title: Labile glutamate signaling onto CA1 pyramidal cells in the developing hippocampus depends mechanistically on input pathway.
abstract: The apical dendrite of hippocampal CA1 pyramidal cells receives information from the entorhinal cortex via the dentate gyrus and CA3 (Schaffer-collateral (SC) input) proximally within the stratum radiatum (SR) and directly from the entorhinal cortex/thalamus distally within the stratum lacunosum-moleculare (SLM). During the early postnatal development, very low/low frequency (0.033-1Hz) activation of previously non-stimulated (naïve) SC synapses (SR-CA1 synapses) results in a stimulus-, but not frequency-, dependent depression which is explained by postsynaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) silencing. This lability of AMPA signaling has been suggested to play a role in the activity-dependent organization of the SR synaptic input. Compared with the SR region the SLM region is matured earlier and may become organized in a different manner. Here, using field recordings of synaptic activity in hippocampal slices from 2nd postnatal week rats, we found that SLM-CA1 synapses are also readily depressed by activity in the very low/low frequency range (0.033-1Hz). The depression was, however, quite distinct from that of SR-CA1 synapses, being frequency dependent and reversing faster following stimulus interruption. Bath application of an AMPA receptor agonist produced only a small (-8%) post-application (10min) depression of SLM-CA1 synapses in contrast to that of SR-CA1 synapses (-33%). The SLM-CA1 synapses did also exhibit less long-term depression than the SR-CA1 synapses. We conclude that in the developing hippocampus the labile glutamate signaling onto CA1 pyramidal cell depends mechanistically on input pathway. The labile AMPA signaling at SLM-CA1 synapses is most likely explained by a presynaptic mechanism with limited amount of postsynaptic AMPA silencing.
authors.affiliation: Department of Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden. Electronic address: rong.ma@gu.se.
authors.forename: Rong
authors.initials: R
authors.lastname: Ma
authors.affiliation: Department of Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Minyi
authors.initials: M
authors.lastname: Xiao
authors.affiliation: Department of Physiology, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Bengt
authors.initials: B
authors.lastname: Gustafsson
mesh_terms: D000818:Animals; D056547:CA1 Region, Hippocampal / Q000378:metabolism*; D003712:Dendrites / Q000502:physiology; D018891:Dentate Gyrus / Q000502:physiology; D005971:Glutamates / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism*; D007395:Interneurons / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D017966:Pyramidal Cells / Q000378:metabolism*; D017208:Rats, Wistar; D015398:Signal Transduction; D013569:Synapses / Q000502:physiology*
chemical_list: D005971:Glutamates
keywords: AMPA silencing; development; hippocampus; synapse; synaptic depression