Inhibition of rubral neurons by a specific ligand for sigma receptors.

1,3-Di-ortho-tolylguanidine (DTG), a compound with marked selectivity for sigma receptors was iontophoretically applied to neurons in the red nucleus and nearby mesencephalic reticular formation. Spontaneous firing of rubral neurons was reduced by DTG in most cases. However, in the reticular formation, less than half of the cells tested showed inhibition; the remaining cells showed either an increase in rate or no consistent response to DTG. This corresponds to the greater density of sigma receptors in the red nucleus and supports previous work which suggests that sigma receptors play a role in the regulation of movement and posture.