Demonstration of thyrotropin-releasing hormone immunoreactivity in neurons of the mouse spinal dorsal horn

Thyrotropin-releasing hormone-like immunoreactivity was demonstrated in neurons within the superficial laminae (I, II, III) of the mouse spinal dorsal horn by light-microscopic peroxidase immunocytochemistry. The immunoreactivity was distributed in a narrow dorsoventral band that enclosed the substantia gelatinosa (lamina II), with a higher concentration along the lamina II/III border. At present, the functional significance of these neurons is unknown. Their existence within the substantia gelatinosa suggests a role in sensory information processing.

Serotoninergic axonal contacts on identified cat spinal dorsal horn neurons and their correlation with nucleus raphe magnus stimulation

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.

Immunocytochemical identification of serotonin axonal contacts on characterized neurons in laminae I and II of the cat dorsal horn

Serotonergic pathways from brainstem to spinal cord play an important role in the modulation of pain perception. To establish where that modulation occurs, we examined serotonin-immunoreactive axonal contacts on individually characterized laminae I and II dorsal horn neurons intracellularly filled with horseradish peroxidase. We found serotonin axonal contacts on marginal, stalked, and islet cells. Contacts preferentially occurred on dendritic shafts rather than on spines. Marginal and stalked cells received the heaviest innervation.