Sickle cell disease in mice is associated with sensitization of sensory nerve fibers

The pain phenotype in sickle cell disease (SCD) patients is highly variable. A small percentage of SCD patients experience many vaso-occlusive crises/year, 5% of patients account for over 30% of pain episodes, while 39% report few episodes of severe pain. Clearly, a better understanding of the pathobiology of SCD is needed to improve its therapy. Humanized sickle cell mice recapitulate several phenotypes of SCD patients and provide a model for the study of SCD pain. Researchers have shown that one strain of humanized SCD mice, the BERK strain, has abnormal pain phenotype. However, the nociception phenotype of another humanized SCD mouse strain, the Townes strain, has not been described. In a large cross-sectional study of BERK and Townes SCD mice, we examined thermosensory response and sensory nerve fiber function using sine-wave electrical stimulation at 2000, 250, and 5 Hz to stimulate preferentially Aβ, Aδ, and C sensory nerve fibers, respectively. We found that BERK and Townes mice, compared to respective controls, had decreases in 2000, 250, and 5 Hz current vocalization thresholds in patterns that suggest sensitization of a broad spectrum of sensory nerve fibers. In addition, the pattern of sensitization of sensory fibers varied according to strain, sex, age, and mouse genotype. In a similarly variable pattern, Townes and BERKs also had significantly altered sensitivity to noxious thermal stimuli in agreement with what has been shown by others. In summary, the analysis of somatosensory function using sine-wave electrical stimulation in humanized sickle cell mice suggests that in SCD, both myelinated and unmyelinated, fibers are sensitized. The pattern of sensory fiber sensitization is distinct from that observed in pain models of neuropathic and inflammatory pain. These findings raise the possibility that sensitization of a broad spectrum of sensory fibers might contribute to the altered and variable nociception phenotype in SCD.     

Loss of spinal substance P pain transmission under the condition of LPA1 receptor-mediated neuropathic pain

In the present study, we first report an in vivo characterization of flexor responses induced by three distinct sine-wave stimuli in the electrical stimulation-induced paw flexion (EPF) test in mice. The fixed sine-wave electric stimulations of 5 Hz (C-fiber), 250 Hz (Aδ-fiber) and 2000 Hz (Aβ-fiber) to the hind paw of mice induced a paw-flexion response and vocalization. The average threshold for paw flexor responses by sine-wave stimulations was much lower than that for vocalization. Neonatally (P3) pretreatment with capsaicin to degenerate polymodal substance P-ergic C-fiber neurons increased the threshold to 5 Hz (C-fiber) stimuli, but not to 250 Hz (Aδ-fiber) and 2000 Hz (Aβ-fiber). The flexor responses to 5 Hz stimuli were significantly blocked by intrathecal (i.t.) pretreatment with both CP-99994 and MK-801, an NK1 and NMDA receptor antagonist, respectively, but not by CNQX, an AMPA/kainate receptor antagonist. On the other hand, the flexor responses induced by 250 Hz stimuli were blocked by MK-801 (i.t.) but not by CP-99994 or CNQX. In contrast, flexor responses induced by 2000 Hz stimuli were only blocked by CNQX treatment. These data suggest that we have identified three pharmacologically different categories of responses mediated through different primary afferent fibers. Furthermore, we also carried out characterization of the in vivo functional sensitivity of each of the sensory fiber types in nerve-injured mice using the EPF test, and found that the threshold to both 250 Hz and 2000 Hz stimulations were markedly decreased, whereas the threshold to 5 Hz stimulations was significantly increased. Thus we found opposing effects on specific sensory fiber-mediated responses as a result of nerve injury in mice. These results also suggest that the EPF analysis is useful for the evaluation of plasticity in sensory functions in animal disease models.     

Formalin injection causes a coordinated spinal cord CO/NO-cGMP signaling system response

Transcutaneous sine-wave stimuli at frequencies of 2000, 250 and 5 Hz (Neurometer) are thought to selectively activate Aβ, Aδ and C afferent fibers, respectively. However, there are few reports to test the selectivity of these stimuli at the cellular level. In the present study, we analyzed action potentials (APs) generated by sine-wave stimuli applied to the dorsal root in acutely isolated rat dorsal root ganglion (DRG) preparations using intracellular recordings. We also measured excitatory synaptic responses evoked by transcutaneous stimuli in substantia gelatinosa (SG) neurons of the spinal dorsal horn, which receive inputs predominantly from C and Aδ fibers, using in vivo patch-clamp recordings. In behavioral studies, escape or vocalization behavior of rats was observed with both 250 and 5 Hz stimuli at intensity of ~0.8 mA (T5/ T250), whereas with 2000 Hz stimulation, much higher intensity (2.14 mA, T2000) was required. In DRG neurons, APs were generated at T5/T250 by 2000 Hz stimulation in Aβ, by 250 Hz stimulation both in Aβ and Aδ, and by 5 Hz stimulation in all three classes of DRG neurons. However, the AP frequencies elicited in Aβ and Aδ by 5 Hz stimulation were much less than those reported previously in physiological condition. With in vivo experiments large amplitude of EPSCs in SG neurons were elicited by 250 and 5 Hz stimuli at T5/ T250. These results suggest that 2000 Hz stimulation excites selectively Aβ fibers and 5 Hz stimulation activates noxious transmission mediated mainly through C fibers. Although 250 Hz stimulation activates both Aδ and Aβ fibers, tactile sensation would not be perceived when painful sensation is produced at the same time. Therefore, 250 Hz was effective stimulus frequency for activation of Aδ fibers initiating noxious sensation. Thus, the transcutaneous sine-wave stimulation can be applied to evaluate functional changes of sensory transmission by comparing thresholds with the three stimulus frequencies.     

Pudendal and median nerve sensory perception threshold: A comparison between normative studies

Background: For the evaluation of sensory innervation, normative data are necessary as a comparison.

Aims: To compare our current perception thresholds (CPTs) with normative data from other research.

Methods: Healthy volunteers were assessed for 2000, 250, and 5?Hz CPTs of the median and pudendal nerve and data were compared with other studies.

Results: Normative data in the studied group n?=?41 (male: 21; female: 20) for the median nerve, 2?kHz, 250?Hz, and 5?Hz were respectively: 241.85?±?67.72 (140–444); 106.27?±?39.12 (45–229); 82.05?±?43.40 (13–271). Pudendal nerve CPTs 250?Hz were: 126.44?±?69.46 (6–333). For men 2?kHz: 349.95?±?125.76 (100–588); 5?Hz: 132.67?±?51.81 (59–249) and women 2?kHz: 226.20?±?119.65 (64–528); 5?Hz: 92.45?±?44.66 (35–215). For the median nerve no statistical differences for gender were shown. For the pudendal nerve, only 250?Hz showed no difference for gender (t-test: 0.516). Comparison of our data with CPTs of other normative data showed no agreement for the pudendal nerve. For the median nerve only 2?kHz showed agreement in three studies and for 5?Hz with one study.

Conclusion: Comparing normative data of multiple studies shows a variety of results and poor agreement. Therefore, referring to normative data of other studies should be handled with caution.     

The release of catecholamines from the adrenal medulla and its modulation by alpha 2-adrenoceptors in the anaesthetized dog

The adrenal nerve of anaesthetized and vagotomized dogs was electrically stimulated (10 V pulses of 2 ms duration for 10 min) at frequencies of 1, 3, 10, and 25 Hz. There was a correlation between the frequency of stimulation and the plasma concentrations of epinephrine, norepinephrine, and dopamine in the adrenal vein, mainly after the 1st min of stimulation and the maximal concentration was reached sooner with higher frequencies of stimulation. Moreover, the relative percentage of catecholamines released in response to the electrical stimulation was not changed by the frequency of stimulation. To test the hypothesis that a local negative feedback mechanism mediated by alpha 2-adrenoceptors exists in the adrenal medulla, the effects of the systemic administration of clonidine (alpha 2-antagonist) on the concentrations of catecholamines in the adrenal vein were evaluated during the electrical stimulation of the adrenal nerve (5 V pulses of 2 ms duration for 3 min) at 3 Hz. Moreover, the effects of the systemic injections of more specific alpha 2-agonist and antagonist (oxymetazoline and idazoxan) were tested on the release of catecholamines in the adrenal vein in response to electrical stimulation of the splanchnic nerve at 1 and 3 Hz frequencies. The injection of 0.5 mg/kg of yohimbine caused a significant increase in the concentrations of epinephrine and norepinephrine in the adrenal vein induced by the electrical stimulation of the adrenal nerve and the injection of 15 micrograms/kg of clonidine had no effects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of Q-switched Nd:YAG laser irradiation on neural impulse propagation: II. Dorsal roots and peripheral nerves.

We have studied the effects of Q-switched Nd:YAG laser irradiation on transmission of neural impulses in sensory nerve fibers in anesthetized rats and cats. Laser light was applied to dorsal roots (rat, cat) and to the sciatic nerve (rat) at increasing pulse energies ranging from 10 to 100 mJ/pulse for 5 minutes each. Compound action potentials recorded from dorsal roots and the sciatic nerve in response to high intensity electrical stimulation during laser application at increasing pulse energies showed a progressive preferential reduction of the slow late component of the electrically evoked response. Preliminary data from multifilament recordings from dorsal roots in cats demonstrated that conduction in small slow conducting fibers was blocked at lower laser pulse energies than in fibers with faster conduction velocities. These results imply, that laser light might have differential effects on slow versus fast conducting sensory nerve fibers. It is most likely that the preferential effect of laser irradiation on slow conducting fibers is mediated by photothermal mechanisms, since temperature increased substantially during laser application.     

High frequency electrostimulation of excitable cells

Reactions of nerve fibers to high frequency electrical stimulation are examined with three nerve models. Switching on the signal produces a single AP at the threshold current. Stronger currents lead into a region of repetitive firing. The firing rate depends on the current and the fibers more distant from the electrode will have a lower rate. The AP's are not synchronized. In the "House-Urban" cochlear implant a 16 kHz carrier is used for stimulation. It is modulated by electrical signals derived from sound pressure. An analysis of the modulation shows which signals can produce APs synchronized with the source signal.     

Post-tetanic potentiation of reciprocal Ia inhibition in human lower limb.

The purpose of this study was to investigate how reciprocal Ia inhibition is changed during muscle fatigue of lower limb muscle, induced with a voluntary contraction or height frequency electrical stimulation. Reciprocal Ia inhibition from ankle flexors to extensors has been investigated in 12 healthy subjects. Hoffmann reflex (H-reflex) in the soleus muscle was used to monitor changes in the amount of reciprocal Ia inhibition from common peroneal nerve as demonstrated during voluntary dorsi or planterflexion and 50 Hz electrical stimulation induced dorsi or planterflexion. The test soleus H-reflex was kept at 20-25% of maximum directly evoked motor response (M response) and the strength of the conditioning common peroneal nerve stimulation was kept at 1.0 x motor threshold. At rest, weak la inhibition was demonstrated in 12 subjects, maximal inhibition from the common peroneal nerve was 28.8%. During voluntary dorsiflexion and 50 Hz electrical stimulation induced dorsiflexion, there absolute amounts of inhibition increased as compared to at rest, and decreased or disappeared during voluntary planterflexion and 50 Hz electrical stimulation induced planterflexion as compared to at rest. During voluntary or electrical stimulation induced agonist muscle fatigue, the inhibition of the soleus H-reflex from the common peroneal nerve was greater during voluntary dorsiflexion (maximal, 11.1%) and 50 Hz (maximal, 6.7%) electrical stimulation induced dorsiflexion than at rest. The inhibition was decreased or disappeared during voluntary planterflexion 50 Hz electrical stimulation induced planterflexion. It was concluded that the results were considered to support the hypothesis that alpha-motoneurones and la inhibitory intemeurones link to antagonist motoneurones in reciprocal inhibition. The diminished reciprocal Ia inhibition of voluntary contraction during muscle fatigue as compared to electrical stimulation, is discussed in relation to its possible contribution to ankle stability.     

Activation and inhibition of the micturition reflex by penile afferents in the cat

Coordination of the urinary bladder and the external urethral sphincter is controlled by descending projections from the pons and is also subject to modulation by segmental afferents. We quantified the effects on the micturition reflex of sensory inputs from genital afferents traveling in the penile component of the somatic pudendal nerve by electrical stimulation of the dorsal nerve of the penis (DNP) in alpha-chloralose anesthetized male cats. Depending on the frequency of stimulation (range, 1-40 Hz), activation of penile afferents either inhibited contractions of the bladder and promoted urine storage or activated the bladder and produced micturition. Stimulation of the DNP at 5-10 Hz inhibited distension-evoked contractions and increased the maximum bladder capacity before incontinence. Conversely, stimulation at 33 and 40 Hz augmented distension-evoked contractions. When the bladder was filled above a threshold volume (70% of the volume necessary for distension-evoked contractions), stimulation at 20-40 Hz activated de novo the micturition reflex and elicited detrusor contractions that increased voiding efficiency compared with distension-evoked voiding. Electrical stimulation of the DNP with a cuff electrode or percutaneous wire electrode produced similar results. The ability to evoke detrusor contractions by activation of the DNP was preserved following acute spinal cord transection. These results demonstrate a clear role of genital afferents in modulating the micturition reflex and suggest the DNP as a potential target for functional restoration of bladder control using electrical stimulation.     

家兔主动脉神经低阈压力感受反射快速重调中枢过程的特征

40只家兔,乌拉坦静脉麻醉。切断双侧主动脉神经(AN)、窦神经及迷走神经。以选择兴奋 AN 有髓传人纤维的条件刺激(0.02ms,50Hz,4—6V,5min)给予切断的 AN 中枢段,模拟导致低阈压力感受反射快速重调的保持压背景,借以诱导快速重调的中枢过程。实验表明:该中枢过程使 AN 有髓纤维传入所激发的压力感受反射降压效应衰减41.82%(P<0.01),肾交感神经活动抑制效应衰减19.31%(P相似文献   

In vitro and in vivo responses of saccular and caudal nucleus neurons in the grassfrog (Rana temporaria).

We present results from in vitro and in vivo studies of response properties of neurons in the saccular and caudal nuclei in the frog. In the in vitro studies the saccular nerve of the isolated brain was stimulated with electrical pulses. In the in vivo experiments, the neurons were stimulated by dorso-ventral vibrations of the intact animal. We identified six response types: (1) primary-like cells with short latencies and follow repetition rates up to 100 Hz; (2) phasic cells responding only to the first pulse in a train; (3) bursting cells firing several spikes in response to any stimulation; (4) late responders with very long latencies; (5) integrator cells showing facilitated responses, and (6) inhibitory cells inhibited by saccular nerve stimulation.The cells have comparable sensitivity and frequency characteristics to the primary fibres (BF 10-80 Hz, thresholds from 0.01 cm/s2) and enable a sophisticated analysis of vibrational stimuli.     

Attenuation of phrenic motor discharge by phrenic nerve afferents

Short latency phrenic motor responses to phrenic nerve stimulation were studied in anesthetized, paralyzed cats. Electrical stimulation (0.2 ms, 0.01-10 mA, 2 Hz) of the right C5 phrenic rootlet during inspiration consistently elicited a transient reduction in the phrenic motor discharge. This attenuation occurred bilaterally with an onset latency of 8-12 ms and a duration of 8-30 ms. Section of the ipsilateral C4-C6 dorsal roots abolished the response to stimulation, thereby confirming the involvement of phrenic nerve afferent activity. Stimulation of the left C5 phrenic rootlet or the right thoracic phrenic nerve usually elicited similar inhibitory responses. The difference in onset latency of responses to cervical vs. thoracic phrenic nerve stimulation indicates activation of group III afferents with a peripheral conduction velocity of approximately 10 m/s. A much shorter latency response (5 ms) was evoked ipsilaterally by thoracic phrenic nerve stimulation. Section of either the C5 or C6 dorsal root altered the ipsilateral response so that it resembled the longer latency contralateral response. The low-stimulus threshold and short latency for the ipsilateral response to thoracic phrenic nerve stimulation suggest that it involves larger diameter fibers. Decerebration, decerebellation, and transection of the dorsal columns at C2 do not abolish the inhibitory phrenic-to-phrenic reflex.     

The frequency selectivity of information-processing channels in the tactile sensory system

The frequency selectivity of the P, NP I, and NP II channels of the four-channel model of mechanoreception for glabrous skin was measured psychophysically by an adaptation tuning curve procedure. The results substantially extend the frequency range over which the frequency selectivity of these channels is known and further confirm the hypothesis that the input stage of each of these channels consists of specific sensory nerve fibers and associated receptors. Specifically, the frequency characteristics of Pacinian nerve fibers, rapidly adapting (RA) nerve fibers, and slowly adapting Type II (SA II) nerve fibers were found to be the peripheral neurophysiological correlates of the P, NP I, and NP II channels, respectively. The finding that the tuning characteristic for a test stimulus of 250 Hz delivered through a small (0.008 cm2) contactor depended dramatically on the duration of the test stimulus whereas the detection threshold did not, provides new evidence in support of the hypothesis that separate NP II and P channels exist.     

VIP and noncholinergic vasodilatation in rabbit submandibular gland

The effect of parasympathetic nerve activation on rabbit submandibular gland (SMG) blood flow and saliva secretion were studied before and after systemic administration of atropine or hexamethonium. The parasympathetic fibers were stimulated electrically (2 and 15 Hz, 10 V, 1 msec) at the plexus around the submandibular salivary duct or at the chorda lingual nerve. In untreated animals, stimulation of parasympathetic fibers caused a frequency-dependent increase of salivary secretion and blood flow in the SMG. Atropine treatment completely abolished saliva secretion at 2 Hz and 15 Hz and the increase in SMG blood flow during stimulation at 2 Hz. Although atropine significantly reduced the vasodilatory response at 15 Hz, the highest blood flow measured under such circumstances was still about 2.5 times the prestimulation value. After hexamethonium administration no blood flow increase or saliva secretion was seen upon chorda lingual stimulation. The concentration of vasoactive intestinal polypeptide (VIP)-like immunoreactivity in the venous effluent of the SMG increased during nerve stimulation. Atropine significantly reduced, and hexamethonium abolished this VIP-output elicited by parasympathetic nerve stimulation. Local infusion of VIP, peptide histidine isoleucine (PHI) and substance P all caused atropine-resistant vasodilation but no salivation. The present data suggest that VIP and possibly PHI play a role in the atropine-resistant vasodilatation in rabbit submandibular gland elicited by parasympathetic nerve stimulation. The contribution of sensory mediators such as substance P released by stimulation of afferent nerves in the chorda lingual nerve to the salivary and vasodilatory responses seems to be of minor importance in the rabbit submandibular gland.     

The frequency selectivity of information-processing channels in the tactile sensory system

The frequency selectivity of the P, NP I, and NP II channels of the four-channel model of mechanoreception for glabrous skin was measured psychophysically by an adaptation tuning curve procedure. The results substantially extend the frequency range over which the frequency selectivity of these channels is known and further confirm the hypothesis that the input stage of each of these channels consists of specific sensory nerve fibers and associated receptors. Specifically, the frequency characteristics of Pacinian nerve fibers, rapidly adapting (RA) nerve fibers, and slowly adapting Type II (SA II) nerve fibers were found to be the peripheral neurophysiological correlates of the P, NP I, and NP II channels, respectively. The finding that the tuning characteristic for a test stimulus of 250 Hz delivered through a small (0.008 cm²) contactor depended dramatically on the duration of the test stimulus whereas the detection threshold did not, provides new evidence in support of the hypothesis that separate NP II and P channels exist.     

Neural stimulation of gluconeogenesis in isolated pyruvate-perfused rat kidneys

To estimate peritubular norepinephrine concentration during renal nerve stimulation, we compared gluconeogenic responses in isolated pyruvate-perfused rat kidneys with electrical nerve stimulation and exogenous norepinephrine. During 2 and 4 Hz stimulation, venous norepinephrine was 1.7 +/- 0.4 and 2.7 +/- 0.9 nmol/L, respectively. Intra-arterial norepinephrine infusion of 60 pmol/min for 20 min (an amount corresponding to that released during 4 Hz stimulation) resulted in venous norepinephrine levels of 3.6 +/- 0.6 nmol/L. Electrical stimuli (1, 2, and 4 Hz) sustained increases in vascular resistance of 2, 5, and 11% during 20 min of stimulation, while the norepinephrine infusion increased resistance gradually by 8% and a bolus (12.5 nmol/L) transiently increased resistance by 2%. All electrical and norepinephrine interventions, except 1 Hz, decreased fractional Cl excretion. Decreased glomerular filtration rate was observed only during 4 Hz stimulation. Gluconeogenesis transiently increased during stimulation at 2 or 4 Hz (12% (p = 0.056) and 15% (p = 0.028]. The 5% increase in gluconeogenesis during norepinephrine infusion did not differ from the increase during 4 Hz stimulation (p = 0.45). An exogenous norepinephrine bolus (12.5 nmol/L) increased gluconeogenesis 60% for 15 min, four time more than the response to 4 Hz nerve stimulation (p = 0.012). Therefore, we conclude that nerve stimulation sufficient to produce sustained vasoconstriction and antinatriuresis raised norepinephrine concentration less than 12 nmol/L on the peritubular surface of the S1 proximal tubule, thus accounting for the small gluconeogenic response.     

Cerebral evoked potentials after rectal stimulation

We obtained reproducible cortical evoked potentials (EPs) in response to electrical stimulation of the rectum with 1 Hz frequency. We found 2 distinctly different EPs in response to rectal stimulation. In 5 females, the EP had an early onset latency (mean 26 msec) with multiple positive and negative peaks. In 10 females, the EP had a later onset latency (mean 52 msec) and a trifid configuration, having a very prominent negative peak. The early onset EPs after rectal stimulation appeared very similar to the wave form of the cortical EPs recorded after pudendal nerve stimulation. Finding similar interpeak latencies in the early onset EP after rectal stimulation and the EP after pudendal nerve stimulation suggests that either the same pathway was used or that rectal stimulation also stimulated the pudendal nerve. It appears that we stimulated visceral afferents when we recorded late onset EPs, because the large EP amplitude declined rapidly with faster stimulation rates and also with greater number of averaging, and the sensation threshold was very unstable, all different to somatosensory EPs.     

Human cerebrocortical potentials evoked by stimulation of the dorsal nerve of the penis

Cortical evoked potentials resulting from stimulation of the dorsal nerve of the penis (DNP) provide a unique opportunity to document the cortical localization of sexual sensory representation in man. The DNP supplies sensory axons to the major portion of the human phallus, including the penile shaft and glans. Animal and human studies indicate that this nerve plays a crucial role in erection and ejaculation. Direct cortical evoked responses to DNP electrical stimulation were recorded in patients undergoing preoperative evaluation for resection of epileptic foci. These studies provided evidence that the primary sensory cortex contains a large area of cortex devoted to the afferent fibers of the DNP and that the sensory field is in a different location than previously described. The location and distribution of this response indicated the need for revision of the traditional concept of the sensory cortical homunculus.     

电刺激猫中脑中央灰质发音区的反应及该区的传入联系

刺激猫中脑中央灰质发音区可引起动物发音、情绪反应以及心律异常、血压升高等变化。同时,本研究还揭示,分别在中脑中央灰质嘴侧和尾侧发音区注入辣根过氧化物酶后,其逆行标记神经元分布相类似;但是,中脑中央灰质发音区和非发音区的传入联系则互不相同。