Biomedical subjects

J W Hu

Publications and source records attributed to J W Hu.

At least 55 records · Page 3Linked to original sources

PubMed1994

Administration of opiate antagonist naloxone induces recurrence of increased jaw muscle activities related to inflammatory irritant application to rat temporomandibular joint region.

1. Our recent studies in rats have demonstrated that the small-fiber excitant and inflammatory irritant mustard oil injected into the temporomandibular joint (TMJ) region can evoke a sustained and reversible increase of electromyographic (EMG) activity in jaw muscles and an acute inflammatory response. The aim of the present study was to test if opioid mechanisms are involved in modulating the EMG increase evoked by mustard oil. 2. Mustard oil injected into the rat TMJ region evoked significant increases of jaw muscle EMG activity; the vehicle mineral oil had no such effect. The increased EMG activity lasted up to 20 min, and by 30 min after the mustard oil injection had returned to control (preinjection) levels, at which time administration of the opiate antagonist naloxone (1.3 mg/kg i.v.) induced a significant recurrence of the increase in EMG activity. This "rekindling" of EMG activity appeared at 5 to 10 min after the naloxone administration and lasted for 10 to 20 min. In contrast, naloxone administration in the animals receiving mineral oil injection into the TMJ region did not "rekindle" the EMG activity, nor did the administration of the peripherally acting opiate antagonist methylnaloxone or the vehicle of naloxone. 3. These findings reveal that the application of the opiate antagonist naloxone produces a recurrence of increased jaw muscle activity reflexively evoked by mustard oil injection into the rat TMJ region. They suggest that central opioid depressive mechanisms activated by the mustard oil-induced afferent barrage limit the duration of the evoked EMG changes.

Afferent Pathways↗

PubMed1994

Precipitation profile of the intravenous induction agents.

To investigate the formation of precipitation between various intravenous agents, we cross-matched the anesthetic agents commonly used in the induction phase. Thiopentone and thiamylal precipitated in combination with non-depolarizing muscle relaxants, lidocaine, morphine, and meperidine. Ketamine and etomidate were naive to these agents. Crystalloidal solutions, such as lactated Ringer, normal saline, and dextrose solution did not contribute to the formation of precipitate. In conclusion, our study indicates that intravenous line must be irrigated before and after thiopentone and/or thiamylal. In order to prevent precipitate formation, mixtures of various drugs should be avoided until in vitro assay is done.

Anesthesia, Intravenous↗

PubMed1994

Propofol modifies recovery from isoflurane-nitrous oxide anesthesia.

A randomized, prospective study was performed to evaluate the hemodynamic changes and recovery characteristics in 60 ASA physical status class I-II unpremedicated patients undergoing gynecological laparotomies with either isoflurane anesthesia only (ISO group) or isoflurane anesthesia followed by propofol infusion (ISO-PRO group). All patients received isoflurane 0.5-1.5% and nitrous oxide (N2O) 66% in oxygen after tracheal intubation. ISO-PRO group (n = 30) received 6 mg kg-1 hr-1 propofol infusion in substitution for isoflurane 25 minutes before the end of surgery. Propofol in ISO-PRO group and isoflurane in ISO group (n = 30) were discontinued 5 minutes before the end of surgery. In both groups, N2O was administered throughout the operation until skin was closed. Hemodynamic measurements were similar between the two groups except at extubation when heart rate and blood pressure were lower in ISO-PRO group. The maximal blood pressure was also lower in ISO-PRO group. In ISO-PRO group, the time required to responsiveness to verbal commands and to orientation were significantly shorter. ISO-PRO group had better Steward's score on arrival at the recovery room and was earlier to get a full score of six. The two groups experienced similar rates of emesis and excitement either two hours or 24 hours postoperatively. We conclude that in relatively long intra-abdominal operations, replacement of isoflurane by propofol infusion 25 minutes before the end of surgery may provide stable maintenance of anesthesia and a faster recovery.

Adult↗

PubMed1993

Tooth pulp deafferentation is not associated with changes in primary afferent depolarization of facial afferent endings in the brain stem.

Previous studies have demonstrated that tooth pulp deafferentation is associated with statistically significant alterations in the low-threshold facial mechanoreceptive field properties of brain stem neurons in trigeminal (V) subnucleus oralis. A loss of spinal afferent-induced presynaptic inhibition as a consequence of a decrease in primary afferent depolarization (PAD) following spinal nerve deafferentation has been invoked as a mechanism underlying deafferentation-induced somatosensory neuroplasticity. Therefore, this study was initiated to determine if these pulp deafferentation-induced neuroplastic changes could be accounted for by an alteration in PAD of low-threshold facial afferent endings in subnucleus oralis of anesthetized rats. In control (unoperated) rats (n = 7) and rats (n = 7) that had undergone mandibular pulp deafferentation 6-10 days previously, antidromic compound action potentials evoked by test stimulation in V subnucleus oralis were recorded in branches of the infraorbital (IO) and supraorbital (SO) nerves, and conditioning stimuli were applied to some of the same nerves. PAD of the afferent endings in oralis of these nerve branches was documented in all animals, and there was no significant difference between the two groups in the incidence or any of the other features of PAD. The features of the PAD were consistent with those described in several previous studies of normal animals. These findings indicate that the reported deafferentation-induced loss of spinal presynaptic regulatory mechanisms cannot be entrapolated to all forms of deafferentation injury and that the mechanoreceptive field changes that can occur in central V somatosensory neurons as a result of tooth pulp deafferentation may not reflect an alteration in PAD.

Action Potentials↗

PubMed1993

Excitatory effects on neck and jaw muscle activity of inflammatory irritant applied to cervical paraspinal tissues.

A study was carried out in 19 anaesthetized rats to determine if the electromyographic (EMG) activity of jaw and neck muscles could be influenced by injection of the inflammatory irritant mustard oil into deep paraspinal tissues surrounding the C1-3 vertebrae. The EMG activity was recorded ipsilaterally in the digastric, masseter and trapezius muscles and bilaterally in deep neck muscles (rectus capitis posterior). In comparison with control (vehicle) injections, mustard oil (20 microliters, 20%) injected into the deep paraspinal tissues induced significant increases in EMG activity in the neck muscles in all the animals and in the jaw muscles in the majority of the animals; the effects of mustard oil were more prominent in the former. The EMG response evoked by mustard oil injection was frequently reflected in two phases of enhanced activity. The early phase of the increase in EMG activity was usually initiated immediately following mustard oil injection (mean latency: 20.4 +/- 17.7 sec) and lasted 1.6 +/- 1.1 min. The second phase occurred 11.3 +/- 7.6 min later and lasted 11.0 +/- 8.1 min. Evans Blue extravasation was apparent in the deep paraspinal tissues surrounding the C1-3 vertebrae after mustard oil injection, and histological examination showed that mustard oil injection induced an inflammatory reaction in the rectus capitis posterior muscle. These results document that injection of the inflammatory irritant mustard oil into deep paraspinal tissues results in a sustained and reversible activation of both jaw and neck muscles. Such effects may be related to the reported clinical occurrence of increased muscle activity associated with trauma to deep tissues.

Animals↗

PubMed1993

Differential effects of cutaneous and deep application of inflammatory irritant on mechanoreceptive field properties of trigeminal brain stem nociceptive neurons.

1. The aim of this study was to determine whether there are differential neuroplastic effects of cutaneous and deep stimuli on the mechanoreceptive field (RF) properties of nociceptive brain stem neurons recorded in trigeminal (V) subnucleus caudalis. 2. A total of 31 caudalis neurons were functionally identified in anesthetized rats as nociceptive neurons receiving convergent cutaneous and deep afferent inputs, and the effects of the small-fiber excitant and inflammatory irritant mustard oil applied to either tongue muscle or facial skin were tested on their cutaneous and deep RFs. 3. The expression of neuroplasticity on the cutaneous and deep RFs of the neurons was found to depend on the site of application of this irritant. Mustard oil injected into the tongue muscle produced a significant and reversible expansion of both the cutaneous and deep RFs. In contrast, application of mustard oil to facial skin resulted in a significant and reversible expansion of the cutaneous RF, but no deep RF expansion occurred. 4. These findings suggest that considerable functional neuroplasticity of the cutaneous and deep RF properties of V nociceptive neurons can be induced by a peripheral inflammatory irritant and that deep inputs are especially effective in evoking these neuroplastic changes.

Animals↗

PubMed1993

Effects of tooth pulp deafferentation on brainstem neurons of the rat trigeminal subnucleus oralis.

The effects of tooth pulp deafferentation on brainstem neuronal properties were examined in the rat trigeminal (V) subnucleus oralis. Deafferentation was produced by removal of the coronal tooth pulp of all left mandibular molars. Neurons in the subnucleus oralis were then electrophysiologically characterized in chloralose/urethane-anesthetized rats at a single postoperative time. The mechanoreceptive field and response properties of low-threshold mechanoreceptive (LTM) neurons in rats studied at postoperative times of 3-4 days, 7-13 days, and 28-40 days were compared to those in control (unoperated) rats. Functional changes in oralis LTM neurons were observed in all tooth-pulp-deafferented rats, but most statistically significant changes were apparent only at the 7- to 13-day postoperative period. In 7- to 13-day pulp-deafferented rats, there was a significant increase in the incidence of neurons with a two-divisional mechanoreceptive field, accompanied by a significant decrease in the incidence of neurons with a maxillary mechanoreceptive field. This group of rats also showed a significant increase in the incidence of neurons with a mechanoreceptive field involving both mandibular and maxillary divisions. For neurons that could be activated by light mechanical stimulation of one or more mandibular or maxillary teeth, the 7- to 13-day pulp-deafferented rats showed a significant increase in the incidence of neurons with such periodontal mechanosensitive inputs involving both mandibular and maxillary divisions. There was also a significant increase in the incidence of spontaneously active neurons in this group of rats. For neurons with a mechanoreceptive field involving mystacial vibrissae, there was a significant increase in all three groups of pulp-deafferented rats in the maximal width of the vibrissal row (i.e., the number of vibrissae in the longest horizontal row of vibrissae, stimulation of which was effective in activating a given neuron). No significant differences were found between groups in the incidence of neurons with a mandibular mechanoreceptive field or in the proportions of neurons with a mechanoreceptive field located in each of several defined orofacial regions. There was also no significant difference between groups in the mean latency to electrical stimulation of the neuronal mechanoreceptive field, or in the proportions of rapidly adapting (RA) and slowly adapting (SA) neurons. These results show many similarities with the functional changes of oralis LTM neurons in the cat following tooth pulp deafferentation, and indicate that the rat may serve as a very useful model for V brainstem neuroplasticity induced by tooth pulp deafferentation.

Afferent Pathways↗

PubMed1992

Development of an orofacial model of acute inflammation in the rat.

An appropriate model was created by the paraperiosteal injection of mustard oil (20% allyl isothiocyanate dissolved in mineral oil) into the periarticular temporomandibular tissue of anaesthetized rats. Inflammation was assessed by the plasma extravasation of Evans' blue dye bound to plasma protein. This was confirmed visually and compared spectrophotometrically with the contralateral untreated control site (p less than 0.0005). A time-course study of the effect of mustard oil on Evans' blue extravasation revealed a gradually increasing effect that was maximal at 30 min after administration, with no further increase at 60 min. A dose-response study showed that giving 30 microliters of 20% mustard oil produced the maximal effect, with no further increase from 50 microliters. To confirm induction of inflammation, polymorphonuclear neutrophil infiltration was assessed morphometrically and found to increase in the treated tissue compared with the contralateral untreated control (p less than 0.001).

Acute Disease↗

PubMed1992

Stimulation of craniofacial muscle afferents induces prolonged facilitatory effects in trigeminal nociceptive brain-stem neurones.

Stimulation of small-diameter afferents supplying deep tissues has been shown to increase the excitability of spinal cord neurones responding to cutaneous afferent inputs. This facilitation has been implicated as integral central mechanisms of deep pain that may contribute to the tenderness and spread and/or referral of pain following injury of deep tissues. In view of the recent documentation of deep craniofacial afferent inputs, as well as cutaneous afferent inputs to the trigeminal (V) spinal tract nucleus, we wished to determine the effects of deep inputs excited by the small-fibre irritant mustard oil on trigeminal nociceptive neurones. The extracellular activity of single brain-stem neurones was recorded in subnuclei caudalis and oralis of the V spinal tract nucleus of anaesthetized rats. The neurones were classified as low-threshold mechanosensitive (LTM), wide dynamic range (WDR) and nociceptive specific (NS) on the basis of their cutaneous mechanoreceptive field properties and their responses evoked by electrical stimulation of their cutaneous afferent inputs. Injection of 5% mustard oil (2-5 microliters) into the deep masseter muscle produced a facilitatory effect in 12 of 27 nociceptive neurones tested in caudalis and in 5 of 12 nociceptive neurones in oralis. This effect was reflected in an expansion of the cutaneous mechanoreceptive field, an increase in spontaneous activity or an increase in responsivity to electrical stimulation of cutaneous afferent inputs to the neurones. The facilitation was reversible and typically became apparent within 3-5 min of the injection, reached its peak at 5-10 min, and lasted for 20-30 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1992

Patterns and plasticity of dental afferent inputs to trigeminal (V) brainstem neurons in kittens.

In the young cat, the natural replacement of deciduous teeth with a permanent dentition may be accompanied by extensive peripheral nerve degeneration and reinnervation. Since we have previously reported significant physiological effects of tooth pulp deafferentation on V brainstem neurons, we wished to determine if deafferentation associated with deciduous tooth exfoliation was accompanied by comparable neuroplastic changes in the brainstem of kittens. We have examined the pulpal afferent terminating pattern within the brainstem as well as the electrophysiological properties of V brainstem neurons during this naturally occurring deafferentation phenomenon. The pattern of the HRP-labelled terminals in different parts of V brainstem subnuclei in kittens was similar to that in adult cats. The highest density of labelled terminals was found in the subnucleus oralis. The properties of subnucleus oralis neurons also showed many similarities between kittens at age of 3-4 months old and adult cats, e.g., (1) in the proportions of neurons activated by tactile stimulation of 1-4 teeth (mandibular and maxillary canines and premolars), (2) the ratio of neurons showing fast adapting or slow adapting responses to dental tactile stimulation, (3) the proportions of neurons activated by electrical pulp stimulation of 1-4 teeth, and (4) the minimal latencies of pulp-evoked responses. However, the incidences of pulpal inputs as well as the convergent pattern to oralis neurons of afferent inputs evoked by periodontal stimulation and electrical pulpal stimulation were less common in kittens than adult cats.

Aging↗

PubMed1991

Mechanisms of pain arising from articular tissues.

This paper reviews the peripheral and central neural mechanisms underlying pain from articular tissues innervated by spinal and trigeminal afferents. The paper especially addresses trigeminal mechanisms related to pain from the temporomandibular joint and its associated craniofacial musculature. Recent studies have shown the existence of articular nociceptive primary afferents that project to the spinal cord dorsal horn and trigeminal brainstem complex. A particular feature of most neurones receiving these deep nociceptive afferent inputs is their responsivity also to cutaneous nociceptive afferent inputs. This suggests the involvement of these neurones not only in the detection of acute articular pain, but also in the hyperalgesia and poor localization, spread, and referral of pain that characterize many painful conditions of joints and other deep structures. While only limited information is available on related higher brain centre mechanisms, convergence and interaction between cutaneous and deep afferent inputs also seem to be a characteristic of somatosensory neurones in the thalamus and somatosensory cerebral cortex. Muscle and autonomic reflexes may be induced by such deep noxious stimuli, but the functional significance of some of these effects (e.g., in relation to clinical concepts of myofascial dysfunction) requires further study in more appropriate functional settings.

Animals↗

PubMed1990

Effects of one- or two-stage deafferentation of mandibular and maxillary tooth pulps on the functional properties of trigeminal brainstem neurons.

We have recently demonstrated that deafferentation of the adult cat's maxillary or mandibular posterior tooth pulps results in statistically significant changes in mechanoreceptive field and response properties of low-threshold mechanoreceptive (LTM) brainstem neurons in trigeminal (V) subnucleus oralis. These effects were however reversible, and the statistically significant changes were apparent only for 1-2 weeks after the deafferentation procedure. The aim of this study was to examine the effects of a more extensive deafferentation involving both maxillary and mandibular pulps. In accordance with our earlier study, the pulps of the teeth were deafferented and, in a 'blind' design, the physiological properties of oralis LTM neurons were studied in each of these animals and compared with those from control, unoperated cats. Statistically significant changes in mechanoreceptive field and response properties were produced in these animals with both maxillary and mandibular quadrants deafferented and were similar to those documented in our earlier study involving deafferentation of only one quadrant. However, as well as occurring at 1-2 weeks after the deafferentation procedures, the changes were still apparent at 4 weeks following the deafferentation. In addition, we also documented that changes could be produced by a two-stage deafferentation procedure involving first the mandibular pulps and then, 3 weeks later, the maxillary pulps. These findings thus demonstrate that an extensive deafferentation procedure involving mandibular as well as maxillary tooth pulps can produce statistically significant changes in the physiological properties of V brainstem neurons of adult cats that may last at least 4 weeks postoperatively.

Action Potentials↗

PubMed1989

Changes in mechanoreceptive field properties of trigeminal somatosensory brainstem neurons induced by stimulation of nucleus raphe magnus in cats.

Experiments were carried out on adult anesthetized cats in which the effects of nucleus raphe magnus (NRM) conditioning stimulation (20 ms) were tested on the responses evoked by orofacial stimuli in single brainstem neurons of trigeminal (V) subnucleus oralis. The NRM stimulation induced inhibition of the responses of 57 of 77 low-threshold mechanoreceptive (LTM) neurons and the one wide-dynamic range (WDR) neuron tested. The duration of the neuronal inhibition ranged from 300-600 ms and the mean threshold for inhibition ranged from 47.8 +/- 4.8 to 102.7 +/- 15 microA depending on the orofacial stimulation site (skin or tooth pulp) and form (mechanical or electrical) of cutaneous stimuli used to evoke neuronal responses. In 20 LTM neurons showing NRM-induced inhibition that were specifically examined for the effects of NRM stimulation on the mechanoreceptive field, one population (n = 11) showed shrinkage (mean 55 +/- 4.4% from control area) of the mechanoreceptive field while the remaining neurons (n = 9) showed no change in mechanoreceptive field size during NRM stimulation. The former group of neurons were also distinguished from the latter neurons by their significantly larger mechanoreceptive field and the activation of the majority of them by electrical stimuli applied outside their mechanoreceptive field. The responses of these neurons evoked by low-threshold inputs from the edge of the mechanoreceptive field were more sensitive to NRM conditioning stimulation than responses evoked from the mechanoreceptive field center, as judged by threshold, magnitude and duration of the NRM-induced inhibition. These findings underscore the sensitivity of LTM neurons to NRM influences. They also reveal a particular population of oralis neurons which have a differential sensitivity of low-threshold inputs evoked from the edge compared to the center of the mechanoreceptive field.

Action Potentials↗

PubMed1989

Effects of tooth pulp deafferentation on nociceptive and nonnociceptive neurons of the feline trigeminal subnucleus caudalis (medullary dorsal horn).

1. Effects of deafferentation of the tooth pulps of the posterior mandibular teeth were studied in single neurons recorded in the ipsilateral subnucleus caudalis of the trigeminal (V) spinal tract nucleus of adult cats and kittens. The functional properties of neurons in each anesthetized animal were determined electro-physiologically in a series of microelectrode penetrations of the subnucleus. 2. The more than 800 neurons investigated could be subdivided on the basis of their cutaneous mechanoreceptive field properties into low-threshold mechanoreceptive (LTM) neurons, wide dynamic range (WDR) neurons, or nociceptive-specific (NS) neurons. Comparisons of neuronal properties were made between control (intact) cats and 7-15 day deafferented cats studied in a blind design, as well as groups of longer term deafferented cats, and kittens undergoing a "natural" deafferentation as a result of exfoliation of primary teeth. 3. There was no apparent change in the somatotopic pattern of organization of the subnucleus in the kittens and pulp-deafferented cats and no statistically significant differences were noted between kittens and control cats in any property except for alterations in the incidence of spontaneously active neurons. 4. Limited but statistically significant alterations were noted in some of the neuronal properties in the deafferented cats. These changes were especially apparent in the LTM neurons. The incidence of spontaneous activity was significantly decreased in the neurons of most long-term deafferented groups of cats. In the 7-15 day deafferented group, significantly more LTM neurons had a mechanoreceptive field involving all three divisions of the V nerve, and there was a significant increase in the incidence of LTM neurons activated by electrical stimulation of intraoral sites. Mechanosensitive neurons responsive only to tap stimuli were found only in the deafferented groups of cats. 5. These alterations in caudalis contrast with previous reports claiming marked hyperexcitability of caudal V brain stem neurons as a consequence of deafferentation and implicating such effects in the development of pain. However, some of the changes are in general not inconsistent with deafferentation-induced changes reported in spinal somatosensory neurons and with the pulp deafferentation-induced changes that we have recently documented in LTM neurons of subnucleus oralis of the V spinal tract nucleus of adult cats.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed1988

Properties of functionally identified nociceptive and nonnociceptive facial primary afferents and presynaptic excitability changes induced in their brain stem endings by raphe and orofacial stimuli in cats.

The activity of 221 single primary afferent units was recorded extracellularly in the trigeminal (V) ganglion of chloralose-anaesthetized cats to examine the receptive field properties of nonnociceptive and nociceptive cutaneous afferents and the effect of conditioning stimulation of the raphe system and orofacial afferents on the antidromic excitability of their brain stem endings in V subnucleus caudalis. In addition to slowly adapting and rapidly adapting low-threshold mechanosensitive afferents, we functionally identified three classes of cutaneous nociceptive afferents: these included A-delta high-threshold mechanoreceptive afferents (A-delta HTMs), C-fiber high-threshold mechanoreceptive afferents (C-HTMs), and C-polymodal nociceptive afferents (CPNs). Most of the CPNs could be activated by light tactile stimuli as well as by heavy pressure and pinch and noxious radiant heat applied to their mechanoreceptive field which usually involved a localized spot (approximately 1 mm in diameter) of skin. In contrast, the C-HTMs and A-delta HTMs could not be activated by radiant heat stimuli although some did show sensitization which was also a feature of the CPNs; they did respond to noxious mechanical stimulation of a localized area of skin. We noted that orofacial conditioning stimulation could produce an increase in antidromic excitability which was considered a reflection of primary afferent depolarization (PAD) in both nociceptive and nonnociceptive afferents innervating the cat's facial skin; nonnoxious mechanical stimuli and electrical stimuli were particularly effective in the low-threshold mechanosensitive afferents and noxious mechanical and high-intensity electrical stimuli were especially effective in the cutaneous nociceptive afferents. Raphe conditioning stimulation also was very effective in inducing PAD in these nociceptive afferents; however, the raphe conditioning effects were not limited to these nociceptive afferents since PAD was also frequently demonstrated in the low-threshold mechanosensitive afferents.

Animals↗

PubMed1988

Effects of temporomandibular joint stimulation on nociceptive and nonnociceptive neurons of the cat's trigeminal subnucleus caudalis (medullary dorsal horn).

1. The extracellular activity of 196 single neurons in subnucleus caudalis (medullary dorsal horn) of the trigeminal (V) spinal tract nucleus was examined in chloralose-anesthesized, paralyzed cats. Electrical, mechanical, and algesic chemical stimuli were applied to the exposed temporomandibular joint (TMJ) in order to activate TMJ afferents. Seventy-eight neurons were studied that responded to electrical stimulation of the TMJ at a mean latency of 9.9 +/- 4.8 (SD) ms. 2. All neurons with TMJ input received additional afferent input, predominantly from facial skin or intraoral sites. Caudalis neurons were classified on the basis of their cutaneous mechanoreceptive field properties as low-threshold mechanoreceptive (LTM), wide dynamic range (WDR), or nociceptive specific (NS); a few neurons unresponsive to cutaneous stimuli were responsive to manipulation of deep subcutaneous structures. A sample of caudalis neurons was tested for responsiveness to electrical TMJ stimulation after the mechanoreceptive field properties of the neurons were determined. In this sample, 24% of the LTM neurons, 29% of the WDR neurons, 36% of the NS neurons, and 57% of the neurons with input from deep structures were responsive to TMJ stimulation. The WDR and NS neurons with TMJ inputs had mechanoreceptive field properties and laminar locations in caudalis that were comparable to those previously described for cutaneous nociceptive neurons in caudalis; also in accordance with recent studies, 74% of the neurons tested showed convergence of tooth pulp and/or hypoglossal (XII) nerve afferent inputs. 3. In contrast to the LTM neurons, the WDR and NS neurons were especially responsive to intense mechanical and algesic chemical stimulation of the TMJ as well as to electrical stimulation of TMJ afferents. For example, 71% of the WDR and NS neurons excited by electrical stimulation of the TMJ afferents and tested for their responsiveness to injections of algesic chemicals (7% NaCl, KCl, bradykinin, histamine) into the TMJ responded to at least one of these chemicals. The temporal characteristics of these responses were quantified. 4. The TMJ afferent inputs to the WDR and NS neurons were considered to be predominantly of a nociceptive character because of (1) the long latency and high threshold of most TMJ-evoked responses, which are consistent with previous demonstrations that small-diameter afferents predominantly supply the TMJ and, (2) the preferential responsiveness to noxious mechanical and chemical stimulation of TMJ afferents of neurons which were functionally identified as cutaneous nociceptive neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1986

Effects of nucleus raphe magnus stimulation on jaw-opening reflex and trigeminal brain-stem neurone responses in normal and tooth pulp-deafferented cats.

Since we have recently shown that tooth pulp deafferentation results in changes in the receptive field properties and activity of brain-stem neurones in the adult cat's subnucleus oralis of the trigeminal (V) spinal tract nucleus, we wished to determine if these changes are associated with alterations in the powerful inhibitory influence that the nucleus raphe magnus (NRM) normally exerts on these neurones and on the related digastric jaw-opening reflex. In control cats or in cats that had undergone mandibular or maxillary tooth pulp deafferentation 7-140 days previously, the effects of NRM conditioning stimulation were tested on jaw-opening reflex responses or oralis neuronal responses evoked by stimulation of the maxillary or mandibular tooth pulp, facial skin, or oral mucosa. No statistically significant difference was noted between control and deafferented animals (n = 32) in the incidence, threshold or time course of NRM-induced inhibition of the reflex responses. Likewise, no difference was noted between control and deafferented animals in these features of the inhibition of oralis neuronal responses. In 276 neurones tested, the high incidence (92%), low threshold (0.08-0.15 mA) and prolonged time course (approximately 400 msec) of NRM-induced inhibition of responses evoked by electrical stimulation of the tooth pulp or by low-intensity electrical or mechanical stimulation of facial skin and oral mucosa were comparable in both groups of animals. These findings indicate that the alterations in properties or oralis neurones subsequent to tooth pulp deafferentation may not be associated with changes in the modulatory influence emanating from the NRM.

Action Potentials↗

PubMed1986

Convergence of cutaneous, tooth pulp, visceral, neck and muscle afferents onto nociceptive and non-nociceptive neurones in trigeminal subnucleus caudalis (medullary dorsal horn) and its implications for referred pain.

Because of the likely involvement of central convergence of afferent inputs in mechanisms underlying referred pain, the activity of single neurones was recorded in the cat's trigeminal (V) subnucleus caudalis (medullary dorsal horn) to test for the presence and extent of convergent inputs to the neurones. In chloralose-anaesthetized or decerebrate unanaesthetized cats, electrical stimuli were applied to afferents supplying facial skin, oral mucosa, canine and premolar tooth pulp, laryngeal mucosa, cervical skin and muscle, and jaw and tongue muscles, and tactile and noxious mechanical and thermal stimuli were applied to skin and mucosa. Considerable proportions of caudalis neurones which could be functionally classified on the basis of their cutaneous receptive field properties as low-threshold mechanoreceptive (LTM), wide-dynamic-range (WDR), or nociceptive-specific (NS) neurones, could be excited by electrical stimulation of several of these afferent inputs. Extensive convergence of afferent inputs, including inputs from skin or mucosal areas outside the neuronal oral-facial receptive field delineated by natural stimuli, was a particular feature of the units classified as cutaneous nociceptive neurones (i.e., WDR and NS). On the basis of antidromic activation, 15% of these WDR and NS neurones were shown to have a direct projection to the contralateral thalamus. The findings question the use of terminology and classifications of somatosensory neurones based only on the cutaneous receptive field properties of the neurones since distinctions between the different neuronal populations become less obvious when properties other than those related to cutaneous afferent inputs are taken into account. Moreover, the observations of extensive convergence of different types of afferents, which was especially apparent in cutaneous nociceptive neurones, also suggest a role for these neurones in mediating deep pain and in spread and referral of pain.

Animals↗