Differences in brain area concentrations of dopamine and serotonin in myers' high ethanol preferring (mHEP) and outbred rats
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Both male and female mHEP rats consume excessive amounts of ethanol and thus offer a rational model for examining biochemical and behavioral differences with non-drinking rat lines. Differences in basal concentrations of 5-hydroxytryptamine (5-HT) and dopamine (DA) correlate with the consumption of ethanol in some ethanol-preferring rat lines. The concentrations of 5-HT and DA were examined by HPLC in five brain areas (prefrontal cortex, hippocampus, nucleus accumbens, striatum and hypothalamus) of ethanol-näive rats and after the oral administration of 0.25 or 1.0 g ethanol/kg in the male and female mHEP rat, the male Wistar rat, and the female Sprague-Dawley rat. The mHEP and control rats that received ethanol were screened for drinking in a 10-day "step-up" 3% to 30% ethanol solutions beginning at postnatal days 40 and 80, and then tested at 150 days of age. The levels of DOPAC in females were lower in the hippocampus of both naïve mHEP and ethanol-treated Sprague-Dawley rats. In striatum, the concentrations of 5-HT and DA were elevated in both mHEP and ethanol-treated Sprague-Dawley female rats. The concentrations of 5-HT and its metabolite, 5-HIAA, were lower in the nucleus accumbens of the ethanol-näive female mHEP rat relative to the female outbred control. In the male rats, the levels of DA, HVA and DOPAC, as well as 5-HT and 5-HIAA were reduced in the hypothalamus of both ethanol-näive mHEP rats and Wistar rats receiving ethanol by gavage. These data demonstrate differences in neurotransmitter activity between the selectively bred mHEP rat and the outbred rat strains. There are few common features found in both the male and the female mHEP rat when compared to their respective controls. Differences in neurotransmitter function in these brain areas may account for some of the behavioral differences previously demonstrated between the two sexes of the mHEP rat.
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