Amphetamine-induced preprodynorphin mRNA expression and κ-opioid receptor binding in basal ganglia of adult rats after prenatal exposure to diazepam

In order to obtain information on the functional state of basal ganglia following prenatal benzodiazepine exposure, preprodynorphin mRNA expression and k-opoid receptors were studied in offspring of timed-pregnant Long Evans rats treated with diazepam (1.25 mg/kg/day) on gestational days 14 to 20. Preprodynorphin mRNA was localized by in situ hybridization using a 33P-labeled oligonucleotide. Relative optical density (ROD) was quantified by image analysis in four quadrants of caudate putamen, in nucleus accumbens and olfactory tubercle of adult male rats. Six hours after functional challenge by injection of D-amphetamine (8 mg/kg s.c)., prenatally vehicle-exposed rats exhibited increased preprodynorphin mRNA (ROD) levels in caudate putamen (dorsolateral 187%, dorsomedial 150%, ventrolateral 153%, ventromedial 140% of control), nucleus accumbens (142%) and olfactory tubercle (213%). Prenatal diazepam exposure attenuated the effect of amphetamine in all regions; statistically significant differences between ROD levels of prenatally vehicle/adult amphetamine-treated and prenatally diazepam/adult amphetamine-treated groups were seen in ventrolateral caudate putamen, nucleus accumbens and olfactory tubercle. Baseline levels and topographical distribution of preprodynorphin mRNA remained unchanged. k-Opioid receptor binding was analyzed in membrane fractions from nucleus accumbens+olfactory tubercle, caudate putamen, and midbrain of male and female offspring using [ 3H]U69593. B max was reduced in nucleus accumbens+olfactory tubercle, but not in caudate putamen or midbrain of adult, prenatally diazepam-exposed male offspring. This effect was not yet seen at earlier postnatal stages (14 and 28 days), and was also absent in females. These data indicate that prenatal exposure to diazepam results in a delayed change in the functional state of dynorphin-containing neurons in several parts of the basal ganglia of adult male offspring. The decreased responsiveness to enhanced dopaminergic transmission may impair the function of basal ganglia circuitry.