Testicular apoptosis is down-regulated during spontaneous recrudescence inwhite-footed mice (Peromyscus leucopus)

Among individuals of many nontropical species, seasonal breeding is timed b y tracking changes in the daily photoperiod. Transfer of rodents to short ( < 12 h of light/day) day lengths for 6 to 14 weeks can induce regression of the testes mediated by apoptosis. After 16 to 20 weeks of short day exposu re, reproductive function is "spontaneously" initiated, and testicular recr udescence is observed. The gonadal mechanisms that underlie testicular recr udescence are not fully understood. If the onset of testicular regrowth tha t occurs during spontaneous recrudescence reflects a down-regulation of apo ptotic signals, then a decline in apoptosis should be noted concurrent with increased testis mass. This experiment sought to assess the role of apopto sis in the restoration of reproductive capacity to photoperiod-inhibited wh ite-footed mice. Males were assigned to long (16:8 LD) or short (8:16 LD) p hotoperiods for 0,14,18,22,26, or 30 weeks. At each of these time points, t estis mass and testosterone concentrations were assessed. In addition, apop totic activity was measured using both in situ terminal deoxynucleotidyl tr ansferase dNTP end labeling (TUNEL) and DNA laddering. Short photoperiod ex posure induced maximal decreases in testicular parameters after 14 weeks (p < 0.05). After 26 weeks of short days, testis mass was no longer different between males housed in long days and those housed in short days. In contr ast, the high incidence of apoptotic TUNEL labeling and DNA laddering obser ved at 14 weeks was reduced to long day values after 22 weeks of short day exposure. Together, our results establish that a decrease in testicular apo ptosis coincides with testicular recrudescence in white-footed mice. The cu rrent study demonstrates a decline in the incidence of testicular cell deat h concomitant with changes in testis mass or length, elucidating a timeline of changes at the cellular level related to the onset of recrudescence.