Photoperiodic influence on the morphology and the androgen receptor level of the ventral prostate gland and seminal vesicles of the Djungarian hamster (Phodopus sungorus)

Photoperiod history-dependent responses to intermediate day lengths engage hypothalamic iodothyronine deiodinase type III mRNA expression

Perihypothalamic thyroid hormone signaling features prominently in the seasonal control of reproductive physiology. Triiodothyronine (T(3)) signaling stimulates gonadal development, and decrements in T(3) signaling are associated with gonadal regression. Type 3 iodothyronine deiodinase (DIO3) converts the prohormone thyroxine (T(4)) into biologically inactive 3,3',5'-triiodothyronine, and in long-day breeding Siberian hamsters exposure to long (LD) and short (SD) photoperiods, respectively, inhibit and stimulate hypothalamic dio3 mRNA expression. Reproductive responses to intermediate-duration photoperiods (IntD) occur in a history-dependent manner; IntDs are interpreted as inhibitory only when preceded by longer photoperiods. Because dio3 expression has only been evaluated under LD or SD photoperiods, it is not known whether hypothalamic dio3 encodes absolute photoperiod duration or the reproductive interpretation of photoperiod. Male Siberian hamsters with and without a prior history of LD were exposed to IntD photoperiods, and hypothalamic dio3 mRNA expression was measured 6 wk later. Hamsters with a LD photoperiod history exhibited gonadal regression in IntD and a marked upregulation of hypothalamic dio3 expression, whereas in hamsters without prior exposure to LD, gonadal responses to IntD were absent, and dio3 expression remained low. Patterns of deiodinase expression in hamsters maintained in chronic IntD photoperiods did not appear to reflect feedback effects of gonadal status. Hypothalamic expression of dio3 does not exclusively reflect ambient photoperiod, but rather the context-dependent reproductive interpretation of photoperiod. Neuroendocrine mechanisms that compare current and prior photoperiods, which permit detection of directional changes in day length, occur either upstream, or at the level, of hypothalamic dio3 expression.

Sexual dimorphism and seasonal variation in submandibular gland histology of Bolomys lasiurus (Rodentia, Muridae)

Wild rodents (Bolomys lasiurus) of both sexes were caught in a cerrado grassland area during the dry (July-September) and rainy (January-March) seasons of Brazil. Fasted animals were perfused with Karnovsky fixative through the left ventricle, under ether anesthesia, and the submandibular gland was processed for embedding in historesin. Histological and histometric data show sexual dimorphism at both seasons. In the volume percentage of the granular convoluted tubules (GCT) and their secretory granules, the males exhibited higher values. The absolute volume occupied by these structures, however, was dimorphic only in the rainy season. The diameter of the GCT, the height of its epithelium, and its total length were also greater in males during the rainy season. The absolute volumes of the acini and of the ductal tree were identical in both sexes in the dry and rainy seasons but the acinar diameter increased in the males and females during the rainy season. The sexual dimorphism and the seasonal variations now described in the B. lasiurus submandibular glands could be explained by the augmented reproductive activity of the males in the rainy period.

Dynamics of the seminal vesicle epithelium

In newborn rodents, seminal vesicle epithelium (SVEP) cells display a poorly developed rough endoplasmic reticulum (RER) and Golgi complex, and they show no signs of secretion. From puberty onward, secretory material starts to appear, and the RER and Golgi complex progressively develop and reorganize until the adult ultrastructure is established around 40-60 days of age. Multivesicular bodies and lysosomes follow in this development but lysosomes evolve to lipofucsin granules with aging. The duration of the secretory cycle in SVEP cells is shorter than in other exocrine cells and the secretory protein pattern depends on the animal species, androgen status, and sexual activity. SVEP cells are also involved in endocytosis, which is coupled to exocytosis, and their endocytic pathway intersects the exocytic pathway in Golgi cisterns. The structure and function of SVEP cells depends mainly on testosterone, but other hormones and factors, such as the neuropeptide VIP, also influence their activity. Castration leads to programmed death and regression of SVEP cells to an extent that depends on the animal species. In addition, castration induces changes in the secretory protein pattern and delays its intracellular transport. Endocytic kinetics is also delayed following castration. Primary cultures of SVEP cells in a bicameral system are proposed as a model to investigate the activities of SVEP cells further.