NEUROCHEMICAL IDENTIFICATION OF A(13) DOPAMINERGIC NEURONAL PROJECTIONS FROM THE MEDIAL ZONA INCERTA TO THE HORIZONTAL LIMB OF THE DIAGONALBAND OF BROCA AND THE CENTRAL NUCLEUS OF THE AMYGDALA

Studies utilizing fluorescent histochemical techniques first revealed that A(13) dopaminergic (DA) perikarya located in medial zona incerta (MZI) project to various regions within the hypothalamus; accordingly, these DA neurons were designated the 'incertohypothalamic' DA neurona l system. More recently, it has been shown that the anterograde neuron al tract tracer Phaseolus vulgaris leucoagglutinin, after injection in to MZI, is identified in nerve terminals outside of the hypothalamus; for example, in horizontal limb of the diagonal band of Broca (HDB) an d central nucleus of the amygdala (cAMY). The purpose of the present s tudy was to determine, using neurochemical techniques, if A(13) DA neu rons project to the HDB and cAMY. Concentrations of dopamine and one o f its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) were determin ed in HDB and cAMY following: (1) electrical stimulation of MZI, (2) e lectrolytic lesion or knife ablation of MZI, and (3) administration of gamma-hydroxybutyric acid (GHBA) into MZI. For comparison, similar me asurements were made in nucleus accumbens (N. Ace.), a terminal region of A(10) DA neurons in the ventral tegmental area (VTA). Electrical s timulation of MZI increased DOPAC concentrations in HDB and cAMY, wher eas electrolytic or ablative lesions of MZI decreased dopamine concent rations in both of these regions. By contrast, neither stimulation nor lesion of MZI had any effect on DOPAC or dopamine concentrations in N . Ace. Intracerebral injection of GHBA into MZI increased dopamine con centrations in MZI and HDB, but not in cAMY or N. Ace. Intracerebral a dministration of GHBA into VTA increased dopamine concentrations in HD B and N. Ace., but not in MZI or cAMY. These results suggest that A(13 ) DA neurons project to HDB and cAMY but not to N. Ace., and HDB recei ves projections from both A(10) and A(13) DA neurons.