Diez-Ala cia e al. T ansla ional Psychia y (2021) 11:302
h ps://doi.o g/10.1038/s41398-021-01430-7
T
ansla ional Psychia y
ARTICLE Open Access
Opposi e al e a ions o 5HT
2A
ecep o b ain
densi y in subjec s wi h schizoph enia: ele ance
o adio ace s pha macological p ofile
Rebeca Diez-Ala cia
1,2,3
, Ca olina Mugu uza
1,2,3
, Guadalupe Ri e o
1,2,3
, Ain zane Ga cía-Bea
1,2
,
Vanessa Gómez-Vallejo
4
,LuisF.Callado
1,2,3
,Jo diLlop
4,5
,Ab ahamMa ín
6,7
and J. Ja ie Meana
1,2,3
Abs ac
The s a us o se o onin 5HT
2A
ecep o s (5HT
2A
Rs) in schizoph enia has been con o e sial. In i o posi on emission
omog aphy neu oimaging and in i o pos -mo em binding s udies ha e epo ed conflic ing esul s abou 5HT
2A
R
densi y. Radio ace s bind di e en ecep o con o ma ions depending on hei agonis , an agonis o in e se agonis
p ope ies. This s udy in es iga es 5HT
2A
R densi y in he pos -mo em p e on al co ex om subjec s wi h
schizoph enia and con ols using h ee adio ace s wi h a di e en pha macological p ofile. The specific binding
pa ame e s o he in e se agonis [
18
F]al anse in, he agonis [
3
H]lyse gic acid die hylamide (LSD) and he an agonis
[
3
H]MDL100907 o b ain co ex memb anes om 20 subjec s wi h schizoph enia and 20 indi idually ma ched con ols
we e e alua ed unde simila me hodological condi ions. Ten schizoph enia subjec s we e an ipsycho ic- ee a dea h.
Sa u a ion cu e analyses we e pe o med by non-linea eg ession o ob ain a maximal densi y o binding si es (B
max
)
and he a fini y o he espec i e adio ace s (K
d
). In schizoph enia subjec s, 5-HT
2A
R densi y was dec eased when
quan ified by [
18
F]al anse in binding, whe eas inc eased when e alua ed by [
3
H]LSD binding. Howe e , [
3
H]
MDL100907 binding was unal e ed. A sligh loss o a fini y (highe K
d
) was obse ed exclusi ely in [
3
H]LSD binding. The
findings we e mo e e iden in an ipsycho ic- ee subjec s han in an ipsycho ic- ea ed subjec s. In conclusion, a
highe p opo ion o he 5-HT
2A
R-ac i e unc ional con o ma ion, which is a he iden ified by agonis adio ace s, was
obse ed in schizoph enia pa ien s. A consequen educ ion o he inac i e 5-HT
2A
R con o ma ion, which is
p e e en ially iden ified by in e se agonis adio ace s, was also ob ained. An agonis adio ace s do no dis inguish
be ween molecula con o ma ions o he ecep o , and acco dingly, he absence o changes was shown. These esul s
a e compa ible wi h he p oposed inc eased unc ional ac i i y o b ain co ical 5-HT
2A
Rs in schizoph enia.
In oduc ion
A ole o se o onin (5-HT) in he pa hophysiology and
he apeu ics o schizoph enia is suppo ed by con e ging
obse a ions
1
. Fi s , simila i ies be ween psycho ic s a es
in psychia ic diso de s and he e ec s o lyse gic acid
die hylamide (LSD) and o he 5-HT ecep o -media ed
psychedelic d ugs (e.g., mescaline and psilocybin) ha e
been desc ibed
2
. Second, co ical se o onin 5HT
2A
ecep o s (5-HT
2A
Rs) seem o be he c i ical a ge o
induce hese psychosis-like esponses
3
, and second-
gene a ion an ipsycho ics such as clozapine, ispe idone
and olanzapine, among o he s, display po en an agonism
p ope ies on 5-HT
2A
Rs. Fu he mo e, since 5-HT plays a
key ole in emo ional p ocessing, i has been p oposed
ha dys egula ion o 5-HT neu o ansmission could
unde lie he nega i e symp oms o schizoph enia
1
. The
5-HT ecep o b ain densi y is ypically assessed in i o
using posi on emission omog aphy (PET)
4
and in i o
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Co espondence: J. Ja ie Meana (ja ie .me[email p o ec ed])
1
Depa men o Pha macology, Uni e si y o he Basque Coun y, Leioa,
Bizkaia, Spain
2
Cen o de In es igación Biomédica en Red de Salud Men al (CIBERSAM),
Leioa, Bizkaia, Spain
Full lis o au ho in o ma ion is a ailable a he end o he a icle
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using pos -mo em issue homogena es and sec ions ( o
a e iew, see Supplemen a y Table S1). E idence shows a
lowe densi y o 5-HT
2A
Rs in he on al co ex o an i-
psycho ic-nai e schizoph enic pa ien s when e alua ed
wi h he e y selec i e (200- o 500- old highe a fini y o
5-HT
2A
Rs s. dopamine D
2
ecep o s (D
2
Rs)) adio ace
[
18
F]al anse in
5–7
. In con as , inconclusi e esul s we e
ob ained wi h o he adio ace s such as [
18
F]se ope one
and [
18
F]N-me hyl spipe one
8–11
, which ha e 10- o 25-
old 5-HT
2A
R selec i i y s. dopamine D
2
Rs
7
. Since D
2
Rs
a e clea ly in ol ed in schizoph enia pa hophysiology and
ea men , he use o hese adio ace s wi h subs an ial
D
2
Ra fini y is conside ed a sou ce o bias o 5-HT
2A
R
de ec ion. On he o he hand, impo an di e ences
among s udies ha e also been ob ained om in i o pos -
mo em s udies in he b ain o subjec s wi h schizo-
ph enia
1,3,12
. Thus, while some s udies desc ibed up-
egula ion o 5HT
2A
Rs, o he s poin ed owa ds he
absence o al e a ions o e en a down- egula ion in he
numbe o binding si es. These appa en disc epancies
among pos -mo em s udies ha e been conside ed in he
con ex o di e en demog aphic and clinical pa ame e s,
he exis ence o di e se pha macological ea men s and
he a ie y o me hodological app oaches
3,12–14
. Mo e-
o e , as d ug- ee popula ions a e di ficul o ob ain o
pos -mo em s udies, he exis ence o long- e m an i-
psycho ic ea men has been conside ed he main
explana o y ac o o di e ences be ween in i o neu-
oimaging s udies in d ug-nai e pa ien s and in i o
findings in pos -mo em b ain. Howe e , less a en ion
has been paid o he pha macological p ope ies, such as
agonis , an agonis o in e se agonis , o he espec i e
d ugs used as adio ace ools o iden i y 5HT
2A
Rs. The
mos common 5HT
2A
R d ugs used o gene a e adi-
oligands o in i o PET s udies ([
18
F]al anse in and [
11
C]
M100907) a e conside ed an agonis s, and he e o s
owa ds he de elopmen o agonis adio ace s ha e
epo ed limi ed success
15
. In ma ked con as , pos -
mo em s udies o 5HT
2A
R quan i a ion in schizoph enia
ha e been pe o med wi h he agonis [
3
H]LSD and he
pa ial agonis [
3
H]ke anse in adio ace s (Supplemen-
a y Table S1). Al hough una ended, he pha macological
p ope ies, such as agonis , an agonis o in e se agonis ,
a e de e minan s o he ecep o con o ma ion iden ified
by he adio ace and, subsequen ly, o he es ima ed
binding densi y
16
.
G-p o ein-coupled ecep o s (GPCRs) and, among
hem, 5HT
2A
Rs display di e en molecula con o ma ions
ha a e in e changeable and s ay in equilib ium
17
. Thus,
he ecep o con o ma ion ha couples o G p o eins is
conside ed o be unc ionally ac i e and ep esen s he
high-a fini y s a e o he ecep o , which is p e e en ially
iden ified by agonis adioligands. Con e sely, in e se
agonis adioligands show p e e ence o bind he low-
a fini y s a e, i.e., he inac i e ecep o con o ma ion,
which is uncoupled om G p o eins. Finally, an agonis
adioligands bind wi h simila a fini y o bo h ecep o
con o ma ions (Fig. 1). The e o e, he binding o agonis
adioligands o he G-p o ein-coupled con o ma ion
should se e as a mo e accu a e measu e o 5HT
2A
R
unc ions and dys unc ions han an agonis binding
18,19
.
In i o s udies ha e e ealed inc eased unc ional cou-
pling o 5HT
2A
Rs o G p o eins in he b ain co ex o
subjec s wi h schizoph enia wi hou al e a ions in o al
alues o ecep o densi y
20
. This finding sugges s ha an
imbalance o 5HT
2A
Rs owa ds he high-a fini y ecep o
con o ma ion migh be p esen in schizoph enia, leading
o o e ac i e G-p o ein-dependen signalling. Unde his
5HT
2A
R o e ac i i y, enhanced agonis adioligand bind-
ing should be expec ed. Con e sely, a dec eased binding
o in e se agonis adioligands o he uncoupled con-
o ma ion migh indica e a dec ease o he low-a fini y
ecep o s a e and p o e he exis ence o an imbalance
be ween coupled and uncoupled 5HT
2A
R con o ma ions
in schizoph enia, wi h ecep o equilib ium displaced
owa ds he ac i e con o ma ional s a e (Fig. 2).
Al hough [
18
F]al anse in and [
11
C]MDL100907 we e
ini ially de eloped as selec i e an agonis adio ace s o
quan i y 5HT
2A
Rs in PET s udies
15
, al anse in has
ecen ly been demons a ed o show in e se agonis
Agonis / [3H]LSD
An agonis / [3H]M100907
In e se agonis / [18F]al anse in
Fig. 1 Con o ma ional s a es o he 5-HT
2A
R. The ecep o con o ma ion coupled o G-p o ein signalling pa hways ep esen s he unc ional s a e
and is p e e en ially iden ified by agonis adioligands such as [
3
H]LSD. The inac i e con o ma ion o he 5-HT
2A
R, which is uncoupled om G
p o eins, is p e e en ially labelled by in e se agonis adioligands such as [
18
F]al anse in. Ac i e and inac i e con o ma ions a e in e changeable s a es
ha s ay in equilib ium
17
. An agonis adioligands, such as [
3
H]MDL100907, bind bo h ecep o con o ma ions and, he e o e, do no dis inguish
be ween unc ional and non- unc ional s a es.
Diez-Ala cia e al. T ansla ional Psychia y (2021) 11:302 Page 2 o 10
p ope ies on 5HT
2A
Rs in pos -mo em human b ain
13,21
.
In ac , [
18
F]al anse in binding is dec eased in he b ain o
pa ien s wi h schizoph enia
5,6
and in p od omal a - isk
s a e subjec s
22
. In con as o PET e alua ions, s udies in
pos -mo em b ain o subjec s wi h schizoph enia ha e
mainly been pe o med wi h he agonis [
3
H]LSD and he
pa ial agonis [
3
H]ke anse in adio ace s (Supplemen-
a y Table S1). No iceably, among pos -mo em s udies,
hose de eloped in an ipsycho ic- ee schizoph enia cases
displayed enhanced 5HT
2A
R densi y in he p e on al
co ex
13,23,24
. Based on all hese obse a ions, i could be
hypo hesized ha 5HT
2A
R agonis s and in e se agonis s
iden i y di e en molecula con o ma ions o his ecep-
o in schizoph enia, leading o opposi e findings. How-
e e , he 5HT
2A
R ecep o binding o agonis , an agonis
and in e se agonis adio ace s has ne e been es ed
unde he same me hodological condi ions.
The aim o he p esen s udy was o in es iga e he
5HT
2A
R densi y in pos -mo em p e on al co ex o
subjec s wi h schizoph enia, using h ee di e en adio-
ace s wi h di e en in insic ac i i y p ope ies (agonis ,
an agonis and in e se agonis ) on his ecep o . [
3
H]LSD,
[
3
H]MDL100907 and [
18
F]al anse in we e selec ed as
ep esen a i e adio ace s wi h well-es ablished pha -
macological p ofiles. LSD is a hallucinogenic d ug wi h
5HT
2A
R pa ial agonis p ope ies
25,26
, and i s
3
H-labelled
o m iden ifies his ecep o unde blocking condi ions o
o he 5-HT ecep o s. MDL100907 is a e y selec i e 5-
HT
2A
R an agonis
27
, whose
18
F- and
11
C-labelled o ms
ha e been used o PET s udies
15,28
. Al anse in is a highly
selec i e 5HT
2A
R in e se agonis
21
, commonly conside ed
as an agonis PET adio ace when labelled wi h
18
F
15
.
The h ee adio ace s we e e alua ed on sa u a ion
binding expe imen s in b ain co ex memb ane homo-
gena es o he same subjec s and unde simila expe i-
men al condi ions. We sough o es he hypo hesis ha
di e en al e a ions o 5HT
2A
R densi y a e ob ained in
schizoph enia depending on he in insic ac i i y p op-
e ies o each adio ace . The esul s would shed ligh on
he uncla ified s a us o b ain 5HT
2A
Rs in schizoph enia.
Subjec s, ma e ials and me hods
Pos -mo em human b ain samples
B ain samples we e ob ained a au opsies pe o med in
he Basque Ins i u e o Legal Medicine, Bilbao, Spain, in
compliance wi h policies o esea ch and e hical boa ds
o pos -mo em b ain s udies. Dea hs we e subjec ed o
e ospec i e sea ching o p e ious medical diagnosis
and ea men using he examine ’s in o ma ion and
eco ds om hospi als and men al heal h cen es. A o al
numbe o 20 b ains om subjec s wi h an e-mo em
diagnosis o schizoph enia acco ding o he Diagnos ic
and S a is ical Manual o Men al Diso de s (DSM-IV,
DSM-IV-TR) we e ma ched o 20 b ains om con ol
subjec s in a pai ed design. Con ol subjec s we e chosen
among he collec ed b ains on he basis o he absence o
neu opsychia ic diso de s o d ug abuse, and an app o-
p ia e sex, s o age ime and pos -mo em in e al (elapsed
ime be ween dea h and issue dissec ion/ eezing) o
ma ch each schizoph enia subjec . Toxicological sc een-
ing o blood samples o all subjec s was pe o med o
de e mine he p esence a dea h o an ipsycho ics, o he
d ugs and e hanol. Acco ding o he absence o p esence
o an ipsycho ic d ugs in his oxicological sc eening,
schizoph enia popula ion was di ided in o wo g oups, a
g oup o an ipsycho ic- ee (n=10) and a g oup o
an ipsycho ic- ea ed (n=10) subjec s. Schizoph enia
and con ol g oups we e simila o sex a io, age, s o age
ime and pos -mo em in e al alues (Supplemen a y
Table S2). Se en een ou o he 20 subjec s in he schi-
zoph enia g oup commi ed suicide. Ma ched con ol
subjec s mainly died by acciden al causes. The e o e, he
mechanism o dea h indica es ha almos all we e iolen
o sudden. Specimens o he do sola e al p e on al co ex
(B odmann’s a ea 9) we e dissec ed a au opsy ollowing
s anda d p ocedu es and immedia ely s o ed a −80 °C
un il assayed. A comple e desc ip ion o he whole
popula ion o subjec s wi h schizoph enia and hei
indi idually ma ched con ols can be ound in Supple-
men a y Table S2. Some o he schizoph enia cases and
con ols ha e been p e iously used o e alua e he [
3
H]
CONTROL
SCHIZOPHRENIA
In acellula signalling
In acellula signalling
Fig. 2 Rep esen a ion o he imbalance be ween 5-HT
2A
R
con o ma ions owa ds he s a e p e e en ially labelled by
agonis s obse ed in he p e on al co ex o subjec s wi h
schizoph enia. The disequilib ium p omo es a G-p o ein
o e ac i a ion in esponse o 5-HT
2A
R agonis s
20
. Based on his
hypo hesis, agonis adioligands should iden i y highe binding si es
and in e se agonis adioligands should label lowe binding si es in
schizoph enia han in con ols. An agonis adioligands would no
disc imina e be ween schizoph enia and con ol subjec s.
Diez-Ala cia e al. T ansla ional Psychia y (2021) 11:302 Page 3 o 10
ke anse in binding densi y
13,24
and G-p o ein ac i a ion
media ed by 5-HT
2A
Rs
20,29
(see Supplemen a y Table S2
o de ails). The p e on al co ex was selec ed as he
egion o in e es based on he mo phological al e a ions
associa ed o schizoph enia
30
and he la ge exp ession o
5-HT
2A
Rs in he a ea
5
.
Ma e ials and d ugs
MDL100907 ( olinanse in) and al anse in we e pu -
chased om Sigma-Ald ich. [
3
H]LSD (86.3 Ci/mmol a
deli e y ime) was ob ained om Pe kinElme Li e and
Analy ical Sciences, Inc., and [
3
H]MDL100907 (80 Ci/
mmol a deli e y ime) was ob ained om ARC Radio-
chemicals. All o he chemicals we e ob ained om s an-
da d sou ces.
Syn hesis o [
18
F]al anse in
[
18
F]al anse in was p oduced in a TRACERlab FXFN
syn hesis module (GE Heal hca e) by adiofluo ina ion o
ni o-al anse in (ABX, Radebe g, Ge many) as p e iously
published
31
. Specific ac i i y a ini ial incuba ion ime (see
below) was in he ange 300–700 GBq/μmol. The a e age
adiochemical yield was 11 ± 4% (end o syn hesis).
Radiochemical pu i y was >97% in all cases.
B ain memb anes p epa a ion
B ain co ex samples we e p ocessed o ob ain
memb ane-en iched homogena es as p e iously desc ibed
13
.
[
18
F]Al anse in, [
3
H]LSD and [
3
H]MDL100907 binding
assays
Comple e sa u a ion binding assays we e pe o med
wi h [
18
F]al anse in (0.03–4 nM, eigh concen a ions),
[
3
H]LSD (0.03–10 nM, en concen a ions) and [
3
H]
MDL100907 (0.007–4 nM, en concen a ions) in o de o
de e mine he densi y (B
max
) and he a fini y (K
d
)o 5-
HT
2A
Rs. Incuba ion was ca ied ou in ubes ([
18
F]al an-
se in) o 96-well pla es ([
3
H]LSD and [
3
H]MDL100907)
and s a ed wi h he addi ion o he b ain memb ane
p epa a ion. Reac ions we e incuba ed o 40 min a 37 °C
o [
18
F]al anse in binding assays and 90 min a 37 °C o
[
3
H]LSD and [
3
H]MDL100907 binding assays. The p e-
sence o MDL100907 (1 µM) o al anse in (10 µM) was
used o de e mine he non-specific binding o [
18
F]al an-
se in and [
3
H]LSD, and o [
3
H]MDL100907, espec i ely.
A e incuba ion, ee adioligand was sepa a ed om
bound adioligand by apid fil a ion unde acuum
h ough GF/C glass fib e fil e s p e-soaked wi h 0.5%
polye hylenimine and coun ed o adioac i i y gamma
coun ing ([
18
F]al anse in; 2470 WIZARD2 Au oma ic
Gamma Coun e , Pe kinElme ) o by liquid scin illa ion
([
3
H]LSD and [
3
H]MDL100907; Mic oBe a T iLux
Coun e , Pe kinElme ). Resul s we e co ec ed o each
adio ace decay. Pai s o cases and con ols we e always
p ocessed a he same ime and all samples we e un in
duplica e.
Da a and s a is ical analyses
Da a ob ained om sa u a ion binding expe imen s o
each subjec we e analysed by non-linea eg ession using
he G aphPad P ism™so wa e. The appa en equilib ium
dissocia ion cons an (K
d
) and he maximum densi y o
specific binding si es (B
max
) we e ob ained. K
d
alues we e
no malized o log ans o ma ion be o e pa ame ic ana-
lyses. All da a we e subjec ed o a G ubbs’s es in o de o
de ec and ejec possible ou lie alues among expe i-
men al g oups. Pea son’s co ela ion coe ficien was
calcula ed o es o a possible associa ion be ween
independen co a iables (age, pos -mo em in e al and
s o age ime) and ecep o densi y. When co ela ion was
significan , analysis o co a iance was pe o med con-
olling o he independen co a iable. One-way analysis
o a iance ollowed by Bon e oni’s pos -hoc es was
used o compa e esul s be ween adioligands. Resul s a e
exp essed as mean±s anda d de ia ion (SD) o indi idual
alues.
S a is ical compa isons be ween g oups we e conduc ed
by non-linea cu e-fi ing coanalysis o all indi idual
binding expe imen s. The selec ion be ween a single-
cu e model (absence o di e ences be ween g oups) and
a wo-cu e model (s a is ical di e ences be ween g oups)
was made by he ex asum-o -squa es F es using
G aphPad P ism™. When s a is ical di e ences be ween
cu es we e ob ained, u he indi idual con as s we e
pe o med o de ec whe he di e ences we e a ibu able
o changes in B
max
and/o K
d
alues be ween g oups
32,33
.
The analysis ha pe mi ed one o mo e o he pa a-
me e s o be sha ed wi hou a significan inc ease in he
esidual a iance was aken as he bes fi . In his non-
linea analysis, esul s (B
max
and K
d
) a e exp essed as he
bes es ima ion pa ame e ± SD. These alues ob ained
om simul aneous non-linea eg ession analyses we e
no used o pa ame ic s a is ical calcula ions.
In all analyses, he le el o s a is ical wo- ailed sig-
nificance was chosen as p=0.05.
Resul s
Specific binding si es o [
18
F]al anse in, [
3
H]LSD and [
3
H]
MDL100907
The indi idual non-linea analysis o each adioligand
binding fi ed o a sa u a ion cu e displaying a single
specific binding si e o high a fini y, compa ible wi h
selec i e de ec ion o 5-HT
2A
Rs. The ecep o densi y
(B
max
) in he o e all popula ion was simila when iden-
ified by [
18
F]al anse in o [
3
H]MDL100907 binding, while
i was significan ly highe when es ima ed by [
3
H]LSD
binding (192 ± 82% o e [
18
F]al anse in, p< 0.01; 210 ±
89% o e [
3
H]MDL100907, p< 0.0001). The binding
Diez-Ala cia e al. T ansla ional Psychia y (2021) 11:302 Page 4 o 10
a fini ies, exp essed by K
d
alues, we e always in he
nanomola ange (K
d
=0.36 ± 0.19 nM o [
18
F]al anse in;
K
d
=1.26 ± 0.86 nM o [
3
H]LSD; K
d
=0.47 ± 0.37 nM o
[
3
H]MDL100907) wi hou significan di e ences be ween
adioligands.
Posi i e co ela ions be ween densi ies ob ained wi h
[
18
F]al anse in and [
3
H]MDL100907 ( =0.332, p< 0.05),
and be ween [
3
H]MDL100907 and [
3
H]LSD ( =0.894,
p< 0.0001) we e ound. In con as , no significan co e-
la ion was ound be ween densi ies ob ained wi h [
18
F]
al anse in and [
3
H]LSD, sugges ing ha hese adi-
oligands could iden i y di e en binding popula ions.
E ec s o demog aphic pa ame e s and pos -mo em
condi ions
The densi y o [
18
F]al anse in binding si es displayed a
nega i e co ela ion wi h he age a dea h ( =−0.341;
p< 0.05). Acco ding o his linea decay, he a e age
dec ease pe decade o 5-HT
2A
Rs was 35 ± 15 mol/mg.
In he case o [
3
H]MDL100907 binding, he e was also a
dec ease o densi y wi h age (30 ± 17 mol/mg pe decade)
ha did no each significan co ela ion ( =−0.283; p=
0.08). No co ela ion be ween age a dea h and densi y o
[
3
H]LSD binding si es was ob ained.
[
18
F]al anse in, [
3
H]LSD and [
3
H]MDL100907 binding
p ope ies we e no significan ly a ec ed nei he by pos -
mo em in e al no by s o age ime a −80 °C.
Compa ison be ween schizoph enia and con ol g oups
The co-analysis o sa u a ion cu es ob ained wi h [
18
F]
al anse in showed a s a is ically significan educ ion o he
densi y o he binding si es in he schizoph enia g oup
compa ed o ma ched con ols. No di e ences in a fini y
we e de ec ed be ween schizoph enia and con ol g oups
(Table 1). When he p esence o an ipsycho ic d ugs was
conside ed, he co-analysis demons a ed a significan
educ ion o [
18
F]al anse in binding si es in an ipsycho ic-
ee subjec s wi h schizoph enia (B
max
=329 ± 24 mol/mg)
s. ma ched con ols (B
max
=410 ± 25 mol/mg) (p<0.05)
(Fig. 3A). In con as , subjec s wi h schizoph enia and
p esence o an ipsycho ic ea men displayed densi y alues
(B
max
=376 ± 18 mol/mg) close o he espec i e ma ched
con ol g oup (B
max
=411 ± 23 mol/mg) (Fig. 3A). No
changes we e obse ed in he a fini y pa ame e s (K
d
=
0.30 ± 0.07 nM in an ipsycho ic- ee schizoph enia g oup
s. K
d
=0.34 ± 0.07 nM in ma ched con ols; K
d
=0.33 ±
0.05 nM in an ipsycho ic- ea ed schizoph enia g oup s.
K
d
=0.29 ± 0.06 nM in ma ched con ols). As expec ed,
hese findings we e confi med by analysis o co a iance
con olling B
max
alue o age.
The co-analysis o sa u a ion cu es ob ained wi h [
3
H]
LSD demons a ed a significan inc ease o binding si es
in subjec s wi h schizoph enia compa ed o ma ched
con ols The co-analysis also demons a ed highe K
d
alues o his adioligand in he schizoph enia g oup han
in con ols (Table 1). When he p esence o an ipsycho ic
d ugs in blood was conside ed, he enhanced ecep o
densi y was main ained in an ipsycho ic- ee schizo-
ph enia subjec s (B
max
=791 ± 69 mol/mg) when com-
pa ed wi h ma ched con ols (B
max
=646 ± 34 mol/mg)
(p< 0.05) (Fig. 3B). Con e sely, an ipsycho ic- ea ed
schizoph enia subjec s displayed ecep o densi y alues
(B
max
=735 ± 63 mol/mg) ha did no di e om hose
in espec i e con ol g oup (B
max
=635 ± 30 mol/mg)
(Fig. 3B). In he case o K
d
alues, he inc ease was sig-
nifican o bo h an ipsycho ic- ee (K
d
=1.45 ± 0.45 nM)
and an ipsycho ic- ea ed (K
d
=1.52 ± 0.44 nM) schizo-
ph enia subjec s compa ed wi h espec i e con ols (K
d
=
0.69 ± 0.15 nM and K
d
=0.77 ± 0.15 nM) (p< 0.05). Re-
e alua ion wi h age as co a ia e main ained simila
esul s. In o de o es whe he he esidual p esence o
an ipsycho ic d ugs could con ibu e o he inc eased K
d
o [
3
H]LSD binding, a co ela ion be ween published K
i
o 5-HT2AR alues
34,35
o d ugs de ec ed in he pos -
mo em oxicological sc eening and indi idual K
d
alues
ob ained o [
3
H]LSD was pe o med. A significan
Table 1 Radioligand binding pa ame e s in he p e on al co ex o subjec s wi h schizoph enia and ma ched con ols.
Schizoph enia Con ol F[d. .,d. .] pValue
B
max
( mol/mg) K
d
(nM) nB
max
( mol/mg) K
d
(nM) n
Mean ± SD Mean ± SD Mean ± SD Mean ± SD
[
18
F]Al anse in 352 ± 15 0.32 ± 0.05 20 410 ± 17 0.32 ± 0.05 20 F[1,288] =6.361 0.0122
[
3
H]LSD 765 ± 47 1.5 ± 0.32 20 640 ± 23 0.73 ± 0.11 20 F[1,311] =8.282 0.0043
[
3
H]MDL100907 324 ± 23 0.29 ± 0.07 20 335 ± 16 0.28 ± 0.04 20 F[1,294] =0.354 0.7023
Fo each adioligand, he wo se s o da a (schizoph enia and con ol) we e fi s analysed sepa a ely. The o e all alue o he sum o squa es and he deg ees o
eedom (d. .) was he sum o he indi idual alues o each fi . Nex , he wo se s o da a we e pooled and analysed simul aneously cons aining hem o sha e one o
wo common pa ame e s (B
max
,K
d
). The pooled fi yielded alues o he sum o squa es and deg ees o eedom. The analysis ha pe mi ed one o wo pa ame e s
o be sha ed wi hou a significan inc ease in he esidual a iance was aken as he bes fi . [
18
F]Al anse in and [
3
H]LSD binding cu es we e conside ed di e en
be ween schizoph enia and con ol. The subsequen analysis demons a ed ha s a is ical di e ences we e adsc ibed o di e en B
max
bu no o K
d
alues. The F, d. .
and p alues displayed co espond o his condi ion. Fo [
3
H]MDL100907, es ima ions ob ained unde equi alen analysis a e shown.
Diez-Ala cia e al. T ansla ional Psychia y (2021) 11:302 Page 5 o 10
co ela ion ( =0.68, p=0.04) was ob ained in
an ipsycho ic- ea ed subjec s.
The co-analysis o cu es ob ained wi h [
3
H]
MDL100907 showed no di e ences o binding si es
be ween subjec s wi h schizoph enia and ma ched con-
ols. The a fini ies we e also simila (Table 1). No di -
e ences we e de ec ed nei he in an ipsycho ic- ee
schizoph enia subjec s (B
max
=324 ± 37 mol/mg; K
d
=
0.34 ± 0.13 nM) wi h espec i e con ols (B
max
=328 ±
23 mol/mg; K
d
=0.32 ± 0.07 nM) no in an ipsycho ic-
ea ed subjec s (B
max
=330 ± 28 mol/mg; K
d
=0.26 ±
0.07 nM) s. ma ched con ols (B
max
=344 ± 22 mol/mg;
K
d
=0.25 ± 0.05 nM) (Fig. 3C). Age a dea h did no
influence he esul s in he analysis o co a iance.
Discussion
The p esen s udy demons a es in pos -mo em human
on al co ex ha al e a ions o 5-HT
2A
Rs obse ed in
schizoph enia a e dependen on he pha macological
p ope ies o he adio ace used o iden i y his ecep o .
Thus, binding assays wi h an agonis ([
3
H]LSD), an
an agonis ([
3
H]MDL100907) and an in e se agonis
([
18
F]al anse in) adio ace conduc ed in simila incuba-
ion condi ions om iden ical samples lead o di e en
esul s. The p esen s udy p o ides e idence ha he
agonis adioligand binding o 5-HT
2A
Rs is inc eased in
schizoph enia, whe eas in e se agonis adioligand bind-
ing is educed, and he an agonis adioligand binding
emains unal e ed. This di e en ial pa e n is ema kable
in an ipsycho ic- ee subjec s, whe eas he p esence o
hese d ugs in blood ends o e e se he 5-HT
2A
R densi y
al e a ions o con ol alues. Un il ecen ly, an equi alen
PET s udy was no easible, mainly due o he lack o
sui able agonis adio ace s o selec i e 5-HT
2A
R iden-
ifica ion
36
. Howe e , he ecen de elopmen o [
11
C]
Cimbi-36
15,18
, a non-selec i e 5-HT
2A/B/C
R agonis
37
,
could help o confi m h ough head- o-head in i o
compa isons be ween an agonis and in e se agonis
adio ace s he findings he e epo ed in he pos -
mo em issue. Ne e heless, he echnical and e hical
easibili y o in i o iden ifica ion o 5-HT
2A
Rs by h ee
di e en PET adio ace s in he same pa ien and sho
ime ame is limi ed. The e o e, in i o pos -mo em
s udies could help o o e come hese d awbacks in he
s udy o neu o ansmi e ecep o molecula al e a ions.
Howe e , o he po en ially con ounding ac o s, especially
he exis ence o p e ious ea men wi h an ipsycho ic
d ugs, add limi a ions o he conclusions o pos mo em
s udies. In ac , he numbe o an ipsycho ic- ee subjec s
included in his ype o s udies is e y limi ed
38
(Supple-
men a y Table S1).
The inc eased densi y o 5-HT
2A
Rs iden ified by he
agonis adio ace [
3
H]LSD confi ms he p oposed highe
unc ional sensi i i y o his ecep o in schizoph enia.
A
B
C
01234
0
100
200
300
400
[
3
H]MDL100907 (nM)
Spec ic bound
( mol/mg p o )
An ipsycho ic- ea ed
schizoph enia (n=10)
An ipsycho ic- ee
schizoph enia (n=10)
Con ol (n=20)
0.0 2.5 5.0 7.5 10.0 12.5
0
200
400
600
800
[
3
H]LSD (nM)
Speci ic bound
( mol/mg p o )
01234
0
100
200
300
400
[
18
F]Al anse in (nM)
Speci ic bound
( mol/mg p o )
Fig. 3 Al e a ions o 5-HT
2A
ecep o densi y in schizoph enia.
Sa u a ion cu es o he specific[
18
F]al anse in (A), [
3
H]LSD (B) and
[
3
H]MDL100907 (C) binding o memb anes o pos -mo em on al
co ex om subjec s wi h schizoph enia and p esence o an ipsycho ic
d ugs in he blood a he ime o dea h (an ipsycho ic- ea ed),
subjec s wi h schizoph enia and no an ipsycho ic d ugs in he blood
(an ipsycho ic- ee), and ma ched con ol subjec s. Each schizoph enia
g oup was analysed s. he espec i e con ol g oup, bu in o de o
cla i y, he e he wo con ol g oups a e shown oge he . The cu es
ep esen he bes -fi es ima ion gene a ed by he non-linea co-
analysis o indi idual esul s in each g oup. The densi y o 5-HT
2A
Rs is
exp essed as he asymp o e alue (B
max
) o he adioligand bound.
The a fini y o he adioligand is exp essed by he concen a ion o
adioligand ha p omo es he hal -maximal bound (K
d
). Poin s
ep esen ing means we e no used o s a is ical analysis.
Diez-Ala cia e al. T ansla ional Psychia y (2021) 11:302 Page 6 o 10
P e ious s udies wi h he pa ial agonis adioligand [
3
H]
ke anse in ha e epo ed simila findings in an ipsycho ic-
ee subjec s
13,24
. Endogenous and exogenous agonis s
bind p e e en ially o he high-a fini y s a e o he ecep o ,
which ep esen s he ac i e unc ional con o ma ion cou-
pled o cell signalling pa hways (Fig. 1). Recen ly, he
assessmen o 5-HT
2A
R coupling o G p o eins in pos -
mo em on al co ex has demons a ed an enhanced
sensi i i y o inhibi o y G
i1
p o eins in esponse o he
agonis (±)DOI (2,5-dime hoxy-4-iodoamphe amine) in
schizoph enia
20
. In conco dance, he p olac in esponse o
he 5-HT- eleasing d ug D- enflu amine
39
, which is con-
side ed a unc ional in i o es dependen on 5-HT
2A/C
Rs
ac i a ion, is enhanced in d ug- ee schizoph enia sub-
jec s
40,41
. The e o e, e idence poin s owa ds a unc ional
hype ac i i y o 5-HT
2A
Rs in schizoph enia. This issue has
esul ed in con o e sy since PET s udies wi h [
18
F]al an-
se in ha e sugges ed dec eased binding po en ial in
an ipsycho ic-nai e schizoph enia pa ien s
5,6
. The p esen
s udy illus a es how he educ ion o [
18
F]al anse in
binding (−20%) is compa ible wi h enhanced binding
(+22%) o agonis adio ace s as [
3
H]ke anse in and [
3
H]
LSD. The compound al anse in has been classically
ega ded as he selec i e 5-HT
2A
R an agonis . Howe e , in
he b ain co ex, his d ug shows in e se agonis p ope -
ies
13,21
, which means p e e en ial labelling o he ecep o
con o ma ion uncoupled om G p o eins. In his way, he
pha macological p ofile o [
18
F]al anse in explains he
educed 5-HT
2A
R densi y epo ed in schizoph enia as a
educ ion o he uncoupled con o ma ion o his ecep o .
G-p o ein-coupled (highe a fini y o agonis s han o
in e se agonis s) and G-p o ein-uncoupled (highe a fini y
o in e se agonis s han o agonis s) ecep o con-
o ma ions a e in e changeable molecula s a es o GPCRs.
In b ains o subjec s wi h schizoph enia, he imbalance
be ween 5-HT
2A
R con o ma ions in a ou o he G-
p o ein-coupled s a e would be exp essed as inc eased
densi y o he agonis [
3
H]LSD binding and educed
densi y o he in e se agonis [
18
F]al anse in binding, as
obse ed in he p esen s udy (Fig. 2). Mo eo e , his
hypo hesis should be suppo ed by he concu en absence
o changes in he 5-HT
2A
R densi y delinea ed by selec i e
an agonis adio ace s. Neu al an agonis d ugs do no
dis inguish among molecula con o ma ions o he ecep-
o and, he eby, a e no sui able ools o de ec he exis-
ence o imbalance be ween 5-HT
2A
R con o ma ional
s a es in schizoph enia. The absence o di e ences o he
an agonis [
3
H]MDL100907 binding be ween schizo-
ph enia and con ol g oups ob ained in he p esen s udy
ag ees wi h his a gumen and suppo s he exis ence o a
unc ional 5-HT
2A
R imbalance in he pa hophysiology o
he diso de . Mo e ecen pos -mo em s udies ha e added
u he weigh o his hypo hesis by showing ha mes-
senge RNA exp ession and o al p o ein immunode ec ion
o 5-HT
2A
Rs a e unal e ed in subjec s wi h schizoph enia
ee o an ipsycho ic ea men
20
.
One appa en inconsis ency o he p esen s udy is he
di e en ecep o binding densi y ob ained be ween
adio ace s. [
3
H]LSD app oxima ely iden ified a wo- old
highe numbe o binding si es han [
18
F]al anse in and
[
3
H]MDL100907. I is widely accep ed ha 5-HT
2A
Rs a e
assembled in o homodime ic and he e odime ic s uc-
u es
24,42
. Recep o oligome s coexis wi h monome ic
o ms (Fig. 4). Dime ic ecep o complex c oss alk o each
o he p omo ing di e en ial modula ion o he ligand
access o he espec i e binding pocke s
36
. In ac , he
binding o pa ial agonis and an agonis s, as ke anse in
and MDL100907, o one o he wo binding si es in he 5-
HT
2A
R homodime in oduces nega i e coope a i i y
e ec s on he p opensi y o a second molecule o he same
d ug o bind he dime
43
. In con as , he hallucinogenic
5-HT
2A
R agonis (±)DOB shows a simila a fini y o he
wo binding si es o he dime
43
. The e o e, i is easible o
p opose ha [
3
H]LSD is able o label he wo binding si es
o he homodime ic 5-HT
2A
R, whe eas [
3
H]MDL100907,
[
18
F]al anse in and [
3
H]ke anse in binding o one o he
ecep o pocke s p e en he own adioligand binding o
he second si e (Fig. 4). This molecula mechanism would
be eflec ed in a wo- old highe densi y when es ima ed
by adio ace s bound o he ull homodime wi h espec
o he densi y ob ained by adio ace s bound only o one
o he monome s ha con o m o he dime . The esul s
shown in he p esen s udy oge he wi h hose in p e-
ious s udies wi h he adio ace [
3
H]ke anse in
13,24
ag ee wi h his hypo hesis o a homodime ic 5-HT
2A
R
s uc u e and unc ion. Ce ainly, he assump ion o he
ecep o oligome iza ion pa adigm should a ec u u e
compa isons be ween adio ace binding p ope ies.
The obse ed decline o 5-HT
2A
R densi y wi h ageing is
a epea ed finding in p e ious pos -mo em
13,24,44
and
PET
45
s udies. This p o ound e ec o ageing p o ides he
a ionale o expe imen al designs based on one- o-one
indi idual ma ching o each schizoph enia case wi h
espec i e con ol, as pe o med he e, a he han he
usual and less igo ous g oup-based ma ching.
The p esence o absence a dea h o an ipsycho ic d ugs
in he blood o subjec s wi h schizoph enia ep esen s
ano he ele an con ounding ac o in adioligand bind-
ing s udies (Supplemen a y Table S1). In he p esen
s udy, he absence o an ipsycho ic d ugs in he ox-
icological analysis does no mean ha hese subjec s
e med as an ipsycho ic- ee we e an ipsycho ic-nai e,
bu a he ha hey we e un ea ed in he nea es an e-
mo em pe iod. The mo e [
18
F]al anse in binding and he
less [
3
H]LSD binding densi ies in an ipsycho ic- ea ed
espec o an ipsycho ic- ee schizoph enia subjec s sug-
ges ha an ipsycho ic ea men would coun e balance
he 5-HT
2A
Rs al e a ions obse ed in schizoph enia.
Diez-Ala cia e al. T ansla ional Psychia y (2021) 11:302 Page 7 o 10
Long- e m ea men wi h second-gene a ion an i-
psycho ics modula es 5-HT
2A
R exp ession in animals
14,24
and could modi y binding pa ame e s due o esidual
p esence o an ipsycho ics ac ing as 5-HT
2A
R an ago-
nis s
20
. Howe e , he possibili y ha obse ed al e a ions
o 5-HT
2A
R densi y (B
max
) in schizoph enia ep esen a
consequence o he cu en o pas long- e m an i-
psycho ic ea men is imp obable. Fi s , he changes o
densi y a e mo e e iden in ecen an ipsycho ic- ee han
in an ipsycho ic- ea ed subjec s. Second, he di e en ial
up- o down- egula ion o 5-HT
2A
Rs associa ed wi h
ecen an ipsycho ic ea men in unc ion o he di e en
adio ace s makes unlikely a esidual compe i i e e ec
be ween he an ipsycho ic and he adioligand o bind he
ecep o pocke . In con as o densi y (B
max
), he
appa en a fini y (K
d
alue) was sensi i e o he esidual
p esence o an ipsycho ic d ugs, al hough his e ec was
only obse ed o [
3
H]LSD binding assays. The finding
easse s he use o agonis adio ace s o be e de ec
he 5-HT
2A
R occupa ion by psychedelic d ugs
46
. Recep o
explo a ion in d ug- ee condi ions is mo e easible by
PET imaging han by e ospec i e pos -mo em binding
s udies. Indeed, mos o he pos -mo em s udies e alu-
a ing 5-HT
2A
Rs in schizoph enia ha e been pe o med in
he b ain o subjec s unde an ipsycho ic ea men , which
p obably led o inconclusi e esul s (Supplemen a y Table
S1). Besides his, when schizoph enia subjec s we e di -
e en ia ed be ween hose unde an ipsycho ic ea men
and hose an ipsycho ic- ee, he pos -mo em adi-
oligand s udies demons a ed up- egula ion o b ain
5-HT
2A
Rs iden ified by agonis /pa ial agonis adio-
ace s
13,20,23,24
. The e o e, in o de o disca d e en ual
bias in pos -mo em s udies, independen and well-
ma ched g oups o an ipsycho ic- ee and an ipsycho ic-
ea ed subjec s should be selec ed and independen ly
analysed.
Ano he po en ial con ounding ac o o conside in he
p esen s udy is he ac ha schizoph enia subjec s died
mos ly om iolen suicide mechanisms. Suicide has been
p oposed as a condi ion ha could influence he e alua-
ion o 5-HT
2A
Rs
47
. Howe e , he e a e se e al s udies in
he on al co ex o suicide ic ims wi h a a ie y o
psychia ic diso de s suppo ing ha suicide unlikely
ep esen s a majo con ounde in 5-HT
2A
R binding
s udies
1,13,48,49
.
In conclusion, he s udy and in e p e a ion o 5-HT
2A
R
dys unc ions in schizoph enia equi es a deep knowledge
o he pha macological p ope ies o he candida e
adio ace s. The dis inc ion o 5-HT
2A
R adio ace s
be ween agonis , an agonis and in e se agonis may shed
ligh on he, up o now, con adic o y esul s. Acco ding
o he di e en pha macological p ofile, he p esen
esul s and mos o he s udies would demons a e an
up egula ion o he ac i e unc ional 5-HT
2A
R con-
o ma ion in he b ain o subjec s wi h schizoph enia.
The p esen esul s suppo he hypo hesis ha 5-
HT
2A
R molecula con o ma ion and/o he ecep o
in e ac ion wi h o he synap ic p o eins migh be al e ed
in schizoph enia. Mo eo e , as p e iously desc ibed, he
an ipsycho ic ea men seems also o modi y he
[3H]LSD
[3H]M100907
[18F]al anse in
Fig. 4 Monome and oligome con o ma ions o he 5-HT
2A
R. The 5-HT
2A
R is exp essed as single monome s bu also as ecep o complexes
cons i u ed by wo o mo e ecep o uni s. The binding o a d ug o one o he monome s o he complex could induce posi i e, nega i e o no
coope a i i y o he binding o o he monome s wi h he complex. Fo example, he binding o he an agonis MDL100907 o he in e se agonis
al anse in o one o he binding pocke s o he homodime in oduces nega i e allos e ic e ec s on he binding o he same d ug o he second
binding pocke
43
. This nega i e coope a i i y would p e en he iden ifica ion o he o al numbe o binding si es. In con as , he binding o
hallucinogenic 5-HT
2A
R agonis such as (±)DOB and LSD o ecep o homodime s does no modi y he es ima ion o he o al numbe o binding
si es
43
. Highe o de 5-HT
2A
R oligome ic and he e ome ic complexes o 5-HT
2A
Rs wi h o he GPCRs a e also easible
24,42
.
Diez-Ala cia e al. T ansla ional Psychia y (2021) 11:302 Page 8 o 10
unc ional s a e o 5-HT
2A
Rs, ying o e e he al e a-
ions ound in an ipsycho ic- ee schizoph enia subjec s.
The e o e, he de elopmen and in i o use o agonis
adio ace s in an ipsycho ic-nai e pa ien s should be
encou aged o alida e he 5-HT
2A
R o e ac i i y he e
p oposed.
Acknowledgemen s
This s udy was suppo ed by he Spanish S a e Resea ch Agency, Minis y o
Science and ERD Funds (SAF-2009-08460, SAF-2017-88126-R, RYC-2017-22412
and CTQ-2017-87637-R), and he Basque Go e nmen (SAIOTEK S-PE13UN019
and IT-1211-19). Pa o his wo k was conduc ed unde he Ma ia de Maez u
Uni s o Excellence P og amme (G an MDM-2017-0720). C.M. and A.G.-B. we e
ecipien s o ellowships om he Ma ie Slodowska-Cu ie P og amme
(Eu opean Union’s Ho izon 2020, G an 747487) and he Basque Go e nmen
p edoc o al aining P og amme, espec i ely. We wish o hank s a membe s,
and especially D . B. Mo en in, o he Basque Ins i u e o Legal Medicine, Bilbao,
Spain, o hei coope a ion in he s udy.
Au ho de ails
1
Depa men o Pha macology, Uni e si y o he Basque Coun y, Leioa,
Bizkaia, Spain.
2
Cen o de In es igación Biomédica en Red de Salud Men al
(CIBERSAM), Leioa, Bizkaia, Spain.
3
Bioc uces Bizkaia Heal h Resea ch
Ins i u e, Ba akaldo, Bizkaia, Spain.
4
CIC BiomaGUNE, Basque Resea ch and
Technology Alliance (BRTA), Donos ia/San Sebas ian, Spain.
5
Cen o de
In es igación Biomédica en Red de En e medades Respi a o ias (CIBERES),
Mad id, Spain.
6
Achuca o Basque Cen e o Neu oscience, Leioa, Bizkaia,
Spain.
7
IKERBASQUE Basque Founda ion o Science, Bilbao, Spain
Conflic o in e es
The au ho s decla e no biomedical financial in e es s o po en ial compe ing
in e es s. The unding sou ces had no ole in he design, collec ion, analysis
and in e p e a ion o da a, w i ing o he epo , o he decision o submi he
a icle o publica ion.
Publishe ’s no e
Sp inge Na u e emains neu al wi h ega d o ju isdic ional claims in
published maps and ins i u ional a filia ions.
Supplemen a y in o ma ion The online e sion con ains supplemen a y
ma e ial a ailable a h ps://doi.o g/10.1038/s41398-021-01430-7.
Recei ed: 1 Oc obe 2020 Re ised: 26 Ap il 2021 Accep ed: 5 May 2021
Re e ences
1. Sel a aj, S., A none, D., Cappai, A. & Howes, O. Al e a ions in he se o onin
sys em in schizoph enia: a sys ema ic e iew and me a-analysis o pos mo em
and molecula imaging s udies. Neu osci. Biobeha . Re . 45, 233–245 (2014).
2. Geye , M. A. & Vollenweide , F. X. Se o onin esea ch: con ibu ions o
unde s anding psychoses. T ends Pha macol. Sci. 29, 445–453 (2008).
3. Gonzalez-Maeso, J. & Seal on, S. C. Psychedelics and schizoph enia. T ends
Neu osci. 32, 225–232 (2009).
4. Pa e son,L.M.,Ko num,B.R.,Nu ,D.J.,Pike,V.W.&Knudsen,G.M.5-HT
adioligands o human b ain imaging wi h PET and SPECT. Med. Res. Re . 33,
54–111 (2013).
5. Rasmussen, H. e al. Dec eased on al se o onin2A ecep o binding in
an ipsycho ic-nai e pa ien s wi h fi s -episode schizoph enia. A ch.Gen.Psy-
chia y 67,9–16 (2010).
6. Rasmussen, H. e al. Low on al se o onin 2A ecep o binding is a s a e
ma ke o schizoph enia? Eu . Neu opsychopha macol. 26,1248–1250 (2016).
7. E i zoe, D. e al. Co ical and subco ical 5-HT
2A
ecep o binding in neu o-
lep ic-naï e fi s -episode schizoph enia pa ien s. Neu opsychopha macology
33, 2435–2441 (2008).
8. T icha d, C. e al. No se o onin 5-HT2A ecep o densi y abno mali y in he co ex
o schizoph enic pa ien s s udied wi h PET. Schizoph . Res. 31,13–17 (1998).
9. Ngan,E.T.,Ya ham,L.N.,Ru h,T.J.&Liddle,P.F.Dec easedse o onin2A
ecep o densi ies in neu olep ic-naï e pa ien s wi h schizoph enia: a PET
s udy using [(18)F]se ope one. Am. J. Psychia y 157,1016–1018 (2000).
10. Ve hoe , N. P. e al. A oxel-by- oxel analysis o [
18
F]se ope one PET da a
shows no subs an ial se o onin 5-HT(2A) ecep o changes in schizoph enia.
Psychia y Res 99, 123–135 (2000).
11. Okubo, Y. e al. Se o onin 5-HT2 ecep o in schizoph enic pa ien s s udied by
posi on emission omog aphy. Li e Sci. 66,2455–2464 (2000).
12. Dean, B. The co ical se o onin2A ecep o and he pa hology o schizo-
ph enia: a likely accomplice. J. Neu ochem. 85,1–13 (2003).
13. Mugu uza, C. e al. Dys egula ed 5-HT(2A) ecep o binding in pos mo em
on al co ex o schizoph enic subjec s. Eu . Neu opsychopha macol. 23,
852–864 (2013).
14. Dean, B., C ossland, N., Boe , S. & Sca , E. E idence o al e ed pos - ecep o
modula ion o he se o onin 2a ecep o in schizoph enia. Schizoph . Res. 104,
185–197 (2008).
15. L’Es ade, E. T. e al. Classics in neu oimaging: he se o one gic 2A ecep o
sys em - om disco e y o mode n molecula imaging. ACS Chem. Neu osci. 9,
1226–1229 (2018).
16. Lopez-Gimenez, J. e al. Mul iple con o ma ions o na i e and ecombinan
human 5-hyd oxy yp amine
2A
ecep o s a e labeled by agonis s and dis-
c imina ed by an agonis s. Mol. Pha m. 60,690–699 (2001).
17. Ba aglia, G., Shannon, M. & Ti ele , M. Guanyl nucleo ide and di alen ca ion
egula ion o co ical S2 se o onin ecep o s. J. Neu ochem. 43,1213–1219
(1984).
18. E up, A. e al. Se o onin 2A ecep o agonis binding in he human b ain wi h
[
11
C]Cimbi-36. J. Ce eb. Blood Flow Me ab. 34,1188–1196 (2014).
19. Colom, M., Vidal, B. & Zimme , L. Is he e a ole o GPCR agonis adio ace s in
PET neu oimaging? F on . Mol. Neu osci. 12, 255 (2019).
20. Ga cía-Bea, A. e al. Se o onin 5-HT2A ecep o exp ession and unc ionali y in
pos mo em on al co ex o subjec s wi h schizoph enia: selec i e biased
agonism ia G
αi1
-p o eins. Eu . Neu opsychopha macol. 29,1453–1463 (2019).
21. Diez-Ala cia, R. e al. Big da a challenges a ge ing p o eins in GPCR signaling
pa hways; combining PTML-ChEMBL models and [
35
S]GTPγS binding assays.
ACS Chem. Neu osci. 10,4476–4491 (2019).
22. Hu lemann, R. e al. 5-HT2A ecep o densi y is dec eased in he a - isk men al
s a e. Psychopha macology 195,579–590 (2008).
23. Whi ake , P. M., C ow, T. J. & Fe ie , I. N. T i ia ed LSD binding in on al co ex
in schizoph enia. A ch. Gen. Psychia y 38,278–280 (1981).
24. Gonzalez-Maeso, J. e al. Iden ifica ion o a se o onin/glu ama e ecep o
complex implica ed in psychosis. Na u e 452,93–97 (2008).
25. Nichols, D. E. Psychedelics. Pha macol. Re . 68,264–355 (2016).
26. Kim, K. e al. S uc u e o a hallucinogen-ac i a ed Gq-coupled 5-HT
2A
se -
o onin ecep o . Cell 182,1574–1588 (2020).
27. Johnson, M. P., Siegel, B. W. & Ca , A. A. [
3
H]MDL 100,907: a no el selec i e 5-
HT2A ecep o ligand. Naunyn Schmiedebe g’sA ch.Pha macol.354, 205–209
(1996).
28. Talbo , P. S. e al. Ex ended cha ac e isa ion o he se o onin 2A (5-HT2A)
ecep o -selec i e PET adio ace
11
C-MDL100907 in humans: quan i a i e
analysis, es - e es ep oducibili y, and ulne abili y o endogenous 5-HT one.
Neu oimage 59,271–285 (2012).
29. Odagaki, Y., Kinoshi a, M., Meana, J. J., Callado, L. F. & Ga cía-Se illa, J. A. 5-HT
2A
ecep o -media ed Gα
q/11
ac i a ion in psychia ic diso de s: a pos mo em
s udy. Wo ld J. Biol. Psychia y h ps://doi.o g/10.1080/15622975.2020.1839967
(2021).
30. Lewis, D. A. & González-Bu gos, G. Neu oplas ici y o neoco ical ci cui s in
schizoph enia. Neu opsychopha macology 33,141–165 (2008).
31. Ma ín, A. e al. PET imaging o se o onine gic neu o ansmission wi h [(11)C]
DASB and [(18)F]al anse in a e ocal ce eb al ischemia in a s. J. Ce eb. Blood
Flow Me ab. 33,1967–1975 (2013).
32. De Lean, A., Munson, P. J. & Rodba d, D. Simul aneous analysis o amilies o
sigmoidal cu es: applica ion o bioassay, adioligand assay, and physiological
dose- esponse cu es. Am.J.Physiol.235,E97–E102 (1978).
33. Mo ulsky,M.J.&Ransnas,L.A.Fi ing cu es o da a using nonlinea
eg ession: a p ac ical and nonma hema ical e iew. FASEB J. 1,365–374
(1987).
34. Lal,S.,Nai ,N.P.V.,Cecy e,D.&Qui ion,R.Le omep omazine ecep o binding
p ofile in human b ain - implica ions o ea men - esis an schizoph enia.
Ac a Psychia . Scand. 87,380–383 (1993).
35. Psychoac i e D ug Sc eening P og am (PDSP) da abase. h ps://pdsp.unc.edu/
da abases/kidb.php(2021).
Diez-Ala cia e al. T ansla ional Psychia y (2021) 11:302 Page 9 o 10
