Hamster supraoptic nucleus: cytoarchitectural, morphometric, and three-dimensional reconstruction.

BACKGROUND

The present paper describes the cytoarchitectonic, morphometric, and three-dimensional characteristics of the golden hamster supraoptic nucleus (SON) in order to provide an anatomical basis for subsequent morphofunctional studies that use this species as an experimental animal. The dimensions (volume and length) and the number of cells of each part of the supraoptic nucleus were obtained, as well as morphometric parameters of their neurons (cross-sectional area and maximum and minimum diameters). A three-dimensional reconstruction of hamster SON has been made in order to know the spatial morphology of this nucleus and to reveal the structural differences between both parts.

METHODS

Ten male adult golden hamsters (Mesocricetus auratus) were used. Animals were anaesthetized and transcardially perfused with 4% paraformaldehyde in 0.1 M phosphate buffer at pH 7.2. The hypothalamic area from seven animals was dissected out, dehydrated, and embedded in paraffin. Serial sections of 10 microns were cut in a coronal plane. Sections were stained with thionin, dehydrated, cleared in eucalyptol, and mounted with Eukitt. To prove the neurosecretory nature to the SON, every fourth section was immunostained against neurophysin by using the peroxidase-antiperoxidase method. To study the neuronal morphometric parameters, all magnocellular neurons of the SON were drawn in sections separated 80 microns with the aid of a camera lucida under 500x magnification. Serial 50 microns thick frozen sections of the hypothalamus from three animals were drawn with camera lucida to determine the volume of the two parts of the SON and to make the three-dimensional reconstruction.

RESULTS

The SON extends rostrocaudally 1.98 +/- 0.03 mm from the preoptic area to the tuberal hypothalamic area. Two classical parts can be clearly delimited: principal (SONp) and retrochiasmatic (SONr). The neuronal population of the two parts of the SON appears constituted only by magnocellular neurons. The volume of the SONp is 0.039 +/- 0.03 mm3 and contains about 762 +/- 93 magnocellular cells, with a density of 19,151.8 cells/mm3. The volume of the SONr is 0.126 +/- 0.03 mm3 and contains about 1,296 +/- 132 neurons with a density of 10,536.6 cells/mm3. The three-dimensional reconstruction reveals that the SONp appears located in a more cephalic, lateral, and dorsal position than the SONr, and a clear discontinuity between the two parts is observed.

CONCLUSIONS

The present study shows that the classically termed SON, in the hamster, clearly consists of two spatially separated neural populations. The SONr is longer than SONp and has the larger volume and higher number of neurons; however, the neurons of the SONr are smaller in cell area than those of the SONp.