Sugar response differences related to sensillum type and location on the labella of Protophormia terraenovae: a contribution to spatial representation of the stimulus.

The chemoreceptor spike activity in response to sucrose in the concentration range 1-500mM was recorded from each of the 11 Intermediate and 13 Large labellar sensilla in the blowfly Protophormia terraenovae. The results showed that: (1) three of the four cells present in each sensillum are activated by sucrose stimulation; (2) differences between the Large and Intermediate types exist in the dose-response profiles of one of these cells (the 'water' cell), possibly reflecting different sugar receptor site populations on the dendritic membranes of homologous cells in the two types; (3) sensilla of both types are differentially responsive to sucrose solutions according to their location on the labellum. These differences may provide elements for a spatial representation of the stimulus source within the sensory coding process.