Ginkgo biloba Extract (GbE) Stimulates the Hypothalamic Serotonergic System and Attenuates Obesity in Ovariectomized Rats

Abstract

Menopause is associated with increased risk to develop obesity but the mechanisms involved are not fully understood. We have shown that Ginkgo biloba extract (GbE) improved diet-induced obesity. Since GbE might be effective in the treatment of obesity related to menopause, avoiding the side effects of hormone replacement therapy, we investigated the effect of GbE on hypothalamic systems controlling energy homeostasis. Wistar rats were either ovariectomized (OVX) or Sham-operated. After 2 months, either 500 mg.kg^-1 of GbE or vehicle were administered daily by gavage for 14 days. A subset of animals received an intracerebroventricular (i.c.v.) injection of serotonin (300 μg) or vehicle and food intake was measured after 12 and 24 h. Another subset was submitted to in vivo microdialysis and 5-HT levels of the medial hypothalamus were measured by high performance liquid chromatography, before and up to 2 h after the administration of 500 mg.kg^-1 of GbE. Additional animals were used for quantification of 5-HT_1A, 5-HT_1B, 5-HT_2C, 5-HTT, and pro-opiomelanocortin hypothalamic protein levels by Western blotting. OVX increased food intake and body weight and adiposity while GbE attenuated these alterations. i.c.v. serotonin significantly reduced food intake in Sham, Sham + GbE, and OVX + GbE groups while it failed to do so in the OVX group. In the OVX rats, GbE stimulated 5-HT microdialysate levels while it reduced hypothalamic 5-HTT protein levels. The results indicate that GbE improved the ovariectomy-induced resistance to serotonin hypophagia, at least in part through stimulation of the hypothalamic serotonergic activity. Since body weight gain is one of the most important consequences of menopause, the stimulation of the serotonergic transmission by GbE may represent a potential alternative therapy for menopause-related obesity.

Keywords: Ginkgo biloba extract; food intake; hypothalamus; in vivo microdialysis; obesity; ovariectomy; serotonin.

FIGURE 1

Timeline of the experimental design.

FIGURE 2

Body mass and food intake during the 8 weeks after ovariectomy or false-ovariectomy. (A) Body mass; (B) body mass gain (% of initial body mass); (C) relative food intake (g.100 g^-1_bw.24 h^-1); and (D) food efficiency (g.kcal^-1) of Sham (n = 48) and OVX rats (n = 49). ^∞p ≤ 0.05 vs. week 0 within the Sham group; ^δp ≤ 0.05 vs. week 0 within the OVX group; ^∗p ≤ 0.05 vs. Sham.

FIGURE 3

Body mass gain and cumulative food intake during the 14 days of GbE therapy, and final fat depots and uterus mass. (A) Body mass gain (% of initial body mass) of Sham (n = 13), Sham + GbE (n = 12), OVX (n = 14), and OVX + GbE (n = 11) groups; (B) visceral adipose tissue depots mass (g.100 g^-1) of Sham (n = 21–24), Sham + GbE (n = 21–23), OVX (n = 18–25), and OVX + GbE (n = 18–23) groups; (C) cumulative food intake (g.100 g^-1_bw.24 h^-1) of Sham (n = 13), Sham + GbE (n = 12), OVX (n = 14), and OVX + GbE (n = 11) groups; (D) uterus mass (g) Sham (n = 21–24), Sham + GbE (n = 21–23), OVX (n = 18–25), and OVX + GbE (n = 18–23) groups. ^∗p ≤ 0.05 vs. Sham; ^#p ≤ 0.05 vs. Sham + GbE; ^&p ≤ 0.05 vs. OVX.

FIGURE 4

Food intake in response to intracerebroventricular serotonin. Relative food intake of (A) Sham (n = 4), (B) Sham + GbE (n = 4), (C) OVX (n = 4), and (D) OVX + GbE (n = 5) in the 12 and 24 h periods after the intracerebroventricular injection of either vehicle or 300 mg 5-HT. ^∗p ≤ 0.05 vs. vehicle.

FIGURE 5

Medial hypothalamic serotonin extracellular levels as measured by in vivo microdialysis. (A) 5-HT levels (% baseline) in 20-min VMH microdialysate samples collected before (baseline –40 to 0 min) and up to 120 min after gavage with either vehicle or 500 mg.kg^-1 of GbE and (B) area under the curve (AUC) of 5-HT extracellular levels during the 120 min of microdialysate collection after gavage of Sham (n = 6–7), Sham + GbE (n = 5–6), OVX (n = 5–10), and OVX + GbE (n = 7–10). ^∗p ≤ 0.05 vs. baseline; ^x p ≤ 0.05 vs. Sham; ^#p ≤ 0.05 vs. Sham + GbE; ^&p < 0.05 vs. OVX; ^δp ≤ 0.05 vs. OVX + GbE.

FIGURE 6

Western blotting analysis of the hypothalamic expression of the proteins serotonin receptors 1A, 1B, and 2C, serotonin transporter (5-HTT), and POMC. (A) 5-HT_1A; (B) 5-HT_1B; (C) 5-HT_2C; (D) POMC; and (E) 5-HTT expression, in % of Sham group expression. Sham (n = 12–13), Sham + GbE (n = 11–12), OVX (n = 12–14), and OVX + GbE (n = 10–11). ^∗p < 0.05 vs. Sham.