Norepinephrine and serotonin alterations following chronic stressor exposure: mouse strain differences.

Exposure to acute uncontrollable foot shock influenced the levels and utilization of norepinephrine (NE) and serotonin (5-HT) in several brain regions. These effects varied between the BALB/cByJ and C57BL/6J mouse strains, with the former displaying more pronounced amine variations. Following repeated exposure to foot shock over 15 days, the decline of NE associated with an acute stressor was abrogated. In the hypothalamus, this was accompanied by high MHPG accumulation, suggesting that the increased NE stemmed from a compensatory increase in synthesis. In the locus coeruleus and prefrontal cortex the accumulation of MHPG declined with repeated exposure, possibly suggesting moderation in utilization. In animals exposed to a chronic unpredictable stressor regimen, the NE decline in the hypothalamus was precluded, but pronounced NE reductions were still evident in the locus coeruleus and prefrontal cortex. The data are related to behavioral impairments associated with stressor application, as well as to the particular vulnerability of BALB/cByJ mice to stressor-induced behavioral impairments.