Bulletin of Experimental Biology and Medicine, Vol. 154, No. 4, February, 2013 PHARMACOLOGY AND TOXICOLOGY
457
Changes in Brain Cortex Sensitivity to Epileptogens under Conditions of Ketogenic Diet
V. I. Kresyun, V. A. Polyasny, V. V. Godovan, and L. S. Godlevsky Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 154, No. 10, pp. 452-454, October, 2012 Original article submitted May 12, 2011 The epileptogenic effects of applications of NMDA and kainic acid solutions to the frontal cortex were attenuated in rats receiving ketogenic diet (80% lipids, 3.3% carbohydrates, and 16.7% proteins) during 4 weeks. Spike latency increased, the power of focal epileptic activity decreased, and focus lifetime was shortened in these animals. Sodium benzylpenicillin and strychnine nitrate less markedly reduced epileptogenic activity. Key Words: focal epileptic activity; penicillin; NMDA; kainic acid; strychnine nitrate Ketogenic diet (KD) is effective in drug-resistant epileptiform syndrome [2]. The development of anticonvulsive effect is associated with activation of the cerebral GABAergic system, inhibition of production and release of proinflammatory cytokines, increase in purinergic mediation, and reduction of the stimulatory amino acid tone [3,4]. Excitability of the cerebral cortex for the epileptogenic effects of neurotoxins with different mechanisms of neurotropic activity in animals receiving KD attracted our attention. We compared the epileptogenic effects of sodium benzylpenicillin (blocker of GABAergic inhibition), kainic acid (glutamate receptor agonist), NMDA (direct stimulant), and strychnine (blocker of glycineinduced inhibition) in rats fed KD [6].
MATERIALS AND METHODS Acute experiment was carried out on male Wistar rats (n=56; 180-250 g). The study was carried out in accordance with the regulations of GLP and Bioethics Committee of Odessa National Medical University (Protocol No. 84, 10.10.2008). The animals were divided into 8 groups (4 experimental and 4 control), 6-8 rats per group. Odessa National Medical University, Ukraine. Address for correspondence:
[email protected]. L. S. Godlevsky
Tracheostomy was carried out under rausch ether narcosis, forced ventilation of the lungs was switched on, and the animals were fixed in a SEZh-3 stereotaxis. Myorelaxation was induced by d-tubocurarine (2 mg/kg intraperitoneally; Orion) and after 0.5% procaine solution infiltration of soft tissues of the head and sites of tissue compression by ear holders, trephination was carried out: the dura mater was dissected and the frontal lobe was exposed. Tissue infiltration by procaine solution was repeated every 1.5-2.0 h. In order to prevent the brain cortex drying, it was regularly humidified by warm saline. Foci of epileptic activity (EPA) were evoked by application of filter paper (2×2 mm), impregnated in the convulsant solution, to the cortical surface. Electric activity was recorded via a monopolar silver chlorine electrode; the indifferent electrode was fixed to the nasal bones of the skull. Bioelectrical signals were recorded on a DX-5000 computer electroencephalograph. Solutions of the following convulsants were prepared ex tempore: sodium benzylpenicillin (10,000 U/ml), NMDA (10 mg/ml; Sigma Aldrich), kainic acid (2 mg/ml), and strychnine nitrate (30 mg/ml; Sigma Aldrich). The animals were fed KD including 80% lipids, 3.3% carbohydrates, and 16.7% proteins [3] for 4 weeks. Controls received common fodder under the same conditions during the same period. The power of focal EPA was expressed in arbitrary units calculated by multiplying the mean fre-
0007-4888/13/15440457 © 2013 Springer Science+Business Media New York
458
Bulletin of Experimental Biology and Medicine, Vol. 154, No. 4, February, 2013 PHARMACOLOGY AND TOXICOLOGY
quency of spike charge generation (oscillations/sec) by their mean amplitude (in mV) during the period of continuous registration (1 min). The duration of the focus existence was recorded from the appearance of the first spike potential until the last spike potential. Only the animals without ictal potentials were included in the analysis. The results were statistically processed by ANOVA and Newman–Keuls test for EPA latent period and power values. The focus lifetimes were compared using Mann–Whitney U test.
RESULTS The latency of spikes induced by application of sodium benzylpenicillin solution (10,000 U/ml) was 5.6±0.7 min in the controls, while in rats fed KD this parameter increased by 1.82 times and reached 10.4±1.3 min; p
