The role of norepinephrine in the expression of learned olfactory neurobehavioral responses in infant rats.

In neonatal rats, norepinephrine (NE) is necessary and sufficient for the acquisition of an olfactory preference and its associated olfactory bulb neural modifications as assessed by [(14)C] 2-deoxyglucose (2-DG) and electrophysiology. In the present studies, we assessed the influence of NE on the expression of a conditioned odor preference and its associated olfactory bulb neural modifications in neonatal rats. On Postnatal Day 5 (PN 5), pups were trained to prefer an odor in a 1-h classical conditioning paradigm. Experimental paired odor-stroke pups received 20 forward pairings of a 10-sec peppermint odor and a 9-sec reinforcing tactile stimulation (stroking). Control pups received either random stroke-odor pairings or were naive (received neither the odor nor stroking). The next day (PN 6), the pups were injected with either an NE β-receptor antagonist, (propranolol or timolol) or saline, 1 h prior to testing. The pups were tested for a behavioral olfactory preference and assessed for differential olfactory bulb activity with [(14)C] 2-DG autoradiography. The results indicate that NE is not necessary for the expression of the learned neurobehavioral response.