Glutamate-induced action potentials are preceded by regenerative prepotentials in rat hippocampal pyramidal cells in vitro.
(1) The responses of CA1 pyramidal cells to short glutamate pulses (10-50 ms) delivered at sensitive spots in the apical dendrites have been analysed by intracellular recording. (2) The glutamate pulses elicited stable depolarizing responses in a dose- and frequency-dependent manner. (3) When a single action potential with a firing probability around 0.5 was elicited, a subtraction procedure showed that a slow depolarizing ramp preceded each spike. We call this ramp the glutamate-induced prepotential (GluPP). (4) In contrast to the upward convex subthreshold depolarization the GluPP was upward concave. (5) The GluPP amplitude and time course increased with depolarization of the membrane, a phenomenon which appears to be connected to the elevation of action potential threshold. (6) The GluPP was regenerative since once started, it ended in an action potential. (7) A specific N-methyl-D-aspartate receptor antagonist, DL-2-amino-5-phosphonovaleric acid (50 microM) reduced the glutamate-induced depolarization, but did not affect the form or amplitude of GluPP, once the latter was induced. (8) It is concluded that short glutamate pulses elicited action potentials through a prepotential mechanism, similar to the slow prepotentials induced by long depolarizing current pulses across the soma membrane. (9) A possible physiological role for the GluPP is discussed.
Institute of Neurophysiology, University of Oslo, Norway.
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D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D004558:Electric Stimulation; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D007478:Iontophoresis; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D011712:Pyramidal Tracts / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011921:Rats, Inbred WKY; D013779:Tetrodotoxin / Q000494:pharmacology
D005971:Glutamates; D018698:Glutamic Acid; D013779:Tetrodotoxin; D015763:2-Amino-5-phosphonovalerate