EFFECTS OF LONG-TERM MALNUTRITION AND REHABILITATION ON THE HIPPOCAMPAL-FORMATION OF THE ADULT-RAT - A MORPHOMETRIC STUDY

We have previously shown that the numerical density of dentate granule and CA3 pyramidal cells of adult rats is reduced after lengthy period s of low-protein diet. In this study, the total number of these neuron s was estimated, together with those for the hilar and CA1 pyramidal c ells in order to obtain a complete and unbiased insight into the effec ts of malnutrition and rehabilitation from malnutrition on the structu re of the hippocampal formation. Groups of 2-month-old rats were fed a low protein diet (8 % casein) for 6, 12 and 18 months and compared wi th age-matched control and recovery rats. The recovery group was fed a low protein diet for 6 months and then switched to normal diet during the same period. Total numbers of neurons of each hippocampal region were calculated from their numerical density, estimated with the physi cal disector, and from the volume of the respective cell layers, after correction for the tissue shrinkage factor. The total number of granu le, hilar, CA1 and CA3 pyramidal cells was reduced in all groups of ma lnourished rats including the recovery group. No differences were foun d between malnourished and recovery groups. These findings indicate th at a prolonged low protein diet, started in adult life, leads to a def icit in neuronal numbers in the hippocampal formation, and that it may also disrupt the normal process of cell acquisition in the dentate gy rus. Moreover, our data support the view that the morphological altera tions induced by a low protein intake are irreversible.