Antiaggressive and motor effects of the DA release inhibitor CGS 10746B

In the present study the effects of a wide range of doses of the dopamine release inhibitor CGS 10746B were evaluated in spontaneous activity and in aggressive behaviour using the paradigm of isolation‐induced aggression. The two higher doses (8 and 16 mg/kg) produced a decrease in spontaneous motor activity. Antiaggressive effects were observed after administration of doses from 4 mg/kg upwards. At this dose, CGS 10746B diminished threat and attack, and although an increase in immobility was observed, no impairment of other motor behaviours was presented. With higher doses, aggression was practically abolished but with a concomitant effect on many other behaviours. When animals were separated depending on their latency of attack, those that showed a long attack latency (LAL) presented a stronger response to 4 mg/kg than those that had a short attack latency (SAL), which were not affected in their aggression by this dose. We can conclude that presynaptic dopamine function is necessary for the normal expression of aggressive behaviours, since CGS 10746B reduces aggression at doses that do not affect spontaneous motor activity. Aggr. Behav. 27:382–390, 2001. © 2001 Wiley‐Liss, Inc.     

Interactions between the effects of food and water motivating operations on food‐ and water‐reinforced responding in mice

Two experiments examined interactions between the effects of food and water motivating operations (MOs) on the food‐ and water‐reinforced operant behavior of mice. In Experiment 1, mice responded for sucrose pellets and then water reinforcement under four different MOs: food deprivation, water deprivation, concurrent food and water deprivation, and no deprivation. The most responding for pellets occurred under food deprivation and the most responding for water occurred under water deprivation. Concurrent food and water deprivation decreased responding for both reinforcers. Nevertheless, water deprivation alone increased pellet‐reinforced responding and food deprivation alone likewise increased water‐reinforced responding relative to no deprivation. Experiment 2 demonstrated that presession food during concurrent food and water deprivation increased in‐session responding for water relative to sessions where no presession food was provided. Conversely, presession water during concurrent food and water deprivation did not increase in‐session responding for pellets. These results suggest that a) the reinforcing value of a single stimulus can be affected by multiple MOs, b) a single MO can affect the reinforcing value of multiple stimuli, and c) reinforcing events can also function as MOs. We consider implications for theory and practice and suggest strategies for further basic research on MOs.     

Apodemus sylvaticus (LOXT) is a suitable mouse strain for testing spatial memory retention in the Morris water maze

Information on the difference in cognitive function between laboratory and wild-caught mice is anecdotal and this question has not been systematically studied. Moreover, studying a wild-caught mouse strain per se may add information to the repertoire of mouse strains available. We aimed to study spatial memory in a wild mouse strain (Apodemus sylvaticus, AS) as compared to two individual laboratory mouse strains.Male AS (n = 20), CD1 (n = 19) and C57BL/6J mice (n = 19), 12–14 weeks old, were used in the experiments. The Morris water maze (MWM) was used for determination of spatial memory and time spent in the target quadrant at time points 5 (D5) and 12 days (D12) was evaluated. During the acquisition phase latency to reach the platform and path length to reach the platform was evaluated.Following four training days on day 5 (D5), time spent in the target quadrant was highest in AS > CD1 > C57BL/6J (P < 0.006). On day 12 (D12), time spent in the target quadrant was significantly higher in AS than in both other strains (P < 0.001).All animals learned the task and during the acquisition phase, latency to reach the platform as well as path length decreased significantly in AS.It is concluded that the AS is the most suitable strain for the evaluation of spatial memory in the MWM and is presenting with memory retention superior to laboratory mouse strains CD1 and C57BL/6J.     

Naloxone differentially alters parental aggression by female mice towards conspecific intruders of differing sex

Lactating mice respond differently to male and female conspecific intruders, displaying defensive attack towards the former and offensive attack towards the latter. Two studies are reported in which the effects of naloxone on this differential response pattern were assessed. In the first study, lactating residents were pretreated with saline or naloxone (0.5, 2.5 mg/kg) and consecutively confronted with intruders of differing sex. Results suggested that attack (offensive) against female conspecifics is more sensitive to the inhibitory effects of opiate-receptor blockade than attack (defensive) on males. This conclusion was strengthened in a follow-up study, in which independent groups of lactating residents were used to further examine the effects of naloxone (0.5 mg/kg) on response to male and female intrusion. Analysis indicated that this low dose of naloxone significantly inhibited attack on female, but not on male, intruders. Indeed, in response to male, but not to female, intrusion, naloxone-treated residents showed a significant increase in fear-related behaviour. Findings are discussed in relation to the motivational differences in the response of lactating mice to intruders of differing sex and to possible mechanisms underlying the reported differential effects of opiate-receptor blockade.     

Hormonal regulation of aggression: Evidence for a relationship among genotype,receptor binding,and behavioral sensitivity to androgen and estrogen

Gonadectomized male mice from the CF-1, CFW, and CD-1 strains were exposed to different androgens (testosterone, dihydrotestosterone, methyltrienolone) or estrogens (estradiol, diethylstilbestrol) and tested for aggressive behavior. Genetic differences in sensitivity to the aggression-promoting property of the various treatments were found. CF-1 mice responded to either androgenic or estrogenic stimulation, CFW males were most sensitive to the estrogen treatments, while CD-1 males responded to androgen but were relatively insensitive to the aggression-promoting property of estrogens. These data suggest that there may be multiple aggression-activating systems and that the functional pathway varies with genotype. Additional experiments examined whether receptor binding in the hypothalamic-preoptic-septal region was related to the genetic differences in behavioral responsiveness. The binding data suggested that sensitivity to the aggression-promoting property of estrogens was related to either a higher concentration of binding sites or to higher affinity binding between estrogen and its receptor. A systematic relationship between dihydrotestosterone binding and behavioral responsiveness to androgen was not found.     

Genetic analysis of “Spontaneous” intermale aggression in mice

“Spontaneous” intermale aggression was investigated in seven inbred strains of mice. A positive interstrain correlation and cross-correlation was found for two indices of fighting intensity, ie, accumulated attacking time and number of attacks. The strain aggressiveness level (percent of mice fighting in each strain) does not correlate with the intensity of aggressive behavior. It has been shown by using a genetical analysis performed on C57BL/6 and BALB/c strains, their reciprocal F₁ hybrids, and back-crosses that these indices of intermale aggression are under different genetic control. Aggressive behavior intensity depends on the additive effects of genes. The control of strain aggressiveness level revealed that a high level of aggressiveness was dominant. No reciprocal effects were found. The level of aggressiveness and the intensity of fighting seem to represent different aspects of aggression and may be controlled by different genetic mechanisms.     

The influence of the Y-chromosome of Rb/1Bg mice on agonistic behaviors

Males of the Rb/lBg and C57BL/10Bg strains, as well as of the Bl0RblF, and RblBlOF1, reciprocal hybrids, were tested for aggression over three daily trials beginning at 50 days of age. The BlORblF, hybrids were sired by Rb/lBg males, and the RblBlOF, hybrids were sired by C57BL/10Bg males. The mean scores for the agonistic acts of chase, wrestle, flank-bite (but not tail rattle or attack), and the mean “aggression” score (but not mean latencies to first agonistic act or first attack) were significantly higher for BlORblF, than for RblBlOF, hybrids. These findings are consistent with the hypothesis that some aspect(s) of the Rb/lBg Y-chromosome strain can influence the occurrence of some of the motor patterns of offense but not defense. The Y-chromosomes of the DBA/1, DBA/2, CBA, and PHH inbred strains have a similar effect on agonistic behaviors.     

Predatory aggression in lines of wild mice selected for interfemale aggression

Mice descending from lines previously selected for high and low levels of interfemale aggression and from a nonselected control line were exposed to live crickets on two consecutive test days. Latencies both to attack and to eat the cricket were recorded. No line or sex differences in attacking were found, although latency to attack decreased over test days. Control line mice were more likely to engage in the eating of the cricket than either the high or low selected lines, suggesting that the selection procedure may have dissociated attacking and eating components of predatory behavior.     

Agonistic behavior and social reactivity of LG/J mice in both an arena and a seminatural setting

In order to determine the relatively long-term effects of having been primed for agonistic behaviors in an arena setting, 28 male LG/J mice were observed for these behaviors in a seminatural environment for a period of 5 days following a 20 min arena test. The mice were first placed in an arena in which they were allowed either immediate physical contact with another strain (control condition) or were briefly separated from another strain by a transparent partition before being allowed physical access to them (priming condition). Subjects, recorded as either having fought or not fought in the arena, were then placed in a 101 cm square seminatural setting. Seven trials, using 8 LGs each (4 arenaexperienced males and 4 naive females), were made, and agonistic behaviors were recorded for the priming and control condition subjects. The results showed that the control condition fighters (CF) like the priming condition fighters (PF) fought in the arena situation, but different agonistic patterns in the seminatural setting were noted. While in the seminatural environment, both CF and PF mice were attacked frequently and submitted frequently, but PF mice attacked opponents more frequently than did CF subjects (p < 0.025) and elicited significantly more submissions from opponent mice than did CF mice (p < 0.025). It is concluded that: (1) there are more and different agonistic behavior patterns available in the more natural environment than in the arena setting, and more specifically (2) there is a greater effect on agonistic behaviors in a seminatural environment for mice that fought when exposed to the arena priming procedure as compared with mice having fought in the arena control condition.