br Material and methods br Results Diagrammatic representati
Material and methods
Results Diagrammatic representations showing the bilateral injection sites in the BNST of all animals used in the present study are presented in Fig. 1.
Discussion The present results provide the first evidence that both CRF1 and CRF2 receptors in the BSNT are involved in cardiovascular adjustments during emotional stress. We have demonstrated that bilateral microinjection of the selective CRF1 receptor antagonist CP376395 into the BNST decreased the pressor and tachycardiac responses caused by acute restraint stress. Conversely, BNST treatment with the selective CRF1 receptor agonist CRF increased restraint-evoked arterial pressure and HR responses and reduced the fall in tail skin temperature. All effects of CRF were inhibited by local BNST pretreatment with CP376395, thus confirming the CRF effects were mediated by activition of local CRF1 receptor. Bilateral microinjection of the selective CRF2 receptor antagonist antisalvagine-30 into the BNST reduced the arterial pressure increase and the drop in tail skin temperature. Bilateral treatment of the BNST with the selective CRF2 receptor agonist Ucn3 increased restraint-evoked pressor and tachycardiac responses and reduced the fall in cutaneous temperature. All effects of Ucn3 were abolished by local BNST pretreatment with antisalvagine-30. In contrast with present findings, some evidence has indicated an opposing role of CRF1 and CRF2 receptors in regulating physiological responses to stress. For instance, studies using mice deficient to either CRF1 or CRF2 receptors have indicated an involvement of CRF1 receptors in the activation of the hypothalamic–pituitary–adrenal (HPA) axis during stress, whereas CRF2 receptors inhibit it , . Although a facilitatory role of CRF1 receptor was further supported by pharmacological studies , , a possible inhibitory influence of CRF2 receptors is controversy once central administration of a selective CRF2 receptor antagonist produced little effect in Science Daily to restraint stress . Previous studies demonstrated that central administration of nonselective CRF receptor antagonists reduced stress-evoked cardiovascular responses , . However, to the best of our knowledge, present study is the first to investigate the specific role of CRF1 and CRF2 receptors in cardiovascular adjustments to emotional stress. It has been reported a regionalization in the BSNT in control of neuroendocrine responses to stress, with rostral regions involved in activation of the HPA axis and posterior division inhibiting it . Consistent with evidence that anterior division is the critical BNST region involved in autonomic control , most of our microinjection sites reached regions of the BSNT anterior division. Therefore, centralization of the microinjection sites in rostral regions of the BNST may have contributed to identification of a similar role of CRF1 and CRF2 receptors in the present study. However, the expression of both CRF receptors was reported in rostral regions of the BNST , , thus supporting present findings. Furthermore, CRF-containing terminals (though to be the endogenous CRF1 ligand) as well as Ucn1- and Ucn3-immunoreactive fibers (thought to be, together with Ucn2, the endogenous ligands of the CRF2 receptors) were identified in BNST anterior division , . A similar role of CRF receptors in the BNST is further supported by demonstration that aversive effects of the CRF in the BNST are mediated by activation of both CRF1 and CRF2 receptors . Thus, CRF1 and CRF2 receptors seem to work sinergically within the BNST. A previous study conducted by our group demonstrated that bilateral BNST neurotransmission inhibition evoked by local treatment with CoCl2 enhanced the HR increase evoked by restraint stress without affecting the arterial pressure response . Similar effect was observed after BNST treatment with a selective α1-adrenoceptor antagonist (i.e., facilitation of restraint-evoked tachycardiac response without affecting pressor effect) , suggesting that the inhibitory role of the BNST in HR response to restraint stress is mediated, at least in part, by the local action of noradrenergic mechanisms. In contrast, present study indicates that activation of CRF1 receptor in the BNST during restraint stress play a facilitatory role in tachycardiac response. Noradrenaline has predominantly an inhibitory influence in the activity of BNST neurons , which is mediated by a facilitation of local GABAergic neurotransmission and inhibition of glutamatergic inputs , , , , . In contrast, CRF1 receptor activation enhances excitatory neurotransmission in the BNST , . These pieces of evidence support the findings of an opposite influence of BNST CRF1 receptor and α1-adrenoceptors in the restraint-evoked tachycardic response. Present findings bring the first evidence of an influence of the BNST in the arterial pressure and skin temperature responses induced by an unconditioned aversive stimulus.