Sexual dimorphism in the subiculum of the rat hippocampal formation

Data accumulated over the last years demonstrate that the hippocampal forma tion of rodents is sexually dimorphic with respect to its functional attrib utes. Neuroanatomical substrates that might contribute to explain these gen der-related differences have been described in the dentate gyrus, and in th e CA3 and CA1 hippocampal fields. However, the subiculum, the source of the major efferent projection of the hippocampal formation, has not been searc hed for the presence of sex-related differences. To address this issue, we have used stereological methods applied to adult rats of both sexes to esti mate the volume of the subiculum, the total number of subicular neurons, an d the total number and size of the synapses established by subicular neuron s. The apical dendritic trees of Golgi-impregnated subicular neurons were a lso quantitatively analyzed. We have found that the volume of the subiculum and of its neuronal layer, and the total number of subicular neurons were greater in males than in females. Conversely, the total dendritic length of the apical arborization of the subicular neurons, and the number of dendri tic spines and axospinous synapses were higher in females than in males. Ho wever, the size of the postsynaptic densities of the individual synapses wa s smaller in female than in male rats and, as a result, the surface area of the total active synaptic zones did not differ between the sexes. These fi ndings provide an additional morphological clue for the comprehension of th e sex dimorphisms within the hippocampal circuitries and, consequently, for a better understanding of the functional sex differences ascribed to the h ippocampal formation. (C) 2000 Elsevier Science B.V. All rights reserved.