GABAergic regulation of light-induced c-Fos immunoreactivity within the suprachiasmatic nucleus

• Published in: Journal of comparative neurology (1911) 1999-09, Vol.411 (4), p.683-692
• Main Authors: Gillespie, C.F., Van Der Beek, E.M., Mintz, E.M., Mickley, N.C., Jasnow, A.M., Huhman, K.L., Albers, H.E.
• Format: Article
• Language: English
• Subjects: Animals; Calbindins; Circadian Rhythm - physiology; circadian rhythms; Cricetinae; entrainment; Fysiologie van Mens en Dier; GABA Agonists - pharmacology; GABA Antagonists - pharmacology; gamma-Aminobutyric Acid - physiology; Human and Animal Physiology; hypothalamus; Immunohistochemistry; Leerstoelgroep Fysiologie van mens en dier; Male; Mesocricetus - metabolism; Mesocricetus - physiology; Microinjections; Nerve Tissue Proteins - analysis; Photic Stimulation; Proto-Oncogene Proteins c-fos - analysis; S100 Calcium Binding Protein G - analysis; Suprachiasmatic Nucleus - chemistry; Suprachiasmatic Nucleus - drug effects; WIAS
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/(SICI)1096-9861(19990906)411:4<683::AID-CNE12>3.0.CO;2-J

Analysis of the photic induction of c‐Fos immunoreactivity (‐ir) within the suprachiasmatic nucleus (SCN) has proven to be a powerful tool with which to study the neurochemical mechanisms involved in phase shifting the circadian clock. Some systemically administered GABAergic drugs inhibit light‐induced phase shifts and c‐Fos‐ir, whereas others inhibit light‐induced phase shifts without affecting c‐Fos‐ir. More recently, we have found that injection of GABAergic drugs directly into the SCN region can have dramatically different effects on light‐induced phase shifts than following their systemic administration. The present study investigated the effects of GABAA and GABAB agonists and antagonists injected into the SCN region on c‐Fos‐ir within the SCN. Microinjection of either a GABAA agonist, muscimol, or a GABAB agonist, baclofen, into the SCN region significantly reduced light‐induced c‐Fos‐ir within the SCN when administered before light exposure at circadian time (CT) 13.5 or CT 19. In contrast, microinjection of a GABAA antagonist, bicuculline, but not a GABAB antagonist, CGP‐35348, into the SCN region increased light‐induced c‐Fos‐ir within the SCN when administered before light exposure at CT 13.5 or CT 19. These data indicate that GABAergic agonists and antagonists injected directly into the SCN region alter light‐induced Fos‐ir in a manner similar to their effects on light‐induced phase shifts. Comparison of these data with previous studies examining the effects of systemically administered GABAergic drugs suggests that GABAB‐active drugs have similar effects whether given systemically or within the SCN, but that GABAA‐active drugs have more complex effects on c‐fos induction and have multiple sites of action. J. Comp. Neurol. 411:683–692, 1999. © 1999 Wiley‐Liss, Inc.