Light SCN direct via the retinohypothalamic RHT pathway

  • Slides: 41
Download presentation
Light →SCN: -direct via the retinohypothalamic (RHT) pathway -indirect via geniculohypothalamic (GHT) pathway

Light →SCN: -direct via the retinohypothalamic (RHT) pathway -indirect via geniculohypothalamic (GHT) pathway

SCN: some morphological features • Parvocellular, paired structure, ~16 -20, 000 neurons in rodent,

SCN: some morphological features • Parvocellular, paired structure, ~16 -20, 000 neurons in rodent, miniscule in man • Phenotypes: multiple potential transmitters – most express GABA (1993 proposal: SCN output is inhibitory) – Peptides: • vasoactive intestinal peptide (VIP) in cells in ventrolateral part; receives retinal input; forms part of the output projection • vasopressin (VP) in cells in dorsomedial part; forms part of the output projection • somatostatin (SS) in cells whose axons remain intrinsic to SCN

Lets consider the neural connections of SCN A schematic outline from Ibata et al

Lets consider the neural connections of SCN A schematic outline from Ibata et al Frontiers in Neuroendocrinology 20: 241 -268, 1999

Notes: 1 -Based on immunocytochemical grounds, SCN can be subdivided into dorsomedial (shell) and

Notes: 1 -Based on immunocytochemical grounds, SCN can be subdivided into dorsomedial (shell) and ventrolateral (core) segments 2 -Retinal input is to the VIPergic neurons in the ventrolateral SCN 3 -output pathways arise from both VIPergic and vasopressinergic neurons in SCN 4 -most projections are local, to hypothalamic sites (exceptions: LGB, TPV)

SCN: techniques to define inputoutput pathways • Using retrograde and/or anterograde transport of suitable

SCN: techniques to define inputoutput pathways • Using retrograde and/or anterograde transport of suitable markers e. g. wheat germ agglutin (WGA)

SCN: techniques to define inputoutput pathways • Using retrograde and anterograde transport of suitable

SCN: techniques to define inputoutput pathways • Using retrograde and anterograde transport of suitable markers e. g. WGA • Using viral retrograde transneuronal traceing (pseudorabies)

Retrograde transneuronal labeling with pseudorabies virus (PRV) injected in the adrenal gland

Retrograde transneuronal labeling with pseudorabies virus (PRV) injected in the adrenal gland

SCN: techniques to define inputoutput pathways • Using retrograde and/or anterograde transport of suitable

SCN: techniques to define inputoutput pathways • Using retrograde and/or anterograde transport of suitable markers e. g. WGA • Using viral retrograde transneuronal tracing (PRV) • Using double label immunocytochemistry to define phenotype (peptides)

PRV (green) A-C: in PVN oxytocin (red) D-E: in SCN vasopressin (red) F: in

PRV (green) A-C: in PVN oxytocin (red) D-E: in SCN vasopressin (red) F: in SCN VIP (red)

Anatomical and functional demonstration of a multisynaptic suprachiasmatic nucleus adrenal (cortex) pathway European Journal

Anatomical and functional demonstration of a multisynaptic suprachiasmatic nucleus adrenal (cortex) pathway European Journal of Neuroscience 11: 15351544, 1999 RM Buijs, J Wortel, JJ van Heerikhuize, MGP Feenstra, GJ Ter Horst, HJ Romijn, A Kalsbeek

Suprachiasmatic nucleus (SCN) • Brain Res. 1972 Jul 13; 42(1): 201 -6. – Loss

Suprachiasmatic nucleus (SCN) • Brain Res. 1972 Jul 13; 42(1): 201 -6. – Loss of a circadian adrenal corticosterone rhythm following suprachiasmatic lesions in the rat. Moore RY, Eichler VB.

The Big PICTURE: influence of the SCN timing system on various functions From Zigmond

The Big PICTURE: influence of the SCN timing system on various functions From Zigmond et al Fundamental Neuroscience, AP 1999

Individual neurons dissociated from rat suprachiasmatic nucleus express independently phased circadian firing rhythms Neuron

Individual neurons dissociated from rat suprachiasmatic nucleus express independently phased circadian firing rhythms Neuron 14: 697 -706, 1995 DK Welsh, DE Logothetis, M Meister and SM Reppert • Within the mammalian hypothalamus, the suprachiasmatic nucleus (SCN) contains a circadian clock for timing of diverse neuronal, endocrine, and behavioral rhythms. • By culturing cells from neonatal rat SCN on fixed microelectrode arrays, we have been able to record spontaneous action potentials from individual SCN neurons for days or weeks, revealing prominent circadian rhythms in firing rate. • Despite abundant functional synapses, circadian rhythms expressed by neurons in the same culture are not synchronized. • After reversible blockade of neuronal firing lasting 2. 5 days, circadian firing rhythms re-emerge with unaltered phases. • These data suggest that the SCN contains a large population of autonomous, single-cell circadian oscillators, and that synapses formed in vitro are neither necessary for operation of these oscillators nor sufficient for synchronizing them.

Electrical synapses coordinate activity in the suprachiasmatic nucleus MA Long, MJ Jutras, BW Connors,

Electrical synapses coordinate activity in the suprachiasmatic nucleus MA Long, MJ Jutras, BW Connors, RD Burwell Nature Neuroscience 8, 61 - 66 (2004) • In the suprachiasmatic nucleus (SCN), the master circadian pacemaker, neurons show circadian variations in firing frequency. There is also considerable synchrony of spiking across SCN neurons on a scale of milliseconds, but the mechanisms are poorly understood. • Using paired whole-cell recordings, we have found that many neurons in the rat SCN communicate via electrical synapses. Spontaneous spiking was often synchronized in pairs of electrically coupled neurons, and the degree of this synchrony could be predicted from the magnitude of coupling. • In wild-type mice, as in rats, the SCN contained electrical synapses, but electrical synapses were absent in connexin 36 -knockout mice. The knockout mice also showed dampened circadian activity rhythms and a delayed onset of activity during transition to constant darkness. • We suggest that electrical synapses in the SCN help to synchronize its spiking activity, and that such synchrony is necessary for normal circadian behavior.

Electrical coupling in SCN- the data • (a) In a well-coupled pair (coupling coefficient

Electrical coupling in SCN- the data • (a) In a well-coupled pair (coupling coefficient = 0. 13), hyperpolarizing current steps resulted in symmetric membrane-potential deflections in the coupled cell. In the left panel, we injected current into cell 1 and recording voltage responses in that cell and its pair. In the right panel, current was injected into cell 2. Traces are averaged from 50 trials. (b) Single action-potential response in a coupled pair in the presence of APV, DNQX and picrotoxin. Shown here is the mean postsynaptic response to 25 spontaneously occurring action potentials (dashed lines = s. e. m. ). (c) Scatterplot of the coupling strength of SCN cell pairs as a function of the time of day recorded. Note the greater incidence of coupling in the middle of the subjective day (ZT 4− 8) as compared the end of the subjective day (ZT 8− 12).

Coupled vs non-coupled SCN cells • All experiments were conducted in the presence of

Coupled vs non-coupled SCN cells • All experiments were conducted in the presence of APV, DNQX and picrotoxin. (a) Examples of intracellular recordings from a pair showing direct electrical coupling (left) and a pair lacking such a connection (right). Below are spike cross-correlograms describing long epochs (>200 s) of spiking data, including the above traces. The time scale for the cross-correlograms is in milliseconds. Correlogram values are normalized by the total spike count. Baseline correlations are subtracted from these analyses. (b) Examples of cell-attached recordings (top) from a coupled (left) and noncoupled (right) pair, and the corresponding spike cross-correlograms (below). (c) The spiking correlation coefficient of electrically coupled pairs is directly related to the strength of coupling. This scatterplot shows data from cellattached recordings ( ) as well as intracellular recordings (

Electrophysiology and circadian behavior in wild -type (WT) and Cx 36 -knockout (KO) mice.

Electrophysiology and circadian behavior in wild -type (WT) and Cx 36 -knockout (KO) mice.

Bridging the gap: coupling single-cell oscillators in the suprachiasmatic nucleus CS Colwell Nature Neuroscience

Bridging the gap: coupling single-cell oscillators in the suprachiasmatic nucleus CS Colwell Nature Neuroscience 8, 10 - 12 (2005) • Top, schematic of pairs of SCN neurons (blue) from wild-type (WT) and Cx 36 -/- mice. Individual SCN neurons contain the molecular machinery necessary to generate circadian oscillations. One gap in our knowledge is the lack of understanding of how these single-cell oscillators are coupled. The new study 3 demonstrates that SCN neurons are coupled through direct electrical connections. This coupling is lost in mice deficient in Cx 36. Bottom, schematics of wheel-running activity records from WT and Cx 36 -deficient mice. Animals maintained in constant darkness show rhythms driven by the endogenous timing system. Each horizontal row represents the activity record for a 24 -hour day. Successive days are plotted from top to bottom. The colored bars represent activity. The WT mice express robust circadian rhythms of locomotor activity with period shorter then 24 h. The onset of activity is typically under precise control. In contrast, the Cx 36 -deficient mice showed rhythms that were weaker and less coherent than controls. Without the Cx 36, the circadian clock still keeps time but lacks the temporal precision that typically characterizes the behavioral output.

A CLOCKWORK WEB: CIRCADIAN TIMING IN BRAIN AND PERIPHERY, IN HEALTH AND DISEASE Michael

A CLOCKWORK WEB: CIRCADIAN TIMING IN BRAIN AND PERIPHERY, IN HEALTH AND DISEASE Michael H. Hastings, Akhilesh B. Reddy & Elizabeth S. Maywood Nature Neuroscience Reviews August 2003

Time after time: inputs to and outputs from the mammalian circadian oscillators David Morsea,

Time after time: inputs to and outputs from the mammalian circadian oscillators David Morsea, Paolo Sassone-Corsi TINS 25: 632 -637, 2002 • • Fig. 1: Rhythmic oscillation of clock gene expression. (a) The mammalian circadian system has two negative feedback loops, one involving inhibition of bmal 1 transcription by a heterodimer of BMAL 1 (brain–muscle Arnt-like protein 1) and CLOCK (left), the other involving inhibition of period ( per) and cryptochrome ( cry) transcription by PER and CRY (right). The two loops are linked by the positive action of PER on bmal 1 transcription and the positive action of the CLOCK–BMAL 1 heterodimer (indicated by the yellow box) on E-boxcontaining promoters. Grey parts of the genes represent promoters; wavy lines indicate that levels of bmal 1, per and cry transcripts oscillate. (b) In the mouse suprachiasmatic nucleus (SCN), per and bmal 1 transcripts oscillate almost 12 h out of phase, with per levels at a maximum around midday. PER and BMAL 1 proteins also oscillate, but PER lags behind per RNA. (c) In peripheral tissues, such as the liver, the same clock gene components oscillate as in the SCN, but with peaks occurring later. The black and white bars above the graphs indicate night and day, respectively.

Nature Reviews Neuroscience 2, 521 -526 (2001); HYPOTHALAMIC INTEGRATION OF CENTRAL AND PERIPHERAL CLOCKS

Nature Reviews Neuroscience 2, 521 -526 (2001); HYPOTHALAMIC INTEGRATION OF CENTRAL AND PERIPHERAL CLOCKS Ruud M. Buijs & Andries Kalsbeek • During sleep, our biological clock prepares us for the forthcoming period of activity by controlling the release of hormones and the activity of the autonomic nervous system. Here, we review the history of the study of circadian rhythms and highlight recent observations indicating that the same mechanisms that govern our central clock might be at work in the cells of peripheral organs. Peripheral clocks are proposed to synchronize the activity of the organ, enhancing the functional message of the central clock. We speculate that peripheral visceral information is then fed back to the same brain areas that are directly controlled by the central clock. Both clock mechanisms are proposed to have a complementary function in the organization of behaviour and hormone secretion.

Interaction between peripheral and central clocks

Interaction between peripheral and central clocks

The Circadian Gene Period 2 Plays an Important Role in Tumor Suppression and DNA

The Circadian Gene Period 2 Plays an Important Role in Tumor Suppression and DNA Damage Response In Vivo Fu, L et al. Cell 111: 41 -50, 2002 • The Period 2 gene plays a key role in controlling circadian rhythm in mice. We report here that mice deficient in the m. Per 2 gene are cancer prone. After γ radiation, these mice show a marked increase in tumor development and reduced apoptosis in thymocytes. The core circadian genes are induced by γ radiation in wild-type mice but not in m. Per 2 mutant mice. Temporal expression of genes involved in cell cycle regulation and tumor suppression, such as Cyclin D 1, Cyclin A, Mdm-2, and Gadd 45α, is deregulated in m. Per 2 mutant mice. In particular, the transcription of c-myc is controlled directly by circadian regulators and is deregulated in the m. Per 2 mutant. Our studies suggest that the m. Per 2 gene functions in tumor suppression by regulating DNA damage-responsive pathways.

Drosophila melanogaster

Drosophila melanogaster