Laboratory rats are considered to be reproductively unresponsive to photoperiod because photoperiod treatments do not induce robust reproductive responses. Groups of 15 young male Fischer 344 (F344) rats were tested for effects of long (16L:8D) and short (8L:16D) photoperiods on testicular development and body mass. Two weeks of short photoperiod inhibited testicular growth, spermatogenesis, and increases in body weight. Testis size became refractory to short photoperiod after 8 wk, but the body weight was lower in short photoperiod for the full 10 wk of the study. In young Harlan Sprague-Dawley rats, in contrast, long and short photoperiod had no effect on either body weight or testis size. Pinealectomized F344 rats had significantly higher body weights and larger testes than did sham-operated controls, suggesting that the effects of photoperiod are mediated, at least in part, by the pineal gland. The F344 strain of laboratory rats is the first in which unmanipulated animals have been found to be robustly affected by photoperiod, indicating that this strain could be a valuable new model for the study of reproductive regulation by photoperiod.
Many temperate-zone species use photoperiod as an environmental cue to regulate reproductive timing. Strains of laboratory rats differ in their responsiveness to photoperiod, with the Fischer 344 (F344) strain being the most responsive known. F344 rats and closely related strains that differ in photoresponsiveness may be useful models to study the mechanisms and genetic basis for photoresponsiveness. We tested two hypotheses: (i) that melatonin mediates photoresponsiveness in F344 rats, as is the case in all other mammals tested, and (ii) that the location, abundance, or affinity of melatonin receptors, as estimated by the amount and location of binding of the radioligand 2-[125I]-iodomelatonin (IMEL) in the brain, might cause variation in photoresponsiveness among rat strains. Melatonin injections 1 h before lights off in a stimulatory photoperiod (L14 : D10) induced reproductive inhibition and reduced weight gain in a manner similar to short days of L8 : D16, while injections of ethanolic saline vehicle did not. Interestingly, melatonin injections administered during an inhibitory photoperiod (L10 : D14) caused greater inhibition of both reproduction and weight gain than short photoperiod alone. Pinealectomized F344 rats implanted subcutaneously with melatonin in a silastic capsule did not differ in testis size or body weight from controls with blank implants. The brains and pars tuberalis of the pituitary from photoresponsive F344 rats and nonphotoresponsive Harlan Sprague-Dawley (HSD) rats were processed for autoradiography using IMEL. We found significantly higher specific IMEL binding in the anterior and posterior regions of the paraventricular nucleus of the thalamus (PVNt) and reuniens nucleus of the thalamus of F344 rats than in the same areas in HSD rats. There were no differences between strains in specific IMEL binding in the medial PVNt, anteroventral and anterodorsal nucleus of the thalamus, suprachiasmatic nucleus, or the pars tuberalis. These results indicate that melatonin mediates photoresponsiveness in F344 rats. In addition, they provide support for the hypothesis that F344 rats may be photoresponsive due to differences from other strains in the location, density, or affinity of melatonin receptors.
Bacillus popilliae grew consistently well in a semisynthetic medium containing a "vitamin-free," salt-free, acid hydrolysate of casein supplemented with dextrose, DL-tryptophan, and thiamine. However, when the casein hydrolysate was replaced with a complete array of amino acids, no growth occurred. The addition of barbituric acid to this synthetic medium resulted in consistent growth. A number of purines, pyrimidines, and other nitrogen-containing compounds were tested, but none was found that would replace barbituric acid. In synthetic media, B. popilliae was found to require biotin, thiamine, and 11 amino acids for growth. Three additional amino acids were stimulatory. Preliminary studies indicated that the nutritional requirements of B. lentimorbus, another species known to be pathogenic for Japanese beetle (Popillia japonica) larvae, were similar to those for B. popilliae.
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