condense ntoes on readings for lecture 5

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Published on 23 Jul 2011
School
Simon Fraser University
Department
Psychology
Course
PSYC 388
Chapter 5 – search for the clock
-motivation = dominant model range of homeostatic drives or motivations that determined behaviour, so if animal became increasingly hungry and at set point it would feed
and if filled calories reservoir the hunger drive would diminish and replaced by another such as thirst drive = rotating repertories of drives and their concomitant behaviours, each
drive take turn at top of hierarchy problem = why particular drives regularly appeared at certain times of day = answer = nocturnal animal active at night so uses up more energy
during night than day so all physiological parameters are higher at night because adaptive and success and controlled by a clock
-homeostatic mechanism takes care of environmental fluctuations (ex. Humidity),but its a fine turner rather than main controller
-hypothalamusregulate blood pressure body temperature, fluid and electrolyte balance, metabolism of fats and carbohydrates and sugar levels, timing of release of hormones (egg)
-lesions in front part of hypothalamus eliminated motile behaviour rhythms
-hypothalamus and thalamus work together to generate sleep/wake cycle
-release of hormones linked to arousal sate of animals and coordination needed to bring it into line = circadian oscillator
-suprachiasmatic nuclei (SCN) =lesion = abolished oestrous cycle and rhythms in behaviour such as drinking and locomotion
-Moores approach = follow light beam as it came through eye and see where it went (known pathway that took light to optic nerve to visual processing ; optic nerves cut before
optic chiasm then LD cycles no longer entrained biological clock; but cut just after optic chiasm LD cycle entrainment unaffected) = suggested distinct pathway separate form
visual projection responsible for transmitting signals for setting clock
~ injected radioactive amino acid into eyes and follow tracer molecules
~ New pathway from eye to SCN = retinohypothalamic tract
~ scn lesion = loss of circadian rhythm of hormone corticosterone, involved in circadian timing of neurosecretion
~ Remove whole SCN destroyed behavioural and endocrine circadian rhythms
-SCN in mammals was clock that regulated several functions with period of ~24hours
-Mid 1970s well established destroying SCN affected timing of various behaviours in mammals but didn’t abolish behaviours themselves = arrhythmic
-SCN isolated (hard because cells locate very close t several major nuclei and tracts) within animal experiment = pattern continued with in SCN itself but rhythmicity abolished in
nearby neurones outside cut suggest endogenous rhythm produced with in SCN an electrical signals carried by neural connections leading away from it (efferents) provided
timing information to other brain regions
-SCN neurones within SCN generate circadian rhythm of electrical activity high in day and low at night; neurones outside SCN showed circadian rhythmcity but out of phase
=peaked in night and lowest during day
-SCN dissected = generates stable rhythm with period of ~ 24 hours and self-sustaining oscillator
-Schwartz found SCN metabolically active during light phase of 12 hours light/12 hours dark cycle and relatively inactive during dark phase = rhythm = rhythm of glucose
utilisation is circadian (evidence) + direct effect when restored circadian activity rhythms in SCNM-lesion rats and hamsters by transplant foetal SCN (no transplant = discernible
pattern of sleep and wake, but regained activity rhythms when received transplant) + mutant golden hamster
-Radioactive 2 –deoxyglucose (2DG) = similar to glucose = insert in vein= slice brain the place on x-ray films = developed films clearly show location of radioacivley labelled 2DG
and intensity of image indicated by amounts of moelculte present in tissue eof slice
-Simple model of mammalian circadian organisation – circadian clock in SCN produces rhythmic output that drives circadian rhythms of activity: drinking, feed, sleep, etc. The
oscillator rhythm locked on to local time by daily entrainment of dawn, dusk/both model show one master clock controlling all rhythmic activity
-Neural projections from SCN = main ones are to areas in hypothalamus, thalamus and midbrain; neurones in scn send direct and indirect projections to neurosecretory CRF
neurones in hypothalamus = corticotrophin- releasing factor regulate resale of ACTH from pituitary gland and rhythmic release of ACTH from pituitary drives release of
corticosterone form adrenal glands
-Corticosterone = key role in animals metabolism because help regulate conversion of amino acids into carbohydrates and glycogen by liver and stimulate glycogen formation in
tissues
-Transplantation studies = transplanted SCN often makes feeble neural connections with host brain ; it restore rhythmicity in rodents but never been entrained by light
-There is a diffusible chemical factor from SCN that helps organise wheel running behaviour = SCN talks to rest of body using both direct neural connections and unknown
diffusible chemical substance because transplanted SCN contained within capsule restored behavioural rhytmicity
-Animals show anticipatory behaviour for food even when SCNs destroyed
-Vertebrate body composed of billions of independent clocks but theres a critical difference between local clock and SCN = only transplanted SC cells can restore rhythicity to
SCN lesion animals
-Studies on food restriction and liver activity suggest theres possible role for behaviour in maintaining internal temporal structure
-Circadian oscillations in liver may respond more directly to enjoyment
-Rat = nocturnal animal = activity at night including liver function and feeding experiment = fed in middle of day = feeding pattern did not affect nocturnal behaviour increased
locomotors and liver function in anticipation of feeding = suggesting Food intake itself can generate an entraining signal for liver and other digestive organs
Food Entrainment
-Light delays CR at dusk and early night, advances CR at late night through dawn
-In many organisms - circadian rhythms can be entrained by non-photic stimuli
-If food availability restricted to fixed time of day = (ex. 4 hour meal alternating with 20 hour fast) for a week or more = free-running rhythms may entrain to mealtime, usually with
daily active phase of circadian rest-activity cycle beginning prior to (anticipating ) mealtime Food unrestricted, CR resume free-running from apparent phase of entrainment
-Food availability can act like light by entraining (setting phase and period) if entire circadian system phase of entrainment = adaptive = ensure they are awake and active prior to
mealtime and metabolically prepared for food ingestion, digestion and absorption (hamster)
-Other species or in presence of LD cycleresponse to daily schedules of food-availability complex = underlying mutli-oscillator circadian system with one pacemaker (SCN) is
entrained primarily by light while most circadian oscillators elsewhere in brain and body are entrained by food
-Uncoupling of circadian oscillators and rhythms by restricted feeding may occur in LL or DD, such that light-entrainable, SCN pacemaker free-runs while food-entrianable
oscillators remain synchronized with mealtime
-Locomotor activity appear to be jointly controlled by both LEP and FEP oscillators while others (ex. Pineal melatonin secretion ) directly regulated by one
-Rats entrained to LD cycle and restricted to single 2-4 hours meal in middle of light period = later increased locomotors activity beginning 1-3 hours before mealtime (food
anticipatory activity) FAA stabilizes
-Expression of 2 CR with different periods indicates joint control of activity by separate light and food entrainable oscillators
-Pineal melatonin secretion – only strong CR that exclusively light-entrainable
-FAA (like hourglass) premeal activity triggered each day when hungry reaches some threshold – food-deprived rats that did not experience regular mid day feeding time do not
exhibit activity waveform similar to food-entrained rats
-FA rhythm established = persist during prolonged bouts of total food deprivation
-FAA explanation = outcome of associative learning process = learn certain phase of light-entrainable circadian pacemaker are predictive of food availability, but food-anticipatory
rhythms emerge and persist normally in rats with complete SCN ablation and in DD or LL
-If meal intervals are outside circadian range (~22-31 hour), anticipatory rhythms don’t emerge (limits to entrainment)
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Document Summary

~ injected radioactive amino acid into eyes and follow tracer molecules. ~ new pathway from eye to scn = retinohypothalamic tract. ~ scn lesion = loss of circadian rhythm of hormone corticosterone, involved in circadian timing of neurosecretion. ~ remove whole scn destroyed behavioural and endocrine circadian rhythms. Scn in mammals was clock that regulated several functions with period of ~24hours. Mid 1970s  well established destroying scn affected timing of various behaviours in mammals but didn"t abolish behaviours themselves = arrhythmic. Scn neurones within scn generate circadian rhythm of electrical activity high in day and low at night; neurones outside scn showed circadian rhythmcity but out of phase. Scn dissected = generates stable rhythm with period of ~ 24 hours and self-sustaining oscillator. Simple model of mammalian circadian organisation circadian clock in scn produces rhythmic output that drives circadian rhythms of activity: drinking, feed, sleep, etc.