Ghrelin levels in different brain regions in Danio rerio exposured to stress

BACKGROUND: Literature data indicated that ghrelin may be a stress neuropeptide in some animals, including Danio rerio. AIM: The aim of the study was to measure the levels of ghrelin in Danio rerio brain (forebrain, midbrain, and hindbrain) after predator exposure (predator stress test) and administration of ghrelin and oxytocin antagonists to assess the role of ghrelin in stress response. MATERIALS AND METHODS: The study used 68 Danio rerio, one predator of Cichlasoma nicaraguensis. Ghrelin levels were measured by enzyme-linked immunosorbent assay. The following pharmacological agents were used: 1) ghrelin antagonist hexapeptide [D-Lys3]-GHRP-6 (Tocris, UK); 2) recombinant peptide analog of ghrelin agrelax with a molecular weight of 3.5 kDa, developed at the IEM (both compounds in equal dosages of 0.333 mg/L); corticoliberin (Tocris) at a dosage of 0.4 mg/L; and oxytocin (Gedeon Richter, Hungary) at a dosage of 3.8 L (0.005 IU/L) per 50 mL of aquarium water (0.019 IU/L). RESULTS: In the control group, ghrelin level was determined only in the hindbrain, and ghrelin levels in the forebrain and midbrain were 4 pg/mg of total protein. Contact with a predator led to a significant increase in ghrelin levels in the forebrain and midbrain, but not in the hindbrain. Thus, in fish forebrain, ghrelin levels increased to 966 12 pg/mg of protein, which is almost a 250-fold increase in the indicator compared with the level in intact animals. In the presence of agrelax, [D-Lys3]-GHRP-6, and oxytocin, ghrelin levels in the forebrain and midbrain of stressed fish decreased approximately equally to 88 3, 97 1, and 115 1 pg/mg protein, respectively. CONCLUSION: Thus, stress exposure (contact with a predator) significantly increases ghrelin levels in the forebrain and midbrain but decreases in the hindbrain. Stress-protective peptides (oxytocin, [D-Lys3]-GHRP-6, and agrelax) decreased ghrelin levels in the forebrain and midbrain, and to a lesser extent, in the hindbrain when exposed to stress.