Immunohistochemical localizations of Orexin-A and the neurokinin 1 receptor in the rat spinal cord

Orexins (hypocretins) are a recently described set of hypothalamic peptides that have been implicated in feeding, neuroendocrine regulation and sleep-wakefulness. The aim of this study was to investigate and compare the distribution of orexin-A-and neurokinin 1 receptor-expressing neurones in the spinal cord of adult Wistar rats using immunohistochemistry. Orexin-A immunoreactive fibres and their terminals were observed in the superficial dorsal horn. Neurokinin 1 receptor positive cells and their processes were also observed in lamina I of the dorsal horn. Although neurokinin 1 cells with orexin-A fibres were concentrated in the marginal layer of the dorsal horn, there was occasional direct anatomic contact between orexin-A and neurokinin 1 receptors in this region. The results of the present study suggest that the functions of the orexins and the neurokinin 1 receptor related to feeding, nociception, sensory information and neuroendocrine functions are possibly mediated via dependent mechanisms. Thus neurokinin 1 containing neurones could potentially receive synaptic inputs from inhibitory and excitatory interneurones in the marginal layer