The ontogeny of ultrasonic vocalizations and other behaviors in male jimpy (jp/Y) mice and their normal male littermates.

Jimpy (jp/Y) male mice have a sex-linked mutation which results in dysmyelination throughout the CNS, causing tremors and behavioral abnormalities. These mice rarely live past 30 days of age. Due to the sex-linked nature of this mutation, both jimpy and normal male pups occur within the same litter. We examined the early behavioral development of these mice by recording their motor behaviors, including slight movement, locomotion and grooming, and their ultrasonic vocalizations (UVs) at 2-day intervals from 2-20 days of age. Jimpy males weighed less than their normal littermates and reached developmental milestones at a later age. They produced fewer UVs than their normal male littermates from 2-8 days of age, after which UVs ceased almost completely in both groups of mice. Jimpy mice spent less time engaged in coordinated motor activities (locomotion and grooming) than normal littermates, and more time engaged in slight movement or remaining inactive. On three of the behavioral measures used (UV production, slight movement, and inactivity) differences were evident early in development (Day 2 postpartum), whereas differences on the other measures (locomotion, grooming) were not evident until later in the developmental period. Our results indicate the importance of using multiple behavioral measures when examining the functional effects of myelin deficiency.