Gustatory receptors

It is interesting that the stimulus compounds used in the study differ widely in their molecular structures, and yet they all interact with antibodies to thaumatin. It is, therefore, probable that a single receptor-structure responds to all sweet stimuli,there being a variation in the relative effectiveness of sweet stimuli across individual nerve-fibers, and the characteristics of all receptor sites do not appear to be identical. Earlier elec-trophysiological studies of single primary, afferent taste-neurons uniformly agreed that individual fibers very often have multiple sensitivities, and that individual, gustatory receptors are part of the receptive field of more than one afferent fiber. " We have yet to learn how these interact, and the nature of their excitatory, or possible inhibitory, relations, or both. 

Recent studies performed using this method have shown that flavanol bitterness decreases from monomer to trimer. Epicatechin was perceived more bitter than catechin and the C4-C6-linked catechin dimer more bitter than other procyanidin dimers with C4-C6 linkages. This may be due to the higher lipophilic character of these molecules facilitating their diffusion to the gustatory receptor. Bitterness of procyanidin fractions in 5% ethanol decreased with their... 

Lepidopterous larvae bear on their mouthparts two pair of styloconic sensilla (see Figure 1). The papilla of each sensillum possesses one terminal pore which gives entrance to the dendritic regions of four gustatory receptor cells. Besides, a fifth cell in each sensillum acts as a mechanoreceptor in detecting positional changes of the papilla (7, ) ... 

Table I. Response spectra of gustatory receptor cells in Pieris brassicae larvae (7,8).

In biting their food and by means of a relatively small number of gustatory receptor cells, the larvae are informed about the composition of nutrients and secondary plant substances. Taste perception, the integration of sensory information in the insect s central nervous system, is not merely a process of summation. Synergistic as well as antagonistic effects between individual compounds can be observed in the food uptake of larvae on artificial diets. 

Different insect species posses different gustatory receptor cells, their response spectra being adapted to the perception of chemical components distributed in their host plant species (9 ). Taste perception in P. brassicae larvae forms a representative example for phytophagous insects, which are able to discriminate a number of compounds like sugars, amino acids, salts, and secondary plant substances acting as feeding inhibitors or feeding incitants (3,6,, 10). 

Drosophila gustatory receptor (GR) genes a gene family that subserves both gustatory and olfactory modalities... 

TM, seven transmembrane domain DOR, Drosophila odorant receptor EAG, electroantennogram GFP, green fluorescent protein GPCR, G-protein coupled receptor GR, gustatory receptor nsyb, neuronal synaptobrevin OR, odorant receptor OSN, olfactory sensory neuron PCR, polymerase chain reaction PN, projection neuron RT-PCR, reverse transcription-polymerase chain reaction SOG, subesophageal ganglion. 

Ueno K., Ohta M., Morita EL, Mikuni Y., Nakajima S., Yamamoto K. and Isono K. (2001) Trehalose sensitivity in Drosophila correlates with mutations in and expression of the gustatory receptor gene Gr5a. Curr. Biol. 11, 1451-1455. 

The influence of the rheology of a particular food material on the perception of its taste or flavor can have two main origins. A physiological effect due to the proximity of the taste and olfactory receptors to the kinesthetic and thermal receptors in the mouth, since then an alteration of the physical state of the material may have an influence on its sensory perception, and an effect related to the bulk properties of the material (e.g., texture, viscosity), since the physical properties of the material may affect the rate and the extent with which the sensory stimulus reaches the gustatory receptors. 

At present, the functional architecture of gustatory receptor gene expression, in particular for sweet and bitter, is being unravelled however, the functional configuration of these receptors as monomer, dimers or oligomers is not clear, and neither are their downstream intracellular signalling cascades, the transmitter used by their host sensory neurons and the precise connectivity of these cells to second-order intemeurons. 

Inoshita T, Tanimura T (2006) Cellular identification of water gustatory receptor neurons and their central projection pattern in Drosophila. Proc Natl Acad Sci USA 103 1094-1099 Ishimoto H, Tanimura T (2004) Molecular neurophysiology of taste in Drosophila. Cell Mol Life Sci 61 10-18... 

Jiao Y, Moon SJ, Montell C (2007) A Drosophila gustatory receptor required for the responses to sucrose glucose and maltose identified by mRNA tagging. Proc Natl Acad Sci USA 104 14110-14115... 

Taste begins with transduction events in receptor cells of the taste buds. There has been a lot of recent progress in our understanding of gustatory receptor mechanisms and transduction. The challenge is to relate molecular mechanisms that are evident at the receptor level to the extensive literature on gustatory neurophysiology and taste-mediated behavior. 

Travers SP, Norgren R. 1991. Coding the sweet taste in the nucleus of the solitary tract Differential roles for anterior tongue and nasoincisor duct gustatory receptors in the rat. J Neurophysiol 65 1372-1380. 

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