Sping Lin

Penicillin as Epileptogenic Agent: Its Effect on an Isolated Neuron

Penicillin induces partial depolarization and increased excitability of the neuronal membrane of crayfish stretch receptor. Such effects suggest that the epileptic focus created by the topical application of penicillin to the mammalian cerebral cortex may result from the lowering of the threshold for impluse initiation by excitatory synaptic action within the neuron population.

The mechanism of action of diphenylhydantoin on invertebrate neurons. I. Effects on basic membrane properties

The effect of diphenylhydantoin (DPH) has been studied on certain membrane properties of the crayfish stretch receptor neuron (SRN) and of neurons in the abdominal and buccal ganglia of Aplysia. DPH decreases the amplitude of post-tetanic hyperpolarization of the SRN, which is thought to be an expression of the electrogenic pump, and does not antagonize the effect of ouabain on this activity. DPH decreases the membrane resistance of all the different types of neurons studied, with little or no change in the resting membrane potential. It decreases the overshoot of the action potential in some of the neurons studied and prolongs the falling phase and the undershoot in other neurons. DPH also decreases repetitive firing. These effects have also been observed at different external concentrations of potassium. It is concluded that DPH, in the different preparations studied, does not have any effect on or decreases the electrogenic pump, but produces changes in other membrane properties which are consistent with its anticonvulsant action.

Ammonia Intoxication: Effects on Cerebral Cortex and Spinal Cord

Abstract: The effect of an acute systemic ammonia intoxication on the metabolic states of the cerebral cortex and the spinal cord of the same animal was studied in the cat. The intravenous infusion of ammonium acetate (2 and 4 mmol/kg body weight/30 min) increased the gross levels of tissue NH4, glutamine, glutamine/glutamate ratio, lactate, and the lactate/pyruvate ratio in the cerebral cortex and the spinal cord. Pyruvate increased, but significantly only in the spinal cord; aspartate decreased, but significantly only in the cerebral cortex. The infusion of ammonium acetate did not significantly change the levels of phosphocreatine, ATP, ADP, AMP, total adenine nucleotides, adenylate energy charge, glucose, glutamate, α‐ketoglutarate, and malate in either tissue. The changes of NH4+, glutamine, and lactate levels as well as gutamine/glutamate and lactate/pyruvate ratios in the spinal cord correlated significantly with the corresponding changes of these metabolites in the cerebral cortex. Thus, cerebral cortex and spinal cord show certain specific and comparable metabolic changes in response to a systemic ammonia intoxication. The effect of ammonia intoxication on the increases of glutamine and lactate levels is discussed.

AN ANALYSIS OF THRESHOLD TEMPERATURES FOR THE DEVELOPMENT OF ONCOPELTUS AND TRIBOLIUM EGGS

T tIE interest of biologists in temperature thresholds of biological processes dates back to the time when R6aumur (1735; see Balehrtdek, 1935) recognized that there was a quantitative relationship between the activities of organisms and the temperature. This may be expressed in various ways. As deduced by later authors, if y is the time required for complete development at temperature t, the relationship may be expressed as follows: y(t-a) =K, (1)

Measurement of adenosine triphosphate content of crayfish stretch receptor cell preparations

Abstract A sensitive and rapid method for the assay of ATP down to 2× 10−14 mole was presented. This was achieved by the use of firefly luciferase-luciferin reaction and a scintillation spectrometer operated on single channel at high voltage. The ATP content of single resting orayfish stretch receptor cell preparations was determined. It was found to be 4.24 picomoles in the absence, and 5.02 picomoles in the presence, of 1 mM glucose.

Acid soluble phosphates in the developing rabbit brain.

AN adequate source of energy is a prerequisite for the orderly maturation of the brain. Since the energy for developmental processes is provided principally through high energy phosphates, information concerning the development of these compounds is of central importance to the understanding of cerebral functional and structural differentiation. Previous reports of levels of high energy phosphates in the developing brain have been sparseandcontradictory and could not be correlated withmorphological and physiological differentiation. This investigation was undertaken to clarify the relationship of these compounds to the maturation of cerebral structure and function. Orthophosphate, phosphoethanolamine, creatine, and ascorbic acid were investigated i n addition to adenosine triphosphate and phosphocreatine because of their relationship to phosphorylation and development.

Ammonia, postsynaptic inhibition and CNS-energy state

Ammonia intoxication decreases the hyperpolarizing action of postsynaptic inhibition. This study examines the metabolic state of the spinal cord during this effect of ammonia intoxication on spinal motoneurons. ATP, ADP, AMP, the adenylate energy charge, glucose, PCr, pyruvate, alpha-ketoglutarate and glutamate were unchanged during the effect of ammonia on the hyperpolarizing action of postsynaptic inhibition. NH4+, glutamine and lactate were increased. Ammonia intoxication affected postsynaptic inhibition without changes of the resting membrane potential, the neuron input resistance, the action potential and EPSPs. The encephalopathy caused by ammonia intoxication is known to occur without an alteration of the tissue energy state. The effect of ammonia intoxication on postsynaptic inhibition can be considered as a cause of the encephalopathy because postsynaptic inhibition is altered without a change of the tissue energy state, the resting membrane potential, the whole neuron resistance, the action potential and EPSPs.

Crayfish ventral nerve cord and hemolymph: Content of free amino acids and other metabolites☆

Abstract 1. 1. Non-protein amino acids and related compounds in the ventral nerve cord (VNC) and the hemolymph of the fresh-water crayfish Orconectes immunis have been determined by ion-exchange chromatography. Some other metabolites have also been measured. 2. 2. A total of twenty-six and twenty-seven amino compounds has been found in the VNC and the hemolymph, respectively. 3. 3. The VNC contained over ten times as much total amino compounds as the hemolymph. 4. 4. Some pharmacologically active amino acids such as GABA, glutamate and aspartate existed in even higher content in the VNC than in the hemolymph. 5. 5. The significance of such disparity in distribution has been discussed.

The effect of diethyl- -fluoroglutarate on phosphates and glutamate in slices of rabbit cerebral cortex.

Abstract— The diethyl ester of α‐fluoroglutarate (DEFG), an inhibitor of glutamate dehydrogenase, was prepared, and its effect on glutamate and phosphates in slices of rabbit cerebral cortex was examined. The primary effect of the drug on cortical slices incubating in a Krebs‐Ringer glucose medium was to decrease the tissue levels of glutamate in association with decreased levels and turnover of high‐energy phosphates. Assimilation of exogenous glutamate by the slices was partially blocked in the presence of the drug and severely depressed oxidative phosphorylation resulted when glutamate and DEFG were both present in the incubation mixture. The results suggested a significant relationship between the activity of cerebral glutamate dehydrogenase and oxidative phosphorylation.

The effect of scorbutus and pentobarbital on the in vivo levels of "energy-rich" phosphates and their turnover in guinea pig cerebral tissue.

Abstract The in vivo cerebral levels of ascorbic acid and “energy-rich” phosphates and turnover of the phosphates were measured in young guinea pigs under different experimental conditions. Pentobarbital-treated scorbutic animals show a cerebral ascorbic acid level twice that of the untreated scorbutic guinea pig. The results also indicate that the combination of scorbutus plus pentobarbital treatment raises the in vivo creatine phosphate level and interferes with the turnover of creatine phosphate and adenosine triphosphate. Boiling water and cold perchloric acid were compared as extracting agents for cerebral organic phosphates. Boiling water results in considerably less creatine phosphate and adenosine triphosphate isolation than does cold perchloric acid, although total creatine and adenine nucleotides extracted by the two remain the same.