Combining in vivo volume-controlled pressure microejection with extracellular unit recording.

We report a method for combining extracellular single-unit recording with pressure ejection, permitting microvolume quantification through the measurement of meniscus movement. Good optimization of both high quality recording and precise determination (in the nanoliter range) of the pressure-ejected volume can be obtained by using a recording electrode affixed to a calibrated, narrow inner diameter ejection pipette.     

Detection of the bladder volume from the neural afferent activities in dogs: experimental results

OBJECTIVE: We evaluate the bladder volume and pressure through recording the bladder afferent activity in the sacral nerve roots in acute experiments of paraplegic dogs. These measurements are intended to report the status of the bladder and to adjust the stimulation parameters of an implantable electric stimulator. METHODS: The extraction of neural information for feedback in functional electrical stimulation is limited by the poor signal to noise ratio (SNR) in the sacral nerve recordings. We propose to inject a very low amplitude sinusoidal current with high SNR to the bladder through the nerve using a tripolar cuff electrode wrapped around the S2 nerve root. The application of this current (0.4 microA peak to peak, 30 Hz) allows detecting bladder afferent activity in its amplitude and the tissues impedance of the nerve. Acute experiments in dogs were performed to evaluate the proposed method. In each dog, the bladder infusion with saline was carried out at both slow and high filling rates. At the same time, the changes in the amplitude of the sinusoidal output voltage V(OUT) were recorded through the cuff nerve electrode. RESULTS: The data obtained from 26 acute experiments using eight dogs demonstrate that the amplitude of the recorded sinusoidal voltage V(OUT) varies proportionally with the bladder pressure during the bladder filling with saline solution. It also demonstrates that the bladder volume can be estimated from the increasing amplitude of the recorded V(OUT). CONCLUSION: This study shows that the increase in the V(OUT) is proportionally related to the increase in bladder pressure. The difference between the recorded V(OUT) during the bladder filling and the baseline V(OUT) can be a useful indicator of the changes in the bladder volume.     

Respiratory motoneuronal activity is altered by injections of picomoles of glutamate into cat brain stem

The local neural circuitry underlying the control of breathing was studied by injecting nanoliter volumes of excitatory amino acids into discrete regions of cat brain stem. Experiments were performed on chloralose-urethane anesthetized, vagotomized, paralyzed, and artificially ventilated cats. Phrenic, intercostal, and recurrent laryngeal nerve discharges were recorded. Multibarrel pipettes were used for recording and pressure ejection of drugs or a dye for marking recording and ejection sites. Ejected volumes were directly monitored for every injection. Injections, proximal to neurons discharging with a respiratory periodicity, of as little of 200 fmol of L-glutamate in 200 pl of saline elicited marked, site-specific increases or decreases in respiratory motoneuronal discharge. N-Methyl-D-aspartic acid and homocysteic acid elicited similar site-specific alterations in respiratory motor output, although some details of the response could differ qualitatively. Responses to all the excitatory agents used were attenuated by concurrent injection of kynurenic acid, DL-2-amino-4-phosphonobutyric acid, or glutamic acid diethyl ester. There was no change in spontaneous phrenic nerve discharge in response to injections of equivalent or larger volumes of saline or lidocaine. These results indicate a heterogeneity in the spatial organization of the brain-stem neural circuitry underlying respiratory control, which has not been described previously. This injection technique may provide a mechanism for probing the neural circuitry underlying other behaviors.     

Augmentation of N-methyl-D-aspartate induced depolarizations by GABA in neocortical and archicortical neurons

The influence of the inhibitory transmitter gamma-aminobutyric acid (GABA) on depolarizations elicited by the excitatory amino acid N-methyl-D-aspartate (NMDA) was tested in neurons of organotypic neocortical tissue cultures (newborn rat) and in CA3 neurons of the hippocampal slice (guinea pig). Drugs were applied through a 3-barrelled micropipette by pressure ejection. Applications of GABA before the ejection of NMDA increased the amplitude of the depolarizations induced by the excitatory amino acid. It is suggested that the enhancement of NMDA responses by GABA may be mainly mediated by an intracellular common pathway.     

Characterization of the techniques of pressure ejection and microiontophoresis using in vivo electrochemistry

Catecholamine levels in frontal cortex were determined in vivo by electrochemical detection after the local application of dopamine (DA) from multibarrel micropipettes by pressure ejection or microiontophoresis. Tissue DA levels were linearly related to microapplication doses with either technique and reached steady state with longer application times. Furthermore, the plateau DA tissue concentrations were clearly related to ejection pressure or iontophoretic current. Using either microapplication technique, the tissue DA levels decreased as distance between the recording electrode and the tip of the drug pipette increased. However, pressure ejected and iontophoretically applied drug differed in their concentration versus time dynamics. Thus, although similar tissue concentrations of drug can be generated by the two techniques, the time dynamics of the drug effects may not be comparable. The quantitative use of these drug application techniques requires a minimal amount of variance in release between pipettes in order to effectively measure small sensitivity differences. Although the 10-fold variance with microiontophoresis does not appear resolvable at present, improved pipette construction techniques permit the variability in dosage to be limited to a maximum of 3-fold with pressure ejection. In addition, the present data also suggest that this variance can be further minimized by holding either ejection duration or ejection pressure constant when establishing dose-response relationships.     

Non-pharmacological effects of the use of microelectrophoresis and pressure ejection of drugs in combination

Pressure ejection of physiological saline from multibarrel micropipette assemblies has been shown to selectively reduce responses of rat spinal cord neurones to electrophoretic ejection of kainate, N-methyl-aspartate and 4-methyl-homoibotenate, but not of quisqualate or L-glutamate. Reduction of response to an excitatory amino acid therefore appears to be correlated with the absence of an active transport system for that amino acid.     

Pressure injections of fluid in the nanoliter range via micropipettes

The relationship between pressure, ejection duration and volume ejected was experimentally determined in vitro for micropipettes with different external tip diameters. The relationship between ejection duration and ejected volume is linear in the steady state (i.e. with ejection durations of 1 s or longer) and at sufficiently high pressures (above about 100 kPa) and for pipettes with a sufficiently high hydrodynamic conductance (larger than 1 pl s⁻¹ kPa⁻¹ at 230 kPa). In this range, flows were found with low Reynolds numbers (smaller than 10), which is consistent with laminar flows. For all but the largest micropipettes, the relationship between pressure and ejected volume is alinear: the pipettes' apparent hydrodynamic conductances increase with increasing pressure. Micropipettes with apparent hydrodynamic conductances between 0.04 and 1400 pl s⁻¹ kPa⁻¹ (at 230 kPa) were tested. Duration-pressure combinations could be defined where the duration-volume relationship was either linear or monotonic. Such duration-pressure combinations were different for pipettes with different apparent hydrodynamic conductances. A quick method is described to measure the pipette's apparent hydrodynamic conductance at the pressure used, corrected for the fluid's viscosity. Measurement of this conductance permits predictable injections of known volumes of fluid in the range of 100 pl to 1 μl with a precision of 10–20%.     

The comparative effects of recombinant hirudin (CGP 39393) and standard heparin on thrombus growth in rabbits

The aim of this study was to compare the ability of standard heparin and recombinant (r-)hirudin, a specific inhibitor of thrombin, to inhibit thrombus growth in a rabbit jugular vein model. Doses of standard heparin and r-hirudin equivalent in prolonging the aPTT were first identified. The ability of these doses to inhibit 125I-fibrin accretion onto preexisting thrombi was then evaluated. 0.5 and 0.75 mg/kg of standard heparin and 0.8 and 1.25 mg/kg of r-hirudin infused over 3 h produced a mean prolongation of the aPTT of 1.5 and 2 times, respectively. In saline treated rabbits 62 +/- 7 micrograms of 125I-fibrin were accreted on the pre-formed thrombi. The lower doses of standard heparin and r-hirudin produced a 125I-fibrin accretion of 44 +/- 5 and 25 +/- 4 micrograms, respectively (p less than 0.01). The two higher doses of standard heparin and r-hirudin produced a 125I-fibrin accretion of 34 +/- 4 and 17 +/- 3 micrograms, respectively (p less than 0.01). The increase in the dose of standard heparin up to 2.5 mg/kg produced a 125I-fibrin accretion of 26 +/- 3 micrograms a 58% reduction when compared with saline. The increase in the dose of r-hirudin up to 5 mg/kg produced a 125I-fibrin accretion of 12 +/- 2 micrograms, an 81% reduction when compared with saline. No further inhibition was observed when the doses of both agents were further increased. We conclude that doses of standard heparin and r-hirudin equivalent in prolonging the aPTT have a different effect on thrombus growth inhibition, r-hirudin being twice as effective as standard heparin. Exclusive inhibition of thrombin without any other inhibiting effect on blood coagulation appears to be sufficient to inhibit thrombus growth. Our results seem to be promising in view of a clinical evaluation of r-hirudin.     

A new method for noninvasive measurement of short-term cerebrospinal fluid pressure changes in humans

Summary Changes in cerebrospinal fluid (CSF) pressure were shown to be reflected by changes in tympanic membrane (TM) tension. Impedance audiometry measures mechanical tension on the TM and was used to detect changes during jugular vein compression in normal students. CSF and perilymph communicate through the cochlear aqueduct, permitting increases in CSF pressure to result in increased pressure on the stapes footplate. This is transmitted to the TM by the ossicles and detected by impedance audiometry. TM tension was also proportional to CSF pressure in cadavers, where CSF pressure was manipulated by saline injection through a lumbar puncture.     

Subjective assessment and cardiovascular response to ischemic pain in young, healthy women users and non-users of oral contraceptives

Experimental pain was introduced in women volunteers, some of whom were taking oral contraceptives. Pain perception and tolerance were the same, regardless of oral contraceptive use. All responded to the introduction of pain with increasing heart rate (HR), blood pressure (BP) and the product of systolic pressure, HR and the left ventricular ejection time (LVET). The users had a more consistent response pattern, and their reported levels of pain were positively and highly correlated with the changes in pre-ejection period (PEP) and the ratio PEP/LVET. Non-users had more variable systolic time interval (STI) responses.     

Traitement de l’hypotension spontanée du liquide cérébrospinal par perfusion épidurale de sérum salé isotonique

Introduction

Spontaneous intracranial hypotension (SIH) is an uncommon cause of secondary headache due to a cerebrospinal fluid (CSF) hypotension. Lumbar epidural blood-patch (LEBP) is the most effective treatment and can be repeated in case of relapse. There is no standard therapeutic strategy for patients free of dural tears who fail to respond to several consecutive blood-patches. We report two cases of SIH successfully treated by an epidural saline infusion after two consecutive LEBP.

Case reports

A 35-year-old woman was admitted to hospital for severe orthostatic headache. The diagnosis of SIH was retained. Two LEBP were performed but with no clinical benefit. Headache disappeared totally after an epidural saline infusion. A second woman, aged 75 years, was admitted for chronic orthostatic headaches. The CSF pressure was low. Search for a dural tear was negative. After two unsuccessful LEBPs, the patient was treated with an epidural saline infusion. Her headache resolved completely and definitely.

Discussion

It is common procedure to search for a dural tear when patients fail to respond to several consecutive LEPB. Surgical repair is however exceptional. An epidural saline infusion might be an efficient therapeutic alternative despite the small number of cases reported in the literature.     

Hydrogen-rich saline injection into the subarachnoid cavity within 2 weeks promotes recovery after acute spinal cord injury

Hydrogen can relieve tissue-damaging oxidative stress, inflammation and apoptosis. Injection of hydrogen-rich saline is an effective method for transporting molecular hydrogen. We hypothesized that hydrogen-rich saline would promote the repair of spinal cord injury induced by Allen''s method in rats. At 0.5, 1, 2, 4, 8, 12 and 24 hours after injury, then once daily for 2 weeks, 0.25 mL/kg hydrogen-rich saline was infused into the subarachnoid space through a catheter. Results at 24 hours, 48 hours, 1 week and 2 weeks after injury showed that hydrogen-rich saline markedly reduced cell death, inflammatory cell infiltration, serum malondialdehyde content, and caspase-3 immunoreactivity, elevated serum superoxide dismutase activity and calcitonin gene-related peptide immunoreactivity, and improved motor function in the hindlimb. The present study confirms that hydrogen-rich saline injected within 2 weeks of injury effectively contributes to the repair of spinal cord injury in the acute stage.     

开颅术后经硬膜下引流管测量颅内压的可行性分析

目的 探讨开颅术后经硬膜下引流管监测颅内压（ICP）的可行性与效果。方法 2020年1月至2022年8月前瞻性选择开颅手术治疗的病人56例,术中将ICP监测探头置入脑室并使用Codman颅内压监护仪连续监护1周（金标准）;同时,应用液压耦合装置经术后留置硬膜下引流管测量ICP（硬膜下法）。结果 56例金标准测得的ICP[（13.34±5.41）mmHg]与硬膜下法测得的ICP[（14.96±5.33）]无统计学差异（P>0.05）。去骨瓣减压术25例金标准测得的ICP[（13.76±5.14）mmHg]与硬膜下法测得的ICP[（14.68±4.71）mmHg]无统计学差异（P>0.05）。未去骨瓣31例金标准测得的ICP[（13.00±5.66）mmHg]与硬膜下法测得的ICP[（15.03±5.80）mmHg]无统计学差异（P>0.05）。硬膜下法测得的ICP与金标准的差值为（1.6±2.1）mmHg;两种方法测得的ICP呈明显正相关（r=0.892,P<0.001）。术后发生颅内感染1例（1.78%）、颅内少量出血1例（1.78%）。结论 与脑室ICP监测相比,开颅术后使用液压耦合装置经硬膜下引流管可以较为准确地监测ICP,方法简单、经济,易于基层医院推广应用。     

Bi-level positive pressure ventilation and adaptive servo ventilation in patients with heart failure and Cheyne-Stokes respiration

OBJECTIVES: Nocturnal positive pressure ventilation (PPV) has been shown to be effective in patients with impaired left ventricular ejection fraction (LVEF) and Cheyne-Stokes respiration (CSR). We investigated the effect of a bi-level PPV and adaptive servo ventilation on LVEF, CSR, and quantitative sleep quality. METHODS: Thirty-seven patients (New York heart association [NYHA] II-III) with LVEF<45% and CSR were investigated by electrocardiography (ECG), echocardiography and polysomnography. The CSR index (CSRI) was 32.3+/-16.2/h. Patients were randomly treated with bi-level PPV using the standard spontaneous/timed (S/T) mode or with adaptive servo ventilation mode (AutoSetCS). After 6 weeks, 30 patients underwent control investigations with ECG, echocardiography, and polysomnography. RESULTS: The CSRI decreased significantly to 13.6+/-13.4/h. LVEF increased significantly after 6 weeks of ventilation (from 25.1+/-8.5 to 28.8+/-9.8%, p<0.01). The number of respiratory-related arousals decreased significantly. Other quantitative sleep parameters did not change. The Epworth sleepiness score improved slightly. Daytime blood pressure and heart rate did not change. There were some differences between bi-level PPV and adaptive servo ventilation: the CSRI decreased more in the AutoSetCS group while the LVEF increased more in the bi-level PPV group. CONCLUSIONS: Administration of PPV can successfully attenuate CSA. Reduced CSA may be associated with improved LVEF; however, this may depend on the mode of PPV. Changed LVEF is evident even in the absence of significant changes in blood pressure.     

Blockade of nicotinic responses in rat retinal ganglion cells by neuronal bungarotoxin

The effects of neuronal bungarotoxin (NBT) on nicotinic acetylcholine responses recorded from rat retinal ganglion cells in culture were studied with patch electrodes. We observed that the concentration of this toxin needed to induce a total blockade of nicotinic currents varied according to the method of toxin application utilized. Rapid addition of 20 microM NBT by pressure ejection from micropipettes produced total blockade of 50-microM acetylcholine-induced currents. In contrast, when added slowly via the physiological solution which continuously superfused the cells, NBT was able to produce a complete blockade of the response at 200 nM. The IC50 determined for NBT by the superfusion method was 55 nM. Recovery from block was slow and incomplete with both drug application methods, although some differences were found. The results are discussed with reference to a scheme in which NBT binds with both low and high affinity to functional nicotinic receptors in rat retinal ganglion cells in culture.     

Resistance to drainage of cerebrospinal fluid: clinical measurement and significance

By infusing saline intrathecally at a constant rate until a new steady-state cerebrospinal fluid (CSF) pressure is attained, one can estimate clinically the apparent resistance (Ra) to drainage of CSF in mm saline/ml./minute. This intrathecal saline infusion test (ITSIT) was performed 36 times on 29 patients with diverse intracranial problems, and the results were analysed and, in most cases, compared with the pneumoencephalogram and the isotope cisternogram. The ITSIT is a safe, simple test to estimate Ra, but factors which are difficult to control (occult leaks from the subarachnoid space; independent fluctuations of CSF pressure) limit its reliability and clinical usefulness. If closely correlated with the clinical syndrome, the pneumoencephalogram, and the isotope cisternogram, an ITSIT may identify decisively the patient who needs a shunt. In addition the ITSIT offers another method by which to investigate the pathophysiological mechanisms of the various states of intracranial hypertension. Results from the test performed on four patients with intracranial hypertension of unknown cause (pseudotumor cerebri) suggest that the underlying mechanism in this condition is probably an impediment to normal CSF drainage.     

Alteration in dendritic morphology of pyramidal neurons from the prefrontal cortex of rats with renovascular hypertension

We have studied, in the rat, the dendritic morphological changes of the pyramidal neurons of the medial part of the prefrontal cortex induced by the chronic effect of high blood pressure. Renovascular hypertension was induced using a silver clip on the renal artery by surgery. The morphology of the pyramidal neurons from the medial part of the prefrontal cortex was investigated in these animals. The blood pressure was measured to confirm the increase in the arterial blood pressure. After 16 weeks of increase in the arterial blood pressure, the animals were sacrificed by overdoses of sodium pentobarbital and perfused intracardially with a 0.9% saline solution. The brains were removed, processed by the Golgi-Cox stain method and analyzed by the Sholl method. The dendritic morphology clearly showed that the hypertensive animals had an increase (32%) in the dendritic length of the pyramidal cells with a decrease (50%) in the density of dendritic spines when compared with sham animals. The branch-order analysis showed that the animals with hypertension exhibit more dendritic arborization at the level of the first to fourth branch order. This result suggests that renovascular hypertension may in part affect the dendritic morphology in this limbic structure, which may implicate cognitive impairment in hypertensive patients.     

Detection of dopamine overflow and diffusion with voltammetry in slices of rat brain

Voltammetric electrodes have been used to monitor extracellular dopamine in rat brain slices. The electrode tips are small enough to be immersed inside the slice. Specificity for dopamine is increased through the use of voltammetry and a cation exchange membrane at the electrode tip. Dopamine overflow is observed in the caudate nucleus following electrical stimulation (60 Hz, 1 s, 3 V) with an adjacent bipolar electrode. The amount of overflow observed is increased when the tissue is perfused with 10 microM cocaine or nomifensine, both recognized inhibitors of dopamine uptake. The ability of dopamine in the perfusion buffer to permeate the slice was monitored with two voltammetric electrodes, one in the cerebral cortex and the other in the caudate nucleus. At a high concentration (100 microM), dopamine rapidly appeared (2.7 +/- 0.4 min) in the interior of the cortex, but dopamine was not observed in the caudate until a significantly later time (8.9 +/- 1.0 min). To examine whether this difference is a reflection of the presence of different uptake systems in the two regions, pressure ejection was employed. In this experiment a double-barrelled pipette was used to eject dopamine or DOPAC at a fixed distance (approximately 70 micron) from the voltammetric electrode. Ejection of small amounts of both substances could be detected in the cortex. When the ejector-detector assembly was moved to the caudate, dopamine could only be observed following pressure ejection after perfusion of the slice with 10 microM nomifensine. Detection of DOPAC was unaffected. All of these experiments indicate that uptake systems in the caudate keep dopamine concentrations very low in the extracellular fluid of the slice.     

A Method for Reducing the Pocket Complications of the Internal Infusion Pumps in Pediatric Patients: A Case Report

Internal infusion pumps are increasingly used as a safe method to deliver drugs in adult patients. However, a formal contraindication of this mode of therapy is the presence of a imbalance between the pump volume and the size of the abdominal wall as occurs in pediatric populations. We describe a method of implantation of an intrathecal infusion pump for baclofen therapy in a 10‐year‐old patient with cerebral palsy. Before the pump implantation we inserted a subcutaneous expander with a reservoir that was filled with saline solution every week. After three sessions, a pocket similar in size to an internal infusion pump was obtained. The result was a pump pocket with soft shaping and no edges that would not generate pressure sores or tissue tension after the pump insertion. This method could extend the use of internal infusion pumps in pediatric populations.     

Characterization in vivo of the NMDA receptor-mediated component of dentate granule cell population synaptic responses to perforant path input.

The NMDA receptor-mediated component of the hippocampal granule cell population excitatory postsynaptic potential response to low frequency (< 0.2 Hz) stimulation of the medial perforant path was characterized in vivo. Extracellular recordings were obtained from the dentate molecular layer in anesthetized rabbits, and glutamatergic and GABAergic antagonists were applied locally by pressure ejection. To measure the NMDA-mediated component, the NMDA receptor antagonist D-5-aminophosphonovalerate (APV) was applied during the constant ejection of physiological saline, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), and/or bicuculline methiodide. In general agreement with the results of attempts by other investigators to identify NMDA responses in vivo, APV did not significantly reduce the response to a single stimulus impulse in the presence of saline. However, an NMDA-mediated response was revealed when alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprianate receptor-mediated current flow was eliminated by applying the non-NMDA receptor antagonist CNQX. The NMDA component was negative-going as predicted, but its duration was considerably less than indicated in other studies of the dentate in vitro. The relative magnitudes of the NMDA and non-NMDA components of the EPSP were found to vary as a function of stimulus intensity or frequency. The NMDA receptor-mediated component represented 12% of the control response and increased to over 25% in response to higher stimulus intensities. A brief, high-frequency burst of impulses evoked a larger NMDA component in the presence of CNQX and was able to evoke an NMDA component in the presence of saline. Surprisingly, short trains of stimulation at lower frequencies typically produced suppression of the NMDA component. In a final series of experiments, it was found that many characteristics of the NMDA component were substantially altered by GABAergic inhibition. In the presence of the GABAA antagonist bicuculline, the magnitude of NMDA receptor-mediated responses was increased and their duration was greatly extended. Additionally, in the presence of bicuculline, the NMDA component facilitated markedly in response to frequencies of stimulus input > 20 Hz. These results indicate in vivo that the initiation and duration of NMDA current flow depend strongly upon the intensity and frequency of perforant path stimulation. In addition, the NMDA response to a single impulse appears to be reduced and truncated by input from GABAA receptor-mediated feedback and/or feedforward inhibition, and this inhibition affects temporal summation of NMDA receptor-mediated responses over a wide range of input frequencies. It is suggested that such inhibition results from the activation of GABAA receptors located on granule cell dendritic shafts.(ABSTRACT TRUNCATED AT 400 WORDS)