5-HT1A RECEPTOR LOCALIZATION ON THE AXON HILLOCK OF CERVICAL SPINAL MOTONEURONS IN PRIMATES

Serotonin (5-HT) has direct and specific effects on the activity of sp inal cord motoneurons. The 5-HT1A receptor has been shown to mediate m otoneuron responses in spinal reflex pathways using the highly selecti ve 5-HT1A receptor agonist 8-OH-DPAT. We have developed an antipeptide antibody that recognizes a specific region (the second external loop) of the 5-HT1A receptor. This 5-HT1A receptor antibody labels populati ons of neurons and glia in the primate cervical spinal cord. The highe st receptor density is present in the superficial lamina of the dorsal horn, around the central canal, and on the axon hillock of large vent ral horn motoneurons. The cellular labeling pattern on motoneurons sho ws a single, densely stained, tapering process emanating from the peri karyon. A more diffuse label is also present throughout the soma. Dend ritic labeling was not apparent. These results suggest that post-synap tic 5-HT1A receptors may be involved in modulating spinal motoneuron a ctivity at the key site of action potential initiation, the axon hillo ck. (C) 1995 Wiley-Liss, Inc.