Multiple messengers in descending serotonin neurons: localization and functional implications

In the present review article we summarize mainly histochemical work dealin g with descending bulbospinal serotonin neurons which also express a number of neuropeptides, in particular substance P and thyrotropin releasing horm one. Such neurons have been observed both in rat, cat and monkey, and may p referentially innervate the ventral horns of the spinal cord, whereas the s erotonin projections to the dorsal horn seem to lack these coexisting pepti des. More recent studies indicate that a small population of medullary raph e serotonin neurons, especially at rostral levels, also synthesize the inhi bitory neurotransmitter gamma-amino butyric acid (GABA). Many serotonin neu rons contain the glutamate synthesizing enzyme glutaminase and can be label led with antibodies raised against glutamate, suggesting that one and the s ame neuron may release several signalling substances, causing a wide spectr um of post- (and pre-) synaptic actions. (C) 2000 Elsevier Science B.V. All rights reserved.