Perineurial cells are the first to traverse gaps of peripheral nerves in silicone tubes

Silicon tubes were used to study the outgrowth and differentiation of the perineurium around the cord bridging the gap between the proximal and distal stumps of the transected sciatic nerve of rats. The sequence of events was investigated at time intervals 3, 7, 12, 18, and 21 days after surgery. Although similar tubulation systems have been used to investigate various aspects of peripheral nerve fibre regeneration, the present study shows for the first time with electron microscopic and immunocytochemical methods that a primitive perineurium bridges the gap as the initial cellular element. This perineurium develops from outgrowing fibroblasts as early as 7 days post surgery, forming a tube which is used as a guiding structure for subsequent cellular elements. The proximal and distal perineurial tubes join between 12 and 18 days after surgery thus representing the first connection between the proximal and distal nerve stumps. Blood vessels, Schwann cells, and axons appear to follow in this sequence.

Spontaneous activity of cat spinal ganglion neurons in vivo

Recordings were made from L4-S1 spinal ganglion neurons of anesthetized cats while their associated dorsal root and the sciatic nerve were left intact, locally anesthetized, or locally anesthetized and sectioned. In all three experimental conditions spontaneous discharges were recorded. These discharges occurred in the absence of any electrical stimulation of the dorsal root or sciatic nerve, and were not due to peripheral exploration of receptive fields or sustained firing in joint or muscle afferents. The spontaneous discharges were relatively rhythmic, and their firing frequency ranged from 5 to 100 impulses per s. Interactions between spontaneous and electrically evoked discharges were observed that depended on the impulse's frequency of firing. High frequency discharges always abolished low frequency impulses regardless of whether these latter were spontaneous or evoked. Extra spikes and postspike events that followed impulses evoked by stimulation of the dorsal root or sciatic nerve were also recorded from some spinal ganglion neurons. These results suggest that spontaneous discharges may originate within the spinal ganglion itself, and that they can occur under normal circumstances.

Ascending afferent regulation of rat midbrain dopamine neurons

Standard, extracellular single-unit recording techniques were used to examine the electrophysiological and pharmacological responsiveness of midbrain dopamine (DA) neurons to selected, ascending afferent inputs. Sciatic nerve stimulation-induced inhibition of nigrostriatal DA (NSDA) neurons was blocked by both PCPA (5-HT synthesis inhibitor) and 5,7-DHT (5-HT neurotoxin), suggesting mediation by a serotonergic (5-HT) system. Direct stimulation of the dorsal raphe (which utilizes 5-HT as a neurotransmitter and inhibits slowly firing NSDA neurons) inhibited all mesoaccumbens DA (MADA) neurons tested. Paradoxically, DPAT, a 5-HT1A agonist which inhibits 5-HT cell firing, enhanced sciatic nerve stimulation-induced inhibition of NSDA neurons. MADA neurons were not inhibited by sciatic nerve stimulation and, therefore, could not be tested in this paradigm. In contrast to the dorsal raphe, electrical stimulation of the pedunculopontine tegmental nucleus preferentially excited slowly firing NSDA and MADA neurons. Thus, both excitatory and inhibitory ascending afferents influence the activity of midbrain DA neurons, and intact 5-HT systems are necessary for sciatic nerve stimulation to alter DA cell activity. However, the role that 5-HT plays in mediating peripheral sensory input remains unclear.

Cerebellar stimulation modulates thalamic noxious-evoked responses

Parafascicular (PF) neurons responding to noxious stimuli and focal electrical stimulation of midbrain, diencephalon, and hypothalamic nuclei, which send projections to PF, modulates the PF spontaneous and noxious-evoked responses. Some cerebellar efferents ascend to PF. This investigation attempted to study the effect of cerebellar stimulation on spontaneous and noxious-evoked PF neuronal activity in rats. It was observed that 26% (73/280) of PF neurons responded to a noxious stimulus. The PF neuronal population exhibits two cell types according to their response pattern following the noxious stimulus. One type of PF neurons were excited (n = 53) and were classified as nociceptive-on cells. The second type of PF neurons responded to noxious stimulus by a decrease in the ongoing firing rate (n = 20) and were classified as nociceptive-off cells. The responses of these two types of nociceptively identified cells were tested following cerebellar lateral nucleus stimulation (Lat.N.S.) utilizing several current intensities. Lat.N.S. with lower intensities (0.1-0.2 mA) elicited suppression of both spontaneous and nociceptive-evoked discharges of the nociceptive-on neurons, although higher intensities (0.4-0.6 mA) elicited excitation on both discharges of this type of neuron. In contrast, Lat.N.S. induced a monophasic intensity-dependent suppression of both the spontaneous and the nociceptive-evoked discharges of the nociceptive-off neurons. The results indicate that Lat.N.S. modulates the nociceptive-evoked responses of PF neurons. The possible role and related pathways of cerebellum in modulating noxious input were discussed.

Reevaluation of the sciatic nerve block

BACKGROUND AND OBJECTIVES

Sciatic nerve blocks are perceived as unreliable, technically demanding, and uncomfortable. With strict criteria to define success rates, we designed a study to examine the efficacy of two techniques of sciatic nerve block.

METHODS

All blocks were performed by a novice in sedated patients using an insulated needle and a nerve stimulator.

RESULTS

Overall success with both techniques was 87.5%. One transient neurologic deficit attributed to the sciatic nerve block was observed; otherwise, the technique provided satisfactory anesthesia without complications.

CONCLUSIONS

Patient acceptance was excellent.

Intrathecal catheterization alone reduces autotomy after sciatic cryoneurolysis in the rat

There is substantial evidence that sciatic cryoneurolysis (SCN, freeze lesion of the sciatic nerve) is a neuropathic pain model in the rat. During characterization of this model, SCN was performed 4 days after either a sham operation or the insertion of an indwelling intrathecal catheter preparatory to selective spinal drug administration. Body weight and autotomy scores were recorded for the next 22 days until sacrifice. The catheter group experienced significant weight loss (7.5%) by 4 days but rapidly regained to parity with the sham group. Autotomy scores and the frequency of severe autotomy (score > 3) were less at day 22 in the catheter group as compared with the sham-control group (p < 0.005, p < 0.03, respectively). Intrathecal catheterization itself effects the degree of behavioral response to neurogenic pain and thus, should be controlled for in studies using nociceptive animal models.

Autotomy and the sciatic functional index

The rat sciatic nerve serves as a good model of nerve regeneration and, as such, is often used in investigations of nerve repair. After transection of the sciatic nerve, rodents frequently scratch and bite their anesthetic foot, resulting in amputation of one or more toes. This is termed autotomy or autophagy. When these rats are part of a study using the sciatic functional index (SFI), autotomy results in unusable data, since necessary foot landmarks have been removed. It would be helpful, therefore, to be familiar with the phenomenon of autotomy and to know which rats are least likely to mutilate themselves. In our experiment involving 64 rats in which the sciatic nerve was transected and repaired, we found that female Sprague-Dawley rats were significantly less likely to perform autotomy than males (33% vs. 65%, P = .04). In addition, we noted that two-thirds of the autotomies that occurred did so by postoperative week 4 and that tabasco sauce did not decrease this activity. We present our experience and a survey of the literature on autotomy and the SFI.

Colocalisation and covariation of c-JUN transcription factor with galanin in primary afferent neurons and with CGRP in spinal motoneurons following transection of rat sciatic nerve

The expression of galanin (GAL) in L5 dorsal root ganglia (DRG) and calcitonin gene-related peptide (CGRP) in motoneurons (MN) of lumbar spinal cord and their colocalisation with the nuclear c-JUN protein was investigated by immunocytochemistry following transection of rat sciatic nerve. Expression of c-JUN in L5 DRG neurons increased 10 h following transection. Between 24 h and 10 days 64%-72% of all neurons were labelled. After 50 and 150 days, the end of the observation period, 62% and 27%, respectively, of neurons were labelled by c-JUN. Expression of GAL started after 24 h, reached a maximum between 2 and 10 days in 40-50% of all neurons and persisted in 37% up to 50 days. After 150 days, GAL-IR had returned to basal levels. Between 24 h and 150 days, 75%-86% of all GAL positive neurons showed a nuclear c-JUN immunoreactivity, the maximal number was visible between 2 and 10 days. After 30 days, small diameter neurons showed a slightly increased colocalisation of GAL and c-JUN compared to large diameter neurons. In motoneurons (MN) of lumbar spinal cord of untreated rats, c-JUN was predominantly visible in small diameter MN. The number of c-JUN labelled MN raised 15 h following sciatic nerve transection in both small and large diameter MN. It reached its maximum after 2 days and declined after 40 days. CGRP showed basal expression exclusively in large MN. Its expression raised after 20 h, showed a maximum after 48 h and returned to control levels after 20 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Is laser repair effective for secondary repair of a focal lesion in continuity?

It is possible to seal nerve ends together with the laser, and this can be effective for sharp injuries that are repaired relatively acutely or primarily. The possibility of utilizing the laser for secondary nerve repair after resection of a lesion in continuity was investigated in a rat sciatic nerve model. After baseline recording of nerve and muscle action potentials (MAP), a 3-mm-long crush injury of the sciatic nerve was performed bilaterally in 12 rats. Two weeks later, the crushed segment was resected, and the nerve on one side was repaired by end-to-end anastomosis using epineurial sutures and on the other side by sealing the nerve ends together with the CO2 laser. At reexploration 50 days postoperatively, all 12 suture repairs were anatomically in continuity and conducted a nerve action potential (NAP), while 10 of the 12 laser-repaired nerves had distracted. Laser repairs not distracted showed electrical and histologic evidence of regeneration. It is concluded that laser repair is not effective for delayed repair of lesions in continuity unless tension at the repair site can be lessened.

Long-term evaluation of nerve regeneration in a biodegradable nerve guide

Nerve regeneration using artificial biodegradable conduits is of increasing interest. The aim of this study is to evaluate the regeneration and maturation of a nerve after long-term implantation (2 years) of a biodegradable poly-L-lactide/poly-epsilon-caprolactone (PLLA/PCL) copolymeric nerve guide in the sciatic nerve of the rat. After harvesting, we evaluated both the regenerated nerves and the controls, using light microscopy, transmission electron microscopy, and morphometric techniques. Remnants of biomaterial were still present after 2 years of implantation, but the foreign body reaction was very mild at this stage, due to the rounded shapes of the polymer debris. Morphometric analysis showed significant differences between the regenerated nerve and the normal sciatic nerve: the number of myelinated fibers is higher, and the mean fiber diameter of the myelinated fibers in the regenerated nerve is smaller. In conclusion, the results demonstrate that the new PLLA/PCL nerve guide can provide optimal conditions for regeneration and maturation of damaged nerves.

Brain-derived neurotrophic factor rescues spinal motor neurons from axotomy-induced cell death

Current ideas about the dependence of neurons on target-derived growth factors were formulated on the basis of experiments involving neurons with projections to the periphery. Nerve growth factor (NGF) and recently identified members of the NGF family of neuronal growth factors, known as neurotrophins, are thought to regulate survival of sympathetic and certain populations of sensory ganglion cells during development. Far less is known about factors that regulate the survival of spinal and cranial motor neurons, which also project to peripheral targets. NGF has not been shown to influence motor neuron survival, and whether the newly identified neurotrophins promote motor neuron survival is unknown. We show here that brain-derived neurotrophic factor (BDNF) is retrogradely transported by motor neurons in neonatal rats and that local application of BDNF to transected sciatic nerve prevents the massive death of motor neurons that normally follows axotomy in the neonatal period. These results show that BDNF has survival-promoting effects on motor neurons in vivo and suggest that BDNF may influence motor neuron survival during development.

Axonal flow blockade induces alpha-CGRP mRNA expression in rat motoneurons

Axonal flow of motoneurons was blocked in the sciatic nerve by the application of vinblastine at a low concentration (100 microM) not considered likely to cause axonal degeneration. The number of motoneurons expressing alpha-calcitonin gene-related peptide (CGRP) mRNA was significantly increased by vinblastine application, while the expression of beta-CGRP mRNA was not influenced. These findings suggest that the synthesis of these two peptides is differentially regulated and that alpha-CGRP mRNA is possibly down-regulated by unknown factor(s) which normally undergo retrograde transport from the periphery.

Insulin-like growth factor II stimulates motor nerve regeneration

Injury to mammalian motor nerves can lead to paralysis, but relatively successful regeneration may occur when conditions are favorable. Elucidation of the mechanism upholding successful regeneration is of theoretical and clinical interest. In this study, the hypothesis that insulin-like growth factor II (IGF-II) can stimulate motor nerve regeneration was tested. When IGF-II was infused continuously near a site of crush on the sciatic nerve, the distance of motor axon regeneration was increased significantly in rats. In contrast, spontaneous regeneration was inhibited when an anti-IGF-II antiserum was infused through a "window" in the epineurium. Thus, infused IGF-II can increase, and endogenous IGFs can support, the regeneration of motor axons in lesioned nerves.

A rat sciatic nerve model for independent assessment of sensory and motor block induced by local anesthetics

The purpose of this study was to develop a reliable model to independently quantify motor and sensory block produced by local anesthetics. The sciatic nerve was blocked in 52 rats by injecting 0.2 mL of 0.125%, 0.25%, 0.5%, or 0.75% bupivacaine (n = 13 for each concentration). Accurate needle placement was achieved using a nerve stimulator at 0.2 mA and 1 Hz. Ten control rats received 0.9% saline (n = 5) or sham nerve stimulation (n = 5). Motor block was assessed by measuring hindpaw grip strength with a dynamometer. Sensory block was determined by measuring hindpaw withdrawal latency from radiant heat. The intensity of both motor and sensory block measured at 30-min intervals was plotted against time until full recovery to obtain the area under the curve. Intergroup comparisons using analysis of variance showed increasing area under the curve with increasing concentrations of bupivacaine for motor blocks (P < 0.05 for all intergroup comparisons except 0.5% vs 0.75%) and sensory blocks (P < 0.05 for all intergroup comparisons). Normal saline or sham nerve stimulation did not result in any motor or sensory block.

Disuse osteopenia is accompanied by downregulation of gene expression for bone proteins in growing rats

Unilateral sciatic neurectomy (USN) resulted in cortical osteopenia in tibiae from the sciatic nerve-sectioned limb of growing rats. The bone deficit resulted from decreased periosteal addition; there were no changes in the indexes of bone resorption. The periosteal bone formation rate was reduced in the nerve-sectioned limb within 7 days of sciatic neurectomy, and this decrease persisted for at least 56 days. Steady-state mRNA levels for bone proteins were determined in periosteum isolated from tibiae and femurs 7 and 14 days after sciatic nerve section. Nerve section resulted in decreased levels of mRNA for osteocalcin, alkaline phosphatase, and possibly the prepro-alpha (I)-subunit of type I collagen (collagen). The effects were more pronounced in tibiae than femurs, corresponding to the greater degree of immobility induced by USN in the former bone. The results demonstrate that decreased bone formation precedes establishment of disuse cortical osteopenia in growing rats with no evidence for a change in bone resorption. Furthermore, the decreased bone formation is associated with, and may be due to, reduced mRNA levels for matrix proteins and other important bone proteins.

Local application of neuropathic organophosphorus compounds to hen sciatic nerve: inhibition of neuropathy target esterase and peripheral neurological impairments

Diisopropyl phosphorofluoridate (DFP), mipafox, cresylsaligenyl phosphate, and phenylsaligenyl phosphate were applied to a 1.5-cm segment of the common trunk of the sciatic nerve in adult hens. At doses of 18-182 micrograms mipafox and 9-110 micrograms DFP, inhibition of neuropathy target esterase (NTE) for the treated segment was over 80%, whereas for the adjacent distal and proximal segments inhibition was under 40%, 15 min after application. NTE was not affected in the peripheral distal terminations arising from the common sciatic nerve (peroneal branches), contralateral sciatic nerve, brain, and spinal cord. A 24-hr study suggested a displacement of the activity-free region toward more distal segments of the nerve. All animals treated with 55 and 110 micrograms DFP or 110 micrograms mipafox lost a characteristic avian retraction reflex in the treated leg 9-15 days after dosing, suggesting peripheral neurological alterations. Only hens dosed at the maximum dose in both extremities presented alterations in motility (Grade 1 or 2 on a 0-8 scale), suggesting no significant central nervous system alterations. Electron microscopy of peroneal branches showed axon swelling and accumulation of smooth endoplasmic reticulum similar to animals dosed systemically (s.c.) with 1-2 mg/kg DFP. The branches also contained granular and electron-dense materials, as well as some intraaxonal and intramyelinic vacuolization. Clinical effects were not observed in animals protected with a 30 mg/kg (s.c.) dose of phenylmethanesulphonyl fluoride. It is concluded that the peripheral neurological effects of local dosing correlate with the specific modification of NTE in a segment of sciatic nerve and that the axon is a more likely target than the perikaryon or nerve terminal in the triggering mechanism of this axonopathy.

Subblocking concentrations of local anesthetics: effects on impulse generation and conduction in single myelinated sciatic nerve axons in frog

Phenomena seen in axons exposed to subblocking doses serve as the basis for interpreting clinical and behavioral observations during onset and recovery of peripheral nerve block. To delineate the changes in excitability and in impulse conduction caused by subblocking concentrations of local anesthetics (LAs) in myelinated peripheral nerve fibers, LAs were applied to excised frog sciatic nerves while impulse conduction was monitored in single axons. For concentrations ranging from 0.01 to 1.2 times the LA concentration needed to block impulse conduction, three measures of susceptibility to LA were made to quantify the action of the drugs on "resting" fibers (firing rates < or = 0.5 Hz): the increase in the threshold for electrical activation of impulses, the increase in conduction latency reflecting the slowing of impulse conduction in the region exposed to LA, and the "critical blocking concentration" of LA just sufficient to prevent impulse conduction in the recorded fiber. Wide interfiber variation in these variables was observed (e.g., for lidocaine, latency increases at block ranged from 66% to 257% of control, blocking concentrations ranged from 0.29 to 1.40 mM), which was not correlated with fiber diameter (as indicated by resting conduction velocity). Mathematical modeling of impulse conduction in fibers exposed to LA demonstrated that the interfiber variation in susceptibility to LA block could result from interfiber differences in the density of sodium and potassium channels. The effects of LA were also studied in active fibers (firing rates > 0.5 Hz). Local anesthetics reversibly inhibited two normally occurring afteroscillations in membrane threshold related to afterpotentials following an impulse. These were "superexcitability," a transient lowering of threshold lasting as long as 1 s, and "depression," a phase of raised threshold peaking within 2-4 s after an impulse and recovering slowly over several minutes. Impulse activity also transiently increased the apparent potency of LAs. Such "use-dependent" increases in threshold and decreases in conduction velocity showed kinetics that were agent specific, lasting 1 s after a burst of impulses for lidocaine and lasting > 10 s for bupivacaine. At low concentrations, within the range of nontoxic plasma concentrations after systemic administration, the predominant actions of LAs on conducting fibers were transient decreases in excitability and conduction velocity in combination with a reduction of intrinsic oscillatory aftereffects of impulse discharge. These effects may degrade decoding of information in discharge patterns without actually blocking conduction of infrequent impulses, suggesting how functional blockade of coordinated movement and perception may occur even without complete blockade of impulse conduction.

Responses of spinothalamic tract neurons to mechanical and thermal stimuli in an experimental model of peripheral neuropathy in primates

1. An experimental peripheral neuropathy (EPN) was induced in three monkeys (Macaca fascicularis) by ligation of spinal nerve L7. Behavioral responses to innocuous mechanical stimuli were tested before and after the surgery. Two weeks after the nerve ligation, the activity of spinothalamic tract (STT) neurons was recorded on both sides of the spinal cord with the animal under general anesthesia. Responses of the STT neurons to the following stimuli applied to the skin were recorded: graded mechanical stimuli (brush, press, pinch and squeeze), von Frey filaments of different bending forces (0.077-19.05 g), 5-s heat stimuli ranging from 39 to 53 degrees C, and 15 s cold stimuli (32-8 degrees C). 2. Innocuous mechanical stimulation of the foot did not evoke hindlimb withdrawal in the animals before surgery. Within 24-48 h after nerve ligation, the animals showed hindlimb withdrawal to the same innocuous stimuli. This behavior was more pronounced on the side of the ligation than on the sham-operated side and more frequent during the second week after the surgery. 3. Responses of 51 STT neurons recorded on the side of the ligation (EPN all group) were compared with responses of 33 STT cells recorded on the sham-operated side (control group) and with records from STT neurons in unoperated animals obtained earlier (reference group). Neurons from the EPN all group were divided into two sets according to their rostrocaudal location (EPN R, rostral to L6/7 border, n = 40; EPN C, caudal to L6/7 border, n = 11). 4. Neurons from the EPN all and EPN R groups had significantly higher background frequencies than those from the control and reference groups. Innocuous brush stimuli evoked mean discharge frequencies of approximately 35 Hz in EPN R neurons and only approximately 15 Hz in both control and reference groups. Increased responsiveness of EPN R neurons to innocuous stimuli was also demonstrated by lower thresholds and higher discharge frequencies to von Frey filament stimulation and by discriminative analysis of the responses evoked by graded mechanical stimuli. 5. The responses of the EPN R neurons to heat stimulation of the skin showed decreased thresholds and increased responses to suprathreshold stimuli, resulting in a significant leftward shift of the stimulus-response curve compared with both reference and control groups. The neurons from the control group showed responses comparable to reference group values. 6. Neurons from the reference group tested with the cooling stimuli showed no evoked response above background.(ABSTRACT TRUNCATED AT 400 WORDS)

Time-dependent regenerative influence of predegenerated nerve grafts on hippocampus

Our previous studies have revealed that the predegeneration facilitated the neurite outgrowth from hippocampus following the peripheral nerve grafts implantation. The aim of the present work is to find whether the stimulative power of peripheral nerve grafts depends on the time lapse after the transection. Autologous predegenerated distal stumps of the rat sciatic nerves were implanted into the hippocampus on the 7th, 14th, 28th, and 35th day following the transection. Six weeks later, horseradish peroxidase conjugated with fluorescein isothiocyanate was injected into the graft and frozen sections of brains were made. Fluorescence microscope examination has shown that FITC-HRP labeled cells were present among the hippocampal neurons in all the brains under examination, excluding these grafted with 14-day predegenerated peripheral nerves. The FITC-HRP labeled neurons were particularly numerous when the 7- and 35-day-old predegenerated stumps were used as grafts.

The non-NMDA antagonist CNQX prevents release of amino acids into the rat spinal cord dorsal horn evoked by sciatic nerve stimulation

Basal extracellular concentrations of 9 amino acids (AAs: aspartate, Asp; glutamate, Glu; asparagine, Asn; serine, Ser; glycine, Gly; threonine, Thr; alanine, Ala; taurine, Tau; and glutamine, Gln) were determined in the spinal cord dorsal horn of anesthetized rats using microdialysis and HPLC techniques. The concentrations of all measured AAs but Gln increased significantly (P < 0.05) during sciatic nerve stimulation at C-fiber strength. The concentration of Tau remained elevated following stimulation, while the other AAs returned to prestimulation values. Addition of the specific non-NMDA antagonist, CNQX, to the perfusing solution prevented the nerve stimulation-evoked AA release. Since the measured increases in extracellular AA concentrations are probably mainly due to activation of interneurons, these results suggest that blockade of non-NMDA receptors prevented activation of interneurons in the dorsal horn and support a major role of non-NMDA receptors at the first synapse of primary afferent fibers in the dorsal horn. Complete block of AA release and decreased basal levels of Glu after infusion of TTX into the dorsal horn also implies increased neuronal activity as the main source of higher AA levels during nerve stimulation.

Increased plasma O2 solubility improves O2 uptake of in situ dog muscle working maximally

A perfluorocarbon emulsion [formulation containing 90% wt/vol perflubron (perfluorooctylbromide); Alliance Pharmaceutical] was used to increase O2 solubility in the plasma compartment during hyperoxic low hemoglobin concentration ([Hb]) perfusion of a maximally working dog muscle in situ. Our hypothesis was that the increased plasma O2 solubility would increase the muscle O2 diffusing capacity (DO2) by augmenting the capillary surface area in contact with high [O2]. Oxygen uptake (VO2) was measured in isolated in situ canine gastrocnemius (n = 4) while working for 6 min at a maximal stimulation rate of 1 Hz (isometric tetanic contractions) on three to four separate occasions for each muscle. On each occasion, the last 4 min of the 6-min work period was split into 2 min of a control treatment (only emulsifying agent mixed into blood) and 2 min of perflubron treatment (6 g/kg body wt), reversing the order for each subsequent work bout. Before contractions, the [Hb] of the dog was decreased to 8-9 g/100 ml and arterial PO2 was increased to 500-600 Torr by having the dog breathe 100% O2 to maximize the effect of the perflubron. Muscle blood flow was held constant between the two experimental conditions. Plasma O2 solubility was almost doubled to 0.005 ml O2 x 100 ml blood-1 x Torr-1 by the addition of the perflubron. Muscle O2 delivery and maximal VO2 were significantly improved (at the same blood flow and [Hb]) by 11 and 12.6%, respectively (P < 0.05), during the perflubron treatment compared with the control. O2 extraction by the muscle remained the same between the two treatments, as did the estimate of DO2.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of purinergic neurotransmission in various cardiovascular reflexes

In urethane-anaesthetized rats the effects of alpha-adrenoceptor antagonists and desensitization of P2-purinoceptors with alpha,beta-methylene ATP on the pressor reflex responses were investigated. Pressor responses were elicited by electrical stimulation of the central end of the sciatic nerve, by asphyxia and by occlusion of the common carotid artery. Responses to sciatic nerve stimulation and to asphyxia, but not those to carotid artery occlusion were entirely suppressed by dihydroergotamine and phentolamine. Under the action of dihydroergotamine the sinocarotid reflex decreased by over 70% in 40% of the experiments. In 60% of experiments the response was only slightly reduced or even augmented, but it was entirely inhibited by subsequent desensitization with alpha,beta-methylene ATP. The magnitude of response to sciatic nerve stimulation was almost unaffected by alpha,beta-methylene ATP, while the response to carotid occlusion was decreased by 40-50%. The recovery of purinoceptor sensitivity to alpha,beta-methylene ATP was accompanied by restoration of the sinocarotid reflex. It is suggested that purinergic neurotransmission plays a considerable role in the pressor sinocarotid reflex, while in the pressor response to stimulation of somatic afferents its role is negligible.

Fading responses in the evoked EMG after rocuronium in cats

This study was performed to evaluate the inhibitory effect on motor nerve terminals by rocuronium using recovery curves of muscle compound action potentials (CAPs) and train-of-four ratios (TOFRs) in anaesthetized cats, and to compare the results with other relaxants reported previously. Recovery curves were derived from the amplitude of the CAP induced in the gastrocnemius muscle by the second of a paired stimulus (test response) to the sciatic nerve and compared with results evoked by the first component (conditioning response). The interval between the paired stimuli was increased stepwise from 7 to 1,000 msec, and the differences in amplitude of the test and conditioning responses were plotted on a graph by relating the changes in paired intervals. The recovery curve after rocuronium was less inhibited than after pancuronium, (100.4 +/- 5.9%, 82.3 +/- 6.7% and 68.5 +/- 6.7% at 60, 100 and 500 msec intervals, compared with 70.3 +/- 3.3%, 59.0 +/- 4.7% and 46.7 +/- 4.3% after pancuronium (P < 0.05). The recovery curves with d-tubocurarine were more depressed than with pancuronium; however, the RC with vecuronium was similar to that of rocuronium. The degree of fade in TOF by rocuronium was also less than those seen with d-tubocurarine and pancuronium. The results obtained suggest that rocuronium has less inhibitory effect on motor nerve terminals than do d-tubocurarine and pancuronium, and has a similar effect to that of vecuronium.

Changes in nerve conduction and Pi/PCr ratio during denervation-reinnervation of the gastrocsoleus muscles of rats

The purpose of this investigation was to study the changes in nerve conduction and phosphate metabolites of the gastrocsoleus muscles of rats during denervation-reinnervation. Sixteen male Sprague-Dawley rats underwent unilateral crush-denervation of the left sciatic nerves at the sciatic notch. Six rats were used for measurement of motor conduction latency and action potential amplitude of the gastrocsoleus muscle by stimulating the sciatic nerve at one, two and eight weeks after nerve crush. The other ten rats were designated for evaluation of the ratio of inorganic phosphorous (Pi) to phosphocreatine (PCr) by a 31P-phosphoenergetic spectrometer at two weeks and eight weeks after nerve crush. None of the sciatic nerves showed conduction to the gastrocsoleus at one or two weeks after nerve crush. At eight weeks postcrush, the motor conduction latency returned to within normal limits, whereas the action potential amplitude was only 55% of the normal. For the eight-week period of study, the Pi/PCr ratio of the normal control muscles ranged between 0.09 +/- 0.02 and 0.11 +/- 0.02 (mean +/- SD). The denervated muscles showed an increase of Pi/PCr ratio by 54% at two weeks postcrush, compared to the respective contralateral control sides. The ratios returned to the normal value by eight weeks postcrush. In summary, these data suggested that the metabolic recovery of the crush-denervated muscle followed the same pattern as the parameters of nerve conduction.

Effects of intrathecal capsaicin and an NK-1 antagonist, CP,96-345, on the thermal hyperalgesia observed following unilateral constriction of the sciatic nerve in the rat

We evaluated the effect of intrathecal (i.t.) capsaicin (CAP) and the NK-1 selective non-peptidic antagonist, CP,96-345, on the thermal hyperalgesia ordinarily observed after unilateral partial ligation of the sciatic nerve in rats. CAP was injected i.t. 2 days after constriction injury. Seven days after partial ligation, the levels of substance P (sP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal polypeptide (VIP) were the same in the left and right dorsal horns of the lesioned rats which were injected with vehicle (VEH). CAP (75 micrograms/15 microliters of 20% 2-hydroxypropyl-beta-cyclodextrin) resulted in an equal reduction (40-50%) in the dorsal horn levels of sP and CGRP, but not VIP. After 7 days, i.t. CAP increased the paw withdrawal latency (PWL) of the non-injured hind paw. In contrast, there was no change in the PWL of the injured paw when compared to that of VEH-treated animals. Thus, CAP did not abolish the hyperalgesic state. We concluded that the thermal hyperalgesia after sciatic nerve constriction injury is not mediated by CAP-sensitive C fibers. CP,96-345 given i.t. at a dose which is physiologically active (400 micrograms) had little effect on the thermal response latency of either the normal or hyperesthetic paw. This provides further evidence that neither the normal pain response nor hyperalgesic state is dependent upon a dorsal horn action of sP.