Photoperiod, melatonin secretion, and sexual maturation in a tropical rodent

Descendants of a sample of cane mice (Zygodontomys brevicauda) trapped at 8 degrees latitude in Venezuela were tested for reproductive photoresponsiveness. This species breeds continuously, year around, despite living in a seasonally harsh habitat. At 50 days of age there were no differences in the weights of the testes or seminal vesicles or in sperm counts of males born and reared on 16L:8D, 13L:11D, 11L:13D, or 8L:16D photoperiods, although there were small differences in body weight. Females born and reared on 16L:8D vs. 8L:16D cycles became pregnant at the same rates and ages when paired with males at 21 or 31 days of age. The daily duration of melatonin secretion depended on the length of the dark phase of the cycle in both sexes. Circulating levels of melatonin were elevated for 8 h on a 16L:8D cycle and for between 9 and 16 h on an 8L:16D cycle. In this tropical species, the neuroendocrine pathway that links photoperiod to reproduction apparently is disconnected somewhere between melatonin and gonadotropin secretion, causing cane mice to be reproductively unresponsive to variation in photoperiod.     

Brain-gonad axis and photoperiodically-stimulated sexual maturation in the slug,Limax maximus

Summary Physiological and endocrine mechanisms mediating long-day (LD 168) triggered sexual maturation were studied in the terrestrial slug,Limax maximus. Our findings were: (1) Maturation was induced in immature slugs seeing only short days (LD 816) after implantation of whole brains from maturing donors, but no development was found in sham-operated control slugs or in animals receiving implants of muscle from mature donors (Table 1). (2) Removal of the optic tentacles did not block maturation in LD 168 or promote maturation in LD 816 (Fig. 1). (3) Gonadectomy (castration) abolished penis development in 9 of 11 slugs exposed to LD 168 for periods of up to 31 weeks (Table 2). The results are consistent with a model forLimax reproductive tract development in which the perception of long days by extraocular receptors results in the secretion of a maturation hormone by the brain followed by the production of a separate male-phase sex hormone by the developing gonad.Abbreviations ASO accessory sex organs - DB dorsal bodies - FPSH female-phase sex hormone - MH maturation hormone - MPSH male-phase sex hormone This work was supported in part by grants from NSF (BNS 78-01408) and NIH (MH 27948) to P.G.S. The assistance of Mr. T.M. Gordon, Mr. J.L. Broyles, and Mr. M. Bullock is gratefully acknowledged.     

Longer life spans and delayed maturation in wild-derived mice

Nearly all the experimental mice used in aging research are derived from lineages that have been selected for many generations for adaptation to laboratory breeding conditions and are subsequently inbred. To see if inbreeding and laboratory adaptation might have altered the frequencies of genes that influence life span, we have developed three lines of mice (Idaho [Id], Pohnpei [Po], and Majuro [Ma]) from wild-trapped progenitors, and have compared them with a genetically heterogeneous mouse stock (DC) representative of the laboratory-adapted gene pool. Mean life span of the Id stock exceeded that of the DC stock by 24% (P < 0.00002), and maximal life span, estimated as mean longevity of the longest-lived 10% of the mice, was also increased by 16% (P < 0.003). Mice of the Ma stock also had a significantly longer maximal longevity than DC mice (9%, P = 0.04). The longest-lived Id mouse died at the age of 1450 days, which appears to exceed the previous longevity record for fully fed, non-mutant mice. The life table of the Po mice resembled that of the DC controls. Ma and Id mice differ from DC mice in several respects: both are shorter and lighter, and females of both stocks, particularly Id, are much slower to reach sexual maturity. As young adults, Id mice have lower levels of insulin-like growth factor 1 (IGF-I), leptin, and glycosylated hemoglobin compared with DC controls, implicating several biochemical pathways as potential longevity mediators. The results support the idea that inadvertent selection for rapid maturation and large body size during the adaptation of the common stocks of laboratory mice may have forced the loss of natural alleles that retard the aging process. Genes present in the Id and Ma stocks may be valuable tools for the analysis of the physiology and biochemistry of aging in mice.     

Epidemiological models with age structure,proportionate mixing,and cross-immunity

Infection by one strain of influenza type A provides some protection (cross-immunity) against infection by a related strain. It is important to determine how this influences the observed co-circulation of comparatively minor variants of the H1N1 and H3N2 subtypes. To this end, we formulate discrete and continuous time models with two viral strains, cross-immunity, age structure, and infectious disease dynamics. Simulation and analysis of models with cross-immunity indicate that sustained oscillations cannot be maintained by age-specific infection activity level rates when the mortality rate is constant; but are possible if mortalities are age-specific, even if activity levels are independent of age. Sustained oscillations do not seem possible for a single-strain model, even in the presence of age-specific mortalities; and thus it is suggested that the interplay between cross-immunity and age-specific mortalities may underlie observed oscillations.     

Long-term effects of accelerated or delayed sexual maturation on reproductive output in wild female house mice (Mus musculus)

The effects of acceleration and delay of puberty in female house mice on survival and reproduction were tested using 6 experimental groups: (1) control females mated at the time of first oestrus, (2) females mated at weaning, (3) females treated with male urine starting at weaning and mated at first oestrus, (4) females housed in groups and mated at first oestrus, (5) females housed alone, treated with urine from grouped females and mated at first oestrus, and (6) females housed alone and mated at 68 days of age. Females caged with males at weaning or treated with male urine and mated at puberty had lower rates of survival to 180 days of age, but did not differ in rates of fertility from mice in the other four treatments. Those females that were housed with males from weaning or treated with male urine also had smaller total numbers of litters, fewer total young, and smaller average litter sizes than did females for which the age of mating was delayed, by grouping or treatment with urine from grouped females, or by being held until age 68 days before mating. Control females mated at first oestrus generally were intermediate or did not differ from the male treatments on these dependent variables. There were no differences in the average number of female young/litter across the 6 treatments. However, females that were delayed in age of first mating had significantly more male young/litter than did females that were accelerated in their sexual development or control females.(ABSTRACT TRUNCATED AT 250 WORDS)     

Indicators of sexual maturation and regression in the female cat flea, Ctenocephalides felis

Differences in the salivary glands, mesenteron epithelium and reproductive organs of female cat fleas, Ctenocephalides felis Bouché (Siphonaptera: Pulicidae), are related to the degree of reproductive maturation or regression. Contrary to previous ideas, blue bodies in the ovarioles are degenerate oocyte nuclei and their presence denotes failure of ripening oocytes to reach full maturity. A distinction between true corpora lutea and pseudo-corpora lutea is established, the presence of the former indicates successful oviposition, and of the latter, failure to complete maturation of eggs. Accurate indicators of sexual maturation and reproductive success are of potential value in assessing relative suitability of various hosts for a given flea species and therefore in assessing the degree of host specificity among fleas.     

Feeding activity,sexual maturation,hormones, and water balance in the female African migratory locust

Feeding activity and water content are examined in relation to sexual maturation in allatectomized, allatectomized-ovariectomized, ovariectomized, and operated control females. Operated control females undergo two distinct phases of active feeding: the first occurs shortly after emergence and is independent of the maturation process; the second phase is associated with sexual maturation and is more intense than the first. The two phases are usually separated by a short period of low food consumption. Removal of the corpora allata, or corpora allata and ovaries, prevents the second phase of active feeding, whereas removal of the ovary alone has less effect.Allatectomized and allatectomized-ovariectomized females have a low water content and small blood volume as compared with the operated controls, but ovariectomized females have a high water content and become distended with blood. Ovariectomy also results in a large accumulation of protein in the blood, whereas in allatectomized and allatectomized-ovariectomized females, the blood protein concentration is only slightly higher than in the operated controls.The observations are discussed, in particular the control of feeding activity, and the rôle of the neuroendocrine system in the adult female. It is suggested that the corpora allata are involved directly in the control of protein synthesis, and that in the maturing female the cerebral neurosecretory system is very active in maintaining water balance.     

Excreted urine,bladder urine,and the delay of sexual maturation in female house mice

A series of experiments tested effects of excreted and bladder urine of group- and singly-caged female house mice (Mus musculus) on sexual maturation of young female mice caged alone or in groups of eight. Puberty was determined by vaginal smears. A maturation-delaying pherompne was present in bladder urine of all female mice and excreted urine of group-caged females, but not in excreted urine from singly-caged females. Test mice treated with bladder urine homogenized with urethras from singly-caged females matured at the same age as controls. Apparently the urethras or associated glands of singly-caged females produce a substance which deactivates the maturation-delaying pheromone contained in bladder urine.     

Sex hormone-dependent brain maturation and sexual behaviour in rats.

In male and female rats the endogenous steroid and gonadotrophin secretion was inhibited by injecting high doses of chlormadinone acetate (CmAc) from day 14 to 24 of life, i. e. during the period of brain maturation. In adulthood the males treated prepubertally with CmAc exhibited reduced sexual activity and fertility, whereas the females did not differ from the controls. More complete sex hormone deficiency during brain maturation was achieved by castration on day 14 of life. Controls were castrated at normal puberty time (40--60 days). Both groups were then substituted with androgens or oestrogens. In the females castrated on day 14 no impairment of sexual behaviour was observed as compared to the later castrated controls. In contrast, the early castrated males showed delayed onset of mounting behaviour. At autopsy, the weights of their sex organs were found to be lower than in the controls despite equal testosterone replacement for several months. These findings speak in favour of a permanently diminished responsiveness to androgens in males having been exposed to more or less severe androgen deficiency during sex specific brain maturation. Hence, the maturation of a male hypothalamus as well as the differentiation appears to depend at least in part on the presence of androgens, whereas in females it runs without hormonal influence.