Response of cutaneous A- and C-fiber nociceptors in the monkey to controlled-force stimuli

The goal of this study was to determine the capacity of primary afferent nociceptive fibers (nociceptors) to encode information about noxious mechanical stimuli in primates. Teased-fiber techniques were used to record from 14 A-fiber nociceptors and 18 C-fiber nociceptors that innervated the hairy skin. Stimulus-response functions were examined with an ascending series of force-controlled stimuli. Stimulus-interaction effects were examined with use of a series of paired stimuli in which the interval between the stimulus pairs was varied systematically. Both A-fiber and C-fiber nociceptors exhibited a slowly adapting response to the stepped force stimuli. The response of the A fibers increased monotonically with increasing force, whereas the response of the C fibers reached a plateau at low force levels. The slope of the stimulus-response function for the A fibers was significantly steeper than that for the C fibers, and the total response was greater. The A fibers also provided more discriminative information regarding stimulus intensity. The C fibers demonstrated a significant fatigue in response when the interstimulus interval between the paired stimuli was 相似文献   

The pharmacokinetics of pravastatin in patients on chronic hemodialysis

Objective: The single-dose and steady-state pharmacokinetics of the HMG CoA reductase inhibitor pravastatin and its two metabolites, SQ 31 906 and SQ 31 945, were evaluated in 12 hemodialysis patients. A single 20-mg i.v. dose was employed, followed by daily oral dosing of 20 mg over four hemodialysis intervals. Results: No statistical differences in the pharmacokinetics of pravastatin or SQ 31 906 were evident when comparing the first and last days of oral dosing with pravastatin. The pharmacokinetic parameters of pravastatin and SQ 31 906 were similar to those of healthy volunteers. SQ 31 945, the inactive polar metabolite, did accumulate in dialysis patients, as evidenced by an accumulation index of 1.7 ± 1.0. Although metabolic clearance is the predominant mode of elimination of pravastatin, hemodialysis clearances of pravastatin, SQ 31 906 and SQ 31 945 will contribute to total body clearance since dialytic clearance ranged from 40 to 80 ml · min⁻¹. Conclusion: Pravastatin can be safely administered in the usual dosages to subjects with renal failure on hemodialysis and no change in dosing is necessary. Received: 7 January 1997 / Accepted in revised form: 12 May 1997     

Activation of an inwardly rectifying K+ conductance by orphanin-FQ/nociceptin in vasopressin-containing neurons.

The orphanin-FQ/nociceptin (OFQ/N) receptor (previously, ORL1, LC132) has been shown to be coupled to an inwardly rectifying K+ conductance in several neuronal populations. Although OFQ/N receptor mRNA is densely expressed in the supraoptic nucleus (SON), little is known about its coupling to effector system(s). The present study examined the effects of OFQ/N on guinea pig magnocellular neurons within the SON using intracellular recording from hypothalamic slices. In the presence of tetrodotoxin, OFQ/N hyperpolarized 48 of 48 SON magnocellular neurons, 24 of which were subsequently identified by immunocytochemistry as arginine vasopressin positive (AVP+). Nineteen of the 48 SON neurons, including 7 which were AVP+, responded to OFQ/N with an outward current that reversed at the K+ equilibrium potential (EK+) and a decrease in slope resistance consistent with the activation of an inwardly rectifying K+ channel. In 4 of these neurons, BaCl2 significantly attenuated both the hyperpolarization and the decrease in slope resistance induced by OFQ/N. Twenty-one SON neurons, 13 of which were AVP+, responded to OFQ/N with an increase in slope resistance which did not reverse at EK+. An additional 5 neurons (2 were AVP+) were treated with the gap junction blocking agent carbenoxolone (CARB). CARB induced a small hyperpolarization, increased slope resistance and significantly reduced the subsequent OFQ/N-induced hyperpolarization. However, when the CARB and CARB plus OFQ/N hyperpolarizations were summed in these 5 cells, they were no different than the OFQ/N hyperpolarization alone. The effect of two putative OFQ/N receptor antagonists was also evaluated. The kappa3-opioid antagonist naloxone benzoylhydrazone was without effect (n = 3), and the 13-amino-acid [Phe1Psi(CH2-NH)Gly2]OFQ/N(1-13)NH2 OFQ/N analog produced a small hyperpolarization on its own in addition to partially antagonizing the effects of OFQ/N (n = 3). Taken together, these results suggest that OFQ/N acts upon SON neurons through two mechanisms, one which hyperpolarizes the neuron by activating an inwardly rectifying K+ conductance, and another which may increase membrane resistance by closing the low-resistance gap junctions.     

Cirrhosis does not affect the pharmacokinetics and pharmacodynamics of clopidogrel

Clopidogrel, a new platelet ADP receptor antagonist used for the prevention of vascular ischemic events, is converted to an active metabolite via the cytochrome P450 system. Patients with cirrhosis may not metabolize drugs normally and may, in addition, have a number of defects in the coagulation system. To assess the effect of cirrhosis on the pharmacokinetics and pharmacodynamics of clopidogrel, the authors performed an open-label, parallel-group study of 12 patients with Child-Pugh Class A or B cirrhosis and 12 matched controls. All 24 subjects received clopidogrel 75 mg PO QD for 10 days. Pharmacokinetics of clopidogrel and the major metabolite SR 26334 were analyzed on Days 1 and 10; pharmacodynamics were assessed by the inhibition of ADP-induced platelet aggregation and by bleeding time prolongation factor. Pharmacokinetic analysis of clopidogrel was limited due to low plasma concentrations arising from rapid hydrolysis to SR 26334. The Cmax at SS for clopidogrel was higher in cirrhotics than in normals. However, exposures to the metabolite SR 26334, as measured by AUC(tau), were comparable. At Day 10, there was not a statistically significant difference in mean inhibition of platelet aggregation (49.2% +/- 38.6% in cirrhotics vs. 66.7% +/- 7.5% in normals) or in bleeding time prolongation factor (1.64 +/- 0.49 in cirrhotics vs. 1.54 +/- 0.87 in normals) between groups. No significant adverse events, including bleeding events, were reported. In conclusion, there were no significant differences in the pharmacokinetics and pharmacodynamics of clopidogrel in this group of subjects with cirrhosis and matched normals. Therefore, no dosage adjustment of clopidogrel is required in patients with Child-Pugh Class A or B cirrhosis.     

Treatment of acute focal cerebral ischemia with prostacyclin

The object of this investigation was to study the effects of prostacyclin (PGI2) upon the evolution of acute focal cerebral ischemia in the cat. Twenty-five fasted adult cats, lightly anesthetized with nitrous oxide, underwent right middle cerebral artery (MCA) occlusion. Eleven cats received an intracarotid infusion of PGI2 in buffered saline pH 10.5 (100 ng/kg/min at 0.01 ml/kg/min), and 11 cats received intracarotid buffered saline pH 10.5 (0.01 ml/kg/min) without therapeutic agents. Treatment with PGI2 was started upon MCA occlusion and continued for 6 hours. Thirty minutes prior to perfusion, the animals were given fluorescein and Evans blue by intravenous injection. The cats were perfused-fixed in vivo with carbon and buffered formalin 6 hours after MCA occlusion. Another 3 cats received tritium labeled intracarotid PGI2, and peripheral venous samples were collected and assayed for PGI2 plasma levels. Mean arterial pressure was stable in PGI2 treated animals during 6 hours of MCA occlusion, while untreated cats had significant progressive hypertension during that period. The rCBF (measured by the intracarotid 133Xe method) decreased markedly in all animals immediately upon MCA occlusion. However, untreated animals had a significant progressive improvement in rCBF during the occlusion period, while PGI2 treated animals had no such improvement. Quantitative EEG changes, gross edema, areas of fluorescein extravasation, patterns of carbon perfusion, and infarct size were not significantly different in the two groups. While most untreated animals had marked Evans blue extravasation after 6 hours of MCA occlusion, most PGI2 treated animals had no such extravasation, indicating some protection of the blood-brain barrier in these animals.     

An electromechanical stimulator system for neurophysiological and psychophysical studies of pain

We have developed a computer-based electromechanical stimulator system suited for neurophysiological and psychophysical studies of pain. The core of the stimulator is a servo-controlled linear motor capable of generating 1 kg of force over a 22-mm range. Forces collinear and tangential to the interchangeable probe tip are calculated using the signal from 3 load cells (resolution: 1/8 g; range: 250 g) arranged in an equilateral triangle. Probe position is measured with an optical encoder (resolution: 1 μm; range: 25 mm). A microprocessor-based digital control system permits smooth switching of feedback control between force or position at the 1-kHz update rate. The stimulator is mounted on a microprocessor-controlled 3-axis translation system that allows automatic movement of the probe over a range of greater than 15 cm to an accuracy of better than 10 μm. The stimulator can be programmed to move in a coordinate system parallel to the skin surface being examined. An IBM-compatible computer is used to command stimulus paradigms and to display real-time motor performance and neural spike-train data. The system has been used to measure the response of nociceptive afferents in monkey to controlled force stimuli applied to various positions within the receptive field.     

Impact of Noise-Attenuating Headphones on Participation in the Home,Community, and School for Children with Autism Spectrum Disorder

Aim: The purpose of this study was to conceptualize the benefits and limitations of using noise-attenuating headphones for children with autism spectrum disorder (ASD) on participation in home, community, and school environments from the perspective of parents and teachers. Methods: Grounded theory methodology was used to guide data collection and analysis. Ten parents and five teachers of children with ASD and auditory hypersensitivity aged 6–12 completed recorded interviews. Interviews were transcribed and crosschecked prior to analysis by two or more researchers. Constant comparison was used during open and axial coding followed by theoretical integration. Results: Participants identified that the use of noise-attenuating headphones increased participation in home, community, and school settings. Barriers and benefits were identified for both around-ear and in-ear headphones. Preparation for use was an identified strategy that reduced the barriers and increased use of the headphones. Additionally, many of the children learned to predict when they needed the headphones and requested their use. Conclusion: Results of the study identified parental and teacher support for the use of noise-attenuating headphones to increase participation in natural environments for children with ASD, as well as suggestions to facilitate use for practicing physical and occupational therapists.     

Accelerated degradation of junctional acetylcholine receptor-α-bungarotoxin complexes in denervated rat diaphragm

[¹²⁵I]α-bungarotoxin was administered to rats in vivo to label acetylcholine receptors in innervated diaphragm, 5-day denervated diaphragm, or diaphragm which had been denervated immediately before labeling. The rate of degradation of junctional toxin-receptor complexes was followed by sacrificing animals at various times after labeling. The rate of degradation of junctional toxin-receptor complexes was significantly faster in 5-day denervated left hemidiaphragm (t 1/2 = 2.0 days) than in innervated left hemidiaphragm (t 1/2 = 10.7 days). The rate of degradation of junctional toxin-receptor complexes in left hemidiaphragm denervated at the time of labeling was essentially identical to that in innervated muscle for 3 days but then increased to a significantly more rapid rate (t 1/2 = 3.7 days in the period 3–13 days after denervation and labelling). These findings support the concert that continous innervation is needed to maintain the metabolic stability of junctional acetylcholine receptors.     

Effect of the mu-opioid agonist DAMGO on medial basal hypothalamic neurons in beta-endorphin knockout mice

The endogenous opioid neurotransmitter beta-endorphin (beta-END), a product of the proopiomelanocortin (POMC) gene, is strongly implicated in the control of the female reproductive cycle, stress responses, and antinociception. Using selective gene targeting, we have generated a strain of mice that do not express any beta-END. These mice exhibit both normal reproduction and normal basal and stress-induced hypothalamic-pituitary-axis activity, but exhibit a significantly attenuated opioid-mediated stress-induced analgesia. To further understand the cellular bases of these responses, we have studied mediobasal hypothalamic (MBH) neurons, including POMC neurons, using whole-cell patch recording in an in vitro slice preparation. Twenty-seven MBH cells were recorded in wild-type and 25 MBH cells were recorded in beta-END knockout mice. Neurons from both genotypes showed a significant positive correlation between DAMGO concentration (from 30 nM to 10 microM) and the induced outward K(+) current. The genotypes did not differ, however, in either the DAMGO-induced maximum outward current response or EC(50), or for the maximal response to the GABA(B) agonist baclofen. Furthermore, quantitative receptor autoradiography utilizing (3)H-DAMGO did not reveal any differences in total mu-opioid receptor binding between genotypes. Therefore, we conclude that the complete absence of beta-END throughout development did not alter either the expression of mu-opioid receptors or their coupling to K(+) channels in MBH neurons.