Ultrastructural aspects of the follicular cells of the pars tuberalis in bats related to the seasonal cycle

The Chiropteran Brain Database: Volumetric Survey of the Hypophysis in 165 Species

For nearly two decades, a database of brain structures from a large sample (272 species) of chiropterans has been widely accessible and used for socioecological analyses of mammals. However, this database remains incomplete since the hypophysis has not been measured. Since this glandular/neural structure has reproductive significance to chiropterans as for other mammals, this investigation was carried out using serial coronal sections of bat brains comprising the Heinz Stephan collection, Düsseldorf, Germany. Complete serially sectioned brains were examined in 313 individuals (165 species, 15 families). Using a well-documented method, hypophyseal volumes were determined from every fourth or sixth section in each individual. The strongest correlation was between body weight and the hypophysis (R(2) = 0.887) and its various components as well as between body weight and adenohypophysis (R(2) = 0.830) and neurohypophysis (R(2) = 0.925). Correlations were also strong for brain weight-adenohypophysis (R(2) = 0.817) and brain weight- neurohypophysis (R(2) = 0.911). Results indicated that: (1) in regression analyses, hipposiderids stand apart as having relatively large adenohypophysis; (2) analysis of residuals generated using least-squares regression of hypophyseal components suggests a trend among microchiropterans where females have a relatively larger adenohypophysis than males. However, this difference is only statistically significant in the largest samples: Phyllostomidae and Vespertilionidae. Pteropodids do not appear to follow this trend. Our findings suggest both phylogenetic and sexual differences in the adenohypophysis in particular, and indicate the need for investigation of larger samples by species, especially those best understood in reproductive and social biology.

Extracellular accumulations in the avian pituitary gland: histochemical analysis in two species of Indian wild birds

Extracellular accumulations of two distinct types, colloid-filled follicles and fibrous-material-containing cysts, were observed in the pituitary gland of two species of Indian wild birds, Halcyon smyrnensis perpulchra and Lonchura striata striata. Colloid follicles were regular structures and distributed throughout the pars distalis (PD). The fibrous cysts were irregular structures, bigger than the colloid follicles and mostly observed towards the ventral margin of the PD. Sometimes disruption of the outer margin with depletion of fibrous material from the cavity was observed. Hormone-secreting cells of various types, anti-adrenocorticotropic-hormone-, anti-prolactin-, anti-growth-hormone- and anti-luteinizing-hormone-immunoreactive cells were encountered bordering both the colloid follicles and fibrous cysts. Neither the colloid nor the fibrous material showed any immunoreaction to any of the pituitary hormone antisera. On histochemical staining colloid was positive to periodic acid-Schiff (PAS) and fibrous materials stained with Alcian blue-PAS-orange G staining. Colloid depositions in the pituitary gland of these two wild birds were correlated to age, more in numbers in the adult birds than in the young ones. Fibrous-material-containing cysts were elucidated in the pituitary gland of adult birds only. These were more prevalent in the pituitary of reproductively active birds. Regular morphology of the colloid follicles, overall distribution in the adenohypophysis and dense nature of deposition of the colloid suggest the accumulation of this type may be the secretory products of both granulated and agranulated pituitary cell types. Absence of immunoreactivity of the colloid against pituitary hormone antisera points out that the storage form may differ chemically from the bioactive hormones. The spatial distribution of fibrous-material-containing cysts mostly towards the ventral PD, observations of immunoreactive cell fragmentations inside the cysts, and their disrupted margins suggest these structures may have some role in discharging the intraglandular degradation products.