Rapid cooling aborts seizure-like activity in rodent hippocampal-entorhinal slices.

PURPOSE: As a preliminary step in the development of an implantable Peltier device to abort focal neocortical seizures in vivo, we have examined the effect of rapid cooling on seizures in rodent hippocampal-entorhinal slices. METHODS: Seizure-like discharges were induced by exposing the slices to extracellular saline containing 4-aminopyridine (50 micromol/L). RESULTS: When we manually activated a Peltier device that was in direct contact with the slice, seizures terminated within seconds of the onset of cooling, sometimes preceding a detectable decrease in temperature measured near the top of the slice. However, activation of the Peltier device did not stop seizures when slices were no longer in direct physical contact with the device, indicating that this was not a field effect. When cooling was shut off and temperature returned to 33 degrees C, bursting sometimes returned, but a longer-term suppressive effect on seizure activity could be observed. In two of our experiments, a custom computer program automatically detected seizure discharges and triggered a transistor-transistor logic pulse to activate the Peltier device. In these experiments, the Peltier device automatically terminated the slice bursting in less than 4 seconds. When the Peltier device was placed in contact with the normal, exposed cortex of a newborn pig, we found that the cortical temperature decreased rapidly from 36 degrees C to as low as 26 degrees C at a depth of 1.7 mm below the cooling unit. CONCLUSIONS: These experiments show that local cooling may rapidly terminate focal paroxysmal discharges and might be adapted for clinical practice.

Anti-aging medicine. 2. Efficacy and safety of hormones and antioxidants.

Little is known about the efficacy and safety of substances that are being promoted to consumers as "anti-aging" therapies. Hormones such as DHEA, human growth hormone, and testosterone tend to decline with aging, but the therapeutic value of replacing them to "normal" physiologic levels has not been substantiated by controlled clinical trials. The best source of antioxidants is a balanced diet, although older patients may benefit from vitamin E supplementation. Providing anti-aging medicine in the primary care setting means practicing good medicine. It means talking to patients who request these therapies and understanding why they want them and how much risk they're willing to take.

Reversible physiological alterations in sympathetic neurons deprived of NGF but protected from apoptosis by caspase inhibition or Bax deletion.

Cell death in nervous system development and in many neurodegenerative diseases appears to be apoptotic or programmed. Withdrawal of nerve growth factor (NGF) from cultures of superior cervical ganglia neurons (SCG) is an excellent model of programmed cell death (PCD), producing apoptosis within 24-48 h. This death can be prevented by treatment with caspase inhibitors or deletion of the proapoptotic Bax gene. Since inhibition of apoptosis is an attractive strategy for the therapy of many neurological diseases and little is known about the function of neurons when apoptosis has been aborted, we examined the electrophysiological properties of NGF-deprived SCG neurons from rats and mice, saved by the caspase inhibitor boc-aspartyl(OMe)fluoromethyl ketone (BAF) or by Bax deletion. Compared to NGF-maintained controls, the resting membrane potentials of BAF-saved neurons were depolarized by 9 mV and the action potentials were prolonged by over 50%. Nicotinic cholinergic current density was depressed by about 50%. Electrophysiological parameters returned to normal within 4 days after NGF restoration. Neurons from Bax-deficient mice were altered differently by NGF withdrawal. There were no detectable changes in resting or action potentials. However, nicotinic current density was reduced just as in BAF-saved rat neurons. There were no observable changes in the processes of individual neurons after 6 days of NGF deprivation in the presence of BAF. Our results indicate that neurons are physiologically altered during pharmacological inhibition of PCD, but fully recover after trophic support is returned.

Abnormal calcium homeostasis and mitochondrial polarization in a human encephalomyopathy.

Patients with several inherited human encephalomyopathies exhibit systemic and neurological symptoms in association with specific mitochondrial mutations. The mechanisms by which these mitochondrial mutations result in cellular injury have not been elucidated. One potential cause of neuronal vulnerability is an inability to effectively buffer intracellular calcium. We report that fibroblasts from patients with one specific inherited encephalomyopathy, MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes) syndrome, have elevated levels of ionized calcium and cannot normally sequester calcium influxes. Quantitative fluorescence imaging demonstrated that this abnormality was associated with a relative decrease in mitochondrial membrane potential compared to control fibroblasts. This documentation of pathological calcium homeostasis in a genetic neurological disease extends the calcium hypothesis of toxic cell injury to human mitochondrial encephalomyopathies.

Adenosine inhibits excitatory but not inhibitory synaptic transmission in the hippocampus.

We examined the effects of adenosine and baclofen on inhibitory (IPSC) and excitatory (EPSC) synaptic currents in dissociated rat hippocampal neurons. Adenosine dramatically reduced monosynaptic EPSCs but failed to diminish IPSCs. This selective effect on EPSCs is likely due to inhibition of excitatory transmitter release because adenosine did not directly alter any properties of postsynaptic neurons. Baclofen depressed both EPSCs and IPSCs to approximately the same extent. These experiments indicate that the presynaptic effects of adenosine and baclofen are clearly separable and that transmitter sensitivities of inhibitory and excitatory neurons can differ. These differences could be exploited in the design of antiepileptic drugs that act at adenosine receptors to limit excitatory neurotransmission without blocking tonic inhibition.

Delayed neurotoxicity of excitatory amino acids in vitro.

The acute neurotoxicity produced by glutamate and related excitatory amino acids is probably caused by depolarization leading to excessive anionic and cationic fluxes and osmotic lysis. Recently, a more delayed form of glutamate neurotoxicity, which is critically dependent upon calcium influx, has been described in cultured neocortex. We investigated this phenomenon in cultures of dispersed rat hippocampal neurons. When these cultures were briefly incubated with various excitatory amino acids in low extracellular chloride, there was no acute toxicity, but a gradual drop-out of neurons occurred over the next day. When calcium was removed from the extracellular medium during amino acid incubation, this late neuronal loss was not seen. Interestingly, blocking excitatory amino acid receptors in cultures after the amino acid exposure also prevented this delayed neuronal death. In addition, these treated cultures contained neurons with normal physiological properties, and had concentrations of adenosine triphosphate that were close to control values. The findings suggest an amino acid-induced calcium influx may elevate the release of endogenous excitatory transmitter, likely glutamate, and/or increase the sensitivity of these neurons to glutamate. These in vitro observations may partially explain the delayed neuronal loss seen in some pathological conditions affecting man.

Ketamine protects hippocampal neurons from anoxia in vitro.

Ketamine, a dissociative, general anesthetic, blocks the excitation produced by activating one class of excitatory amino acid receptors, the N-methyl-D-aspartate receptor in the rat. We have found that ketamine can protect hippocampal neurons in culture and slice from anoxia. When added to cultures immediately prior to anoxic exposure, ketamine prevented the neuronal destruction seen after a day of anoxia. Neurons appeared undamaged and had normal resting and action potentials. Adenosine triphosphate levels in ketamine-protected anoxic cultures were approximately two-thirds of normal controls. Ketamine also prevented the irreversible loss of the population spike seen in hippocampal slices after prolonged perfusion with anoxic buffer. These results suggest that ketamine may have therapeutic potential in preventing anoxic damage from stroke in man.

Glutamate and the pathophysiology of hypoxic--ischemic brain damage.

Information obtained over the past 25 years indicates that the amino acid glutamate functions as a fast excitatory transmitter in the mammalian brain. Studies completed during the last 15 years have also demonstrated that glutamate is a powerful neurotoxin, capable of killing neurons in the central nervous system when its extracellular concentration is sufficiently high. Recent experiments in a variety of preparations have shown that either blockade of synaptic transmission or the specific antagonism of postsynaptic glutamate receptors greatly diminishes the sensitivity of central neurons to hypoxia and ischemia. These experiments suggest that glutamate plays a key role in ischemic brain damage, and that drugs which decrease the accumulation of glutamate or block its postsynaptic effects may be a rational therapy for stroke.

Electrophysiology of Duchenne dystrophy myotubes in tissue culture.

Single myotubes from cultures of 6 patients with Duchenne muscular dystrophy and 6 patients whose biopsy specimens lacked histological abnormality were studied with intracellular physiological recording. Average resting membrane potentials were 47.8 +/- 2.3 mV and 47.0 +/- 1.5 mV for the control and Duchenne cultures, respectively. Action potentials elicited at a standard resting potential of -80 mV were 97.3 +/- 4.0 mV and 98.6 +/- 8.2 mV for the two groups. Maximum rate of rise of action potentials was 154.2 +/- 25.2 V/sec for control and 143.1 +/- 37.1 V/sec for Duchenne myotubes. Action potentials mediated by an influx of calcium ions were seen only when the myotubes from both groups were bathed in high concentrations of calcium and 4-aminopyridine (20 mM and 1 mM, respectively). Thus, the plasma membrane of Duchenne dystrophy myotubes does not have active electrical properties that differ from those in controls. Previous reports of low resting membrane potentials in biopsies studied acutely may reflect secondary changes in degenerating fibers.

Congenital astrocytoma presenting with intracerebral hematoma. Case report.

A massive left intracerebral hematoma was surgically evacuated from a 2-week-old infant. Pathological examination showed that the hemorrhage had developed within a fibrillary astrocytoma. Neonatal intracerebral hemorrhage should raise the question of congenital tumor because such a hemorrhage in this age group is rarely the result of trauma, bleeding diathesis, or vascular malformation.

Cerebrovascular changes in neurofibromatosis.

Vascular changes in neurofibromatosis are most commonly described in the renal arteries. In the present study, two children with neurofibromatosis and cerebral vascular occlusive changes demonstrated by cerebral angiography are reported. Although focal neurological findings in children with neurofibromatosis are often due to tumours, the sudden development of neurological symptoms in such cases should alert paediatricians to the possibility of cerebral vascular disease.