The terminal nerve projects centrally in the hamster.

The projections of the peripheral and intracerebral portions of the hamster terminal nerve were examined with lesion and immunocytochemical techniques. After transection, proximal processes of the terminal nerve accumulate luteinizing hormone-releasing hormone-immunoreactive material, while the distal processes disintegrate and are no longer stained. It thus becomes possible to determine the direction of conduction of terminal nerve axons. The results of transection at the level of the cribriform plate, along the olfactory bulb, and in the ventral forebrain were all consistent in indicating a centripetal direction of conduction. Immunoreactive material collected distal to the lesion at each of these levels. All peripheral lesions eliminated processes coursing into and through the terminal ganglion at the base of the ventral forebrain. These lesions left intact, however, the terminal ganglion projections to the accessory olfactory bulb and ventral forebrain. These results indicate a centripetal projection from terminal neurons in the nasal cavity, along the olfactory bulbs and within the terminal ganglion to successively more caudal levels. This suggests that neural messages are conveyed from nasal cavity to the brain through this route. Because immunoreactive fibers were found within the sensory epithelium of the vomeronasal organ a sensory and/or sensory modulatory action is suggested.