Dorsomedial portion of the ventromedial hypothalamus participation on tonic immobility defensive behavior and locomotion after Canabidiol administration

• Grant number: 13/19458-7
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2014
• End date: January 31, 2015
• Field of knowledge: Biological Sciences - Physiology - Physiology of Organs and Systems
• Principal Investigator: Leda Menescal de Oliveira
• Grantee: Angélica Limoli Silva
• Host Institution: Faculdade de Medicina de Ribeirão Preto (FMRP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil

Abstract

Evidence has demonstrated that endocannabinoid and the CB1 receptors are involved in mood disease, as anxiety and defensive behavior. An endocannabinoid interaction with endogenous opioid and serotonin (5-HT) systems may also participate in defensive behavior responses. Some neural substrates have an important participation in tonic immobility defensive behavior response, and the hypothalamus is a structure that modulates behavior response involved on emotions and physiological responses. Other studies showed that the ventromedial hypothalamus modulated some defensive responses elicited in a situation of intense fear, like a prey/predator confrontation. Flight and tonic immobility responses are of observed in this situation. In this way, in the current study, our objective is to investigate the effect of systemic and central cannabidiol administration, subcutaneously and on the dorsomedial part of the hypothalamus ventromedial, respectively, on tonic immobility defensive behavior and motor activity in guinea pigs (Cavia porcellus). The animals will be divided into 8 experimental groups: on group 1 the animals will receive saline (0.5 ml) subcutaneously followed by saline (0.2 µl) microinjection on the ventromedial hypothalamus, dorsomedial part (HVMdm); in group 2 the animals will be injected with canabidiol (CBD; canabinoid agonist) at 3 mg/kg/0.5 ml dose subcutaneusly + saline (0.2 µl) microinjection on HVMdm; on group 3 we will inject 3 mg/kg of the CBD subcutaneusly followed by AM251 (100 pmol) microinjection on HPMdm; on group 4 the animals will receive a subcutaneusly injection of the saline (0.5 ml) + AM251 (100 pmol) microinjection on HVMdm; on group 5 the animals will receive a CBD (30 nmol) microinjection at HVMdm; on group 6 the animals will be microinjected with AM251 (100 pmol) followed (10 minutes) by CBD (30 nmol) on HVM dm; on group 7 the animals will be microinjected with AM251 (100 pmol) on HVMdm; on group 8 the animals will microinject with saline (0.2 µl) on HVMdm. After each experiment, the animals were anesthetized by intramuscular sodium pentobarbital and then will be intracardially perfused with saline followed by 10% formalin. The brains will be removed and maintained in formalin solution for 24 h, and cryoprotected in 30% sucrose for at least 48 h. Serial 40µ coronal brain sections will be cut using a cryostat (21 æC), will be mounted on gelatin-coated slides, and stained with Cresyl Violet (0.25%; Sigma-Aldrich, St. Louis, MO, USA) to localize the positions of the microinjection sites according to the atlas of Rössner atlas. (AU)