Effect of Stimulation of the Paraventricular Hypothalamic Nucleus on Noxious-Evoked Fos-immunoreactlvity In the Rat lumbar Spinal Cord

• The paraventricular nucleus of the hypothalamus (PVH) provides a prominent descending projection to the superficial dorsal horn, and contains a number of neuropeptides that are know to influence nociceptive processing. In the present study, we injected formalin subcutaneously into the hind paws of unanesthetized rats and studied the noxious-evoked Fos protein expression in the dorsal horn following simultaneous unilateral injection of the glutamate receptor agonist kainic acid into the PVH. Although some cases displayed less Fos-inununoreactivity in the lumbar spinal cord on the side ipsilateral to the PVH activation than on the contralateral side, others displayed no side differences, and one case showed more labeling in the ipsilateral dorsal horn than on the contralateral side, Because different parts of the PVH were activated in the different experiments, the present observations suggest that the different peptide expressing populations of spinal cordprojecting neurons in PVH may have different, and perhaps opposing functions in the spinal dorsal horn.

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MEDICIN

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