Distributed chemoreception

The matching dichotomy of sensilla construction and neuroanatomical organization of sensory neuropils suggests that in crustaceans chemical information is received and processed in two fundamentally different modes. One mode is Olfaction which we define as chemoreception mediated by the aesthetasc - OL pathway the second mode is Distributed Chemoreception, which we define as chemoreception mediated by bimodal sensilla on all appendages and the associated striated neuropils that serve as local motor centers. Distributed chemoreception not only comprises taste, which we define as contact chemoreception in the context of... 

Analysis of the relative distribution and expression of OR/VNOR genes would clarify the variety of functional chemoreceptive divisions amongst this transitional group. 

Thus, in various insect species, the expression of CSP occurs in many different tissues, especially in the legs and contact sensory organs. The differences between CSPs and OBPs in tissue distribution and developmental expression suggest that the roles of these proteins in chemoreception may also be different. CSPs may have a broader function than OBPs, functioning in more systems than olfaction and taste, perhaps as general molecule carriers but especially involved in the transport of contact sensory molecules. 

It irritates skin and mucous membranes. In terms of chemoreception, it irritates the trigeminal nerve. Capsaicin binds to the vanilloid receptor subtype 1 (VRl). Birds lack this receptor. Since they cannot sense capsaicin, they eat and distribute seeds of red hot peppers. Medically capsaicin is used as painkiller (analgesic). 

Milsom WK. New insights into gill chemoreception receptor distribution and roles in water and air breathing fish. Respir Physiol Neurobiol. 2012 184 326-39. 

Contact chemoreception of the dry plant surface is basically different from the well-studied perception of aqueous solutions. Since the stimulating compounds are in a dry state it may be that their distribution is not continuous and/or at a very low concentration. Thus not every contact between a sensillum tip and the plant would result in a stimulation. Although speculative, this may explain the specific behavior of various insect species after contacting plant leaves two female flies (P. rosae, D. brassicae) perform so called oviposition runs, on host leaves of about 20-30 s duration (Stadler, 1977,1978). Locusts make rapid vibrations (10-15 times per second) with the palps contacting the potential food plant surface. Blaney and Duckett (1975) showed that this palpation increases the amount of sensory input to the CNS by allowing disadap-tation of chemoreceptors between contacts. This must also be true for the tarsal hairs of two flies mentioned above. Some butterflies use the fore tarsi to drum or tap the plant surface prior to oviposition (Ma and Schoonhoven, 1973 ... 

In conclusion, the distribution of NOS immunoreactivity and the pharmacological and physiological evidence analyzed and discussed here support the proposal that CB endogenous NO exerts a tonic inhibitory effect on CB chemoreception. Clearly, NO in low concentration is a broad inhibitory modulator of the chemoreception process in the CB. NO may modulate chemoreception by regulating the CB vascular tone, the oxygen delivery to the chemoreceptor cells, and the excitability of glomus cells and petrosal sensory neurons. 

Disproportionately more is known about O2 chemoreception in mammals despite the fact that they make up only about 10% of known vertebrate species. There seems to be a general phylogenetic trend with 02-sensitive chemoreceptors having a more diffuse, intemal/extemal distribution in lower vertebrates to the more localized interior receptor groups in aortic and carotid bodies of mammals This concentration of chemoreceptor loci follows the phylogenetic trend seen in the internalization and reduction of gill arches. 

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