Integrity of perforant path fibers and the frequency of action potential independent excitatory and inhibitory synaptic events in dentate gyrus granule cells

Abstract

Whole-cell voltage clamp recordings in 400 microns thick hippocampal slices revealed discrete excitatory and inhibitory postsynaptic currents which persisted at synapses on granule cells following abolition of action potentials with 1 microM tetrodotoxin (TTX). The conductances associated with excitatory amino acid and GABAA receptor mediated events had mean peaks of 200 and 800 pS, and decayed monoexponentially with time constants of 5.6 and 5.3 ms. At a holding potential close to the normal resting membrane potential of granule cells (-80 to -90 mV), the frequency of glutamate/aspartate mediated spontaneous excitatory postsynaptic currents (sEPSCs) was decreased from 2.04 Hz in slices cut parallel to the plane of the perforant path to 0.87 Hz in slices cut in a plane that disrupted the distal perforant path fibres, suggesting that presynaptic integrity influences the rate of action potential independent neurotransmitter release. The orientation of the slicing had no effect on the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs).

Glutamatergic and Nonglutamatergic Neurons of the Ventral Tegmental Area Establish Local Synaptic Contacts with Dopaminergic and Nondopaminergic Neurons

“…The remaining events are likely due to vesicle fusion events that are independent of action potential-induced depolarization of the axon terminal. Such action potential independent events have been observed in many parts of the central nervous system (e.g., Staley and Mody, 1991; Farrant and Cull-Candy, 1991; Hubbard 1961), including at both glutamate and GABA synapses in the VTA (e. g. Deng et al, 2009; Xiao et al, 2008; Xiao et al, 2009; Margolis et al, 2005; Margolis et al, 2008). We observed a slight decrease in the amplitude of spontaneous EPSCs following the application of TTX.…”

The pro-convulsant actions of corticotropin-releasing hormone in the hippocampus of infant rats

“…Brains were cooled in 4°C artificial cerebrospinal fluid (ACSF), composed of (in mM): 126 NaCl, 2.5 KCl, 26 NaHCO 3 , 2 CaCl 2 , 2 MgCl 2 , 1.25 NaH 2 PO 4 and 10 glucose. Horizontal whole brain slices 27 (450 μm) were prepared with the use of a Vibratome tissue sectioner (Lancer Series 1000). The brain slices were sagittally bisected into two hemispheric components and preincubated submerged in a temporary storage chamber containing oxygenated ACSF at 32°C for 1 h before any experimental manipulations.…”

Synaptic Communication among Hippocampal Interneurons: Properties of Spontaneous IPSCs in Morphologically Identified Cells

“…oriens and alveus border and may project mainly along the longitudinal axis of the hippocampus (Acsády et al, 1996a) (L. Acsády, personal communication) to innervate horizontal interneurons including O-LM cells in this layer (Acsády et al, 1996b). This anatomical finding together with the higher probability of recording spontaneous synaptic events originating from long, intact axon collaterals (Staley and Mody, 1991) would ensure a higher probability of recording O-LM cell sIPSCs in a slice cut in the longitudinal plane. Therefore, we investigated the possibility that cutting a slice along the longitudinal axis of the hippocampus may better preserve the inhibitory inputs onto O-LM cells.…”