Strain differences in anxiety-like behavior: association with corticotropin-releasing factor.

The purpose of the current study was to relate basal corticotropin-releasing factor (CRF) mRNA level in the central nucleus of the amygdala (CeA) with anxiety-like behavior using three strains of rat reported to exhibit a range of behavioral and neuroendocrine responses to stress. Anxiety-like behavior was determined for Fischer (F344), Wistar, and Wistar-Kyoto (WKY) rats with an elevated plus-maze and CRF mRNA level was measured using in situ hybridization. WKY rats exhibited more anxiety-like behavior on the elevated plus-maze than both F344 (p's < 0.01) and Wistar rats (p's < 0.05). WKY rats had higher basal levels of CRF mRNA in the CeA than F344 rats (p < 0.05) with a trend toward higher levels than Wistar rats (p = 0.06). Wistar rats had similar indices of anxiety with F344 rats and comparable levels of CRF mRNA in the CeA. Basal plasma corticosterone was similar for all three strains and repeated experience with the plus-maze had no effect on basal corticosterone levels or CRF mRNA levels in the paraventricular nucleus of the hypothalamus (PVN) for Wistar or WKY rats. Consistent with reported hyperactivity of the hypothalamopituitary adrenal axis of F344 rats with repeated stress, we observed elevated corticosterone following repeated exposure to the elevated plus-maze in F344 rats (p < 0.01) with a trend toward increased CRF mRNA levels in the PVN (p = 0.09). Heightened expression of CRF in the CeA of WKY rats may be involved in anxiety-like behaviors observed in this strain.