Changes in neurotransmitter levels associated with the deficiency of some essential amino-acids in the diet

B i ish Jou nul o Nui i ion (1992), 68, 409420 409 Changes in neu o ansmi e le els associa ed wi h he de iciency o some essen ial amino acids in he die BY JOSE L. VENERO, ANTONIO J. HERRERA, ALBERT0 MACHADO AND JOSEFINA CAN0 Depn amen o de Bioy hica, B oma nlogia y Toxicologia, Uni e sidnd de Se illa, C/ P~nj. Ga cia Conzulez sln, 41012-Se illu, Spain (Recei ed I1 Feb ua y 1991 -Accep ed 23 Augus 1991) The con en s o dopamine (DA) and se o onin (5-HT) and hei me aboli es we e measu ed in a subs an ia nig a and co pus s ia um ollowing die a y changes, including es ic ion o p o ein con en (low-p o ein die ; LPD) and he con en s o se e al la ge neu al amino acids (isoleucine, leucine, me hionine, phenylalanine, yp ophan and aline) o 25 d. The LPD p oduced an inc ease in he concen a ion o y osine (TYR) in he wo egions o he b ain s udied. This e ec was also obse ed wi h all amino acid de iciencies s udied excep o aline in he subs an ia nig a, yp ophan in he s ia um and phenylalanine in bo h egions. Likewise, he concen a ion o 5-hyd oxyindolace ic acid (5- HIAA), he main me aboli e o 5-HT, inc eased in he subs an ia nig a bu no in he s ia um a e LPD, as well as wi h all he amino acid de iciencies s udied, wi h he excep ion o yp ophan de iciency. In his case he e was a d ama ic e ec on all componen s o he se o onine gic sys em, wi h dec eases in he concen a ion o yp ophan (TRP ; p ecu so ), 5-HT and 5-HIAA. This beha iou clea ly shows an in e ela ionship be ween p ecu so (TRP) a ailabili y and 5-HT syn hesis and me abolism. Wi h aline de iciency, dopamine gic and se o onine gic sys ems demons a ed opposi e e ec s in he subs an ia nig a and he co pus s ia um, and he beha iou o he wo monoamines was also opposi e wi hin each s uc u e. The signi icance o hese changes is discussed. Subs an ia nig a : S ia um : Malnu i ion : Monoamines The amino acid composi ion o a p o ein, pa icula ly he essen ial amino acid po ion, is c ucial o nu i ion. Mos die a y p o eins, especially hose de i ed om ege able sou ces, a e poo in some essen ial amino acids (Schoe ield & Boo h, 1983). The in ake o hese essen ial amino acids is impo an in such unc ions as p o ein syn hesis and g ow h (S e n e ul. I976 : Wes & Kempe , 1976). Se e al amino acids a e also in ol ed in biogenic amine biosyn hesis, while o he s a e hemsel es neu o ansmi e s. The impac o p o ein malnu i ion on he b ain has been examined a di e en s ages o li e, p ima ily du ing de elopmen and ma u a ion (Winick & Rosso, 1973; Winick, 1989). The e ec o loading o de iciency o essen ial amino acids such as yp ophan, phenylalanine o y osine has also been e alua ed (Mille e al. 1976, 1977a; Du ing e al. 1989; Wes e ink & De V ies, 1991) in an e o o de e mine he esul ing impac on he syn hesis and concen a ion o neu o ansmi e subs ances (Fe ns om & Wu man, I97 1 ; Mille e al. 1977h). Howe e , li le a en ion has been ocused on he compa a i e e ec o di e en essen ial amino acid de ici s and neu o ansmi e syn hesis in adul s. Taking in o accoun he eal possibili y o malnu i ion a some ime du ing he adul s age, we s udied i s e ec on some aspec s o b ain unc ion. The p esen s udy was designed o de e mine he e ec o a die a y de iciency in some o h ps://doi.o g/10.1079/BJN19920098 Published online by Camb idge Uni e si y P ess 410 J. L. VENERO AND OTHERS he essen ial amino acids on he le el o biogenic amines ac ing as neu o ansmi e s in di e en a eas o he cen al ne ous sys em. The e ec o he biogenic amines se o onin (5-HT) and dopamine (DA), hei espec i e p ecu so s yp ophan (TRP) and y osine (TYR), and hei me aboli es 5-hyd oxyindolace ic acid (5-HIAA, 3,4-dihyd oxy- phenylace ic acid (DOPAC), 3-me hyoxy y amine (3-MT) and homo anillic acid (HVA) was in es iga ed, because i is known ha hese neu o ansmi e s a e in luenced by di e en amino acids, especially yp ophan and phenylalanine, as p ecu so s o indolamines and ca echolamines espec i ely. A he same ime, hey a e anspo ed ac oss he blood-b ain ba ie by he la ge neu al amino acid anspo sys em, so hey mus compe e wi h aline, leucine, isoleucine, y osine and me hionine o access o he ca ie -binding si e (Pa d idge, 1983). Fo hese easons hese amino acids we e selec ed. The wo egions selec ed o he s udy we e he co pus s ia um and he subs an ia nig a o he a because hey a e ex emely ich in neu o ansmi e con en , allowing measu emen o changes in hei concen a ions, and because in human pa ien s wi h a ious neu ological diso de s changes in biogenic amine le els ha e been desc ibed in hese a eas. Thus, Pa kinson’s disease is associa ed wi h a degene a ion o dopamine gic cell bodies o he pa s compac o he subs an ia nig a (Hi sch e al. 1988) and a dec ease in DA concen a ion in he s ia um (Ma sden, 1982). The nig o-s ia al sys em has also been epo ed o be in ol ed in o he neu ological diso de s. Fo ins ance, Hun ing on’s disease is associa ed wi h se e e degene a ion and cell loss in he co pus s ia um, whe e e e en neu ons o all he s ia al neu o ansmi e s a e a ec ed (Enna e al. 1977; Penney & Young, 1982; Scheel-K uge , 1986). Likewise, he e is degene a ion o he melanin-pigmen ed neu ons in he subs an ia nig a in Alzheime ’s disease (Mann e al. 1982). The e ec s we e s udied in adul a s: (1) ed on he s anda d con ol die (CD); (2) ed on a low-p o ein die supplemen ed wi h all essen ial amino acids (LPD; his die ha ing all he nu i ional equi emen s ecommended by Na ional Academy o Sciences (1978)) ; (3) ed on a low-p o ein die -supplemen ed wi h all essen ial amino acids excep one. The indings suppo he hypo hesis ha a de iciency in some o hese amino acids induces changes in biogenic amine le els. In some cases, he e is a dec ease in he concen a ion o dopamine o se o onin ha could exace ba e an incipien pa hological disease ela ed o hese le els. EXPERIMENTAL METHODS Animuls and ea men Thi y- wo male Wis a a s weighing 150-200 g and bo n in ou labo a o y we e used. Animals we e housed in eigh g oups ( ou a s pe cage) unde a 12 h ligh -da k cycle. They we e ed on a s anda d comme cial die (Panlab) un il adminis a ion o he expe imen al die s: CD, LPD and LPD wi hou one o he essen ial amino acids o be es ed. The composi ion o hese die s was as ollows. CD. This con ained (g/kg) 180 lac albumin, 220 suc ose, 440 dex in, and 1 10 a , wi h he emainde o he die composed o i amins and mine als ( a die co ec o i amin and mine als, Incole -1 ; Inco esa, Leon). The o al amino acid composi ion is shown in Table 1. LPD. This was an isoene ge ic die con aining (g/kg) 5 lac albumin, 270 suc ose, 560 dex in, and 110 a , as well as lysine 14.6, h eonine 5.0, a ginine 14.9, his idine 5.4, me hionine 4.8, isoleucine 5, leucine 7.5, phenylalanine 8.0, yp ophan 2.6, aline 6.0, wi h he emainde o he die composed o i amins and mine als. De ails o he amino acid composi ion o LPD a e shown in Table 1. h ps://doi.o g/10.1079/BJN19920098 Published online by Camb idge Uni e si y P ess EFFECT OF DIET IN NEUROTRANSMITTER LEVELS 41 1 Table 1. Amino acid composi ion (glkg) o con ol die (CD) and low-p o ein die (LPD) - ~ Amino acids CD LPD Aspa ic acid 14 5 04 Glu amic acid 16 1 04 Aldnine 32 01 A ginine 21 14 9 Cys eine 11 8 03 Phenyldlanine 80 82 Glycine 54 01 His idine 56 01 Isoleucine 12 7 53 Leucine 20 7 80 Lyaine 21 2 15 2 Me hionine 19 48 P oline 28 01 Se ine 89 02 Ty osine 88 03 Th eonine 10 I 53 Valine 86 62 ASpd dglne I9 3 05 Glu d nine 71 02 __ T yp ophan 99 29 - ~~ Expe imen a1 die s Six di e en expe imen al die s we e p epa ed. The composi ion o each die was iden ical o LPD excep o he omission o me hionine, isoleucine, leucine, phenylalanine, yp ophan o aline. Th oughou he s udy all a s we e gi en ood and wa e ad lib. The die s we e ed o 25 d be o e each expe imen . The ood in ake was eco ded daily and co ec ed o spillage. All animals we e decapi a ed be ween 10.00 and 11.00 hou s and he whole b ain was quickly emo ed. The mesencephalon was di ided in o wo pa s, wi h an incision om he en al side a he caudal bo de eminence unning pe pendicula o he long axis o he mesencephalon. The wo subs an ia nig as we e hen easily iden i ied, and dissec ed ee o he su ounding issue, including he en al egmen al a ea (A lo). The esul ing po ion was ozen in liquid ni ogen, as was a simila ly-p epa ed po ion o he s ia um. The o al ime-pe iod equi ed o isola ion o each po ion was less han 3 min. Measu emen o biogenic amines Analyses we e pe o med by means o a high-pe o mance liquid ch oma og aph equipped wi h a Kon on 420 pump wi h elec ochemical de ec ion (Bioanaly ical Sys em, LC-4B). Measu emen o he biogenic amines and hei me aboli es was pe o med acco ding o me hods desc ibed in de ail elsewhe e (Vene o e al. 1989). Typical expe imen al ch oma og ams a e shown in Fig. 1. Ch oma og ams we e eco ded on a Me ck-Hi achi in eg a o (model D-2000). Accu a e in eg a ing op ions we e equi ed o in eg a ing TYR in bo h subs an ia nig a and s ia um, and DOPAC in he s ia um. In o de o ob ain an adequa e in eg a ion o bo h me aboli es, a ail op ion was chosen o in eg a ing TYR, and a pe pendicula d op o DOPAC. h ps://doi.o g/10.1079/BJN19920098 Published online by Camb idge Uni e si y P ess 412 J. L. VENERO AND OTHERS 4 2 I 3 Fig. 1. Ch oma og ams o dopamine (DA), se o onin (5-HT) and hei me aboli es om: (A) a s ia al issue a e 25 d on a low-p o ein die ; (B) a s ia al issue a e 25 d on a yp ophan-de icien die . J, injec ion peak; 1, y osine; 2, dopamine; 3, 3,4-dihyd oxyphenylace ic acid : 4, 5-hyd oxy-3-indolace ic acid; 5, 3-me h- oxy y amine; 6, 5-HT; 7, homo anillic acid; 8, yp ophan. Fo de ails o die s, see pp. 41041 1 and Table 1. S a ly ical analysis Biogenic amine con en s om animals ed on CD and LPD we e compa ed using S uden ’s es . Da a om LPD and he di e en amino acid-de icien die s we e analysed by means o one-way analysis o a iance (ANOVA). Obse ed mean di e ences we e e alua ed using he Sche ee es (pa ame ic es ). Food in ake and body-weigh loss we e compa ed using S uden ’s es . RESULTS Food in ake and hody-weigh loss The e we e no signi ican di e ences in ood in ake (g/animal pe d) be ween CD and LPD and he di e en expe imen al die s: CD 16.7 (SE 1.4), LPD and expe imen al die s 15.2 (SE 1.4). The e we e no di e ences in body-weigh loss (YO): CD 10.6 (SE 0.9), LPD and expe imen al die s 13.2 (SE 2.1). The ac ha all ea men s led o a ce ain deg ee o body- weigh loss could be a ibu ed o he low pala abili y o he die s. This is suppo ed by he inding ha he highes loss a e was eco ded du ing he i s week o he ea men s. Howe e , om day 8 o 25 (be o e dea h) he espec i e body-weigh s emained almos unchanged. E ec o LPD on neu o ansmi e le els The e we e no signi ican changes in he se o onine gic sys em, excep o 5-HTAA which inc eased in he subs an ia nig a wi h LPD when compa ed wi h CD (38.0%; P < 0.01 ; Table 2). Mo eo e , li le change was ound in he concen a ion o 5-HT in he wo egions a e LPD, bu he e was an inc ease in he subs an ia nig a and a dec ease in he s ia um. Wi hin he dopamine gic sys em, an inc ease in he concen a ion o TYR a e LPD was seen in bo h s uc u es (42.2% in he subs an ia nig a, 25.4% in he s ia um; P < 0.01; Tables 3 and 5). h ps://doi.o g/10.1079/BJN19920098 Published online by Camb idge Uni e si y P ess EFFECT OF DIET IN NEUROTRANSMITTER LEVELS 413 Table 2 E lec s o a iou die s on he concen a ion (ng/g we issue) o se o onin (5- HT) and i s me aboli es in he subs an ia nig a o a s HIAA SEM 18 7, d 23) (The combined SEM and d o each compound we e TRP SEM 54 2, d 21, 5-HT SEM 48 7, d 21, 5- ~ ~ ~ ~~~~~~____~ ~ -~ ~~~~~~ ______________~ Die ? TRP 5-HT 5-HIAA ___.- ~ __ ______~~____ ~~ CD 3386 4 2018 4 452 4 LPD 35189 2164 9 624 51 LPD de icien in Isoleucine 3344 I 2001 8 582 4 Leucine 3727 9 1811 5** 6408 Me hionine 3312 8 17037** 6277 Phenylalanine 3344 3 18195* 6423 T yp ophan 1731 9** 1051 4** 250 I** Valine 3526 9 17145** 5757 __ ~ ~ -~ ____ ~ ~~~_____ ~~-~ ~ ~ ~ ~ __ ________~. ~~ ____~ CD, con ol die , LPD, low-p o ein die , TRP, yp ophan, 5-HIAA, 5-hyd oxyindolace ic acid Mean alues o amino acid-de icien die s we e signi ican ly di e en om hose o LPD (one-way analysis o a iance ollowed by Sche ee es ) * P < 0 05, ** P < 0 01 Fo de ails o die s, see pp 41041 1 and Table I Mean alue o LPD was signi ican ly di e en om ha o CD (S uden ’s es ) 1 P < 0 01 Table 3. E ec s o a ious die s on he concen a ion (ng/g we issue) o dopamine (DA) and i s me aboli es in he subs an ia nig a o a s (Thecombineds~~andd o eachcompound we e:TYRs~~212.1,d 21; DASEM 18.1,d 21;DOPAC SEM 3.6. d 21 ; 3-MT SEM 2.6, d 21 ; HVA SEM 46, d 21) . .~ - ~~~ --.-- . - ___ ___~._____..._____ ~~ .~ ~~ ~- ~ ~~-_____ Die ? TY R DA DOPAC 3-MT HVA CD 6083.2 7105 102.2 51.1 130.5 LPD 8655,6$ 769.7 98.0 47.8 138.7 ___________.____ ~~ __.__~~ LPD de icien in: Isoleucine 8053.0 572.7** I1 1.7 56.9 109.8* Leucine 10803.6** 649.0* 139.8** 50.0 131.7 Me hionine 8 767.4 762.7 115.7 51.5 124.3 T yp ophan 7 905.2 584.9** 110.7 53.7 131.5 Valine 7 108* 838.8 139.5** 5 .6 178.9** Phenylalanine 6813.5** 550.2** 80.8 509 119.1 ~ .~ ~~ ___ __~ ~~~ ~~~.~.____~ ~~ ~~ ~~ ~ ~ ___.______~~__~ CD, con ol die ; LPD, low-p o ein die : TYR, y osine; DOPAC, 3.4-dihyd oxyphenylace ic acid; 3-MT, 3- Mean alues o amino acid-de icien die s we e signi ican ly di e en om hose o LPD (one-way analysis 1- Fo de ails o die s, see pp. 41041 1 and Table I. Mean alue o LPD was signi ican ly di e en om ha o CD (S uden ’s es ): $ P < 04,)l. me hoxy y dmine ; HVA, homo anillic acid. o a iance ollowed by Sche ee es ): * P < 0.05, ** P < 0.01. Subs an ia nig a sdeucin de ici . This de ici had no e ec on he se o onine gic sys em. Wi hin he dopamine gic sys em his de ici was associa ed wi h a dec ease in he concen a ions o DA (-25.6%; P < 0.01) and HVA (-21.0%; P < 0.05) compa ed wi h ha o LPD (Table 3). Leucine de ici . Compa ed wi h LPD his de ici induced a dec ease in he concen a ion o 5-HT (-16.3%, P < 0.01; Table 2). The 5-HIAA: 5-HT a io was also inc eased compa ed wi h ha ob ained wi h LPD (20.6 %). Wi h espec o he dopamine gic sys em, 15 NUT 68 h ps://doi.o g/10.1079/BJN19920098 Published online by Camb idge Uni e si y P ess 414 J. L. VENERO AND OTHERS he e was an inc ease in he concen a ions o TYR and DOPAC when compa ed wi h hose ob ained wi h LPD (24.8 and 41.8 YO o TYR and DOPAC espec i ely; P < 0.01 ; Table 3), whe eas DA concen a ions dec eased (- 15.6 YO, P < 0.05 ; Table 3). The e lux o DA, quan i ied as D0PAC:DA a io (Al a e al. 1987), was also inc eased compa ed wi h ha ob ained wi h LPD (69.2 YO). Me hionine dejici . This de ici caused a dec ease In he concen a ion o 5-HT when compa ed wi h ha ound wi h LPD (-21.3 YO; P < 0.01 ; Table 2). Howe e , he e lux o 5-HT, measu ed as 5-HIAA:5-HT a io, inc eased wi h espec o LPD (27.5%). No s a is ical change was de ec ed in he dopamine gic sys em a e his de ici . Phenylulunine de ici . De ici o his amino acid caused a dec ease in he concen a ion o 5-HT when compa ed wi h ha ob ained wi h LPD (- 15.9%; P < 0.05; Table 2). The u no e o 5-HT, measu ed as 5-HIAA : 5-HT a io, inc eased compa ed wi h ha ound wi h LPD (20.6 YO). Wi hin he dopamine gic sys em he e was a signi ican dec ease in he concen a ions o TYR (-21.2%; P < 0.01) and DA (-28.4%; P < 0.01) compa ed wi h hese ob ained wi h LPD (Table 3). T yp ophan de ici . This de ici had a d ama ic e ec on all componen s o he se o onine gic sys em, showing a ela ionship be ween p ecu so a ailabili y and 5-HT syn hesis. Thus, he e was a dec ease in he concen a ions o TRP (- 50.7 YO), 5-HT (- 5 1.4 "/o) and 5-HIAA (- 59.9 YO ; P < 0.0 I) compa ed wi h hose ob ained wi h LPD (Table 2). Wi h espec o he dopamine gic sys em his de ici dec eased he concen a ion o DA wi h espec o LPD (-24.0%; P < 0.01 ; Table 3); he D0PAC:DA a io was inc eased compa ed wi h ha ob ained wi h LPD (46.1 %). Valine de$ci . This de ici caused a dec ease in he concen a ion o 5-HT when compa ed wi h ha o LPD (-20.8%, P < 0.01) (Table 2). Wi hin he dopamine gic sys em he concen a ions o DOPAC and HVA we e inc eased compa ed wi h hose ob ained wi h LPD (42.3 YO o DOPAC and 28.9 YO o HVA; P < O.Ol), and ha o TYR dec eased (- 17.8 O/O ; P < 0.05 ; Table 3). Mo eo e , he DOPAC : DA a io was inc eased compa ed wi h ha ound wi h LPD (30.7%). S ia um Isoleucine de ici . This de ici had no e ec on he se o onine gic sys em. Wi hin he dopamine gic sys em, only HVA concen a ion dec eased compa ed wi h ha ob ained wi h LPD (- 32.9 YO ; P < 0.01 ; Table 5). Leucine de ici . De ici o leucine caused a dec ease in he concen a ion o 5-HT compa ed wi h ha ob ained wi h LPD (- 24.8 YO, P < 0.05 ; Table 4). In he dopamine gic sys em he e was an inc ease in he concen a ions o TYR and DOPAC compa ed wi h hose ound wi h LPD (83.4 YO o TYR and 42.7 YO o DOPAC; P < O.Ol), and a dec ease in HVA ( - 10.8 % ; P < 0.0 1 ; Table 5); he DOPAC : DA a io was inc eased compa ed wi h ha wi h LPD (31.2%). Me himine de ici . De ici o me hionine caused only a dec ease in he TRP concen a ion compa ed wi h ha ob ained wi h LPD (-25.6%, P < 0.01) in he se o onine gic sys em (Table 4). In he dopamine gic sys em he e was a dec ease in he concen a ions o TYR (- 27.6 YO, P < 0.05) and HVA (- 22.7 YO, P < 0.01) when compa ed wi h hose o LPD (Table 5). Phenylalanine de ici . This de ici only had an e ec on he dopamine gic sys em. Thus, he e was a dec ease in he concen a ions o TYR (-33.7 %, P < 0.01) and HVA compa ed wi h hose o LPD (-21.3Y0, P < 0.01; Table 5). These esul s we e accompanied by an inc eased DOPAC : DA a io wi h espec o LPD (25.0 %). T yp ophan de ici . This de ici , as o he subs an ia nig a, had a ma ked in luence on all he componen s o he se o onine gic sys em. Thus, he e was a dec ease in he h ps://doi.o g/10.1079/BJN19920098 Published online by Camb idge Uni e si y P ess EFFECT OF DIET IN NEUROTRANSMITTER LEVELS 415 Table 4. E ec s o a ious die s on he concen a ion (ng/g we issue) o se o onin (5-HT) and i s me aboli es in he s ia um o a s (The combined SEM and d o each compound we e: TRP SEM 134.6, d 21; 5-HT SEM 39.7, d 22; 5-HIAA SEM 10.5, d 24) ~~ . ~~~ ._ ~ ~ ~ ___~_________________ Die TRP 5-HT 5-HIAA .~ ~~ ____~ ~ ~__.___._______~ CD 4623.7 1056.4 28 1.8 LPD 4677.3 9 10.6 301.6 LPD de icien in : Isoleucine 3994.4 1131.2 3 15.2 Leucine 4961.1 684.3* 256.9 Me hionine 3476.6** 1021.5 295.2 Phenylalanine 4437.9 843.5 288.6 T yp ophan 2440.6** 5663** 135,9** Valine 4895.7 1169,2* 290.2 ~____~ ~____~.~~ ~~~~~ ~ ~~~ ~ ~________.____.~~.~-~.-~.~~- ~~ CD, con ol die : LPD, low-p o ein die : TRP, yp ophan ; 5-HIAA, 5-hyd oxyindolace ic acid. Mean alues o amino acid-de icien die s we e signi ican ly di e en om hose o LPD (one-way analysis Fo de ails o die s, see pp. 41041 I and Table 1. o a iance ollowed by Sche ee es ): * P < 0.05; ** P < 0.01, Table 5. E lec s o a ious die s on he concen a ion (ng/g we issue) o dopumine (DA) and i s me aboli es in he s ia um o u s (The combined SEM and d o each compound we e: TYR SEM 376.4, d 21 ; DA SEM 396.7, c 24: DOPAC SEM 83.2, d 23; 3-MT SEM 22.8, d 24; HVA SEM 25.8, d 23) ~~ ~~ ~~~~ ~. ~~~~~ ~ ~~ ~~ .~ ~___ _____.~~..~..~_____~ ~ Die TYR DA DOPAC 3-MT HVA ~~ ~~ ~~~ ~. CD 5 950.8 12 220.4 1903.4 547.1 889.7 LPD 7466.7$ 12599.9 1989.3 549.9 882.0 LPD de icien in : Isoleucine 6 646.0 10548.2 2170.4 505.9 591.2** Leucine 13 693,0** 13 606.6 2839.8** 640.1 786.0** Me hionine 5402.3 1 1208.6 21 17.7 649.9 681,8** Phenylalanine 4944.6** 10844.9 2112.5 518.1 694.3** T yp ophan 6682.4 1228 1.0 1987.2 582.7 586.0** Valine 7 502. I 83990** I482.8** 412.2** 414.5** ~~~ ~ - ~~~~~ ~ ~ ~~ ~. ~~ ~~ CD, con ol die ; LPD, low-p o ein die ; TYR, y osine; DOPAC, 3,4-dehyd oxyphenylace ic acid; 3-MT, 3- Mean alues o amino acid-de icien die s we e signi ican ly di e en om hose o LPD (one-way analysis Fo de ails o die s, see pp. 41041 1 and Table 1. Mean alue o LPD was signi ican ly di e en om ha o CD (S uden 's c es ): $ P < 0.01. me hoxy y amine ; HVA, homo anillic acid. o a iance ollowed by Sche ee es ) : * P < 0.05, ** P < 001. concen a ion o TRP (-474 YO), 5-HT (- 55.1 %) and 5-HIAA (- 55.1 YO; P < 0.01 ; Table 4). In con as o he se o onine gic sys em, in he dompamine gic sys em he e was only a dec ease in he HVA concen a ion, compa ed wi h ha ob ained wi h LPD (- 33.5 % ; P < 0.01) (Table 5). Vulinp de ici . Wi hin he se o onine gic sys em, only an inc ease in 5-HT concen a ion compa ed wi h LPD was de ec ed (28.3 '4 ; P < 0.05 ; Table 4). In he dopamine gic sys em he e ec was opposi e o ha seen in he subs an ia nig a ollowing his de ici . Thus, excep TYR, he concen a ions o all componen s o his neu o ansmi e sys em we e 15-2 h ps://doi.o g/10.1079/BJN19920098 Published online by Camb idge Uni e si y P ess 416 J. L. VENERO AND OTHERS dec eased wi h espec o LPD: DA -33.3 %, DOPAC -25.4%, 3-MT -25.0% and HVA -53.0% (P < 0.01 ; Table 5). DISCUSSION We ha e s udied he changes in neu o ansmi e con en in adul animals ed on die s de icien in some essen ial amino acids o a sho pe iod o ime (25 d). This si ua ion may be ound in some pa hological condi ions and may be impo an in olde pe3ple. Thus, wi h age he e is an inc ease in he appea ance o some pa hological diseases such as Pa kinson’s, ela ed o he concen a ion o a ious neu o ansmi e s in di e en a eas o he cen al ne ous sys em. I he s a e o malnu i ion a ec s he neu o ansmi e con en i could mean an enhancemen o he isk o his kind o disease. The low-p o ein die supplemen ed wi h all essen ial amino acids me all he ecommended nu i ional equi emen s (Na ional Academy o Sciences, 1978) ; his is con i med by he low le el o e ec ound on he concen a ions o he biogenic amines in bo h egions s udied. Howe e , cau ion mus be exe cised because some di e ences be ween CD and LPD we e de ec ed These include a s a is ical inc ease in he concen a ion o TYR in bo h egions, and o 5-HIAA in he subs an ia nig a. O he changes, al hough no s a is ically signi ican , we e hose ound o 5-HT in bo h egions, wi h an inc ease in one and a dec ease in he o he . O he changes ound, only ha o TYR appea ed o be ela ed o he low die a y p o ein con en , since simila e ec s we e ound in he wo egions s udied which was con a y o he changes seen in he se o onine gic sys em. Wi h he a ailable in o ma ion i is di icul o explain he di e ences in TYR concen a ion be ween CD and LPD. Taking in o accoun ha phenylalanine does no ac as a p ecu so o TYR in he cen al ne ous sys em ( he e is no phenylalanine hyd oxylase (EC 1.14.16.1) ac i i y in he b ain), he inc ease seen in TYR wi h LPD could be ela ed o a majo e lux o TYR o he b ain ia he la ge neu al amino acid anspo sys em. Fo his o occu , ni ogen om essen ial amino acids would be necessa y o syn hesize non-essen ial amino acids, including TYR, o i is possible ha phenylalanine is con e ed enzymically o y osine by phenylalanine hyd oxylase, in pe iphe al issues, o bo h. The la e possibili y seems o be plausible because o he simila i y in he phenylalanine con en in CD and LPD (see Table I). E ec o sonie essen id amino mid de$ciencies in he se o onine gic sys em Die a y de iciency a ec ed 5-HT me abolism in bo h egions s udied, being mo e ob ious in he subs an ia nig a. No able was he inc ease in he concen a ion o 5-HIAA in he subs an ia nig a. A simila e ec was ound in his s uc u e in isoleucine-de icien a s, and in ensi ied in leucine, me hionine and phenylalanine de iciencies. Mo eo e , wi h he la e ea men s he inc ease in 5-HIAA was also accompanied by a signi ican dec ease in he concen a ion o 5-HT wi h espec o CD and LPD. The di e en egional e ec s on 5-HT me abolism associa ed wi h he di e en amino acid de iciencies could be due o he di e en o igins o he 5-HT. The 5-HT in he subs an ia nig a comes p incipally om he neu onal cell bodies and e minals (Fuxe, 1965; Unge s ed , 1971; Olsen & Seige , 1972), whe eas in he s ia um i comes only om aphe nuclei e minals (Bobillie e al. 1976; Van de Kooi, 1979). The dec ease in 5-HT con en could be due o an accele a ion o 5-HT u no e such as ha desc ibed in se o onine gic ne e e minals inju ed by 5,7- dihyd oxy yp amine (S achowiak e al. 1986). In he la e condi ion he le els o 5-HT and 5-HIAA we e educed in he hippocampus and sep um a e he lesion. Howe e , as he magni ude o his dec ease was much lowe o 5-HIAA con en , he 5-HIAA: 5-HT a io was inc eased. As 5-HIAA is he majo me aboli e o 5-HT in he b ain, an inc ease h ps://doi.o g/10.1079/BJN19920098 Published online by Camb idge Uni e si y P ess EFFECT OF DIET IN NEUROTRANSMITT’ER LEVELS 417 in he 5-HIAA: 5-HT a io may indica e an accele a ed u no e o 5-HT. This possibili y is suppo ed by a p e ious epo ha o ma ion o 5-[’H]HIAA om [3H]TRP in he medulla and spinal co d inc eased a e 5,7-dihyd oxy yp amine adminis a ion (Ge son & Baldessa ini, 1974). In he p esen s udy a simila e ec was also ound in he s ia um when he e was a leucine o aline de iciency. These indings sugges ha in a s ed on LPD b ain p o ec ion dec eases somewha , especially in he subs an ia nig a. The lack o p o ec ion was mo e signi ican when he e was a de iciency in leucine, nie hionine o phenylalanine. These indings a e simila o hose ob ained by inducing di e en kinds o damage (Ge son & Baldessa ini, 1974; S achowiak e a/. 1986). I we ela e he magni ude o he damage o he inc ease in he 5-HTAA : 5-HT a io, i is highes wi h he me hionine- de icien die . This ac may be ela ed o he ole o me hionine, since his is a sulphu - con aining essen ial amino acid which is in ol ed in he syn hesis o cys eine. Cys eine is a undamen al componen o he pep ide glu a hione. This pep ide cons i u es he majo non-p o ein sulphu a ed componen o all o ganisms and is in ol ed in se e al impo an p ocesses including de oxi ica ion (Sies e al. 1983) and he oxida i e me abolism o cen al ca echolamines (Ho he sall e ul. 1982). Thus, glu a hione is undamen al in main aining he cellula edox s a e (Reed e al. 1983). A de ici o me hionine p oduces a ma ked dec ease in hepa ic glu a hione concen a ion and should a ec b ain glu a hione concen a ion, al hough o a lesse ex en . This e ec may also be he esul o a dec ease in p o ec ion agains oxida i e damage as has been epo ed in a i amin E-de icien die (A. Cas aEo, J. Cano & A. Machado, unpublished esul s). This may be impo an since li le is known abou he mechanisms behind he degene a i e p ocess leading, o example. o Pa kinson’s disease, bu i has been sugges ed ha oxic species e ol ed om he ca abolism o ca echols may be in ol ed in he pa hogenesis (Cohen, 1983; Fo ns ed e al. 1990). A de ici o yp ophan a ec ed 5-HT me abolism in bo h egions s udied (5-HT and i s me aboli e 5-HIAA dec eased). Since 5-HT in he b ain is syn hesized om he essen ial amino acid TRP, hese esul s a e in acco dance wi h he ac ha he a e o 5-HT syn hesis in he b ain depends on he a ailabili y o his p ecu so (Fe ns om & Wu man, 1971 ; Ca lsson & Lindq is , 1978). Nume ous expe imen s ha e demons a ed ha an inc ease in b ain TRP no only inc eases he a e o 5-HT syn hesis bu also inc eases he whole-b ain concen a ion o 5-HIAA (Fe ns om & Wu man, 1971). Thus, a dec ease in TRP concen a ion may be expec ed o p oduce a dec ease in 5-HIAA. This inding may be impo an since, in some illnesses such as oxici y, TRP is adminis e ed as a sca enge (Gomez-Reino e a . 1983) wi hou knowing he e ec o his ea men on he ee plasma TRP and subsequen TRP and 5-HT concen a ions in he b ain. Besides, li le is known abou whe he adicals can oxidize TRP and how his would a ec 5-HT concen a ion. Howe e , om he amino acid composi ion o CD and LPD (9.9 g TRP in CD and 2.9 g in LPD), only a la ge educ ion in he TRP con en o he die (i.e. 0.3 g TRP in he TRP- de icien die ) may lead o a deple ion o he TRP pool in he b ain. The e ec s o he aline-de icien die we e unusual. In he subs an ia nig a he e ec on he se o onine gic sys em was simila o ha ound wi h o he amino acid de iciencies, being he e e se o ha in he s ia um (5-HT concen a ion dec eased in he subs an ia nig a and inc eased in he s ia um). E ec o some essen ial amino acid d@iencies in he dopamine gic sys em When he ca echolamine le els we e s udied he e was a no able inc ease in TYR concen a ion a e he adminis a ion o each o he p o ein-de icien die s in bo h egions s udied. This e ec was p oduced by LPD and i was main ained in all amino acid de iciencies s udied wi h he excep ion o he phenylalanine-de icien die . The maximum h ps://doi.o g/10.1079/BJN19920098 Published online by Camb idge Uni e si y P ess