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.     

Leg kinematics and muscle activity during treadmill running in the cockroach, Blaberus discoidalis: II. Fast running

We have combined kinematic and electromyogram (EMG) analysis of running Blaberus discoidalis to examine how middle and hind leg kinematics vary with running speed and how the fast depressor coxa (Df) and fast extensor tibia (FETi) motor neurons affect kinematic parameters. In the range 2.5–10 Hz, B. discoidalis increases step frequency by altering the joint velocity and by reducing the time required for the transition from flexion to extension. For both Df and FETi the timing of recruitment coincides with the maximal frequency seen for the respective slow motor neurons. Df is first recruited at the beginning of coxa-femur (CF) extension. FETi is recruited in the latter half of femur-tibia (FT) extension during stance. Single muscle potentials produced by these fast motor neurons do not have pronounced effects on joint angular velocity during running. The transition from CF flexion to extension was abbreviated in those cycles with a Df potential occurring during the transition. One effect of Df activity during running may be to phase shift the beginning of joint extension so that the transition is sharpened. FETi is associated with greater FT extension at higher running speeds and may be necessary to overcome high joint torques at extended FT joint angles. Accepted: 24 May 1997     

The conformations of polypeptide chains where the main-chain parts of successive residues are enantiomeric. Their occurrence in cation and anion-binding regions of proteins.

We have investigated the shapes of polypeptides where successive residues have main-chain phi,psi conformations of opposite hand. A graph not unlike a Ramachandran plot is presented illustrating the various possible conformations. All are ring-shaped or extended. Some of these conformations occur in native proteins, the commonest approximating to a feature we propose calling a nest, described in the accompanying paper, where the main-chain NH groups point inwards relative to the ring and give rise to an anion-binding site. Another conformation is related but more extended and is found uniquely in the four stretches of polypeptide that line the tetrameric K(+) channel; their CO groups bind the K ions in the channel. In a different ring-shaped conformation that we propose calling a catgrip, the main-chain CO groups point into the ring; this is employed for specific Ca ion binding in the annexin, phospholipase A2 and subtilisin loops, and the regularly arranged beta-roll loops of the serralysin protease family.     

AN INTRODUCTORY STUDY ON THE ECOLOGY OF HYRAX (DENDROHYRAX BRUCEI AND PROCAVIA JOHNSTONI) IN THE SERENGETI NATIONAL PARK

1. Dendrofoyrax brucei and Procavia johnstoni populations have been studied in kopjes surrounding the senior author's house.
2. The two species have been described and a short historical review of the Hyracoidea is given. Some notes are made concerning "Hyraceum".
3. The kopjes under study are described, being typical of granite outcrops in the Serengeti region.
4. The adaptations of both species of hyrax for the kopje habitat are described. Observations are made on the diurnal activity patterns in relation to climatic conditions.
5. A list of all plants available to the animals is presented, and those eaten by either species are indicated. Comment is made on the lack of overlap in the diets of the two species, and this is suggested as being partly due to lack of pressure on food resources.
6. A discussion on the possible evolution of the kopje-dwelling habit is held, which concludes that reconvergence may have taken place as a result of forest giving way to woodland and plains.