Biological rhythms Control of Animal Behavior Flashcards
What is biological rhythm?
Cycle of activity that occurs on a predictable basis; can be hourly, daily, monthly, yearly
Jean Jacque de Mairan
Studied mimosa plants
Mimosa plants opened during the day and closed at night
They discovered that even when the mimosa plant was moved to a dark area during the day, it still followed the pattern of opening during the day and closing at night
Three rules or laws governing biological rhythms
1 – Endogenous: inherent to the organism, comes from within organism
Example: Actogram of rat on wheel, about etrainment and free running periods
2 – Circadian rhythms persist under constant conditions
3 – Rhythms are trainable (such as training of accurate “timing” for organisms to eat, shelter, etc. to survive and thrive)
Entrained behavior
biological clock lines up with environmental cycle, the cycle that is inherent to a certain organism
Free running behavior
when the sleep-wake pattern varies less or greater than 24 hours (23-25 hours instead)
Example of Entrained behavior and free running behavior
Activity record of a rat
Etrained behavior was for the rat to run on a wheel when it was dark outside, and then stop when there was light outside
When placed in a dark environment 24/7, the animal show constant night activity at first
As time went on, the wake time shifted from constant darkness (creating a phase delay cycle, which is greater than 24 hours)
Phase delay
biological cycle greater than 24 hours, actogram activity chart lines will shift forward slowly
Phase advance
biological cycle less than 24 hours, actogram activity chart lines will shift backward slowly
Zeitgeber
“time giver”
Sunlight (most important cue!) and other environmental cues(food, etc.)
SCN
Suprachiasmatic Nucleus
Getting info about light into SCN
Direct pathway: Retino-hypothalmic tract
Indirect pathway as well
Retino-hypothalmic tract
light info travels to brain, brain interprets
Evidence info passes by SCN, “samples” light
Bulb of eye -> optic nerve -> chiasma -> optic tract, pass by thalamus
Evidence of accuracy of direct pathway retino-hypothalmic tract
When the retino-hypothalamus tract is severed, the organism has random periods of activity (they are NOT entrained, they are arrhythmic!)
When removing photoreceptors (rod and cones), the animal can entrain, since other light sensitive receptors still present
Removing the entirety of the eye causes no entrainment
Describe example of Indirect pathway
Melatonin: made by pineal gland, increased secretion when dark (vice versa)
Example: reptiles, birds have pineal closer to surface, can penetrat skull and cause above effects w/melatonin
Name Clocks outside of the SCN
pineal, eyes, optic lobe, brain
Describe the process of biological rhythms on a molecular basis
This process described occurs over the course of approx. 24 hours (in mammals)
Production of 2 proteins, Clock and Bmal, and binding together to move to nucleus
The combined proteins connect to 2 genes (promoter regions) to increase rate of transcription and translation; creates more proteins
Clock and Bmal turn into per and cry genes; Proteins leave nucleus and form complex (with possible other proteins that were produced INDEPENDENTLY); Formation of trimer, complex produces actions
Complex creates temporary inhibition (negative feedback) of transcription and translation when production too high; Trimer complex breaks down eventually, allowing active Clock/Bmal once again
What structures can serve as the pacemaker or “master clock” controlling circadian rhythms in vertebrates and invertebrates?
Address later
What experimental evidence suggests that the SCN is the master clock? Know at least two.
A transplant study shows evidence that the rhythms can be restored by inserting SCN wild type tissue into an organism with mutant/lesioned SCN
A lesion study showed the animal had arrhythmic behaviors with a damaged SCN
A transplant study showed removal and replacement of single SCN and double SCN creates a phase advance in organism (22, then 20 hours in day) when placed in mutant organism
What do SCN transplant studies using the tau mutant hamster (single and double) tell us about circadian rhythms?
This shows homozygous mutant hamsters gain extremely short circadian periods down to approx. 20 hours
This showed a gene expression influence in SCN tissues that create the short periods in circadian period
What cues can be used as zeitgebers?
The major one is sunlight, it can also be environmental cues (maybe food, weather, etc.)
What happens to rhythms during free running conditions? How do we get an animal to experience free running?
The organism can have a shift in wake-sleep schedules; it can create phase delays or phase advances in organisms
An organism can experience free running by being exposed to constant state of darkness or light (rat example)
What happens to the onset of behavioral activity during a phase advance and phase delay?
phase delay results in periods of greater than 24 hours in sleep wake cycle, organism wakes later and sleeps later
Phase advance results in periods less than 24 hours in sleep wake cycle, organism wakes earlier and sleeps earlier
What effect does lesioning the SCN have on behavior?
Lesioning the SCN creates arrhythmic behavior, organism has sporadic biological rhythm from SCN damage
What was one of Dr. Menaker’s biggest contributions to the field of circadian biology?
Studying genes in the circadian cycle
Bred single allele mutations amongst experiments
Discovered single allele mutation in hamster that’s in free running condition had clock of approx. 22 hours, which was never seen before
Further studies showed double mutation in organisms created shorter clock at approx. 20 hours
