Hyperemotionality induced by lesions in the olfactory system of the rat.

* Present address: Biological Research Lab., Tanabe Seiyaku Co ., Ltd., Osaka, Japan. Abstract-In order to clarify the neural mechanisms underlying the hyperemotion ality induced by bilateral olfactory bulb ablations in rats, changes in emotional be havior were measured after various parts of the secondary olfactory structures had been lesioned and olfactory bulb ablations had been carried out. When the anterior olfactory nuclei, lateral olfactory tracts and prepiriform cortices were bilaterally lesioned simultaneously with olfactory bulb ablations, many rats died from lack of food in take, while on the contrary, the rats with bilateral lesions in the olfactory tubercle, anterior olfactory nuclei and olfactory bulb developed marked hyperemotionality immediately after the lesioning. Hyperemotionality of the latter rats included not only hyperreactivity similar to that observed in the septal rat but also a muricide of 90% in incidence, which is similar to rats with olfactory bulb ablations. From these results, it can be concluded that changes in the activity of the olfactory tubercle were the most important for the development of hyperemotionality following bilateral ablations of the olfactory bulb in the rat.