Long-Term Enhancement of Synchronized Oscillations by Adrenergic Receptor Activation in the Olfactory Bulb

Department of Physiology and Biophysics, and Neuroscience Program, University of Colorado at Denver and Health Sciences Center, Denver, Colorado Submitted 8 December 2007; accepted in final form 3 February 2008 The noradrenergic system is widely thought to be important for associative learning in the olfactory system through actions in the first processing structure, the main olfactory bulb (MOB). Here, we used extracellular local field potential (LFP) and patch-clamp recordings in rat MOB slices to examine norepinephrine (NE)-induced long-term changes in circuit properties that might underlie learning. During responses to patterned olfactory nerve stimulation mimicking the breathing cycle, NE induced a long-term increase in gamma frequency (30–70 Hz) synchronized oscillations. The enhancement persisted long after washout of NE ( 70 min), depended on the combined actions of NE and neuronal stimulation, and seemed to be caused by enhanced excitatory drive on the mitral/granule cell network that underlies rapid gamma oscillations. The last effect, increased excitation, was manifested as an increase in evoked long-lasting depolarizations (LLDs) in mitral cells. From a functional perspective, the observed long-term cellular and network changes could promote associative learning by amplifying odor-specific signals. Address for reprint requests and other correspondence: N. Schoppa, Dept. of Physiology and Biophysics, UCDHSC at Fitzsimons, Mail Stop 8307, PO Box 6511, Aurora, CO 80045 (E-mail: Nathan.Schoppa{at}UCHSC.edu )