Previously, we have reported that brain regions that are thought to be involved in motivated behavior are altered in animals undergoing repeated exposures to immobilization stress. The goal of the present study was to determine the effects of recovery from this type of stress on these same mesolimbic brain regions. For this purpose, adult male Sprague-Dawley rats were initially exposed to immobilization stress either once (2. h) or repeatedly (2. h × 10. days). Rats were then either allowed to recover from the stressor for a shorter (2. days) or longer period of time (9. days) in their home cages. At the end of this recovery period, rats were euthanized and trunk blood and brains were processed for serum corticosterone (CORT) and neurochemistry, respectively. Brain mRNA levels were determined via in situ hybridization for the opioid preprodynorphin (DYN) and its cognate receptor (kappa, KOR), in striatal and accumbal subregions. A pattern of selective transcriptional activation emerged in the four resultant treatment conditions where a short recovery from either a single or repeated exposure to immobilization produced increases in KOR-mRNA levels in striatal and nucleus accumbens (Acb) subregions. Relative to controls, these differences were diminished after a longer recovery period. Interestingly, DYN-mRNA levels were unchanged after the shorter recovery period and after single or repeated immobilizations but appeared to be induced after a longer recovery period after repeated immobilizations. A relative amount of weight loss occurred after immobilization following repeated but not single exposure to stress. In addition, only those rats recovering from repeated stress exposures had higher CORT levels compared with non-immobilized controls. These results suggest that recovery from immobilization stress may alter the motivational system after as little as a single immobilization and that a possible dysphoric effect on appetitive behavior may be reflected by an altered striatal dynorphin system.
- Nucleus accumbens
ASJC Scopus subject areas
- Experimental and Cognitive Psychology
- Behavioral Neuroscience