Functional changes in waking and sleeping rats after lesions in the olfactory pathways.

Food deprived control rats presented the following characteristics: (1) in a two-choice behavioral test, the animals explored significantly more the side of the cage odorized by a food odor (FO) than the non odorized one; (2) FO presentations in slow wave sleep (SWS) aroused them significantly more often than in a food satiated condition; (3) during wakefulness, the multiunit mitral cell responsiveness towards FO was selectively enhanced. The same 3 parameters have also been tested in animals where projections of one olfactory bulb were completely sectioned, or intact either in the medial or in the lateral part of one peduncle; the other olfactory peduncle was completely severed. The results showed that waking rats needed both medial and lateral projection pathways to perform normally in the food odor detection task, and to display the normal mitral cell excitability. However, in SWS, one medial pathway at least was needed to mediate normal rates of neocortical arousal in response to FO stimulations. The results are considered in terms of functional complementarity/redundance of the medial and lateral olfactory pathways.