Acute stress-induced increases in thalamic CRH mRNA are blocked by repeated stress exposure

Corticotropin-releasing hormone (CRH) coordinates multiple aspects of the s tress response. Recently, CRH mRNA has been identified in two regions of th e thalamus: the posterior nuclear group (Po), and a region located at the i nterface of the central medial and ventral posteromedial nucleus (parvicell ular part) (CM-VPMpc). Previous studies demonstrated that in both regions C RH mRNA increases following I h of restraint stress, suggesting involvement of thalamic CRH in processing somatosensory and visceral information relat ed to stress. The current study was proposed to further understand the effe cts of repeated and acute restraint stress on levels of thalamic CRH mRNA. Adult male rats were assigned to one of four groups in a 2 (repeated stress , no repeated) X2 (acute. no acute) design. Brain sections were processed f or CRH mRNA in situ hybridization. ANOVA revealed no main effects of acute or repeated stress in either thalamic region. However. significant interact ions between acute and repeated stress for levels of CRH mRNA were found fo r both regions of the thalamus. Compared to the no stress condition. acute restraint significantly increased CRH mRNA in the Po (39%) and the CM-VPMpc (32%). Repeated restraint did not alter baseline CRH mRNA levels. but bloc ked the acute restraint-induced effects. Thus, while acute stress increases levels of thalamic CRH mRNA, repeated exposure to the same stressor is wit hout effect and prevents the acute response. These findings add to data est ablishing a role for thalamic CRH in the stress response and suggest a mech anism that may underlie habituation to repeated stress exposure. (C) 2001 E lsevier Science B.V. All rights reserved.