Effects of prenatal phenobarbital on benzodiazepine receptor development

Hippocampal gamma-aminobutyric acid and benzodiazepine receptors after early phenobarbital exposure

Mice were exposed to phenobarbital (PhB) prenatally (PreB offspring) by feeding their mothers 3 g/kg PhB in milled food on gestation days 9-18, or neonatally by directly injecting pups of intact mothers with daily dose of 50 mg PhB on postnatal days 2-21 (NeoB offspring). At age 22 or 50 days, the offspring were tested for gamma-aminobutyric acid (GABA) up take in the hippocampus and in the rest of the brain. In addition, [3H]muscimol and [3H]flunitrazepam binding in the hippocampus and cortex were measured in the offspring at age 22 and 50 days. Long-term decrease in GABA uptake was found in the NeoB group. A 23% decrease was found in 22-day-old mice (P < 0.001) and a 22% decrease in 50-day-old mice (P < 0.05). In addition, there was a 22% decrease in GABA uptake in the brain of 22-day-old PreB mice (P < 0.05). An increase of 52% in [3H]muscimol binding (P < 0.001) and 45% (P < 0.001) in [3H]flunitrazepam binding were measured in the hippocampus in the 22-day-old NeoB mice; no differences were found in affinity. The differences were short-term and could no longer be detected at age 50 days. No differences were found in the cortex; unlike NeoB, PreB mice did not differ from controls. The results suggest upregulation of the GABAergic system in early PhB exposed mice.

Effect of prenatal and neonatal chronic exposure to phenobarbital on central and peripheral benzodiazepine receptors

Phenobarbital (PhB) was administered to pregnant mice during days 9-18 of gestation. [3H]Muscimol binding to cerebellum, [3H]flunitrazepam binding to cerebellum and olfactory bulb, and [3H]PK 11195 binding to olfactory bulb, heart and kidney were assay in the of offspring at 22 and 50 days of age. The chronic prenatal administration of PhB did not affect either gamma-aminobutyric acid (GABA) receptors, central benzodiazepine receptors (CBR), or peripheral benzodiazepine binding sites (PBS) in these tissues. In the next stage of the study, we investigated a possible modulatory effect of chronic postnatal PhB treatment during days 2-21 of age on the same receptors measured at 22 and 50 days of age. PhB exposure of neonates resulted in a significant down-regulation of GABA receptors and CBR in the cerebellum and of PBS in the heart. The effects were demonstrated on day 22 of age and were undetectable by day 50 of age. CBR at the olfactory bulb and PBS at the olfactory bulb and kidney were not altered by the drug treatment. It is concluded that in utero exposure to PhB does not affect benzodiazepine receptor ontogenesis, and the effects of postnatal treatment are transitory only.

Age-related changes in multiple neurotransmitter systems in the monkey brain

Age-associated changes in cholinergic, monoaminergic and amino acid neurotransmitter systems were analyzed in 14 brain regions of 23 rhesus monkeys that ranged in age from 2 to 37 years. In the frontal pole, the levels of choline acetyltransferase (ChAT) activity, the density of [3H]ketanserin (serotonin type-2) binding sites and endogenous levels of dopamine, homovanillic acid and serotonin, all expressed per milligram of protein, decreased significantly with aging. In precentral motor cortex, ChAT activity decreased; in parietal and occipital cortex, the number of [3H]ketanserin binding sites decreased while the number of Na+-independent [3H]glutamate binding sites increased with age. In the caudate nucleus, endogenous levels of norepinephrine decreased. This descriptive study indicates that the aging monkey may be a very useful model for future investigations of age-associated transmitter abnormalities similar to those that occur in humans.

Individual differences in aging: behavioral and neurobiological correlates

The goal of this experiment was to determine the correlations among different behavioral and neurobiological measures in aged rats. Aged Sprague-Dawley rats were given a battery of cognitive and sensorimotor tests, followed by electrophysiological assessment of sleep and biochemical measurements of various neurotransmitter systems. The behavioral tests included the following: Activity level in an open field; short-term and long-term memory of a spatial environment as assessed by habituation: spatial navigation, discrimination reversal, and cue learning in the Morris water pool; spatial memory in a T-maze motivated by escape from water; spatial memory and reversal on the Barnes circular platform task; passive avoidance; motor skills. Sleep was assessed by electrographic cortical records. The following neurotransmitter markers were examined: Choline acetyltransferase; the density of nicotinic, benzodiazepine and glutamine receptors in the cortex and caudate nucleus; endogenous levels of norepinephrine, dopamine, and serotonin in the cortex and hippocampus. The duration of bouts of paradoxical sleep was strongly correlated with several cognitive measures and selected serotonergic markers. This finding suggests that changes in sleep patterns and brain biochemistry contribute directly to deficits in learning and memory, or that the same neurobiological defect contributes to age-related impairments in sleep and in learning and memory.