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Background and Purpose The existence of functional Kv7 channels in thalamocortical ( TC) relay neurons and the effects of the K+-current termed M-current ( IM) on thalamic signal processing have long been debated. Immunocytochemical evidence suggests their presence in this brain region. Therefore, we aimed to verify their existence, pharmacological properties and function in regulating activity in neurons of the ventrobasal thalamus ( VB). Experimental Approach Characterization of Kv7 channels was performed by combining in vitro, in vivo and in silico techniques with a pharmacological approach. Retigabine (30 μM) and XE991 (20 μM), a specific Kv7 channel enhancer and blocker, respectively, were applied in acute brain slices during electrophysiological recordings. The effects of intrathalamic injection of retigabine (3 mM, 300 nL) and/or XE991 (2 mM, 300 nL) were investigated in freely moving animals during hot-plate tests by recording behaviour and neuronal activity. Key Results Kv7.2 and Kv7.3 subunits were found to be abundantly expressed in TC neurons of mouse VB. A slow K+-current with properties of IM was activated by retigabine and inhibited by XE991. Kv7 channel activation evoked membrane hyperpolarization, a reduction in tonic action potential firing, and increased burst firing in vitro and in computational models. Single-unit recordings and pharmacological intervention demonstrated a specific burst-firing increase upon IM activation in vivo. A Kv7 channel-mediated increase in pain threshold was associated with fewer VB units responding to noxious stimuli, and increased burst firing in responsive neurons. Conclusions and Implications Kv7 channel enhancement alters somatosensory activity and may reflect an anti-nociceptive mechanism during acute pain processing. [ABSTRACT FROM AUTHOR]

Key points During the behavioural states of sleep and wakefulness thalamocortical relay neurons fire action potentials in high frequency bursts or tonic sequences, respectively., The modulation of specific K+ channel types, termed TASK and TREK, allows these neurons to switch between the two modes of activity., In this study we show that the signalling lipids phosphatidylinositol 4,5-bisphosphate (PIP2) and diacylglycerol (DAG), which are components of their membrane environment, switch on and shut off TREK and TASK channels, respectively., These channel modulations contribute to a better understanding of the molecular basis of the effects of neurotransmitters such as ACh which are released by the brainstem arousal system., The present report introduces PIP2 and DAG as new elements of signal transduction in the thalamus., Abstract The activity of two-pore domain potassium channels (K2P) regulates the excitability and firing modes of thalamocortical (TC) neurons. In particular, the inhibition of two-pore domain weakly inwardly rectifying K+ channel (TWIK)-related acid-sensitive K+ (TASK) channels and TWIK-related K+ (TREK) channels, as a consequence of the stimulation of muscarinic ACh receptors (MAChRs) which are coupled to phosphoinositide-specific phospholipase C (PLCβ), induces a shift from burst to tonic firing. By using a whole cell patch-clamp approach, the contribution of the membrane-bound second messenger molecules phosphatidylinositol 4,5-bisphosphate (PIP2) and diacylglycerol (DAG) acting downstream of PLCβ was probed. The standing outward current ( ISO) was used to monitor the current through TASK and TREK channels in TC neurons. By exploiting different manoeuvres to change the intracellular PIP2 level in TC neurons, we here show that the scavenging of PIP2 (by neomycin) results in an increased muscarinic effect on ISO whereas increased availability of PIP2 (inclusion to the patch pipette; histone-based carrier) decreased muscarinic signalling. The degree of muscarinic inhibition specifically depends on phosphatidylinositol phosphate (PIP) and PIP2 but no other phospholipids (phosphatidic acid, phosphatidylserine). The use of specific blockers revealed that PIP2 is targeting TREK but not TASK channels. Furthermore, we demonstrate that the inhibition of TASK channels is induced by the application of the DAG analogue 1-oleoyl-2-acetyl- sn-glycerol (OAG). Under current clamp conditions the activation of MAChRs and PLCβ as well as the application of OAG resulted in membrane depolarization, while PIP2 application via histone carrier induced a hyperpolarization. These results demonstrate a differential role of PIP2 and DAG in K2P channel modulation in native neurons which allows a fine-tuned inhibition of TREK (via PIP2 depletion) and TASK (via DAG) channels following MAChR stimulation. [ABSTRACT FROM AUTHOR]

Background and Purpose: The existence of functional K(v)7 channels in thalamocortical (TC) relay neurons and the effects of the K(+)-current termed M-current (I(M)) on thalamic signal processing have long been debated. Immunocytochemical evidence suggests their presence in this brain region. Therefore, we aimed to verify their existence, pharmacological properties and function in regulating activity in neurons of the ventrobasal thalamus (VB)., Experimental Approach: Characterization of K(v)7 channels was performed by combining in vitro, in vivo and in silico techniques with a pharmacological approach. Retigabine (30 μM) and XE991 (20 μM), a specific K(v)7 channel enhancer and blocker, respectively, were applied in acute brain slices during electrophysiological recordings. The effects of intrathalamic injection of retigabine (3 mM, 300 nL) and/or XE991 (2 mM, 300 nL) were investigated in freely moving animals during hot-plate tests by recording behaviour and neuronal activity., Key Results: K(v)7.2 and K(v)7.3 subunits were found to be abundantly expressed in TC neurons of mouse VB. A slow K(+)-current with properties of IM was activated by retigabine and inhibited by XE991. K(v)7 channel activation evoked membrane hyperpolarization, a reduction in tonic action potential firing, and increased burst firing in vitro and in computational models. Single-unit recordings and pharmacological intervention demonstrated a specific burst-firing increase upon I(M) activation in vivo. A K(v)7 channel-mediated increase in pain threshold was associated with fewer VB units responding to noxious stimuli, and increased burst firing in responsive neurons., Conclusions and Implications: K(v)7 channel enhancement alters somatosensory activity and may reflect an anti-nociceptive mechanism during acute pain processing., (© 2015 The British Pharmacological Society.)