"Central" and "peripheral" benzodiazepines and kinetics of lindane-induced toxicity

Lindane-induced generation of reactive oxygen species and depletion of glutathione do not result in necrosis in renal distal tubule cells

Lindane is a chlorinated hydrocarbon pesticide, currently used in prescription shampoos and lotions to treat scabies and lice infestations. Lindane is known to be nephrotoxic; however, the mechanism of action is not well understood. In other organ systems, lindane produces cellular damage by generation of free radicals and oxidative stress. Morphological changes were observed in lindane-treated Madin-Darby canine kidney (MDCK) cells indicative of apoptosis. Lindane treatment induced time-dependent reactive oxygen species (ROS) generation. Onset of ROS generation correlated with an initial increase in total glutathione (GSH) levels above control values, with a subsequent decline in a time-dependent manner. This decline may be attributed to quenching of free radicals by GSH, thereby decreasing the cellular stores of this antioxidant. Necrotic injury was assessed by measuring lactate dehydrogenase (LDH) leakage from the cell after lindane exposure. No significant LDH leakage was noted for all concentrations tested over time. Generation of ROS and alterations in cellular protective mechanisms did not result in necrotic injury in MDCK cells, which corresponds with our morphological findings of lindane-induced apoptotic changes as opposed to necrosis in MDCK cells. Thus, lindane exposure results in oxidative damage and alterations in antioxidant response in renal distal tubule cells, followed by cell death not attributed to necrotic injury.

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.

Self-biting induced by activation of L-type calcium channels in mice: serotonergic influences

The L-type calcium channel activator +/-Bay K 8644 has recently been shown to provoke self-injurious biting in young mice. Since the serotonergic systems have been implicated in the expression of self-injurious behavior in both humans and animals, the present studies tested whether drugs influencing serotonin systems could modify the ability of +/-Bay K 8644 to cause this behavior. The ability of +/-Bay K 8644 to provoke self-biting behavior was increased by the serotonin uptake inhibitor fluoxetine or the monoamine oxidase inhibitor clorgyline. On the other hand, the ability of +/-Bay K 8644 to provoke self-biting was decreased by depletion of serotonin with p-chlorophenylalanine or 5,7-dihyroxytryptamine. These results suggest that the ability of +/-Bay K 8644 to provoke self-injurious behaviors may be mediated by serotonergic influences.

PK 11195 reduces the brain availability of lindane in rats and the convulsions induced by this neurotoxic agent

The effect of pretreatment with PK 11195, a ligand of the 'peripheral-type' benzodiazepine receptor (PBR), on convulsions induced by lindane (gamma-hexachlorocyclohexane, gamma-HCH) in rats was examined, to determine whether the mechanism of this convulsant activity may be mediated through the PBR. PK 11195 elicited a protective effect against the convulsant activity of orally administered lindane. It reduced the frequency of animals exhibiting convulsions and delayed the time to onset of these seizures. The concentration of lindane in the brain was found to be significantly lower in PK 11195 pretreated rats and a high correlation between blood and brain lindane concentrations was obtained. When similar experiments were repeated with alpha-HCH, a non-convulsant isomer of HCH, brain and blood concentrations were again found to be significantly reduced in PK 11195 pretreated animals. We conclude that the 'anticonvulsant' action of PK 11195 was not due to an interaction of PK 11195 and lindane on common CNS target sites, but by an action of PK 11195 on the gastrointestinal tract of the animal, delaying the absorption of lindane into the bloodstream.

Modulation of noradrenaline release from hippocampal slices by hexachlorocyclohexane isomers. Effects of GABAergic compounds

The effects of hexachlorocyclohexane (HCH) isomers and some GABAergic compounds on [3H]noradrenaline (NA) release from rat hippocampal slices prelabelled with 80 nM [3H]NA were determined. The convulsant gamma-HCH isomer facilitated (EC50 = 21 microM) and the depressant delta-HCH isomer reduced (EC50 = 48 microM) the Ca(2+)-dependent K(+)-evoked release of [3H]NA, whereas alpha- and beta-HCH isomers did not show any effect. Moreover, alpha- and delta-HCH isomers antagonized the facilitation of evoked [3H]NA release induced by the gamma-HCH isomer. The GABAergic convulsant drugs, bicuculline, picrotoxin and pentylenetetrazol, did not cause any modification of the evoked [3H]NA release even at high concentrations. Neither bicuculline nor picrotoxin blocked the effects of HCH isomers on K(+)-evoked release of [3H]NA. Exposure of slices to diazepam reduced the K(+)-evoked release of [3H]NA (EC50 = 33 microM) in a manner similar to that of the delta-HCH isomer. In addition, diazepam (50 microM) blocked the gamma-HCH effect and caused an additive inhibitory response with the delta-HCH isomer. On the other hand, diazepam and delta-HCH induced a time-dependent Ca(2+)-independent enhancement of basal [3H]NA release. The results suggest that modulation of [3H]NA release in the hippocampus by HCH isomers may be involved in the central actions of these compounds, and that sites other than the classic GABAA receptor may underlie their presynaptic mechanisms of action.

Ro 5-4864, like picrotoxin, enhances EPSP-spike coupling in the freely behaving rat

To help determine its mechanism of action, the convulsant benzodiazepine Ro 5-4864 was administered (15-20 mg/kg) intraperitoneally (IP) and electrophysiological and behavioral effects were compared; parallel studies were conducted with picrotoxin (PTX; 1 mg/kg). Both PTX and Ro 5-4864 produced myoclonic seizures, primarily between 15-40 min after administration; myoclonus was followed by more severe seizures after PTX. Both Ro 5-4864 and PTX produced a maximal increase in amplitude and decrease in threshold of the population spike (PS) evoked in the dentate gyrus (DG) by stimulation of the dorsal perforant path prior to peak seizure activity; start latency of the PS and initial slope and amplitude of the population slow wave (SW) were not changed. Amplitude of the PS was already increased by 5 min after administration of Ro 5-4864 and was maximally increased 1.8- to 3-fold, depending on stimulus intensity, usually by 10 min. Similarly, by 20 min after administration, PTX had also increased PS amplitude in the absence of an effect on PS latency or the SW. The increase in PS amplitude without concomitant changes in the SW suggests that Ro 5-4864 enhanced coupling between the excitatory postsynaptic potential (EPSP) and firing of the postsynaptic neurons, i.e., it enhanced E-S coupling, as has also been suggested for PTX. The similarity in the effects of Ro 5-4864 and PTX suggests that antiGABAergic effects, perhaps along feedforward inhibitory pathways, are involved in both the seizures and enhanced E-S coupling.

Toxicokinetics of Ro 5-4864, lindane and picrotoxin compared

The effects produced by IP administration of these three agents in the rat were compared because of in vitro evidence that each modulates the picrotoxinin site of the GABAA receptor. For each, hypothermia had the lowest threshold and convulsions the next, with hypophagia produced only by the highest dose of either Ro 5-4864 or lindane. Convulsant effects had a shorter latency and a shorter duration than did hypothermia. Hypophagia, when present, lasted the longest. Myoclonus was the seizure type with the lowest threshold for all three agents. At the highest dose, lindane produced a high incidence of maximal clonic (hopping) seizures, whereas Ro 5-4864 and picrotoxin produced a high incidence of maximal tonic seizures instead. On a mole/kg basis, picrotoxin was 40 times more effective than the other two agents and produced seizures which started later, peaked later, and persisted longest. Ro 5-4864 and lindane were effective at equimolar concentrations and, in combination, produced effects which suggested either dose-addition or synergism. The data are consistent with the hypothesis that the toxic effects of both Ro 5-4864 and lindane may be attributable, at least in part, to an action at a subpopulation of GABAA receptors.

Kinetics and thresholds of several indices of lindane-induced toxicity

The effects of lindane, administered either IP (4, 6 or 8 mg/kg in dimethylsulfoxide, 0.5 ml/kg) or PO (30, 40 or 50 mg/kg in oil, 1 ml/kg), were compared in male rats. Effects appeared later and lasted longer after PO administration. After either route, convulsant effects occurred first and were over before hypothermic effects were maximal. Also, hypothermia subsided before hypophagia ended. After IP administration, hypothermia had the lowest threshold and convulsions the next lowest; reduced food intake was produced only by the highest dose, which also produced 43% deaths. By contrast, after PO administration, all doses reduced food intake and produced hypothermia, but deaths did not occur after even the highest dose. The different time courses and thresholds for the different indices of toxicity suggest that different target sites or mechanisms may be involved. Thus, effects on the gut, in addition to effects on the brain, may account for the longer duration and greater sensitivity of reduced food intake, compared to lethal and hypothermic effects, after PO administration of lindane. After administration of lindane IP, peripheral vasodilation (as demonstrated by an increase in tail temperature) preceded colonic hypothermia. This could be explained if lindane inappropriately activated heat-loss mechanisms.