Differential effects of lorazepam on sleep and activity in C57BL/6J and BALB/cJ strain mice

Abstract

Compared to C57BL/6 mice, BALB/c mice exhibit greater 'anxiousness' on behavioural tests of anxiety, and can show significantly longer sleep disruptions after exposure to anxiogenic situations. Relative to C57BL/6 mice, BALB/c mice also have reduced benzodiazepine (BZ) receptor densities in the brain and fivefold less BZ receptor density in the amygdala, a region important in anxiety and in the control of arousal. Lorazepam is a BZ receptor full agonist and has been used to treat both anxiety and insomnia. Differences between C57BL/6 and BALB/c mice raise the question of whether BZ agonists would impact sleep and activity differentially in the two strains. We examined the effects of two doses of lorazepam (0.5 and 1.5 mg kg(-1)) or saline alone (0.2 mL) on sleep and activity in C57BL/6 (n = 8) and BALB/c (n = 7) mice. Compared to saline, both doses of lorazepam significantly increased non-rapid eye movement (NREM) and reduced activity in both strains. In C57BL/6 mice, rapid eye movement (REM) was increased at both doses. In BALB/c mice, the 0.5 mg kg(-1) dose had no significant influence on REM, whereas REM was reduced significantly after the 1.5 mg kg(-1) dose. The results demonstrate significant differences between C57BL/6 and BALB/c mice in the effects of lorazepam on REM, whereas the effects on NREM and activity were similar. Strain differences in the number of BZ receptors in the amygdala, but not other brain regions, suggests possible site specificity in the effects of lorazepam on REM. These differences in BZ-binding sites in the amygdala could be a significant factor in differences in the sleep response between C57 and BALB/c mice.

Figure 1

Selected sleep parameters and activity plotted in time-matched blocks for non-disturbed baseline and following injections of SAL in C57BL/6J and BALB/cJ mice. Values are means±SEM. Block data are plotted in two 5-h blocks for the light period and two 6-h blocks for the dark period. The results for significant two-way ANOVAs are indicated above the appropriate bars for entire 22-h recording period. F- and p-values are presented for significant main effect across treatments for NREM and for interactions across treatment and block for REM and activity. Stars indicate significant differences (*p <0.05, **p <0.01) compared to baseline conducted with Tukey test.

Figure 2

Latency to NREM, REM and difference score (REM latency – NREM latency) in minutes following injections of SAL, LZA (0.5 mg/kg) and LZB (1.5 mg/kg) in C57BL/6J and BALB/cJ mice. Values are means±SEM. The results for significant ANOVAs are indicated above the appropriate bars for the analyses between treatments. F- and p-values are presented for main effect across treatments. Stars indicate significant differences (*p <0.05, **p <0.01, ***p <0.001) compared to SAL conducted with Tukey test. # illustrates significant difference (p < 0.05) between strains (t-test).

Figure 3

Selected sleep measures plotted in blocks after injections of SAL, LZA (0.5 mg/kg) and LZB (1.5 mg/kg) in C57BL/6J and BALB/cJ mice. Values are means±SEM. Block data are plotted in two 5-h blocks for the light period and two 6-h blocks for the dark period. The results for significant two-way ANOVAs are indicated above the appropriate bars for entire 22-h recording period. F- and p-values are presented for main effect across treatments. Stars indicate significant differences (*p <0.05, **p <0.01, ***p <0.001) compared to SAL conducted with Tukey test.

Figure 4

NREM, REM and total sleep plotted as a percentage change relative to those of control (SAL) for LZA (0.5 mg/kg) and LZB (1.5 mg/kg) injections during total 22-h, 10-h light and 12-h dark periods in C57BL/6J and BALB/cJ mice. Values are means±SEM. t- and p-values for significant differences between strains are indicated above the appropriate bas.

Figure 5

Activity is plotted hourly (Upper) and blocks (Lower) after injections of SAL, LZA (0.5 mg/kg) and LZB (1.5 mg/kg) in C57BL/6J and BALB/cJ mice. Values are means±SEM. Block data are plotted in two 5-h blocks for the light period and two 6-h blocks for the dark period. The results for significant two-way ANOVAs are indicated above the appropriate bars for entire 22-h recording period. F- and p-values are presented for main effect across treatments. Stars indicate significant differences (**p <0.01, ***p <0.001) compared to SAL conducted with Tukey test.

Figure 6

Activity plotted as a percentage change relative to that of control (SAL) for LZA (0.5 mg/kg) and LZB (1.5 mg/kg) injections during total 22-h, 10-h light and 12-h dark periods in C57BL/6J and BALB/cJ mice. Values are means±SEM. t- and p-values for significant differences between strains are indicated under the appropriate bas.