Effects of microinjections of Group II metabotropic glutamate agents into the amygdala on sleep

Abstract

Systemic administration of the Group II metabotropic glutamate (mGlu) receptor agonist, LY379268 (LY37), dose-dependently suppresses rapid eye movement sleep (REM) whereas systemic administration of the mGlu II receptor antagonist, LY341495 (LY34), increases arousal. Group II mGlu receptors are highly expressed in the amygdala, a brain region involved in the regulation of sleep and arousal. To determine whether the amygdala is involved in mediating the effects of Group II mGlu agents on sleep, we microinjected LY37 and LY34 into the basal amygdala (BA) and the central nucleus of the amygdala (CNA) and recorded sleep and wakefulness. Wistar rats were implanted with electrodes for recording sleep and with bilateral cannulae aimed into BA for drug administration. Different groups of rats received bilateral microinjections of LY37 into BA at two dosage ranges (3.2 mM, 5.3 mM or 10.7 mM or 0.1 nM, 2.0 nM or 10.0 nM) or one dosage range of LY34 (1.0 nM, 30.0 nM or 60.0 nM). Microinjections into CNA were conducted at one dosage range for LY37 (0.1 nM, 2.0 nM or 10.0 nM) and for LY34 (1.0 nM, 30.0 nM or 60.0 nM). All drugs or vehicle alone were administered in a counterbalanced order at 5-day intervals. Following microinjection, sleep was recorded for 20 h. Microinjection of LY37 into BA at both nM and mM concentrations significantly decreased REM without significantly altering NREM, total sleep or wakefulness. The high dosage of LY34 in BA significantly suppressed NREM and total sleep. Microinjections of LY37 or LY34 into CNA had no significant impact on sleep. We suggest that Group II mGlu receptors may influence specific cells in BA that control descending output (via the CNA or bed nucleus of the stria terminalis) that in turn regulates pontine REM generator regions.

Figure 1

Selected sleep parameters (mean±SEM) plotted for 2h periods for rats that received intra-amygdala microinjections of the millimolar range of LY37 (L: 3.2 mM; M: 5.3mM; H: 10.7 mM): REM (A), NREM (B), REM episode number (C) and average REM episode duration (D). VEH: vehicle control; L: 3.2mM; M: 5.3mM; H: 10.7mM. The dark bar on the X-axis indicates the dark period.

Figure 2

Plots of total REM amounts (A), REM average duration (B) and REM episode number (C) in 4h blocks (mean±SEM) after microinjection into the amygdala of the nanomolar range of LY37 (L: 0.1nM, M: 2nM or H: 10nM) or VEH (vehicle). The dark bar on the X-axis indicates the dark period. *, P<0.05, significant difference relative to VEH; ++, P<0.05, significant difference between drug conditions. Comparisons were conducted using Tukey tests.

Figure 3

Plots of total NREM amounts (A), total sleep (B), NREM average duration (B) and NREM episode number (C) in 4h blocks (mean±SEM) after microinjection into the amygdala of the nanomolar range of LY37 (L: 0.1nM, M: 2nM or H: 10nM) or VEH (vehicle). The dark bar on the X-axis indicates the dark period. There were no significance differences across treatments for any of the measures.

Figure 4

Line drawings showing placements of microinjection cannulae in the (A) basal amygdala (BA) and (B) central nucleus of the amygdala (CNA). Dark triangles indicate injection sites for millimolar concentrations of LY37. Dark squares indicate injection sites for nanomolar microinjections of LY37. Gray circles indicate injection sites for the antagonist.