Anita K. Pearson

Effects of mammalian gonadotropins (FSH and LH) on the testes of the lizard Anolis carolinensis

Responses of the testis to mammalian FSH and LH were examined in the lizard Anolis carolinensis at different times of year and at different temperatures. Small amounts of FSH (0.1 mU/day) maintain testis weight and the accessory structures (epididymis and sex segment of kidney) and promote the development of new germ cells in surgically hypophysectomized lizards at 31° during the spring. Ovine LH has the same actions but much higher doses are required. With testosterone the rate of posthypophysectomy regression is reduced but no new germ cells develop. Both ovine FSH and LH stimulate spermatogenesis and interstitial cell activity in “physiologically” hypophysectomized Anolis at 31° in the fall. The development of accessory sexual structures requires a higher dose of gonadotropin than does complete spermatogenesis; only the early stages of spermatogenesis—up to the spermatid stage—occur with low doses of gonadotropin. Comparison of several preparations of ovine gonadotropins (from NIH and Papkoff) indicates that the potency of FSH is many hundred times greater than that of LH with regard to the stimulation of spermatogenesis and interstitial cell activity in the lizard. At 20°, the high doses of gonadotropin required to initiate the development of accessory sexual structures cause an abnormal—edematous—response in the germinal epithelium. Normal spermatogenic recrudescence at 20° is mimicked best by a relatively low dose of gonadotropin which does not promote interstitial cell activity. The observed thermal effects and differential dose sensitivity of various testicular responses suggest that annual cycles of spermatogenesis and interstitial cell activity in reptiles may result from variations in the level of a single gonadotropin (or gonadotropic-complex). A scheme is proposed whereby low temperatures suppress circulating gonadotropins so that only the early stages of spermatogenesis occur, while increased temperatures elevate gonadotropin production which leads to the development of accessory sexual structures and spermiation.

Biology of the bamboo Chusquea culeou (Poaceae: Bambusoideae) in southern Argentina

Over a period of 7 years the biology and phenotypic variability of Chusquea culeou were studied at 5 locations in cool temperate forests of southern Argentina. Excavated rhizomes had an average of 1.1 successful rhizome buds, and an average of 2.1 years elapsed between successive generations of rhizomes. Rhizome buds usually develop within the first four years after a rhizome forms. Height, volume and weight of a culm can be calculated from its diameter 1 m above the ground. Culm size, length of foliage leaf blades, and pattern of secondary branching differed among study sites. Dead culms were numerous and commonly remained erect for more than 7 years after dying. New culm shoots appear in spring and reach full size within a few months. Shoots can grow more than 9 cm/day. Less than half of the shoots survived a year; most were killed by moth larvae. Multiple primary branch buds emerge through the culm leaf sheaths in the second spring. The mean number of branch buds at mid-culm nodes varied between 34.8 and 81.5, and the mean number of primary branches was between 22.8 and 40.8. Number and length of branches, and number and length of foliage leaf blades at each node is related to the position of the node on a culm. Most branches grow about 3 cm and produce 1 to 3 foliage leaves annually. Foliage leaf blades generally live 2 years or more; few survive 6 years. Relative lengths of foliage leaf blades and their spacing along a branch permit recognition of annual cohorts. Both gregarious and sporadic flowering have been reported, and every year a few isolated plants flower and die. Length of the life cycle is unknown. Seedlings require up to 15 years to produce culms of mature size. Foliage branches may live more than 23 years, and culms may survive 33 years. Extensive loss of new shoots to predation suggests that gregarious flowering may be driven by a need to escape parasitism. C. culeou clumps expand slowly. Average annual rate of increase of the number of live culms in a clump was 4.6%. Methods of seed dispersal are undocumented. A dense stand of Chusquea culeou had an estimated phytomass of 179 tons/hectare (dry weight), 28% of which was underground. Net annual production was about 16 t/ha dry weight.

Morphology and immunocytochemistry of the turtle pituitary gland with special reference to the pars tuberalis

SummaryExamination of pituitaries from young and adult turtles representing four families, reveals that in addition to the abundant juxtaneural pars tuberalis (JuxPT) found in this class of reptiles, there is generally a substantial amount of pars tuberalis (PT) tissue closely associated with the pars distalis (PD). The PT forms a cortical layer especially conspicuous around the anterior tip of the PD in some species (Trionyx, Kinosternon, Sternotherus), or it forms a thick dorsal layer of tissue irregularly extending onto the sides of the PD in others (Pseudemys, Chrysemys, Lepidochelys, Chelonia).Immunocytochemical studies using unlabelled second antibody and peroxidase-antiperoxidase reveal that in turtles of all ages, the PT tissue allied with the PD (the PTinterna) is composed primarily of cells containing glycoprotein hormones (FSH, LH and TSH), especially the gonadotropins. The juxPT, however, consists mainly of secretory cells unstained by the antisera tested and includes only a small number of gonadotropes and thyrotropes. Although usually widely distributed in the testudinate adenohypophysis, the great majority of gonadotropes and thyrotropes present in the hatchling are in the PTinterna. It is probable that a concentration of these cells in the PTinterna is widespread among vertebrates.In all turtles examined, lactotropes occur principally in the anterior and ventral part of the PD proper; somatotropes are posterior and dorsal. Corticotropes are concentrated as the lactotropes in the anterior PD, but some are also scattered throughout the posterior half of the gland. Lactotropes, corticotropes, and with a few exceptions, somatotropes, do not occur in PT tissue in the turtle.

A stereological analysis of the ultrastructure of the lungs of wild mice living at low and high altitude.

Stereological analysis of the ultrastructural composition of the pulmonary alveolo‐capillary region of mice living at sea level compared with that of the same species (Phyllotis darwini) genetically adapted to life at 4,660 m reveals a trend at high altitude towards a greater volume percentage of tissue components. On a weight‐specific basis, non‐circulating tissue occupies a significantly greater volume in high‐altitude mice, but air space and capillary contents are not correspondingly greater. Since the arithmetic mean thickness of the tissue layers and of the air‐blood barrier are the same in the two altitudinal groups, the average alveolus must have a smaller volume in the high‐altitude mice.

Ultrastructure of the pars distalis of the lizard Anolis carolinensis with special reference to the identification of the gonadotropic cell

SummaryFive categories of granulated cells were distinguished by their ultrastructural features, and quantitative analyses were made of the pars distalis cells in normal and castrated lizards. The gonadotropin-producing cell was identified on the basis of its uniform distribution in the gland as well as from cytological changes resulting from castration. The secretory granules of the gonadotropic cell vary in size (100–500 mμ) and density, and lipid bodies are commonly present. Following castration, the endoplasmic reticulum proliferates, forming many small, rough-surfaced, dilated cisternae which do not coalesce greatly as in other vertebrate species. Degranulation is accompanied by hypertrophy and hyperplasia of the mitochondria and by the appearance in the cytoplasm of conspicuous clusters of microfilaments. The designated gonadotropic cell was the only class of secretory cell showing consistent changes following three weeks of castration.In addition to the uniformly distributed gonadotrope cell, two secretory cells occur mainly in the rostral half of the gland, and two in the caudal half. Tentative identification of the cell types is discussed in the light of available information on the localization of the hormones in the pars distalis of this species.

Ontogeny and immunocytochemical differentiation of the pituitary gland in a sea turtle, Caretta caretta

SummaryIn the sea turtle Caretta caretta the dorsal wall of the pituitary anlage and the apex of the hypophyseal angle are derived from stomodeal epithelium adherent to the neural epithelium of the diencephalon; a substantial part of the ventral wall of the anlage is derived from epithelium of mixed origin (stomodeum and foregut). Distribution of immunoreactive cells in the embryonic gland suggests that pituitary peptide hormones (adrenocorticotropin, ACTH; melanotropin, MSH; prolactin, PRL; growth hormone, GH) are synthesized in cells from the dorsal wall, while cells producing glycoprotein hormones (luteinizing hormone, LH; thyrotropin, TSH) trace their lineage to ventral and ventrolateral areas of the anlage that include some endoderm.Mesenchymal movements mold the epithelial anlage in two steps, delineating first the posterior and subsequently the anterior area of the gland. During the former process the lateral lobes are defined, and material immunoreactive with antiserum to ACTH appears in epithelial cells of presumptive pars distalis (PD) and pars intermedia (PT). Delineation of the anterior end of the pituitary gland occurs as the hypophyseal stalk forms, approximately one-fourth through ontogenesis. Shortly thereafter, immunoreactions demonstrate synthetic activity of distinctively distributed cells containing ACTH, PRL, GH, LH and TSH.In Caretta the lateral lobes of the pituitary anlage give rise to a distinct layer of tissue around the PD (pars tuberalis interna, PTint) and a thick layer on the floor of the hypothalamus (juxtaneural pars tuberalis, juxPT). In the pituitaries of late embryos, juxPT tissue proximal to the PD contains many cells immunoreactive with LH antiserum; whereas cells in distal areas of the juxPT do not react with any antisera tested. LH-cells also occur in large numbers in the PTint and in the posterior PD where tissues of the partes tuberalis and dístalis are continuous. Cells reactive with antiserum to TSH are found in small numbers in the PTint, and in larger numbers along with the LH-cells in the posterior PD. PRL-cells occur in the anterior PD, GH-cells in the posterior. ACTH-cells are found primarily in the anterior two-thirds of the PD.

Embryonic differentiation of the pituitary in a snake (Thamnophis brachystoma)

SummaryThe adenohypophysis of Thamnophis is produced from the stomodeal epithelium in two steps: a diverticulum, enlarging by addition of epithelium to its basal end, defines the posterior end of the gland, and a subsequent infolding promoted by mesenchymal movements occurs in epithelium anterior to the original diverticulum and forms the anterior end of the anlage and the hypophyseal stalk. Immediately thereafter the pars intermedia (PI) is demarcated, first by a luminal, subsequently by an external constriction, and secretion granules are found in the gland. At this time granulated cells are rare in the PI, and in the pars distalis (PD) they are more frequent in the anterior end. Secretion granules occur in cells away from the surface of the residual lumen; the lumen is lined by presumptive stellate cells. The early appearance of secretion granules in cells of the embryonic pituitary, and the presence in the hypophyseal stalk of both mucussecreting cells and cells with granules similar to those of the PD suggest that some differentiation occurs in the stomodeal epithelial cells before the definitive pouch is formed.The absence of lateral lobes in the embryonic hypophysis precludes the development of the pars tuberalis in Thamnophis.

Granular pneumocytes and altitude: a stereological evaluation.

SummaryStereological analysis demonstrates that the granular pneumocytes of mice native to high altitude (4660 m) are significantly larger than those of the same species (Phyllotis darwini) living at sea level. Such cells have larger nuclei and a significantly greater volume of mitochondria. There are both more and larger lamellar bodies in high altitude granular pneumocytes, resulting in about four times more surfactant per cell at high altitude.

The double nucleus of the sertoli cell in the lizard Anolis carolinensis

Over 90% of the Sertoli cells in the testes of adult lizards (Anolis carolinensis) are binucleate. The nuclei occur in closely associated pairs in the basal cytoplasm of the Sertoli cells that line the testis tubules. The two nuclei of a pair are of similar volume, and each usually contains one conspicuous rounded nucleolus. The average volume of individual nuclei varies from 367.8 microm(3) in spermatogenically active testes in March to 172.5 microm(3) in September, when testes are regressed. The irregular shape of the Sertoli nuclei is particularly pronounced during testicular regression. Until initiation of spermatogenesis in hatchling lizards, Sertoli cells have a single nucleus containing patches of hetcrochromatin. With the appearance of prophase stages of primary spermatocytes, a few paired Sertoli nuclei can be found, and the nuclei increasingly exhibit the homogeneous euchromatic nucleoplasm of the adult. The average volume of individual nuclei in lizards under 4 months of age is less than a third the volume of Sertoli nuclei in reproductively active adults. The appearance of binucleate cells at this time documents a doubling of the amount of desoxynucleic acid in Sertoli cells preparatory to their growth and expanded functions during spermatogenesis.

Endocrine Function and Reproductive Impairment in an Irradiated Population of the Lizard Uta stansburiana

This study describes gonadal changes in lizards (Uta stansburiana) exposed to chronic low levels of γ radiation (1.5-10 R/day) under field conditions and attempts to evaluate endocrine involvement in these changes. Reproductive impairment in irradiated males is demonstrated during the breeding season by reduced testes weights and by seminiferous tubules devoid of germ cells. Ultrastructural morphology of Leydig cells, plasma testosterone levels, and developed accessory sex structures indicate normal steroidogenesis in such males; cytology of the pituitary gonadotropes and pituitary gonadotropin content indicate normal gonadotropin levels. These findings suggest that low levels of radiation affect the spermatogenic process directly, rather than through damage to the pituitary. Comparable irradiation causes complete resorption of ovarian tissue in some female Uta. The oviducts are atrophic and the pituitary gonadotropes hyperactive. Resemblance of gonadotropes to those of castrated animals and reduced pitui...