THE TYPES OF NEURON IN SPINAL DORSAL HORN WHICH POSSESS NEUROKININ-1 RECEPTORS

In order to provide further information about the types of spinal neur on which possess neurokinin-1 receptors, we have carried out pre-embed ding immunocytochemistry on sections of rat lumbar spinal cord with an antiserum raised against a synthetic peptide corresponding to part of the sequence of the receptor, and combined this with post-embedding i mmunocytochemistry to detect GABA and glycine. Numerous neuronal cell bodies showing neurokinin-1 receptor-immunoreactivity were seen in lam ina I, laminae III-VI, the lateral spinal nucleus and the area around the central canal. Most of the cells observed in lamina III were small and had relatively restricted dendritic trees which could often not b e followed into lamina II, however some larger cells in laminae III an d IV had dendrites which extended through lamina II and into lamina I. Cells of the latter type are likely to represent a major target of su bstance P released from small-diameter primary afferents in the superf icial dorsal horn. The great majority (255 out of 283) of spinal neuro ns which possessed neurokinin-1 receptor-immunoreactivity, including a ll of those in lamina I, were not GABA- or glycine-immunoreactive, how ever a few cells in the deep part of the dorsal horn and the lateral s pinal nucleus and several cells near the central canal were GABA-immun oreactive, and some of these were also glycine-immunoreactive. These r esults suggest that substance P acts through neurokinin-1 receptors ma inly on excitatory neurons within the spinal cord.