Deletion of presynaptic adenosine A1 receptors impairs the recovery of synaptic transmission after hypoxia

Abstract

Adenosine protects neurons during hypoxia by inhibiting excitatory synaptic transmission and preventing NMDA receptor activation. Using an adeno-associated viral (AAV) vector containing Cre recombinase, we have focally deleted adenosine A 1 receptors in specific hippocampal regions of adult mice. Recently, we found that deletion of A 1 receptors in the CA1 area blocks the postsynaptic responses to adenosine in CA1 pyramidal neurons, and deletion of A 1 receptors in CA3 neurons abolishes the presynaptic effects of adenosine on the Schaffer collateral input [J Neurosci 23 (2003) 5762]. In the current study, we used this technique to delete A 1 receptors focally from CA3 neurons to investigate whether presynaptic A 1 receptors protect synaptic transmission from hypoxia. We studied the effects of prolonged (1 h) hypoxia on the evoked field excitatory postsynaptic potentials (fEPSPs) in the CA1 region using in vitro slices. Focal deletion of the presynaptic A 1 receptors on the Schaffer collateral input slowed the depression of the fEPSPs in response to hypoxia and impaired the recovery of the fEPSPs after hypoxia. Delayed responses to hypoxia linearly correlated with impaired recovery. These findings provide direct evidence that the neuroprotective role of adenosine during hypoxia depends on the rapid inhibition of synaptic transmission by the activation of presynaptic A 1 receptors. KeywordsCA1; Schaffer collaterals; electrophysiology; AAV; Cre recombinase; inducible knock-out mice Extracellular adenosine levels in the CNS increase after head injury, seizures, hypoxia, hypoglycemia and ischemia (Winn et al., 1979(Winn et al., , 1981Zhu and Krnjevic, 1993;Headrick et al., 1994;Dunwiddie, 1999). Neuronal damage in these conditions is primarily caused by excessive release of glutamate (Simon et al., 1984;Obrenovitch and Urenjak, 1997;Sattler et al., 2000), and adenosine protects neurons by activating A 1 receptors that reduce glutamate release and NMDA receptor activation (Fredholm, 1997;Sweeney, 1997;de Mendonca et al., 2000). Accordingly, protection against hypoxia and ischemia can be achieved by increasing extracellular levels of adenosine through inhibition of adenosine degradation or reuptake (Gidday et al., 1995;Miller et al., 1996;Jiang et al., 1997 antagonists or increased breakdown of extracellular adenosine exacerbates neuronal loss from hypoxia and ischemia (Sweeney, 1997;de Mendonca et al., 2000).In the CA1 region, hypoxia and ischemia disrupt synaptic transmission, protein synthesis, maintenance of ATP levels, cytoskeletal integrity, and neuronal morphology (Lipton, 1999;Wang et al., 1999). However, hypoxia also induces release of adenosine (Dale et al., 2000;Frenguelli et al., 2003) which rapidly depresses synaptic transmission and neuronal firing (Lipton and Whittingham, 1979;Fowler, 1989;Gribkoff et al., 1990). This inhibition of neuronal activity prevents glutamatergic excitotoxicity, allowing full recovery from hypoxia (Sebastiao et al., 2001). These effects are primarily mediated by adenos...

[60]Fullerene derivative modulates adenosine and metabotropic glutamate receptors gene expression: a possible protective effect against hypoxia

“…In line with this, the observed increase in A 1 ARs gene expression by t3ss derivative, as it has been previously reported in SK-N-MC cells [23], could be related to the described protective role exerted by these receptors during hypoxic conditions [30]. …”

Interleukin-6 Upregulates Neuronal Adenosine A1 Receptors: Implications for Neuromodulation and Neuroprotection

“…The amplitude of postsynaptic AMPA-induced currents was not affected by CPA (5 nM) in control conditions (106.0 ± 7.4% of control, n ¼ 3). When the concentration of CPA was increased to 100 nM, AMPA-evoked currents were still not significantly modified (p40.05), which solely confirmed the limited contribution of postsynaptic adenosine A 1 receptors to the modulation of synaptic transmission (Arrigoni et al, 2005); it did not preclude, however, that the upregulation of postsynaptic or somatic A 1 receptors might assume functional relevance in other experimental paradigms, a possibility which we explored and were able to demonstrate further below using a different in vitro model (see data on neuronal cultures).…”

Modulators of Nucleoside Metabolism in the Therapy of Brain Diseases

“…Adenosine, via activation of A 1 Rs is considered to be an important neuroprotectant against ischemic damage in the adult brain, although there is still controversy regarding the underlying mechanisms [15, 86–89]. Surprisingly, A 1 R activation does not protect the developing brain and impairs cerebral maturation [90] and adenosine receptor antagonists reduce ischemic brain injury in neonatal mice [91].…”