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

J Comp Neurol. 1999 Sep 6;411(4):683-92.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calbindins
  • Circadian Rhythm / physiology*
  • Cricetinae
  • GABA Agonists / pharmacology
  • GABA Antagonists / pharmacology
  • Immunohistochemistry
  • 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
  • gamma-Aminobutyric Acid / physiology*

Substances

  • Calbindins
  • GABA Agonists
  • GABA Antagonists
  • Nerve Tissue Proteins
  • Proto-Oncogene Proteins c-fos
  • S100 Calcium Binding Protein G
  • gamma-Aminobutyric Acid