Adenosine receptor activation is responsible for prolonged depression of synaptic transmission after spreading depolarization in brain slices

Abstract

Spreading depolarization (SD) is a slowly propagating, coordinated depolarization of brain tissue, which is followed by a transient (5–10 min) depression of synaptic activity. The mechanisms for synaptic depression after SD are incompletely understood. We examined the relative contributions of action potential failure and adenosine receptor activation to the suppression of evoked synaptic activity in murine brain slices. Focal micro-injection of KCl was used to induce SD and synaptic potentials were evoked by electrical stimulation of Schaffer collateral inputs to hippocampal area CA1. SD was accompanied by loss of both presynaptic action potentials (as assessed from fiber volleys) and field excitatory postsynaptic potentials (fEPSPs). Fiber volleys recovered rapidly upon neutralization of the extracellular DC potential, whereas fEPSPs underwent a secondary suppression phase lasting several minutes. Paired-pulse ratio was elevated during the secondary suppression period, consistent with a presynaptic mechanism of synaptic depression. A transient increase in extracellular adenosine concentration was detected during the period of secondary suppression. Antagonists of adenosine A1 receptors (DPCPX or 8-CPT) greatly accelerated fEPSP recovery and abolished increases in paired-pulse ratio normally observed after SD. The duration of fEPSP suppression was correlated with both the duration of the DC shift and the area of tissue depolarized, consistent with the model that adenosine accumulates in proportion to the metabolic burden of SD. These results suggest that in brain slices, the duration of the DC shift approximately defined the period of action potential failure, but the secondary depression of evoked responses was in large part due to endogenous adenosine accumulation after SD.

Spreading Depolarization-Induced Adenosine Accumulation Reflects Metabolic Status In Vitro and In Vivo

“…In 21% O 2 conditions, SD-evoked adenosine transients were easily detected from 250 μm slices, with accumulations approximately fourfold larger than in 95% O 2 conditions ( Figures 4A and 4B), and adenosine signals were more dramatically increased in the same detected from cortex than from hippocampal CA1 (P o 0.05, n = 5,5 slices from two animals), likely because the area of depolarized tissue was larger. 16 Adenosine Accumulation was Observed After SD In Vivo and Correlated with Direct Current Duration Figure 5 shows that transient accumulation of adenosine was detected with SD in vivo. Figure 5D shows representative traces in one animal.…”

“…22 Adult C57Bl/6 mice (n = 20) were anesthetized with ketamine/xylazine, decapitated, and brain slices were prepared as described previously. 16 From each animal, a series of coronal slices was prepared at 250 μm, 350 μm, and 450 μm thicknesses, and a distribution of rostral, intermediate, and caudal slices of each thickness was included in each series of experiments. Slices recovered in artificial cerebrospinal fluid (aCSF) at 35°C for 1 hour then were held at room temperature until being used for experiments.…”

“…15 Thus, extracellular adenosine serves as an integrator of net metabolic status. We have recently used electrochemical detection methods in brain slices to verify that adenosine accumulates after K + -induced SD, 16 possibly indicating the severity of this metabolic challenge. Whether adenosine accumulation can be detected after SD in vivo is not yet clear.…”

The Stroke-Migraine Depolarization Continuum

“…SD seems to initiate spreading depression because the sustained depolarization exceeds the inactivation threshold for the action potential generating channels (Kager et al, 2002). The depression nevertheless outlasts the depolarization, suggesting that it is maintained by other mechanisms such as intracellular zinc, calcium, and/or adenosine accumulation (Carter et al, 2013;Lindquist and Shuttleworth, 2012). A new SD can start before the depression caused by the preceding SD has finished (Dohmen et al, 2008;Dreier et al, 2006;Fabricius et al, 2006).…”

Real-time monitoring of extracellular adenosine using enzyme-linked microelectrode arrays

“…As a result, we have provided a novel sensor that selectively measures extracellular adenosine and produces minimal damage to the brain tissue (Hinzman et al, 2015;Rutherford et al, 2007) permitting real-time monitoring in discrete brain regions. The major advantage of the self-referenced design is the ability to subtract out false signals from major interferents and the enzymatic break-down products (inosine and xanthine) that a single electrode may fail to distinguish (Llaudet et al, 2003), which require additional experimental controls to identify the source of signal (Lindquist and Shuttleworth, 2012). The self-referenced configuration of the MEA and low LOD (0.04 mM) allow measurement of the basal adenosine concentration, which has been previously found to range 0.04-10 mM in the rat brain (Latini and Pedata, 2001).…”