circadian rhythm Flashcards
calendar cells
cells responsible for long term time keeping
melatonin target cells
how do calendar cells decode melatonin duration?
use a clock-gene based mechanism
melatonin signal generator
LD cycle —> photoreceptors in the retina —> pineal glands which release melatonin or SCN circadian cell —> which go to other cell targets
melatonin decoder in the pituitary gland
LD= short night = less melatonin signal time SD= long night and more melatonin signal time
this melatonin signal goes to calendar cell —> lactotroph/PRL —> hair papilla, hepatocyte, luteal cell
which receptors of calendar cells pick up melatonin?
MTI receptors
long term changes in prolactin secretion in the pelage/moult cycle
prolonged SD results in the development of prolactin secretion and the reversion from white to agouti pelage
exposure to prolonged LD results in the initial refractory response that merges into the expression into the expression of circannual cycle; horn growth is suppressed during winter
refractory period
insensitive phase to prolactin secretion
calendar cells have inhibition of prolactin secretion which occurs over a long time before it recovers
two models of the photoperiod
amplitude model - changes in the amplitude of clock gene expression
phase control- based on relationships between proteins
proteins dimerise, meet in the nucleus and act on gene expression, chance of proteins meeting in the LD is lower, in SD chance of them meeting is higher and get higher gene transcription
symptoms of jetlag
constipation- clock is coupled to digestive system
retrieving information- mental performance
retrograde amnesia
zeitgeber
time giver- resetting stimulus that functions as a time cue
light
molecular clockworks of circadian rhythms
positive elements = CLKC and BMAL
negative elements are PER and CRY
PER and CRY dimerise and inhibit the positive elements in the nucleus
negative elements undergo ubiquitination and phosphorylation to prevent further inhibition
regulation of clockwork genes
CLOCK and BMAL dimerise and bind to the promoters of the dock controlled genes and induce the transcription of many genes including PER and CRY
PER and CRY dimerise and interact with CLKOCK and BMAL, initiating their degradation
SCN
paired nuclei at the base of the hypothalamus just above the optic chiasm
r
where does SCN receive input from?
retinohypothalamic tract
projections from the SCN
PVN - relaying information to the periphery, ARC - feeding centres , LHA- behaviour