P2 receptor-types involved in astrogliosis in vivo

1. In the nucleus accumbens (NAc) of rats, the involvement of P2X and P2Y receptors in the generation of astrogliosis in vivo, was investigated by local application of their respective ligands. The agonists used had selectivities for P2X1,3 (alpha,beta-methylene adenosine 5'-triphosphate; alpha,beta-meATP), P2Y1,12 (adenosine 5'-O-(2-thiodiphosphate; ADP-beta-S) and P2Y2,4,6 receptors (uridine 5'-O-(3-thiotriphosphate; UTP-gamma-S). Pyridoxalphosphate-6-azophenyl-2,4-disulphonic acid (PPADS) was used as a non-selective antagonist. The astroglial reaction was studied by means of immunocytochemical double-labelling with antibodies to glial fibrillary acidic protein (GFAP) and 5-bromo-2'-deoxyuridine (BrdU). 2. The agonist-induced changes in comparison to the artificial cerebrospinal fluid (aCSF)-treated control side reveal a strong mitogenic potency of ADP-beta-S and alpha,beta-meATP, whereas UTP-gamma-S was ineffective. The P2 receptor antagonist PPADS decreased the injury-induced proliferation when given alone and in addition inhibited all agonist effects. 3. The observed morphogenic changes included hypertrophy of astrocytes, elongation of astrocytic processes and up-regulation of GFAP. A significant increase of both GFAP-immunoreactivity (IR) and GFA-protein content (by using Western blotting) was found after microinfusion of alpha,beta-meATP or ADP-beta-S. In contrast, UTP-gamma-S failed to increase the GFAP-IR. The morphogenic effects were also inhibited by pre-treatment with PPADS. 4. A double immunofluorescence approach with confocal laser scanning microscopy showed the localisation of P2X3 and P2Y1 receptors on the GFAP-labelled astrocytes. 5. In conclusion, the data suggest that P2Y (P2Y1 or P2Y12) receptor subtypes are involved in the generation of astrogliosis in the NAc of rats, with a possible minor contribution of P2X receptor subtypes.