Central cannabinoid regulation of food intake in chickens
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ABSTRACT Marijuana has been used for medicinal and recreational purposes for thousands of years. Many people think of marijuana in the context of an illegal drug. Because of the antimarijuana attitude, research with cannabinoids was neglected for a long time. Although this substance is related to social problems, scientists are interested in its action and possible medicinal properties. Since the identification of the structure of Î 9--tetrahydrocannabinol, the main psychoactive ingredient of marijuana, there has been increased interest in this compound. Following the discovery of two cannabinoid receptors, CB1 and CB2 receptors, it was determined that CB1 receptors are in high density in the central nervous system while CB2 receptors are found primarily in the immune system. The endogenous cannabinoid ligands, anandamide and 2-arachidonoylglycerol, were observed in the central nervous system and peripheral tissues. Endocannabinoids differ from other "classical" neurotransmitters because they do not appear to be stored in synaptic vesicles, and they act as retrograde messengers within the brain. The endogenous cannabinoid signaling system includes cannabinoid receptors, their endogenous ligands called endocannabinoids, and the proteins for their synthesis and inactivation. The cannabinoid system appears to act as a neuromodulatory system. During the past ten years, the endogenous cannabinoid system has been implicated in a variety of physiological functions including pain reduction, motor regulation, learning, memory, and reward. Because obesity and eating disorders are prevalent, scientists are working at the molecular level to study the mechanisms controlling body weight and regulation of food intake. Several of the neuropeptides present in hypothalamic nuclei contribute to energy balance and food intake regulation. Endogenous cannabinoid and cannobinoid receptors are found in the hypothalamus and are associated with the regulation of food intake. Although the mechanisms whereby cannabinoids influence food intake remain unclear, results suggest that the cannabinoid system will be an important target in future studies in obesity. Most research on cannabinoids has focused on their role in food intake regulation in mammalian species. It is important to determine the role of endocannabinoids in other species. The effect of intracerebroventricular injection of agonists and antagonists of both CB1 and CB2 receptors in 8 to 11 week-old male Single Comb White Leghorn and 3 to 6 weeks old male broilers was investigated. It was found that agonists of both the CB1 and CB2 receptor increased food intake significantly; however, the CB2 receptor agonist had a stronger and longer lasting effect. Antagonists of both receptors decreased food intake significantly. The CB1 receptor antagonist appeared to block both cannabinoid receptors in birds, whereas the CB2 receptor antagonist did not block both receptors. Previous studies have indicated that the CB2 receptor is found only outside the brain and spinal cord, and is involved with the immune system. From the present results, it appears that both cannabinoid receptors are present in the chicken brain. Furthermore, the CB2 receptor may also be localize in the chicken brain. There are also differences in cannabinoid system between Leghorn and broilers. Key words: Chickens, Cannabinoid, Endogenous cannabinoid, Food intake.
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