Congenital insensitivity to noxious stimuli

NGF-dependent neurons and neurobiology of emotions and feelings: Lessons from congenital insensitivity to pain with anhidrosis

NGF is a well-studied neurotrophic factor, and TrkA is a receptor tyrosine kinase for NGF. The NGF-TrkA system supports the survival and maintenance of NGF-dependent neurons during development. Congenital insensitivity to pain with anhidrosis (CIPA) is an autosomal recessive genetic disorder due to loss-of-function mutations in the NTRK1 gene encoding TrkA. Individuals with CIPA lack NGF-dependent neurons, including NGF-dependent primary afferents and sympathetic postganglionic neurons, in otherwise intact systems. Thus, the pathophysiology of CIPA can provide intriguing findings to elucidate the unique functions that NGF-dependent neurons serve in humans, which might be difficult to evaluate in animal studies. Preceding studies have shown that the NGF-TrkA system plays critical roles in pain, itching and inflammation. This review focuses on the clinical and neurobiological aspects of CIPA and explains that NGF-dependent neurons in the peripheral nervous system play pivotal roles in interoception and homeostasis of our body, as well as in the stress response. Furthermore, these NGF-dependent neurons are likely requisite for neurobiological processes of 'emotions and feelings' in our species.

Proposal for a standardized protocol for the systematic orofacial examination of patients with Hereditary Sensory Radicular Neuropathy

AIM

To apply a standardized protocol for the orofacial evaluation of two adult siblings (one male and one female) with Hereditary Sensory Radicular Neuropathy (HSRN) that presented with dental problems.

SUMMARY

The systematic evaluation consisted of (a) clinical questionnaire; (b) radiographs [orthopantomography and computarized tomography (CT)]; (c) orofacial psychophysical tests (pain, thermal, mechanical and electrical sensation); and (d) histology of gingiva and pulp (optical and transmission electronic microscopy). The female patient had complete insensitivity to orofacial pain and partial facial heat sensitivity, and received dental treatment without anaesthesia or pain. She had a severe and painless jaw infection due to pulp necrosis in tooth 37. The male patient had partial insensitivity to orofacial pain and required anaesthesia for dental treatment. Histological examination of gingivae and pulpal tissue revealed an altered proportion of unmyelinated and myelinated sensory nerve fibres.

KEY LEARNING POINTS

* Patients with HSRN may present with significant, silent dental disease. * A standard protocol is helpful when evaluating such patients. * If the opportunity arises, evaluation of pulp tissue may reveal an altered proportion of myelinated and unmyelinated nerve fibres. This may avoid the more estabilished sural nerve biopsy.

Dental neuroplasticity, neuro-pulpal interactions, and nerve regeneration

This review covers current information about the ability of dental nerves to regenerate and the role of tooth pulp in recruitment of regenerating nerve fibers. In addition, the participation of dental nerves in pulpal injury responses and healing is discussed, especially concerning pulp regeneration and reinnervation after tooth replantation. The complex innervation of teeth is highly asymmetric and guided towards specific microenvironments along blood vessels or in the crown pulp and dentin. Pulpal products such as nerve growth factor are distributed in the same asymmetric gradients as the dentinal sensory innervation, suggesting regulation and recruitment of those nerve fibers by those specific factors. The nerve fibers have important effects on pulpal blood flow and inflammation, while their sprouting and cytochemical changes after tooth injury are in response to altered pulpal cytochemistry. Thus, their pattern and neuropeptide intensity are indicators of pulp status, while their local actions continually affect that status. When denervated teeth are injured, either by pulp exposure on the occlusal surface or by replantation, they have more pulpal necrosis than occurs for innervated teeth. However, small pulp exposures on the side of denervated crowns or larger lesions in germ-free animals can heal well, showing the value of postoperative protection from occlusal trauma or from infection. Current ideas about dental neuroplasticity, neuro-pulpal interactions, and nerve regeneration are related to the overall topics of tooth biomimetics and pulp/dentin regeneration.

Indolent corneal ulcers in a patient with congenital insensitivity to pain with anhidrosis: a case report and literature review

PURPOSE

To report a case of bilateral corneal neurotrophic ulcer in patient with congenital insensitivity to pain with anhidrosis (CIPA) and review the literature.

CASE REPORT

A 6 year-old boy presented with bilateral central corneal sterile ulcer, decreased corneal sensitivity, moderately altered corneal reflex and normal tearing response. History taken, systemic evaluation and medical chart review were undertaken.

DISCUSSION

Fifty-two cases of CIPA have been reported worldwide. Fourteen cases had corneal involvement. The clinical picture of our patient is characteristic of CIPA.

CONCLUSIONS

Congenital insensitivity to pain with anhidrosis may present as neurotrophic corneal ulcer. We report herewith, this vision threatening corneal congenital abnormality. Early diagnosis and prompt treatment are mandatory to prevent corneal complications such as scarring and perforation.

Congenital insensitivity to pain with anhidrosis: ocular and systemic manifestations

PURPOSE

To report the incidence and severity of the ophthalmologic manifestations in patients with congenital insensitivity to pain with anhidrosis.

METHODS

Fifteen Bedouin children with congenital insensitivity to pain with anhidrosis underwent complete ocular examination, including refraction and assessment of corneal sensation, and a detailed neurologic examination, including measurement of median nerve motor and sensory conduction. Patients with corneal ulcers were treated appropriately.

RESULTS

In the 15 children (eight girls and seven boys, with a mean age of 3.75 +/- 2.67 years; range, 9 months to 9 years), corneal sensation was absent in both eyes. Corneal opacities were present in 10 children, five of whom had bilateral corneal opacities. Corneal ulcers were found in seven children, two of whom had bilateral ulcers, and in three children the ulcers recurred. The corneal ulcers were characterized by very poor healing. The surgical procedures included four lateral tarsorrhaphies, two corneal patch grafts, and one penetrating keratoplasty. All the patients had self-inflicted injuries varying from skin ulcers, burns, and bone fractures to autoamputations of fingertips and tongues. Many patients showed delayed healing and repair of bone and skin injuries. All patients had attacks of hyperpyrexia, moderate mental retardation, and hypotonicity with absent superficial sensation to light touch. Results of median nerve motor and sensory conduction studies were within normal limits.

CONCLUSIONS

The patients with congenital insensitivity to pain and anhidrosis and absent corneal sensation showed a marked tendency to develop corneal ulcers that healed poorly. Congenital insensitivity to pain and anhidrosis, although rare, should be considered in the differential diagnosis of neurotrophic keratitis.

Thalamic nociceptive mechanisms in cats, influenced by central conditioning stimuli

Field potentials and single cell activity evoked by tooth pulp (TP) stimulation were studied in the ventrobasal (VB) complex of the cat. The experiments were performed using a conditioning-test paradigm. Evoked cell activity or field potentials following TP stimulation was used as a test. Conditioning stimulus was given to different regions of the thalamic central lateral nucleus (CL). Conditioning electrical stimulation in medial (ML 2.8-3.6 mm) parts of CL induced a depression of the TP evoked response in 10 cells. Stimulation sites in lateral CL (ML 3.6-4.2 mm) induced facilitation in eight cells and decreased activity in seven cells. Tooth pulp evoked field potentials in thalamus were facilitated by a preceding stimulation in lateral CL. Cells in the lateral parts of CL are suggested to induce an increased activity in cells in the VB complex which mediate nociceptive information. This effect is suggested to be mediated via a CL induced disinhibition at a reticular thalamic (RE) or at a VB complex level. The medial parts of CL seem to give a traditional feedback inhibition on VB cells. Such an effect is also suggested to be mediated via the RE complex. The importance of these findings are discussed with relation to changes in the thalamus that may occur following long lasting nociceptive stimulation.

Relationship between vertex potentials and magnitude of pre-pain and pain sensations evoked by electrical skin stimuli

Vertex potentials evoked by painful and non-painful electrical skin stimuli were recorded in 10 healthy male volunteers. Peak-to-peak amplitudes of the major vertex potential components were compared with subjective rating of the stimuli. While a significant correlation was observed between peak-to-peak amplitudes and stimulus rating following non-painful stimuli, generally no such correlation was present following stimulations above the pain threshold. These findings suggest that vertex potentials elicited by electrical skin stimuli may reflect central processing of non-noxious afferent information rather than of pain-related information.

Pain and tooth pulp evoked potentials

The purpose of this study was to verify whether the late components (N 140) of TPEPs were a reliable index of pain intensity. In the group with acute pain, except for higher amplitudes of the second negative wave, the plateau phenomenon has been noted. Analgesic and placebo effects indicated that the method used offers more objective than subjective components, because the real value of amplitudes is about 10% of control values for analgesic and between 60 and 70% for placebo. Shorter latency periods were observed in all parts of evoked potentials in the patients suffering from trigeminal neuralgia, as occurrence of a greater number of waves; while amplitudes on the affected side were significantly higher than on the healthy side.

Short latency trigeminal evoked potentials: normative data and clinical correlations

A very short latency trigeminal evoked potential (STEP) to electrical stimulation of the upper lip has been recorded from over the scalp. This potential consists of 5 distinct peaks within the 12 msec range. Normative data were obtained from 25 healthy volunteers. The impact of the stimulus rate and intensity on the response was studied in each subject. These results were compared to those of 19 patients suffering from lesions involving the trigeminal system in its peripheral aspect or the brain-stem. The STEP was consistently abnormal whenever the involved side was stimulated. Changes in peak latencies and in interpeak latency differences (IPLD) correlated well with clinical and radiological findings and improved with the removal of the offending lesion. The STEP proved to be a reliable method for evaluating the trigeminal system in its peripheral and central pathways; it may thus serve as an additional parameter for studying brain-stem functions.

The long-latency component of cerebral evoked potentials in anesthetized cats

A late component of the cortical evoked potential elicited by somatosensory afferent input was studied in cats anesthetized with alpha-chloralose. Cortical evoked potentials were recorded from the somatosensory-motor cortex during stimulation of the sural nerve with graded intensities. The stimulus intensity was adjusted to activate A alpha beta fibers only, then both A alpha beta and A delta fibers, and both A and C fibers, as judged by afferent volleys monitored from the sural nerve proximal to the stimulating site. In addition to early components reported previously, a very late component was identified at a latency of 400 to 600 msec following stimulation of the sural nerve with intensities above threshold for A delta fibers. A further increase in stimulation intensity to include activation of C fibers did not reveal any more components. This late component was depressed by a systemic intravenous injection of morphine (2 mg/kg), and intravenous naloxone (0.1 mg/kg) reversed the effect of morphine. The late component of the evoked potential could also be recorded from subcortical tissue after decortication of the sensorimotor cortex. From these results, it appears that a very late component of the cortical evoked potential can be recorded from cats anesthetized with alpha-chloralose. The late component is evoked by activation of peripheral A delta fibers. Furthermore, its morphine sensitivity suggests that this component may be elicited by nociceptive afferent fibers. If further investigations prove this, the late component, which is analogous to human long-latency potentials, could be used in an experimental model for pain research.

Projection of tooth pulp afferents to the thalamus of the cat. I. Focal potentials and thalamocortical connections

Electrical stimulation of tooth pulp afferents in cats evoked short latency focal potentials in the basal ventromedial nucleus of thalamus (VMB), in the border zone between this nucleus and the arcuate nucleus of the ventrobasal complex (VBA), and in the marginal zone of VBA and the external nucleus of the ventrobasal complex (VBX). No responses were found in the centre of VBA and VBX. Very few responses were found in the intralaminar region. The projection from the tooth pulps was bilateral, but the best responses following stimulation of the ipsi- and the contralateral tooth pulps could be evoked at slightly different locations within VMB. The mean latency of the responses was shorter following stimulation of the contralateral tooth pulp than following stimulation of the ipsilateral one. Electrical stimulation in VMB, VBA, and VBX evoked focal potentials in thalamocortical projection fibres, which were recorded from in the white matter below areas SI and SII after decortication by suction. Conditioning stimulation of the tooth pulps suppressed these responses within 200 ms if the stimulating electrode was placed at the border between VBA and VMB, suggesting that tooth pulp stimulation activates a thalamocortical projection with a postexcitatory inhibition. Finally, lesions were made in the thalamus and their effects were checked on the cortical responses to tooth pulp stimulation. If the lesion included the region of VMB bordering to VBA the cortical responses decreased in amplitude. It is concluded that VMB and the borderzone between VMB and VBA are important relays between the nociceptors of the tooth pulp and the sensory cortex.

Sensory innervation of periodontal ligament of rat molars consists of unencapsulated Ruffini-like mechanoreceptors and free nerve endings

The trigeminal ganglion (TG) of adult rats was injected with 3H-amino acids to label periodontal receptors by axonal transport; 20-24 hours after injection, samples of molar ligament were prepared for autoradiography and electron microscopy. Four types of neurites labeled from TG were found in the avascular ligament fiber regions: large, complex, Ruffini-like endings, lacking a capsule, but with finger extensions touching ligament collagen; smaller Ruffini-like endings, lacking a capsule and neural fingers; free bundles of unmyelinated axons; and free, small, myelinated axons. The vascular channels plus associated loose connective tissue that perforate the ligament contained labeled preterminal ensheathed axons, small Ruffini endings, and free unmyelinated or small myelinated axons. The incidence of labeled endings was about 5 X greater next to the lower third of the root than in the upper two-thirds or beneath the root. The TG myelinated axons (diameter range 2-15 microns) entered the ligament in sheathed nerve bundles; these branched to form numerous small preterminal axons that were surrounded by a periaxonal fluid space and a perineurial sheath. Terminal axons branched from nodes of Ranvier, left the preterminal chamber, and followed an extended branching course through the collagen fibers. Large, complex Ruffini-like endings had numerous mitochondria and were partially covered by special lamellar Schwann cells and complex basal lamina; vesicles and multivesicular bodies were found near exposed regions of the receptor. Smaller Ruffini-like endings lacked neural fingers and had a simpler structure and less elaborate Schwann cells. The structure of Ruffini-like endings was highly varied; thus a structural continuum may exist from the largest, most complex to the smallest, simplest Ruffini-like receptor. The TG unmyelinated axons entered the ligament in ensheathed bundles; they then branched into free bundles that were found in the avascular ligament or near blood vessels. No encapsulated receptors were found.

Dental sensory receptors

Teeth are innervated by unmyelinated sympathetic axons, and by unmyelinated and small myelinated sensory axons. Some sensory axons in teeth are terminal branches of larger parent axons, so that conduction from teeth to CNS in trigeminal nerves includes C-fiber, A-delta, and A-beta velocities. Sensory dental axons contain acetylcholine or substance P-like immunoreactivity. The sympathetic axons contain noradrenalin. Other neuropeptides may also be present, such as vasoactive intestinal peptide and serotonin. Dental axons of mature teeth of many species (man, monkey, cat, rodents, fish) are essentially the same, but continuously erupting teeth have smaller and fewer axons. Free sensory nerve endings in mature teeth are found in the peripheral plexus of Raschkow, the odontoblastic layer, the predentin, and the dentin. Free nerve endings are most numerous in those regions near the tip of the pulp horn, where more than 40% of the dentinal tubules can be innervated. Many dentinal tubules contain more than one free nerve ending. Intradentinal axons can extend as far as 0.2 mm into dentin but usually end less than 0.1 mm from the pulp. Some sensory endings also occur along pulpal blood vessels. In continuously erupting teeth nerve endings do not enter the dentin but remain within the pulp. Nerve endings in dentin are labeled by axonal transport. They are therefore as viable and active as the nerve endings in pulp. The axoplasm of the free nerve endings contains organelles typical of other somatosensory receptors. These organelles are most common in the successive beaded regions along the free nerve endings and include mitochondria, clear and dense-core vesicles, multivesicular bodies, profiles of smooth endoplasmic reticulum, and relatively few microtubules and neurofilaments. The beads can vary in size from about 0.2 to 2.0 microns and can have varying amounts of receptor organelles. The interbead axonal regions are thin and contain mainly microtubules and neurofilaments. Nerve endings are associated with companion cells after they leave the coronal nerve bundles; these companion cells include Schwann cells, fibroblasts, and odontoblasts. There is no good evidence of gap junctions or synapses between nerve endings and odontoblasts. Instead, the two cell types form appositions that have a 20-40 nm extracellular cleft and parallel apposed plasmalemmas but no unusual membrane-associated material. No special organelles occur in the odontoblastic cytoplasm at these sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Actions of GABA, glycine, methionine-enkephalin and beta-endorphin compared with electrical stimulation of nucleus raphe magnus on responses evoked by tooth pulp stimulation in the medial reticular formation in the cat

In decerebrate, cerebellectomized cats, a comparison was made between the effects of electrical stimulation in nucleus raphe magnus (NRM) and iontophoretic application of GABA, glycine, met-enkephalin and beta-endorphin on the responses of neurones in the medial brain stem reticular formation to tooth pulp stimulation. NRM stimulation, GABA, glycine and enkephalin produced a short lasting inhibition of tooth pulp evoked responses whilst the time course of the inhibition produced by beta-endorphin was much slower, often lasting up to 1 h following a 3-7 min ejection period. The effects of GABA and glycine could be antagonised by iontophoresis of bicuculline and strychnine respectively whilst intravenous injection of naloxone antagonised the inhibition induced by the opioid peptides. In most neurones tested, inhibition of tooth pulp evoked responses by NRM stimulation was blocked by iontophoretic application of bicuculline but not by strychnine or naloxone (i.v.). We conclude that GABA may act as a transmitter which mediates the inhibitory effects of NRM on the responses of reticular neurones to tooth pulp stimulation. Thus GABA may be involved in stimulation produced analgesia.

Sensory evoked response to electrical stimulation of the trigeminal nerve in humans

Electrical stimulation of the upper and lower lips of normal subjects evoked a consistent response recorded from over the face area of the ipsi- and contralateral hemispheres. This response consisted of seven discrete waves. Peak latencies ranged from as early as 8 msec to 115 msec. Stimulation of the lower lip evoked a response of lower amplitude and reversed polarity, as compared to te upper lip stimulation response. The data support the validity of the trigeminal sensory evoked response in the evaluation of the trigeminal pathways. Previously reported methods are reviewed and compared.

Habituation to bearable experimental pain elicited by tooth pulp electrical stimulation

Stimulation (1/10 sec, 1-2 msec) of the tooth pulp of volunteers was carried out for 120 min at an intensity that produced bearable pain. Cortical evoked potentials, electroencephalographic activity, electromyograms of the superciliary and masseter muscles and galvanic skin response were recorded. Every 30 min, without suspending the stimulation, the subjects were questioned with respect to the sensations accompanying the stimuli. A progressive decrease in all polygraphic responses was observed which coincided with a decrease in the reported sensation of pain. This effect could be reversed by applying heterosensorial stimulation (questioning). It is suggested that this is a phenomenon of habituation to pain since dishabituation, potentiation of habituation, and habituation to dishabituation were found.

Congenital insensitivity to pain with anhidrosis

A nine-year-old child presented with congenital insensitivity to pain and anhidrosis. Quantitative studies and electron microscopy of the cutaneous branch of the radial nerve revealed almost complete absence of small myelinated and unmyelinated fibers and a disproportionate number of nerve fibers with a diameter of 6-10 micrometers. A grouping of both type 1 and type 2 muscle fibers was also seen. We suggest that this disease entity is not caused by a hereditary sensory neuropathy, but rather that it derives from a developmental defect.

Brain evoked potentials are functional correlates of induced pain in man

Electrical potentials evoked by 5 intensities of painful dental stimulation were recorded at the scalp. During testing, volunteers indicated subjective painfulness by verbal pain ratings and visual analogue scales. Evoked potentials (EPs) to each intensity, observed between 50 and 400 msec, were characterized by 4 waveform components. The peak-to-peak amplitudes, but not the peak latencies, of all 4 EP components systematically increased with increased stimulation. The amplitudes of the two earlier components correlated with stimulus intensity when the effect of subjective painfulness was controlled, but this was not the case for the later components. In contrast, the amplitudes of the two later components were associated with subjective painfulness but not with stimulus intensity. A strong linear relationship was observed between subjective painfulness and peak-to-peak amplitude for the EP component observed between 175 and 260 msec. The data suggest that the earlier EP components may reflect sensory transmission processes while the later components indicate brain activity when pain is perceived.

Nasoenteric feeding

CT findings were reviewed in 68 patients with untreated head and neck lymphoma. More than half of the patients with either Hodgkin's disease or non-Hodgkin's lymphoma were detected in the earlier stages (stage I or II). Four types of abnormalities were identified with CT: nodal involvement alone (type 1), extranodal involvement alone (type 2), a combination of extranodal and nodal disease (type 3), and multifocal extranodal disease with or without nodal involvement (type 4). In the 18 patients with Hodgkin's disease, a subgroup of mixed cellularity was most common; type 1 was the prevailing CT presentation, and no type 2 or 4 lesions were observed. In the 50 patients with non-Hodgkin's lymphoma, diffuse large-cell lymphoma was the most common histologic subtype, and the most common CT presentation was type 2, followed by type 3. Lymphomatous nodes may be extensive and confluent, but often they are smaller than 2 cm and rarely are necrotized. The most frequent extranodal sites of head and neck lymphomas are Waldeyer's ring, paranasal sinuses, and nasal cavity. Extranodal lymphoma cannot be differentiated reliably from the more commonly occurring carcinoma, although it is less often associated with invasion and destruction of adjacent bony structures. Multiple sites of extranodal involvement, with or without neck lymphadenopathy, may suggest a diagnosis of non-Hodgkin's lymphoma.

Sensation evoked by bipolar intrapulpal stimulation in man

Bipolar intrapulpal stimulation was applied to human teeth using the same procedure as in animal experiments. The effects of variation of stimulus parameters on the quality of sensation were studied. A prepain sensation exists which cannot be explained by diffusion of the stimulus to periodontal tissues. When the intensity of stimulation is increased, the prepain sensation is gradually replaced by a pinprick sensation. With long, high intensity stimulation, an acute long lasting very painful sensation appears. To evoke a pinprick sensation the best stimulation seems to be a 50 msec train (0.5 msec, 300 Hz, 0.5 mA). Longer train duration and a higher intensity of current are necessary to evoke a long lasting, acute very painful sensation. Since the exclusively Adelta and C nerve fiber content of the dental pulp is well documented and since it is possible to avoid current diffusion outside the dental pulp cavity, the tooth pulp implantation seems to be a good technic for studying pain, as long as the investigator uses adequate stimulation.

Detection and decision factors in pain perception in young and elderly men

The effect of age on ability to discriminate between levels of electrical stimulation of tooth pulp and willingness to report shocks as painful was evaluated using the Sensory Decision Theory. While threshold did not increase with age for tooth pulp stimulation as is often observed for thermal pain thresholds, a significant age deficit in ability to discriminate between suprathreshold shocks was observed. Significant changes with age in willingness to report the electrical shocks as painful were also observed. These results indicate that changes with age in pain perception are complex, involving not only possible discrimination deficits but also changes in bias for and against labeling noxious events as painful. These findings stress the need for within individual comparisons of laboratory techniques for evoking acute pain experiences where variables such as age are under consideration.

Behavioral evidence showing the predominance of diffuse pain stimuli over discrete stimuli in influencing perception

This experiment was directed toward determining the relative effectiveness of discrete and diffuse pain stimuli in influencing perception and behavior. Shocks to the footpads were used to activate the discrete pain pathways and shocks to the upper canine teeth to activate the diffuse pain pathways. In the first phase of this experiment, cats were trained to escape from foot shock in a shuttle box. Current applied to the feet was varied in ascending and descending sequences for each animal according to the psychophysical method of limits and each animal was trained until stable thresholds for escape responding were achieved. In the second phase of the experiment, the effect on behavior of simultaneous activation of both the discrete and diffuse pain systems was assessed. The principal finding is this experiment was that excape responding that was well established when foot shock was presented alone was routinely abolished on trials when tooth shock and foot shock were presented together. These results were interpreted as indicating that the diffuse pain system was prepotent in influencing behavior when both the discrete and diffuse pain systems were activated simultaneously.