Conformational Requirements of Acetylcholine Analogues and Local Anaesthetics

ATTEMPTS have been made to view the roles of acetylcholine and of cholinergic agonists as triggering permeability changes in excitable membranes through attachment to acetylcholine receptor biopolymers^1,2. Similarly, it has been proposed that local anaesthetics might block nerve conduction through attachment to axonal acetylcholine receptors^3,4. These considerations raise a number of questions. Are certain specific conformations essential for molecules related to acetylcholine either to “trigger” or to “block” depolarization of excitable membranes ? Are the conformations of such molecules identical in the crystal and in solution ? What are the rotational barriers to conformational alteration of such molecules ?     

Egg laying, maternal care and development of young in the scolopendromorph centipede, Cormocephalus anceps anceps Porat

The methods used to observe the construction of the brood chamber and rearing of the young by the female Cormocephalus anceps are described. The period of egg laying and the maternal care, essential for the survival of both eggs and brood, were observed and the behaviour of the female during this time is recorded. Two broods were successfully reared to first year adolescent stages in the laboratory. The two embryonic and three adolescent stages are briefly described and their developmental times recorded. Subsequent stages of development are noted by increase in size until sexual maturity is attained in the second year. The length of life and number of broods per female remains to be investigated.     

Ontogeny of Glucocorticoid Binding in Rodent Brain

Neonatal treatment with corticosterone can differentially andpersistently reduce either the basal level of plasma corticosteroneor the amplitude of the adult diurnal rhythm in the rat dependingon the age at which exposure to the steroid occurs. This alterationof basal secretion by hormonal manipulation during the firstpostnatal week may be related to the high levels of corticosteronefound in pituitary cell nuclei following exposure of the immaturerat to exogenous corticoid. The ontogenetic course of cytosolbinding in the pituitary suggests a mechanism by which suchvulnerability may occur. The hypothalamus was the only brain region found to have a constantlevel of cell nuclear binding throughout development, althoughit closely resembles the brain as a whole with regard to thedevelopment of cytosol binding sites. The significant postnatalneurogenesis of the hippocampus is reflected in a large postnatalrise in both cytosol and nuclear binding of corticosterone.This increase would appear to be due in part to a delay in bindingcompetence by the pyramidal and granule cells of the hippocampus.The autoradiographic evidence indicates that in the immaturerat the retention of steroid by hippocampal pyramidal cellscorrelates directly with the embryonic age of the neuron. Likewise,the oldest granule cells are the most heavily labelled granulecells in the dentate gyrus, while newly arrived cells do notconcentrate corticosterone. This would suggest that an eventin cellular differentiation occurs sometime after the cellsare "in position," which permits the binding of glucocorticoidsby these hippocampal neurons.     

In Vivo Incorporation of a Polyunsaturated Fatty Acid into the sn-C-1 and sn-C-2 Positions of Tetrahymena Glycerophospholipids1

The glycerophospholipids of the protozoon Tetrahymena pyriformis W are unique in that the polyunsaturated fatty acid γ-linolenate (18:3Δ^6,9,12) is a major component of both the sn-C-1 and sn-C-2 positions. Tetrahymena were incubated with [1-¹⁴C]γ-linolenate. The positional distribution of the radiolabeled fatty acid in the three major glycerophospholipids was determined. [1-¹⁴C]γ-linolenate was found at both carbons of the three lipids, in general agreement with the mass distribution of γ-linolenate, except for markedly greater labeling at the sn-C-2 position of phosphatidylcholine. We hypothesize that an acyltransferase exists in Tetrahymena that can esterify γ-linolenate at both carbons during glycerophospholipid biosynthesis.     

Cytology of two species of winged bean, Psophocarpus tetragonolobus (L.) DC. and P. scandens (Endl.) Verde. (Leguminosae)

Karyotype morphology of Psophocarpus tetragonolobus and P. scandens is described and the behaviour of chromosomes at meiosis discussed. Both species have a chromosome number of 2n = 18 and similar karyotypes of a sort unusual within the Phaseolinae. Differences between the species in detailed morphology of the chromosomes agree with data from external morphology, palynology and crossability in indicating that P. scandens cannot be the immediate wild ancestor of domesticated P. tetragonolobus . Study of meiotic chromosomes and analysis of qualitative and quantitative variation in Papua New Guinean P. tetragonolobus suggest that there are few restrictions to recombination other than those imposed by predominant self-pollination, The bearing of these data on the taxonomic relationships of Psophocarpus and on chromosomal evolution within the Phaseolinae is discussed.     

Insights on Species Richness and Turnover from Long-Term Ecological Research: Fishes in North Temperate Lakes

SYNOPSIS. We examined eleven years of annual survey data onfish assemblages in seven lakes. Expectations based on biogeographicliterature were that, owing to the isolation of lakes, fishspecies structure should be relatively stable and species turnoverlow. Our original objective was to determine whether lakes houserelatively stable fish assemblages or ones with high rates ofspecies turnover. Methodological issues became apparent thatcaused us to consider issues of rare species and sample sufficiency.Ourdata were from samples rather than complete counts and rarespecies could have been missed. In our results mean annual richnesswas considerably lower than cumulative richness. In addition,species turnover was overestimated and decreased exponentiallyas the number of yearsbetween observation increased. Samplingvariability might explain these results; however, given thesame number of survey years, cumulative richness increased withthe number of years between observations. Apparently extinctionsand invasions occurred even within eleven years, but uncertaintyremains because rare taxa can be missed and their appearancesand disappearances in the record influence estimates of richnessand turnover. To compensate for this problem we removed raretaxa and corrected turnover rates by removing an estimate ofsampling error (the turnover rate between adjacent years). Evenusing these conservative approaches, estimates of turnover amonglakes ranged from 0.36% to 0.50% per year. Because the thresholdfor species detection by most sampling regimes is greater thanzero, survey data are expected to underestimate species richnessand overestimate species turnover even with standardized methods.Conservation biologists should evaluate claims of decline inspecies richness against such considerations     

Evidence for parasitoid‐induced premature mortality in the Argentine stem weevil

The Argentine stem weevil Listronotus bonariensis Kuschel (Coleoptera: Curculionidae) is an exotic pest of New Zealand ryegrass and the adult‐stage is parasitized by the introduced solitary endoparasitoid Microctonus hyperodae Loan (Hymenoptera: Braconidae: Euphorinae). This biological control agent is effective, although, under both laboratory and field conditions, an unexplained source of premature mortality in the weevils is observed after exposure to M. hyperodae. This premature mortality may be affected to varying degrees by the length of time of parasitoid exposure, the physiological conditions of the host, and the host to parasitoid ratios, although it occurs naturally without any physical interruption to the parasitoid ovipositional process. In the present study, the premature mortality reported in earlier studies is confirmed and it is conjectured to be the result of injection of parasitoid venom without an egg. Moreover, the lack of premature mortality resulting from longer exposure periods indicates that there might be a curative effect resulting from subsequent oviposition; the egg reverses the toxic effect induced by the injection of venom only. As discussed, this phenomenon may not be restricted to the L. bonariensis/M. hyperodae system and, accordingly, there are evolutionary, biosecurity and general pest management questions to be considered.     

Additive effects of predator diversity on pest control caused by few interactions among predator species

1. Studies of the impact of predator diversity on biological pest control have shown idiosyncratic results. This is often assumed to be as a result of differences among systems in the importance of predator–predator interactions such as facilitation and intraguild predation. The frequency of such interactions may be altered by prey availability and structural complexity. A direct assessment of interactions among predators is needed for a better understanding of the mechanisms affecting prey abundance by complex predator communities. 2. In a field cage experiment, the effect of increased predator diversity (single species vs. three‐species assemblage) and the presence of weeds (providing structural complexity) on the biological control of cereal aphids were tested and the mechanisms involved were investigated using molecular gut content analysis. 3. The impact of the three‐predator species assemblages of aphid populations was found to be similar to those of the single‐predator species treatments, and the presence or absence of weeds did not alter the patterns observed. This suggests that both predator facilitation and intraguild predation were absent or weak in this system, or that these interactions had counteracting effects on prey suppression. Molecular gut content analysis of predators provided little evidence for the latter hypothesis: predator facilitation was not detected and intraguild predation occurred at a low frequency. 4. The present study suggests additive effects of predators and, therefore, that predator diversity per se neither strengthens nor weakens the biological control of aphids in this system.