Arg-vasopressin content in the suprachiasmatic nucleus of rat pups: circadian rhythm and its development

The effect of maternal stress activation on the offspring during lactation in light of vasopressin

Although it is obvious that preconceptional effects as well as stressors during pregnancy profoundly influence the progeny, the lactation period seems to be at least as important. Here we summarize how maternal stressors during the lactation period affect the offspring. As vasopressin is one of the crucial components both for stress adaptation and social behavior, special emphasis was given to this neuropeptide. We can conclude that stressing the mother does not have the same acute effect on the hypothalamo-pituitary-adrenocortical axis (as the main target of stress adaptation) of the pups as stressing the pups, but later endocrine and behavioral consequences can be similar. Vasopressin plays a role in acute and later consequences of perinatal stressor applied either to the mother or to the offspring, thereby contributing to transmitting the mothers' stress to the progeny. This mother-infant interaction does not necessarily mean a direct transmission of molecules, but rather is the result of programming the brain development through changes in maternal behavior. Thus, there is a time lag between maternal stress and stress-related changes in the offspring. The interactions are bidirectional as not only stress in the dam but also stress in the progeny has an effect on nursing.

Development, maturation, and necessity of transcription factors in the mouse suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) of the hypothalamus is the master mammalian circadian clock. The SCN is highly specialized because it is responsible for generating a near 24 h rhythm, integrating external cues, and translating the rhythm throughout the body. Currently, our understanding of the developmental origin and genetic program involved in the proper specification and maturation of the SCN is limited. Herein, we provide a detailed analysis of transcription factor (TF) and developmental-gene expression in the SCN from neurogenesis to adulthood in mice (Mus musculus). TF expression within the postmitotic SCN was not static but rather showed specific temporal and spatial changes during prenatal and postnatal development. In addition, we found both global and regional patterns of TF expression extending into the adult. We found that the SCN is derived from a distinct region of the neuroepithelium expressing a combination of developmental genes: Six3, Six6, Fzd5, and transient Rx, allowing us to pinpoint the origin of this region within the broader developing telencephalon/diencephalon. We tested the necessity of two TFs in SCN development, RORα and Six3, which were expressed during SCN development, persisted into adulthood, and showed diurnal rhythmicity. Loss of RORα function had no effect on SCN peptide expression or localization. In marked contrast, the conditional deletion of Six3 from early neural progenitors completely eliminated the formation of the SCN. Our results provide the first description of the involvement of TFs in the specification and maturation of a neural population necessary for circadian behavior.

The retina-attached SCN slice preparation: an in vitro mammalian circadian visual system

The suprachiasmatic nucleus (SCN), the mammalian circadian pacemaker, receives information about ambient light levels through the retinohypothalamic tract. This information resets the molecular clock of SCN neurons, thereby entraining overt animal behavior and physiology to the solar cycle. Progress toward functional characterization of retinal influences on the SCN has been hampered by limitations of established experimental paradigms. To overcome this hurdle, the authors have developed a novel in vitro preparation of the rat retinohypothalamic circuit that maintains functional connectivity between the retinas and the SCN. This method permits whole-cell patch-clamp recordings from visually identified, light-responsive SCN neurons. Using this preparation, the authors have found that in the SCN, light-evoked responses are partly driven by the melanopsin photosensory system of the intrinsically photosensitive retinal ganglion cells and that SCN neurons exhibit light adaptation. The authors have also been able to generate this preparation from mice, demonstrating the feasibility of applying this method to transgenic mice.

Circadian dynamics of vasopressin in mouse selection lines: translation and release in the SCN

Arg8-vasopressin (AVP), a circadian clock-controlled gene product, is released from the hypothalamic suprachiasmatic nuclei (SCN) in mice in a circadian fashion. Previously reported differences in two mouse lines, initially selected for thermoregulatory nest-building behavior (building small nests (S-mice) or big nests (B-mice)) with different circadian organization of behavior and in number of SCN-AVP immunoreactive neurons, were further investigated. We confirmed and expanded the finding that S-mice exhibited constant high levels of SCN-AVP content with no apparent circadian rhythmicity, whereas B-mice had lower numbers of AVP positive cells which varied with time of day. We found that AVP mRNA expression levels at midnight and midday were similar in both lines, as established by in situ hybridization. When AVP transport and release were blocked by colchicine, SCN-AVP immunoreactivity was similar in both lines. This suggests that differences in SCN-AVP content depend on transport or release. Organotypic SCN cultures of B-mice showed more AVP release per neuron than cultures of S-mice. These results reveal that on a mechanistic level the mouse lines differed in transport and/or release of AVP in the SCN, rather than differential regulation of AVP gene transcription or number of AVP immunoreactive neurons.

Neurogenesis and ontogeny of specific cell phenotypes within the hamster suprachiasmatic nucleus

The hamster suprachiasmatic nucleus (SCN) is anatomically and functionally heterogeneous. A group of cells in the SCN shell, delineated by vasopressin-ergic neurons, are rhythmic with respect to Period gene expression and electrical activity but do not receive direct retinal input. In contrast, some cells in the SCN core, marked by neurons containing calbindin-D28k, gastrin-releasing peptide (GRP), substance P (SP), and vasoactive intestinal polypeptide (VIP), are not rhythmic with respect to Period gene expression and electrical activity but do receive direct retinal input. Examination of the timing of neurogenesis using bromodeoxyuridine indicates that SCN cells are born between embryonic day 9.5 and 12.5. Calbindin, GRP, substance P, and VIP cells are born only during early SCN neurogenesis, between embryonic days 9.5-11.0. Vasopressin cells are born over the whole period of SCN neurogenesis, appearing as late as embryonic day 12.5. Examination of the ontogeny of peptide expression in these cell types reveals transient expression of calbindin in a cluster of dorsolateral SCN cells on postnatal days 1-2. The adult pattern of calbindin expression is detected in a different ventrolateral cell cluster starting on postnatal day 2. GRP and SP expression appear on postnatal day 8 and 10, respectively, after the retinohypothalamic tract has innervated the SCN. In summary, the present study describes the ontogeny-specific peptidergic phenotypes in the SCN and compares these developmental patterns to previously identified patterns in the appearance of circadian functions. These comparisons suggest the possibility that these coincident appearances may be causally related, with the direction of causation to be determined.

Circadian- and temperature-specific effects of early deprivation on rat maternal care and pup development: Short-term markers for long-term effects?

We compare the effects on pup body weight and on maternal care of 4-hr separation from dam and littermates on postnatal Days 1 to 14 (early deprivation, ED) under different thermal and circadian conditions. ED was performed at either 21 degrees C (Cold), or 32 degrees C (Warm), and either during the light or dark phase. The comparison group was nonhandling (NH), either under a nonreversed (Light) or reversed (Dark) cycle. At weaning, Cold ED pups were of lower body weight than Warm ED pups, and Warm ED pups were of lower body weight than NH pups. Light and Dark ED pups received high care at reunion relative to NH, and Cold ED pups received higher care at several hours postreunion relative to Warm ED and NH pups. We propose that reduced pup weight and increased maternal care are short-term markers for the severity of Cold ED, and that this manipulation could therefore impact negatively on emotionality and cognition in adulthood.

Vasopressin immunoreactivity and release in the suprachiasmatic nucleus of wild-type and tau mutant Syrian hamsters

Despite the prominent role of the Syrian hamster (Mesocricetus auratus) in studies of circadian rhythms, there are no data available on the temporal dynamics of the neuropeptide vasopressin (AVP), a major output system of the suprachiasmatic nucleus (SCN). We studied the hamster SCN-AVP system in vivo across the light period and in vitro using long-term organotypic SCN cultures. Additionally, we compared wild-type and tau mutant hamsters with an endogenous circadian period of approximately 24 h and approximately 20 h, respectively. The in vivo study revealed no differences in the number of SCN-AVP neurons between the two genotypes of hamsters studied at three time points across the light period of the circadian cycle. A significantly higher level of AVP-immunoreactivity, however, was found in the SCN of wild-type compared to tau mutant hamsters at the beginning and in the middle of the light period, but not at the end of the light period. SCN-AVP cell number and immunostaining decreased significantly across the light period in wild-type hamsters, but not in tau mutants. The in vitro study revealed a significantly higher rate of AVP release per 24 h from the tau mutant SCN compared to the wild-type SCN. Robust circadian oscillations in AVP release were not found in either type of hamster. These results may suggest that the SCN-AVP system of hamsters, irrespective of genotype, is relatively weak compared to other species. Moreover, the tau mutation seems to influence the SCN-AVP system by enhancing the rate of AVP release and by reducing AVP content and its daily fluctuation.

Ontogenetic formation of the ability of rats to count time endogenously and its relationship with the level of anxiety

Improvements in the ability to count time endogenously with maturation in rats depends on the normal age dynamics of anxious-phobic state and is associated with the state of the peripheral compartment of the sympatheticoadrenal system. Increases in the lengths of locomotive excursions were accompanied by decreases in anxious-phobic state and increases in the quality of time-keeping. In rats aged three and six months (but not in one-month-old rats), the ability to count time endogenously showed a parabolic relationship with initial anxious-phobic state: the most precise and efficient counting of time intervals needs a certain intermediate level of anxiety, covering a relatively narrow range. Anxious-phobic states beyond this optimum, either increases or decreases, lead to degradation of chronometric ability.

Regulation of hypothalamic arginine vasopressin messenger ribonucleic acid and pituitary arginine vasopressin content in fetal sheep: effects of acute tonicity alterations and fetal maturation

OBJECTIVE

Fetal arginine vasopressin contributes to fetal and amniotic fluid homeostasis by increasing water resorption in the kidney and, at higher plasma levels, circulatory homeostasis by vasopressor effects. In utero and neonatal exposure of rat pups to prolonged alterations in plasma osmolality may permanently alter (imprint) pituitary arginine vasopressin content and adult responses to osmotic challenges. Our objective was to investigate fetal developmental changes and the impact of maternal dehydration and maternal hyponatremia on fetal pituitary arginine vasopressin content and hypothalamic arginine vasopressin messenger ribonucleic acid expression.

STUDY DESIGN

Ten pregnant ewes with singleton fetuses (135 +/- 1 day) were chronically prepared with maternal vascular catheters. Ewes were assigned to receive water deprivation (n = 4) [desamino, D-Arg8]-arginine vasopressin-induced plasma hyponatremia (n = 3), or 4 days of observation (n = 3). Three additional pregnant ewes with preterm (110 +/- 1 day) singleton fetuses were also included for a study of maturational effects. Daily maternal blood samples were analyzed for determination of plasma arginine vasopressin, electrolytes, and osmolality. After the study protocol, fetuses were operatively delivered, umbilical blood samples obtained, and fetuses put to death for pituitary and hypothalamic tissues. Pituitary arginine vasopressin content was determined by radioimmunoassay, and hypothalamus arginine vasopressin messenger ribonucleic acid expression was detected by Northern blotting.

RESULTS

Dehydration significantly (P < .05) increased, and hyponatremia significantly decreased maternal plasma sodium concentration compared with controls. Fetal plasma sodium concentration significantly changed in parallel with maternal values (dehydration: 139 +/- 1 to 150 +/- 1 mEq/L; hyponatremia: 138 +/- 1 to 128 +/- 5 mEq/L). Fetal hypothalamic arginine vasopressin messenger ribonucleic acid expression and pituitary content did not change in relation to these relatively acute alterations in plasma tonicity. However, among all animals, arginine vasopressin messenger ribonucleic acid expression was significantly negatively correlated with pituitary arginine vasopressin content (r2 = 0.563; P = .02). Arginine vasopressin messenger ribonucleic acid expression was significantly lower in both preterm and near-term fetuses (P < .05) than that in the maternal ewe, although pituitary arginine vasopressin content (in micrograms per milligram of protein) was significantly greater in preterm fetuses (P < .01, vs maternal; P < .05, vs near term).

CONCLUSIONS

The significant inverse relation between arginine vasopressin content and arginine vasopressin messenger ribonucleic acid suggests a dynamic arginine vasopressin synthesis-content feedback relationship is functional in the near-term fetus. Although relatively acute periods of maternal hypertonicity or hypotonicity do not alter fetal pituitary arginine vasopressin content or hypothalamic arginine vasopressin messenger ribonucleic acid expression, longer-term plasma tonicity alterations may potentially have an impact on the fetal arginine vasopressin hypothalamic-pituitary axis.

Circadian rhythm of Arg-vasopressin contents in the suprachiasmatic nucleus in relation to corticosterone

Circadian rhythms of locomotor activity and adrenal glucocorticoid are controlled by the suprachiasmatic nucleus (SCN), the center of a biological clock, in mammals. Arg-vasopressin (AVP) contents in the SCN play a role in endogenous circadian rhythm during the absence of time cues. The AVP-containing neurons in the SCN are considered to transmit a circadian signal to the other parts of the brain. The circadian rhythms of AVP in the SCN in relation to the plasma corticosterone and locomotor activity were investigated. Under the light-dark cycle, plasma corticosterone levels were reciprocally correlated with the AVP content in the SCN. Under free-running conditions with constant dim light, AVP rhythms were reciprocally synchronized with the locomotor activity. The correlation of AVP with plasma corticosterone is different at different times of the day both under the LD cycle and constant dim light. Dexamethasone (i. p., 0.1 mg/100) increased the AVP contents, and this tendency was significantly greater during the dark period. These results indicate that corticosterone in the blood may regulate the circadian rhythm through AVP variation in the SCN.

Constant bright light (LL) during lactation in rats prevents arrhythmicity due to LL

Light has a strong effect on the circadian system. Light-dark (LD) cycles are the main zeitgebers for practically all organisms, and the exposure of animals to constant bright light (LL) alters the manifestation of circadian rhythms. In rats, exposure to LL in adulthood produces an arrhythmic pattern in their motor activity, with a large number of ultradian components. In previous experiments, we found that rats born and kept under LL during lactation develop, after weaning, a circadian rhythm which is maintained for at least a couple of months. Here, we examined motor activity rhythms under LL of two groups of rats which differed in the lighting conditions under which they were kept during lactation: 1) rats kept under LL during lactation (LL-rats), which manifested a circadian rhythm after weaning, and 2) rats kept under constant darkness (DD-rats), which were arrhythmic after weaning. We investigated whether the presence of rhythmicity under LL in LL-rats is a transitory effect or whether it persists throughout most of the life of the rat. Moreover, we examined motor activity rhythms of both groups of rats under different lighting conditions to find out other possible differences in the manifestation of their circadian rhythms. Results showed that there are no differences in the capacity of entrainment of both groups of rats to LD cycles or in the rhythm that rats show under DD. Most of the LL-rats maintained their circadian rhythms for the duration of the experiment (1 year), although we found differences in the rhythms manifested between males and females. We found that most of the LL-males became arrhythmic; consequently, at the end of the experiment, there were no differences in the number of males showing circadian rhythm in the LL- and DD-groups. Most of the females in the LL-group showed a clear circadian rhythm under LL during the entire experiment. Thus, LL during lactation has a protective effect against the disruptive effect of LL on the circadian rhythm, although it is only clearly manifested in females.

AVP rhythm in the suprachiasmatic nucleus in relation to locomotor activity under constant light

To examine the roles of Arg-vasopressin (AVP)- and vasoactive intestinal peptide (VIP)-containing neurons in the suprachiasmatic nucleus (SCN) in production of circadian rhythmicity of locomotor activity, variations in the contents of AVP and VIP in punched-out SCN tissue and locomotor activity were measured under a light-dark cycle as well as under conditions of constant light for up to 3 weeks. Under the light-dark cycle, contents of AVP and VIP, and locomotor activity showed marked circadian rhythmicity. Under constant light, AVP content showed circadian rhythmicity until 3 weeks, while VIP rhythm disappeared from the first week with decreases in its content. Locomotor activity showed a free-running circadian rhythm for more than 3 weeks under constant light conditions in most cases. These results suggest that AVP but not VIP in the SCN may be involved in the generation of locomotor activity rhythm under conditions of constant light.

GABAergic control of Arg-vasopressin release from suprachiasmatic nucleus slice culture

gamma-Aminobutyric acid (GABA) is contained in many neurons in the suprachiasmatic nucleus (SCN), and is considered to be a circadian entraining factor. Arg-vasopressin (AVP)-containing neurons represent one of the output paths from the SCN to other brain areas. We examined the effects of GABA, muscimol (GABA-A agonist), bicuculline (GABA-A antagonist), baclofen (GABA-B agonist) and phaclofen (GABA-B antagonist) on AVP release using SCN slice preparations in culture. SCN slices were prepared from coronally sliced brain tissue and cultured in organic tissue culture dishes with DMEM/N2 medium in a CO2 (5%) incubator. The culture medium was changed at 3-h intervals until 9 h after 3 h application of each drug. Concentrations of AVP in 1 ml aspirates of the medium were analyzed by EIA. Muscimol (1, 10 microM) increased and bicuculline (1, 10, 100 microM) decreased the AVP release 3-6 h after application. However, baclofen and phaclofen had no apparent effects on AVP release. Riluzole (0.1 mM) and nipecotic acid (1 mM), GABA uptake inhibitors, increased AVP release 3-6 h after application. These results indicate that GABA promotes AVP release mediated by GABA-A receptors in the SCN.