Longitudinal analysis of the behavioural phenotype in R6/1 (C57BL/6J) Huntington's disease transgenic mice

Huntington's disease is caused by a single mutation on the HTT gene which produces an expansion in the number of glutamine repeats present in the huntingtin protein. This mutation results in an array of motor, cognitive and behavioural problems mediated by a progressive loss of striatal neurons and brain atrophy. The identification of behavioural phenotypes in mouse models of the disease provides a baseline of efficacy for therapeutic interventions. The R6/1 mouse line carries ∼115 CAG repeats and has an aggressive form of the disease. The aim of the present study was to undertake longitudinal behavioural characterisation of this mouse line in order to quantify the time course and severity of disease progression. In the present study, when compared to wildtype littermates, male R6/1 heterozygous mice demonstrated a progressive weight loss from 3 months of age. The R6/1 carriers also demonstrated a relatively stable motor coordination deficit on the rotarod, and progressive impairments on each aspect of the balance beam test: latency to orientate and traverse the beam; number of fore- and hind-limb footslips. The R6/1 carriers were less reactive to acoustic startle stimuli and displayed less inhibition to prepulse warning stimuli than their wildtype littermates. In the Morris water maze, the R6/1 carriers demonstrated a deficit on latency to find the platform and path length measures, which was apparent by 3 months of age but not further progressive. They also demonstrated fewer entries into the target zone during probe trials. The data from the present study demonstrate that the R6/1 mouse has a profound behavioural phenotype that includes motor and cognitive deficits, but that not all of these deficits were robustly progressive in nature.