Paraventricular nucleus modulates autonomic and neuroendocrine responses to acute restraint stress in rats

The paraventricular nucleus of the hypothalamus (PVN) has been implicated in several aspects of neuroendocrine and cardiovascular control. The PVN contains parvocellular neurons that release the corticotrophin release hormone (CRH) under stress situations. In addition, this brain area is connected to several limbic structures implicated in defensive behavioral control, as well to forebrain and brainstem structures involved in cardiovascular control. Acute restraint is an unavoidable stress situation that evokes corticosterone release as well as marked autonomic changes, the latter characterized by elevated mean arterial pressure (MAP), intense heart rate (HR) increases and decrease in the tail temperature. We report the effect of PVN inhibition on MAP and HR responses, corticosterone plasma levels and tail temperature response during acute restraint in rats. Bilateral microinjection of the nonspecific synaptic blocker CoCl2 (1 mM/100 nL) into the PVN reduced the pressor response; it inhibited the increase in plasma corticosterone concentration as well as the fall in tail temperature associated with acute restraint stress. Moreover, bilateral microinjection of CoCl2 into areas surrounding the PVN did not affect the blood pressure, hormonal and tail vasoconstriction responses to restraint stress. The present results show that a local PVN neurotransmission is involved in the neural pathway that controls autonomic and neuroendocrine responses, which are associated with the exposure to acute restraint stress.