Differential c-Fos immunoreactivity in arousal-promoting cell groups following systemic administration of caffeine in rats

J Comp Neurol. 2006 Oct 10;498(5):667-89. doi: 10.1002/cne.21084.


Despite the widespread use of caffeine, the neuronal mechanisms underlying its stimulatory effects are not completely understood. By using c-Fos immunohistochemistry as a marker of neuronal activation, we recently showed that stimulant doses of caffeine activate arousal-promoting hypothalamic orexin (hypocretin) neurons. In the present study, we investigated whether other key neurons of the arousal system are also activated by caffeine, via dual immunostaining for c-Fos and transmitter markers. Rats were administered three doses of caffeine or saline vehicle during the light phase. Caffeine at 10 and 30 mg/kg, i.p., increased motor activities, including locomotion, compared with after saline or a higher dose, 75 mg/kg. The three doses of caffeine induced distinct dose-related patterns of c-Fos immunoreactivity in several arousal-promoting areas, including orexin neurons and adjacent neurons containing neither orexin nor melanin-concentrating hormone; tuberomammillary histaminergic neurons; locus coeruleus noradrenergic neurons; noncholinergic basal forebrain neurons that do not contain parvalbumin; and nondopaminergic neurons in the ventral tegmental area. At any dose used, caffeine induced little or no c-Fos expression in cholinergic neurons of the basal forebrain and mesopontine tegmentum; dopaminergic neurons of the ventral tegmental area, central gray, and substantia nigra pars compacta; and serotonergic neurons in the dorsal raphe nucleus. Saline controls exhibited only few c-Fos-positive cells in most of the cell groups examined. These results indicate that motor-stimulatory doses of caffeine induce a remarkably restricted pattern of c-Fos expression in the arousal-promoting system and suggest that this specific neuronal activation may be involved in the behavioral arousal by caffeine.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Arousal / drug effects*
  • Arousal / physiology
  • Behavior, Animal
  • Brain* / cytology
  • Brain* / drug effects
  • Brain* / metabolism
  • Caffeine / administration & dosage*
  • Cell Count / methods
  • Central Nervous System Stimulants / administration & dosage*
  • Dose-Response Relationship, Drug
  • Gene Expression Regulation / drug effects
  • Immunohistochemistry / methods
  • Male
  • Motor Activity / drug effects
  • Neurons / drug effects*
  • Proto-Oncogene Proteins c-fos / genetics
  • Proto-Oncogene Proteins c-fos / metabolism*
  • Rats
  • Rats, Wistar
  • Tyrosine 3-Monooxygenase / metabolism
  • Vesicular Acetylcholine Transport Proteins / metabolism


  • Central Nervous System Stimulants
  • Proto-Oncogene Proteins c-fos
  • Slc18a3 protein, rat
  • Vesicular Acetylcholine Transport Proteins
  • Caffeine
  • Tyrosine 3-Monooxygenase