Effects of locus ceruleus and olfactory bulb stimulation on rat olfactory tubercle neuron activity

The effects of electrical stimulation of the olfactory bulb and the locus ceruleus on olfactory tubercle neurons were examined in rat models. Ipsilateral stimulation of the olfactory bulb produced excitation in 31% of olfactory tubercle neurons tested and inhibition in 17%. Twenty-two percent of the olfactory tubercle neurons were excited, whereas 9% were inhibited by ipsilateral stimulation of the locus ceruleus. Contralateral stimulation of the locus ceruleus produced similar responses in the same neuron entities. A negative-positive evoked potential was recorded in the olfactory tubercle after ipsilateral and contralateral stimulation of the locus ceruleus. Thirty-three percent of the olfactory tubercle neurons that responded orthodromically or antidromically to stimulation of the olfactory bulb were excited by ipsilateral stimulation of the locus ceruleus. In contrast, only 10% responded with excitation to ipsilateral stimulation of the locus ceruleus among the olfactory tubercle neurons that were unresponsive to stimulation of the olfactory bulb. These findings suggest that olfactory tubercle neurons that receive input from or sending output to the olfactory bulb are influenced by the noradrenergic system of the locus ceruleus. A possible role of the olfactory tubercle in olfactory transduction will also be discussed.