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At least 19 recordsLinked to original sources
PubMed1978

Light- and electron microscopic localization of vasopressin or a vasopressin-like substance in the neurons of the rat suprachiasmatic nucleus.

In the suprachiasmatic nucleus of the rat light microscopic immunostaining for vasopressin reveals a distribution pattern of the immunoreactive material different from that known for the supraoptic nucleus. Among non-stained neurons positive-reacting perikarya display a cap- or tip-like labeling. The area of the suprachiasmatic nucleus is marked by delicate vasopressin-positive fibers. At the ultrastructural level the reaction product, after incubation with anti-vasopressin, is localized in small elementary granules unevenly distributed over the cytoplasm. Groups of axons containing specifically labeled granules contact non-reacting fibers.

Animals↗
PubMed2026

GIRK Channels Regulate Circadian Rhythms of Excitability in Prokineticin 2 Neurons of the Suprachiasmatic Nucleus and Modulate Behavioral Circadian Rhythms.

The suprachiasmatic nucleus (SCN), the central circadian clock in mammals, generates robust yet adaptable circadian rhythms through electrically mediated coordination among heterogeneous peptidergic neuronal populations with presumed cell type-specific roles. Previous studies have proposed that circadian changes in membrane excitability of individual SCN neurons arise from time-of-day-dependent shifts in the relative balance of subthreshold Na+ and K+ conductances. Although multiple channels have been implicated in these processes, how nocturnally dominant K+ conductances are implemented in a cell type-specific manner remains poorly understood. Prokineticin 2 (Prok2) has been identified as a SCN signaling peptide essential for behavioral circadian regulation; however, the electrophysiological properties of Prok2-expressing neurons and the mechanisms underlying their diurnal rhythmicity remain largely unexplored. Here, using electrophysiological approaches in mice of either sex, we show that Prok2 neurons exhibit diurnal variations in electrical properties, with higher excitability during the day and reduced excitability at night, and that G-protein-coupled inwardly rectifying potassium (GIRK) channel-mediated basal current contributes to nighttime hyperpolarization. Immunofluorescence and single-cell RT-PCR analyses revealed that GIRK1 and GIRK3 are the predominant GIRK subunits expressed in Prok2 neurons. Moreover, Prok2 neuron-specific deletion of GIRK3 using in vivo genome editing resulted in significant nocturnal depolarization and induced abnormalities in behavioral rhythms, including delayed activity onset and circadian period lengthening, with altered SCN network activity. Together, these findings suggest that tonic, G-protein-dependent regulation of GIRK channels provides a night-specific inhibitory mechanism that contributes to intrinsic diurnal neuronal excitability in Prok2 neurons and supports the regulation of behavioral circadian rhythms.

Animals↗
PubMed1979

Persistence of circadian rhythmicity in a mammalian hypothalamic "island" containing the suprachiasmatic nucleus.

The experimental work described tested the prosposition that the suprachiasmatic nucleus of the hypothalamus is an autonomous circadian pacemaker. Simultaneous recording from two extracellular electrodes indicated neural (multiple unit) activity at two sites in the brain, one of which is in or near the suprachiasmatic nucleus and the other in one of many other brain locations. Both sites in intact rats displayed clear circadian rhythmicity of spontaneous neural activity. In experimental animals, a Halasz knife was used to create an island of hypothalamic tissue that contained the suprachiasmatic nuclei. In such animals that were also blinded by bilateral ocular enucleation, circadian rhythmicity was lost at all brain locations recorded outside the island, but it persisted within the island that contained the suprachiasmatic nuclei. The rhythmicity of the island is thus not dependent on afferent inputs from elsewhere in the brain.

Action Potentials↗
PubMed1978

Neonatal suprachiasmatic nucleus ablation: absence of functional and morphological plasticity.

Neonatal ablation of the suprachiasmatic nucleus in the rat has two important consequences. First, the direct projection from the retina to the suprachiasmatic nucleus fails to develop and no other retinal projection to any hypothalamic nucleus is formed. Second, circadian rhythms in drinking and spontaneous locomotor activity to not appear in these rats when they are tested as adults, and the females exhibit constant vaginal estrus. These observations indicate that the central neural mechanisms responsible for the generation and entrainment of circadian rhythmicity in the rat are not capable of either the functional or morphological plasticity characteristic of other developing neural systems.

Animals↗
PubMedDate not supplied

Effects of suprachiasmatic nucleus lesions on hypothalamic LH-releasing hormone (LHRH) content and gonadotropin secretion in the ovariectomized (OVX) female rat.

Suprachiasmatic nucleus lesions in OVX rats blocked progesterone-induced gonadotropin surges without affecting tonic levels of these hormones or the expression of estrogen negative feedback. In addition, these lesions resulted in a decrease in LHRH content of tissue rostral and caudal to the lesion. These results suggest that the effect of suprachiasmatic nucleus lesions on phasic gonadotropin secretion may be due to the interruption of LHRH input to the median eminence from rostral centers known to be important in this event.

Animals↗
PubMed1978

Retinal afferents form Gray-type-I and type-II synapses in the suprachiasmatic nucleus (rat).

The synapses of optic nerve afferents in the suprachiasmatic nucleus (SCN) usually form Gray type I (asymmetrical) synapses, but about 13% show clear-cut Gray type II ( symmetrical) active zones. Some presynaptic elements form a Gray type I--active zone with one dendrite and a Gray type II-active zone with another postsynaptic element at the same time. It is discussed whether this variabilility is related to a simultaneous excitatory and inhibitory action, to a variable activity or efficiency of the synapses or to various stages of maturation.

Animals↗
PubMed2025

The suprachiasmatic nucleus regulates brown fat thermogenesis in male mice through an adrenergic receptor ADRB3-S100B signaling pathway.

The suprachiasmatic nucleus (SCN), the central circadian pacemaker, orchestrates daily metabolic rhythms, yet its role in substrate selection and thermogenic adaptation under stress remains insufficiently understood. Here, we show that SCN lesioning abolishes the adaptive suppression of brown adipose tissue (BAT) thermogenesis typically observed during time-restricted feeding in subthermoneutral environments (TRF-STE), a paradigm that imposes concurrent nutrient and thermal stress. Contrary to wild-type responses, SCN-lesioned mice maintain elevated BAT thermogenic activity, despite impaired lipolysis, instead shifting toward glucose-driven heat production. This phenotype is accompanied by sustained sympathetic tone and β3-adrenergic receptor (ADRB3) signaling in BAT. Mechanistically, we identify a SCN-regulated ADRB3-S100B signaling axis underlying this metabolic reprogramming. S100B, a nutrient-sensitive calcium-binding protein, is upregulated in BAT following SCN disruption, where it promotes thermogenesis by stimulating brown adipocyte proliferation and suppressing senescence. Functional studies reveal that S100B is both necessary and sufficient for sustaining BAT thermogenesis under TRF-STE. Furthermore, diverse SCN disruption models, including light-induced circadian arrhythmia, N-Methyl-D-aspartic acid (NMDA) excitotoxicity, and Caspase-3-mediated ablation, consistently elevate S100B expression in BAT, reinforcing its role as a convergent effector of SCN-regulated metabolic adaptation. Thus, in intact animal, the SCN restrains the ADRB3-S100B module, gating BAT thermogenic output in accordance with energetic availability. Disruption of SCN output lifts this restraint, unmasking a latent ADRB3-S100B program that preserves thermogenesis when lipid fuel is limited. These findings reveal a previously unrecognized role of the SCN in governing thermogenic flexibility and fuel partitioning, and position the ADRB3-S100B axis as a potential target for mitigating circadian misalignment and metabolic disease.

Animals↗
PubMedDate not supplied

Suprachiasmatic nucleus responsiveness to photic and basal hypothalamic stimulation.

In view of the demonstrated role of light and of the suprachiasmatic nucleus (SCN) in the maintenance of circadian rhythms related to endocrine functions and as the mediobasal hypothalamus (MBH) controls neuroendocrine activity, the effects of light and MBH stimulation on the electrical activity of SCN neurons were studied in rats. Out of 253 cells studied in the SCN, 32 cells were antidromically activated, while 65 cells responded orthodromically to MBH stimulation. In another series of experiments out of 95 suprachiasmatic neurons, 11 were antidromically activated by MBH stimulation and 18 different SCN cells responded to continuous light. The present data, which demonstrate photic responses in suprachiasmatic neurons and direct projections from the SCN to MBH, are discussed in view of the current knowledge on the role of the retinohypothalamic tract and the SCN in the control of circadian rhythms.

Animals↗
PubMed1979

Suprachiasmatic nucleus neurones: excitation and inhibition mediated by the direct retino-hypothalamic projection in female rats.

The suprachiasmatic nucleus (SCN) of female rats was surveyed with microelectrodes under urethane anaesthesia. In rats with bilateral transection of the optic tracts, repetitive three pulses of 100 Hz applied to the contralateral optic nerve excited 8 and inhibited 11 other of the 86 SCN units examined. Transection of the optic tract did not significantly influence frequency of occurrence of the SCN units that were excited or inhibited by stimulation of the optic nerve. Certain SCN units responded to both of contralateral and ipsilateral stimulations of the optic nerve, indicating that bilateral visual inputs converge on the same single SCN neurones. Oscillatory responses with a period of 100--200 msec were occasionally produced by stimulation of the optic nerve. Flash stimuli with relatively weak intensity, even insufficient for producing wavelets in electroretinograms, produced an excitation and inhibition in SCN units. The mean firing rates were significantly altered by either electrical or flash stimuli repeated 500 times at 0.97 Hz in those units which showed no transitory response. Some of the SCN neurones receiving visual inputs were identified to be the tuberoinfundibular neurone and some other SCN neurones were found to receive converging inputs both from the optic nerve and from the axon collaterals of tuberoinfundibular neurones.

Animals↗
PubMed1979

Neonatal suprachiasmatic nucleus lesions: effects on the development of circadian rhythms in the rat.

Previous studies of the effects of suprachiasmatic nucleus (SCN) destruction and visual pathway transections in adult rodents have revealed the primary significance of the SCN and the retinohypothalamic (RH) projection in the generation and entrainment of circadian rhythms. In the present study we found that complete ablation of the SCN in 2-day-old rats, prior to its innervation by the RH projection, permanently eliminates circadian rhythms in spontaneous locomotor activity and drinking; activity and drinking appear randomly distributed over the light-dark cycle. In addition, females exhibit long periods of constant vaginal cornification and an absence of normal estrous cycles. These effects are independent of the animal's visual status; that is, they occur in blinded as well as sighted animals. Incomplete SCN lesions results in partial disruption of rhythmic functions such as damping of circadian rhythms in activity and/or drinking, irregular estrous cycling, and/or complete disruption of only one or two of these measures of rhythmicity. The absence of spared functions after early SCN destruction is consistent with the high degree of specificity for the SCN exhibited by developing RH fibers and further emphasizes the significance of the SCN in circadian rhythm generation. Neither morphological nor functional plasticity has been found following neonatal ablation of the SCN in the rat.

Animals↗
PubMed1978

Persistent estrus and blockade of progesterone-induced LH release follows lesions which do not damage the suprachiasmatic nucleus.

Very small electrolytic lesions were made over the anterior or posterior portion of the optic chiasm in mature female rats showing normal estrous cycles. Lesions over the posterior portion of chiasm destroyed the suprachiasmatic nucleus of the hypothalamus (SCN) while the anterior lesions destroyed a small neural structure, here designated as the medial preoptic nucleus (MPN). Both lesions were effective in inducing persistent vaginal estrus, but when animals were ovariectomized and treated with exogenous and progesterone it was found that lesions including the MPN alone, but not the SCN alone, eliminated the positive feedback effects of this steroid regimen on LH release.

Animals↗
PubMed1979

Pineal N-acetyltransferase and hydroxyindole-O-methyltransferase: control by the retinohypothalamic tract and the suprachiasmatic nucleus.

The visual pathway and central neural structures involved in the photic and endogenous regulation of the activity of pineal N-acetyltransferase and hydroxyindole-O-methyltransferase were investigated. The results indicate that the visual pathway regulating both enzymes is the retinohypothalamic tract, and that the inferior accessory optic tract is clearly not involved in the regulation of hydroxyindole-O-methyltransferase activity, as has been previously thought. In addition, the suprachiasmatic nucleus was found to be necessary for the generation of a rhythm in N-acetyltransferase activity in blinded animals, and to be responsible for the tonic elevation of hydroxyindole-O-methyltransferase activity in blinded animals. Finally, it was concluded that the rapid and large daily changes in N-acetyltransferase activity seen in a normal lighting cycle and the much slower and smaller changes in hydroxyindole-O-methyltransferase activity seen only after weeks in constant lighting conditions are mediated by the same neural tract; the different time courses of the effects of environmental lighting may be explained on the basis of different intracellular regulatory mechanisms.

Acetylserotonin O-Methyltransferase↗
PubMed1979

Regularly firing neurones in the rat suprachiasmatic nucleus.

The spontaneous discharge of some suprachiasmatic neurones in vivo and in vitro was found to exhibit a very constant interspike interval. In vivo these cells were comparatively rare and appeared to be mutually coupled. The findings are discussed in relation to coupled oscillator theories of circadian rhythm generation.

Animals↗