Alterations in mice dopamine receptor characteristics after early exposure to phenobarbital

Altered brain sensitivity to ethanol in mice after MPTP treatment

Previous studies demonstrated the role of the dopaminergic receptors in brain sensitivity to ethanol. The present study was designed to assess the relative contribution of the nigrostriatal component to this brain sensitivity. Adult male C57BL mice were given 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine (MPTP) injections (30 mg/kg daily for 2 consecutive days). The treatment decreased the striatal dopamine level by 35% from the control level, and the number (Bmax) of dopaminergic receptors was increased by 67%. Ethanol-induced sleep time was reduced in the MPTP-treated mice, as compared to controls, and this gap progressively widened during the 3 weeks of testing to 29%. Brain ethanol levels upon awakening increased by 22%. The results suggest that the nigrostriatal dopaminergic pathways play a major role in determining brain sensitivity to ethanol which may represent an important component in the addictive process.

Alterations in hippocampal cholinergic receptors and hippocampal behaviors after early exposure to nicotine

Mice were exposed to nicotine prenatally by injecting the mother with 1.5 mg/kg nicotine SC twice daily on gestation days 9-18 (PreN mice) or neonatally by daily SC injections of 1.5 mg/kg nicotine on postnatal days 2-21 (NeoN mice). At age 50 days, hippocampal muscarinic receptors Bmax of PreN and NeoN mice were 58% and 79% above control, respectively (p less than 0.01); Kd was unaffected by early nicotine exposure. Eight-arm maze performance of nicotine-exposed animals fell behind control level. Both PreN and NeoN made approximately 10% less correct responses in the first eight trials than controls throughout the test period (p less than 0.01). By the last day of testing, PreN needed 23% and NeoN 31% more trials than controls to enter all arms (p less than 0.001). In addition, PreN needed 35 and NeoN 42% more days than controls to reach criterion (p less than 0.05). Similarly, while 61% of controls reached criterion by day 6 only 17% of PreN and 25% of NeoN reached criterion (p less than 0.01). In the Morris maze, PreN needed from 43-119% more time to reach the platform (p less than 0.001). In the spatial probe test, PreN animals made 35% fewer crosses over the area of the missing platform (p less than 0.001). The study suggests that nicotine administered to the fetus or neonate alters septohippocampal chemistry and induces deficits in hippocampus-related behaviors. The possible reversal of the behavioral changes by manipulating the cholinergic innervations should be the subject of future investigations.

Chronic ACTH treatment increases striatal dopamine D-2 receptor binding in developing rat brain

ACTH has been reported to decrease elevated levels of dopamine metabolites in the CSF of patients with infantile spasms who respond clinically to ACTH therapy. To study the possible role of dopamine receptors in the effect of ACTH, we treated rat pups for thirty days with 40 IU/kg subcutaneously of porcine ACTH or with normal saline. Using 10 nM 3H-spiperone and sulpiride to determine nonspecific binding, specific binding of D-2 receptors increased significantly (46%) in the striata of ACTH-treated rats when compared to controls. No significant difference in specific binding was found in the nucleus accumbens. Protein concentration was significantly decreased by ACTH treatment. Saturation studies will be necessary to determine if the increase in dopamine receptor binding induced by a high dose of ACTH represents a change in receptor density or affinity. The effect of lower clinical doses of ACTH on dopamine receptors warrants study.

Differential effects of prenatal exposure to phenobarbital on the behaviour and neurochemistry of CBA and C57BL/6J mice

Pregnant C57BL/6J and CBA mice were administered 60 mg/kg phenobarbital intraperitoneally from days 10 to 16 of gestation. On day 18 of pregnancy half of the control and drug-treated mice were killed and the embryonic brains removed for cell cultures. The remaining mice were allowed to have their litter. After cross-fostering the mice were used for behavioural studies. Pups born to drug-treated CBA mice had birth-weights similar to controls, but their weights had fallen behind controls by day 18 after birth. They were slower at attaining mature responses in tests for sensory motor development and became progressively more hyperactive (three times more active at day 18) compared to controls. Drug-exposed C57 pups also had birth weights similar to controls. After cross-fostering, 19% of control and 31% of drug-exposed pups died, but the remaining drug-exposed pups showed no deficits in weight gain. In contrast to drug-treated CBA pups, drug-exposed C57 pups were slightly quicker in attaining mature responses in some tests. There was no difference in activity between them and their controls. In neurochemical analyses, uptake of neurotransmitters by cerebral cultures from CBA showed that uptake of GABA was increased by 5%, choline by 95%, dopamine 120%, serotonin 165% and noradrenaline by 160% in cultures from drug exposed embryos compared to controls. In cerebral cultures from C57, GABA uptake was reduced by 18%, choline 33%, dopamine 35% and noradrenaline by 25%. Only serotonin uptake was increased by 182% compared to controls. Differences between C57 and CBA were also apparent in the uptake of neurotransmitters by neuronal cultures from the mesencephalon.(ABSTRACT TRUNCATED AT 250 WORDS)

Normal zinc and iron concentrations in mice after early exposure to phenobarbital

Zinc and iron levels were studied in mice with early (pre/neonatal) exposure to phenobarbital, as the levels of these trace metals are known to be correlated with specific behaviors shown in our previous and present experiment to be affected by early phenobarbital administration. Mice were exposed to phenobarbital prenatally or neonatally. At adulthood they showed marked reduction from control in all parameters of eight-arm maze performance (P less than 0.001). Since zinc is known to be correlated with this behavior, it was subsequently studied in barbiturate exposed animals. The differences between barbiturate exposed and control offspring for zinc levels in plasma, brain and hippocampus did not reach statistical significance. Our previous studies have shown that the number of dopamine receptors and the resulting apomorphine-induced climbing behavior is altered after early exposure to phenobarbital. The effect of iron level on dopamine receptors is now well established. Subsequently, a group of mice were tested for iron levels in their brain and liver. No significant differences were found. It is suggested that deficits in the hippocampal behaviors, mainly eight-arm maze, after early exposure to phenobarbital are not related to changes in zinc levels. Similarly, early phenobarbital-induced alternation in dopamine receptors and the resulting dopaminergic behaviors are not related to changes in iron levels.