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Cholinergic influence on memory facilitation induced by angiotensin II in rats
Neuropeptides (1990) 16,157-162 @ Longman Group UK Ltd 1990
Cholinergic Influence on Memory Facilitation Induced by Angiotensin II in Rats D. 1. YONKOV
and V. P. GEORGIEV
Department of Experimental Pharmacology, Institute of Physiology, Acad. G. Bontchev Str., 61. 23, 1113 Sofia, Bulgaria
Bulgarian Academy
of Sciences,
Abstract-The influence of the cholinesterase inhibitor galanthamine (Nivalin), of the cholinergic agonist oxotremorine, and of the muscarinic cholinergic antagonist scopolamine on the retention-improving effect of angiotensin II (AT II) was studied in male Wistar rats trained and tested for retention (24h later) using two paradigms: two-way active avoidance (shuttle-box) and passive (step-through) avoidance. AT II and the cholinergic agonists, administered together potentiated their retention-improving effects, while scopolamine abolished the memory effect of AT II. It is suggested that brain cholinergic neurotransmission participates in the mechanisms of the memory-facilitating effect of AT II.
Introduction
Earlier studies of ours have shown that angiotensin II (AT II) at small doses (0.1-0.5 pg) administered intracerebroventricularly (icv) shortly before or immediately after training improves memory processes in rats trained and tested for retention on active and passive avoidance tasks (1). This effect of AT II might be due to its interaction with the AT-binding sites in brain, because it is antagonised by saralasin (an A T II receptor antagonist). Participation of brain dopaminergic and GABAergic neurotransmission in the mechanism of the memory-facilitating effect of AT II has been suggested (2, 3, 4, 5, 6, 7). Data in the literature
Date received 16 October 1989 Date accepted 15 February 1990
and the results of our earlier studies have shown an active participation of brain cholinergic neurotransmission in memory processes (8, 9, 10, 11). Many authors have suggested an important !role of the brain cholinergic and of some other ineurotransmitters in memory formation and storage (for review see 12). Worthy of note is the fact that the centrally acting cholinolytics cause profound changes in different behavioural responses and - particularly in learning and retention. It is thought that these changes are related to the animal species, the training task, the dose and the time af drug application, etc. (13). The aim of the present study was to examine the participation of cholinergic neurotransmission in the mechanism of memory-enhancing effect of angiotensin II.
157
158 Materials and Methods The experiments were carried out on 230 male Wistar rats, weighing 180-200g. The animals were kept under standard laboratory conditions (12h light-dark cycles, 20°C free access to food and water). Three hours before training the rats were surgically prepared for intracerebroventricular (icv) administration of AT II. The following coordinates for injection into the right lateral cerebral ventricle were used: 1 mm posterior to the coronary suture; 1.5mm laterally from the midline and 4.5mm below the skull. Rats were trained and tested for retention using two paradigms: two-way active avoidance (shuttlebox) (14) and passive (step-through) avoidance (15). The conditioned signal used in the shuttle-box training was a combined presentation of sound and light for 4s, followed by electrical footshock (a.c. 20-30V) on the grid-floor until the rat escaped to the opposite side (or up to 11s). The intertrial interval was 15-20s. The training session was completed after reaching the criterion of 6 out of 7 consecutive avoidance responses. If the rat did not reach the learning criterion in 50 successive trials learning was considered impossible. Retention (relearning) test was given 24h after the end of the training session and in some experiments - 7 days later, too. Learning and retention were estimated by the number of training trials necessary for reaching the learning criterion. The apparatus for step-through passive avoidance test consisted of two compartments separated by a hand-operated slide-door; an outer one, painted white and an inner one, painted black. A single 1OOW bulb was positioned 6Ocm above the platform in the outer compartment. Alternation current electrical footshock (40V) was administered through the grid-floor of the inner compartment. The rats were trained in one-trial session. Every rat was placed in the outer compartment, facing the door. One minute later the door was raised and the latency to cross from the outer to the inner compartment was recorded. After the animal entered the dark compartment, the door was closed and footshock was delivered for 1 s. Immediately after that the rat was replaced in the home cage. Retention was assessed 24h later
NEUROPEPTIDES
using a procedure indentical to that for training, except that footshock was not delivered. For 180s the latency of the rat to cross from the outer platform into the inner compartment was recorded. The latency was expressed in percentage. The following drugs and doses were used: angiotensin II (AT II - Ciba Geigy) - 0.1 u,g per rat icv; oxotremorine (Sigma) - 0.10, 0.25, and 0.50mg/kg i.p.; nivalin (Pharmachim) - 0.50 and l.Omg/kg s.c.; scopolamine (Sigma) - 2.0mg/kg i.p. The drugs were dissolved in saline and applied immediately after training alone or in the following combinations: AT II + oxotremorine (0.25 mg/ kg, or + nivalin (O.jmg/kg), or + scopolamine (2.0mglkg). The controls were treated with saline 0.1 mYlOOg body weight i.p. and 10 Fg per rat icv. The results from the shuttle-box experiments were analyzed statistically by the analysis of variance (ANOVA) followed by Newman-Keuls test for multiple means comparisons. F-ratios, degrees of freedom and p-values were taken into account where the effects were significant. In all comparisons between particular groups ~~0.05 was considered significant. The results expressed in percentage were statistically analyzed using x2 test. Results Active avoidance No significant
differences between the investigated groups of rats were found in training session. The effects of oxotremorine and nivalin at different doses on retention were evaluated using two individual two-way ANOVA - for oxotremorine and for nivalin. The factors were: oxotremorine (0,0.25 and 0.5mg/kg) and nivalin (0,O.j and 1 .Omg/kg), chosen as independent factors and the retention tests (24 h and 7 d) for every experiment - as repeated measure. Oxotremorine /F (2,27) = 68.67, p < O.OOl/and nivalin /F (2,36) = 60.70, p < O.OOl/ significantly influenced retention. There was no interaction between the two factors in the provided analysis. In individual post-hoc comparisons oxotremorine at the two doses and nivalin at a dose of lmg/kg significantly decreased the number of necessary trainings in the two retention tests, i.e.
159
CHOLINERGIC INFLUENCE ON MEMORY FACILITATION INDUCED BY ANGIOTENSIN II IN RATS
1
Rotrntion
-2Ch
AT II scopolamine of AT II (Fig. 3).
abolished the retention
effect
Passive avoidance
Fig. 1 Influence of oxotremorine on the retention effect of AT II in shuttle-box test (Mean + SEM). Groups: 1 - Controls; 2 - AT II 0.1 pg; 3 - Oxotremorine 0.25 mg/kg; 4 - AT II + Oxotremorine. ‘P < 0.01 (vs. 1); XP < 0.01 (4 vs. 2); +P < 0.01 (4 vs. 3).
No differences between the tested groups of rats were found in training session. AT II at a dose of 0.1 pg improved retention, i.e. it tended to increase the percentage of the latenties to cross from the outer to the inner compartment . Oxotremorine at doses of 0.10 and 0.25 mg/ kg significantly improved retention. Oxotremorine O.lOmg/kg and AT II 0.1 pg admihistered together potentiated their own memory-enhancing effects, while oxotremorine at a dose of 0.25mg/kg had no influence on the AT II effect (Fig. 4). Nivalin OSmg/kg slightly improved retention, but abolished the retention effect of AT II (Fig. 6). Discussion
they improved retention. Nivalin 0.5 mg/kg had no significant effect (Table). The effect of the combination of AT II with oxotremorine, nivalin or scopolamine on retention was evaluated using two-way ANOVA. The factors in the first analysis were: AT II (0 and 0.1 Fg) and oxotremorine (0 and 0.25mg/kg); in the second one - AT II (0 and 0.1 pg/kg); in the third one - AT II (0 and 0.1 kg) and scopolamine (0 and 2mglkg). The results showed a significant influence of oxotremorine, scopolamine and AT II on retention: oxotremorine /F (1,36) = 160.54, p < O.OOl/, scopolamine /F (1,36) = 18.13, p < O.OOl/ and AT II /F (1,36) = 34.02, 178.81 and 18.13, p < 0.001 -in all cases/. The combination of AT II and nivalin significantly influenced retention /F (1,36) = 25.87, p < O.OOl/. In individual post-hoc comparisons AT II or oxotremorine significantly improved retention, while nivalin at the dose used exerted no effect. The combined administration of AT II and oxotremorine potentiated their own memory-improving effects (Fig. 1). Nivalin injected in combination with AT II potentiated the memory-enhancing effect of AT II (Fig. 2). Scopolamine administered alone slightly impaired retention. In combination with
The present results showed that the immediate post-trial injection of the centrally acting/muscarinic cholinergic agonist oxotremorine (16) and the anticholinesterase drug nivalin (galan hamine) facilitated the retention of the rats in bo9 h active and passive avoidance tasks and potenti?ated the
1
Rotrntion-2Lh
Lo-
+ 2 x
30-
E
2
6
0
.5 20:
X *
lok
1
2
3
II 4
Influence of nivalin on the retention effect of AT II in shuttle-box test (Mean + SEM). Groups: 1- Controls; 2 - AT II 0.1 pg; 3 - Nivalin: 0.5 mg/kg; 4 - AT II + Nivaiin. ‘P < 0.01 (vs. 1); “P < 0.01 (4 vs. 2); *P < 0.01 (4 vs. 3).
Fig. 2
160
NEUROPEPTIDES
Retml~on -2Lh
the increased endogenous acetyl-choline after inhibition of cholinesterase. This holds true also for other cholinergic agonists (9, 12, 19). The present results on the dose-dependent effects of oxotremorine are in agreement with data of Baratti et al. (20). In our experiments the higher dose of oxotremorine (0.5 mg/kg) did not influence retention because central and autonomic effects caused by this muscarinic agonist might modify retention in non specific way (18). Our data strongly suggest a complex interaction between cholinergic receptors and AT II binding sites in brain structures involved in the regulation of memory consolidation. Frontoparietal cortex, hippocampus, striatum, nucl. basalis magnocellularis (basal forbrain) are among the structures rich
a I
3
2
b
Fig. 3 Influence of scopolamine on the retention effect of AT II in shuttle-box test (Mean _+SEM). Groups: 1 - Controls; 2 - AT II 0.1 ug; 3 - Scopolamine 2mg/kg; 4 - AT II + Scopolamine. *P < 0.01 (vs. 1); “P < 0.01 (4 vs. 2); “P < 0.01 (4 vs. 3).
oxotremorine and nivalin-facilitated retention. Scopolamine impaired retention (in active avoidance paradigm mainly). This effect of scopolamine was diminished when the cholinolytic was combined with AT II. The retention-improving effect of AT II was decreased by scopolamine. All these findings suggest an influence on memory consolidation. Thus, the improved retention after oxotremorine was probably due to an influence on memory consolidation due to an activation of brain muscarinic cholinergic receptors (17, 18). The facilitated retention after post-trial nivalin could be attributed to an activation of both muscarinic and nicotinic brain cholinoreceptors due to
Table
Influence
of oxotremorine
Retrntion-2Ch
1
2
3 4
3’ 4’
Fig. 4 Inthtence of oxotremorine on the retention effect of AT II on rats in step-through passive avoidance task. Groups: 1 - Controls; 2 - AT II 0.1 ug; 3 - Oxotremorine O.lOmg/kg; 3’ - Oxotremorine 0.25 mg/kg; 4 - AT II + Oxotremorine O.lOmg/kg; 4’ - AT II + Oxotremorine 0.25mglkg. *P < 0.05 (vs. 1); +P < 0.05 (4’ vs. 3’).
and nivalin on memory retention of albino rats in shuttle-box.
Mean + SEM.
Number of training trials Groups 1. 2. 3. 4. 5.
Controls Oxotremorine Oxotremorine Nivalin Nivalin
*P < 0.01 and **P < 0.001 (vs. 1).
Doses m&kg
No
0.25 0.50 0.50 1.00
10 10 10 10 10
Retention 24 h 34.5 20.5 25.5 32.7 21.9
+ + + + +
1.0 0.9** 2.7* 2.5 2.0**
Retention 7d 31.4 14.2 lg.9 24.9 19.4
+ + + + +
1.0 1.7’; 3.2: 3.2 2.0**
CHOLINERGIC INFLUENCE ON MEMORY FACILITATION INDUCED BY ANGIOTENSIN II IN RATS Retention-2Ch
161
References I. Georgiev, V. P. and Yonkov, D. I. (1985). Participation of
2.
3.
I
2
34
Influence of nivalin on the retention effect of AT II on rats in step-through passive avoidance task. Groups: 1 - Controls; 2 - AT II 0.1 ug; 3 - Nivalin O.Smg/kg; 4 - AT II + Nivalin. *P < 0.05 (4 vs. 1). Fig. 5
4.
5.
Retmtion-2Ch
6.
7.
: ‘2 50 . 4
8. 0 1
2
34
Fig. 6 Influence of scopolamine on the retention effect of AT II on rats in step-through passive avoidance task. Groups: 1 - Controls; 2 - AT II 0.1 kg; 3 - Scopolamine 2mg/kg; 4 - AT II + Scopolamine.
in cholinergic innervation (21) and in AT II binding sites (22). The results and the data about the influence of saralasin, DAergic and GABAergic agonists and antagonists on the pre- and post-trial effects of AT II (1,3,5,7,23) suggest a complex interaction between these systems in memory processes. In conclusion, cholinergic neurotransmission participates in retention and in the mechanisms of the retention-improving effect of AT II in active and passive avoidance.
9.
10.
11.
12. 13.
angiotensin II in learning and memory. I. Interaction of angiotensin II with saralasin. Methods and Findings of Experimental and Clinical Pharmacology 7: 8,41.%418. Georgiev, V. and Yonkov, D. (1985). Interactions between angiotensin II with saralasin and dopammergic agents in active avoidance. In: Borsy, J. et al., (eds) Dopamine, aging and disease. Akademiai Kiado, Budapest, p. 109-112. Georgiev, V. P., Yonkov, D. I. and Kambourova, T. S. (1988). Interaction between angiotensin II and baclofen in shuttle-box and passive avoidance performance. Neuropeptides 12: 155-158. Georgiev, V. P. (1987). Interactions of angiotensin 1IIwith brain neurotransmission in behavioural reactions. In: Stoytchev, Ts. et al. (eds) Trends in the pharmacology of neurotransmission. Publishing House of the Bulgarian Academy of Sciences, Sofia, p. 92-98. Yonkov, D. I., Georgiev, V. P. and Opitz, M. J. (1986). Participation of angiotensin II in learning and memory. II. Interaction of angiotensin II with dopaminergic drugs. Methods and Findings of Experimental and Clinical Pharmacology 8: 3,203-206. Yonkov, D. I., Georgiev, V. P., Kambourova, T. S. and Opitz, M. J. (1987). Participation of angiotensin II in learning and memory. III. Interaction of angiotensin II with GABAergic drugs. Methods and Findings of Experimental and Clinical Pharmacology 9: 4, 203-208. Yonkov, D., Georgiev, V. and Kambourova, T. (1989). Further evidences for the GABAergic influence on memory. Interaction of GABAergic neurotransfnission with angiotensin II in memory processes. Methods and Findings of Experimental and Clinical Pharmacology 11: 10, (in press). Coyle, J. T., Price, D. L. and De Long, M. R. (1983). Alzheimer’s disease: a disorder of cortical chdlinergic innervation. Science 219: 1184-1190. Haroutunian, V., Barues, E. and Davis, K. L. (1985). Chohnergic modulation of memory in rats. Psychopharmacology 87: 267-271. Gamzu, E., Vincent, G., Verderese, A., Boff, E., Lee, L. and Davidson, A. (1986). Pharmacological protection against memory retrieval deficits as a method of discovering new therapeutic agents. In: Fischer. A. et al. (eds) Alzheimer’s and Parkinson’s deseases - strategies for research and development. Plenum Press, New York, London, p. 375-391. Yonkov, D. I., Kambourova, T. S. and Todorov, 1. K. (1988). Significance of the interactions of the brain choIinergic and dopaminergic neurotransmitter systems in cognitive processes. Competes rendus de I’Academie bulgare des Sciences 41: 127-130. Kruglikov, R. I. (1981). Neurochemical mechanisms in learning and memory. Nauka, Moscow, (in Russian). Heise, G. A. (1981). Behavioral methods for measuring effects of drugs on learning and memory in animals. Medical Research Reviews 4: 535-538.
162 14. Yonkov, D. I., Petkov, V. V., Roussinov, K. S. and Vuglenova, Y. V. (1983). New model of apparatus for two-way avoidance (Shuttle-box) for pharmacological memory studies of small laboratory animals. Competes rendus de 1’Academie bulgare des Sciences 36: 1123-I 126. 15. Yonkov, D. I., Petkov, V. D. and Kambourova, T. S. (1986). A new model of apparatus for inhibitory “Stepthrough” avoidance for memory studies in small laboratory animals. Competes rendus de I’Academie bulgare des Sciences 39: 141-144. 16. Choi, R. L., Roth M. and Jenden, D. J. (1973). A regional study of acetylcholine turnover in rat brain and the effects ofoxotremorine. Proc. West. Pharmacol. Sot. 16: 188190. 17. Elrod, K. and Buccafusco, J. J. (1988). An evaluation of the mechanism of scopolamine-induced impairment of two passive avoidance protocols. Pharmacology Biochemistry and Behavior 29: 15-20. 18. McGaugh, J. L. (1973). Drug facilitation of learning and memory. Annual Reviews of Pharmacology and Toxicology 13: 229-241. 19. Flood, J. F., Landry, D. W. and Jarvik, M. S. (1981).
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20.
21.
22.
23.
Cholinergic receptor interactions and their effects on long-term memory processing. Brain Research 215: 177183. Baratti, C. M., Introini, I. B., Huygens P. and Gusovsky, F. (1983). Possible cholinergic-dopaminergic link in memory facilitation induced by oxotremorine in mice. Psychopharmacology 80: 161-163. Beninger, R. J., Ihamandas, K., Baegman, R. J. and El-Dfraowy, S. R. (1986). Effects of scopolamine and unilateral lesions of the basal forbrain on T-maze spatial discrimination and alternation in rat. Pharmacology Biochemistry and Behavior 24: 1353-1360. Gehlert, D. R., Speth, R. S. and Wamsley, J. K. (1986). Distribution of (iz51) angiotensin II binding sites in the rat brain: a quantitative autoradiographic study. Neuroscience 18: 837-856. Georgiev, V., Gyorgy., Yonkov, D., Getova, D., Markovska, V. and Petkova, B. (1985). Dopaminergic influence on the effects of angiotensin II in behavioural reactions. Physiologia Bohemoslovaka 34: Suppl., 45-48.
Cholinergic Influence on Memory Facilitation Induced by Angiotensin II in Rats D. 1. YONKOV
and V. P. GEORGIEV
Department of Experimental Pharmacology, Institute of Physiology, Acad. G. Bontchev Str., 61. 23, 1113 Sofia, Bulgaria
Bulgarian Academy
of Sciences,
Abstract-The influence of the cholinesterase inhibitor galanthamine (Nivalin), of the cholinergic agonist oxotremorine, and of the muscarinic cholinergic antagonist scopolamine on the retention-improving effect of angiotensin II (AT II) was studied in male Wistar rats trained and tested for retention (24h later) using two paradigms: two-way active avoidance (shuttle-box) and passive (step-through) avoidance. AT II and the cholinergic agonists, administered together potentiated their retention-improving effects, while scopolamine abolished the memory effect of AT II. It is suggested that brain cholinergic neurotransmission participates in the mechanisms of the memory-facilitating effect of AT II.
Introduction
Earlier studies of ours have shown that angiotensin II (AT II) at small doses (0.1-0.5 pg) administered intracerebroventricularly (icv) shortly before or immediately after training improves memory processes in rats trained and tested for retention on active and passive avoidance tasks (1). This effect of AT II might be due to its interaction with the AT-binding sites in brain, because it is antagonised by saralasin (an A T II receptor antagonist). Participation of brain dopaminergic and GABAergic neurotransmission in the mechanism of the memory-facilitating effect of AT II has been suggested (2, 3, 4, 5, 6, 7). Data in the literature
Date received 16 October 1989 Date accepted 15 February 1990
and the results of our earlier studies have shown an active participation of brain cholinergic neurotransmission in memory processes (8, 9, 10, 11). Many authors have suggested an important !role of the brain cholinergic and of some other ineurotransmitters in memory formation and storage (for review see 12). Worthy of note is the fact that the centrally acting cholinolytics cause profound changes in different behavioural responses and - particularly in learning and retention. It is thought that these changes are related to the animal species, the training task, the dose and the time af drug application, etc. (13). The aim of the present study was to examine the participation of cholinergic neurotransmission in the mechanism of memory-enhancing effect of angiotensin II.
157
158 Materials and Methods The experiments were carried out on 230 male Wistar rats, weighing 180-200g. The animals were kept under standard laboratory conditions (12h light-dark cycles, 20°C free access to food and water). Three hours before training the rats were surgically prepared for intracerebroventricular (icv) administration of AT II. The following coordinates for injection into the right lateral cerebral ventricle were used: 1 mm posterior to the coronary suture; 1.5mm laterally from the midline and 4.5mm below the skull. Rats were trained and tested for retention using two paradigms: two-way active avoidance (shuttlebox) (14) and passive (step-through) avoidance (15). The conditioned signal used in the shuttle-box training was a combined presentation of sound and light for 4s, followed by electrical footshock (a.c. 20-30V) on the grid-floor until the rat escaped to the opposite side (or up to 11s). The intertrial interval was 15-20s. The training session was completed after reaching the criterion of 6 out of 7 consecutive avoidance responses. If the rat did not reach the learning criterion in 50 successive trials learning was considered impossible. Retention (relearning) test was given 24h after the end of the training session and in some experiments - 7 days later, too. Learning and retention were estimated by the number of training trials necessary for reaching the learning criterion. The apparatus for step-through passive avoidance test consisted of two compartments separated by a hand-operated slide-door; an outer one, painted white and an inner one, painted black. A single 1OOW bulb was positioned 6Ocm above the platform in the outer compartment. Alternation current electrical footshock (40V) was administered through the grid-floor of the inner compartment. The rats were trained in one-trial session. Every rat was placed in the outer compartment, facing the door. One minute later the door was raised and the latency to cross from the outer to the inner compartment was recorded. After the animal entered the dark compartment, the door was closed and footshock was delivered for 1 s. Immediately after that the rat was replaced in the home cage. Retention was assessed 24h later
NEUROPEPTIDES
using a procedure indentical to that for training, except that footshock was not delivered. For 180s the latency of the rat to cross from the outer platform into the inner compartment was recorded. The latency was expressed in percentage. The following drugs and doses were used: angiotensin II (AT II - Ciba Geigy) - 0.1 u,g per rat icv; oxotremorine (Sigma) - 0.10, 0.25, and 0.50mg/kg i.p.; nivalin (Pharmachim) - 0.50 and l.Omg/kg s.c.; scopolamine (Sigma) - 2.0mg/kg i.p. The drugs were dissolved in saline and applied immediately after training alone or in the following combinations: AT II + oxotremorine (0.25 mg/ kg, or + nivalin (O.jmg/kg), or + scopolamine (2.0mglkg). The controls were treated with saline 0.1 mYlOOg body weight i.p. and 10 Fg per rat icv. The results from the shuttle-box experiments were analyzed statistically by the analysis of variance (ANOVA) followed by Newman-Keuls test for multiple means comparisons. F-ratios, degrees of freedom and p-values were taken into account where the effects were significant. In all comparisons between particular groups ~~0.05 was considered significant. The results expressed in percentage were statistically analyzed using x2 test. Results Active avoidance No significant
differences between the investigated groups of rats were found in training session. The effects of oxotremorine and nivalin at different doses on retention were evaluated using two individual two-way ANOVA - for oxotremorine and for nivalin. The factors were: oxotremorine (0,0.25 and 0.5mg/kg) and nivalin (0,O.j and 1 .Omg/kg), chosen as independent factors and the retention tests (24 h and 7 d) for every experiment - as repeated measure. Oxotremorine /F (2,27) = 68.67, p < O.OOl/and nivalin /F (2,36) = 60.70, p < O.OOl/ significantly influenced retention. There was no interaction between the two factors in the provided analysis. In individual post-hoc comparisons oxotremorine at the two doses and nivalin at a dose of lmg/kg significantly decreased the number of necessary trainings in the two retention tests, i.e.
159
CHOLINERGIC INFLUENCE ON MEMORY FACILITATION INDUCED BY ANGIOTENSIN II IN RATS
1
Rotrntion
-2Ch
AT II scopolamine of AT II (Fig. 3).
abolished the retention
effect
Passive avoidance
Fig. 1 Influence of oxotremorine on the retention effect of AT II in shuttle-box test (Mean + SEM). Groups: 1 - Controls; 2 - AT II 0.1 pg; 3 - Oxotremorine 0.25 mg/kg; 4 - AT II + Oxotremorine. ‘P < 0.01 (vs. 1); XP < 0.01 (4 vs. 2); +P < 0.01 (4 vs. 3).
No differences between the tested groups of rats were found in training session. AT II at a dose of 0.1 pg improved retention, i.e. it tended to increase the percentage of the latenties to cross from the outer to the inner compartment . Oxotremorine at doses of 0.10 and 0.25 mg/ kg significantly improved retention. Oxotremorine O.lOmg/kg and AT II 0.1 pg admihistered together potentiated their own memory-enhancing effects, while oxotremorine at a dose of 0.25mg/kg had no influence on the AT II effect (Fig. 4). Nivalin OSmg/kg slightly improved retention, but abolished the retention effect of AT II (Fig. 6). Discussion
they improved retention. Nivalin 0.5 mg/kg had no significant effect (Table). The effect of the combination of AT II with oxotremorine, nivalin or scopolamine on retention was evaluated using two-way ANOVA. The factors in the first analysis were: AT II (0 and 0.1 Fg) and oxotremorine (0 and 0.25mg/kg); in the second one - AT II (0 and 0.1 pg/kg); in the third one - AT II (0 and 0.1 kg) and scopolamine (0 and 2mglkg). The results showed a significant influence of oxotremorine, scopolamine and AT II on retention: oxotremorine /F (1,36) = 160.54, p < O.OOl/, scopolamine /F (1,36) = 18.13, p < O.OOl/ and AT II /F (1,36) = 34.02, 178.81 and 18.13, p < 0.001 -in all cases/. The combination of AT II and nivalin significantly influenced retention /F (1,36) = 25.87, p < O.OOl/. In individual post-hoc comparisons AT II or oxotremorine significantly improved retention, while nivalin at the dose used exerted no effect. The combined administration of AT II and oxotremorine potentiated their own memory-improving effects (Fig. 1). Nivalin injected in combination with AT II potentiated the memory-enhancing effect of AT II (Fig. 2). Scopolamine administered alone slightly impaired retention. In combination with
The present results showed that the immediate post-trial injection of the centrally acting/muscarinic cholinergic agonist oxotremorine (16) and the anticholinesterase drug nivalin (galan hamine) facilitated the retention of the rats in bo9 h active and passive avoidance tasks and potenti?ated the
1
Rotrntion-2Lh
Lo-
+ 2 x
30-
E
2
6
0
.5 20:
X *
lok
1
2
3
II 4
Influence of nivalin on the retention effect of AT II in shuttle-box test (Mean + SEM). Groups: 1- Controls; 2 - AT II 0.1 pg; 3 - Nivalin: 0.5 mg/kg; 4 - AT II + Nivaiin. ‘P < 0.01 (vs. 1); “P < 0.01 (4 vs. 2); *P < 0.01 (4 vs. 3).
Fig. 2
160
NEUROPEPTIDES
Retml~on -2Lh
the increased endogenous acetyl-choline after inhibition of cholinesterase. This holds true also for other cholinergic agonists (9, 12, 19). The present results on the dose-dependent effects of oxotremorine are in agreement with data of Baratti et al. (20). In our experiments the higher dose of oxotremorine (0.5 mg/kg) did not influence retention because central and autonomic effects caused by this muscarinic agonist might modify retention in non specific way (18). Our data strongly suggest a complex interaction between cholinergic receptors and AT II binding sites in brain structures involved in the regulation of memory consolidation. Frontoparietal cortex, hippocampus, striatum, nucl. basalis magnocellularis (basal forbrain) are among the structures rich
a I
3
2
b
Fig. 3 Influence of scopolamine on the retention effect of AT II in shuttle-box test (Mean _+SEM). Groups: 1 - Controls; 2 - AT II 0.1 ug; 3 - Scopolamine 2mg/kg; 4 - AT II + Scopolamine. *P < 0.01 (vs. 1); “P < 0.01 (4 vs. 2); “P < 0.01 (4 vs. 3).
oxotremorine and nivalin-facilitated retention. Scopolamine impaired retention (in active avoidance paradigm mainly). This effect of scopolamine was diminished when the cholinolytic was combined with AT II. The retention-improving effect of AT II was decreased by scopolamine. All these findings suggest an influence on memory consolidation. Thus, the improved retention after oxotremorine was probably due to an influence on memory consolidation due to an activation of brain muscarinic cholinergic receptors (17, 18). The facilitated retention after post-trial nivalin could be attributed to an activation of both muscarinic and nicotinic brain cholinoreceptors due to
Table
Influence
of oxotremorine
Retrntion-2Ch
1
2
3 4
3’ 4’
Fig. 4 Inthtence of oxotremorine on the retention effect of AT II on rats in step-through passive avoidance task. Groups: 1 - Controls; 2 - AT II 0.1 ug; 3 - Oxotremorine O.lOmg/kg; 3’ - Oxotremorine 0.25 mg/kg; 4 - AT II + Oxotremorine O.lOmg/kg; 4’ - AT II + Oxotremorine 0.25mglkg. *P < 0.05 (vs. 1); +P < 0.05 (4’ vs. 3’).
and nivalin on memory retention of albino rats in shuttle-box.
Mean + SEM.
Number of training trials Groups 1. 2. 3. 4. 5.
Controls Oxotremorine Oxotremorine Nivalin Nivalin
*P < 0.01 and **P < 0.001 (vs. 1).
Doses m&kg
No
0.25 0.50 0.50 1.00
10 10 10 10 10
Retention 24 h 34.5 20.5 25.5 32.7 21.9
+ + + + +
1.0 0.9** 2.7* 2.5 2.0**
Retention 7d 31.4 14.2 lg.9 24.9 19.4
+ + + + +
1.0 1.7’; 3.2: 3.2 2.0**
CHOLINERGIC INFLUENCE ON MEMORY FACILITATION INDUCED BY ANGIOTENSIN II IN RATS Retention-2Ch
161
References I. Georgiev, V. P. and Yonkov, D. I. (1985). Participation of
2.
3.
I
2
34
Influence of nivalin on the retention effect of AT II on rats in step-through passive avoidance task. Groups: 1 - Controls; 2 - AT II 0.1 ug; 3 - Nivalin O.Smg/kg; 4 - AT II + Nivalin. *P < 0.05 (4 vs. 1). Fig. 5
4.
5.
Retmtion-2Ch
6.
7.
: ‘2 50 . 4
8. 0 1
2
34
Fig. 6 Influence of scopolamine on the retention effect of AT II on rats in step-through passive avoidance task. Groups: 1 - Controls; 2 - AT II 0.1 kg; 3 - Scopolamine 2mg/kg; 4 - AT II + Scopolamine.
in cholinergic innervation (21) and in AT II binding sites (22). The results and the data about the influence of saralasin, DAergic and GABAergic agonists and antagonists on the pre- and post-trial effects of AT II (1,3,5,7,23) suggest a complex interaction between these systems in memory processes. In conclusion, cholinergic neurotransmission participates in retention and in the mechanisms of the retention-improving effect of AT II in active and passive avoidance.
9.
10.
11.
12. 13.
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