Changes in spontaneous spike activities recorded from murine frontal cortex networks grown on substrate-integrated microelectrodes were used to determine the dissociation constant (KB) of three GABAA antagonists. Neuronal networks were treated with fixed concentrations of GABAA antagonists and titrated with muscimol, a GABAA receptor agonist. Muscimol decreased spike activity in a concentration dependent manner with full efficacy (100% spike inhibition) and a 50% inhibitory concentration (IC50) of 0.14 ± 0.05 µM (mean ± SD, n=6). At 10, 20, 40 and 80 µM bicuculline, the muscimol IC50 values were shifted to 4.3 ± 1.8 µM (n=6), 6.8 ± 1.7 µM (n=6), 19.3 ± 3.54 µM (n=10) and 43.5 µM (n=2), respectively (mean ± SD). Muscimol titration in the presence of 10, 20, 40 µM of gabazine resulted in IC50s values of 20.1 (n=2), 37.17 (n=4), and 120.45 (n=2), respectively. In the presence of 20, 80, and 160 µM of TMPP (trimethylolpropane phosphate) the IC50s were 0.86 (n=2), 3.07 (n=3), 6.67 (n=2) µM, respectively. Increasing concentrations of GABAA antagonists shifted agonist log concentration-response curves to the right with identical efficacies, indicating direct competition for the GABAA receptor. A Schild plot analysis with linear regression resulted in slopes of 1.18 ± 0.18, 1.29 …

Taxonomic composition and spatio-temporal variability of macroinvertebrates inhabiting snags were examined from an 8-km segment of the Elm Fork of the Trinity River. Seventy-seven macroinvertebrate taxa were collected from submerged wood during the study. Assemblages were highly variable spatially and temporally, especially among seasons. An ordination of species and environment did not find snag taxa to have striking correlations with many of the selected environmental variables, although there were some trends in flow-mediated species distributions. There were significant seasonal differences in the abundances of some taxa, particularly among the Chironomidae (Diptera). The Tribe Orthocladiini was numerically abundant during the winter, while the Tribes Chironomini and Tanytarsini dominated the summer and autumn. Additionally, this study included a secondary production and microdistribution analysis of a population of the caddisfly Cyrnellus fraternus. Distributions of C. fraternus were restricted to snags, the most stable substratum for retreat building and for resisting periodic high waters. Larvae were not found in the soft sand and mud benthic habitats near submerged wood. The insects were multivoltine with a minimum of three generations per year. Pupae were collected July through September and adults emerged from May through October. The population overwintered as larvae. Estimated annual production was 1,015.4 …