Tetrodotoxin functions as a stress relieving substance in juvenile tiger puffer Takifugu rubripes

• DOI: 10.1016/j.toxicon.2019.09.024
• Publication Date: 2019-09-30T05:50:03Z
• Authors: Masafumi Amano; Noriko Amiya; Minami Takaoka; Haruka Sato; Tomohiro Takatani; Osamu Arakawa; Yoshitaka Sakakura
• Keywords: Brain Chemistry; Behavior, Animal; Hydrocortisone; Corticotropin-Releasing Hormone; Body Weight; Gene Expression; Tetrodotoxin; 04 agricultural and veterinary sciences; TTX; Stress; Cortisol; 630; ACTH; Takifugu; Adrenocorticotropic Hormone; CRH; Pituitary Gland; Animal Fins; Animals; 0401 agriculture, forestry, and fisheries; RNA, Messenger; Tiger puffer

We tested whether tetrodotoxin (TTX) functions as a stress relieving substance in puffer fish. We orally administered TTX to the juveniles of hatchery-reared non-toxic tiger puffer Takifugu rubripes and measured the effects of TTX on brain corticotropin-releasing hormone (CRH) mRNA expression and plasma cortisol levels in comparison with effects in non-toxic juveniles. Firstly, the reciprocal connections of CRH and adrenocorticotropic hormone (ACTH) were confirmed by dual-label immunohistochemistry. CRH-immunoreactive (ir) cell bodies were detected in the hypothalamus and CRH-ir fibers were observed to project to ACTH-ir cells in the rostral pars distalis of the pituitary. Next, a TTX-containing diet (2.35 mouse units (517 ng)/g diet) or a non-toxic diet were fed to the fish for 28 days under a recirculating system. Standard length and body weight became significantly larger in the TTX-treated group. The degree of loss of the caudal fin, which is an indicator of the degree of agonistic interactions, where high values show a higher loss of caudal fin of a fish due to nipping by other individuals, was significantly lower in the TTX-treated group. Relative CRH mRNA expression levels in the brain and cortisol levels in the plasma were significantly lower in the TTX-treated group. These results indicate that TTX functions as a stress relieving substance by affecting the CRH-ACTH-cortisol axis and reducing agonistic interactions in tiger puffer juveniles.