Anxiety and stress disorders are the most commonly occurring of all mental illnesses, and current treatments are less than satisfactory. So, the discovery of novel approaches to treat anxiety disorders remains an important area of neuroscience research. Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system, and G-protein-coupled metabotropic glutamate (mGlu) receptors function to regulate excitability via pre- and postsynaptic mechanisms. Various mGlu receptor subtypes, including group I (mGlu(1) and mGlu(5)), group II (mGlu(2) and mGlu(3)), and group III (mGlu(4), mGlu(7) and mGlu(8)) receptors, specifically modulate excitability within crucial brain structures involved in anxiety states. In addition, agonists for group II (mGlu(2/3)) receptors and antagonists for group I (in particular mGlu(5)) receptors have shown activity in animal and/or human conditions of fear, anxiety or stress. These studies indicate that metabotropic glutamate receptors are interesting new targets to treat anxiety disorders in humans.

Two-pore domain potassium (K 2P ) channel expression is believed to underlie the developmental emergence of a potassium leak conductance [I K(SO) ] in cerebellar granule neurons (CGNs), suggesting that K 2P function is an important determinant of the input conductance and resting membrane potential. To investigate the role that different K 2P channels may play in the regulation of CGN excitability, we generated a mouse lacking TASK-1, a K 2P channel known to have high expression levels in CGNs. In situ hybridization and real-time PCR studies in wild-type and TASK-1 knock-outs (KOs) demonstrated that the expression of other K 2P channels was unaltered in CGNs. TASK-1 knock-out mice were healthy and bred normally but exhibited compromised motor performance consistent with altered cerebellar function. Whole-cell recordings from adult cerebellar slice preparations revealed that the resting excitability of mature CGNs was no different in TASK-1 KO and littermate controls. However, the modulation of I K(SO) by extracellular Zn 2ϩ , ruthenium red, and H ϩ was altered. The I K(SO) recorded from TASK-1 knock-out CGNs was no longer sensitive to alkalization and was blocked by Zn 2ϩ and ruthenium red. These results suggest that a TASK-1-containing channel population has been replaced by a homodimeric TASK-3 population in the TASK-1 knock-out. These data directly demonstrate that TASK-1 channels contribute to the properties of I K(SO) in adult CGNs. However, TASK channel subunit composition does not alter the resting excitability of CGNs but does influence sensitivity to endogenous modulators such as Zn 2ϩ and H ϩ .

In mammals, identifying the contribution of specific neurons or networks to behavior is a key challenge. Here we describe an approach that facilitates this process by enabling the rapid modulation of synaptic inhibition in defined cell populations. Binding of zolpidem, a systemically active allosteric modulator that enhances the function of the GABA A receptor, requires a phenylalanine residue (Phe77) in the γ2 subunit. Mice in which this residue is changed to isoleucine are insensitive to zolpidem. By Cre recombinase-induced swapping of the γ2 subunit (that is, exchanging Ile77 for Phe77), zolpidem sensitivity can be restored to GABA A receptors in chosen cell types. We demonstrate the power of this method in the cerebellum, where zolpidem rapidly induces significant motor deficits when Purkinje cells are made uniquely sensitive to its action. This combined molecular and pharmacological technique has demonstrable advantages over targeted cell ablation and will be invaluable for investigating many neuronal circuits.A classical approach to the study of brain function is selective lesioning. Unfortunately, the interpretation of data from such studies can be confounded by compensatory changes, whereby unrelated systems are recruited to alleviate, if only partially, any deficit. A complementary method involves reversibly silencing, albeit with little or no cell-type selectivity, the activity of a pathway or nucleus through cooling or stereotaxic drug administration (for example, see refs. 1,2). Reversible approaches have advantages over permanent lesioning. First, the effects of acute regional inactivation cannot be easily overcome by compensatory changes, because the inactivated system is altered only briefly

Inhalation anesthetics activate and cannabinoid agonists inhibit TWIK-related acid-sensitive K ϩ channels (TASK)-1 two-pore domain leak K ϩ channels in vitro. Many neuromodulators, such as noradrenaline, might also manifest some of their actions by modifying TASK channel activity. Here, we have characterized the basal behavioral phenotype of TASK-1 knockout mice and tested their sensitivity to the inhalation anesthetics halothane and isoflurane, the ␣ 2 adrenoreceptor agonist dexmedetomidine, and the. TASK-1 knockout mice had a largely normal behavioral phenotype. Male, but not female, knockout mice displayed an enhanced acoustic startle response. The knockout mice showed increased sensitivity to thermal nociception in a hot-plate test but not in a tail-flick test. The analgesic, sedative, and hypothermic effects of WIN55212-2 (2-6 mg/kg s.c.) were reduced in TASK-1 knockout mice. These results implicate TASK-1-containing channels in supraspinal pain pathways, in particular those modulated by endogenous cannabinoids. TASK-1 knockout mice were less sensitive to the anesthetic effects of halothane and isoflurane than wild-type littermates, requiring higher anesthetic concentrations to induce immobility as reflected by loss of the tail-withdrawal reflex. Our results support the idea that the activation of multiple background K ϩ channels is crucial for the high potency of inhalation anesthetics. Furthermore, TASK-1 knockout mice were less sensitive to the sedative effects of dexmedetomidine (0.03 mg/kg s.c.), suggesting a role for the TASK-1 channels in the modulation of function of the adrenergic locus coeruleus nuclei and/or other neuronal systems.

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