Microinjection of morphine within nucleus raphe magnus and dorsal horn neurone activities related to nociception in the rat

1980 ◽  
Vol 189 (2) ◽  
pp. 467-481 ◽  
Author(s):  
Daniel Le Bars ◽  
Anthony H. Dickenson ◽  
Jean Marie Besson
Keyword(s):  
Dorsal Horn ◽  
Nucleus Raphe Magnus ◽  
Dorsal Horn Neurone ◽  
Raphe Magnus

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.

Quantitative comparison of inhibition in spinal cord of nociceptive information by stimulation in periaqueductal gray or nucleus raphe magnus of the cat

1983 ◽  
Vol 50 (6) ◽  
pp. 1433-1445 ◽  
Author(s):  
G. F. Gebhart ◽  
J. Sandkuhler ◽  
J. G. Thalhammer ◽  
M. Zimmermann
Keyword(s):  
Electrical Stimulation ◽  
Dorsal Horn ◽  
Periaqueductal Gray ◽  
Neuronal Responses ◽  
Descending Inhibition ◽  
Nucleus Raphe Magnus ◽  
Mean Intensity ◽  
C Fibers ◽  
Raphe Magnus ◽  
The Mean

The descending inhibition of spinal neuronal responses by focal electrical stimulation in the periaqueductal gray (PAG) or nucleus raphe magnus (NRM) was quantitatively studied and compared in the anesthetized, paralyzed cat. All 60 dorsal horn neurons studied were driven by electrical stimulation of hindlimb cutaneous nerves at strengths supramaximal for activation of A-alpha,delta- and C-fibers, and 52 also responded to noxious radiant heating (50 degrees C, 10 s) of the skin of the foot- or toepads; 8 units had receptive fields in the hairy skin of the hindlimb. All neurons studied also responded to mechanical stimuli; recording sites were located in laminae I-VI of the dorsal horn. The inhibition of spinal neuronal heat-evoked responses by stimulation in the PAG or NRM differed quantitatively when examined on the same spinal neurons. Inhibition of heat-evoked spinal neuronal responses occurred at a lower threshold of stimulation in the NRM than in the PAG. The mean intensity of stimulation in the NRM producing an attenuation to 50% of the control 50 degrees C heat-evoked response was significantly lower than the mean intensity of stimulation in the PAG producing a 50% attenuation of the same spinal units. The mean magnitude of inhibition produced by stimulation in the NRM was significantly greater than that produced on the same spinal units by the same intensity of stimulation in the PAG. However, stimulation in the NRM and PAG produced the same mean percent change in inhibition per 100-microA increase in the intensity of stimulation. Thus, the slopes of the recruitment of descending inhibition from the PAG and the NRM as a function of increasing intensities of stimulation are the same; the lines of recruitment of inhibition are parallel. When examined on the same dorsal horn units, stimulation in the PAG influenced their intensity coding to graded noxious heating of the skin differently than did stimulation in the NRM. The responses of the class 2 and class 3 spinal units examined to increasing temperatures of heat applied to the skin was a monotonic linear function throughout the temperature range studied (42-50 degrees C). Stimulation in the PAG decreased the slope of the stimulus-response function (SRF) without affecting unit thresholds of response, thus influencing the gain control of nociceptive transmission in the dorsal horn. Stimulation in the NRM produced a parallel shift to the right of the SRF, influencing the set point and threshold of response.(ABSTRACT TRUNCATED AT 400 WORDS)

19. A comparison of visceral and noxious somatic influences on neurons in rat nucleus raphe magnus

1985 ◽  
Vol 308 (1136) ◽  
pp. 425-425
Keyword(s):  
Urinary Bladder ◽  
Dorsal Horn ◽  
Spinal Dorsal Horn ◽  
Diffuse Noxious Inhibitory Controls ◽  
Nucleus Raphe Magnus ◽  
Spinal Dorsal ◽  
Raphe Magnus ◽  
Noxious Stimuli

The activities of certain neurons in the spinal dorsal horn can be depressed by widespread noxious stimuli (Le Bars et al. 1979), A phenomenon usually referred to as ‘diffuse noxious inhibitory controls’ (d.n.i.c.). Similar effects have been demonstrated following distension of the urinary bladder or colon (Cadden, this meeting). D.n.i.c. are thought to be mediated by a pathway which relays in the medullary nucleus raphe magnus (n.r.m.) (Dickenson et al. 1980). The aims of the present study were to determine whether neurons in n.r.m. could be influenced by visceral and somatic stimuli that produce d.n.i.c., and whether any such neurons have spinally projecting axons.

Sign in / Sign up

Export Citation Format

Share Document