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Two distinct types of repetitive bursting activity mediated by NMDA in hypothalamic neurons in vitro
Author(s) -
Poulain Pierre
Publication year - 2001
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.0953-816x.2001.01677.x
Subject(s) - bursting , nmda receptor , neuroscience , tetrodotoxin , slice preparation , chemistry , biophysics , patch clamp , glutamate receptor , electrophysiology , biology , receptor , biochemistry
Hypothalamic magnocellular dorsal nucleus neurons were recorded from adult guinea pig brain slices with the whole‐cell patch‐clamp technique to determine the effects of N ‐methyl‐ d ‐aspartate (NMDA) applied in the bath or by iontophoresis. In a majority of cells (59 of 77, 76.6%), rhythmic bursting discharges were evoked by specific activation of NMDA receptors when the membrane was more negative than −60 mV. This endogenous rhythmic activity was resistant to tetrodotoxin. It was suppressed by removal of extracellular Mg 2+ , indicating the involvement of the voltage‐dependent block of the NMDA channel by Mg 2+ . Application of thapsigargin showed that rhythmic activity did not depend on the release of Ca 2+ from reticulum stores. Blockers of Ca 2+ conductances Ni 2+ and nifedipine had no effects on the bursts. Their repolarization did not involve the activation of a strophantidin‐ or ouabain‐sensitive pump, but partly depended on an apamine‐sensitive Ca 2+ ‐dependent K + current. In a small subset of cells (9 of 69, 13%), specific activation of NMDA receptors induced another type of bursting activity which consisted of repetitive low‐threshold spikes sustaining bursts of action potentials. Rhythmic low‐threshold spikes subsisted in the presence of tetrodotoxin but were suppressed by Ni 2+ . Increasing the amount of NMDA brought about a switch from the rhythmic low‐threshold spike burst firing to the rhythmic bursting activity observed for the majority of cells. The present data show for the first time that NMDA receptor activation can induce two independent rhythmic bursting behaviours in the same neuron, probably depending on the strength of the glutamatergic drive.