1 4 3 Circadian Rhythms BIO 361T Fall 2014 1 In all mammalian species diurnal and nocturnal melatonin peaks in the middle of the night In the experiment below rats were kept in constant darkness DD A one hour pulse of light in the left panel was sufficient to signal the onset of day A daily infusion of melatonin in the right panel was sufficient to signal the onset of night a How would you describe the rhythmicity of behavior in DD Free running b What happens to the rhythmicity when a pulse of either light or melatonin is given at the same time every day Entrained slightly shorter period c Most mammalian tissues have receptors for melatonin particularly neurons in the SCN Explain why exogenous from outside the animal s body melatonin affects entrainment in mammals The pineal gland releases melatonin into the circulation and it binds to many cells including SCN neurons feedback Thus exogenous melatonin will also bind the SCN which is what entrains the pineal in mammals d Melatonin is often used to adjust sleep cycles due to insomnia shift work jet lag and other disruptions to circadian rhythms but its effects are not consistent The graph below shows on average how time of day corresponds to the effects of taking melatonin Note that the time scale is circadian time not clock time it is based on light vs dark which comes at different times depending on location and time of year For example if melatonin is taken at dusk 12 00 there will be a 2 hour phase advance your body will behave as if it is two hours earlier Why does melatonin seem to have no effect around 18 00 Melatonin is naturally high in the middle of the night 2 2 Blindness can have several different causes but most blind mammals can still entrain to light as can all blind non mammalian vertebrates However if the retina is completely absent mammals are unable to entrain to light Explain these differences that correspond to taxa and pathology Retinal cells are necessary for entrainment in mammals because that is what responds to light These results suggest that the retinal cells necessary for sight are not the same ones that entrain the SCN Non mammalian vertebrates do not entrain through the retina as their pineal gland is close enough to the surface to detect light 3 The actograms below contrast wild type mice with melanopsin knock out mice Use them to answer the questions below a Does the mutant still display circadian rhythmicity How can you tell Yes still regular periods of behavior and no behavior b Is the mutant able to entrain to light How can you tell No active inactive cycle does not line up with light dark on graph c Is the mutant period longer or shorter than WT How can you tell Shorter activity starts earlier each day period must be 24 hours d Hypothesize as to whether the mutant would be able to entrain to another cue such as being fed at 08 00 every day Explain your answer Yes because melanopsin is only involved with entraining to light 3 4 The actograms below are from the following experimental procedure Two intact animals were entrained to light artificially with a 12 12 LD cycle but at different hours one was given light from 10 00 to 22 00 the other was given light from 23 00 to 11 00 Two other animals of the same species had their pineal glands artificially removed Pinx and were kept in LL constant light The pineal glands from the entrained animals were removed and transplanted into the Pinx ed animals a Did this experiment use a nocturnal or diurnal species Diurnal b How would you describe the Pinx ed animals based on their actograms Arrhythmic c Explain the observation in b in terms of the animal s physiology No pineal gland so no central clock Peripheral clocks get out of sync and animal as a whole is arrhythmic d What would you expect the Pinx actograms to look like in the presence of an LD cycle Explain your answer The same If the animal is not even rhythmic there is no rhythm to entrain e What can you conclude about the pineal transplants based on the last actograms What effect did they have on their recipients Explain any observations in terms of the underlying physiology The rhythm and entrainment was transplanted with the pineal As these are grafts this must be due to diffusible factors like hormones not direct neural connections which would not grow back 4 f Did this experiment use invertebrates non mammalian vertebrates or mammals Non mammalian vertebrates as pinx ing mammals would not obliterate all rhythmicity and restoring the pineal in mammals would not transplant entrainment 5 The graphs below show relative levels of expression of several clock genes in humans and how they change throughout a 24 hour period Note that the x axis is circadian time not clock time so use the light dark bar for reference The left panel is under normal conditions and the right panel is after chronic jet lag a Each night bmal expression peaks Why does expression of cry rev erb and per increase soon after Because bmal is a transcription factor that activates expression of these genes b What is happening in the cell to make per and cry expression decrease PER and CRY are removing CLK and BMAL inhibiting their own expression c How does per and cry expression begin to increase again the next morning PER and CRY degrade and CLK and BMAL can bind again
View Full Document
Unlocking...