title: Serotoninergic axonal contacts on identified cat spinal dorsal horn neurons and their correlation with nucleus raphe magnus stimulation.
abstract: This study examined the distribution of serotoninergic (5-HT) immunoreactive axonal contacts on spinal laminae I and II neurons by combining the intracellular horseradish peroxidase (HRP) method with immunocytochemistry. In addition, the 5-HT distribution was correlated with effects produced by electrical stimulation within the nucleus raphe magnus (NRM). Responses of lamina I neurons and lamina II stalked cells to noxious stimulation were markedly suppressed during NRM stimulation. In contrast, responses of nociceptive lamina IIa islet or non-nociceptive lamina IIb islet cells remained unchanged during nucleus raphe magnus stimulation. These inhibitory influences were positively correlated with the distribution of 5-HT immunoreactive contacts on these neurons. Nociceptive lamina I neurons and lamina II stalked cells received a significantly greater number of contacts (average of 74 and 63, respectively) than either nociceptive lamina IIa islet or non-nociceptive lamina IIb islet cells (average of 25 and eight contacts, respectively). Irrespective of cell type, most 5-HT contacts occurred on dendritic shafts rather than spines. These data reveal a differential distribution of 5-HT contacts on neurons in spinal laminae I and II, and indicate that at least a portion of the NRM modulation of dorsal horn neuronal activity is serotoninergic and concentrated on the dendritic shafts of nociceptive lamina I neurons and lamina II stalked cells.
mesh_terms: D000818:Animals; D001931:Brain Mapping; D002415:Cats; D004558:Electric Stimulation; D007124:Immunoenzyme Techniques; D009434:Neural Pathways / Q000033:anatomy & histology; D011903:Raphe Nuclei / Q000033:anatomy & histology* / Q000502:physiology; D012701:Serotonin / Q000378:metabolism / Q000502:physiology*; D013116:Spinal Cord / Q000033:anatomy & histology* / Q000502:physiology
chemical_list: D012701:Serotonin