Faculty Bibliography

Infant rat pups were exposed to a novel odor (orange or cedar) while they received tactile stimulation (stroking of the body) or were presented with odor or stroking alone. The effects of these treatments were assessed on pups' performance in a huddling test (Experiment 1 and 2) and an independent feeding test (Experiment 3). During these tests, only pups that had received the simultaneous presentation of the odor and stroking exhibited an increase in huddling and feeding. The increase in these behaviors was dependent on the presence of the conditioned odor during testing.

In Experiment 1, 3-6-day-old rats were simultaneously exposed to an unfamiliar odor which they will normally avoid (orange extract) and the odor of maternal saliva, or to either orange alone or saliva alone. One hour later, in a two-odor choice test, those pups which were simultaneously exposed to orange and saliva exhibited an enhanced orientation to the orange odor. In Experiment 2, orange odor was presented while pups were exposed to the odor of saliva, or while they received one of two types of tactile stimulation (stroking or tailpinching). Pups in control groups were first presented with saliva or tactile stimulation and then the orange odor. Pups that had received any of the three simultaneous exposure treatments subsequently exhibited an enhanced orientation toward the orange odor, but not the pups in the control groups. The results suggest that the tendency of neonates to avoid a novel odor can be reversed by pairing that odor with events that elicit significant increases in behavioral activity. The possibility that this phenomenon reflects a classical conditioning process is discussed.

During Postnatal Days 1-28, male Wistar rat pups were simultaneously exposed to an odor and reinforcing tactile stimulation similar to that normally received from the dam. Controls received only the odor, only the stimulation, or neither of these stimuli. Ss that received simultaneous odor and tactile stimulation displayed both a behavioral odor preference and an enhanced 2-deoxyglucose uptake in specific olfactory bulb glomeruli. Results suggest that early olfactory learning enhances the neural response to odors that have acquired attractive value and that attentional processes cannot account for the olfactory-based behavioral changes.

Previous studies have shown that rat pups have an enhanced metabolic activity to familiar odors in specific glomeruli of the olfactory bulb. The present study examined extracellularly recorded mitral cell responses to odors in this glomerular region, in odor-familiar and odor-unfamiliar pups. Mitral cells in odor-familiar pups had significantly fewer excitatory and more inhibitory responses to the familiar odor than controls. There were no differences between groups in responses to a novel odor. These results demonstrate that neonatal exposure to odors selectively alters subsequent mitral cell responsiveness to that odor

Nutritive deprivation, suckling deprivation, gastronintestinal fill, and milk availability contribute to the control of sucking (as measured by jaw-muscle electromyograph) and ingestion of milk (provided via a tongue cannula) in 11-13-day-old rat pups. Depriving pups of the opportunity to suckle reliably increases subsequent sucking and milk intake. Intraoral delivery of milk also increases sucking, regardless of whether or not pups are suckling-deprived. Gastrointestinal preloads have no effect on sucking if pups are not receiving milk, but reliably block the increase in sucking which accompanies milk delivery. Finally, milk delivered to the pup's mouth prior to a suckling opportunity can either enhance or attenuate subsequent sucking depending on whether pups are allowed to consume milk while suckling. In all cases, a particular mode of sucking ("rhythmic" sucking) is most affected by experimental manipulation, and appears to be an important component of the pup's ingestive behavior.

In Exp I, 11-23 day old Wistar rat pups sucked more frequently when receiving tiny intermittent pulses of milk than when receiving no milk and continued to suck at a high rate for at least 30 min after cessation of milk delivery. In Exps II and III, it was found that Ss 13-28 days of age engaged in more frequent sucking if receiving milk continuously rather than intermittently; this increased rate of sucking persisted for at least 24 hrs after cessation of milk delivery. Ss given experience with continuous milk delivery from 14 to 18 days of age also spent significantly more time attached to the nipple at 19 days of age than did Ss in control groups. It is concluded that experience with different milk delivery schedules can affect subsequent sucking and nipple attachment behavior.