HAMSTER SUPRAOPTIC NUCLEUS - CYTOARCHITECTURAL, MORPHOMETRIC, AND 3-DIMENSIONAL RECONSTRUCTION

Background: The present paper describes the cytoarchitectonic, morphom etric, and three-dimensional characteristics of the golden hamster sup raoptic nucleus (SON) in order to provide an anatomical basis for subs equent morphofunctional studies that use this species as an experiment al animal. The dimensions (volume and length) and the number of cells of each part of the supraoptic nucleus were obtained, as well as morph ometric 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 nucl eus and to reveal the structural differences between both parts. Metho ds: Ten male adult golden hamsters (Mesocricetus auratus) were used. A nimals were anaesthetized and transcardially perfused with 4% paraform aldehyde in 0.1 M phosphate buffer at pH 7.2. The hypothalamic area fr om seven animals was dissected out, dehydrated, and embedded in paraff in. Serial sections of 10 mu m were cut in a coronal plane. Sections w ere stained with thionin, dehydrated, cleared in eucalyptol, and mount ed with Eukitt. To prove the neurosecretory nature to the SON, every f ourth section was immunostained against neurophysin by using the perox idase-antiperoxidase method. To study the neuronal morphometric parame ters, all magnocellular neurons of the SON were drawn in sections sepa rated 80 mu m with the aid of a camera lucida under 500 x magnificatio n. Serial 50 mu m 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 pre optic area to the tuberal hypothalamic area. Two classical parts can b e clearly delimited: principal (SONp) and retrochiasmatic(SONr). The n euronal population of the two parts of the SON appears constituted onl y by magnocellular neurons. The volume of the SONp is 0.039 +/- 0.03 m m(3) and contains about 762 +/- 93 magnocellular cells, with a density of 19,151.8 cells/mm(3). The volume of the SONr is 0.126 +/- 0.03 mm( 3) and contains about 1,296 +/- 132 neurons with a density of 10,536.6 cells/mm(3). The three-dimensional reconstruction reveals that the SO Np appears located in a more cephalic, lateral, and dorsal position th an the SONr, and a clear discontinuity between the two parts is observ ed. Conclusions: The present study shows that the classically termed S ON, in the hamster, clearly consists of two spatially separated neural populations. The SONr is longer than SONp and has the larger volume a nd higher number of neurons; however, the neurons of the SONr are smal ler in cell area than those of the SONp. (C) 1994 Wiley-Liss, Inc.