Effects of isolation and environmental complexity on brain and pineal organ

Effects of environmental complexity and deprivation on brain anatomy and histology: a review

During the last 20 years the anatomical plasticity of the brain in response to sensory stimulation has been clearly demonstrated. This paper reviews the effects of environments rich in sensory stimulation versus those which are stimulus poor. Effects have been noted at all levels from the gross anatomical to the electromicroscopic. As compared to their stimulus-deprived counterparts, animals reared in complex environments tend to display greater cerebral weight and length and cortical depth. The greatest effects occur in the occipital cortex where histological studies have revealed expanded neuron perikaryonal and nuclear size and dendritic branching, more dendritic spines, alterations in synaptic numbers and morphology, and greater numbers of neuroglia. Different cortical areas and layers respond to different degrees. Some responses have also been noted in the underlying hippocampus, particularly in the dentate gyrus. The emerging data present a picture of a dynamic, plastic brain adapting homeostatically to the demands of its environment.

Cholinergic mechanisms in scent marking behavior by Mongolian gerbils (Meriones unguiculatus)

The Mongolian gerbil reared in Japan manifested scent marking behavior in the similar behavioral topography as described by foreign researchers. The frequency of marking was affected by early isolation housing; isolated male gerbils exhibited a higher frequency of marking than aggregated males. The marking behavior was suppressed by scopolamine (1.5 mg/kg, IP), whereas methylscopolamine was ineffective. In order to elucidate the possible neural mechanisms, acetylcholinesterase (ACh-E) and choline acetyltransferase (Ch-Ac) activities were measured in 8 discrete areas of the brain (the cortex, striatum, amygdala, hypothalamus, midbrain, hippocampus, olfactory bulbs, and pons plus medulla oblongata). There was, however, no significant difference between isolated and aggregated gerbils in either ACh-E or Ch-Ac activity in any of the brain areas. These results suggest that other neural events, such as changes in the ACh turnover rate or in ACh release, may participate in the manifestation of scent marking behavior.