Pain suppression induced by electrical stimulation of the pontine parabrachial region. Experimental study in cats

Cholinergic stimulation by microinjection of drugs into a region surrounding the lateral half of the brachium conjunctivum selectively produces a non-opiate form of pain suppression in the cat. Since this suppression does not appear to involve neural systems that mediate morphine analgesia, stimulation of this pontine parabrachial region (PBR) may potentially be useful for control of human pain resistant or tolerant to opiate treatment. Because of technical problems associated with the clinical use of microinjection techniques in the human brain, we investigated whether electrical stimulation of the PBR can produce pain suppression similar to pain suppression produced by cholinergic stimulation. The results indicate that electrical stimulation of an area generally corresponding to the PBR can also produce significant pain suppression. Although the PBR is a region previously implicated in a variety of behavioral and physiological functions, the stimulation parameters that produce maximal pain suppressive effects (namely, low frequency and relatively low intensity) were not associated with noticeable changes in such functions. The prolonged onset period and persistent analgesic effects outlasting the period of stimulation--features that have been reported in other studies of brain stimulation-produced pain suppression--were observed in the present study. The time course of pain suppression did not parallel other changes in behavioral and physiological functions. These data indicate that electrical stimulation of the PBR, under certain stimulation parameters, can activate previously demonstrated neural populations related to pain suppression without affecting neural elements contributing to other behavioral or physiological functions. The authors suggest that electrical stimulation of the PBR may be clinically applicable for treatment of human pain.     

Coma associated with flaccidity produced by fluid-percussion concussion in the cat. II: Contribution of activity in the pontine inhibitory system

In the preceding paper we reported that concussive levels of fluid-percussion head injury can produce transient flaccidity of postural muscles associated with other indices of coma. This reversible coma associated with flaccidity follows an initial period of generalized areflexia and occurs in the absence of EEG slow waves. The present study investigated the physiological mechanisms underlying the flaccidity following concussive head injury be recording dorsal and ventral root potentials of the spinal cord. Studies indicated that, during the initial period of generalized areflexia, afferent input transmission was depressed although the excitability of motoneuronal pools was increased. In contrast, during periods of flaccidity, spinal cord somatomotor functions were depressed while transmission of afferent inputs was recovering. Systematic transection of the brain stem showed that activity within structures lying between collicular and midpontine levels is necessary to produce this latter condition. Cholinergic activation of pontine inhibitory areas within this same region of the rostral pons can produce profound descending inhibitory influences on postural somatomotor function in conjunction with other features of coma including suppression of eye-opening responses. Such effects occur without EEG slow waves. Moreover, other data indicate that local rates of glucose utilization within this pontine inhibitory area increase following concussive head injury. Thus, it is possible that a predominance of activity within the pontine inhibitory area could provide at least one neural basis for the reversible comatose state following concussive head injury characterized by close association between flaccidity and other indices of coma. Possible relationships of these data to clinically observed features of concussion are discussed.     

Activation of the rostral pontine reticular formation increases the spinal glycine level and inhibits bladder contraction in rats

PURPOSE: We examined the mechanism involved in the inhibition of bladder activity in rats by stimulating the rostral pontine reticular formation (RPRF) using carbachol, flavoxate and propiverine, and by analysis of amino acid levels in the lumbosacral cord. MATERIALS AND METHODS: A total of 82 female rats were anesthetized with urethane. Under isovolumetric conditions physiological saline, carbachol, flavoxate or propiverine was injected into the RPRF or intravenously. Changes in bladder activity and amino acid levels in the lumbosacral cord were examined. RESULTS: Injection of carbachol or flavoxate (0.3 microM each) into the RPRF abolished bladder contraction but there was no change after injection of physiological saline or propiverine. Intravenous injection of flavoxate or propiverine (0.1 to 10 mg/kg each) inhibited bladder contraction. Amino acid analysis revealed that injection of carbachol into the RPRF increased glutamate and glycine levels in the lumbosacral cord, while injection of flavoxate into the RPRF or intravenously caused an increase in glycine the lumbosacral cord. Injection of propiverine into the RPRF or intravenously did not influence lumbosacral cord amino acid levels. CONCLUSIONS: These results suggest that the RPRF has an important role in the inhibition of bladder contraction and carbachol or flavoxate can activate descending RPRF neurons and inhibit bladder contraction via spinal glycinergic neurons.     

脑干网状结构内注射腺苷A1受体激动剂对大鼠的镇痛作用

目的 观察脑干网状结构内注射腺苷A1受体激动剂苯基异丙基腺苷(R-PIA)对大鼠的镇痛作用及其机制.方法 雄性SD大鼠,建立脑干网状结构内置管模型,置管后1周模型制备成功的60只大鼠随机分为12组(n=5)对照组、R-PIA0.5组、R-PIA1.0组、R-PIA2.0组、茶碱(腺苷受体阻滞剂)组、DPCPX(腺苷A1受体阻滞剂8-环戊二丙基黄嘌呤)组、格列本脲(ATP-敏感型钾通道阻滞剂)组、4-AP(电压依赖型钾通道阻滞剂4-氨基吡啶)组、R-PIA2.0+茶碱组、R-PIA2.0+DPCPX组、R-PIA2.0+格列本脲组、R-PIA2.0+4-AP组.前8组注射生理盐水后15 min分别注射生理盐水、R-PIA0.5μg、R-PIA 1.0μg、R-PIA 2.0μg、茶碱5.0μg、DPCPX 1.0μg、格列本脲5.0μg、4-AP 5.0μg;后4组注射R-PIA 2.0μg前15min分别注射茶碱5.0μg、DPCPX 1.0μg、格列本脲5.0μg、4-AP 5.0μg,每次给药容积均为0.3μl(用生理盐水稀释).用热辐射法测定注射R-PIA后5、15、30、45、60、90min大鼠甩尾反应潜伏期(TFL),痛阈以MPE[(给药后TFL-TFL的基础值)/(10.0-TFL的基础值)×100%]表示.结果 脑干网状结构内注射R-PIA 0.5～2.0μg有镇痛作用,且呈剂量依赖性,这种作用可被茶碱和DPCPX完全阻滞,被格列本脲和4-AP部分阻滞.结论 脑干网状结构内注射R-PIA对大鼠有一定的镇痛作用,通过作用腺苷A1受体,与开放ATP-敏感型和电压依赖型钾通道有关.     

鞘内注射腺苷A1受体激动剂对吗啡和可乐定镇痛作用的影响

目的 观察鞘内注射腺苷A1受体激动剂苯基异丙基腺苷(R-PIA)对吗啡和可乐定镇痛作用的影响.方法 健康雄性SD大鼠,鼠龄8～10周,体重250～300g,鞘内置管成功的85只大鼠随机分为17组,每组5只,对照组、R-PIA0.4组、R-PIA0.8组、R-PIA1.0组、茶碱组、吗啡2.0组、吗啡5.0组、可乐定2.0组、可乐定15.0组、R-PIA+吗啡2.0组、R-PIA+吗啡5.0组、R-PIA+可乐定2.0组、R-PIA+可乐定15.0组、可乐定+吗啡组均鞘内注射生理盐水,15min后分别注射生理盐水、R-PIA 0.4μg、R-PIA 0.8μg、R-PIA 1.0 μg、茶碱50 μg、吗啡2.0μg、吗啡5.0μg、可乐定2.0μg、可乐定15.0μg、R-PIA 0.4μg+吗啡2.0μg、R-PIA 0.4μg+吗啡5.0μg、R-PIA 0.4μg+可乐定2.0μg、R-PlA 0.4μg+可乐定15.0μg、可乐定2.0μg+吗啡2.0μg;R-PIA+吗啡+茶碱组、R-PIA+可乐定+茶碱组、可乐定+吗啡+茶碱组鞘内注射茶碱50μg,15 min后分别注射R-PIA 0.4μg+吗啡5.0μg、R-PIA 0.4μg+可乐定15.0μg、可乐定2.0μg+吗啡2.0μg,每次给药容积均为10μl.注药后5、10、20、30、40、60min时测定大鼠热辐射甩尾反应潜伏期(TFL),用最大效应百分比(MPE)[(注药后TFL-TFL的基础值)/(10.0-TFL的基础值)γ100%]评价镇痛效果.结果 高剂量R-PIA、吗啡、可乐定可升高MPE,R-PIA可增强吗啡、可乐定的镇痛作用,可被茶碱完全阻断,吗啡可增强可乐定的镇痛作用,可被茶碱部分阻断;可乐定可增强吗啡的镇痛作用.结论 大鼠鞘内注射R-PIA可增强吗啡和可乐定的镇痛作用,其机制可能与活化脊髓内腺苷受体有关.     

Alterations in cholinergic and purinergic signaling in a model of the obstructed bladder

PURPOSE: There is increasing evidence that purinergic signaling may have a role in the generation of detrusor contractions in the pathologically unstable human bladder. However, study of the rabbit model of partial bladder outlet obstruction showed a loss in cholinergic and purinergic innervation after 3 months. We examined changes in the cholinergic and purinergic components contributing to nerve mediated detrusor contraction in a rabbit model of detrusor instability secondary to bladder outlet obstruction during the early hypertrophic stage. MATERIALS AND METHODS: Partial bladder outlet obstruction was surgically induced in adult male rabbits. At 3 weeks detrusor strips were obtained and contractions were produced by electrical field stimulation in the presence of 1 microM. atropine and/or 30 microM. of the P2-purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2'4'-disulfonic acid, and after adding 1 microM. tetrodotoxin. Purinergic and cholinergic components were calculated and compared with those from sham operated controls. RESULTS: The cholinergic or atropine sensitive component was frequency dependent, that is smaller at lower frequencies. The cholinergic component was decreased in the early obstructed bladder. The pyridoxalphosphate-6-azophenyl-2'4'-disulfonic acid sensitive purinergic component was frequency dependent, that is larger at lower frequencies. The purinergic component was increased in the early obstructed bladder. The overall electrical field stimulation response or the response to KCl was unaltered in the obstructed group. There was no difference in the response in strips from the bladder neck and dome. CONCLUSIONS: The purinergic component of nerve mediated detrusor contraction is increased and the cholinergic component is decreased in early stages of bladder obstruction in this rabbit model.     

Central cholinergic depletion induced by 192 IgG-Saporin alleviates the sedative effects of propofol in rats

We examined the effect of central cholinergic depletion on thesedative potency of propofol in rats. Depletion was producedby intracerebroventricular administration of an immunotoxinspecific to cholinergic neurones (192 IgG-Saporin; 2 µg).As a result of this lesion, acetylcholine concentration wasreduced by about 40% in the frontoparietal cortex and in thehippocampus but was essentially normal in the striatum and cerebellum.Sedation in rats was assessed as the decrease in locomotor activity.Sedative potency of propofol (30 mg kg^–1 i.p.) was reducedby about 50% in rats who received the injection of 192 IgG-Saporinas compared to controls. These results show that a central cholinergicdepletion alleviates the sedative effect of propofol, and indicatesthat basal forebrain cholinergic neurones might mediate partof the sedative/hypnotic effects of propofol. Br J Anaesth 2000; 85: 869–73     

Computational evaluation of platelet activation induced by a bioprosthetic heart valve

It is known that bioprosthetic heart valves (BHVs) have better hemodynamics and lower thromboembolic events compared with their mechanical counterparts; however, patients implanted with BHVs still face the potential of such complications. The risk of a clinical thromboembolism is on average 0.7% per year in patients with tissue valves in sinus rhythm. In this study, we developed a computational fluid dynamic (CFD) model of a BHV implanted in an aortic root and investigated the BHV-induced platelet activation using a damage accumulation model previously applied to mechanical valves. The CFD model was validated against published experimental data, including the flow velocity profile across the valve and the transvalvular pressure drop, and close matches were obtained. Hemodynamic performance measures such as flow velocity, turbulent kinetic energy, and wall shear stress were explored. Lagrangian particle tracking was used to calculate the extent of platelet activation for central bulk flow and flow in the vicinity of the leaflets. A peak flow of 2.22 m/s was observed at 40 msec after peak systole in the vicinity of a fold at the base of the leaflets. With the platelet activation expressed as 0-100% of activation threshold levels, mean damage on one pass was 2.489 × 10(-7)% and maximum damage on one pass was 8.778 × 10(-4)%. Our results suggested that the potential for BHV-induced platelet activation was low and that the leaflet's fully open geometry might play a role in the extent of blood element damage.     

Coma associated with flaccidity produced by fluid-percussion concussion in the cat. I: Is it due to depression of activity within the brainstem reticular formation?

This study is the first attempt to characterize neurological and behavioural consequences of fluid-percussion concussive head injury in the cat. Both animals initially anaesthetized by N2O as well as unanaesthetized, chronically prepared animals were subjected to injury. Injury with a fluid-pressure wave of 1.9-2.5 atm (duration 21-24 ms) produced a brief generalized areflexia. Following this initial response, injury greater than 2.1 atm frequently produced a period associated with hypotonia of postural muscles and suppression of postural motor responses (flaccidity). A close association between flaccidity and other indices of coma such as absence of eye-opening responses was noted. These consequences of injury can occur without fatal apnoae, circulatory collapse or overt intraparenchymal haemorrhages. This result suggests that mechanical stress predominantly restricted to the brain stem in fluid percussion may be sufficient, at least in the cat, to produce coma associated with flaccidity which has been previously documented for acceleration concussion. There was no evidence that fluid percussion produced EEG depression similar to the effects of lesions in the mesencephalic reticular activating system (RAS). Thus, depression of general levels of brain activity including those within the RAS seems not be necessary for production of this form of reversible coma.     

A model of reversible obstructive jaundice in the rat

A model of reversible, extrahepatic biliary obstruction is described. Vessel loop blockade of the biliary tree results in obstructive jaundice while removal of the exteriorized vessel loop provides internal biliary drainage without subsequent laparotomy. This technique combined with a system for chronic venous infusion and arterial blood sampling in the unrestrained rat is ideal for long-term metabolic studies of obstructive jaundice. Male Fisher 344 rats (275-350 g) underwent either the combined procedure of total biliary tract blockade and vascular access or sham operation. Mean serum bilirubin was significantly elevated (12.7 +/- 8.9 mg/dl) in the experimental group and following relief of biliary obstruction significantly dropped below 1 mg/dl in all animals except one. Concomitant changes in alkaline phosphatase, glutamate oxaloacetate transaminase, and glutamate pyruvate transaminase were seen. Experimental and control rats initially lost weight following laparotomy; however, mean body weight stabilized by the 5th postoperative day and was similar in both groups on the 10th postoperative day. This combined procedure is a simple, effective and reproducible method of obstructive jaundice.     

The use of URYX for reversible vasectomy in a rabbit model

URYX is a biocompatible polymer of ethylene vinyl alcohol dissolved in a dimethyl sulfoxide (DMSO) carrier to allow injection of a very low-viscosity fluid into tissue. Once the material comes into contact with body tissue or fluid, the DMSO rapidly dissipates from the polymer, which results in a precipitate of a coherent solid mass. The purpose of the present study was to determine whether URYX can effectively occlude the vas deferens and whether patency can be restored by redissolving the URYX in vivo using the solvent DMSO. Eight male New Zealand White rabbits (age range, 25-41 weeks; mean age, 33.9 +/- 7.5 weeks; mean weight, 4.0 +/- 0.2 kg) were used in 2 experiments (E1 and E2). In E1, 3 rabbits underwent unilateral vasectomy, and the contralateral vas was injected with either 0.05 or 0.10 mL of URYX, to determine the amount of URYX required to cause obstruction. Two animals underwent bilateral vasectomy, to serve as controls. In E2, 3 animals underwent bilateral URYX injection and were compared with the bilateral vasectomy control rabbits used in E1. After 1 month of initial bilateral URYX treatment, all animals in E2 underwent attempted unilateral reversal with 1.5 mL of DMSO injected into 1 occluded vas deferens. Two end points were evaluated-a clinical end point assessed by semen analyses and a pathological end point assessed by histological analysis of treated tissues, to assess for safety. A 1.5-cm infrapubic incision was made to expose both vasa in anesthetized rabbits. The vasal injection of URYX was performed with a 30-gauge needle. Vasectomy was performed by excision of a 1-cm segment of the vas deferens and subsequent ligation with a 6-0 prolene suture. Semen was collected using an artificial vagina 2-3 times/wk before and 1 month later, after injection treatments and vasectomy. Manual sperm counts were performed. All animals were sacrificed, and tissues (distal vas, injection site, proximal vas, cauda epididymis, caput epididymis, and testis) were harvested and examined for the presence of URYX. The inflammatory response of the wall and adventitia of the vas deferens was given a score (0-15) based on the sum of grades (0 = none, 1 = mild, 2 = moderate, and 3 = severe) for the following categories: foreign body giant cell reaction, granulation tissue, lymphocytes, eosinophils, and scarring, as evaluated by a single pathologist (J.M.). Vasal injection with 0.05 mL of URYX was not sufficient to cause occlusion. Both animals injected with 0.1 mL of URYX were effectively occluded. The injection of occluded vasa with DMSO did not dissolve the URYX plug in the vas lumen. There was no significant difference in vasal inflammatory response scores between vasal units treated with URYX only and vasal units in the vasectomy model. Vasal units subjected to URYX followed by DMSO demonstrated greater inflammatory response scores than vasal units treated with URYX followed by normal saline, URYX alone, or vasectomy. Epididymal and testicular histology remained unaffected in all vasal units in E1. The vasal units in E2 subjected to URYX followed by normal saline showed no histological abnormalities of the epididymis and testis. However, those vasal units subjected to URYX followed by DMSO in E2 showed evidence of adhesions, necrosis, and degenerating cells in the epididymis and a focal foreign body giant cell reaction in the testis. The bilateral vasal injection of URYX can result in azoospermia in the rabbit model. Reversal with subsequent DMSO injection was not achieved. A minimal inflammatory response of the vas deferens was observed with URYX injection alone; however, DMSO following URYX injection resulted in increased vasal inflammation, in addition to epididymal and testicular changes.     

A reversible model of acute hepatic failure by temporary hepatic ischemia in the pig

BACKGROUND: To evaluate new therapies for human fulminant hepatic failure, a suitable large animal model is needed. The purpose of this study was to develop a reversible surgical model of acute hepatic liver failure by transient ischemia in pigs. MATERIALS AND METHODS: Under general anesthesia, an end-to-side portacaval shunt was performed in 17 pigs and tape was laid around the hepatoduodenal ligament. Two days after construction of the functional portacaval shunt, 13 ambulant pigs underwent transient total liver ischemia by tightening of the tape around the hepatoduodenal ligament for 5.5 h. During ischemia, 10% glucose was continuously infused intravenously to prevent hypoglycemia. RESULTS: Ten animals (77%) died with hepatic coma after a mean duration of 22.5 +/- 1.9 h. The 3 remaining animals survived more than 5 days and were sacrificed. In dying animals, encephalopathy was observed 14 +/- 1.7 h after the onset of ischemia. During ischemia, similar progressive decrease of fibrinogen, platelets, prothrombin time, and factors V and VII activities was observed in dying and surviving animals. Just before death, mean prothrombin and factors V and VII activities were respectively 22 +/- 2, 21 +/- 4.4, and 24 +/- 5%. At 22 h, plasma ammonia and lactate levels were respectively 705 +/- 93 micromol/L and 10.5 +/- 0.4 mmol/L in dying animals and 249 +/- 75 micromol/L and 2.9 +/- 0.1 mmol/L in surviving animals (P < 0.01). Estimation of the percentage liver cells necrosed was 74 +/- 4.7% in the survivors and 86 +/- 5.5% in animals who died of hepatic coma (NS). CONCLUSIONS: This model is reproducible and reversible and should allow the quantitative evaluation of new technologies, such as bioartificial liver, for the support of hepatic failure in humans.     

Photobiomodulation increases cell viability via AKT activation in an in vitro model of diabetes induced by glucose neurotoxicity

Lasers in Medical Science - Peripheral neuropathy (PN) is a serious complication of diabetes mellitus (DM) and is known to be resistant to conventional treatment. Photobiomodulation (PBM) is...