Library

Notes: Abstract: Accumulation of intracellular Ca2+ is known to be critically important for the expression of NMDA receptor-mediated glutamate neurotoxicity. We have observed, however, that glutamate can also increase the neuronal intracellular Mg2+ concentration on activation of NMDA receptors. Here, we used conditions that elevate intracellular Mg2+ content independently of Ca2+ to investigate the potential role of Mg2+ in excitotoxicity in rat cortical neurons in vitro. In Ca2+-free solutions in which the Na+ was replaced by N-methyl-d-glucamine or Tris (but not choline), which also contained 9 mM Mg2+, exposure to 100 µM glutamate or 200 µM NMDA for 20 min produced delayed neuronal cell death. Neurotoxicity was correlated to the extracellular Mg2+ concentration and could be blocked by addition of NMDA receptor antagonists during, but not immediately following, agonist exposure. Finally, we observed that rat cortical neurons grown under different serum conditions develop an altered sensitivity to Mg2+-dependent NMDA receptor-mediated toxicity. Thus, the increase in intracellular Mg2+ concentration following NMDA receptor stimulation may be an underestimated component critical for the expression of certain forms of excitotoxic injury.

Notes: Abstract— Two membrane fractions were obtained from electric organ tissue of the electric eel by sucrose gradient centrifugation of tissue homogenates. Electron microscopic examination showed that both fractions contained mainly vesicular structures (microsacs). Both the light and heavy fractions had a-bungarotoxin-binding capacity and Na+-K+ ATPase activity, while only the light fraction had AChE activity. The polypeptide patterns of vesicles derived from both the light and heavy fractions were examined by SDS-polyacrylamide gel electrophoresis and found to be very similar. The ratio of protein to phospholipid in the light vesicles was much lower than in the heavy vesicles, but the relative amounts of individual phospholipids in the two fractions were similar.A marked difference in the permeability of the light and heavy vesicles was observed by measuring efflux of both [14C]sucrose and 22Na+, and also by monitoring volume changes induced by changing the osmotic strength of the medium. All three methods showed the heavy vesicles to be much more permeable than the light ones. Only the light vesicles displayed increased sodium efflux in the presence of carbamylcholine.The AChE in the light fraction does not appear to be membrane-bound, but is rather a soluble enzyme, detached from the membrane during homogenization, which migrates on the gradient similarly to that of the light vesicles. This is supported by the fact that the bulk of the AChE is readily removed by washing the vesicles. Moreover, under the conditions employed in our sucrose gradient separations,‘native’14 S + 18 S AChE exists in the form of aggregates which migrate very similarly to the major peak of AChE activity of tissue homogenates.Separated innervated and non-innervated surfaces of isolated electroplax were obtained by microdissection. α-Bungarotoxin-binding capacity was observed only in the innervated membrane. About 80% of the AChE was in the innervated membrane, and about 70% of the Na+-K+ ATPase in the non-innervated membrane.The data presented indicate that the light and heavy vesicle fractions separated by sucrose gradient centrifugation are not derived exclusively from the innervated and non-innervated membranes respectively, as previously suggested by others, but contain membrane fragments from both sides of the electroplax. The separation of two populations on sucrose gradients may be explained both by the differences in permeability and in protein to phospholipid ratios.

Notes: —Levorphanol (10-3 M) reversibly blocked conduction in the giant axon of the squid and axons from the walking legs of spider crab and lobster. Similar concentrations of levallorphan and dextrorphan blocked conduction in the squid giant axon. Under the same experimental condition morphine caused an approximately 40 per cent decrease in spike height. Levorphanol did not affect the resting potential or resistance of the squid axon. Spermidine, spermine and dinitrophenol had little or no direct effect on the action potential nor did they alter the potency of levorphanol. Concentrations of levorphanol as low as 5 × 10-5 M blocked repetitive or spontaneous activity in the squid axon induced by decreasing the divalent cations in the medium. After exposure to tritiated levorphanol, the axoplasm and envelope of the squid axon accumulated up to 500 per cent of the concentration of tritium found in the external medium, dependent on time of exposure, and other variables. At pH 6 the levels of penetration were 33-50% of those found at pH 8, which correlates with our observation that levorphanol is about 33 % as potent in blocking the action potential at pH 6. The penetrability of levorphanol was not affected by spermidine, dinitrophenol or cottonmouth moccasin venom. Levorphanol did not alter the penetration of [C14]acetylcholine nor did it render the squid axon sensitive to it. The block of axonal conduction by compounds of the morphine series is discussed both as to possible mechanisms and significance.

Notes: Abstract— Squid axonal preparations consisting of the giant axon plus adhering small nerve fibres were incubated for 30 min with phospholipase A (1, 0.2 and 0.025 mg/ml); phospholipase C (10 and 0.5 mg/ml) or lysolecithin (1 and 0.2 mg/ml) followed by another 30 min incubation in normal sea water. The axoplasm and envelope (sheath) of the axonal preparation were then separated and the phospholipids and free amino acids determined. The released amino acids were also measured in the incubation solutions. Compared to phospholipase C, phospholipase A caused a much greater reduction in the free amino acid content of axoplasm and envelope; and a concomitant much greater increase in amino acids released into the incubation solutions, even when phospholipase A was used in concentrations which caused less phospholipid splitting than phospholipase C. Lysolecithin had a much weaker effect than phospholipase A. It is concluded that disruption of hydrophobic binding has a much greater effect on the structure of the non-lipid portion of the axonal membranes than does disruption of hydrophilic (electrostatic) forces of interaction. Our results can be interpreted in terms of the protein-crystal or mosaic models of membrane structure whereas they do not support the unit membrane hypothesis.

Notes: The knee-chest position for lumbar spine surgery is favoured because decreased filling of the epidural veins is associated with reduced peroperative bleeding. However, the position may be unfavourable from a circulatory point of view. In the present study, non-invasive assessment of circulation in the lower limbs was performed in 21 unanaesthetised, healthy volunteers who were placed in the surgical knee-chest position. Measurements included blood flow velocity (colour Doppler ultrasonography), oscillotonometric arterial blood pressure from upper and lower limbs and pulse oximetry from a toe. There was a statistically significant reduction in the posterior tibial artery flow velocity, maximally 31.6%, when the subject was moved from the prone to the knee-chest position. An enlargement of the trunk-femoral angle at the hip did not improve arterial flow. In 10 of the 21 volunteers, no flow in the posterior tibial vein was detected in the knee-chest position. In spite of the deteriorated blood flow, pulse oximetry indicated sufficient capillary flow in the very periphery of the lower limb. The change from prone to knee-chest position resulted in an increase in arterial blood pressure of the upper limb; the increase in diastolic arterial pressure was statistically significant (p 〈 0.001). It is concluded that the surgical knee-chest position involves deterioration of both the arterial and venous flow of the lower limbs. This should be considered in patients undergoing surgery in this position and, in particular, in those at risk of developing cardiovascular complications.

Notes: A perivascular catheter technique (PVT) and a nerve stimulator technique (NST) for axillary brachial plexus block were compared in terms of quality: complete, incomplete or failed blocks. In a randomised series, 30 PVT blocks and 30 NST blocks were performed by three staff anaesthetists. In the NST group, surgical anaesthesia was always achieved, whereas in the PVT group, four blocks required supplementation with general anaesthesia. In both groups eight patients needed supplementation with addilioncd conduction blocks of 1–3 peripheral nerves. It is concluded that a nerve stimulator technique may increase the success rate of axillary brachial plexus block to some extent.

Notes: The quality of anaesthesia provided by three dosages of prilocaine. 40 ml 0.5%. 20 ml 1%, or 40 ml 1%. administered in random order, for intravenous regional anaesthesia of the lower extremity below the knee was compared in six volunteers. Limited sensory blockade was achieved in the groups with 40 ml 0.5% and 20 ml I% during the 30-minute test period. One subject was not fully anaesthetised with any of the dosages used. Recovery was rapid (mean 12–13 minutes) in these two groups. In two subjects given 40 ml of 1%. complete recovery took 90 minutes. At 30 minutes, the degree of flexion remaining in the great toe (control 100%) was 4% in the groups who received 40 ml Of 0.5% and 1 %, but 34% in those who received 20 ml of I% respectively. Full motor recovery was achieved in 8–9 minutes. Five of six volunteers who received the 400-mg dose experienced subjective signs of central nervous system side effects when the cuff was released. In this group, the mean plasma level of prilocaine at 2 minutes was 1.22 μg/ml. maximum 2.12 μg/ml. In a radiological examination, no leak of contrast medium under the tourniquet cuff (300 mmHg) was detected. The development of anaesthesia was fastest following the largest dose, but the large number of central side effects makes that dosage less suitable for clinical work.

Notes: The effect of the addition of 0.1 mg or 0.2 mgfentanyl to 40 ml 0.5% prilocaine in intravenous regional anaesthesia of the arm was investigated in 37 patients in a randomised, double-blind study. The characteristics of the sensory and motor block were studied. There was no difference in the speed of onset of analgesia in the groups (mean latency approximately 4 min in each group). However, significantly more patients in thefentanylO.2 mg group (7/12) had complete anaesthesia at 15 min than in the fentanyl 0.1 mg group (1/13) and the control group (2/12) (p 〈 0.05). There were no differences in the incidence of tourniquet pain immediately before cuff deflation (tourniquet time 45–87 min). After cuff deflation, in those patients who complained of wound pain within 30 min, on average the pain appeared later in the fentanyl 0.2 mg group (six patients, mean 14.3 min) than in the control group (eight patients, mean 9.4 min) (ns). In the fentanyl groups, the incidence of central nervous system side effects was greater than in the control group (fentanyl 0.1 mg 7/13 patients, fentanyl 0.2 mg 6/12 patients, control 1/12 patients) (p 〈 0.05). The plasma concentrations of prilocaine after cuff deflation were higher, in a dose-dependent fashion, in the fentanyl groups than in the control group, but the concentrations of prilocaine and fentanyl did not correlate with the symptoms. Postoperative nausea occurred only in the patients who had received fentanyl.

Notes: Propofol and methohexitone given in equipatent doses were compared for anaesthesia for thermocoagulation of trigeminal rootlets. Thirty-eight patients received two to six injections of the induction agents in one therapy session. The increase in arterial blood pressure during coagulation was significantly lower in the propofol group. Respiratory problems were encountered more often in those who received methohexitone (7/19 patients) than propofol (2/19 patients). There was a small but significant increase in blood propofol concentrations as well as in methohexitone plasma concentrations after repeated injections. Individual wake-up times increased to a statistically significant extent in relation to the number of doses of the induction agent but the increases were clinically unimportant (maximal mean change approximately 2 minutes). There were no differences in wake-up times between the two anaesthetic groups.