Peripheral noxious stimulation induces CREM expression in dorsal horn: involvement of glutamate

Thermal washout curves have been proposed as noninvasive tools for analysing lower airway dimensions and pulmonary blood flow, but how upper airway heat transfer affects these washout curves is unclear. The present study was designed to compare extrathoracic and tracheobronchial contributions to thermal washout curves. Respiratory frequency, air ambient temperature, and body core temperature (tc) were varied in six male subjects before and after immersion in cold (1.1 degrees C) water for up to 2 h under three conditions: 1) control: ambient temperature (tamb) = 25 degrees C, rectal temperature change (delta tre) = 0 degrees C; 2) pre-immersion: tamb = 4 degrees C, delta tre = 0 degrees C; and 3) post-immersion: tamb = 25 degrees C, delta tre = -0.7 degrees C. Both peak expiratory nasal (tpn) and oral (tpo) airstream temperatures were measured. Each subject was tested twice. Expiratory tpo was generally higher than tpn in all conditions. Increasing breathing rates lowered tpn and tpo in the control and cold air environments. Orifice temperatures, which are presumed to reflect upper airway blood temperatures, correlated with both tpn and tpo. Lowering tc had no effect on washout curves during quiet breathing and affected only tpn during rapid breathing. The results suggest that while tracheobronchial conditions may contribute to thermal washout curves, extrathoracic conditions predominate. Strong correlations between orifice temperatures, peak expiratory nasal temperatures and peak expiratory oral temperature demonstrate the dominant role of upper airway heat exchange in determining thermal washout curves.     

Diffuse noxious inhibitory controls reduce the expression of noxious stimulus-evoked Fos-like immunoreactivity in the superficial and deep laminae of the rat spinal cord

Behavioral and electrophysiological studies have shown that a noxious stimulus applied to one part of the body can reduce the response to a subsequent noxious stimulus elsewhere on the body. This phenomenon is referred to as diffuse noxious inhibitory controls (DNIC). In the present study we used immunocytochemical labeling for the Fos protein product of the c-fos proto-oncogene to determine the location of lumbar spinal nociresponsive neurons that are inhibited by a spatially remote noxious stimulus. Repetitive hindpaw pinch evoked pronounced Fos-like immunoreactivity in the superficial and deep laminae of the lumbar spinal cord. Placing the tail in 50 degrees C water before each hindpaw pinch significantly reduced Fos-like immunoreactivity in these regions. These data demonstrate that nociresponsive neurons in both the superficial and deep laminae of the spinal cord are sensitive to inhibition by a spatially remote noxious conditioning stimulus.     

Effect of continuous spinal remifentanil infusion on behaviour and spinal glutamate release evoked by subcutaneous formalin in the rat

Four mutants of Arabidopsis thaliana that are deficient in adenine phosphoribosyl transferase (APRT) activity have been isolated by selecting for germination of seeds and growth of the plantlets on a medium containing 2,6-diaminopurine (DAP), a toxic analog of adenine. In all mutants, DAP resistance is due to a recessive nuclear mutation at a locus designated apt. The mutants are male sterile due to pollen abortion after meiosis. Furthermore, it has been shown that metabolism of cytokinins is impaired in the mutant BM3, which has the lowest level of APRT activity among the mutants tested. However, three different cDNAs encoding APRT have been isolated in A. thaliana and this raised the question of the nature of the mutation which results in low APRT activity. The mutation was genetically mapped to chromosome I and lies within 6 cM of the phenotypic marker dis2, indicating that the mutation affects the APT1 gene, a result confirmed by sequencing of mutant alleles. The mutation in the allele apt1-3 is located at the 5' splicing site of the third intron, and eliminates a BstNI restriction site, as verified by Southern blotting and PCR fragment length analysis.     

Antinociceptive action of vaginocervical stimulation in rat spinal cord: 2-DG analysis

Using [14C] 2-deoxyglucose (2-DG) autoradiography with computerized densitometric analysis, unilateral foot pinch was found to significantly increase the relative optical density in laminae I and II of the ipsilateral, compared to the contralateral, spinal cord at lumbar 5 (L5). However, during vaginocervical mechanostimulation applied concurrently with the unilateral foot pinch, no comparable difference was observed. No response to foot pinch was observed in other laminae of the spinal cord at L5, and no effects comparable to the above were observed at L3. These findings indicate that vaginocervical mechanostimulation suppresses neural responses to noxious foot pinch stimulation selectively at the laminae I and II level of the spinal cord at L5, but not at L3.     

Regional changes in forebrain activation during the early and late phase of formalin nociception: analysis using cerebral blood flow in the rat

This is the first neural imaging study to use regional cerebral blood flow (rCBF) in an animal model to identify the patterns of forebrain nociceptive processing that occur during the early and late phase of the formalin test. We measured normalized rCBF increases by an autoradiographic method using the radiotracer [99mTc]exametazime. Noxious formalin consistently produced detectable, well-localized and typically bilateral increases in rCBF within multiple forebrain structures, as well as the interpeduncular nucleus (Activation Index, AI = 66) and the midbrain periaqueductal gray (AI = 20). Structures showing pain-induced changes in rCBF included several forebrain regions considered part of the limbic system. The hindlimb region of somatosensory cortex was significantly activated (AI = 31), and blood flow increases in VPL (AI = 8.7) and the medial thalamus (AI = 9.0) exhibited a tendency to be greater in the late phase as compared to the early phase of the formalin test. The spatial pattern and intensity of activation varied as a function of the time following the noxious formalin stimulus. The results highlight the important role of the limbic forebrain in the neural mechanisms of prolonged persistent pain and provide evidence for a forebrain network for pain.     

PAG-microinjected dipyrone (metamizol) inhibits responses of spinal dorsal horn neurons to natural noxious stimulation in rats

Recently, we have shown that rapid eye movement sleep deprivation (REM-SD) in animals with lesions of the nigro-striatal pathway facilitates turning behavior and such increase still occurred even in the presence of dopaminergic grafts. The objective of this work was to determine which DA receptors are preferentially involved. The results showed that the D2 receptor antagonist sulpiride decreases significantly turning behavior of lesioned animals, with no effect whatsoever of the D1 antagonist SCH 23390. When lesioned animals were REM sleep deprived, the D1 but not the D2 receptor antagonist prevented the increase of turning induced by REM-SD. This work suggests that the increase of post-synaptic supersensitivity induced by REM-SD in nigro-striatal lesioned animals is mediated by D1 receptors.     

Differential c-fos expression in the nucleus of the solitary tract and spinal cord following noxious gastric distention in the rat

c-Fos has been used as a marker for activity in the spinal cord following noxious somatic or visceral stimulation. Although the viscera receive dual afferent innervation, distention of hollow organs (i.e. esophagus, stomach, descending colon and rectum) induces significantly more c-Fos in second order neurons in the nucleus of the solitary tract and lumbosacral spinal cord, which receive parasympathetic afferent input (vagus, pelvic nerves), than the thoracolumbar spinal cord, which receives sympathetic afferent input (splanchnic nerves). The purpose of this study was to determine the contribution of sympathetic and parasympathetic afferent input to c-Fos expression in the nucleus of the solitary tract and spinal cord, and the influence of supraspinal pathways on Fos induction in the thoracolumbar spinal cord. Noxious gastric distention to 80 mmHg (gastric distension/80) was produced by repetitive inflation of a chronically implanted gastric balloon. Gastric distension/80 induced c-Fos throughout the nucleus of the solitary tract, with the densest labeling observed within 300 microns of the rostral pole of the area postrema. This area was analysed quantitatively following several manipulations. Gastric distension/80 induced a mean of 724 c-Fos-immunoreactive nuclei per section. Following subdiaphragmatic vagotomy plus distention (vagotomy/80), the induction of c-Fos-immunoreactive nuclei was reduced to 293 per section, while spinal transection at T2 plus distention (spinal transection/80) induced a mean of 581 nuclei per nucleus of the solitary tract section. Gastric distension/80 and vagotomy/80 induced minimal c-Fos in the T8-T10 spinal cord (50 nuclei/section), but spinal transection/80 induced 200 nuclei per section. Repetitive bolus injections of norepinephrine produced transient pressor responses mimicking the pressor response produced by gastric distension/80. This manipulation induced minimal c-Fos in the nucleus of the solitary tract and none in the spinal cord. It is concluded that noxious visceral input via parasympathetic vagal afferents, and to a lesser extent sympathetic afferents and the spinosolitary tract, contribute to gastric distention-induced c-Fos in the nucleus of the solitary tract. The induction of c-Fos in the nucleus of the solitary tract is significantly greater than in the viscerotopic segments of the spinal cord, which is partially under tonic descending inhibition, but is not subject to modulation by vagal gastric afferents. Distention pressures produced by noxious gastric distention are much greater than those produced during feeding, suggesting that c-Fos induction in the nucleus of the solitary tract to noxious distention is not associated with physiological mechanisms of feeding and satiety. The large vagal nerve-mediated induction of c-Fos in the nucleus of the solitary tract following gastric distension suggests that parasympathetic afferents contribute to the processing of noxious visceral stimuli, perhaps by contributing to the affective-emotional component of visceral pain.     

Gender differences in pain perception and patterns of cerebral activation during noxious heat stimulation in humans

The purpose of the present study was to determine whether gender differences exist in the forebrain cerebral activation patterns of the brain during pain perception. Accordingly, positron emission tomography (PET) with intravenous injection of H2(15)O was used to detect increases in regional cerebral blood flow (rCBF) in normal right-handed male and female subjects as they discriminated differences in the intensity of innocuous and noxious heat stimuli applied to the left forearm. Each subject was instructed in magnitude estimation based on a scale for which 0 indicated 'no heat sensation'; 7, 'just barely painful' and 10, 'just barely tolerable'. Thermal stimuli were 40 degrees C or 50 degrees C heat, applied with a thermode as repetitive 5-s contacts to the volar forearm. Both male and female subjects rated the 40 degrees C stimuli as warm but not painful and the 50 degrees C stimuli as painful but females rated the 50 degrees C stimuli as significantly more intense than did the males (P=0.0052). Both genders showed a bilateral activation of premotor cortex in addition to the activation of a number of contralateral structures, including the posterior insula, anterior cingulate cortex and the cerebellar vermis, during heat pain. However, females had significantly greater activation of the contralateral prefrontal cortex when compared to the males by direct image subtraction. Volume of interest comparison (t-statistic) also suggested greater activation of the contralateral insula and thalamus in the females (P < 0.05). These pain-related differences in brain activation may be attributed to gender, perceived pain intensity, or to both factors.     

Opioid antagonist profile of SC nor-binaltorphimine in the formalin paw assay

The antinociceptive effects of mu and kappa agonists were examined after the systemic administration of the opioid antagonists nor-binaltorphimine (nor-BNI) and naloxone in the late response or tonic nociceptive phase of the mouse formalin assay. Initially, SC morphine (ED50, 0.97 mg/kg), racemic U-50488H (ED50, 0.79 mg/kg), (-)U-50488 (ED50, 0.41 mg/kg), and another agonist PD 117,302 (ED50, 0.28 mg/kg) were found to produce graded increases in the level of antinociception as measured by this procedure; naloxone, administered immediately before morphine and U-50488H, antagonized their antinociceptive actions. The effects of morphine and U-50488H then were evaluated 10 min to 96 h after the administration of nor-BNI. Subcutaneous nor-BNI at 30.0 mg/kg, but not at 3.0 or 10.0 mg/kg, attenuated the antinociceptive effects of morphine and U-50488H when the interval separating nor-BNI and the agonists was kept constant at 1 h. Time-course analysis of the effects of combinations of nor-BNI with morphine led to irregular findings: 10.0 mg/kg of nor-BNI lessened the effects of morphine (2.0 mg/kg) if the dosing interval was 10 min, whereas 30.0 mg/kg of nor-BNI attenuated the effects of morphine (2.0 mg/kg) if the dosing interval was 1 or 4 h; 10.0 mg/kg of nor-BNI also diminished the antinociceptive effects of U-50488H (1.7 mg/kg) only if the interval spacing the two drugs was 24 h. In comparison, a threefold higher dose of nor-BNI (30.0 mg/kg) reduced the effects of U-50488H (1.7 mg/kg) if the interval was 1 h or more. In these latter experiments, the antagonist effects of SC nor-BNI (30.0 mg/kg) were evident up to 96 h posttreatment. These results show that the mu opioid antagonist activity of nor-BNI is variable and that the kappa opioid antagonist selectivity of nor-BNI is a function of dose and treatment interval and is long-lasting even after systemic administration.     

Morphine-3-glucuronide (M3G) potentiates noxious stimulus-evoked Fos protein-like immunoreactivity in the rat spinal cord

The effect of morphine-3-glucuronide (M3G) on noxious stimulus-evoked Fos protein-like immunoreactivity in the rat spinal cord were assessed by ABC method. It was found that a dose-dependent increase of Fos-like immunoreactive neurons could be induced by M3G intrathecal injection followed by formaline injection into hindpaw. With high dosage M3G (1.1 x 10(-7) mole), dense Fos-like labelling was found in the superficial and the deep dorsal horn bilaterally, While with low dosage M3G (5.4 x 10(-8) and 1.1 x 10(-8) mole), most of the positively labelled neurons were only found in laminae I and II of the ipsilateral dorsal horn to the injured paw. The above results revealed that M3G exerts a potentiating effect on the noxious stimulus-evoked Fos protein-like immunoreactivity in the rat spinal cord.     

Somatotopic and laminar organization of fos-like immunoreactivity in the medullary and upper cervical dorsal horn induced by noxious facial stimulation in the rat

The distribution of fos-like-immunoreactivity (fos-LI) in the medullary and upper cervical dorsal horn was examined following noxious facial stimulation, in order to evaluate the use of fos as a marker for neuronal activation in trigeminal nociceptive pathways. Control animals that received urethane anesthesia and no facial stimulation showed substantial bilateral labeling in the trigeminal complex that was restricted to one rostrocaudal level, at the transition between the medullary dorsal horn (nucleus caudalis) and nucleus interpolaris. Noxious mechanical stimulation (pinch) of different facial sites produced labeling in the ipsilateral dorsal horn whose distribution varied predictably with the rostrocaudal and dorsoventral position of the facial stimulation site, such that rostral facial sites were represented rostrally in the dorsal horn and dorsal sites were represented ventrolaterally. The cornea was exceptional among the facial stimulation sites in that it had a specific representation at two distinct rostrocaudal levels, in C1 and the interpolaris-caudalis transition region; the position of the rostral peak was somatotopically inappropriate, based on the representation of other facial sites. The proportion of labelling in laminae III-IV relative to laminae I-II was higher with noxious mechanical stimulation than with noxious thermal (55 degrees C) or chemical (subcutaneous injection of capsaicin) stimulation. The proportion of labelling in laminae III-IV produced by electrical stimulation of the infraorbital nerve was no greater than that produced by pinch. The results suggest that fos-LI mapping can be a useful method for the investigation of somatotopy but is subject to serious limitations when used for the investigation of laminar organization. The results also suggest that the interpolaris-caudalis transition region may have properties that are distinct from those of the rest of the trigeminal complex, possibly related to an involvement in autonomic function.     

Neuron discharges in the rat auditory cortex during electrical intracortical stimulation

Cocaine and cocaine-associated cues elicit craving in addicts and reinstate cocaine-seeking behavior in rats. Craving and cocaine-seeking behavior may be mediated by withdrawal-induced changes in dopamine (DA) neurotransmission in the amygdala. To examine whether there are concomittant changes in cocaine-seeking behavior and extracellular DA levels during withdrawal, experimental rats were trained to self-administer cocaine (0.75 mg/kg i.v.). After 14 daily 3-hour training sessions, animals underwent either a 1-day, 1-week, or 1-month withdrawal period. Extracellular DA levels were assessed during baseline, extinction, cue reinstatement, and cocaine (15 mg/kg i.p.) reinstatement of cocaine-seeking behavior (i.e., defined as the difference in nonreinforced lever presses on an active minus inactive lever). Cocaine-seeking behavior became more intense during the course of cocaine withdrawal. Additionally, basal and cocaine-induced extracellular DA levels were enhanced after the 1-month withdrawal period. We suggest that the former may reflect a persistent elevation in tonic extracellular DA levels in the amygdala, whereas the latter may reflect a persistent elevation in phasic extracellular DA levels.     

Changes in descending pain threshold related to rate of noxious stimulation.

Measured detection threshold, pain threshold, and pain tolerance for electrical stimulation in 20 healthy male volunteer medical students, using the psychophysical method of limits. The ascending rate of stimulation was held constant, but 5 different descending rates were employed. The descending pain threshold decreased significantly with increases in the descending speed of stimulation, but all other response parameters remained constant. It is proposed that several factors, including adaptation to pain and emotional reactivity associated with relief of pain, caused these results. Simple reaction time was excluded as a significant variable. It is suggested that descending pain parameters require more systematic study, especially since the relief of suffering may be more closely related to clinical pain than experimentally-induced ascending pain parameters. (21 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Expression of Fos protein in the rat central nervous system in response to noxious stimulation: effects of chronic inflammation of the superior cervical ganglion

OBJECTIVES: To compare treatments of complete fractures of the third metacarpal (MC) or metatarsal (MT) bone in horses and to identify factors that could impact prognosis. DESIGN: Retrospective case series. ANIMALS: 25 horses with fractures of the third MC or MT bone that were treated by use of internal fixation, external coaptation, or both. PROCEDURE: Medical records from the Veterinary Medical Data Base of horses treated for fractures of third MC or MT bone at Texas A&M University from 1980 to 1994 and Purdue University from 1980 to 1996 were reviewed. Information on signalment, results of physical and radiographic examinations, treatment, and outcome were obtained. For horses that had radiographic evidence of healing, long-term follow-up information was obtained by telephone contact with owners or referring veterinarians. RESULTS: Age, sex, weight, and limb affected were not related to outcome; however, affected horses were younger than the general hospital populations. Seventeen horses had open fractures at referral. Infection was the most common complication after surgery, with open fractures more likely to become infected. Nonunion in an infected fracture was the most common reason for postoperative failure (7 horses). Long-term follow-up was available for 16 horses; 11 of these had no complications related to surgical repair. CLINICAL IMPLICATIONS: Fractures of the MC or MT bone are not always associated with a poor prognosis in horses. Proper case selection, rigid fracture stabilization, and efforts to prevent or treat infection will improve success rate.     

Activation and recovery of the PGE2-mediated sensitization of the capsaicin response in rat sensory neurons

Pro-inflammatory prostaglandins are known to enhance the sensitivity of sensory neurons to various modalities of stimulation, including the excitatory chemical agent, capsaicin. In this report, we examined the capacity of prostaglandin E2 (PGE2) to enhance the capsaicin response recorded from sensory neurons isolated from embryonic rats and grown in culture. Previous work demonstrated that the cyclic adenosine 3',5'-monophosphate pathway mediates initiation of the PGE2-induced sensitization, however, little is known about the pathways regulating the recovery from sensitization. Therefore, we examined the neuronal transduction cascades that control the duration of sensitization. Treatment with PGE2 enhanced the capsaicin-evoked current by two- to threefold, however, this sensitization was transient even in the continued presence of prostaglandin. The duration of sensitization produced by PGE2 was related inversely to the extracellular Ca2+ concentration with the shortest recovery times observed in cells exposed to 2 mM Ca2+-Ringer. Inclusion of the Ca2+ chelator, bis-(o-aminophenoxy)-N, N,N',N'-tetraacetic acid, in the recording pipette greatly lengthened the period of sensitization. Pretreatment with either the nitric oxide synthase inhibitor, nitro-L-arginine methyl ester (L-NAME), or the inhibitor of the cyclic guanosine 3', 5'-monophosphate (GMP)-dependent protein kinase, KT-5823, before the application of PGE2 increased the duration of sensitization even in the presence of 2 mM Ca2+. In contrast, after attaining maximal sensitization in 2 mM Ca2+-Ringer containing L-NAME, the addition of either nitric oxide donors (3-morpholinosydnonimine or s-nitroso-n-acetylpenicillamine) or 8-Br-cyclic GMP led to a rapid decrease in the level of sensitization. In the absence of sensitization, nitric oxide-cyclic GMP modulating agents had no effect on the capsaicin-evoked current. Therefore, these results suggest that capsaicin-induced elevations in intracellular Ca2+ levels lead to an enhanced production of cyclic GMP, via the nitric oxide pathway, that ultimately activates cyclic GMP-dependent protein kinase. This protein kinase inactivates or terminates the sensitization produced by PGE2 by an as yet unidentified mechanism.     

Characterization of the foot withdrawal response to noxious radiant heat in the rat

The rat foot withdrawal response to noxious radiant heat has been used as a model of nociception that is particularly useful for measurements of unilateral changes in nociceptive responses. The purpose of these studies was to characterize the foot withdrawal response to graded rates of noxious skin heating. Response latencies and both surface and subsurface temperatures produced by 6 different intensities of radiant heat were measured to determine whether response latency is an appropriate measure of nociceptive threshold. With constant intensity heating, the temperature of the skin surface increased as logarithmic function of time, while subsurface temperature increased linearly with time. In contrast, a heating function that linearly increased the temperature at the skin surface increased the subsurface temperature as an exponential function of time. These results and published reports of nociceptive afferent recordings which used similar skin heating parameters, indicate that nociceptive foot withdrawal responses occur at about the same skin temperature as the activation of nociceptors. These results also indicate that since constant intensity heating produces linear increases in the subsurface temperature, then response latency can be used as an accurate measure of changes in nociceptive threshold produced by drug treatments. These observations lead to the conclusion that the foot withdrawal response latency is a valid and useful measure of nociceptive threshold in rodents.     

Gas exchange kinetics during functional electrical stimulation in subjects with spinal cord injury

We examined the kinetics of VO2, VCO2, and VE following the onset of unloaded leg cycling, and in recovery, in six patients with spinal cord injury (SCI). Exercise was produced by functional electrical stimulation (FES) of the quadriceps, hamstrings, and gluteal muscles. End-exercise VO2 (1.03 +/- 0.16 l.min-1), VCO2 (1.20 +/- 0.22 l.min-1) and VE (41 +/- 10 l.min-1) were elevated compared to values typically seen in healthy ambulatory subjects performing similar unloaded cycling. Mean response times for the on transients (MRTon) were both long and variable across subjects for VO2 (165 +/- 62 s), VCO2 (173 +/- 58 s), and VE (202 +/- 61 s). Recovery kinetics showed much less intersubject variability, and for five of six subjects were faster than the equivalent exercise MRT for all three variables (MRToff for VO2 of 103 +/- 28 s, VCO2 136 +/- 20 s, and VE 144 +/- 34 s), but P > 0.05 for all three. Size of the O2 deficit (1.96 +/- 0.90 l) and end-exercise lactate (7.05 +/- 1.65 mmol.l-1) were similar to values reported for healthy sedentary subjects performing maximal voluntary exercise, but the end-exercise heart rate (102 +/- 16 bpm) was lower than expected for this intensity of exercise. In conclusion, FES-induced unloaded cycling leads to exaggerated responses of pulmonary gas exchange and long time constants in patients with SCI. The delayed kinetics may be due in part to a blunted increase in heart rate in addition to severe deconditioning.