Chemosensory activity

Zapata P. Chemosensory activity in the carotid nerve effects of pharmacological agents. In Gonzalez C, ed. The Carotid Body Chemoreceptors. New "Vork Springer Austin Landes, 1997 119-146. 

Zuazo A, Zapata P. Effects of 6-hydroxy-dopamine on carotid body chemosensory activity. Neurosci Lett 1978 9 323-328. 

When we studied the effects of SNP on carotid chemosensory responses to excitatory and inhibitory stimuh in paralyzed and artificially ventilated cats (15), we found that SNP increased basal chemosensory discharges. This result was completely unexpected, since NO donors reduced or had no effect on basal chemoreceptor activity in the cat CB superfused or perfused in vitro (3-6,16). A major difference between CB preparations in situ and in vitro is the presence of large amounts of endothehum and vascular smooth muscle tissue in situ. Since endothehum and smooth muscle cells are required to activate SNP for releasing NO (27), it is likely that large amounts of NO released from SNP in situ may account for the increased chemosensory activity. 

Chugh DK, Katayama M, Mokashi A, Dehout DE, Ray DK, Lahiri S. Nitric oxide-related inhihition of carotid chemosensory activity in the cat. Respir Physiol 1994 97 147-152. 

Heme oxygenase 1 and 2 (HO-1 and HO-2) catalyze the formation of CO and molecular oxygen is required for CO synthesis (67). HO-2 is constitutively expressed in type 1 cells and inhibition of HO-2 by zinc protoporphyrin-9 augments the sensory activity of the carotid body (67). These observations indicate that type I cells of the carotid bodies are capable of producing CO and that CO is inhibitory to the carotid body activity. Consistent with this notion is the findings of Lahiri and Acker (44), who reported that low doses of CO inhibit chemosensory activity of the isolated rat carotid bodies. Future studies may provide insight as to the role of CO in the carotid body function. 

Rimold M, Chemiack NS, Prabhakar NR. Effect of adenosine on chemosensory activity of the cat carotid body. Respir Physiol 1990 80 299-306. 

Ituniaga R, Larrain C, Zapata P. Effects of dopaminergic blockade upon carotid chemosensory activity and its hypoxia-induced excitation. Brain Res 1994 663 145-154. 

Natural stimuli of the carotid body (low PO2, acidification) have no effect on PG neurons, but stimuli-related responses can be recorded only in cocultures of carotid body and PG cells. The reconstitution of synaptic contacts between carotid body cells and PG neurons appears to be necessary for the generation of chemosensory activity. 

Taste-active chemicals react with receptors on the surface of sensory cells in the papillae causing electrical depolarization, ie, drop in the voltage across the sensory cell membrane. The collection of biochemical events that are involved in this process is called transduction (15,16). Not all the chemical steps involved in transduction are known however, it is clear that different transduction mechanisms are involved in different taste quaUties different transduction mechanisms exist for the same chemical in different species (15). Thus the specificity of chemosensory processes, ie, taste and smell, to different chemicals is caused by differences in the sensory cell membrane, the transduction mechanisms, and the central nervous system (14). 

Later in intra-uterine life, the human infant is susceptible to early chemical prompting, but again the affector route is not known with certainty. Neonatal discrimination in favour of familiar (maternal) amniotic fluid is demonstrable, suggesting that the foetus already has active chemosensory capacities (Schaal, 1998). Smell and taste are operative in the near full-term foetus since it shows detection of about 120 mg/day maternal intake of anethole (as anise condiments) within a few days before parturition this exposure induced subsequent preferential responses by babies to anethole (Schaal et ai, 2000). The human neonate is not likely to have its organ as a fully functioning chemosensor,... 

In support of this contention, the carrier protein Aphrodisin makes an early appearance in vaginal secretions. In pre-pubertal hamsters, it thus indicates chemosensory preparation for the onset of female maturity (Magert, 1999). The proven ability of the AOS to modulate the CNS-pituitary-gonadal axis by advancing or retarding endocrine activity (Chap. 5), underlines its role as primarily the chemosensor of the reproductive system. The adaptive consequence of responses, which allows an avoidance of premature breeding, or of a postponement of puberty, would seem to be advantageous. 

The heterogeneity of the VN primary neurones is reflected in their modes of chemosensory preferences. The relative binding efficiencies for distinct odourant types onto the membrane sites is indeed functionally partitioned. When urinary fractions from male mice were applied to VN cells of females, stimulation by a lipophilic and volatile odourant fraction activated only the Gi protein-expressing cells. In contrast, Go activation was elicited by one of the lipocalin superfamily the MUP fraction containing an a-2-globulin (Krieger, 1999). This observation... 

Dudley C.A. and Moss R.L. (1999). Activation of an anatomically distinct subpopulation of accessory olfactory bulb neurons by chemosensory stimulation. Neuroscience 91, 1549-1556. 

A review of their biological activity. Phycologia 42 332-350 Weissburg MJ (2000) The fluid dynamical context of chemosensory behavior. Biol Bull 198 188-202... 

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