Mapping of the mouse anonymous DNA fragment, D16Ros2, to human chromosome 3

Thechakragati mouse: A mouse model for rapidin vivo screening of antipsychotic drug candidates

The chakragati (ckr) mouse is a serendipitously discovered insertional transgenic mutant that exhibits circling and hyperactivity. Studies of social behavior, sensorimotor gating and ventricular anatomy suggest that the ckr mouse models aspects of schizophrenia. The underlying genetic and neurodevelopmental mechanisms remain to be elucidated but appear to result in a hemispheric asymmetry in striatal D(2)-like dopamine receptors. The circling is inhibited by administration of antipsychotic drugs and so lends itself to in vivo prospective screening for novel molecules with antipsychotic-like activity. Using the ckr mouse we have applied an in vivo first approach to screening for antipsychotic drug candidates. This offers the advantage of early indication of central nervous system bioavailability and potential toxicological concerns. Additionally, in vivo first screening in the ckr mouse is not biased by any particular neurotransmitter hypothesis of the disease, and so has the potential to identify compounds modifying the behavioral output by novel mechanisms of interaction with the underlying brain circuitry. Thus, in contrast to the classical strategy of hypothesis-driven in vitro screening for drugs fitting a "receptor model" of the disease, the ckr mouse screen has greater potential to identify lead molecules for a new generation antipsychotics with novel mechanisms of action.

Specificity of behavioral and neurochemical dysfunction in the chakragati mouse: a novel genetic model of a movement disorder

The chakragati (ckr) mouse is a transgenic insertional mutant that displays lateralized circling behavior, locomotor hyperactivity, hyperexcitability as well as body weight deficits. The mutation is autosomal and recessive. We have previously found that ckr mice have bilateral asymmetric elevations in striatal dopamine (DA) D2-like (D2, D3 and/or D4), but not D1-like (D1 and/or D5) receptors. Predictably, these mice increase turning in response to the D2-like agonist quinpirole and spontaneously rotate contralateral to the striatal side with the higher D2-like receptors. The overall objective of the present study was to assess the neurochemical specificity of the mutation in ckr mouse, particularly since motor behaviors can be elicited by a multitude of brain regions and neurotransmitter systems within the basal ganglia. Using quantitative receptor autoradiography, we examined the regional distribution of DA uptake sites and 5-HT1A, 5-HT1B/1D, GABAA and mu opioid receptors. Also, we wanted to determine whether increased behavioral laterality as seen in rotation is evident with another test of laterality, such as lateral paw preference. The ckr mice showed greater paw preferences than normal mice; however, neither the degree nor direction of these preferences correlated with rotational behavior. The ckr mice showed moderate decreases in the density of DA uptake sites in all subregions of the striatum, but not in the nucleus accumbens or olfactory tubercle. Interestingly, these decreases in ckr mice were not accompanied by a reduction in striatal tissue DA content. 5-HT1 and mu opiate receptor populations were normal in ckr mice. However, GABAA sites in the mediodorsal thalamus and superior colliculus were bilaterally and asymmetrically elevated in ckr mice. These data are consistent with the idea that the motor phenotypes of the ckr mouse result from specific disturbances within nigro-striatal, striato-pallido-thalamic and striato-nigro-collicular circuitry. The implications of these and past findings are discussed in relation to current thinking about hyperkinetic motor syndromes in humans involving reduced basal ganglia outflow.

Asymmetric elevation of striatal dopamine D2 receptors in the chakragati mouse: neurobehavioral dysfunction in a transgenic insertional mutant

We have previously reported the discovery of a transgenic insertional mutant, recently named the chakragati (ckr) mouse, which displays lateralized circling, locomotor hyperactivity, hyperreactivity, as well as body weight deficits. Since lateralized dopamine function is associated with circling behavior we sought to determine whether dopamine (DA) D1 and D2 receptors were asymmetrically distributed in the striata of adolescent and adult ckr mice using receptor autoradiography. Stereotypic and rotational responses to quinpirole served as behavioral indices of D2 receptor function. The ckr mice showed hemispherically asymmetric elevations in DA D2 receptors in the lateral subregions of the striatum whereas medial regions of the striatum were symmetrically and bilaterally elevated (overall elevation = 30%). As a group, ckr mice had higher D2 receptor levels on the side which was contralateral to the preferred direction of spontaneous nocturnal rotation. Striatal D1 receptors and mesolimbic D2 and D1 receptors of ckr mice were neither elevated nor differentially asymmetric. Young adult ckr mice showed dose-dependent increases in net rotations in response to quinpirole whereas normal mice showed no change from baseline levels. Both groups showed similar stereotypic responses. Older adult ckr mice, however, showed dose-dependent reductions in rotation after quinpirole whereas normal mice turned at baseline levels. Older ckr mice also displayed significantly greater stereotyped sniffing behavior. This unique mutant provides a novel genetic model of basal ganglia dysfunction, and may be useful in studying aspects of neuropsychiatric disorders associated with dopaminergic abnormalities.