Testicular regression in response to food restriction and short photoperiod in white-footed mice (Peromyscus leucopus) is mediated by apoptosis

Short day lengths or reduced food availability are salient cues for small m ammals that breed seasonally. Photoperiod-mediated gonadal regression in wh ite-footed mice (Peromyscus leucopus) is a slow, orderly process that invol ves testicular apoptosis. Testicular regression in response to restricted c aloric intake is relatively rapid, and it is generally reversed quickly by ad libitum (ad lib) feeding. To determine the contribution of apoptotic cel l death during food restriction, and to examine possible interactions with photoperiod, mice housed in long (16L:8D) or short (8L:16D) photoperiods we re fed either ad lib or 70% of their average ad lib intake. Testes were rem oved at 2, 4, 6, or 8 wk of experimental treatment. Apoptotic activity was determined by in situ TUNEL labeling and assessment of DNA laddering. Signi ficant (P < 0.05) gonadal regression in response to short days was first de tected at 8 weeks in mice fed ad lib. Food-restricted, long-day mice also s howed significant testicular regression at 8 wk. Combined exposure to short day lengths and food restriction resulted in significant testicular regres sion at 6 wk (P < 0.05). TUNEL labeling was slightly, though significantly, elevated in germ cells at 2 and 4 wk in long-day food-restricted mice (P < 0.05). TUNEL labeling was also elevated in short-day food-restricted males at these early times but then increased nearly 5-fold at 6 and 8 wk in the se mice (P < 0.001). DNA laddering confirmed elevated apoptosis. Overall ap optotic activity negatively correlated with paired testis mass, plasma test osterone, and spermatogenic index measurements in both ad lib and food-rest ricted males. Few histological markers of necrotic cell death were observed in any group. Taken together, these results suggest that testicular regres sion in response to limited caloric intake or short days is mediated by apo ptosis.