Lecture 13.1: Dormancy and Muscle Atrophy

Question 1

What is dormancy?

Answer 1

‘physiological time out’ involving adjustments that reduce metabolic demands to enhance survival in response to harsh environmental condition

Question 2

What is the classic definition of hibernation?

Answer 2

state of inactivity and reduced responsiveness to stimuli

Question 3

What is the advanced (Geiser’s) definition of hibernation?

Answer 3

regulated state where metabolic rate is reversibly suppressed to < 10% of resting values for several days, with corresponding decreases in Tb

• involves a fall in Tb below 10ºC (controlled drop in body temperature), and its metabolic rate falls by over 90% for longer than 1 day

Question 4

What is torpor?

Answer 4

similar to hibernation, but the decrease in metabolic rate and Tb are less severe and lasts < 24 hours before being reversed

Question 5

Do small animals hibernate?

Answer 5

yes – the most profound demonstration of hibernation is observed in small mammals, where Tb can decrease to as low as 2ºC

Question 6

Do large animals hibernate?

Answer 6

yes – no mammal larger than 10 kg will undergo a decrease in Tb to meet Geiser’s definition (advanced definition) of hibernation, but they still hibernate

Question 7

What are the 3 axes of dormancy that can differentiate dormancy types across animal taxa?

Answer 7

• induction
• recalcitrance
• magnitude

Question 8

Axes of Dormancy

What does induction and recalcitrance describe?

Answer 8

describe the degree to which the dormancy is endogenously PROGRAMMED and centrally mediated (ie. driven by central nervous system and endogenous time-keeping mechanisms) vs. RESPONSIVE (a direct response to an adverse environment)

Question 9

Axes of Dormancy

Induction – Programmed vs. Responsive

Answer 9

• programmed: committed before environment deteriorates
• responsive: immediate response to limiting factor

Question 10

Axes of Dormancy

Recalcitrance – Programmed vs. Responsive

Answer 10

• programmed: high recalcitrance, refractory
• responsive: no recalcitrance, environmentally sensitive

Question 11

Axes of Dormancy

What does magnitude describe?

Answer 11

describes the dormancy-specific degree of plasticity in a range of traits, including metabolic rate

• deep: inactive, profound metabolic suppression
• shallow: active, mild metabolic suppression of physiological traits and conditions

Question 12

What is the dormancy spectrum?

Answer 12

differentiates the dormancy types across animal taxa

• programmed vs. responsive
• deep vs. shallow

two extremes

• programmed and deep
• responsive and shallow

Question 13

Name some organisms and where they are on the dormancy spectrum.

Answer 13

• long-tongued nectar bat – shallow and responsive
• edible dormouse – deep and responsive
• arctic ground squirrel – deep and programmed
• short-beaked echidna – shallow and programmed

Question 14

What is estivation?

Answer 14

dormancy in response to a hot arid environment to address food scarcity and the dry environment

• involves controlled loss of water (up to 80% water loss)
• involves decrease in basal metabolic rate
• goal is survival
• ie. desert frogs

Question 15

What is diapause?

Answer 15

developmentally programmed dormancy

• usually timed to a harsh environmental condition
• ie. Artemia sp. (brine shrimp)

Question 16

What are obligate hibernators?

Answer 16

hibernators that follow an endogenous circannual rhythm and hibernate each year, regardless of environmental conditions (ie. very cold, food scarcity)

• PROGRAMMED for hibernation every year
• ie. ground squirrel

Question 17

What are facultative hibernators?

Answer 17

mammals where the expression and characteristics of hibernation is not consistent and depends largely on the environment

• if one year the environment is not harsh and food is still available, hibernation time may differ or may not occur at all
• ie. Syrian hamster

Question 18

What are the three broad phases of obligate hibernation?

Answer 18

• preparation
• hibernation period – smaller phases within include initiation, maintenance, potentiation
• emergence (activation)

Question 19

Time Course of Obligate Hibernation

What happens to metabolism and cell cycle, locomotor activity, reproductive activity, and energy storage during the preparation phase?

Answer 19

all high

Question 20

Time Course of Obligate Hibernation

What happens to metabolism and cell cycle, locomotor activity, reproductive activity, and energy storage during the hibernation period phase?

Answer 20

• metabolism and cell cycle, locomotor activity, and reproductive activity decrease
• energy storage stays high, then gradually decreases towards the end of hibernation

Question 21

Time Course of Obligate Hibernation

What happens to metabolism and cell cycle, locomotor activity, reproductive activity, and energy storage during the emergence (activation) phase?

Answer 21

traits return to high level of activity

Question 22

What are interbout arousals (IBA)?

Answer 22

transient state of activity in which the animal will recover active-like physiological parameters such as body temperature, heart rate, and blood pressure

Question 23

What are the 6 characteristics of hibernation?

Answer 23

• reduced Tb
• metabolic suppression
• insulin resistance
• water loss
• decreased physiological functions – ie. heart rate, ventilation
• inactivity

Question 24

Metabolic Suppression Before Cooling

What happens in ground squirrels?

Answer 24

• metabolic rate declines before body temperature decreases
• lower Tb facilitates further reductions in metabolic rate through thermodynamic effects

Question 25

Mitochondrial Metabolism Describe the maximal metabolic rate of mitochondria in muscles of hibernating vs. non-hibernating squirrels.

Answer 25

- maximal metabolic rate of mitochondria is lower in muscle from hibernating than non-hibernating squirrels - hibernation-induced decrease in mitochondrial metabolism is due to differential phosphorylation of complex I and II of ETS

Question 26

Describe the mechanisms of metabolic rate suppression.

Answer 26

Na+/K+ ATPase and protein synthesis are down regulated during hibernation - Na+/K+ ATPase activity is lower in almost all tissues of hibernating animals – due to phosphorylation - during hibernation in squirrels, [14 C] leucine is not incorporated into the brain, liver, and heart – shows that no protein synthesis was occurring - protein synthesis downreguated by phosphorylation of critical enzymes

Question 27

Regulation of Fuel Selection During Hibernation What is pancreatic triglyceride lipase (PTL)?

Answer 27

enzyme that breaks down triglyceride

Question 28

Regulation of Fuel Selection During Hibernation What is pyruvate dehydrogenase kinase 4 (PDK4)?

Answer 28

enzyme that inhibits carbohydrate oxidation

Question 29

Regulation of Fuel Selection During Hibernation What fuel is used pre-hibernation?

Answer 29

mainly carbohydrates are used in the pancreas to secrete insulin - high level of insulin in the serum facilitates use of carbohydrates or carbohydrate oxidation - high level of insulin inhibits function of PTL – prevents breakdown of triglyceride - high level of insulin inhibits function of PDK4 – allows carbohydrate oxidation to occur (inhibitor is inhibited)

Question 30

Regulation of Fuel Selection During Hibernation What fuel is used during hibernation?

Answer 30

switch to using more fatty acids - pancreas makes insulin and it accumulates in the pancreas, therefore the serum level of insulin is low - no inhibition of PTL – triglycerides and white adipose tissue can be broken down to fatty acids, and go to lipid oxidation - no inhibition of PDK4 – carbohydrate oxidation is inhibited

Question 31

Heat Production During Emergence Describe the changes in temperature once hibernation starts, and once hibernation ends.

Answer 31

- once hibernation starts and temperature decreases to torpor state, there is IBA arising in temperature along with other physiological aspects (regulated pattern of IBA) - upon the initiation of arousal, core body temperature increases over a very short time course - mechanisms of heat production allow rapid increase in high temperature occurring once hibernation period is over

Question 32

Do animals function normally after a long period of activity?

Answer 32

yes – animals go through long period of inactivity, but still come back active and function normally - can maintain tissue or re-use/bring them back to an active and functional level after a period of inactivity - these studies are important because they are applicable to other things - ie. astronauts’ muscle mass also decreases, and they go through some changes - ie. people who were in a coma