Chronic Peripheral Administration of Kappa-Opioid Receptor Antagonist Advances Puberty Onset Associated with Acceleration of Pulsatile Luteinizing Hormone Secretion in Female Rats

Puberty in mammals is timed by an increase in gonadotropin-releasing hormone (GnRH) secretion. Previous studies have shown involvement of the two neuropeptides, kisspeptin and neurokinin B (NKB), in controlling puberty onset. Little is known about the role of the other key neuropeptide, dynorphin, in controlling puberty onset, although these three neuropeptides colocalize in the arcuate kisspeptin neurons. The arcuate kisspeptin neuron, which is also referred to as the KNDy neuron, has recently been considered to play a role as an intrinsic source of the GnRH pulse generator. The present study aimed to determine if attenuation of inhibitory dynorphin-kappa-opioid receptor (KOR) signaling triggers the initiation of puberty in normal developing female rats. The present study also determined if stimulatory NKB-neurokinin 3 receptor (NK3R) signaling advances puberty onset. Female Wistar-Imamichi rats were weaned and intraperitoneally implanted with osmotic minipumps filled with nor-binaltorphimine (nor-BNI), a KOR antagonist, or senktide, a NK3R agonist, at 20 days of age. Fourteen days of intraperitoneal infusion of nor-BNI or senktide advanced puberty onset, manifested as vaginal opening and the first vaginal estrus in female rats. Frequent blood sampling showed that nor-BNI significantly increased luteinizing hormone (LH) pulse frequency at 29 days of age compared with vehicle-treated controls. Senktide tended to increase this frequency, but its effect was not statistically significant. The present results suggest that the inhibitory input of dynorphin-KOR signaling plays a role in the prepubertal restraint of GnRH/LH secretion in normal developing female rats and that attenuation of dynorphin-KOR signaling and increase in NKB-NK3R signaling trigger the onset of puberty in female rats.     

Muscle type‐specific effect of myostatin deficiency on myogenic regulatory factor expression in adult double‐muscled Japanese Shorthorn cattle

To clarify muscle type‐specific effect of myostatin on myogenic regulatory factors (MRFs), we examined mRNA expression of MRFs in five skeletal muscles of normal (NM) and myostatin‐deficient double‐muscled (DM) adult Japanese Shorthorn cattle by quantitative reverse‐transcribed PCR. Among the four MRFs, namely, Myf5, MyoD, myogenin, and MRF4, MyoD expression was different among the muscles of the DM cattle (P < 0.01) but not of the NM cattle. Meanwhile, MyoD expression was significantly elevated only in masseter (MS) muscle in the DM cattle due to the myostatin deficiency (P < 0.05). Myf5 and MRF4 expression in semitendinosus (ST) was higher in the DM than in the NM cattle (P < 0.05). According to analysis of myosin heavy chain (MyHC) isoform expression, more MyHC‐2x and ‐2a and less ‐slow isoforms were expressed in the longissimus and ST muscles compared to the MS muscle in both cattle (P < 0.05), but no significant difference in MyHC expression was observed between the NM and DM cattle. Taken together, myostatin has influences on Myf5 and MRF4 expression in faster‐type muscles and on MyoD expression in slower‐type muscles, suggesting a possible muscle type‐specific effect of myostatin in skeletal muscle growth and maintenance.     

Immunolocalization of steroidogenic enzymes and their expression during the breeding season in the testes of wild raccoon dogs (Nyctereutes procyonoides)

The objective of this study was to investigate immunolocalization of steroidogenic enzymes 3βHSD, P450c17 and P450arom and their expression during the breeding season in wild male raccoon dogs. The testicular weight, size and seminiferous tubule diameters were measured, and histological and immunohistochemical observations of testes were performed. The messenger RNA expression (mRNA) of 3βHSD, P450c17 and P450arom was measured in the testes during the breeding season. 3βHSD was found in Leydig cells during the breeding and non‐breeding seasons with more intense staining in the breeding season. P450c17 was identified in Leydig cells and spermatids in the breeding season, whereas it was present only in Leydig cells in the non‐breeding season. The localization of P450arom changed seasonally: no immunostaining in the non‐breeding season; more extensive immunostaining in Leydig cells, Sertoli cells and elongating spermatids in the breeding season. In addition, 3βHSD, P450c17 and P450arom mRNA were also expressed in the testes during the breeding season. These results suggested that seasonal changes in testicular weight, size and seminiferous tubule diameter in the wild raccoon dog were correlated with spermatogenesis and immunoreactivity of steroidogenic enzymes and that steroidogenic enzymes may play an important role in the spermatogenesis and testicular recrudescence and regression process.     

Effects of intramuscular fat deposition on the beef traits of Japanese Black steers (Wagyu)

Effects of intramuscular fat deposition on the chemical composition, tenderness, and free amino acids (FAA) concentration of beef were studied using various classified carcasses of 21 Japanese Black (Wagyu) steers. The Beef Marbling Standard (BMS) No., judged on the market in 1998, and fat content, ranged from 2 to 10 and 4.8 to 39.0% in the M. longissimus thoracis, respectively. Moisture content was negatively correlated with the fat content (r =?0.98, P < 0.01). In contrast, protein content was relatively constant up to approximately 23% fat, corresponding to BMS No.4, and decreased as the fat content increased. Cooking loss was also constant up to approximately 28% fat, corresponding to BMS No.4, and markedly decreased with fat content increase. The beef in these cases were, however, classified into BMS No. around 9 and 11, respectively, according to the BMS model in 1988. A negative correlation was found between the shear‐force value and the fat content (r =?0.83, P < 0.05). Most FAA concentrations on the wet weight of meat were correlated negatively with the fat content, except glutamine, and this negative relationship was still observed when the concentrations were recalculated on the basis of protein. These results indicate that higher marbling Wagyu beef (above approx. 23% fat) would have an extremely lower content of protein, which would partly explain the lower cooking loss and FAA with fat increase. In addition, some other reasons not relating to protein content (e.g. high fat content preventing the breakdown of protein to FAA) seem to explain the negative correlation between fat and FAA.     

Analysis of weed vegetation of no-tillage upland fields based on the multiplied dominance ratio

The objective of the present study was to clarify the characteristics of weed vegetation in no-tillage upland fields in Japan. Vegetation surveys were conducted in two stages and the obtained data were analyzed based on the multiplied dominance ratio. The first was a two-year survey of a no-tillage field and a tilled field where no-tillage or tillage farming had been carried out for more than 10 years. The no-tillage field surveyed exhibited a different seasonal succession from the tilled field. Summer annuals dominated the tilled field in summer, and winter annuals dominated in spring. Perennials occupied the no-tillage field in spring; summer annuals also dominated in summer. The second survey was of 19 and 22 fields, including some no-tillage fields, in the summer of 2000 and the spring of 2001. The vegetation in both summer and spring was classified into three vegetation types, principally dependent on the no-tillage periods: types I and II consisted mainly of tilled and under 3-year-old no-tillage fields, and type III comprised no-tillage fields three years old or over. Type II vegetation was characterized primarily by the presence of biennials and perennials of Asteraceae, and type III by perennials, such as sweet vernalgrass ( Anthoxanthum odoratum ), in addition to the same species as type II. Summer annuals such as southern crabgrass ( Digitaria ciliaris ) were abundant in many fields in summer regardless of the vegetation types.