Nociceptive neurons in rat superior colliculus: response properties, topography, and functional implications

1989 ◽  
Vol 62 (2) ◽  
pp. 510-525 ◽  
Author(s):  
J. G. McHaffie ◽  
C. Q. Kao ◽  
B. E. Stein
Keyword(s):  
Superior Colliculus ◽  
Dynamic Range ◽  
The Body ◽  
Body Parts ◽  
Power Functions ◽  
Noxious Heat ◽  
Nociceptive Neurons ◽  
Tactile Stimuli ◽  
Noxious Stimuli ◽  
Wdr Neurons

1. Extracellular recordings were made from single superior colliculus neurons in urethane-anesthetized rats in response to mechanical and/or thermal stimulation of the skin. In addition to those activated by low-threshold (LT) tactile stimuli, many neurons responded preferentially, or solely, to noxious stimuli. Two functionally defined subtypes of nociceptive neurons were distinguished: wide-dynamic-range (WDR) neurons, which responded optimally to noxious stimuli but also to innocuous stimuli; and nociceptive-specific (NS) neurons, which responded solely to frankly noxious stimuli. The thermal thresholds were 42-45 degrees C, and the stimulus-response relationships were positively accelerating power functions with exponents of 2.9 (WDR) and 3.1 (NS). 2. WDR neurons also responded to cooling of the skin to temperatures below 24 degrees C. Like noxious heat responses, cold responses were monotonically graded as the intensity of the cold stimulus was increased. Thus the temperature sensitivity of thermal-sensitive neurons in the superior colliculus appeared to be tuned to detect large deviations from ambient skin temperature in either direction once threshold is reached. 3. LT neurons were somatotopically organized, with the head and forelimbs rostral and the trunk and hindlimbs caudal. The limbs were generally represented further lateral in the structure, whereas more proximal body parts were more medial. Nevertheless, there was extensive overlap of body parts especially in areas of transition. Thus, a "block-to-block" or "area-to-area" rather than a "point-to-point" representation of the body surface was evident. 4. The nociceptive representation did not violate the general LT somatotopy but neither was it coextensive. Virtually all nociceptive neurons had trigeminal receptive fields and were thus heavily represented in the rostral superior colliculus, where the LT face representation was also located. No nociceptive neurons were present in the caudal one-third of the structure. A general dorsal-to-ventral segregation of somatosensory neurons also was noted, so that in a given electrode penetration, LT neurons usually were the most superficial, WDR neurons were just below these, and NS neurons were deepest of all. 5. The presence of overlapping LT and nociceptive trigeminal representations in the superior colliculus seems particularly adaptive in view of the fact that rodents use their vibrissae for exploring their environment and thus put rostral body parts at risk during such behaviors.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses of monkey medullary dorsal horn neurons during the detection of noxious heat stimuli

1989 ◽  
Vol 62 (2) ◽  
pp. 437-449 ◽  
Author(s):  
W. Maixner ◽  
R. Dubner ◽  
D. R. Kenshalo ◽  
M. C. Bushnell ◽  
J. L. Oliveras
Keyword(s):  
Dorsal Horn ◽  
Stimulus Intensity ◽  
Dynamic Range ◽  
Thermal Stimulus ◽  
Mechanical Stimuli ◽  
Behavioral Task ◽  
Noxious Heat ◽  
Nociceptive Neurons ◽  
Medullary Dorsal Horn ◽  
Wdr Neurons

1. We examined the activity of thermally sensitive trigeminothalamic neurons and nonprojection neurons in the medullary dorsal horn (trigeminal nucleus caudalis) in three monkeys performing thermal and visual detection tasks. 2. An examination of neuronal stimulus-response functions, obtained during thermal-detection tasks in which noxious heat stimuli were applied to the face, indicated that wide-dynamic-range neurons (WDR, responsive to innocuous mechanical stimuli with greater responses to noxious mechanical stimuli) could be subclassified based on the slope values of linear regression lines. WDR1 neurons exhibited significantly greater sensitivity to noxious heat stimulation than WDR2 neurons or nociceptive-specific neurons (NS, responsive only to noxious stimuli). 3. In one behavioral task, the monkeys detected 1.0 degrees C increases in noxious heat from preceding noxious heat stimuli ranging from 44 to 48 degrees C. WDR1, WDR2, and NS neurons increased their discharge frequency as a function of the intensity of the first noxious heat temperature (T1) as well as the final temperature (T2). The responses of WDR1 neurons were greater than those produced by WDR2 or NS neurons across all the temperatures examined. The order of stimulus presentation affected the responses of WDR1 neurons to 1.0 degrees C increases in the noxious heat range but not those of WDR2 or NS neurons. 4. In a second behavioral task, the monkeys detected small increases in noxious heat (0.2-0.8 degrees C) from a first temperature of 46 degrees C. Although the responses of all three classes of neurons were monotonically related to stimulus intensity, WDR1 neurons exhibited greater sensitivity to small temperature increases than either WDR2 or NS neurons. 5. Subpopulations of all three classes of neurons exhibited responses that were independent of thermal stimulus parameters or sensory modality and that only occurred during the behavioral task. These task-related responses were time-locked to specific behavioral events associated with trial initiation and trial continuation. 6. These data provide evidence that a subpopulation of WDR neurons is the dorsal horn cell type most sensitive to small increases in noxious heat in the 45-49 degrees C temperature range and provides the most information about stimulus intensity. The findings support the view that nociceptive neurons have the capacity to precisely encode stimulus features in the noxious range and that WDR neurons are likely to participate in the monkeys' ability to perceive the intensity of such stimuli.

scholarly journals Effects of a Cannabinoid Agonist on Spinal Nociceptive Neurons in a Rodent Model of Neuropathic Pain

2006 ◽  
Vol 96 (6) ◽  
pp. 2984-2994 ◽  
Author(s):  
Cheng Liu ◽  
J. Michael Walker
Keyword(s):  
Neuropathic Pain ◽  
Receptive Field ◽  
Nerve Injury ◽  
Dynamic Range ◽  
Rodent Model ◽  
Field Size ◽  
Neural Basis ◽  
Noxious Heat ◽  
Nociceptive Neurons ◽  
Wdr Neurons

The effects of the synthetic cannabinoid WIN 55,212–2 on heat-evoked firing of spinal wide dynamic range (WDR) neurons were examined in a rodent model of neuropathic pain. Fifty-eight WDR neurons (1 cell/animal) were recorded from the ipsilateral spinal dorsal horns of rats with chronic constriction injury (CCI) and sham-operated controls. Relative to sham-operated controls, neurons recorded in CCI rats showed elevations in spontaneous firing, noxious heat-evoked responses, and afterdischarge firing as well as increases in receptive field size. WIN 55,212–2 (0.0625, 0.125, and 0.25 mg/kg, intravenous) dose-dependently suppressed heat-evoked activity and decreased the receptive field areas of dorsal horn WDR neurons in both nerve injured and control rats with a greater inhibition in CCI rats. At the dose of 0.125 mg/kg iv, WIN 55,212–2 reversed the hyperalgesia produced by nerve injury. The effect of intravenous administration of WIN 55,212–2 appears to be centrally mediated because administration of the drug directly to the ligated nerve did not suppress the heat-evoked neuronal activity in CCI rats. Pretreatment with the cannabinoid CB1 receptor antagonists SR141716A or AM251, but not the CB2 antagonist SR144528, blocked the effects. These results provide a neural basis for reports of potent suppression by cannabinoids of the abnormal sensory responses that result from nerve injury.

Spinothalamic and spinohypothalamic tract neurons in the sacral spinal cord of rats. II. Responses to cutaneous and visceral stimuli

1996 ◽  
Vol 75 (6) ◽  
pp. 2606-2628 ◽  
Author(s):  
J. T. Katter ◽  
R. J. Dado ◽  
E. Kostarczyk ◽  
G. J. Giesler
Keyword(s):  
Spinal Cord ◽  
Dorsal Horn ◽  
Dynamic Range ◽  
Receptive Fields ◽  
High Threshold ◽  
Mechanical Stimuli ◽  
Power Functions ◽  
Nociceptive Neurons ◽  
Wdr Neurons ◽  
Sacral Spinal Cord

1. A goal of this study was to determine whether neurons in the sacral spinal cord that project to the diencephalon are involved in the processing and transmission of sensory information that arises in the perineum and pelvis. Therefore, 58 neurons in segments L6-S2 were activated antidromically with currents < or = 30 microA from points in the contralateral diencephalon in rats that were anesthetized with urethan. 2. Responses to mechanical stimuli applied to the cutaneous receptive fields of these neurons were used to classify them as low-threshold (LT), wide dynamic range (WDR) or high-threshold (HT) neurons. Twenty-two neurons (38%) responded preferentially to brushing (LT neurons). Eighteen neurons (31%) responded to brushing but responded with higher firing frequencies to noxious mechanical stimuli (WDR neurons). Eighteen neurons (31%) responded only to noxious intensities of mechanical stimulation (HT neurons). LT neurons were recorded predominantly in nucleus proprius of the dorsal horn. Nociceptive neurons (WDR and HT) were recorded throughout the dorsal horn. 3. Cutaneous receptive fields were mapped for 56 neurons. Forty-five (80%) had receptive fields that included at least two of the following regions ipsilaterally: the rump, perineum, or tail. Eleven neurons (20%) had receptive fields that were restricted to one of these areas or to the ipsilateral hind limb. Thirty-eight neurons (68%) had cutaneous receptive fields that also included regions of the contralateral tail or perineum. On the perineum, receptive fields usually encompassed perianal and perivaginal areas including the clitoral sheath. There were no statistically significant differences in the locations or sizes of receptive fields for LT neurons compared with nociceptive (WDR and HT) neurons. 4. Thirty-seven LT, WDR, and HT neurons were tested for their responsiveness to heat stimuli. Five (14%) responded to increasing intensities of heat with graded increases in their firing frequencies. Thirty-two LT, WDR, and HT neurons also were tested with cold stimuli. None responded with graded increases in their firing frequencies to increasingly colder stimuli. There were no statistically significant differences among the responses of LT, WDR, and HT neurons to either heat or cold stimuli. 5. Forty LT, WDR, and HT neurons were tested for their responsiveness to visceral stimuli by distending a balloon placed into the rectum and colon with a series of increasing pressures. Seventeen (43%) exhibited graded increases in their firing frequencies in response to increasing pressures of colorectal distention (CrD). None of the responsive neurons responded reproducibly to CrD at an intensity of 20 mmHg, and all responded at intensities of > or = 80 mmHg. More than 90% responded abruptly at stimulus onset, responded continuously throughout the stimulus period, and stopped responding immediately after termination of the stimulus. 6. Thirty-one neurons were tested for their responsiveness to distention of a balloon placed inside the vagina. Eleven (35%) exhibited graded increases in their firing frequencies in response to increasing pressures of vaginal distention (VaD). The thresholds and temporal profiles of the responses to VaD were similar to those for CrD. Twenty-nine neurons were tested with both CrD and VaD. Thirteen (45%) were excited by both stimuli, four (14%) responded to CrD but not VaD, and one (3%) was excited by VaD but not CrD. Neurons excited by CrD, VaD, or both were recorded throughout the dorsal horn. 7. As a population, WDR neurons, but not LT or HT neurons, encoded increasing pressures of CrD and VaD with graded increases in their firing frequencies. The responses of WDR neurons to CrD differed significantly from those of either LT or HT neurons. Regression analyses of the stimulus-response functions of responsive WDR neurons to CrD and VaD were described by power functions with exponents of 1.6 and 2.4, respectively.(ABSTRACT TRUNCATED)

Investigating mechanisms behind offset analgesia: Effect on spinal responses during thermal stimulation

2014 ◽  
Vol 5 (3) ◽  
pp. 207-208
Author(s):  
Thomas Kronborg Larsen ◽  
Andreas Egmose ◽  
Marianne Enggaard ◽  
Rósa Hugosdóttir ◽  
Federico Arguissain ◽  
...  
Keyword(s):  
Dynamic Range ◽  
Tibialis Anterior Muscle ◽  
Noxious Heat ◽  
Baseline Trial ◽  
Nociceptive Neurons ◽  
Pain Ratings ◽  
Subjective Pain ◽  
Wdr Neurons ◽  
Perceptual Mechanism ◽  
Stimulation Of

AbstractIntroductionOffset analgesia (OA) is a temporal perceptual mechanism in which subjective pain ratings decrease disproportionally when a noxious heat stimulus is decreased by 1–3 ◦C. Whether OA is a peripheral, spinal or supraspinal mechanism remains unknown. The stimulation of afferent nociceptors in the foot, leads to a spinal nociceptive withdrawal reflex (NWR) which is mediated through the wide dynamic range (WDR) neurons and therefore under descending control. We hypothesized that OA affects the spinal nociceptive neurons resulting in an attenuation of the NWR during OA.MethodsFour heat stimulations profiles were applied to the lower legs divided into four segments of 5 s, 5 s, 5 s, and 15 s, respectively: Offset Analgesia Trial (OAT) (48, 49, 48, 48 ◦C), Offset Baseline Trial (OBT) (48, 49, 32, 32 ◦C), Constant Heat Trial (CHT) (4 × 48 ◦C), and Baseline Trial (BT) (4 × 32 ◦C). Subjects rated the pain intensity continuously using a visual analog scale (VAS). NWR were evoked by electrical stimulation of the plantar foot and assessed once during each segment by recording EMG from the tibialis anterior muscle.ResultsVAS-ratings were lower during the third period of OAT compared to CHT (p < 0.001). However, there was no difference (p > 0.05) comparing the NWR size between OAT, OBT, CHT, and BT throughout the time periods.ConclusionsThe NWR was not affected by OA suggesting that spinal WDR plays a limited role in the OA mechanism. Whether peripheral- or supraspinal mechanisms are responsible the OA phenomenon remains unknown.

Cannabinoid Suppression of Noxious Heat-Evoked Activity in Wide Dynamic Range Neurons in the Lumbar Dorsal Horn of the Rat

1999 ◽  
Vol 81 (2) ◽  
pp. 575-583 ◽  
Author(s):  
Andrea G. Hohmann ◽  
Kang Tsou ◽  
J. Michael Walker
Keyword(s):  
Dorsal Horn ◽  
Dynamic Range ◽  
Cb1 Receptors ◽  
Intraventricular Administration ◽  
Wide Dynamic Range ◽  
Noxious Heat ◽  
Nociceptive Neurons ◽  
Evoked Activity ◽  
Wdr Neurons ◽  
Wide Dynamic Range Neurons

Cannabinoid suppression of noxious heat-evoked activity in wide dynamic range neurons in the lumbar dorsal horn of the rat. The effects of cannabinoid agonists on noxious heat-evoked firing of 62 spinal wide dynamic range (WDR) neurons were examined in urethan-anesthetized rats (1 cell/animal). Noxious thermal stimulation was applied with a Peltier device to the receptive fields in the ipsilateral hindpaw of isolated WDR neurons. To assess the site of action, cannabinoids were administered systemically in intact and spinally transected rats and intraventricularly. Both the aminoalkylindole cannabinoid WIN55,212-2 (125 μg/kg iv) and the bicyclic cannabinoid CP55,940 (125 μg/kg iv) suppressed noxious heat-evoked activity. Responses evoked by mild pressure in nonnociceptive neurons were not altered by CP55,940 (125 μg/kg iv), consistent with previous observations with another cannabinoid agonist, WIN55,212-2. The cannabinoid induced-suppression of noxious heat-evoked activity was blocked by pretreatment with SR141716A (1 mg/kg iv), a competitive antagonist for central cannabinoid CB1 receptors. By contrast, intravenous administration of either vehicle or the receptor-inactive enantiomer WIN55,212-3 (125 μg/kg) failed to alter noxious heat-evoked activity. The suppression of noxious heat-evoked activity induced by WIN55,212-2 in the lumbar dorsal horn of intact animals was markedly attenuated in spinal rats. Moreover, intraventricular administration of WIN55,212-2 suppressed noxious heat-evoked activity in spinal WDR neurons. By contrast, both vehicle and enantiomer were inactive. These findings suggest that cannabinoids selectively modulate the activity of nociceptive neurons in the spinal dorsal horn by actions at CB1 receptors. This modulation represents a suppression of pain neurotransmission because the inhibitory effects are selective for pain-sensitive neurons and are observed with different modalities of noxious stimulation. The data also provide converging lines of evidence for a role for descending antinociceptive mechanisms in cannabinoid modulation of spinal nociceptive processing.

Responses of primate SI cortical neurons to noxious stimuli

1983 ◽  
Vol 50 (6) ◽  
pp. 1479-1496 ◽  
Author(s):  
D. R. Kenshalo ◽  
O. Isensee
Keyword(s):  
Receptive Field ◽  
Cortical Neurons ◽  
Receptive Fields ◽  
The Body ◽  
Thermal Stimulation ◽  
Discharge Frequency ◽  
Mechanical Stimuli ◽  
Noxious Heat ◽  
Nociceptive Neurons ◽  
Heat Pulses

Recordings were made from single SI cortical neurons in the anesthetized macaque monkey. Each isolated cortical neuron was tested for responses to a standard series of mechanical stimuli. The stimuli included brushing the skin, pressure, and pinch. The majority of cortical neurons responded with the greatest discharge frequency to brushing the receptive field, but neurons were found in areas 3b and 1 that responded maximally to pinching the receptive field. A total of 68 cortical nociceptive neurons were examined in 10 animals. Cortical neurons that responded maximally to pinching the skin were also tested for responses to graded noxious heat pulses (from 35 to 43, 45, 47, and 50 degrees C). If the neuron failed to respond or only responded to 50 degrees C, the receptive field was also heated to temperatures of 53 and 55 degrees C. Fifty-six of the total population of nociceptive neurons were tested for responses to the complete series of noxious heat pulses: 46 (80%) exhibited a progressive increase in the discharge frequency as a function of stimulus intensity, and the spontaneous activity of two (4%) was inhibited. One population of cortical nociceptive neurons possessed restricted, contralateral receptive fields. These cells encoded the intensity of noxious mechanical and thermal stimulation. Sensitization of primary afferent nociceptors was reflected in the responses of SI cortical nociceptive neurons when the ascending series of noxious thermal stimulation was repeated. The population of cortical nociceptive neurons with restricted receptive fields exhibited no adaptation in the response during noxious heat pulses of 47 and 50 degrees C. At higher temperatures the response often continued to increase during the stimulus. The other population of cortical nociceptive neurons was found to have restricted, low-threshold receptive fields on the contralateral hindlimb and, in addition, could be activated only by intense pinching or noxious thermal stimuli delivered on any portion of the body. The stimulus-response functions obtained from noxious thermal stimulation of the contralateral hindlimb were not different from cortical nociceptive neurons with small receptive fields. However, nociceptive neurons with large receptive fields exhibited a consistent adaptation during a noxious heat pulse of 47 and 50 degrees C. Based on the response characteristics of these two populations of cortical nociceptive neurons, we conclude that neurons with small receptive fields possess the ability to provide information about the localization, the intensity, and the temporal attributes of a noxious stimulus.4+.

scholarly journals Non-informative vision improves spatial tactile discrimination on the shoulder but does not influence detection sensitivity

2020 ◽  
Vol 238 (12) ◽  
pp. 2865-2875
Author(s):  
Fabrizio Leo ◽  
Sara Nataletti ◽  
Luca Brayda
Keyword(s):  
Tactile Stimulation ◽  
Detection Threshold ◽  
Receptive Fields ◽  
Judgment Task ◽  
The Body ◽  
Detection Sensitivity ◽  
Body Parts ◽  
Tactile Acuity ◽  
Tactile Stimuli ◽  
Numerosity Judgment

Abstract Vision of the body has been reported to improve tactile acuity even when vision is not informative about the actual tactile stimulation. However, it is currently unclear whether this effect is limited to body parts such as hand, forearm or foot that can be normally viewed, or it also generalizes to body locations, such as the shoulder, that are rarely before our own eyes. In this study, subjects consecutively performed a detection threshold task and a numerosity judgment task of tactile stimuli on the shoulder. Meanwhile, they watched either a real-time video showing their shoulder or simply a fixation cross as control condition. We show that non-informative vision improves tactile numerosity judgment which might involve tactile acuity, but not tactile sensitivity. Furthermore, the improvement in tactile accuracy modulated by vision seems to be due to an enhanced ability in discriminating the number of adjacent active electrodes. These results are consistent with the view that bimodal visuotactile neurons sharp tactile receptive fields in an early somatosensory map, probably via top-down modulation of lateral inhibition.

α2-Adrenoceptors Modulate NMDA-Evoked Responses of Neurons in Superficial and Deeper Dorsal Horn of the Medulla

1998 ◽  
Vol 80 (4) ◽  
pp. 2210-2214 ◽  
Author(s):  
Kai-Ming Zhang ◽  
Xiao-Min Wang ◽  
Angela M. Peterson ◽  
Wen-Yan Chen ◽  
Sukhbir S. Mokha
Keyword(s):  
Dorsal Horn ◽  
Dynamic Range ◽  
Inhibitory Effect ◽  
Male Rats ◽  
Evoked Responses ◽  
Superficial Dorsal Horn ◽  
Nociceptive Neurons ◽  
Adrenoceptor Antagonist ◽  
Medullary Dorsal Horn ◽  
Wdr Neurons

Kai-Ming Zhang, Xiao-Min Wang, Angela M. Peterson, Wen-Yan Chen, and Sukhbir S. Mokha. α2-Adrenoceptors modulate NMDA-evoked responses of neurons in the superficial and deeper dorsal horn of the medulla. J. Neurophysiol. 80: 2210–2214, 1998. Extracellular single unit recordings were made from neurons in the superficial and deeper dorsal horn of the medulla (trigeminal nucleus caudalis) in 21 male rats anesthetized with urethan. NMDA produced an antagonist-reversible excitation of 46 nociceptive as well as nonnociceptive neurons. Microiontophoretic application of a preferential α2-adrenoceptor (α2AR) agonist, (2-[2,6-dichloroaniline]-2-imidazoline) hydrochloride (clonidine), reduced the NMDA-evoked responses of 86% (6/7) of nociceptive-specific (NS) neurons, 82% (9/11) of wide dynamic range (WDR) neurons, and 67% (4/6) of low-threshold (LT) neurons in the superficial dorsal horn. In the deeper dorsal horn, clonidine inhibited the NMDA-evoked responses of 94% (16/17) of NS and WDR neurons and 60% (3/5) of LT neurons. Clonidine facilitated the NMDA-evoked responses in 14% (1/17) of NS, 9% (1/11) of WDR, and 33% (2/6) of LT neurons in the superficial dorsal horn. Idazoxan, an α2AR antagonist, reversed the inhibitory effect of clonidine in 90% (9/10) of neurons, whereas prazosin, an α1-adrenoceptor antagonist with affinity for α2BAR, and α2CAR, were ineffective. We suggest that activation of α2ARs produces a predominantly inhibitory modulation of the NMDA-evoked responses of nociceptive neurons in the medullary dorsal horn.

Halothane Suppression of Spinal Sensory Neuronal Responses to Noxious Peripheral Stimuli Is Mediated, in Part, by Both GABAAand Glycine Receptor Systems

2002 ◽  
Vol 97 (2) ◽  
pp. 412-417 ◽  
Author(s):  
Masanori Yamauchi ◽  
Hiroshi Sekiyama ◽  
Steven G. Shimada ◽  
J. G. Collins
Keyword(s):  
Dynamic Range ◽  
Glycine Receptor ◽  
Gamma Aminobutyric Acid ◽  
Neuronal Responses ◽  
General Anesthetic ◽  
Gaba A ◽  
Low Threshold ◽  
Noxious Stimuli ◽  
Evoked Activity ◽  
Wdr Neurons

Background A major effect of general anesthesia is lack of response in the presence of a noxious stimulus. Anesthetic depression of spinal sensory neuronal responses to noxious stimuli is likely to contribute to that essential general anesthetic action. The authors tested the hypothesis that gamma-aminobutyric acid receptor type A (GABA(A)) and strychnine-sensitive glycine receptor systems mediate halothane depression of spinal sensory neuronal responses to noxious stimuli. Methods Extracellular activity of single spinal dorsal horn wide dynamic range (WDR) neurons was recorded in decerebrate, spinal cord transected rats. Neuronal responses to noxious (thermal and mechanical) and nonnoxious stimuli were examined in the drug-free state. Subsequently, cumulative doses (0.1-2.0 mg/kg) of bicuculline (GABA(A) antagonist) or strychnine (glycine antagonist) were administered intravenously in the absence or presence of 1 minimum alveolar concentration (MAC) of halothane. Results Halothane, 1.1%, depressed the response of WDR neurons to both forms of noxious stimuli. Antagonists, by themselves, had no effect on noxiously evoked activity. However, bicuculline and strychnine (maximum cumulative dose, 2.0 mg/kg) partially but significantly reversed the halothane depression of noxiously evoked activity. Similar results were seen with most, but not all, forms of nonnoxiously evoked activity. In the absence of halothane, strychnine significantly increased neuronal responses to low threshold receptive field brushing. Conclusion Halothane depression of spinal WDR neuronal responses to noxious and most nonnoxious stimuli is mediated, in part, by GABA(A) and strychnine-sensitive glycine systems. A spinal source of glycine tonically inhibits some forms of low threshold input to WDR neurons.

Response Properties and Organization of Nociceptive Neurons in Area 1 of Monkey Primary Somatosensory Cortex

2000 ◽  
Vol 84 (2) ◽  
pp. 719-729 ◽  
Author(s):  
Dan R. Kenshalo ◽  
Koichi Iwata ◽  
Maurice Sholas ◽  
David A. Thomas
Keyword(s):  
Somatosensory Cortex ◽  
Dynamic Range ◽  
Receptive Fields ◽  
Primary Somatosensory Cortex ◽  
Isolated Cells ◽  
Nociceptive Neurons ◽  
Response Properties ◽  
Stimulus Response ◽  
Noxious Mechanical Stimulation ◽  
Wdr Neurons

The organization and response properties of nociceptive neurons in area 1 of the primary somatosensory cortex (SI) of anesthetized monkeys were examined. The receptive fields of nociceptive neurons were classified as either wide-dynamic-range (WDR) neurons that were preferentially responsive to noxious mechanical stimulation, or nociceptive specific (NS) that were responsive to only noxious stimuli. The cortical locations and the responses of the two classes of neurons were compared. An examination of the neuronal stimulus-response functions obtained during noxious thermal stimulation of the glabrous skin of the foot or the hand indicated that WDR neurons exhibited significantly greater sensitivity to noxious thermal stimuli than did NS neurons. The receptive fields of WDR neurons were significantly larger than the receptive fields of NS neurons. Nociceptive SI neurons were somatotopically organized. Nociceptive neurons with receptive fields on the foot were located more medial in area 1 of SI than those with receptive fields on the hand. In the foot representation, the recording sites of nociceptive neurons were near the boundary between areas 3b and 1, whereas in the hand area, there was a tendency for them to be located more caudal in area 1. The majority of nociceptive neurons were located in the middle layers (III and IV) of area 1. The fact that nociceptive neurons were not evenly distributed across the layers of area 1 suggested that columns of nociceptive neurons probably do not exist in the somatosensory cortex. In electrode tracks where nociceptive neurons were found, approximately half of all subsequently isolated neurons were also classified as nociceptive. Low-threshold mechanoreceptive (LTM) neurons were intermingled with nociceptive neurons. Both WDR and NS neurons were found in close proximity to one another. In instances where the receptive field shifted, subsequently isolated cells were also classified as nociceptive. These data suggest that nociceptive neurons in area 1 of SI are organized in vertically orientated aggregations or clusters in layers III and IV.

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