The methamphetamine-sensitive circadian oscillator is dysfunctional in a transgenic mouse model of Huntington's...

A progressive disintegration of the rest-activity rhythm has been observed in the R6/2 mouse model of Huntington's disease (HD). Rest-activity rhythm is controlled by a circadian clock located in the suprachiasmatic nuclei (SCN) of the hypothalamus, although SCN-independent oscillators such as the methamphetamine (MAP)-sensitive circadian oscillator (MASCO) can also control rhythmicity, even in SCN-lesioned animals. We aimed to test whether or not the administration of MAP could restore a normal rest-activity rhythm in R6/2 mice, via the activation of the MASCO. We administered chronic low doses of MAP to wild-type (WT) and presymptomatic (7-8 weeks) R6/2 mice, in constant darkness. As expected, ~40% of the WT mice expressed a rest-activity rhythm controlled by the MASCO, with a period of around 32 h. By contrast, the MASCO was missing from almost 95% of the R6/2 mice, even at early stages of disease. Interestingly, although the MASCO was deficient, initially MAP was able to stabilize the day/night activity ratio in R6/2 mice and delay the onset of disintegration of the rest-activity rhythm driven by the SCN. Furthermore, in presymptomatic R6/2 mice treated with L-DOPA, a MASCO-like component began to emerge, although this never became established. Our data show a major dysfunction of the MASCO in presymptomatic R6/2 mice that is likely to be due to an early abnormality of the catecholaminergic systems. We suggest that the dysfunction of the MASCO in humans could be partially responsible for circadian disturbances observed in HD patients, as well as patients with other neurological diseases in which both catecholaminergic and circadian abnormalities are present, such as Parkinson's disease and schizophrenia.