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The repeated administration of subconvulsant doses of pentylenetetrazol (PTZ) produced a progressive sensitization to the effects of this compound (i.e., chemical kindling) in the rat. A very similar time-course for PTZ-induced kindling was observed using two different treatment schedules: 1) one injection every day (30 mg/kg, IP), and 2) one injection (30 mg/kg, IP) every second day. When these treatment schedules were used for eight consecutive weeks, more than 80% of the rats displayed convulsions by the end of treatment. In contrast, only 20% of the rats were sensitized if PTZ was administered twice daily at the dose of 15 mg/kg, IP. The increased sensitivity to the convulsant effect of PTZ was still present one year after completion of the chronic treatment. Moreover, rats kindled with PTZ showed an enhanced susceptibility to convulsions induced by different inhibitors of central GABAergic function, such as the chloride channel blocker picrotoxin, the benzodiazepine receptor ligands FG 7142 and Ro 15-4513, and the inhibitor of GABA synthesis isoniazid. In contrast, the sensitivity to the convulsant action of the glycine receptor antagonist strychnine was unchanged by repeated PTZ administration. It is suggested that kindling produced by PTZ may be associated with a persistent reduction in the inhibitory function of the GABAergic system in the brain.

The intracerebroventricular injection of ACTH1-24 (0.1-10 micrograms) produced a dose-dependent decrease of punished licking periods in the conflict test in rats. The same treatment failed to modify unpunished behavior. A similar effect was produced by alpha-MSH (0.25-5 micrograms), whereas ACTH4-10 and ACTH11-24 were ineffective in doses up to 10 micrograms. The proconflict effect of ACTH1-24 was completely antagonized by diazepam (1.5 mg/kg IP) and partially by the benzodiazepine receptor antagonist Ro 15-1788 (5 mg/kg IP). The results are in line with a possible "anxiogenic" action of ACTH1-24.

The hypnotic drug quazepam and its active metabolite 2-oxo-quazepam (2-oxo-quaz) are two benzodiazepines (BZ) containing a trifluoroethyl moiety on the ring nitrogen at position 1, characterized by their preferential affinity for Type I BZ recognition sites. In the present study we characterized the binding of 3H-2-oxo-quaz in discrete areas of the human brain. Saturation analysis demonstrated specific and saturable binding of 3H-2-oxo-quaz to membrane preparations from human cerebellum. Hill plot analysis of displacement curves of 3H-flunitrazepam (3H-FNT) binding by 2-oxo-quaz yielded Hill coefficients of approximately 1 in the cerebellum and significantly less than 1 in the cerebral cortex, hippocampus, caudate nucleus, thalamus and pons. Self and cross displacement curves for 3H-FNT and 3H-2-oxo-quaz binding in these brain areas indicated that 2-oxo-quaz binds with different affinities to two populations of binding sites. High affinity binding sites were more abundant in the cerebellum (95% of total sites), cerebral cortex, hippocampus and thalamus, whereas low affinity sites were predominant in the caudate nucleus and pons. Competition studies of 3H-2-oxo-quaz (2 nM) and 3H-FNT (0.5 nM) using unlabelled ligands indicated that compounds which preferentially bind to Type I sites are more potent at displacing 3H-2-oxo-quaz than 3H-FNT from cerebral cortex membrane preparations. The results suggest that 3H-2-oxo-quaz may be used for selectively studying Type I BZ recognition sites in the human brain.

The changes in the number and sensitivity of benzodiazepine and GABA binding sites in the rat retina during postnatal development, adulthood and ageing and their functional relationship at different ages have been studied. Data indicate an increase in the total number of both GABA and benzodiazepine binding sites with age. In contrast, the activation of retinal benzodiazepine receptor binding by GABA is significantly reduced in aged rats with respect to young adult and newborn rats. Moreover, the activation of retinal benzodiazepine receptor binding induced by dark exposure of the animals is present in young adult rats but is lost in aged rats. These results suggest that in the retina of aged rats there is an increase of GABA and benzodiazepine receptors which have lost their functional connection.

A novel beta-carboline with benzodiazepine-like properties has recently been synthesized. We compared the effect of the i.v. administration of this drug, ZK 93423, with diazepam on the activity of nigral pars reticulata neurons which are known to be very sensitive to the inhibitory effect produced by GABA-mimetics and benzodiazepines. ZK 93423 (0.05-1.0 mg/kg) inhibited reticulata cells in a dose-related manner up to the cessation of their activity. Since the maximal rate-inhibition elicited by diazepam (1.0 mg/kg) was some 55% of baseline, ZK 93423 showed a much greater potency. Moreover, the firing depression by ZK 93423 was prevented and reversed by two benzodiazepine receptor antagonists: Ro15-1788 and ZK 93426. However, the dosage of Ro15-1788 required for these actions was at least five times higher than that for the blockade of the diazepam effect. The results indicate that the beta-carboline agonist ZK 93423 decreases the activity of reticulata neurons more effectively than diazepam.

The aim of the present study was to investigate the ability of different benzodiazepine recognition site antagonists (Ro 15-1788 and ZK 93426) and inverse agonists (Ro 15-4513, FG 7142 and CGS 8216) to induce abstinence signs in diazepam-dependent cats. Different groups of cats were challenged with each of the benzodiazepine recognition site ligands under investigation 24 hours after the last dose of chronic treatment with diazepam (7 mg/kg, IP at 8.00 a.m. and 8.00 p.m. for 21 consecutive days). The benzodiazepine derivatives Ro 15-4513 and Ro 15-1788 precipitated an abstinence syndrome within minutes after IP administration. The pyrazoloquinoline derivative CGS 8216 also induced withdrawal signs that were less severe and had a longer latency than those elicited by Ro 15-4513 and Ro 15-1788. Abstinence signs included tremors, increased muscle tone, irritability, fear, arched-back posture, pupillary dilation and vocalizations. On the other hand, the beta-carboline derivatives ZK 93426 and FG 7142 failed to precipitate abstinence signs in diazepam-dependent cats when given at doses that prevented the acute effects of diazepam. Our results demonstrate that the ability to induce withdrawal signs in diazepam-dependent cats depends on the chemical structure of the challenge drug (i.e., benzodiazepine or pyrazoloquinoline), since beta-carboline antagonists like ZK 93426 and partial inverse agonists like FG 7142 lack this property.

3H-GABA binding was studied in cortical membranes from cerebral cortex of handling-habituated and naive rats after the in vitro addition of Ro15-1788. At low concentrations (10(-8), 10(-9) M) Ro15-1788 increased the total number of low affinity 3H-GABA binding sites in brain tissue from naive rats but failed to modify 3H-GABA binding in tissue from handling-habituated ones. On the contrary, Ro15-1788 at higher concentrations (10(-5), 10(-6)M) decreased the total number of low affinity 3H-GABA binding sites in tissue from handling-habituated rats but failed to modify 3H-GABA binding in tissue from naive animals. Ro15-1788 (10(-7)M) failed to modify significantly low affinity 3H-GABA binding in membranes from both naive and handling-habituated rats. However, this concentration abolished the effect of beta-carbolines and diazepam on 3H-GABA binding in membranes from naive and handling-habituated rats, respectively. The changes in the affinity of 3H-GABA binding were inversely related to the changes in the number. The results suggest that: a) the action "in vitro" of Ro15-1788 on low affinity 3H-GABA binding depends from its concentration at the benzodiazepine recognition sites; b) the benzodiazepine recognition site has a modulatory role in the control of the function of GABA-ergic receptor. Our data might explain the conflicting results obtained with this compound "in vivo".

Long-term (20 days) treatment with methyl mercury (MeHg) increases the total number of benzodiazepine binding sites and decreases essentially the content of cyclic GMP in the cerebellar cortex. In contrast, this treatment fails to modify the content of GABA and cyclic AMP, GAD activity and GABA binding sites in the same brain area. The changes in cyclic GMP and benzodiazepine binding sites in the cerebellar cortex are discussed in relation to the motor disturbances associated with MeHg intoxication.

The aim of the present study was to compare the ability of Ro 15-4513 and FG 7142, two inverse agonists for benzodiazepine recognition sites, to antagonize the EEG effects of ethanol in freely moving rats. Ethanol (2.5 g/kg, p.o.) induced sedation and ataxia associated with a progressive suppression of the fast cortical activities and an enhancement of low frequencies in both cortical and hippocampal tracings. In contrast, Ro 15-4513 (2 mg/kg, i.p.) and FG 7142 (10 mg/kg, i.p.) both caused a state of alertness associated with desynchronized cortical activity and theta hippocampal rhythm as well as spiking activity which was predominantly observed in the cortical tracings. When rats were treated with FG 7142 or RO 15-4513 either before or after ethanol, a reciprocal antagonism of the behavioral and EEG effects of ethanol and of the partial inverse agonists was observed. These data support the view that the anti-ethanol effects of Ro 15-4513 may be related to its partial inverse agonist properties.