Roderick Wong

Interanimal aggression and hyperreactivity following hypothalamic infusion of local anesthetic in the rat.

Abstract Temporary lesions were made by infusing a local anesthetic, lidocaine (2%), into the medial hypothalamus or adjacent areas of male hooded rats. Bilateral infusions of 1 μl, at a rate of 1 μl/3 min, were made every 5 min over a 20 min period. Reactivity to the experimenter, muricide, and intermale aggression were assessed following each 1 μl injection. Each of these behaviors was produced by injections along the descending columns of the fornix, in the anterior one-third of the ventromedial hypothalamic nucleus, and more posteriorly between the ventromedial nucleus and the fornix. The appearance of hyperreactivity, muricide, and intermale aggression were corelated with one another. The time of their appearance during the infusion period was similar for different infusion sites along the anterior-posterior length of the medial hypothalamus. Infusion of lidocaine into the medial forebrain bundle did not induce an increase in the behaviors measured. It is suggested that two systems, one modulating interanimal aggressiveness and another modulating reactivity (defensiveness) are being affected by these injections. The systems, while distinct, overlap in the medial hypothalamus. They are not localized solely in the ventromedial nucleus.

Recall and clustering of verbal materials among normal and poor readers

The recall and clustering of verbal materials among normal and poor readers was investigated. The results indicated quantitative differences between the two groups of readers. More importantly, the results also indicated that normal readers were able to maximize extra given time to learn and organize materials for remembering. Additionally, they were able to generate their own mnemonic strategies in the absence of instructional cues. The results were interpreted in terms of the poor reader’s unadaptiveness to the experimental task. Such unadaptiveness appears to be a function of production deficiency in mnemonic strategies.

Adrenocortical responsiveness to novelty in the hamster

The adrenocortical response to increasing periods of exposure to a novel cage, as well as the effects of returning hamsters to their familiar home cages, were examined. We found that a five min exposure to a novel cage was insufficient to activate the pituitary-adrenal system, but that cortisol levels increased significantly as duration of exposure increased from 15 to 30 min. In contrast, returning hamsters to their home cages for at least 15 min following the 15 min novel cage exposure produced a significant drop in plasma levels of cortisol. Finally we found that males exhibit a greater cortisol response to novelty than females, indicating a sexual dimorphism which is the reverse of that reported in other rodents.

Defensive aggression and testosterone-dependent intermale social aggression are each elicited by food competition ☆

Castrated rats with medial hypothalamic lesions or sham lesions and castrated rats with testosterone implants or sham implants were placed on a 23-hr food deprivation schedule, adapted to a highly palatable liquid food, and then housed in pairs. The pairs were observed in competition for the highly palatable food over a 4-min period on each of six days. On the first three days, the food was dispensed in a way that allowed only one animal at a time to drink while during the second three days both animals could drink simultaneously. The pairs of animals were then separated, individually adapted to a bland liquid food, and paired with a different animal for a second series of competition tests. With highly palatable food as the incentive, rats made hyperdefensive by medical hypothalamic lesions were more successful at maintaining access to the food and more aggressive than their sham-lesioned competitors on tests when food access was restricted to a single animal but not on tests when both animals could drink simultaneously. With bland food as the incentive, lesioned animals were not consistently more successful in maintaining access to the food but were significantly more aggressive than their cagemates. With the highly palatable food, castrated males with testosterone implants were neither more successful in maintaining access to the food nor more aggressive than their cagemates with sham implants. However, when paired with an unfamiliar cagemate in preparation for competition tests with the bland food, most rats with testosterone implants attacked the new cagemate using a lateral attack and displaying piloerection.(ABSTRACT TRUNCATED AT 250 WORDS)

Infantile handling and the facilitation of discrimination and reversal learning

One group of rats was removed from their home cage and received daily handling from Days 3–21, while the control group of litter mates remained in the cage and did not receive any treatment. On Day 22 all rats were weaned and they were housed in individual cages until they were 60 days old. After two pretraining days, subjects were given daily blocks of one free and three forced trials in the T-maze and were rewarded with food after making the correct response. Following 20 days of training and testing on black-white discrimination, subjects were given 10 days of reversal training with four daily trials. Results indicate that the handled animals showed faster running and a greater number of correct choices than the control rats during both the acquisition and reversal learning phases of the experiment.

A comparative analysis of feeding and hoarding in hamsters and gerbils.

Male and female hamsters and gerbils were randomly assigned to one of three groups. The animals were tested under ad lib feeding conditions or food deprived until they had lost either 10% or 20% of their predeprivation body weight. They were given a 30-min. hoarding test for three consecutive days. The results indicated that although food-deprived gerbils ate more than control gerbils, deprivation had no significant effect on the food intake of hamsters. A sex difference was also evident in the food intake of gerbils; males ate more than did females. Although there was a sex and species difference in the amount of hoarding, deprivation had no significant effect on the amount of hoarding. The implications of these results for of different models of hoarding are discussed. These models contrast hoarding as a defensive response in the regulation of body weight or as an anticipatory activity that is influenced by other selection pressures.

Infantile handling and successive spatial reversal learning in rats.

The successive reversal learning methodology was used to compare the learning ability of rats which had received preweaning stimulation with those that had not been handled. The results showed that most of the male handled rats had completed seven reversals and that none from the other groups made it within 500 trials. Most of the female handled rats reached five reversals and most of the male nonhandled rats attained four reversals. The female nonhandled rats achieved only three reversals. It was suggested that the successive reversal learning methodology is likely to reveal group differences when the data are analyzed in terms of the number of reversals attained by the animals from different treatment groups within a fixed number of test trials. However, this methodology is less likely to reveal treatment effects when the data are analyzed for intratask group differences.

Consummatory behavior and adrenocortical responsiveness in the hamster

In this study we examined the effects of consummatory behavior on adrenocortical activity in the golden hamster (Mesocricetus auratus). We found that: (1) Animals tested in their home cage began drinking faster and drank more water than animals tested in a novel cage. (2) Basal levels of cortisol were not elevated following 24 hr water deprivation. (3) Placement in a novel cage produced significant cortisol elevations. However, if water was available, cortisol levels were reduced and did not differ significantly from presession (basal) levels. (4) Opportunity to drink while in the home cage produced no significant change in cortisol. All animals were water-deprived for 24 hr prior to testing and no sex differences were observed on any of these measures. In a second experiment we examined adrenocortical inhibition in water-deprived animals tested in a novel cage which was Empty or which allowed access to Food, Water or Sanicel bedding. Presence of food did not reduce cortisol levels; however, presence of either water or Sanicel reduced plasma corticoids to basal levels.

Aldactazide-induced sodium appetite in rats

Rats were presented with a choice between water and 2.0% (0.34M) NaC1 solution and their fluid intake was measured for 7 days. Then the rats were injected with Aldactazide-A on odd days and with 0.88% (0.15M) NaC1 solution on even days. This procedure was repeated for 12 days at which time the animals had received six tests under each of the injections. The results indicated that the rats consumed more hypertonic saline solution when injected with Aldactazide than they did with isotonic NaC1 injections. The water intake of these animals was not affected by the different injections. With repeated Aldactazide injections the animals showed an increase of saline consumption over the six sessions. These results suggest that Aldactazide is an effective agent for inducing sodium appetite in rats.

Gerbils reared by rats: effects on adult open-field and ventral marking activity.

At 72 hr after birth gerbil litters were divided and half the pups fostered to lactating mother rats whose own pups were removed. Remaining pups were returned to their natural mothers. Rat-reared gerbils weighed more at weaning than control gerbils but there was no weight difference at 100 days. When tested in the open-field as adults, rat-reared gerbils were found to locomote and to rear less than controls. The fostering treatment had no clear-cut effects on frequency of ventral marking, although there was a large sex difference for this measure. No sex differences in open-field activity were found.