Altered baroreflex responses in alpha7 deficient mice.

The autonomic nervous system controls and coordinates several cardiovascular functions, including heart rate, arterial pressure, blood flow and vasomotor tone. Neuronal nicotinic acetylcholine receptors (nAChRs) are the interface between the nervous system and the cardiovascular system, but it is not known which nAChR subtypes regulate autonomic function in vivo. Nicotinic AChRs containing the alpha7 subunit are a candidate subtype in autonomic ganglia. Stimulation of these nAChRs can increase neurotransmitter release via presynaptic mechanisms, as well as mediate fast synaptic transmission via postsynaptic mechanisms. To investigate the role of the alpha7 nAChR subunit in cardiac autonomic function, we measured baroreflex-mediated responses in alpha7 null mice. Here we show that the alpha7 null mice have impaired sympathetic responses to vasodilatation, as sodium nitroprusside infusion triggered a 48% heart rate increase in wild type mice but only a 21% increase in the alpha7 nulls (P < 0.001). The mutant mice developed supersensitivity to adrenergic agonists, although norepinephrine release from sympathetic nerve terminals could be elicited through mechanisms alternative to nAChR stimulation. Baroreflex-mediated parasympathetic responses were normal in alpha7 null mice. The decreased baroreflex-mediated tachycardia in alpha7 mutant mice indicates that alpha7-containing nAChRs participate in the autonomic reflex that maintains blood pressure homeostasis. The alpha7 mutant mice may serve as a model of baroreflex impairment arising from autonomic dysfunction.

A molecular evolutionary framework for the phylum Nematoda.

Nematodes are important: parasitic nematodes threaten the health of plants, animals and humans on a global scale; interstitial nematodes pervade sediment and soil ecosystems in overwhelming numbers; and Caenorhabditis elegans is a favourite experimental model system. A lack of clearly homologous characters and the absence of an informative fossil record have prevented us from deriving a consistent evolutionary framework for the phylum. Here we present a phylogenetic analysis, using 53 small subunit ribosomal DNA sequences from a wide range of nematodes. With this analysis, we can compare animal-parasitic, plant-parasitic and free-living taxa using a common measurement. Our results indicate that convergent morphological evolution may be extensive and that present higher-level classification of the Nematoda will need revision. We identify five major clades within the phylum, all of which include parasitic species. We suggest that animal parasitism arose independently at least four times, and plant parasitism three times. We clarify the relationship of C. elegans to major parasitic groups; this will allow more effective exploitation of our genetic and biological knowledge of this model species.

18S rRNA suggests that Entoprocta are protostomes, unrelated to Ectoprocta.

The Ento- and Ectoprocta are sometimes placed together in the Bryozoa, which have variously been regarded as proto- or deuterostomes. However, Entoprocta have also been allied to the pseudocoelomates, while Ectoprocta are often united with the Brachiopoda and Phoronida in the (super)phylum Lophophorata. Hence, the phylogenetic relationships of these taxa are still much debated. We determined complete 18S rRNA sequences of two entoprocts, an ectoproct, an inarticulate brachiopod, a phoronid, two annelids, and a platyhelminth. Phylogenetic analyses of these data show that (1) entoprocts and lophophorates have spiralian, protostomous affinities, (2) Ento- and Ectoprocta are not sister taxa, (3) phoronids and brachiopods form a monophyletic clade, and (4) neither Ectoprocta or Annelida appear to be monophyletic. Both deuterostomous and pseudocoelomate features may have arisen at least two times in evolutionary history. These results advocate a Spiralia-Radialia-based classification rather than one based on the Protostomia-Deuterostomia concept.

18S rRNA data indicate that Aschelminthes are polyphyletic in origin and consist of at least three distinct clades.

The Aschelminthes is a collection of at least eight animal phyla, historically grouped together because the absence of a true body cavity was perceived as a pseudocoelom. Analyses of 18S rRNA sequences from six Aschelminth phyla (including four previously unpublished sequences) support polyphyly for the Aschelminthes. At least three distinct groups of Aschelminthes were detected: the Priapulida among the protostomes, the Rotifera-Acanthocephala as a sister group to the protostomes, and the Nematoda as a basal group to the triploblastic Eumetazoa.