Modulation of olfactory-driven behavior by metabolic signals: role of the piriform cortex.

Olfaction is one of the major sensory modalities that regulates food consumption and is in turn regulated by the feeding state. Given that the olfactory bulb has been shown to be a metabolic sensor, we explored whether the anterior piriform cortex (aPCtx)-a higher olfactory cortical processing area-had the same capacity. Using immunocytochemical approaches, we report the localization of Kv1.

Nutrient Sensing: Another Chemosensitivity of the Olfactory System.

Olfaction is a major sensory modality involved in real time perception of the chemical composition of the external environment. Olfaction favors anticipation and rapid adaptation of behavioral responses necessary for animal survival. Furthermore, recent studies have demonstrated that there is a direct action of metabolic peptides on the olfactory network.

Cellular and molecular cues of glucose sensing in the rat olfactory bulb.

In the brain, glucose homeostasis of extracellular fluid is crucial to the point that systems specifically dedicated to glucose sensing are found in areas involved in energy regulation and feeding behavior. Olfaction is a major sensory modality regulating food consumption. Nutritional status in turn modulates olfactory detection.

Modulation of olfactory sensitivity and glucose-sensing by the feeding state in obese Zucker rats.

The Zucker fa/fa rat has been widely used as an animal model to study obesity, since it recapitulates most of its behavioral and metabolic dysfunctions, such as hyperphagia, hyperglycemia and insulin resistance. Although it is well established that olfaction is under nutritional and hormonal influences, little is known about the impact of metabolic dysfunctions on olfactory performances and glucose-sensing in the olfactory system of the obese Zucker rat. In the present study, using a behavioral paradigm based on a conditioned olfactory aversion, we have shown that both obese and lean Zucker rats have a better olfactory sensitivity when they are fasted than when they are satiated.

Insulin modulates network activity in olfactory bulb slices: impact on odour processing.

Odour perception depends closely on nutritional status, in animals as in humans. Insulin, the principal anorectic hormone, appears to be one of the major candidates for ensuring the link between olfactory abilities and nutritional status, by modifying processing in the olfactory bulb (OB), one of its main central targets. The present study investigates whether and how insulin can act in OB, by evaluating its action on the main output neurons activities, mitral cells (MCs), in acute rat OB slices.

Olfaction under metabolic influences.

Recently published work and emerging research efforts have suggested that the olfactory system is intimately linked with the endocrine systems that regulate or modify energy balance. Although much attention has been focused on the parallels between taste transduction and neuroendocrine controls of digestion due to the novel discovery of taste receptors and molecular components shared by the tongue and gut, the equivalent body of knowledge that has accumulated for the olfactory system, has largely been overlooked. During regular cycles of food intake or disorders of endocrine function, olfaction is modulated in response to changing levels of various molecules, such as ghrelin, orexins, neuropeptide Y, insulin, leptin, and cholecystokinin.

Modulation of spontaneous and odorant-evoked activity of rat olfactory sensory neurons by two anorectic peptides, insulin and leptin.

In mammals, the sense of smell is modulated by the status of satiety, which is mainly signaled by blood-circulating peptide hormones. However, the underlying mechanisms linking olfaction and food intake are poorly understood. Here we investigated the effects of two anorectic peptides, insulin and leptin, on the functional properties of olfactory sensory neurons (OSNs).

5-Hydroxytryptamine action in the rat olfactory bulb: in vitro electrophysiological patch-clamp recordings of juxtaglomerular and mitral cells.

The olfactory bulb, first relay of olfactory pathways, is densely innervated by serotoninergic centrifugal fibers originating from the raphe nuclei. Although serotonin innervation was reported to be involved in olfactory learning in mammals, the action of this neurotransmitter on its putative cellular targets has been never described through unitary recordings. This lack of data initiated the present study where the effects of 5HT on juxtaglomerular and mitral cells are analyzed using whole-cell recordings on olfactory bulb slices.

Taurine action on mitral cell activity in the frog olfactory bulb in vivo.

Taurine (TAU) is a free amino acid that is particularly abundant in the olfactory bulb. In the frog, TAU is located in the terminations of the primary olfactory axons and in the granular cell layer. TAU action seems to be associated with gamma amino butyric acid (GABA), the main inhibitory neurotransmitter involved in the processing of the sensory signal.

GABA(B) receptor-mediated inhibition of mitral/tufted cell activity in the rat olfactory bulb: a whole-cell patch-clamp study in vitro.

GABA, the major inhibitory neurotransmitter involved in information processing in the olfactory bulb, is hypothesized to act through GABA(B) receptors by depressing primary neurotransmitter release at the level of olfactory nerve axon endings. The present study was designed to analyze GABA(B) receptor-mediated inhibition mechanisms by performing whole-cell patch-clamp recordings of mitral/tufted cell activity in the rat in vitro. To do so, GABA(B) receptor-mediated action was mimicked by baclofen and antagonized by saclofen.

Sensory information processing in the frog olfactory pathways. Experimental basis for modeling studies.

In the frog, unitary electrophysiological recordings have been extensively used to investigate odor processing along the olfactory pathways. By comparing spontaneous and odor-evoked activities of neuroreceptor, mitral and cortical cells, we have collected fundamental data relating to coding abilities of the three olfactory levels, the olfactory mucosa, the bulb and the cortex. Based on a synthesis of our experimental data related to GABAergic and dopaminergic involvement in the olfactory bulb, this paper aims to match this information with computational data and to discuss some questions on bulbar processing.

Odor coding properties of frog olfactory cortical neurons.

Until now, in amphibians, response odor properties of primary cortical neurons had never been investigated. Furthermore, very few data on this subject are available in other species. This prompted us to explore the functional properties of olfactory cortical neurons at rest and in response to odors.

Action of vasopressin on hypoglossal motoneurones of the rat: presynaptic and postsynaptic effects.

The distribution of vasopressin binding sites in the hypoglossal nucleus of newborn rats was determined using autoradiography on film and a radioiodinated vasopressor antagonist. These sites predominated in the ventromedial and dorsal divisions of the nucleus. The effect of vasopressin on hypoglossal neurones was studied in brainstem slices of newborn animals, using the single-electrode voltage-clamp technique.

Somatic Acetylcholine Release in Rabbit Nodose Ganglion.

In the rabbit, as in various other species, the presence of a cholinergic vagal afferent contingent has been demonstrated previously using biochemical and immunohistological approaches at the nodose ganglion level, where vagal afferent cell bodies are located. This structure is completely devoid of synaptic contacts. In the present study, somatic acetylcholine release is demonstrated on different types of in vitro rabbit nodose ganglion preparations (fragments of nodose tissue or isolated cell bodies) using chemiluminescent detection.

Choline uptake in cholinergic nodose cell bodies.

Isolated living cell bodies were obtained by mechanical and enzymatic dissociation from adult rabbit nodose ganglion followed by separation of fibres and cells using a Percoll gradient. A purification yield of 45% was measured. Based on previous results obtained in whole ganglion and showing the presence of cholinergic cell bodies among the afferent fibres of the vagus nerve, this preparation was used to study choline uptake by neuron cell somata.