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Abstract
The norepinephrine-releasing neurons in the locus coeruleus (LC) are well known to regulate wakefulness/arousal. They display active firing during wakefulness and a decreased discharge rate during sleep. We have previously reported that LC neurons express large numbers of GABAB receptors (GABABRs) located at peri-/extrasynaptic sites and are subject to tonic inhibition due to the continuous activation of GABABRs by ambient GABA, which is significantly higher during sleep than during wakefulness. In this study, we further showed using western blot analysis that the activation of GABABRs with baclofen could increase the level of phosphorylated extracellular signal-regulated kinase 1 (ERK1) in LC tissue. Recordings from LC neurons in brain slices showed that the inhibition of ERK1/2 with U0126 and FR180204 accelerated the decay of whole-cell membrane current induced by prolonged baclofen application. In addition, the inhibition of ERK1/2 also increased spontaneous firing and reduced tonic inhibition of LC neurons after prolonged exposure to baclofen. These results suggest a new role of GABABRs in mediating ERK1-dependent autoregulation of the stability of GABABR-activated whole-cell current, in addition to its well-known effect on gated potassium channels, to cause a tonic current in LC neurons.
Highlights
Γ-Aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the forebrain
We examined pERK1/2 levels in locus coeruleus (LC) tissue punched from slices (Fig. 1A) bathed in 50 μM baclofen, a GABAB receptors (GABABRs) agonist, and the vehicle, artificial cerebrospinal fluid containing synaptic blockers, using western blot analysis
We provide biochemical and electrophysiological evidence showing that GABABRs can mediate the autoregulation of GABABR-activated whole-cell current through the activation of extracellular signal-regulated kinase 1 (ERK1) in LC neurons
Summary
Γ-Aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the forebrain. By acting at ionotropic GABAA receptors (GABAARs) located within the synaptic acting zone, GABA can rapidly increase the membrane permeability to Cl- in target neurons and produce fast phasic inhibitory transmission. This type of signaling is referred to as conventional synaptic transmission and features a specific method of communication between neurons with high temporal and spatial precision that enables the presynaptic neuron to shape the spiking pattern of the postsynaptic neuron. We further show that the activation of ERK1 signaling pathways by GABABRs could prevent a rapid decline in the GABABR-activated whole-cell membrane current and help stabilize tonic inhibition
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