Projections from the rostral ventrolateral medulla to brainstem monoamine neurons in the rat

Following the iontophoretic deposition of Phaseolus vulgaris leucoagglutinin (PHA-L) into the rostral ventrolateral medulla (RVL), two-color immunoperoxidase staining was employed to demonstrate contiguity between PHA-L-immunoreactive (PHA-LI) varicose fibers and boutons and brainstem monoaminergic cells. Black-stained PHA-LI cells in the deposition site were found to be located among amber-stained phenylethanolamine N-methyl transferase-immunoreactive (PNMT-I) neurons of the C1 cell group. RVL projections were contiguous with PNMT-I neurons of the C1, C2 and C3 cell groups, with tyrosine hydroxylase-immunoreactive (TH-I) neurons of the A1, A2 and A5 cell groups, and with serotonin-immunoreactive (5-HT-I) neurons of the B1, B2 and B3 cell groups. Preliminary findings of this study have been presented previously (Soc. Neurosci. Abstr., 15 (1989) 451).