Differentiated Response to Sugars among Labellar Chemosensilla in Drosophila

Abstract

Recent findings have indicated that the Gr genes for putative gustatory receptors of Drosophila melanogaster are expressed in a spatially restricted pattern among chemosensilla on the labellum. However, evidence for a functional segregation among the chemosensilla is lacking. In this work, labellar chemosensilla were classified and numbered into three groups, L-, I- and S-type, based on their morphology. Electrophysiological responses to sugars and salt were recorded from all the accessible labellar chemosensilla by the tip-recording method. All the L-type sensilla gave good responses to sugars in terms of action potential firing rates, while the probability for successful recordings from the I-type and S-type sensilla was lower. No differences were found in the responses to sugars between chemosensilla belonging to the same type; however, dose-response curves for several different sugars varied among the sensilla types. The L-type sensilla gave the highest frequency of nerve responses to all the sugars. The I-type sensilla also responded to all the sugars but with a lower magnitude of firing rate than the L-type sensilla. The S-type sensilla gave a good response to sucrose, and lower responses to the other sugars. These results suggest that there might be variations in the expression level or pattern of multiple receptors for sugars among the three types of chemosensilla. The expression pattern of six Gr genes was examined using the Gal4/UAS-GFP system, and sensilla were identified according to the innervation pattern of each GFP-expressing taste cell. None of the spatial expression patterns of the six Gr genes corresponded to the sugar sensitivity differences we observed.

A Drosophila gustatory receptor required for the responses to sucrose, glucose, and maltose identified by mRNA tagging

“…Autospike 3.1 software (Syntech) was used to acquire the action potentials (9.6-kHz sampling rate) and to analyze the frequencies. For most sugars we used 100 mM, which is the concentration typically used in previous analyses (28,35). We used 50 mM sucrose because this sugar induced a much higher frequency of action potentials than other sugars.…”

“…4A). In Drosophila, sugar-induced action potentials can be detected in the GRNs in L, I, or S type bristles, although the highest frequencies and rates of response occur in L type sensilla (35). Therefore, we applied sugars to L type bristles and compared the frequencies of action potentials in wild type and in the Gr64 ab mutant.…”

A microfluidics-based method for measuring neuronal activity in Drosophila chemosensory neurons

“…The fruit fly Drosophila melanogaster is widely used as a genetic model organism to uncover basic mechanisms of taste coding and odor perception [1][2][3][4][5][6][7] . Recent insights into the molecular and functional mechanisms of sensory perception in Drosophila have been achieved by the use of single-sensillum recordings of adult taste or olfactory sensilla 1,4,[8][9][10][11][12][13] . This method enables sensitive measurements of action potential patterns and shows whether responses are excitatory or inhibitory, but drawing final conclusions about the individual firing neuron is difficult, as each sensillum contains two to four neurons 14 .…”

Electrophysiological Recording From <em>Drosophila</em> Labellar Taste Sensilla

“…On the labellum, the number and location of sensilla is stereotyped. There are three morphological classes of sensilla based on length: the long (L), intermediate (I), and short (S) sensilla 7,8 . Each sensillum contains either two (I-type) or four (L-and S-type) gustatory receptor neurons (GRNs) 9 .…”

“…Each sensillum contains either two (I-type) or four (L-and S-type) gustatory receptor neurons (GRNs) 9 . Different GRNs respond to different categories of taste stimuli: bitter, sugar, salt and osmolarity 7,10 and express different subsets of gustatory receptors 8,[11][12][13] . Only I and S-type sensilla contain bitter-responsive GRNs 8,10 .…”