Evidence for GABA involvement in midbrain control of medullary neurons that modulate nociceptive transmission

Brain Res. 1986 Nov 5;397(1):37-46. doi: 10.1016/0006-8993(86)91367-3.


The effects of GABA-related compounds microinjected into the midbrain periaqueductal gray (PAG) on the tail-flick reflex (TF) and on the activity of tail-flick related neurons in the rostral ventromedial medulla (RVM), were studied in barbiturate anesthesized rats. Neurons whose activity either decreased (off-cells) or increased (on-cells) immediately prior to TF were examined. Bicuculline and picrotoxin microinjected into the ventrolateral aspect of the caudal PAG inhibited the TF, increased the spontaneous activity of the off-cells and decreased that of the on-cells. Concomitant with the increase in TF latency, the TF-related deceleration of the off-cells and acceleration of the on-cells were reduced. These effects were reversed by a microinjection of muscimol (MUS) into the PAG. The analgesic effect of morphine microinjected into the PAG was also reversed by a MUS microinjection at the same site. These results support the hypothesis that a GABAergic synapse inhibits cells in the PAG which modulate nociceptive transmission at the spinal level through actions on neurons in the RVM.

Publication types

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

MeSH terms

  • Action Potentials / drug effects
  • Animals
  • Bicuculline / pharmacology
  • Male
  • Medulla Oblongata / drug effects
  • Medulla Oblongata / physiology*
  • Morphine / antagonists & inhibitors
  • Muscimol / pharmacology
  • Neural Pathways / physiology
  • Pain / physiopathology*
  • Pain Measurement
  • Periaqueductal Gray / drug effects
  • Periaqueductal Gray / physiology*
  • Picrotoxin / pharmacology
  • Rats
  • Rats, Inbred Strains
  • gamma-Aminobutyric Acid / physiology*


  • Picrotoxin
  • Muscimol
  • gamma-Aminobutyric Acid
  • Morphine
  • Bicuculline