European Journal of Pharmacology, 198 (1991) 109-112
109
© 1991 Elsevier Science Publishers B.V. 0014-2999/91/$03.50 ADONIS 001429999100415Z EJP 20834
Short communication
Antagonism by propyl-fl-carboline-3-carboxylate of passive avoidance impairment induced by diazepam T a d a s h i Nagatani and Tsuneyuld Y a m a m o t o l Department of Pharmacology, Nobeoka Medicines Laboratory, Life Science Research Laboratories, Asahi Chemical Industry Co., Ltd., 6-2700 Asahi-machi, Nobeoka, Miyazaki 882, Japan and 1 Department of Pharmacology, Faculty of Pharmaceutical Sciences, Kyushu University 62, Fukuoka 812, Japan Received 20 March 1991, accepted 9 April 1991
We investigated the effects of propyl-/3-carboline-3-carboxylate (/3-CCP) on learning and memory tasks in a passive avoidance test in mice to clarify whether/3-CCP is an agonist or antagonist at benzodiazepine (BZP) receptors. At doses up to 10 mg/kg i.v., /3-CCP had no effect on mice in the passive avoidance test. Diazepam impaired passive avoidance behavior and methyl-/3-carboline-3-carboxylate(/3-CCM) enhanced it./3-CCP blocked these effects of diazepam and/3-CCM in a dose-dependent manner similar to the effect of Ro15-1788. These effects of/3-CCP, which are thought to be mediated by BZP receptors, indicate that/3°CCP is an antagonist in the passive avoidance test. /3-CCP (propyl-/3-carboline-3-carboxylate); Diazepam; Learning and memory; Passive avoidance behaviour
1. Introduction
Recently, benzodiazepine (BZP) has been shown to impair the performance of subjects in tasks involving learning and memory in clinical and animal studies (Peterson and Cohneim, 1980; Sanger and Joly, 1985; Venault et al., 1986). In contrast, methyl-/3-carboline3-carboxylate (/3-CCM) has been reported to enhance performance in learning and memory tasks (Venault et al., 1986). Since these effects of diazepam and/3-CCM in animal studies were blocked by Ro15-1788, BZP receptors seem to play a role in learning and memory mechanisms. Ligands of central BZP receptors are classified into three overlapping groups: agonist, antagonist and inverse agonist. Diazepam has been classified as an agonist and /3-CCM has been classified as an inverse agonist because the pharmacological effects of/3-CCM (e.g. proconflict and convulsant effect) are opposite to those of BZP (Prado de Carvalho et al., 1984; Nagatani et al., 1988). Propyl-/3-carboline-3-carboxylate (/3-CCP), like /3-CCM, has high affinity for central BZP receptors, but the classification of/3-CCP as a BZP ligand is
Correspondence to: T. Nagatani, Department of Pharmacology, Nobeoka Medicines Laboratory, Life Science Research Laboratories, Asahi Chemical Industry Co., Ltd., 6-2700 Asahi-Machi, Nobeoka,
Miyazaki 882, Japan.
uncertain although an earlier report (Valin et al., 1982) indicated that fl-CCP blocked convulsions induced by /3-CCM in baboons. We attempted to clarify whether/3-CCP is a BZP ligand in learning and memory, using a passive avoidance apparatus.
2. Materials and methods
2.1. Animals The subjects were male ddY mice (Seiwa Experimental Animals Ltd.) weighing 24-28 g. They were housed in 30 x 30 × 13 cm plastic cages in groups of 10, with free access to food and water at all times except while the tests were performed. 2.2. Apparatus and procedure A modification of the one-trial passive avoidance task described by Jarvic and Essman (1960) was used. The apparatus consisted of an illuminated small chamber (transparent plastic walls and ceiling, 10 × 15 × 10 cm) and a darkened chamber (opaque black plastic walls and ceiling, 16 x 16 x 14 cm). The two chambers were connected by a passage with a guillotine door (8 cm wide). This apparatus was put in a sound- and light-proof box with a small pinhole window. In train-
ing se~,;ions the mice were gently placed in the illuminated chamber, facing the opposite direction to the guillotine door. As soon as they e n t e r e d the d a r k e n e d chamber, the guillotine door was closed a n d an electrical foot shock (2 mA, I s or 1 m A , 1 s) was administered (acquisition session). The mice were removed from this d a r k e n e d c h a m b e r immediately after shock administration a n d r e t u r n e d to their h o m e cage. Twenty-four hours after this acquisition session, the mice were again plated in the illuminated c h a m b e r and the latency to enter the d a r k e n e d c h a m b e r was recorded (test session). However, the trial was terminated if the mice r e m a i n e d in the illuminated c h a m b e r for 300 s. D r u g s were administered three times: just prior to the acquisition session, immediately after the acquisition session and just prior to the test session.
23. Dntgs The following drugs were used: propyl-/3-carboline3-carbox3,1ate (/3-CCP, Asahi Chemical Ind. Co., Ltd.), methyl-/3-carboline-3-carboxylate (/3-CCM, Asahi Chemical Ind. Co., Ltd.), diazepam (Cercine, T a k e d a Pharmaceutical Co.), and Ro15-1788 (Asahi Chemical Ind. Co., Ltd.). /3-CCM was dissolved in 0.9% NaCI with 1 drop of 1 N H C i / 5 m l . / 3 - C C P a n d Ro15-1788 were suspended in 1% methylcellulose a n d 0.1% T w e e n 80, respectively. /3-CCM and /3-CCP were administered i.v. Ro15-1788 and d i a z e p a m w e r e a d m i n i s t e r e d i.p. in a constant volume of 0.01 m l / g . T h e t r e a t m e n t time of each drug upon administration prior to the training or the test session was as follows: 10 min for /3-CCM a n d / 3 - C C P , 15 min for Ro15-1788 and 30 min for diazepam. W h e n / 3 - C C P was a d m i n i s t e r e d in combination with /3-CCM, the t r e a t m e n t time of /3-CCP was 12 min.
2.4. Statistical treatment D a t a for groups of mice are expressed as m e d i a n latencies to e n t e r the d a r k e n e d c h a m b e r , a n d comparisons between the groups were m a d e using the Kruskal-Wallis test.
3. Results
As shown in table 1, the m e a n (_+ S.E.) latency to enter the d a r k e n e d c o m p a r t m e n t of the control group on the test session was 286.5 _+ 8.1 s w h e n the electric current intensity was 2 mA, 1 s. D i a z e p a m r e d u c e d the latency in this condition in a d o s e - d e p e n d e n t m a n n e r when it was administered prior to the acquisition session (table 1). fl-CCP itself, like f l - C C M and Ro151788, did not have a significant effect on the latency periods, when administered prior to the acquisition
TABLE 1 Effects on mice of/3-carbolines and diazepam and Ro15-1788 in a passive avoidance test. a Controls were rats that did not receive any drug. b Latencies are expressed as mean values ( _+S.E.). (A) Latency measured whetl the electric current intensity was 2.0 mA, 1 s. (B) Latency measured when the electric current intensity was 0.5 mA, 1 s. Each drug was administered prior to the acquisition session. The treatment time of each drug was as follows: fl-CCP 10 min i.v., /3-CCM l0 min i.v., diazepam 30 min i.p. and Ro15-1788 15 min i.p. Significant differences from the control value: c p < 0.05, a p < 0.01, P < 0.005 by KruskaI-Wallis test. Drug (A) Control ~ -CCP -CCP -CCP 3-CCP 3-CCP 3-CCM 3-CCM 3-CCM 3-CCM ~-CCM Diazepam Diazepam Diazepam Diazepam Ro15-1788 Ro15-1788 Ro15-1788 (B) Control
/3-CCP fl-CCP fl-CCP fl-CCP /3-CCP /3-CCM fl-CCM /3-CCM fl-CCM fl-CCM Diazepam Diazepam Diazepam Diazepam Ro15-1788 Ro15-1788 Ro15-1788
Dose (mg/kg) 0.1 0.3 1
3 10 0.03 0.1 0.3 1 3 0.1 0.3 1
3 3 10 30 -
0.1 0.3 1 3 10 0.01 0.03 0.1 0.3 1 0.1 0.3 1
3 3 10 30
N
Latency (s) b
45 10 10
286.5_+ 8.1 298.4_+ 6.7 276.4_+ 5.8 288.4_+ 6.4 298.4_+ 2.0 294.0_+ 6.0 284.2_+ 14.0 279.0 _+21.0 253.2 _+20.0 258.0 _+20.9 199.7_+51.1 268.4_+ 12.0 149.9 _+38.0 d 46.8_+ 18.0 e 23.7_+ 8.9 e 284.8 _+15.3 288.6_+ 8.2 273.5 _+13.6
10
10 10 10 10 10 10 10 10 10 10 10 8 8 8 40 10 10 I0 10 10 10 10 10 10 10 10 10 10 10 10 10 10
35.6_+ 4.8 34.7_+ 7.2 33.0_+ 6.6 39.2_+ 4.6 41.0_+ 14.6 36.2_+ 9.4 70.4 _+17.2 85.0_+ 16.7 c 97.2_+ 19.8 c 120.6 _+26.4 c 92.5_+ 3.6 c 33.6_+ 2.7 24.2_+ 1.9 c 17.4_+ 3.7 c 9.6_+ 2.0 e
34.2_+ 6.3 39.3_+ 4.8 37.7_+ 10.1
session u n d e r these test conditions (table 1). N o n e of the drugs affected the latency periods w h e n they were a d m i n i s t e r e d aRer the acquisition session or prior to the test session (data not shown). The m e a n (_+ S.E.) latency of the control g r o u p was r e d u c e d to 35.6 _+ 4.8 s w h e n the electric c u r r e n t intensity was changed to 0.5 m A (table 1). U n d e r these conditions, d i a z e p a m also reduced the latency in a d o s e - d e p e n d e n t m a n n e r w h e n it was a d m i n i s t e r e d prior to the acquisition session (table 1). N e i t h e r / 3 - C C P nor Ro15-1788 affected the m e a n latency w h e n adminis-
111 (A)
4. Discussion 70 60
-'(n
5O
=,, 40 f.1 c
o
,.J
30
20 10
l
i 1 3 10 0.1 0.3 1 1 3 10 ( m g l k g ) `8- CCP `8- CCM Ro15 - 1788
Control
Diazepam ( 3 mg / kg )
(B) 150
~" 100
I
:),, o
,,J
0
n
Control
h nii
3 10 0.3 1 3 1 0 0.03 0.1 0.31 ( m g / k g ) 0.3 `8- CCP Ro15 - 1788 Diazepam
,8- CCM ( 0.3 mg / kg ) Fig. 1. (A) Effects on mice of/3-CCP, 3-CCM and Ro15-1788 on the impairment effect induced by diazepam in a passive avoidance task. (B) Effects on mice of fl-CCP, Ro15-1788 and diazepam on the enhancement effect induced by/3-CCM in a passive avoidance task. /3-CCP and fl-CCM were administered i.v. and Ro15-1788 and diazepam were administered i.p. The treatment time of each drug was as follows: 10 min for/3-CCP and fl-CCM, 15 min tor Ro15-1788 and 30 min for diazepam. Each drug was administered prior to the acquisition session. Asterisks denote significant differences from the values when diazepam was administered alone or the value when fl-CCM was administered alone. Closed triangles denote significant differences from the control value. * P < 0.05, * * P < 0.01, * * * P < 0.005 by Kruskal-Wallis test.
tered prior to the acquisition session. However,/3-CCM prolonged the latency significantly when it was administered prior to the acquisition session (table 1). The impairment effect of diazepam and the enhancement effect of/3-CCM were not observed when these agents were administered immediately after the acquisition session or just prior to the test session respectively (data not shown). Like/3-CCM and Ro15-1788,/3-CCP clearly blocked the impairment effect of diazepam (fig. 1A). These blocking effects of each drug were seen only when the drugs were administered prior to the acquisition session (data not shown). The enhancement effect of /3-CCM was also blocked by /3-CCP, Ro151788 and diazepam when they were administered just prior to the acquisition session (fig. 1B). The blocking effect of these drugs was not seen when they were administered immediately after the acquisition session or just prior to the test session (data not shown).
A number of clinical studies and animal experiments have shown that diazepam impairs performance in learning and memory tasks. In addition, Venault et al. (1986) have reported that /3-CCM enhances performance in learning and memory tasks. In this study, we confirmed the impairment effect of diazepam and the enhancement effect of/3-CCM in a passive avoidance test. Additionally, these effects of diazepam and /3CCM were blocked by pretreatment with Ro15-1788. These findings are in accordance with those of Venault et al. (1986). We found that the blocking activity of Ro15-1788 was exerted only when the drug was administered together with diazepam or/3-CCM prior to the acquisition session. Diazepam and /3-CCM seemed to exert their effects in passive avoidance tasks through a BZP receptor. In this study, we showed that ~-CCP did not have an effect on a passive avoidance behavior when it was administered alone. However,/3-CCP blocked not only the impairment effect of diazepam but also the enhancement effect of/3-CCM in a dose-dependent manner. Like the blocking effect of Ro15-1788, this blocking effect of/3-CCP was observed only when the drug was administered prior to the acquisition session and together with diazepam or/3-CCM. As/3-CCP did not have an effect on spontaneous motor activity at the doses used,/3-CCP seemed to exert its blocking effect by competition through a BZP receptor. We did not observe the enhancement effect of /3CCM when the current electric intensity was 2.0 mA. It is possible that since the motivation was so intense, the latency was long in non-drug-treated rats (286.5 + 8.1, mean + S.E.), and /3-CCM could not exert its enhancing effect under these conditions. /3-CCP has high affinity for the central BZP receptor and has various pharmacological activities. We reported previously that /3-CCP has a mild anti-conflict effect (Nagatani et al., 1988) as well as the ability to prolong the duration of immobility in the forced swimming test, as does diazepam (Nagatani et al., 1987). In addition, the presence of y-aminobutyric acid (GABA) increases the affinity of fl-CCP for the BZP receptor, and /3-CCP enhances GABA affinity (Nielsen et al., 1981; Doble et al., 1982; Skerrit et al., 1983). These findings suggest that/3-CCP is an agonist. In conclusion, /3-CCP itself did not have an effect on passive avoidance behavior, but blocked both the impairment effect of diazepam and the enhancement effect of/3-CCM. These effects of/3-CCP are thought to be exerted through the BZP receptor, as are the effects of Ro15-1788. /3-CCP, similar to Ro15-1788, seems to fit the classification of an antagonist in passive avoidance tasks.
Ac ~l~r~owledgement 1"his research ~as supported in part by a Grant-in-Aid for Scientific Research(C~ from the Ministry. of Education, Science and Culture of Japan.
Refe~nces Doble, A., I.L. Martin and D.A. Richards, 1982, GABA modulation precicts biological actix~ty of ligands for the benzodiazepine rece3tor, Br. J. Pharmacol. 76, 238. Jar¢ic, M.E. and W.B. Essam, 1960, A simple one-trial learning situation for mice. Psychol. Rep. 6, 290. Nagatani, T., T. Yamamoto, T. Sugihara and S. Ueki, 1987, The effect of agonist at the GABA-benzodiazepine receptor complex on the duration of immobility of mice in the forced swimming test, European J. Pharmacol. 142, 17. Nagatani, T., T. Yamamoto, T. Sugihara and S. Ueki, 1988, The effect of agonist at the GABA-benzodiazepine-receptor complex on the proconflict effect induced by fl-CCM and pentetrazol in rots, Jap. J. Pharmacoi. 46, 267.
Nielsen, M., H. Schou and C. Braestrup, 1981, 3H-Propyl-fl-carbolate binds specificially to brain benzodiazepine receptors. J. Neurochem. 36, 276. Peterson, R.C. and M.M. Cohneim, 1980, Diazepam and human memory: influence on acquisition, retrieval and state-dependent learning, Prog. Neuro-Psychopharmacol. 4, 81. Prado de Carvalho, P., L.G. Grecksch, E,A. Cavalheiro, R.H. Dodd, G. Chapouthier and J. Rossier, 1984, Characterization of convulsion induced by methyl-fl-carboline-3,carboxylate in mice, European J. Pharmacol. 103, 287. Sanger, D.J. and D. Joly, 1985, Anxiolytic drugs and the acquisition of conditioned fear in mice, Psychopharmacelogy 85, 284. Skerrit, J.H., G.A. Johnston and C. Braestrup, 1983, Modulation of GABA binding to rat brain membranes by alkyl-fl-carboline-3carboxylate esters, European J. Pharmacol. 86, 299. Vaiin, A., R.H. Dodd, D.R. Liston, P. Potier and J. Rossier, 1982, Methyl-/3-carboline-induced convulsions are antagonized by Ro15-1788 and by propyl-fl-carboline, European J. Pharmacel. 85, 93. Venault, P., G. Chapouthier, L.P. Carvalho, J. Simiand, M. Morre, R.H. Dodd and J. Rossier, 1986, Benzodiazepine impairs and B-carboline enhances performance in learning and memory tasks, Nature 321,864.
109
© 1991 Elsevier Science Publishers B.V. 0014-2999/91/$03.50 ADONIS 001429999100415Z EJP 20834
Short communication
Antagonism by propyl-fl-carboline-3-carboxylate of passive avoidance impairment induced by diazepam T a d a s h i Nagatani and Tsuneyuld Y a m a m o t o l Department of Pharmacology, Nobeoka Medicines Laboratory, Life Science Research Laboratories, Asahi Chemical Industry Co., Ltd., 6-2700 Asahi-machi, Nobeoka, Miyazaki 882, Japan and 1 Department of Pharmacology, Faculty of Pharmaceutical Sciences, Kyushu University 62, Fukuoka 812, Japan Received 20 March 1991, accepted 9 April 1991
We investigated the effects of propyl-/3-carboline-3-carboxylate (/3-CCP) on learning and memory tasks in a passive avoidance test in mice to clarify whether/3-CCP is an agonist or antagonist at benzodiazepine (BZP) receptors. At doses up to 10 mg/kg i.v., /3-CCP had no effect on mice in the passive avoidance test. Diazepam impaired passive avoidance behavior and methyl-/3-carboline-3-carboxylate(/3-CCM) enhanced it./3-CCP blocked these effects of diazepam and/3-CCM in a dose-dependent manner similar to the effect of Ro15-1788. These effects of/3-CCP, which are thought to be mediated by BZP receptors, indicate that/3°CCP is an antagonist in the passive avoidance test. /3-CCP (propyl-/3-carboline-3-carboxylate); Diazepam; Learning and memory; Passive avoidance behaviour
1. Introduction
Recently, benzodiazepine (BZP) has been shown to impair the performance of subjects in tasks involving learning and memory in clinical and animal studies (Peterson and Cohneim, 1980; Sanger and Joly, 1985; Venault et al., 1986). In contrast, methyl-/3-carboline3-carboxylate (/3-CCM) has been reported to enhance performance in learning and memory tasks (Venault et al., 1986). Since these effects of diazepam and/3-CCM in animal studies were blocked by Ro15-1788, BZP receptors seem to play a role in learning and memory mechanisms. Ligands of central BZP receptors are classified into three overlapping groups: agonist, antagonist and inverse agonist. Diazepam has been classified as an agonist and /3-CCM has been classified as an inverse agonist because the pharmacological effects of/3-CCM (e.g. proconflict and convulsant effect) are opposite to those of BZP (Prado de Carvalho et al., 1984; Nagatani et al., 1988). Propyl-/3-carboline-3-carboxylate (/3-CCP), like /3-CCM, has high affinity for central BZP receptors, but the classification of/3-CCP as a BZP ligand is
Correspondence to: T. Nagatani, Department of Pharmacology, Nobeoka Medicines Laboratory, Life Science Research Laboratories, Asahi Chemical Industry Co., Ltd., 6-2700 Asahi-Machi, Nobeoka,
Miyazaki 882, Japan.
uncertain although an earlier report (Valin et al., 1982) indicated that fl-CCP blocked convulsions induced by /3-CCM in baboons. We attempted to clarify whether/3-CCP is a BZP ligand in learning and memory, using a passive avoidance apparatus.
2. Materials and methods
2.1. Animals The subjects were male ddY mice (Seiwa Experimental Animals Ltd.) weighing 24-28 g. They were housed in 30 x 30 × 13 cm plastic cages in groups of 10, with free access to food and water at all times except while the tests were performed. 2.2. Apparatus and procedure A modification of the one-trial passive avoidance task described by Jarvic and Essman (1960) was used. The apparatus consisted of an illuminated small chamber (transparent plastic walls and ceiling, 10 × 15 × 10 cm) and a darkened chamber (opaque black plastic walls and ceiling, 16 x 16 x 14 cm). The two chambers were connected by a passage with a guillotine door (8 cm wide). This apparatus was put in a sound- and light-proof box with a small pinhole window. In train-
ing se~,;ions the mice were gently placed in the illuminated chamber, facing the opposite direction to the guillotine door. As soon as they e n t e r e d the d a r k e n e d chamber, the guillotine door was closed a n d an electrical foot shock (2 mA, I s or 1 m A , 1 s) was administered (acquisition session). The mice were removed from this d a r k e n e d c h a m b e r immediately after shock administration a n d r e t u r n e d to their h o m e cage. Twenty-four hours after this acquisition session, the mice were again plated in the illuminated c h a m b e r and the latency to enter the d a r k e n e d c h a m b e r was recorded (test session). However, the trial was terminated if the mice r e m a i n e d in the illuminated c h a m b e r for 300 s. D r u g s were administered three times: just prior to the acquisition session, immediately after the acquisition session and just prior to the test session.
23. Dntgs The following drugs were used: propyl-/3-carboline3-carbox3,1ate (/3-CCP, Asahi Chemical Ind. Co., Ltd.), methyl-/3-carboline-3-carboxylate (/3-CCM, Asahi Chemical Ind. Co., Ltd.), diazepam (Cercine, T a k e d a Pharmaceutical Co.), and Ro15-1788 (Asahi Chemical Ind. Co., Ltd.). /3-CCM was dissolved in 0.9% NaCI with 1 drop of 1 N H C i / 5 m l . / 3 - C C P a n d Ro15-1788 were suspended in 1% methylcellulose a n d 0.1% T w e e n 80, respectively. /3-CCM and /3-CCP were administered i.v. Ro15-1788 and d i a z e p a m w e r e a d m i n i s t e r e d i.p. in a constant volume of 0.01 m l / g . T h e t r e a t m e n t time of each drug upon administration prior to the training or the test session was as follows: 10 min for /3-CCM a n d / 3 - C C P , 15 min for Ro15-1788 and 30 min for diazepam. W h e n / 3 - C C P was a d m i n i s t e r e d in combination with /3-CCM, the t r e a t m e n t time of /3-CCP was 12 min.
2.4. Statistical treatment D a t a for groups of mice are expressed as m e d i a n latencies to e n t e r the d a r k e n e d c h a m b e r , a n d comparisons between the groups were m a d e using the Kruskal-Wallis test.
3. Results
As shown in table 1, the m e a n (_+ S.E.) latency to enter the d a r k e n e d c o m p a r t m e n t of the control group on the test session was 286.5 _+ 8.1 s w h e n the electric current intensity was 2 mA, 1 s. D i a z e p a m r e d u c e d the latency in this condition in a d o s e - d e p e n d e n t m a n n e r when it was administered prior to the acquisition session (table 1). fl-CCP itself, like f l - C C M and Ro151788, did not have a significant effect on the latency periods, when administered prior to the acquisition
TABLE 1 Effects on mice of/3-carbolines and diazepam and Ro15-1788 in a passive avoidance test. a Controls were rats that did not receive any drug. b Latencies are expressed as mean values ( _+S.E.). (A) Latency measured whetl the electric current intensity was 2.0 mA, 1 s. (B) Latency measured when the electric current intensity was 0.5 mA, 1 s. Each drug was administered prior to the acquisition session. The treatment time of each drug was as follows: fl-CCP 10 min i.v., /3-CCM l0 min i.v., diazepam 30 min i.p. and Ro15-1788 15 min i.p. Significant differences from the control value: c p < 0.05, a p < 0.01, P < 0.005 by KruskaI-Wallis test. Drug (A) Control ~ -CCP -CCP -CCP 3-CCP 3-CCP 3-CCM 3-CCM 3-CCM 3-CCM ~-CCM Diazepam Diazepam Diazepam Diazepam Ro15-1788 Ro15-1788 Ro15-1788 (B) Control
/3-CCP fl-CCP fl-CCP fl-CCP /3-CCP /3-CCM fl-CCM /3-CCM fl-CCM fl-CCM Diazepam Diazepam Diazepam Diazepam Ro15-1788 Ro15-1788 Ro15-1788
Dose (mg/kg) 0.1 0.3 1
3 10 0.03 0.1 0.3 1 3 0.1 0.3 1
3 3 10 30 -
0.1 0.3 1 3 10 0.01 0.03 0.1 0.3 1 0.1 0.3 1
3 3 10 30
N
Latency (s) b
45 10 10
286.5_+ 8.1 298.4_+ 6.7 276.4_+ 5.8 288.4_+ 6.4 298.4_+ 2.0 294.0_+ 6.0 284.2_+ 14.0 279.0 _+21.0 253.2 _+20.0 258.0 _+20.9 199.7_+51.1 268.4_+ 12.0 149.9 _+38.0 d 46.8_+ 18.0 e 23.7_+ 8.9 e 284.8 _+15.3 288.6_+ 8.2 273.5 _+13.6
10
10 10 10 10 10 10 10 10 10 10 10 8 8 8 40 10 10 I0 10 10 10 10 10 10 10 10 10 10 10 10 10 10
35.6_+ 4.8 34.7_+ 7.2 33.0_+ 6.6 39.2_+ 4.6 41.0_+ 14.6 36.2_+ 9.4 70.4 _+17.2 85.0_+ 16.7 c 97.2_+ 19.8 c 120.6 _+26.4 c 92.5_+ 3.6 c 33.6_+ 2.7 24.2_+ 1.9 c 17.4_+ 3.7 c 9.6_+ 2.0 e
34.2_+ 6.3 39.3_+ 4.8 37.7_+ 10.1
session u n d e r these test conditions (table 1). N o n e of the drugs affected the latency periods w h e n they were a d m i n i s t e r e d aRer the acquisition session or prior to the test session (data not shown). The m e a n (_+ S.E.) latency of the control g r o u p was r e d u c e d to 35.6 _+ 4.8 s w h e n the electric c u r r e n t intensity was changed to 0.5 m A (table 1). U n d e r these conditions, d i a z e p a m also reduced the latency in a d o s e - d e p e n d e n t m a n n e r w h e n it was a d m i n i s t e r e d prior to the acquisition session (table 1). N e i t h e r / 3 - C C P nor Ro15-1788 affected the m e a n latency w h e n adminis-
111 (A)
4. Discussion 70 60
-'(n
5O
=,, 40 f.1 c
o
,.J
30
20 10
l
i 1 3 10 0.1 0.3 1 1 3 10 ( m g l k g ) `8- CCP `8- CCM Ro15 - 1788
Control
Diazepam ( 3 mg / kg )
(B) 150
~" 100
I
:),, o
,,J
0
n
Control
h nii
3 10 0.3 1 3 1 0 0.03 0.1 0.31 ( m g / k g ) 0.3 `8- CCP Ro15 - 1788 Diazepam
,8- CCM ( 0.3 mg / kg ) Fig. 1. (A) Effects on mice of/3-CCP, 3-CCM and Ro15-1788 on the impairment effect induced by diazepam in a passive avoidance task. (B) Effects on mice of fl-CCP, Ro15-1788 and diazepam on the enhancement effect induced by/3-CCM in a passive avoidance task. /3-CCP and fl-CCM were administered i.v. and Ro15-1788 and diazepam were administered i.p. The treatment time of each drug was as follows: 10 min for/3-CCP and fl-CCM, 15 min tor Ro15-1788 and 30 min for diazepam. Each drug was administered prior to the acquisition session. Asterisks denote significant differences from the values when diazepam was administered alone or the value when fl-CCM was administered alone. Closed triangles denote significant differences from the control value. * P < 0.05, * * P < 0.01, * * * P < 0.005 by Kruskal-Wallis test.
tered prior to the acquisition session. However,/3-CCM prolonged the latency significantly when it was administered prior to the acquisition session (table 1). The impairment effect of diazepam and the enhancement effect of/3-CCM were not observed when these agents were administered immediately after the acquisition session or just prior to the test session respectively (data not shown). Like/3-CCM and Ro15-1788,/3-CCP clearly blocked the impairment effect of diazepam (fig. 1A). These blocking effects of each drug were seen only when the drugs were administered prior to the acquisition session (data not shown). The enhancement effect of /3-CCM was also blocked by /3-CCP, Ro151788 and diazepam when they were administered just prior to the acquisition session (fig. 1B). The blocking effect of these drugs was not seen when they were administered immediately after the acquisition session or just prior to the test session (data not shown).
A number of clinical studies and animal experiments have shown that diazepam impairs performance in learning and memory tasks. In addition, Venault et al. (1986) have reported that /3-CCM enhances performance in learning and memory tasks. In this study, we confirmed the impairment effect of diazepam and the enhancement effect of/3-CCM in a passive avoidance test. Additionally, these effects of diazepam and /3CCM were blocked by pretreatment with Ro15-1788. These findings are in accordance with those of Venault et al. (1986). We found that the blocking activity of Ro15-1788 was exerted only when the drug was administered together with diazepam or/3-CCM prior to the acquisition session. Diazepam and /3-CCM seemed to exert their effects in passive avoidance tasks through a BZP receptor. In this study, we showed that ~-CCP did not have an effect on a passive avoidance behavior when it was administered alone. However,/3-CCP blocked not only the impairment effect of diazepam but also the enhancement effect of/3-CCM in a dose-dependent manner. Like the blocking effect of Ro15-1788, this blocking effect of/3-CCP was observed only when the drug was administered prior to the acquisition session and together with diazepam or/3-CCM. As/3-CCP did not have an effect on spontaneous motor activity at the doses used,/3-CCP seemed to exert its blocking effect by competition through a BZP receptor. We did not observe the enhancement effect of /3CCM when the current electric intensity was 2.0 mA. It is possible that since the motivation was so intense, the latency was long in non-drug-treated rats (286.5 + 8.1, mean + S.E.), and /3-CCM could not exert its enhancing effect under these conditions. /3-CCP has high affinity for the central BZP receptor and has various pharmacological activities. We reported previously that /3-CCP has a mild anti-conflict effect (Nagatani et al., 1988) as well as the ability to prolong the duration of immobility in the forced swimming test, as does diazepam (Nagatani et al., 1987). In addition, the presence of y-aminobutyric acid (GABA) increases the affinity of fl-CCP for the BZP receptor, and /3-CCP enhances GABA affinity (Nielsen et al., 1981; Doble et al., 1982; Skerrit et al., 1983). These findings suggest that/3-CCP is an agonist. In conclusion, /3-CCP itself did not have an effect on passive avoidance behavior, but blocked both the impairment effect of diazepam and the enhancement effect of/3-CCM. These effects of/3-CCP are thought to be exerted through the BZP receptor, as are the effects of Ro15-1788. /3-CCP, similar to Ro15-1788, seems to fit the classification of an antagonist in passive avoidance tasks.
Ac ~l~r~owledgement 1"his research ~as supported in part by a Grant-in-Aid for Scientific Research(C~ from the Ministry. of Education, Science and Culture of Japan.
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