Combined modulating effects of the general arousal and the specific hunger arousal on the olfactory bulb responses in the rat.

The combined modulating effects of the general level of arousal and specific hunger arousal on the olfactory bulb responses were investigated in the rat. Vigilance state parameters and multi-unit mitral cell activity were recorded in freely moving animals stimulated by control odours and by their usual food odour, either in the hungry or the satiated state. The nutritionally modulated bulb responses towards food odour were observed only for high arousal level (wakefulness). In rapid eye movement sleep (REMS), no olfactory response occurred. In slow wave sleep (SWS), one observed either a high bulb responsiveness to stimuli with neocortical arousal, or a general inexcitability. Each odorous stimulus in SWS elicited a higher neocortical arousal rate in the hungry than in the satiated state, as did food odour compared with control odours in both nutritional states. In SWS, a progressive alteration of the nutritionally modulated responses occurred at first at the bulb level and later for inner structures. Rats fed 2 h a day displayed a reversed circadian sleep-waking cycle and a lower SWS proportion compared with rats fed ad libitum. The hunger arousal could quantitatively and qualitatively modulate the activity of structures regulating the sleep-waking pattern.