The effects of focal stimulation in nucleus raphe magnus and periaqueductal gray on intracellularly recorded neurons in spinal laminae I and II

1986 ◽  
Vol 56 (3) ◽  
pp. 555-571 ◽  
Author(s):  
A. R. Light ◽  
E. J. Casale ◽  
D. M. Menetrey
Keyword(s):  
Brain Stem ◽  
Periaqueductal Gray ◽  
The Other ◽  
Descending Pathways ◽  
Nucleus Raphe Magnus ◽  
Raphe Magnus ◽  
Low Threshold ◽  
Conductance Increase ◽  
Small Conductance ◽  
Postsynaptic Mechanism

Single neurons in spinal laminae I and II of cats were recorded intracellularly while stimulating in nucleus raphe magnus (NRM) and periaqueductal gray (PAG) with monopolar tungsten microelectrodes. Brain stem stimulation inhibited about one-half of the nociceptive-specific neurons, whereas the other half was unaffected. Brain stem stimulation inhibited about one-half of the multireceptive neurons, but the other half was excited and then inhibited. Brain stem stimulation inhibited about one-third of the low-threshold neurons, one-half was excited then inhibited, and one-fifth showed no effect. In all classes of neurons, the inhibition was produced by an inhibitory postsynaptic potential (IPSP) that began with a latency of approximately 25 ms and lasted approximately 400 ms following a single stimulus. The IPSP occurred with a small conductance increase and was reversed by hyperpolarizing currents applied to the cell. These data indicate that NRM and PAG modulated laminae I and II neurons via a postsynaptic mechanism. The conduction velocity of this descending pathway was calculated to range from 6.1 to 66.6 m/s with an average of 13.8 m/s. These data also indicate heterogeneity in the pathway, since some neurons were inhibited, whereas other neurons were excited then inhibited by descending stimulation. Finally, these data indicate specificity in these descending pathways since nearly one-half of neurons that had low-threshold inputs were excited by brain stem stimulation, whereas nearly all nociceptive-specific neurons were either inhibited or unaffected.

Influence of cold and warm acclimation on neuronal responses in the lower brain stem

1987 ◽  
Vol 65 (6) ◽  
pp. 1281-1289 ◽  
Author(s):  
P. Hinckel ◽  
W. T. Perschel
Keyword(s):  
Brain Stem ◽  
Guinea Pigs ◽  
Metabolic Activation ◽  
Maximum Activity ◽  
Descending Pathways ◽  
Nucleus Raphe Magnus ◽  
Average Maximum ◽  
Raphe Magnus ◽  
Lower Brain Stem ◽  
Excitatory Responses

Neurons in two lower brain stem areas, the nucleus raphe magnus and the subcoeruleus region, have been shown to be part of the thermoafferent system. It is concluded from microcut experiments in unanaesthetized guinea pigs that inhibition of shivering caused by nucleus raphe magnus stimulation is mediated partly by ascending and partly by descending efferents of the nucleus raphe magnus. Electrical stimulation of the subcoeruleus area caused excitatory metabolic responses. Interruption of the ascending efferents of the subcoeruleus area did not prevent the metabolic activation. It is concluded that the excitatory responses are partly mediated by descending efferents of the subcoeruleus area. The descending pathways project mainly to motoneurone pools and to dorsal horn cells. In cold-acclimated guinea pigs, the average maximum activity of bell-shaped subcoeruleus cold-responsive units was reduced significantly in comparison with cold-responsive neurons in animals acclimated to normal room temperature. Furthermore, peak activity of warm-responsive units in the nucleus raphe magnus was larger in cold-acclimated animals than in animals acclimated to normal room termperature. These neuronal changes may contribute via descending lower loops and via ascending upper loops to long-term slope reduction of metabolic cold defence and shivering threshold displacements.

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

1983 ◽  
Vol 49 (4) ◽  
pp. 932-947 ◽  
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.

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

1983 ◽  
Vol 49 (4) ◽  
pp. 948-960 ◽  
Author(s):  
J. O. Dostrovsky ◽  
Y. Shah ◽  
B. G. Gray
Keyword(s):  
Dorsal Horn ◽  
Dynamic Range ◽  
Periaqueductal Gray ◽  
Nucleus Raphe Magnus ◽  
Nucleus Reticularis ◽  
Medullary Dorsal Horn ◽  
Significant Difference ◽  
Raphe Magnus ◽  
Somatosensory Responses ◽  
Wdr Neurons

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.

Sign in / Sign up

Export Citation Format

Share Document