This review considers the questions of the structural-functional organization of the central nucleus (CN) of the amygdaloid body (AB) of the brain in relation to new data on its involvement in the formation of stress reactions and adaptive behavior in animals. Data are presented on the distribution of neuropeptides, neurotransmitters, and modulators in the CN. It is noted that the CN, appearing at the earliest stages of establishment of the AB, is reorganized with it and reflects the evolution of the whole AB. Detailed data are presented on the cytoarchitectonics of the CN of the AB, its heteromorphousness, and subdivision into zones (subnuclei) based on the use of different study methods and assessment criteria. The neuronal organization of the CN and its subnuclei is considered; detailed descriptions of different types of neurons are provided, with consideration of their topographies, sizes, and shapes and of their perikarya, the orientation and type of branching of their dendrites, the organization of the spine apparatus, and axon structure. The characteristics of the development of the CN of the AB in the ontogenesis of mammals and man are discussed. Analysis of published data and our own results supports the role of the CN not only as an intra-amygdalar integrative center, but also as one of the major channels for the afferent and efferent connections of the AB with the rest of the brain.
The dorsomedial nucleus (MEd), located in the posterior part of the corticomedial section of the amygdaloid body (AB), is one of the major areas of sexual dimorphism [1,6], which forms during the period of sexual differentiation of the brain [9, 16]. This nucleus is formed from populations of small and intermediate-sized neurons, most of which are characterized by large, dark-staining nuclei and a narrow rim of perikaryon [3]. Impregnation with silver nitrate using the Golgi method has established that the neurons of this nucleus have long, poorly branched axons [7], which have a tendency to be located on the surfaces of vessels [2]. It has been suggested that these ceils are neurotransducer cells.The aim of the present work was to study the ultrastructure of MEd neurons with the morphological signs of neurosecretory activity. MATERIALS AND METHODSStudies were carried out using adult white Wistar rats weighing 300-320 g. Specimens for study were collected using an MBS-9 magnifier, fixed in cold 2.5% gintaraldehyde in phosphate buffer, and processed using standard methods [5]. Sections were prepared on an LKB ultramicrotome, contrasted with lead citrate [17], and studied in an IEM 2000 EX transmission electron microscope with primary magnification of • RESULTS AND DISCUSSION All the neurons in the MEd can be divided into two large groups: dark and light. Dark neurons, which make Department of Human and Animal Morphology and Physiology (director Professor L. B. Kalimullina), Bashkir State University, Ufa. 503up about 88% of all neurons in this structure, are characterized by high electron density in both the nucleus and cytoplasm. Light neurons have an electron-transparent cytoplasmic matrix, providing a background on which all ultrastructural components are clearly visible. There are also transitional types of neuron, in which a light nucleus is combined with a cytoplasm which is dark, because of its high content of electron-dense granular material (Fig. le).At low magnification, groups of dark neurons could be seen distributed between other structures of the neuropil. The bodies of these cells were spherical, oval, or polygonal in shape. The sizes of the dark neurons also varied, though most were intermittent-sized or small (%14 ~tm) and were separated by distances of 10-40 ~tm.The nuclei of dark neurons were large, occupying a significant proportion of the cell body; the cytoplasm formed a narrow rim (see Fig. la, c, d). The nuclear outline was always irregular, as the surface had both buds and invaginations of cytoplasm. In some neurons, these cytoplasmic invaginations were very deep (see Fig. lc). In these cases, sections across the center of the nucleus revealed islets of cytoplasm; there were no changes in the nuclear membranes. The width of the perinuclear space differed in different areas (see Fig. le) and varied from 50 to 200 nm. Ribosomes could be seen on the surface of the outer nuclear membrane, located in dense rows. This membrane was connected with the membranes of the rough endoplasmic reticulum (E...
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