Alterations in dopamine D3 receptors in the circling (ci3) rat mutant

Significance of F3/Contactin gene expression in cerebral cortex and nigrostriatal development

F3/Contactin is a neuronal surface glycoprotein, which plays a general role in neural development and, in particular, in neuronal and oligodendrocyte differentiation. In a previous study using the F3/EGFP transgenic mice, which express an EGFP reporter under control of the regulatory region from the mouse F3/Contactin gene, the activation of the F3/Contactin promoter was found to correlate with granule and Purkinje neuron differentiation in developing cerebellar cortex. Here we report that in developing cerebral cortex and basal ganglia the F3/Contactin gene is mostly activated during early commitment of neuronal precursors, thus indicating a region-specific profile of its developmental activation. We also report that, in the same structures of F3/EGFP mice, a downregulation of the endogenous F3/Contactin gene occurs, which correlates with upregulation of the dopaminergic phenotype and with locomotor pattern abnormalities. Therefore, F3/EGFP transgenic mice exhibit morphological and functional phenotypes recapitulating those arising from imbalance of the striatal dopaminergic pathway. As for the underlying mechanisms, we postulate that in F3/EGFP mice F3/Contactin downregulation results from the ability of transgene promoter sequences to interfere with the activation of the endogenous gene, thus realizing an F3/Contactin knockdown model, while dopaminergic upregulation is consistent with a general F3/Contactin inhibitory effect on the neuronal phenotype.

Comparative analysis of anxiety-like behaviors and sensorimotor functions in two rat mutants, ci2 and ci3, with lateralized rotational behavior

There is increasing evidence that developmental anomalies of cerebral asymmetry are involved in the etiology of psychiatric disorders, including schizophrenia, depression and anxiety. Thus, rodents with abnormal cerebral lateralization are interesting tools to study the association between such anomalies and behavioral dysfunction. The most studied indicator of cerebral asymmetry in the rat is that of circling or rotational behavior. We have recently described two rat mutants, ci2 and ci3, in which lateralized rotational behavior occurs either spontaneously or in response to external stimuli, such as new environment or handling. While cochlear and vestibular defects are found in ci2 rats, ci3 rats do not exhibit any inner ear abnormalities. The abnormal motor response to external stimuli raised the possibility that the circling rat mutants may be more likely to express anxiety-related behavior in tests of emotionality. In the present study, we characterized anxiety-related behaviors of ci2 and ci3 rats in the open field, elevated plus-maze and light/dark exploration test. Furthermore, sensorimotor functions of these rats were evaluated by the rotarod, accelerod and wire hang tests. Heterozygous (ci2/+) littermates or rats of the respective background strains (LEW, BH.7A) were used as controls. In contrast to our expectation, both mutants demonstrated less anxiety-related behavior than controls in tests of emotionality. Ci3 rats exhibited normal sensorimotor functions, whereas marked impairment was observed in ci2 rats, which is most likely a consequence of the vestibular dysfunction in these animals. The acoustic startle response (ASR) and prepulse inhibition of ASR did not differ between ci3 rats and controls. The reduced emotionality of the mutant rats indicated by the present experiments may not be specifically linked to anxiety per se, but is maybe more reflective of impulsivity or the inability to normally perceive or process potentially threatening situations. Based on previous findings of dysfunctions of the central dopamine system in ci2 and ci3 mutant rats, we assume that alterations in dopaminergic activity are involved in the maladaptive behavior observed in the present study.