Effects of age and photoperiod on reproduction and the spleen in the marsh rice rat (Oryzomys palustris).

To examine the interactions between age and photoperiod on reproduction and spleen weights, we exposed adult male and female rice rats of various ages to photoperiods of 16:8-h light-dark photoperiods (16L:8D) or 12L:12D. After 10 wk, animals were killed and the following data were recorded: weights of testes, seminal vesicles, uterus, ovaries, body, and spleen and, in addition, vaginal patency. Young adult males displayed a greater degree of testicular and seminal vesicle regression in short photoperiods than did older males; the testes of most older males did not regress in response to short photoperiods. Spleen weight was unresponsive to short photoperiods in all males, but was affected by age. Females, however, exhibited reproductive organ regression and decreased vaginal patency in response to short photoperiods at all ages examined. Body weights were affected by photoperiod in young females, and, as in males, photoperiod had no effect on spleen weights. These data suggest that the reproductive response to photoperiod in adult male rice rats declines with age, whereas in adult females it does not.

Humanitarian aid operations in Republica Srpska during Operation Resolute 2.

The humanitarian aid experience of a unit in Bosnia is described. Data are presented for primary care clinics undertaken, showing the range of conditions and age of patients seen. The role of the civilian aid agencies involved is described, together with recommendations for future training requirements for similar operations.

Pineal gland and melatonin affect testicular status in the adult marsh rice rat (Oryzomys palustris).

The effects of the presence or absence of the pineal gland and of melatonin administration were examined on testicular maintenance, regression, and recrudescence in adult male rice rats. Pinealectomy at the beginning of the study caused significant testicular regression in animals housed on both long (16L:8D) and short (12L:12D) photoperiods (Experiment 1). Sham-operated males maintained testicular weight on 16L:8D and underwent testicular regression on 12L:12D. The magnitude of testicular regression in pinealectomized animals was reduced relative to that of sham-operated animals housed on a short photoperiod and occurred on a different time course. Animals pinealectomized after testicular regression had occurred on 12L:12D demonstrated delayed photostimulated testicular recrudescence when housed on 16L:8D, while spontaneous testicular recrudescence was unaffected in animals maintained on 12L:12D (Experiment 2). Administration of melatonin via subcutaneous implants at the beginning of the study (Experiment 3) produced similar effects on testicular function attributed to pinealectomy in Experiment 1. Finally, melatonin implants administered after the testes regressed on 12L:12D delayed both photostimulated and spontaneous testicular recrudescence in animals housed on long or short photoperiods, respectively (Experiment 4). These results suggest a role for both the pineal gland and melatonin at various stages of the annual reproductive cycle of the male rice rat.

Effects of prenatal and postnatal photoperiods and of the pineal gland on early testicular development in the marsh rice rat (Oryzomys palustris).

Prepubertal male rice rats are responsive reproductively to photoperiod early in postnatal development. Testicular growth was inhibited in animals gestated and reared to 28 days of age on photoperiods ranging from 8 to 13 h of light per day, and stimulated in animals reared on 14 h or more of light per day, suggesting a critical photoperiod between 13 and 14 h for testicular growth. In addition, postnatal photoperiod markedly affected testicular development in animals exposed to various prenatal and postnatal photoperiods. Postnatal exposure to constant light unmasked effects of the prenatal photoperiod on testicular development. Exposure of rice rats to short or long photoperiods during the period of lactation (Days 1-14 of life) affected testicular maturation. In addition, alteration of the photoperiod experienced after Day 14 of life (post-lactational) markedly affected testicular development and was the primary factor determining whether maturation would occur. Finally, pinealectomy had little to no effect on the magnitude of testicular development in animals maintained on the presurgical photoperiod, but did prevent animals from demonstrating the appropriate testicular response to a new photoperiod after surgery. These data suggest that early testicular development in rice rats is affected by the prenatal and postnatal photoperiod and that the pineal gland is involved in the transduction of this environmental information.

Effects of photoperiod on pineal melatonin in the marsh rice rat (Oryzomys palustris).

Pineal melatonin content was examined under four different photoperiods (10L:14D, 12L:12D, 14L:10D, and 16L:8D) in adult female rice rats (Experiment 1). Pineal melatonin was basal during the light and increased beginning 1 hr after lights off. Within 2 hr after lights off, melatonin increased to levels that were maintained throughout the dark period. In all but one photoperiod (10L:14D), melatonin remained elevated prior to light onset and decreased markedly within one hour after lights on. In addition, the duration of pineal melatonin was inversely related to the length of the photoperiod. In Experiment 2, the time course of pineal melatonin content on 16L:8D was examined every 20 min during the first hour after lights off and the first hour after lights on. Melatonin content increased gradually during the first hour and decreased markedly within 20 min after lights on. These data show that pineal melatonin in female rice rats is regulated by photoperiod.

Photoperiod and melatonin affect testicular growth in the marsh rice rat (Oryzomys palustris).

Reproduction in rice rats is subject to photoperiodic control and the pineal gland mediates this effect. We examined the effects of the pineal gland hormone melatonin on testicular weight when administered via implants, injections, and infusions. Testicular weight was modified by photoperiod and the size of the melatonin implant. Twenty-millimeter implants suppressed testicular weight in rice rats housed on 12- and 16-hr photoperiods, while those housed on a 14-hr photoperiod were more sensitive to melatonin; in these animals 10- and 20-mm implants inhibited testicular weight. Melatonin implants also prevented rice rats from responding to a change in photoperiod with the appropriate alteration of testicular growth. Melatonin injections inhibited testicular growth when administered before lights out on LD 14:10, but not on LD 16:8. Morning injections had no effect on either photoperiod. Finally, 12-hr duration melatonin infusions inhibited testicular growth in pinealectomized rice rats on LD 16:8, while 6-hr duration infusions were without effect. These data show that the pineal, through the secretion of melatonin, is a phototransducing organ intimately involved in testicular growth in rice rats.

Effect of photoperiod on gonadal maintenance and development in the marsh rice rat (Oryzomys palustris).

Reproductive responsiveness to photoperiod was examined in adult and prepubertal rice rats. In Experiment 1, adult males on 16L:8D and 14L:10D maintained testicular size, while exposure to 12L:12D and 10L:14D resulted in testicular regression, followed by spontaneous testicular recrudescence. Adult females (Experiment 2) on long photoperiods had larger uterine and ovarian weights at most times examined and maintained vaginal patency compared to females on short photoperiods. Reproductive development of male rice rats (Experiment 3) was stimulated on 16L:8D and 14L:10D with rapid testicular development occurring by 12 weeks of age, while in males reared on 12L:12D and 10L:14D reproductive development proceeded slowly and was completed at approximately 26 weeks of age. Females on 16L:8D and 14L:10D experienced rapid uterine development compared to those on 12L:12D and 10L:14D. Ovarian weights on 14L:10D were significantly greater than ovarian weights on 12L:12D. Finally, vaginal patency was attained more rapidly on 16L:8D than on 14L:10D and was markedly inhibited on 12L:12D and 10L:14D. These data show that reproduction in adult male and female rice rats is regulated, at least in part, by photoperiod and that reproductive development in juveniles is also under photoperiodic control.