Electrophysiological analysis of the nasal chemical senses in garter snakes

Electroolfactogram and electrovomeronasogram recordings were made from garter snakes stimulated with vapor of amyl acetate, butanol and of earthworm wash. The olfactory epithelium was more sensitive than the vomeronasal epithelium to all three stimuli. Volatiles from prey washes were capable of stimulating the olfactory epithelium when delivered as airstreams. The vomeronasal epithelium was sensitive only to the air delivery of vapor of amyl acetate. Single unit recordings from the mitral cell layer of the accessory olfactory bulb of garter snakes were made in response to liquid delivery of a variety of chemical stimuli including classical odorants, amino acids and proteins derived from prey. All three classes of stimuli altered unit firing in the accessory olfactory bulb. Amyl acetate, earthworm wash, goldfish wash and non-volatile amino acids delivered as liquid stimuli to the vomeronasal epithelium produced responses in the accessory olfactory bulb that were more distinct and reliable than the electrovomeronasogram responses to airborne odorants recorded at the periphery. Both excitatory and inhibitory responses were observed in the accessory olfactory bulb of garter snakes. The direction of the response to a given stimulus differed for different neurons. Responses were frequently biphasic and could last longer than 50 seconds. Individual neurons responded to different classes of stimuli suggesting that they are broadly tuned.