Adenosine A1 and A2A receptors are co-expressed in pyramidal neurons and co-localized in glutamatergic nerve terminals of the rat hippocampus

Adenosine is a neuromodulator that controls neurotransmitter release through inhibitory A(1) and facilitatory A(2A) receptors. Although both adenosine receptor-mediated inhibition and facilitation of glutamate release have been observed, it is not clear whether both A, and A(2A) receptors are located in the same glutamatergic nerve terminal or whether they are located on different populations of these terminals. Thus, we have tested if single pyramidal glutamatergic neurons from the hippocampus simultaneously expressed A(1) and A(2A) receptor mRNA and if A(1) and A(2A) receptors were co-localized in hippocampal glutamatergic nerve terminals. Single cell PCR analysis of visually identified pyramidal neurons revealed the simultaneous presence of A(1) and A(2A) receptor mRNA in four out 16 pyramidal cells possessing glutamatergic markers but not GABAergic or astrocytic markers. Also, A(1) and A(2A) receptor immunoreactivities were co-localized in 26 +/- 4% of nerve terminals labeled with antibodies against vesicular glutamate transporters type 1 or 2, i.e. glutamatergic nerve terminals. This indicates that glutamatergic neurons in the hippocampus co-express A(1) and A(2A) receptors and that these two receptors are co-localized in a subset of glutamatergic nerve terminals. (c) 2005 IBRO. Published by Elsevier Ltd. All rights reserved.