| Abstract: | A study was made of microinjections of antagonists of various neuromodulators on the dynamics of inhibition of the spino-bulbo-spinal reflexes which were evoked by stimulation of the central gray matter (PAG) in rats anesthetized with chloralose. Injections were made into the reticular gigantocellular nucleus (GN), which is the basic supraspinal center of this reflex. Administering methysergide (a blocker of serotonin receptors) was accompanied by significant (two to four times) diminution of inhibition evoked by PAG stimulation with a short, high-frequency series of stimuli. Long inhibition caused by long, rhythmic stimulation of the PAG was diminished less significantly: from 6–10 to 2.5–4 min. When the opiate receptors of the GN neurons were blocked with naloxone, duration of inhibition was reduced by two to five times. The most clearly expressed diminution of both types of inhibitions was noted with injections of haloperidol, an antagonist of catecholamines. Our data indicate that evidently all of these neuromediator (neuromodulator) systems participate in inhibition of high-threshold, reflex activity of the reticular formation evoked by stimulation of the PAG, but their participation in this process is unequal.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 455–463, July–August, 1991. |
