Size, form and orientation of the neuronal perikarya and nuclei in the nucleus infundibularis of the male rat.

Size, form and orientation of nerve cells of the Nucleus infundibularis have been analyzed in frontal, horizontal and sagittal semithin sections of Vestopal-embedded hypothalami of the male rat. Morphometric studies were performed with a semiautomatic image analyzing system. By combining data from three different planes of section the three-dimensional size, shape and orientation of perikarya and nuclei in the different parts of the Nucleus infundibularis as well as gradients in mediolateral, rostrocaudal and ventrodorsal directions were examined. Additionally, cell density, volume and relation of the volumes of nucleus and perikaryon were determined. In all parts of the Nucleus infundibularis there occur cells exhibiting different sizes, forms and orientations. The mean values, however, show a rostrocaudal decrease and a mediolateral increase of the cell volumes with a maximum in the rostral, ventral and lateral parts and a minimum in the caudal, ventral and medial parts. In the entire Nucleus infundibularis there is a preferred orientation of the cell axes parallel to the wall of the third ventricle. Spherically-formed cells occur mainly in the rostral and basal parts, elongated and flattened cells in the caudal and dorsal parts. The nucleus-perikaryon relation is small in the rostral, lateral and ventral parts, large in the caudal, medial and dorsal parts. The cell density increases from rostral to caudal and decreases from medial to lateral. The results are discussed with respect to histochemical and immunohistochemical localization of substances relevant to neuroendocrine and neurotropic processes. This investigation exemplarily shows that different planes of section may lead to different descriptions of number and morphology of cells, and that a morphological analysis of nerve cells is only reliable from three-dimensional reconstruction using more than one direction of sectioning.