The influence of stomach distention on feeding in the nudibranch mollusk Melibe leonina

Although research on satiation has revealed much about the effect of sensory inputs on motivational state, we have yet to fully understand exactly how satiating signals influence the neural circuits underlying specific behaviors. One organism that is well suited for addressing this question is the nudibranch Melibe leonina, because its feeding activity is easily quantified, it has translucent skin that makes the stomach easy to observe, and it has large, identifiable neurons that are very suitable for subsequent analysis of the neural correlates of satiation. In this study our goal was to document the time course of satiation in Melibe, and determine if stomach distention contributes to satiation. When exposed to brine shrimp (Artemia), Melibe immediately commenced stereotypic oral hood movements to capture prey, and continued to do so for approximately five hours. Individuals eventually stopped, despite the continued presence of food, and the slowing and eventual termination of oral hood closures was correlated with distension of the stomach caused by the ingested Artemia. We obtained further evidence that stomach distension is one of the underlying causes of satiation by injecting artificial non-nutritive food into the stomach, and by cutting open part of the stomach wall to prevent it from filling and distending. The first treatment caused satiation to occur more rapidly, while the second treatment delayed satiation. Both results demonstrate that in Melibe stomach distention has a major impact on the motivation to feed. These findings provide the framework for subsequent studies designed to determine precisely how stomach distention influences feeding circuits.     

Genetic mapping of meander tail, a mouse mutation affecting cerebellar development

The meander tail mouse harbors a recessive mutation on chromosome 4 that affects the anterior lobes of the cerebellum and the caudal vertebrae. Examination of the mea/mea cerebellum reveals that the complete disorganization of all cell types seen in the anterior lobes is separated by a sharp and consistent boundary from the normal cytoarchitecture of the posterior lobes. In the absence of any biochemical information regarding the affected gene product, attempts to clone the gene must rely on the strategy of reverse genetics. As an initial step in this process we have constructed a genetic linkage map spanning 68 cM of chromosome 4 using an intersubspecific phenotypic backcross. The loci included in this analysis are Calb, Ggtb, Lv, b, Ifa, mea, D4Rp1, Glut-1, Lck, Lmyc-1, and Eno-1. This analysis positions the mea phenotypic locus in the interval between Ifa and Glut1. These results also further define regions of homology between mouse chromosome 4 and human chromosomes 8, 1, and 9. This linkage map provides the means to evaluate candidate genes, and to identify tightly linked markers useful for cloning the meander tail locus.     

Stage-specific proteinases of Leishmania mexicana mexicana promastigotes

Four distinct bands of cysteine proteinase activity were detected when stationary-phase populations of Leishmania mexicana mexicana were subjected to gelatin-SDS-PAGE. The highest mobility band contained at least three isoforms separable by mono Q anion exchange chromatography. These high mobility activities were distinct from all the major amastigote enzymes. Stationary-phase promastigote populations also contained two acid-activable precursor forms of the promastigote-specific band. It is suggested that these promastigote-specific activities occur in the infective metacyclic stage of the parasite and may have a role in parasite survival upon inoculation into a mammal.     

The influence of seed apparency,nutrient content and chemical defenses on dietary preference in Dipodomys ordii

Summary Physical, nutritional and defensive qualities of seeds differ in the extent to which they influence granivore preference. In a study aimed to quantifying those differences, Ord's kangaroo rats (Dipodomys ordii) were found to prefer the seeds of just three of twenty-nine species: Cryptantha crassisepala, Oryzopsis hymenoides and Salsola kali. Oryzopsis hymenoides was most preferred during the early plant growth season (April–July); preference for S. kali peaked during late (August–November) and dormant (December–March) seasons; and greatest preference for C. crassisepala occurred during dormant and early seasons. Regression of forage ratios, averaged across seasons, against seed length, mass, abundance, patchiness, percent nitrogen, energy content, and chemical defenses showed seed length to be the most important predictor of seed preference. Seed length combined with nitrogen (protein) content and levels of two defensive compounds, saponins and non-protein amino acids, to account for 68% of the variation in seed preference. The importance of seed length rather than biomass indicated that there are limits to the ability of D. ordii to detect small seeds and that small size facilitated escape of dispersed seeds. Seasonality in preference suggested, however, that seed escape was encountered by predispersal harvesting of newly maturing seeds still on plants. Maximization of protein intake contradicted previously published observations, but presumably reflected low nitrogen availability. In addition to small size, the presence of saponins or non-protein amino acids in seeds was sufficient to negate the positive influence of higher protein content.