Mice selected for differences in sensitivity to a benzodiazepine receptor inverse agonist vary in intermale aggression

Phenotypic differences between fast and slow methionine sulfoximine-inbred mice: seizures, anxiety, and glutamine synthetase

Seizures induced by the convulsant methionine sulfoximine (MSO) resemble human "grand mal" epilepsy, and brain glutamine synthetase is inhibited. We recently selected two inbred lines of mice: sensitive to MSO (MSO-Fast) and resistant (MSO-Slow). In the present study, the selection pressure was increased and consanguinity established. To gain insight into the mechanisms of epileptogenesis, we studied the behaviour of MSO-Fast and MSO-Slow mice based on their responses to various convulsants and anticonvulsants, and also the kinetics of glutamine synthetase. The results show that increasing the number of generations of sib-crossings resulted in an increase in the differences between MSO-Fast and MSO-Slow mice. The dose-response curve of MSO-dependent seizures demonstrated that the MSO-Slow mice were highly insensitive to MSO-dependent seizures compared with MSO-Fast inbred mice that were highly sensitivity. The MSO-Slow were resistant to convulsions induced by various convulsants having different mechanisms of action, whereas those in the MSO-Fast line were more sensitive to kainic acid-induced seizures. These data, in addition to the effects of anticonvulsant, strongly suggest that glutamatergic pathways are most likely involved in MSO-dependent seizures, rather than GABAergic ones. This hypothesis is corroborated by the glutamine synthetase activity, which is more elevated in the MSO-Slow line. Behaviour tests showed that MSO-Slow were less anxious than MSO-Fast. Collectively, these results showed that glutamatergic pathways could be involved in the epileptogenic action of MSO, which may be related to the glutamate/glutamine cycle in the brain.

Behavioral effects of ventilated micro-environment housing in three inbred mouse strains

Animal facilities aim to combine animal welfare with cost-efficiency and limited care staff requirements, and individually ventilated cage (IVC) systems were developed towards these goals. While IVC have great sanitary advantages both for the animals but also for the care staff, these systems involve potentially deleterious features such as high levels of air renewal, noise, and subtle vibrations of the racks because of the air filtering system used, but also reduce the frequency of stressful cage changes. It is unknown in how far these conditions may influence the animals' behavior. This issue becomes critical as many facilities are switching to IVC systems, possibly complicating replication of data or biasing ongoing studies. We investigated the effects of IVC housing in mice on different behaviors including anxiety, exploration, and learning in males and females of three common and phenotypically distant strains. Results demonstrate robust effects of IVC in multiple behavioral tests with the direction of the effect strongly dependent on strain and sex. These data should serve to alert researchers that a switch to IVC housing during the course of an experiment has the potential to bias results in a serious manner. In addition, behavioral baseline data will have to be re-established once the switch has been completed.

Enhanced Activity of DNA Polymerase Iota in Mouse Brain Cells Is Associated with Aggressiveness

Recent studies performed with crude extracts of mouse tissues showed that the activity of DNA-polymerase iota (Pol iota) can be detected only in brain and testis extracts. To assess whether the activity of Pol iota is associated with animal behavior, we determined Pol iota activity in brain extracts of mice of two lines sharply differing in aggressiveness (RSB and RLB). We found that Pol iota activity in the mice with aggressive behavior was three times higher than in the less aggressive mice. The possible relationship between the activity of Pol iota and animal behavior is discussed.

Benzodiazepines and heightened aggressive behavior in rats: reduction by GABA(A)/alpha(1) receptor antagonists

RATIONALE

Positive modulators of the benzodiazepine/GABA(A) receptor complex can heighten aggressive behavior; the GABA(A)/alpha(1) subunit may play a critical role in benzodiazepine-modulated aggressive behavior.

OBJECTIVE

The carboline derivatives, beta-CCt and 3-PBC, antagonists with preferential action at the GABA(A) receptors with alpha(1) subunits, may antagonize benzodiazepine-heightened aggression, thus implicating the alpha(1) subunit in heightened aggression.

METHODS

The GABA(A) receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4c]-pyridin-3-ol (THIP) (0.01-3.0 mg/kg), and the benzodiazepine receptor agonists midazolam (0.3-3.0 mg/kg) and triazolam (0.003-3.0 mg/kg) were administered to adult male resident rats to assess the drugs' effects on their aggressive behavior toward an intruder. Then beta-CCt (0.3-10.0 mg/kg) and 3-PBC (0.3-17.0 mg/kg) were each administered in conjunction with midazolam. The salient elements of aggressive and non-aggressive behavior were measured by analyzing video recordings and encoding each behavioral act and posture in terms of its frequency and duration of occurrence.

RESULTS

Midazolam significantly increased the duration of aggressive behaviors at 1.0 and 1.7 mg/kg, and triazolam increased attack bite frequency at 0.03 mg/kg, both implicating GABA(A) receptors with benzodiazepine binding sites in aggressive behavior. In the present dose range, THIP did not affect any behaviors. The broad-spectrum benzodiazepine antagonist, flumazenil (1.0 mg/kg), antagonized the aggression-heightening effects of midazolam. beta-CCt (0.3-10.0 mg/kg) and 3-PBC (0.3-17.0 mg/kg) also antagonized the aggression-heightening effects of midazolam (1.0 mg/kg).

CONCLUSIONS

These results implicate both the GABA(A) gamma and alpha(1) subunits in benzodiazepine-heightened aggression.

Mouse lines differing in sensitivity to beta-CCM differ in tasks used for testing antidepressants

Two lines of mice, previously selected for their sensitivity (BS) or their resistance (BR) to an anxiogenic benzodiazepine (BZ) receptor inverse agonist, methyl beta-carboline-3-carboxylate (beta-CCM), have recently been shown to present several differences in anxiety. In the present study, attempt was made to extend their behavioral profile in two situations classically used for testing antidepressant drugs. Reassessment of locomotor performance of these new populations confirmed that the motor activity of BR mice was lower than that of BS mice. In both the forced-swimming and the tail suspension tests, the immobility time of BS mice was significantly higher than that of BR mice. In the tail suspension test, two administrations of imipramine (30 mg/kg i.p., 5 h and 30 min before testing) significantly reduced the immobility time of BS mice but not of BR mice. From these data, it appears that BS mice are more "depressed" than BR mice. Thus, these selectively bred lines may represent potentially useful animal models to investigate behavioral, neurochemical and neuroendocrine correlates of antidepressant action.

Divergent levels of anxiety in mice selected for differences in sensitivity to a convulsant agent

Spontaneous behavior patterns were assessed in eight different behavioral situations in two lines of mice, BR and BS, previously selected for their sensitivity to an anxiogenic benzodiazepine (BZ) receptor inverse agonist, Methyl beta-carboline-3-carboxylate (beta-CCM). BR is highly resistant, and BS, highly sensitive to beta-CCM-induced seizures. Tests used included an assessment of general locomotor activity, several situations classically used for measuring fear-motivated behaviors (open field, thigmotaxis, elevated plus-maze, light-dark discrimination, staircase), a test for measuring exploration (holeboard), and a test for measuring nociception (hot-plate). In the absence of beta-CCM, the results provide evidence of reduced motor activity and higher levels of anxiety in the BR line as compared to the BS line.