Peptides. Vol. 7, pp. 11-13, 1986. © Ankho International Inc. Printed in the U.S.A. 0196-9781/86 $3.00 + .00

The Effect of fl-(Tyrg)Melanotropin-(9-18) on Active Avoidance Behavior,

Electroconvulsive Shock-Induced Amnesia and T-Discrimination

Learning of Rats

G Y U L A T E L E G D Y , L , ~ S Z L 0 Vt~CSEI, I B O L Y A B O L L O K A N D A N D R E W V. S C H A L L Y *

Department o f Pathophysiology, University Medical School, Szeged, P.O.B. 531, H-6701, Hungary *Endocrine and Polypeptide Laboratory, Veterans Administration Medical Center

and Tulane University School o f Medicine, New Orleans, LA

Rece ived 21 F e b r u a r y 1985

TELEGDY, G., L. VI~CSEI, I. BOLLOK AND A. V. SCHALLY. The effi'ct offl-(Tyra)melanotropin-(9-18) on active avoidance behavior, electroconvulsive shock-induced amnesia and T-discrimination learning of rats. PEPTIDES 7(1) 11-13, 1986.--The effect of fl-(Tyrg)melanotropin-(9-18) was investigated on active avoidance behavior, electroconvul- sive shock (ECS)-induced amnesia and T-discrimination learning in rats. The decapeptide inhibited the extinction of active avoidance behavior. It was also able to block ECS-induced amnesia if the treatment was performed immediately, or 4 hr or 20 hr after the ECS. In the T-discrimination paradigm the peptide facilitated spatial discrimination learning and reversal learning. These results suggest that/3-(Tyrg)melanotropin-(9--18) can influence learning and memory processes in different behavioral tests.

/3-(Ty&)MSH~ ,~ Avoidance behavior Amnesia T-discrimination learning

fl-(Tyrg)MELANOTROPIN-(9-18) was isolated by Schally and coworkers [6] from pig hypothalami, and was shown to have the following sequence: H-Tyr-Phe-Arg-Trp-Gly-Ser- Pro-Pro-Lys-Asp-OH. The peptide exerted some MSH-like activity on frog skin, but was ineffective on pituitary quar- ters in releasing ACTH, GH, LH, FSH, TSH. It did cause stimulation of pituitary prolactin release, but had no lypoly- tic or opioid activity [6].

Our earlier experiments showed that the decapeptide al- ters brain transmitter levels [3], influences dopaminergic mechanisms [9,11], antagonizes morphine-induced analgesia [8] and increases passive avoidance latency [10]. All these experiments indicated that the decapeptide is effective in influencing brain functions. Furthermore, the passive avoidance experiment suggested that the peptide might also act on memory processes.

In these experiments the effects of two different doses of the decapeptide on active avoidance behavior and ECS- induced amnesia were studied. It was proposed that a-MSH acts to increase attention to stimuli, based on findings that a-MSH increases the rate of learning of reversals on two- choice discrimination problems [5]. In the third part of the present study the effect of the decapeptide (which is closely related to fl-MSH) on T-discrimination learning was investi- gated.

METHOD

Peptide: fl-(Ty&)melanotropin-(%18) was synthetized by a solid-phase method [6].

Subjects

Experiments were performed on male CFY rats weighing 160-180 g. They were kept under a standard 12 hr illumina- tion schedule (light on 6.00 a.m.). Food and water were available ad lib. All experiments started at 8.00 a.m.

Surgical Method

The animals were anesthetized with pentobarbital-Na (Nembutal, 35 mg/kg IP) and a cannula was placed into a lateral cerebroventricle and fixed to the skull with dental cement. The rats were used after a recovery period of 5 days. The correct positioning of the cannula was checked by dis- section of the brain.

Behavioral Methods

Active avoidance behavior. Active avoidance condition- ing was performed in a platform jumping conditioning appa- ratus [7].

The conditional stimulus (CS) was the light of a 40 W

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FIG. I. Effects of/3-(TyrS)MSH~ ~ on active avoidance behavior, k~ control (4/xl saline ICV); • /3-(Tyr'~)MSH, t~ (1 p,g/4 /*1 ICV): • /3-(TyrS)MSH:~ .s (4 /zg/4 /*1 ICV). ( ) Number of animals used. + p<0.05 (M.W. test), + + - p < 0 . 0 2 (M.W. test), O=p<0.05 (K.W. test), OO=p<0.02 (K.W. test).

electr ic bulb, while the uncondit ional stimulus (US) was an electr ic shock of 0.2 mA del ivered through the grid f loor of the apparatus to the paws of the rat. Each day for three consecu t ive days, 10 trials were performed, at an interval of 60 sec. On the fourth day ext inct ion trials were run and the US was no longer applied. The CS was presented for a max imum of 10 sec, or it was terminated as soon as the animal made the response. Animals which made at least 8 condit ional avoidance responses out of 10 trials in the first ext inct ion session were used for fur ther exper iments . These animals were al located to different groups (control, 1 /xg/4 /zl, 4 /,tg/4 /zl in t racerebroventr icular ly (ICV)), and were t reated immedia te ly after the first ext inct ion session. The second and third sessions were per formed 3 hr and 6 hr after t rea tment on day 4. A fourth ext inct ion session was run on day 5, 24 hr after single injection of the peptide or saline.

Amnesia. The rats were trained in a one-trial learning pass ive avoidance apparatus [1]. Briefly, the apparatus con- sisted of an i l luminated platform at tached to a larger com- par tment . Rats were placed on the platform and al lowed to enter the dark compar tment . Since rats prefer dark to light, they normally entered within 15 sec. The additional trials were given on the fol lowing day. After the second trial, un- avoidable electric shocks (0.4 mA, 2 sec) were del ivered through the grid floor of the dark compar tment . Af ter this single learning trial, the rats were immediate ly r emoved from the apparatus . Retrograde amnesia was induced in the animals by ECS t rea tment (Minicoma, 0.5 sec, 220 V, posi- tion 2) immedia te ly after the learning trial. Trea tment with the peptide was per formed immediate ly , or 4 hr, 20 hr or 23 hr after the ECS. The animals were tested 24 hr after train- ing./3-(Tyr~)melanotropin-(9-18) was administered in a dose o f 1 /zg or 4 /zg in a vo lume of 4 /zl saline into the lateral cerebrovent r ic le . The control animals rece ived physiological saline. In every session, animals t reated with foot shock, foot shock + ECS (both group treated with saline) or foot shock + ECS + fl-(Tyrg)melanotropin-(9-18) ( I beg/4/xl or 4 / ,g/4/ ,1 ICV) were used.

A versively motivated spatial discrimination luarning. The exper iment was per formed according to Bureg e t a / . [2], with slight modificat ion. Briefly, on the first day animals were trained to avoid foot shocks by always going to the right arm of the T-apparatus. The animals were placed on the start (far end of the stem) and after 10 sec electr ic shocks (0.5 sec, 50 Hz, 0.2 mA) were applied a max imum of five times. The

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FIG. 2. Effect of ~-(qyr")MSH~ > on electroconvulsive shock (ECS)-induced amnesia. Open column denotes foot shock ~ saline (4/*1 1CV); slashed column denotes lbot shock - ECS ~ saline 14 ,ul ICV): wavy column denotes foot shock + ECS + /3-(Tyr")MSH, ~, (I /zg/4 ,u,I ICV): dotted column denotes foot shock + ECS • /3-(Tyr~)MSH, ,~ (4 /xg/4 #1 ICV). Number in bars is number of animals used. ~ p<0.05 (M.W. test), ++-i><0.02 (M.W. test). + + + p<0 .0 l (M.W. test), O O - p < 0.02 {K .W. tesl). 0 0 0 p<0 .0 l (K.W. tcst).

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i ~ ~ o~ FIG. 3. Effect of/3-(I'yr~gMSH, t, on T-discrimination learning. :L control (4 /,1 saline ICV): • ,8-(Tyr'4)MSH~, ~ (1 /,g/4 /xl ICV); • ,8-(Tyr")MSHr. ~ (4 /,g/4 /a.I ICV). Number in bars is number of animals used. The ordinate represents total number of incorrect choices per trial until 9 correct choices were reached. + p<0.05 (M.W. test), O=p<0.05 (K.W. test), OO=p<0.02 (K.W. test).

shocks made the animal cont inue the search until the goal in the right arm was reached. The rat was left there for the remainder of the interval (20 sec) and then placed on the start. The training cont inued until the cri terion of 9 correct choices. The total number of incorrect choices was recorded (uncondit ional response). On the next day, the safe goal area was shifted to the o ther arm of the T-maze. On the third day, the task was reversed again. The decapept ide (1 /zg/4/xl, 4 /zg/4/zl ICV) was adminis tered immediate ly before the train- ing session on all three days. The controls received saline (4 /zl ICV).

Statistical Analysis

The U test of Mann-Whitney (M.W. test) was used to compare placebo vs. peptide data. Kruskal-Wall is ' test (K.W. test) was used across t reatments .

R E S U L T S

(/3-(Tyr:bmelanotropin-(9-18) inhibited the ext inct ion of

/3-(TYR9)MELANOTROPIN-(9-18) AND BEHAVIOR 13

active avoidance behavior at 3 hr, 6 hr and 24 hr after the treatment (Fig. 1).

As concerns ECS-induced amnesia, it was found that the avoidance latency of the animals treated with foot shock and saline was approximately 130 sec. If the animals received ECS, the avoidance latency decreased significantly. If treatment with the decapeptide was performed immediately or 4 hr or 20 hr after the ECS, the peptide had an antiamnesic effect. If the treatment was performed 1 hr before the test session, the decapeptide did not influence the amnesia (Fig. 2).

/3-(Tyra)melanotropin-(9-18) facilitated the performance of T-discrimination learning on the 1st and 2rid day. On the third day the learning performance of the peptide-treated animals did not differ from that of the control group (Fig. 3).

ment was performed immediately, or 4 hr or 20 hr after the ECS. As the ECS and peptide treatment interval increased, the effect of the substance decreased. In an earlier study, we found that /3-(Tyra)melanotropin-(9--18) increased passive avoidance latency if the treatment was performed 30 rain before the foot shock, but was ineffective if the treatment was performed 30 min before the 24 hr test session [12]. It suggests that the decapeptide influences memory consolida- tion rather than the memory retrieval processes.

Reversal learning has been postulated to be a measure of attention [4]. The decapeptide administration facilitated learning of the discrimination task, which indicated that the substance might influence attention. There are, however, numerous cognitive skills involved in reversal learning which may be influenced by MSH. In conclusion however it seems that the improvement both of the memory and the attention induced by fl-(Tyrg)melanotropin-(9-18) are important fac- tors of the extinction inhibition induced by the decapeptide.

DISCUSSION

In the present study /3-(Tyr9)melanotropin-(9--18) inhib- ited the extinction of active avoidance behavior. Delay of extinction of active avoidance behavior may be due to in- creased selective attention to the conditioned stimulus of the light signal, a more general state of arousal, enhanced moti- vation, or an improvement in memory function. (%18) was kindly provided by Dr. D. H. Coy, Veterans Administra-

The decapeptide had an antiamnesic effect if the treat-

ACKNOWLEDGEMENT

This work was supported by the Scientific Research Council, Hungarian Ministry of Health ( 16/4-10/502/T)./3-(Tyr9)melanotropin -

tion Medical Center, New Orleans, LA.

R E F E R E N C E S

1. Ader, R., A. W. M. Weijnen and P. Moleman. Retention of a passive avoidance response as a function of the intensity and duration of electric shock. Psychosom Sci 26: 126-128, 1972.

2. Bureg, J., O. Bure~ova and J. P. Huston. Techniques andBasic Experiments fi)r the Study ~f Brain and Behavior. Amsterdam: Elsevier, 1976.

3. Fekete, M., G. Telegdy, A. V. Schally and D. H. Coy. Effects of/3-(Tyrg)melanotropin-(9-18) decapeptide on catecholamine disappearance and serotonin accumulation in discrete brain re- gions of rats. Neuropeptides 1: 377-382, 1981.

4. Macintosh, N. J. Selective attention in animal discrimination learning. Psychol Bull 64: 124-150, 1965.

5. Sandman, C. A., L. H. Miller, A. J. Kastin and A. V. Schally. Neuroendocrine influence on attention and memory. J Comp Physiol 80: 54-58, 1972.

6. Schally, A. V., R. C. C. Chang, W. Y. Huang, D. H. Coy, A. J. Kastin and T. W. Redding. Isolation, structure, biological char- acterization and synthesis of fl-(Tyra)melanotropin-(%18) de- capeptide from pig hypothalami. Proc Nutl Acad Sci USA 77: 3947-3951, 1980.

7. Telegdy, G., J. Hadnagy and K. Liss~ik. The effect of gonads on conditioned avoidance behavior of rats. Actu Physiol Hung 339: 439-446, 1968.

8. Telegdy, G., L. V6csei, A. V. Schally and D. H. Coy. The effects of/3-(Tyra)melanotropin4%18) and H-Phe-lle-Tyr-His- Ser-Tyr-Lys-OH on the analgesic action of morphine. Neuro- pharmacology 22: 131-134, 1983.

9. Vrcsei, L., I. Boll6k, G. Telegdy, D. H. Coy and A. V. Schally. Effect of intracerebroventricular administration of/3-(Tyrg)mel - anotropin-(9-18) on rotation behavior induced by substantia nigra lesion. Neuropeptides 3: 435-442, 1983.

10. Vrcsei, L., G. Telegdy, A. V. Schally and D. H. Coy. Effects of /3-(Tyrg)melanotropin-(9-18) decapeptide on passive and active avoidance behavior and on open-field activity of rats. Peptides 2: 389-391, 1981.

11. Vrcsei, L., G. Telegdy, A. V. Schally and D. H. Coy. Effects of /3-(Tyrg)melanotropin-(9-18) on apomorphine-induced stereo- typed cage-climbing and on striatal dopamine release in mice. Comparative studies with amphetamine. Neuropeptides 3: 91-96, 1982.