Effects of differential environments on the cerebral anatomy of rats as a function of previous and subsequent housing conditions

Abstract

After 1 month in enriched or impoverished environments, groups of rats were housed for an additional month in either the same or the opposite environment. The cross-over design allowed us to see whether or not the cerebral effects of differential environments are modified by subsequent housing conditions, and also whether or not such effects might be influenced by previous experience. Differential housing for 1 month was associated with significant alterations in the weight and length of the cerebrum, the thickness of the occipital cortex, and the relative number of neurons and oligodendrocytes, and no change in the ratio of astrocytes to neurons. The effects of enrichment were not reduced in animals that were previously impoverished. When impoverishment followed enrichment, certain effects appeared to diminish, notably, the increase in cortical thickness. Other effects, however, such as the increase in the ratio of oligodendrocytes to neurons, were very stable. The gross cerebral alterations associated with differential housing did not differ significantly after 2 as opposed to 1 month's exposure, but the effects on neuronal density and the ratio of oligodendrocytes to neurons in layers V and VI of the cortex were, paradoxically, significantly smaller with the longer duration. We suggest that this decrease is due to the continuation of processes induced in the first month of differential experience rather than to their dissipation.

Review: Environmental enrichment and brain repair: harnessing the therapeutic effects of cognitive stimulation and physical activity to enhance experience‐dependent plasticity

“…The cellular effects of EE, which are presumably dependent on molecular changes, include enhanced adult neurogenesis [108,129–133] and synaptic plasticity [134–139]. Specific neuronal cell populations have been shown to be activated by EE [140] and the effects in the brain extend to glia [141–143]. However, a range of other cellular effects have been described, including those impacting on metabolism [144], the immune system [145–148] and the HPA‐axis [47,149–151].…”

Learning-Dependent Synaptic Modifications in the Cerebellar Cortex of the Adult Rat Persist for at Least Four Weeks

“…The persistence of some of the anatomical changes described above has been examined in reversal experiments in which animals are reared in a complex environment followed by a period of time in standard labora-tory cages. These studies have shown that the increased cortical weight (Katz and Davies, 1984) and dendritic arborization (Camel et al, 1986) observed in rats reared in a complex environment tend to persist. Some of the behavioral consequences of complex housing, such as improved performance on a Hebb-Williams maze, may also persist (Forgays and Read, 1962).…”

Environmental conditions influence hippocampus‐dependent behaviours and brain levels of amyloid precursor protein in rats

“…Environmental enrichment or restriction can also affect cerebral size, neuron size, number of glial cells, dendritic branching, spine density, and number of synapses (e.g. Bennett et al ., 1964; Rosenzweig et al ., 1971; Volkmar & Greenough, 1972; West & Greenough, 1972; Globus et al ., 1973; Diamond et al ., 1975; Katz & Davies, 1984), as well as the turnover of several neurotransmitters (Jones et al ., 1992; Myhrer et al ., 1992; Fulford et al ., 1994; Escorihuela et al ., 1995). Little is known concerning the mechanisms that underlie these structural and chemical effects.…”