SINGLE-LABEL AND DOUBLE-LABEL IMMUNOCYTOCHEMICAL STUDY OF THE OVINE SUPRACHIASMATIC NUCLEUS (SCN) - GABAERGIC AND PEPTIDERGIC RELATIONSHIPS

This study evaluated the neuropeptide and neurotransmitter content of the ovine suprachiasmatic nucleus (SCN) using both single- and double- label immunocytochemical methods. Single-label immunocytochemistry ide ntified a few lightly labeled gamma aminobutyric acid (GABA) cells wit hin the SCN as well as a dense plexus of fibers staining positive for the GABA biosynthetic enzyme, glutamic acid decarboxylase (GAD). Vasoa ctive intestinal polypeptide (VIP) fibers exhibited a similar distribu tion to GAD fibers; VIP cells were found throughout the SCN, as well a s in the paraventricular (PVN) and supraoptic nuclei. Both GAD and VIP fibers exited dorsally from the SCN towards the PVN. Neurophysin (NP) and neuropeptide-Y (NPY) fibers were sparsely distributed throughout the SCN. Double-label immunocytochemistry revealed that GAD varicositi es were often in close apposition to VIP cells. These results confirm the presence of GABAergic elements within the sheep SCN. Furthermore, they raise the possibility of a GABAergic modulation of VIP neuronal a ctivity within the ovine SCN.