[Ultrastructure of neurons and synapses of the lateral hypothalamic area in the rat]

Ultrastructural organization of the lateral hypothalamic area (LHA) has been studied in Wistar rats. Structural peculiarities of neurons and interneuronal connections in the anterior, middle and posterior parts of the LHA have been demonstrated. In the anterior and middle parts, neurons of middle size (17-22 mcm) make the most of the cellular population; large neurons (35-50 mcm) predominate in the posterior part of the LHA. Small cells are diffusely distributed in all the parts. Two types of axons are defined: axons of the I type--with round light, and some of them, with large granular synaptic vesicles; axons of the II type contain smaller and polymorphous light synaptic vesicles. The axons form axodendritic and axosomatic synapses. The former predominate in all parts of the LHA. The axons of the I type form, mainly, asymmetrical, and the axons of the II type--symmetrical contacts. Most of the synapses are formed by the axons of the I type, overwhelmed majority of the synapses are axodendritic. Differences in localization and in distribution of the axodendritic synapses in different parts of the LHA are revealed. In the anterior part of the LHA the axodendritic synapses form synaptic muffs around large and middle dendrites, and more seldom around small and spine-shaped processes of the dendrites. In the middle and posterior parts of the LHA no synaptic muffs are revealed.