Inactivation of adenosine A2A receptor impairs long term potentiation in the accumbens nucleus without altering basal synaptic transmission

The nucleus accumbens is considered to be critically involved in the control of complex motivated behaviors. By modulating its glutamatergic excitatory input, mesolimbic dopaminergic afferents have been implicated in the reinforcing properties of drugs of abuse. However. they might not represent the only path for influencing the accumbens output. The aim of this study was to investigate possible modulation of synaptic transmission at this glutamatergic synapse by adenosine receptors. The standard field potential recording technique was used on brain slices from wild-type and A(2A) receptor-deficient mice. Neither the stimulus-response relationship nor paired-pulse facilitation was altered in the mutant mice. In both genotypes, the activation of A(1) receptors by 2-chloro-N-6-cyclopentyladenosine reduced the field excitatory postsynaptic potential (fEPSP) slope to a similar extent. In wild-type slices, activation or blockade of A(2A) receptors by 2-[4-(carboxyethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenosine and 4-(2-[7-amino-2-(2- furyl)[1,2,4]-triazolo-[2,3-a][1.3,5]triazin-5-ylamino]ethyl)phenol. respectively, did not modify the synaptic transmission. Moreover, a long lasting pre-activation of these A(2A) receptors did not influence the A I receptor-mediated reduction in fEPSP slope. Long term potentiation (LTP) of the alpha -amino-3-hydroxy-5-methyl-4-isoxazole proprionate (AMPA) receptor-mediated synaptic transmission could be elicited in both wild-type and A(2A) receptor-deficient mice. However, LTP appeared to be quantitatively modulated by the A(2A) receptor pathway since the level of potentiation was reduced in A(2A) receptor-deficient mice as well as in slices or wild-type mice in which the A(2A) receptor pathway was blocked. The involvement of the cAMP-dependent protein kinase was supported by the reduction in potentiation level in slices of wild-type mice treated with adenosine 3',5'-cyclic monophosphorothiotate, 8-(4-chlorophenylthio)-Rp isomer, an inhibitor of this enzyme. These data provide evidence that the adenosine acting at the A(2A) receptor is implicated in events directly or indirectly related to LTP induction in the accumbens whereas it is not involved in the regulation of the basal AMPA receptor-mediated excitatory synaptic transmission. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.