Maciej Nalecz

Metabolic approach of absence seizures in a genetic model of absence epilepsy, the GAERS: Study of the leucine-glutamate cycle

We suggest that a dysregulation of energy metabolism in the brain of genetic absence epilepsy rats from Strasbourg (GAERS) could create a specific cerebral environment that would favor the expression of spike‐and‐wave discharges (SWD) in the thalamocortical loop, largely dependent on glutamatergic and γ‐aminobutyric acid (GABA)‐ergic neurotransmissions. We tested several aspects of metabolic activity in the brain of GAERS compared to a genetic strain of nonepileptic (NE) rats. Glucose metabolism was higher in all brain regions of GAERS compared to those of NE rats along the whole glycolytic and aerobic pathways, as assessed by regional histochemical measurement of lactate dehydrogenase and cytochrome oxidase activities. Branched‐chain amino acids (BCAA) and α‐ketoisocaproate (α‐KIC), the ketoacid of leucine, when injected intraperitoneally, increased the number of SWD in GAERS but had only a slight effect on their duration. These data speak in favor of a BCAA‐ or α‐KIC‐induced change in neuronal excitability. Leucine and α‐KIC decreased the concentration of glutamate in thalamus and cortex without affecting GABA concentrations. Thus, BCAA and α‐KIC, by decreasing glutamatergic neurotransmission, could favor GABAergic neurotransmission, which is known to increase the occurrence of seizures in GAERS. Finally, the transport of [1‐14C]α‐KIC in freshly isolated cortical neurons was lower in GAERS than in NE rats, and this difference was shown to be of metabolic origin. The addition of gabapentin, a specific inhibitor of BCAA transaminase (BCAT), reduced the transport of [1‐14C]α‐KIC in GAERS and NE rats to a level that became identical in both strains. This strain‐dependent change was not related to a difference in the activity of BCAT, which was identical in GAERS and NE rats. The exact origin of this apparent metabolic dysregulation of energy metabolism in GAERS that could underlie the origin of seizures in that strain remains to be explored further.

Modulation of absence seizures by branched-chain amino acids: correlation with brain amino acid concentrations

The occurrence of absence seizures might be due to a disturbance of the balance between excitatory and inhibitory neurotransmissions in the thalamo-cortical loop. In this study, we explored the consequences of buffering the glutamate content of brain cells on the occurrence and duration of seizures in Genetic Absence Epilepsy Rats from Strasbourg (GAERS), a genetic model of generalized non-convulsive epilepsy. Branched-chain amino acids (BCAAs) and alpha-ketoisocaproate (alpha-KIC), the ketoacid of leucine were repeatedly shown to have a critical role in brain glutamate metabolism. Thus, GAERS were injected by intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) route with these compounds, then the effects on seizures were evaluated on the electroencephalographic recording. We also measured the concentration of amino acids in thalamus and cortex after an i.p. injection of leucine or alpha-KIC. Intracerebroventricular injections of leucine or alpha-KIC did not influence the occurrence of seizures, possibly because the substances reached only the cortex. BCAAs and alpha-KIC, injected intraperitoneally, increased the number of seizures whereas they had only a slight effect on their duration. Leucine and alpha-KIC decreased the concentration of glutamate in thalamus and cortex without affecting GABA concentrations. Thus, BCAAs and alpha-KIC, by decreasing the effects of glutamatergic neurotransmission could facilitate those of GABAergic neurotransmission, which is known to increase the occurrence of seizures in GAERS.

Modulation of pentylenetetrazol-induced seizure activity by branched-chain amino acids and α-ketoisocaproate

Branched-chain amino acids, and mainly leucine act as nitrogen donors in the cerebral glutamate-glutamine cycle, thereby reducing brain excitability. Rats equipped with cortical electrodes received 300 mg/kg of leucine, isoleucine, valine or the ketoacid of leucine, alpha-ketoisocaproate at 2 h before the induction of seizures by 40 mg/kg pentylenetetrazol. Control groups received saline or a commercial mixture of amino acids, Vamine(R). Leucine and isoleucine increased the latency to absence-like and tonic-clonic seizures but did not influence the duration of the tonic-clonic seizure. Vamine(R), valine and alpha-ketoisocaproate had no effect. These data are consistent with the role of leucine in buffering brain glutamate concentration.

Electrocatalytic Determination of Glucose in a Ringer's Solution by Pulse-Voltammetry

Improvement of the electrocatalytic method of glucose determination was achieved by applying the pulse voltammetry technique. This technique, compared. to previously applied cyclic voltammetry, enhances selectivity of a platinum-black working electrode for glucose measurement. A low catalytic load working electrode has been used which is less susceptible to poisoning and has longer term stability. With cyclic voltammetry previously applied, those electrodes were limited by their narrow concentration range for glucose detection. By applying a pulsing technique, these electrodes exhibit linearity up to a glucose concentration 200 mg/dl with correlation coefficients greater than 0.9. The pulse voltammetry diminishes interference by low molecular weight serum components such as serum urea. Concentrations from 20. to 40 mg/di had an interference of 4 percent compared to 40 percent with cyclic voltammetry. Further investigations are carried on to adopt pulse voltammetry for direct measurements of glucose in body fluids.

A hall effect accelerometer

Abstract This paper describes a new measurement technique for accelerometers, using the Hall effect in semiconductors. The mechanical system of the accelerometer consists of a mass suspended from the frame by a flat spring. The acceleration to be measured is proportional to the deflection of the other end of the spring. The mechanical displacements are measured by the Hall voltage, with the Hall generator mounted at the end of the spring and moving in a nonuniform magnetic field. When the gradient of the magnetic field is linear, then the Hall voltage is proportional to the measured acceleration. Two magnetic systems with permanent magnets are discussed. Using the Hall generator (Bell Inc. BH 200) with the gradient equal to about 10,000 gauss/millimeter, earth accelerations from 1 g. to 10 −4 g. can be measured on the linear scale.

Carnitine Transport and Physiological Function in Neurones

Carnitine (4-N-trimethylammonium-3 hydroxybutyric acid) facilitates in the eukaryotic cell the transfer of acyl compounds, mainly long-chain fatty acids, from the cytosol to the mitochondrial matrix (1). The pathway, well characterized for peripheral tissues like liver, kidney or muscles, includes the synthesis of acylcarnitine derivatives from their acylCoA forms by the enzymes localized at the outer side of the outer mitochondrial membrane (for instance palmitoylcarnitine transferase I). Acylcarnitines are further translocated through the inner mitochondrial membrane by a carnitine carrier and subsequently, on the inner side of this membrane the acyl moieties are transferred to CoASH by a different carnitine acyl transferase (e.g. palmitoylcarnitine transferase II). The carnitine carrier responsible for the central tranlocation step catalyses an uniport of carnitine or its exchange with acylcarnitines (2). This system of carnitine-dependent transport of fatty acids into the mitochondria, the so-called “carnitine shuttle”, delivers substrates for β-oxidation.

BLOOD GLUCOSE MONITORING SYSTEM FOR ARTIFICIAL PANCREAS

Abstract The blood-glucose analyser for bed-side automatic insulin infusion system (“artificial pancreas”) has been designed. In the analyser the electrocatalytic amperometric glucose sensor was used as the glucose detector. The sensors selectivity was improved utilising the effect of concentration saturation of coreactans influences. The blood-glucose analysing system was tested “in vivo” in animal experiments with good results.

Control Aspects of Programmed DRUG Administration

Abstract The trend towards increasing the reliability and efficiency of pharmacological therapy is associated with searching for new methods of drug administration. The programmers and infusion pumps enabling the realization of this task have been designed. As for pumping units: a few syringe pumps with a stepping driving motor for intermittent infusion and an original membrane micropump driven by electromagnet for repetitive injection have been used. The constructed dosing units can deliver a constant drug infusion rate and/or a high infusion rate. The complex transients are approximated by step or by segment curves. Theoretical comparison between intermittent infusion and repetitive injection using the one compartment model is considered.

Blood Glucose Monitoring System for Artificial Pancreas

Abstract The blood-glucose analyser for bed-side automatic insulin infusion system (“artificial pancreas”) has been designed. In the analyser the electrocatalytic amperometric glucose sensor was used as the glucose detector. The sensors selectivity was improved utilising the effect of concentration saturation of coreactans influences. The blood-glucose analysing system was tested “in vivo” in animal experiments with good results.

Control Aspect of Artificial Internal Organs 1

Abstract Problems and difficulties encountered in designing and construction of artificial internal organs are revued. Investigation and modelling of Mosystems cooperating with the artificial organ, control of particular parameters within the artificial organ itself and interfacing of the two components are indicated to create the main control problems. Current tasks of control in relation to total artificial heart, cardiac pacing, intraaortic balloon pump, artificial respiration, artificial lung, artificial pancreas and artificial kidney are discussed.