Further Studies of Body Growth and Brain Development in ‘Small-for-Dates’ Rats

Rats were growth-retarded either from conception to 5 postnatal days (FNR or ‘small-for-dates’ group) or from 5 to 25 postnatal days (IR group) by underfeeding their mothers or foster-mothers. All young were fed ad libitum from weaning till they were killed at 15–24 weeks. The body weight of the FNR rats was 36% less than that of controls at 5 days and remained significantly less throughout their lives. Their adult nose-rump and tail lengths were slightly but significantly shorter than those of controls, but they did not differ in total body fat. TR rats weighed less than control and FNR rats from 10 days onwards, and they were leaner than both groups at death. They grew more in nose-rump and tail length between 35 and 115 days than the other groups, but were still significantly shorter than the controls at 115 days. This ‘catch-up’ may be related to their relative skeletal immaturity (assessed radiographically) at the time of the body growth spurt. Brain growth was impaired in both FNR and IR rats, though in different ways. Cerebellar growth was selectively affected in IR but not in FNR rats. Total synaptosomal protein (a probable measure of synapse number) was lower in the brains of both experimental groups in proportion to their brain weight deficits.