Molecular genetic approaches to investigate individual variations in behavioral and neuroendocrine stress responses.

A large response range can be observed in both behavioral and neuroendocrine responses to environmental challenges. This variation can arise from central mechanisms such as those involved in the shaping of general response tendencies (temperaments) or involves only one or the other output system (behavioral vs. endocrine response). The participation of genetic factors in this variability is demonstrated by family and twin studies in humans, the comparison of inbred strains and selection experiments in animals. Those inbred strains diverging for specific traits of stress reactivity are invaluable tools for the study of the molecular bases of this genetic variability. Until recently, it was only possible to study biological differences between contrasting strains, such as neurotransmitter pathways in the brain or hormone receptor properties, in order to suggest structural differences in candidate genes. The increase of the power of molecular biology tools allows the systematic screening of significant genes for the search of molecular variants. More recently, it was possible to search for genes without any preliminary functional hypothesis (mRNA differential expression, nucleic acid arrays, QTL search). The approach known as quantitative trait loci (QTL) analysis is based on the association between polymorphic anonymous markers and the phenotypical value of the trait under study in a segregating population (such as F2 or backcross). It allows the location of chromosomal regions involved in trait variability and ultimately the identification of the mutated gene(s). Therefore, in a first step, those studies skip the 'black box' of intermediate mechanisms, but the knowledge of the gene(s) responsible for trait variability will point out to the pathway responsible for the phenotypical differences. Since variations in stress-related responses may be related to numerous pathological conditions such as behavioral and mood disorders, drug abuse, cardiovascular diseases or obesity, and production traits in farm animals, these studies can be expected to bring significant knowledge for new therapeutic approaches in humans and improved efficiency of selection in farm animals.

Dpp and Hedgehog mediate neuron-glia interactions in Drosophila eye development by promoting the proliferation and motility of subretinal glia.

Neuron-glia interactions are crucial for the establishment of normal connectivity in the nervous system during development, but the molecular signals involved in these interactions are largely unknown. Here we show that differentiating photoreceptors in the developing Drosophila eye influence the proliferative and migratory behavior of the subretinal glia through the diffusible factors Decapentaplegic (Dpp) and Hedgehog (Hh). We demonstrate that proliferation and migration of the glia are separable processes, and that Dpp promotes both the proliferation and motility of the glia, whereas Hh appears to promote only their motility; neither specifies the direction of migration. We present evidence that Dpp and Hh act on the glia in parallel and through the regulation of transcription. Finally, we show that ectopic migration of subretinal glia can result in the ectopic projection of photoreceptor axons. Our study suggests a novel function for Hh in regulating migratory behavior and provides further evidence for a complex mutual dependence between glial and neuronal cells during development.

GR 127935 reduces basal locomotor activity and prevents RU 24969-, but not D-amphetamine-induced hyperlocomotion, in the Wistar-Kyoto hyperactive (WKHA) rat.

The hyperlocomotor effect of the serotonin (5-HT)1A,B receptor agonist 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole (RU 24969) has been repeatedly reported. However, 5-HT1A receptors, 5-HT1B receptors (or both) have been claimed to mediate this effect of RU 24969. These contradictory data possibly arise from protocol differences, especially those related to animal species, drugs, and activity assessment. Herein, the influence of a pretreatment with the selective 5-HT1B,D receptor antagonist N-[4-methoxy3-(4-methyl-1-piperazinyl)phenyl]-2'-methyl-4'-(5me thyl-1,2,4-oxadiozol-3-yl)-biphenyl-4-carboxamide (GR 127935; 1, 3.3 and 10 mg/kg IP) on the hyperlocomotor effect of a 5 mg/kg (IP) dose of RU 24969 was studied in Wistar-Kyoto Hyperactive (WKHA) rats. In a first series of experiments, it was confirmed that RU 24969 (2.5 and 5 mg/kg), administered 10 min after the onset of activity recordings, increases locomotion dose-dependently (cage crossings). In a second series of experiments, administration of GR 127935 10 min after the onset of activity recordings promoted a dose-dependent decrease in basal activity (and rearings) and prevented (3.3 and 10 mg/kg) RU 24969-elicited locomotor activity. On the other hand, GR 127935 was ineffective against RU 24969-induced inhibition of rearings. Lastly, it was observed that 3.3 mg/kg GR 127935 did not affect the number of cage crossings and rearings displayed by rats administered 1.5 mg/kg D-amphetamine. This study shows that 5-HT1B receptors play a major role in the hyperlocomotor effect of RU 24969, at least under our experimental setting. Whether these receptors also play a tonic role in the high locomotor activity displayed by WKHA rats remains to be determined.

A major quantitative trait locus influences hyperactivity in the WKHA rat.

The syndrome of hyperactivity describes behavioural disorders existing mainly in children and characterized by increased levels of motor activity, inattention and impulsivity. Overall the aetiology is poorly understood due to the heterogeneity of the pathology although psychological, biological and social factors acting singly or in concert are generally thought to be involved. In animal studies the observed hyperactivity phenotype results from relative participation of exploration, emotionality and general activity. Studies using brain lesions, neuropharmacology and gene knock-out strategies have shown that specific elements of the brain dopaminergic system can subserve hyperactivity. Evidence of a genetic contribution comes from family and twin studies but also from the ability to select divergent animal lines on the basis of their differential activity. The Wistar-Kyoto (WKY) and Wistar-Kyoto hyperactive (WKHA) rats are such strains--distinct for their low and high activity scores in a novel environment, respectively. Here, we report the detection of a major hyperactivity-related QTL on chromosome 8, explaining 29% of the variance of an intercross between these strains. This study represents the first behavioural QTL analysis in rat and provides a new starting point for biologically categorizing different forms of hyper-activity.

Behavioral and neuroendocrine reactivity to stress in the WKHA/WKY inbred rat strains: a multifactorial and genetic analysis.

Genetic factors have been shown to influence the nature and the intensity of the stress responses. In order to understand better the genetic mechanisms involved, we have studied the behavioral and neuroendocrine responses to novel environments in the WKHA/WKY inbred strains and we have investigated the genetic relationships between these traits in a segregating F2 intercross. The animals were submitted to behavioral tests known to provide both indices of activity and fear (activity cages, open field and elevated plus-maze). The plasma levels of prolactin, ACTH, corticosterone, glucose and renin activity were determined after a 10-min exposure to novelty. Our results showed that WKHA rats, compared to WKYs, were more active in a familiar as well as in novel environments. They exhibited also less anxiety-related behaviors and lower neuroendocrine responses. A principal component analysis performed on the behavioral F2 results defined three independent factors: general activity, anxiety and defecation, none of them being correlated with the neuroendocrine measures. Thus this study suggests that these different responses to stress are independent components that may have distinct molecular bases.