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Institute of Zoology University of Veterinary Medicine Hannover Centre for Systems Neuroscience Hannover

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Niveau: Supérieur, Doctorat, Bac+8
Institute of Zoology University of Veterinary Medicine Hannover Centre for Systems Neuroscience Hannover in cooperation with the Laboratory for Neurobiology of Rhythms University Louis Pasteur Strasbourg Torpor and timing: Impact of endogenously controlled hypothermia on the circadian system of two hamster species. Thesis Submitted in Partial Fulfilment of the requirements for the degree Dr. rer. nat. at the University of Veterinary Medicine Hannover by Annika Herwig Kiel, Germany Hannover, Germany 2007

  • veterinary medicine

  • has been

  • van burd gohn

  • djungarian hamsters

  • stops ticking during

  • european doctoral

  • büst doch up

  • hannover


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Language English
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Institute of Zoology
University of Veterinary Medicine Hannover
Centre for Systems Neuroscience Hannover
in cooperation with the
Laboratory for Neurobiology of Rhythms
University Louis Pasteur Strasbourg




Torpor and timing:
Impact of endogenously controlled hypothermia on
the circadian system of two hamster species.

Thesis
Submitted in Partial Fulfilment of the requirements for the degree

Dr. rer. nat.

at the University of Veterinary Medicine Hannover
by

Annika Herwig
Kiel, Germany


Hannover, Germany 2007


1. Supervisor: Prof. Stephan Steinlechner, University of Veterinary Medicine Hannover
2. Supervisor: Dr. Michel Saboureau, University Louis Pasteur, Strasbourg

Advisory Committee:
Prof. Wolfgang L?scher, University of Veterinary Medicine Hannover
Prof. Alexandru Stan, Hannover Medical School
Dr. Paul PØvet, University Louis Pasteur, Strasbourg
Prof. Fran?ois Lasbennes, University Louis Pasteur, Strasbourg

First Evaluation :
Prof. Stephan Steinlechner, University of Veterinary Medicine Hannover
Dr. Michel Saboureau, University Louis Pasteur, Strasbourg
Prof. Wolfgang L?scher, University of Veterinary Medicine Hannover
Prof. Alexandru Stan, Hannover Medical School
Dr. Paul PØvet, University Louis Pasteur, Strasbourg
Prof. Fran?ois Lasbennes, University Louis Pasteur, Strasbourg

Second Evaluation:
Prof. Franziska Wollnik, University of Stuttgart

Date of oral examination: 26.04.2007




Ms Annika Herwig was a member of the European Doctoral College of the Universities of
Strasbourg during the preparation of his/her PhD, from 2004 to 2007, class name Périclès.
She has benefited from specific financial supports offered by the College and, along with
his/her mainstream research, has followed a special course on topics of general European
interests presented by international experts. This PhD research project has been led with the
collaboration of two universities: the University of Veterinary Medicine Hannover and the
University Louis Pasteur in Strasbourg.





















?Van Burd d?tt ik ober doch ne gohn, ne??
?Och du D sbattel, kannst du ok van Burd gohn?
B st doch up See, is doch all Woter m di r?m.?
Gorch Fock „Seefahrt ist not!“


Contents

Chapter 1 Introduction 1

Chapter 2 Daily torpor alters multiple gene expression in 13
suprachiasmatic nuclei and pineal gland of the
Djungarian hamster (Phodopus sungorus)

Chapter 3 Daily torpor affects the molecular machinery of the 21
circadian clock in Djungarian hamsters (Phodopus sungorus)

Chapter 4 Trans pineal microdialysis in the Djungarian hamster 39
(Phodopus sungorus): a tool to study seasonal changes of
circadian clock activities

Chapter 5 In vivo melatonin measurement during torpor in the 53
Djungarian hamster (Phodopus sungorus)

Chapter 6 The circadian clock stops ticking during hibernation 65

Chapter 7 Histamine H3 receptor and Orexin A expression during 77
daily torpor in the Djungarian hamster (Phodopus sungorus)

Chapter 8 Discussion 91

References 101

Summary 119


Zusammenfassung 121

Résumé 123

Acknowledgements 125

Publications 128





















Abbreviations

AA-NAT Arylalkylamine-N-acetyltransferase
ARC Arcuate nucleus
AVP Arginine-vasopressin
CLOCK Circadian locomotor output cycles kaput
CRY Cryptochrome
CNS Central nervous system
HP Hibernation protein
DD Constant darkness
DLG Dorsal lateral geniculate
DMH Dorso-medial hypothalamus
H1-4R Histamine 1-4 receptor
LD Long day
L:D Light:dark
LP Long photoperiod
MRMetabolic rate
NA Noradrenaline
OX1R Orexin receptor 1
OX2R Orexin receptor 2
PER Period
REV-ERBα Orphan nuclear receptor
RORα Retinoid-orphan receptor
SCN Suprachiasmatic nuclei
T Ambient temperature a
T Body temperature b
Τ Endogenous period
TMTuberomammilary nucleus
VLPO ventrolateral preoptic area
ZT Zeitgeber-time
1
Introduction
















1 Chapter 1

Introduction

Our earth rotates around itself once a day and around the sun once a year, which is why most
organisms face periodic changes of their environment. The alteration of day and night is the
most important Zeitgeber in our lives and build the framework for all doings. Activity and
resting, food and water intake are only the most obvious behaviours that are timed. However,
also most physiological processes like body temperature, hormone release, moods and
emotions underlie rhythmicity triggered by the light dark cycle (FOSTER and KREITZMAN
2004). The ratio of day and night length changes throughout the year and with it the
conditions of living. Humans mostly elude those seasonal variations by electric light, central
heating and always available food stocks, but animals have evolved different strategies to live
with and adapt to varying conditions of light, temperature, food supply or predator abundance.
Seasonal influences are extremely marked at high latitudes, where changes in external
conditions are most drastic. Some species, especially birds, migrate over long distances to
exploit local resources as best as possible (GWINNER 1996). Mammals often anticipate
profound environmental changes throughout the year facilitating survival in winter when
energy supply is low, but metabolic costs are high. Generally reproduction and growth are
shut down in less inviting seasons. Reproduction is strictly bound to times of the year when
resources cover the demanding energy costs of pregnancy and lactation and warrant survival
of the offspring. Some species increase their body weight during summer in order to live on
fat reserves in winter, until food availability improves again in spring. Others, especially
small mammals that can only store a low amount of fat relative to their body mass, even
decrease their body weight towards winter lower body mass costs less energy. Many
mammals like sheep, deer, rabbits or bears change their fur to a better insulating coat to
decrease heat loss. For endotherms, thermoregulation is the highest expenditure in cold
seasons. The rate of heat production is proportionally enhanced to the rate of heat loss to
maintain body temperature (T ) at the desired level allowing maximal physical performance. b
Energy costs for endotherms are eight times higher than for ectotherms of comparable body
size and ambient temperature (T ) (ELSE and HULBERT 1981) and cannot always be a
afforded.

2 Chapter 1
Torpor
To lower metabolic costs, many species evolved endogenously controlled hypothermia which
is probably the most powerful tool for saving energy in harsh seasons. Those heterotherms
appear to use mainly two different forms of torpor to adapt to their environment and their
physiological needs as best as possible: hibernation or prolonged torpor in ?true hibernators
and daily torpor in the daily heterotherms (Fig. 1). Deep hibernators like e.g. European
hamsters (Cricetus cricetus), European ground squirrels (Spermophilus citellus) or Syrian
hamsters (Mesocricetus auratus) show a controlled decrease in T to values approaching b
ambient temperature (T ) during the hibernation season which can last 6-7 months. Periods of a
deep torpor are interrupted by regular arousals and brief 1-2 day periods of euthermia every 5
to 20 days (K?RTNER and GEISER 2000). Mostly, the preferred T during deep hibernation b
ranges between 1 and 6 C, but some species like the Arctic ground squirrel can even tolerate
supercooling at -3 C (BARNES 1989). Hibernating mammals reduce their metabolic costs by
around 90% (HELDMAIER et al. 2004) which allows survival entirely on body fat that has
been stored prior to winter, making this economizing strategy most effective. Thus, energy
intake and expenditure in hibernators are not balanced on a daily, but rather a yearly basis.
Smaller animals like the Djungarian hamster (Phodopus sungorus), various bat species,
hummingbirds and also lemurs predominantly undergo bouts of daily torpor (GEISER 2004,
DAUSMANN 2004). During this relatively shallow form of torpor they decrease T b
depending on T to barely lower than 15 ?C. Generally, daily torpor is restricted to the a
circadian resting phase of the animal, hence not exceeding a duration of some hours (GEISER
2004, HELDMAIER et al. 2004). During a bout of daily torpor the extent of hypothermia and
hypometabolism, i.e. energy saving, is usually less pronounced than in deep hibernation.
Nevertheless, a 60-70% reduction in energy requirements is reached, also because feeding-
related activities are strongly reduced in torpid animals (RUF et al. 1991, 1993, SCHMID et
al. 2000). The advantage of daily torpor compared to deep hibernation is that territorial and
social activities can be maintained during the torpor season. Generally, daily torpor is less
strictly seasonal in most species and therefore can also be used as a response to acute energy
shortage.
It has been questioned whether different forms of hypothermia underlie different mechanisms,
but so far physiological properties have turned out to be very similar (HELDMAIER et al.
2004).
3 Chapter 1



Figure 1: Examples of daily torpor (upper panel) and hibernation (lower panel) over 20 days in
midwinter. The minimum T achieved during a daily torpor bout of this Djungarian hamster, which was b
kept at 15 C T does not drop below 20 C. Note that daily torpor is not expressed every day. During a,
deep hibernation preferred T of golden-mantled ground squirrels generally lies at around 6 C at 5 C b
T . Regular arousals occur every 7-8 days in this example (modified from RUBY et al. 2003). a

First, metabolic rate is reduced, followed by a drop in T which can be precisely regulated and b
maintained at low degrees, before rapidly increasing again to the normometabolic and
normothermic state (GEISER and HELDMAIER 1995, LOVEGROVE et al. 1999,
4
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