Efferent connections of the olfactory bulb in the cat. An experimental study with silver impregnation methods

Abstract

Abstract After lesions of the olfactory bulb with some involvement of the anterior olfactory nucleus in the cat the ensuing degeneration was studied with both the Nauta and the Glees silver impregnation techniques. Preterminal and terminal degeneration was found in the anterior olfactory nucleus, pars lateralis and pars externa; the rostrolateral part of the olfactory tubercle; prepyriform and periamygdaloid cortices; anterior amygdaloid area; nucleus of the lateral olfactory tract and nucleus corticalis of amygdala, homolaterally. On the contralateral side the degeneration was restricted to the pars externa of the anterior olfactory nucleus and to the granular layer and the inner part of the internal plexiform layer of the olfactory bulb. In the olfactory tubercle and pyriform cortex the degeneration was located in the plexiform layer in which there were seen degenerating axo‐dendritic synaptic contacts on the ascending dendrites of the pyramidal cells. The olfactory projection fibers which reach the contralateral anterior olfactory nucleus and bulb course through the anterior limb of the anterior commissure. In the olfactory bulb the fibers were found to end not only among the neuropil of the internal pleximorm and granular layers but also as axo‐somatic contacts on the granular cells. The mitral cells and the periglomerular layer were completely free from degeneration. No degeneration was observed homolaterally in the rest of the amygdaloid complex, septal areas, bed nucleus of the anterior commissure, interstitial nucleus of the stria terminalis or hippocampus.