Stimulation of P2Y1 Receptors Causes Anxiolytic-like Effects in the Rat Elevated Plus-maze: Implications for the Involvement of P2Y1 Receptor-Mediated Nitric Oxide Production

Abstract

The widespread and abundant distribution of P2Y receptors in the mammalian brain suggests important functions for these receptors in the CNS. To study a possible involvement of the P2Y receptors in the regulation of fear and anxiety, the influences of the P2Y(1,11,12) receptor-specific agonist adenosine 5'-O-(2-thiodiphosphate) (ADPbetaS), the P2X(1,3) receptor agonist alpha,beta-methylene ATP (alpha,betameATP), the unspecific P2 receptor antagonist pyridoxalphosphate-6-azopheny l-2',4'-disulfonic acid (PPADS), and the specific P2Y(1) receptor antagonist N(6)-methyl-2'-deoxyadenosine-3',5'-bisphosphate (MRS 2179) on the elevated plus-maze behavior of the rat were investigated. All tested compounds were given intracerebroventricularly (0.5 microl). ADPbetaS (50 and 500 fmol) produced an anxiolytic-like behavioral profile reflected by an increase of the open arm exploration. The anxiolytic-like effects were antagonized by pretreatment with PPADS (5 pmol) or MRS 2179 (5 pmol). Both compounds caused anxiogenic-like effects when given alone. Furthermore, the anxiolytic-like effects of ADPbetaS could be antagonized by pretreatment with the nitric oxide synthase (NOS) inhibitor N(w)-nitro-L-arginine methyl ester (L-NAME). In addition, the anxiogenic-like effects of PPADS were reversed by the pretreatment with L-arginine (500 pmol), which is the natural substrate for NOS, but not by D-arginine (500 pmol), which is not. Immunofluorescence staining revealed the presence of P2Y(1) receptors on neurons in different brain regions such as hypothalamus, amygdala, hippocampus and the periaqueductal gray. Furthermore, the colocalization of P2Y(1) receptors and neuronal NOS (nNOS) on some neurons in these regions could be demonstrated. The highest density of P2Y(1)- and nNOS-immunoreactivity was detected in the dorsomedial hypothalamic nucleus. Taken together, the present results suggest that P2Y(1) receptors are involved in the modulation of anxiety in the rat. The anxiolytic-like effects after stimulation of P2Y(1) receptors seem to be in close connection with the related nitric oxide production.