Gabaergic control of olfactory learning in young rats

Olfactory learning in young rats correlates with neural plasticity in the o lfactory bulb, and involves noradrenergic modulation of reciprocal dendrode ndritic synapses between mitral cells and GABAergic granule cells. The purp ose of this study was to examine, in vivo, the consequences of manipulating bulbar GABA transmission during training. In the first experiment, postnat al day 11 rat pups were trained in an olfactory associative learning task w ith citral odor and foot shock as the conditioned and unconditioned stimuli , respectively. The pups received continuous infusion of saline or the GABA (A) receptor agonist muscimol into the olfactory bulbs throughout a 30-min training session. The pups were then tested on postnatal day 12 for a prefe rence for or an aversion to citral odor. Saline-infused control pups develo ped an aversion to citral odor. The GABA(A) receptor agonist muscimol impai red this aversive learning in a dose-dependent manner. In the second experi ment, pups were exposed to the odor for 30 min while receiving continuous i ntrabulbar infusion of a low or high dose of the GABA(A) receptor antagonis t bicuculline, without any other reinforcer. Depending on whether a low (0. 2 nmol/bulb) or high (1.0 nmol/bulb) dose of bicuculline was infused, the p ups showed a preference or an aversion for citral odor after infusion of lo w and high doses, respectively. These results indicate that disinhibition of mitral cells in the olfactory bulb is critical for olfactory learning in young rats, and suggest that the degree of disinhibition is an important determinant in acquiring either pr eference or aversion for the conditioned odor. (C) 1999 IBRO. Published by Elsevier Science Ltd.