BSci 3230 Lecture Notes PDF

NOTE ! These files are provided for the sole purpose of assisting BSci 3230 students to study for exams in the class. Some of the material in these files may be copyrighted, and it is not OK for you to share these files with anyone who is not a student in this class or to use them for any purpose ot...

NOTE ! These files are provided for the sole purpose of assisting BSci 3230 students to study for exams in the class. Some of the material in these files may be copyrighted, and it is not OK for you to share these files with anyone who is not a student in this class or to use them for any purpose other than to study for BSci 3230. Thanks, Carl Johnson  BSci 3230 From Genes to Behavior and Back Again From Genes to Behavior Feedback at every step; e.g., SCN networks control behavior, but behavior feeds back to modulate SCN amplitude Functional relevance of multi-oscillator structure For nocturnal rodents, SCN activity and locomotor activity are inversely correlated Aging and exercise have opposite effects on the SCN clock Note: many of the slides included in this lecture are courtesy of Dr. Johanna Meijer, University of Leiden, Netherlands  Feedback flow at every control level Genes Membrane potential necessary TTFL for rhythms Neuron Ion channels Network activity enhances Electrical activity SCN neuron amplitude SCN network Neural circuits Activity/exercise can enhance SCN amplitude and cause phase shifts Behavior Entrainment & Seasons Environment (e.g., LL, photoperiod, T-cycle)  Circadian Behavior: cell-based or network-dependent? Is the rhythm from the SCN based on coupling of cell-autonomous oscillators or is the rhythm dependent on an emergent network of non- oscillating cells ? single dissociated SCN neurons are rhythmic in vitro Isolated SCN neurons on “multielectrode plate” (MEP) 50µm We already discussed these data in Lecture 12  Circadian Behavior: cell-based or network-dependent? Isolated SCN neurons can free- run with different periods (therefore, they are not synchronized), and tetrodotoxin (TTX) will stop firing activity but after washout, the recovered rhythm is in phase with the pretreatment rhythm We already discussed these data in Lecture 12  SCN: composed of ~40,000 neurons in Human total of heterogeneous cell types Mouse Primates Coronal Slice Horizontal Slice  Evidence for multi-oscillator system within the SCN Per-luc molecular rhythms in SCN: Electrical activity in SCN: electrical activity of single unit activity SCN subpopulations: SCN recordings: Electrical activity Yamaguchi et al. Science 2003 Individual SCN neurons are active at different phases, but are coupled together in networks that Schaap et al. PNAS 2003 give coherent rhythms in the entire SCN population  The SCN are functionally and anatomically composed of at least two regions AVP/VIP PVN,SPZ etc VIII Dorso- Shell medial rat SCN mouse SCN (AVP/GABA) (AVP/GABA) Raphe Core Ventro- lateral IGL (VIP/GRP/ 5H T GABA) (VIP/GRP/GABA) A BA Optic chiasm G N PY/ ate/ RHT G lu t a m VIP = Vasoactive intestinal peptide AVP = Arginine Vasopressin, aka Vasopressin retina PACAP (VP), aka antidiuretic hormone (ADH) 5HT = serotonin GRP = Gastrin-releasing peptide NPY = Neuropeptide Y PACAP = Pituitary adenylate cyclase- GABA = gamma-amino butyric acid activating polypeptide  Core : Shell: receives major afferents from eyes projects efferent outputs VIP/GRP neurons predominate AVP neurons predominate Gating/photic induction Autonomous Per mRNA rhythms SCN neurons are (>90%) GABAergic in both core and shell Spatial differences in circadian vs. light-induced mPer1 expression: CT4 No light CT16 No light CT 16 30min light pulse Optic Chiasm Shigeyoshi et al. Cell 91: 1043-53, 1997. (also see 2nd Human Lecture) Antle & Silver, TINS 28:145-151, 2005  Evidence for multi-oscillator system within the SCN Left/Right SCN are normally coupled, but sometimes become uncoupled during “splitting” in LL (hamster data shown) Per 1 Per 1 Bmal 1 de la Iglesia, Meyer, Carpino & Schwartz, Science 290:799, 2000  SCN networks/Neural Circuits Clocks within cells: Multiple interlocked feedback loops Core neurons: Photic induction, interface with environment Shell neurons: Autonomous rhythms Left/Right SCN: Additional coupling Targets Antle & Silver TINS 28: 145-151 (2005)  Functional relevance of multi-oscillator structure Precision many oscillators ( i.e., SCN neurons) coupled Robustness together lead to these advantages Resilience Adaptation to photoperiods: phase differences among SCN neurons contribute to photoperiodic adaptation  Beyond the Single Cell: Building a Precise SCN Clock intact animal (wheel-running) SCN slice SCN slice SCN slices isolated SCN neurons Herzog et al., J Biol Rhythms 19:35, 2004  Beyond the Single Cell: Building a Robust SCN Clock Mouse mPer2::luc cultures of Mice, 22.51 h mPer2::luc SCN explants, 22.53 h isolated SCN neurons: Cry1-/- mPer2::luc isolated neurons (Cry1-/-) Cry1-/- mPer2::luc isolated neurons (wild type) The proportion of rhythmic (black) vs arhythmic (white) SCN WT neurons from low-density cultures compared with high-density cultures van der Horst et al., Nature 398:627,1999 Webb et al., PNAS 106:16493, 2009 Liu et al., Cell 129:605, 2007  Functional relevance of multi-oscillator structure Adaptation to photoperiods: phase differences among SCN neurons contribute to photoperiod adaptation of the SCN Electrical Phase differences between (neural) activity of neurons contribute to the SCN in photoperiod adaptation of vivo LD 8:16 LD 8:16 the SCN. Simulation of a short photoperiod resulted in a narrow population Locomotor pattern with a high activity of amplitude rhythm. the animal Simulation of longer LD 12:12 prior to photoperiods by larger electrical assays phase distribution of the neurons rendered lower- LD 12:12 amplitude rhythms with a broader peak. The interpretation at this time is SCN has LD 16:8 that the circadian FRP & lower amplitude of individual amplitude in neurons is unchanged, but LD 16:8 long days the coupling between them is changed by photoperiod. Therefore, seasonal encoding is a NETWORK property Schaap et al. PNAS 2003  Functional relevance of multi-oscillator structure Adaptation to photoperiods: Building a Photoperiodic SCN Clock Electrical activity Rat (c-fos photoinduction) LD 8:16 SCN slices from animals previously in long days show lower amplitude and less synchrony Electrical activity LD 16:8 Sumová et al., PNAS 92:7754, 1995 van der Leest et al., Curr Biol 17:468, 2007 Therefore, seasonal encoding is a NETWORK property  Functional relevance of multi-oscillator structure C57BL/6 mouse (hypothalamic slice) Adaptation to photoperiods: Building a Photoperiodic SCN SCN has Clock lower amplitude in long days Seasonal/Photoperiodic encoding is a NETWORK property mPer2::luc mouse (in vitro slice) Core region of SCN shows big differences in peak time as compared with other regions in longer photoperiods (Coronal Slices) Evans et al., Neuron 80:973, 2013  Functional relevance of multi-oscillator structure Adaptation to photoperiods: Building a Photoperiodic SCN Clock Yoshikawa et al. Sci. Rep. 2017 Therefore, seasonal encoding is a NETWORK property  Functional relevance of multi-oscillator structure What’s in the core of the SCN ? VIP neuropeptides, which appear to coordinate different regions within the SCN. What happens in VIP-knockout mice ? VIP- VIP- In VIP-knockout mice, there is no “memory” of the photoperiod in terms of the duration of activity after release from LD to DD Lucassen et al. EJN 2012 Is Aging of the Clock and the SCN a Network Problem? Young animals: SCN rhythms have a higher amplitude rhythm of young neural activity than older animals old Young animals: SCN cells in synch & in phase Old animals: SCN cells out of synch & sometimes in antiphase (because of weak coupling?) Farajnia et al. J. Neurosci. 2012 Is Aging of the Clock and the SCN a Network Problem? Both old SCNs and SCNs from animals on long days have reduced amplitude rhythms Could we treat circadian and young sleep problems in the elderly by restoring network function ?? old Could exercise/activity and/or enforced L/D cycles be non- drug ways to restore & enhance rhythms in the elderly? Can we test that idea in mice? Farajnia et al. J. Neurosci. 2012 First, is locomotor activity of rodents an appropriate measure? Could running wheel activity be a pathological behavior of caged mice? No! Even wild mice spontaneously love to play on running wheels! video courtesy of Dr. Johanna Meijer Exposure to T-cycles affects behavior and the SCN Activity peaks near the end of night in short T-cycles, and near the beginning of night in long T-cycles Houben, Coomans and Meijer, PLoS One 2014  Exposure to T-cycles affects behavior and the SCN T=22 T=26 MUA = multi-unit activity (electrical activity of the SCN) Troughs of SCN neural activity (MUA) occur near the end of night in short T-cycles, and near the beginning of night in long T-cycles Houben, Coomans and Meijer, PLoS One 2014  Exposure to T-cycles affects behavior and the SCN MUA = multi-unit activity (electrical activity of the SCN) actogram For nocturnal rodents on T- T26 SCN MUA activity cycles, SCN activity is low when activity is high averaged locomotor activity Does activity in actogram the SCN suppress locomotor T23 SCN MUA activity activity? averaged locomotor activity Houben, Coomans and Meijer, PLoS One 2014  Locomotor activity and SCN activity (MUA) are inversely correlated Injection of tetrodotoxin (TTX) or control vehicle (aCSF = artificial cerebrospinal fluid) directly into the SCN: Injection of Injection of minutes minutes locomotor activity MUA = multi-unit activity (SCN electrical activity) Houben, Coomans and Meijer, PLoS One 2014  Spontaneous locomotor activity and SCN activity (MUA) are inversely correlated spontaneous locomotor activity Van Oosterhout et al., PLoS One 2012 Spontaneous activity and SCN activity (MUA) are inversely correlated MUA = multi-unit activity (electrical activity of the SCN) PIR = Passive Infrared Detector to pick up movements from the animal Courtesy of Dr. Johanna Meijer  SCN activity during rest vs. activity When movement (locomotor activity) was detected during a 10 sec recording bin, the number of SCN spikes counted in that bin is represented by a black dot (and red line). Grey dots show multiunit activity data points from bins when no movement was detected (and blue line). This implies feedback of SCN activity locomotor activity to the corresponding with SCN activity movement corresponding with no SCN. movement Van Oosterhout et al., PLoS One 2012  Hypothesis: phasing of locomotor activity (i.e., exercise) can enhance or suppress SCN amplitude For nocturnal rodents: SCN activity corresponding with no when behavioral activity movement is concentrated during the night and is absent during the day, the amplitude of the SCN electrical activity rhythm should be maximized when behavioral activity SCN activity occurs during the day and rest occurs at night, corresponding with movement the SCN amplitude is negatively affected and should show a reduced amplitude of the rhythm Activity (spontaneous or induced) Van Oosterhout et al., PLoS One 2012 Activity-induced Phase Shifting; Feedback to the SCN ? Acceleration of Transients: When hamsters are placed in a new running wheel, they jump into it and run for a long time to check it out: “novelty-induced wheel running” activity: running wheel Without novel running wheel With novel Activity-induced Phase Shifting; Feedback to the SCN ? Hamsters: Acceleration of Transients: 1-h light pulse Phase Shift (h) running wheel Without novel 3-h novelty-induced wheel running Phase Shift (h) running wheel With novel 0 4 8 12 16 20 24 Circadian Time (h) Activity-induced Phase Shifting; Feedback to the SCN ? Hamsters: 1-h light pulse Human Exercise PRC: Phase Shift (h) 3-h novelty-induced wheel running Phase Shift (h) (Clock Time?) Human subjects performed 1-h moderate treadmill exercise for 3 consecutive days at 0 4 8 12 16 20 24 one of eight phases of the day/night cycle Circadian Time (h) Youngstedt et al. (2019) J Physiol 597: 2253–2268 Long-term exposure to LL affects behavior/metabolism and the SCN control group (LD always) LD to LL to LD group LD continuously LL for 24 weeks, then LD +/- S.D. Long-term exposure to LL affects behavior/metabolism and the SCN MUA = multi-unit activity (electrical activity of the SCN) Mouse#1 Mouse#2 Location of electrode Day-active and night-active animals: SCN shows same phase Regardless of phasing of locomotor activity, SCN metabolism and activity always peaks in the day Unlike nocturnal animals, for day-active animals (like ourselves) we will probably find that locomotor activity and SCN activity are positively correlated, and therefore activity in the day will enhance the SCN rhythm for us. Schwartz et al., Brain Res 274:184, 1983  Feedback flow at every control level Genes Membrane potential necessary TTFL for rhythms Neuron Ion channels Network activity enhances Electrical activity SCN neuron amplitude SCN network Neural circuits Activity/exercise can enhance SCN amplitude and cause phase shifts Behavior Entrainment Seasons Environment (e.g., LL, photoperiod, T-cycle)  Some Take-home messages: 1. The multi-oscillator and network structure of the SCN has functional relevance, including precision, robustness, and seasonal (PP) encoding. 2. SCN output has acute effects on behavior; in nocturnal animals, SCN activity and locomotor activity are inversely correlated. 3. Properly phased activity/behavior can enhance amplitude of SCN rhythms. 4. Long days (PP) and aging both correlate with lower amplitude SCN rhythms. 5. Aging and exercise have opposite effects on the SCN. 6. Provide running wheels to nocturnal rodents to enhance their health? 7. Potential human applications: provide L/D cycles in the ICU, neonatal units, etc. (not LL as is commonly practiced now); exercise is important to reinforce and enhance rhythms (especially in older people?).