Synaptic transmission and paired-pulse behaviour of CA1 pyramidal cells in hippocampal slices from a hibernator at low temperature: importance of ionic environment

doi:10.1016/0006-8993(95)00524-T

Brain Research

Volume 689, Issue 1, 14 August 1995, Pages 9-20

https://doi.org/10.1016/0006-8993(95)00524-T Get rights and content

Abstract

To investigate the effects of ionic changes possibly associated with hibernation, hippocampal slices prepared from golden hamsters were studied in artificial cerebrospinal fluid (ACSF) of variable composition (K⁺ 3–5 mM, Ca²⁺ 2–4 mM, Mg²⁺ 2–4 mM, pH 7.0–7.7) at temperatures of 15–20°C, just above the temperature below which synaptic transmission is blocked. Population action potentials (population spikes, PSs) of CA1 pyramidal cells were evoked by stimulation of the Schaffer collaterals/commissural fibers with paired pulses (interpulse interval 50 ms, interval pairs 30 s). The responses evoked at given temperatures were investigated as a function of extracellular ion concentrations. In ACSF containing 3 mM K⁺, 2 mM Ca²⁺ and 2 mM Mg²⁺, PSs could be evoked at temperatures of > ∼ 16°C whereas at lower temperatures synaptic transmission was blocked. The threshold temperature was slightly higher for the first (PS1) than for the second PS (PS2) evoked by paired-pulse stimulation. The slices displayed paired-pulse facilitation (PPF) at all temperatures. Elevation of [K⁺]₀ from 3 to 5 mM depressed the amplitudes of both PS1 and PS2, with a stronger effect on PS2. PPF was reduced and, at near-threshold temperatures, turned into paired-pulse depression (PPD). Elevation of [Ca²⁺]₀ from 2 to 4 mM increased the amplitude of PS1. The amplitude of PS2, in contrast, was reduced at near-threshold temperatures. PPF turned into PPD. Elevation of [Mg²⁺]₀ from 2 to 4 mM reduced the amplitudes of both PS1 and PS2, with a stronger effect on PS1. Accordingly, PPF was increased. Acidification by 0.3 pH units strongly depressed the amplitudes of PS1 as well as PS2 and increased PPF. Alkalization by 0.4 pH units had only weak effects in the opposite direction. Changes in the ionic composition comparable to those investigated in the present study presumably occur in the brain interstitium of hamsters during entrance into hibernation. According to our results, such changes depress synaptic transmission at low temperatures in the hamster hippocampus in vitro. This modulation may be important for the regulation of neuronal activity during entrance into hibernation.

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¹: Present address: Institut für Physiologie der Charité, Tucholskystr. 2, D-10117 Berlin, Germany.

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Synaptic transmission and paired-pulse behaviour of CA1 pyramidal cells in hippocampal slices from a hibernator at low temperature: importance of ionic environment

Abstract

Brain Res.

EEG Clin. Neurophysiol.

Neurosci. Lett.

Brain Res.

Brain Res.

Brain Res.

Exp. Neurol.

J. Therm. Biol.

Brain Res.

Neurosci. Lett.

Neurosci. Lett.

Brain Res.

Neurosci. Lett.

Brain Res.

Brain Res.

Progr. Neurobiol.

Neurosci. Lett.

J. Neurosci. Meth.

Brain Res. Bull.

Gen. Pharmacol.

Brain Res.

Exp. Neurol.

Exp. Neurol.

J. Therm. Biol.

Neurosci. Lett.

Neuroscience

Brain slice methods

Feed-forward dendritic inhibition in rat hippocampal pyramidal cells studied in vitro

J. Physiol.

Pathways of post-synaptic inhibition in the hippocampus

J. Neurophysiol.

Effects of CO2 and interstitial pH changes on synaptic transmission in CA1 region of rat hippocampus in vitro

Concentration of carbon dioxide, interstitial pH and synaptic transmission in hippocampal formation of the rat

J. Physiol.

Paired-pulse and frequency facilitation in the CA1 region of the in vitro rat hippocampus

J. Physiol.

Paired-pulse depression of monosynaptic GABA-mediated inhibitory postsynaptic responses in rat hippocampus

J. Physiol.

Neurotransmitter release and its facilitation in crayfish: III. Amplitude of facilitation and inhibition of entry of calcium into the terminal by magnesium

Pflügers Arch.

Effects of CO₂ and interstitial pH changes on synaptic transmission in CA1 region of rat hippocampus in vitro