Contributions to the comparative anatomy of the amygdaloid nuclei of mammals with some experiments of their destruction or stimulation.

Abstract

Summary The results of comparative-anatomical and experimental studies on amygdala disclosed the following facts: 1) The division of amygdaloid niiclei into two groups, basolateral and corticomedial seems to be not fully adequate in regard to the functional differences, because results of the stimulation experiments in our laboratory indicate for certain coincidence of effectiveness with autonomous function. From the view angle of fiber connection, this way of division ought also not to be highly evaluated. 2) The intermediate principal nucleus (nucleus T of Volsch large-celled lateral part of the basal nucleus of American authors) is generally divided into two parts, namely, dorsal and ventral portions. The ventral portion of that of the bat is particularly large and together with the large lateral principal nucleus nucleus M of Volsch, lateral nucleus of American authors) constitutes a characteristic of bat amygdala. The reason for its largeness was found, by means of destruction experiment of the amygdaln, in a close connection with the flight activity. Presumably intermediate prinripal nucleus participates in the extrapyramidal motor function; the lateral principal nucleus is generally large in most animals and functionally seems to inhibit motor activity. 3) The medial principal nucleus (nucleus T of Volsch, small-celled medial part of the basal nucleus of American authors) remains maldeveloped in some lower animals. In general, it grows distinctly larger in the caudal level. According to the result of the investigations undertaken in our laboratory, the said nucleus is chiefly related to autonomic nervous system. The above mentioned lateral and intermediate principal nuclei (T and T) also seem to have some relation, partially at least with autonomic nervous system. 4) The so-called medial nucleus in higher animals (D of Volsch) is generally maldeveloped. This nucleus, together with cortical nucleus (B of Volsch), participates partially also in autonomic nerve function. The central nuclei of higher animals (E and E of Volsch) are also underdeveloped 5) The periamygdaloid cortex (Pam1, Pam2 and Pam3 of Rose) receives the fibers from the lateral olfactory tract and evidently participates in olfactory function, but it also causes both extrapyramidal and autonomic reflexes probably by way of the amygdalar connection. Of the said cortical portions what are particularly closely related with amygdala are the portions Pam2 and Pam3. However, the portion Pam3 has not been differentiated yet in the lower animals. 6) When the bilateral amygdala of a young animal is destroyed early in life, growth gets markedly inhibited. In such an animal. atrophy of the parotid gland, thyroid gland, hypophysis, adrenal gland and pancreatic gland was observed. As the cause of this developmental disturbance there are two nervous routes assumable, namely, the route through amygdala hypothalamus anterior lobe of hypophysis general inner secretory glands and the route through amygdala salivary glands inner secretory disturbance of the latter. In the latter connection, the pituitary gland also may participate in the process. We should be particularly cautious about applying bilateral amygdalectomy to human subjects as there is a possibility of the occurrence of disturbances long after the operation. 7) That amygdala participates in salivation was verified by our experiments and the following facts also came to be clear as the result thereof: the portion Pam2 of periamygdaloid cortex has a particularly close connection with the secreting function of parasympathetic origin; of all the amygdaloid nuclei, the medial principal nucleus (T) has an especially close relation with saliva secretion of sympathetic origin, while the intermediate principal nucleus (T), cortical nucleus (B), medial nucleus (D) and hippocampus secret saliva of a parasympathetic origin. Unilateral stimulation produces secretion of bilateral salivary glands. The fibers starting from such portions seem to be led directly toward hypothalamus further to reach the lower part of the brain.