Bed nucleus of the stria terminalis noradrenergic system modulates contextual fear conditionig: involvement of crf1 receptors and nmda-no pathway

SC Hott, FV Gomes, DLM Uliana, LBM Resstel. University of S ã o Paulo, Ribeir ã o Preto, Brazil

Some evidence showed that during aversive situations noradrenaline releases is increased in bed nucleus of the stria terminalis (BNST) [1]. Previous studies showed that BNST noradrenergic neurotransmission is involved with conditioned emotional response (CER) by activation of both α1 and β1-adrenergic receptors [2]. In addition, BNST β1-adrenergic receptors activation increases the local release of glutamate in a manner dependent of CRF1 receptors [3]. Thus, we investigated the participation of the CRFergic, glutamatérgic and nitrergic systems in the modulation of CER by the BNST noradrenergic neurotransmission induced by contextual fear conditioning (CFC) in rats. Male Wistar rats (240-270g) with cannulae implanted bilaterally into the BNST were submitted to a 10min conditioning session (3 footshocks, 0.85 mA, 2s). 24h later, the behavioral and autonomic responses (mean arterial pressure - MAP; heart rate - HR and cutaneous temperature of the tail - CT) evoked by aversive context were measured during test session. The Institution’s Animal Ethics Committee approved the housing conditions and experimental procedures (process number: 119/2010). It were administered 0.1µL of saline, reboxetine (2nmol; n=6-9), a potent and selective inhibitor of noradrenaline uptake or CRF agonist urocortin (0.01nmol; n=5-7). Moreover, it were administrated vehicle, α1 and β1-adrenergic receptors antagonist WB4101 (1.7nmol; n=5) and CGP20712 (4.5nmol; n=6) respectively, CRF1 antagonist CP376395 (2.7nmol; n=6-7),NMDA receptor antagonist AP7 (1nmol; n=6) and neuronal NO synthase inhibitor NPLA (0.4nmol; n=5-6) 5 min before the reboxetine or urocortin. Compared to control animals, reboxetine significantly increased freezing behavioral and autonomic responses after re-exposure to the aversive context. These effects were blocked for WB4101 and CGP20712 (freezing: F5,29=4.7, P<0.01; PAM: F5,435=30.8, P<0.001; FC: F5,435=56.8, P<0.001; TC: F5,435=29.9, P<0.001), CP376395 (freezing: F3,18=13.0, P<0.001; MAP: F3,270=46.4, P<0.001; HR: F3,270=69.5, P<0.001; CT: F3,270=18.4, P<0.001), AP7 (freezing: F3,20=5.4, P<0.01; PAM: F3,300=81.9, P<0.001; FC: F3,300=63.4, P<0.001; TC: F3,300=57.7, P<0.001) and NPLA (freezing: F3,17=19.2, P<0.001; PAM: F3,255=51.5, P<0.001; FC: F3,255=71.2, P<0.001; TC: F3,255=81.5, P<0.001). Similar to reboxetina, urocortin significantly increased the CER after re-exposure to the aversive context. These effects were blocked for CP376395 (freezing: F4,30=8.2, P<0.001; MAP: F4,450=34.2, P<0.001; HR: F4,450=8.8, P<0.001 and CT: F4,450=20.5 P<0.001) and also for AP7 (freezing: F3,22=18.3, P<0.001; PAM: F3,330=53.4, P<0.001; FC: F3,330=23.2, P<0.001; TC: F3,330=46.1, P<0.001) and NPLA(freezing: F3,18=11.3, P<0.001; PAM: F3,255=24.2, P<0.001; FC: F3,255=88.8, P<0.001; TC: F3,255=23.9, P<0.001), but not WB4101 and CGP20712 (P>0.05). These results show that the stress increases the release of noradrenaline which act on α1 and β1-adrenoceptor and promotes direct depolarization of CRF neurons in the BNST. The increase in extracellular CRF levels lead to a facilitation of NMDA-NO pathway on BNST, suggesting the existence of a BNST norepinephrine-CRF-glutamate pathway modulating the expression of CFC in rats.

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2. Hott, S.C., et al., Both alpha1- and beta1-adrenoceptors in the bed nucleus of the stria terminalis are involved in the expression of conditioned contextual fear. Br J Pharmacol, 2012. 167(1): p. 207-21.

3. Nobis, W.P., et al., beta-Adrenergic Receptors Enhance Excitatory Transmission in the Bed Nucleus of the Stria Terminalis Through a Corticotrophin-Releasing Factor Receptor-Dependent and Cocaine-Regulated Mechanism. Biol Psychiatry, 2011.