ASSOCIATION OF SPINAL-LAMINA-I PROJECTIONS WITH BRAIN-STEM CATECHOLAMINE NEURONS IN THE MONKEY

In addition to giving primary projections to the parabrachial and peri aqueductal gray regions, ascending lamina I projections course through and terminate in brainstem regions known to contain catechol aminergi c cells. For this reason, double-labeling experiments were designed fo r analysis with light and electron microscopy. The lamina I projection s in the Cynomolgus monkey were anterogradely labeled with Phaseolus v ulgaris leucoagglutinin (PHA-L) and catecholamine-containing neurons w ere labeled immunocytochemically for tyrosine hydroxylase (TH). Light level double-labeling experiments revealed that the terminations of th e lamina I ascending projections through the medulla and pens strongly overlap with the localization of catecholamine cells in: the entire r ostrocaudal extent of the ventrolateral medulla (Al caudally, C1 rostr ally); the solitary nucleus and the dorsomedial medullary reticular fo rmation (A2 caudally, C2 rostrally): the ventrolateral pens (A5); the locus coeruleus (A6); and the subcoerulear region, the Kolliker-Fuse n ucleus, and the medial and lateral parabrachial nuclei (A7). At the li ght microscopic level: close appositions between PHA-L-labeled lamina I terminal varicosities and TH-positive dendrites and somata were obse rved, particularly in the Al, A5 and the A7 cell groups on the contral ateral side. At the electron microscopic level, examples of lamina I t erminals were found synapsing on cells of the ventrolateral catecholam ine cell groups in preliminary studies. The afferent input relayed by these lamina I projections could provide information about pain, tempe rature, and metabolic state as described previously. Lamina I input co uld impact interactions of the catecholamine system with higher brain centers modulating complex autonomic, endocrine, sensory, motor, limbi c and cortical functions such as memory and learning. Nociceptive lami na I input to catecholamine cell regions with projections back to the spinal cord could form a feedback loop for control of spinal sensory, autonomic and motor activity.