Placed in a test chamber (26 cm L612 cm W612 cm H) containing 1 cm deep bedding of clean, fresh wood chips, and was acclimated to the test condition in which a clean, dry cotton-tipped applicator was inserted 4 cm deep through a hole on the lid for 15 min following an i.c.v. injection of drugs or vehicle. The sniffing behavior was defined as when 
the mouse was orienting towards the tip of replaced applicator absorbed with distilled water, almond extract (1:100 dilution, Supercook, Leeds, UK) or vanilla extract (1:100 dilution, Supercook, Leeds, UK) with its nose within 2 cm or closer to the tip. The sniffing behavior was recorded for 2 min in each trial. The sequence of replaced applicator was water, water, water, almond, almond, almond, vanilla, vanilla and vanilla, with 1 min 
interval. Habituation is defined as a progressive decrease inolfactory sniffing time towards a repeated presentation of the same odor stimulus and used to evaluate whether an animal can distinguish the same odor. Dishabituation is defined by a reinstatement of sniffing when a novel odor is presented, and used to Triptorelin assess whether an animal can detect a different odor [20?22]. The test chambers were rinsed with distilled water and the bedding was changed before each test. The animals were videorecorded and an experimenter blind to the treatment analyzed the animal behavior.Food intake testIt is well-known that olfaction is closely related to food intake in mammals, especially in rodents [23,24]. To determine whether the change of olfaction following NPS administrations influences food ingestion, the amount of food intake was respectively measured at 0.5, 1, 2, 4 and 24 h after central administration of vehicle (n = 10)NPS Facilitates Olfactory FunctionFigure 4. Latency to find the buried food following i.c.v. injection of vehicle, NPS or [D-Val5]NPS and NPS + [D-Val5]NPS in mice. Values are means 6 SEM (n = 10 mice in each group). * p,0.05, ** p,0.001. Data were analyzed by one-way ANOVA and followed by Fisher’s LSD test. doi:10.1371/journal.pone.0062089.gor NPS (0.5 or 1 nmol, n = 9 in each group) in mice fasted for 32 h.ImmunohistochemistryTissue preparation. One and a half hour after NPS (0.5 nmol, n = 4) or vehicle 1 ml (n = 5) i.c.v. administration, animals were anesthetized with over dose of chloral hydrate (400 mg/kg), and perfused via the ascending aorta with 30 ml saline containing heparin (1 U/ml) followed by 4 paraformaldehyde in 0.1 M phosphate buffer (PB). Brains were 15755315 removed, post-fixed in the same fixative overnight and immersed in 30 sucrose solution in 0.1 M PB at 4uC for 36 h, and coronally sectioned (30 mm) on a cryostat (CM1900, Leica Micro-systems, Heidelberg, Germany) at 220uC and the sections were collected into 0.01 M sodium phosphate buffer (PBS). Fos immunohistochemistry. The floating sections were rinsed in 0.01 M PBS (pH 7.4), treated 30 min in 0.3 H2O2 in PBS, and incubated in blocking solution (10 bovine serum in PBS) for 1 h. Then the sections were incubated with a rabbit AZ 876 polyclonal antibody against c-Fos (1:5,000, sc-253, Santa Cruz Biotechnology, Santa Cruz, CA, USA) diluted in PBS containing 1 bovine serum for 48 h at 4uC on an agitator. After rinsing in PBS, sections were incubated with a biotinylated goat anti-rabbit IgG (1:1000, AP132B, Millipore, Temecula, CA, USA) then with horseradish peroxidase conjugated streptavidin (1:2,000, SA202, Millipore, Temecula, CA, USA). Both incubations were carried out on an agitator at 4uC o.Placed in a test chamber (26 cm L612 cm W612 cm H) containing 1 cm deep bedding of clean, fresh wood chips, and was acclimated to the test condition in which a clean, dry cotton-tipped applicator was inserted 4 cm deep through a hole on the lid for 15 min following an i.c.v. injection of drugs or vehicle. The sniffing behavior was defined as when the mouse was orienting towards the tip of replaced applicator absorbed with distilled water, almond extract (1:100 dilution, Supercook, Leeds, UK) or vanilla extract (1:100 dilution, Supercook, Leeds, UK) with its nose within 2 cm or closer to the tip. The sniffing behavior was recorded for 2 min in each trial. The sequence of replaced applicator was water, water, water, almond, almond, almond, vanilla, vanilla and vanilla, with 1 min interval. Habituation is defined as a progressive decrease inolfactory sniffing time towards a repeated presentation of the same odor stimulus and used to evaluate whether an animal can distinguish the same odor. Dishabituation is defined by a reinstatement of sniffing when a novel odor is presented, and used to assess whether an animal can detect a different odor [20?22]. The test chambers were rinsed with distilled water and the bedding was changed before each test. The animals were videorecorded and an experimenter blind to the treatment analyzed the animal behavior.Food intake testIt is well-known that olfaction is closely related to food intake in mammals, especially in rodents [23,24]. To determine whether the change of olfaction following NPS administrations influences food ingestion, the amount of food intake was respectively measured at 0.5, 1, 2, 4 and 24 h after central administration of vehicle (n = 10)NPS Facilitates Olfactory FunctionFigure 4. Latency to find the buried food following i.c.v. injection of vehicle, NPS or [D-Val5]NPS and NPS + [D-Val5]NPS in mice. Values are means 6 SEM (n = 10 mice in each group). * p,0.05, ** p,0.001. Data were analyzed by one-way ANOVA and followed by Fisher’s LSD test. doi:10.1371/journal.pone.0062089.gor NPS (0.5 or 1 nmol, n = 9 in each group) in mice fasted for 32 h.ImmunohistochemistryTissue preparation. One and a half hour after NPS (0.5 nmol, n = 4) or vehicle 1 ml (n = 5) i.c.v. administration, animals were anesthetized with over dose of chloral hydrate (400 mg/kg), and perfused via the ascending aorta with 30 ml saline containing heparin (1 U/ml) followed by 4 paraformaldehyde in 0.1 M phosphate buffer (PB). Brains were 15755315 removed, post-fixed in the same fixative overnight and immersed in 30 sucrose solution in 0.1 M PB at 4uC for 36 h, and coronally sectioned (30 mm) on a cryostat (CM1900, Leica Micro-systems, Heidelberg, Germany) at 220uC and the sections were collected into 0.01 M sodium phosphate buffer (PBS). Fos immunohistochemistry. The floating sections were rinsed in 0.01 M PBS (pH 7.4), treated 30 min in 0.3 H2O2 in PBS, and incubated in blocking solution (10 bovine serum in PBS) for 1 h. Then the sections were incubated with a rabbit polyclonal antibody against c-Fos (1:5,000, sc-253, Santa Cruz Biotechnology, Santa Cruz, CA, USA) diluted in PBS containing 1 bovine serum for 48 h at 4uC on an agitator. After rinsing in PBS, sections were incubated with a biotinylated goat anti-rabbit IgG (1:1000, AP132B, Millipore, Temecula, CA, USA) then with horseradish peroxidase conjugated streptavidin (1:2,000, SA202, Millipore, Temecula, CA, USA). Both incubations were carried out on an agitator at 4uC o.