Early neuromotor behavior in craniosynostotic rabbits.

Objective: Clinical studies have shown both abnormal and normal mental and psychomotor development in patients with craniosynostosis. However, a number of confounding variables make study comparisons difficult. For these reasons, the present study describes early neuromotor development in an homogeneous rabbit model of craniosynostosis.

Design: Fifty-three newborn New Zealand white rabbit kits were used: 13 were wild-type, normal control rabbits; 23 had delayed-onset coronal suture synostosis (onset is approximately 57 to 74 days post conception); and 17 had early-onset coronal suture synostosis (onset is approximately 21 to 25 days post conception). All rabbits were observed individually and blindly in an open field, daily for 2 minutes, from birth through the first 14 days of life. The first day of emergence of 10 different mature behaviors and developmental events (in developmental order of appearance: falling, righting, cliff avoidance, first sign of fur, body elevation, head elevation, circling, dragging, eye opening, and hopping) was recorded for each kit. Daily activity levels (grid crossing), and body weights were also recorded.

Results: Significant group (p <.05) differences were observed in 9 of 11 measures. Both synostosed groups had significantly (p <.05) accelerated onset of behavior in 8 of 9 measures, compared with wild-type controls. The early-onset synostosis group had significantly (p <.05) accelerated onset in five of eight measures, compared with wild-type controls, and three of eight measures, compared with the delayed-onset synostosis group.

Conclusions: Synostotic rabbits showed precocious neuromotor development possibly through frontal lobe constrictions and altered brain activity from increased intracranial pressure, although primary genetic effects cannot be ruled out.