INVOLVEMENT OF HYPOTHALAMIC CORTICOTROPIN-RELEASING FACTOR NEURONS INBEHAVIORAL-RESPONSES TO NOVELTY IN RATS

The purpose of this experiment was to investigate whether endogenous c orticotropin-releasing factor (CRF) within the paraventricular nucleus of the hypothalamus (PVN) is involved in the alteration of locomotor activity related to a novel, presumably stressful, environment in rats . Impairment of the function of CRF-containing neurons was effected by immunotargeting ricin A chain toxin to these cells with a monoclonal antibody to CRF (CRF-MAb/toxins). CRF-MAb/toxins administered into the PVN 2 weeks prior to testing produced an increase in locomotor activi ty during exposure to novel environment photocell cages. This behavior al activation was maintained throughout the 120 min experimental sessi on, but was not present when the rats where introduced to the same pho tocell cages after extensive habituation. These results suggest that t he effect induced by CRF-MAb/toxin treatment was related to the explor ation of the novel environment, and was not due to a generalized locom otor hyperactivity. This effect was accompanied by a 53% and 61% CRF d ecrease in the hypothalamus and the median eminence, respectively. Inj ection of CRF-MAb/toxins into the ventromedial nucleus of the hypothal amus did not modify the locomotor activity in either unfamiliar or fam iliar conditions. These data suggest that CRF neurons within the PVN m ay participate not only in the activation of the pituitary adrenal axi s associated with stressors but also as physiological mediators of the behavioral responses to stress.