39 in this part of these studies, it
was found that dopamine D2-like receptor blockade increased the POMC mRNA this website levels in the hypothalamus, a site with a different function than POMC mRNA levels in the anterior pituitary.39 These findings suggest that activation of the dopamine D2 receptor may play a tonic inhibitory tone on hypothalamic POMC gene expression. However, neither dopamine D2 blockade nor acute binge cocaine altered POMC mRNA levels in the amygdala, the anterior pituitary, or the neurolntermedlate level of the pituitary. Also, dopamine D1 receptor Inhibitors,research,lifescience,medical blockade had no impact on hypothalamic POMC expression. Thus, these results both suggest a possible specific role for dopamine D2 in at least acute cocaine effects on hypothalamic POMC gene expression.39 To further our studies on the relative role of the D1-like and D2-like (and also D3-like, which are D2-like) dopamine receptors in Inhibitors,research,lifescience,medical the setting of drug abuse, and, specifically the impact of binge-pattern cocaine administration, we have conducted studies using D1-/- or D3-/- selective Inhibitors,research,lifescience,medical dopamine receptor gene deletion mice.40
In these studies, we examined mu-opioid receptor gene expression in response to binge-pattern cocaine. We found that, at basal state, there was a significant Inhibitors,research,lifescience,medical increase in mu-opioid receptor mRNA levels in the frontal cortex of both the D1-/- and D3-/- dopamine receptor gene deletion mice, as compared with each of their wild-type controls.40 However, there were no differences in basal levels of mu-oploid gene expression in the nucleus accumbens or in the caudate-putamen in these gene deletion mice. Strikingly, and in an opposite direction from some of our earlier findings in wild-type rat models, acute binge cocaine 15 mg/kg x 3 doses resulted
in the Inhibitors,research,lifescience,medical restoration of frontal cortex mu-opioid receptor ADAMTS5 mRNA levels in the gene deletion mice to the levels of those in wildtype mice.40 Further, in the nucleus accumbens core, after acute binge cocaine, there was an actual decrease in mu-opioid receptor levels in the D1-/- mutant mice, whereas in that brain region there was an increase in mu-opioid receptor gene expression in D3-/- mice.40 The opposite pertained in the caudate-putamen, with an increase in mu-opioid receptor levels after binge cocaine in the caudate-putamen of the D1-/- mice and a decrease in the dopamine D3-/- mice.40 In addition, a decrease in basal orexin mRNA levels was found in the lateral hypothalamus of the D3-/- mice, which did not change with cocaine.