The projections of the A8, A9 and A10 dopaminergic cell bodies: evidence for a nigral-hypothalamic-median eminence dopaminergic pathway.

Using the microdissection method of Palkovits and a sensitive microassay for dopamine (DA) and norepinephrine (NE), the CNS projections of the nigral A8, A9 and A10 dopaminergic cell bodies have been determined in rat brain. Following bilateral electrolytic lesions of the A8-A9-A10 region, DA levels fell significantly in the following areas: dorsal septal nucleus (85%), olfactory tubercle (75%), lateral amygdaloid nucleus (75%), habenula (75%), parietal cortex (75%), cingulate cortex (70%), cerebellum (50%), thalamic paraventricular nucleus (50%), and preoptic suprachiasmatic nucleus (45%). Of particular interest was the finding of a 40% fall in the dopamine levels of the median eminence after such lesions. Concentrations of NE in these same areas following lesions of the A8-A9-A10 region were unchanged. These findings suggest that the nigral A8, A9 and A10 dopaminergic cell bodies, project diffusely to many different areas of cortex, hypothalamus, and brain stem, and, more importantly, provide evidence for a previously unsuspected dopaminergic pathway from substantia nigra to median eminence, an area intimately concerned with neuroendocrine regulation.