Nitric oxide in the olfactory epithelium

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Schwann Cell Responses and Plasticity in Different Dental Pulp Scenarios

Mammalian teeth have evolved as dentin units that enclose a complex system of sensory innervation to protect and preserve their structure and function. In human dental pulp (DP), mechanosensory and nociceptive fibers form a dense meshwork of nerve endings at the coronal dentin-pulp interface, which arise from myelinated and non-myelinated axons of the Raschkow plexus (RP). Schwann cells (SCs) play a crucial role in the support, maintenance and regeneration after injury of these fibers. We have recently characterized two SC phenotypes hierarchically organized within the coronal and radicular DP in human teeth. Myelinating and non-myelinating SCs (nmSCs) display a high degree of plasticity associated with nociceptive C-fiber sprouting and axonal degeneration in response to DP injuries from dentin caries or physiological root resorption (PRR). By comparative immunolabeling, confocal and electron microscopy, we have characterized short-term adaptive responses of SC phenotypes to nerve injuries, and long-term changes related to aging. An increase of SCs characterizes the early responses to caries progression in association with axonal sprouting in affected DP domains. Moreover, during PRR, the formation of bands of Büngner is observed as part of SC repair tracks functions. On the other hand, myelinated axon density is significantly reduced with tooth age, as part of a gradual decrease in DP defense and repair capacities. The remarkable plasticity and capacity of SCs to preserve DP innervation in different dental scenarios constitutes a fundamental aspect to improve clinical treatments. This review article discusses the central role of myelinating and non-mSCs in long-term tooth preservation and homeostasis

Epithelial sentinels or protozoan parasites?: Studies on isolated rodlet cells on the 100th anniversary of an enigma Centinelas epiteliales o parásitos protozoarios?: Estudios en células rodlet aisladas en el centenario de un enigma

Rodlet cells are an unusual cell type found exclusively in teleost fishes. Their principal characteristics are a fibrous capsule and arrow or club-like structures pointing towards the apex of the cell, which are called rodlets. Rodlet cells were first described by Thelohan (1892) as undetermined sporozoan fish parasites, and soon after named Rhabdospora thelohani by Laguesse (1895). In 1906, a presently ongoing controversy started, with Plehn's independent characterization of rodlet cells as endogenous glandular cells, and a prompt refutation by Laguesse (1906). Both maintained their position, and during the following century both views continued to coexist with varying popularity, while additional interpretations of rodlet cell function were proposed. Here I present observations of live rodlet cells from the olfactory epithelium of the marine teleost Isacia conceptionis. Rodlet ejection was monitored and the fate of rodlet cells and ejected rodlets was tracked for up to 12 h. While rodlet cells died within a few hours, usually after rodlet expulsion, the rodlets remained stable over the observation period. These results are discussed in the light of the current hypotheses regarding rodlet cell functionLas células "rodlet" son un tipo celular poco usual que se encuentra exclusivamente en peces teleósteos. Sus características principales son tener una cápsula fibrosa y estructuras en forma de lanza que apuntan hacia el ápice de la célula, denominadas "rodlet". Las células "rodlet" fueron descritas por primera vez por Thelohan (1892) como parásitos esporozoarios no determinados de peces, y poco después bautizados por Laguesse (1895) como Rhabdospora thelohani. En 1906, con la caracterización independiente realizada por Plehn de estas células como células glandulares endógenas, y la pronta refutación por Laguesse (1906), comienza una controversia que se ha mantenido hasta hoy. Ambos defendieron su posición, y durante el siglo siguiente ambas visiones continuaron coexistiendo con variada popularidad, al mismo tiempo que se proponían interpretaciones alternativas sobre la función de las células "rodlet". Aquí presento observaciones de células "rodlet" vivas del epitelio olfatorio del teleósteo marino I. conceptionis. Se monitoreó la expulsión de los "rodlets", el destino de las células "rodlet", y se siguió la trayectoria de los "rodlets" expulsados durante 12 h. No obstante las células "rodlet" murieron dentro de unas pocas horas, generalmente después de la expulsión de los "rodlets", los "rodlets" siguieron siendo estables durante el período de observación. Se discuten estos resultados teniendo en cuenta las hipótesis actuales sobre la función de estas célula

Excitation, inhibition, and suppression by odors in isolated toad and rat olfactory receptor neurons

. Excitation, inhibition, and suppression by odors in isolated toad and rat olfactory receptor neurons. Am J Physiol Cell Physiol 279: C31-C39, 2000.-Vertebrate olfactory receptor neurons (ORNs) exhibit odor-induced increases in action potential firing rate due to an excitatory cAMP-dependent current. Fish and amphibian ORNs also give inhibitory odor responses, manifested as decreases in firing rate, but the underlying mechanism is poorly understood. In the toad, an odor-induced Ca 2ϩ -activated K ϩ current is responsible for the hyperpolarizing receptor potential that causes inhibition. In isolated ORNs, a third manner by which odors affect firing is suppression, a direct and nonspecific reduction of voltage-gated and transduction conductances. Here we show that in whole cell voltage-clamped toad ORNs, excitatory or inhibitory currents were not strictly associated to a particular odorant mixture. Occasionally, both odor effects, in addition to suppression, were concurrently observed in a cell. We report that rat ORNs also exhibit odor-induced inhibitory currents, due to the activation of a K ϩ conductance closely resembling that in the toad, suggesting that this conductance is widely distributed among vertebrates. We propose that ORNs operate as complex integrator units in the olfactory epithelium, where the first events in the process of odor discrimination take place. olfactory transduction; excitatory current; inhibitory current; odor suppression THOUSANDS TO MILLIONS of olfactory receptor neurons (ORNs) in the olfactory epithelium enable vertebrates to perceive a wide diversity of odor molecules (for a review, see Ref. 3). Each sensory cell is thought to express a single type or at most a few types of receptor molecule in its chemosensory cilia, where odor transduction occurs. A matter of great interest is how the olfactory system discriminates between the myriad of different odorants and how odor perception is achieved by the nervous system. Central to this problem is the question of how odors are coded and to what extent the olfactory epithelium, the olfactory bulb, and higher brain structures participate in coding. In this framework, an understanding of the physiological properties of the receptor neurons is fundamentally important

Olfactory transduction in ciliated receptor neurons of the Cabinza grunt, Isacia conceptionis (teleostei: haemulidae)

The ciliated receptor neurons of fish olfactory organs are thought to transduce amino acids through a cAMP-dependent transduction pathway, but direct physiological evidence for this hypothesis remains scarce and is confined to catfish and trout. We investigated olfactory transduction in a marine fish, the Cabinza grunt Isacia conceptionis (Perciformes, Teleostei). The olfactory epithelium was characterized using light and electron microscopy, and isolated ciliated receptor neurons were recorded with the perforated patch-clamp technique. Cells were stimulated with puffer pipettes containing amino acid odourants, IBMX plus forskolin or 8bromo-cAMP. All three stimuli triggered transient inward currents at a holding potential of -70 mV and responses with outward-rectifying current-voltage relationships. The characteristics of the transduction currents induced by each stimulus were similar across cells and indistinguishable within the same cell, supporting the hypothesis of a cAMP pathway

Nitric oxide activates a potassium current in olfactory receptor neurons from Caudiverbera caudiverbera and Xenopus laevis

The putative role of nitric oxide (NO) in the physiology of olfactory receptor neurons (ORNs) is controversial. Here we report that pulses of NO caused an outward current in voltage-clamped isolated olfactory neurons. The I-V relation of this effect, its sensitivity to charybdotoxin and its dependence on external potassium suggest that NO activates a K+-conductance. As blockers of soluble guanylyl cyclases failed to affect the current, we conclude that NO opens K+-channels in a cGMP-independent manner

NADPH diaphorase is developmentally regulated in rat olfactory epithelium

In vertebrate olfactory receptor neurons, NO synthase (NOS) has been detected in embryonic and early postnatal stages. However, expression of the enzyme in the mature epithelium is still controversial. We analyzed the developmental expression pattern of the histochemical NOS-marker NADPH diaphorase (NADPHd) in the olfactory epithelium of young rats. NADPHd was expressed in a small subset of olfactory receptor neurons as early as PO. Between P0 and P24 the number of labeled neurons increased 10-fold, stabilizing thereafter. Whereas NADPHd was generally found in the somata, a transitory dendritic expression was observed between P2 and P5. This dynamic postnatal regulation of the cellular distribution of NADPHd appears to reflect developmental processes within the olfactory epithelium. © 2001 Lippincott Williams & Wilkins