257.20/NN33 - Mechanisms behind gamma band activity in the pedunculopontine nucleus (PPN).?

LUSTER BR; HYDE J; DONOFRIO S; URBANO FJ; GARCIA-RILL E

Washington, DC

Congreso; 2014 SOCIETY FOR NEUROSCIENCE MEETING, Washington D.C., Nov. 15-19.; 2014

Society for Neuroscience

The pedunculopontine nucleus (PPN) is a component of the brainstem Reticular Activating System (RAS), and is active during waking and paradoxical sleep. High frequency, especially beta/gamma band activity drives our cognitive function during waking and REM sleep, two markedly different states of awareness. Previous results show that every cell in the PPN plateaus at gamma band frequencies and this high frequency activity is mediated by high threshold, voltage-dependent N- and P/Q-type Ca2+ channels. However, these results do not indicate whether some PPN cells manifest this high frequency activity through only P/Q-type Ca2+ channels or only N-type Ca2+ channels. The proposed studies were designed to determine whether some PPN cells have only N-, only P/Q-, or both N- and P/Q-type Ca2+ channels, and determine how many have neither one of these. Sagittal slices containing the PPN were cut at 400 μm from 9-17 day rat pups, an age at which developmental changes have shifted and plateaued. Slices were recorded and perfused with oxygenated aCSF in a perfusion chamber containing the synaptic blockers (SB): gabazine (GABAA antagonist), strychnine (glycine antagonist), 6-cyano-7-nitroquinoxaline-2,3-dione (AMPA/kainate receptor antagonist), and APV (NMDA receptor antagonist), and also Tetrodotoxin (TTX) to block sodium channels. Whole cell patch-clamp experiments (current and voltage clamp modes) were performed at body temperature (~36.5°C) using a Multiclamp 700B amplifier. Capacity transients were cancelled using computer-controlled circuitry and series resistance was compensated in all experiments (>35%, ranging from 5-16). PPN neurons were identified as to cell type (type I has LTS, type II has IA, type III has LTS+IA) using voltage and current clamp I-V curves. We found that all rat PPN cell types (n=50) showed gamma oscillations in the presence of SB+TTX when membrane potential was depolarized using current ramps. PPN neurons showed gamma oscillations when voltage-clamped at holding potentials above -30 mV. The N-type calcium channel blocker CgTx partially reduced gamma oscillations (decrease of 34% compared to control, p>0.05), while the P/Q-type blocker AgA abolished the remainder. Both ω-CgTx and ω-Aga blocked voltage-dependent calcium currents. These results suggest that all cells in the PPN have both N- and P/Q-type Ca2+channels, and that voltage-dependent P/Q- and, to a lesser extent, N-type calcium channels mediate gamma oscillations in the PPN.