BILATERAL 6-OHDA LESIONS OF THE LOCUS-COERULEUS IMPAIR ASSOCIATIVE OLFACTORY LEARNING IN NEWBORN RATS

On postnatal day 4 (PN4) Wistar rat pups were anesthetized and receive d bilateral infusions of 6-OHDA into the locus coeruleus or received v ehicle infusions. On PN6 pups were trained in a classical conditioning paradigm with intra-oral milk infusions as the UCS and citral odor as the CS. Pups were trained in either 'paired', 'odor-only', 'milk-only ' or 'backward' (milk then odor) conditions. On PN7 acquisition of a l earned odor preference to the CS was tested in a two-odor choice test. HPLC analysis showed that locus coeruleus lesions significantly reduc ed olfactory bulb NE content but had no effect on olfactory bulb DA or 5-HT levels compared to controls. Pups receiving locus coeruleus lesi ons did not differ in behavioral response patterns during training com pared to their littermate, vehicle controls. However, locus coeruleus lesions impaired acquisition of conditioned odor preferences. These re sults suggest that NE output from the locus coeruleus is critical for early olfactory learning.