Muscarinic Modulation of High Frequency Oscillations in Pedunculopontine Neurons

Abstract

We previously reported that persistent application of the non-specific cholinergic agonist carbachol (CAR) increased the frequency of calcium channel-mediated oscillatory activity in pedunculopontine nucleus (PPN) neurons, which we identified as dependent on voltage-gated, high-threshold P/Q-type channels. Here, we tested the hypothesis that M2 muscarinic receptors and G-proteins associated with M2 receptors mediate the increase in oscillatory frequency in PPN neurons. We found, using depolarizing ramps, that patch clamped 9–12 day old rat PPN neurons (n = 189) reached their peak oscillatory activity around −20 mV membrane potential. Acute (short duration) application of CAR blocked the oscillatory activity through M2 muscarinic receptors, an effect blocked by atropine. However, persistent (long duration) application of CAR significantly increased the frequency of oscillatory activity in PPN neurons through M2 receptors [40 ± 1 Hz (with CAR) vs. 23 ± 1 Hz (without CAR); p < 0.001]. We then tested the effects of the G-protein antagonist guanosine 5′-[β-thio] diphosphate trilithium salt (GDP-β-S), and the G-protein agonist 5′-[γ-thio] triphosphate trilithium salt (GTP-γ-S). We found, using a three-step protocol in voltage-clamp mode, that the increase in the frequency of oscillations induced by M2 cholinergic receptors was linked to a voltage-dependent G-protein mechanism. In summary, these results suggest that persistent cholinergic input creates a permissive activation state in the PPN that allows high frequency P/Q-type calcium channel-mediated gamma oscillations to occur.

Modulation of gamma oscillations in the pedunculopontine nucleus by neuronal calcium sensor protein-1: relevance to schizophrenia and bipolar disorder

“…Furthermore, Na ϩ and Ca 2ϩ influx triggered by membrane depolarization has been described to mediate a biphasic stimulatory effect followed by an inhibitory regulation of adenylyl cyclase in cerebellar granule cells (Cooper et al 1998). The biphasic effects described here could be mediated by a rapid recruitment of calcium channels and its known downstream intracellular modulatory machinery (e.g., intracellular G-protein modulation; Kezunovic et al 2013) by NCS-1 at 1 M, while a more extreme [Ca 2ϩ ]-buffering by NCS-1 at 5-10 M could interfere with downstream elements. Future experiments are needed to further confirm this hypothesis.…”

Cholinergic and endocannabinoid neuromodulatory effects overlap on neurons of the pedunculopontine nucleus of mice

“…Muscarinic and nicotinic cholinergic [3,4,5] serotonergic [6,7], GABAergic [8] effects have been already described, as well as modulatory effects by orexin, ghrelin [9] or endocannabinoids [10,11]. These effects overlap in certain cases: neurons hyperpolarized by serotonin are hyperpolarized by stimulation of muscarinic acetylcholine receptors (mAChR) as well [6], and orexin and ghrelin depolarizes the same neuronal population [9].…”

Role of Calcium Channels in Bipolar Disorder

“…Both P/Q and N-type Ca 2+ channel modulation by G-proteins can involve either voltage-dependent or independent mechanisms [135–137]. In PPN neurons, M2 muscarinic receptors mediated a voltage-dependent inhibition of Ca 2+ currents [125,138]. However, the present results showed a G-protein mediated voltage-independent inhibition that was mediated by Li + that further reduced I 2 /I 1 I Ca ratio values.…”

“…We assume that activation of muscarinic cholinergic receptors will trigger a G protein coupled pathway [125] that releases InsP3, which acts with cytoplasmic NCS-1 to bind to the InsP3 receptor in the endoplasmic reticulum to release intracellular calcium. Consequently, it is that release that potentiates calcium channel mediated currents.…”

“…The biphasic effects described here could be mediated by a rapid recruitment of calcium channels and its known downstream intracellular modulatory machinery (e.g. intracellular G-protein modulation [125]) by NCS-1 at 1 μM, while a more extreme [Ca 2+ ]-buffering by 5–10 μM NCS-1 could interfere with downstream elements. Future experiments are needed to further confirm this hypothesis.…”