Increased dopamine and norepinephrine concentrations in primate CSF following amphetamine and phenylethylamine administration

Brain Research, 186 (1930) 469473 O Elsevier/North-Holland Biomedical Press

469

Increased dopamine and norepinephrine concentrations in primate CSF following amphetamine and phenylethylamine administration M A R K , J. PERLOW, C. C. CHIUEH, C. R A Y M O N D LAKE and R I C H A R D JED WYATT

Laboratory of Clinical Psychopharmacology, Division of Special Mental Health Research, Intramural Research Program, National Institute of Mental Health, Saint Elizabeths Hospital, Washington, D.C. 20032 and ( C.C.C. and C.R.L.) Laboratory of Clinical Science, National Institute of Mental Health, Bethesda, Md. (U.S.A.) (Accepted November 29th, 1979)

Key words: dopamine - - norepinephrine - - CSF - - amphetamine - - phenylethylamine

The psychotic behavior observed in individuals following the administration of large doses of amphetamine (AMPHET) is similar to the psychotic behavior of paranoid schizophrenics 2,5. This similarity has prompted investigators to use AMPHET-induced behavioral abnormalities in animals as a model of acute psychosis 19, and to seek endogenous compounds that have AMPHET-like activity in psychotic individuals. Phenylethylamine (PEA) has been suggested as one such potential psychotogen 17,21. It is present in animal and human nervous tissue s,la,21 and, in at least some studies, has been shown to be excreted in greater than normal amounts in the urine of some schizophrenic patientsT, 16. Phenylethylamine's similarities to A M P H E T are great: (1) although shorter acting, PEA-induced behavioral abnormalities are in many respects identical to those produced by AM PH ET administration 3,10,12,20; (2) structurally A M P H E T is a-methylated PEA; (3) A M P H E T - and PEA-induced behaviors are blocked by neuroleptics6,19,21; and (4) both PEA and A M P H E T increase the utilization of catecholamines by promoting synaptic release and inhibiting reuptake6,18. Here we demonstrate in the waking primate that A M P H E T and PEA significantly increase the concentration of dopamine (DA) and norepinephrine (NE) the cerebrospinal fluid (CSF), and that this increase corresponds to the relative duration of action of the two compounds. Adult, male, rhesus monkeys (5.5-6.5 kg, n = 4) were adapted to chronic restraint in primate chairs in sound-attenuated chambers with the lights on from 06.00 to 18.00 h, and off from 18.00 to 06.00 h. In all animals a polyethylene catheter was inserted, percutaneously, between lumbar vertebra into the subarachnoid sFace. The catheter was advanced such that the open end stopped in the high cervical or cisternal subarachnoid space. CSF was withdrawn continuously (approximately 1 ml/h) from the awake animal by a peristaltic pump and automatically collected into polypropylene tubes as 3 h fractions. CSF remained at room temperature in the collecting tubing

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Fig. 1. Effect of amphetamine (AMPHET) (0.75 mg/kg, i.m.) and saline on the concentration of D A and NE in the CSF of rhesus monkeys, (n - 4). The baseline value (100K) is the mean of the concentrations of the - - 6 to - - 3 h and --3 to 0 h samples of the saline-treated animals. The arrow indicates the time (0 h) the drugs were administered. Using a Student's t-test: (*) indicates P < 0.05 and (**) indicates P < 0.005 as compared with control value at the same time period.

tor approximately 2 h before refrigeration at 4 °C. The refrigerated samples were removed every 24 h and stored at --70 °C until assayed. Each 3 h sample was collected in tubes containing 0.2 ml of a stabilizing solution composed of one part concentrated perchloric acid and one part of a solution with 19)~o E G T A (ethyleneglycol-bis-(amino-ethylether) N, N-tetraacetic acid), 1.2 ~ MgCIz4H20 in 2 M Tris-HCl buffer (pH 9.6). The samples were assayed for DA and NE by a radioenzymatic paperchromatographic method 4. The mean ( ± S.E.M.) CSF concentration of NE and DA prior to drug administration (--3 to 0 h) was 232 ± 37 and 149 ~ 11 pg/ml respectively. The administration of a dose of A M P H E T (0.75 mg/kg, i.m. Sigma, St. Louis) similar to what might be used by an abuser of the drug al produced an immediate increase in the concentration of NE and DA to 177°/o and 126~ of pre-drug concentrations, respectively. These elevated concentrations persisted with little change over the subsequent 12 h. The slight increase in locomotor activity lasted for at least 6 h (period of observation was limited by the onset of the dark period). The administration of 75 mg/kg of PEA (i.m., Regis Chemical, Morton Grove, Ill.) caused an immediate increase in the

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Fig. 2. Effect of phenylethylamine (PEA) (75 mg/kg and 150 mg/kg, i.m.) and saline on the concentration of D A and NE in the CSF of rhesus monkeys, (n -- 4). The baseline value (100 %) is the mean of the concentration of the - - 6 to - - 3 h and - - 3 to 0 h samples of the saline-treated animals. The arrow indicates the time (0 h) the drugs were administered. Using a Student's t-test: (*) indicates P < 0.05 and (**) indicates P < 0.005 as compared with control value at the same time period.

concentration of NE and DA to 396 ~ and 233 ~ ofpre-drug concentrations, respectively. The elevated levels fell rapidly after drug injections, so that by 6 h for DA, and 9 h for NE, CSF concentrations were within the normal limits. Behaviorally, this dose of PEA was able to initiate an increase in visual searching behavior (checking) that lasted less than one hour 2°. At a higher dose, PEA (150 mg/kg) markedly increased NE and DA concentrations in the CSF, 2213 ~ and 690 ~ ofpre-drug concentrations at 0 to 3 h, respectively. Lower, but still elevated, levels persisted for 9-12 h. This dose of PEA markedly increased total body locomotor activity for the period of observation, with maximal activity occurring 1-3 h following drug administration. By measuring the concentration of NE and DA in the CSF rather than by measuring the concentrations of their metabolites, we have been able to demonstrate that A M P H E T and PEA increase the release of catecholamines in the brain of an awake primate. Using a dose of A M P H E T more than 10 times higher than the one used here, Baker and Ridley 1were unable to demonstrate any increase in the concentration of the DA metabolite, homovanillic acid (HVA), in the CSF; an increase in HVA was, however, observed 4-10 h after A M P H administration in animals pre-

472 treated with probenecid. The causes for this a p p a r e n t discrepancy are discussed in earlier p u b l i c a t i o n s 14. In a d d i t i o n to the issues previously addressed it is recognized that A M P H E T has slight i n h i b i t o r y effect on m o n o a m i n e oxidase 6 which could delay or prevent the f o r m a t i o n o f H V A as well as slow the b r e a k d o w n of D A and NE. It seems, from our experience, that m e a s u r e m e n t s o f N E a n d D A in the C S F , in c o n t r a s t to their metabolites, are sensitive indicators o f catecholamine release14,15. In previous p u b l i c a t i o n s we were able to d e m o n s t r a t e a daily r h y t h m int he concentration o f N E and H V A in ventricular CSF14,15. These c o m p o u n d s were released into the C S F from the ventricular surfaces near the tip o f the intracranial cannula. The absence o f any r h y t h m in the c o n c e n t r a t i o n o f N E a n d D A in this study is p r o b a b l y s e c o n d a r y to the catheter tip's location in the cisternal-cervical space. In this position the circadian elevations and troughs were p r o b a b l y blunted as a result o f mixing o f C S F in the ventricular a n d the s u b a r a c h n o i d spaces. In conclusion PEA and A M P H E T cause the release o f N E and D A into the C S F in the a w a k e rhesus monkey. The time course o f the change in the CS F c o n c e n t r a t i o n of these catecholamines corres p o n d s to the relative d u r a t i o n o f action o f P E A and A M P H E T . This in turn suggests t h a t the release o f catecholamines accounts for some o f the behavioral effects o f the two c o m p o u n d s z,9. While the lower dose o f P E A is 100 times greater than A M P H E T , the increases in N E a n d D A were less t h a n after A M P H E T . A l t h o u g h presently unknown, this difference m a y be related to the fact t h a t P E A is readily m e t a b o l i z e d by m o n o a m i n e oxidase 21. P E A could be m e t a b o l i z e d by muscle, liver, b l o o d etc. long before it gets into the brain. A M P H E T is not a g o o d substrate for M A O (see ref. 6). I f A M P H E T ' s m e c h a n i s m o f action is t h o u g h P E A (see ref. 3) it still m a y be a localized mechanism.

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