Effect of basolateral amygdala and ventromedial hypothalamic lesions on ingestion and taste preference in rat

Background and objectives: Amygdaloid nuclei and the hypothalamic structures are known to have intimate functional relationships. But to date the nature of this relationship has not been completely understood. In the present study, this relationship was evaluated. Methods: Lesions were performed in basolateral nucleus of amygdala (BLA) and the ventromedial hypothalamus (VMH) in the same rats sequentially to evaluate both the individual, as well as combined effects of lesions of these two centres. Food intake, water intake and the body weight were studied before and after the lesions. Results: The first lesion of BLA or VMH increased the food and water intake significantly (P<0.01). But in the VMH lesioned rats, further lesioning of BLA, reduced the intensity of the hyperphagia. This suggested a kind of interrelationship between these centres, pointing out that intact BLA was instrumental in the development of VMH induced hyperphagia. To further assess the interactions of these two centres, three bottle free choice taste preference tests were undertaken by using sweet, salty solution along with tap water. The lesion of the BLA increased the intake of sweet tasting saccharin solution. This preference was retained even after the lesion of the VMH in the same rats. Interpretation and conclusion: Therefore it appeared as if the VMH neurons might not be involved in the sweet taste preference following BLA lesion, suggesting involvement of some other pathway for taste selection responses. But the development of full fledged VMH lesion induced hyperphagia could occur only in the presence of intact BLA.