Endocrine and cardiovascular rhythms differentially adapt to chronic phase-delay shifts in rats

Sex differences in the rodent medial prefrontal cortex - What Do and Don't we know?

The prefrontal cortex, particularly its medial subregions (mPFC), mediates critical functions such as executive control, behavioral inhibition, and memory formation, with relevance for everyday functioning and psychopathology. Despite broad characterization of the mPFC in multiple model organisms, the extent to which mPFC structure and function vary according to an individual's sex is unclear - a knowledge gap that can be attributed to a historical bias for male subjects in neuroscience research. Recent efforts to consider sex as a biological variable in basic science highlight the great need to close this gap. Here we review the knowns and unknowns about how rodents categorized as male or female compare in mPFC neuroanatomy, pharmacology, as well as in aversive, appetitive, and goal- or habit-directed behaviors that recruit the mPFC. We propose that long-standing dogmatic concepts of mPFC structure and function may not remain supported when we move beyond male-only studies, and that empirical challenges to these dogmas are warranted. Additionally, we note some common pitfalls in this work. Most preclinical studies operationalize sex as a binary categorization, and while this approach has furthered the inclusion of non-male rodents it is not as such generalizable to what we know of sex as a multidimensional, dynamic variable. Exploration of sex variability may uncover both sex differences and sex similarities, but care must be taken in their interpretation. Including females in preclinical research needs to go beyond the investigation of sex differences, improving our knowledge of how this brain region and its subregions mediate behavior and health. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Simulated Chronic Jet Lag Affects the Structural and Functional Complexity of Hippocampal Neurons in Mice

There has been a long history that chronic circadian disruption such as jet lag or shift work negatively affects brain and body physiology. Studies have shown that circadian misalignment act as a risk factor for developing anxiety and mood-related depression-like behavior. Till date, most studies focused on simulating jet lag in model animals under laboratory conditions by repeated phase advances or phase delay only, while the real-life conditions may differ. In the present study, adult male mice were subjected to simulated chronic jet lag (CJL) by alternately advancing and delaying the ambient light-dark (LD) cycle by 9 h every 2 days, thereby covering a total of 24 days. The effect of CJL was then examined for a range of stress and depression-related behavioral and physiological responses. The results showed that mice exposed to CJL exhibited depression-like behavior, such as anhedonia. In the open field and elevated plus maze test, CJL-exposed mice showed increased anxiety behavior compared to LD control. In addition, CJL-exposed mice showed an increased level of serum corticosterone and proinflammatory cytokine, TNF-α in both serum and hippocampus. Moreover, CJL-exposed mice exhibited a reduction in structural complexity of hippocampal CA1 neurons along with decreased expression of neurotrophic growth factors, BDNF and NGF in the hippocampus compared to LD control. Taken together, our findings suggest that simulated chronic jet lag adversely affects structural and functional complexity in hippocampal neurons along with interrelated endocrine and inflammatory responses, ultimately leading to stress, anxiety, and depression-like behavior in mice.

Circadian disruption during fetal development promotes pathological cardiac remodeling in male mice

Disruption of circadian rhythms during fetal development may predispose mice to developing heart disease later in life. Here, we report that male, but not female, mice that had experienced chronic circadian disturbance (CCD) in utero were more susceptible to pathological cardiac remodeling compared with mice that had developed under normal intrauterine conditions. CCD-treated males showed ventricular chamber dilatation, enhanced myocardial fibrosis, decreased contractility, higher rates of induced tachyarrhythmia, and elevated expression of biomarkers for heart failure and myocardial remodeling. In utero CCD exposure also triggered sex-dependent changes in cardiac gene expression, including upregulation of the secretoglobin gene, Scgb1a1, in males. Importantly, cardiac overexpression of Scgb1a1 was sufficient to induce myocardial hypertrophy in otherwise naive male mice. Our findings reveal that in utero CCD exposure predisposes male mice to pathological remodeling of the heart later in life, likely as a consequence of SCGB1A1 upregulation.

An update on the role and potential mechanisms of clock genes regulating spermatogenesis: A systematic review of human and animal experimental studies

Circadian clocks can be traced in nearly all life kingdoms, with the male reproductive system no exception. However, our understanding of the circadian clock in spermatogenesis seems to fall behind other scenarios. The present review aims to summarize the current knowledge about the role and especially the potential mechanisms of clock genes in spermatogenesis regulation. Accumulating studies have revealed rhythmic oscillation in semen parameters and some physiological events of spermatogenesis. Disturbing the clock gene expression by genetic mutations or environmental changes will also notably damage spermatogenesis. On the other hand, the mechanisms of spermatogenetic regulation by clock genes remain largely unclear. Some recent studies, although not revealing the entire mechanisms, indeed attempted to shed light on this issue. Emerging clues hinted that gonadal hormones, retinoic acid signaling, homologous recombination, and the chromatoid body might be involved in the regulation of spermatogenesis by clock genes. Then we highlight the challenges and the promising directions for future studies so as to stimulate attention to this critical field which has not gained adequate concern.

Artificial Dim Light at Night during Pregnancy Can Affect Hormonal and Metabolic Rhythms in Rat Offspring

Artificial light at night (ALAN) is considered an environmental risk factor that can interfere with the circadian control of the endocrine system and metabolism. We studied the impact of ALAN during pregnancy on the hormonal and biochemical parameters in rat pups at postnatal (P) days P3, P10, and P20. Control dams (CTRL) were kept in a standard light-dark regime, and ALAN dams were exposed to dim ALAN (<2 lx) during the whole pregnancy. A plasma melatonin rhythm was found in all CTRL groups, whereas in ALAN pups, melatonin was not rhythmic at P3, and its amplitude was lowered at P10; no differences were found between groups at P20. Plasma corticosterone was rhythmic at P20 in both groups, with decreased mesor in ALAN pups. Plasma thyroid hormones exhibited an inconsistent developmental pattern, and vasopressin levels were suppressed at the beginning of the dark phase at P20 in ALAN compared to CTRL. Glucose and cholesterol showed significant daily rhythms in CTRL but not in ALAN offspring at P3. Exposure to ALAN during pregnancy disturbed the development of daily rhythms in measured hormones and metabolites, suggesting that ALAN during pregnancy can act as an endocrine disruptor that can interfere with the normal development of the progeny.

Hypotensive effects of melatonin in rats: Focus on the model, measurement, application, and main mechanisms

The hypotensive effects of melatonin are based on a negative correlation between melatonin levels and blood pressure in humans. However, there is a positive correlation in nocturnal animals that are often used as experimental models in cardiovascular research, and the hypotensive effects and mechanism of melatonin action are often investigated in rats and mice. In rats, the hypotensive effects of melatonin have been studied in normotensive and spontaneously or experimentally induced hypertensive strains. In experimental animals, blood pressure is often measured indirectly during the light (passive) phase of the day by tail-cuff plethysmography, which has limitations regarding data quality and animal well-being compared to telemetry. Melatonin is administered to rats in drinking water, subcutaneously, intraperitoneally, or microinjected into specific brain areas at different times. Experimental data show that the hypotensive effects of melatonin depend on the experimental animal model, blood pressure measurement technique, and the route, time and duration of melatonin administration. The hypotensive effects of melatonin may be mediated through specific membrane G-coupled receptors located in the heart and arteries. Due to melatonin's lipophilic nature, its potential hypotensive effects can interfere with various regulatory mechanisms, such as nitric oxide and reactive oxygen species production and activation of the autonomic nervous and circadian systems. Based on the research conducted on rats, the cardiovascular effects of melatonin are modulatory, delayed, and indirect.

Disrupted Circadian Control of Hormonal Rhythms and Anticipatory Thirst by Dim Light at Night

AIMS

Our study addresses underlying mechanisms of disruption of the circadian timing system by low-intensity artificial light at night (ALAN), which is a growing global problem, associated with serious health consequences.

METHODS

Rats were exposed to low-intensity (∼2 lx) ALAN for 2 weeks. Using in situ hybridization, we assessed 24-h profiles of clock and clock-controlled genes in the suprachiasmatic nuclei (SCN) and other hypothalamic regions, which receive input from the master clock. Moreover, we measured the daily rhythms of hormones within the main neuroendocrine axes as well as the detailed daily pattern of feeding and drinking behavior in metabolic cages.

RESULTS

ALAN strongly suppressed the molecular clockwork in the SCN, as indicated by the suppressed rhythmicity in the clock (Per1, Per2, and Nr1d1) and clock output (arginine vasopressin) genes. ALAN disturbed rhythmic Per1 expression in the paraventricular and dorsomedial hypothalamic nuclei, which convey the circadian signals from the master clock to endocrine and behavioral rhythms. Disruption of hormonal output pathways was manifested by the suppressed and phase-advanced corticosterone rhythm and lost daily variations in plasma melatonin, testosterone, and vasopressin. Importantly, ALAN altered the daily profile in food and water intake and eliminated the clock-controlled surge of drinking 2 h prior to the onset of the rest period, indicating disturbed circadian control of anticipatory thirst and fluid balance during sleep.

CONCLUSION

Our findings highlight compromised time-keeping function of the central clock and multiple circadian outputs, through which ALAN disturbs the temporal organization of physiology and behavior.

Telemetric data collection should be standard in modern experimental cardiovascular research

Cardiovascular (CV) health is often expressed by changes in heart rate and blood pressure, the physiological record of which may be affected by moving, anaesthesia, handling, time of day and many other factors in rodents. Telemetry measurement minimises these modulations and enables more accurate physiological recording of heart rate and blood pressure than non-invasive methods. Measurement of arterial blood pressure by telemetry requires implanting a catheter tip into the artery. Telemetry enables us to sample physiological parameters with a high frequency continuously for several months. By measuring the pressure in the artery using telemetry, we can visualize pressure changes over a heart cycle as the pressure wave. From the pressure wave, we can subtract systolic, diastolic, mean and pulse pressure. From the beat-to-beat interval (pressure wave) and the RR' interval (electrocardiogram), we can derive the heart rate. From beat-to-beat variability, we can evaluate the autonomic nervous system's activity and spontaneous baroreflex sensitivity and their impact on CV activity. On a long-term scale, circadian variability of CV parameters is evident. Circadian variability is the result of the circadian system's activity, which synchronises and organises many activities in the body, such as autonomic and reflex modulation of the CV system and its response to load over the day. In the presented review, we aimed to discuss telemetry devices, their types, implantation, set-up, limitations, short-term and long-term variability of heart rate and blood pressure in CV research. Data collection by telemetry should be, despite some limitations, standard in modern experimental CV research.

Chronic circadian phase advance in male mice induces depressive-like responses and suppresses neuroimmune activation

Altered working and sleeping schedules during the COVID-19 pandemic likely impact our circadian systems. At the molecular level, clock genes form feedback inhibition loops that control 24-hr oscillations throughout the body. Importantly, core clock genes also regulate microglia, the brain resident immune cell, suggesting circadian regulation of neuroimmune function. To assess whether circadian disruption induces neuroimmune and associated behavioral changes, we mimicked chronic jetlag with a chronic phase advance (CPA) model. 32 adult male C57BL/6J mice underwent 6-hr light phase advance shifts every 3 light/dark cycles (CPA) 14 times or were maintained in standard light/dark cycles (control). CPA mice showed higher behavioral despair but not anhedonia in forced swim and sucrose preferences tests, respectively. Changes in behavior were accompanied by altered hippocampal circadian genes in CPA mice. Further, CPA suppressed expression of brain-derived neurotrophic factor (BDNF) and pro-inflammatory cytokine interleukin-1 beta in the hippocampus. Plasma corticosterone concentrations were elevated by CPA, suggesting that CPA may suppress neuroimmune pathways via glucocorticoids. These results demonstrate that chronic circadian disruption alters mood and neuroimmune function, which may have implications for shift working populations such as frontline health workers.

Dim Light at Night Impairs Daily Variation of Circulating Immune Cells and Renal Immune Homeostasis

Dim light at night (dLAN) has become a pervasive part of the modern world, and growing evidence shows its association with increased health risks. Though this link is attributed to a disturbed circadian clock, the underlying mechanisms that can explain how circadian disruption from dLAN causes negative health effects remain unclear. Here, we exposed rats to a light–dark cycle (12:12 h) with low-intensity light at night (~2 lx) for 2 and 5 weeks and explored the steady-state pattern of circulating immune cells and renal immune-related markers, which are well controlled by the circadian clock. After 5 weeks, dLAN impaired the daily variation in several types of white blood cells, especially monocytes and T cells. Two-week dLAN caused a reduction in blood monocytes and altered gene expression of macrophage marker Cd68 and monocyte-attracting chemokine Ccl2 in the kidney. Interestingly, dLAN decreased renal 3-nitrotyrosine levels and resulted in up-regulation of the main endogenous antioxidant pathways, indicating a disturbance in the renal redox balance and an activation of compensatory mechanisms. These effects paralleled the altered renal expression of the molecular clock components and increased plasma corticosterone levels. Together, our results show that chronic exposure to dLAN weakened the circadian control of daily variation of circulating immune cells and disturbed renal immune and redox homeostasis. Consequences of this dLAN-disturbed immune balance on the ability of the immune system to cope with other challenges should by clarified in further studies.

A mixture of diethylhexyl, diisononyl and dibutyl phthalate decreased anogenital distance, postnatal testosterone levels, and changed social behavior in Wistar rats

Phthalates are chemicals interfering with the function of testosterone and are suspected to play a role in the emergence of neurodevelopmental diseases. This could be due to interference with brain development for which optimal testosterone levels are essential. We investigated the effect of prenatal and early postnatal exposure to a phthalate mixture on the anogenital distance (AGD), plasma testosterone levels and social behavior in rats. Pregnant rats were exposed to a mixture of diethylhexyl, diisononyl and dibutyl phthalate, each at a dose of 4.5 mg/kg/day, from gestational day 15 to postnatal day 4. A social interaction test was performed to assess sociability in the three ontogenetic stages (weaning, puberty, adulthood). AGD was measured in adulthood to assess changes in prenatal testosterone levels. Plasma testosterone levels were measured in adults by a radioimmunoassay. The total frequency and time of socio-cohesive interactions were decreased in phthalate exposed females in weaning, puberty and adulthood. Phthalate exposed males showed a decrease in the frequency of social interactions in weaning only. Shorter anogenital distance was observed in adult males exposed to phthalates. Decreased testosterone levels were observed in the exposed group in both sexes. Our results suggest that early developmental phthalate exposure may play an important role in the hormonal and behavioral changes associated with several neurodevelopmental diseases.

Working with Inadequate Tools: Legislative Shortcomings in Protection against Ecological Effects of Artificial Light at Night

The fundamental change in nocturnal landscapes due to the increasing use of artificial light at night (ALAN) is recognized as being detrimental to the environment and raises important regulatory questions as to whether and how it should be regulated based on the manifold risks to the environment. Here, we present the results of an analysis of the current legal obligations on ALAN in context with a systematic review of adverse effects. The legal analysis includes the relevant aspects of European and German environmental law, specifically nature conservation and immission control. The review represents the results of 303 studies indicating significant disturbances of organisms and landscapes. We discuss the conditions for prohibitions by environmental laws and whether protection gaps persist and, hence, whether specific legislation for light pollution is necessary. While protection is predominantly provided for species with special protection status that reveal avoidance behavior of artificially lit landscapes and associated habitat loss, adverse effects on species and landscapes without special protection status are often unaddressed by existing regulations. Legislative shortcomings are caused by difficulties in proving adverse effect on the population level, detecting lighting malpractice, and applying the law to ALAN-related situations. Measures to reduce ALAN-induced environmental impacts are highlighted. We discuss whether an obligation to implement such measures is favorable for environmental protection and how regulations can be implemented.