0129 LOCAL THALAMIC RETICULAR NUCLEUS INHIBITION OF T-TYPE CALCIUM CHANNELS REDUCES SLEEP SPINDLES IN MICE

Abstract

Parvalbumin (PV)-containing GABAergic thalamic reticular neurons (TRN) express Cav3.3 T-type calcium channels that are thought to generate burst firing necessary for spindle generation. Cav3.3 is a risk gene for schizophrenia, where spindle abnormalities are present. The role of Cav3.3 in the control of sleep and spindles has been examined using global Cav3.3 knockout mice but not with acute, local pharmacological blockade. Therefore, here we examined the inhibitory effect of a selective T-type inhibitor, TTA-P2, in TRN on sleep and spindles. In vitro recordings were made from identified TRN PV neurons in slices from mice (13-22d) expressing a red fluorescent protein in PV neurons. In vivo, mice (N=8) were implanted with bilateral microdialysis cannulae targeting TRN (AP -0.7, ML ±1.3, DV -4.0) and electrodes (EEG/EMG) for sleep-wake recordings. A custom Matlab script detected individual spindles (10-15Hz) in the EEG, allowing analysis of drug effects on spindle density (spindles/min) during NREM sleep. Data was compared with the ACSF-day values and related to the histological location of the probe. TRN-PV neurons exhibited low-threshold spikes/inward currents after removal of hyperpolarizing currents/voltage steps respectively, which were blocked by TTA-P2 (3 µM, n=4), confirming the expression of low threshold T-type Ca channels in TRN PV neurons. In 6/8 mice with probe locations in TRN (uni- or bi-lateral), TTA-P2 infusion at ZT2-6 significantly decreased (-27.0 ± 11.6%, p=0.008) spindle density (ACSF: 4.25 ± 0.19; TTA-P2: 3.13 ± 0.37) without any significant effect on amplitude or duration. There was no effect on NREM sleep duration, delta (0.5-4Hz) or slow-wave activity (0.5–1.5Hz). Localized pharmacological inhibition of T-type calcium channels within TRN selectively decreased NREM spindle density without an effect on NREM sleep. These results contrast with those observed with a constitutive, global knockout of Cav3.3, where sleep fragmentation was observed in addition to reduced spindles (Astori et al., 2011). Veterans Affairs Medical Research Service Awards, 5I01BX001356, I01BX001404, 1IK2BX002130, R21-NS079866, RO1-MH039683, PO1-HL095491, R21 NS093000, R03 MH107650, JTM received partial salary compensation and funding from Merck MISP, but has no conflict of interest with this work.