Deviations in brain development of F2 generation on caloric undernutrition and scope of their prevention by rehabilitation: alterations in dendritic spine production and pruning of pyramidal neurons of lower laminae of motor cortex and visual cortex.

This is a report of comparison of developmental changes of spine densities on the different categories of dendrites of neocortical pyramidal neurons (V and VI layers of motor and visual areas) of Wistar rat, during 11-150 days of age, under conditions of normal nutrition and under chronic caloric but not protein deprivation. The studied animals were of F2 generation born to parents undernourished to a degree that their weights were only 40-50% of normal control. At such a level they would be active, reproduce, and not morbid. Similar level of undernutrition also continued in the F2 group studied. A group of undernourished animals was also, for rehabilitation, put on normal diet from 21 days of age. Visual and motor cortical area pieces were impregnated by Stensaas' rapid Golgi method. Spines were counted on successive 20-micron segments (I-IV) of both apical and basal dendritic main shafts as well as primary and secondary branches. The spine count per segment (density) in the normal population reached exuberant values by 26-50 days of age and later underwent a progressive decline or pruning by 30-50% or more by 150 days of age. The degrees of exuberance and pruning varied in different categories of dendrites, generally being more conspicuous in motor than visual cortex, and more in basal than apical dendrites. Under the conditions of chronic caloric restriction, the phenomenon of exuberance was retarded and pruning was not observed. On the contrary, there was a progressive increase in the spine densities on both basal and apical dendrites, in motor and visual cortex. By 150 days of age, the spine densities were not only greater than the final counts for respective segments in the normal animal, but even greater than the exuberant counts. Postweaning caloric rehabilitation had only a modest impact against this deviation. Preliminary data (intersections) of dendritic branching also indicated a similar pattern of changes (lag followed by increase), but of a lesser degree. These alterations in neuronal development are interpreted as biological adaptations evoked in shaping the homeostasis of the organism's brain and behaviour by factors of nurture.