CONSTITUTIVE EXPRESSION OF CALMODULIN-BINDING PHOSPHOPROTEIN GAP-43 IN RAT SEROTONERGIC AND NORADRENERGIC CELL GROUPS WHICH PROJECT TO THE SPINAL-CORD

In situ hybridization was combined with serotonin (5-hydroxytryptamine , 5-HT) or tyrosine hydroxylase immunocytochemistry and with Fluoro-Go ld retrograde labeling of bulbo-spinal pathways in order to investigat e the expression of GAP-43 mRNA in monoamine cell groups of the adult rat brain stem. Consistent with previous reports, GAP-43 mRNA was obse rved in serotonin and dopamine cell groups in the pens. In addition, G AP-43 expressing cells were observed in all the major monoamine cell g roups in the medulla. Thus the BI, B2 and B3 serotonin cell groups all showed high GAP-43 expression and all contained many GAP-43 expressin g serotonin cells with spinal cord projections. The Al, A2, A5 and A6 noradrenalin cell groups also showed high GAP-43 expression, although cells with spinal cord projections were largely restricted to the A5 g roup and A6 subcoeruleus region. In all areas, GAP-43 expressing cells with spinal cord projections were also observed which were not seroto nergic or noradrenergic.