The effects of chemical or surgical deafferentation on [3H]-acetylcholine release from rat spinal cord.

Cholinergic modulation of nociceptive transmission through both nicotinic and muscarinic receptors in the spinal cord represents an important mechanism in pain signaling. However, what neuronal elements release acetylcholine and how release might change in response to deafferentation are unclear. The present studies demonstrated Ca++- and K+-dependent release of [3H]-acetylcholine from slices of regional areas of rat spinal cord. That [3H]-acetylcholine was synthesized from [3H]-choline was demonstrated by the lack of [3H]-acetylcholine release following incubation with either the choline uptake inhibitor hemicholinium or the choline acetyltransferase inhibitor bromoacetylcholine. Rats treated neonatally with capsaicin or with spinal nerve ligation as adults showed a significantly decreased K+-stimulated release of [3H]-acetylcholine from dorsal horn but not ventral horn lumbar spinal cord slices. In rats subjected to dorsal rhizotomy, while basal release from lumbar dorsal spinal cord slices was reduced, K+-stimulated [3H]-acetylcholine release, while decreased, was not significantly different compared with controls. The data presented here show that there are regional differences in the release of acetylcholine from spinal cord and that this release can be modulated by chemical or surgical deafferentation. These results also indicate that the source of acetylcholine in the dorsal cord originates mainly from resident somata and their collaterals, interneurons and/or descending terminals, with only very minor contributions coming from primary afferents. The present data help to further elucidate the role of acetylcholine in spinal signaling, particularly with respect to the effects of nerve injury and nociceptive neurotransmission.