Abstract: 60

APOPTOSIS MEDIATES TESTICULAR REGRESSION INDUCED BY PHOTOPERIOD OR FOOD RESTRICTION IN WHITE-FOOTED MICE.

Kelly A. Young¹ , Barry R. Zirkin^{1 *}, Randy J. Nelson^{1 2 *}
Department of Biochemistry, Divison of Reproductive Biology, The Johns Hopkins School of Hygiene and Public Health, Baltimore, MD USA ¹
Departments of Psychology and Neuroscience, The Johns Hopkins University, Baltimore, MD USA ²

Many temperate-zone rodents breed seasonally. Exposure to simulated winter conditions including restricted food intake or short photoperiod can trigger germ cell loss and cause testicular regression. Regression induced by short photoperiod in white-footed mice (Peromyscus leucopus) is a 10-12 week process. Food restriction interacts with photoperiod, resulting in a faster atrophy of the testis. The mechanisms by which germ cells are lost in response to the combined cues of limited food intake and short photoperiod remain unspecified. To determine if testicular regression induced by short days, food restriction, or both, was due to apoptosis, necrosis, or a combination, ad-lib fed or 30% food-restricted white-footed mice were exposed to either long (16L:8D) or short (8L:16D) photoperiods for 2, 4, 6, or 8 weeks. Apoptotic activity was determined by terminal transferase end labeling (TUNEL) and quantitative 3’-end autoradiography (laddering) of apoptotic DNA fragments. Necrotic death was determined by histological examination of morphological alterations typical of necrosis. At Week 8, relative testis mass decreased 47.7% in short day ad lib males and 74.0% in food-restricted short day males as compared to long day ad lib-fed males (p< 0.05). TUNEL labeling in food restricted short day males was increased at Week 8 by 37.0% and 86.0% as compared to ad lib males in short or long days, respectively (p< 0.05). DNA laddering confirmed increases in apoptosis. Few histological indicators of necrosis such as swollen cells or macrophage presence, were observed in any group. Thus, apoptotic cell death appears to mediate testicular regression in response to short photoperiod, and apoptosis is further increased when food restriction is combined with short days.

    This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.