EFFECT OF IMMOBILIZATION STRESS ON TRANSCRIPTIONAL ACTIVITY OF INDUCIBLE IMMEDIATE-EARLY GENES, CORTICOTROPIN-RELEASING FACTOR, ITS TYPE-1 RECEPTOR, AND ENKEPHALIN IN THE HYPOTHALAMUS OF BORDERLINE HYPERTENSIVE RATS

The effects of immobilization on the expression of immediate-early gen e c-fos and nerve growth factor-inducible (NGFI)-B mRNAs, corticotropi n-releasing factor (CRF) mRNA, CRF heteronuclear RNA (hnRNA), CRF rece ptor types 1 and 2 alpha mRNA, and enkephalin hn/mRNA were investigate d in the hypo thalamic paraventricular nucleus of Wistar-Kyoto (WKY) r ats and borderline hypertensive rats (BHRs). Rats were deeply anesthet ized 0, 30, 60, and 180 min after the beginning of the immobilization session (60 min maximum). BHR paraventricular nuclei displayed slight differences in their resting levels of NGFI-B mRNA and CRF hnRNA, bath being significantly elevated compared with those of WKY rats. Convers ely, basal levels of enkephalin primary transcript were significantly lower in BHRs. Immobilization, however, induced transient Variations i n the hybridization signals for all evaluated genes within the paraven tricular nucleus (except for GRF 2 alpha receptor). Immediate-early ge ne mRNA levels were higher and more prolonged in BHRs than in WKY rats . This heightened neuronal activation in the BHRs was associated with a more rapid increase in CRF mRNA expression (30 min) compared with th at in WKY rats (60 min). It is interesting that a transient rise in CR F hnRNA levels was detected in stressed WKY rats, whereas the BHR grou p displayed a progressive decline in this transcript, being significan tly below resting levels 180 min after the immobilization session. The stress-induced expression of CRF type 1 receptor mRNA was similar in both strains. Moreover, no significant differences were observed for e nkephalin hn/mRNA in either strain during the immobilization session. Therefore, the hypothalamic paraventricular nucleus appears to be invo lved in the functional hyperreactivity of the hypothalamic-pituitary-a drenal and autonomic axes to stress observed in BHRs, which may lead u ltimately to a stress-induced hypertensive state.