Intrinsic photosensitive retinal ganglion cells in the diurnal rodent, Arvicanthis ansorgei.

Intrinsically photosensitive retinal ganglion cells (ipRGCs) represent a new class of photoreceptors which support a variety of non-image forming physiological functions, such as circadian photoentrainment, pupillary light reflex and masking responses to light. In view of the recently proposed role of retinal inputs for the regulation of diurnal and nocturnal behavior, we performed the first deep analysis of the ipRGC system in a diurnal rodent model, Arvicanthisansorgei, and compared the anatomical and physiological properties of ipRGCs with those of nocturnal mice. Based on somata location, stratification pattern and melanopsin expression, we identified two main ipRGC types in the retina of Arvicanthis: M1, constituting 74% of all ipRGCs and non-M1 (consisting mainly of the M2 type) constituting the following 25%.

The output signal of Purkinje cells of the cerebellum and circadian rhythmicity.

Measurement of clock gene expression has recently provided evidence that the cerebellum, like the master clock in the SCN, contains a circadian oscillator. The cerebellar oscillator is involved in anticipation of mealtime and possibly resides in Purkinje cells. However, the rhythmic gene expression is likely transduced into a circadian cerebellar output signal to exert an effective control of neuronal brain circuits that are responsible for feeding behavior.

Heterogeneity of intrinsically photosensitive retinal ganglion cells in the mouse revealed by molecular phenotyping.

Intrinsically photosensitive retinal ganglion cell (ipRGC) types can be distinguished by their dendritic tree stratification and intensity of melanopsin staining. We identified heavily stained melanopsin-positive M1 cells branching in the outermost part of the inner plexiform layer (IPL) and weakly melanopsin-positive M2 cells branching in the innermost layer of the IPL. A third type can be distinguished by the displacement of the soma to the inner nuclear layer and has morphological similarities with either M1 cells or M2 cells, and is termed here displaced or M-d cells.

Activation of glycine receptor phase-shifts the circadian rhythm in neuronal activity in the mouse suprachiasmatic nucleus.

In mammals, the master clock in the suprachiasmatic nucleus (SCN) of the hypothalamus is composed of numerous synchronized oscillating cells that drive daily behavioural and physiological processes. Several entrainment pathways, afferent inputs to the SCN with their neurotransmitter and neuromodulator systems, can reset the circadian system regularly and also modulate neuronal activity within the SCN. In the present study, we investigated the function of the inhibitory neurotransmitter glycine on neuronal activity in the mouse SCN and on resetting of the circadian clock.

Pineal projections in the zebrafish (Danio rerio): overlap with retinal and cerebellar projections.

The pineal organ in fishes is a photoreceptive organ with dual outputs, neuroendocrine and neural. The neural projections of the zebrafish pineal were experimentally studied by means of tract-tracing with carbocyanine dyes (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), 3,3'-dioctadecyloxacarbocyanine perchlorate (DiO)). Double-labeling experiments were also performed in order to investigate the degree of overlapping of pineal, retinal or cerebellar projections in zebrafish.

Orexin A modulates neuronal activity of the rodent suprachiasmatic nucleus in vitro.

In mammals, as in rats and mice used in the present study, the major internal timekeeping mechanism is located in the suprachiasmatic nucleus (SCN). It is composed of a complex tissue of multiple, individual oscillator cells that drive numerous physiological and endocrine processes via an electrical and humoral output. Several afferent input systems can interact with the clock mechanism and lead to phase-resetting actions.

The mammalian molecular clockwork controls rhythmic expression of its own input pathway components.

The core molecular clockwork in the suprachiasmatic nucleus (SCN) is based on autoregulatory feedback loops of transcriptional activators (CLOCK/NPAS2 and BMAL1) and inhibitors (mPER1-2 and mCRY1-2). To synchronize the phase of the molecular clockwork to the environmental day and night condition, light at dusk and dawn increases mPer expression. However, the signal transduction pathways differ remarkably between the day/night and the night/day transition.

Nitric oxide synthase in photoreceptive pineal organs of fish.

Photoreceptor cells in the fish pineal gland transduce light-dark information differentially into a neuroendocrine melatonin message; distinguishing features are the presence or absence of endogenous oscillators that drive these rhythms. In the present study, we have analysed the presence and distribution of nitric oxide (NO) synthase in both pineal types by NADPH-diaphorase (NADPHd) histochemistry and determined the effects of NO donors on cGMP formation and melatonin production. NADPHd staining was confined to photoreceptor cells in clock-driven pineal organs of zebrafish and goldfish as evidenced by a codistribution with S-antigen-immunoreactivity (-ir) or cyclic GMP-ir and, in the pineal of the trout, to cells that are S-antigen negative.

Circadian activity rhythms and phase-shifting of cultured neurons of the rat suprachiasmatic nucleus.

The mammalian suprachiasmatic nucleus (SCN) is the major endogenous pacemaker that coordinates various daily rhythms including locomotor activity and autonomous and endocrine responses, through a neuronal and humoral influence. In the present study we examined the behavior of dispersed individual SCN neurons obtained from 1- to 3-day-old rats cultured on multi-microelectrode arrays (MEAs). SCN neurons were identified by immunolabeling for the neuropeptides arginine-vasopressin (AVP) and vasoactive intestinal polypeptide (VIP).

Immunochemical, ultrastructural and electrophysiological investigations of bone-derived stem cells in the course of neuronal differentiation.

Numerous reports have highlighted the use of mesenchymal stem cells (MSC) for tissue engineering because of the capacity of the cells to differentiate along the osteogenic, chondrogenic or adipogenic pathway. As MSC also display neuronal morphologies under appropriate culture conditions, the differentiation capacity of stem cells seems to be more complex than initially thought, but it requires careful characterization of the cells. This is especially the case because recently it has been suggested that neuronal differentiation of stem cells is only an artifact.

Suprachiasmatic nuclei grafts restore the circadian rhythm in the paraventricular nucleus of the hypothalamus.

The mammalian suprachiasmatic nucleus (SCN) controls the circadian rhythm of many physiological and behavioral events by an orchestrated output of the electrical activity of SCN neurons. We examined the propagation of output signals from the SCN into the hypothalamus, especially into the region of the paraventricular nucleus, through multimicroelectrode recordings using acute and organotypic brain slices. Circadian rhythms in spontaneous firing rate with a period close to 24 hr were demonstrated in the SCN, in directly adjacent hypothalamic regions, and in the region of the paraventricular nucleus of the hypothalamus, an important center for the integration of neuroendocrine, homeostatic, and autonomic functions.

Evolution of photosensory pineal organs in new light: the fate of neuroendocrine photoreceptors.

Pineal evolution is envisaged as a gradual transformation of pinealocytes (a gradual regression of pinealocyte sensory capacity within a particular cell line), the so-called sensory cell line of the pineal organ. In most non-mammals the pineal organ is a directly photosensory organ, while the pineal organ of mammals (epiphysis cerebri) is a non-sensory neuroendocrine organ under photoperiod control. The phylogenetic transformation of the pineal organ is reflected in the morphology and physiology of the main parenchymal cell type, the pinealocyte.

The pituitary adenylate cyclase-activating polypeptide modulates glutamatergic calcium signalling: investigations on rat suprachiasmatic nucleus neurons.

Circadian rhythms generated by the hypothalamic suprachiasmatic nucleus (SCN) are synchronized with the external light/dark cycle by photic information transmitted directly from the retina via the retinohypothalamic tract (RHT). The RHT contains the neurotransmitters glutamate and pituitary adenylate cyclase-activating polypeptide (PACAP), which code chemically for 'light' or 'darkness' information, respectively. We investigated interactions of PACAP and glutamate by analysing effects on the second messenger calcium in individual SCN neurons using the Fura-2 technique.

Analyses of signal transduction cascades reveal an essential role of calcium ions for regulation of melatonin biosynthesis in the light-sensitive pineal organ of the rainbow trout (Oncorhynchus mykiss).

Signal transduction processes regulating melatonin production in the light-sensitive trout pineal organ were investigated by immunocytochemical and immunochemical demonstration of phosphorylated cyclic AMP-responsive element-binding protein (pCREB) and measurements of cyclic AMP, melatonin, and calcium levels. Melatonin levels were tightly controlled by light and darkness. Elevation of cyclic AMP levels by 8-bromo-cyclic AMP, forskolin, and 3-isobutyl-1-methylxanthine increased the levels of pCREB and melatonin in light- or dark-adapted pineal organs in vitro.

Photoendocrine signal transduction in pineal photoreceptors of the trout. Role of cGMP and nitric oxide.

This study describes the presence and distribution of cGMP-immunoreactivity and of the nitric oxide (NO) synthesizing enzyme, NO synthase (NOS), as demonstrated by use of the NADPH-diaphorase technique in directly light sensitive pineal organ of the trout. Cyclic GMP immunohistochemistry revealed immunoreactivity in pineal photoreceptor cells that were identified by double-labeling with S-antigen, whereas NADPH-positive structures were located adjacent to these photoreceptor cells. Since NO is known to stimulate synthesis of cGMP, these results indicate a role for NO in pineal function, e.

Responses of neurones of the rat suprachiasmatic nucleus to retinal illumination under photopic and scotopic conditions.

1. We have examined the responses of neurones in the suprachiasmatic nuclei (SCN) of the rat to retinal illumination under photopic and scotopic conditions to identify the types of photoreceptor input to these nuclei. 2.

Pituitary adenylate cyclase-activating polypeptide and melatonin in the suprachiasmatic nucleus: effects on the calcium signal transduction cascade.

The suprachiasmatic nucleus (SCN) harbors an endogenous oscillator generating circadian rhythms that are synchronized to the external light/dark cycle by photic information transmitted via the retinohypothalamic tract (RHT). The RHT has recently been shown to contain pituitary adenylate cyclase-activating polypeptide (PACAP) as neurotransmitter/neuromodulator. PACAPergic effects on cAMP-mediated signaling events in the SCN are restricted to distinct time windows and sensitive to melatonin.

Photic regulation of pineal function. Analogies between retinal and pineal photoreception.

Light absorbed by a photopigment in a photoreceptor cell causes a photochemical reaction converting the 11-cis retinal chromophore into the all-trans configuration. These changes lead to a series of events that causes cGMP hydrolysis, a following decrease of cGMP in the cytoplasm of the photoreceptor outer segment and a closure of cGMP-gated cationic channels. As a consequence of these processes the membrane hyperpolarizes.

The pituitary adenylate cyclase-activating polypeptide-induced phosphorylation of the transcription factor CREB (cAMP response element binding protein) in the rat suprachiasmatic nucleus is inhibited by melatonin.

The mammalian hypothalamic suprachiasmatic nucleus (SCN) is an endogenous pacemaker generating circadian rhythms. SCN activity is synchronized with environmental light/dark cycles by photic information primarily transmitted via the retinohypothalamic tract (RHT). The SCN controls synthesis and release of melatonin, the hormone of the pineal gland.

Regulation of melatonin production and intracellular calcium concentrations in the trout pineal organ.

The present in vitro study correlates measurements of the melatonin production from trout pineal organs with those of the intracellular calcium concentration in pinealocytes. Melatonin production increases with decreasing irradiance and shows maximal values in darkness. Some pinealocytes exhibit spontaneous calcium oscillations, although most of them have a stable basal calcium concentration.

Central projections of the parapineal organ of the adult rainbow trout (Oncorhynchus mykiss).

Neural connections of the small parapineal organ of the adult rainbow trout were experimentally investigated by using a lipophilic carbocyanine dye as a tracer. The dye was applied to the parapineal organ, to the pineal organ, or to the left or right habenular ganglion. The parapineal organ mainly projected via a coarse parapineal tract to a conspicuous neuropil in the rostrodorsal part of the left habenular ganglion.

Diazepam increases melatonin secretion of photosensitive pineal organs of trout in the photopic and mesopic range of illumination.

The pineal organ of teleost fish receives photic information directly through specialized photoreceptor cells that transmit their light response to second-order neurons and respond also with an endocrine light-dependent melatonin signal. In the present study we have analyzed the action of diazepam, a full agonist of the benzodiazepine receptor, on the photic regulation of the endocrine melatonin response of cultured trout pineal organs. Melatonin release of explanted pineal organs was clearly dependent on the irradiance of incident light with a maximum change during mesopic illuminations.

Secretion of the methoxyindoles melatonin, 5-methoxytryptophol, 5-methoxyindoleacetic acid, and 5-methoxytryptamine from trout pineal organs in superfusion culture: effects of light intensity.

The teleost pineal organ is a photoreceptive endocrine organ that synthesizes the hormone melatonin through specialized intrapineal photoreceptor cells in a light-dependent manner. The present study investigated whether the methoxyindoles 5-methoxytryptophol (5-MTOL), 5-methoxyindoleacetic acid (5-MIAA), and 5 methoxytryptamine (5-MT) correspond to melatonin secretion synthesized and released from explanted, superfused pineal organs in response to direct light stimulation and whether their release is correlated with the level of dark adaptation. Melatonin release in superfusion cultures using Hank's buffer was clearly dependent on irradiance of the incident light and increased with decreasing light intensity from an average release of 1 ng/pineal/hr in light-adapted pineal glands to about 9 ng/pineal/hr in dark-adapted pineal glands.

Secretion of methoxyindoles from trout pineal organs in vitro: indication for a paracrine melatonin feedback.

Synthesis and release of the pineal hormone melatonin is in all vertebrates primarily regulated by the light/dark cycle. In pineal organs of teleost fish, like in other non-mammalian vertebrates, melatonin formation is regulated by a direct photoreception of the pineal organ. We performed measurements in explanted, perifused pineal organs of the rainbow trout, Oncorhynchus mykiss, to examine whether melatonin can influence its own production.

Benzodiazepines influence melatonin secretion of the pineal organ of the trout in vitro.

The effect of benzodiazepines (BZP) on melatonin release was investigated in the pineal gland of the rainbow trout, Oncorhynchus mykiss, maintained under in vitro perifusion culture conditions. Melatonin and the methoxyindoles 5-methoxytryptophol (5-MTOL), 5-methoxyindoleacetic acid (5-MIAA), and 5-methoxytryptamine (5-MT) were determined directly in samples of the superfusion medium by HPLC with electrochemical detection. Melatonin release was significantly increased by addition of diazepam and clonazepam in a dose-related and reversible manner.