DIFFERENTIAL-EFFECTS OF CRH INFUSION INTO THE CENTRAL NUCLEUS OF THE AMYGDALA IN THE ROMAN HIGH-AVOIDANCE AND LOW-AVOIDANCE RATS

Roman-high (RHA/Verh) and low (RLA/Verh) avoidance rats are selected a nd bred For rapid learning versus non-acquisition of two-way, active a voidance behaviour in a shuttle box. RHA/Verh rats generally show a mo re active coping style than do their RLA/Verh counterparts when expose d to various environmental challenges. The central nucleus of the amyg dala (CeA) is known to be involved in the regulation of autonomic, neu roendocrine and behavioural responses to stress and stress-free condit ions, and it is considered in relation to coping strategies. Corticotr opin-releasing hormone (CRH) seems to be a key factor in the control o f the CeA output. Neuroanatomical studies have revealed that the major ity of CRH fibers from the CeA have direct connections with autonomic regulatory nuclei in the brainstem, e.g. lateral parabrachial nucleus (lPB), ventrolateral periaquaductal gray (vlPAG). The modulating effec ts of CRH (30 ng) on CeA activity were studied by infusion of CRH into the CeA in freely moving male RHA/Verh and RLA/Verh rats under stress -free conditions. Heart-rate and behavioural activities were repeatedl y measured before, during and after local administration of CRH or veh icle, after which early gene product FOS immunocytochemistry and CRH-m RNA in situ hybridisation were carried out in selected brain areas. CR H infusion into the CeA caused a long lasting increase in heart-rate a nd behavioural activation in the RHA/Verh rats, leaving the RLA/Verh r ats unaffected. As a result of CRH infusion, the number of FOS positiv e cells in the CeA and lPB of RLA/Verh rats was increased whereas an o pposite response was found in the RHA/Verh rats. However. CRH into the CeA of the Roman rat lines induced no pronounced effects on FOS stain ing in the vlPAG and CRH mRNA levels in the CeA. These results indicat e that the CRH system of the CeA, connected with the output brainstem areas, is differentially involved in cardiovascular and behavioural re sponses. (C) 1998 Elsevier Science Ltd. All rights reserved.