LOCALIZATION OF 5-HT3 RECEPTORS IN THE RAT SPINAL-CORD - IMMUNOHISTOCHEMISTRY AND IN-SITU HYBRIDIZATION

SPECIFIC antibodies raised against a fusion protein containing the ami no acid sequence of the putative second intracellular loop of the clon ed 5-HT3-A receptor subunit were used for the immunohistochemical visu alization of 5-HT3 receptors in the rat spinal cord. A dense 5-HT3-lik e immunoreactivity was found in the superficial layers of the dorsal h orn, which closely matched the labelling of 5-HT3 binding sites by [I- 125]iodo-zacopride. This immunostaining was markedly decreased followi ng unilateral rhizotomy, consistently with a preferential location of 5-HT3 receptors on terminals of primary afferent fibres, and with the presence of 5-HT3 mRNA in dorsal root ganglia. However, a significant proportion of 5-HT3 receptors persisted after rhizotomy, and the corre sponding mRNA was found in the dorsal horn of the spinal cord. 5-HT3 r eceptors are therefore also located on intrinsic neurones of the spina l cord.