Module 9

Question 1

A master circadian pacemaker is located in the ______

Answer 1

Suprachiasmatic nucleus, which is in the hypothalamus

Question 2

In the 1920s, Curt Richter pioneered ______

Answer 2

The use of running wheels to study daily rhythms in

rats

Question 3

What is a fishing expedition/unbiased mapping?

Answer 3

Making lesions in various brain regions, and removing various body organs

Question 4

In mammals, photoreception is mediated by the _____, and visual information is sent to the brain through _____

Answer 4

• retina

- the optic nerve

Question 5

What are the output neurons of the retina?

Answer 5

Retinal ganglion cells

Question 6

What is the titrated amino acid autoradiography method?

Answer 6

Attaching a weakly radioactive H isotope (3H, titrium) to amino acids, which are injected into the vitreous chamber of the eye, gradually taken up by retinal ganglion cells, which end up in different synapses - the radioactivity of these synapses tells where the 3H ended up

Question 7

Moore et al. used titrated amino acid autoradiography to discover the ______, which ______

Answer 7

• retinohypothalamic tract (RHT)

- is a short pathway supplying neurons from the optic chiasm to the suprachiasmatic nucleus

Question 8

What is the first area in the brain to get information from the retina?

Answer 8

The suprachiasmatic nucleus

Question 9

What happens when the SCN is lesioned in blind rats?

Answer 9

Behavioural rhythms are eliminated

Question 10

After removal of the SCN, what happens to a rat’s sleep schedule?

Answer 10

The circadian rhythm is replaced by a ~3h rhythm

Question 11

What are the implications of the fact that most mammalian species can maintain homeostasis even after SCN removal?

Answer 11

Circadian and homeostatic controls are mediated by separate mechanisms

Question 12

What is the evidence that the SCN is indeed a master pacemaker?

Answer 12

• SCN lesions eliminate free-running light-entrainable rhythms, permanently
• SCN stimulation shifts rhythms
• SCN neurons oscillate at single-cell and population levels
• SCN transplants restore rhythms, transferring characteristics of the donor

Question 13

For the SCN clock to be shifted by light, SCN neurons must be ________

Answer 13

Activated or suppressed by neurotransmitters released by axons from retinal ganglion cells

Question 14

Electrical stimulation of rat/hamster SCN mimics _____

Answer 14

Phase shift effects of light pulses

Question 15

Intra-SCN injection of ____ (chemical stimulation) in hamsters mimics _____

Answer 15

• NPY

- The phase shift effects of arousal

Question 16

The SCN uses low levels of glucose in the _____, and high levels of glucose in the _____

Answer 16

• subjective night

- subjective day

Question 17

SCN activity is ____ when locomotor activity is

Answer 17

high

Question 18

What happens when the SCN is completely severed of connections to the rest of the brain?

Answer 18

The SCN continues to oscillate, but all other brain regions are arrhythmic

Question 19

What happens to SCN tissue that is isolated from euthanized animals?

Answer 19

It continues to exhibit circadian oscillations

Question 20

The sparrow becomes arrhythmic in dim light when the _____ is removed, but circadian rhythms return after a ______

Answer 20

• pineal gland

- transplant

Question 21

In rats, what age is best for an SCN donor?

Answer 21

Embryonic

Question 22

The axons of the retinal ganglion cells form the _____

Answer 22

Optic nerves

Question 23

How do knife cuts to sever the optic tracts behind the optic chiasm affect LD entrainment, and what does this indicate?

Answer 23

• They don’t affect LD entrainment

- There must be another pathway between the optic nerve and the optic tract