DOPAMINE AND 5-HT RECEPTOR SENSITIVITY DOES NOT CORRELATE WITH NEOSTRIATAL DOPAMINE OR 5-HT CONTENT

To explore associations of neostriatal (NST) endogenous levels of dopa mine (DA) and serotonin (5-HT) with sensitivity of their receptors, gr aded doses of 6-hydroxydopamine HBr (0 to 400 mu g, ICV; 6-OHDA; desip ramine pretreatment, 20 mg/kg IP) were given to rats' between birth (P 0) and P 42. Numbers of vacuous chewing movements (VCMs) induced by S KF 38393 or m-chlorophenylpiperazine (m-CPP), respective DA D-1 and 5- HT2 agonists, were subsequently determined. Enhanced SKF 38393-induced VCMs occurred when NST DA was reduced 97%-98% by high dose 6-OHDA (10 0-134 mu g) at P 0 or P 3, but not in rats with 95%-97% loss in DA pro duced by 6-OHDA at P7 (134 mu g) or P3 (67 mu g). Enhanced m-CPP-induc ed VCMs occurred even when NST 5-HT content was not elevated after 6-O HDA (134 mu g at P 10). Accordingly, D-1 and 5-HT receptor sensitivity is not correlated with respective NST DA and 5-HT contents. The stage of ontogeny at the time of DA denervation may be the governing influe nce on receptor sensitivity.