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

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

Localization of three forms of gonadotropin-releasing hormone in the brain and pituitary of the self-fertilizing fish, Kryptolebias marmoratus

The localization of gonadotropin-releasing hormone (GnRH) in the brain and pituitary of the self-fertilizing mangrove killifish Kryptolebias marmoratus was examined by immunohistochemistry and in situ hybridization to understand its neuroendocrine system. The genome assembly of K. marmoratus did not have any sequence encoding GnRH1, but sequences encoding GnRH2 (chicken GnRH-II) and GnRH3 (salmon GnRH) were found. Therefore, GnRH1 was identified by in silico cloning. The deduced amino acid sequence of the K. marmoratus GnRH1 (mature peptide) was identical to that of the medaka GnRH. GnRH1 neurons were detected in the ventral part of the preoptic nucleus by immunohistochemistry and in situ hybridization, and GnRH1-immunoreactive (ir) fibers were observed throughout the brain. GnRH1-ir fibers were in close contact with luteinizing hormone (LH)-ir cells in the pituitary using double immunohistochemistry. GnRH2 neurons were detected in the midbrain tegmentum by immunohistochemistry and in situ hybridization. Although GnRH2-ir fibers were observed throughout the brain, they were not detected in the pituitary. GnRH3 neurons were detected in the lateral part of the ventral telencephalic area by both methods. GnRH3-ir fibers were observed throughout the brain, and a few GnRH3-ir fibers were in close contact with LH-ir cells in the pituitary. These results indicate that GnRH1 and possibly GnRH3 are responsible for gonadal maturation through LH secretion and that all three forms of GnRH function as neurotransmitters or neuromodulators in the brain of K. marmoratus

Unique morphological characteristics of Japanese sand lances, genus Ammodytes, possibly endemic along the northern Sanriku Coast

Herein, we report a unique morphological characteristic of Japanese sand lances, genus Ammodytes, inhabiting the northern Sanriku Coast. Japanese sand lances are distributed widely in Japanese coastal waters and possess vivid spots on the both sides of their head, which reflect environmental light and can be visually observed. However, the population in Otsuchi Bay, Iwate completely lacks these spots, which is mutual in the sympatric species A. japonicus and A. heian. This difference in the local population in the Otsuchi Bay relative to those in other localities has been likely overlooked because the spots quickly disappear after the fish dies; therefore, they are not recognizable in preserved specimens. Furthermore, the population in Sendai Bay, Miyagi consists of individuals with these spots present (75%) and absent (25%), suggesting an immigration of the latter from the northern Sanriku Coast. Microscopic observation revealed that the spots are iridophore-like cells because of their oval shape and the absence of pigments and are probably connected to the nervous system. The present study should encourage future research to clarify the taxonomy and population structure of Japanese sand lances, whose stock has been decreasing and for which a management plan is urgently needed.Short Not

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

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

Localization of three forms of gonadotropin-releasing hormone in the brain and pituitary of the self-fertilizing fish, Kryptolebias marmoratus

The localization of gonadotropin-releasing hormone (GnRH) in the brain and pituitary of the self-fertilizing mangrove killifish Kryptolebias marmoratus was examined by immunohistochemistry and in situ hybridization to understand its neuroendocrine system. The genome assembly of K. marmoratus did not have any sequence encoding GnRH1, but sequences encoding GnRH2 (chicken GnRH-II) and GnRH3 (salmon GnRH) were found. Therefore, GnRH1 was identified by in silico cloning. The deduced amino acid sequence of the K. marmoratus GnRH1 (mature peptide) was identical to that of the medaka GnRH. GnRH1 neurons were detected in the ventral part of the preoptic nucleus by immunohistochemistry and in situ hybridization, and GnRH1-immunoreactive (ir) fibers were observed throughout the brain. GnRH1-ir fibers were in close contact with luteinizing hormone (LH)-ir cells in the pituitary using double immunohistochemistry. GnRH2 neurons were detected in the midbrain tegmentum by immunohistochemistry and in situ hybridization. Although GnRH2-ir fibers were observed throughout the brain, they were not detected in the pituitary. GnRH3 neurons were detected in the lateral part of the ventral telencephalic area by both methods. GnRH3-ir fibers were observed throughout the brain, and a few GnRH3-ir fibers were in close contact with LH-ir cells in the pituitary. These results indicate that GnRH1 and possibly GnRH3 are responsible for gonadal maturation through LH secretion and that all three forms of GnRH function as neurotransmitters or neuromodulators in the brain of K. marmoratus