Nuzzling in the gray short-tailed opossum. I: Delivery of odors to vomeronasal organ.

Nuzzling in the gray short-tailed opossum (Monodelphis domestica) is exhibited in response to conspecific odor deposits and is involved in chemosensory recognition. Nuzzling consists of bouts of repeated forward rubbing motions (with intermittent tapping) with the ventral aspect of the snout over the odor source, while moistening it with naso-oral secretions. The role of nuzzling in odorant d delivery to the vomeronasal organ (VNO) was investigated. Five opossums were allowed to nuzzle conspecific odor deposits mixed with 3H-proline. Histological sections of the snouts processed for autoradiography revealed very strong labeling of the VNOs, primarily the nonsensory epithelium. No labeling was observed in the olfactory epithelium. Unilateral closure of the oral opening to the nasopalatine canal resulted in labeling of the contralateral VNO only, implicating oral access to the VNO. Several distinctive structures appear to be associated with chemical access. An experiment in which 16 males and 16 females were given a preference test of dried nuzzling secretion versus dried distilled water established that the naso-oral secretions deposited during nuzzling do not have properties of scent marks.