Mamillary body in the rat: A cytoarchitectonic, golgi, and ultrastructural study

The present study provides a comprehensive light and electron microscopic analysis of the anatomical organization of the rat mamillary body. The cytoarchitecture and morphology of mamillary neurons were investigated with the aid of Nissl‐stained and Golgi‐impregnated sections cut in transverse, horizontal, and sagittal planes. The ultrastructural features of the mamillary nuclei were correlated with observations made on Golgi material. The mamillary body is comprised of a lateral and a medial nucleus, the latter being subdivided into five major subnuclei: pars lateralis, pars basalis, pars medialis, pars medianus, and pars posterior. The perikarya are medium‐sized or small with the proportions of each differing among subnuclei. The largest perikarya are found in the lateral mamillary nucleus (cell area 257.0 μm2) and have 2‐5 radially oriented aspiny dendrites that are often beaded. Small cells predominate in the pars lateralis (cell area 116.3 μm2) and pars basalis (cell area 118.3 μm2), whereas the pars medialis (cell area 196.7 μm2), pars medianus (cell area 136.5 μm2), and pars posterior (cell area 154.6 μm2) contain mainly medium‐sized cells. The dendrites of most cells in the medial nucleus are radially oriented and exhibit a variety of spines including numerous short stubby spines, spines with thin necks that end in spherical swellings, and long thin spines. Neuronal somata are often closely apposed with no intervening glial processes and contain eccentrically located nuclei with one or more invaginations of the nuclear envelope.