High‐Frequency Repetitive Firing of Cat Lumbosacral Motoneurones Stimulated by Long‐Lasting Injected Currents

Abstract

Abstract Kernell, D. High‐frequency repetitive firing of cat lumbosacral motoneurones stimulated by long‐lasting injected currents . Acta physiol. scand. 1965. 65 . 74–86. Repetitive discharges were initiated in motoneurones by steady currents injected through an intracellular micro‐electrode. At weaker currents, producing firing rates up to on the average 51 (30–84) imp/sec, the steady discharge frequency was approximately linearly related to current strength ( cf . Granit, Kernell and Shortess 1963 a ). Several cells were capable of setting up steady discharges only within this so‐called “primary” range. In many other cells, steady repetitive firing was obtained even with stronger currents. There were in the latter two ranges of steady firing, the primary one referring to weak and a “secondary” referring to stronger stimulating currents, each approximately fitted by a separate straight line in the graphs relating impulse frequency to current strength. The straight line wich referred to steady firing within the secondary range had a 2–6 times steeper slope than the one characterizing the primary range. Motoneurones capable of maintained firing within the secondary range could reach steady firing rates of the order of 125 (88–195) imp/sec. The maximal impulse frequency within the primary range was about the same initially in the discharge as later on. The findings are discussed also with regard to the repetitive firing of reflexly activated motoneurones.