Abstract
Neuropeptide Y (NPY) plays an important role in regulating appetite and hunger in vertebrates. In the hypothalamus, NPY stimulates food intake under the control of the nutritional status. Previous studies have shown the presence of NPY and receptors in rodent olfactory system, and suggested a neuroproliferative role. Interestingly, NPY was also shown to directly modulate olfactory responses evoked by a food-related odorant in hungry axolotls. We have recently demonstrated that another nutritional cue, insulin, modulates the odorant responses of the rat olfactory mucosa (OM). Therefore, the aim of the present study was to investigate the potential effect of NPY on rat OM responses to odorants, in relation to the animal's nutritional state. We measured the potential NPY modulation of OM responses to odorant, using electro-olfactogram (EOG) recordings, in fed and fasted adult rats. NPY application significantly and transiently increased EOG amplitudes in fasted but not in fed rats. The effects of specific NPY-receptor agonists were similarly quantified, showing that NPY operated mainly through Y1 receptors. These receptors appeared as heterogeneously expressed by olfactory neurons in the OM, and western blot analysis showed that they were overexpressed in fasted rats. These data provide the first evidence that NPY modulates the initial events of odorant detection in the rat OM. Because this modulation depends on the nutritional status of the animal, and is ascribed to NPY, the most potent orexigenic peptide in the central nervous system, it evidences a strong supplementary physiological link between olfaction and nutritional processes.
Highlights
Most animals, including humans, rely on their sense of smell for food seeking, food choice and the appreciation of food palatability [1,2]
The present study provides the first demonstration of the Neuropeptide Y (NPY) involvement in the acute modulation of olfactory sensory neuron (OSN) responses to odorants in rats
We show that this modulation depends on the nutritional status, which regulates the Y1 receptor (Y1R) expression in the olfactory mucosa (OM)
Summary
Most animals, including humans, rely on their sense of smell for food seeking, food choice and the appreciation of food palatability [1,2]. Olfactory neural processing is closely linked to the physiological and nutritional status of an organism: the olfactory system is more active [3,4,5] and its sensitivity [6] is increased under starvation, whereas both activity and acuity are reduced after satiation [3,4,5,6]. While this relationship has been known for several decades, the signaling systems and the mechanisms underlying the modifications of the olfactory activity induced by the nutritional state were only recently explored. Among numerous physiological functions (for review see [28,29]), NPY plays a pivotal role in the control of food intake, mainly through central hypothalamic sites, in numerous animal species [17,30,31,32,33,34,35,36]
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