Effects of intertrial reinforcers on rats' timing behavior

Two experiments were conducted to assess the effects of non-contingent intertrial interval (ITI) reinforcers on rats' discrimination of duration. In the first experiment, rats' discrimination of a 2 vs. 8 s of light was significantly disrupted when reinforcers were presented in the ITI. Disruption was not different on short (2 s) and long (8 s) trials. The second experiment showed that this disruptive effect was not specific to trials preceded by ITI reinforcers; responding on empty ITI trials run in the same session as ITI-reinforcer trials was also disrupted. This disruption however was not as great as on the ITI-reinforcer trials. The results of these experiments show that ITI reinforcers affect timing discriminations in much the same way they affect classical conditioning and delayed matching to sample. However, detailed examination of the results suggests that the deleterious effects of ITI reinforcers in these different paradigms might be produced by different rather than the same mechanism. The results also support the conclusion that pre-trial reinforcement “priming” produces disruption rather than facilitation in complex tasks.     

Aggressive behavior of pregnant mice toward males.

Aggressive behavior toward male intruders was compared between pregnant, pseudopregnant, and virgin females during a series of successive daily encounters. The pregnant and the pseudopregnant females obtained significantly higher scores than the virgins. Changes in ovarian activity may be a determinant of the female aggression toward males.     

Aggressive behavior of the white-eye mutant crickets, Gryllus bimaculatus

Aggressive behavior of white-eye mutant crickets was investigated and compared with that of wild-type crickets. In the dark, wild-type pairs performed long-lasting fights with significantly higher aggressive levels compared to those in the light. In contrast, fights between two white-eye mutants were not significantly different with those between two wild-type crickets both in duration and the aggressive levels. Ethograms of aggressive behavior showed that the mutants could show typical sequentially escalating fight with the same behavioral categories as the wild-type crickets. These results indicate that the white-eye mutants are able to express normal aggressive behavior.     

Aggressive behavior in birds: an experimental model for studies of brain-steroid interactions

1. Although testosterone (T) stimulates aggressiveness in males of many vertebrate species, it is now known that the full expression of T actions in the central nervous system requires aromatization to estradiol (E2) and subsequent binding of formed E2 to its receptor. 2. We have recently confirmed these as rate-limiting steps in the control of sex-related and individual differences in aggressiveness of the Japanese quail (Coturnix coturnix japonica). 3. In this review, we describe some of the neuroendocrine factors which control aggression with a focus on our recent studies in quail.     

Aggressive behavior in female golden hamsters: development and the effect of repeated social stress

In male golden hamsters, agonistic behavior matures during puberty, changing from play fighting to adult-like aggression. In addition, this transition is accelerated by repeated social subjugation early in puberty. However, little is known about the development of agonistic behavior in females. In the present study, we compared the development of agonistic behavior in male and female golden hamsters. Furthermore, we also tested the effects of repeated social subjugation on the development of agonistic behavior during puberty. Hamsters were tested for agonistic behavior in the presence of a smaller intruder at different intervals during puberty. Several observations were made. First, the frequency of attacks remained stable in females, while varying in males. Second, the transition from play fighting to adult-like aggression occurred at earlier time periods in females than in males. Finally, a clear transitional period marked by attacks focused on the flanks was observable in males around mid-puberty. However, this transitional period was not apparent in females. In addition, juvenile females were exposed to aggressive adult males or females. In both cases, repeated exposure to stress had no statistically significant effect on the development of agonistic behavior. After 2 weeks of subjugation, exposure to aggressive adults had no effect on serum cortisol levels, indicating that juvenile females habituate to repeated social stress. These data show significant sex differences in the development of agonistic behavior and adaptation to repeated stress in juvenile golden hamsters.     

Aggressive behavior and change in salivary testosterone concentrations predict willingness to engage in a competitive task

The current study investigated relationships among aggressive behavior, change in salivary testosterone concentrations, and willingness to engage in a competitive task. Thirty-eight male participants provided saliva samples before and after performing the Point Subtraction Aggression Paradigm (a laboratory measure that provides opportunity for aggressive and defensive behavior while working for reward; all three involve pressing specific response keys). Baseline testosterone concentrations were not associated with aggressive responding. However, aggressive responding (but not point reward or point protection responding) predicted the pre- to post-PSAP change in testosterone: Those with the highest aggressive responding had the largest percent increase in testosterone concentrations. Together, aggressive responding and change in testosterone predicted willingness to compete following the PSAP. Controlling for aggression, men who showed a rise in testosterone were more likely to choose to compete again (p = 0.03) and controlling for testosterone change, men who showed the highest level of aggressive responding were more likely to choose the non-competitive task (p = 0.02). These results indicate that situation-specific aggressive behavior and testosterone responsiveness are functionally relevant predictors of future social behavior.     

Aggressive behavior of adult meadow voles (Microtus pennsylvanicus) towards young

Summary Field evidence indicates that adult microtines, especially females, may be a major cause of poor juvenile survival and this may be instrumental in their population regulation. This suggests that males and females behave differently towards young animals. To examine how adult males, nonlactating females, and lactating females behave towards strange young, I introduced young animals into the home cage of the adults. Lactating females were most aggressive towards young; most males investigated them; most nonlactating females ignored them. However, discriminant function analysis indicated a great deal of overlap in the behavior of the classes. None of the classes behaved differently towards young of either sex. Females did not vary their behavior during lactation. Behavior varied among lactating females, with 55% showing little aggression and 20% showing a great deal. Most lactating females showed similar behavior in each of their bouts: docile females remained docile, aggressive females remained aggressive. I conclude that lactating females are most aggressive towards strange young. These results are consistent with the field evidence, which suggests that adult females depress juvenile survival and recruitment and that the main culprits are breeding females.     

Further evidence of joint time-place control of rats' behavior: results from an 'open hopper' test

Rats were trained on an interval time-place task. Food was intermittently available on each of four levers for 4 min in a 16-min session. After baseline training the rats received 'open hopper' sessions in which food was available on all levers for all of the 16-min sessions. Despite the absence of any contingencies for doing so, the rats continued to press the levers in the 'correct' sequence, for roughly the 'correct' amount of time. This confirms that the rat behavior was controlled, in part, by a representation of an elapsed interval of time. The rats responding was more variable in 'open hopper' sessions and error increased (in an exponential fashion) as the session proceeded. This finding suggests that the rats may have used shifts in the location of food availability to minimize the accumulation of error throughout baseline sessions.     

Aggressive behavior and dominance hierarchies in female sable antelope,Hippotragus niger: Implications for captive management

Social interactions of adult female sable antelope, Hippotragus niger, were observed at the National Zoological Park's Conservation and Research Center. Aggressive behavior was quantified for two herds containing 8 and 11 females. Aggression was lowest at calving, and highest near the time of conception. Dominance hierarchies were strictly linear and stable over time. Dominance rank was highly correlated with age, with the oldest females achieving highest rank. High-ranking females initiated more aggression and were more likely to behave aggressively towards a newly introduced adult female. The newly introduced individual was the victim of prolonged, intense group chases and was permanently excluded from the herd. Low-ranking females directed more aggression at yearling herd members than did high-ranking females. Temporary absences by herd members resulted in long-lasting, substantial increases in received aggression upon their return. Because of their aggressive nature, sable antelope present a challenge to captive management. © 1993 Wiley-Liss, Inc.     

Tumor radiosensitivity and apoptosis

With approximately 50% of all cancer patients receiving radiation therapy at some point in their treatment, increasing the sensitivity of tumor cells to the lethal effects of irradiation has the potential to significantly improve the rate of recovery from many malignancies. The major biological determinant of radiotherapy failure is tumor radioresistance. It is well known that tumors from the same histological group and stage of development are extremely heterogeneous in their sensitivity to radiotherapy. There are many factors which could affect tumor radiosensitivity. One cellular mechanism common to various therapeutic regiments, including radiation, is killing tumor cells via apoptosis. However, this killing is not always efficient. In this review the link between tumor sensitivity to radiation treatment and the capacity of tumor cells to be killed by apoptotic mechanisms will be discussed.     

Aggressive howling in wolves

During two studies that investigated the responses of wolf packs to either human simulations or pre-recorded playbacks of wolf, Canis lupus, howling, single adult wolves from five different packs approached my location and howled on a total of six occasions. The howls uttered by these close-approaching wolves were significnatly deeper in pitch than comparable samples of howls recorded from animals that did not approach. In addition, howls of two of the five animals differed in structure from most of the other howls recorded during both studies. These close-approach howls were characterized by the presence of harmonically unrelated frequency sidebands near the end of the howl. This feature was rate in howls recorded during occasions when wolves kept their distance. These results indicate that the structure of wolf howling during aggressive interactions with strange wolves follows Morton's (1977) motivation-structural rules, which state that natural selection will favour the use of low-frequency, harsh sounds by hostile animals. This relationship follows from the physical constraints of vocal production: animals of larger size can produce sounds of lower pitch and harsher tonal quality. As body size is a primary determinant in the outcome of aggressive interactions, vocalizations signalling size (i.e.low-pitched, harsh sounds) will be of selective value for individuals engaged in aggressive interactions.