Non-linear dynamics of neurochemical modulation of mosquito oviduct and hindgut contractions.

Microphysiological techniques and computer-based methods of data acquisition and analysis were used to investigate the dynamics of neurochemical action on spontaneous contractions of continuously perfused oviducts and hindguts isolated from female mosquitoes (Aedes aegypti). Proctolin, leucomyosuppressin (LMS), serotonin and octopamine, which are known to modulate insect muscle contractions, and a mosquito neuropeptide, Aedes Head Peptide I (Aea-HP-I), which inhibits host-seeking behavior, were tested in the bioassays. LMS depressed contractile activity in oviducts at concentrations above 10(-12) mol l-1, but hindguts did not respond to concentrations below 10(-6) mol l-1. Hindgut contractions spontaneously restarted in 10(-6) mol l-1 LMS, but only washing out LMS restored activity in oviducts. LMS changed the amplitude of the oviduct contractions, but the dynamics of contraction remained steady. Following recovery of contractions in LMS, hindgut tissues contracted with a more regular pattern. Serotonin and octopamine had an identical action on oviduct and hindgut tissues. At concentrations greater than 10(-8) mol l-1, serotonin eliminated the refractory period between contractions and thus increased the contraction frequency of oviducts. Though the contractions appeared chaotic, state-series analysis proved that serotonin-treated oviducts contracted rhythmically. Above 10(-6) mol l-1, serotonin extinguished normal hindgut peristalsis and induced regular fluttering of the anteriormost portion of the hindgut, an effect possibly related to diuresis following the blood meal. Proctolin failed to stimulate both oviduct and hindgut contractions at concentrations up to 10(-6) mol l-1, but at 10(-8) mol l-1 induced contractions of cricket hindgut preparations. Aea-HP-I had no effect on either tissue at 10(-6) mol l-1 or lower concentrations. State-series analysis, based on simple manipulations of experimental data, permitted direct observation of the dynamics of oviduct and hindgut contractile activity.