Contextual modulation of androgen effects on agonistic interactions.

Seasonal changes in steroid hormones are known to have a major impact on social behavior, but often are quite sensitive to environmental context. In the bi-directionally sex changing fish, Lythrypnus dalli, stable haremic groups exhibit baseline levels of interaction. Status instability follows immediately after male removal, causing transiently elevated agonistic interactions and increase in brain and systemic levels of a potent fish androgen, 11-ketotestosterone (KT). Coupling KT implants with a socially inhibitory environment for protogynous sex change induces rapid transition to male morphology, but no significant change in social behavior and status, which could result from systemically administered steroids not effectively penetrating into brain or other tissues. Here, we first determined the degree to which exogenously administered steroids affect the steroid load within tissues. Second, we examined whether coupling a social environment permissive to sex change would influence KT effects on agonistic behavior. We implanted cholesterol (Chol, control) or KT in the dominant individual (alpha) undergoing sex change (on d0) and determined the effects on behavior and the degree to which administered steroids altered the steroid load within tissues. During the period of social instability, there were rapid (within 2 h), but transient effects of KT on agonistic behavior in alphas, and secondary effects on betas. On d3 and d5, all KT, but no Chol, treated females had male typical genital papillae. Despite elevated brain and systemic KT 5 days after implant, overall rates of aggressive behavior remained unaffected. These data highlight the importance of social context in mediating complex hormone-behavior relationships.

Chloride channels in apical membrane patches of stellate cells of Malpighian tubules of Aedes aegypti.

Stellate cells of Aedes aegypti Malpighian tubules were investigated using patch-clamp methods to probe the route of transepithelial Cl(-) secretion. Two types of Cl(-) channel were identified in excised, inside-out apical membrane patches. The first Cl(-) channel, type I, had a conductance of 24 pS, an open probability of 0.816+/-0.067, an open time of 867+/-114 ms (mean +/- s.e.m., four patches) and the selectivity sequence I(-)>Cl(-)(much greater than) isethionate>gluconate. The I(-)/Cl(-)>>isethionate>gluconate. The I(-)Cl(-) permeability ratio was 1.48, corresponding to Eisenman sequence I. The type I Cl(-) channel was blocked by 2,2'-iminodibenzoic acid (DPC) and niflumic acid (2-[3-(trifluoromethyl)anilo]nicotinic acid). The removal of Ca(2+) from the Ringer's solution on the cytoplasmic side had no effect on channel activity. The second Cl(-) channel, type II, had a conductance of 8 pS, an open probability of 0.066+/-0.021 and an open time of 7.53+/-1.46 ms (mean +/- s.e.m., four patches). The high density and halide selectivity sequence of the type I Cl(-) channel is consistent with a role in transepithelial Cl(-) secretion under control conditions, but it remains to be determined whether these Cl(-) channels also mediate transepithelial Cl(-) secretion under diuretic conditions in the presence of leucokinin.