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Neuronal and synaptic measurements in the visual cortex of adult rats after undernutrition during normal or
K S Bedi1, R F Massey, J L Smart
1Department of Anatomy, University of Queensland, St. Lucia, Brisbane, Australia.
Insights
Early life undernutrition and isolation interact to alter brain development in rats. Artificial rearing alone did not cause lasting changes in synapse-to-neuron ratios in the visual cortex.
Area of Science:
- Neuroscience
- Developmental Biology
- Animal Models
Background:
- Early life undernutrition is linked to brain morphology changes.
- The role of mother-infant interactions versus direct undernutrition effects is unclear.
Purpose of the Study:
- To investigate if artificial rearing (environmental isolation) or undernutrition has a greater impact on brain morphology.
- To examine the interaction between early life undernutrition and environmental isolation on synapse-to-neuron ratios.
Main Methods:
- Four groups of male hooded rats were used: mother-reared control (MRC), mother-reared undernourished (MRU), artificially reared control (ARC), and artificially reared undernourished (ARU).
- Artificial rearing involved isolation from days 5-21 with gastric infusion.
- Undernutrition occurred from days 5-25.
- Stereological analysis of visual cortex (layers II-IV) was performed at light and electron microscopic levels to determine synapse-to-neuron ratios.
Main Results:
- Synapse-to-neuron ratios were similar in MRC and ARC rats (approx. 7000).
- MRU rats showed an increased ratio (approx. 8300), while ARU rats showed a decreased ratio (approx. 5000).
- The interaction between rearing method and nutrition was statistically significant (p<0.001), driven by changes in synapse density.
Conclusions:
- Environmental isolation and undernutrition interact to cause significant morphological changes in the adult rat brain.
- Artificial rearing alone did not lead to permanent alterations in interneuronal connectivity.
- The findings highlight the critical interplay between nutrition and social environment during early development.
Abstract:
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.