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The effects of sulfated and nonsulfated cholecystokinin octapeptides on electroconvulsive shock-induced retrograde amnesia after. Intracerebroventricular administration in rats
Neuropeptides
4 : 127-135,
I984
THE EFFECTS OF SULFATED AND PEPTIDES ON ELECTROCONVULSIVE AFTER. INTRACEREBROVENTRICULAR Tibor
I
Botond
Penke
2
NONSULFATED CHOLECYSTOMININ SHOCK-INDUCED RETROGRADE ADMINISTRATION IN RATS
, I
‘Department of Pathophysiology University Medical Chemistry, Hungary /Reprint requests 531,
I
2
, and
and ‘Department School, H-6701 to GT/
Gyula
OCTAAMNESIA
Telegdyl
of Medicinal Szeged, P.O. B.
ABSTRACT The effects of several doses of intracerebroventricularly injected cholecystokinin octapeptide sulfate ester (Ccl<-8-SE) and nonsulfated scholecystokinin octapeptide (Ccl<-8-NS) were studied on electroconvulsive shock (ECS)-induced retrograde as measured in a one-trial step-through passive aamnesia, voidance paradigm, Both Ccl<-8-SE and Ccl<-8-NS were able to attenuate amnesia slightly when they were injected into rats 10 min prior to ECS treatment, possibly by reducing the severity of the ECS-induced seizures. Of the treatments carried out immediately after ECS, only the 0.8 pmole dose of Ccl<-8-NS could significan,tly restore retrograde amnesia. After treatment 20 min prior to testing 24-hr retention, no effect of the peptides was observed. The lacl< of a dose-dependency and of any effect on retrieval raises the possibility that the Ccl< octapeptides influence memory processes by an indirect mechanism. INTRODUCTION In recent years cholecystokinin has been found to be an important brain and a broad range of investigations peptide, is in progress, using several methodological approaches, to clarify its physiological significance in the central nervous system and its possible therapeutic applications. The neuropharmacological effects of cholecystokinin octapeptide are analgesia (1,2), central depression or a neuroleptic-like effect (3,4,5), centrally induced hyperglycemia (6), hypothersatiety induction (for reviews see refs. lO,ll, mia (7,8,9), pituitary effects (13). 12) I and anterior Several behavioral effects reported from our laboratory.
of cholecystokinin Cholecystokinin 127
have octapeptide
been sul-
fate ester (Ccl<-8-SE) and nonsulfated cholecytokinin octapeptide (Ccl<-8-NS) depressed the acquisition and facilitated the extinction of active avoidance and conditioned feeding behavior after intracerebrove-ttricular (icv.) administration (14, Both octapeptides were able to enhance the latencies of 15). passive avoidance behavior after intraperitoneal (16) or icv. injection (17). The physiological significance of the lstter effect was indicated by the fact that the central injection of cholecystokinin antisera could produce opposite changes in the passive avoidance latencies (18). As the peptides which contribute tomsmory processes (e.g. exert potent effects in ACTH or vasopressin) , and therefore the passive avoidance behavioral paradigm, are also active in attenuating retrograde amnesia induced by various agents (-For a review see ref. 19), it seemed worthwhile to investigate the effects of cholecystokinin on retrograde amnesia. In the experiments presented here the actions of Ccl<-~-SE and CCI<-8-NS on electroconvulsive shock-induced amnesia were studied after administration, icv. METHODS CFY male rats weighing 150-180 g were used in the experiments. The animals were maintained under standard conditions in rooms with controlled lighting (lights on from 6 am to 6 pm) and were given access to commercial food and tap water. A stainless steel guide cannula was implanted into the lateral brain ventricle and fixed to the skull with dental cement and acrylate resin for icv. treatment. Behavioral testing began after a one-week recovery period. The correct positioning of the cannula was checked by injecting methylene blue dye and by dissecting the brain after the experiment had been completed. the one-trial step-through learning As an amnesia model, paradigm of Ader and coworkers (20) -for passive avoidclnce beRats were trained in a two-compartment appahavior was used. ratus consisting of a large dark box with a grid floor, and a brightly illuminated runway attached to the front center hole of the dark compartment. On Day 1, after a 2-min adaptation in the dark compartment, the rats were placed on the runway, facing away from the hole, and allowed to enter the box through a sliding door. They were given two more trials separated by Rats prefer dark to light, and ran into the dark 1 hr on Day 2. compartment within 10 sec. Immediately after the second trial on Day 2, rats received an electric footshocl< (0.85 mA, 3 set) delivered th’rough the grid floor; they were then rapidly removed from the box and an ECS was given through ear-clip electrodes (190 V, 0.5 set, Minicoma ECS equipment). One of the control groups was submitted only to footshock (learning trial) and no ECS was given. Retention of passive avoidance behavior was measured on Day 3, 24 hr fcii.lowing th’e learning trial, by placing the animal on the runway and measuring the time until
128
it
entered
the
dark
compartment,
or
up
to
300
sec.
Several doses of Ccl<-8-SE and Ccl<-8-NS dissolved in ~aor saline alone in the control group, were injected line, in a volume of 2 /u1 with a microsyringe. The cholecysicv. tokinin octapeptides were synthetized by Penke and coworkers (21). Statistical evaluation of the results was performed by analysis of variance kitlowed by Student’s t-test.
RESULTS The effects of Ccl<-8-SE and Ccl<-8-NS on ECS-induced amnesia were studied in three series of experiments. In the first one, icv. administration was carried out 10 min before the learning trial, i.e. before the electric footshock and ECS treatment. The results obtained are summarized in Figure 1. The ECS treatment deteriorated the passive avoidance response (p(O.001 as compared to the control group without ECS treatOf the doses tested, ment). 8.0 pmole Ccl<-8-SE and 80 pmole Ccl<-8-NS significantly (by t-test) reversed the action of ECS, and there was a tendency to increase the latencies in the 80 pmole CCK-8-SE-treated group and in the groups treated with 0.8 or 8.0 pmole Ccl<-8-NS. These latter effects were not signifilatency
(secl
X X
100
I
80
I x
!i_L 0
60 40 20 111, 12 C-ECS
. . .
0
0
0
0
0
0
0
0
0
0
0
0
l?
lo
12
0
12 C
08 a.0 a0 pmole
CCK-B-SE
icv
CCK- B-NS
Figure 1. The effects of Ccl<-8-SE and Ccl<-8-NS on ECS-induced amnesia when treatment was carried out 10 min prior to the learning trial and ECS. C - ECS: saline-treated group without ECS treatment ; C: saline-treated group. The figures at the bottom of the bars indicate the number of animals used. 0.0: p(O.001 vs. C - ECS; x: ~(0.05; xx: p(O.01 vs. control group (t-test).
129
latency (set)
160.
loo80.
0 0
60. :.
40s ZO-
C-ECS
c
08
80
80
0 0
0 0
08
8.0
80
pmole icv
CCK-8-NS
CCK-8-SE
Figure 2. The effects of Ccl<-8-SE and amnesia when treatment was carried out ECS treatment (or following the learning For abbreviations see Fig. 1. group).
Latency
0 0
CCK-8-NS on ECS-induced immediately following trial in the C - ECS
kec)
1601401201 oo-
8060. 4020C,
xs
c
0.8 8.0 80 CCK-8-SE
0.8 8.0 80 pmole icv. CCK-
8-NS
Figure 3, The effects of Ccl<-8-SE and Ccl<-8-NS on amnesia when treatment was carried out 20 min prior the 24-hr retention. l o: p
130
ECS-induced to testing For fur-
cant because of groups F(6,70)=1.46;
the
large not
variances significant).
(for
the
ECS-treated
In the second series, icv. treatment was performed immediately after the tonic-clonic seizures induced by ECS (or immediately after the learning trial in the control group miFigure 2 shows that only 0.8 pmole Ccl<-8nus ECS treatment). -NS prevented the development of retrograde amnesia when the latencies were tested 24 hr later (for the ECS-treated groups F(6,96)=3.72; p< 0.01). Solutions were administered icv. to the animals 20 min before testing the 24-hr retention on Day 3 in the third series of experiments. Neither Ccl<-8-SE nor Ccl<-8-NS could reverse ECS-induced retrograde amnesia in the doses tested; moreover, the 8 pmole dose of Ccl<-~-NS somewhat reduced the latencies (t=2,01, df=23; O.lO>p>D.O5; analysis of variance for the ECS-treated groups: F(6,78)=0.72; not significant, Fig. 3). DISCUSSION A behavioral response is always an outcome of very complex brain processes influenced by external and internal stiincluding the experimental treatment. The passive avoidmuli, ance response measured as retention latencies can be modified by several mechanisms. There were discrepancies in the present experiments between the results obtained with treatment performed before the learning trial or immediately after ECS treatment. In the first case both Ccl<-8-SE and Ccl<-8-NS increased the latencies, whereas in the second case only the lowest dose of Ccl<-8-NS did so. In our recent experiments (22) Ccl<-8-SE and Ccl<-8-NS were demonstrated to reduce the severity of electroshock-induced seizures 10 min after icv. injection under a similar dose regimen, and therefore the increased latencies observed after pretrial treatment would mean the manifestation of the anticonvulsive activity of the octapeptides in a memory test. A detailed analysis of the data revealed that Ccl<-8 treatment before the learning trial increased the proportion of animals showing very long latencies, and thus the variance of the data increased. This could be one explanation for the lack of a dose-dependency, but more numerous sample data would be needed to demonstrate the exact relationships. The effect of 0.8 pmole Ccl<-8-NS injected immediately after ECS seems to be the specific prevention of retrograde amnesia. In our previous experiments (17) Ccl<-8-SE and Ccl<-~-NS dose-dependently enhanced the latencies of passive avoidance behavior when icv. injections were given immediately after the learning trial. The threshold dose of the effect was 0.8 pmole In the present experiments, only 0.8 pmole Ccl<-8-NS could produce a specific antiamnesic effect when peptides were injected
131
immediately after the ECS treatment. Cholecystokinin octapeptides could not promote or restore the recall of the memory trace disrupted by the ECS treatment, though it was shown that the 0.8 pmole dose of both octapeptides enhanced the latencies of passive avoidance behavior when they were injected 20 min before the retention test (17). it seems that the Ccl< octapeptides restore the Generally, retrograde amnesia less actively than they increase the performance of passive avoidance behavior, and therefore different mechanisms may be responsible for the memory facilitatory In another assumption the mechanism and antiamnesic effects, but the CCI< octapeptides act indirectly by moduis the same, lating the effects of other endogenous neurohormones contributing tb memory processes, Our latter suggestion is strongly supported by the results which demonstrated the high activities of vasopressin and oxytocin on memory processes and their opposite effects (23,24), and the very potent antiamnesic effects of vasopressin (25,26; for a review see ref. 19), together with those of Beinfeld and coworkers (27,28) and Vanderhaeghen’s group (29,30) on the existence of CCI< peptides in the posterior pituitary and in the paraventricular and supraand on the parallel changes of CCI< and posterior optic nuclei, pituitary hormone levels after physiological and surgical maAs ACTH also has memory-promoting and antiamnesic nipula tions. in spite of the controversies, there is effects (20,25) and, an interaction between cholecystokinin-gastrin-like peptides and ACTH, which has already been’demdnstrated morphologically (31,32) and physiologically (33,34), the alteration of the memory effects of endogenous ACTH by CCI< is atso presumable. ACKNOWLEDGEMENTS
cil,
This work Hungarian
was supported Ministry of
by the Scientific Health (16/4-10/502/T).
Research
Coun-
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(1981) Suppressive action of on the behavioral effects Journal of Pharmacology 75,
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(1982) Sedative action of cholecystokiI
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Morley 3E, Levine AS, Lindblad S. (1981) Intraventricular cholecystokinin octapeptide produces hypothermia in European Journal of Pharmacology 74, 249-251.
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Effect of cholecystokinin in the rat, Japanese
Zetler G. (1982) Cholecystokinin and caerulein analogues: Effects the mouse. Neuropharmacology 21,
octaJournal
octapeptide, caerulein on thermoregulation 795-801.
rats.
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(1978) Current status of cholecystoHsiao S, short-term satiety hormone, Neuroscience and Reviews 2, 79-87.
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Mueller I<, Ikinin as a Biobehavioral
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Smith GP, Gibbs J, (1981) Thornton J. A progress report.
12.
Morley -from
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Vijayan E, Samson WI<, McCann SM. vitro effects of cholecystokinin tin, growth hormone and thyrotropin Brain Research 172, 295-302.
14.
Fekete M, Szabo A, Balazs M, Penke B, Telegdy G. (1981) Effects of intraventricular administration of cholecystokinin octapeptide sulfate ester and unsulfated cholecystokinin octapeptide on active avoidance and conditioned feeding behaviour of rats. Acta Physiologica Academiae Scientiarum Hungaricae 58, 39-45.
15.
Telegdy brain.
JE. (1982) gut to brain.
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Jerome C, Pi-Sunyer The satiety effect Peptides 2, Suppl.
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M,
Kadar T. Medicine
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(1979) In vivo on gonadotropin, release in
(1982) 2, 2-5.
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and in .prolacthe rat,
Cholecystokinin
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16.
Fekete M, /
17.
G. (1981) Modulation of passive Fekete M, Telegdy l
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Modulation octapep-
the
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Fekete M, Lonovics passive avoidance cular administration Neu ropep t ides 1,
19.
;rd;;ed . Plenum
J, Telegdy G. (1981) behaviour of rats by of cholecystokinin 363-369.
D, Gispen In: Gainer, Press, New
WH. (1977) Behavioral H. (ed.) Peptides York, p. 397-448.
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Ader R, Weijnen passive avoidance and duration of 125-128.
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Penke B, Toth GI<, Zarandi M, Nagy A, Kovacs I<. (1981) new synthesis of tyrosine-o-sulfated peptides containing methionine. In: Brunfeldt , I<. (ed.) Peptides 1980. Proceedings of the 16th European Peptide Symposium. Scriptor, Coppenhagen, p. 253-257.
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Telegdy G, I
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H, De Wied D. (1974) The effects Rigter H, van Riezen ACTH and vasopressin analogues on C02-induced retrograde amnesia in rats. Physiology and Behavior 13, 381-388.
26.
Walter R, Hoffman PL, Flexner JB, Flexner LB. (1975) Neurohypophyseal hormones, analogs, and fragments: Their effect on puromycin-induced amnesia. Proceedings of the National Academy of Sciences U.S.A. 68, 880-884.
27.
Beinfeld kinin in 2, 77-79.
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Beinfeld MC, Meyer DI<, Brownstein MD. (1980) CholecystoIkinin octapeptide in the rat hypothalamo-neurohypophysial Nature 288, 376-378, system.
29.
Vanderhaeghen J-J, Lotstra F, de Mey J, Gilles C. (1980) Immunohistochemical localization of cholecystokininand gastrin-like peptides in the brain and hypophysis of the Proceedings of the National Academy of Sciences rat. U.S.A. 77, 1190-1194.
MC, the
Meyer central
DI<, Brownstein MD. (1981) nervous system. Peptides
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Cholecysto2, Suppl.
30.
Deschepper C, Lotstra F, Vandesande F, Vanderhaeghen J-J. (1983) Cholecystokinin varies in the posterior pituitary and external median eminence of the rat according to factors affecting vasopressin and oxytocin. Life Sciences 32, 2571-2577.
31.
Lotstra F, Vanderhaeghen J-J, Vandesande F, Gilles C. (1980) Relationship of gastrin family peptides with oxyACTH and M-MSH cells, tocin, A study in hypophysis and hypothalamus using immunohistochemistry, radioimmunoassays and chromatography. Neuroscience Letters Suppl. 5, s209.
32.
Larsson L-I, in corticotrophs
33.
Fekete M, Bokor M, Penke Effects of cholecystokinin on brain monoamines and chemistry International
34.
Porter JR, Sander Ikinin octapeptide Regulatory Peptides
This manuscript
Received Accepted
Rehfeld and
JF. (1981) melanotrophs.
Pituitary Science
B,
gastrins occur 213, 768-770.
Kovacs I<, Telegdy octapeptide and its plasma corticosterone. 3, 165-169.
LD. ;1981) The on pituitary-adrenal 2., 245-252.
effect
G. (1981) fragments Neuro-
of cholecystohormone secretion.
was delayed by fire in the editor's off ice.
28/II/83 24101184
135
4 : 127-135,
I984
THE EFFECTS OF SULFATED AND PEPTIDES ON ELECTROCONVULSIVE AFTER. INTRACEREBROVENTRICULAR Tibor
I
Botond
Penke
2
NONSULFATED CHOLECYSTOMININ SHOCK-INDUCED RETROGRADE ADMINISTRATION IN RATS
, I
‘Department of Pathophysiology University Medical Chemistry, Hungary /Reprint requests 531,
I
2
, and
and ‘Department School, H-6701 to GT/
Gyula
OCTAAMNESIA
Telegdyl
of Medicinal Szeged, P.O. B.
ABSTRACT The effects of several doses of intracerebroventricularly injected cholecystokinin octapeptide sulfate ester (Ccl<-8-SE) and nonsulfated scholecystokinin octapeptide (Ccl<-8-NS) were studied on electroconvulsive shock (ECS)-induced retrograde as measured in a one-trial step-through passive aamnesia, voidance paradigm, Both Ccl<-8-SE and Ccl<-8-NS were able to attenuate amnesia slightly when they were injected into rats 10 min prior to ECS treatment, possibly by reducing the severity of the ECS-induced seizures. Of the treatments carried out immediately after ECS, only the 0.8 pmole dose of Ccl<-8-NS could significan,tly restore retrograde amnesia. After treatment 20 min prior to testing 24-hr retention, no effect of the peptides was observed. The lacl< of a dose-dependency and of any effect on retrieval raises the possibility that the Ccl< octapeptides influence memory processes by an indirect mechanism. INTRODUCTION In recent years cholecystokinin has been found to be an important brain and a broad range of investigations peptide, is in progress, using several methodological approaches, to clarify its physiological significance in the central nervous system and its possible therapeutic applications. The neuropharmacological effects of cholecystokinin octapeptide are analgesia (1,2), central depression or a neuroleptic-like effect (3,4,5), centrally induced hyperglycemia (6), hypothersatiety induction (for reviews see refs. lO,ll, mia (7,8,9), pituitary effects (13). 12) I and anterior Several behavioral effects reported from our laboratory.
of cholecystokinin Cholecystokinin 127
have octapeptide
been sul-
fate ester (Ccl<-8-SE) and nonsulfated cholecytokinin octapeptide (Ccl<-8-NS) depressed the acquisition and facilitated the extinction of active avoidance and conditioned feeding behavior after intracerebrove-ttricular (icv.) administration (14, Both octapeptides were able to enhance the latencies of 15). passive avoidance behavior after intraperitoneal (16) or icv. injection (17). The physiological significance of the lstter effect was indicated by the fact that the central injection of cholecystokinin antisera could produce opposite changes in the passive avoidance latencies (18). As the peptides which contribute tomsmory processes (e.g. exert potent effects in ACTH or vasopressin) , and therefore the passive avoidance behavioral paradigm, are also active in attenuating retrograde amnesia induced by various agents (-For a review see ref. 19), it seemed worthwhile to investigate the effects of cholecystokinin on retrograde amnesia. In the experiments presented here the actions of Ccl<-~-SE and CCI<-8-NS on electroconvulsive shock-induced amnesia were studied after administration, icv. METHODS CFY male rats weighing 150-180 g were used in the experiments. The animals were maintained under standard conditions in rooms with controlled lighting (lights on from 6 am to 6 pm) and were given access to commercial food and tap water. A stainless steel guide cannula was implanted into the lateral brain ventricle and fixed to the skull with dental cement and acrylate resin for icv. treatment. Behavioral testing began after a one-week recovery period. The correct positioning of the cannula was checked by injecting methylene blue dye and by dissecting the brain after the experiment had been completed. the one-trial step-through learning As an amnesia model, paradigm of Ader and coworkers (20) -for passive avoidclnce beRats were trained in a two-compartment appahavior was used. ratus consisting of a large dark box with a grid floor, and a brightly illuminated runway attached to the front center hole of the dark compartment. On Day 1, after a 2-min adaptation in the dark compartment, the rats were placed on the runway, facing away from the hole, and allowed to enter the box through a sliding door. They were given two more trials separated by Rats prefer dark to light, and ran into the dark 1 hr on Day 2. compartment within 10 sec. Immediately after the second trial on Day 2, rats received an electric footshocl< (0.85 mA, 3 set) delivered th’rough the grid floor; they were then rapidly removed from the box and an ECS was given through ear-clip electrodes (190 V, 0.5 set, Minicoma ECS equipment). One of the control groups was submitted only to footshock (learning trial) and no ECS was given. Retention of passive avoidance behavior was measured on Day 3, 24 hr fcii.lowing th’e learning trial, by placing the animal on the runway and measuring the time until
128
it
entered
the
dark
compartment,
or
up
to
300
sec.
Several doses of Ccl<-8-SE and Ccl<-8-NS dissolved in ~aor saline alone in the control group, were injected line, in a volume of 2 /u1 with a microsyringe. The cholecysicv. tokinin octapeptides were synthetized by Penke and coworkers (21). Statistical evaluation of the results was performed by analysis of variance kitlowed by Student’s t-test.
RESULTS The effects of Ccl<-8-SE and Ccl<-8-NS on ECS-induced amnesia were studied in three series of experiments. In the first one, icv. administration was carried out 10 min before the learning trial, i.e. before the electric footshock and ECS treatment. The results obtained are summarized in Figure 1. The ECS treatment deteriorated the passive avoidance response (p(O.001 as compared to the control group without ECS treatOf the doses tested, ment). 8.0 pmole Ccl<-8-SE and 80 pmole Ccl<-8-NS significantly (by t-test) reversed the action of ECS, and there was a tendency to increase the latencies in the 80 pmole CCK-8-SE-treated group and in the groups treated with 0.8 or 8.0 pmole Ccl<-8-NS. These latter effects were not signifilatency
(secl
X X
100
I
80
I x
!i_L 0
60 40 20 111, 12 C-ECS
. . .
0
0
0
0
0
0
0
0
0
0
0
0
l?
lo
12
0
12 C
08 a.0 a0 pmole
CCK-B-SE
icv
CCK- B-NS
Figure 1. The effects of Ccl<-8-SE and Ccl<-8-NS on ECS-induced amnesia when treatment was carried out 10 min prior to the learning trial and ECS. C - ECS: saline-treated group without ECS treatment ; C: saline-treated group. The figures at the bottom of the bars indicate the number of animals used. 0.0: p(O.001 vs. C - ECS; x: ~(0.05; xx: p(O.01 vs. control group (t-test).
129
latency (set)
160.
loo80.
0 0
60. :.
40s ZO-
C-ECS
c
08
80
80
0 0
0 0
08
8.0
80
pmole icv
CCK-8-NS
CCK-8-SE
Figure 2. The effects of Ccl<-8-SE and amnesia when treatment was carried out ECS treatment (or following the learning For abbreviations see Fig. 1. group).
Latency
0 0
CCK-8-NS on ECS-induced immediately following trial in the C - ECS
kec)
1601401201 oo-
8060. 4020C,
xs
c
0.8 8.0 80 CCK-8-SE
0.8 8.0 80 pmole icv. CCK-
8-NS
Figure 3, The effects of Ccl<-8-SE and Ccl<-8-NS on amnesia when treatment was carried out 20 min prior the 24-hr retention. l o: p
130
ECS-induced to testing For fur-
cant because of groups F(6,70)=1.46;
the
large not
variances significant).
(for
the
ECS-treated
In the second series, icv. treatment was performed immediately after the tonic-clonic seizures induced by ECS (or immediately after the learning trial in the control group miFigure 2 shows that only 0.8 pmole Ccl<-8nus ECS treatment). -NS prevented the development of retrograde amnesia when the latencies were tested 24 hr later (for the ECS-treated groups F(6,96)=3.72; p< 0.01). Solutions were administered icv. to the animals 20 min before testing the 24-hr retention on Day 3 in the third series of experiments. Neither Ccl<-8-SE nor Ccl<-8-NS could reverse ECS-induced retrograde amnesia in the doses tested; moreover, the 8 pmole dose of Ccl<-~-NS somewhat reduced the latencies (t=2,01, df=23; O.lO>p>D.O5; analysis of variance for the ECS-treated groups: F(6,78)=0.72; not significant, Fig. 3). DISCUSSION A behavioral response is always an outcome of very complex brain processes influenced by external and internal stiincluding the experimental treatment. The passive avoidmuli, ance response measured as retention latencies can be modified by several mechanisms. There were discrepancies in the present experiments between the results obtained with treatment performed before the learning trial or immediately after ECS treatment. In the first case both Ccl<-8-SE and Ccl<-8-NS increased the latencies, whereas in the second case only the lowest dose of Ccl<-8-NS did so. In our recent experiments (22) Ccl<-8-SE and Ccl<-8-NS were demonstrated to reduce the severity of electroshock-induced seizures 10 min after icv. injection under a similar dose regimen, and therefore the increased latencies observed after pretrial treatment would mean the manifestation of the anticonvulsive activity of the octapeptides in a memory test. A detailed analysis of the data revealed that Ccl<-8 treatment before the learning trial increased the proportion of animals showing very long latencies, and thus the variance of the data increased. This could be one explanation for the lack of a dose-dependency, but more numerous sample data would be needed to demonstrate the exact relationships. The effect of 0.8 pmole Ccl<-8-NS injected immediately after ECS seems to be the specific prevention of retrograde amnesia. In our previous experiments (17) Ccl<-8-SE and Ccl<-~-NS dose-dependently enhanced the latencies of passive avoidance behavior when icv. injections were given immediately after the learning trial. The threshold dose of the effect was 0.8 pmole In the present experiments, only 0.8 pmole Ccl<-8-NS could produce a specific antiamnesic effect when peptides were injected
131
immediately after the ECS treatment. Cholecystokinin octapeptides could not promote or restore the recall of the memory trace disrupted by the ECS treatment, though it was shown that the 0.8 pmole dose of both octapeptides enhanced the latencies of passive avoidance behavior when they were injected 20 min before the retention test (17). it seems that the Ccl< octapeptides restore the Generally, retrograde amnesia less actively than they increase the performance of passive avoidance behavior, and therefore different mechanisms may be responsible for the memory facilitatory In another assumption the mechanism and antiamnesic effects, but the CCI< octapeptides act indirectly by moduis the same, lating the effects of other endogenous neurohormones contributing tb memory processes, Our latter suggestion is strongly supported by the results which demonstrated the high activities of vasopressin and oxytocin on memory processes and their opposite effects (23,24), and the very potent antiamnesic effects of vasopressin (25,26; for a review see ref. 19), together with those of Beinfeld and coworkers (27,28) and Vanderhaeghen’s group (29,30) on the existence of CCI< peptides in the posterior pituitary and in the paraventricular and supraand on the parallel changes of CCI< and posterior optic nuclei, pituitary hormone levels after physiological and surgical maAs ACTH also has memory-promoting and antiamnesic nipula tions. in spite of the controversies, there is effects (20,25) and, an interaction between cholecystokinin-gastrin-like peptides and ACTH, which has already been’demdnstrated morphologically (31,32) and physiologically (33,34), the alteration of the memory effects of endogenous ACTH by CCI< is atso presumable. ACKNOWLEDGEMENTS
cil,
This work Hungarian
was supported Ministry of
by the Scientific Health (16/4-10/502/T).
Research
Coun-
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