Morphometry of cytoarchitecture of the lateral hypothalamic area in the rat.

The cytoarchitecture of the lateral hypothalamic area (LHA) in rats was studied with cresyl violet-stained coronal celloidin sections and with sections of the brain impregnated by a Golgi method. Unimodality was established in the frequency distribution histogram of both the somatic cross-sectional area of the LHA neurons and somatic shape (elongation and circularity). The predominant somatic orientation was in the dorsomedial-ventrolateral direction: bimodality of the frequency distribution of somatic orientation was denied. These findings suggest that the LHA neurons examined in the present study are not subdivisible on the basis of the somatic area, shape or orientation. Although the neurons were classified into eight types based upon the dendritic pattern, those in the LHA largely consisted of only three of them; Type III (dendrites extending in two directions along the long axis of soma), Type IV (three directions) and Type VIII (four directions) jointly accounted for 97.1 percent of the total neurons examined. This finding suggests that the parameter of dendritic pattern serves an important purpose in the typing of the rat LHA neurons. The orientation of intrinsic dendrites and intrinsic axons in the LHA has also been described.