Extracellular adenosine concentrations during in vitro ischaemia in rat hippocampal slices

Abstract

1 The application of an ischaemic insult in hippocampal slices results in the depression of synaptic transmission, mainly attributed to the activation of A 1 adenosine receptors by adenosine released in the extracellular space. 2 To estimate the concentration of endogenous adenosine acting at the receptor level during an ischaemic episode, we recorded ®eld e.p.s.ps (fe.p.s.ps) from hippocampal slices, and evaluated the ability of the selective A 1 receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), to reverse the fe.p.s.p. depression induced by in vitro ischaemia. A relationship between the IC 50 of an antagonist and the endogenous concentration of a neurotransmitter has been used for pharmacological analysis. 3 The complete and reversible depression of fe.p.s.p. in the CA1 region induced by 5 min ischaemia was decreased in the presence of DPCPX (50 ± 500 nM). 8-Phenyltheophylline (10 mM) abolished the depression of fe.p.s.ps during the ischaemic period, while a small (peak eect 12+4%) decrease in fe.p.s.ps was observed during the initial phase of reperfusion. 4 In the time-interval of maximal depression of fe.p.s.ps., IC 50 and adenosine concentration changed as function of time with a good degree of correlation. The maximal value of adenosine concentration was 30 mM. 5 Our data provide an estimation of the adenosine concentration reached at the receptor level during an ischaemic episode, with a higher time discrimination (15 s) than that achieved with any biochemical approach. This estimation may be useful in order to establish appropriate concentrations of purinergic compounds to be tested for their pharmacological eects during an ischaemic episode.

Role of adenosine A3 receptors on CA1 hippocampal neurotransmission during oxygen–glucose deprivation episodes of different duration

“…3 show that periods of 2-or 5-min OGD induced, respectively, a partial or complete reduction of synaptic potential amplitude that was always reversible upon reperfusion with normal oxygenated aCSF. These results are in agreement with our previous studies [13,27,28].…”

“…Unlike prolonged (7-min) OGD, depression of synaptic responses caused by OGD episodes of short duration (2 or 5 min) is fully reversible [13,27,28] and is not sufficient to trigger AD. The decrease in fEPSP depression or the faster recovery of fEPSP amplitude during the selective block of A 3 receptors indicates an inhibitory role of A 3 receptors on synaptic transmission during brief OGD.…”

“…The decrease in fEPSP depression or the faster recovery of fEPSP amplitude during the selective block of A 3 receptors indicates an inhibitory role of A 3 receptors on synaptic transmission during brief OGD. We previously demonstrated that depression of synaptic potentials during 2-or 5-min OGD is almost completely antagonized in the presence of the selective A 1 adenosine receptor antagonist DPCPX [10,27,28]. Most of the known neuroprotective effects of adenosine during ischemia both in vivo and in vitro are attributed to the depression of synaptic activity induced by the activation of A 1 receptors.…”

“…After 3.5 min of reperfusion in normal, glucose-containing aCSF, fEPSPs progressively reappeared and reached a complete recovery within 10 min from the beginning of reperfusion. Because it has been demonstrated that a second 5-min OGD episode, 50 min after the end of the first one, is followed by an appreciably faster recovery of fEPSPs [27], the effect of the selective A 3 antagonist was studied in a separate group of slices. MRS1523 (100 nM, n = 7), applied 10 min before, during, and 5 min after OGD application.…”

“…Prolonged, severe episodes of OGD bring about the irreversible depression of neurotransmission and the appearance of AD [14,25], a phenomenon strictly correlated with the extent of brain damage during ischemia both in vivo and in vitro [26]. Brief periods of ischemia are followed by complete recovery of neurotransmission and imply shorter times of A 3 receptor stimulation by endogenous adenosine released during the ischemic episode [10,13,27,28].…”