Heterotopic nociceptive EMG-reactions in M. masseter

Peculiarities of EMG-reactions of m. masseter to noxious homo- and heterotopic stimulation were studied on healthy volunteers. Homotopic noxious electrical stimulation of n. mentalis elicited several successive responses in m. masseter consisting of R-component, early exteroceptive suppression period, early excitation period, late exteroceptive suppression period, and late excitation period. Heterotopic noxious stimulation (forehead, ear lobe, index finger) induced only the late exteroceptive suppression period and late excitation period. It is concluded that the excitatory components have a reflex nature, and that the late exteroceptive suppression period is formed under the effect of central cerebral structures, which mediate their influence via the spinal-corticospinal return loop.     

Exteroceptive suppression of the trapezius muscle produced by mental nerve stimulation in normal subjects.

The purpose of the present study was to evaluate the similarities and differences in exteroceptive suppression produced by mental nerve stimulation between the masseter and trapezius muscles. Six normal subjects were studied using various intensities of stimulation. Although the duration and degree of exteroceptive suppression were increased with stimulus intensity in the masseter muscle, they did not correlate with stimulus intensity in the trapezius muscle. The latency and duration in the trapezius muscle were almost the same as those in the masseter muscle. The degrees in the masseter muscle were significantly larger than those in the trapezius muscle. Exteroceptive suppression of the trapezius muscle might have a similar mechanism as that of the masseter muscle, but it may be mediated by the separate interneurons. The projection from the trigeminal afferent to the trapezius motoneuron might be smaller than that to the masseter motoneuron.     

Interactive effects of catastrophizing and suppression on responses to acute pain: a test of an appraisal × emotion regulation model

We examined whether people who tend to catastrophize about pain and who also attempt to regulate negative thoughts and feelings through suppression may represent a distinct subgroup of individuals highly susceptible to pain and distress. Ninety-seven healthy normal participants underwent a 4-min ischemic pain task followed by a 2-min recovery period. Self-reported pain and distress was recorded during the task and every 20 s during recovery. Participants completed the Pain Catastrophizing Scale and the White Bear Suppression Inventory. Repeated measures multiple regression analysis (using General Linear Model procedures) revealed significant 3-way interactions such that participants scoring high on the rumination and/or helplessness subscales of the Pain Catastrophizing Scale and who scored high on the predisposition to suppress unwanted thoughts and feelings reported the greatest pain and distress during recovery. Results suggest that pain catastrophizers who attempt to regulate their substantial pain intensity and distress with maladaptive emotion regulation strategies, such as suppression, may be especially prone to experience prolonged recovery from episodes of acute pain. Thus, emotion regulation factors may represent critical variables needed to understand the full impact of catastrophic appraisals on long-term adjustment to pain.     

Brainstem evaluation in children with primary nocturnal enuresis

We investigated the brainstem integrity in children with primary nocturnal enuresis (PNE) using auditory brainstem responses (ABR), blink reflex and exteroceptive suppression of the masseter muscle. We examined 23 children with PNE (16 male, 7 female; mean age: 10.4 years) and 19 control subjects (11 male, 8 female; mean age: 11.8 years). ABR parameters such as wave latencies, amplitudes and interpeak latencies and blink reflex parameters such as R1 and R2 amplitude and latencies were not significantly different between the 2 groups. Although S2 parameters of the exteroceptive suppression of the masseter muscle were easily and completely obtained from the control subjects, in the PNE group S2 onset latency and duration were not recorded in 26% of the study children (n = 6) (P = 0.01). S2 duration time was significantly lowered in the enuretic group (left side: P = 0.001 and right side: P = 0.003). S2 duration time changes in the enuretic group supports a possible brainstem dysfunction in children with PNE.     

肾素-血管紧张素系统构建在高血压胚胎起源学说中的重要性

流行病学资料表明,低出生全重儿是成年期高血压等诸多疾病发生的高危因素[1].     

Cardiopulmonary baroreflex stimulation and blood pressure-related hypoalgesia

Results from both experimental animals and humans suggest that baroreflex stimulation may be involved in blood pressure-related hypoalgesia. However, most of this research, especially in the area of human experimentation, has focused on sinoaortic baroreceptors. Cardiopulmonary baroreflex stimulation may also be an important moderator of pain. Sixty-six healthy male undergraduates varying in risk for hypertension participated in an experimental protocol in which painful mechanical finger pressure was presented three times in a counterbalanced fashion. One pain stimulus was preceded by 6 min of supine rest, another by a period of rest interspersed with periodic Valsalva manoeuvres, and another by a period in which cardiopulmonary baroreceptors were stimulated by passive leg elevation. Significantly lower pain was reported by men with relatively elevated systolic blood pressure following leg elevation but not the other conditions. Cardiopulmonary baroreflex stimulation was documented by increased forearm blood flow and other data obtained via impedance cardiography. These results suggest that blood pressure related hypoalgesia may be at least partially related to cardiopulmonary baroreflex stimulation.     

Participation of the hippocampus in the facilitatory effect of an exteroceptive stimulus on milk ejection

Summary The auditory exteroceptive stimulus emanating from a lactating rat and the litter while suckling was used to facilitate milk ejection in another induced mother suckled by her own litter. Sectioning of the tractus corticohypothalamicus medialis (TCM) or the columns of the fornix, prevented the facilitatory effect of the exteroceptive stimulus on milk ejection. Sham operated induced mothers gave significantly more milk than non-induced rats. Electrolytic lesioning of the stria terminalis did not affect normal milk ejection nor the response to the exteroceptive stimulus. It is proposed that the hippocampus through the TCM may facilitate the suckling-induced milk ejection when an appropiate exteroceptive stimulus is applied. Neither the lesion of the stria terminalis nor the section of the fornix or the TCM seems to alter the normal suckling-induced milk ejection. A general modulatory role of the limbic system is described.     

Suppression of pain-related thoughts and feelings during pain-induction: sex differences in delayed pain responses

Women tend to report greater acute and chronic pain intensity than men, and various mechanisms have been proposed to account for these sex differences. Suppression has been related to amplified pain intensity, and thus we examined whether sex differences in the use of suppression partly explained the discrepancy between men and women on pain report. Participants (N = 222; women: 55%) underwent a cold pressor, during which half the sample was randomly assigned to suppress pain-related thoughts and feelings and the other half was not. A 2-min recovery period followed the cold pressor. Ten min later, all participants were exposed to another physical stimulus (a massage device). Significant condition × Sex interactions were found for pain intensity, sensory ratings from the McGill Pain Questionnaire and unpleasantness ratings for the massage device, such that: (a) men in the No Suppression condition reported lower pain and unpleasantness than women in the same condition; (b) men in Suppression condition reported greater pain and unpleasantness then men in No Suppression condition, but equivalent pain and unpleasantness to women in No Suppression condition; (c) differences between men and women on pain in No Suppression condition were partly mediated by women’s report of greater spontaneous use of avoidance/suppression during the cold pressor. Results using an “addition” paradigm (i.e., manipulating use of suppression) and a “take away” (i.e., mediation) paradigm converge to suggest that women spontaneously use suppression to regulate pain more than men, and that the differential use of suppression partly explains the tendency for women to report greater pain intensity than men.     

Acquisition of conditioned suppression and responsivity to thermal stimulation in spontaneously hypertensive,renal hypertensive and normotensive rats

The acquisition of conditioned suppression of instrumental responding and responsivity to thermal stimulation were assessed in spontaneously hypertensive rats of the Okamoto-Aoki strain (SHRs), renal hypertensive rats of the Wistar-Kyoto strain (WKYs), and normotensive WKY rats. Spontaneously hypertensive rats showed significantly faster acquisition of conditioned suppression than age-matched WKY normotensive rats. This acquisition difference between SHRs and normotensive WKYs was maintained even following chronic preexposure to shock alone; a treatment that retarded normal acquisition of conditioned suppression. In contrast, renal hypertensive WKYs acquired conditioned suppression at the same rate as age-matched normotensive WKYs. Spontaneously hypertensive rats and renal hypertensive WKYs both showed significantly longer latencies than normotensive WKYs to respond to thermal stimulation using a hot-plate assay. These outcomes suggest that the relationship between blood pressure and the acquisition of conditioned suppression in SHRs is either pleiotrophic or a consequence of random fixation, and that acquisition of conditioned suppression may serve as a valuable marker variable of hypertension in the SHR. The dissociation between acquisition of conditioned suppression and responsivity to thermal stimulation suggests that different mechanisms may mediate nociceptive responses to shock and thermal stimulation in these models of hypertension.     

The effect of an exteroceptive stimulus on the concentration of melanocyte-stimulating hormone in the pituitary of lactating rats

1. A study was made of the effect of an exteroceptive stimulus, produced by a team of lactating rats and of litters while suckling, on the pituitary melanocyte-stimulating hormone (MSH) activity of a group of lactating rats.2. After being isolated for 9 hr from their litter, one group of lactating rats was killed after being allowed to nurse for 30 min, another group was subjected to the exteroceptive stimulus for 15 min and then killed. Control rats were killed after 9 hr of isolation from the litter without being subjected to either suckling or the exteroceptive stimulus.3. The group of rats which had suckled their young showed a pituitary MSH activity equal to 35 +/- 2.29%, and the group exposed to the exteroceptive stimulus an activity equal to 59.5 +/- 3.16% of that in the control animals.4. When deaf rats were used, only the suckled mother showed a decrease of the pituitary MSH activity which was similar to that obtained with the normal suckled mother, indicating that the exteroceptive stimulus depended on hearing for its effect.5. A light dose of sodium pentobarbitone was sufficient to block the effect of suckling and the auditory stimuli on the pituitary MSH activity.6. The role of the central nervous system in this phenomenon and the possibility that MSH is implicated in the process of lactation are discussed.     

Exaggeration of blood pressure-related hypoalgesia and reduction of blood pressure with low frequency transcutaneous electrical nerve stimulation

Reduced pain perception has been observed in hypertensive individuals and normotensive individuals at risk for high blood pressure and may involve increased endogenous opioid release or receptor sensitivity. The present study examined the issue by administering two subjectively similar but physiologically different forms of the pain-reducing procedure transcutaneous electrical nerve stimulation (TENS). Men varying in resting blood pressure and parental history of hypertension participated in three testing sessions during which was presented (a) high-frequency (100 Hz) TENS; (b) low-frequency (2 Hz) TENS, the type believed to elicit endogenous opioid activity; or (c) no-TENS stimulation. Measurements of blood pressure (BP) and other physiological variables were obtained during this period. Afterwards, two pain stimuli were presented: a series of electric shocks and 5 min of arm ischemia. There was a significant negative association between pain and resting systolic blood pressure (SBP), and pain and parental history of hypertension in the no-TENS and high-frequency TENS conditions that was significantly strengthened by administration of low-frequency TENS. As well, low-frequency TENS produced a modest but significant acute reduction in SBP, especially among those with higher resting levels. These results provide further evidence that opioid mechanisms are involved in blood pressure-related hypoalgesia and blood pressure regulation.     

Empirical contributions

To evaluate the possible negative association between risk for hypertension and pain sensitivity in women, 24 healthy young adult women with a parental history of hypertension and 24 without a parental history of hypertension participated in 2 laboratory sessions in which electric shock and the cold-pressor test were administered. To assess the possible role of stress-induced analgesia in blood pressure-related hypoalgesia, the sessions were identical with the exception of the fact that participants were exposed to a stressful 20-min videogame before the pain stimuli on one occasion and a nonstressful control task on the other. Women with a parental history of hypertension and high blood pressure reactivity to the videogame displayed a reduced sensitivity to electric shock on both days, suggesting that risk for hypertension is associated with reduced sensitivity to at least some pain stimuli in women. Blood pressure reactivity to stress-associated baroreceptor stimulation was not implicated as a mediator of decreased pain perception. However, other analyses revealed an effect of family history on shock pain only among women who reported relatively high anxiety, suggesting that other aspects of the stress response may be involved in this phenomenon. This research was supported by the Heart and Stroke Foundation of Quebec and an Academic Challenge grant from the state of Ohio     

Anger inhibition and pain: conceptualizations, evidence and new directions

Anger and how anger is regulated appear to affect acute and chronic pain intensity. The inhibition of anger (anger-in), in particular, has received much attention, and it is widely believed that suppressing or inhibiting the verbal or physical expression of anger is related to increased pain severity. We examine theoretical accounts for expecting that anger inhibition should affect pain, and review evidence for this claim. We suggest that the evidence for a link between trait anger-in (the self-reported tendency to inhibit anger expression when angry) and acute and chronic pain severity is quite limited owing to a number of factors including a inadequate definition of trait anger-in embodied in the popular anger-in subscale of Spielberger's Anger Expression Inventory, and a strong overlap between trait anger-in scores and measures of general negative affect (NA). We argue that in order to determine whether something unique to the process of anger inhibition exerts direct effects on subsequent pain intensity, new conceptualizations and approaches are needed that go beyond self-report assessments of trait anger-in. We present one model of anger inhibition and pain that adopts elements of Wegner's ironic process theory of thought suppression. Findings from this emerging research paradigm indicate that state anger suppression (suppression manipulated in the laboratory) may indeed affect sensitivity to subsequent painful stimuli, and we outline potentially productive avenues of future inquiry that build on this model. We conclude that although studies employing correlational designs and self-reports of trait anger-in have not upheld the claim that anger inhibition affects pain severity, evidence from studies using new models suggests that actually inhibiting anger expression during a provocative event may increase perceived pain at a later time.     

Decreased pain perception and risk for hypertension: considering a common physiological mechanism.

For almost two decades, researchers have demonstrated that hypertension is reliably associated with decreased perception of pain. More recently, a growing body of evidence has begun to suggest that hypoalgesia is not a consequence of high blood pressure, as the phenomenon precedes the onset of hypertension in individuals at risk for the disorder. This article provides a review of empirical evidence of decreased pain perception in normotensive persons with a family history of hypertension, elevated resting blood pressure, or exaggerated cardiovascular reactivity to stress. Based on the existing evidence, hypoalgesia is argued to be a correlate of dysregulation of central nervous system structures involved in both pain control and cardiovascular regulation in individuals who are genetically predisposed to develop high blood pressure. As such, hypoalgesia may serve as a valuable method of identifying individuals at greatest risk for hypertension.     

The effect of an exteroceptive stimulus on milk ejection in lactating rats

1. The exteroceptive stimulus emanating from a lactating rat and the litter while suckling was used to induce milk ejection in another lactating mother 15 min before the replacement of her own litter. The effect of the external stimulus on milk ejection during one 30 min period and four 15 min periods of nursing was studied.2. After being isolated for 9 hr the litter from the mother subjected to the exteroceptive nursing stimulus (induced rat) obtained a significantly greater amount of milk during 30 min of nursing than that obtained by the litter from the control mother.3. When deaf mother rats were used the gain of milk by the litter showed no difference between the control and the induced mother. This result indicated that the effective external stimulus is an auditory one and is probably produced by the mother rat and the young while suckling.4. The administration of oxytocin (Syntocinon, Sandoz) 20 m-u./100 g body wt., 15 min before the replacement of the litter produced a milk ejection similar to that obtained under the influence of the auditory stimulus. This would indicate that the exteroceptive stimulus probably evokes the release of oxytocin from the neurohypophysis.5. When nursing was performed in four periods of 15 min each the litter of the control mother obtained milk only in the second period of nursing while the litter of the induced mother obtained milk in all four periods of nursing and the amount of milk obtained in the whole hour was greater than that from the control rat.6. The administration of oxytocin just before the replacement of the litter every 15 min produced milk ejection only in the first two periods of suckling in the control rats but the induced rats were capable of ejecting milk during all four periods.7. The most satisfactory conclusion for the results obtained is that the C.N.S. regulates both the release of oxytocin in response to suckling and the response of the mammary gland to oxytocin, in the lactating rat.     

The proposed mechanism of action during different pain management techniques on expression of cytolytic molecule perforin in patients after colorectal cancer surgery

The postoperative period is accompanied with neuroendocrine, metabolic and immune alteration which is caused by tissue damage, anesthesia, postoperative pain and psychological stress. Postoperative pain contributes to dysfunction of immune response as a result of interaction between central nervous and immune system. The postoperatively activated hypotalamo-pituitary-adrenocortical axis, sympathic and parasympathic nerve systems are important modulators of immune response. According to bidirectional communication of immune and nervous system, appropriate postoperative pain management could affect immune response in postoperative period. Although the postoperative suppression of immune response has been reported, a very little are known about the influences of different pain management techniques on cytotoxic function of immune cells in patients with colorectal cancer in early postoperative period. Perforin is a cytotoxic molecule expressed by activated lymphocytes which has a crucial role in elimination of tumor cells and virus-infected cells, mostly during the effector's phase of immune response. Immune compromise during the postoperative period could affect the healing processes, incidence of postoperative infections and rate and size of tumor metastases disseminated during operation. The pharmacological management of postoperative pain in patients with malignancies uses very different analgesic techniques whose possible influence on cytotoxic functions of immune cells are still understood poor. For decades the most common way of treating postoperative pain after colorectal cancer surgery was intravenous analgesia with opiods. In the last decade many investigations pointed out that opiods can also contribute to postoperative suppression of immune response. Epidural analgesia is a regional anesthesia technique that acts directly on the origin of pain impulses and pain relief can be achieved with small doses of opiods combined with local anesthetics. Local anesthetics potentate analgesic properties of opiods but per se are also acting as antiinflammatory drugs. Afferent neural blockade by epidural analgesia attenuates neuroendocrine stress response. We propose that epidural analgesia could be more convenient that intravenous analgesia in maintenance of immunological homeostasis that is altered by surgical stress, tumor growth and pain.     

The effects of sensitization and social isolation on maternal behavior in the virgin rat

Thirty-three out of 67 virgin Sprague-Dawley rats spontaneously retrieved 5–10-day-old foster pups in a pretest. The 34 rats not responding immediately were randomly divided into three groups to study the effects of direct and exteroceptive exposure to young on the induction of maternal behavior. Retrieving, licking and crouching behavior appeared in a higher proportion of cage rats (n = 12) which received a fresh group of pups to live with throughout each day than in control rats (n = 10) that had only 5 min daily exposure. However basket rats (n = 12) also became maternal merely by exposure to exteroceptive stimuli from pups living in baskets fixed to the cage wall. In a second experiment, virgin rats that spontaneously retrieved pups were socially isolated for 2–4 weeks. As a result, a 50–60% decrease in the number of rats showing retrieval was found not only in an independent sample of rats (n = 20) but also in a related group (n = 13) that practiced the response in the week between a pretest and Week 2 in isolation. Therefore, the results demonstrate that exteroceptive cues from pups alone may be sufficient to induce maternal behavior in nonspontaneously retrieving virgin rats, and that isolation from pups and other social stimuli reduce retrieving behavior in initially responsive virgin rats.     

THE EFFECTS OF AWARENESS AND SUCCESSIVE INHIBITION ON INTEROCEPTIVE AND EXTEROCEPTIVE CONDITIONING OF THE GALVANIC SKIN RESPONSE

The general conclusion from Soviet studies of interoceptive conditioning has been that interoceptive conditioning is unconscious, established at a slower rate, and is more resistant to extinction than exteroceptive conditioning. Forty-eight paid volunteer subjects were classically conditioned to both interoceptive (0 and 50 degree C. water in an intubated balloon located between the bronchial and diaphragmatic constrictions of the esophagus) and exteroceptive CSs (256 and 512 Hz tones at 60 db). Significant interoceptive and exteroceptive conditioning of the GSR was obtained using responses occurring within the interstimulus or first interval (FIR) as well as the post-UCS or second interval (SIR). FIR conditioning progressed at a slower rate to interoceptive than to exteroceptive stimulation whereas SIR conditioning was equally effective to both modes of stimulation. Unawareness of interoceptive stimulation or their reinforcement contingencies tended to eliminate FIR but not SIR conditioning. Although not statistically supported, successive inhibitory-excitatory compounding of interoceptive and exteroceptive CSs indicated stronger response tendencies to the interoceptive CSs when equated to exteroceptive conditioning strength. These results demonstrate the complexity of GSR conditioning when CS modality, response types, and awareness of CS-UCS contingencies are considered.     

Implication of endogenous beta-endorphin in the inhibition of the morphine-induced rewarding effect by the direct activation of spinal protein kinase C in mice

It has often been proposed that opioid addiction does not arise as a consequence of opioid treatment for pain. Recently, we demonstrated that activated protein kinase C (PKC) in the spinal cord associated with chronic pain-like hyperalgesia suppressed the morphine-induced rewarding effect in mice. In the present study, we investigated whether a gene deletion for an endogenous mu-opioid peptide beta-endorphin could affect pain-like behavior and the suppression of the morphine-induced rewarding effect by the direct activation of PKC in the spinal cord. We found that activation of spinal PKC by intrathecal (i.t.) treatment with phorbol 12,13-dibutyrate (PDBu), a specific PKC activator, caused thermal hyperalgesia, pain-like behaviors and suppression of the morphine-induced rewarding effect. This suppression of morphine reward was eliminated in mice that lacked beta-endorphin. In contrast, thermal hyperalgesia and pain-like behaviors were not affected in beta-endorphin knockout mice. These results suggest that the activation of PKC in the spinal cord may play an essential role in the suppression of the morphine-induced rewarding effect in mice with neuropathic pain through the constant release of beta-endorphin.     

Effects of naltrexone on electrocutaneous pain in patients with hypertension compared to normotensive individuals

An opioid mechanism may help explain hypertensive hypoalgesia. A double-blind placebo-controlled design compared the effects of opioid blockade (naltrexone) and placebo on electrocutaneous pain threshold, pain tolerance, and retrospective McGill Pain Questionnaire ratings in 35 unmedicated patients with essential hypertension and 28 normotensive individuals. The hypertensives experienced less pain than normotensives during the assessment of their pain tolerance; however, this manifestation of hypertensive hypoalgesia was not moderated by naltrexone. These findings fail to support the hypothesis that essential hypertension is characterised by relative opioid insensitivity.