Photoresponsive Fischer 344 Rats are Reproductively Inhibited by Melatonin and Differ in 2‐[125I] Iodomelatonin Binding from Nonphotoresponsive Sprague‐Dawley Rats

摘要: Many temperate-zone species use photoperiod as an environmental cue to regulate reproductive timing. Strains of laboratory rats differ in their responsiveness photoperiod, with the Fischer 344 (F344) strain being most responsive known. F344 and closely related strains that photoresponsiveness may be useful models study mechanisms genetic basis for photoresponsiveness. We tested two hypotheses: (i) melatonin mediates rats, is case all other mammals tested, (ii) location, abundance, or affinity receptors, estimated by amount location binding radioligand 2-[125I]-iodomelatonin (IMEL) brain, might cause variation among rat strains. Melatonin injections 1 h before lights off a stimulatory (L14 : D10) induced inhibition reduced weight gain manner similar short days L8 D16, while ethanolic saline vehicle did not. Interestingly, administered during inhibitory (L10 D14) caused greater both reproduction than alone. Pinealectomized implanted subcutaneously silastic capsule not testis size body from controls blank implants. The brains pars tuberalis pituitary photoresponsive nonphotoresponsive Harlan Sprague-Dawley (HSD) were processed autoradiography using IMEL. found significantly higher specific IMEL anterior posterior regions paraventricular nucleus thalamus (PVNt) reuniens same areas HSD rats. There no differences between medial PVNt, anteroventral anterodorsal thalamus, suprachiasmatic nucleus, tuberalis. These results indicate In addition, they provide support hypothesis due density, receptors.