Muscarinic Modulation of Intrinsic Burst Firing in Rat Hippocampal Neurons

Rony Azouz, Morten S. Jensen, Yoel Yaari

Research output: Contribution to journalArticlepeer-review

28 Scopus citations

Abstract

Intracellular recordings in rat hippocampal slices were used to examine how exogenous and endogenous cholinergic agonists modulate the firing pattern of intrinsically burst‐firing pyramidal cells. About 24% of CA1 pyramidal cells generated all‐or‐none, high‐frequency bursts of fast action potentials in response to intracellular injection of long positive current pulses. Application of carbachol (5 μM) converted burst firing in these neurons into regular trains of independent spikes. Acetylcholine (5 μM) exerted a similar effect, provided acetylcholine esterase activity was blocked with neostigmine (2 μM). Atropine (1 μM) reversed this cholinergic effect, indicating its mediation by muscarinic receptors. Cholinergic agonists also caused mild neuronal depolarization but the block of intrinsic burst firing was independent of this effect. Repetitive stimulation of cholinergic fibres in the presence of neostigmine (2 μM) evoked a slow cholinergic excitatory postsynaptic potential (EPSP) lasting about a minute. During the slow EPSP, burst firing could not be evoked by depolarizing pulses and the neurons fired in regular mode. These effects were prevented by pretreatment with atropine (1 μM). Exogenously applied cholinergic agonists and endogenously released acetylcholine also reduced spike frequency accommodation and suppressed the long‐duration afterhyperpolarization in burst‐firing pyramidal cells in an atropine‐sensitive manner. A membrane‐permeable cAMP analogue (8‐bromo‐cAMP; 1 mM) also reduced frequency accommodation and blocked the long‐duration afterhyperpolarization, but did not affect intrinsic burst firing at all. Taken together, the data show that muscarinic receptor stimulation transforms the stereotyped, phasic response of burst‐firing neurons into stimulus‐graded, tonic discharge.

Original languageEnglish
Pages (from-to)961-966
Number of pages6
JournalEuropean Journal of Neuroscience
Volume6
Issue number6
DOIs
StatePublished - 1 Jan 1994
Externally publishedYes

Keywords

  • acetylcholine
  • hippocampal slice
  • pyramidal cell
  • rat

ASJC Scopus subject areas

  • Neuroscience (all)

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