Astroglial elements in the suprachiasmatic nucleus of the golden hamster and the rat - Comparative morphological study using immunocytochemistry

Astroglial elements in the suprachiasmatic nucleus (SCN) in golden hamsters and rats were investigated by GFAP immunocytochemistry and a computer-assisted analyzing system. Serial frontal sections, including the SCN region, were prepared and GFAP immunoreactivity in the following areas were measured as optical density (O. D.) per area (O. D./mu m(2)): (1) the whole SCN region, (2) the ventrolateral portion (VLSCN), where vasoactive intestinal peptide (VIP) neurons were mainly distributed, (3) the dorsomedial portion, where arginine vasopressin (AVP) neurons were mainly distributed, and (4) as determined by unilateral intraocular injection of cholera toxin B subunit, the area where retinohypothalamic tract (RHT) fibers were distributed. In the rat, GFAP immunoreactivity was observed throughout the SCN, particularly in the VLSCN, while in the golden hamster, astroglial elements enclosed the whole region of the SCN. In addition, quantitative analysis revealed that the O. D. of the GFAP immunoreactivity in the VLSCN, where VIP neurons and the RHT fibers were distributed, were significantly higher than those in other regions of the SCN. These results strongly suggested that the astroglial elements, VIP neurons and PI-IT fibers have close morphological interactions, although delicate differences were demonstrated in both species.