The role of olfactory bulb norepinephrine in early olfactory learning.

Wistar rat pups were implanted with bilateral olfactory bulb cannulas on postnatal day 5 (PN5). On PN6, pups were trained in an olfactory classical conditioning task with peppermint odor as the CS and tactile stimulation/stroking as the UCS. Pups were randomly assigned to either PAIRED, BACKWARD or ODOR-only conditions. Half the pups in each group received intrabulbar infusions of 100 microM propranolol and half received intrabulbar infusions of saline during the training session. Propranolol infusions blocked acquisition of the learned odor preference expressed by PAIRED saline-infused pups. Diffusion of the infusate was checked in additional pups by infusing [3H]NE and performing LSC analysis. Infusate concentration did not significantly differ between the anterior and posterior halves of the bulb, but were sharply lower in the olfactory peduncle and more posterior areas. The results suggest that olfactory bulb NE is critical for early olfactory learning.