Comparative morphology of the pituitary gland in Australian flying foxes (megachiroptera: genus Pteropus)

Abstract

Background: Investigations of reproductive endocrinology of flying foxes (genus Pteropus) have been hampered by inadequate information on the normal morphology of the megachiropteran pituitary. Methods: The novel technique of graphical three-dimensional (3-D) reconstruction, supported by more traditional anatomical techniques, have now been used to examine the shapes of, the interrelations between, the lobes of the pituitary of the little red flying fox, Pteropus scapulatus. Statistical analysis of data from three species tested whether there were changes in pituitary size with annual cycles in function, particularly with key stages of reproduction. Results: In the three species of Australian flying foxes examined, the hypophyseal cleft is closed; the pars intermedia extends over the rostral, ventral, and lateral surfaces of the neural lobe. The pars distalis is broad rostrally and extends over two-thirds of the lateral and ventral pars intermedia. The hypophyseal recess is broad at the median eminence, then narrows and extends through the infundibulum to, but not into, the neural lobe. In adult animals the pituitary weight was 10.0 ± 0.3 mg (mean ± s.e.) in P. scapulatus, 14.7 ± 0.5 mg in Pteropus poliocephalus (greyheaded flying foxes), and 18.7 ± 1.5 mg in Pteropus alecto (black flying foxes). Pituitary weight was not significantly affected by reproductive stage. Conclusions: Thus histologically, the adenohypophysis and neurohypophysis are similar to those of other mammals. Comparative differences in pituitary size reflected differences in species body size rather than cyclical reproduction.