Abstract
The striatum is the most prominent nucleus in the basal ganglia and plays an important role in motor movement regulation. The cholinergic interneurons (ChIs) in striatum are involved in the motion regulation by releasing acetylcholine (ACh) and modulating the output of striatal projection neurons. Here, we report that muscarinic ACh receptor (M receptor) agonists, ACh and Oxotremorine (OXO-M), decreased the firing frequency of ChIs by blocking the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. Scopolamine (SCO), a nonselective antagonist of M receptors, abolished the inhibition. OXO-M exerted its function by activating the Gi/o cAMP signaling cascade. The single-cell reverse transcription polymerase chain reaction (scRT-PCR) revealed that all the five subtypes of M receptors and four subtypes of HCN channels were expressed on ChIs. Among them, M2 receptors and HCN2 channels were the most dominant ones and expressed in every single studied cholinergic interneuron (ChI).Our results suggest that ACh regulates not only the output of striatal projection neurons, but also the firing activity of ChIs themselves by activating presynaptic M receptors in the dorsal striatum. The activation of M2 receptors and blockage of HCN2 channels may play an important role in ACh inhibition on the excitability of ChIs. This finding adds a new G-protein coupled receptor mediated regulation on ChIs and provides a cellular mechanism for control of cholinergic activity and ACh release in the dorsal striatum.
Highlights
As a prominent nucleus in the basal ganglia, striatum serves as a center of input and integration for cortical, thalamic, and midbrain afferents
In scRT-PCR experiments, the cells selected preferentially in morphology transcribed choline acetyltransferase (ChAT) mRNA while glutamate decarboxylase 67 (GAD67) products were not detected (Figure 1B), which could exclude the contamination of medium-size spiny neurons (MSNs)
Our present results demonstrate that cholinergic interneurons (ChIs) expressed M receptor and hyperpolarization-activated cyclic nucleotide-gated (HCN) channel abundantly, and their spontaneous firing can be modulated by application of M receptor agonist or HCN channel blocker
Summary
As a prominent nucleus in the basal ganglia, striatum serves as a center of input and integration for cortical, thalamic, and midbrain afferents. ChIs only take a small fraction of striatal neurons (1–3%), but have widespread connections throughout the striatum (Kawaguchi et al, 1995; Tepper and Bolam, 2004). They synthesize, transport, and secrete acetylcholine (ACh; Woolf and Butcher, 1981; Wang et al, 2006; Ding et al, 2010; Goldberg et al, 2012). Increased release of ACh by ChIs has been shown to contribute to structural changes and distorted network function in the striatum (Pisani et al, 2007)
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