GABAergic modulation of lindane (gamma-hexachlorocyclohexane)-induced seizures

The main objective of this work was to study the role of the GABAergic system on the convulsions elicited by the organochlorine insecticide lindane. The concentration of lindane in rat brain at the onset of the first tonic convulsion was taken as the endpoint for the neurotoxic action of the insecticide administered by intravenous infusion. Pretreatment with the GABA agonists muscimol and progabide, the GABA uptake blocker SK&F 89976-A, the GABA transaminase inhibitor gamma-acetylenic GABA, and the GABA indirect agonist phenobarbital significantly increased the threshold concentration of lindane in brain required to induce convulsions. The GABA agonist THIP, the GABA competitive antagonist bicuculline, and the prodrug cetyl-GABA had no effect on the brain level of lindane required to induce seizures. The noncompetitive GABA antagonists, picrotoxinin and pentylenetetrazol, significantly decreased the brain concentration of lindane needed to elicit convulsions. The concentration of GABA in the brain of lindane-treated rats was only modified by the significant increase produced after gamma-acetylenic GABA pretreatment. These results show that the convulsions elicited by lindane can be facilitated by some GABA antagonists and antagonized by GABA mimetics, especially those that enhance GABA functionality. The present data are consistent with the proposed in vitro competition of lindane for the picrotoxinin binding site associated with the Cl- ionophore of the GABAA receptor, and suggest that lindane may also interact in vivo with this site.     

The effect of non-convulsant doses of lindane on temperature and body weight

The effect of lindane (gamma-HCH) on temperature, food intake and body weight was studied in male and female rats after single or repeated non-convulsant oral doses. A single dose of 30 mg/kg induced a significant decrease of core temperature (0.4 degrees C in males and 0.66 degrees C in females) 5 h after administration when compared to the control value. Lindane-induced hypothermia was strongly potentiated (1.45 degrees C) by cold stress when rats were kept at 4 degrees C. The same dose of lindane produced a significant decrease in body weight gain (-85% in males and -219% in females compared to the control gain), accompanied by a diminution of food intake, 24 h after administration. No decrease in both parameters was observed when alpha- or delta-HCH isomers 30 mg/kg were tested. After daily administration with 10 mg/kg lindane for 7 days, no hypothermic effects were observed. However, a slight but significant decrease in body weight gain was recorded over the treatment period. This effect was also accompanied by a reduced food intake. The observed stereoselective effects of HCH isomers on core temperature and body weight could be a useful model to study the mechanisms of lindane neurotoxicity at low subconvulsant doses.     

Convulsant effect of lindane and regional brain concentration of GABA and dopamine

Lindane (gamma-hexachlorocyclohexane) is an organochlorine insecticide with known neurotoxic effects. Its mechanism of action is not well understood although it has been proposed that lindane acts as a non-competitive antagonist at the gamma-aminobutyric acid (GABA)-A receptor. We studied the effect of lindane (150 mg/kg) on the GABAergic and dopaminergic systems by measuring the concentration of GABA, dopamine and its metabolites in 7 brain areas at the onset of seizures. All animals suffered tonic convulsions at 18.3 +/- 1.4 min after lindane administration. The concentration of GABA was only slightly but significantly decreased in the colliculi without modifications in the other areas. The concentration of dopamine was increased in the mesencephalon and that of its metabolite DOPAC was also increased in the mesencephalon and the striatum.     

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.     

Regional effects on the cerebral concentration of noradrenaline, serotonin and dopamine in suckling rats after a single dose of lindane.

The effect of a low single dose of lindane (gamma-hexachlorocyclohexane) on monoaminergic neurotransmission during brain postnatal development was studied in 8-, 15-, 22- and 29-day-old suckling rats. Concentrations of noradrenaline, serotonin, dopamine and their metabolites were determined in eight cerebral regions 1 h after dosing (20 mg/kg lindane per os). All these aminergic systems were altered in a regional- and age-related pattern. Decreases of noradrenaline in regions rich with noradrenergic terminals together with increases of the ratio 5-HIAA/serotonin and DOPAC/dopamine suggest, as a whole, an enhanced release of the monoamines. This increased neuronal activity does not exclude an initial action of lindane on the inhibitory GABAergic system that would activate the neurotransmitter release in other systems shortly after a single administration of the neurotoxic agent.     

Effect of lindane at repeated low doses

The relationship between brain concentration of lindane and its convulsant effect have been studied in rats after repeated low doses of lindane. The mean brain plateau concentration was achieved in 5-8 days. The doses administered (5, 12 and 20 mg/kg) and the brain concentration of lindane at the plateau were highly correlated. The incidence rate of response (percentage of rats with tonic convulsions) was also highly correlated with the log of concentration of lindane in brain for all doses and days studied. A decrease in brain concentration of lindane was observed after 12 days of daily administration at doses of 5 and 12 mg/kg but not at the highest dose (20 mg/kg).     

The Role of nitric oxide in convulsions induced by lindane in rats

Lindane is an organochloride pesticide and scabicide. It evokes convulsions mainly trough the blockage of GABA_A receptors. Nitric oxide (NO), gaseous neurotransmitter, has contradictor role in epileptogenesis due to opposite effects of l-arginine, precursor of NO syntheses (NOS), and L-NAME (NOS inhibitor) observed in different epilepsy models. The aim of the current study was to determine the effects of NO on the behavioral and EEG characteristics of lindane-induced epilepsy in male Wistar albino rats.The administration of l-arginine (600, 800 and 1000 mg/kg, i.p.) in dose-dependent manner significantly increased convulsion incidence and severity and shortened latency time to first convulsion elicited by lower lindane dose (4 mg/kg, i.p.). On the contrary, pretreatment with L-NAME (500, 700 and 900 mg/kg, i.p.) decreased convulsion incidence and severity and prolonged latency time to convulsion following injection with a convulsive dose of lindane (8 mg/kg, i.p.). EEG analyses showed increase of number and duration of ictal periods in EEG of rats receiving l-arginine prior to lindane and decrease of this number in rats pretreated with L-NAME.These results support the conclusion that NO plays a role of endogenous convulsant in rat model of lindane seizures.     

The effects of lindane, DDT, and chlordecone on avoidance responding and seizure activity

Male adult Fischer-344 rats were given various doses of lindane (0, 15, and 30 mg/kg, po), chlordecone (0, 25, 50, or 100 mg/kg, ip), or p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT) (0, 25, 50, or 100 mg/kg, po) and tested for their ability to perform a two-way shuttle box task or to learn and retain a step-through passive avoidance response. Administration of p,p'-DDT or chlordecone 3 hr prior to acquisition did not affect the number of shuttle box avoidance responses made during a 60-trial training task, while responses during the intertrial interval (ITI) were decreased. Rats receiving 15 or 30 mg/kg of lindane made fewer avoidance responses, but did not differ from controls in terms of the number of responses during the ITI. When 30 mg/kg lindane was given 3 hr prior to passive avoidance acquisition, retention was impaired 7 days later; the lower dose of lindane, and all doses of chlordecone or p,p'-DDT had no effect under these conditions. When these chemicals were given immediately after passive avoidance training, animals treated with lindane were not affected. Animals receiving 100 mg/kg of p,p'-DDT or chlordecone displayed marked signs of toxicity and animals tested 7 days after training showed an impaired retention. Pretreatment with anticonvulsants such as phenobarbital and chlordiazepoxide, which may enhance GABA-mediated responses, blocked the disruptive effects of lindane (30 mg/kg) on shuttle box avoidance. The seizure-related activity produced by a higher dose of lindane (60 mg/kg) and kainic acid, a hippocampal excitotoxin, was also blocked by phenobarbital and chlordiazepoxide. Pretreatment with phenytoin, which is thought to bind to the inactivation gates of sodium, had no effect on the effects produced by lindane or kainic acid. These data suggest that treatment with nonconvulsant doses of lindane can interfere with the ability to acquire and use new information and that these effects may be associated with alterations in GABA.     

The potency of gamma-1,2,3,4,5,6-hexachlorocyclohexane (lindane)

The potency of gamma-1,2,3,4,5,6-hexachlorocyclohexane (lindane) as a convulsant was examined in rats by infusion into a tail vein of the unrestrained animal using a lipid emulsion as vehicle and a dose rate of 200 micrograms/min. The concentration of drug in brain rose linearly up to a convulsant level, the rate of rise increasing with relative organ mass. The decline from a convulsant level was biphasic with half times of, respectively, 30 min and 3 days. Convulsant concentrations (CC) in brain were within the range obtained with other modes of administration and exhibited normal distribution but there was a moderate influence of sex, the ovarian cycle, and age on the individual response. The minimally effective and the mean convulsant doses recorded in the survey were, respectively, 1.5 and 2.4 mg/kg and, thus, of the same order as doses reportedly convulsant in the American cockroach as well as, under certain circumstances, in man. In the neonate, the mean CC in brain was 2.5 as against 4.5 micrograms/g wet weight in the adult. An argument is put forward to support the contention that this difference might be largely accounted for by the maturational increase in the lipid content of the brain. The argument uses an approximation to the mean CC in brain water which is 70 nmol/l in both the young suckling and the adult and corresponds to concentrations in which the drug reportedly effects neuroexcitation in the cockroach nervous system or binds to the ionophore of GABA-A receptors in rat brain membranes. The findings call for convulsive states in children after dermal application of lindane to be considered in terms of individual factors favouring rapid absorption as well as in terms of individual supersensitivity of the nervous system.     

Effects of glycine and other inhibitory amino acid neurotransmitters on strychnine convulsive threshold in mice

The effects of glycine and other inhibitory amino acid neurotransmitters on strychnine convulsive threshold were studied in mice. The mean intravenous threshold dose for strychnine to produce its convulsive effects in briefly restrained mice was determined to be 1.386 +/- 0.035 mg/kg. The dose of strychnine produced 100% postconvulsive mortality in all the mice tested. Intraperitoneal administration of various doses (100-500 mg/kg) of glycine, beta-alanine and L-threonine, 15-20 minutes prior to strychnine infusion produced an increase of 13.92%, 25.73% and 17.15% respectively in strychnine convulsive threshold in mice. Diazepam, known to produce its anticonvulsant, sedative and muscle relaxant effects through its interaction either with central GABA or glycine receptors was found to be the most potent (48.39%) in increasing strychnine convulsive threshold. Taurine and Baclofen were found to be ineffective in raising strychnine convulsive threshold in mice. These observations favor the possible use of either glycine or beta-alanine in addition to diazepam in treating clinical cases of strychnine neurotoxicoses.     

Effect of lindane on the myelination process in the rat

After lindane administration at several doses, brain myelin fractions of litters of male and female Wistar rats show a significant diminution of CNP (2′,3′-cyclic nucleotide 3′-phosphodiestera activity. Furthermore, the immunohistochemical study of brains by means of a MBP (myelin basic protein) specific antibody reveals myelin deficits in some brain regions after lindane treatment. This loss of myelin protein is dose dependent. The deficit in myelin cannot be attributed to undernourishment of lindane-administered rats. This work shows the vulnerability of the developing central nervous system (CNS) to lindane and the correlation between a decrease in the CNPase activity and a deficit of MBP during the period of study of these animals.     

Relationship between lindane concentration in blood and brain and convulsant response in rats after oral or intraperitoneal administration

The relationships between brain and blood concentrations of lindane and its convulsant effects have been studied in rats after different po and ip doses. A good correlation was observed between dose and the frequency and time to onset of tonic seizures, the intensity of the response and lethality. An oral ED₅₀ (84 mg/kg) and an ip ED₅₀ (131 mg/kg) for the half-maximal incidence rate of lindane-induced tonic seizures was determined. The incidence of response was directly proportional to the log of lindane concentration in brain and blood, with an EC₅₀ of 5.3 g/g and 1.5 g/ml, respectively. The threshold concentration of lindane eliciting tonic seizures was estimated to be 5 g/g in brain and 1.5 g/ml in blood. The kinetics of lindane in brain and blood were examined after a single 60 mg/kg po or ip dose over a period from 5 min to 1 week. Concentrations of lindane in brain and blood were found to be highly correlated.     

Effect of repeated exposure to lindane and cadmium on lindane metabolism in rats

The effects of daily administration of cadmium and lindane for 35 days on the metabolism of lindane in rats were investigated. The results indicate that cadmium induces a significant inhibition of lindane metabolism, since the group dosed with lindane plus cadmium had a significantly higher concentration of lindane in plasma and tissues than the group dosed with lindane alone. The inhibition in the metabolic rate of lindane is associated with the cadmium-induced alterations in the disposition of essential trace elements, Zn, Cu and Fe, in the liver.     

Chlorinated phenols as metabolites of lindane. Evaluation of the degree of conjugation in rat urine

After lindane was administered to rats in a single oral dose, the time profile of the degree of conjugation of the main phenolic metabolites was evaluated. In all urine samples 2,3-dichlorophenol, 2,4,5- and 2,4,6-trichlorophenol, and 2,3,5,6-tetrachlorophenol were constantly present. 2,3,5,6-Tetrachlorophenol and then 2,4,6-trichlorophenol were the prevalent metabolites in all cases. The degree of conjugation did not correlate with the dissociation constant of individual chlorinated phenols. Phenol conjugation declined with time after administration.     

Plasma absorption and ultrastructural changes of rat testicular cells induced by lindane

This paper describes, for the first time, how topical application in rats of a commercial preparation of lindane widely used in public health, at similar doses and routes of administration as in humans, leads to rapid absorption and accumulation of lindane in the testes. An early peak of absorption was detected in plasma 6 h after topical treatment of male Wistar rats with a commercial preparation of 1% lindane (Plomurol). Higher plasma levels were observed after repetitive doses of 60 mg/kg b.w., the amount recommended for the treatment of scabies and pediculosis in humans in several countries. A residue level of 7.4 +/- 0.67 microg/g was found in testicular tissue 6 h after a single daily topical application for 4 consecutive days. The ultrastructural study of testicular interstitial cells exposed to dermal application of lindane (Plomurol) revealed widespread damage of a great number of Leydig cells, some of which were completely disintegrated.     

Effects of midazolam,DMCM and lindane on potentiated startle in the rat

Forty-eight male Wistar rats were exposed to contingent light-shock combinations and 48 rats received light and shock stimuli in a random order. One day after fear conditioning the animals were tested for startle potentation after injection of midazolam (0, 0.5, 1.0, 2.0 mg/kg, IP) or DMCM (methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate; 0, 0.1, 0.2, 0.4 mg/kg IP) or lindane (0, 7.5, 15.0, 30.0 mg/kg PO). Midazolam attenuated potentiated startle dose dependently and the inverse benzodiazepine agonist DMCM had the opposite effect. The effects of lindane on startle amplitudes were identical to those of DMCM, indicating that lindane has anxiogenic effects on behavior. It is suggested that the anxiogenic effects of lindane are mediated by an effect at the GABA-ionophore complex.     

Differential effects of gamma-hexachlorocyclohexane (lindane) on pharmacologically-induced seizures

Gamma-hexachlorocyclohexane (gamma-HCH), the active ingredient of the insecticide lindane, has been shown to decrease seizure threshold to pentylenetrazol (PTZ) 3 h after exposure to gamma-HCH and conversely increase threshold to PTZ-induced seizures 24 h after exposure to gamma-HCH (Vohland et al. 1981). In this study, the severity of response to other seizure-inducing agents was tested in mice 1 and 24 h after intraperitoneal administration of 80 mg/kg gamma-HCH. One hour after the administration of gamma-HCH, the activity of seizure-inducing agents was increased, regardless of their mechanism, while 24 h after gamma-HCH a differential response was observed. Seizure activity due to PTZ and picrotoxin (PTX) was significantly decreased; however, seizure activity due to 3-mercaptopropionic acid (MPA), bicuculline (BCC), methyl 6,7-dimethoxy-4-ethyl-B-carboline-3-carboxylate (DMCM), or strychnine (STR) was not different from control. In vitro, gamma-HCH, pentylenetetrazol and picrotoxin were shown to inhibit 3H-TBOB binding in mouse whole brain, with IC₅₀ values of 4.6, 404 and 9.4 M, respectively. MPA, BCC, DMCM, and STR showed no inhibition of 3H-TBOB (t-butyl bicyclo-orthobenzoate) binding at concentrations of 100 m. The pharmacological challenge data suggest that tolerance may occur to seizure activity induced by PTZ and PTX 24 h after gamma-HCH, since the response to only these two seizure-inducing agents is decreased. The in vitro data suggest that the site responsible for the decrease in seizure activity 24 h after gamma-HCH may be the GABA-A receptor-linked chloride channel.     

Effects of lindane on oocyte maturation and preimplantation embryonic development in the mouse

Lindane, an organochlorine insecticide, is suspected of preimplantation embryonic toxicity based on in vitro experiments with bovine and murine embryos. To verify this hypothesis in vivo we tested lindane for developmental alterations during early embryonic cleavage in the mouse. Two treatment schedules were tested: three daily doses of 15 or 25mg/kg b.w. lindane were orally administered to female mice either before mating or immediately after mating. Morphologic alterations (lysis or fragmentation of blastomeres, developmental arrest) of two-cell embryos and morulae were evaluated by inverted microscopy. In addition, cytologic abnormalities and cell proliferation delay, possibly induced during the first four cleavage cycles, were evaluated by fluorescent microscope analysis of the number and morphology of blastomere nuclei. A statistically significant increase of degenerating two-cell embryos was induced by exposure of preovulatory oocytes to the highest tested lindane dose. Early cleavage embryos exposed to the same dose showed a lower average number of blastomeres per morula, as well as a 40% reduction of the mitotic index with respect to matched controls. However, mean values in individual litters were variable and litter analysis did not show a lindane-related effect. One possible mechanism for the observed effects could be the recently demonstrated inhibitory action of lindane on gap junction-mediated cell communication between oocyte and cumulus cells. A comparison between human exposure levels and experimental doses based on measured and predicted blood concentrations suggests that there are ample margins of safety for human embryonic development at the present exposure levels.     

The effect of p-bromomethamphetamine (V-111), a selective serotoninergic amphetamine, on the convulsive seizure excitability threshold in mice

The effect of p-bromomethamphetamine (V-111), a selective serotoninergic amphetamine analogue, on convulsive seizure excitability threshold was evaluated in male albino mice. It was found to be most effective in subcutaneous doses of 15 mg/kg and intracerebroventricular doses of 25 fig per mouse. In a single dose of 15mg/kg, V-111 elevated the pentylenetetrazol threshold when the latter was applied at 30 min, 1 hr or 3 hr; after this time V-111 decreased the threshold. The effect of V-111 on the pentylenetetrazol threshold was changed by drugs which influence serotoninergic synaptic transmission.

p-Chlorophenylalanine decreased the threshold while 5-hydroxytryptophan, imipramine and the combination of 5-hydroxytryptophan and imipramine increased it. Nialamide caused no change in the threshold. The changes in the convulsive seizure excitability threshold are considered to be due to inhibition of intraneuronal 5-hydroxytryptamine and dopamine uptake and alteration of the brain level of 5-hydroxytryptamine induced by V-111.     

Convulsions in weanling rabbits after a single topical application of 1% lindane.

There have been sporadic reports of adverse effects of lindane (γ-hexachlorocyclohexane) in children treated for scabies. These effects usually consisted of tremors, convulsions, anorexia, and possible stunting of growth. Weanling rabbits (6 weeks old; 1.0 kg) given a single topical application of 1% lindane at a dose reportedly used in infants (60 mg/kg) exhibited severe anorexia and convulsions; death occurred in some cases. The effects were more pronounced in weanlings in which the skin was inflamed or not completely intact. In contrast, young adult rabbits (2–3 kg) given the same dose showed only some anorexia and possibly mild excitement. Concentrations of lindane in whole blood of weanlings at the time of convulsion (approximately 24 hr after dosing) ranged from 0.7 to 2.5 μg/ml. These findings suggest a rather pronounced sensitivity of weanlings to lindane in comparison to adults.