Georges Chapouthier

Biological bases of anxiety

Anxiety is a complex psychological and behavioural trait, related to behavioural responses as different as seizures, memory, impulsivity or aggression. The biological bases analysed in the present article involve neurotransmitter systems, specific regions in the brain and genetic factors. The genetic approach is given special emphasis as it offers, in rodents, a promising field for acquiring knowledge on biological factors modulating anxiety.

Genetic difference in sensitivity to β-carboline: Evidence for the involvement of brain benzodiazepine receptors

The convulsive effects of methyl beta-carboline-3-carboxylate (beta-CCM), a benzodiazepine receptor ligand, are different in two inbred strains of mice: BALB/cBy mice are more sensitive to beta-CCM than C57BL/6J mice. In the present article, we report the effects of [3H]flunitrazepam binding in these two strains, which suggest a possible explanation of the differences in their sensitivity to beta-CCM by the involvement of brain benzodiazepine receptors.

Cognitive enhancing properties of β-CCM infused into the nucleus basalis magnocellularis of the rat

Peripheral administration of various benzodiazepine derivatives or beta-carbolines (inverse agonists at benzodiazepine receptors), has been shown to affect memory. In this study, the effect of local infusion of a beta-carboline-methyl beta carboline-3-carboxylate (beta-CCM) into the nucleus basalis magnocellularis (NBM) of rats was examined in a two-trial recognition task. The results show that beta-CMM (3 micrograms/0.5 microliter) enhances recognition performance when injected both before or immediately after the acquisition trial. These effects appear to be mediated by a benzodiazepine (BZD) receptor since they were blocked by pretreatment with Ro 15-1788, a BZD receptor antagonist. This study supports the involvement of the NBM in cognitive processes, and demonstrates that these processes can be influenced by alteration of GABAergic neurotransmission.

Involvement of regions of the 4th and 7th chromosomes in the open-field activity of mice.

Reactivity to a new environment was studied in mice, using an open-field procedure in two strains, C57BL/6By and ABP/Le, the F1 populations and the intercrosses F2 and backcross segregating populations. The analysis of the behavioral traits: peripheral and central activities, leaning, rearing and defecation in the parental strains made it possible to show that the ABP/Le strain was more reactive than C57BL/6By. In addition, the study of segregating, for four phenotypic markers, in F2 and backcross populations strongly suggested that two autosomal regions were involved in the control of open-field behavior: one in chromosomal region comprising the b locus on chromosome 4 and one in chromosomal region comprising the p locus on chromosome 7.

Methyl β-carboline-3-carboxylate enhances performance in a multiple-trial learning task in mice

In contrast to diazepam, a benzodiazepine receptor (BZ-R) ligand, which impairs memory processing, methyl beta-carboline-3-carboxylate (beta-CCM), another BZ-R ligand, administered before a training session, enhances performance in a retention test. This action, however, has only been demonstrated in single trial or single session learning protocols. The present report extends these results to a multiple-trial learning procedure in mice (brightness discrimination in a T-maze with negative reinforcement). The animals were trained for sessions of ten trials per day for six consecutive days. In a first experiment, the sessions during the first three days took place after administration of beta-CCM (0.3 mg/kg), diazepam (2.5 mg/kg) or saline. In a second experiment, especially designed to study the effects of beta-CCM, during the first three days animals received beta-CCM (0.3 mg/kg), Ro 15-1788 (15 mg/kg), beta-CCM + Ro 15-1788, vehicles of these drugs or saline. In the first experiment, performance was improved by beta-CCM and impaired by diazepam in the first three sessions as well as in the final three. In the second experiment, beta-CCM alone, as well as Ro 15-1788 improved performance, and the simultaneous administration of the two drugs suppressed these effects. These results suggest that the performance enhancing effects of beta-CCM observed in single trial learning protocols, during the retention test, can already be observed during drug treatment. They confirm that beta-CCM has an action on acquisition (learning). As the effects of beta-CCM are suppressed by the simultaneous administration of Ro 15-1788, our results could suggest a role for benzodiazepine receptors in learning. This question is discussed.

Spatio-temporal analysis of locomotion in BALB/cByJ and C57BL/6J mice in different environmental conditions

We analysed spatial and temporal characteristics of mouse locomotion and investigated whether mouse gait differed between strains and environments. To this end, we used two inbred strains of mice (BALB/cByJ and C57BL/6J) known for their contrasting inherent level of anxiety, in three different visual surroundings. The animal position was determined relative to each environment. Gait cycle, defined as the sequence of limb movements, was analysed relative to time. We also recorded spatial parameters of gait such as stride length, track width and footfall characteristics. These measures allowed us to obtain an accurate description of locomotion and to assess subtle modifications of the gait. We found that mice adjusted their position in space, posture and gait in order to either stabilize their body on the ground in a potentially unsafe environment, or to optimize propulsion and maneuverability in a safer location. In addition, the two strains of mice used different strategies, suggesting that the inherent level of emotionality may affect the organization of locomotion in mice. We further concluded that higher structures of the central nervous system are involved in the online control of locomotion.

Opposite effects of cholinergic agents and benzodiazepine receptor ligands in a passive avoidance task in rats.

Benzodiazepine (Bzd) agonist, diazepam (Dzp) and inverse agonist methyl beta-carboline-3-carboxylate (beta-CCM); acetylcholinesterase inhibitor, physostigmine (Physo) and muscarinic antagonist, scopolamine (Scopo), were investigated for their mnesic effect in a passive avoidance (PA) task in rats. Impairments were observed after Dzp- and/or Scopo-pretraining treatments. Physo was without effect but antagonized the Dzp-induced impairments. beta-CCM enhanced acquisition and antagonized the Scopo-induced impairing effect. All these drugs had no effect in posttraining administration.

Association of autosomal loci with the grooming activity in mice observed in open-field

We studied the reactions of mice when placed in an open-field environment and counted the grooming score in response to novelty. We used animals from Mendelian F2s and backcrosses, obtained from the parental strains ABP/Le and C57BL/6By, to test the hypothesis that the differences in this behavior were due to genetic variation at loci associated with visible recessive markers. Furthermore, the analysis of the segregating populations by means of non parametric Collins method was used to test the one segregating unit hypothesis. We provide evidence for genes involved in the variation of grooming activity and situated close to the locus se on chromosome 9. Although the one-locus hypothesis was ruled out in the general analysis, a possible major gene effect in some crosses suggests a maternal environment effect.

Comparison between the effects of the benzodiazepine receptor ligands methyl beta-carboline-3-carboxylate and diazepam in two learning situations in mice

Benzodiazepines are known to induce profound amnesia in man. In this report, we show, in mice, that whereas benzodiazepine diazepam indeed impairs performance, methyl beta-carboline-3-carboxylate gB-CCM), an inverse agonist of the benzodiazepine receptor, on the contrary enhances performance. The two learning situations used were one-trial passive avoidance and multiple-trial light-dark discrimination in a T-maze. Since these effects are blocked by Ro 15–1788, a specific antagonist of the benzodiazepine receptor, they are likely to be mediated by the benzodiazepine receptor. They seem to involve action on learning rather than on memory.

A mouse mutant strain highly resistant to methyl β-carboline-3-carboxylate-induced seizures

The convulsant properties of methyl β-carboline-3-carboxylate (β-CCM) were evaluated in the TaT-fm/GncTa+/+Tfm strain carrying the tabby coat color (Ta) and/or the testicular feminization (Tfm) gene. When injected intraperitoneally within a 5–60 mg/kg dose range, β-CCM-induced convulsions in less than 25% of the mice, thus providing evidence for a high resistance of this strain, as compared to classical strains of mice. However, this strain responds normally to the convulsant pentylenetetrazol (PTZ), suggesting a specific resistance to β-CCM. Both the Ta gene and the TaTfm/Gnc genetic background were involved in the high resistance to β-CCM. In addition, concentrations of neurosteroids and benzodiazepine binding, both modulating GABAA receptor efficacy, have been measured in order to elucidate the biological mechanisms of drug resistance.