Descending inhibitory influences from periaqueductal gray, nucleus raphe magnus, and adjacent reticular formation. II. Effects on medullary dorsal horn nociceptive and nonnociceptive neurons

Abstract

1. This study examined the inhibitory effects elicited by brain stem stimulation on the somatosensory responses of trigeminal medullary dorsal horn (subnucleus caudalis of the spinal trigeminal nucleus) neurons. Single-unit extracellular recordings were obtained in chloralose-anesthetized cats. Neurons were classified as wide dynamic range (WDR), nociceptive specific (NS), or low-threshold mechanoreceptive (LTM). Conditioning stimuli were delivered to the periaqueductal gray (PAG), nucleus cuneiformis (CU), nucleus raphe magnus (NRM), nucleus reticularis gigantocellularis (NGC), and nucleus reticularis magnocellularis (NMC). 2. Over 97% of the neurons tested could be inhibited by stimulation in all regions except PAG. Stimulation in the PAG inhibited 91% of the neurons tested. There was no statistically significant difference in the incidence of inhibition of WDR and NS nociceptive (noci) neurons and the LTM nonnociceptive (nonnoci) neurons. 3. Mean stimulation intensities necessary to produce inhibition were determined for each neuron from each stimulation site. The current thresholds necessary to inhibit the responses of noci neurons were found to be significantly lower, on the average, than those of nonnoci neurons at stimulation sites in the PAG, CU, and NGC. 4. Inhibition of the responses of WDR neurons required a lower mean current than for NS neurons but was statistically significant only for PAG and NGC. Thresholds for inhibiting the responses of NS neurons were similar to those for inhibiting the responses of LTM neurons for all regions except CU, where LTM thresholds were markedly but not significantly higher. 5. Stimulation thresholds were found to be lowest in NMC, while in NGC, NRM, and CU they were all similar and slightly higher. Stimulation in the PAG required the highest currents to produce inhibition. 6. These results indicate that stimulation in NRM and PAG not only inhibits the responses of noci neurons but also those of nonnoci neurons. Furthermore, stimulation in reticular regions adjacent to NRM and PAG is frequently even more effective in inhibiting the responses of both noci and nonnoci neurons. In addition, WDR neurons are more effectively inhibited than NS or LTM neurons. These results are compared with those obtained using similar methods in cat lumbar dorsal horn.

Sensory suppression during feeding

“…Because VMM stimulation modulates the cellular responses and behavioral reactions evoked by both noxious and innocuous inputs (33)(34)(35), a generalized decrease in reactivity to somatosensory stimulation may accompany feeding, allowing an animal to nourish itself without being distracted by every falling leaf or gust of wind. Taken together, our work has shown that decreases in ON cell firing and increases in OFF cell firing occur during sleep, eating, drinking, and micturition (21,22,31).…”

Systemic Morphine Inhibits Dorsal Horn Projection Neurons through Spinal Cholinergic System Independent of Descending Pathways

“…Spinal dorsal horn neurons are subject to modulation by the supraspinal descending pathways. For example, stimulation of the periaquaductal gray and rostral ventromedial medulla inhibits dorsal horn neurons (Dostrovsky et al, 1983;Basbaum and Fields, 1984). However, the role of the descending pathways in the analgesic effect and inhibition of ascending dorsal horn neurons produced by systemic opioids is not fully known.…”

“…Both systemic and spinal local application of opioids produces potent analgesia and inhibition of dorsal horn neurons (Yaksh and Rudy, 1977;Sastry and Goh, 1983;Yaksh and Noueihed, 1985;Magnuson and Dickenson, 1991). The spinal dorsal horn neurons are subject to descending modulation from supraspinal sites such as the periaquaductal gray, locus coeruleus, and rostral ventromedial medulla (Dostrovsky et al, 1983;Bodnar et al, 1990;Urban and Smith, 1994;Pan et al, 2004). Some studies suggest that the analgesic effect of opioids may be mediated by descending inhibition of dorsal horn neurons (Basbaum and Fields, 1984;Wigdor and Wilcox, 1987;Chiang and Zhuo, 1989).…”

Bloqueio anestésico do nervo occipital maior na profilaxia da migrânea

“…Mecanismos de inibição central e periférica aparecerão em diferentes sítios cerebrais na tentativa de restabelecer este equilíbrio [13][14][15][16][17][18][19][20][21] . O tempo necessário para que isto ocorra, corresponde a duração média das crises de migrânea.…”