AI Article Synopsis

  • Cholinergic transmission, particularly through muscarinic acetylcholine receptors (mAChRs), plays a role in learning and memory, but its effects in the neocortex are not well understood, prompting research using rat neocortical slices.
  • The cholinergic agonist carbachol (CCh) was found to increase neuronal firing while simultaneously reducing synaptic transmission, with varying effects based on which specific mAChR antagonists were administered.
  • The study concluded that different mAChRs mediate distinct effects: M₁ mAChR increases neuronal firing, M₂ mAChR decreases inhibition, and M₄ mAChR causes depression of excitatory transmission, suggesting a

Article Abstract

Background: Cholinergic transmission has been implicated in learning, memory and cognition. However, the cellular effects induced by muscarinic acetylcholine receptors (mAChRs) activation are poorly understood in the neocortex. We investigated the effects of the cholinergic agonist carbachol (CCh) and various agonists and antagonists on neuronal activity in rat neocortical slices using intracellular (sharp microelectrode) and field potential recordings.

Results: CCh increased neuronal firing but reduced synaptic transmission. The increase of neuronal firing was antagonized by pirenzepine (M₁/M₄ mAChRs antagonist) but not by AF-DX 116 (M₂/M₄ mAChRs antagonist). Pirenzepine reversed the depressant effect of CCh on excitatory postsynaptic potential (EPSP) but had marginal effects when applied before CCh. AF-DX 116 antagonized the depression of EPSP when applied before or during CCh. CCh also decreased the paired-pulse inhibition of field potentials and the inhibitory conductances mediated by GABA(A) and GABA(B) receptors. The depression of paired-pulse inhibition was antagonized or prevented by AF-DX 116 or atropine but only marginally by pirenzepine. The inhibitory conductances were unaltered by xanomeline (M₁/M₄ mAChRs agonist), yet the CCh-induced depression was antagonized by AF-DX 116. Linopirdine, a selective M-current blocker, mimicked the effect of CCh on neuronal firing. However, linopirdine had no effect on the amplitude of EPSP or on the paired-pulse inhibition, indicating that M-current is involved in the increase of neuronal excitability but neither in the depression of EPSP nor paired-pulse inhibition.

Conclusions: These data indicate that the three effects are mediated by different mAChRs, the increase in firing being mediated by M₁ mAChR, decrease of inhibition by M₂ mAChR and depression of excitatory transmission by M₄ mAChR. The depression of EPSP and increase of neuronal firing might enhance the signal-to-noise ratio, whereas the concomitant depression of inhibition would facilitate long-term potentiation. Thus, this triade of effects may represent a "neuronal correlate" of attention and learning.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3416661PMC
http://dx.doi.org/10.1186/1471-2202-13-42DOI Listing

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