The effects of azapirones on serotonin1A neurons of the dorsal raphe.

1. The effects of buspirone, gepirone, ipsapirone and tandospirone on spontaneously discharging serotonergic neurons of the dorsal raphe were determined under the same experimental conditions. 2. Buspirone, gepirone, ipsapirone and tandospirone were equally efficacious and acted in a dose-dependent manner to totally inhibit the spontaneous activity of serotonergic neurons. 3. Based on their effects six min after administration (i.p.), their ED50 values were: buspirone, 134 micrograms/kg; ipsapirone, 220 micrograms/kg; gepirone, 225 micrograms/kg; tandospirone, 198 micrograms/kg. 4. The similarity of these ED50 data suggest that they share a similar chemical structure that binds to the 5-HT1A receptor, most likely it is "N-C-C-C-C-N" aliphatic backbone. 5. Buspirone and tandospirone required 4 or more min to totally block the spontaneous activity, while gepirone and ipsapirone blocked it in 3 min. 6. The dose-response curves from buspirone and tandospirone demonstrated enough dissimilarity to the dose-response curves from gepirone and ipsapirone to suggest differences in their rates of absorption, and/or differences in the production of active and inactive metabolites.

The phylogenetic status of arthropods, as inferred from 18S rRNA sequences.

Partial 18S rRNA sequences of five chelicerate arthropods plus a crustacean, myriapod, insect, chordate, echinoderm, annelid, and platyhelminth were compared. The sequence data were used to infer phylogeny by using a maximum-parsimony method, an evolutionary-distance method, and the evolutionary-parsimony method. The phylogenetic inferences generated by maximum-parsimony and distance methods support both monophyly of the Arthropoda and monophyly of the Chelicerata within the Arthropoda. These results are congruent with phylogenies based on rigorous cladistic analyses of morphological characters. Results support the inclusion of the Arthropoda within a spiralian or protostome coelomate clade that is the sister group of a deuterostome clade, refuting the hypothesis that the arthropods represent the "primitive" sister group of a protostome coelomate clade. Bootstrap analyses and consideration of all trees within 1% of the length of the most parsimonious tree suggest that relationships between the nonchelicerate arthropods and relationships within the chelicerate clade cannot be reliably inferred with the partial 18S rRNA sequence data. With the evolutionary-parsimony method, support for monophyly of the Arthropoda is found in the majority of the combinations analyzed if the coelomates are used as "outgroups." Monophyly of the Chelicerata is supported in most combinations assessed. Our analyses also indicate that the evolutionary-parsimony method, like distance and parsimony, may be biased by taxa with long branches. We suggest that a previous study's inference of the Arthropoda as paraphyletic may be the result of (a) having two few arthropod taxa available for analysis and (b) including long-branched taxa.