[Regulation of TH activity by GAD immunoreactivity in rat peri-LC after chronic variable stress]

Locus coeruleus (LC) is the major component of noradrenergic neurons in the brain. The corticotropin-releasing hormone (CRH) and norepinephrine (NE) are suggested to play a role in modulating the central stress response. In a previous study we observed a decrease of the basal level of tyrosine hydroxylase (TH) immunoreactivity (-ir) in the LC of rats treated with chronic variable stress (CVS) for 14 days. Furthermore a novel stressor produced an enhanced response of the TH-ir after CVS. In the present study we examined the effect of CVS on the glutamic acid decarboxylase (GAD)-ir activity of periaqueductal gray (PAG), prepositus hypoglossi (PrH) and peri-LC. The GAD-ir was significantly increased in PrH and peri-LC after CVS. The footshock-induced reactivity in the GAD-ir was decreased in both regions after CVS. Moreover, we investigated the influence of the CRH receptor antagonist, alphah-CRH (i.c.v.) on the CVS-induced activation of the TH-ir in the LC. The alphah-CRH i.c.v. diminished the enhanced-TH reactivity by novel stressor after CVS. Our results suggest that the GABA activity in peri-LC and PrH might regulate the LC-TH response, and also the CRH input from central nucleus of amygdala (CeA) and/or the bed nucleus of stria terminalis (BNST) might regulate the TH reactivity.