GABAergic regulation of light-induced c-Fos immunoreactivity within the suprachiasmatic nucleus.
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 GABA(A) and GABA(B) agonists and antagonists injected into the SCN region on c-Fos-ir within the SCN. Microinjection of either a GABA(A) agonist, muscimol, or a GABA(B) 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 GABA(A) antagonist, bicuculline, but not a GABA(B) 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 GABA(B)-active drugs have similar effects whether given systemically or within the SCN, but that GABA(A)-active drugs have more complex effects on c-fos induction and have multiple sites of action.
Gillespie
C F
CF
Laboratory of Neuroendocrinology and Behavior, Departments of Biology and Psychology, Georgia State University, Atlanta, Georgia 30303, USA.
Van Der Beek
E M
EM
Mintz
E M
EM
Mickley
N C
NC
Jasnow
A M
AM
Huhman
K L
KL
Albers
H E
HE
D000818:Animals; D064026:Calbindins; D002940:Circadian Rhythm / Q000502:physiology*; D006224:Cricetinae; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D008647:Mesocricetus / Q000378:metabolism / Q000502:physiology*; D008845:Microinjections; D009419:Nerve Tissue Proteins / Q000032:analysis*; D010775:Photic Stimulation; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis*; D064030:S100 Calcium Binding Protein G / Q000032:analysis; D013493:Suprachiasmatic Nucleus / Q000737:chemistry* / Q000187:drug effects; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D064026:Calbindins; D018755:GABA Agonists; D018756:GABA Antagonists; D009419:Nerve Tissue Proteins; D016760:Proto-Oncogene Proteins c-fos; D064030:S100 Calcium Binding Protein G; D005680:gamma-Aminobutyric Acid