Microinjection of muscimol into caudal periaqueductal gray lowers body temperature and attenuates increases in temperature and activity evoked from the dorsomedial hypothalamus

Brain Res. 2006 May 30;1092(1):129-37. doi: 10.1016/j.brainres.2006.03.080. Epub 2006 May 4.


Microinjection of the neuronal inhibitor muscimol into the midbrain lateral/dorsolateral periaqueductal gray (l/dlPAG) suppresses increases in heart rate (HR) and mean arterial pressure (MAP) evoked by microinjection of the GABA(A) receptor antagonist bicuculline methiodide (BMI) into the dorsomedial hypothalamus (DMH) in rats. Injection of BMI into the DMH also increases body temperature (Tco) and motor activity. Here, our goal was to extend previous findings by examining the effect of microinjection of muscimol into the PAG on these thermogenic and behavioral responses in conscious freely moving rats. Microinjection of muscimol (300 pmol and 1 nmol) alone into the l/dlPAG reduced baseline Tco without affecting activity, HR, or MAP. Similar injection of a dose that failed to alter baseline Tco (100 pmol) suppressed the increases in Tco evoked from the DMH and significantly attenuated DMH-induced increases in locomotor activity. Whereas microinjection of 1 nmol muscimol into the ldlPAG abolished the increases in Tco evoked from the DMH and in fact lowered body temperature to a degree similar to that seen after this dose of muscimol alone, 1 nmol muscimol at adjacent sites outside the targeted region of the PAG had no significant effect on DMH-induced increases in Tco or any other parameter. These results indicate a role for neuronal activity in the l/dlPAG in (1) the temperature and behavioral responses to disinhibition of neurons in the DMH, and (2) the maintenance of basal body temperature in conscious freely moving rats.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Blood Pressure / drug effects
  • Blood Pressure / physiology
  • Body Temperature / drug effects
  • Body Temperature / physiology*
  • Body Temperature Regulation / drug effects
  • Body Temperature Regulation / physiology
  • Dorsomedial Hypothalamic Nucleus / drug effects
  • Dorsomedial Hypothalamic Nucleus / physiology*
  • Dose-Response Relationship, Drug
  • GABA Agonists / pharmacology
  • Heart Rate / drug effects
  • Heart Rate / physiology
  • Male
  • Motor Activity / drug effects
  • Motor Activity / physiology
  • Muscimol / pharmacology*
  • Neural Inhibition / drug effects
  • Neural Inhibition / physiology
  • Neural Pathways / drug effects
  • Neural Pathways / physiology*
  • Neurons / drug effects
  • Neurons / physiology
  • Periaqueductal Gray / drug effects
  • Periaqueductal Gray / physiology*
  • Rats
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology
  • Thermogenesis / drug effects
  • Thermogenesis / physiology
  • gamma-Aminobutyric Acid / metabolism


  • GABA Agonists
  • Muscimol
  • gamma-Aminobutyric Acid