Medullary substrates of descending spinal inhibition activated by intravenous administration of [d-Ala2]methionine enkephalinamide in the rat

A confocal laser microscopic study of enkephalin-immunoreactive appositions onto physiologically identified neurons in the rostral ventromedial medulla

“…The enkephalins, leu-enkephalin, met-enkephalin, and several C-terminal extended forms of enkephalin, have a widespread distribution in the CNS (Murakami et al, 1987;Mansour et al, 1988) and are concentrated in pain modulatory regions of the brainstem including the RVM (Khachaturian et al, 1983;Williams and Dockray, 1983;Guthrie and Basbaum, 1984). Despite extensive literature on the enkephalinergic modulation of pain transmission (Azami et al, 1982;Akil et al, 1984;Dickenson and Le Bars, 1987;Randich et al, 1987;Basbaum and Besson, 199 1;Vaught, 1991), the mechanisms by which endogenous opioids produce antinociception in vivo remain obscure.…”

Further Characterization of Nociception-Related and Arterial Pressure-Related Neuronal Responses in the Nucleus Reticularis Gigantocellularis of the Rat

“…Some information is presently available to support a role for this opioid in the modulation of the interactive effect of noxious and hypertensive stimuli on the respon siveness of NRGC neurons. First, the endogenous opioids, including the enkephalins, are intimately related to the central regulation of nociception [4,16,29,30,38] and circulation [1,27,28,30,31,36], Second, results from our laboratory and others have further shown that the NRGC is actively involved in the antinociceptive [8,17,22,33] and cardiovascular suppressive [19,37] ac tions of morphine and the enkephalins. Third, opioid receptors [2] and enkephalinergic fiber terminals [18,32,35] have been identified in the medullary reticular forma tion, including the NRGC.…”