Collateral projections of nucleus raphe dorsalis neurones to the caudate-putamen and region around the nucleus raphe magnus and nucleus reticularis gigantocellularis pars α in the rat

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.

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Analgesic effects of serotonin microinjection into nucleus raphe magnus and nucleus raphe dorsalis evaluated by the monosodium urate (MSU) tonic pain model in the rat

Brain Research ◽

10.1016/0006-8993(87)90874-2 ◽

1987 ◽

Vol 426 (2) ◽

pp. 205-211 ◽

Cited By ~ 18

Author(s):

Masahiko Inase ◽

Hiroshi Nakahama ◽

Taisuke Otsuki ◽

Jiazhi Fang

Keyword(s):

Monosodium Urate ◽

Pain Model ◽

Nucleus Raphe Magnus ◽

Analgesic Effects ◽

Raphe Magnus ◽

Tonic Pain ◽

Raphe Dorsalis

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Descending inhibitory influences from periaqueductal gray, nucleus raphe magnus, and adjacent reticular formation. I. Effects on lumbar spinal cord nociceptive and nonnociceptive neurons

Journal of Neurophysiology ◽

10.1152/jn.1983.49.4.932 ◽

1983 ◽

Vol 49 (4) ◽

pp. 932-947 ◽

Cited By ~ 115

Author(s):

B. G. Gray ◽

J. O. Dostrovsky

Keyword(s):

Spinal Cord ◽

Brain Stem ◽

Periaqueductal Gray ◽

Spinal Cord Dorsal Horn ◽

Lumbar Spinal Cord ◽

Nucleus Raphe Magnus ◽

Nucleus Reticularis ◽

Raphe Magnus ◽

Lumbar Spinal ◽

The Brain

1. This study examined the inhibitory effects of conditioning stimuli delivered to the periaqueductal gray (PAG), nucleus cuneiformis (CU), nucleus raphe magnus (NRM), nucleus reticularis gigantocellularis (NGC), and nucleus reticularis magnocellularis (NMC) on functionally identified neurons of the lumbar spinal cord dorsal horn in chloralose-anesthetized or decerebrate cats. 2. Neurons were classified according to their responses to a variety of cutaneous stimuli as low-threshold mechanoreceptive (LTM), wide dynamic range (WDR), or nociceptive specific (NS). The major aim of this study was to determine whether there was a difference in the effectiveness of the brain stem stimulation-produced inhibition of nociceptive (noci) neurons (consisting of both WDR and NS neurons) and the LTM non-nociceptive (nonnoci) neurons. There were no statistical differences in the susceptibility of WDR and NS neurons to brain stem-induced inhibition. 3. Most neurons tested could be inhibited by stimulation of any of the brain stem regions tested. In all cases the percentage of noci neurons inhibited from a given region was higher than the percentage of nonnoci neurons; however, this difference was only statistically significant in the case of NMC stimulation. 4. Threshold current intensities necessary to produce inhibition were determined for each neuron from each stimulation site. Although there was a trend for noci neurons to require slightly lower current intensities, there was in fact no statistically significant difference in the inhibitory thresholds between noci and nonnoci neurons for any of the regions tested. 5. A comparison of the mean threshold currents for the five regions studied revealed that the lowest stimulation currents were obtained in NMC with NRM, CU, NGC, and PAG, each requiring progressively higher current intensities in order to produce inhibition. 6. These results indicate that stimulation in PAG and NRM not only inhibits the responses of noci neurons but also those of nonnoci neurons. Moreover, stimulation in reticular regions adjacent to these two regions is effective in inhibiting the responses of both noci and nonnoci neurons.

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