University of Alberta, Edmonton - May 2 - 6, 2006

M FOLEY¹, R GARY CHIANG^1,2, MJ O’DONNELL^1
1Department of Biology, McMaster University, Hamilton, ON and ²Department of Biology, Redeemer University College, Ancaster, ON

Serotonin reduces the rate of ongoing electrical activity recorded extracellularly from axons of neurosecretory cells associated with the hypocerebral ganglion in the blood-feeding insect, Rhodnius prolixus.

Electrical activity of axons and terminals of neurosecretory cells (NSC’s) can be recorded extracellularly from the cephalic aorta of Rhodnius.   Cell bodies of many of these NSC’s are located in the hypocerebral ganglion (HG), a structure associated with the retrocerebral complex.   The HG is involved in feeding, which accounts for its nervous connections to the salivary glands, but the physiological role of its neurosecretions in the aorta is unclear.   The purpose of this study was to document whether NSC’s associated with the cephalic aorta respond to serotonin, a substance known to be released in Rhodnius at the time of feeding.   When exposed to concentrations of 10-6 M serotonin or less, we found that discharge rate was reduced.   Rate increased after serotonin was removed, but did not return to initial levels.   This finding suggests that the act of feeding may lead to a reduction in neurosecretion released by the HG.   The physiological significance of these findings will be discussed.

R TORY & R GARY CHIANG
Department of Biology, Redeemer University College, Ancaster, ON

The differential effect of minimal doses of juvenile hormone III on the development of the male and female climbing apparatus in blood-feeding insect, Rhodnius prolixus.

The ability of adult Rhodnius to climb smooth surfaces is due to the presence on the first two pairs of legs of a small “fleshy pad” situated at the end of the tibia.   These pads are absent in nymphs, and we have previously shown that the formation of these pads is highly sensitive to JHIII applied topically to L5 animals on day 1 after feeding.   The present work has verified this earlier finding showing that JHIII affected development of these pads in concentrations as low as 0.4 µg/animal.   We have also shown that at the same concentration of JHIII from 0.4 to 1.0 µg/animal, the male pads are not as reduced in size as those of the female. Being less sensitive to JH suggests that the male climbing apparatus may play a more essential role than that of the female.   This role may be associated with the male’s ability to copulate.