bay-60-6583 and 1-3-dipropyl-8-cyclopentylxanthine

Adenosine is an endogenous neuromodulator exerting its biological functions via four receptor subtypes, A

Topics: Adenosine; Adenosine A2 Receptor Agonists; Aminopyridines; Animals; Brain; CA1 Region, Hippocampal; Excitatory Postsynaptic Potentials; Glucose; Glutamic Acid; Hippocampus; Male; Neuronal Plasticity; Oxygen; Rats; Rats, Wistar; Receptor, Adenosine A2A; Receptor, Adenosine A2B; Synapses; Synaptic Transmission; Xanthines

Adenosine is a neuromodulator mostly acting through A1 (inhibitory) and A2A (excitatory) receptors in the brain. A2B receptors (A(2B)R) are G(s/q)--protein-coupled receptors with low expression in the brain. As A(2B)R function is largely unknown, we have now explored their role in the mouse hippocampus. We performed electrophysiological extracellular recordings in mouse hippocampal slices, and immunological analysis of nerve terminals and glutamate release in hippocampal slices and synaptosomes. Additionally, A(2B)R-knockout (A(2B)R-KO) and C57/BL6 mice were submitted to a behavioural test battery (open field, elevated plus-maze, Y-maze). The A(2B)R agonist BAY60-6583 (300 nM) decreased the paired-pulse stimulation ratio, an effect prevented by the A(2B)R antagonist MRS 1754 (200 nM) and abrogated in A(2B)R-KO mice. Accordingly, A(2B)R immunoreactivity was present in 73 ± 5% of glutamatergic nerve terminals, i.e. those immunopositive for vesicular glutamate transporters. Furthermore, BAY 60-6583 attenuated the A(1)R control of synaptic transmission, both the A(1)R inhibition caused by 2-chloroadenosine (0.1-1 μM) and the disinhibition caused by the A(1)R antagonist DPCPX (100 nM), both effects prevented by MRS 1754 and abrogated in A(2B)R-KO mice. BAY 60-6583 decreased glutamate release in slices and also attenuated the A(1)R inhibition (CPA 100 nM). A(2B)R-KO mice displayed a modified exploratory behaviour with an increased time in the central areas of the open field, elevated plus-maze and the Y-maze and no alteration of locomotion, anxiety or working memory. We conclude that A(2B)R are present in hippocampal glutamatergic terminals where they counteract the predominant A(1)R-mediated inhibition of synaptic transmission, impacting on exploratory behaviour.

Topics: 2-Chloroadenosine; Acetamides; Adenosine A1 Receptor Agonists; Adenosine A1 Receptor Antagonists; Adenosine A2 Receptor Agonists; Adenosine A2 Receptor Antagonists; Aminopyridines; Animals; Exploratory Behavior; Glutamic Acid; Hippocampus; Male; Maze Learning; Mice, Inbred C57BL; Mice, Knockout; Purines; Receptor, Adenosine A1; Receptor, Adenosine A2B; Synaptic Transmission; Vesicular Glutamate Transport Proteins; Xanthines

Adenosine mediates vascular responses through four receptor subtypes: A(1), A(2A), A(2B), and A(3). The role of A(2A) receptors in aortic vascular tone was investigated using A(2A) adenosine receptor (AR) knockout (A(2A)KO) and corresponding wild-type (A(2A)WT) mice. Isolated aortic rings from A(2A)WT and A(2A)KO mice were precontracted with phenylephrine (10(-7) M), and concentration responses for adenosine analogs and selective agonists/antagonists were obtained. Nonselective adenosine analog (NECA; EC(50) = 6.78 microM) and CGS-21680 (A(2A)AR selective agonist; EC(50) = 0.013 microM) produced concentration-dependent relaxation (maximum of 25% and 28% relaxation at 10(-5) M NECA and CGS-21680, respectively) in A(2A)WT aorta. In A(2A)KO aorta, NECA (EC(50) = 0.075 microM) induced concentration-dependent contraction (maximum contraction of 47% at 10(-6) M; P < 0.05 compared with A(2A)WT), whereas CGS-21680 produced no response. SCH-58261 (10(-6) M; A(2A)AR selective antagonist) abolished both NECA- and CGS-21680-mediated vasorelaxation in A(2A)WT (P < 0.05), whereas no change was observed in A(2A)KO. When DPCPX (10(-5) M; A(1) selective antagonist) was used in NECA concentration response, greater vasorelaxation was observed in A(2A)WT (50% vs. 25% in controls at 10(-5) M; P < 0.05), whereas lower contraction was seen in A(2A)KO tissues (5% vs. 47% in controls at 10(-6) M; P < 0.05). Aortic endothelial function, determined by response to acetylcholine, was significantly higher in WT compared with KO (66% vs. 51%; P < 0.05). BAY 60-6583 (A(2B) selective agonist) produced similar relaxation in both KO and WT tissues. In conclusion, A(2A)AR KO mice had significantly lower aortic relaxation and endothelial function, suggesting that the A(2A)AR plays an important role in vasorelaxation, probably through an endothelium-dependent mechanism.

Topics: Acetylcholine; Adenosine; Adenosine-5'-(N-ethylcarboxamide); Aminopyridines; Animals; Aorta; Dose-Response Relationship, Drug; Endothelium, Vascular; Female; Flavins; Gene Expression Regulation; In Vitro Techniques; Male; Mice; Mice, Knockout; Phenethylamines; Pyrimidines; Receptor, Adenosine A1; Receptor, Adenosine A2A; Receptor, Adenosine A2B; Triazoles; Vasoconstriction; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents; Xanthines