Brain somatostatin receptor 2 mediates the dipsogenic effect of central somatostatin and cortistatin in rats: role in drinking behavior

Abstract

Intracerebroventricular injection of stable somatostatin (SST) agonists stimulates food and water intake in rats. We investigated the receptor subtype(s) involved in the dipsogenic effect of intracerebroventricular injection of SST agonists, mechanisms of action, and role. In nonfasted and non-water-deprived male rats with chronic intracerebroventricular cannula, intake of water without food or food without water was monitored separately to avoid any interactions compared with intracerebroventricular vehicle. SST-14 and cortistatin (CST-14) (1 μg/rat icv) increased water intake by 3.1- and 2.7-fold, respectively, while both peptides did not alter food intake at 1 h postinjection in the light phase. By contrast, the stable pan-somatostatin agonist ODT8-SST (1 μg/rat icv) increased both water and food intake by 4.9- and 3.7-fold, respectively. S-346-011, a selective receptor 2 (sst2) agonist (1 μg/rat icv) induced water ingestion, while sst1 or sst4 agonist, injected under the same conditions, did not. The sst2 antagonist S-406-028 (1 μg/rat icv) prevented the 1-h water intake induced by intracerebroventricular ODT8-SST and CST-14. Losartan (100 μg/rat icv), an angiotensin receptor 1 (AT1) antagonist, completely blocked the water consumption induced by intracerebroventricular ODT8-SST, whereas intracerebroventricular injection of S-406-028 did not modify the intracerebroventricular ANG II-induced dipsogenic response. The sst2 antagonist reduced by 40% the increase of the 3-h water intake in the early dark phase. These data indicate that SST-14 and CST-14 interact with sst2 to exert a potent dipsogenic effect, which is mediated downstream by angiotensin-AT1 signaling. These data also indicate that sst2 activation by brain SST-14 and/or CST-14 may play an important role in the regulation of drinking behavior.

Keywords: angiotensin receptor 1; brain; cortistatin; somatostatin agonists; water intake.

Fig. 1.

Effects of intracerebroventricular injection of ODT8-somatostatin (SST), SST-14, and cortistatin (CST)-14 on food intake without water. Nonfasted and non-water-deprived rats were injected (10 μl/rat icv) with vehicle (saline), ODT8-SST, SST-14, or CST-14 (all 1 μg/rat icv), and food intake was measured for 1 h in rats that had no access to water. Data are expressed as means ± SE of 5 or 6 rats per group. **P < 0.01 vs. vehicle.

Fig. 2.

ODT8-SST, SST-14, and CST-14 injected intracerebroventricularly increased water intake without food. Nonfasted and non-water-deprived rats were injected (10 μl/rat icv) with vehicle (saline), ODT8-SST, SST-14, or CST-14 (all 1 μg/rat icv), and water intake was measured in rats without access to food during the 0–10- and 10–60-min periods postinjection; then data were cummulated over the 60-min period. Data are expressed as means ± SE of 5 or 6 rats per group. *P < 0.05, **P < 0.01 vs. vehicle.

Fig. 3.

The intracerebroventricular injection of selective the sst₂ agonist, unlike the sst₁ or sst₄ agonists increased water intake without food. Nonfasted and non-water-deprived rats were injected (10 μl/rat icv) with vehicle (saline) or selective sst₁, sst₂, or sst₄ agonists (all 1 μg/rat icv). Water intake was measured in rats without access to food during the 0–10- and 10–60-min periods postinjection; then data were cummulated over the 60-min period. Data are expressed as means ± SE of 5 or 6 rats per group. **P < 0.01 vs. vehicle.

Fig. 4.

The selective sst₂ antagonist injected intracerebroventricularly blocked water intake induced by intracerebroventricular ODT8-SST and CST-14. Nonfasted and non-water-deprived rats were pretreated (5 μl/rat icv) with vehicle (saline) or the selective sst₂ antagonist (1 μg/rat icv) followed by vehicle (saline), ODT8-SST, or CST-14 (both 1 μg/rat icv) and water intake without food was measured during the 0–10- and 10–60-min periods after the intracerebroventricular injection. Data are expressed as means ± SE of 5 or 6 rats per group. *P < 0.05, **P < 0.01 vehicle plus agonists vs. vehicle plus saline. †P < 0.05, ‡P < 0.01 sst₂ antagonist plus agonists vs. vehicle plus respective agonists.

Fig. 5.

Intracerebroventricular injection of the selective AT₁ antagonist losartan blocked the ODT8-SST-induced water intake, while the selective sst₂ antagonist did not block the water intake induced by ANG II. Nonfasted and non-water-deprived rats were pretreated (5 μl/rat icv) with saline or losartan (100 μg/rat icv) followed by ODT8-SST (1 μg/rat icv), or were pretreated with saline or selective sst₂ antagonist (1 μg/rat icv) followed by ANG II (52 ng/rat icv). Water intake without food was measured at 10 and 60 min post injection. Data are expressed as means ± SE; n = 6 rats per group. **P < 0.01 saline plus agonists vs. saline plus saline. ‡P < 0.01 losartan plus ODT8-SST vs. saline plus ODT8-SST. #P < 0.01 saline plus ANG II vs. saline plus ODT8-SST. Sal, saline; Los, losartan; ODT8, ODT8-SST; sst₂At, sst₂ antagonist.

Fig. 6.

ODT8-SST injected intracerebroventricularly induced c-Fos expression in the supraoptic nucleus (SON) and magnocellular paraventricular nucleus (PVN), but not in subfornical organ (SFO) or median preoptic nucleus (MnPO). Nonfasted and non-water-deprived rats were injected (10 μl icv) with vehicle (saline) or ODT8-SST (1 μg/rat) and euthanized 90 min later for brain immunohistochemical analysis. The representative images of the SON (A and E), PVN (B and F), SFO (C and G), and MnPO (D and H) following saline (A--D) or ODT8-SST (E--H) are shown. * and # indicate the MnPO areas divided by the anterior commissure. Scale bars: 100 μm, except for MnPO (300 μm). SON, supraoptic nucleus; PVN, paraventricular nucleus of the hypothalamus; mp, medial parvocellular; lm, lateral magnocellular; SFO, subfornical organ; MnPO, median preoptic nucleus.

Fig. 7.

The selective sst₂ antagonist blocked the physiological water intake in the early dark phase. Rats were injected (10 μl/rat icv) with vehicle (saline) or sst₂ selective antagonist (1 μg/rat icv) 30 min before lights were turned off at 6:00 PM. Water intake without food was measured during the 0–1- and 1–3-h periods; then data were cumulated over the 0–3-h period. Data are expressed as means ± SE of 6 rats per group. *P < 0.05 vs. vehicle.