Participation of endocannabinoid system in the bed nucleus of the stria terminalis on conditioned emotional response modulation in rats: participation of glutamatergic and nitrergic neurotransmissions

Author(s)

Anna Bárbara Borges de Assis

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2021-12-10

Examining board members

Leonardo Resstel Barbosa Moraes; Norberto Cysne Coimbra; Fernando Eduardo Padovan Neto; Fabiana Cardoso Vilela

• Advisor: Leonardo Resstel Barbosa Moraes

Abstract

The endocannabinoid system role of fear and anxiety responses is widely described, mostly mediated via type 1 and 2 cannabinoid receptors (CB1 and CB2, respectively). CB1 receptor activation negatively modulates the release of several neurotransmitters, including glutamate. However, the CB2 receptor role in neuronal activity is not yet fully understood, but it is suggested that they also act through glutamate levels modulation. Glutamate is the main excitatory neurotransmitter of the central nervous system (CNS). Thus, CB1 receptors play a fundamental role in neuronal excitability by NMDA receptors. Furthermore, it is well established that NMDA receptors activation induce nitric oxide (NO) synthesis in the CNS. NO can diffuse to the synaptic cleft and act at neuronal excitability modulation. Previous data from our group demonstrated the essential role of NMDA receptors and NO in the conditioned emotional response (CER) evoked by the contextual fear conditioning (CFC) in the bed nucleus of the stria terminalis. The Bed Nucleus of the Stria Terminalis (BNST) is a limbic structure responsible for integration of autonomic, neuroendocrine and behavioral information during aversive situations. However, the endocannabinoid system role in this structure is not fully elucidated, despite studies demonstrating its presence in BNST. Thus, our aim was to evaluate the role of CB1 (AM251) and CB2 (AM630) receptors\' antagonists in BNST in responses induced by CFC, and also to assess whether CB1 receptors act via NMDA/NO. For this, Wistar rats (240 - 270g) were submitted to stereotaxic surgery for bilateral implantation of cannulas in the BNST, for drug administration. Five days after, the animals were submitted to the CFC protocol, performed on 3 consecutive days. The habituation session consisted of a 10-min-long exposure to the footshock chamber without shock delivery. Four hours later animals were placed back into the same experimental chamber, and three electric footshocks were delivered (Conditioning). Twenty-four hours after the conditioning, the surgery for a catheter implantation into the femoral artery was performed to do the cardiovascular recording. Behavior (freezing time) and autonomic (Mean arterial pressure-MAP; Heart rate-HR and cutaneous temperature-CT) measurements were carried out on the next day after femoral surgery. Pharmacological compounds and vehicle were administered into the NLET, 10 minutes before re-exposure to the conditioned context (Test). Our results demonstrated that both CB1 and CB2 receptor antagonism increased the CER expression. Furthermore, the administration of an NMDA receptor antagonist, neuronal NO synthase inhibitor, NO scavenger and soluble guanylate cyclase (sGC) enzyme inhibitor prevented the CB1 antagonist effect. Our results suggest that CB1 and CB2 receptors modulate the expression of CER. Moreover, we suggest that the modulation of CER via CB1 receptors in BNST involves activation of NMDA receptors, NO production by nNOS, NO diffusion in the synaptic cleft and activation of the enzyme sGC in the presynaptic terminal. Therefore, the BNST endocannabinoid system possibly represents an important neurotransmission in the regulation and integration of emotional responses. (AU)

• FAPESP's process: 17/16913-6 - Possible involvement of the endocannabinoid system in the bed nucleus of stria terminalis on the contextual fear conditioning responses in rats
• Grantee: Anna Bárbara Borges de Assis
• Support Opportunities: Scholarships in Brazil - Doctorate