Abstracts

Adensine is an inhibitory synaptic modulator in the central nervous system (CNS). The main adenosine receptor in the CNS is A1R and its activation inhibits neurotransmitter release and hyperpolarizes neurons. Since adenosine release appears to be activity dependent, it may play an important role in regulating synaptic activity during periods of heightened neuronal firing such as occur during epileptiform activity. We investigated the effects of temporary blockade of adenosine receptors on neuronal firing in an in vitro model of interictal activity.
We tested the effects of the adenosine A1 receptor (A1R) antagonists theophylline (250 [mu]M) or DPCPX (100 nM), on the CA3 burst probability using extracellular and intracellular recordings. Hippocampal coronal slices were prepared from 4-6 week old Sprague-Dauley rats. Spontaneous bursting of the CA3 network was induced by blockade of GABA[sub]A[/sub] and [sub]B[/sub] conductances with 100mM picrotoxin and 1mM CGP55845A, respectively. Intracellular recordings were performed in the presence of picrotoxin (100[mu]M), CGP55845A (1 [mu]M), and dAP5 (50[mu]M).
Repetitive 10 min applications of adenosine A1R blockers resulted in progressive decreases in extracellular CA3 burst frequency on washout. This effect was independent of NMDARs, MgluR receptors, L-type calcium channels or PKC activation. Activation of PKA during A1R blockade resulted in cessation of CA3 network bursting during the wash of A1R blockade. This decrease in CA3 burst frequency could be observed during subsequent adenosine A1R blockades, suggesting that A1R activation is not necessary for its expression. Preliminary voltage clamp intracellular recordings revealed a decrease in the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) without a change in the average sEPSC amplitude, suggesting a presynaptic locus of this effect.
These data suggest that temporary blockade of A1R results in lasting decrease in CA3 network burst probability. This decrease in network activity together with the decrease in sEPSCs frequency at CA3 excitatory synapses suggest that transient A1R blockade results in a long-term decrease in glutamate release probability. Together, these data suggest that therapeutic manipulations of adenosine activity during interictal or ictal epileptiform activity may induce long lasting decreases in the excitation of epileptic networks.
[Supported by: NIH]