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Volume 17, Number 11, Issue of June 1, 1997 pp. 4406-4414
Copyright ©1997 Society for Neuroscience

Temperature Dependency of Basal and Evoked Release of Amino Acids and Calcitonin Gene-Related Peptide from Rat Dorsal Spinal Cord

Received Jan. 17, 1997; revised March 3, 1997; accepted March 12, 1997.

David M. Dirig¹, Xiao-Ying Hua², and Tony L. Yaksh^{1, 2}

Departments of ¹ Pharmacology and ² Anesthesiology, University of California, San Diego, La Jolla, California 92093-0818

Moderate hypothermia significantly diminishes consequences of spinal and cerebral anoxia. One component of this neuroprotection has been hypothesized to be suppression of excitotoxic transmitter release. Whether this suppression is attributable to reduced hypoxic injury that induces release or an alteration of the release process itself is unclear. We sought to characterize the temperature sensitivity (Q₁₀) of basal and evoked calcitonin gene-related peptide (CGRP) and amino acid release from dorsal horn slices of rat spinal cord over a range of temperatures from 40 to 8°C. At 40°C, potassium (60 mM) and capsaicin (10 µM) evoked a 21- and 32-fold increase in basal CGRP concentrations, respectively. Capsaicin had no effect on glutamate release, but potassium evoked a 2.7-fold increase. Release evoked by either potassium or capsaicin was reduced in a biphasic fashion with declining temperature. Over the range of 40 to 34°C, the Q₁₀ values for evoked release for CGRP were 11.3 (potassium) and 39.7 (capsaicin) and for glutamate, 5.5 (potassium). Over the range of 34 to 8°C, Q₁₀ values were near unity for all evoked release (0.8 and 1.3 for CGRP and 1.2 for glutamate). Although serine, glycine, glutamine, taurine, and citrulline showed no evoked release, basal levels were reduced at temperatures below 34°C. The pronounced temperature dependency of evoked transmitter release between 40 and 34°C is consistent with the profound cerebral protection observed with mild hypothermia in which metabolic activity is only slightly depressed.

Key words: hypothermia; hyperthermia; glutamate; CGRP; spinal cord superfusion; evoked transmitter release; dorsal horn; capsaicin

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