106 Trakia Journal of Sciences, Vol. 12, Suppl. 1, 2014 Trakia Journal of Sciences, Vol. 12, Suppl. 1, pp 106-109, 2014 Copyright © 2014 Trakia University Available online at: http://www.uni-sz.bg ISSN 1313-7050 (print) ISSN 1313-3551 (online) INCREASE IN THE NUMBER OF CB1 IMMUNOPOSITIVE NEURONS IN THE AMYGDALOID BODY AFTER ACUTE COLD STRESS EXPOSURE E. Dzhambazova 1 , B. Landzhov 2 , L. Malinova 2 , Y. Kartelov 2 , S. Abarova 2 1 Department of Chemistry, Biochemistry, Physiology and Pathophysiology, Faculty of Medicine, Sofia University St. Kl. Ohridski, Sofia, Bulgaria 2 Department of Anatomy, Histology and Embryology, Faculty of of Medicine, Medical University, Sofia, Bulgaria ABSTRACT PURPOSE: According literature data the animal's response to stress depends not only upon the state and conditions of the animal but also upon the nature of the stressor itself. It is known that stress have wide- ranging effects on neuroendocrine, autonomic, immune, and hormonal function. Different research groups have shown induction of acute physical stress by low temperature exposure which have been reported to impair motor activity, modulate pain perception, anxiety and depression-like behaviors in the animals. Considerable work has established the amygdaloid body as a key site involved in the generation of fear and anxiety responses, the assignment of emotional salience to external stimuli, the coordination of affective, autonomic, and behavioral responses. The aim of our study was to examine the effect of cold stress on density of CB1 receptors in the amygdaloid body. METHODS: Immunocytochemistry and morphometric analysis were used to determined density of CB1 immunopositive neurons in the amygdaloid body of male Wistar rats exposed to acute cold stress. RESULTS: Our morphometric studies reveal that cold stress significantly increased (around 40 %) density of CB1 immunopositive neurons in the rat amygdaloid body compared with control group. CONCLUSIONS: Our results confirm that temperature fluctuation induces stress and endocanabinoid system is involved. Key words: cold stress, endocannabinoids, amygdaloid body INTRODUCTION The term ‘stress’ generally indicates an internal (i.e.,infection, psychological condition) or external (i.e., physical danger or damage) circumstance that threatens the homeostasis of the organism. Thus, stress results in a discrepancy, either real or perceived, between the demands of a situation and the organism’s resources (1). Exposure to a stressor is immediately followed by somatic and neuro- physiological reactions involving peripheral organs such as adrenals, cardiovascular and respiratory systems, metabolism, and also brain ____________________________ *Correspondence to: E. Dzhambazova, Department of Chemistry, Biochemistry, Physiology and Pathophysiology, Faculty of Medicine, Sofia University St. Kl. Ohridski, Sofia, Bulgaria, е-mail: elena.dzambazova@abv.bg areas such as the prefrontal cortex, amygdala, hippocampus, nucleus accumbens, and hypothalamus (2). Considerable work has established the amygdaloid body as a key site involved in the generation of fear and anxiety responses, the assignment of emotional salience to external stimuli, the coordination of affective, autonomic, and behavioral responses. It is known that the endocannabinoid system (ECS), formed by cannabinoid receptors (CB1 and CB2), their endogenous lipid ligands (endocannabinoids, ECBs), and the machinery for synthesis and degradation of ECBs plays a key role in the psychoneuroendocrine responses to stress. The ECS participates in multiple brain circuits implicated in stress reactions, learning, and extinction of fear, emotional regulation, and reward processes. The endocannabinoid CB1