Journal of Neuroscience, Vol 6, 701-713, Copyright © 1986 by Society for Neuroscience
Characterization of inhibition of the spinal nociceptive tail-flick reflex in the rat from the medullary lateral reticular nucleus
GF Gebhart and MH Ossipov
Inhibition of the spinal nociceptive tail-flick (TF) reflex by focal
electrical stimulation in the caudal medulla was examined and characterized
in lightly pentobarbital-anesthetized rats. Systematic mapping studies
revealed that inhibition of the TF reflex was produced at low intensities
of stimulation (12.5-25 microA) only from the lateral reticular nucleus
(LRN). Areas dorsal and medial to the LRN required higher intensities of
stimulation to produce descending inhibition of the TF reflex, likely
reflecting spread of current to the LRN at these higher intensities of
stimulation (50-100 microA). At threshold inhibitory intensities of
stimulation in the LRN, changes in blood pressure were not produced.
Strength-duration characterization of stimulation and the microinjection of
glutamate into the LRN at the same site where focal electrical stimulation
was effective suggest that the descending inhibition produced arises from
activation of cell bodies in the LRN. The intrathecal administration of a
variety of pharmacological antagonists revealed the descending inhibition
produced by stimulation in the LRN to be mediated at least in part by
spinal alpha 2-adrenoceptors. These findings, together with previous
observations, suggest a role for the LRN in the centrifugal modulation of
spinal nociceptive transmission.