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B J Sessle

Publications and source records attributed to B J Sessle.

At least 37 records · Page 2Linked to original sources
PubMed2001

Temporomandibular-evoked jaw muscle reflex: role of brain stem NMDA and non-NMDA receptors.

This study investigated the possible involvement of brain stem excitatory amino acid receptor mechanisms and the trigeminal subnucleus caudalis (Vc) in temporomandibular joint (TMJ)-evoked reflex jaw muscle activity. Glutamate injected into the TMJ of anesthetized rats reflexly evoked activity in the jaw muscles. Application of lidocaine, but not saline, to the surface of the caudal brainstem overlying Vc significantly suppressed TMJ-evoked jaw muscle activity, while application of NMDA or non-NMDA receptor antagonists also significantly attenuated jaw muscle activity. These results provide evidence that Vc is a critical relay in the TMJ-evoked reflex activation of the jaw muscles, and that both NMDA and non-NMDA receptor mechanisms may contribute to these effects.

Anesthetics, Local↗
PubMed2001

Superficial and deep convergent nociceptive neurons are differentially affected by N-methyl-D-aspartate applied on the brainstem surface of the rat medullary dorsal horn.

The activation of N-methyl-D-aspartate receptors is implicated in the spinal and trigeminal processing of nociceptive information conveyed by convergent (wide dynamic range) neurons and particularly in C-fiber-evoked responses elicited by repetitive and high-intensity electrical stimulation of the neuronal receptive field. In this study, the effects of intrathecal NMDA application on the electrically evoked nociceptive responses of trigeminal subnucleus caudalis convergent neurons have been investigated. The total C-fiber-evoked activity triggered by 30 successive stimuli was divided into two components: the C-fiber input response and the 'wind-up' response. Application of 0.1 microg (in 50 microl) of NMDA evoked a bi-directional effect on the total C-fiber-evoked activity of 19 neurons tested. A significant increase in the total C-fiber-evoked activity was observed 15-25 min after the NMDA application for nine neurons located in superficial laminae II and III. In contrast, a significant decrease in the total C-fiber-evoked activity was observed 5-25 min after the NMDA application for 10 neurons located more deeply, in lamina V. The NMDA-induced modifications seen in the total C-fiber-evoked activity were likely a reflection of a significant increase or decrease in neuronal activity evoked by the C-fiber input rather than wind-up of the responses since the latter was not significantly modified by the NMDA application. These results provide evidence for a possible inhibitory role for NMDA-dependent interneurons of the superficial laminae of the medullary dorsal horn on the nociceptive activity of deep convergent neurons.

Animals↗
PubMed2001

Neuroplasticity induced by tooth pulp stimulation in trigeminal subnucleus oralis involves NMDA receptor mechanisms.

We have recently demonstrated that application of the mustard oil (MO), a small-fiber excitant and inflammatory irritant, to the rat maxillary molar tooth pulp induces significant increases in jaw muscle electromyographic (EMG) activity and neuroplastic changes in trigeminal (V) subnucleus caudalis. Since subnucleus oralis (Vo) as well as caudalis receives projections from molar pulp afferents and is also an integral brain stem relay of afferent input from orofacial structures, we tested whether MO application to the exposed pulp induces neuroplastic changes in oralis neurons and whether microinjection of MK-801, a noncompetitive NMDA antagonist, into the Vo influences the pulp/MO-induced neuroplastic changes in chloralose/urethan-anesthetized rats. Single neuronal activity was recorded in Vo, and neurons classified as low-threshold mechanoreceptive (LTM), wide dynamic range (WDR), nociceptive-specific (NS), deep (D), or skin/mucosa and deep (S + D). The spontaneous activity, mechanoreceptive field (RF) size, mechanical threshold, and response to suprathreshold mechanical stimuli applied to the neuronal RF were assessed prior to and throughout a 40- to 60-min period after MO application to the maxillary molar pulp. In animals pretreated with saline microinjection (0.3 microl) into the Vo, MO application to the pulp produced a significant increase in spontaneous activity, expansion of the pinch or deep RF, decrease in the mechanical threshold, and increase in response to suprathreshold mechanical stimuli of the nociceptive (WDR, NS, and S + D) neurons except for those nociceptive neurons having their RF only in the intraoral region. The pulpal application of MO did not produce any significant neuroplastic changes in LTM neurons. Furthermore, in animals pretreated with MK-801 microinjection (3 microg/0.3 microl) into the Vo, MO application to the pulp did not produce any significant changes in the RF and response properties of nociceptive neurons. In other animals pretreated with saline (0.3 microl) or MK-801 (3 microg/0.3 microl) microinjected into the Vo, mineral oil application to the pulp did not produce any significant changes in RF and response properties of nociceptive neurons. These findings indicate that the application of MO to the tooth pulp can induce significant neuroplastic changes in oralis nociceptive neurons and that central NMDA receptor mechanisms may be involved in these neuroplastic changes.

Animals↗
PubMed2001

Characteristics of glutamate-evoked temporomandibular joint afferent activity in the rat.

Injection of glutamate into the rat temporomandibular joint (TMJ) capsule can reflexly induce a prolonged increase in the electromyographic (EMG) activity of the jaw muscles, however, the characteristics of TMJ afferents activated by glutamate have not been investigated. In the present study, we examined the effect of glutamate injection into the TMJ capsule on jaw muscle EMG activity and the extracellularly recorded activity of single trigeminal afferents that had receptive fields in the TMJ tissue and antidromically identified projections to the brain stem subnucleus caudalis (Vc) in rats of both sexes. Glutamate (0.05--1.0 M, 10 microl) injection into the TMJ capsule evoked EMG activity in a dose-related manner; however, at concentrations of 0.5 and 1.0 M, glutamate-evoked digastric muscle responses were greater in female than in male rats. In experiments where jaw muscle EMG and afferent activity were recorded simultaneously, glutamate (0.5 M, 10 microl) injection into the TMJ capsule evoked activity in the jaw muscles as well as in 27 (26 A delta and 1 C-fiber afferent) of 34 trigeminal afferents that could be activated by blunt mechanical stimulation of the TMJ tissue. In these experiments, glutamate-evoked jaw muscle activity was significantly increased for 6 min after the glutamate injection, whereas afferent activity was significantly increased only during the first minute after the glutamate injection. The glutamate-evoked afferent activity was inversely related to conduction velocity and, in afferents with conduction velocities <10 m/s, was significantly greater in female (n = 6) than in male (n = 10) rats. These results suggest that glutamate excites putative nociceptive afferents within the TMJ to a greater degree in female than in male rats. This sex-related difference in afferent discharge may, in part, underlie sex-related differences in glutamate-evoked jaw muscle EMG activity.

Animals↗
PubMed2001

Sex-related differences in human pain and rat afferent discharge evoked by injection of glutamate into the masseter muscle.

Animal studies have suggested that tissue injury-related increased levels of glutamate may be involved in peripheral nociceptive mechanisms in deep craniofacial tissues. Indeed, injection of glutamate (0.1-1 M, 10 microl) into the temporomandibular region evokes reflex jaw muscle responses through activation of peripheral excitatory amino acid receptors. It has recently been found that this glutamate-evoked reflex muscle activity is significantly greater in female than male rats. However, it is not known whether peripheral administration of glutamate, in the same concentrations that evoke jaw muscle activity in rats, causes pain in humans or activates deep craniofacial nociceptive afferents. Therefore we examined whether injection of glutamate into the masseter muscle induces pain in male and female volunteers and, since masseter afferent recordings were not feasible in humans, whether glutamate excites putative nociceptive afferents supplying the masseter muscle of male and female rats. Injection of glutamate (0.5 M or 1.0 M, 0.2 ml) into the masseter muscle of both men and women caused significantly higher levels of peak pain, duration of pain, and overall pain than injection of isotonic saline (0.2 ml). In addition, glutamate-evoked peak and overall muscle pain in women was significantly greater than in men. In rats of both sexes, glutamate (10 microl, 0.5 M) evoked activity in a subpopulation of masseter muscle afferents (n = 36) that projected to the subnucleus caudalis, an important relay of noxious input from the craniofacial region. The largest responses to glutamate were recorded in muscle afferents with the slowest conduction velocities (2.5-5 m/s). Further, glutamate-evoked masseter muscle afferent activity was significantly greater in female than in male rats. These results indicate that glutamate injection into the masseter muscle evokes pain responses that are greater in women than men and that one possible mechanism for this difference may be a greater sensitivity to glutamate of masseter muscle afferents in females. These sex-related differences in acute experimental masseter muscle pain are particularly interesting given the higher prevalence of many chronic muscle pain conditions in women.

Adult↗
PubMed2001

Sleep bruxism: an oromotor activity secondary to micro-arousal.

Spontaneous rhythmic masticatory muscle activity (RMMA) during sleep occurs in relation to transient activation in the cerebral and autonomic nervous systems of normal subjects and in patients with sleep bruxism (SB). In this study, we made a quantitative assessment of the sequential changes in cortical electroencephalographic (EEG) and autonomic-cardiac activities associated with micro-arousals preceding RMMA episodes. We matched 10 SB patients with 10 normal subjects. The onset of RMMA episodes was defined in terms of the onset of activation in the suprahyoid muscles. In SB patients, an increase in cortical EEG activity was observed 4 seconds before the onset of suprahyoid activity in 79% of episodes. A significant acceleration in heart rate was initiated one cardiac cycle before RMMA onset. A clear sequence of cortical to autonomic-cardiac activation precedes jaw motor activity in SB patients. This suggests that SB is a powerful oromotor manifestation secondary to micro-arousal.

Adult↗
PubMed2000

Acute and chronic craniofacial pain: brainstem mechanisms of nociceptive transmission and neuroplasticity, and their clinical correlates.

This paper reviews the recent advances in knowledge of brainstem mechanisms related to craniofacial pain. It also draws attention to their clinical implications, and concludes with a brief overview and suggestions for future research directions. It first describes the general organizational features of the trigeminal brainstem sensory nuclear complex (VBSNC), including its input and output properties and intrinsic characteristics that are commensurate with its strategic role as the major brainstem relay of many types of somatosensory information derived from the face and mouth. The VBSNC plays a crucial role in craniofacial nociceptive transmission, as evidenced by clinical, behavioral, morphological, and electrophysiological data that have been especially derived from studies of the relay of cutaneous nociceptive afferent inputs through the subnucleus caudalis of the VBSNC. The recent literature, however, indicates that some fundamental differences exist in the processing of cutaneous vs. other craniofacial nociceptive inputs to the VBSNC, and that rostral components of the VBSNC may also play important roles in some of these processes. Modulatory mechanisms are also highlighted, including the neurochemical substrate by which nociceptive transmission in the VBSNC can be modulated. In addition, the long-term consequences of peripheral injury and inflammation and, in particular, the neuroplastic changes that can be induced in the VBSNC are emphasized in view of the likely role that central sensitization, as well as peripheral sensitization, can play in acute and chronic pain. The recent findings also provide new insights into craniofacial pain behavior and are particularly relevant to many approaches currently in use for the management of pain and to the development of new diagnostic and therapeutic procedures aimed at manipulating peripheral inputs and central processes underlying nociceptive transmission and its control within the VBSNC.

Acute Disease↗
PubMed1999

Effects of functional disruption of lateral pericentral cerebral cortex on primate swallowing.

Bilateral cold block of the intracortical microstimulation (ICMS)-defined swallow cortex markedly affected the ability of monkeys to carry out swallowing. Significant changes also occurred in swallow-related electromyographic (EMG) activity patterns. These findings provide further evidence that the lateral pericentral cortex plays a critical role in the initiation and regulation of swallowing in the primate.

Animals↗
PubMed1999

Effects of pre-emptive local anaesthesia on tooth pulp deafferentation-induced neuroplastic changes in cat trigeminal brainstem neurones.

Previous work has shown increased excitability of brainstem neurones in the trigeminal (V) subnucleus oralis following the deafferentation produced by tooth-pulp removal. The present study was designed to determine if the changes in oralis neuronal properties seen in cats 1-2 wk after the deafferentation could be blocked by local anaesthesia of the Vth nerve proximal to the sites of pulp injury just before the actual deafferentation. The response properties of neurones recorded in V subnucleus oralis were determined in anaesthetized cats. One or two weeks before neuronal recording, the pulps of the posterior mandibular teeth were removed under local mandibular anaesthesia in one group of cats (group A) and without local anaesthesia in a second group (group B); a third group (group C) had no pulp removal but received local anaesthesia. Consistent with the earlier data, there was a significantly increased incidence of neurones having an enlarged mechanoreceptive field, spontaneous activity and habituating tap sensitivity in group B compared to group C, but no significant differences were found between the two deafferented groups (A and B). As local anaesthesia did not prevent the development of pulp deafferentation-induced changes in the oralis neurones, it is unlikely that an afferent barrage of impulses induced by the deafferentation procedure was responsible for the neuroplastic changes that subsequently developed in the V subnucleus oralis.

Anesthetics, Local↗
PubMed1999

Involvement of trigeminal subnucleus caudalis (medullary dorsal horn) in craniofacial nociceptive reflex activity.

We have previously shown that an increase in electromyographic (EMG) activity of digastric (DIG) and masseter (MASS) muscles can be reflexly evoked by injection into the rat's temporomandibular joint (TMJ) region of the small-fibre excitant and inflammatory irritant mustard oil (MO). Since the trigeminal (V) subnucleus caudalis (Vc, i.e. medullary dorsal horn) has traditionally been viewed as an essential brainstem relay site of nociceptive information from craniofacial tissues, an EMG study was carried out in 45 anaesthetized rats to determine if Vc is involved in the MO-evoked increases in jaw muscle EMG activity. The effects of histologically confirmed surgical or chemical lesions of Vc on this evoked EMG activity were tested in different groups of rats. MO injection into the left TMJ region of intact rats evoked bilateral increases in EMG activity of DIG and MASS which could be significantly reduced by surgical transection of the left caudal brainstem at the obex level; MO injection into the right TMJ region in these same rats still readily evoked increases in EMG activity. A sagittal section medial to Vc or transection at the level of the second cervical spinal segment did not produce any significant reduction in the reflexly evoked EMG activity. Neurones in Vc, as opposed to fibres of passage, appear to be important for the MO-evoked EMG activity, since injection into Vc of the neurotoxic chemical ibotenic acid significantly reduced the mustard oil-evoked EMG activity. The Vc also appears to play a role in the activation of contralateral V motoneurons, as evidenced by the activation of the contralateral DIG and MASS muscles by the injection of MO into the left TMJ region of intact rats and by the reduction of this evoked EMG activity in the contralateral DIG and MASS of rats with a surgical transection or ibotenic acid lesion of the left Vc. These findings suggest that Vc may be a critical element in the neural pathways underlying the reflex responses evoked bilaterally in DIG and MASS muscles by noxious stimulation of the TMJ region.

Animals↗
PubMed1999

Neural mechanisms and pathways in craniofacial pain.

Many free nerve endings of small-diameter afferents (A-delta or C nerve fibres) respond to craniofacial noxious stimuli and a number of neurochemicals are involved in their activation or sensitization. The small-diameter nociceptive afferents project to the trigeminal (V) brainstem complex where they can excite nociceptive neurones that have been categorized as either nociceptive-specific (NS) or wide dynamic range (WDR). These neurones project to other brainstem regions or to the contralateral thalamus. The lateral and medial thalamus contain NS and WDR neurones which have properties and connections with the overlying cerebral cortex or other thalamic regions indicative of a role for most of them in the sensory-discriminative, affective or other dimensions of pain. Some of the V brainstem NS and WDR neurones respond exclusively to cutaneous sensory inputs and have features indicating their involvement in acute superficial craniofacial pain. Many of the neurones, however, receive convergent inputs from afferents supplying other craniofacial tissues (e.g. cerebrovascular, muscle) as well as skin, and are likely involved in deep pain, as well as spread and referral that is typically seen in headache and several craniofacial pain conditions involving deep tissues. Convergence may also be an important factor underlying the neuroplastic changes in V neuronal properties that may occur with peripheral injury or inflammation. These changes include a prolonged enhancement of the cutaneous as well as deep afferent inputs to most NS and WDR neurones and expansion of their cutaneous or deep mechanoreceptive field and increased EMG activity in the jaw musculature. They involve NMDA, non-NMDA and opioid neurochemical mechanisms within peripheral tissues as well as within the CNS. Such modulatory effects on brainstem neuronal properties reflect the functional plasticity of the central V system, and may be involved in the development of headache and other conditions that manifest craniofacial pain.

Brain Stem↗
PubMed1999

C-fiber depletion alters response properties of neurons in trigeminal nucleus principalis.

The effects of C-fiber depletion induced by neonatal capsaicin treatment on the functional properties of vibrissa-sensitive low-threshold mechanoreceptive (LTM) neurons in the rat trigeminal nucleus principalis were examined in adult rats. Neonatal rats were injected either with capsaicin or its vehicle within 48 h of birth. The depletion of unmyelinated afferents was confirmed by the significant decrease in plasma extravasation of Evan's blue dye induced in the hindlimb skin of capsaicin-treated rats by cutaneous application of mustard oil and by the significant decrease of unmyelinated fibers in both the sciatic and infraorbital nerves. The mechanoreceptive field (RF) and response properties of 31 vibrissa-sensitive neurons in capsaicin-treated rats were compared with those of 32 vibrissa-sensitive neurons in control (untreated or vehicle-treated) rats. The use of electronically controlled mechanical stimuli allowed quantitative analysis of response properties of vibrissa-sensitive neurons; these included the number of center- and surround-RF vibrissae within the RF (i.e., those vibrissae which when stimulated elicited >/=1 and <1 action potential per stimulus, respectively), the response magnitude and latency, and the selectivity of responses to stimulation of vibrissae in different directions with emphasis on combining both the response magnitude and direction of vibrissal deflection in a vector analysis. Neonatal capsaicin treatment was associated with significant increases in the total number of vibrissae, in the number of center-RF vibrissae per neuronal RF, and in the percentage of vibrissa-sensitive neurons that also responded to stimulation of other types of orofacial tissues. Compared with control rats, capsaicin-treated rats showed significant increases in the response magnitude to stimulation of surround-RF vibrissae as well as in response latency variability to stimulation of both center- and surround-RF vibrissae. C-fiber depletion also significantly altered the directional selectivity of responses to stimulation of vibrissae. For neurons with multiple center-RF vibrissae, the proportion of center-RF vibrissae with net vector responses oriented toward the same quadrant was significantly less in capsaicin-treated compared with control rats. These changes in the functional properties of principalis vibrissa-sensitive neurons associated with marked depletion of C-fiber afferents are consistent with similarly induced alterations in LTM neurons studied at other levels of the rodent somatosensory system, and indeed may contribute to alterations previously described in the somatosensory cortex of adult rodents. Furthermore, these results provide additional support to the view that C fibers may have an important role in shaping the functional properties of LTM neurons in central somatosensory pathways.

Animals↗
PubMed1999

Activation of peripheral GABAA receptors inhibits temporomandibular joint-evoked jaw muscle activity.

We have previously shown that injection of mustard oil or glutamate into rat temporomandibular joint (TMJ) tissues, an experimental model of acute TMJ injury, can reflexly induce a prolonged increase in the activity of both digastric (jaw-opener) and masseter (jaw-closer) muscles. In this study, GABA was applied to the TMJ region by itself or in combination with glutamate, and the magnitude of evoked jaw muscle electromyographic (EMG) activity was measured. Application of GABA alone to the TMJ region did not evoke significant jaw muscle EMG activity when compared with normal saline controls. In contrast, co-application of GABA and glutamate into the TMJ region decreased the magnitude of glutamate-evoked EMG activity. This GABA-mediated inhibition of glutamate-evoked EMG activity followed an inverse dose-response relationship with an estimated median inhibitory dose (ID50) of 0.17 +/- 0.05 (SE) micromol and 0.031 +/- 0.006 micromol for the digastric and masseter muscles, respectively. Co-administration of the GABAA receptor antagonist bicuculline (0.05 micromol) but not the GABAB receptor antagonist phaclofen (0.05 or 0. 15 micromol) reversed the suppressive actions of GABA, indicating that this action of GABA may be mediated by peripheral GABAA receptors located within the TMJ region. Our results suggest that activation of peripheral GABAA receptors located within the TMJ region could act to decrease the transmission of nociceptive information.

Animals↗
PubMed1999

Features of cortically evoked swallowing in the awake primate (Macaca fascicularis).

Although the cerebral cortex has been implicated in the control of swallowing, the output organization of the cortical swallowing representation, and features of cortically evoked swallowing, remain unclear. The present study defined the output features of the primate "cortical swallowing representation" with intracortical microstimulation (ICMS) applied within the lateral sensorimotor cortex. In four hemispheres of two awake monkeys, microelectrode penetrations were made at </=1-mm intervals, initially within the face primary motor cortex (face-MI), and subsequently within the cortical regions immediately rostral, lateral, and caudal to MI. Two ICMS pulse trains [35-ms train, 0.2-ms pulses at 333 Hz, </=30 microA (short train stimulus, T/S); 3- to 4-s train, 0.2-ms pulses at 50 Hz, </=60 microA (continuous stimulus, C/S)] were applied at </=500-micron intervals along each microelectrode penetration to a depth of 8-10 mm, and electromyographic (EMG) activity was recorded simultaneously from various orofacial and laryngeal muscles. Evoked orofacial movements, including swallowing, were verified by EMG analysis, and T/S and C/S movement thresholds were determined. Effects of varying ICMS intensity on swallow-related EMG properties were examined by applying suprathreshold C/S at selected intracortical sites. EMG patterns of swallows evoked from various cortical regions were compared with those of natural swallows recorded as the monkeys swallowed liquid and solid material. Results indicated that swallowing was evoked by C/S at approximately 20% of 1,569 intracortical sites where ICMS elicited an orofacial motor response in both hemispheres of the two monkeys, typically at C/S intensities </=30 microA. In contrast, swallowing was not evoked by T/S in either monkey. Swallowing was evoked from four cortical regions: the ICMS-defined face-MI, the face primary somatosensory cortex (face-SI), the region lateral and anterior to face-MI corresponding to the cortical masticatory area (CMA), and an area >5 mm deep to the cortical surface corresponding to both the white matter underlying the CMA and the frontal operculum; EMG patterns of swallows elicited from these four cortical regions showed some statistically significant differences. Whereas swallowing ONLY was evoked at some sites, particularly within the deep cortical area, swallowing was more frequently evoked together with other orofacial responses including rhythmic jaw movements. Increasing ICMS intensity increased the magnitude, and decreased the latency, of the swallow-related EMG burst in the genioglossus muscle at some sites. These findings suggest that a number of distinct cortical foci may participate in the initiation and modulation of the swallowing synergy as well as in integrating the swallow within the masticatory sequence.

Animals↗