Raphe-spinal and subcoeruleo-spinal modulation of temperature signal transmission in rats

Abstract

1. 1.Extracellular recordings were made from dorsal horn cells responsive to temperature changes in the innocuous range (10–40°C) of scrotal skin temperature in the lumbosacral segment of urethane-anesthetized rats. The temperature responsive dorsal horn cells (65) were classified into two groups: warm-responsive cells (48) showing an increase in firing rate by skin warming, “warm-response”, and cold-responsive cells (17) showing an increase in firing rate by skin cooling, “cold-response”. The effects of electrical stimulation in the nucleus raphe magnus (NRM) and subcoeruleus region (SC) on their firing activity were studied. 2. 2.The effects of electrical stimulation in the NRM as well as in the SC were found to consist in partial or complete depression of warm- or cold-responses. The background activity mostly remained unaffected. 3. 3.Depression of the temperature response by NRM stimulation occured in most (95%) of warm-responsive cells, whereas SC stimulation depressed the majority (79%) of cold-responsive cells. 4. 4.In four warm-responsive cells, NRM-evoked depression of their temperature responses was partially antagonized by the serotonin antagonist methysergide (1 mg/kg, i.v.), suggesting the NRM-evoked depression was mediated serotonergic raphe-spinal pathways. 5. 5.The results suggest that the raphe- and subcoeruleo-spinal descending pathways modulate the spinal transmission of warm and cold signals contributing to central thermoregulation.