Imprinting on prey odours in ferrets (Mustela Putorius F. Furo L. ) and its neural correlates

The effect of different feeding conditions during ontogeny was investigated in the carnivorous ferret. Behavioral tests and cardiac responses towards known and unknown odours as well as food choice tests showed that in this species olfaction plays an important role for prey recognition. Yet, the knowledge of the prey odours has to be learned during a sensitive phase which was found to exist between postnatal days 60 and 90. In adult ferrets, searching for prey can be elicited reliably by familiar odours, unknown odours are not reacted to. The maturation of the granule cells of the ferret olfactory bulb around the time of prey odour imprinting has been analysed. Rapid Golgi impregnation studies reveal a temporal overshoot in the development of the spines on the external dendrites of the granule cells. Electron microscopical examinations of the synaptic contacts in the external plexiform layer indicate that the time course of synapse and reciprocal synapse formation is similar to that of the formation of the spines on the external dendrites. The results show that the maturation of the external plexiform layer with respect to the number of dentritic spines and synapses, occurs at a time when the animal is most sensitive to olfactory imprinting stimuli.