BACKGROUND AND PURPOSE The bed nucleus of the stria terminalis (BNST) is a limbic structure that is involved in the expression of conditioned contextual fear. Among the numerous neural inputs to the BNST, noradrenergic synaptic terminals are prominent and some evidence suggests an activation of this noradrenergic neurotransmission in the BNST during aversive situations. Here, we have investigated the involvement of the BNST noradrenergic system in the modulation of behavioural and autonomic responses induced by conditioned contextual fear in rats. EXPERIMENTAL APPROACH Male Wistar rats with cannulae bilaterally implanted into the BNST were submitted to a 10 min conditioning session (6 footshocks, 1.5 ma/ 3 s). Twenty‐four hours later freezing and autonomic responses (mean arterial pressure, heart rate and cutaneous temperature) to the conditioning box were measured for 10 min. The adrenoceptor antagonists were administered 10 min before the re‐exposure to the aversive context. KEY RESULTS L‐propranolol, a non‐selective β‐adrenoceptor antagonist, and phentolamine, a non‐selective α‐adrenoceptor antagonist, reduced both freezing and autonomic responses induced by aversive context. Similar results were observed with CGP20712, a selective β1‐adrenoceptor antagonist, and WB4101, a selective α1‐antagonist, but not with ICI118,551, a selective β2‐adrenoceptor antagonist or RX821002, a selective α2‐antagonist. CONCLUSIONS AND IMPLICATIONS These findings support the idea that noradrenergic neurotransmission in the BNST via α1‐ and β1‐adrenoceptors is involved in the expression of conditioned contextual fear.

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Edited by: Mark Chapleau New Findings r What is the central question of this study?Classically, areas of the brainstem are involved in the cardiac baroreceptor reflex. However, forebrain areas, such as the hippocampus, may also modulate the cardiac baroreflex function. r What is the main finding and its importance?According to the hippocampal subarea recruited dorsoventrally, the baroreflex function can be either facilitated or inhibited. These results are according to the new topographical division proposed for the hippocampus, i.e. it can be divided into functionally and anatomically different regions along its dorsoventral axis.From a neuroanatomical point of view, we may split the hippocampal formation into the dorsal (DH) and ventral hippocampus (VH). Although the basic intrinsic circuitry of the hippocampus seems to be maintained throughout its longitudinal axis, dorsal and ventral portions connect differently with cortical and subcortical areas and express different gene patterns, being functionally distinct. Differential stimulation of the DH or VH can evoke either an increase or a decrease in blood pressure, heart rate and sympathetic activity. However, to the best of our knowledge, specific involvement of the hippocampus and its different subareas in the baroreflex function remains to be investigated. In the present work, therefore, we evaluated the involvement of hippocampal subareas arranged on the dorsoventral axis in cardiac baroreflex modulation. Our results suggest that inhibition of hippocampal subareas by CoCl 2 , a calcium-dependent synaptic neurotransmission blocker, differentially affects baroreflex sensitivity; administration of CoCl 2 into the DH increased cardiac baroreflex function, whereas it diminished cardiac baroreflex function when administered into the VH. In contrast, administration of CoCl 2 into intermediate portions of the hippocampus did not affect the baroreflex response. Our findings suggest that the hippocampus influences baroreflex function according to the hippocampal subarea recruited dorsoventrally.

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