NeuroanatomyComplex organization of mouse and rat suprachiasmatic nucleus
Section snippets
Experimental procedures
Adult male albino rats (N=21; Sprague–Dawley, Taconic Farms, Germantown, NY, USA) and male inbred C57BL/6J mice (N=23; Jackson Laboratory, Bar Harbor, ME, USA) housed under a 12-h light/dark photoperiod, were anesthetized using ketamine (100mg/kg; Wyeth Pharmaceuticals, Madison, NJ, USA) and xylazine (10mg/kg; Ben Venue Laboratories, Bedford, OH, USA). Animals were placed in a stereotaxic instrument and cholera toxin subunit B (CT-B) conjugated to Alexa 594 (item C-34777, Molecular Probes,
Mouse
The SCN is easily defined by either of two criteria, ventral periventricular cells staining more intensely for Nissl substance than those in the surrounding hypothalamus (Fig. 1A) or the location of intensely GABA-IR neurons (Fig. 2A) which are abundant and clearly distinguishable throughout most of the SCN, although less so in the periventricular dorsomedial part of the nucleus. As indicated in Fig. 1A, cells staining darkly for Nissl substance tend to be rounder than those in adjacent
Discussion
The SCN can be satisfactorily distinguished from adjacent hypothalamus by the presence of a variety of neural indicators. Nissl substance stains darkly in SCN neurons and is an easily used characteristic identifying neurons throughout the entire SCN (Card and Moore 1991, Abrahamson and Moore 2001). Presence of GABA-IR in most, if not all, SCN neurons also renders this phenotype a good cellular marker of the nucleus (Abrahamson and Moore 2001, Moore and Speh 1993, Morin and Blanchard 2001).
Conclusion
In summary, investigators using a variety of methods have provided data suggesting two, three or even four divisions within the rodent SCN, depending upon the indicators used to define divisions (see (Morin and Allen, 2006) for a review). The present analysis of SCN cell types and terminal fields in the mouse and rat demonstrates an organizational complexity that does not readily fit a simple descriptive scheme. Moreover, rhythmically dynamic changes in apparent organization that have been
Acknowledgments
Supported by NIH grants MH64471 and NS22168 to L.P.M.
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- 1
Present address: Graduate School and University Center, City University of New York, Hunter College, 695 Park Avenue, New York, NY 10021.
- 2
Present address: Department of Psychiatry, Millhauser Laboratories, Room HN607, New York University School of Medicine, 550 First Avenue, New York, NY.