Intraventricular 5,7-Dihydroxytryptamine Increases Thyrotropin-Releasing Hormone Content in Regions of Rat Brain

Rats received intraventricular (i.v.t.) injections of 5,7-dihydroxytryptamine (5,7-DHT) (100-600 micrograms). Some animals also received intraperitoneal injections of the 5-hydroxytryptamine uptake blocker fluoxetine (FX) (20 mg/kg) or the norepinephrine uptake blocker desmethylimipramine (DMI) (48 mg/kg) 30-90 min prior to i.v.t. 5,7-DHT. Rats were killed between 2 and 35 days following i.v.t. 5,7-DHT, brains were dissected, and regions were assayed for thyrotropin-releasing hormone (TRH) by radioimmunoassay. Dose-dependent increases in TRH content following i.v.t. 5,7-DHT were noted in the brainstem and hippocampus. DMI pretreatment blocked the increase in hippocampal TRH, but not in brainstem TRH. FX pretreatment was ineffective in blocking any increases in TRH content. These results suggest differential regulation of regional TRH content by interactions with specific neurotransmitter systems.     

THE POPCORN WOLBACHIA INFECTION OF DROSOPHILA MELANOGASTER: CAN SELECTION ALTER WOLBACHIA LONGEVITY EFFECTS?

Wolbachia popcorn ( w MelPop), a life-shortening strain of Wolbachia, has been proposed as an agent for suppressing transmission of dengue fever following infection of the vectoring mosquito Aedes aegypti . However, evolutionary changes in the host and Wolbachia genomes might attenuate any life span effects mediated by w MelPop. Here we test for attenuation by selecting strains of Drosophila melanogaster infected with w MelPop for early and late reproduction in three independent outcrossed populations. Selection caused divergence among the lines in longevity. This divergence was mostly associated with the host genetic background rather than the Wolbachia infection, although there were also interactions between the host and Wolbachia genomes. Development time, viability, and productivity were not altered by selection. The implications of these results are discussed in light of the intended use of w MelPop for suppressing disease transmission.     

Archaeal diversity and a gene for ammonia oxidation are coupled to oceanic circulation

Evidence of microbial zonation in the open ocean is rapidly accumulating, but while the distribution of communities is often described according to depth, the other physical factors structuring microbial diversity and function remain poorly understood. Here we identify three different water masses in the North Water (eastern Canadian Arctic), defined by distinct temperature and salinity characteristics, and show that they contained distinct archaeal communities. Moreover, we found that one of the water masses contained an increased abundance of the archaeal alpha-subunit of the ammonia monooxygenase gene ( amoA ) and accounted for 70% of the amoA gene detected overall. This indicates likely differences in putative biogeochemical capacities among different water masses. The ensemble of our results strongly suggest that the widely accepted view of depth stratification did not explain microbial diversity, but rather that parent water masses provide the framework for predicting communities and potential microbial function in an Arctic marine system. Our results emphasize that microbial distributions are strongly influenced by oceanic circulation, implying that shifting currents and water mass boundaries resulting from climate change may well impact patterns of microbial diversity by displacing whole biomes from their historic distributions. This relocation could have the potential to establish a substantially different geography of microbial-driven biogeochemical processes and associated oceanic production.     

Low-nutrient induction of abnormal chlamydial development: A novel component of chlamydial pathogenesis?

Abstract The intracellular development of chlamydiae in McCoy cells incubated in Eagle's minimal essential medium lacking all 13 amino acids was examined both by fluorescence and electron microscopy and by infectivity titration. Aberrant development occurred in almost all inclusions of strains of Chlamydia trachomatis and C. psittaci with the production of abnormal forms which differed in size, shape and internal structure from normal reticulate and elementary body forms. Detailed analysis of the response of C. trachomatis L2 strain 434 to graded reductions in amino acid level showed that infectivity was reduced and morphological abnormality increased as amino acid concentrations were lowered from 33 to 0% of amino acids present in minimal essential medium. Reversion of inclusions to normal and reappearance of infectious forms occured on restoration of amino acids and further incubation. It is suggested that aberrant development may account for the presence in vivo of non-cultivable chlamydiae and that such development can arise via tryptophan deprivation mediated by local release of interferon gamma.     

Parasite species richness in carnivores: effects of host body mass, latitude, geographical range and population density

Aim  Comparative studies have revealed strong links between ecological factors and the number of parasite species harboured by different hosts, but studies of different taxonomic host groups have produced inconsistent results. As a step towards understanding the general patterns of parasite species richness, we present results from a new comprehensive data base of over 7000 host–parasite combinations representing 146 species of carnivores (Mammalia: Carnivora) and 980 species of parasites.
Methods  We used both phylogenetic and non-phylogenetic comparative methods while controlling for unequal sampling effort within a multivariate framework to ascertain the main determinants of parasite species richness in carnivores.
Results  We found that body mass, population density, geographical range size and distance from the equator are correlated with overall parasite species richness in fissiped carnivores. When parasites are classified by transmission mode, body mass and home range area are the main determinants of the richness of parasites spread by close contact between hosts, and population density, geographical range size and distance from the equator account for the diversity of parasites that are not dependent on close contact. For generalist parasites, population density, geographical range size and latitude are the primary predictors of parasite species richness. We found no significant ecological correlates for the richness of specialist or vector-borne parasites.
Main conclusions  Although we found that parasite species richness increases instead of decreases with distance from the equator, other comparative patterns in carnivores support previous findings in primates, suggesting that similar ecological factors operate in both these independent evolutionary lineages.     

Opening the Social Gateway: Early Vocal and Social Sensitivities in Brown-Headed Cowbirds (Molothrus ater)

The organization of cowbird ( Molothrus ater ) social groups affords individuals living in the groups different opportunities for learning and also structures trajectories of social development. Here, we studied the influence of adults on social organization of very young cowbirds. In three experiments, we housed juvenile birds in large, seminatural environments that either contained or did not contain adult conspecifics. We then observed the social associations and vocalizations of juveniles in each environment. The presence of adults in the social environment influenced the assortment and singing patterns of juveniles, although throughout the three experiments adults rarely interacted physically with juveniles. Juveniles housed with adults interacted with other juveniles more often and sang significantly less often than juveniles housed without adults. Effects of adult presence or absence on social organization and singing patterns emerged extremely rapidly and could be reversed quickly. Taken as a whole, the experiments revealed that very young cowbirds, in the first days of independence from their hosts, were sensitive to, and reacted rapidly to, the composition of their social environment. Specifically, presence of other age classes of individuals within the group increased juvenile associations and delayed production of vocalizations by juvenile males. Self-organization within the social group produced different social environments, which could in turn create different gateways for social learning and vocal development.