The Effects of Environmental Manipulation On The Morphology of The Neonate Rat Brain

Abstract

The intent of the present research endeavor was to determine the effect of differential environment on some morphological aspects of the immature rat brain. All litters of Long-Evans rats were reduced to three male pups per mother at birth. At six days of age three groups were formed: 1. One mother with her three pups remained in the standard colony cage (Unifamily Environment, UFE). 2. Three mothers with three pups each were placed together in a single large cage (Multifamily Environment, MFE). 3. Three mothers with three pups each were placed together in a single large cage with exploratory apparatus (Enriched Condition-Multifamily Environment, EC-MFE). The UFE vs. EC-MFE cohort was divided into three age groups to be sacrificed at 14,19, and 28 days of age. Cortical depth and neuronal nuclei from Nissl-stained histological preparations were measured in the somatosensory and occipital cortices. Neuronal measurements were also made in the lateral geniculate nucleus. A modified ‘hit’ method was employed to determine the percent neuronal constituent in the somatosensory cortex and lateral geniculate body. The results were as follows: There were no marked cortical depth differences between 28-day-old UFE and MFE animals in either the somatosensory or occipital cortices. The EC-MFE animals had significantly greater cortical depths than the UFE animals in all age groups with the exception that the visual cortex was not significantly different in the two groups at 14 days of age. The neuronal nuclear and perikaryon areas in the somatosensory cortex were significantly greater in the EC-MFE animals than in the UFE animals in the 28-day-old animals. The neuronal nuclear area in the occipital cortex also showed such differences. The enriched vs. more restricted environments did bring about cortical differences which demonstrated more plasticity in the neonate than in the adult rat brain.