Unilateral lesions of the olfactory tubercle modifying general arousal effects in the rat olfactory bulb.

The centrifugal control exerted by different arousal states on the rat olfactory bulb was investigated. The olfactory tubercle was unilaterally coagulated with either 1 mA or 3 mA current. The vigilance state parameters and multiunit mitral cell activity were recorded in freely moving rats, stimulated either by their usual food odor or by isoamyl acetate, in a hungry or a satiated state. In each animal, a unilateral lesion affected resting activity and the relative proportion of positive (excitatory) and negative (inhibitory) responses in the same way in both olfactory bulbs; these effects were proportional to the extent of the lesion. In wakefulness, a nutritional modulation of the bulb responses for food odor existed in spite of a slight decrease in the general arousal level. In slow wave sleep (SWS), when compared to a control group, the rats with lesions showed an increase of neocortical desynchronization induced by olfactory stimulation, and a large decrease of mitral cell excitability. Inhibition of the olfactory input, which normally develops during SWS, could involve mainly mesencephalic neurons reaching the olfactory tubercle and the bulb via the ventral part of the medial forebrain bundle.