ATTENTION, AROUSAL REGULATION & INHIBITORY CONTROL IN FMR1 KNOCKOUT MICE: A MOUSE MODEL OF FRAGILE X SYNDROME

Ji-sook Moon, Ph.D. Cornell University 2006

Fragile X syndrome (FXS) is the most common inherited form of mental retardation, occurring in roughly 1/4000 males and 1/8000 females. An abnormal expansion of a trinucleotide CGG repeat sequence in the fmr1 gene results in transcriptional silencing of this gene, which codes for the Fragile X Mental Retardation Protein (FMRP). The loss of FMRP, directly and/or indirectly, gives rise to the FXS phenotype, which includes a characteristic set of anatomic and cognitive/behavioral features. The present studies were designed to test the hallmark areas of dysfunction (i.e. attention, inhibitory control, hyperarousal, and emotional regulation) seen in human FXS and further characterize spared and impaired functions in fmr1 KO mice. The performance of F1 hybrid fmr1 KO mice (a C57BL/6J x FVB/NJ cross) and wild-type (WT) littermate controls were evaluated on a series of tasks designed to assess inhibitory control and various aspects of attention, Reversal Learning Task, and Associate Learning Task. Regulation of arousal and emotion, two domains affected in FXS, was also evaluated in these tasks by examining the animals reaction to the unexpected presentation of potent olfactory distractors (in the Distraction task), as well as their reaction to committing an error on the previous trial. The present studies provided the first evidence that the hallmark deficits in human FXS -- impaired attention, inhibitory control, and arousal regulation are also impaired in the fmr1 mouse model of FXS. In addition, these findings demonstrate that attentional dysfunction and impaired inhibitory control are most prominent when task contingencies change and when the animal has just committed an error situations that arouse or disturb the mice. Analysis of videotapes further demonstrates that arousal regulation is impaired in the fmr1 KO mice. Additionally, the fmr1 KO mice were not impaired in associative learning, transfer of learning, or reversal learning. The present results provide strong support for the validity of this animal model for future studies designed to elucidate the pathogenic process in human FXS and to test new therapies.