Differential co-localisation of the P2X₇ receptor subunit with vesicular glutamate transporters VGLUT1 and VGLUT2 in rat CNS

Presynaptic P2X7 receptors are thought to play a role in the modulation of transmitter release and have been localised to terminals with the location and morphology typical of excitatory boutons. To test the hypothesis that this receptor is preferentially associated with excitatory terminals we combined immunohistochemistry for the P2X7 receptor subunit (P2X 7R) with that for two vesicular glutamate transporters (VGLUT1 and VGLUT2) in the rat CNS. This confirmed that P2X7R immunoreactivity (IR) is present in glutamatergic terminals; however, whether it was co-localised with VGLUT1-IR or VGLUT2-IR depended on the CNS region examined. In the spinal cord, P2X7R-IR co-localised with VGLUT2-IR. In the brainstem, co-localisation of P2X7R-IR with VGLUT2-IR was widespread, but co-localisation with VGLUT1-IR was seen only in the external cuneate nucleus and spinocerebellar tract region of the ventral medulla. In the cerebellum, P2X7R-IR co-localised with both VGLUT1 and VGLUT2-IR in the granular layer. In the hippocampus it was co-localised only with VGLUT1-IR, including in the polymorphic layer of the dentate gyrus and the substantia radiatum of the CA3 region. In other forebrain areas, P2X7R-IR co-localised with VGLUT1-IR throughout the amygdala, caudate putamen, striatum, reticular thalamic nucleus and cortex and with VGLUT2-IR in the dorsal lateral geniculate nucleus, amygdala and hypothalamus. Dual labelling studies performed using markers for cholinergic, monoaminergic, GABAergic and glycinergic terminals indicated that in certain brainstem and spinal cord nuclei the P2X7R is also expressed by subpopulations of cholinergic and GABAergic/glycinergic terminals. These data support our previous hypothesis that the P2X7R may play a role in modulating glutamate release in functionally different systems throughout the CNS but further suggest a role in modulating release of inhibitory transmitters in some regions.