Lecture 13.1: Dormancy and Muscle Atrophy Flashcards
What is dormancy?
‘physiological time out’ involving adjustments that reduce metabolic demands to enhance survival in response to harsh environmental condition
What is the classic definition of hibernation?
state of inactivity and reduced responsiveness to stimuli
What is the advanced (Geiser’s) definition of hibernation?
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
What is torpor?
similar to hibernation, but the decrease in metabolic rate and Tb are less severe and lasts < 24 hours before being reversed
Do small animals hibernate?
yes – the most profound demonstration of hibernation is observed in small mammals, where Tb can decrease to as low as 2ºC
Do large animals hibernate?
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
What are the 3 axes of dormancy that can differentiate dormancy types across animal taxa?
- induction
- recalcitrance
- magnitude
Axes of Dormancy
What does induction and recalcitrance describe?
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)
Axes of Dormancy
Induction – Programmed vs. Responsive
- programmed: committed before environment deteriorates
- responsive: immediate response to limiting factor
Axes of Dormancy
Recalcitrance – Programmed vs. Responsive
- programmed: high recalcitrance, refractory
- responsive: no recalcitrance, environmentally sensitive
Axes of Dormancy
What does magnitude describe?
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
What is the dormancy spectrum?
differentiates the dormancy types across animal taxa
- programmed vs. responsive
- deep vs. shallow
two extremes
- programmed and deep
- responsive and shallow
Name some organisms and where they are on the dormancy spectrum.
- long-tongued nectar bat – shallow and responsive
- edible dormouse – deep and responsive
- arctic ground squirrel – deep and programmed
- short-beaked echidna – shallow and programmed
What is estivation?
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
What is diapause?
developmentally programmed dormancy
- usually timed to a harsh environmental condition
- ie. Artemia sp. (brine shrimp)
What are obligate hibernators?
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
What are facultative hibernators?
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
What are the three broad phases of obligate hibernation?
- preparation
- hibernation period – smaller phases within include initiation, maintenance, potentiation
- emergence (activation)
Time Course of Obligate Hibernation
What happens to metabolism and cell cycle, locomotor activity, reproductive activity, and energy storage during the preparation phase?
all high
Time Course of Obligate Hibernation
What happens to metabolism and cell cycle, locomotor activity, reproductive activity, and energy storage during the hibernation period phase?
- metabolism and cell cycle, locomotor activity, and reproductive activity decrease
- energy storage stays high, then gradually decreases towards the end of hibernation
Time Course of Obligate Hibernation
What happens to metabolism and cell cycle, locomotor activity, reproductive activity, and energy storage during the emergence (activation) phase?
traits return to high level of activity
What are interbout arousals (IBA)?
transient state of activity in which the animal will recover active-like physiological parameters such as body temperature, heart rate, and blood pressure
What are the 6 characteristics of hibernation?
- reduced Tb
- metabolic suppression
- insulin resistance
- water loss
- decreased physiological functions – ie. heart rate, ventilation
- inactivity
Metabolic Suppression Before Cooling
What happens in ground squirrels?
- metabolic rate declines before body temperature decreases
- lower Tb facilitates further reductions in metabolic rate through thermodynamic effects
Mitochondrial Metabolism
Describe the maximal metabolic rate of mitochondria in muscles of hibernating vs. non-hibernating squirrels.
- 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
Describe the mechanisms of metabolic rate suppression.
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
Regulation of Fuel Selection During Hibernation
What is pancreatic triglyceride lipase (PTL)?
enzyme that breaks down triglyceride
Regulation of Fuel Selection During Hibernation
What is pyruvate dehydrogenase kinase 4 (PDK4)?
enzyme that inhibits carbohydrate oxidation
Regulation of Fuel Selection During Hibernation
What fuel is used pre-hibernation?
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)
Regulation of Fuel Selection During Hibernation
What fuel is used during hibernation?
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
Heat Production During Emergence
Describe the changes in temperature once hibernation starts, and once hibernation ends.
- 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
Do animals function normally after a long period of activity?
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
