Interactions between melatonin and prolactin during gestation in mink (Mustela vison)

Immature female mink, 8 weeks of age in July, were treated with implants releasing melatonin. Mating, which induced ovulation, took place during the normal breeding season in the following March. Circulating prolactin and progesterone concentrations did not undergo the expected gestational increases, and no embryos implanted. A similar absence of gestational changes in prolactin and progesterone values ensued in primiparous mink treated with the melatonin implant 2-3 days after the second of 2 matings. Administration of exogenous sheep prolactin (0.5 mg/day) by minipump induced precocious elevation of progesterone concentrations in mated mink. Prolactin administration overcame the effects of melatonin, in that the corpora lutea were activated and embryos implanted, but exogenous prolactin resulted in degeneration of implanted embryos both in the presence and absence of chronic melatonin. The results suggest that melatonin has a single effect in alteration of gestation in mink; i.e. the prevention of prolactin secretion. Hyperprolactinaemia may inhibit embryo development in this species.     

Endogenous mink (Mustela vison) type C virus isolated from sarcoma virus-transformed mink cells.

A previously described type virus stock (designated PP-1R), isolated by cocultivating baboon cells with mink cells transformed by Kirsten sarcoma virus (64J1), has been further cloned and characterized. End point-diluted stocks of PP-1R have been obtained that are free of focus-forming activity and lack both Kirsten sarcoma and primate type C viral sequences. Nucleic acid hybridization experiments show that the cloned virus (MiLV) is an endogenous, genetically transmitted virus of the mink (Mustela vison). MiLV replicates in canine, feline, and 64J1 mink cells but not in an untransformed mink cell line. Multiple viral gene copies can be detected in the DNA of normal mink cells in culture and in normal mink tissues; related endogenous viral genes are also detected in several related Mustela species. The virus codes for a p30 protein very closely related antigenically to that of feline leukemia virus but contains p15 and p12 proteins that are antigenically distinct. The mink cell line, Mv1Lu, and its Kirsten sarcoma-transformed derivatives, 64J1, express relatively low levels of type C viral RNA related to MiLV and normally do not produce detectable levels of MiLV p30 protein or complete, infectious viral particles. Infection of sarcoma virus-transformed mink cells with baboon type C virus, however, can augment the level of expression of endogenous mink viral RNA and can result in the synthesis and packaging of mink viral RNA and p30 antigen in extracellular virions. Since the Mv1Lu cell line and its tranformed derivatives have become widely used in studies of retroviruses, the possibility of activating endogenous mink viral genes should be considered by investigators working with these cells.     

The pars intermedia of the mink,Mustela vison

Summary The pars intermedia of intact and experimental female minks has been studied by light, electron and fluorescence microscopy. The general structure of the mink intermediate lobe is described. Two main cell types are recognized. One, termed glandular cell, predominates in number and is characterized by the presence of electron-dense granules about 200 nm in diameter and numerous large vesicles up to 300 nm in diameter. The other, termed stellate cell, is devoid of cytoplasmic vesicles and granules and possesses microfilaments, junctional complexes and elongated processes inserted between the glandular cells. Different treatments (photostimulation and administration of hypertonic saline and metopirone) induced morphological reactions in the glandular cells. The significance of these changes and the possibility of a functional relation between the pars intermedia and ACTH secretion are discussed.Numerous nerve fibres and axon terminals containing electron-dense granules (60–120 nm) and electron-lucent vesicles (30–40 nm) are observed throughout the pars intermedia.With the histochemical fluorescence method of Falck-Hillarp a rich system of delicate fluorescent varicose fibres, sometimes provided with irregular swellings or droplets, is observed in the pars intermedia and also in the pars nervosa. Microspectrofluorometrically these fibres exhibit the spectral characteristics of catecholamines. All the cells of the pars intermedia and a large number of cells in the pars distalis show a yellowish weak fluorescence, which becomes much stronger after combined formaldehyde-ozone treatment. This cellular fluorophore shows the same microspectrofluorometric characteristics as does the fluorophores of tryptamine and of certain peptides with NH₂-terminal tryptophan.Supported by the Swedish Fur Breeders' Association and the Swedish Natural Science Research Council (grant No. 2124). Thanks are due to Miss W. Carlsson and Miss Y. Lilliemarck for their helpful technical assistance.Supported by the Harald and Greta Jeanssons Stiftelse and by the Ford Foundation. The skilful technical assistance of Mrs. Eva Svensson and Miss Annika Borgelin is greatfully acknowledged.     

Isolation and cultivation of blastocyst-derived stem cell lines from American mink (Mustela vison).

Ten embryonic stem (ES) cell lines from mink blastocysts were isolated and characterized. All the lines had a normal diploid karyotype; of the ten lines studied, five had the XX and five had the XY constitution. Testing of the pluripotency of the ES-like cells demonstrated that 1) among four lines of genotype XX, and X was late-replicating in three; both Xs were active in about one-third of cells of line MES8, and analysis of glucose-6-phosphate dehydrogenase revealed no dosage compensation for the X-linked gene; 2) when cultured in suspension, the majority of lines were capable of forming "simple" embryoid bodies (EB), and two only showed the capacity for forming "cystic" multilayer EBs. However, formation of ectoderm or foci of yolk sac hematopoiesis, a feature of mouse ES cells, was not observed in the "cystic" EB; 3) when cultured as a monolayer without feeder, the ES cells differentiated into either vimentin-positive fibroblast-like cells or cytokeratin-positive epithelial-like cells (less frequently); neural cells appeared in two lines; 4) when injected into athymic mice, only one of the four tested lines gave rise to tumors. These were fibrosarcomas composed of fibroblast-like cells, with an admixture of smooth muscular elements and stray islets of epithelial tissue; (5) when the ES cells of line MES1 were injected into 102 blastocyst cavities and subsequently transplanted into foster mothers, we obtained 30 offspring. Analysis of the biochemical markers and coat color did not demonstrate the presence of chimaeras among offspring. Thus the cell lines derived from mink blastocysts are true ES cells. However, their pluripotential capacities are restricted.     

The development of homeothermy in mink (Mustela vison)

In mink (Mustela vison) kits newborn mortality is very high. One of the major causes of death is hypothermia. The objectives of this study were to observe the development of thermoregulation in mink kits, and their ability to maintain their body temperature during the postnatal period (1-50 days of age). Based on the kit's body weight (BW), and rectal and ambient temperature measurements during cold (+4 degrees C) and warm (+40 degrees C) exposures, a homeothermy index (HI) and cooling and warming rates were calculated. No significant differences in the body temperatures were found between the kits and the dam after 36 days of age. The kits were able to maintain homeothermy by 22 days of age (HI 90%). The body cooling rate was 0.88+/-0.04 degrees C min(-1) on day 1 but only 0.35+/-0.03 degrees C min(-1) at 22 days of age. The body WR was lower: day 1, 0.85+/-0.04 degrees C min(-1) and 0.22+/-0.03 degrees C min(-1) at 22 days of age. All measured and calculated thermophysiological variables were significantly influenced by BW and age of the kit.     

Ultrasonographic analysis of gestation in mink (Mustela vison)

Mink are seasonal breeders that display an obligate delay preceding implantation and a post implantation gestation of 31 d. The purpose of this study was to evaluate gestational parameters in mink by ultrasonography. A total of 92 female mink were mated twice during the period from March 2 to 20. The mink were scanned once and allowed to whelp (n=55); or scanned at 3 to 5-d intervals until parturition (n=13); or immediately subjected to autopsy (n=24) after scanning. Embryonic age was calculated from the date of parturition or from crown rump length. Uterine swelling diameter and fetal head size were correlated with embryonic age. The gestational sac grew rapidly once implantation had occurred. Uterine swellings of 4 to 5 mm in diameter were found on Days 2 to 4 post implantation and increased through Days 18 to 20, at which time they began to elongate due to the longitudinal growth of the fetus. Fetal cardiac activity could be detected on Days 10 to 12 post implantation in live embryos. The heart frequency was 198 +/- 3.0 beats per minute and did not vary from Days 12 to 30 post implantation. Fetal head diameter of 5 mm was first detected on Day 19 post implantation and grew gradually to 9 to 10 mm at parturition. It was not possible to accurately assess the number of conceptuses in utero. We conclude that ultrasonography can be employed in mink to diagnose pregnancy, to predict the parturition date and to determine the presence of live fetuses.     

Lesions in mink (Mustela vison) infected with giant kidney worm (Dioctophyma renale).

Adult Dioctophyma renale occupied the enlarged renal pelvis of the right kidney of naturally infected mink. Lesions in the kidney parenchyma consisted of connective tissue proliferation in the interstitial tissue, tubular atrophy and fibrosis, and periglomerular fibrosis. The luminal surface of the renal pelvis wall was formed of numerous papillae covered with transitional epithelium. The nematodes in the lumen were bathed in an albuminous fluid containing red blood cells, epithelial cells and D. renale eggs. The left (uninfected) kidney was 60% larger than the left kidney of normal mink.     

Three twinning types in mink (Mustela vison) embryogeny

The frequency of emergence of monochorial twins in the postimplantational embryogeny of the American mink and their karyotypes were studied. Monochorial pairs were found in which embryos had different karyotypes: 2n, XX and 2n, XY or 2n and 3n. This fact contradicts the notion that monochorial twins should be monozygotic and genetically identical but confirms our earlier hypothesis that a third twinning type exists in mink: monozygotic but genetically different. The mechanism of the emergence of this twinning type in mammals is discussed. It is suggested that the high (up to 4.5%) frequency of its emergence in the American mink is related to obligate embryonic diapause, causing abnormal fertilization.     

The food of feral mink (Mustela vison) in Scotland

Feral American mink ( Mustela vison ) thrive in Scotland. The potential impact of the mink on the native fauna was investigated through its food. Fifty-five stomachs and 33 scats were analysed by identifying the indigestible remains. Fish formed the main prey (49% occurrence) and birds and mammals 28% and 23% respectively. Most of the fish eaten were Salmonidae (brown trout and salmon). No remains of eels were found.
Mink may compete with otters for food, but the smaller prey taken by the mink and its greater use of land separates it from the otter. Mink seem to be occupying a vacant feeding niche in Scotland.     

Duration of copulation and fertility in the mink, Mustela vison

In mink, restricting the duration of copulation (相似文献   

Exogenous melatonin elevates the plasma leptin and thyroxine concentrations of the mink (Mustela vison)

Eight male and eight female minks were given exogenous melatonin as subcutaneous implants. The plasma leptin and thyroxine concentrations were measured. The leptin concentrations showed clear seasonal variations and differences between the experimental groups. In September most of the control females had undetectable plasma leptin concentrations, but the melatonin-treated females had detectable concentrations significantly higher than the leptin levels of the controls. Most of the males had undetectable leptin concentrations, too. In October the plasma leptin levels had increased significantly in all the groups except the control males. The melatonin-treated minks had significantly higher leptin levels than the controls. There was a significant rise in the thyroxine levels from September to October and the melatonin-treated groups had significantly higher thyroxine levels than the controls. The effects of exogenous melatonin are very pronounced in the mink. Melatonin elevates the plasma leptin and thyroxine levels possibly by direct and indirect mechanisms.     

Mapping of 53 loci in American mink (Mustela vison)

Fifty-three genes were mapped in the American mink genome using polymerase chain reaction (PCR)-based analysis of a Chinese hamster-American mink somatic cell hybrid panel. Heterologous primers designed for cat gene mapping were used in this study. Forty-nine of these loci were localized into expected chromosome regions according to Zoo-FISH data, whereas four loci--ALPL, CDC20, ERF-2, and Fc(Mv)23617--were mapped out of expected conserved regions. PCR products amplified with primers corresponding to these four markers were partly sequenced and verified using BLAST. The results showed the homology to be more than 90% between mink and human or cat counterparts. At present, the gene map of American mink has expanded to 127 loci.     

Observations on thermoregulatory ontogeny of mink (Mustela vison)

(1) We measured cooling rate for neonatal mink during a 10min coldroom (3.9 degrees C) exposure and subsequent warming rate during a 20min incubator (37.2 degrees C) exposure, the behaviour of the kits and the changes in their pelage between 1 and 46d of age, in an attempt to monitor the ontogeny of their thermoregulatory capacity. (2) Body weight of the 1d old kits averaged only 12.8+/-2.3g (n=4), but they gained weight rapidly reaching 226.1+/-28.3g (males, n=4) and 207.6+/-16.1g (females, n=4) at 30-31d of age, and 562.3+/-43.2g (males, n=3) and 435.7+/-35.5g (females, n=4) at 45-46d of age. (3) Body cooling rate (C(rate) ( degrees C/min); n=80) was affected by the age (between 1 and 31d), BW, initial rectal temperature (T(r0)), and sex of the kits, in addition to their body posture (P(cold), 1=extended, 2=curled-up) during coldroom exposure. C(rate) ( degrees C/min)=-0.34-0.02age-0.002BW+0.05T(r0)-0.06sex-0.20P(cold) (R(2)=0.75). (4) Body warming rate (W(rate) ( degrees C/min); n=80) was influenced by the age(2) and rectal temperature of the kit after the coldroom exposure (T(r10)). W(rate)( degrees C/min)=1.24+0.0002age(2)-0.04T(r10) (R(2)=0.76). (5) Kit fur fibre length increased from 5.45+/-0.63mm (males, n=2) and 6.20+/-0.20mm (females, n=3) at 22-23d of age to 9.43+/-1.44mm (males, n=4) and 8.70+/-1.89mm (females, n=4) at 30-31d of age, and to 12.93+/-0.47mm (males, n=3) and 11.38+/-0.41mm (females, n=4) at 45-46d of age, the growth averaging about 0.26mm per day. (6) Under normal circumstances newborn mink kits are hypothermic.Their thermoregulation develops only gradually and is dependent on increase in body mass, insulation and behavioural thermoregulation. Their strategy of survival is based on the ability to withstand hypothermia and on the nutrition and warmth provided by the dam.     

Characterization of oligosaccharides in milk of a mink, Mustela vison

Carbohydrates were extracted from a sample of milk from a mink, Mustela vison (Family Mustelidae). Free neutral and acidic oligosaccharides were isolated from the carbohydrate fraction and their chemical structures were compared with those of white-nosed coati (Nasua narica, Procyonidae) and harbour seal (Phoca vitulina, Phocidae) that we had studied previously. The ratio of free lactose to milk oligosaccharides was similar to that in milk of the white-nosed coati; in both species, this ratio was much lower than that in the milk of most eutherians. The neutral oligosaccharides of mink milk had alpha(1-3)-linked Gal or alpha(1-2)-linked Fuc residues at their non-reducing ends, as in the neutral oligosaccharides of white-nosed coati milk. Some of the neutral and acidic oligosaccharides, determined here, had been found also in harbour seal milk, but the harbour seal oligosaccharides did not contain alpha(1-3)-linked Gal residues.     

Underwater predatory behaviour of the American mink (Mustela vison)

Fishing behaviour of the American mink ( Mustela vison Schreber) was investigated in the laboratory. Data were recorded using ciné film and tape recorded commentaries. Three species of prey were presented to mink, namely, carp ( Cyprinus curpio ), goldfish ( Carassius auratus ) and minnows ( Phoxinus phoxinus ).
It was found to be necessary to train ranch-bred mink to enter water and catch fish; young mink appeared to be easier to train than adults. Mink spent 5–20 sec under water when fishing; prey had usually previously been located from an aerial vantage point. Predatory behaviour was highly organized sequentially whereas fish were more prone to indulge in unpredictable stratagems; the behaviour of mink and fish were highly correlated.
The mink's efficiency in catching fish was related to prey size (smaller individuals being more vulnerable to capture) and shoaling. Minnows, which form highly organized shoals, were less easily caught when present in large numbers; this was not true of a loosely shoaling species, the carp.
Of the three species of prey presented, vulnerability to capture took the form goldfish> carp> minnow; these differences, however, may have been influenced by the fish's previous experience of underwater predators.     

LH release in mink (Mustela vison). Pattern of the LH surge and effect of metabolic status

The mink is a seasonal breeder with induced ovulation and delayed implantation. Reproductive processes are strongly influenced by energy supply and body condition. Items for which there is paucity or complete lack of data were the main objectives of this study: the temporal relationship between copulation and the pre-ovulatory LH surge and the influence of energy supply on LH release. A total of 30 yearling female mink with a well defined metabolic status was used. Twelve females kept in the laboratory were measured in six consecutive one-week balance periods each including the measurement of heat production by means of indirect calorimetry, and 18 females were kept under conventional farm conditions. The animals were fed so as to maintain energy balance (CON), flush fed by 2 weeks food restriction followed by 2 weeks refeeding (FLUSH), or kept in a negative energy balance (NEG). Plasma concentrations of the thyroid hormones, IGF-1 and insulin were determined weekly (n = 12), or 1 week after change in energy supply to the FLUSH group (n = 18). On the day of mating, blood samples for LH and oestradiol-17beta (E2) were taken before and immediately after mating and then 4, 8, 12, 24, 30 and 48 h thereafter. Frequent blood samplings, each lasting 60 min, were taken during the LH surge from two other females surgically fitted with venous access ports. Peak concentrations of LH were recorded on the first sampling, an average 16 min after mating. The concentrations remained elevated for 12 h, but almost decreased to basal values 24 h after mating. Plasma E2 was high before mating and peak values were attained 4 h after mating after which it decreased. Energy supply had no significant influence on LH and E2, but there was a tendency for a more sluggish LH release in NEG animals. The lack of response in FLUSH animals was explained by these animals having a lower intake of metabolisable energy than CON animals, the total intake not being significantly different from the NEG group. Plasma concentrations of thyroid hormones, IGF-1 and insulin were not significantly affected by the treatment, but in FLUSH animals the values mirrored energy supply, and in the NEG group, the values tended to decrease during the course of the experiment. It was concluded that the pre-ovulatory LH surge is an immediate response to mating, and that reproductive activity in the mink is maintained over a wide range of energy supply and body condition.     

Effect of aleutian gene on mink (Mustela vison) growth

The correlation between the skin size of Mustela vison mink and the combination of the alleles of aleutian colour gene has been shown. The studied relation can be presented as ppAa > ppAA > ppaa.     

The feeding ecology of mink (Mustela vison) in coastal habitat

The diet of a coast-living population of mink was investigated from the scats collected over a three-year period, and compared with information on the availability of principal prey species. Lagomorphs were the single most important prey, and predation upon them matched the abundance of rabbits as determined by monthly counts. Aquatic foraging was particularly important, with rockpool-inhabiting fish accounting for 29–1% occurrence of food items. Fish predation was more pronounced during winter months when lagomorph prey was less available. Crustacean prey, particularly the shore crab, Carcinus maenas , occurred frequently in the diet. Seabirds figured regularly in the diet; these were either taken as carrion from the strand-line or through predation on breeding colonies during the summer months.