Olfactory learning in the rat neonate soon after birth

Abstract

The first hours of a newborn rat's life entail locating and attaching to the mother's nipple not only for nutrition but also for protection and warmth. The present study sought to characterize olfactory learning in the rat neonate immediately after birth. Newborn rats were exposed to an odor at various time periods soon after birth and tested for behavioral activation and attachment to a surrogate nipple in the presence of this odor at 4-5 hr postpartum. Regardless of when pups were presented the odor (0, 1, or 2 hr after birth) motor activity was greater among pups previously exposed to the odor than pups with no odor experience. Similarly, latency to attach to the nipple in the presence of the odor was lower among odor-preexposed pups, especially when odor exposure began within an hour of cesarean delivery. Odor exposure immediately after birth for just 15 min was sufficient to increase motor activity and to decrease latency to attach to a similarly scented surrogate nipple. These results suggest that olfactory experience very soon after birth can shape subsequent olfactory responses. The relative importance of the dearth of postnatal experience or of elevated neurochemicals immediately after birth and possible associative mechanisms underlying this learning is discussed.

Figure 1

Schematic depiction of the odor exposure container.

Figure 2

Experiment 1. These graphs illustrate the mean (± SE) of a) latency to attach to and b) percent total time attached to a scented surrogate nipple as a function of time of odor exposure. Also depicted are the mean (± SE) values of c) head movements and d) burst movements during the first minute of presentation of the scented surrogate nipple. For all graphs: gray bars = pups with prior odor exposure; white bars = pups with no prior odor exposure. For graph b) percent total time attached: vertical stripes = male rats, horizontal stripes = female rats. †Figure 2C (120–180) significant effects were found only for males * indicates p <.05

Figure 3

Experiment 2. These graphs illustrate the mean (± SE) of a) latency to attach to and b) percent total time attached to a scented surrogate nipple as a function of duration of prior odor exposure. Also depicted are the mean (± SE) values of c) head movements and d) burst movements during the first minute of presentation of the scented surrogate nipple. * indicates p <.05