High-threshold Ca2+ channels behind gamma band activity in the pedunculopontine nucleus (PPN).

Brennon Luster,Stasia D'Onofrio,Edgar Garcia-Rill,Francisco Urbano

doi:10.14814/phy2.12431

Abstract

The pedunculopontine nucleus (PPN) is part of the Reticular Activating System, and active during waking and REM sleep. Previous results showed that all PPN cells plateau at gamma frequencies and intrinsic membrane oscillations in PPN neurons are mediated by high-threshold N- and P/Q-type Ca2+ channels. The present study was designed to determine whether some PPN cells have only N-, only P/Q-, or both N- and P/Q-type Ca2+ channels. We used patch-clamp recordings in PPN cells in slices from anesthetized rat pups in the presence of synaptic receptor blockers (SB) and Tetrodotoxin (TTX), and applied ramps to induce intrinsic membrane oscillations. We found that all PPN cell types showed gamma oscillations in the presence of SB+TTX when using current ramps. In 50% of cells, the N-type Ca2+ channel blocker ω-Conotoxin-GVIA (ω-CgTx) reduced gamma oscillation amplitude, while subsequent addition of the P/Q-type blocker ω-Agatoxin-IVA (ω-Aga) blocked the remaining oscillations. Another 20% manifested gamma oscillations that were not significantly affected by the addition of ω-CgTx, however, ω-Aga blocked the remaining oscillations. In 30% of cells, ω-Aga had no effect on gamma oscillations, while ω-CgTx blocked them. These novel results confirm the segregation of populations of PPN cells as a function of the calcium channels expressed, that is, the presence of cells in the PPN that manifest gamma band oscillations through only N-type, only P/Q-type, and both N-type and P/Q-type Ca2+ channels.

Highlights

The pedunculopontine nucleus (PPN) is a component of the brainstem Reticular Activating System (RAS), and is the only RAS nucleus active during both waking and paradoxical or rapid eye movement (REM) sleep
We tested 25 neurons to study Ca2+ currents: 20 were tested using a single-step protocol to determine the differential effects of channel blockers, while five were tested using a multiple ramp protocol to determine the effects of each Ca2+ channel blocker across multiple depolarizing levels and the effects of the unspecific Ca2+ channel blocker Cad
On the other hand, increased ERK1/2 signaling in the PPN is associated with maintenance of sleep via suppression of waking (Desarnaud et al 2011), while activation of intracellular protein kinase A (PKA) in the PPN instead contributed to REM sleep recovery following REM sleep deprivation (Datta and Desarnaud 2010). These authors showed that during REM sleep, pCREB activation in PPN cholinergic neurons was induced by REM sleep, and that PPN intracellular PKA activation, and a transcriptional cascade involving pCREB, occurred only in cholinergic neurons (Datta et al 2009). These results suggest that waking in vivo may be modulated by the CaMKII pathway while REM sleep may be modulated by the cAMP/PKA pathway in the PPN (Urbano et al 2014)

Summary

Introduction

The pedunculopontine nucleus (PPN) is a component of the brainstem Reticular Activating System (RAS), and is the only RAS nucleus active during both waking and paradoxical or rapid eye movement (REM) sleep. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society. Gamma frequency oscillations are evident during REM sleep, when our skeletal muscles undergo atonia and we experience neurogenic surrealistic dreaming (Llinas and Pare 1991)

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