Differential modulation of glutamatergic and cholinergic synapses by calcineurin in hippocampal CA1 fast-spiking interneurons

doi:10.1016/j.brainres.2004.01.025

Brain Research

Volume 1004, Issues 1–2, 9 April 2004, Pages 125-135

https://doi.org/10.1016/j.brainres.2004.01.025 Get rights and content

Abstract

How signaling molecules in inhibitory interneurons modulate and coordinate the integration of synaptic inputs remains largely unknown. We investigated the kinetics and modulation of glutamatergic and cholinergic synapses on CA1 fast-spiking interneurons in hippocampal slices by using whole-cell clamp recording. Spontaneous synaptic currents mediated by either AMPA-type glutamate or nicotinic acetylcholine receptors on the interneurons can be classified into fast, slow and fast–slow based on their duration and decay phase. Effects of calcineurin, calmodulin-dependent protein phosphatase, on these two groups of synapses were examined by infusing an autoinhibitory peptide of calcineurin (CaN-AIP) into the recording neurons. CaN-AIP enhanced the amplitude of glutamatergic fast-EPSCs, as well as both amplitude and frequency of cholinergic fast-EPSCs. No significant changes in slow-EPSCs were observed during the infusion of CaN-AIP. Our results indicate that signal transmission at synapses, which are mediated by either AMPA-type glutamate or nicotinic acetylcholine receptors, appears different in the kinetics. The selective influence of calcineurin on different synapses in fast-spiking interneurons may play an important role in coordinating thousands of synaptic inputs in order to set neuronal excitability at proper levels.

Introduction

Each cerebral inhibitory neuron terminates on thousands of principal neurons to regulate their synchronous activity and neural behaviors [1], [8], [9], [19], [26], [47]. The execution of such regulatory functions requires a precise setting of excitability that largely depends on the integration of various synaptic inputs at inhibitory interneurons. Several types of excitatory synapses, e.g., glutamatergic and cholinergic, have been identified in interneurons [8], [14], [26]. Less is known about how the activities of these synapses are modulated and coordinated. The elucidation of the modulation of synapse function at inhibitory interneurons is of critical importance because their extensive terminations control neural behaviors.

Ionotropic glutamate and nicotinic acetylcholine receptors (nAChR) are present in cerebral inhibitory interneurons, where AMPA-type glutamate and α7-nACh receptors mediate the rapid synaptic signals, whereas the time-course of kainate and α4β2-ACh receptor-mediated EPSCs appears to be slow [2], [3], [7], [8], [25], [28], [42], [43]. However, the kinetics of such receptor-mediated activities at unitary synapses has not been documented. Moreover, nAChRs in brain slices were studied by applying acetylcholine onto neurons. Electrical signals recorded under this condition may be primarily generated from extrajunctional receptors, and may not reveal how synaptic events shape neuronal excitation. It raises the need to investigate the activities and modulation of receptors that are anchored into the postsynaptic densities [18], i.e., synaptic receptors.

Calcium (Ca²⁺) signal is detected in cerebral inhibitory interneurons [5], and affects glutamatergic synaptic transmission [32], [35]. Ca²⁺/calmodulin (CaM) and CaM-dependent protein kinases up-regulate glutamatergic synapses in hippocampal interneurons [46]. Does calcineurin (CaN), Ca²⁺/CaM-dependent protein phosphatase that is sensitive to changes in intracellular Ca²⁺/CaM levels [16], regulate the activity of glutamatergic synapses in interneurons? In addition, the desensitization of nAChRs in the cultured cells was modulated by CaN [15], [20]. How do signaling molecules modulate the activities of nAChRs that anchor into postsynaptic densities? To attempt to elucidate these questions, we examined the effects of CaN on cholinergic and glutamatergic unitary synapses by infusing CaN autoinhibitory peptide (AIP) into CA1 fast-spiking interneurons in hippocampal slices. Our results demonstrate that CaN differentially modulates the features of cholinergic and glutamatergic synapses.

Section snippets

Hippocampal slices and solution

Slices (400 μm) were prepared from Sprague–Dawley rats in postnatal days (PND) 18–22. Rats were anesthetized by the inhalation of methoxyflurane (2 ml in 4l bell jar) and then decapitated by a guillotine. Tissue blocks including hippocampus and partial cortex were quickly isolated in oxygenated (95% O₂ and 5% CO₂) ice-cold artificial cerebrospinal fluid (ACSF), in which 0.5 mM CaCl₂ and 4 mM MgSO₄ were used to reduce excitation. Slices were cut with a Vibratome, and then held in oxygenated

The kinetics of glutamatergic and cholinergic synaptic currents

Spontaneous EPSCs were recorded in CA1 fast-spiking neurons of hippocampal slices (postnatal days 18–22) to document the kinetics of unitary synaptic currents. Although we should define this parameter by analyzing events at a single synapse recorded from the synaptically coupled neurons (see below), the recording of sEPSCs allows screening all types of synaptic events at each neuron under the same conditions. The decay phase of sEPSCs was measured for the analysis of synapse kinetics.

The decay

Discussion

Based on analyzing the kinetics of synaptic events, we can identify three types of kinetically different glutamatergic or cholinergic synapses in hippocampal CA1 inhibitory neurons Fig. 1, Fig. 2. Calcineurin selectively limits the activities of these synapses with fast kinetics Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8. Such results were consistently observed whenever sEPSCs, mEPSCs or uEPSCs, which manifest events at unitary synapses, were recorded. Together with different functional groups of

Acknowledgments

We thank Drs. M. Richter and J. Orr for critically reading the manuscript.

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Research reportDifferential modulation of glutamatergic and cholinergic synapses by calcineurin in hippocampal CA1 fast-spiking interneurons

Abstract

Introduction

Section snippets

Hippocampal slices and solution

The kinetics of glutamatergic and cholinergic synaptic currents

Discussion

Acknowledgments

Neuroscience

Cell

Neurosci. Res.

Neuron

Brain Res.

Neurosci. Res.

J. Biol. Chem.

Trends Neurosci.

Curr. Opin. Neurobiol.

Trends Neurosci.

Neuron

TINS

Neuron

Neurochem. Int.

Gating of GABAergic inhibition in hippocampal pyramidal cells

Ann. N.Y. Acad. Sci.

Nicotinic receptor activation in human cerebral cortical interneurons: a mechanism for inhibition and disinhibition of neuronal network

J. Neurosci.

Interneuron-specific Ca2+ responses linked to metabotropic and ionotropic glutamate receptors in rat hippocampal slices

Eur. J. Neurosci.

Regulation of a4b2 nicotinic receptor desensitization by calcium and protein kinase C

Mol. Pharmacol.

Interneurons of the hippocampus

Hippocampus

Immunocytochemical localization of calcineurin in adult and developing primary visual cortex of cats

Exp. Brain Res.

Recovery from desensitization of neuronal nicotinic acetylcholine receptors of rat chromaffin cells is modulated by intracellular calcium through distinct second messengers

J. Neurosci.

Nitric oxide acts as a postsynaptic signaling molecule in calcium/calmodulin-induced synaptic potentiation in hippocampal CA1 pyramidal neurons

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Research report
Differential modulation of glutamatergic and cholinergic synapses by calcineurin in hippocampal CA1 fast-spiking interneurons