James E. Cottrell

Prevention of Nitroprusside-Induced Cyanide Toxicity with Hydroxocobalamin

To investigate hydroxocobalamins role in preventing cyanide intoxication from sodium nitroprusside, we studied two groups of patients. One group received nitroprusside alone, and the other received nitroprusside and hydroxocobalamin. Red-cell and plasma cyanide levels were 83.44 +/- 23.12 and 3.51 +/- 1.01 microgram per 100 ml after nitroprusside alone and were 33.18 +/- 17.29 and 2.18 +/- 0.65 microgram per 100 ml after nitroprusside plus hydroxocobalamin. Acidosis developed in patients with red-cell cyanide levels higher than 75 microgram per 100 ml. When hydroxocobalamin infusion was stopped before sodium nitroprusside infusion was discontinued, blood cyanide levels and base deficit increased in a manner similar to that in the untreated group. The dose of nitroprusside used in each group did not differ statistically. These data show that hydroxocobalamin prevents cyanide transfer from red cells and plasma to tissue after nitroprusside metabolism, and thereby prevents cyanide toxicity from large intravenous doses of the drug.

the Effect of Thiopental and Propofol on Nmda- and Ampa-mediated Glutamate Excitotoxicity

Background: Glutamate excitotoxicity has been implicated as an important cause of ischemic, anoxic, epileptic, and traumatic neuronal damage. Glutamate receptor antagonists have been shown to reduce anoxic, ischemic, and epileptic damage. The effects of thiopental and propofol on N‐methyl‐D‐aspartate (NMDA) and alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole proprionate (AMPA)‐induced neuronal damage were investigated in this study. Methods: The Schaffer collateral pathway was stimulated, and a postsynaptic‐evoked population spike was recorded from the CA1 pyramidal cell layer of rat hippocampal slices. The recovery of the population spike amplitude was an indicator of neuronal viability. The duration of NMDA (25 micro Meter) or AMPA (15 or 10 micro Meter) treatment was 10 min. Thiopental (600 micro Meter), propofol (112 micro Meter), or the vehicle was present 15 min before, during, and 10 min after the NMDA or AMPA treatment. Results: Thiopental prolonged the time required to completely block the population spike after the addition of NMDA or AMPA. Thiopental improved the recovery of the population spike after 25 micro Meter NMDA (79% vs. 44%) and 15 micro Meter AMPA (50% vs. 15%). Propofol worsened the recovery of the population spike from NMDA‐induced damage. The recovery was 8% with propofol compared with 40% with NMDA alone. Propofol did not significantly alter the AMPA‐induced neuronal damage. Conclusions: Thiopental attenuates NMDA‐ and AMPA‐mediated glutamate excitotoxicity. This may be one way barbiturates reduce anoxic, ischemic, and epileptic damage. Propofol enhances NMDA‐induced neuronal damage. These results demonstrate that thiopental and propofol have different properties with respect to glutamate excitotoxicity.

The importance of sodium for anoxic transmission damage in rat hippocampal slices: mechanisms of protection by lidocaine.

1. The effect of sodium influx on anoxic damage was investigated in rat hippocampal slices. Previous experiments demonstrated that a concentration of tetrodotoxin which blocks neuronal transmission protects against anoxic damage. In this study we examined low concentrations of lidocaine (lignocaine; which do not block neuronal transmission), for their effect on recovery of the evoked population spike recorded from the CA1 pyramidal cell layer. 2. Recovery of the population spike, measured 60 min after a 5 min anoxic period, was 4 +/‐ 2% of its preanoxic, predrug level. Lidocaine concentrations of 10, 50, and 100 microM significantly improved recovery to 56 +/‐ 12, 80 +/‐ 7 and 70 +/‐ 14%, respectively. 3. Lidocaine (10 microM) did not alter the size of the evoked response before anoxia and had no significant effect on potassium levels or calcium influx during anoxia. It did, however, reduce cellular sodium levels (146 +/‐ 7 vs. 202 +/‐ 12 nmol mg‐1) and preserve ATP levels (2.17 +/‐ 0.07 vs. 1.78 +/‐ 0.07 nmol mg‐1) during anoxia. All values were measured at the end of 5 min of anoxia except those for Ca2+ influx which were measured during 10 min of anoxia. 4. High concentrations of lidocaine (100 microM) did not improve recovery significantly over that observed with 10 microM. They also had no significantly greater effects on sodium levels than 10 microM lidocaine (137 +/‐ 12 vs. 146 +/‐ 7 nmol mg‐1); however, 100 microM lidocaine significantly improved potassium (202 +/‐ 18 vs. 145 +/‐ 6 nmol mg‐1) and ATP (2.57 +/‐ 0.06 vs. 2.17 +/‐ 0.07 nmol mg‐1) levels, while reducing calcium influx (7.76 +/‐ 0.12 vs. 9.24 +/‐ 0.39 nmol mg‐1 (10 min)‐1) when compared with 10 microM lidocaine. 5. We conclude that sodium influx and ATP depletion are of major importance in anoxic damage since 10 microM lidocaine reduced these changes during anoxia and improved recovery of the population spike. In addition, our results indicate that the properties of the sodium channel are altered during anoxia, since sodium influx is blocked by a concentration of lidocaine that does not affect the population spike in the preanoxic period.

Magnesium and cobalt, not nimodipine, protect neurons against anoxic damage in the rat hippocampal slice.

Brain tissue, maintained in vitro, was used to determine whether agents that block calcium entry into neurons can improve the recovery of evoked responses after anoxia. The hippocampus was dissected from a rat brain and sliced perpendicular to its long axis such that its main neuronal circuits remain functional. A pathway in the slice was stimulated electrically, and an extracellular potential, the evoked population spike, recorded from the neurons postsynaptic to that pathway. A bipolar stimulating electrode was placed in either the perforant path or the Schaeffer collaterals and a monopolar metal microelectrode placed, respectively, in either the dentate granule cell layer or the CA1 pyramidal cell layer. The slices were maintained in vitro by superfusing them with oxygenated (95% O2, 5% CO2) artificial cerebrospinal fluid (aCSF). In order to generate anoxia, the tissue was superfused with aCSF bubbled with 95% N2, 5% CO2 for either 5 or 10 min. All drugs examined were present in the aCSF before, during, and immediately after the anoxic period. Percentage recovery was expressed as the amplitude of the evoked population spike 60 min after anoxia divided by its preanoxic amplitude. Protection in this model is defined as a significant (P < 0.05) improvement in percentage recovery compared with the recovery of untreated slices. There was no recovery of the response recorded from untreated dentate granule cells after 10 min of anoxia (0 ± 0%, n = 5; mean ± SE), whereas 5 min of anoxia was sufficient to cause damage to the untreated CA1 pyramidal cells (4 ± 3%, n = 6). When nimodipine (10−7 M) was present, there was no significant improvement in the recovery of the evoked population spike from either the dentate granule cells (11 ± 11%, n = 5) or the CA1 pyramidal cells (5 ± 5%, n = 5). Cobalt (2 mM), which had improved the recovery of dentate granule cells,1 protected the CA1 pyramidal cells from anoxic damage (64 ± 12%, n = 5). Magnesium (10 mM) significantly improved recovery of both the dentate granule cells (76 ± 5%, n = 5) and the CA1 pyramidal cells (35 ± 10%, n = 8) after anoxia in this in vitro model. ATP levels during anoxia were measured in order to determine how magnesium might protect against the anoxic damage. ATP was maintained at a significantly higher level during anoxia when 10 mM magnesium was present in the bathing medium (1.7 ± 0.2 vs. 1.1 ± 0.15 nM/mg dry weight). Nimodipine did not maintain ATP levels during anoxia. The authors conclude that magnesium and cobalt, but not nimodipine, protect against anoxic damage to the hippocampus in this in vitro model. Any potential clinical benefit of magnesium (cobalt is highly toxic) would have to be tested in an in vivo model, and serious problems such as the limited permeability of the blood-brain barrier to magnesium would have to be overcome. Their results support the importance of calcium influx as one trigger for anoxic damage.

Lidocaine attenuates apoptosis in the ischemic penumbra and reduces infarct size after transient focal cerebral ischemia in rats

Lidocaine is a local anesthetic and antiarrhythmic agent. Although clinical and experimental studies have shown that an antiarrhythmic dose of lidocaine can protect the brain from ischemic damage, the underlying mechanisms are unknown. In the present study, we examined whether lidocaine inhibits neuronal apoptosis in the penumbra in a rat model of transient focal cerebral ischemia. Male Wistar rats underwent a 90-min temporary occlusion of middle cerebral artery. Lidocaine was given as an i.v. bolus (1.5 mg/kg) followed by an i.v. infusion (2 mg/kg/h) for 180 min, starting 30 min before ischemia. Rats were killed and brain samples were collected at 4 and 24 h after ischemia. Apoptotic changes were evaluated by immunohistochemistry for cytochrome c release and caspase-3 activation and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) for DNA fragmentation. Cytochrome c release and caspase-3 activation were detected at 4 and 24 h after ischemia and DNA fragmentation was detected at 24 h. Double-labeling with NeuN, a neuronal marker, demonstrated that cytochrome c, caspase-3, and TUNEL were confined to neurons. Lidocaine reduced cytochrome c release and caspase-3 activation in the penumbra at 4 h and diminished DNA fragmentation in the penumbra at 24 h. Lidocaine treatment improved early electrophysiological recovery and reduced the size of the cortical infarct at 24 h, but had no significant effect on cerebral blood flow in either the penumbra or core during ischemia. These findings suggest that lidocaine attenuates apoptosis in the penumbra after transient focal cerebral ischemia. The infarct-reducing effects of lidocaine may be due, in part, to the inhibition of apoptotic cell death in the penumbra.

Intramedullary pressure in syringomyelia: clinical and pathophysiological correlates of syrinx distension.

OBJECTIVE The pathophysiological effects of syrinx distension are incompletely understood. Although it is generally assumed that the accumulation of fluid within syrinx cavities can contribute to neurological dysfunction, there are no reports describing intramedullary pressure in syringomyelia. The purpose of the current study was to measure syrinx pressures in patients with progressive clinical deterioration and to correlate these data with neurological deficits and intraoperative physiological findings. METHODS Intramedullary fluid pressure was measured manometrically in 32 patients undergoing syrinx shunting procedures. The data were correlated with syrinx morphology, intraoperative somatosensory evoked potentials, laser Doppler measurements of local spinal cord blood flow (six patients), and neurological findings before and after syrinx decompression. RESULTS Syrinx pressures recorded under atmospheric conditions ranged from 0.5 to 22.0 cm H2O (mean = 7.7 cm). There was a significant elevation of the cardiac pulse (mean = 0.7 cm H2O) and the respiratory pulse (mean = 1.1 cm H2O) that was consistent with raised cerebrospinal fluid pressure. Syrinx pressures decreased to subatmospheric levels after surgical drainage. In 18 of 24 patients with predrainage somatosensory evoked potential abnormalities, syrinx decompression produced a consistent reduction of N20 latencies (mean change = 0.49 ms +/- 0.094 SE right, P = 0.002; 0.61 ms +/- 0.089 SE left, P = 0.001) and a similar but less consistent increase in N20 amplitudes (mean change = 0.17 mV +/- 0.103 SE right, P = 0.115; 0.31 mV +/- 0.097 SE left, P = 0.027). Measurements of local spinal cord blood flow revealed very low baseline values (mean = 12.2 arbitrary units +/- 13.9 standard deviation), which increased to intermediate levels (mean = 144.7 arbitrary units +/- 42.6 standard deviation) after syrinx decompression. Patients with syrinx pressures greater than 7.7 cm H2O tended to have more rapidly progressive symptoms, exhibited greater improvements after shunting, and had a higher incidence of postoperative dysesthetic pain. CONCLUSION The current study is the first to measure intramedullary pressure in a human disease. Evidence is presented that distended syringes are associated with varying levels of raised intramedullary pressure that can accentuate or induce neurological dysfunction by the compression of long tracts, neurons, and the microcirculation. Symptoms referrable to raised intramedullary pressure are potentially reversible by syrinx decompression.

Intrapulmonary shunting during induced hypotension.

The effect of sodium nitroprusside (SNP) and nitroglycerin (TNG) on pulmonary shunting (&OV0422;s/&OV0422;t) in 14 consenting adults [nine with normal lung function and five with chronic obstructive pulmonary disease (COPD)] was studied under general anesthesia. &OV0422;s/&OV0422;t significantly increased (p > 0.005) from 5.19% to 8.81%, whereas pulmonary arterial pressure (PAP) decreased from 18.5 to 8 torr (p > 0.005) and pulmonary vascular resistance (PVR) decreased from 235 to 147.75 dynes sec/cm5 (p > 0.025) when SNP was administered to patients with normal lung function. Nitroglycerin increased &OV0422;s/&OV0422;t from 5.13% to 6.19% (p > 0.005), whereas PAP decreased from 18 to 10 torr (p > 0.005) and PVR decreased from 237 to 162.6 dynes sec/cm5 (p > 0.025) in these patients. In patients with COPD, SNP and TNG produced no significant changes in &OV0422;s/&OV0422;t, PAP, or PVR. Cardiac output remained unchanged in both groups of patients. Various mechanisms to explain these results can be postulated. When hypotension is induced in patients with normal pulmonary function, PAP decreases and the effect of gravity puts more blood through dependent areas where most of the shunt units are. In patients with COPD, destructive vascular changes increase PAP, preventing vasodilators from decreasing PVR. In addition, dilation of hypoxic pulmonary vasoconstriction (if present) by SNP and TNG will occur independent of the two previously mentioned mechanisms. These results provide evidence that SNP-and TNG-induced hypotension may cause significant impairment in pulmonary gas exchange in patients with normal lung function. In patients with COPD pulmonary gas exchange is not affected after deliberate hypotension with SNP or TNG.

Neuroprotective effect of low-dose lidocaine in a rat model of transient focal cerebral ischemia.

Background A low concentration of lidocaine (10 &mgr;m) has been shown to reduce anoxic damage in vitro. The current study examined the effect of low-dose lidocaine on infarct size in rats when administered before transient focal cerebral ischemia. Methods Male Wistar rats (weight, 280–340 g) were anesthetized with isoflurane, intubated, and mechanically ventilated. After surgical preparation, animals were assigned to lidocaine 2-day (n = 10), vehicle 2-day (n = 12), lidocaine 7-day (n = 13), and vehicle 7-day (n = 14) groups. A 1.5-mg/kg bolus dose of lidocaine was injected intravenously 30 min before ischemia in the lidocaine 2-day and 7-day groups. Thereafter, an infusion was initiated at a rate of 2 mg · kg−1 · h−1 until 60 min of reperfusion after ischemia. Rats were subjected to 90 min of focal cerebral ischemia using the intraluminal suture method. Infarct size was determined by image analysis of 2,3,5-triphenyltetrazolium chloride–stained sections at 48 h or hematoxylin and eosin–stained sections 7 days after reperfusion. Neurologic outcome and body weight loss were also evaluated. Results The infarct size was significantly smaller in the lidocaine 2-day group (185.0 ± 43.7 mm3) than in the vehicle 2-day group (261.3 ± 45.8 mm3, P < 0.01). The reduction in the size of the infarct in the lidocaine 7-day group (130.4 ± 62.9 mm3) was also significant compared with the vehicle 7-day group (216.6 ± 73.6 mm3, P < 0.01). After 7 days of reperfusion, the rats in the lidocaine group demonstrated better neurologic outcomes and less weight loss. Conclusions The current study demonstrated that a clinical antiarrhythmic dose of lidocaine, when given before and during transient focal cerebral ischemia, significantly reduced infarct size, improved neurologic outcome, and inhibited postischemic weight loss.

The barbiturate thiopental reduces ATP levels during anoxia but improves electrophysiological recovery and ionic homeostasis in the rat hippocampal slice

The barbiturate anesthetic thiopental enhances recovery of the evoked population spike recorded from rat hippocampal slices after short periods of anoxia. Thiopental reduces changes in sodium, potassium and calcium but enhances the fall in ATP levels during anoxia. The postsynaptic population spike recorded from the CA1 pyramidal cell region of the slices treated with thiopental (600 microM) recovered to 67% of the preanoxic amplitude after 3.5 min of anoxia. There was less recovery (24%) when a lower concentration of thiopental (250 microM) was used. Untreated slices recovered to only 10% of their preanoxic amplitude after 3.5 min of anoxia. Other studies have demonstrated that maintaining ATP levels during anoxia may be an important mechanism of protection. In contrast to those studies, thiopental was protective although it enhanced the fall of ATP levels after 3.5 min of anoxia in the CA1 region and after 3.5 and 5 min in the dentate region. Thus enhanced recovery of the population spike with thiopental is not due to its preservation of ATP levels. This result allows a clear separation of improved ATP levels during anoxia from other mechanisms of protection. We therefore looked for other mechanisms of protection. Sodium and potassium levels were measured after 10 min of anoxia. In untreated tissue, sodium levels in the slice rose and potassium levels fell significantly. In thiopental-treated tissue, changes in sodium and potassium caused by anoxia and by veratridine under normoxic conditions were significantly reduced. During anoxia calcium-45 uptake increases; thiopental significantly reduces this uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Compensation for PKMζ in long-term potentiation and spatial long-term memory in mutant mice

PKMζ is a persistently active PKC isoform proposed to maintain late-LTP and long-term memory. But late-LTP and memory are maintained without PKMζ in PKMζ-null mice. Two hypotheses can account for these findings. First, PKMζ is unimportant for LTP or memory. Second, PKMζ is essential for late-LTP and long-term memory in wild-type mice, and PKMζ-null mice recruit compensatory mechanisms. We find that whereas PKMζ persistently increases in LTP maintenance in wild-type mice, PKCι/λ, a gene-product closely related to PKMζ, persistently increases in LTP maintenance in PKMζ-null mice. Using a pharmacogenetic approach, we find PKMζ-antisense in hippocampus blocks late-LTP and spatial long-term memory in wild-type mice, but not in PKMζ-null mice without the target mRNA. Conversely, a PKCι/λ-antagonist disrupts late-LTP and spatial memory in PKMζ-null mice but not in wild-type mice. Thus, whereas PKMζ is essential for wild-type LTP and long-term memory, persistent PKCι/λ activation compensates for PKMζ loss in PKMζ-null mice. DOI: http://dx.doi.org/10.7554/eLife.14846.001