An extreme supernormal period in cerebellar parallel fibres

Abstract

SUMMARY1. The electrical responses produced by stimulation at the surface of the cerebellar cortex have been studied in anaesthetized cats.2. The propagation of the underlying activity is attributed to parallel fibres, but the mode of generation of the potential changes is less certain.3. The threshold for a second response is up to 40 % lower following a conditioning stimulus, and the responses to test stimuli less strong than the conditioning stimulus are correspondingly potentiated.4. A second stimulus given 22 msec after the first produces a response which propagates 15-20 % faster along the folium.5. The reduction of the threshold and the increase of the propagation velocity are as large with small (but above threshold) conditioning shocks as with large shocks.6. Both after-effects are present from 5 to 100 msec after a conditioning stimulus, with maximal values at about 10-30 msec.7. The fibre conduction velocity inferred from collision experiments agrees with that inferred from the propagation velocity of the responses, and shows a similar increase after conditioning.8. A second shock does not recruit a new and faster population of parallel fibres.9. Under the conditions of electrical stimulation the after-effects are probably restricted to those fibres which are active during conditioning.

Proceedings of the Physiological Society, 18–19 January 1974, St.Thomas's Hospital Meeting: Communications

“…injection of pentolinium tartrate was inhibited. This confirms a previous conclusion that hypotensive drugs can induce antidiuresis by causing a reflex release of vasopressin in response to a fall of arterial blood pressure (Bisset & Lewis, 1962 A synchronous shock to the parallel fibres of the mammalian cerebellum results in a supernormal period lasting 100-200 msec, during which, at the peak of the effect, a second volley is conducted 15-20 % faster than the initial volley (Gardner-Medwin, 1972). We have found a similar phenomenon in the olfactory nerve of the tortoise.…”

Comparison of the after‐effects of impulse conduction on threshold at nodes of Ranvier along single frog sciatic axons.

“…It has been suggested that superexcitability is correlated with long depolarizing after-potentials seen in myelinated fibres from peripheral nerves (Gasser, 1935;Gardner-Medwin, 1972;Merrill, Wall & Yaksh, 1978;Raymond & Lettvin, 1978;Barrett & Barrett, 1982;Bostock & Grafe, 1985) and that post-tetanic afterhyperpolarization (Gasser & Grundfest, 1936) from an electrogenic pump (Connelly, 1959;Rang & Ritchie, 1968;Schoepfli & Katholi, 1973) causes depression (Bergmans, 1968 a, b;Bliss & Rosenberg, 1979;Raymond, 1979;Bostock & Grafe, 1985). Several findings support this view of mechanisms.…”

Effects of nerve impulses on threshold of frog sciatic nerve fibres.

“…In the rabbit (Lorente de No & Graham, 1936) and cat (Gasser & Grundfest, 1936;Gardner-Medwin, 1972), the period of the oscillation appears shorter so that the phases are over more quickly. A period of ringing in threshold of mammalian nerves was reported by Gasser & Grundfest (1936) after long tetani at high frequencies.…”

“…Furthermore, when conduction velocity changes with activity, it is likely that there are correlated threshold changes, since such changes, distributed along the fibre, result in altered velocity of impulse propagation. In a variety of investigations, threshold changes are implicated from the conduction velocity measurements (Bullock, 1951;Gardner-Medwin, 1972; Kocsis, Vander Maelen & Kitai, 1977;George, 1977), and one variable can often be used as a measure of the other.…”