Normal Prenatal and Postnatal Development of the Hooded Rat and the Effects of Prenatal Treatment with Growth Hormone

Abstract

<p>The prenatal and postnatal development of the rat has been investigated under normal conditions and following treatment of the mother with growth hormone during pregnancy.</p> <p>Whereas most structural measure of normal body and brain development changed in a continuous fashion through the fetal and neonatal stages, the net change in brain DNA (cellularity) was biphasic; the first phase occurring in the fetal stage and the second over the second and third postnatal weeks. Daily treatment of the pregnant rat with growth hormone has no detectable effect on litter-size, placenta weight, or body and brain measures of the fetus in late gestation. However, the treatment did produce two definite effects: (i)prolongation of the gestation period; (ii) an increase in body-weight of the gravid rat which was maintained, in part, throughout lactation. Autopsy on postnatal day 40 showed that a definite growth response had occurred.</p> <p>Naturally occurring differences in maternal body-weight were subsequently studied. Body-weight of the mother was not related to gestation period, litter-size, or birth-weight of the offspring, but was found to be inversely correlated with nest-time. Heavy mothers spent less time with their litters, and imparted a slight developmental precocity to them, compared with light mothers. In the open-field in adulthood, activity level was correlated positively, and defecation level negatively, with the amount of time the mother had spent with the litter in the first two weeks of life. A temperature-dependent model for maternal nursing behaviour was proposed.</p> <p>Prenatal treatment with growth hormone resulted in changes in maternal behaviour in the direction predicted on the basis of body-weight. Offspring from growth hormone mothers showed no developmental precocity when age was dated from conception. Previously reported differences in adult brain structure and behaviour of growth hormone offspring were attributed to a postnatal influence of the growth hormone-treated mother.</p>