Spontaneous and evoked activities of anterior thalamic neurons during waking and sleep states

In contrast with most dorsal thalamic nuclei, the anterior thalamic (AT) complex is devoid of input from the reticular (RE) thalamic nucleus. Instead, it is interposed in a limbic circuit linking the mammillary bodies (MB) to various allo- and periallocortical fields. To investigate the electrophysiological consequences of this peculiar pattern of connectivity, a sample of 92 AT cells, physiologically identified by their short-latency response to MB stimulation, was recorded in chronically-implanted animals and compared to a group of rostral intralaminar centralis-paracentralis (CL-PC) thalamic neurons receiving a dense innervation from the RE nucleus. Numerous similarities were found between the state-related fluctuations in spontaneous and evoked activities of AT and CL-PC neurons. For instance, both types of cells displayed stereotyped, high-frequency (250-300 Hz) bursts of 2-4 spikes in S and a more tonic discharge pattern in W and D. However, the high-frequency bursts of the S state occurred randomly in AT cells, whereas in CL-PC neurons they appeared rhythmically in clusters closely related to spindle waves. In addition, we found that a period of decreased responsiveness consistently followed the ortho- or antidromic activation of AT an CL-PC cells. This inhibitory period lasted less than 80 ms in AT cells and contrasted with the much longer (less than or equal to 120 ms) period of decreased excitability observed in CL-PC neurons during S. We suggest that these differences reflect the lack of RE input to the AT group.(ABSTRACT TRUNCATED AT 250 WORDS)

pH adjustment of local anesthetic solutions with sodium bicarbonate: laboratory evaluation of alkalinization and precipitation

pH adjustment of several commonly administered local anesthetic solutions was evaluated in the laboratory. The pH achieved after the addition of sodium bicarbonate and the onset of precipitation for alkalinized solutions were recorded. Solutions of 2-chloroprocaine and lidocaine readily alkalinized to near physiological pH without precipitation. Mepivacaine solutions exhibited a tendency for delayed precipitation (18-20-minute latency for 1.5% mepivacaine) above neutral pH. Bupivacaine and etidocaine solutions precipitated after the addition of small amounts of sodium bicarbonate and could not be alkalinized to physiologic pH. Two commercially available sodium bicarbonate preparations, 4% (wt/vol) and 8.4% (wt/vol), were compared and produced similar pH changes and precipitation behavior. The data obtained for pH and time to precipitation for local anesthetic solutions alkalinized with sodium bicarbonate may be useful for practical application in the clinical setting.

Perioperative analgesia with subarachnoid fentanyl-bupivacaine for cesarean delivery

Addition of fentanyl to bupivacaine administered for spinal anesthesia for cesarean delivery was evaluated in 56 ASA physical status 1 term parturients. Preservative-free saline was added to 0, 2.5, 5, 6.25, 12.5, 25, 37.5, or 50 micrograms fentanyl to make a 1 ml total volume, which was injected intrathecally prior to bupivacaine in a double-blind, randomized fashion. Vital signs, sensory level, motor block, pain score, and side effects were recorded every 2 min for the first 12 min and then at 15, 30, 45, and 60 min and at 30-min intervals until the patient complained of pain. At delivery maternal vein, umbilical artery, and umbilical vein blood gases were obtained. Apgar scores at 1 and 5 min were recorded. Early Neonatal Neurobehavioral Scales (ENNS) were performed on days 1 and 2. Side effects and opioid requirements were recorded for the first 24 h. All of the patients in the control group reported a pain score greater than 0 during surgery and 67% required intraoperative opioids. None of the patients who received greater than or equal to 6.25 micrograms fentanyl required intraoperative opioids. Complete analgesia (time from injection to first report of pain) lasted 33.7 +/- 30.8 min (mean +/- SD) in the control group and increased to 130 +/- 30 min (P less than 0.05) with addition of 6.25 micrograms fentanyl. Duration of effective analgesia (time from injection to first parenteral opioid) was 71.8 +/- 43.2 min in the control group and increased (P less than 0.05) to 192 +/- 74.9 min with addition of 6.25 micrograms fentanyl.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of bupivacaine- and ropivacaine-induced conduction blockade in the isolated rabbit vagus nerve

Ropivacaine (LEA-103) is a new amino-amide local anesthetic agent the chemical structure and anesthetic properties of which are similar to bupivacaine. Preliminary studies in animals indicate that the CNS toxicities of ropivacaine and bupivacaine are similar, but that ropivacaine may have less arrhythmogenic effects than bupivacaine. The current study arrhythmogenic effects than bupivacaine. The current study was designed to compare the in vitro potency, onset and recovery from block of ropivacaine and bupivacaine using an isolated rabbit vagus nerve model. The effect of varying concentrations of ropivacaine and bupivacaine on the compound action potential of A and C nerve fibers was assessed to determine whether motor and sensory fibers have different sensitivities to the two agents. The results showed that the depressant effect of bupivacaine was 16% greater than that of ropivacaine on motor fibers, but only 3% greater on sensory fibers. An analysis of variance indicated that this was a statistically significant difference (P = 0.028). Thus, at the concentrations tested, ropivacaine appears to produce relatively less blockade of motor fibers than does bupivacaine but with similar sensory blockade. The onset of this difference became significant as early as five minutes after the drug exposure was begun. No significant differences in recovery times were observed.

The role of reticular activating system in altering medial preoptic neuronal activity in anesthetized rats

The influence of the ascending reticular activating system (ARAS) on the medial preoptic unit activity was studied in urethane anesthetized rats. Alterations in the unit activity were also correlated with cortical EEG changes. A fourth of the medial preoptic units showed alterations in their discharges with cortical EEG changes. These units were also influenced by high frequency stimulation of ARAS, which simultaneously produced EEG desynchronization. On the other hand they were generally not influenced by 1 Hz stimulation of ARAS. These results indicate that the anatomically demonstrated projections from midbrain (forming ARAS), involving very few synapses, may not be involved in the regulation of sleep-wakeful function of the medial preoptic area. Interaction of some of the inputs at the medial preoptic area is discussed.

Precordial Doppler monitoring and pulse oximetry during cesarean delivery: detection of venous air embolism

Venous air embolism (VAE) is a potential but rare complication of cesarean delivery that can be associated with morbidity and death. Uterine sinuses are susceptible to the entrance of air during cesarean delivery. To define the incidence of VAE and its relation to arterial oxygen saturation (SaO2) and consequent electrocardiographic (ECG) changes, a prospective study was undertaken in which precordial Doppler monitoring was conducted during cesarean delivery. Concomitant, SaO2 and ECG were recorded in 78 patients. Fifty-one of 78 (65%) of the subjects had Doppler changes consistent with VAE. Of these, 37 patients (72%) showed a decreased SaO2, (average decline 5.2%). The remainder of the patients with Doppler changes showed no SaO2 change. Twenty of the patients with Doppler changes and decreased SaO2 complained of chest pain and dyspnea. Three of these patients exhibited ECG changes including ST segment depression. Although all ECG changes resolved spontaneously without sequelae, the potential clearly existed for life threatening embolic events. Thus, precordial Doppler monitoring of cesarean delivery patients demonstrated a surprisingly high incidence of Doppler changes consistent with VAE. Some episodes were associated with a significant reduction in SaO2 and rarely with ECG changes.

Epidural butorphanol-bupivacaine for analgesia during labor and delivery

A double-blind, randomized, dose-response study of a combination of 0.25% bupivacaine combined with 0, 1, 2, or 3 mg of butorphanol was studied in 40 laboring parturients. The optimal dose of butorphanol combined with 8.5 to 10 ml 0.25% bupivacaine was 2 mg; with 2 mg, the duration of analgesia was significantly greater and the time to onset of analgesia significantly shorter than when no butorphanol was added, and the amount of bupivacaine could be reduced 50%. Adverse fetal effects were not observed except that of a low amplitude sinusoidal fetal heart rate pattern with doses of 3 mg butorphanol. All neonatal observations were normal. It is concluded that epidural butorphanol can be a useful and safe adjunct to bupivacaine used for epidural analgesia during labor.

Enhanced myocardial preservation by nicotinic acid, an antilipolytic compound: mechanism of action

The cardioprotective effects of an antilipolytic compound, nicotinic acid, on arrested-reperfused myocardium were investigated in the isolated in situ pig heart preparation. Hearts were preperfused for 15 min in the presence of (5-3H)-glucose and (U-14C)-palmitic acid. Half of the hearts were then perfused with 0.08 mM nicotinic acid for an additional 15-min period, while the remaining control hearts received unmodified perfusion. Arrest was then induced in all animals for 2 h using hypothermic K+ cardioplegia, followed by 60 min of normothermic reperfusion. In control hearts, there were significantly greater levels of long-chain acyl Co-A and acyl carnitine and lower levels of membrane phospholipids than in the nicotinic acid group. While nicotinic acid inhibited beta-oxidation during pre-ischemia and reperfusion, it also prevented the degradation of membrane phospholipids. The net result was a reduction of free fatty acid accumulation during arrest and reperfusion in the nicotinic acid group. Glycolysis, as reflected in 3H2O production, was significantly increased by nicotinic acid administration. In the control heart as compared to the nicotinic acid group, the incorporation of 14C-label from palmitate into triglyceride and cholesterol during arrest was enhanced, while incorporation into phospholipids was depressed. The cardioprotective effects of nicotinic acid were demonstrated by decreased release of creatine kinase and improved coronary blood flow, and cardiac contractility in the reperfused myocardium supplemented with nicotinic acid compared to the control group. These results suggest that nicotinic acid significantly protects the arrested-reperfused myocardium by a) preventing elevation of myocardial fatty acid levels, b) stimulating glycolysis by limiting fatty acid oxidation, c) inhibiting degradation of membrane phospholipids, and d) preventing accumulation of fatty acid metabolites with harmful detergent properties.

Delivery temperature of heated intravenous solutions during rapid infusion

Warming of intravenous fluids may help to prevent shivering and hypothermia in the surgical patient. Increasing the fluid temperatures to as high as 60 degrees C has been suggested. An in vitro study was performed in which temperature changes following the rapid infusion of heated lactated Ringer's solution within a vein were measured. When 1 L of solution was warmed to 55 degrees C and then was infused over 4 min, local model vein temperatures rose from 37 degrees C to 44 degrees C. This effect of possible regional tissue heating may well occur in vivo. It is known that the rate of human blood cell hemolysis and membrane enzymatic function is affected by temperature. Further efforts need to be directed toward appreciating the effects of warmed intravenous fluids upon intact physiologic preparations and red blood cells.

Chronically administered progesterone decreases halothane requirements in rabbits

The MAC for halothane is 25% lower in pregnant than that in nonpregnant ewes. The reason for this is uncertain, but changes in both steroidal and endogenous opiate have been implicated. This study was undertaken to assess the effect of exogenous progesterone on minimal alveolar concentrations (MAC) of halothane in ovariectomized rabbits. Minimal alveolar concentration of halothane was determined in 84 female rabbits, 37 intact (group A), 20 ovariectomized and injected with inert carrier peanut oil (group B), and 27 ovariectomized and injected with progesterone in peanut oil (group C). Minimal alveolar concentration in group A, 1.68 +/- 0.06% (mean +/- SEM), did not differ significantly from that in group B rabbits, 1.77 +/- 0.06%. However, MAC in progesterone-treated rabbits, 1.48 +/- 0.06%, was significantly lower than the MAC of the other two groups (P less than 0.01). Plasma progesterone concentrations in group A, B, and C were 5.28 +/- 0.62 ng/ml, 6.83 +/- 2.00 ng/ml, and 37.33 +/- 4.25 ng/ml, respectively. These results suggest that experimental treatment with progesterone can reduce the amount of halothane required to produce anesthesia and may explain the phenomenon of decreased need of inhalation anesthetic in human parturients.

ZnO-on-Si mode conversion resonator

A two-port admittance matrix model is presented to describe the operation of the surface-acoustic-wave (SAW) mode conversion resonator. A unique treatment of the transducer coupling is applied to the specific case of the mode conversion device. The model takes into account the simultaneous presence of propagating Rayleigh and Sezawa waves and allows an equivalent circuit to be constructed to describe the resonator behavior. The model makes it possible to determine the reflector array separation and the interdigital transducer placement necessary for resonance and maximum coupling. Finally, experimental results are shown as verification of the device theory.

Fetal surgery and general anesthesia: a case report and review

Fetal surgery, in utero, is now a viable option for some congenital conditions due to recent advances in ultrasound and microsurgical technology. Previous reports of anesthesia for such procedures have focused on spinal or epidural conduction techniques. General endotracheal anesthesia may have several advantages in this setting. In addition to maternal anesthesia, general anesthesia can provide fetal neuromuscular block (without direct fetal injection of blocking agents) and uterine relaxation. It may also blunt fetal response to surgical stimulation.

Developmental neurophysiology of mammalian peripheral nerves and age-related differential sensitivity to local anaesthetic

Using an in vitro nerve preparation, we have studied the relative electrophysiological properties of myelinated and unmyelinated nerve fibres in the vagus nerve of 1-, 9- and 36-month-old rabbits and their sensitivity to local anaesthetic. The baseline (values before infusion of local anaesthetic) mean amplitude and conduction velocity (CV) of the compound action potential (APc) were recorded and the nerve was exposed to a range of concentrations (0.5-4.0 mmol litre-1) of lignocaine for periods sufficient to attain equilibrium block. There was an increase in the amplitude of the A fibre elevation from the 1-month to the 9- and 36-month-old rabbits. The CV of the A and B fibres increased significantly with age, while the CV of the C fibres did not change. The ED50 values of lignocaine for reduction of the A fibre elevation in the 1-, 9- and 36-month-old rabbits were 0.66, 0.94 and 0.85 mmol litre-1, respectively. The respective values for the B fibres were 0.74, 1.21 and 0.82 mmol litre-1, while those of the C fibres were 1.50, 2.44 and 2.07 mmol litre-1. In general, nerves from young and old rabbits were more sensitive to local anaesthetic-induced conduction blockade, suggesting that smaller doses of local anaesthetic are required clinically for anaesthesia in paediatric and older age groups.

A small nonconjugative plasmid encoded for streptomycin-resistant character in Shigella dysenteriae

Conjugative transfers of drug-resistant plasmids in Shigella dysenteriae type 1 isolated from the epidemic in West Bengal were unsuccessful. The plasmids were non-transmissible in spite of having the fertility factor F, genetically labelled with kanamycin-resistant transposon Tn903 (pWS 7). A small 2.5 kb nonconjugative plasmid encoded for the streptomycin-resistant character. Cured plasmid-less strains of S. dysenteriae 1 showed resistance to sulfonamides.

Rapid minipreparations of bacteriophage lambda DNA

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Decreased incidence of tourniquet pain during spinal anesthesia with bupivacaine. A possible explanation

In a previous report, the incidence of tourniquet pain was found to be 25% with bupivacaine and 60% with tetracaine (P less than 0.05) spinal anesthesia. On the other hand, tetracaine is more potent than bupivacaine in abolishing the single-compound action potential in vitro in isolated nerves. These conflicting observations may be reconciled if bupivacaine produced greater frequency-dependent conduction blockade of nerve action potentials. This hypothesis was tested in C fibers of isolated, desheathed rabbit vagus nerves. The nerves were supramaximally stimulated at frequencies of 9 or 15 Hz. After a control period, the nerves were exposed to bupivacaine (0.2 mM) or tetracaine (0.02 mM) for 30 minutes. The local anesthetics were then washed out by continuous constant-rate perfusion. The decline and recovery of the first and last action potential amplitudes of the train were measured. Bupivacaine and tetracaine produced similar depression of the first action potential of the 9-Hz and 15-Hz trains. However, bupivacaine caused a delayed recovery of the last action potential of the 15-Hz train but not of the 9-Hz train. These results show that bupivacaine produces greater frequency-dependent conduction blockade of C fibers than does tetracaine. These findings offer a possible explanation as to why spinal anesthesia with bupivacaine results in a lower incidence of tourniquet pain than tetracaine.

Single neuronal activities from CA3 region of hippocampus during conditioning, in mobile unanaesthetised conscious rabbits

Single neuronal activities of 93 units from CA3 region of hippocampus were studied in unanaesthetised mobile rabbits. Effects of repeated reinforced conditioned stimuli (CS+) were observed on these neuronal firing pattern. The conditioned stimuli (CS) consisted of a tone 600 Hz for 6 seconds which was reinforced by a subcutaneous electrical shock (0.4 V, frequency 250 sec, and pulse width 300 microsec) for one second duration (CS+). Ten such CS+ were applied at the gap of 5 min, in between. As majority of CA3 neurons showed irregular spontaneous activities-the histograms drawn after calculation of interspike intervals showed a definite pattern of discharge which could be compared before, during and after multiple CS+. Two groups of neurons could be identified by their resting firing pattern. One group consisting of 21 neurons (22.5% approximately) showed complex spikes, with spike frequency less than 2 to 8 per sec. They were complex spike cells (CSC). The other group consisting of majority of neurons (72 neurons, 77.5% approximately) showed comparatively high spike frequency greater than 8 to 40 per sec (theta cells). Both the group of neurons reacted tonically to CS+. All complex spike cells and 54% of theta cells showed inhibitory reaction and 46% of theta cells showed excitatory reaction to CS+. But with repeated presentation (4th to 5th) of CS+ the reaction gradually declined and finally after tenth CS+ it disappeared and resting firing pattern was observed. Thus it seems that the neurons of CA3 region have an intrinsic habituation capability. The probable cause, mechanism and the significance for the habituation has been discussed here.

Enhanced myocardial preservation by nicotinic acid, an antilipolytic compound. Improved cardiac performance after hypothermic cardioplegic arrest

The effect of nicotinic acid, an antilipolytic drug, on myocardial preservation was studied on the basis of cardiac performance after 2 hours of cardioplegic arrest. Isolated in situ pig hearts were subjected to 120 minutes of hypothermic potassium (35 mEq) crystalloid cardioplegic arrest followed by 60 minutes of reperfusion. The experimental group received nicotinic acid 0.08 mmol/L 15 minutes before cardioplegic arrest, whereas the control group received 15 minutes of unmodified perfusion. There was a marked decline in myocardial creatine phosphate levels during cardioplegic arrest in both groups that returned to the baseline level during reperfusion without a significant intergroup difference, and adenosine triphosphate levels remained stable throughout the experiment in both groups. Myocardial oxygen consumption during reperfusion was significantly higher in hearts treated with nicotinic acid, which was consistent with a significantly greater cardiac contractile force as evaluated by isovolumetric left ventricular pressure measurements. There appeared to be less cardiac membrane damage as measured by creatine kinase release during reperfusion, which was significantly inhibited by treatment with nicotinic acid. The present study supports the conclusion that nicotinic acid improves cardiac performance after hypothermic cardioplegic arrest.