- Email: [email protected]
Intracranial self-stimulation distinguishes between two benzodiazepine antagonists
Neuroscience Letters, 47 (1984) 173-177 Elsevier Scientific Publishers Ireland Ltd.
173
NSL 02740 INTRACRANIAL SELF-STIMULATION DISTINGUISHES BETWEEN TWO BENZODIAZEPINE ANTAGONISTS
SHARON PELLOWl, SANDRA E. FILE1 AND L.J. HERBERG 2 IMRC Neuropharmacology Research Group, Department of Pharmacology, The School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N l A X and ~Experimental Psychology Laboratory, Institute o f Neurology, Queen Square, London WC1N 3BG (U.K.)
(Received February 20th, 1984; Revised version received March 15th, 1984; Accepted March 16th, 1984)
Key words: benzodiazepine antagonists - chlordiazepoxide - self-stimulation
Low doses of Ro 15-1788 and CGS 8216 were without effect on variable-interval self-stimulation, but completely abolished the enhancement of responding produced by chlordiazepoxide (5 mg/kg). Higher doses of Ro 15-1788, unlike other benzodiazepine receptor antagonists, produced an increase in response rates similar to that found after chlordiazepoxide. This result is consistent with its suggested action as a partial agonist. The combination of a high (benzodiazepine-like) dose of Ro 15-1788 with chlordiazepoxide produced a depression of responding similar to that seen with high doses of benzodiazepines. High doses of CGS 8216 produced a depression of self-stimulation, which was not reversed by chlordiazepoxide (5 mg/kg). Thus, the present procedure is able to distinguish contrasting behavioural effects of benzodiazepine antagonists.
Since the discovery o f benzodiazepine binding sites in the C N S [15, 20], a variety o f c o m p o u n d s have been discovered that displace 3H-benzodiazepines f r o m their binding sites a n d that reverse their p h a r m a c o l o g i c a l actions. These include the imidazodiazepine, R o 15-1788, the pyrazoloquinoline, C G S 8216, and alkyl /3carboline-3-carboxylates [2, 12, 21]. These c o m p o u n d s have intrinsic activity generally in the direction opposite to that o f benzodiazepines. Thus, C G S 8216 is anxiogenic in various tests o f anxiety, [5, 14, 19] and proconvulsant (4, 13] in rodents. R o 15-1788 is also anxiogenic in the social interaction test [7] and the openfield novelty procedure [11]; but unlike C G S 8216 it has anticonvulsant activity at low doses [1, 9, 13] and at high doses actually takes on certain benzodiazepine-like properties [3, 16]. Response to intracranial self-stimulation at threshold currents on a variableinterval 10-s schedule o f reinforcement is sensitive to the effects o f benzodiazepines a n d other G A B A e r g i c c o m p o u n d s [10] and to the effects o f the/~-carboline F G 7142 [18]. We therefore wished to investigate a n y intrinsic actions o f R o 15-1788 and C G S 8216 on self-stimulation p e r f o r m a n c e , and to see if they could reverse the e n h a n c e m e n t usually p r o d u c e d by chlordiazepoxide [10]. 0304-3940/84/$ 03.00 © 1984 Elsevier Scientific Publishers Ireland Ltd.
174
Under halothane anesthesia, male hooded PVG rats (Banting and Kingman Ltd.) weighing 200-230 g at time of surgery were stereotaxically implanted in the midlateral hypothalamus with twisted bipolar stainless-steel electrodes (0.25 mm diameter). Coordinates were 1.0 mm posterior to bregma, 1.3 mm to the left of the midline and 9.0 mm below the skull surface [17]. Electrode placements were determined from enlarged photographic projections of 50-t~m frozen sections at the end of the experiments. After recovery (1 week) rats were trained to operate a pedal for a 0.5-s 50-Hz sinewave reinforcing impulse available on a variable-interval schedule of 10-s mean duration. The stimulating current for each rat was fixed at the lowest intensity that elicited steady and sustained responding. During test sessions, animals were allowed to respond for self-stimulation for 45 min, of which the last 30 min provided a pre-injection baseline. The rat was then injected and allowed to selfstimulate for a further 60 min. Response rates were recorded automatically at 5-min intervals; drug effects were determined from the rate recorded during the second 15-min period after injection, expressed as a percentage of the pre-injection baseline, and compared with the corresponding rate after control injections. Two groups of rats received the following drug treatments in a random order: Group 1 (n=6): vehicle, Ro 15-1788 (2, 10, 20 and 50 mg/kg), CDP (5 mg/kg), and Ro 15-1788 (2 and 50 mg/kg) + CDP (5 mg/kg). Group 2 (n=6): control, CGS 8216 (2, 10 and 20 mg/kg), CDP (5 mg/kg), and CGS 8216 (2 and 10 mg/kg) + CDP (5 mg/kg). Rats were tested no more than once every 48 h. Ro 15-1788 and CGS 8216 were suspended in distilled water with a drop of Tween 20; chlordiazepoxide hydrochloride (CDP) (Roche Products) was dissolved in distilled water. Control injections consisted of distilled water, with or without a drop of Tween 20 as appropriate. Drugs were injected intraperitoneally in a volume of 2 ml/kg. CDP (5 mg/kg) significantly enhanced self-stimulation (P< 0.05, Wilcoxon test, see Fig. la, b); this effect was reversed by Ro 15-1788 at 2 mg/kg (P<0.05, Fig. la), and by CGS 8216 (2 and 10 mg/kg, P<0.05, see Fig. lb); these results are consistent with previous research using other procedures [12, 21]. At the low doses neither Ro 15-1788 nor CGS 8216 showed any intrinsic activity (see Fig. 1); however, at higher doses they had contrasting effects on self-stimulation. When it was given alone, Ro 15-1788 overall had a significant effect on selfstimulation (X2= 13.86, P<0.01, Friedman analysis of variance), but post hoc analysis with Wilcoxon matched-pairs signed-ranks tests showed that this was mainly due to the 50 mg/kg dose (P< 0.05, see Fig. la) which enhanced self-stimulation compared with controls. This suggests that at high doses Ro 15-1788 acts like a low dose of a benzodiazepine, which is particularly likely in the light of other behavioural studies showing benzodiazepine-like activity with high doses of Ro 15-1788, which have led to the proposal that Ro 15-1788 may be a partial agonist at benzodiazepine receptors [3, 16]. CGS 8216 had a significant overall effect on self-stimulation (X2 = 15.2, P < 0.005, Friedman analysis of variance), and post hoc analysis showed that higher doses of
175
a)
b) 200
200 Ot
I
~.
150
150
L.. 0.. o E; 0
E
100
1O0
50
50
d'l I
U3
t
0
i
i
,
5 10
I
,J
20
50
0
t
0
t
J
I
5 10
J
20
DOSE ( m g l k g ) Fig. I. Mean (+ S.E.M.) self-stimulation rate (variable interval, 10 s) in the second 15-min period after injection for rats given: (a) control, Ro 15-1788 (2-50 mg/kg), chlordiazepoxide (5 mg/kg) alone and in combination with Ro 15-1788 (2 and 50 mg/kg); and (b) control, CGS 8216 (2-20 mg/kg), chlordiazepoxide (5 mg/kg) alone and in combination with CGS 8216 (2 and 10 mg/kg). (O) Ro 15-1788 (a) and CGS 8216 alone (b); (A) chlordiazepoxide alone; (i) chlordiazepoxide + Ro 15-1788 (a), or CGS 8216 (b).
CGS 8216, unlike Ro 15-1788, depressed self-stimulation significantly below control rates ( P < 0.05, see Fig. lb). This is consistent with previous reports demonstrating reduced behaviour with CGS 8216 in the social interaction [5] and punished drinking [19] procedures; however, Ro 15-1788, like CGS 8216, also reduces social interaction at doses o f l0 m g / k g [7] and has intrinsic activity in the open-field novelty procedure [11] and on exploratory head-dipping [8], and so it was surprising that no effects were observed with Ro 15-1788 until doses at which it becomes benzodiazepine-like. We were then interested to See whether C D P could reverse the intrinsic activity obtained with higher doses of Ro 15-1788, and CGS 8216. Even though when given alone both Ro 15-1788 (50 m g / k g ) and chlordiazepoxide elevated self-stimulation, the combination produced a significant depression in self-stimulation compared with controls ( P < 0 . 0 5 , Wilcoxon test, see Fig. la). Behaviourally, these effects resemble those produced by higher doses of benzodiazepines [10], but the pharmacological basis o f the effects is unclear. A partial agonist in combination with a full agonist would not produce an additive effect (except perhaps at very low concentrations). Until the pharmacological basis of the effects of benzodiazepines on intracranial self-stimulation is more thoroughly investigated, we will be unable to
176
provide an adequate explanation for this finding. Similarly, an unexpected interaction between Ro 15-1788 and CDP was observed for exploratory behaviour in the holeboard test [8]. Response after the combined administration of CGS 8216 (10 mg/kg) and CDP (5 mg/kg) was also significantly reduced compared with controls (P< 0.05) and was not significantly different from CGS 8216 (10 mg/kg) alone (see Fig. lb). CDP (5 mg/kg) has been shown to reverse the reduction in self-stimulation produced by the t3-carboline FG 7142 [18] which is also thought to interact with benzodiazepine binding sites. The effect of CGS 8216 was no stronger than that of FG 7142, and so the inability of CDP to reverse the intrinsic activity of CGS 8216 on self-stimulation is consistent with previous suggestions (ref. 6, and File and Pellow, in preparation) that CGS 8216 at higher doses may have additional actions at brain systems unrelated to benzodiazepine binding sites. It is at these higher doses that other intrinsic actions of CGS 8216 have been observed, including an anxiogenic effect that also could not be reversed by CDP (File and Pellow, in preparation). It is necessary to consider whether the effects of Ro 15-1788 and CGS 8216 on self-stimulation were secondary to other pharmacological actions: neither drug has any effect on locomotor activity [5, 8] and so the results cannot be explained in terms of sedation. These two antagonists differ in their effects on seizure activity: Ro 15-1788 is anticonvulsant and CGS 8216 is proconvulsant. However, the current levels used in the present procedure were near threshold, and reward pulses could be obtained only at mean intervals of not less than 10 s; seizure activity is therefore unlikely to have played an important role. We conclude that intracranial selfstimulation provides another behavioural measure that can distinguish between these two antagonists. S.E.F. is a Wellcome Trust Senior Lecturer. We are grateful to Hoffman-La Roche for the gift of Ro 15-1788 and Ciba-Geigy for CGS 8216; and to the Medical Research Council for support. 1 Albertson, T.E., Bowyer, J.F. and Paule, M.G., Modification of the anticonvulsant efficacy of diazepam by Ro 15-1788 in the kindled amygdaloid seizure model, Life Sci., 31 (1982) 1597-1601. 2 Braestrup, C., Nielsen, M. and Olsen, C.E., Urinary and brain 13-carboline-3-carboxylates as potent inhibitors of brain benzodiazepine receptors, Proc. nat. Acad. Sci. U.S.A., 77 (1980) 2288-2292. 3 Dantzer, R. and Perio, A., Behavioural evidence for partial agonist properties of Ro 15-1788, a benzodiazepine receptor antagonist, Europ. J. Pharmacol., 81 (1982) 655-658. 4 File, S.E., Proconvulsant action of CGS 8216, Neurosci. Lett., 35 (1983) 317-320. 5 File, S.E. and Lister, R.G., Quinolines and anxiety: anxiogenic effects of CGS 8216 and partial anxiolytic profile of PK 9084, Pharmacol. Biochem. Behav., 18 (1983) 185-188. 6 File, S.E. and Lister, R.G., Interactions of ethyl-B-carboline-3-carboxylate and Ro 15-1788 with CGS 8216 in an animal model of anxiety, Neurosci. Lett., 39 (1983) 91-94. 7 File, S.E., Lister, R.G. and Nutt, D.J., The anxiogenic action of benzodiazepine antagonists, Neuropharmacology, 21 (1982) 1033-1037. 8 File, S.E., Lister, R.G. and Nutt, D.J., Intrinsic actions of benzodiazepine antagonists, Neurosci. Lett., 32 (1982) 165-168.
177 9 Greksch, G., Prado de Carvalho, L., Venault, P., Chapouthier, G. and Rossier, J., Convulsions induced by a submaximal dose of pentylenetetrazol in mice are antagonised by the benzodiazepine antagonist, Ro 15-1788, Life Sci., 32 (1983) 2579-2584. 10 Herberg, L.J. and Williams, S.F., Anticonflict and depressant effects by GABA agonists and antagonists, benzodiazepines and non-GABAergic anticonvulsants on self-stimulation and locomotor activity. Pharmacol. Biochem. Behav., 19 (1983) 625-633. 11 Hoffman, D.K. and Britton, D.R., Anxiogenic-like properties of benzodiazepine antagonists, Neurosci. Abstr., 9 (1983) 129. 12 Hunkeler, W., Mohler, H., Pieri, L., Polc, P., Bonetti, E.P., Cumin, R., Schaffner, R. and Haefely, W., Selective antagonists of benzodiazepines, Nature (Lond.), 290 (1981) 514-516. 13 Jensen, L.H., Petersen, E.N. and Braestrup, C., Audiogenic seizures in DBA/2 mice discriminate sensitively between low efficacy benzodiazepine receptor agonists and inverse agonists, Life Sci., 33 (1983) 393-399. 14 Kehr, W. and Stephens, D.N., Further evidence that central benzodiazepine receptor ligands may exhibit anxiogenic properties, Brit. J. Pharmacol., in press. 15 Mohler, H. and Okada, T., Benzodiazepine receptors: demonstration in the CNS, Science, 198 (1977) 849-85 I. 16 Nutt, D.J., Cowen, P.J. and Little, H.J., Unusual interactions of benzodiazepine receptor antagonists, Nature (Lond.), 295 (1982) 436-438. 17 Pellegrino, L.J., Pellegrino, A.S. and Cushman, A.J., A stereotaxic atlas of the rat brain, Plenum, New York, 1979. 18 Pellow, S., Herberg, L.J. and File, S.E., The effects of a ~-carboline, FG 7142, on intracranial selfstimulation in the rat, Pharmacol. Biochem. Behav., in press. 19 Petersen, E.N., Jensen, L.H., Honore, T. and Braestrup, C., Differential pharmacological effects of benzodiazepine receptor inverse agonists. In G. Biggio and E. Costa (Eds.), Benzodiazepine Receptor Recognition Site Ligands: Biochemistry and Pharmacology, Raven Press, New York, 1983. 20 Squires, R.F. and Braestrup, C., Benzodiazepine receptors in rat brain, Nature (Lond.), 266 (1977) 732-734. 21 Yokoyama, N., Ritter, B. and Neubert, A.D., 2-Arylpyrazolo[4,3-c]quinolin-3-ones: novel agonist, partial agonist and antagonist of benzodiazepines, J. med. Chem., 25 (1982) 337-339.
173
NSL 02740 INTRACRANIAL SELF-STIMULATION DISTINGUISHES BETWEEN TWO BENZODIAZEPINE ANTAGONISTS
SHARON PELLOWl, SANDRA E. FILE1 AND L.J. HERBERG 2 IMRC Neuropharmacology Research Group, Department of Pharmacology, The School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N l A X and ~Experimental Psychology Laboratory, Institute o f Neurology, Queen Square, London WC1N 3BG (U.K.)
(Received February 20th, 1984; Revised version received March 15th, 1984; Accepted March 16th, 1984)
Key words: benzodiazepine antagonists - chlordiazepoxide - self-stimulation
Low doses of Ro 15-1788 and CGS 8216 were without effect on variable-interval self-stimulation, but completely abolished the enhancement of responding produced by chlordiazepoxide (5 mg/kg). Higher doses of Ro 15-1788, unlike other benzodiazepine receptor antagonists, produced an increase in response rates similar to that found after chlordiazepoxide. This result is consistent with its suggested action as a partial agonist. The combination of a high (benzodiazepine-like) dose of Ro 15-1788 with chlordiazepoxide produced a depression of responding similar to that seen with high doses of benzodiazepines. High doses of CGS 8216 produced a depression of self-stimulation, which was not reversed by chlordiazepoxide (5 mg/kg). Thus, the present procedure is able to distinguish contrasting behavioural effects of benzodiazepine antagonists.
Since the discovery o f benzodiazepine binding sites in the C N S [15, 20], a variety o f c o m p o u n d s have been discovered that displace 3H-benzodiazepines f r o m their binding sites a n d that reverse their p h a r m a c o l o g i c a l actions. These include the imidazodiazepine, R o 15-1788, the pyrazoloquinoline, C G S 8216, and alkyl /3carboline-3-carboxylates [2, 12, 21]. These c o m p o u n d s have intrinsic activity generally in the direction opposite to that o f benzodiazepines. Thus, C G S 8216 is anxiogenic in various tests o f anxiety, [5, 14, 19] and proconvulsant (4, 13] in rodents. R o 15-1788 is also anxiogenic in the social interaction test [7] and the openfield novelty procedure [11]; but unlike C G S 8216 it has anticonvulsant activity at low doses [1, 9, 13] and at high doses actually takes on certain benzodiazepine-like properties [3, 16]. Response to intracranial self-stimulation at threshold currents on a variableinterval 10-s schedule o f reinforcement is sensitive to the effects o f benzodiazepines a n d other G A B A e r g i c c o m p o u n d s [10] and to the effects o f the/~-carboline F G 7142 [18]. We therefore wished to investigate a n y intrinsic actions o f R o 15-1788 and C G S 8216 on self-stimulation p e r f o r m a n c e , and to see if they could reverse the e n h a n c e m e n t usually p r o d u c e d by chlordiazepoxide [10]. 0304-3940/84/$ 03.00 © 1984 Elsevier Scientific Publishers Ireland Ltd.
174
Under halothane anesthesia, male hooded PVG rats (Banting and Kingman Ltd.) weighing 200-230 g at time of surgery were stereotaxically implanted in the midlateral hypothalamus with twisted bipolar stainless-steel electrodes (0.25 mm diameter). Coordinates were 1.0 mm posterior to bregma, 1.3 mm to the left of the midline and 9.0 mm below the skull surface [17]. Electrode placements were determined from enlarged photographic projections of 50-t~m frozen sections at the end of the experiments. After recovery (1 week) rats were trained to operate a pedal for a 0.5-s 50-Hz sinewave reinforcing impulse available on a variable-interval schedule of 10-s mean duration. The stimulating current for each rat was fixed at the lowest intensity that elicited steady and sustained responding. During test sessions, animals were allowed to respond for self-stimulation for 45 min, of which the last 30 min provided a pre-injection baseline. The rat was then injected and allowed to selfstimulate for a further 60 min. Response rates were recorded automatically at 5-min intervals; drug effects were determined from the rate recorded during the second 15-min period after injection, expressed as a percentage of the pre-injection baseline, and compared with the corresponding rate after control injections. Two groups of rats received the following drug treatments in a random order: Group 1 (n=6): vehicle, Ro 15-1788 (2, 10, 20 and 50 mg/kg), CDP (5 mg/kg), and Ro 15-1788 (2 and 50 mg/kg) + CDP (5 mg/kg). Group 2 (n=6): control, CGS 8216 (2, 10 and 20 mg/kg), CDP (5 mg/kg), and CGS 8216 (2 and 10 mg/kg) + CDP (5 mg/kg). Rats were tested no more than once every 48 h. Ro 15-1788 and CGS 8216 were suspended in distilled water with a drop of Tween 20; chlordiazepoxide hydrochloride (CDP) (Roche Products) was dissolved in distilled water. Control injections consisted of distilled water, with or without a drop of Tween 20 as appropriate. Drugs were injected intraperitoneally in a volume of 2 ml/kg. CDP (5 mg/kg) significantly enhanced self-stimulation (P< 0.05, Wilcoxon test, see Fig. la, b); this effect was reversed by Ro 15-1788 at 2 mg/kg (P<0.05, Fig. la), and by CGS 8216 (2 and 10 mg/kg, P<0.05, see Fig. lb); these results are consistent with previous research using other procedures [12, 21]. At the low doses neither Ro 15-1788 nor CGS 8216 showed any intrinsic activity (see Fig. 1); however, at higher doses they had contrasting effects on self-stimulation. When it was given alone, Ro 15-1788 overall had a significant effect on selfstimulation (X2= 13.86, P<0.01, Friedman analysis of variance), but post hoc analysis with Wilcoxon matched-pairs signed-ranks tests showed that this was mainly due to the 50 mg/kg dose (P< 0.05, see Fig. la) which enhanced self-stimulation compared with controls. This suggests that at high doses Ro 15-1788 acts like a low dose of a benzodiazepine, which is particularly likely in the light of other behavioural studies showing benzodiazepine-like activity with high doses of Ro 15-1788, which have led to the proposal that Ro 15-1788 may be a partial agonist at benzodiazepine receptors [3, 16]. CGS 8216 had a significant overall effect on self-stimulation (X2 = 15.2, P < 0.005, Friedman analysis of variance), and post hoc analysis showed that higher doses of
175
a)
b) 200
200 Ot
I
~.
150
150
L.. 0.. o E; 0
E
100
1O0
50
50
d'l I
U3
t
0
i
i
,
5 10
I
,J
20
50
0
t
0
t
J
I
5 10
J
20
DOSE ( m g l k g ) Fig. I. Mean (+ S.E.M.) self-stimulation rate (variable interval, 10 s) in the second 15-min period after injection for rats given: (a) control, Ro 15-1788 (2-50 mg/kg), chlordiazepoxide (5 mg/kg) alone and in combination with Ro 15-1788 (2 and 50 mg/kg); and (b) control, CGS 8216 (2-20 mg/kg), chlordiazepoxide (5 mg/kg) alone and in combination with CGS 8216 (2 and 10 mg/kg). (O) Ro 15-1788 (a) and CGS 8216 alone (b); (A) chlordiazepoxide alone; (i) chlordiazepoxide + Ro 15-1788 (a), or CGS 8216 (b).
CGS 8216, unlike Ro 15-1788, depressed self-stimulation significantly below control rates ( P < 0.05, see Fig. lb). This is consistent with previous reports demonstrating reduced behaviour with CGS 8216 in the social interaction [5] and punished drinking [19] procedures; however, Ro 15-1788, like CGS 8216, also reduces social interaction at doses o f l0 m g / k g [7] and has intrinsic activity in the open-field novelty procedure [11] and on exploratory head-dipping [8], and so it was surprising that no effects were observed with Ro 15-1788 until doses at which it becomes benzodiazepine-like. We were then interested to See whether C D P could reverse the intrinsic activity obtained with higher doses of Ro 15-1788, and CGS 8216. Even though when given alone both Ro 15-1788 (50 m g / k g ) and chlordiazepoxide elevated self-stimulation, the combination produced a significant depression in self-stimulation compared with controls ( P < 0 . 0 5 , Wilcoxon test, see Fig. la). Behaviourally, these effects resemble those produced by higher doses of benzodiazepines [10], but the pharmacological basis o f the effects is unclear. A partial agonist in combination with a full agonist would not produce an additive effect (except perhaps at very low concentrations). Until the pharmacological basis of the effects of benzodiazepines on intracranial self-stimulation is more thoroughly investigated, we will be unable to
176
provide an adequate explanation for this finding. Similarly, an unexpected interaction between Ro 15-1788 and CDP was observed for exploratory behaviour in the holeboard test [8]. Response after the combined administration of CGS 8216 (10 mg/kg) and CDP (5 mg/kg) was also significantly reduced compared with controls (P< 0.05) and was not significantly different from CGS 8216 (10 mg/kg) alone (see Fig. lb). CDP (5 mg/kg) has been shown to reverse the reduction in self-stimulation produced by the t3-carboline FG 7142 [18] which is also thought to interact with benzodiazepine binding sites. The effect of CGS 8216 was no stronger than that of FG 7142, and so the inability of CDP to reverse the intrinsic activity of CGS 8216 on self-stimulation is consistent with previous suggestions (ref. 6, and File and Pellow, in preparation) that CGS 8216 at higher doses may have additional actions at brain systems unrelated to benzodiazepine binding sites. It is at these higher doses that other intrinsic actions of CGS 8216 have been observed, including an anxiogenic effect that also could not be reversed by CDP (File and Pellow, in preparation). It is necessary to consider whether the effects of Ro 15-1788 and CGS 8216 on self-stimulation were secondary to other pharmacological actions: neither drug has any effect on locomotor activity [5, 8] and so the results cannot be explained in terms of sedation. These two antagonists differ in their effects on seizure activity: Ro 15-1788 is anticonvulsant and CGS 8216 is proconvulsant. However, the current levels used in the present procedure were near threshold, and reward pulses could be obtained only at mean intervals of not less than 10 s; seizure activity is therefore unlikely to have played an important role. We conclude that intracranial selfstimulation provides another behavioural measure that can distinguish between these two antagonists. S.E.F. is a Wellcome Trust Senior Lecturer. We are grateful to Hoffman-La Roche for the gift of Ro 15-1788 and Ciba-Geigy for CGS 8216; and to the Medical Research Council for support. 1 Albertson, T.E., Bowyer, J.F. and Paule, M.G., Modification of the anticonvulsant efficacy of diazepam by Ro 15-1788 in the kindled amygdaloid seizure model, Life Sci., 31 (1982) 1597-1601. 2 Braestrup, C., Nielsen, M. and Olsen, C.E., Urinary and brain 13-carboline-3-carboxylates as potent inhibitors of brain benzodiazepine receptors, Proc. nat. Acad. Sci. U.S.A., 77 (1980) 2288-2292. 3 Dantzer, R. and Perio, A., Behavioural evidence for partial agonist properties of Ro 15-1788, a benzodiazepine receptor antagonist, Europ. J. Pharmacol., 81 (1982) 655-658. 4 File, S.E., Proconvulsant action of CGS 8216, Neurosci. Lett., 35 (1983) 317-320. 5 File, S.E. and Lister, R.G., Quinolines and anxiety: anxiogenic effects of CGS 8216 and partial anxiolytic profile of PK 9084, Pharmacol. Biochem. Behav., 18 (1983) 185-188. 6 File, S.E. and Lister, R.G., Interactions of ethyl-B-carboline-3-carboxylate and Ro 15-1788 with CGS 8216 in an animal model of anxiety, Neurosci. Lett., 39 (1983) 91-94. 7 File, S.E., Lister, R.G. and Nutt, D.J., The anxiogenic action of benzodiazepine antagonists, Neuropharmacology, 21 (1982) 1033-1037. 8 File, S.E., Lister, R.G. and Nutt, D.J., Intrinsic actions of benzodiazepine antagonists, Neurosci. Lett., 32 (1982) 165-168.
177 9 Greksch, G., Prado de Carvalho, L., Venault, P., Chapouthier, G. and Rossier, J., Convulsions induced by a submaximal dose of pentylenetetrazol in mice are antagonised by the benzodiazepine antagonist, Ro 15-1788, Life Sci., 32 (1983) 2579-2584. 10 Herberg, L.J. and Williams, S.F., Anticonflict and depressant effects by GABA agonists and antagonists, benzodiazepines and non-GABAergic anticonvulsants on self-stimulation and locomotor activity. Pharmacol. Biochem. Behav., 19 (1983) 625-633. 11 Hoffman, D.K. and Britton, D.R., Anxiogenic-like properties of benzodiazepine antagonists, Neurosci. Abstr., 9 (1983) 129. 12 Hunkeler, W., Mohler, H., Pieri, L., Polc, P., Bonetti, E.P., Cumin, R., Schaffner, R. and Haefely, W., Selective antagonists of benzodiazepines, Nature (Lond.), 290 (1981) 514-516. 13 Jensen, L.H., Petersen, E.N. and Braestrup, C., Audiogenic seizures in DBA/2 mice discriminate sensitively between low efficacy benzodiazepine receptor agonists and inverse agonists, Life Sci., 33 (1983) 393-399. 14 Kehr, W. and Stephens, D.N., Further evidence that central benzodiazepine receptor ligands may exhibit anxiogenic properties, Brit. J. Pharmacol., in press. 15 Mohler, H. and Okada, T., Benzodiazepine receptors: demonstration in the CNS, Science, 198 (1977) 849-85 I. 16 Nutt, D.J., Cowen, P.J. and Little, H.J., Unusual interactions of benzodiazepine receptor antagonists, Nature (Lond.), 295 (1982) 436-438. 17 Pellegrino, L.J., Pellegrino, A.S. and Cushman, A.J., A stereotaxic atlas of the rat brain, Plenum, New York, 1979. 18 Pellow, S., Herberg, L.J. and File, S.E., The effects of a ~-carboline, FG 7142, on intracranial selfstimulation in the rat, Pharmacol. Biochem. Behav., in press. 19 Petersen, E.N., Jensen, L.H., Honore, T. and Braestrup, C., Differential pharmacological effects of benzodiazepine receptor inverse agonists. In G. Biggio and E. Costa (Eds.), Benzodiazepine Receptor Recognition Site Ligands: Biochemistry and Pharmacology, Raven Press, New York, 1983. 20 Squires, R.F. and Braestrup, C., Benzodiazepine receptors in rat brain, Nature (Lond.), 266 (1977) 732-734. 21 Yokoyama, N., Ritter, B. and Neubert, A.D., 2-Arylpyrazolo[4,3-c]quinolin-3-ones: novel agonist, partial agonist and antagonist of benzodiazepines, J. med. Chem., 25 (1982) 337-339.