Melatonin rhythms and pineal structure in a tropical bat, Anoura geoffroyi, that does not use photoperiod to regulate seasonal reproduction

Abstract: It has been hypothesized that pineal structure and function might differ between temperate zone and tropical species of mammals because of lower amplitudes of seasonal change in photoperiod and, in some areas, less seasonal climatic variation. Anoura geoffroyi produce a single offspring in November or December of each year on the Caribbean island of Trinidad, at 10°N latitude in the deep tropics. Previous work has shown that this population lacks reproductive responses to photoperiod, and must be enforcing seasonal breeding using a non-photoperiodic cue. Anoura geoffroyi have a minute, thin, and rod-like pineal gland. Throughout much of its length, the pineal courses irregularly within the ventrolateral wall of the great cerebral vein. This intimate relationship may have functional implications. Despite having a very small pineal gland, this species produced a nocturnal rise in serum melatonin. Serum melatonin levels in most individuals were below or near undetectable levels during the light period and rose to a peak averaging 100 pg/ml in the last third of the dark period. Our results indicate that, although the pineal gland of A. geoffroyi is extremely small, serum melatonin levels are comparable to those of other mammals.     

Seasonal covariation of the circadian phases of rectal temperature and slow wave sleep onset

There is a scarcity of well-controlled studies of the seasonal variation in circadian rhythmicity. In the present study, the circadian phase of rectal temperature and the onset of slow wave sleep were studied in a series of twelve 24-h experiments, one each month of the year, for six healthy subjects under controlled conditions in a climatic chamber. In winter, as compared with summer, the average circadian rhythm of rectal temperature was phase delayed by 45 min, and the average onset of slow wave sleep was phase delayed by 40 min. The temporal relationship between the circadian phase of rectal temperature and the timing of slow wave sleep was maintained throughout the year. Habitual rising and retiring times covaried as well. Furthermore, the circadian rhythm of rectal temperature followed the timing of the photoperiod across the year, but had a much smaller range of seasonal variation. Apparently, the seasonal variation in the photoperiodic zeitgeber is largely compensated for by the stabilizing influence of secondary zeitgebers. However, in healthy subjects some effect of photoperiodic variation can still be observed.     

Immunohistochemical Localization of Neuropeptide Y in Nerves of the Male Genital Tract of the Photoperiodically Responsive Djungarian Hamster, Phodopus Sungoras/Immunhistochemische Lokalisation von Neuropeptid Y in Nerven der männlichen Genitalorgane des photoperiodisch sensiblen Djungarischen Zwerghamsters, Phodopus sungorus

Neuropeptide Y (NPY) was demonstrated by immunohistochemistry in nerves of the male genital tract of Phodopus sungorus at long (LD 16:8) und short (LD 8:16) photoperiods. No immunoreactive nerve fibres could be demonstrated in the testis, caput and corpus epididymidis and the ventral prostate gland. Dense networks of NPY-containing nerve fibers were demonstrated in the smooth muscle layer of the sperm-transporting duct, beginning in the cauda epididymidis with increasing density towards the distal part of the ductus deferens, and in the smooth muscle layer of the seminal vesicles. At short photoperiods, the density of the NPY-containing nerve plexus decreased only in the smooth muscle layer of the ductus deferens. A "trophic" influence of the large smooth muscle cells of the ductus deferens on their nerves not only in regard to their noradrenaline, but also on their NPY content is discussed.     

Neuropeptide Y in the female reproductive tract of the rat. Distribution of nerve fibres and motor effects

The spontaneous firing of single neurones in the region of the lateral reticular nucleus was the subject of a pharmacological study employing microiontophoretic and systemic application of adrenoceptor agonists and antagonists. Both iontophoretic noradrenaline and systemic clonidine depressed neuronal firing. The depressions were consistently reversed by the alpha-2 antagonist RX781094. Other adrenergic antagonists, prazosin and sotalol, were ineffective. The results suggest the existence of alpha-2 receptors in this region of the brain.     

The Pars Tuberalis: The Missing Link in the Photoperiodic Regulation of Prolactin Secretion?

The endocrine function of the pars tuberalis of the pituitary gland has been an enigma for many years. Recent work suggests that one of its primary functions in seasonal mammals is to mediate photoperiodically regulated changes in prolactin secretion via an unidentified factor called tuberalin.     

Seasonal changes in the expression of neuropeptide Y and pro-opiomelanocortin mRNA in the arcuate nucleus of the ovariectomized ewe: relationship to the seasonal appetite and breeding cycles

Sheep experience well-documented seasonal changes in reproductive activity and voluntary food intake (VFI). Within the hypothalamus, neurones that express neuropeptide Y (NPY) and pro-opiomelanocortin (POMC) have been implicated in the regulation of reproduction and appetite. In this study, we aimed to determine the extent to which the expression of these two neuronal systems is linked to the seasonal reproductive cycle and/or the seasonal appetite cycle. VFI in our sheep reaches a nadir in August with no difference occurring between December and February. We examined the brains of ovariectomized (OVX) female sheep (n=5-7) that were killed during the breeding season (February) or during the early or late nonbreeding season (August and December, respectively). The brains of these animals were perfused with paraformaldehyde and processed for in situ hybridization histochemistry, using ribonucleotide probes labelled with 35S. The number of NPY and POMC cells and the number of silver grains per cell were counted using an image analysis system. For NPY, the number of cells counted in the arcuate nucleus/median eminence region and the number of silver grains per cell was significantly lower in animals killed during August than in animals killed in February or December. The number of grains per cell over NPY cells was also significantly lower in animals killed during August. For POMC, the number of cells was lower in February than in August and December. Similarly, the number of grains per cell for POMC were lower in February than in August and December. VFI was significantly lower in animals during August than at other times of the year. We conclude that in OVX ewes: (i) NPY gene expression is lower at the time of the year when VFI is reduced and (ii) POMC gene expression is greater at the time of the nonbreeding season than during the breeding season. Because these results were obtained in OVX animals, the changes appear to be independent of alterations in the secretion and/or action of ovarian steroids. Thus, the activity of NPY neurones appears to relate to changes in appetite whereas changes in POMC expression may be relevant to the seasonal breeding cycle.     

Vitamin D,folate, and potential early lifecycle environmental origin of significant adult phenotypes

Background and objectives: Vitamin D and folate are highly UV sensitive, and critical for maintaining health throughout the lifecycle. This study examines whether solar irradiance during the first trimester of pregnancy influences vitamin D receptor (VDR) and nuclear folate gene variant occurrence, and whether affected genes influence late-life biochemical/clinical phenotypes.Methodology: 228 subjects were examined for periconceptional exposure to solar irradiance, variation in vitamin D/folate genes (polymerase chain reaction (PCR)), dietary intake (food frequency questionnaire (FFQ)) and important adult biochemical/clinical phenotypes.Results: Periconceptional solar irradiance was associated with VDR-BsmI (P = 0.0008^wk7), TaqI (P = 0.0014^wk7) and EcoRV (P = 0.0030^wk6) variant occurrence between post-conceptional weeks 6–8, a period when ossification begins. Similar effects were detected for other VDR gene polymorphisms. Periconceptional solar irradiance was also associated with 19 bp del-DHFR (P = 0.0025^wk6), and to a lesser extent C1420T-SHMT (P = 0.0249^wk6), a folate-critical time during embryogenesis. These same genes were associated with several late-life phenotypes: VDR-BsmI, TaqI and ApaI determined the relationship between dietary vitamin D and both insulin (P < 0.0001/BB, 0.0007/tt and 0.0173/AA, respectively) and systolic blood pressure (P = 0.0290/Bb, 0.0299/Tt and 0.0412/AA, respectively), making them important early and late in the lifecycle. While these and other phenotype associations were found for the VDR variants, folate polymorphism associations in later-life were limited to C1420T-SHMT (P = 0.0037 and 0.0297 for fasting blood glucose and HbA1c levels, respectively). We additionally report nutrient–gene relationships with body mass index, thiol/folate metabolome, cognition, depression and hypertension. Furthermore, photoperiod at conception influenced occurrence of VDR-Tru9I and 2R3R-TS genotypes (P = 0.0120 and 0.0360, respectively).Conclusions and implications: Findings identify environmental and nutritional agents that may interact to modify gene–phenotype relationships across the lifecycle, offering new insight into human ecology. This includes factors related to both disease aetiology and the evolution of skin pigmentation.     

Short photoperiod restores ventral subicular lesion-induced deficits in affective and socio-cognitive behavior in male Wistar rats

Photoperiod (day-length) has enduring effects on an organism's physiological functions like metabolism and behavioral phenotypes including cognition and affect. Circadian rhythm manipulations are potentially effective non-pharmacological strategies in the management of central nervous system insults. In our previous study, we demonstrated the efficacy of short photoperiod regime (SPR; 06/18 hr light-dark cycle) in establishing functional recovery in ventral subicular lesion (VSL) rats. The present study further demonstrates the efficacy of SPR in mitigating anxiety and depression as well as facilitating socio-cognitive behavior in VSL rats. VSL elevated the basal plasma corticosterone levels, increased anxiety, anhedonia, and behavioral despair with decreased self-care. The VSL rats also exhibited a considerable degree of impaired social cognition, in terms of altered social preference and social novelty. Exposure to SPR for 21 days mitigated the anxiety- and depressive-like phenotypes as well as improved social cognition significantly. Thus, the study demonstrated the effectiveness of SPR strategy in reversing most of the behavioral deficits caused by VSL. SPR, perhaps, would have regulated the hypothalamo-pituitary-adrenal axis responsiveness as we observed a decrease in plasma corticosterone levels following SPR in VSL rats. The study implies the need for developing a task-dependent SPR strategy to achieve complete behavioral recovery as the functional demands of each behavior is distinct. In summary, the study highlights the efficacy of photoperiod manipulation as a novel, non-pharmacological approach in mitigating the affective and cognitive deficits associated with neuropsychiatric disorders such as bipolar disorder and Alzheimer's disease wherein circadian rhythm alterations are implicated.     

Influences of season and of temperature, photoperiod, and subcutaneous melatonin infusion on the glomerular filtration rate of ewes

Abstract: Influences of season and of temperature, photoperiod, and subcutaneous melatonin infusion on glomerular filtration rate (GFR) were measured in ewes. There was a seasonal difference of GFR between summer (June-August) and winter (December-February) in Tokyo (35°, 35°N); GFR was significantly ( P < 0.05) higher in summer (4.2 ± 0.3 ml/ min/kg) than in winter (3.0 ± 0.2 ml/min/kg). GFR was measured after exposure to three types of photoperiod, 24L: 0D, 12L: 12D, and 0L: 24D, for 7 to 8 days. The value for GFR obtained at 20°C was significantly lower ( P < 0.05) with 0L: 24D than with the other two photoperiodic conditions. GFR obtained during subcutaneous melatonin infusion (20μg/hr for 16 hr/ day for 7 days) with 24L: 0D conditions was significantly ( P < 0.05) lower (2.5 ± 0.1 ml/min/kg) than without infusion (3.8 ± 0.3 ml/ min/kg) and was about the same as that obtained in animals under 0L: 24D conditions. At 30°C, GFR exhibited no difference between the 3 photoperiodic conditions and was always lower than that found at 20°C. Possible influences of melatonin on GFR are discussed.