Gabaergic fibers from substantia nigra para reticulata modulate escape bahavior induced by midbrain central gray stimulation

Eletrical stimulation or microinjection of GABA antagonists into the dorsal periaqueductal gray (DPAG) produces escape behavior. In order to determine whether the nigrocollicular gabaergic fibers exert some control over this behavior, rats bearing kainic acid lesion of the substantia nigra pars reticulata were submitted to microinjections of bicuculline or electrical stimulation of the DPAG at the escape threshold. Rats thus treated exhibited a significant decrease in the escape threshold while bicuculline increased the expression of flight behavior. These results suggest an inhibitory control of gabaergic fibers from the substantia nigra pars reticulata on aversive behavior induced by DPAG stimulation

Independence of aversive and pain mechanisms in the dorsal periaqueductal gray matter of the rat

Electrical stimulation of the dorsal periaqueductal gray (DPAG) elicits autonomic responses similar to those following peripheral pain stimulation. The present study analyzes the effects of morphine and midazolan applied to the same DPAG sites on the autonomic responses induced by both types of stimulation. Both drugs attenuated the increase in heart rate and blood pressure induced by DPAG stimulation while attenuating only the increase in heart rat induced by pain stimulation. These results suggest that the neural substrates of the autonomic expression of the DPAG and pain stimulation are different although they may partially overlap