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C R Kramer

Publications and source records attributed to C R Kramer.

6 recordsLinked to original sources
PubMed2000

Ultrastructural observations on sperm storage in the ovary of the platyfish, Xiphophorus maculatus (Teleostei: poeciliidae): the role of the duct epithelium.

Sperm storage is an important phenomenon occurring in viviparous and oviparous teleosts and contributes to the reproductive life history of these forms. There is a paucity of morphological studies on sperm storage in fishes. The majority of these have been confined to the light level of investigation. In this report, we describe, at the ultrastructural level, sperm storage in the viviparous platyfish, Xiphophorus maculatus. Female platyfish, as is typical of the poeciliids, are capable of storing viable sperm for up to several months within the ovary and gonoduct. We observed that sperm stored within inseminated platyfish became associated with specific epithelial cells (SACs) lining the oviduct. Two forms of association were seen: 1) sperm were found within deep surface pits and pockets, and 2) the spermatozoa were taken up and incorporated within the cytoplasm of the SACs. Junctional complexes in the form of tight junctions (zona occludens) and desmosomes at the apico-lateral surfaces of the SACs were prevalent. The junctions could have contributed to allograft survival of the haploid heterogenetic sperm cells within the female's reproductive tract. Our results shed light on the mechanism of sperm storage in the platyfish and could serve as a model for other poeciliid species and teleosts that are capable of storing sperm.

Animals↗
PubMed1997

Neuropeptide Y (NPY) induces gonad reversal in the protogynous bluehead wrasse, Thalassoma bifasciatum (Teleostei: Labridae).

Female-to-male sex transformation in the protogynous marine fish Thalassoma bifasciatum is the culmination of a neuroendocrine cascade triggered by social and behavioral cues. We have previously shown that the hypothalamus and pituitary gland, key components of the neuroendocrine axis, play a significant role in gender reversal of this species. However, nothing is known about the possible involvement of other brain factors with the hypothalamo-pituitary gland axis in this fish. One such factor, neuropeptide Y (NPY) has been shown to effect a direct or indirect control of GtH-II release in gonochoristic teleosts. In view of this finding, we have investigated the role of NPY on sex reversal in T. bifasciatum. Females (n = 38) were injected intraperitoneally thrice weekly with NPY at a dose of 0.02 microgram/gbw dissolved in 0.6% saline. Controls (n = 48) received equal volumes of saline. Fish were sacrificed at 1, 4, 6, and 8 weeks. By the end of 8 weeks, 81.6% of the NPY-treated fish showed signs of gonad reversal ranging from early (n = 25) to mid- (n = 3) and late stage (n = 3). Furthermore, the effects of NPY appeared to be dependent on duration of treatment. At 6 and 8 weeks, the ovaries of four and three fish, respectively, were markedly degenerated. Our findings shed new light on the neuroendocrine control of sex reversal in T. bifasciatum and in hermaphroditic forms in general.

Animals↗
PubMed1989

Human chorionic gonadotropin (hCG) induces gonad reversal in a protogynous fish, the bluehead wrasse, Thalassoma bifasciatum (Teleostei, Labridae).

Female to male successive hermaphroditism (protogyny) is common in several groups of marine fish. Thalassoma bifasciatum, the bluehead wrasse (Labridae), found in the reefs of the Caribbean normally undergoes sex reversal after receiving behavioral cues. This report deals with the successful use of human chorionic gonadotropin (hCG) in inducing gonad reversal in this species. Eighty percent (n = 40) of the treated fish showed signs of reversal in 1-6 weeks; only 11% (n = 54) of the control (nontreated) group showed signs of reversal during the same period. The number of fish undergoing reversal increased with the length of the treatment period, 55% after 1 week, 100% after 6 weeks. A bluehead color pattern, typical of the terminal male phase, also appeared more frequently in the longer treated groups. To determine the efficacy of hCG in inducing gonad reversal, morphological criteria for reversal had to be established. For the majority of treated fish, the presence of both spermatogenic cysts and degenerating oocytes was sufficient to label these gonads unambiguously as undergoing reversal. However, at the extremes of this process, i.e., onset (early) and endpoint (late) stages, ambiguity could arise in identifying a gonad as undergoing reversal, and, therefore, key criteria were established for these stages. In our hands, the most consistent and reliable criterion for the early stage reversal was appearance of male germ line cells, clusters of "spermatogonial-like" cells. For the late stage, recognizable remnants of late-state oocytes had to be present. Some details of the histological changes that occur during early, middle, and late stages of reversal are also described. It is suggested that these results with hCG shed new light on the endocrine control of gonad reversal in T. bifasciatum.

Animals↗
PubMed1987

Sex reversal in wrasses. I. Uptake of testosterone by the gonads and the central nervous system and its aromatization in the CNS of Thalassoma duperrey (Teleostei: Labridae).

3H-Labelled testosterone, injected into the peritoneal cavity of T. duperrey is taken up by the central nervous system and the gonads. In the brain maximal uptake occurs within 1 to 2 h whereas maximal uptake in the gonads takes place within 1/2 to 1 h. Relatively large amount of radioactivity were eliminated into water: the elimination reached 8% of the injected dose in 4 h. The brain and the gonads are capable of aromatizing injected androgen, forming estrone, estradiol and more polar metabolites (i.e. containing more than 2 hydroxyl groups) and water soluble derivatives (possibly either the sulfates, or glucuronides). The uptake, and metabolism, may be higher in males as compared to females.

Animals↗
PubMed1985

Sex differentiation of somatic tissue in the unsexualised gonad primordia of the embryos of three species of poeciliid fish.

The structure of the gonad primordia is described in the embryos of three species of poeciliid fish. Prior to the sexualisation of the germ cells, a dimorphism exists based upon the gonadal somatic features. This serves as a basis for distinguishing between male and female specimens. Presumptive males are characterised by the presence in at least one of their gonad primordia of a conspicuous stalk whereas in presumptive females, a stalk is completely lacking.

Animals↗