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DISAGGREGATION OF BRAIN POLYSOMES INDUCED BY ELECTROCONVULSIVE TREATMENT

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  • Six electric shocks were given at intervals of 12–15 min to male rabbits mrussels Hare strain, 34–3.5 kg) with temporo-frontal placement of the electrodes. Rectangular pulses (110 v, 20 msec, interpulse 10 msec) were provided for 0.5 sec. with an electrophysiological stimulator (Grass Medical Instruments, Quincy, Mass., U.S.A.). Immediately after the last convulsion the animal was decapitated, the cerebral cortex quickly removed and placed in ice-cold 0-32 M-Sucrose in TMK. buffer (0.01 m-tris pH 7.3, 2mm-MgCl2, 0.01 M-KCl). The subsequent operations were carried out keeping the material at 0–4°. The tissue, weighing 3–35 g, was minced and homogenized with an equal volume of this medium in a Potter-Elvehjem glass homogenizer, fitted with a teflon pestle allowing a clearance of about 1 mm. Motor speed was adjusted at about 1000 rev/min and the strokes applied very gently for 1 min. The homogenate was centrifuged at 800 g for 5 min and then at 20,000 g for 12 min (in the same tube) using a Servall RP2 regrigerated centrifuge. The supernatant fraction was made 1% in DOC, layered onto a 17–40 per cent linear sucrose gradient in TMK buffer, and centrifuged at 4° (23,500 rev/min; 4.5 hr) in the SW 25.1 or SW 25.2 rotor of the Spinco Model L2 ultracentrifuge. One experimental and one control sample were always centrifuged in the same run to ensure a more accurate comparison of the profiles. The tube content was collected in twenty-seven fractions by means of an ISCO automatic fractionator (Instrument Specialities Co., Lincoln, Nebr., U.S.A.) recording continuously the absorbancy at 254 mμ and of a fraction collector of the same apparatus. When radioactive aminoacids ([14C]amhoacids mixture, 40 mc/m-atom carbon, New England Nuclear Corp., Boston, Mass., U.S.A.) were injected in the subarachnoidal space, the procedure was that described elsewhere (Vesco and Giuditta 1967).

Abstract

—The ribosome–polysome equilibrium of rabbit cerebral cortex is considerably modified after elicitation of epileptic seizures by means of electroshock. Under this condition the number of free ribosomes increases approximately 80 per cent at the expense of a comparable decrease in the polysomal population.

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