Effects of post-trial administration of naloxone and beta-endorphin on shock-induced fighting in rats

To study the involvement of endogenous opioid peptides in the development of shock-induced fighting, naloxone (2 mg/kg) or beta-endorphin (10 micrograms/kg) was administered subcutaneously immediately after the session and during nine consecutive daily sessions to rats repeatedly exposed to electric shocks. beta-Endorphin blocked the development of shock-induced fighting while naloxone facilitated it but only when shock-induced fighting occurred at a low rate. The effects of beta-endorphin were time dependent since when beta-endorphin was injected 90 min after the shock session instead of immediately after, its impairing effect disappeared. In addition, naloxone blocked the impairment produced by beta-endorphin. Differential postsession treatment of each member of pairs of rats with naloxone and beta-endorphin resulted in a higher probability of rats treated with naloxone to be dominant over rats treated with beta-endorphin in the test situation. These results are discussed in relation with the possible involvement of endogenous opioids in the modulation of the physiological consequences of defensive behavioral responses to shock.     

Tolerance to cocaine's rate-increasing effects upon repeated administration.

Four squirrel monkeys responded daily under a fixed-interval 5-min or 8-min schedule of food-pellet delivery. Cocaine (0.03 to 1.7 mg/kg) and saline were injected before occasional daily sessions (acute administration). Some doses of cocaine produced substantial overall increases in response rate for 3 of the subjects; effects were less substantial for the remaining subject, who exhibited modest increases in response rate early in the session and during the middle portion of the intervals. A dose that increased response rate when administered acutely was then administered before each session (chronic administration). Chronic administration resulted in a reduction in the increases in response rate seen under acute administration for all subjects.     

The effects of phencyclidine and chlordiazepoxide on target biting of confined male mice

Target-biting of confined mice increases following delivery of tail shock and decreases during a tone that precedes the shock. Both phencyclidine and chlordiazepoxide reduced biting (dose dependently) following shock and had no effect on biting during the tone. These observations are discussed in reference to previous reports, which infer that the effects of phencyclidine and chlordiazepoxide on aggression might depend upon the baseline rate of the behavior.     

Effects of novel odors on intermale attack behavior in mice

Offensive, defensive, and nonagonistic social behaviors of resident male mice toward unfamiliar intruders were examined during exposure to the novel odors of chocolate or sheep's wool. Both novel odors reduced lateral attacks and boxing when compared to familiar sawdust odor. Chocolate, but not sheep's wool, also reliably increased flight behavior by residents. Neither social behaviors nor self-grooming were affected by these odors. The novel odors had no effect upon, or actually decreased, the defensive responses of intruders towards residents. The equivalent effectiveness of both predator and nonpredator odors in elevating risk assessment and suppressing attack during firsttime exposure, and the decreased potency of cat odors following repeated exposure, suggests that novelty contributes to the enhanced defensiveness seen among subjects during initial exposure to predator odors. © 1995 Wiley-Liss, Inc.     

Analysis of the targets and tactics of conspecific attack and predatory attack in northern grasshopper mice onychomys leucogaster

Comparisons of tactics of fighting between species are often difficult to make since the body targets attacked may differ. Thus it becomes difficult to assess whether differences in fighting tactics are due to species-specific differences in the tactics themselves or due to the different targets attacked. A solution to this problem is to analyse the tactics of a species that attacks different targets under different circumstances. In this way, differences in tactics can be more readily attributed to differences in targets. In this study, resident male northern grasshopper mice (Onychomys leucogaster) were tested against intruding male conspecifics and against laboratory mice (Mus musculus domesticus). Conspecifics were mainly bitten on the lower dorsum, whereas prey were bitten and killed by bites to the nape of the neck. Therefore, it was possible to analyze the tactics of attack by grasshopper mice when attacking different body targets. For example, in order to defend the lower dorsum and the nape, both intruding conspecifics and prey adopted an upright defensive posture. Resident grasshopper mice used the lateral attack tactic to gain access to the lower flanks but not the nape. This illustrates that the lateral attack tactic is not merely a tactic suitable for overcoming the upright defense tactic, but is used in this context only when the target attacked is on the opponent's posterior dorsum. Such withinpecies comparison enables the identification of the contextual rules which govern the use of fighting tactics. © 1992 Wiley-Liss, Inc.     

The Daily Stress Inventory: Validity and effect of repeated administration

The Daily Stress Inventory (DSI) is a self-report measure of minor stressors which is administered daily. One test of the validity of a measure of daily stress is its sensitivity to the difference between the stressors of workdays and those of weekends. A second concern in establishing the validity of a test administered repeatedly is that self-monitoring may influence the obtained scores. The present study investigated these two issues using a sample of 70 community adults who reported full-time employment. These subjects provided a week of self-monitoring with the DSI. The results indicated that the DSI was sensitive to the difference between weekends and weekdays. The analyses of the effect of repeated administration suggested that the first day of self-monitoring may differ from the other days of self-monitoring. When the first day was eliminated, there was no significant difference among the days of self-monitoring, and the difference between the weekdays and the weekends remained. The data suggest that the DSI is a valid measure of the construct of daily stress and that any influence of repeated self-monitoring with the scale may be easily resolved.     

Relationship between attack and feeding in the insect predatory behavior of grasshopper mice

In grasshopper mice, the consequences of feeding and state of hunger affect the predatory attack to a limited extent. The purpose of this study was: (1) to establish other ways that attack and feeding were connected besides the two effects already mentioned; and (2) to determine if caching of dead prey could account for the limited connection between attack and feeding. Experiment 1 showed that attack and feeding were connected as part of a reaction chain. Experiment 2 showed that both shared a common maturational process despite the fact that each response achieved an improved efficiency in a different way. Experiment 3 showed that caching prey was not correlated with the killing of a prey and thus could not account for the limited connection between attack and feeding. It is proposed that a highly canalized attack response specifically buffered against the effects of feeding and hunger plays an important role in the mouse's carnivorous life style.     

Chronic administration of propranolol impairs inhibitory avoidance retention in mice

Adrenergic systems are importantly involved in memory storage processes. As such, agents that alter adrenergic receptors, such as "beta-blockers," also alter memory storage. However, the anxiety literature cautions that beta-adrenergic receptor antagonists, such as propranolol, may have different behavioral effects with acute vs chronic dosing. The effects of chronic propranolol specifically on memory modulation are unknown. This study was designed to evaluate the effects of chronic propranolol on retention for an aversive task, in which there is endogenous adrenergic activation. Adult male ICR mice were given daily injections of one of four doses of propranolol (2, 4, 8, and 12 mg/kg) or 0.9% NaCl vehicle for 15 days prior to, and continuing during, behavioral tests of exploration and retention. Exploratory behavior, as an index of anxiety level, was measured in a conventional elevated plus-maze, whereas retention of an aversive experience was measured in a step-through inhibitory avoidance apparatus. Sensitivity to aversive footshock was also evaluated. Compared to controls, propranolol-treated mice showed a dose-dependent decrease in retention for the inhibitory avoidance task, but no effect on anxiety on the plus-maze or on footshock sensitivity. Taken together with results from previous studies, it is apparent that propranolol can have different behavioral effects when administered acutely vs chronically, and its chronic effects significantly impair memory storage processes. Since these drugs are typically used chronically, and often in older adults, they could contribute to functional memory impairments.     

Shock source and intensity: Variables in shock-induced fighting

Alternating current, direct current, and rectified alternating current shock were compared at four shock intensities to assess differential influences on shock-induced fighting in rats. At higher shock intensities, the data paralleled the Campbell and Masterson (1969) equal aversion function, but at lower shock intensities, differences among shock types with respect to frequencies of shock-induced fighting were obtained. These results suggested that, at lower shock intensities, shock type is a variable in shock-induced aggression research with rats.     

Increased stress-induced intra-hippocampus corticosterone rise associated with memory impairments in middle-aged mice

The present study investigates the relationships between hippocampal corticosterone concentrations and memory retrieval performance in stress and non-stress conditions, in both young (6 month-old) and middle-aged (16 month-old) mice. For this purpose, the time-course evolution of stress-induced corticosterone rise in the dorsal hippocampus (dHPC) was investigated in both young and middle-aged mice. In parallel, the evolution of memory retrieval patterns was assessed using a contextual serial discrimination task (CSD). Finally, metyrapone (corticosterone synthesis inhibitor) was administered in order to evaluate the stress-induced impact of corticosterone rise on contextual memory retrieval in middle-aged animals.Results showed that: (i) non-stressed middle-aged mice exhibited a memory retrieval pattern opposite to that of non-stressed young animals, but similar to that of stressed young mice; (ii) the impact of stress on memory performance was transient (90 min) in young, as compared to middle-aged mice (120 min); (iii) dHPC basal (non-stress) corticosterone level was significantly increased by ageing; (iv) acute stress induced a rapid (15 min) and transient (90 min) dHPC corticosterone rise in young mice, while exhibiting greater magnitude and duration (120 min) in middle-aged animals; and (v) both the stress-induced endocrinal and memory effects were blocked by metyrapone in young and middle-aged mice.Finally, to our knowledge, the present work is the first study to directly measure the corticosterone rise in the hippocampus following exposure to stress and to directly correlate the corticosterone changes in the hippocampus with memory performance in both young and middle-aged mice.     

Reduction in paradoxical sleep after L-dopa administration in rats

The EEG and EMG activity of two groups of rats (N = 8 each) was recorded during one experimental and 5 control days. On the experimental day, one group received 125.0 mg/kg L-dopa preceded by 50.0 mg/kg benserazide hydrochloride. The other group received 1.0 mg/kg haloperidol, immediately before the recording session. After L-dopa plus benserazide administration the total time and the number of episodes of paradoxical sleep and slow wave sleep decreased significantly compared to control sessions.     

Differential effect of handling on adult aggression in male mice bidirectionally selected for attack latency

Individual variation in intermale aggression is to a significant degree based upon genetic variation, but environmental factors can also exert their influence on the level of aggression. Moreover, genotype–environment interactions are a well‐known phenomenon. In the present experiment, I tested whether cage size or handling during development had an influence on adult attack latency scores. To be able to study a genotype–environment interaction, mice from two bidirectionally on attack latency selected lines were used. The size of the cage in which the mice grew up had no long‐term effect on aggression, neither in the high‐ nor in the low‐aggressive line. Handling, however, significantly increased the adult aggression of males from the low‐aggressive line. Despite the differential effect of handling on genetically high‐ and low‐aggressive mice, handling was not able to undo the marked differences in attack latencies between mice from both lines. Aggr. Behav. 25:365–368, 1999. © 1999 Wiley‐Liss, Inc.