Lipopolysaccharide-induced depressive-like behavior is associated with α₁-adrenoceptor dependent downregulation of the membrane GluR1 subunit in the mouse medial prefrontal cortex and ventral tegmental area

Abstract

Background: Chronic stress-induced depressive-like behavior is relevant to inflammatory immune activation. However, the neurobiological alterations in the brain following the central inflammatory immune activation remain elusive.

Methods: Therefore, we investigated the neurobiological alterations during depressive-like behavior induced in mice by systemic administration of lipopolysaccharide (LPS; 1.2 mg/kg administered twice at a 30-min interval via intraperitoneal injection).

Results: At 24 h after the second administration of LPS, an increased immobility time in the tail suspension test and the forced swimming test were observed, as well as reduced sucrose preference. Protein levels of the AMPA receptor GluR1 were significantly decreased at the plasma membrane in the medial prefrontal cortex (mPFC) and ventral tegmental area (VTA), while levels of the GluR2 were increased at the plasma membrane in the nucleus accumbens (NAc) at 24h after LPS. However, total GluR1 and GluR2 protein levels in the mPFC, VTA, and NAc were not affected by LPS. Moreover, LPS facilitated release of noradrenaline in the mPFC and VTA, but not in the NAc. Consistently, systemic administration of prazosin, an α1-adrenoceptor antagonist, blocked the LPS-induced downregulation of the membrane GluR1 subunit in both the mPFC and VTA and also blocked the upregulation of the membrane GluR2 subunit in the NAc. Intracerebroventricular administration of prazosin 30 min before LPS injection abrogated the LPS-induced depressive-like behaviors. In opposition, administration of propranolol, a β-adrenoceptor antagonist, did not affect the LPS-induced downregulation of GluR1, the upregulation of GluR2, or the depressive-like behavior.

Conclusions: These results suggest that LPS-activated α1-adrenoceptor-induced downregulation of membrane GluR1 in the mPFC and VTA is associated with inflammation-induced depressive-like behavior.

Keywords: 1-adrenoceptor; depressive-like behavior; immune system; neuronal plasticity; reward system; α.

Figure 1.

Mice were injected with LPS (1.2mg/kg) twice with a 30min interval. The locomotor activity was measured at either 4 or 24h after LPS injection. The mobility time of mice in the open field was recorded over each 6min period, and results are presented as mouse locomotor activity (A; control, n=6; LPS, n=6). Change in body weight at 24h post-LPS was measured. The body weight of each mouse was measured at 5min before and 24h after LPS injection (B; control, n=6; LPS, n=6). The duration of immobility during the TST at 24h post-LPS was recorded for 6min (C; control, n=6; LPS, n=6). The duration of immobility during the FST at 24h post-LPS was recorded each for 6min (D; control, n=6; LPS, n=6). Sucrose preference was measured at 24h post-LPS (E; control, n=6; LPS, n=6) and 24–48h post-LPS (F; control, n=6; LPS, n=6) and the percentage of sucrose intake against total intake was calculated. All data are presented as means ± SEM. Statistically significant effects of LPS injection (**p < 0.01) are noted.

Figure 2.

Representative western blot of the protein level of membrane and total GluR1, GluR2, and NR1 in mouse mPFC (A), NAc (H), and VTA (O) with at 4h and 24h post-LPS injection (1.2mg/kg, twice at 30min interval). Representative graphs of the protein levels of membrane GluR1 (B; control, n=4; LPS, n=4), GluR2 (C; control, n=4; LPS, n=4), and NR1 (D; control, n=4; LPS, n=4) in the mPFC; of the total protein level of GluR1 (E; control, n=4; LPS, n=4), GluR2 (F; control, n=4; LPS, n=4), and NR1 (G; control, n=4; LPS, n=4) in the mPFC; of the protein levels of membrane GluR1 (I; control, n=4; LPS, n=4), GluR2 (J; control, n=4; LPS, n=4), and NR1 (K; control, n=4; LPS, n=4) in the NAc; of the total protein levels of GluR1 (L; control, n=4; LPS, n=4), GluR2 (M; control, n=4; LPS, n=4), and NR1 (N; control, n=4; LPS, n=4) in the NAc; of the protein levels of membrane GluR1 (P; control, n=4; LPS, n=4), GluR2 (Q; control, n=4; LPS, n=4), and NR1 (R; control, n=4; LPS, n=4) in the VTA; and of the total protein levels of GluR1 (S; control, n=4; LPS, n=4), GluR2 (T; control, n=4; LPS, n=4), and NR1 (U; control, n=4; LPS, n=4) in the VTA. The graph indicates the percentage of control (saline) levels. All data are presented as mean ± SEM. Statistically significant effects of LPS injection (*p < 0.05, **p < 0.01) are noted.

Figure 3.

Schematic drawing of the histological reconstruction of coronal sections from the mPFC (A), the NAc (C), and the VTA (E) in the microdialysis studies. Each symbol represents the approximate microdialysis probe placement for the sampling of the artificial cerebrospinal fluid containing the noradrenaline. LPS-induced facilitation of noradrenaline release in the mPFC (B, n=5), the NAc (D, n=5) and the VTA (F, n=5). Drawings were adapted from the digital Paxinos and Franklin Mouse Brain Atlas; the numbers on the left upper side of the drawings indicate the distance (in millimeters) anterior (+) and posterior (-) to bregma. Mice were injected with LPS (1.2mg/kg, twice at a 30min interval) and microdialysate effluents were collected from the mPFC (B), NAc (D), and VTA (F) at 30min intervals, starting at 30min before LPS injection (i.e., at the end of the preceding 90min stabilization period) and ending 90min after the LPS injection. Values are the mean ± SEM. *p < 0.01 relative to content of noradrenaline (pg/30 μl) at 0min are noted.

Figure 4.

Effects of pretreatment with prazosin (Prazo) or propranolol (Proprano) on LPS-induced alterations of the GluR1 and GluR2 subunits protein levels at the plasma membrane fraction and total extracts of the mouse mPFC (A-E), NAc (F-J), and VTA (K-O) at 4 and 24h post-LPS injection. Prazosin and propranolol were injected intracerebroventricularly at 30min before LPS injection (1.2mg/kg, twice at 30min interval). The graph indicates the percentage of control (saline) levels. Representative graph for the protein level of membrane GluR1 (B; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) and GluR2 (C; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) in the mPFC; of the total protein levels of GluR1 (D; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) and GluR2 (E; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) in the mPFC; of the protein levels of membrane GluR1 (G; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) and GluR2 (H; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) in the NAc; of the total protein levels of GluR1 (I; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) and GluR2 (J; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) in the NAc; of the protein levels of membrane GluR1 (L; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) and GluR2 (M; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) in the VTA; and of the total protein level of GluR1 (N; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) and GluR2 (O; control, n=5; LPS, n=5; prazosin + LPS, n=5; propranolol + LPS, n=5) in the VTA. All data are presented as mean ± SEM. Statistically significant effects of LPS injection (*p < 0.01) are noted.

Figure 5.

Prazosin or propranolol were injected intracerebroventricularly 30min before the LPS injections (1.2mg/kg, twice at a 30min interval). (A) The locomotor activity was measured at either 4 or 24h following the relevant injection. The mobility time in the open field was recorded every 6min, and results are presented as mouse locomotor activity (control, n=6; LPS, n=6; prazosin + LPS, n=6; propranolol + LPS, n=6). (B) Changing body weight at 24h post LPS was measured. The body weight of each mouse was measured at 5min before and 24h after LPS or saline injection (control, n=6; LPS, n=6; prazosin + LPS, n=6; propranolol + LPS, n=6). (C) The duration of immobility during the tail suspension test at 24h post LPS was recorded for each 6min test (control, n=6; LPS, n=6; prazosin + LPS, n=6; propranolol + LPS, n=6). (D) The duration of immobility during the forced swim test at 24h post LPS or saline was recorded for each 6min test (control, n=6; LPS, n=6; prazosin + LPS, n=6; propranolol + LPS, n=6). Sucrose preference was measured at the first 24h post LPS (E; control, n=6; LPS, n=6; prazosin + LPS, n=6; propranolol + LPS, n=6) and at 24–48h post LPS or saline (F; control, n=6; LPS, n=6; prazosin + LPS, n=6; propranolol + LPS, n=6), and the percentage of sucrose intake against total intake was presented. All data are presented as the mean ± SEM. Statistically significant effects of LPS injection (*p < 0.01) are noted.