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Abstract

The fields of origin of the amygdalofugal pathways in the albino rat were studied by using the Fink-Heimer technique to stain degenerating fibers and terminals in brains of animals sacrificed four and seven days after small unilateral lesions of the amygdale. A surprisingly restricted field of origin was found for the supracommissural stria terminalis — the component projecting to the ventromedial nucleus of the hypothalamus Only a lesion in the most posterior part of the cortical nucleus produced degeneration in this pathway. The postcommissural stria terminalis which apparently distributes to the bed nucleus of the stria terminalis and preoptic area originates in a more widespread area including parts of both the basolateral and corticomedial complexes. Although intense terminal degeneration could be seen within the amygdala following all lesions, long fibers projecting into the anterior amygdaloid area, lateral preoptic area and lateral hypothalamus were found only after lesions in which fibers of passage from periamygdaloid cortex could have been interrupted. Convincing evidence, therefore, of a long axon ventral amygdalofugal pathway of the rat was not found in this study.