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The Journal of neuroscience : the official journal of the Society for Neuroscience

Target-Dependent Compartmentalization of the Corelease of Glutamate and GABA from the Mossy Fibers.


PMID 28100750

Abstract

The mossy fibers (MFs) corelease glutamate and GABA onto pyramidal cells of CA3 during development, until the end of the third postnatal week. However, the major target cells of the MF are the interneurons of CA3. Therefore, it has been shown that the interneurons of the hilus and stratum lucidum receive this dual monosynaptic input on MF stimulation. Because the plasticity of glutamatergic transmission from the different terminals of the MF is target specific, we here asked whether the corelease of glutamate and GABA was also subjected to a target-dependent compartmentalization. We analyzed the occurrence and plasticity of MF simultaneous glutamatergic-GABAergic signaling onto interneurons of the different strata of CA3 in rats during the third postnatal week. We show the coexistence of time-locked, glutamate receptor and GABA receptor-mediated mono synaptic responses evoked by MF stimulation in interneurons from stratum lucidum and stratum radiatum, but not in interneurons from stratum lacunosum-moleculare. As expected from the transmission of MF origin, MF GABAergic responses were depressed by the activation of metabotropic glutamate receptors. Strikingly, while MF glutamatergic responses underwent LTD, the simultaneous MF GABAergic responses of stratum lucidum interneurons, but not of stratum radiatum interneurons, displayed a Hebbian form of LTP that was mimicked by PKC activation. PKA activation potentiated MF glutamatergic responses of stratum radiatum interneurons, whereas in stratum lucidum interneurons only GABAergic responses were potentiated. We here disclose that the corelease of glutamate and GABA, as well as their plasticity are compartmentalized in a target-dependent manner, showing counterbalanced compensatory plasticity of two neurotransmitters released by different terminals of the same pathway. The mossy fibers transiently corelease glutamate and GABA onto pyramidal cells of CA3. We here describe that they can also corelease these amino acids onto interneurons, in a target-dependent manner. Many interneurons in stratum lucidum and stratum radiatum receive both signals, while those in stratum lacunosum-moleculare exclusively receive a glutamatergic signal. It is noteworthy that glutamatergic LTD, which is known to exist on stratum lucidum interneurons, coexists in the same pathway with a presynaptic form of GABAergic LTP, while interneurons of stratum radiatum, despite receiving this dual signaling, do not display such plasticity. The GABAergic LTP is mimicked with PKA or PKC activation. We disclose compartmentalized corelease of glutamate and GABA and its differential plasticity from a single pathway onto different interneuron sets.

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