Association of an odor with activation of olfactory bulb noradrenergic β-receptors or locus coeruleus stimulation is sufficient to produce learned approach responses to that odor in neonatal rats

These experiments examined the sufficiency of pairing an odor with either intrabulbar activation of noradrenegic beta-receptors or pharmacological stimulation of the locus coeruleus to support learned odor preferences in Postnatal Day 6-7 rat pups. The results showed that pups exposed to odor paired with beta-receptor activation limited to the olfactory bulb (isoproterenol, 50 mu M) displayed a conditioned approach response on subsequent exposure to that odor. Furthermore, putative stimulation of the locus coeruleus (2 mu M idazoxan or 2 mM acetylcholine) paired with odor produced a subsequent preference for that odor. The effects of locus coeruleus stimulation could be blocked by a pretraining injection of the beta-receptor antagonist propranolol (20 mg/kg). Together these results suggest that convergence of odor input with norepinephrine release from the locus coeruleus terminals within the olfactory bulb is sufficient to support olfactory learning.