No abstract

Psychostimulants induce neuroadaptations in excitatory and fast inhibitory transmission in the ventral tegmental area (VTA). Mechanisms underlying drug-evoked synaptic plasticity of slow inhibitory transmission mediated by GABAB receptors and G protein-gated inwardly rectifying potassium (GIRK/Kir3) channels, however, are poorly understood. Here, we show that one day after methamphetamine (METH) or cocaine exposure, both synaptically-evoked and baclofen-activated GABABR-GIRK currents were significantly depressed in VTA GABA neurons, and remained depressed for 7 days. Presynaptic inhibition mediated by GABABRs on GABA terminals was also weakened. Quantitative immunoelectron microscopy revealed internalization of GABAB1R and GIRK2, which occurred coincident with dephosphorylation of Ser783 in GABAB2R, a site implicated in regulating GABABR surface expression. Inhibition of protein phosphatases recovered GABABR-GIRK currents in VTA GABA neurons of METH-injected mice. This psychostimulant-evoked impairment in GABABR signaling removes an intrinsic brake on GABA neuron spiking, which may augment GABA transmission in the mesocorticolimbic system.

The binding pockets of Cys-loop receptors are dominated by aromatic amino acids. In the GABA A receptor ␣ 1 Phe65, ␤ 2 Tyr97, ␤ 2 Tyr157, and ␤ 2 Tyr205 are present at the ␤ 2 /␣ 1 interface and have been implicated in forming an important part of the GABA binding site. Here, we have probed interactions of these residues using subtle chemical changes: unnatural amino acid mutagenesis was used to introduce a range of Phe analogs, and mutant receptors expressed in oocytes were studied using voltage-clamp electrophysiology. Serial mutations at ␤ 2 97 revealed a ϳ20-fold increase in EC 50

BackgroundGABAA receptors are members of the Cys-loop family of neurotransmitter receptors, proteins which are responsible for fast synaptic transmission, and are the site of action of wide range of drugs [1]. Recent work has shown that Cys-loop receptors are present on immune cells, but their physiological roles and the effects of drugs that modify their function in the innate immune system are currently unclear [2]. We are interested in how and why anaesthetics increase infections in intensive care patients; a serious problem as more than 50% of patients with severe sepsis will die [3]–[6]. As many anaesthetics act via GABAA receptors [7], the aim of this study was to determine if these receptors are present on immune cells, and could play a role in immunocompromising patients.Principal FindingsWe demonstrate, using RT-PCR, that monocytes express GABAA receptors constructed of α1, α4, β2, γ1 and/or δ subunits. Whole cell patch clamp electrophysiological studies show that GABA can activate these receptors, resulting in the opening of a chloride-selective channel; activation is inhibited by the GABAA receptor antagonists bicuculline and picrotoxin, but not enhanced by the positive modulator diazepam. The anaesthetic drugs propofol and thiopental, which can act via GABAA receptors, impaired monocyte function in classic immunological chemotaxis and phagocytosis assays, an effect reversed by bicuculline and picrotoxin.SignificanceOur results show that functional GABAA receptors are present on monocytes with properties similar to CNS GABAA receptors. The functional data provide a possible explanation as to why chronic propofol and thiopental administration can increase the risk of infection in critically ill patients: their action on GABAA receptors inhibits normal monocyte behaviour. The data also suggest a potential solution: monocyte GABAA receptors are insensitive to diazepam, thus the use of benzodiazepines as an alternative anesthetising agent may be advantageous where infection is a life threatening problem.

The 5-HT 3 receptor is a member of the Cys-loop family of ligandgated ion channels. The extracellular domains of these proteins contain six amino acid loops (A-F) that converge to form the ligand binding site.