Extrasynaptic glycine receptors of rodent dorsal raphe serotonergic neurons:a sensitive target for ethanol

Alcohol abuse is a significant medical and social problem. Several neurotransmitter systems are implicated in ethanol's actions, with certain receptors and ion channels emerging as putative targets. The dorsal raphe (DR) nucleus is associated with the behavioural actions of alcohol, but ethanol actions on these neurons are not well understood. Here, using immunohistochemistry and electrophysiology we characterise DR inhibitory transmission and its sensitivity to ethanol. DR neurons exhibit inhibitory 'phasic' postsynaptic currents mediated primarily by synaptic GABAA receptors (GABAAR) and to a lesser extent by synaptic glycine receptors (GlyR). In addition to such phasic transmission mediated by the vesicular release of neurotransmitter, the activity of certain neurons may be governed by a 'tonic' conductance resulting from ambient GABA activating extrasynaptic GABAARs. However, for DR neurons extrasynaptic GABAARs exert only a limited influence. By contrast, we report that unusually the GlyR antagonist strychnine reveals a large tonic conductance mediated by extrasynaptic GlyRs, which dominates DR inhibition. In agreement, for DR neurons strychnine increases their input resistance, induces membrane depolarization and consequently augments their excitability. Importantly, this glycinergic conductance is greatly enhanced in a strychnine-sensitive fashion, by behaviourally-relevant ethanol concentrations, by drugs used for the treatment of alcohol withdrawal and by taurine, an ingredient of certain 'energy drinks' often imbibed with ethanol. These findings identify extrasynaptic GlyRs as critical regulators of DR excitability and a novel molecular target for ethanol

Inhibition of Dopamine Transporter sctivity by G protein beta gamma subunits

Uptake through the Dopamine Transporter (DAT) is the primary mechanism of terminating dopamine signaling within the brain, thus playing an essential role in neuronal homeostasis. Deregulation of DAT function has been linked to several neurological and psychiatric disorders including ADHD, schizophrenia, Parkinson’s disease, and drug addiction. Over the last 15 years, several studies have revealed a plethora of mechanisms influencing the activity and cellular distribution of DAT; suggesting that fine-tuning of dopamine homeostasis occurs via an elaborate interplay of multiple pathways. Here, we show for the first time that the βγ subunits of G proteins regulate DAT activity. In heterologous cells and brain tissue, a physical association between Gβγ subunits and DAT was demonstrated by co-immunoprecipitation. Furthermore, in vitro pull-down assays using purified proteins established that this association occurs via a direct interaction between the intracellular carboxy-terminus of DAT and Gβγ. Functional assays performed in the presence of the non-hydrolyzable GTP analog GTP-γ-S, Gβγ subunit overexpression, or the Gβγ activator mSIRK all resulted in rapid inhibition of DAT activity in heterologous systems. Gβγ activation by mSIRK also inhibited dopamine uptake in brain synaptosomes and dopamine clearance from mouse striatum as measured by high-speed chronoamperometry in vivo. Gβγ subunits are intracellular signaling molecules that regulate a multitude of physiological processes through interactions with enzymes and ion channels. Our findings add neurotransmitter transporters to the growing list of molecules regulated by G-proteins and suggest a novel role for Gβγ signaling in the control of dopamine homeostasis.Jennie Garcia-Olivares, Delany Torres-Salazar, William A. Owens, Tracy Baust, David P. Siderovski, Susan G. Amara, Jun Zhu, Lynette C. Daws, Gonzalo E. Torre

Intravenous Hypnotic Agents: From Binding Sites to Loss of Consciousness

All the intravenous hypnotic drugs important for clinical anesthesiology reversibly unsettle functional brain networks, in order to undermine the information transfer on which consciousness depends. Three classes of intravenous hypnotic drugs are the most used nowadays: the carboxylated imidazole derivate propofol, the short-acting benzodiazepine midazolam, and the barbiturates, which show action on GABAA Receptors, potentiating gamma-aminobutyric acid (GABA) action. The dissociative agent ketamine, instead, mainly exerts its effects by reversibly blocking the activity of N-methyl-D-aspartate receptors while the most recent dexmedetomidine is an alpha-2 adrenergic receptor agonist. Nevertheless, other receptors are also involved in anesthesia determining, that is voltage-gated and ligand-gated ion channels and it is probable that each intravenous hypnotic agent alters neuronal activity acting at different levels and at multiple sites in a way not yet entirely clear