EFFERENT PROJECTIONS FROM THE REGION OF THE MEDIAL ZONA INCERTA CONTAINING A(13) DOPAMINERGIC-NEURONS - A PHA-L ANTEROGRADE TRACT-TRACING STUDY IN THE RAT

Potential efferent projections of A(13) dopaminergic (DA) neurons were identified in the present study by examining the distribution of labe lled fibers following iontophoretic injection of the anterogradely tra nsported lectin Phaseolus vulgaris leucoagglutinin (PHA-L) into the me dial zona incerta (MZI), the region of the diencephalon containing A(1 3) DA neuronal perikarya. One week after injection, PHA-L labelled fib ers were found throughout the brain with the heaviest labelling occurr ing ipsilateral to the injection site in the anterior hypothalamic are a, lateral hypothalamus, lateral preoptic area, horizontal diagonal ba nd of Broca, and parvocellular region of the paraventricular nucleus. Moderate labelling was observed in the ipsilateral median preoptic nuc leus, lateral septum, lateral aspect of the bed nucleus of the stria t erminalis, and central nucleus of the amygdala. Moderate labelling was also found in the contralateral MZI and parvocellular region of the p araventricular nucleus. Light labelling was detected in the ipsilatera l medial preoptic area, supraoptic nucleus, ventromedial nucleus, arcu ate nucleus, vertical limb of the diagonal band of Broca, and in the c ontralateral lateral hypothalamus. Few immunopositive fibers were pres ent in the dorsomedial nucleus of the hypothalamus or the magnocellula r region of the paraventricular nucleus. These results reveal that neu rons located in the MZI (possibly A(13) DA neurons) have ipsilateral e fferent axonal projections to a variety of brain regions including the lateral hypothalamus, lateral preoptic area, and the limbic structure s at the diencephalic-telencephalic juncture.