Olfactory and other afferent connections of the hippocampus in the rabbit, rat, and cat

Abstract

After lesions of the olfactory bulb, coarse degenerating fibers were traced by the method of Nauta and Gygax through the lateral olfactory tract to superficial terminations in the prepiriform and periamygdaloid cortex and olfactory tubercle. Fine degenerated fibers were traced from the bulb through the anterior limb of the anterior commissure to terminations among the less superficial cells of the prepiriform cortex and olfactory tubercle. No fibers from the bulb reached the hippocampus or entorhinal area in these three species. After lesions in the olfactory tubercle, prepiriform cortex, or preoptic area, however, degenerated fibers were traced to the entorhinal area, subiculum, and hippocampus. There were some species differences in the distribution of these fibers, but a clear anatomical basis was found for the relay of olfactory impulses to the hippocampus. Rabbit and rat brains with lesions affecting the medial forebrain bundle at various levels were examined. Degenerated fibers were found to ascend through the bundle to the septum and fornix, and to be distributed from the fimbria throughout the extent of the ipsilateral hippocampus, passing right down to the ventral pole.