Hyperphagia resulting from gut denervation in the sea slug, Pleurobranchaea

Previous research suggests that gut distension by ingested bulk plays an important role in the regulation of food intake in gastropod molluscs. The present study tested whether the bilateral stomatogastric nerves which innervate the esophagus and crop in Pleurobranchaea form a neural pathway carrying information about gut distension to the central nervous system. The posterior branches of the paired stomatogastric nerves were surgically exposed and sectioned in seven experimental animals while the nerves were simply exposed and not sectioned in seven sham-operated control animals. In three, subsequent, daily feeding sessions, the experimental subjects consumed a greater amount of food in terms of percentage of body weight than the control subjects. The experimental animals also gained a greater percentage of body weight and later were found to contain much more food within their guts. The results support the hypothesis that stretch receptors which innervate the gut and which have axons in the stomatogastric nerves form an important negative feedback pathway for the control of feeding in the sea slug.     

Time horizons in rats foraging for food in temporally separated patches

An important tenet of optimal foraging theory is that foragers compare prey densities in alternative patches to determine an optimal distribution of foraging behavior over time. A critical question is over what time period (time horizon) this integration of information and behavior occurs. Recent research has indicated that rats do not compare food density in a depleting patch with that in a rich patch delayed by an hour or more (Timberlake, 1984). In the present research we attempted to specify over what time period a future rich patch would affect current foraging. The effect of future food was measured by early entry into the rich patch (anticipation) and by a decrease in food obtained in the depleting patch (suppression). The rats showed anticipation of a rich patch up to an hour distant, but suppressed current feeding only if the rich patch was 16 min distant or less. The suppression effect appeared mediated by competition for expression between anticipatory entries into the rich patch and continued foraging in the depleting patch. These results suggest that optimal foraging is based on a variety of specific mechanisms rather than a general optimizing algorithm with a single time horizon.     

Mechanisms underlying satiation of feeding behavior of the mollusc Aplysia

Animals filled almost to satiation by nonnutritive bulk do not satiate when they ingest a small amount of seaweed. This suggests that satiation is not triggered by chemostimulation of an anteriorly located "hot spot." Inflation of a balloon placed in the gut of the animal results in satiation as reflected in a number of different parameters of feeding behavior. The suppressive effect of a relatively brief inflation is rapidly and fully reversible, although repeated inflation and deflation appeared to produce slowly reversible or irreversible effects. The parameters of the changes in feeding during gut inflation are comparable to those of normal animals that are slowly fed individual pieces of food. The inflation volume needed to satiate the animal is a function of the rate of inflation--more rapid inflations requiring larger volumes. Cutting of the esophageal nerves results in a significant increase in the volume needed to satiate the animals, but nevertheless they eventually cease feeding and generally do not show a burst gut. The evidence indicates that the satiation that eventually occurs in nerve-sectioned animals, at least in part, is due to depression of feeding following very prolonged sensory stimulation. The data suggest that for a rapidly consumed meal, satiation results primarily due to distension-related gut signals conveyed by the esophageal nerves, whereas for very slowly consumed meals, the former factor interacts with a process associated with sensory stimulation, such as receptor adaptation. The current results indicate that balloon distension can serve as a reasonable stimulus in experiments in simplified preparations in which the nervous system can be studied.     

Social structure features in three inbred strains of mice, C57Bl/6J, Balb/cj, and NIH: a comparative study

Some features of social living were investigated in three inbred strains of mice: C57Bl/6j, Balb/cj, and NIH. Five social behaviors--Aggression, Submission, Allogrooming, Social Rest and Rest Alone, as well as Wheel Running Activity--were recorded 2 h daily for a week, in 26 groups of seven male mice living in an enriched environment. Dominants and subordinates among strains shared some behavioral characteristics, but strain contributions upon social structure were also detected. Similarities among strains included the appearance of a single dominant mouse per group rated as the most aggressive, besides from being the animal presented with most Submissions. Allogrooming was more frequent among subordinates than among dominants and subordinates. Differences among strains were that agonistic behavior among subordinates was higher in the Balb/cj and NIH groups than in the C57Bl/6j mice. NIH mice were recorded in Rest Alone more often than mice from the other strains. C57Bl/6j dominants showed higher rates of Wheel Running Activity than subordinates.     

Long-term memory formation in chicks is blocked by 2-deoxygalactose, a fucose analog

When day-old chicks are trained on a passive avoidance task there is enhanced synthesis of glycoproteins. Bilateral intracerebral injections of 20 mumole of 2-deoxygalactose (2-D-gal), administered just before and just after training on the task, produce amnesia for the avoidance. Amnesia develops slowly over the first hour and persists for at least 24 h subsequently. If 2-D-gal injections are administered 4 h prior to the training or delayed for 3 h after training, no amnesia occurs. Apart from a brief initial suppression of pecking following injection there are no effects of 2-D-gal on other observed behaviors of the birds. Within the first hour this dose of 2-D-gal inhibits [3H]fucose incorporation into acid-insoluble material by 26% (or 68%, calculated relative to free pool fucose). The amnestic effect of 2-D-gal is not shown by galactose, glucose, fucose, or 2-D-glucose. Injecting 40 mumole of galactose simultaneously with the 2-D-gal abolishes the 2-D-gal-induced amnesia; 40 mumole of fucose, however, does not abolish the amnesia. The utility of 2-D-gal as an agent for analyzing the role of glycoproteins in memory formation is discussed.     

Hippocampal associative cellular responses: dissociation with behavioral responses revealed by a transfer-of-control technique

Multiunit activity was recorded in the CA3 field of the dorsal hippocampus in freely moving rats during classical conditioning and subsequent presentation of the CS on operant baselines for food reward as well as shock avoidance. Rats were first trained in a nonsignaled bar-pressing-dependent shock omission task and in a food-motivated lever-pressing task (60-s VI). Five sessions with presentations of a previously habituated tone as a CS paired with footshock as a US were then given. Testing was carried out by presenting the CS alone while behavioral responses were maintained by reinforcement in both instrumental tasks on alternate sessions. As expected, the CS induced a marked suppression of lever pressing for food reward and a marked enhancement of bar-pressing for shock avoidance. The analysis of the frequency of multiunit discharges to the CS revealed that the hippocampal cellular responses established during classical conditioning were maintained while two different behavioral responses were exhibited to the CS. The results showed that the associative response of hippocampal neurons may be dissociated from the Pavlovian conditioned responses the CS elicits. They support the hypothesis that hippocampal cellular responses represent a neural index of the acquired CS-US associative representation.     

Pavlovian analysis of interactions between hunger and thirst

In four experiments we examined the effect of an irrelevant drive on classical conditioning with food and water. In the first experiment the irrelevant drive weakened the conditioned response in extinction. In Experiments 2 and 3, this suppressive effect was found also in acquisition. Furthermore, the presence of an irrelevant drive during nonreinforced presentations of the conditioned stimulus was found to protect the conditioned response from extinction. Experiment 4 showed that the depressive effect of the irrelevant drive is manifested only when the relevant drive is present. Taken together, these results suggest that an irrelevant drive can influence conditioned responding by modulating the representation of the unconditioned stimulus.     

Kinematic form and scaling: further investigations on the visual perception of lifted weight

Observers are able to judge accurately the weight lifted by another person when only the motions of reflective patches attached to the lifter's major limb joints and head can be seen (Runeson & Frykholm, 1981). What properties of these complex kinematic patterns allow judgments of weight to be made? The pattern of variation in velocity of the lifted object over position is explored as a source of information for weight: It is found to provide limited information. How are variations in kinematic patterns scaled to allow judgments of weight, a kinetic quantity? The possibility of a source of information for scaling in the kinematics is investigated. Judgments based only on patch-light displays are accurate to a degree that is improved by an extrinsic scaling basis. Finally, the sensitivity to scaling of alternative metrics used in judging is explored. Intrinsic metrics are discovered to be less sensitive to the absence of an extrinsic basis for scaling.     

Perceptual normalization of vowels produced by sinusoidal voices

When listeners hear a sinusoidal replica of a sentence, they perceive linguistic properties despite the absence of short-time acoustic components typical of vocal signals. Is this accomplished by a postperceptual strategy that accommodates the anomalous acoustic pattern ad hoc, or is a sinusoidal sentence understood by the ordinary means of speech perception? If listeners treat sinusoidal signals as speech signals however unlike speech they may be, then perception should exhibit the commonplace sensitivity to the dimensions of the originating vocal tract. The present study, employing sinusoidal signals, raised this issue by testing the identification of target /bVt/, or b-vowel-t, syllables occurring in sentences that differed in the range of frequency variation of their component tones. Vowel quality of target syllables was influenced by this acoustic correlate of vocal-tract scale, implying that the perception of these nonvocal signals includes a process of vocal-tract scale, implying that the perception of these nonvocal signals includes a process of vocal-tract normalization. Converging evidence suggests that the perception of sinusoidal vowels depends on the relation among component tones and not on the phonetic likeness of each tone in isolation. The findings support the general claim that sinusoidal replicas of natural speech signals are perceptible phonetically because they preserve time-varying information present in natural signals.