Ascending olfactory information and centrifugal influxes contributing to a nutritional modulation of the rat mitral cell responses

A nutritional modulation of electrical mitral cell multiunit responses was studied in three groups of rats, with either a unilateral section of the olfactory peduncle (OP) or of the lateral olfactory tract (LOT), or with unilaterally damaged olfactory mucosa (zinc sulphate treatment). The control and lesion-side activity was chronically recorded in the bulbs of hungry and satiated animals receiving series of 10 identical stimulations with a food odor and odors non-associated to nutrition. Patterns of positive, negative and null responses were thus collected. In the control-side bulbs of the LOT and OP groups, as in intact animals, the percentage of positive responses was maximal in hungry rats receiving food odor, and minimal in satiated rats receiving isoamyl acetate, as a result of the nutritional modulation of responses. In the lesion-side bulbs of the LOT group, activation increased irrespective of the nutritional state of the animal and the nutritional meaning of the odorant. This shift was reproduced in the lesion-side bulbs of the OP group. In these animals, no nutritional modulation was observed, an effect ascribed to the disruption of activating fibers in the anterior limb of the anterior commissure (AAC). The zinc sulphate treated animals displayed a lack of olfactory responses in the treated-side bulbs, and no response modulation in the control-side bulbs, where the percentage of positive responses for non-alimentary odors was slightly increased, presumably as a consequence of the suppression of interbulbar inhibition. The results are discussed in terms of the quantity of olfactory information necessary for the centrifugal nutritional modulation to be released. The neuronal circuits subserving these various effects in the bulb are considered.