Modification of seizures elicited by the benzodiazepine Ro 5-3663--a comparison with picrotoxin

Reversal of propoxur-induced impairment of memory and oxidative stress by 4'-chlorodiazepam in rats

Carbamate pesticides like propoxur have been shown to adversely affect memory and induce oxidative stress on both acute and chronic exposure. The present study was designed to explore the modulation of the effects of propoxur over cognitive function by progesterone (PROG) and 4'-chlorodiazepam (4CD). Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus, transfer latency (TL) on a plus maze and spatial navigation test on Morris water maze. Oxidative stress was assessed by examining brain malondialdehyde (MDA) and reduced glutathione (GSH) levels and catalase (CAT) activity. A significant reduction in SDL and prolongation of TL and spatial navigation test was found for the propoxur (10 mg/kg/d; p.o.) treated group at weeks 6 and 7 as compared with control. One-week treatment with 4CD (0.5 mg/kg/d; i.p.) antagonized the effect of propoxur on SDL, spatial navigation test as well as TL; whereas, PROG failed to modulate this effect at a dose of 15 mg/kg/d, i.p. Propoxur produced a statistically significant increase in the brain MDA levels and decrease in the brain GSH levels and CAT activity. Treatment with 4CD at the above dose attenuated the effect of propoxur on oxidative stress whereas PROG (15 mg/kg/d; i.p.) failed to influence the same. The results of the present study thus show that 4-CD has the potential to attenuate cognitive dysfunction and oxidative stress induced by toxicants like propoxur in the brain.

Reversal of lindane-induced impairment of step-down passive avoidance and oxidative stress by neurosteroids in rats

Neurosteroids (NS) are recognized as important modulators of functioning of the nervous system. Lindane, an organochlorine pesticide has been shown to adversely affect memory and induce oxidative stress on both acute and chronic exposure. The present study was designed to explore the modulation of effects of lindane over cognitive function by progesterone (PROG), pregnenolone sulfate (PREG-S) and 4'-chlorodiazepam (4CD). Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus and transfer latency (TL) on a plus maze. Oxidative stress was assessed by examining brain malondialdehyde (MDA) and non-protein thiol (NP-SH) levels. A significant reduction in SDL was found for the lindane treated group at weeks 6 and 7 as compared to control (p<0.001). One-week treatment by PREG-S or 4CD antagonized the effect of lindane on SDL. PROG failed to modulate the effect of lindane on SDL. Lindane caused a significant prolongation of TL as compared to control (p<0.001) from second week onwards. One-week administration of PROG, PREG-S or 4CD was unable to reverse this prolongation of TL. Lindane produced a statistically significant increase in the brain MDA levels (p<0.001) and significant decrease in the brain NP-SH levels (p<0.001). Treatment with PREG-S and 4CD attenuated the effect of lindane on MDA (p<0.001) and NP-SH levels. PROG failed to influence oxidative stress induced by lindane. Results of the present study thus show that some NS have potential in reversing cognitive dysfunction and oxidative stress induced by toxicants like lindane in the brain.

Cueing effects of anxiolytic benzodiazepines (DZP and Ro 11-3128): stereospecificity and antagonism by the convulsant benzodiazepine Ro 5-3663

Two groups of gerbils were trained in a T-maze to discriminate between the vehicle condition (4 ml/kg) and either of the benzodiazepine (BDZ) agonists diazepam (DZP) and Ro 11-3128; administration (5.6 mg/kg) was IP 5 min prior to training onset. Once trained, novel doses and drugs were assessed in test sessions interposed between the regular training days. A dose-related generalization effect occurred with both compounds (range 0.1-5.6 mg/kg), the effect being similar at both the 5 and 15 min test intervals; the two intervals were evaluated after a single injection. The lack of generalization of Ro 11-3624 (range 5.6-56 mg/kg) indicates a stereoisomeric separation of BDZ agonist activity. Ro 5-4864 (range 17.5-56 mg/kg), an agent chemically/structurally related to DZP, did not produce DZP responding at either of the two test inverals; clear-cut convulsant activity occurred at the 15 min interval. The convulsant BDZ compound Ro 5-3663 (3 and 10 mg/kg) antagonized the DZP stimulus irrespective of whether Ro 5-3663 was given either prior to, simultaneously with, or shortly after the DZP injection.

Intrinsic actions of the benzodiazepine receptor antagonist Ro 15-1788

The imidazodiazepine Ro 15-1788 is a benzodiazepine receptor antagonist that was initially reported to be lacking in intrinsic activity in a variety of test situations in which benzodiazepine-like effects can be identified. However, many recent studies have shown that this compound does indeed have intrinsic activity in a variety of behavioural, neurological, electrophysiological and biochemical preparations in both animals and man. The purpose of the present review is firstly to describe these intrinsic actions, and secondly to consider to what extent these intrinsic actions of Ro 15-1788 have implications for current concepts of the functioning of the benzodiazepine receptor.

Convulsant component of a depressant benzodiazepine

The convulsant influence of high doses of diazepam, in the presence of the benzodiazepine receptor antagonist Ro 15-1788, was studied in rats. Animals were implanted with permanent cortical screw electrodes for EEG recording. EEG spiking and accompanying clonic activity was observed in rats receiving greater than or equal to 200 mg/kg diazepam, followed 10 minutes later by Ro 15-1788 (20 mg/kg). Pentylenetetrazole and picrotoxin seizure thresholds, measured during constant rate iv infusion, were significantly lowered by pretreatment with diazepam (250 mg/kg) and Ro 15-1788 (20 mg/kg) administered 30 and 20 minutes, respectively, before seizure threshold measurement. It is proposed that this convulsive activity of diazepam is mediated through the picrotoxinin receptor.

Antagonism of flurazepam and other effects of Ro15-1788, PK8165 and Ro5-4864 on the GABA-A receptor complex in rat cuneate nucleus

In slices of rat cuneate nucleus, responses to the GABA-A receptor agonist muscimol were potentiated by flurazepam. The maximal potentiation by 1 microM flurazepam was antagonized by the neuronal benzodiazepine receptor ligand Ro15-1788 3 microM, by the quinoline derivative PK8165 0.1 microM and by the peripheral-type benzodiazepine receptor ligand Ro5-4864 0.1 microM. Another ligand for the peripheral-type benzodiazepine receptor, PK11195 10 microM, enhanced the potentiating effect of a submaximal concentration of flurazepam 0.1 microM and prevented the antagonism of flurazepam by Ro5-4864. At much higher concentrations of these drugs, additional effects were seen. Ro15-1788 30 microM and PK11195 30 microM each caused small potentiations of muscimol while Ro5-4864 30 microM caused a small antagonism. Ro15-1788 30 microM, PK8165 100 microM and Ro5-4864 30 microM all antagonized the potentiation of muscimol by pentobarbitone 10 microM; also, PK8165 and Ro5-4864 enhanced the potency of picrotoxin as an antagonist of muscimol. It is concluded that both Ro5-4864 and PK8165 have several distinct effects on the GABA-A receptor complex, all of which could result in reduced responses to muscimol.

Pro- and anti-convulsant drug effects in combination with the convulsant benzodiazepine Ro 5-4864

The effects of several compounds believed to act at the GABA-benzodiazepine receptor complex and which have anticonvulsant or proconvulsant properties when administered in combination with picrotoxin and pentetrazol (leptazol, pentylenetetrazole) were investigated in combination with the convulsant benzodiazepine Ro 5-4864. Tracazolate (25-100 mg kg-1) failed to affect convulsions induced by Ro 5-4864; however, they were prevented by treatment with CL 218,872 (20 mg kg-1). Compounds having proconvulsant activity in combination with a subthreshold dose of Ro 5-4864 were: CL 218,872 (5 mg kg-1), and CGS 8216 (20 mg kg-1) and FG 7142 (40 mg kg-1), two compounds characterized as 'inverse agonists' at benzodiazepine receptors. The phenylquinolines PK 8165 and PK 9084, originally believed to have anxiolytic properties, had no significant effect in combination with Ro 5-4864 (25-100 mg kg-1). The convulsant profile of Ro 5-4864 is compared with that of picrotoxin and pentetrazol.