Neurogenesis occurs in the dentate gyrus of the hippocampus throughout the life of a rodent, but the function of these new neurons and the mechanisms that regulate their birth are unknown. Here we show that significantly more new neurons exist in the dentate gyrus of mice exposed to an enriched environment compared with littermates housed in standard cages. We also show, using unbiased stereology, that the enriched mice have a larger hippocampal granule cell layer and 15 per cent more granule cell neurons in the dentate gyrus.

More hippocampal neurons in adult mice living in an enriched environment

Neuronal plasticity is a central theme of modern neurobiology, from cellular and molecular mechanisms of synapse formation in Drosophila to behavioural recovery from strokes in elderly humans. Although the methods used to measure plastic responses differ, the stimuli required to elicit plasticity are thought to be activity-dependent. In this article, we focus on the neuronal changes that occur in response to complex stimulation by an enriched environment. We emphasize the behavioural and neurobiological consequences of specific elements of enrichment, especially exercise and learning.

Neural consequences of environmental enrichment.

http://zeta.math.utsa.edu/~yxk833/METROPOLIS/REFERENCES/Rosenzweig.pdf

Psychobiology of plasticity: effects of training and experience on brain and behavior

The fetal and even the young brain possesses a considerable degree of plasticity. The plasticity and rate of neurogenesis in the adult brain is much less pronounced. The present study was conducted to investigate whether housing conditions affect neurogenesis, learning, and memory in adult rats. Three-month-old rats housed either in isolation or in an enriched environment were injected intraperitoneally with bromodeoxyuridine (BrdU) to detect proliferation among progenitor cells and to follow their fate in the dentate gyrus. The rats were sacrificed either 1 day or 4 weeks after BrdU injections. This experimental paradigm allows for discrimination between proliferative effects and survival effects on the newborn progenitors elicited by different housing conditions. The number of newborn cells in the dentate gyrus was not altered 1 day after BrdU injections. In contrast, the number of surviving progenitors 1 month after BrdU injections was markedly increased in animals housed in an enriched environment. The relative ratio of neurogenesis and gliogenesis was not affected by environmental conditions, as estimated by double-labeling immunofluorescence staining with antibodies against BrdU and either the neuronal marker calbindin D28k or the glial marker GFAp, resulting in a net increase in neurogenesis in animals housed in an enriched environment. Furthermore, we show that adult rats housed in an enriched environment show improved performance in a spatial learning test. The results suggest that environmental cues can enhance neurogenesis in the adult hippocampal region, which is associated with improved spatial memory.

Enriched environment increases neurogenesis in the adult rat dentate gyrus and improves spatial memory.

http://jtoomim.org/brain-training/aerobic%20execise%20and%20improved%20neuropsychological%20function%20in%20older%20adults.pdf

Aerobic exercise training and improved neuropsychological function of older individuals.

ANIMALS that have been exposed to environmental stimulation develop marked differences in brain structure and biochemistry when compared with animals that have not been exposed in this way1–4. Factors influencing the magnitude of these changes are the duration of rearing and the age of the animals when the environmental separation takes place. Most studies have focused on young animals because the brain is thought to be more plastic at this stage. As a result, temporal analyses of the induced changes have usually been limited to fairly short periods of environmental exposure early in the animal's life. Rosenzweig et al.3 have suggested that, in rats differentially reared from weaning, the induced differences in brain weight reach a maximum during the first 30 d of separation, after which they decrease. But the evidence for this biphasic response has been based on relatively short periods of differential rearing (15–160 d).

T Konstantinos

Papers

Environmentally-induced changes in the brains of elderly rats