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Biomedical subjects

W B Neaves

Publications and source records attributed to W B Neaves.

At least 37 records · Page 2Linked to original sources
PubMed1982

The chorioallantoic placenta of the spotted hyena (Crocuta crocuta Erxleben): an electron microscopic study.

The histology and ultrastructure of the chorioallantoic placenta of the spotted hyena have been studied in three specimens obtained in the field and fixed promptly with glutaraldehyde. Observations revealed that the interhemal membrane at its minimal thickness is hemomonochorial, consisting of a continuous layer of syncytial trophoblast, a basal lamina, and fetal capillary endothelium. Cytotrophoblastic cells form a discontinuous layer beneath the syncytial trophoblast and are distinguished by the presence of numerous extracted lipid droplets in their cytoplasm. A network of extracellular spaces, incorrectly identified as cisternae of endoplasmic reticulum by earlier investigators, occurs beneath the maternal surface of the syncytial trophoblast. These spaces contain moderately dense, nonfibrillar material resembling the intrasyncytial lamina previously described only in the hemochorial placenta of certain bats. Hence, these spaces may contain remnants of maternal capillary basal lamina following displacement of the endothelium by extensions of syncytial trophoblast at an early stage of placental development.

Allantois↗
PubMed1981

The steroidogenic capacity of the aging rat testis.

Factors bearing on the steroidogenic capacity of the aging testis have been examined in Sprague-Dawley rats between 3 and 24 months of age. Neither the number nor the binding affinity of testicular receptors for 125I-hCG changed with age. The ability of the aging testis to synthesize cholesterol from octanoate was similarly undiminished. Testicular conversion of cholesterol to pregnenolone, the gonadotropin-responsive, rate-limiting portion of the androgenic pathway, remained near young adult levels with advancing age. The rate at which the testis converted pregnenolone to testosterone actually increased by almost 25% in the oldest rats. Hence, the steroidogenic capacity of the Sprague-Dawley rat testis does not decline with advancing age.

Aging↗
PubMed1981

The androgen status of aging male rats.

In male Sprague-Dawley rats between 3-24 months of age, plasma concentrations of testosterone declined by more than 50% while concentrations of LH in plasma remained relatively constant. During the same interval, body weight rose almost 50%, suggesting that total circulating amounts of testosterone, assuming a proportional expansion of plasma volume, remained relatively constant with increasing age and that total LH in the circulation actually increased in older rats. This assumption was justified by demonstrating that blood plasma volume increased in proportion to body weight over the range of ages and weights represented by rats in this study. Plasma testosterone levels achieved after the injection of gonadotropin were significantly lower in the oldest rats, but when adjusted for increased plasma volume, total testosterone added to the circulation in response to injected gonadotropin did not diminish with age. Age-related change was not detected in testosterone secretion by decapsulated rat testes, either under control conditions or after the addition of gonadotropin to the incubation medium. The average volume of individual Leydig cells remained near young adult values with advancing age, while the total number of Leydig cells per testis rose slightly in the oldest rats. Hence, diminished androgen status in old rats could not be attributed to functional or numerical deficits in the Leydig cell population. Instead, low plasma testosterone levels may have resulted from two interrelated extratesticular phenomena, dilution of secreted hormone with the expanded volume of plasma in a significantly larger body mass, and failure of LH levels to rise sufficiently to stimulate additional testosterone secretion. (Endocrinology 108: 712, 1981)

Aging↗
PubMed1980

Exchange of skin grafts among monozygotic quadruplets in armadillos.

Skin grafting experiments, with long-term follow-ups, on three litters of armadillo quadruplets born in our laboratory have confirmed the familiar rule that grafts exchanged between monozygotic littermates are not rejected as a consequence of alloimmune reactions. A possible explanation of the striking discrepancy between the present findings and those of a previous study is uncertainty about the relationships of the previous animals, which were obtained from a commercial dealer at 10 days of age.

Animals↗
PubMed1980

The relationship of biopsy evaluations and testicular measurements to over-all daily sperm production in human testes.

Enumeration of homogenization-resistant spermatids in testicular homogenates provided a rapid and precise means of characterizing human spermatogenesis in quantitative terms. This technique was applied to simulated biopsy specimens as small as 10 mg of testicular parenchyma and yielded values for daily sperm production per gram of testicular parenchyma (DSP/gm) that were highly correlated with over-all DSP/gm values for paired testes (r = +0.86) and DSP/pair of testes (r = +0.93). In 12 autopsy cases representing a 100-fold range of sperm production rates, the average difference between DSP/gm values obtained from simulated biopsy specimens and from entire testes was not significantly different from zero (P < 0.05). The small amount of testicular parenchyma required for this determination indicated that both DSP data and routine histologic observations can be collected from the material included in a conventional testicular biopsy. Various measurements related to testicular size were positively but weakly correlated with DSP/testis (values for r ranged from +0.45 to +0.66). Hence, testicular size was a relatively poor index of sperm production in this study.

Adolescent↗
PubMed1980

Sexual dimorphism of the phallus in spotted hyaena (Crocuta crocuta).

The weight of the skinned phallus and the diameter of its shaft and glans did not differ significantly in the two sexes of spotted hyaena, but phallus length was greater in males. The urethra of the penis was surrounded by corpus spongiosum, while the urogenital canal of the clitoris was suspended beneath the erectile bodies in loose connective tissue, an arrangement compatible with dilatation of the canal during copulation and parturition. The average width of the phallic meatus in juvenile females exceeded that in males of any age and, in adults, the clitoridal meatus was > 10 times the width of the penile meatus. A robust retractor muscle situated dorsal to the urogenital canal further distinguished the clitoris from the penis; this muscle may play an important role in facilitating copulation.

Animals↗
PubMed1979

The annual testicular cycle in an equatorial colony of lesser rock hyrax, Heterohyrax brucei.

Adult males from a colony of lesser rock hyrax found near the equator in Kenya exhibited an annual cycle of testicular activity characterized by intense spermatogenesis and elevated androgen status from May to July. Average masses of testes and seminal vesicles taken in these months were almost fourfold greater than those from September to January. During the months of peak testicular activity average diameters of Leydig cells and seminiferous tubules were increased by approximately one half and total tubule length was doubled, compared with values for the quiescent months. Variable testicular development occurred during transitional intervals preceding and following peak testicular activity. From February to Aril thickening of the seminiferous epithelium and appearance of spermatozoa in the caput epididymidis signalled re-establishment of sperm production. In August shedding of germinal cells from the epithelium heralded impending failure of spermatogenesis. Evidence of an annual testicular cycle contradicted the prevalent belief that equatorial hyrax breed all year and suggested that the testicular cycle is a conservative element of hyracoid reproductive strategy.

Animals↗
PubMed1979

The lymphatic drainage of the rat prostate and its status as an immunologically privileged site.

Recent suggestions that the rat prostate is an alymphatic, immunologically privileged site stimulated further investigation of its status using a variety of techniques. Fixation of certain organs by vascular perfusion of glutaraldehyde followed by plastic embedding avoids the distortion and stromal reorganization that often obscures evidence of lymphatic vessels in conventional histological preparations. When applied to the rat prostate, this technique revealed small lymphatic vessels at irregular intervals throughout the sparse stroma. Ink injected into the prostate drained from the organ into iliac lymph nodes within 3 to 4 hr. Enlargement of iliac lymph nodes within 1 week after injection of parental strain lymphoid cells into the prostate of F1 rats confirmed the drainage pattern. Ink and lymphoid cell injections into the bladder wall yielded comparable results, although ink reached iliac nodes sooner than it did in prostate injections. Immunological privilege was investigated by determining survival of skin allografts implanted in the prostate. Skin-into-prostate grafts bearing either major or minor histocompatibility antigens were rejected within a few days of similar orthotopic grafts. The inability of the rat prostate to allow significantly prolonged allograft survival as well as its demonstrated lymphatic drainage argues against an immunologically privileged status.

Animals↗
PubMed1978

Attrition of the human Leydig cell population with advancing age.

Existing evidence suggests that the aging human male experiences a gradual decline in testosterone production, a phenomenon that should be reflected in the Leydig cell population of the testis. It has been proposed that Leydig cells diminish in number with increasing age, but conflicting claims characterize reports of this topic. We have reinvestigated this possibility by histometric analysis of perfused testes from 25 men ranging from 18 to 87 years of age. Average single Leydig cell volume (2,943 +/- 623 micrometer 3, X +/- S.D.) did not change significantly with increasing age (r = 0.24, P greater than 0.2), suggesting that surviving cells remain active. Total testis weight (43.5 +/- 13.9 g) also did not change with age (r = 0.04, P greater than 0.5). However, both total Leydig cell volume and the absolute number of Leydig cells per individual decreased significantly as functions of age (r = -0.71, P less than 0.002, and r = -0.61, P less than 0.005, respectively). Analysis of relationship between these two parameters indicates that the total volume of Leydig cell cytoplasm contained within the human testis is determined by the number of cells present. Our results show that a pair of young adult testes endowed with more than 700 million Leydig cells at 20 years of age may be expected to undergo an attrition rate of approximately 80 million cells per subsequent decade of life. Thus, Leydig cell attrition is an important correlate of declining androgen status in aging men.

Adolescent↗
PubMed1978

Clinical and endocrinological evaluation of patients with congenital microphallus.

Eight patients with congenital microphallus were investigated. Plasma luteinizing hormone, follicle-stimulating hormone, testosterone and androstenedione levels were obtained in all cases. In addition, the response to the administration of human chorionic gonadotropin, luteinizing horomone-releasing hormone and adrenocorticotropic hormone, the assessment of testicular histology by electron microscopy and the measurement of dihydrotestosterone formation by preputial skin were determined in some patients. The results of these studies were compared to similar studies in 6 normal prepubertal boys, 4 boys with bilateral cryptorchidism, 1 male infant with anorchia and 1 adult with hypogonadotropic hypogonadism. The clinical and endocrinological findings in the 8 patients with microphallus can be divided into 2 distinct categories. In 5 patients the disorder is familial, gonadotropin levels are low and there is a normal response to stimulation with chorionic gonadotropin. The data are compatible with the possibility that 3 (possibly 5) of the 8 patients with microphallus have hypogonadotropic hypogonadism. In the other group the cases are sporadic, serum luteinizing hormone and follicle-stimulating hormone levels are elevated and plasma testosterone failed to increase after short-term treatment with chorionic gonadotropin. In these patients a primary testicular disorder appears to be responsible. Experimental and clinical evidence suggests that microphallus results from defective testicular function during the second and third trimesters of pregnancy, either as the result of defective gonadotropin secretion or defective androgen synthesis.

Adolescent↗