Effect of lindane on the myelination process in the rat

Prenatal β-Hexachlorocyclohexane (β-HCH) Exposure and 7-Year Child IQ in the CHAMACOS Birth Cohort

Fetal and infant exposures to β-hexachlorocyclohexane (β-HCH) occur through placental and breastmilk transfers. No studies have examined the relationship between β-HCH and child intelligence quotient (IQ). This study examined associations between in utero β-HCH exposure and cognitive development in 7-year-old children. Data from women and children (n = 256) participating in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) birth cohort study were evaluated. We assessed exposure to β-HCH by measuring maternal serum concentration during pregnancy. We administered the Wechsler Intelligence Scale for Children (WISC), Fourth Edition, to children at age 7. Analyses were adjusted for maternal age, country of birth, work status, parity, and other pesticide exposures, language used for child cognitive assessment, and duration of breastfeeding. Higher serum β-HCH concentrations were associated with higher cognitive scores across all unadjusted models for the full-scale and sub-scale cognitive tests. In the adjusted models, a 10-fold increase in serum β-HCH concentration was associated with a 4.5-point increase in Working Memory IQ score (95% CI, 0.6 to 8.3; p = 0.02). We observed no significant interaction by length of breastfeeding or sex on associations. Our findings suggest that prenatal exposure to β-HCH is not adversely related to IQ at age 7 in a cohort of Mexican American children with fairly high exposure in utero as measured by maternal serum levels. Future research must replicate these findings in other study cohorts of women and children.

Developmental neurotoxicity of succeeding generations of insecticides

Insecticides are by design toxic. They must be toxic to effectively kill target species of insects. Unfortunately, they also have off-target toxic effects that can harm other species, including humans. Developmental neurotoxicity is one of the most prominent off-target toxic risks of insecticides. Over the past seven decades several classes of insecticides have been developed, each with their own mechanisms of effect and toxic side effects. This review covers the developmental neurotoxicity of the succeeding generations of insecticides including organochlorines, organophosphates, pyrethroids, carbamates and neonicotinoids. The goal of new insecticide development is to more effectively kill target species with fewer toxic side effects on non-target species. From the experience with the developmental neurotoxicity caused by the generations of insecticides developed in the past advice is offered how to proceed with future insecticide development to decrease neurotoxic risk.

Responsiveness of cerebral and hepatic cytochrome P450s in rat offspring prenatally exposed to lindane

Prenatal exposure to low doses of lindane has been shown to affect the ontogeny of xenobiotic metabolizing cytochrome P450s (CYPs), involved in the metabolism and neurobehavioral toxicity of lindane. Attempts were made in the present study to investigate the responsiveness of CYPs in offspring prenatally exposed to lindane (0.25 mg/kg b. wt.; 1/350th of LD(50); p. o. to mother) when challenged with 3-methylcholanthrene (MC) or phenobarbital (PB), inducers of CYP1A and 2B families or a sub-convulsant dose of lindane (30 mg/kg b. wt., p. o.) later in life. Prenatal exposure to lindane was found to produce an increase in the mRNA and protein expression of CYP1A1, 1A2, 2B1, 2B2 isoforms in brain and liver of the offspring at postnatal day 50. The increased expression of the CYPs in the offspring suggests the sensitivity of the CYPs during postnatal development, possibly, to low levels of lindane, which may partition into mother's milk. A higher increase in expression of CYP1A and 2B isoenzymes and their catalytic activity was observed in animals pretreated prenatally with lindane and challenged with MC (30 mg/kg, i. p. x 5 days) or PB (80 mg/kg, i. p. x 5 days) when young at age (approx. 7 weeks) compared to animals exposed to MC or PB alone. Further, challenge of the control and prenatally exposed offspring with a single sub-convulsant dose of lindane resulted in an earlier onset and increased incidence of convulsions in the offspring prenatally exposed to lindane have demonstrated sensitivity of the CYPs in the prenatally exposed offspring. Our data assume significance as the subtle changes in the expression profiles of hepatic and cerebral CYPs in rat offspring during postnatal development could modify the adult response to a later exposure to xenobiotics.

Behavioral and monoaminergic changes after lindane exposure in developing rats

The effects of lindane on behavior and central monoaminergic systems were studied in rat pups at 15 days of postnatal age. Pups were previously given nonconvulsant lindane PO doses, either a single 20 mg/kg or 7-day repeated 10 mg/kg doses. Both treatment schedules improved the passive avoidance acquisition but only the acute administration prolonged the step-through latency. Acute lindane decreased the motor activity, whereas the repeated dosing increased it. Increases of the ratio 5-HIAA/serotonin in several brain regions and of the ratio DOPAC/dopamine in the mesencephalon after a single dose of lindane suggest an enhanced monoaminergic turnover. In contrast, repeated lindane doses decreased monoamine/metabolite ratios excluding the striatum, where an increase of DOPAC/dopamine ratio correlates with the higher motor activity of these animals. It is postulated that both the imbalance of the central monoaminergic systems and the lindane-induced GABAergic blockade may be the basis of the behavioral alterations.

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.

Behavioral changes induced in developing rats by an early postnatal exposure to lindane

The purpose of this study was to determine whether the behavioral developmental pattern was altered by an early postnatal exposure to lindane. Male and female offspring of Wistar rats were daily orally administered with a nonconvulsant dose of lindane (10 mg/kg) during 7 days either the 1st or the 2nd postnatal week days. Effects on pups were evaluated with a reduced developmental neurotoxicological test battery. Body weight evolution, neuromotor reflexes (surface righting, cliff avoidance and tail hang reflex) and spontaneous motor activity were analyzed from day 1 after birth up to day 28. The body weight pattern was unaffected by treatment with lindane and no signs of overt toxicity were observed. Lindane-treated pups showed an increased positive response of the neuromotor reflexes. Furthermore, lindane produced hyperactivity, especially manifested between days 12 and 16. A peak of activity was reached at day 16 in lindane-treated group, while control animals had a maximum between days 20 and 24. These results suggest that low nonconvulsant doses of lindane may induce behavioral changes in developing rats.