The aim of this experiment was to clarify if the entopeduncular nucleuscan modulate the pain threshold through habenular nucleus mediated the actionbetween nuclei entopeduncular and habenular. L-glutamic acid (excitatory acid thai can excite the neuron body ratherthan passed fibers)

bicuculline (a GABA receptor antagonist)

lidocaine andGABA were injected into entopeduncular and habenular nuclei respectivelythrough the implanted cannula. Pain threshold was measured by the latencyof avoidance response (tail-flick) elicited by radiant heat applied to the tailskin of animals before and after intracerebral injection. In some cases single-unit activity in the habenular nucleus was recorded when the entopeduncularnucleus was electrically stimulated.