Biomedical subjects
Publications and source records attributed to G Chapouthier.
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.
The capacity to attack a passive standard opponent in a resident-intruder test and the GAD activity in the olfactory bulbs were measured in 140 male mice from seven different inbred mouse strains. The effect of the non-pseudo autosomal region of the Y-chromosome (YNPAR) on these two phenotypes has also been investigated using a quartet of reciprocal strains congenic for the YNPAR. A strong negative correlation was found between the two variables but the YNPAR is not involved. This result suggests that males of more attacking strains have a lower olfactory threshold, making the olfactory discrimination of the opponent easier and its identification as a stranger more efficient.
The propensity for anxiety-related behavior has been studied by comparing two highly inbred strains of mice, ABP/Le and C57BL/6ByJ, in two behavioral procedures, open-field and light-dark preference. Their Mendelian F2 population allowed us to evaluate the putative involvement of four easily identifiable loci in anxiogenic processes. In fact, chromosomal regions containing the brown, pink-eyed dilution and short-ear loci on the 4th, 7th and 9th chromosomes respectively are associated with anxiety-related behavior patterns. In addition, binding of [3H]flumazenil to brain GABA(A) receptors was measured as a biochemical index that may be associated with observed behavior patterns.
A study of the effect of Ginkgo biloba extract (EGb 761) has shown enhancing effects on training in adult and aged Swiss mice. An analysis of inbred mice has confirmed this sensitivity to EGb 761, but depending on the strains, with different effects at different ages. The most interesting results are related to improvements in performances observed with aged mice of the DBA/2J strain. The results obtained with inbred strains in the study of the mossy fibers of the hippocampus make it possible to suggest a link between the improvements in training and the histological structure of the hippocampus. This possibility, which can be confirmed by further studies, is presented here.
The linkage-testing strain of ABP/Le mice carries six mutations which express in easily identifiable phenotypes. By crossing this strain with a traditional inbred strain (C57BL/6ByJ) which is the 'wild type' for the mutated ABP/Le loci, we produced Mendelian populations, intercrosses and backcrosses so as to estimate whether the sensitivity to methyl beta-carboline-3-carboxylate (beta-CCM), a benzodiazepine receptor inverse agonist, and anxiety-related behaviour could be related to a common genetically determined substrate. We have shown that one locus on chromosome 9 is associated with beta-CCM-induced seizures and three loci on chromosomes 4, 7 and 9 are associated with anxiogenic processes. Analysis of [3H]flumazenil binding suggested a possible involvement of a Bmax decrease in both beta-CCM-induced seizures and anxiogenic processes. The putative common genetic regulation of both mechanisms is discussed.
Analysis of beta-CCM induced seizures in three inbred strains of mice, ABP/Le, C57BL/6J and C57BL/6ByJ, and their F1s and F2s progeny, allowed identification of a putative seizure susceptibility controlling locus on chromosome 9 near the short-ear locus. The involvement of a gene in the medial segment of this chromosome in both seizure activity and GABA-controlled behaviour is discussed.
The convulsant properties of methyl beta-carboline-3-carboxylate (beta-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, beta-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 beta-CCM. Both the Ta gene and the TaTfm/Gnc genetic background were involved in the high resistance to beta-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.
A model to explain individual differences in mice for the propensity to attack male conspecifics is proposed. In the first part of the paper, the relation between olfaction and intermale aggression is discussed emphasizing the importance of olfactory cues provided by the opponent and their subsequent processing by the attacking male. The physiological role of GABA in the olfactory pathway is presented in the second part of the paper. The third part investigates the possible modulating action of steroids on the GABA-A receptor complex, intermale aggression, and olfaction. We hypothesize that at least part of the individual differences in the propensity to attack may be explained by a differential olfactory recognition and discrimination of the opponent as a stranger through a differential processing threshold of the olfactory cues provided by the urine of the opponent. A possible modulation of this threshold by steroids, especially testosterone, is also discussed.
The capacity of males to attack a passive standard opponent in a resident-intruder test and the preferences in a dark/light choice situation were measured in 200 male mice from 10 different inbred mouse strains. Large strain differences were found for all variables recorded, i.e., the proportion of attacking males, the time spent in the brightly lit box, and the number of transitions between the lit and the dark boxes. A strong negative correlation was found between the first two variables. This result suggests that males of more attacking strains have a higher level of anxiety but do not differ for their level of activity. An involvement of GABA as mediating factor is suggested.
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.
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.
beta-CCM is a beta-carboline known to have properties opposite to those of benzodiazepines. Our approach was to analyze, in mice, the genetic mechanisms involved in beta-CCM-induced myoclonic seizures using recombinant congenic strains and F1 hybrids issued from these strains. Our aim was to define the extent of the multigenic character of beta-CCM-induced myoclonic seizures, while also evaluating the distribution of the strength of the genes implicated in this trait. The results show that the control of reactivity to beta-CCM is multigenic with notable epistatic involvement.
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.
In a light-dark choice situation, the alpha-2 adrenoceptor antagonist idazoxan shows anxiogenic-like effects, which cannot be blocked by the alpha-2 adrenoceptor agonist clonidine, or by the benzodiazepine receptor antagonist Ro 15-1788. In a conditioned conflict situation, both idazoxan and the alpha-2-adrenoceptor yohimbine show anxiogenic-like effects; the effect of idazoxan could not be blocked by clonidine or Ro 15-1788. These data suggest that systems other than alpha-2 adrenoceptors or benzodiazepine receptors must be found to explain these anxiogenic-like properties.
The Morris water-maze has been designed to test spatial orientation ability, learning and memory processes. In order to improve the analyse of the organization of the trajectory of rats, during the training phase, a computer program was elaborated. The study of the effect of a benzodiazepine, diazepam, was chosen to illustrate and validate this methodological approach. Results showed that rats pre-treated with diazepam (2 mg/kg) presented an impairment of spatial learning associated with the occurrence of a stereotyped circular swimming behaviour.
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.
Recombinant congenic strains (RCS) represent a series of related strains, each of which carries a small fraction of the genome of one strain ("donor" strain) on the genetic background of another strain ("background" strain). Recombinant inbred strains (RIS) are commonly used to identify major gene segregation and linkage and associations between behavior and quantitative trait loci, whereas recombinant congenic strains (RCS) open other complementary leads. The variability in the reactivity of RCS to a trait is thus the expression of few minor-effect genes originating from the donor strain, because the probability that major genes are present in any one RCS is low. Unlike RIS in which minor-effect genes are often masked by major genes, RCS enable the effects of minor genes to be studied. With our method, for a given trait, an estimate can be made of the gene strength distribution as well as an estimate of the minimal number of genes involved having a certain strength.
The beta-carbolines, methyl-beta-carboline-3-carboxylate (beta-CCM) and 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) are known to have pharmacological properties opposite to those of agonistic benzodiazepines. Convulsions induced by these drugs lead to differential patterns, such as clonus, myoclonic or tonic seizures. In 10 different inbred strains of mice we investigated whether the responsiveness to the two drugs was the same, irrespective of the pattern of convulsions. We found the same ranking in the responsiveness of the strains to both drugs in the case of myoclonic seizures. No such correlation could be found for clonus or tonic seizures. Our conclusion is that the same genetic factors determine myoclonic seizures, whereas a plurality of mechanisms underly the other patterns. Thus, myoclonic seizures seem to be the most appropriate index for evaluating the convulsant action of beta-carbolines in genetic experiments.