Stress-induced sensitization of dopamine and norepinephrine efflux in medial prefrontal cortex of the rat.

We examined whether prior exposure to chronic cold (17-28 days, 5 degrees C) alters basal or stress-evoked (30-min tail shock) catecholamine release in medial prefrontal cortex, nucleus accumbens, and striatum, using in vivo microdialysis. Basal norepinephrine (NE) concentrations in medial prefrontal cortex did not differ between chronically cold-exposed rats and naive control rats (2.7 +/- 0.3 vs. 2.5 +/- 0.2 pg/20 microliters respectively). Basal dopamine (DA) efflux in any of the brain regions was not significantly different between chronically cold-exposed rats and naive rats. However, a trend for lower basal DA efflux in the cold-exposed relative to naive rats was observed in medial prefrontal cortex (1.5 +/- 0.2 vs. 2.2 +/- 0.3 pg/20 microliters, respectively), nucleus accumbens (3.7 +/- 0.8 vs. 5.4 +/- 0.9 pg/20 microliters, respectively), and striatum (4.4 +/- 0.5 vs. 7.2 +/- 1.5 pg/20 microliters, respectively). In medial prefrontal cortex of rats previously exposed to cold, tail shock elicited a greater increase from baseline in both DA and NE efflux relative to that measured in naive rats (DA, 2.3 +/- 0.3 vs. 1.2 +/- 0.1 pg, respectively; NE, 3.8 +/- 0.4 vs. 1.4 +/- 0.2 pg, respectively). However, in nucleus accumbens or striatum of rats previously exposed to cold, the stress-induced increase in DA efflux was not significantly different from that of naive rats (nucleus accumbens, 1.8 +/- 0.7 vs. 1.5 +/- 0.3 pg, respectively; striatum, 1.9 +/- 0.4 vs. 2.6 +/- 0.7 pg, respectively). Thus, both cortical NE projections and cortically projecting DA neurons sensitize after chronic exposure to cold. In contrast, subcortical DA projections do not sensitize under these conditions.