SUMMATION AND INHIBITION FOLLOWING CONTRALATERAL STIMULATION OF THE TARSAL CHEMORECEPTORS OF THE BLOWFLY

¹ Department of Biology, The Johns Hopkins University, Baltimore 18, Md.

Acceptance thresholds of the tarsal chemoreceptors of the blowfly, Phormia regina, for sucrose and rejection thresholds for HCl, NaCl, and propanol have been determined. Comparisons were made of the thresholds of one-legged and two-legged flies. Comparisons were also made of rejection thresholds determined (a) on one leg exposed to a mixture of sucrose and unacceptable compound and (b) on two contralateral legs, one of which was exposed to sucrose alone and the other to an unacceptable compound alone, the exposure being simultaneous. The following results were obtained:

(1) The bilateral threshold for sucrose is lower than the unilateral threshold.

(2) For sucrose the decrease of bilateral over unilateral threshold is never greater than can be satisfactorily accounted for on a simple probability basis.

(3) Unacceptable compounds terminate the response to sucrose even when applied to the leg not receiving sucrose, i.e., they can act contralaterally as well as ipsilaterally.

(4) There is a greater rejection when two opposing stimuli act on one leg than when they stimulate two contralateral legs.

(5) Unacceptable compounds also "sum" contralaterally.

(6) Supplementation also occurs in the response of thirsty flies to water.

(7)The prevention of proboscis extension to water and sucrose by unacceptable compounds is predominantly a central phenomenon.

(8) Available evidence favors the interpretation that there are at least two distinct sets of receptors on the tarsi, sugar receptors and non-sugar receptors.