Functional organization of the bed nucleus of the stria terminalis

This thesis examined the functional organization of the bed nucleus of the stria terminalis (BNST), a poorly known brain region. Two series of experiments were performed. First, in anesthetized rats, we compared antidromic response latencies in anterior BNST (BNSTa) and central amygdala (CeA) neurons to brainstem stimuli. The frequency distribution of latencies was unimodal in BNSTa neurons (~10 ms) and bimodal in CeA cells (~10 and ~30 ms). After stria terminalis (ST) lesions, only short-latency antidromic responses were observed. Since BNST and CeA share excitatory basolateral amygdala (BL) inputs, lengthening the path of CeA axons might allow synchronization of BNSTa and CeA impulses to brainstem when activated by BL inputs. Consistent with this, the latency difference between CeA and BNSTa neurons to BL stimuli approximated that seen between the antidromic responses of BNSTa cells and CeA neurons with long-conduction times. These results point to a hitherto unsuspected level of temporal coordination between CeA and BNSTa neurons, supporting the idea of shared functions. Second, in behaving rats, we recorded BNST neurons in anterolateral (BNST-AL) and anteromedial (BNST-AM) regions under spontaneous conditions and during auditory fear conditioning. The firing rates of BNST- AL and AM neurons were highest in paradoxical sleep, lowest during slow-wave sleep and intermediate during wakefulness. During habituation, most neurons were unresponsive to the conditioned stimulus (CS). After fear conditioning, many BNST-AL neurons developed inhibitory responses to the CS whereas in BNST- AM, neurons with positive CS responses prevailed. The behavior of BNST-AM and AL neurons during contextual fear paralleled their CS responsiveness: BNST-AM neurons fired at higher rates during contextual freezing than movement whereas BNST-AL cells did the opposite. However, in contrast with cued fear where similar proportions of BNST- AM and AL neurons were CS responsive, many more BNST-AM than AL neurons showed differential activity in relation to contextual freezing. These findings point to regional differences in the activity of BNST-AL and AM in relation to learned fear, raising the possibility that they exert opposite influences on fear output networks. The stronger recruitment of BNST-AM neurons during contextual relative to cued fear may account for BNST’s selective involvement in the former.Ph. D.Includes bibliographical referencesIncludes vitaby Frank Nag