Microglia express three isoforms of the NADPH oxidase, Nox1, Nox2 and Nox4, with the potential to produce superoxide (O2·). Microglia also express neurotransmitter receptors, which can modulate microglial responses. In this study, microglial activity of Nox1, Nox2 and Nox4 in primary rat cultured microglia or the rodent BV2 cell line were altered by microglial neurotransmitter receptor modulation. Glutamate, GABA or ATP triggered microglial O2· production via Nox activation. Nox activation was elicited by agonists of metabotropic mGlu3 receptors and by group III receptors, by GABAA but not GABAB receptors, and by purinergic P2X7 or P2Y2/4 receptors but not P2Y1 receptors, and inhibited by metabotropic glutamate receptor 5 antagonists. The neurotransmitters also modulated Nox mRNA expression and NADPH activity. The activation of Nox by BzATP or GABA promoted a neuroprotective phenotype whilst the activation of Nox by glutamate promoted a neurotoxic phenotype. Taken together, these data indicate that microglial neurotransmitter receptors can signal via Nox to promote neuroprotection or neurotoxicity. This has implications for the subsequent neurotoxic profile of microglia when neurotransmitter levels may become skewed in neurodegeneration. : Microglial neurotransmitter receptors couple to intracellular superoxide generation Microglia express a wide range of neurotransmitter receptors but little is known about the signalling cascades activated when these receptors are stimulated. Stimulation of glutamate, GABA or ATP receptors triggered intracellular superoxide production in microglia. Theese findings will help to target therapies to known receptors on microglia to modulate the wayward microglial responses detected in a wide range of neurodegenerative diseases.(Figure is included in full-text article.)