Changes in levels of GnRH in the brain and pituitary and GTH in the pituitary in male masu salmon,Oncorhynchus masou,from hatching to maturation

Levels of two types of gonadotropin-releasing hormone (salmon GnRH and chicken GnRH-II) in the brain and pituitary, and content of gonadotropin (GTHIβ and IIβ) in the pituitary were measured in male masu salmon from hatching to gonadal maturation for three years in order to clarify the involvement of GnRHs in precocious maturation. Underyearling precocious males were distinguishable in summer of year 1 and were marked by an increased GSI. Spermiation was observed among these individuals thereafter every autumn. Pituitary GTHIβ content in both precocious and immature males, and GTHIIβ content in precocious males showed seasonal fluctuations — high in autumn and low in winter. Pituitary GTHIIβ content was low in immature males. Pituitary sGnRH content in precocious males increased from spring to autumn during the three-year period. sGnRH concentrations in discrete brain areas showed seasonal changes — high during autumn to winter and low in summer. Concentrations in the olfactory bulbs and hypothalamus increased significantly in association with testicular maturation during year 3. sGnRH concentrations in the hypothalamus were significantly higher in precocious males than in immature males; this was possibly due to positive feedback of steroid hormones. cGnRH-II was undetectable in the pituitary and no distinct changes were observed in its concentration in the brain in relation to maturation. The phenomenon of underyearling precocious maturation is considered to be triggered before the onset of early summer. It is suggested that males which mature precociously are larger in size and contain much sGnRH in the pituitary before the outward signs of precocity appear; sGnRH may stimulate GTH II synthesis and induce precocious maturation.     

Differential expression of histochemical characteristics in the developing olfactory receptor cells in a flatfish, barfin flounder (Verasper moseri)

Differentiation of the histochemical characteristics of the olfactory receptor cells (ORC) was examined by immunohistochemistry for protein gene product 9.5 (PGP 9.5) and calretinin (CR) and lectin histochemistry for Phaseolus vulgaris agglutinin-L (PHA-L) in the developing olfactory epithelium (OE) of the barfin flounder. PGP 9.5 immunoreactivity was diffuse and CR immunoreactivity was restricted at day 7, but these immunoreactivities became intense in the OE toward day 91. Crypt cells were first identified at day 56. PHA-L staining was faint at day 28, but became intense toward day 91. These findings suggest that PGP 9.5-immunopositive cells, CR-immunopositive cells, crypt cells and PHA-L-reactive cells differentiate independently in the developing OE and constitute subsets of the ORC in the OE.     

Areolae of the Placenta in the Antarctic Minke Whale (Balaenoptera bonaerensis)

In this study, we examined the existence and structure of areolae and the steroidogenesis of areolar trophoblast cells in the Antarctic minke whale placenta morphologically and immunohistochemically. Placentas were collected from the 15th, 16th and 18th Japanese Whale Research Program under Special Permit in the Antarctic (JARPA) and 1st JARPA II organized by the Institute of Cetacean Research in Tokyo, Japan. The opening and cavity of fetal areolae formed by taller columnar trophoblast cells (areolar trophoblast cells) with long microvilli and a bright cytoplasm, as compared with the trophoblast cells of the chorionic villi interdigitating with the endometrial crypts, were recognized in observations of serial sections. The opening of the areolar cavity was hidden by chorionic villi with areolar trophoblast cells. Furthermore, a closed pouch-like structure lined by tall columnar cells similar to areolar trophoblast cells within the stroma of chorionic villi was noticed and continued to the areolar cavity, with the opening seen on serial sections. In a surface investigation of the chorion and endometrium by SEM, maternal (endometrial) areolae irregularly surrounded by endometrial folds were obvious. Moreover, we distinguished areolar trophoblast cells with long microvilli attached with many blebs from trophoblast cells. In our immunohistochemical observations, a steroidogenic enzyme, cytochrome P450 side chain cleavage enzyme (P450scc), was detected with strong immunoreactivity in trophoblast cells. However, areolar trophoblast cells showed weak or no immunoreactivity for P450scc.     

Immune response during the onset of coliform mastitis in dairy cows vaccinated with STARTVAC®

The immune response during the onset of coliform mastitis in vaccinated cows was investigated by measuring lactoferrin (LF), interleukin-8 ( IL-8), and interleukin-1β (IL-1β) concentrations and somatic cell counts in 28 milk samples at the onset of acute coliform mastitis (ACM) and 73 milk samples at the onset of peracute coliform mastitis (PCM). Vaccinated ACM, unvaccinated ACM, and vaccinated PCM showed significantly higher values for LF and IL-1β levels than unvaccinated PCM (p < .01). The IL-8 concentration was lower in vaccinated PCM than in unvaccinated PCM (p < .05). There was no significant difference in somatic cell counts for each parameter. There were no significant differences in the parameters between vaccinated and unvaccinated ACM cows, or vaccinated ACM and PCM cows. From the above results, it is suggested that mastitis vaccination improved the early immune response, particularly at the onset of PCM, and played a large role in host defense against the initial infection.     

Effects of Low pH on Upstream Migratory Behavior in Land-Locked Sockeye Salmon Oncorhynchus nerka

The effects of low pH on upstream migratory behavior in land-locked sockeye salmon Oncorhynchus nerka were examined using 2-way flow-through channels. Homing mature salmon captured at the mouth of their native stream were used. When neutral (pH 6.7) hatchery water of the same origin as native stream water was allowed to flow through both channels, fish showed active swimming into both channels during a 48 hrs period. When water pH in one channel was lowered by the addition of sulfuric acid, salmon completely ceased upstream swimming behavior into areas of pH lower than 6.0, and swam up into only neutral areas. In the lower pond of the 2-way channels, fish also avoided acidic areas even when average pH was 6.2. Since it has been reported that extremely slight changes in pH such as in the pH 6 range inhibits spawning behavior in this species, it is suggested that land-locked sockeye salmon have a sensitive ability to perceive even slight acidity, and avoid environments which may be deleterious to their offspring.     

Photic and circadian regulation of self-feeding activity in ayu

ABSTRACT:   The self-feeding rhythms of ayu Plecoglossus altivelis altivelis were examined. Individual ayu (mean body weight 40 g) were held in 60-L glass tanks equipped with self-feeders. Six of 14 fish learned self-feeding during the experiment. Under two different light–dark (LD) conditions (16 h:8 h and 8 h:16 h LD), self-feeding was synchronized to the LD cycle, and feeding occurred almost exclusively during the light phase. During exposure to constant light (LL), circadian feeding rhythms were observed. These results indicate self-feeding rhythms in ayu are restricted to the light phase under LD conditions and are controlled by the circadian clock under LL conditions.     

Toxicity of wild juvenile “komonfugu” Takifugu flavipterus in the Bay of Sanriku Coast,Tohoku Area,Northern Japan

To clarify the mechanism of tetrodotoxin (TTX) accumulation in pufferfish, we compared the toxicity of two sets of wild juvenile “komonfugu” Takifugu flavipterus. The first set was sampled from Onisawa Fishing Port (FP) located in Okirai Bay, the Pacific Coast of Sanriku, Tohoku Area, Northern Japan. The second set was collected from the Onisawa FP and reared in an outdoor laboratory tank supplied with different seawater (Yoshihama Bay). The fish were sampled regularly and on the same days. The amount of TTX (mouse unit (MU)/fish) in the fish at Onisawa FP increased until 20 days and thereafter it did not change, while the amount of TTX in the fish in the laboratory tank remained low, and the TTX concentration (MU/g fish) decreased. Next, we compared the toxicity of wild juvenile T. flavipterus collected from Okirai Bay (Onisawa FP and Okirai FP) and Yoshihama Bay (Yoshihama FP). Large differences in TTX levels were observed among the fish from the three FPs. The amounts and concentrations of TTX in the fish at Onisawa FP were higher than those in the fish from the other two FPs. These results indicate that a large variation in toxic activity exists in the juvenile T. flavipterus in the bay of the Sanriku Coast.

     

Quantitative studies of the in vitro production of pipecolic acid by rumen protozoa and its degradation by rumen bacteria

An in vitro study was conducted to quantitatively investigate the metabolism of pipecolic acid (Pip), a neuromodulator, by mixed rumen bacteria (B), mixed rumen protozoa (P), a combination of B and P (BP), species‐enriched rumen protozoal suspension (Polyplastron sp., Diploplastron sp., entodinia and Entodinium caudatum) and pure cultures of several isolates of rumen bacteria (Prevetolla bryantii, Prevetolla albensis, Streptococcus bovis, Veillonella parvula, Megasphaera elsdenii and Ruminococcus albus). Only P produced Pip from L‐lysine (1.0 mmol/L L‐Lys) at a rate of 83.5 ± 1.6 µmol/L/h and even in BP, Pip was produced from L‐Lys by P and increased at a rate of 31.2 ± 3.8 µmol/L/h. Pip production by P was highest when the substrate (L‐Lys) concentration was 6 mmol/L and then the rate was 580 ± 36 µmol/L/h. Pipecolic acid production by P suspension enriched with different species of protozoa showed that Polyplastron sp. had the highest Pip production rate of 0.907 ± 0.092 µmol/L/mg protozoal protein per h, and Diploplastron sp. had the lowest rate of 0.55 ± 0.13 µmol/L/mg protozoal protein per h. The addition of D‐Lys (1.0 mmol/L) as a substrate to the P suspension revealed that P were also able to produce Pip from D‐Lys, though at a lower rate (1/3) compared with L‐Lys (1.0 mmol/L), suggesting the presence of epimerases in P. It was confirmed that B were unable to produce Pip from L‐ or D‐Lys. Only B degraded Pip (1.0 mmol/L) after a lag phase at a rate of 56.0 ± 1.5 µmol/L/h. The B suspension was able to degrade D‐Lys, though the products were not identified. Pip degradation by pure culture of some species of rumen bacteria showed that P. bryantii and R. albus had the highest rate followed by P. albensis, S. bovis and M. elsdenii with a low rate of Pip degradation. Veillonella parvula showed no ability to degrade Pip. The results suggest that a fairly large proportion of rumen‐produced Pip is likely to be absorbed by the host animal before degradation by rumen bacteria.