Differential vulnerability of the subiculum and entorhinal cortex of the adult rat to prolonged protein deprivation

Protein deprivation experienced in adult life leads to deficits in the number of hippocampal granule and CA3‐CA1 pyramidal cells and to changes in the dendritic domain of granule cells and CA3 pyramids. To obtain a more complete insight into the effects of malnutrition on the limbic system of the adult rat we have analyzed the subiculum and the entorhinal cortex (neuronal layers II, III, and V‐VI) in groups of 8‐month‐old rats fed with a low‐protein diet (8% casein) since the age of 2 months and in age‐matched control rats. Stereological methods were employed to estimate the total number of neurons in the subiculum and layers II, III, and V‐VI of the entorhinal cortex and the volume of the respective cell layers. Moreover, to evaluate whether protein deprivation affects the dendritic domains of the neurons from these regions we have analyzed, in Golgi‐impregnated material, the dendritic trees of the pyramidal cells of the subiculum and of the stellate neurons of the entorhinal cortex layer II applying quantitative and metric methods. The volume of the subiculum and the total number of its neurons were reduced in malnourished animals. In these animals we also found marked regressive changes in the apical and basal dendritic trees of the pyramidal subicular neurons. However, the spine density was increased in malnourished rats. No differences in the volume of the neuronal layers of the entorhinal cortex or in the total number of their neurons were found between protein‐deprived and control rats, and no alterations were depicted in the dendritic trees of the stellate neurons of layer II. We can thus conclude that the effects of long‐term protein deprivation are region specific and that the resulting structural alterations are confined to the three‐layered components of the hippocampal region. Hippocampus 1998;8:33–47. © 1998 Wiley‐Liss, Inc.