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Pain is a complex experience consisting of sensory, affective, behavioural and physiological components. The management of pain is therefore best achieved with an approach which acknowledges that the experience of pain is produced through the interaction of biological, psychological and sociocultural factors. Effective pain management requires preoperative patient engagement and education to manage expectations regarding pain relief and an inpatient pain service to coordinate the implementation of evidence-based postoperative pain management protocols and facilitate continuous staff education. Multimodal postoperative analgesia, built on an opioid-sparing ethos, is an essential component of perioperative pain management. Effective pain management enhances recovery after surgery by facilitating early patient mobilization, a reduction in respiratory and cardiac complications and amelioration of the stress response to surgery with consequent improved wound healing. Inadequate pain control can contribute to prolonged hospitalization and the development of chronic postsurgical pain. [ABSTRACT FROM AUTHOR]

The presence of pain is a protective mechanism that serves to prevent the body from further harm. However, when pain becomes pathological, it becomes a socio-economic disease burden that impacts a significant portion of the population. This article aims to discuss the physiology of pain that forms the basis for understanding the processes that allow pain to become chronic. It describes the definition of pain and the various types of pain receptors involved in the processing and perception of pain. The physiology, pathways and processes involved in the activation and ongoing experience of pain are well described in terms of four distinct events, known as transduction, transmission, modulation, and perception. The events described lend emphasis to the subjectivity of pain and the importance of a multidisciplinary approach to the effective management of chronic pain conditions. [ABSTRACT FROM AUTHOR]

Pregnancy-induced anti-nociception is a continuous dialogue between increased levels of endogenous opioids, activation of spinal kappa and delta receptors as well as altered hormonal concentrations. Pain of labour is a multi-factorial subjective algesic experience. It has two components: visceral and somatic. Understanding the interplay between various factors can help in developing newer pain-relieving strategies during labour. Labour pain is an excellent model of acute pain, which is highest on the pain rating scale when compared to other painful life experiences. The two major pathways that attenuate nociceptive inputs in the dorsal horn consist of local control from inhibitory interneurons and the descending inhibitory system from the supra-spinal level. Pain inhibitory neurotransmitters, such as serotonin, noradrenaline, glycine, and GABA, play an important role in pain modulation at the inhibitory interneurons and the descending pain inhibitory system. Labour pain is a nociceptive experience that not only involves inhibitory neurotransmitters but other contributing factors such as hormonal levels, previous experiences, stress, and socioeconomic factors. Visceral/peripheral factors are also important for the subjective experience of pain. Therefore, more studies are warranted to understand the role of pain inhibitory neurotransmitters in central and peripheral modulation of labour pain. [ABSTRACT FROM AUTHOR]

Pain is a complex experience consisting of sensory, affective, behavioural and physiological components. Pain management is therefore best achieved through an approach which acknowledges the complex interaction between biological, psychological and sociocultural factors. Effective pain management requires preoperative patient engagement and education in order to manage expectations and a structured inpatient service to facilitate evidence-based postoperative pain management and continuous staff education. Multimodal postoperative analgesia, built on an opioid-sparing ethos, is an essential component of perioperative pain management. Effective pain management facilitates early mobilization and a reduction in respiratory and cardiac complications and reduces the stress response to surgery which in turn improves wound healing and recovery. Inadequate pain control can lead to morbidity and mortality including prolonged hospital stays and the development of chronic postoperative pain. [ABSTRACT FROM AUTHOR]

Following a surgical procedure, pain is a physiological response which requires medical and nursing intervention. The physiological process of pain is described, with a specific review of the literature around the use of local anaesthetic following thoracic surgery as part of multi-modal care. [ABSTRACT FROM AUTHOR]

Central sensitization is a physiological mechanism associated with enhanced sensitivity and pain responses. At present, central sensitization cannot be determined directly In humans, but certain signs and symptoms may be suggestive of it. Although central sensitization has received increasing attention in the clinical literature, there is a risk that certain distinctions are being lost. This paper summarizes current knowledge of the physiology of central sensitization and its possible manifestations in patients, in order to inform a debate about the relevance of central sensitization for physical therapists. It poses 6 challenges associated with the application of central sensitization concepts in clinical practice and makes suggestions for assessment, treatment, and use of terminology. Physical therapists are asked to be mindful of central sensitization and consider potential top-down as well as bottom-up drivers, in the context of a person-centered bio-psychosocial approach. [ABSTRACT FROM AUTHOR]

In spite of systematic investigations, the existence of a specific cortex that could encode for the intensities of somatosensory stimuli, including within nociceptive ranges, is still a matter of debate. The present consensus is that pain is expressed in a distributed network made of thalamus, SII, insula, ACC, and, less consistently, SI. Here we argument that there must be an entrance to this network. The common denominator to every functional imaging study is that the subjects can distinguish between noxious and non-noxious stimuli, or between two different intensities of noxious stimuli. This is associated with a consistent activation of the insula-SII cortices while activations in other brain areas may be missing or sub-significant. In other words, the operculo-insular cortex activations are the most robust pain-related activations across studies, whatever the manipulation of the pain components, except the discriminative one. Intra-cerebral recordings also pointed out this piece of cortex as being able to encode for pain intensity. As a last physiological argument, stimulating directly the brain with small intensities standardized electrical shocks elicited pain sensations selectively if the electrode was in the operculo-insular cortex. Human models of disease confirmed that epileptic discharges in the insular cortex can produce ictal pain. Insular epilepsy (or propagation of discharges to the insular cortex) is the only focal epilepsy to be possibly associated with painful symptoms. Finally, unique and focal lesions of the posterior operculo-insular cortices were able to remove (or at least to impair) thermosensory and nociceptive functions. Thus, the operculo-insular area can be presented as the only area in the brain to respond to the features of a primary thermosensory and nociceptive cortex. This area is likely to be the starting point of the nociceptive-related networks. Future investigations are necessary to determine how this "pain symphony" between these different brain areas is temporally orchestrated. Developments of new targets for functional neurosurgery could benefit of such localized and initiating processes, for instance focal neurostimulations. [ABSTRACT FROM AUTHOR]

Abstract Pain is a complex experience consisting of sensory, affective, behavioural and physiological components. Pain management is therefore best achieved through an approach which acknowledges the complex interaction between biological, psychological and sociocultural factors. Effective pain management requires preoperative patient engagement and education in order to manage expectations and a structured inpatient service to facilitate evidence-based postoperative pain management and continuous staff education. Multimodal postoperative analgesia, built on an opioid-sparing ethos, is one component of postoperative pain management and is essential for achieving patient satisfaction and enhanced recovery. Effective pain management facilitates early mobilization and a reduction in respiratory and cardiac complications, reducing the stress response to surgery in turn improving wound healing and recovery. Inadequate pain control can lead to higher morbidity and mortality, prolonged hospital stays and the development of chronic postoperative pain. [ABSTRACT FROM AUTHOR]

Pain recognition, assessment, and management is a primary focus and an integral part of veterinary rehabilitation. Evidence-based pain mitigation protocols will use both pharmacologic tools and nonpharmacologic methods to create a customized, safe, and effective treatment plan. A multimodal, patient-centered approach will allow for the best outcomes for pain relief and improved quality of life., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Pain should be regarded as a complex experience consisting of sensory, affective, behavioural and physiological components. Pain management is therefore best achieved by an approach which acknowledges the complex interactions between biological, psychological and sociocultural factors. Effective pain management requires thorough patient preparation and education to manage expectations and a robustly structured inpatient service for postoperative pain management and continuous staff education. Postoperative analgesia is one component of postoperative pain management and is essential for achieving patient satisfaction and enhanced recovery. Effective pain management facilitates early mobilization and a reduction in respiratory and cardiac complications reducing the stress response to surgery in turn improving wound healing and recovery. Inadequate pain control can lead to higher morbidity and mortality, prolonged hospital stay and the development of chronic postoperative pain. [ABSTRACT FROM AUTHOR]

During the past decades, worldwide clinical and scientific interest in dry needling (DN) therapy has grown exponentially. Various clinical effects have been credited to dry needling, but rigorous evidence about its potential physiological mechanisms of actions and effects is still lacking. Research identifying these exact mechanisms of dry needling action is sparse and studies performed in an acupuncture setting do not necessarily apply to DN. The studies of potential effects of DN are reviewed in reference to the different aspects involved in the pathophysiology of myofascial triggerpoints: the taut band, local ischemia and hypoxia, peripheral and central sensitization. This article aims to provide the physiotherapist with a greater understanding of the contemporary data available: what effects could be attributed to dry needling and what are their potential underlying mechanisms of action, and also indicate some directions at which future research could be aimed to fill current voids. [ABSTRACT FROM AUTHOR]

The current understanding of pain processing mechanisms, the different pharmacologic drugs, and other nonpharmacologic means that can be used to manage postobstetric operation pain are reviewed. [Copyright &y& Elsevier]

Objectives: Pain neuroscience education (PNE) has been shown to be effective in reducing pain in people with chronic musculoskeletal pain. Knowledge of pain physiology is necessary to undertake PNE, and a measure for such knowledge is necessary. The Knowledge and Attitudes of Pain (KNAP), a comprehensive assessment of knowledge, attitudes, and beliefs regarding pain for healthcare practitioners, was developed in 2020 through the assessment of construct validity, reliability, and responsiveness in Dutch and English. This study aimed to conduct cross-cultural adaptation of the KNAP into Japanese and to verify test-retest reliability among Japanese undergraduate physical therapy and occupational therapy students., Methods: Cross-cultural adaptation was performed using Beaton's five-step process. Subsequently, the KNAP was completed by participants with a 2-week interval. The study included second-, third-, and fourth-year undergraduate physical therapy and occupational therapy students., Results: A total of 50 students participated in the pilot test and a Japanese version of KNAP was created. Thirty-nine students completed the Japanese version of KNAP twice. Of the 30 items on the KNAP, the quadratic weighted kappa value was less than 0.4 for only one item (item 15), but reliability was interpreted as sufficient for the overall score, with an intraclass correlation coefficient (95% confidence interval) for the total score of 0.89 (0.80-0.94)., Conclusions: This study has developed the Japanese KNAP, which has shown preliminary evidence of adequate test-retest reliability in Japanese undergraduate physical therapy and occupational therapy students., Competing Interests: CONFLICTS OF INTEREST: The authors report no conflicts of interest., (2022 The Japanese Association of Rehabilitation Medicine.)

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Background: Dry needling (DN) is often used for the treatment of muscle pain among physiotherapists. However, little is known about the mechanisms of action by which its effects are generated. The aim of this randomized controlled trial was to determine if the use of DN in healthy subjects activates the sympathetic nervous system, thus resulting in a decrease in pain caused by stress., Methods: Sixty-five healthy volunteer subjects were recruited from the University of Alcala, Madrid, Spain, with an age of 27.78 (SD = 8.41) years. The participants were randomly assigned to participate in a group with deep DN in the adductor pollicis muscle or a placebo needling group. The autonomic nervous system was evaluated, in addition to local and remote mechanical hyperalgesia., Results: In a comparison of the moment at which the needling intervention was carried out with the baseline, the heart rate of the dry needling group significantly increased by 20.60% (SE = 2.88), whereas that of the placebo group increased by 5.33% (SE = 2.32) ( p = 0.001, d = 1.02). The pressure pain threshold showed significant differences between both groups, being significantly higher in the needling group (adductor muscle p = 0.001; d = 0.85; anterior tibialis muscle p = 0.022, d = 0.58)., Conclusions: This work appears to indicate that dry needling produces an immediate activation in the sympathetic nervous system, improving local and distant mechanical hyperalgesia.

Postoperative pain is a major health care issue. Several factors have contributed to inadequate postoperative pain control, including a lack of understanding of preemptive pain management strategies, mistaken beliefs and expectations of patients, inconsistencies in pain assessment practices, use of as-needed analgesics that patients must request, and lack of analgesic regimens that account for inter-individual differences and requirements. Untreated acute pain has the potential to produce acute neurohumoral changes, neuronal remodeling, and long-lasting psychological and emotional distress, and may lead to prolonged chronic pain states. To effectively manage postoperative pain, nurses must be able to adequately assess pain severity in diverse patient populations, understand how to monitor physiological changes associated with pain and its treatment, be prepared to address the psychosocial experiences accompanying pain, and know the consequences of inadequate analgesia. It is important for nurses to be aware of relevant research and evidence-based guidelines that are available to guide pain assessments and patient-monitoring practices. [Copyright &y& Elsevier]

1. In anesthetized rats, recordings were made within the medullary subnucleus reticularis dorsalis (SRD) from neurons that exhibited convergence of nociceptive inputs from the entire body. Neurons with total nociceptive convergence (TNC) responded to suprathreshold percutaneous electrical stimuli (2-ms duration) with an early and a late peak due to activation of A delta- and C-fibers, respectively, no matter which part of the body was stimulated. Neurons with partial nociceptive convergence (PNC) responded to the same stimuli with an A delta-peak regardless of which part of the body was stimulated and with a C-peak of activation from some, mainly contralateral, parts of the body. The characteristics of the responses of these neurons to the application of graded intensities of electrical, thermal, and mechanical stimuli were analyzed. 2. All TNC neurons and 85% of PNC neurons responded to A delta- and C-fiber activation following percutaneous electrical stimulation of the contralateral hindpaw. With regard to A delta-fiber-evoked responses, a linear relationship between the logarithm of the applied current and the magnitude of the responses was found within the 0.25- to 6.0-mA and 0.5- to 24-mA ranges for TNC and PNC neurons, respectively; however, these curves were essentially similar. With regard to C-fiber-evoked responses, such a linear relationship was found within the 1.5- to 6.0-mA range for both types of SRD neurons, although the TNC neurons presented larger C-fiber-evoked responses than did the PNC neurons. 3. TNC and PNC neurons linearly increased their discharges during the application of noxious thermal stimuli to the contralateral hindpaw within the range 44-52 degrees C; the mean responses evoked by noxious heat from TNC neurons were of higher magnitude than those from PNC neurons. The majority of SRD neurons presented long-lasting afterdischarges, especially with the highest temperature employed (52 degrees C). 4. TNC neurons monotonically increased their discharges during graded mechanical or thermal stimulation of the tail. When mechanical stimuli were applied, a linear relationship was found between the logarithm of the strength of the mechanical stimulus and the neuronal discharges, in the 5.3- to 7.4-N/cm2 range. With thermal stimulation, TNC neurons linearly increased their discharges in the 44-52 degrees C range. When increasing amounts of the tail were immersed in a 50 degrees C waterbath, TNC neurons increased their discharges within a restricted range of tail surface areas (0.9-5.7 cm2); further increases in the stimulated surface size were not followed by increases in firing rate.(ABSTRACT TRUNCATED AT 400 WORDS)

Two cross-sectional studies were made of the recovery of tactile and pain sensitivity in subjects having skin flaps in the region of the chest and neck as a result of tumor excision. In experiment 1, stimuli ranging from 2.46 to 17.10 gm of force were delivered by von Frey hairs to the flaps and comparable normal sites in 35 subjects at times ranging from 1 month to 10 years after surgery. No subjects perceived stimuli of less than 11.80 gm, thermal, or moving touch applied to flaps, whereas 21 percent perceived 11.80 gm or greater force (judged as painful applied to normal skin). The results of experiment 2 showed that these findings were not due to visual information available to subjects. Possible explanations for the fact that these results are radically different from those reported in the literature are discussed.

New approaches in the design of analgesics emerged from the discovery that serotonin (5HT) is involved in the descending system (brain to spinal cord) that inhibits signals from peripheral nociceptors. However, the simple hypothesis that 5HT is a transmitter in this system requires elaboration, since not all agonists of 5HT are analgesics. In this commentary, the following questions are discussed: (a) do 5HT systems influence all responses to all types of noxious stimuli?, (b) is a 5HT synapse a necessary link in the analgesic system, (c) what is the location of the relevant 5HT receptor?, and (d) what is the relevant 5HT receptor subtype? The need for more adequate definition of the relevant 5HT receptor is stressed. Once this is achieved, a more rational approach to analgesic drug discovery will be provided by the design of selective agonists of this receptor.

The threshold of flinch-jump response to electric footshock was measured after adrenalectomy (ADX) in male albino rats. The ADX-rats showed higher threshold from the 2nd to 6th postoperative days than the sham-operated animals. Daily subcutaneous administration of 100 micrograms/100 g b.w. corticosterone (CS) led to restoration of the footshock sensitivity of ADX-rats. The same effect was observed following dexamethasone (DEX) treatment. DEX but not CS administration resulted in a decrease of the footshock sensitivity in the sham-operated rats. On the 9th and 18th days after adrenalectomy, in contrast to the early postoperative period, the threshold for footshock sensitivity was significantly lower than in sham-operated controls. It is suggested that an excess release of endogenous opiates from the pituitary are involved in the changes of pain threshold under the conditions studied.

Envisaging the phenomenon of pain within the concept of systems theory, different, mutually coherent system levels can be noted of interest, namely the existential person level, the psychological behavioural level and the organismal neurophysiological level. Viewed from this angle, and considering pain to be a signal indicating the whole system's integrity being threatened, the experience of pain can be seen as associated with an intrinsic system function: the pain function. This function is initiated in painful conditions with respect to the system as a whole, rather than being a symptomatic phenomenon lodged--in terms of cause and effect--in distinct system levels. The syndrome of chronic pain may therefore be regarded as a specific state resulting from a pathological derangement in the course of that function. In respect of the different ways in which the system, by way of this function, can cope with a painful event, various possible correlations may be pointed out with regard to the conditions of the system levels in concern. As to the specific course of the pain function--the system's 'answer' to the threatening condition--the pre-existing state of system's integrity can be proposed to be of major importance; the integrity being in clinical terms consonant with a given state of 'health'. Thus chronic pain may be considered as a pathological state resulting from the reaction to painful conditions of an already unhealthy individual. In view of this concept on (chronic) pain several implications can be pointed out with regard to the leading notions on chronic pain, as well as to the general therapeutic approach to be considered.

The axonal tract tracing technique using the transport in both the retrograde and orthograde directions of wheat-germ agglutinin conjugated to horseradish peroxidase permitted the observation of both retrogradely labelled spinal neurons and anterogradely labelled thalamic fiber terminals in the same animal after injections of the compound in the nucleus reticularis gigantocellularis, thus allowing the definition of the spino-reticulo-thalamic pathway which relays in this nucleus in the rat. Results of the present study are in favor of the existence of a pathway originating mostly in the spinal ventral horn and ending in the intralaminar nuclei of the thalamus, in particular in the nucleus center median, after a relay in the nucleus reticularis gigantocellularis. Origin and termination of this pathway seem to be well differentiated from those of the direct spino-thalamic tract. The results are discussed with reference to the possible involvement of this pathway in some aspects of pain transmission. It is suggested, in particular, that the direct spino-thalamic system which relays in the thalamic ventrobasal complex, presents the features required of a structure playing a role in the sensory-discriminative aspects of pain transmission; in contrast, the spino-reticulo thalamic system defined here could be involved in some motor and/or behavioral responses related to pain.

The selective vulnerability of myelinated axons in lesions of peripheral nerve is incompletely understood and appears somewhat at variance with the energy conservation attached to saltation in these fibers. We evaluated the relative energy requirement of resting A and C fibers in rabbit vagus nerve by measuring the amplitude of the components of the compound action potential at 5-10 min intervals during incubation in Ringer-bicarbonate solutions containing 0-20 mM glucose. In nerves in which the perineurial sheath was retained intact the A components remained at control amplitude with 20 mM glucose but, after a plateau period, declined increasingly rapidly with 5, 2, 1, 0.5 and 0 mM glucose. 2mM glucose sufficed to maintain control amplitude of the C fiber component. In desheathed nerves the A component remained at control amplitude with 5 mM glucose but declined increasingly rapidly with 2, 1, 0.5 and 0 mM glucose; 0.5 mM glucose sufficed to maintain control amplitude to C fibers. The depressed potentials generally recovered incompletely after transfer to glucose 5 mM (desheathed) or 20 mM (sheathed); however, the partial recovery was more rapid and more nearly complete in the C fiber group than in the A fiber group (P less than 0.05). The data demonstrate that resting A fibers are much more susceptible to energy lack in vitro than resting C fibers. This suggests that deprivation of energy may be a factor in the preferential destruction of large fibers, termed fiber dissociation, which characterized several syndromes of chronic pain.

A case is reported in which initial anginal pain was localized to the area of the left posterior teeth. Subsequently the patient reported that at certain times he experienced pain in the area of the left posterior teeth with concomitant chest pain while at other times the pain was confined to the teeth.

Rat were exposed to 80% nitrous oxide in oxygen for 1 and 18 h. Met-enkephalin levels in the dorsal raphé, medial thalamus, periaqueductal grey, raphé magnus and locus coeruleus were measured by radioimmunoassay in control and treated animals. There was no change in Met-enkephalin levels at either time point in any of the brain areas examined.

1. The response properties of neurons of the spinocervicothalamic pathway were studied in anesthetized macaque monkeys. Graded innocuous and noxious mechanical stimuli, including sinusoidal vibration and thermal pulses, were applied to the cutaneous receptive fields. 2. Forty-nine cells in the lateral cervical nucleus (LCN) were identified by antidromic activation from the ventral posterior lateral (VPL) nucleus of the contralateral thalamus. Twelve spinocervical tract (SCT) cells in the lumbosacral enlargement of the spinal cord were identified by antidromic activation from stimulation of the ipsilateral dorsolateral funiculus below C3 but not above C1. 3. Latencies for antidromic activation of LCN neurons averaged 2.3 ms, corresponding to a mean conduction velocity of approximately 17 m/s. Mean latency for orthodromic activation of LCN neurons following electrical stimulation of peripheral nerves was 12.6 ms. Overall mean conduction velocity for the monkey spinocervicothalamic pathway was estimated to be 29 m/s. 4. Most LCN cells had receptive fields on hairy skin, but some had input from glabrous skin and a few had subcutaneous fields. The receptive fields of most SCT cells had a glabrous skin component. Receptive fields tended to be smaller for SCT than LCN cells even for fields on a comparable part of the distal hindlimb. 5. Based on their responses to a series of mechanical stimuli (brushing, pressure, pinch, and squeeze), LCN and SCT cells were classified as low-threshold (LT), wide dynamic range (WDR), or high-threshold (HT) neurons. Most of the cells were in the LT or WDR classes. Thus the spinocervicothalamic pathway in the monkey differs from the spinothalamic tract (STT), in that STT cells are generally of the WDR or HT classes. 6. With the use of discriminant analysis, LCN and SCT neurons were allocated to categories determined from a k-means cluster analysis of the responses of 318 STT cells. The LCN and SCT neurons were in different proportions in the various categories than were STT cells, suggesting differences in the signaling properties of the spinocervicothalamic and spinothalamic paths. 7. Innocuous steady indentation of the skin failed to excite any of the neurons tested. Thus no positive evidence was obtained for an input to LCN neurons from slowly adapting mechanoreceptors. 8. Sinusoidal vibratory stimuli were used to test the ability of LCN and SCT neurons to follow repeated innocuous mechanical stimuli. Vibration at 10 Hz and an amplitude of 100 micron resulted in repetitive discharges in most LCN neurons and half the SCT neurons tested; many LCN neurons had thresholds below 25 micron.(ABSTRACT TRUNCATED AT 400 WORDS)

Thresholds of two behavioral responses to noxious pressure of the hindpaws (withdrawal, vocalization) were analyzed before and 3 weeks after a lesion of various quadrants of the spinal cord at the cervical level. The threshold of the spinal reflex could not be modified. Threshold of vocalization elicited by the pressure of one hindpaw was significantly increased when, and only when, the opposite ventrolateral quadrant was cut. These results emphasize the role of the lateral spinothalamic tract in the transmission of noxious messages.

1. Recordings were made from 67 neurons in the nucleus gracilis (NG) of anesthetized macaque monkeys. All of the cells were activated antidromically from the ventral posterior lateral (VPL) nucleus of the contralateral thalamus. Stimuli used to activate the cells orthodromically were graded innocuous and noxious mechanical stimuli, including sinusoidal vibration and thermal pulses. 2. The latencies of antidromic action potentials following stimulation in the VPL nucleus were significantly shorter for cells in the caudal compared with the rostral NG. The mean minimum afferent conduction velocity of the afferent conduction velocity of the afferent fibers exciting the NG cells was 52 m/s, as judged from the latencies of the cells to orthodromic volleys evoked by electrical stimulation of peripheral nerves. The overall conduction velocity of the pathway from peripheral nerve to thalamus was approximately 40 m/s. 3. Cutaneous receptive fields on the distal hindlimb usually occupied an area equivalent to much less than a single digit. However, a few cells had receptive fields up to or exceeding the area of the foot. 4. NG cells were classified by their responses to graded mechanical stimulation of the skin as low threshold (LT) or wide dynamic range (WDR). No high-threshold NG cells were found. A special subcategory of pressure-sensitive LT (SA) neurons was recognized. Many of these cells were maximally responsive to maintained indentation of the skin. The sample of NG cells differed from the population of primate spinothalamic and spinocervicothalamic pathways so far examined, in having a larger proportion of LT neurons and a smaller proportion of WDR cells. A few NG cells responded best to manipulation of subcutaneous tissue. 5. Discriminant analysis permitted the NG cells to be assigned to classes determined by a k-means cluster analysis of the responses of a reference set of 318 primate spinothalamic tract (STT) cells. There were four classes of cells based on normalized responses of individual neurons and another four classes based upon responses compared across the population of cells. The NG cells were allocated to the various categories in different proportions than either primate STT cells or spinocervicothalamic neurons, consistent with the view that the functional roles of these somatosensory pathways differ. 6. Some of the pressure-sensitive NG cells were excited when the skin was stretched, suggesting an input from type II slowly adapting (Ruffini) mechanoreceptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrical stimulation of medial brainstem sites produces potent analgesia in rats that is either opioid- or non-opioid-mediated depending on the specific brain region stimulated. Footshock stress also causes opioid and non-opioid forms of analgesia in rats depending on the exact parameters of footshock administered. We now report that opioid, but not non-opioid, stress analgesia demonstrates cross-tolerance with opioid, but not non-opioid, stimulation-produced analgesia. This finding suggests that opioid forms of stimulation-produced and stress-induced analgesia share a common substrate.

Pain-related somatosensory evoked potentials (SEPs) following CO2 laser stimulation were analyzed in normal volunteers. Low power and long wavelength CO2 laser stimuli to the hand induced a sharp pain which was associated with a large positive component, P320, recorded over the scalp. Amplitude decreased and latency increased with reduction in stimulus intensity and subjective pain feeling. P320 was maximal at the vertex but was distributed widely over the scalp. There were no topographic differences between left- and right-hand stimulation, or between hand and chest stimulation. Lidocaine injection to produce anesthetic nerve block resulted in loss of P320, but the potential was relatively preserved during ischemic nerve block. No potential corresponding to P320 could be recorded following electrical or mechanical tactile stimulation. We consider P320 to be generated by impulses arising from pain stimuli and ascending through A delta fibers. We propose the thalamus as a generator source from considering its scalp topography, but pain-specific cognition or perception may also be involved in generating this potential.

Tactile, two-point discrimination, thermal change detection and heat pain thresholds as well as oral stereognostic ability, warmth scaling and heat pain tolerance were compared in a group of 72 subjects with burning mouth syndrome (BMS) and 43 age- and sex-matched control subjects. No differences were found between the BMS and control subjects for any of the sensory modalities tested except for heat pain tolerance. Pain tolerance was significantly decreased for the BMS subjects at the tongue tip, a site of clinical pain in approximately 85% of the subjects tested in this study, but not at the cutaneous lower lip which was a site of pain only in approximately 17% of the subjects tested in this study. In addition, no differences in heat pain tolerance were found at the cutaneous lower lip between the control subjects and the BMS subjects who reported pain on the mucosal lower lip (approximately 49% of subjects), but heat pain tolerance was significantly decreased at this site for those BMS subjects tested without pain on the mucosal lower lip (approximately 51% of subjects). These findings do not suggest a psychogenic origin for the alteration of heat pain tolerance in the BMS subjects, but suggest instead specific changes in their peripheral or central sensory functions.

Extracellular action potentials were recorded from antidromically identified, tonically firing cells in the hypothalamic paraventricular nucleus (PVN) of ovariectomized, estrogen-treated female rats under urethane anesthesia. Genital or somatic sensory stimuli, or electrical stimulation of the nerves innervating the pelvis were applied. Uterine horn or vaginal distension each excited 33% of the neurons tested. Probing of the cervix had no effect. Hindpaw pinch produced excitation in 39% and inhibition in 11% of the neurons tested. Non-noxious somatic stimuli had no effect. Stimulation of the uterine afferent nerves, the hypogastric and pelvic nerves, excited 55% and 30% of the neurons tested, respectively. Stimulation of a somatic nerve of the hindleg, the sciatic nerve, activated 80% of the neurons tested. These results indicate that specific sensory afferents arrive at the PVN from the uterus; in addition, somatic afferents converge in this hypothalamic nucleus.

A recent model for control of spinal and medullary nociceptive neurons (Basbaum and Fields, 1984) incorporates a gamma-aminobutyric acid-ergic (GABA-ergic) cell into this circuitry and indicates that such elements could act as one substrate for presynaptic inhibition of primary afferents. This concept is supported by a variety of pharmacological and electrophysiological studies. We therefore examined the distribution of GABA-ergic activity in trigeminal subnucleus interpolaris (Vi) by focusing on the types of cells, together with dendritic and synaptic profiles, that are immunocytochemically labeled with an antiserum against glutamic acid decarboxylase (GAD). GAD occurred throughout Vi but was most concentrated in the ventrolateral quadrant and interstitial nucleus. It was localized to groups of small neurons with two to three primary dendrites, and within numerous punctate profiles suggestive of synaptic elements. Electron microscopy revealed labeled dendrites, some of which were postsynaptic to scalloped terminals of presumptive primary afferents. Other labeled dendritic elements, which were quite variable in size, engaged both GAD-labeled and unlabeled synapses. Most GAD synapses displayed clear round vesicles and formed contacts with unlabeled perikarya and a variety of dendritic processes. Numerous GAD-positive synapses were also incorporated into axoaxonic clusters, in which the GAD element was presynaptic to scalloped terminals. Others engaged in serial arrays with other unlabeled terminals, which, in turn, were presynaptic to dendrites. Occasionally, GAD synapses formed contacts with GAD-positive dendrites. These data show that GABA is localized to a variety of neuronal elements in ventrolateral Vi and the interstitial nucleus. These occur in spatial arrangements providing an anatomical substrate for postsynaptic modulation of activity in this area. GABA terminals also appear to be involved in a presynaptic inhibitory mechanism, which may, in some instances, affect transmission in primary afferents.

Exposure to painful or stressful stimuli produces an analgesic reaction which can persist for 1-2 h post-stress. In the typical stress-induced analgesia study the subject is not permitted to alter or exert control over the aversive event to which it is exposed. That is, its behavior affects neither the duration or intensity of the event. The experiments reported here attempted to determine whether this inability of the subject to control the aversive event is an important determinant of stress-induced analgesia, or whether simple exposure to painful events is a sufficient condition for its production. In the first experiment rats were given either escapable electric shocks (the subject's behavior could terminate the shock), equal amounts of inescapable shock, or no shock. Tail-flick to radiant heat was assessed 30 min later. The group given inescapable shock was strongly analgesic, while the group given an equal amount of escapable shock was only mildly analgesic. Thus the controllability of the shock or the availability of a coping response determined the antinociceptive reaction which followed. The second experiment revealed that this differential effect of controllability on tail-flick responding is masked, shortly after the end of the shock session, by a transient analgesic effect of shock which is not sensitive to the controllability dimension. The implications of these results for stress-induced analgesia and the activation of opioid systems are discussed.

Neonatal administration of monosodium glutamate (MSG) produces in rats neurotoxic degeneration of the circumventricular system, including the medial-basal hypothalamus, depleting several neuropeptides and neurotransmitters in this area. In addition, a number of behavioral and neuroendocrine responses are impaired, including a significant decrease in the analgesic response to cold-water swims (CWS). The present study examined whether the alterations in the analgesic responses following CWS and 2-deoxy-D-glucose (2-DG) induced by neonatal MSG treatment were due either to direct alterations in a pain-inhibitory system, or alternatively, to alterations in a system that processes the stressful consequences or properties of a stimulus. To accomplish this, the analgesic, hypothermic, and locomotor responses following CWS and the analgesic, hyperphagic, and locomotor responses following 2-DG were assessed in rats treated neonatally (days 2, 4, 6, 8, and 10) with either MSG or a vehicle solution. MSG-treated rats displayed significant reductions in both their analgesic and hypothermic responses following CWS, suggesting that MSG treatment impairs an animal's ability to process sufficiently the stimulus properties of the swim as stressful. While MSG treatment potentiated 2-DG analgesia, it reduced 2-DG hyperphagia, suggesting that MSG treatment also impairs coping responses to glucoprivation. These data indicate the importance of the circumventricular system in the coding of stimuli as potential stressors and in the subsequent activation of requisite systems necessary to provide a sustained, coordinated, and synchronous coping response.

Spontaneous discharges and nociceptive responses of 47 parafascicularis thalami (PF) neurons were recorded extracellularly and comparisons were made between the effects of these discharges following focal dorsal raphe stimulation (DRS) and bilateral pinnal electrical stimulation (PES). Eighty-three percent of PF neurons (N = 39) responded to noxious stimulus, about 69% of the PF responsive cells (N = 27) were excited during noxious stimuli and thus categorized as "nociceptive-on" cells. The remaining 31% (N = 12) were suppressed by the noxious stimuli, and were categorized as "nociceptive-off" cells. DRS and PES attenuated the spontaneous activity of the "nociceptive-on" neurons as well as the noxious input to these cells, while the spontaneous activity of the "nociceptive-off" cells was suppressed only following DRS and not following PES. Moreover, PES displayed disinhibiting properties, namely, it reduced the suppression effects elicited by noxious input. In conclusion, it was demonstrated that both focal DRS and noninvasive PES were effective in modulating pain input to single neurons in the PF.