Biological rhythms Control of Animal Behavior

Question 1

What is biological rhythm?

Answer 1

Cycle of activity that occurs on a predictable basis; can be hourly, daily, monthly, yearly

Question 2

Jean Jacque de Mairan

Answer 2

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

Question 3

Three rules or laws governing biological rhythms

Answer 3

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)

Question 4

Entrained behavior

Answer 4

biological clock lines up with environmental cycle, the cycle that is inherent to a certain organism

Question 5

Free running behavior

Answer 5

when the sleep-wake pattern varies less or greater than 24 hours (23-25 hours instead)

Question 6

Example of Entrained behavior and free running behavior

Answer 6

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)

Question 7

Phase delay

Answer 7

biological cycle greater than 24 hours, actogram activity chart lines will shift forward slowly

Question 8

Phase advance

Answer 8

biological cycle less than 24 hours, actogram activity chart lines will shift backward slowly

Question 9

Zeitgeber

Answer 9

“time giver”

Sunlight (most important cue!) and other environmental cues(food, etc.)

Question 10

SCN

Answer 10

Suprachiasmatic Nucleus

Question 11

Getting info about light into SCN

Answer 11

Direct pathway: Retino-hypothalmic tract
Indirect pathway as well

Question 12

Retino-hypothalmic tract

Answer 12

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

Question 13

Evidence of accuracy of direct pathway retino-hypothalmic tract

Answer 13

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

Question 14

Describe example of Indirect pathway

Answer 14

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

Question 15

Name Clocks outside of the SCN

Answer 15

pineal, eyes, optic lobe, brain

Question 16

Describe the process of biological rhythms on a molecular basis

Answer 16

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

Question 17

What structures can serve as the pacemaker or “master clock” controlling circadian rhythms in vertebrates and invertebrates?

Answer 17

Address later

Question 18

What experimental evidence suggests that the SCN is the master clock? Know at least two.

Answer 18

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

Question 19

What do SCN transplant studies using the tau mutant hamster (single and double) tell us about circadian rhythms?

Answer 19

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

Question 20

What cues can be used as zeitgebers?

Answer 20

The major one is sunlight, it can also be environmental cues (maybe food, weather, etc.)

Question 21

What happens to rhythms during free running conditions? How do we get an animal to experience free running?

Answer 21

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)

Question 22

What happens to the onset of behavioral activity during a phase advance and phase delay?

Answer 22

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

Question 23

What effect does lesioning the SCN have on behavior?

Answer 23

Lesioning the SCN creates arrhythmic behavior, organism has sporadic biological rhythm from SCN damage

Question 24

What was one of Dr. Menaker’s biggest contributions to the field of circadian biology?

Answer 24

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