Narcotic analgesia: fentanyl reduces the intensity but not the unpleasantness of painful tooth pulp sensations.

Forty subjects rated the magnitude of painful electrical stimulation of tooth pulp before and after the intravenous administration of either fentanyl, a short-acting narcotic, or a saline placebo. The responses were choices of verbal descriptors from randomized lists of either sensory intensity (that is, weak, mild, intense) or unpleasantness (annoying, unpleasant, distressing) descriptors. The fentanyl significantly reduced the sensory intensity without reducing the unpleasantness of the tooth pulp stimuli, indicating that the mechanisms of narcotic analgesia may include a significant attenuation in pain sensation in addition to effects on pain reaction. These results stress the importance of using multiple measures of pain.

Pain and self-reported health in Canadian children.

BACKGROUND: Despite increasing attention to the epidemiology of pain, relatively little is known about the association between pain and health in children. In particular, no studies have examined this relationship in the general population of children in Canada. OBJECTIVES: To assess the association between self-reported pain experiences and health in school children in southeastern Ontario. Health measures included perceived health status, psychological complaints and satisfaction with school. METHODS: A total of 495 nine- to 13-year-old school children completed the Pain Experience Interview -- Short Form and health-related questions from the Health Behaviour in School-aged Children questionnaire. RESULTS: Of the 495 children in the present study, 8% rated their health as 'fair' to 'poor', 56% reported experiencing at least one of four psychological symptoms more than once a week and 24% said they disliked school. The strongest associations existed between headaches and poor self-rated health (OR=10.1; 95% CI 1.3 to 78.3), recurrent pain and psychological outcomes (OR=3.6; 95% CI 2.0 to 6.3), and recurrent pain and disliking school (OR=3.6; 95% CI 1.9 to 6.7). DISCUSSION: These findings indicate that common childhood pains are associated with childhood health. Further studies are needed to assess the causal relationship between pain and health in children, to obtain a more comprehensive understanding of the personal and economic impact of childhood pain, and to monitor changes in the lives of children living with chronic pain.

Death of motorneurons during the postnatal loss of polyneuronal innervation of rat muscles.

A study was made of the decline in the number of motor neurons and axons of the brachial spinal cord of the rat during postnatal development. The injection of horseradish peroxidase (HRP) into the biceps muscle showed that it was innervated by motor neurons located in the dorsolateral position of the lateral motor column in segments C5 and C6; HRP injections into the triceps muscle showed that it was innervated by motor neurons located in the ventrolateral position of the lateral motor column in segments C7 and C8. There was no change in the position of these motor neuron pools between birth and maturity. However, there was a decline in the number of neurons in each pool during the postnatal period; over 35% of the neurons present at birth had disappeared by maturity. This loss of neurons was uniform throughout the rostrocaudal extent of each pool. It was accompanied by a similar percentage loss in the number of axons in a ventral root at the branchial level (C8). Electrophysiological measurements showed that the disappearance of motor neurons was accompanied by a loss in the polyneuronal innervation of synaptic sites in the biceps muscle. The possibility that a decrease in the number of neurons contributes to the loss of polyneuronal innervation is discussed.

The spatial distribution, intensity and unpleasantness of acute dental pain.

The distribution, intensity and unpleasantness of acute dental pain were studied in 196 patients. Dental pain was classified by source according to 7 anatomical sites: dentinal, pulpal, pulpal and periapical, periapical, pericoronal, papillar, and periodontal. The distribution of dental pain was classified by the frequency of pain spread throughout the sample, by the extent of pain spread for a particular pain source, that is, the number of vectors of spread, and by the pain reference locations in the face and head. Pain-intensity and pain-unpleasantness were assessed on Visual Analogue Scales. The frequency and extent of pain spread varied as a function of source. However, specific patterns of pain spread were not associated with particular pain sources. There was considerable overlap in patterns of spread between maxillary and mandibular pain sources. The frequency and extent of pain spread was correlated positively with both pain intensity and pain unpleasantness. The correlation between pain ratings and pain spread may be attributed to central mechanisms and interactions between trigeminothalamic neurons. Spatial overlap of pain from maxillary and mandibular pain sources may be due to the large receptive fields of wide dynamic range neurons, that can extend beyond one trigeminal division. These observations indicate that the spatial distribution of acute dental pain is not sufficient as a diagnostic tool for indentifying pain source.

Non-pain and pain sensations evoked by tooth pulp stimulation.

This study investigated the quality and magnitude of sensations evoked by electrical tooth pulp stimulation. Detection threshold (the minimum current intensity that evoked a sensation) and pain threshold were determined for tooth pulp stimuli varying in frequency from 5 to 500 Hz. The effect of frequency and intensity of tooth pulp stimulation on the magnitude of sensations was assessed using visual analog scales and verbal descriptor scales. Detection thresholds were stable over experimental sessions and independent of the frequency of the stimulating current. Pain threshold varied as a function of frequency with a minimum value at 100 Hz. Stimuli that evoked non-pain sensations at low frequencies evoked pain sensations when frequency was increased from 5 to 100 Hz. Subjects were able to scale non-pain sensations over a range of stimulus intensities and frequencies. The lowest currents evoked sensations that were non-painful and were of constant magnitude despite changes in the frequency of stimulation. Higher stimulus currents evoked sensations that were non-painful at low stimulus frequencies and painful at high stimulus frequencies. Sensation magnitude at each stimulus intensity increased as a function of frequency. Temporal summation occurred in proportion to stimulus intensity. These findings suggest that the non-pain sensations evoked in tooth pulp are mediated by a distinct population of afferents that are not involved in the coding of pain. High frequency stimulation that increased the discharge rate of the lowest threshold pulpal afferents resulted in no summation of non-pain sensation and never produced pain. However, high frequency stimulation evoked greater magnitude sensations at higher stimulus currents, indicating that central summation mechanisms were critical for higher threshold afferents signaling more intense non-pain and pain sensations.

Pediatric pain: interacting behavioral and physical factors.

Pain in infants, children, and adolescents warrants study from a developmental, behavioral, and physiological perspective because maturation of physical, emotional, and cognitive systems influences the way in which pain is experienced and expressed. Pediatric pain is an underdeveloped area ripe for study within the realm of developmental and behavioral pediatrics, as noted by documentation of its undertreatment in children. The focus of this paper is to present issues relevant to the study of pain in children, using the example of the recurrent abdominal pain syndrome to illustrate points regarding epidemiology, assessment, and intervention. It is the opinion of these authors that pediatric pain must be understood from a developmental perspective in both clinical and nonclinical populations of children. Multidisciplinary approaches to research in pain aids in understanding the development of nociceptive transmission and inhibitory systems, the development of pain expression, and the influence of context on pain experience and behavior. The goal of research in pediatric pain is to understand these systems within a developmental context so that preventive and therapeutic intervention strategies can be developed to reduce children's distress and pain-related disability.

Electrical responses of cultured porcine thyroid cells to adrenergic agents.

The membrane potential of cultured porcine thyroid follicular cells depolarized by up to 20 mV from the resting value of about -73 mV on exposure to beta-adrenoceptor agonists. A similar response was induced by TSH or dibutyryl cyclic AMP. alpha-Adrenoceptor agonists were without effect. The receptor subtype was shown to be (at least predominantly) beta 2 by the order of potency for beta-agonists (isoprenaline approximately equal to fenoterol much greater than adrenaline greater than noradrenaline) and by the relative potency of selective beta-antagonists (ICI 118,551 much greater than atenolol). The alpha-agonist phenylephrine had no effect on the TSH response but weakly inhibited the beta-agonist response. Rather than a physiological antagonism between alpha- and beta-adrenoceptor-mediated responses, this effect was shown to be due to the weak beta-antagonist effect of phenylephrine since the alpha-antagonist phentolamine failed to potentiate the depolarizing response to the mixed agonist noradrenaline, and also failed to block the inhibitory action of phenylephrine on the beta-agonist effect. Sensitivity to beta-agonist was enhanced by omission of serum from the culture medium and reduced by exposure to beta-agonists or a high concentration of TSH or dibutyryl cyclic AMP.

Effect of epidermal growth factor on the membrane potential of cultured porcine thyroid cells.

Cultured porcine thyroid cells maintained in media containing TSH exhibited a membrane potential of -50 mV, and hyperpolarized by about 10 mV within 1 h of the addition of epidermal growth factor (EGF; 10 ng/ml). Follicle cells had depolarized to -45 mV after 4 h of exposure to EGF. Cells maintained in dibutyryl cyclic AMP (dbcAMP) did not alter their membrane potential when exposed to EGF for up to 4 h. Cultures washed to remove the TSH or dbcAMP hyperpolarized to -75 mV within 30 min, and a reversible depolarization to -60 mV was observed on addition of EGF. It was concluded that EGF acts as a physiological antagonist of TSH and also exerts a separate depolarizing influence on cultured thyroid cells.

Electrical responses of cultured thyroid cells to serotonin.

Cultured porcine thyroid cells, maintained in the differentiated state by dibutyryl cyclic AMP, responded to serotonin (5-HT; 10 nmol/l to 1 mumol/l) with a depolarization of the membrane potential, but did not respond to histamine (100 mumol/l) or dopamine (1 mumol/l). The resting membrane potential of these cells was about -71 mV, maximal concentrations of 5-HT (1 mumol/l) inducing a depolarization to approximately -53 mV. Methysergide or phenoxybenzamine, but not propranolol, abolished the response to 5-HT. Sensitivity to 5-HT was reduced by previous exposure of cultures to TSH, the beta-adrenoceptor agonist salbutamol or 5-HT itself.

The regression of synapses formed by a foreign nerve in a mature axolotl striated muscle.

A study has been made of the factors which determine that the terminals of a foreign flexor nerve at synaptic sites in a unrodele extensor muscle regress on return of the original extensor nerve. The quantal content (m) of the endplate potential (EPP) at flexor nerve terminal synapses, during innervation of a previously denervated extensor muscle, increased in about 8 weeks to reach the same size as at normal extensor nerve terminals; the same time was taken for m to reach normal size at extensor nerve terminals when these reinnervated their own muscle. At flexor nerve terminals, m decreased eventually to zero if the extensor nerve terminals returned within about 6 weeks of synapse formation by the flexor nerve terminals to the same or an immediately adjacent synaptic site to that occupied by these terminals. During this decrease in m at flexor nerve terminals, stimulation of the flexor nerves in the presence of horseradish peroxidase (HRP) showed HRP-labelled flexor nerve terminals present only in those regions of the extensor muscle in which the electrical signs of flexor nerve terminals were observed, indicating that the decrease in m at regressing flexor terminals was accompanied by their vacating synaptic sites. However, flexor nerve terminals failed to regress from the extensor muscle on return of the original nerve supply if the flexor nerve allowed to form synapses for more than about 10 weeks before the return of the extensor nerve.

Evaluating a child's pain.

Much recent attention has focused on the development and refinement of pain measures, as well as on the use of more effective pain control methods for infants, children, and adolescents. This article reviews the primary categories of pediatric pain measures, with a specific focus on the selection of the most appropriate behavioral, physiologic, or subjective method for assessing a child's pain. The optimum pain measure depends on the age and cognitive level of a child, the type of pain experienced, and the situation in which the pain occurs. While no single measure is adequate for all children for all types of acute, recurrent, and chronic pain, it is possible to choose practical, valid, and reliable methods for evaluating any child's pain experience.

Development of the World Health Organization Guidelines on Cancer Pain Relief and Palliative Care in Children.

Assess pain regularly throughout the course of treatment. Follow the WHO Analgesic Ladder for selecting pain-relief drugs, that is, a stepwise approach to analgesic management, where a child's pain severity determines the level of analgesics. Use practical cognitive, behavioral, physical, and supportive therapies, combined with appropriate drug treatment. Administer adequate analgesics doses "by the clock," that is, at regular times, not PRN. Use oral routes for administering analgesics, and avoid painful routes of administration, whenever possible. Administer a sufficient analgesic dose to allow children to sleep throughout the night. Anticipate and treat side effects aggressively.

Phantom limb sensations in adolescents: a case study to illustrate the utility of sensation and pain logs in pediatric clinical practice.

Although the nature of pain following amputations has been well documented for adults, little research has been conducted to determine the incidence, prevalence, and nature of phantom limb sensations and pains in children and adolescents. This case study documents the nature of phantom limb sensation (intensity, quality, location, duration, and frequency) for a 15-yr-old adolescent after leg amputation. She completed a brief sensation/pain log, consisting of quantitative and qualitative scales, for 28 days after surgery. She experienced phantom limb sensations, which spread from her toes to encompass her entire leg by day 10 after surgery. The pattern of spread was not consistent throughout this period. The quality of sensations remained relatively constant and was described as itching and tingling. The phantom sensations were not experienced consistently throughout the day, but were experienced as discreet episodes. Both the duration and frequency of these episodes decreased throughout the 28 days. Similarly, the intensity of her phantom sensations decreased gradually throughout this period. This case study illustrates how it is possible to integrate research with health care delivery in a practical manner, to obtain prospective information about the nature of childhood sensory experiences.

Psychological aspects of pain perception.

Interest in the assessment and management of pain increased dramatically after 1965, when the gate control theory was introduced. This increase is concurrent with enormous advances in our understanding of the plasticity and complexity of pain processing. New information about internal pain-inhibitory systems and the factors that trigger them has revolutionized traditional approaches to pain control. This article describes some of the new information on the factors that influence human pain perception, specifically the environmental and psychological factors that modify how pain is experienced. Pain is a complex, multidimensional perception that varies in quality, strength, duration, location, and unpleasantness. The strength and unpleasantness of pain is neither simply nor directly related to the nature and extent of tissue damage. Even newborn infants may experience different pains from the same stimulus, because of the differences in the situations in which it is administered. Pain experiences can range from an inability to perceive pain, regardless of the strength of stimulation, to the actual perception of pain in a limb that has been amputated. The perception of, expression of, and reaction to pain are influenced by genetic, developmental, familial, psychological, social and cultural variables. Psychological factors, such as the situational and emotional factors that exist when we experience pain, can profoundly alter the strength of these perceptions. Attention, understanding, control, expectations, and the aversive significance can affect pain perceptions. Consequently, the understanding of pain requires not only understanding of the nociceptive system, but recognition and control of the many environmental and psychological factors that modify human pain perceptions.

Masseter inhibitory periods and sensations evoked by electrical tooth pulp stimulation in patients with oral-facial pain and mandibular dysfunction.

The masseter inhibitory period (silent period) and sensations evoked by tooth-pulp stimulation were examined in 12 healthy subjects and 12 patients with oral-facial pain and mandibular dysfunction (MPD). Trains of 30 pulses were applied to an upper incisor and the threshold intensities for detecting sensation, for detecting pain sensation and for the masseter inhibitory period were determined. Masseter activity was monitored during tooth stimulation by electromyographic recordings from surface electrodes. Electrical tooth stimulation elicited three different configurations of masseter inhibitory periods in both groups: single, double and merged. MPD patients exhibited a greater proportion of single inhibitory periods. The combined average total durations of the three types of configurations were less in MPD. The findings are consistent with the hypothesis that there is an increase in excitability of the central masseter motorneuron pool in MPD, resulting in a reduction in the effective duration of the masseter inhibitory period. The higher incidence of single inhibitory periods in MPD patients also could result from this increased central excitatory state. There was no difference between masseter inhibitory periods evoked in either painful or non-painful muscles, and no particular configuration associated with pain sensation. The findings do not support the hypothesis that nociceptive input contributes to the increase in duration of the silent period in MPD. Although there were no significant differences between masseter inhibitory period threshold, detection thresholds or pain threshold for both groups, MPD patients had detection thresholds higher than their masseter inhibitory thresholds. These effects may be related to differential central neural influences on sensory-discriminative and reflex pathways in the trigeminal system.

The treatment of temporomandibular joint syndrome through control of anxiety.

Following a negative experience with general anesthesia, a 20-yr-old woman developed anxiety and an inability to relax concomitant with temporomandibular joint dysfunction and pain syndrome. Systematic countering of anxiety by relaxation successfully removed her anxiety and led to a complete resolution of her symptoms. Follow-up at 16 months indicated maintenance of treatment gains and no recurrence of the symptoms during the previous 12 months.

Pain in the pediatric patient: practical aspects of assessment.

A child's pain is plastic and complex. In order to more effectively alleviate suffering, emphasis must shift from an exclusive focus on the source of tissue damage to a more comprehensive focus that includes factors that modulate pain. Evaluating a child's pain requires an integrated approach. Clinicians always should ask a child directly about his or her pain experience to determine the sensory characteristics. Clinicians also should assess situational factors to develop strategies to modify their impact. Then, a child's pain intensity should be measured regularly to monitor the effectiveness of interventions. Interviews, structured questionnaires, and simple rating scales are the primary tools to assess pain for most children older than 5 years of age. For infants, toddlers, and cognitively impaired children, physicians must infer the presence and severity of pain by evaluating changes in children's behavioral and physiological states. Parents and the health professionals who work most closely with children with particular handicaps can provide valuable information about the presence and severity of a child's pain because they often can recognize extremely subtle behavioral cues that indicate distress. A standardized but flexible approach is necessary to assess a child's pain. Pain assessment, like pain management, is a continuous process. Pain intensity rating scales should be used so children can provide a direct rating of their pain intensity and pain effect. Patients should receive some guidance about how to use the information from rating scales to develop consistent and objective criteria to know when children require analgesics and then to evaluate the effectiveness of those medications.

The role of situational variables in pain control.

The understanding of human pain perception, nociceptive systems, and analgesia is complicated by the variety of psychological, social and contextual variables that may interact with noxious sensory input to produce inexplicable changes in the strength, unpleasantness or quality of pain that is experienced. Consequently, many clinical and experimental studies aim to elucidate the mechanism by which psychological variables affect both neural coding and the resulting pain perception. Recently, more attention has focused on situational variables as important modifiers of pain and analgesic efficacy. Situational variables refer to the specific combination of psychological and contextual factors that exist in a particular pain situation. These variables represent a unique interaction between the individual experiencing pain and the context in which the pain is experienced.This article reviews the role of situational variables for modifying multiple dimensions of pain perception. Observations from human and animal research studies have been integrated to illustrate the potential of situational variables for enhancing or for reducing pain that is produced by a noxious stimulus. Clinical and experimental research designs are presented which may be used to identify relevant situational variables, to determine their effect on pain perception, to assess their interaction with analgesic efficacy, and to evaluate their mechanisms of action.