The effect of environmental stimulation on brain weight in previously undernourished rats

Effects of environmental enrichment on cortical depth and Morris-maze performance in B6D2F2 mice exposed prenatally to ethanol

Pregnant mice were fed a liquid diet with 25% of the calories as ethanol from day 5 to 17 of gestation; controls received equivalent amounts of diet with maltose-dextrin substituted isocalorically for the ethanol. Two male weanlings from each litter were assigned randomly to an enriched or isolated environmental condition. After 6 weeks in these environments measures of brain growth were obtained, including thickness of frontal, parietal, and occipital cortex (study 1), or their behavioral capabilities were assessed in a Morris water maze (study 2). Ethanol decreased birth weight (both studies), postweaning body weight (study 2), and brain weight (study 1), while the enriched animals in both studies were heavier. Ethanol decreased the thickness of the occipital cortex only. All groups demonstrated learning by showing a decrease in latency to locate the hidden platform over the 5 days of testing; this was supported by their spending most time in the target quadrant during the probe trial. The latencies of the enriched animals were shorter than the isolated; covariance analysis indicated that this was not due solely to their faster swimming speed.

Neuronal and synaptic measurements in the visual cortex of adult rats after undernutrition during normal or artificial rearing

It is possible that the reported effects of early life undernutrition on brain morphology may be due to alterations in mother-infant interactions and not directly to undernutrition. We have investigated this possibility by comparing artificially reared with mother-reared rats. Four groups of black-and-white hooded male rats were reared. These consisted of mother reared control (MRC), mother reared undernourished (MRU), artificially reared control (ARC) and artificially reared undernourished (ARU). Artificially reared rats were raised in isolation away from their mothers from 5 to 21 days of postnatal age. They were fitted with a gastric cannula through which 'milk' was infused automatically. The period of undernutrition lasted from 5 to 25 postnatal days, following which the animals were fed ad libitum until 312 days of age. Rats from each group were then killed by perfusion with buffered 2.5% glutaraldehyde. Pieces of visual cortex from each rat were postfixed in osmium tetroxide and embedded in resin. Stereological procedures at the light and electron microscopical levels were used to estimate the synapse-to-neuron ratios in cortical layers II to IV. Both MRC and ARC rats had about 7000 synapses per neuron. However, this ratio was about 8300 in MRU rats whilst it was only about 5000 in ARU animals. The rearing x nutrition interaction was statistically significant at the 0.1% level. These changes in the synapse-to-neuron ratio were mainly due to alterations in the numerical densities of the synapses rather than that of neurons. These results demonstrate that environmental isolation, as a result of artificial rearing procedures, and concurrent undernutrition during the first three weeks of postnatal life, interact with one another to produce marked morphological changes in the adult rat brain. However, environmental isolation was not, by itself, sufficient to cause permanent changes in interneuronal connectivity.

Effects of early life undernutrition in artificially-reared rats. 2. Subsequent behaviour

Four groups of rat pups were reared: mother-reared control (well-fed) and undernourished (MRC, MRU) and artificially-reared control and undernourished (ARC, ARU). AR rats were fed expressed rats' milk (days 5-7), mixtures of rats' milk and milk substitute (days 8-16), and milk substitute only (days 17-20) by intermittent infusion via a gastric cannula. Undernutrition, imposed from 5-25 days, was effected initially by underfeeding the mother (MRU) or by infusing restricted quantities of milk (ARU). Weaning was at 21 days and undernutrition from 21-25 days was by restricting the supply of solid food. All rats were fed ad lib from 25 days. From 18 weeks, male rats were subjected to 3 behavioural tests: open field, social behaviour (encounters between rats of like treatment group) and bar-pressing for food (CRF, FR5, VI 1', VI 2' and Extinction). Previously undernourished rats responded at higher rates on FR5, received fewer rewards on VI 2' and displayed more aggression during social interaction. These findings may reflect direct effects of nutrition on brain growth. In the open field and social situations ARU were generally less active than ARC animals, whereas MRU and MRC rats differed little. These results are discussed in terms of MRU pups being maternally "buffered" against the worst effects of undernutrition and ARC rats displaying characteristics of "early stimulated" animals.

The comparative effects of early-life undernutrition and subsequent differential environments on the dendritic branching of pyramidal cells in rat visual cortex

Male rats were either undernourished or fed normally from birth to day 21, after which time food was made freely available. At 1 month of age littermate pairs from both nutritional groups were housed in either enriched or impoverished conditions for 30 days and then killed for brain measurements. Significant deficits due to undernutrition were observed in the weight and size of the cerebrum, but not in the thickness or area of the visual cortex. Although there were large differences of between 21 and 39% in the number of higher-order basal dendrites of layers II and III pyramidal cells, and of about 19% in the distal ring intersections, none except the fourth-order branches and intersections at 100 micron from the cell body approached statistical significance. Changes in cerebral weight and size also occurred as a result of differential housing, with the enriched rats showing increased values relative to their impoverished littermates. In contrast to the nutritional treatment, differential housing significantly affected cortical thickness and area, as well as basal dendritic branching of the pyramidal cells. Enriched rats had relative increases of 26% in the number of fifth-order branches and 45-80% in the number of distal ring intersections.

The separate and combined effects of early undernutrition and environmental complexity at different ages on cerebral measures in rats

Rats were either undernourished or fed normally during the suckling period, then at 1 and 5 months of age littermates were housed in enriched or impoverished environments for 30 days. The undernutrition caused lasting reductions in the weight and size of the cerebrum and in parameters of the hippocampus, but significant deficits were not observed in the thickness and area of the occipital cortex. Differential housing differed from early undernutrition in that its largest effects were on cortical parameters, but the effects of the two conditions did partly overlap. This meant that some nutritionally induced deficits could be modified later by manipulating environmental complexity. The cerebral response of the previously undernourished rats to differential environments was not distinguishable from that of well-fed controls on the basis of the gross anatomical changes that were measured. Furthermore, no significant differences were found between the environmental effects in young and mature rats, although the latter's response tended to be somewhat less for most parameters.

The effects of early-life undernutrition and subsequent environment on morphological parameters of the rat brain

The investigation examines the extent to which lasting effects of early-life undernutrition on the brain of rats can be modified by manipulating the amount of environmental stimulation later. Infant rats were undernourished during the vulnerable brain growth spurt in the lactation period; then after two months of unrestricted feeding, they were placed in enriched or impoverished environments. Measurements of the forebrain, posterior cerebral cortex and hippocampus showed that neither undernutrition nor environmental stimulation affected the brain uniformly and that some parameters were more susceptible to one condition than the other. Where nutritional and environmental conditions affected the same anatomical dimensions, their combined effects appeared to be additive rather than synergistic.

Sex differences in effects of environmental stimulation on brain weight of previously undernourished rats

Neonatally undernourished male and female rats were housed under differential (enriched vs standard) environmental conditions during refeeding from 30 days post-partum (dpp). Animals were killed at 170 dpp and whole brain, forebrain and cerebellar weights compared with those of normally-fed, differentially housed control animals. A sex difference was observed in the response to environmental enrichment. Enriched females showed significantly increased brain weights, irrespective of previous nutritional history. Enriched males failed to show any significant alteration in brain weight. Autopsy results indicated that the enriched condition was stressful to males but not to females. The results cast doubt on the notion that infantile undernutrition may limit later effects of differential experience on the brain.