Hibernation triggers and cryogens: Do they play a role in hibernation?

Cump. Biochem. Physiol. Vol. 118A, No. 4, pp. 1125-l 133, 1997 Copyright 0 1997 Elsevier Science Inc. All rights reserved.

ISSN 0300-9629/97/$17.00 PI1 SO300.9629(97)00239.9

ELSEVIER

REVIEW

Hibernation Triggers and Cryogens: Do They Play a Role in Hibernation? S . Vybiral and L. Janskj DEPARTMENTOF COMPARATIVE PHYSIOLOGY,FACULTY OF SCIENCE,CHARLES UNIVERSITY, PRAGUE, THE CZECH REPUBLIC

1997. 0 1997 Elsevier Science Inc.

COMP BLOCHEMPHYSIOL118A;4:1125-1133.

KEY WORDS.

Hibernation triggers, cryogens, DADLE, met-enkephalin,

is made possible by the lowering of the threshold

INTRODUCTION Hibernation

is a seasonal phenomenon

triggered by changes

in environmental

factors, namely by light, temperature,

food availability.

Hibernation

continuous

phenomenon

can be characterized

and

as a dis-

consisting of series of short hiber-

nating bouts, lasting several hours or days. Different levels of hypothermia have been observed among hibernating species, while bears may not lower body temperature

below 3O”C, in smaller hibernators,

peratures close to 5°C have been commonly bernation

can be characterized

body tem-

observed. Hi-

not only by the level of hy-

pothermia and by the frequency of hibernation bouts, but also by the duration of the prehibemation period, of the hibernation

season and by other parameters

(35,38).

these parameters should be taken into consideration analyzing the effect of environmental

All when

factors or humoral

substances on hibernation. Hibernation

is a strictly controlled

cess, characterized homeostasis control

thermoregulatory

for hibernation,

body temperature

meotherms,

hibernators

After several weeks

during which the animals

very precisely,

as do other ho-

suddenly lower body temperature

within a few hours. After a bout of hibernation, moregulatory normothermic companied

pro-

by the resetting of the control of thermal

to low body temperatures.

of preparation

thermoregulation

threshold

is spontaneously

level again. Additionally,

the ther-

returned hibernation

by changes in feeding behavior-periods

perphagia are followed by periods of anorexia,

to the is acof hy-

which is re-

flected in changes in body mass (63). Hypothalamic control centers play a crucial role in regulation of body temperature during hibernation. Hibernation

Address reprint requests to: L. Jansky, Dept. of Comparative Physiology, Faculty of Science, Charles University, 128 00 Prague 2, Vinicni 7, Czech Republic. Tel. 42-2-21953247; Fax 42-2-299713. Received 17 August 1996; revised 8 April 1997; accepted 24 April 1997.

for induc-

tion of thermoregulatory

responses, such that body tempera-

ture can be maintained

at a level close to the ambient tem-

perature (25,26,31,81). Changes in the sympathetic

tone and an altered hor-

monal status are also typical for hibernation. cies, involution

are a necessary prerequisite for hibernation to gonads, many other endocrine

(36). In addition

glands also undergo pro-

found changes during preparation is, therefore,

In most spe-

of gonads and absence of gonadal steroids

for hibernation

(92).

tempting to speculate that in hibernating

mals the change in thermoregulatory by action of humoral substances

threshold

It

ani-

is triggered

(42).

Several naturally occurring substances, namely neuropeptides, may lower the thermoregulatory threshold and induce changes similar to those observed during hibernation. There is substantial evidence that intrahypothalamic broventricular

administration

hypothermia

even in nonhibernators

neuropeptides are effective ACTH,

(enkephalins, in normal

MSH)

91). Neuropeptides hibernation

(37).

induces

Some

of the

bombesin, CCK)

while the others

(AVP,

in febrile animals only (7,24,

appear to be promlising

candidates

as

triggers, since they do not only induce changes

in body temperature Increased

neurotensin,

animals,

are effective

or intracere-

of neuropeptides

but also influence

levels of neuropeptides

food intake

(37).

have been demonstrated

in hibernating animals (48,64,68,69). When analyzing the effect of humoral substances on body temperature control of hibernators and nonhibemators it should be differentiated between the mode of action of cryogens and hibernation induction triggers (HIT). Some substances, derived from tissues or urine, may induce hypothermia, not only in hibernating but also in nonhibernating Chemically

species. These substances are called cryogens. they are probably of different character. The

search for cryogens has a long history. In 1932, Nitsche and

S. Vybiral and L. Janskq

1126

Maier (67) injected

an extract of a hibernator’s

tissue into nonhibernators reduction Wendt

and hibernators

of body temperature

species. Only a heterogenous

lymphatic

and obtained

a

and oxygen consumption.

(96) and Hook (33) found that an extract from the

brown adipose tissue (BAT)

lowered metabolic

rate in rats.

Kroll(5 1) observed a sleep-like state in cats following injections

of brain

hedgehogs.

extracts

Zirm (99)

from hibernating temperature extracts

from hibernating

hamsters

also observed that extracts

hedgehogs

and

of BAT

produced a lowering of body

in mice. No such effect was seen with BAT

from nonhibernating

other than BAT.

hedgehogs

On the contrary,

or from tissues

neither

Allen (62), Bigelow et al. (6), nor Johannsen

Morrison

and

(41) were able

preparation has been obtained

from the blood of woodchucks and 13-lined ground squirrels (73). Recently,

Horton et al. (34) described a hibernation

specific 88 kDa protein in the plasma of deeply hibernating woodchucks, and Bruce et al. (9) presented evidence that the albumin-bound hibernation substance is of opioid character, however. Regrettably, the effect of the HIT on individual hibernation parameters (durations of prehibemation

season) has never been studied

in detail. The experimental

conditions

ture) have not always been exactly specified and sometimes the hibernation

animals in nonhibernators.

was not followed. Furthermore,

the existence of an antimetabolic termed

hormone, which was later

untaboIone. He presented

evidence

that

extracts

from the brain of aestivating lung fish, when injected

intra-

venously into white rats, induced a state of torpor followed by a drop of body temperature of 3°C (88). These effects were not seen following

injections

of active fish. This observation [cited in (86)].

Similarly,

brains of hibernating

of extracts from brains

was confirmed by Reinhard

i.v. injections

of extracts

from

ground squirrels lowered the body

under which hiber-

nation behaviour has been studied (e.g., ambient tempera-

to confirm any effects of brown fat extracts from hibernating In 1963, Swan (85) postulated

period, hiber-

nation bout or hibernation

behaviour

of the control group of animals

stances on body temperature

the effect of HIT-like control

sub-

of normotherms

has

not been studied at all. Recently,

Japanese researchers dis-

covered (47,90)

proteins” in the blood of

that “hibernation

chipmunks even decrease during hibernation. Because homeiothermic slow-wave sleep and hibernation appear to be manifestations

of physiologically

related pro-

cesses, it has been also thought that the biochemical

mecha-

nisms underlying these states would share similar properties. A large number of sleep-inducing

peptides (e.g., DSIP) have

temperature of albino rats. Again, extracts from normother-

been isolated from the plasma, urine, milk, and tissues of

mic ground squirrels were without any effect (89). Recently,

sleeping animals and chemically

it was found that peptides isolated from the brain of hiber-

see (29,53)].

nating ground squirrels decrease body temperature

kines and muramyl peptides (55,56).

when injected

intraperitoneally

(98).

Finally, Kluger et al.

(44) and Cox et al. (16) described a hypothermic a substance from human urine in rabbits. Gordon duced hypothermia

of rats,

in mice using i.p. injections

between

hibernation

established,

(28) in-

seem rather to induce an hyperthermic

of mouse

ger” (HIT),

induction

derived from the blood of hibernating

and able to induce hypothermia

trig-

animals

the other hand, i.p. injected

in awake hibernators

has

been suggested by Dawe and Spurrier in 1969. When blood from hibernating

13-lined ground squirrels was injected

in-

this connection, substances

e.g. cyto-

No firm homologies

however [for review see (54)], and sleep factors

induced hyperthermia of a so-called “hibernation

[for review

triggers and sleep factors have been

effect of

urine. The existence

characterized

Other peptides are also somnogenic,

reaction (77,79).

in mice but not in rats (30,97).

it should be noted, however,

that usually induce hyperthermia

toxin) at thermoneutrality bient temperatures

On

DSIP reduces amphetaminethat some (e.g.,

may be hypothermic

In

endo-

at low am-

(23).

It should be also noted that, in addition

to the HITS,

travenously into summer active animals of the same species,

expression

the recipient

within 2 days. Evidently,

changes in energy balance. Reduced glucose availability has

no gonadal involution was necessary to induce hypothermia

been found to induce torpor in Djungarian hamsters (18). A new hypothesis linking thermostatic and glucostatic con-

began to hibernate

under these conditions. stance Serum

The existence

of the trigger sub-

was reported later in other hibernating species. dialyzate from hibernating woodchucks or arctic

of the daily torpor can also be influenced

trol of the hypothalamus Finally, Stanton

by

has been presented recently (32).

et al. (83) reported that continuous

in-

ground squirrels appeared to induce hibernation in summer active 13-lined ground squirrels (19-22,82). On the other hand, while HIT appeared to be effective in ground squir-

tracerebroventricular infusions of melatonin prolong the duration of hibernation bouts in golden-mantled ground squirrels. The role of the pineal in inducing hibernation has

rels, woodchucks (19), bats (12) and bears (11,66,80), transfusions of the blood from hibernating animals to other species (golden hamster, Djungarian hamster, Richardson’s

not been clearly established yet, however. It appeared to be important for the occurrence of spontaneous torpor in

ground squirrels) failed to induce hibernation, suggesting that the effect may be species specific (1,27,43,61). HIT has been characterized as thermolabile small protein, closely associated with the plasma albumin fraction (74), the structure and effects being similar across different

animals fed ud l&turn, but not in starved animals (84). In golden hamsters, pinealectomy had little effect on hibernation (38). Since there is increasing evidence in the literature that endogenous opioids may be also involved in hibernation [( 13,17,49,95);

for details see Discussion],

in this study ex-

Hibernation

1127

Triggers and (Iryogens

100

body core temperature on the activity control

%

rabbits.

50

body

temperature

41

40

39

42

“C

FIG. 1. Scheme of the activation of thermoregulatory effectors in a normotherm (rabbit) in response to changes in central body temperature. [CT = cold thermogenesis, PVMT = peripheral vasomotor tone, HL = respiratory evaporative heat loss; (37) 1.

drops

below

which

38.5”C

operational

range of the temperature

its maximal

thus being

central

of the peripheral to reach

of these

and 4O”C, respectively,

and

vice

1°C. On the other

hand,

increases

to above

highest

tone

values

the operational

38.5”C,

and panting

at about

range

39.5” ahout

being

of the body tempera-

The

in control

extent

of the

interthreshold

zone

intrahypothalamically

(DADLE)

in concentrations

was

of 5, 25

or 50 ,ug. A dose of 500 pug was used for intravenous periments

were performed

sponses

to analyze

of a normotherm

injections

after

(DADLE,

of enkephalins

fect of plasma studied

(rabbit)

thermoregulatory

from hibernating

European

of hibernation-like

hibernating

Ef-

hamsters

conditions

substances

tions.

Met-enkephalin

pothalamus

intrahypothalamic

met-enkephalin).

under the same experimental

the existence

re-

was also

in the blood of

blood

The simple

measurement

to a peripheral

of the body temperature

injection

of a substance

provides

physiological

role of the substance

the changes

Therefore,

to analyze

ture control ministered detailed individual (CT),

directly

at 5°C. Serum

volume

of plasma

the

was stored

at

into the hypothala-

experiments,

1 ml of plasma

was

intravenously.

to the

cooling

heat

vasomotor

lease of the vasomotor

tone

must To

(cold

(PVMT)

et al. (40) and Janskf central

be ad-

clarify the

was used

effecters

an enkephalin

the threshold

substances,

warming

that

the

for shivering,

the interthreshold

regulatory

mechanisms

lamic

to stimulate

D-AlaZ-D-Leu-

but leaves the threshold

tone

enlarging

of body temperature

method

derivate

Enkephalin (DADLE), when injected in pharmacological doses (50 pug) into the hypothalamus of the rahbit, lowers

on body tempera-

hypothalamus.

of the

the

may be unspecific.

the substances

loss (panting-REHL).

manipulation

about

used in body temperature

of these

and

It was found

in a thermoneutral

the effect of opioids precisely,

RESULTS

response

information

in body temperature

thermoregulatory

see Janski

enabled

only limited

of action

peripheral

evaporative details

centers

mode

of intestinal

at 10°C was

after ohtaining

AND METHODS

environment control:

injec-

into the hy-

hibernating

Immediately

was centrifuged

- 20°C. The injected also injected

MATERIALS

hamsters

mus was 10 ~1. In other

animals.

was injected

in doses of 0.1, 0.5, 1 .O, 2.5, and 5.0 pg. by decapitation.

sample,

to indicate

(met-EK)

Blood from European obtained

is

animals.

In this study, D-Ala2-D-Leu5-Enkephalin injected

the cold

can be also estimated from the slopes of the slopes indicating a higher thermosensitivity

versa.

minimal

at 37.5”C,

input stimulating

The thermosensitivity

ture controller curves, steeper

ef-

change When

cold thermogenesis

vasomotor

their

in

central

in this case is

intensity

about

body temperature

1.0” and 1S”C.

T hp.

of the

for the activation

to reach

the release 36

a signal

is activated

are activated 37

or warming effecters

any deviation

from the threshold,

represents

thermogenesis

36

cooling

fectors. Intensities of CT, PVMT, and REHL then proportionally to changes in body core temperature.

when

f

intestinal

thermoregulatory

Obviously,

body temperature 38.5”C,

during

of individual

and panting

zone and leaving

out of action changes

thermosensitivity

within

(0. 8°C).

of the warm

for re-

unchanged, a certain

Apparent defence

thus

the thermorange

hypothamechanisms

(PVMT, REHL) appears to he lowered (Fig. 2). The effect of DADLE is short-lasting and is followed hy a nonsig-

thermogenesis and respiratory

For experimental (37). The

method

temperature

input,

nificant

hyperthermia

DADLE

(5 pg) are without

(Fig.

(500 ,ug) of this substance

3). Lower effect.

cc>ncentrations

Intravenous

of

applications

are also ineffective.

Intrahypothalamic injections of met-enkephalin (0.5 pup) induced a slight febrile-like hyperthermia due to the shift

while leaving the peripheral temperature input relatively unaffected. This allowed expressing the activity of individual thermoregulatory effecters and the apparent hypothalamic thermosensitivity as simple functions of central body

of thresholds of all thermoregulatory effecters upwards, without influencing the apparent hypothalamic thermosen-

temperature and to estimate the thermoregulatory olds for individual thermoregulatory effecters.

sitivity (Fig. 4). Additional experiments

Figure

1 schematically

shows

the effects

thresh-

of changes

in

plasma

from hibernating

with European

i.v. or i.h. hamsters

injections

of

did not reveal

S. Vybiral and L. Janski

( IO). Hibernating reactions

animals showed seasonal variations in the

to naloxone

and opiates (5,941.

Specific

opioid

binding in the brain also decreased during hibernation

(3).

Further it was found that the delta opioid receptors were involved in the control of hibernation agonist opioid production

(72) and that delta

increased during hibernation

of

black bears (9). Opioids were involved in the initiative regulatory steps of hibernation

of ground squirrels (13). In con-

trast, Kulpa et al. (57) found that naloxone did not alter the onset of hibernation

administration

and the weight gain

in 13-lined ground squirrels. Opioids also modulate gonadotropin tion

and may thus control

gonadal

and prolactin secreactivity

and conse-

quently hibernation behaviour. Opioid peptides lower the production of gonadotropins (60). The reduction of LH and FSH production

induced by exposure to short photoperiod

can be prevented by naloxone

(14), suggesting that the pho-

toperiod effect is mediated by opioids. Opiates also lower the sensitivity of the hypothalamic

pituitary axis to testos-

terone feedback (15). Prolactin levels increase after administration of endorphins

(78).

In contrast to all these findings, other evidence suggests that opioid peptides, mus of normotherms

when injected

into the hypothala-

induce hyperthermia

and hyperphagia,

while nonopioid peptides appear to be hypothermic petite-inhibiting (37). The results presented

in this paper do not fully support

earlier tindings that a delta opioid-DADLE-can a long-lasting

and ap-

hypothermic

induce

effect (71) and do not indicate

that changes in body temperature control observed after inFIG. 2. Relationship between central body temperature and the intensity of individual thermoregulatory effecters (PVMT = Tsk, REHL = RR, CT = 0,) in rabbits after intrahypothalamic injections of DADLE (50 pg). Black symbols represent control values, white symbols represent values after treatment.

any effect on the activity of thermoregulatory

effectors-

trahypothalamic

injections

occurring during entrance injections

of met-enkephalin

thermic. This is not consistent centrations

the intrahy-

are slightly hyper-

with findings that brain con-

of met-enkephalin

increase during hibernation

(58), but it rather agrees with the findings of Beckman (2), that ICV infusions of this substance result in shortening of the hibernation.

(Fig. 5).

ture control

Our results do not indicate any changes in body temperaof rabbits after intrahypothalamic

of plasma from hibernating

injections

hamsters. This contrasts

findings that in a nonhibernator

DISCUSSION

are similar to those

Our data show that, in contrast to DADLE, pothalamic

the threshold body temperature and the apparent hypothalamic thermosensitivity of rabbits remained unchanged

(monkey)

with

infusions or HIT

into the cerebral ventricle produced a transient fall in body

The hypothesis of an opioid peptide control of hibernation had been presented by Margules et al. (59) in 1979. Later, it has been found that the functional properties of one or several brain opioid peptide systems are altered during hibernation and that opioid peptides may modulate the CNS control of hibernation (2). Continuous microinfusions of naloxone in the cerebral ventricle produced a dose-dependent decrease in duration of hibernation bouts (4) and naltrexone decreased the length of sleeping bouts (52). Naloxone-treated

of DADLE

into hibernation.

ground squirrels also hibernated

less frequently

temperature, a long-term reduction of the animal’s intake of food, bradycardia and an opiate-like modification in behaviour (65,75). Extracts of brains from hibernating ground squirrels lowered heart rate and increased coronary flow and oxygen consumption of isolated perfused rat hearts (87). HIT also altered renal functions in the monkey (70). Albumin fraction from the blood of hibernating black bears suppressed the induced contractility of the guinea pig ileum and naloxone reversed this effect (8,9). A peptide isolated from the brain of hibernating ground squirrels decreased the

1129

Hibernation Triggers and Cryogens

FIG. 3. Effect of different doses of DADLE on shift of the threshold for shivering during the early (O-60 min [black columns]) and late phase ( 120-180 min [white columns]) of cooling.

heart rate of chicken substances occurring

embryos (50).

Thus, it appears that

in the blood or tissues of hibernating

animals may alter different physiological not influence the body temperature

functions,

On the basis of all the data presented to conclude,

m agreement

evidence for the existence vincing.

Experiments

but do

control. above, we tend that the

of an universal HIT is not con-

in this direction

have been going on

for about 60 years without considerable

success. Several ex-

perimental approaches were used to reach this goal. Extracts BAT)

or body fluids (blood,

urine) of hibernating

or nonhibernating

jected subcutaneously,

i.p. or i.v. into normotherms

animals were inor sum-

mer active hibernators with inconsistent results. Furthermore, HITS do not seem to have a universal hypothermic effect, neither

in hibernators

to find, isolate, and identify a universal substance induce a hypometabolic

with Wang et al. (93),

from various tissues (brain,

active hibernators and none of the hibernation triggers has been chemically identified yet. It appears that the attempts

nor in nonhibernators.

There

have been unsuccessful. evidence

state in a homeiothermic Although

that opioids are connected

able to organism

there exists increasing with hypometabolic

states, it seems unlikely that a single opioid substance could be responsible

for changes in the hormonal

status, feeding

behavior and body temperature control ohserved during hibernation. There exist, however, substances of peptidergic character that induce hypothermia

in normal nonhibernating

animals

(cryogens). Intrahypothalamic administrations of bombesin seem to induce changes in body temperature control similar to those observed during hibernation administered

intrahypothalamically

(7). Bombesin,

when

in very low doses, shifts

is also a serious problem concerning the specificity of the HIT effects. Compared to current methodologies many of these previous experiments were methodically imperfect. In

the threshold for all thermoregulatory effecters downward and lowers the apparent hypothalamic thermosensitivity (39). The effect of bombesin may persist for several hours

some cases the depression of metabolism and body temperature might be due to an anaphylatic shock. Additionally,

or even days. Thermoregulatory responses to i.h. injections of bombesin resemble those occurring during entrance

HITS have never been injected

into hibernation.

into the hypothalamus

of

Interestingly,

the hypothermic

effects of

1130

S. Vybiral

and L. Jansky

RR

02

*c 5.2

FIG. 4. Relationship between central body temperature and the intensity of thermoregulatory effecters (PVMT = Tsk, REHL = RR, CT = 0,) in rabbits after intrahypothalamic injections of met-enkephalin (0.5 pg). Black symbols represent control values, white symbols represent values after treatment.

bombesin

can be blocked by the administration

of nalox-

one (7).

FIG. 5. Relationship between central body temperature and intensity of individual thermoregulatory effecters (PVMT = T,h, REHL = RR, CT = 0,) in rabbits 20 mm after intrahypothalamic injections of plasma from hibernating European hamsters. Black symbols represent control values, white symbols represent values after treatment.

(0.1-l

pg) induce a slight hyperthermia

all thermoregulatory Intrahypothalamic

due to the shift of

effecters to higher body temperatures. injections

of plasma from hibernating

European hamsters do not influence the body temperature SUMMARY

control

in rabbits.

A survey of the literary evidence on cryogens and hibernation induction triggers is given and the results of experiments on the effect of hypothalamic or i.v. injections of opioids and plasma from hibernating

European hamsters on

body temperature control of rabbits are presented. Pharmacological doses of a delta opioid-DADLE

(25 or

50 pg), when injected into the anterior hypothalamus, induce a small and short-lasting hypothermic effect in cold exposed rabbits, due to the downward shift of the temperature threshold for shivering. Lower doses (5 pug) are without effect, similarly as i.v. administrations (500 pg/kg) of this substance. Intrahypothalamic injections of met-enkephalin

References Abbots, B.; Wang, L.C.H.; Glass, J.D. Absence of evidence for a hibernation “trigger” in blood dialyzate of Richardson’s ground squirrel. Cryobiology 16:179-183;1979. Beckman, A.L. Functional aspects of brain upioid peptide systems in hibernation. In: Heller, H.C.; Musacchia, X.1.; Wang, L.C.H. (eds). Living in the Cold. Physiological and Biochemical Adaptations. New York: Elsevier Science Inc.; 1986:225234. Beckman, A.L.; Dean, R.R.; Wamsley, J.K. Hippocampal and cortical opioid receptor binding: Changes related to the hibernation state. Brain Res. 386:223-231;1986. Beckman, A.L.; Llados-Eckman, C. Antagonism of brain opi-

Hibernation

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19. 20.

21.

Triggers

and Cryogens

oid peptide action reduces hibernation bout duration. Brain Res. 328:201-205;1985. Beckman, A.L.; Llados-Eckman, C.; Stanton, T.L.; Adler, M.W. Physical dependence on morphine fails to develop during the hibernating state. Science 212:1527-1529;1981. Bigelow, W.; Trimple, A.S.; Schonbaum, E.; Kovats, L. A report on studies with Mannota monax. 1. Biochemical and pharmacological investigations of blood fat. Ann. Acad. Sci. Fenn. A. 4,71:37-50;1964. Brown, M.; Rivier, J.; Vale, W. Actions of bombesin, thyrotropin releasing factor, prostaglandin El and naloxone on thermoregulation in the rat. Life Sci. 20:1681-1688;1977. Bruce, D.S.; Ambler, D.I.; Henschel, I.M.; Oeltgen, P.R.; Nilekami, S.P.; Amstrup, S.C. Suppression of guinea pig ileum induced contractility by plasma albumin of hibernators. Pharmacol. Biochem. Behav. 43:199-203;1992. Bruce, D.S.; Bailey, E.C.; Setran, D.P.; Tramell, M.S.; Jacobson, D.; Oeltgen, P.R.; Horton, N.D.; Heilgren, EC. Circannual variations in bear plasma albumin and its opioid-like effects on guinea pig ileum. Pharmacology Biochemistry and Behavior 55:885-889;1996. Bruce, D.S.; Cope, G.W.; Elam, T.R.; Ruit, K.A.; Oeltgen, P.R. Opioids and hibernation. 1. Effects of naloxone on bear HIT’s depression of guinea pig ileum contractility and on induction of summer hibernation in the ground squirrel. Life Sci. 41:2107-2113;1987. Bruce, D.S.; Darling, N.K.; Seeland, K.J.; Oeltgen, P.R.; Nilekani, S.P.; Amstrup, S.C. Is the polar bear (Ursus maritimus) a hibernator? Continued studies on opioids and hibernatmn. Pharmacol. Biochem. Behav. 35:705-711;1990. Bruce, D.S.; Tuggy, M.L.; Pearson, P.J. Summer hibernation induced in ground squirrels (Citellus tridecemlineatus) by urine or plasma from hibernating bats (Myotis lucifugus or Eetesicus fuscus). Cryobiology 21:371-374;1984. Cai, Yi-Peng; Ye, Zu-Cheng; Li, Zi-Wei. Interrelationship of endogenous opioids and neurotransmitters in hibernation modulation in ground squirrels. In: Geiser, F.; Hulbert, A.J.; Nicol, SC. (eds). Adaptations to the Cold: Tenth lnternational Hihernation Symposium. Armidale: University of New England Press; 1996. Chen, H.J.; Torgovnik, _I.; McMillan, L.; Randall, S. Age difference in endogenous opiate modulation of short photoperiod-induced testicular regression in golden hamsters. J. Endocrinol. lOl:l-6;1984. Cicero, T.J.; Schainker, B.A.; Meyer, E.R. Endogenous opioids participate in the relation of the hypothalamic-pituitaryluteinizing hormone axis and testosterone’s negative feedback control of luteinizing hormone. Endocrinology 104: 12861291;1979. Cox, P.A.; Rothenburg, B.A.; Kluger, M.J. Characterization of an rndogenous cryogen that appears in the urine. Am. J. Physiol. 243:R241-R244;1982. Cui, Y.; Lee, T.F.; Wang, L.C.H. State-dependent changes of brain endogenous opioids in mammalian hibernation. Brain Res. Bull. 40:129-133;1996. Dark, J.; Miller, D.R.; Zucker, 1. Reduced glucose availability induces torpor in Siberian hamsters. Am. J. Physiol. 267: R496-R501;1994. Dawe, A.R.; Spurrier, W.A. Hibernation induced in ground squirrels by blood transfusion. Science 163:298-299;1969. Dawe, A.R.; Spurrier, W.A. The blood-borne “trigger” for natural mammalian hibernation in the 13-lined ground squirrel and the woodchuck. Cryobiology 9:163-172;1972. Dawe, A.R.; Spurrier, W.A. Summer hibernation of infant (six week old) 13-lined ground squirrels, Citellw aidecemlineatus. Cryobiology 11:33-43;1974.

1131

22. Dawe, A.R.; Spurrier, W.A.; Armour, J.A. Summer hibernation induced from cryogenically preserved blood “trigger.” Science 168:497-498;1970. 23. Derijk, R.H.; Van Kampen, M.; Van Rooijen, N.; Berkenbosch, F. Hypothermia to endotoxin involves reduced thermogenesis, macrophage-dependent mechanisms, and prostaglandins. Am. J. Physiol. 266:Rl-R8;1994. 24. Ehymayed, H.M.; Janskq, L. A discrete mode of the antipyretie action of AVP, a-MSH and ACTH. Physiol. Res. 41: 57-61;1992. 25. Florant, G.L.; Heller, H.C. CNS regulation of body temperature in euthermic and hihernating marmots. Am. J. Physiol. 232:R203-R208;1977. 26. Florant, G.L.; Turner, B.M.; Heller, H.C. Temperature regulation during wakefulness, sleep, and hibernation in marmots. Am. J. Physiol. 235:R82-R88;1978. 27. Floster, W.A. Failure to initiate hibernation with blood from the hibernating arctic ground squirrel, Citellus undulates, and Eastern woodchuck, Marmota monax. J. Therm. Biol. 3:93; 1978. 28. Gordon, C.J. Induction of regulated hypothermia in mice by urine administration. J. Therm. Biol. 15:97-101;1990. 29. Graf, M.V.; Kastin, A.J. Delta-sleep-inducing peptide (DSIP): An update. Peptides 7:1165-1187;1986. 30. Graf, M.V.; Kastin, A.].; Coy, D.H.; Zadina, J.E. DSIP reduces amphetamine-induced hyperthermia in mice. Physiol. Behav. 33:291-295;1984. 3 1. Heller, H.C.; Colliver, G.W. DNS regulation of body temperature during hibernation. Am. J. Physiol. 227:583-589;1974. 32. Himms-Hagen, J. Role of brown adipose tissue thermogenesis in control of thermoregulatory feeding in rate: A new hypothesis that links thermostatic and glucostatic hypotheses for control of food intake. Proc. Sot. Exp. Biol. Med. 208:I 59169;1995. 33. Hook, W.E. Effect of crude peanut oil extracts of brown fat on metabolism of white fat. Proc. Sot. Exp. Biol. Med. 45: 37-40;1940. 34. Horton, N.D.; Oeltgen, P.R.; Kaftani, D.J.; Su, T-P.; Bruce, D.S.; Krober, AS.; Jones, J.F. Biochemical characterization of a hibernation-specific 88 kDa protein derived from the plasma of deeply hibernating woodchucks. In: Geiser, F. (ed). Adaptations to the Cold: Tenth International Hibernation Symposium. Armidale, NSW: University ofNew England Press; 1996. 35. Jansk_i, L. Pineal, gonads and hibernation. Pineal Res. Rev. 4:141-181;1986. 36. Janskq, L. Gonads and hihemation. In: Heller, H.C.; Musacchia, X.J.; Wang, L.C.H. (eds). Living in the Cold. New York: Elsevier Science Inc.; 1986:331-340. 37. Janskq, L. Neuropeptides and the central regulation of body temperature during fever and hibernation. J. Therm. Biol. 15: 329%347;1990. 38. Jansk$, L.; Kahlerovi, Z.; Nedoma, J.; Andrews, J.F. Humoral control of hihernation in golden hamsters. In: Musacchia, X.J.; Janskf, L. (eds). Survival in the Cold: Hibernation and Other Adaptations. Amsterdam: Elsevier North Holland, Inc.; 1981:13-22. 39. Janski, L.; Reidel, W.; Simon, E.; Simon-Oppermann, C.; Vybiral, S. Effect of bombesin on thermoregulation of the rahbit. Pfliig. Arch. 409:318-322;1987. 40. Janskq, L.; Vybiral, S.; Moravec, J.; Nachizel, J.; Reidel, W.; Simon, E.; Simon-Oppermann, C. Neuropeptides and temperature regulation. J. Therm. Biol. 11:79-83;1986. 41. Johannsen, B.W. Effects of drugs on hibernation. In: Schijnbaum, E.; Lomax, P. (eds). The Pharmacology of Thermoregulation. Basel: Karger; 1973:364-381. 42. Kalter, V.G.; Folk, G.E., Jr. Humoral induction ot mammalian

1132

hibernation. Comp. Biochem. Physiol. 63A:7-13;1979. 43. Karjalainen, M.; Hohtola, E.; Hissa, R. No metabolic suppression in the Djungarian hamster or rat by injections of plasma from the winter-sleeping brown bear. J. Therm. Biol. 19:321325;1994. 44. Kluger, M.J.; Tumbull, A.J.; Cranston, W.I.; Wing, A.J.; Gross, M.P.; Rothenburg, B.A. Endogenous cryogen excreted by the kidneys. Am. J. Physiol. 241:R271-276;1981. 45. Kolaeva, S.G.; Kramarova, L.I.; Yarygin, K.N. The role of opioids and TRH in the hibernation bout/arousal cycle of ground squirrels Citellus undulates. In: Malan, A.; Canguilhem, B. (eds). Living in the Cold II. Montrough, London, Paris: John Libbey Eurotext; 1989:461-466. 46. Kolaeva, S.G.; Lee, T.F.; Wang, L.C.H.; Paproski, S.M. Effect of intracerebroventricular injection of neokyotorphin on the thermoregulatory responses in rats. Brain Res. Bull. 25:407410;1990. 47. Kondo, N.; Joh, T. Endogenous circannual rhythm of hibernation-specific proteins (HP) associated with hibernation in chipmunks. In: Geiser, F.; Hulbert, A.J.; Nicol, S.C. (eds). Adaptations to the Cold: Tenth International Hibernation Symposium. Armidale, NSW: University of New England Press; 1996. 48. Kramarova, L.I.; Kolaeva, S.H.; Yukhananov, R.Y.; Rozhanets, V.V. Content of DSIP enkephalins and ACTH in some tissues of active and hibernating ground squirrels (Citellus suslicus). Comp. Biochem. Physiol. 74C:31-33;1983. 49. Kramarova, L.I.; Lee, T.F.; Ciu, Y.; Wang, L.C.H. State-dependent variation in inhibitory effect of (D-Ala2, D-Leu5)enkephalin on hippocampal serotonin release in the ground squirrel. Life Sci. 48:175-181;1991. 50. Kramarova, L.; Ziganshin, R.; Timoshenko, M.; Mikhaleva, I.; Karnaukhov, V. The peptide Thr-Ser-Lys-Tyr isolated from the brain of hibernating ground squirrels (Spertnophilus undufuMs) decreases the heart rate of chicken embryos. In: Geiser, F.; Hulbert, A.J.; Nicol, S.C. (eds). Adaptations to the Cold: Tenth International Hibernation Symposium. Armidale: University of New England Press; 1996. 51. Kroll, F.W. Gibt es einem humoralen Schafstoff im Schlafhim? Deutsch. Med. Wschr. 77:879-880;1952. 52. Kromer, W. Naltrexone influence on hibernation. Experientia 36:581-582;1980. 53. Krueger, J.M. Sleep-promoting factor S: Characterization and analogues. In: Sleep 1982. Sixth Sur. Congress on Sleep Research, Zurich 1982. Basel: Karger; 1983:106. 54. Krueger, J.M.; Shoham, S. Homologies between sleep factors and hibernation triggers. In: Heller, H.C.; Musacchia, X.J.; Wang, L.C.H. (eds). Living in the Cold. New York: Elsevier Science Inc.; 1986:235-243. 55. Krueger, J.M.; Walter, J.; Dinarello, C.A.; Wolff, S.M.; Chedid, L. Sleep-promoting effects of endogenous pyrogen (interkeukin-1). Am. J. Physiol. 246:R994-R999;1984. 56. Krueger, J.M.; Walter, J.; Karnovski, K.L.; Chedid, L.; Choay, J.P.; Lefrancier, P.; Lederer, E. Muramyl peptides. J. Exp. Med. 159:68;1984. 57. Kulpa, C.M.; Mammajiwalla, S.N.; Christman, L.M.; Beebe, J.A.; Hall, K.D. Persistence of weight gain and hibernation onset in juvenile thirteen-lined ground squirrels (Spermophilus ticemlineatus) in spite of long-term administration of naloxone. Comp. Biochem. Physiol. 85C:363-367;1986. 58. Lee, T.F. Niimberger, F.; Jourdan, M.L.; Wang, L.C.H. Possible involvement of septum in seasonal changes in thermoregulatory responses to MET-enkephalin amide in ground squirrels. In: Schonbaum, E.; Lomax, P. (eds). Thermoregulation: Research and Clinical Applications. Basel: Kruger; 1989:200203.

S. Vybiral and L. Janski

59. Margules, D.L.; Goldman, B.; Finck, A. Hibernation: An opioid-dependent state? Brain Res. Bull. 4:721-724. 60. Meites, J.; Bruni, J.F.; Van Vugh, D.A.; Smith, A.F. Relation of endogenous opioid peptides and morphine to neuroendocrine functions. Life Sci. 24:1325-1336;1979. 61. Minor, J.C.; Bishop, D.A.; Badger, C.R., Jr. The golden hamster and the blood-borne hibernation trigger. Cryobiology 15: 557-562~1978. 62. Morrison, P.R.; Allen, W.T. Temperature response of white mice to implants of brown fat. J. Mammal. 43:13-17;1962. 63. Mrosovsky, N.; Fisher, K.C. Sliding set points for body weight in ground squirrels during the hibernation season. Can. J. Zool. 48:241-247;1970. 64. Muchlinski, A.E.; Ho, F.J.; Chew, P.; Yamada, T. The concentrations of four neuropeptides in various brain areas of summer active and hibernating Spermophilus lateralis. Comp. Biochem. Physiol. 74C:185-189;1983. 65. Myers, R.D.; Oeltgen, P.R.; Spurrier, W.A. Hibernation “trigger” injected in brain induces hypothermia and hypophagia in the monkey. Brain Res. Bull. 7:691-695;1981. 66. Nelson, R.A.; Folk, G.F.; Pfeifler, E.W.; Craighead, J.J.; Jonkel, C.J.; Steiger, D.I. Behavior, biochemistry, and hibernation in black, grizzly and polar bears. Int. Conf. Bear Res. Manag. 5:284-290;1283. 67. Nietschke, A.; Maier, E. Uber das Vergiftungbild nach Injektion von Extrakten aus lymphatischem Bewebe (P-Substanz) und seine Beziehung zum Winterschlaf. A. Ges. Exp. Med. 82~215%226;1932. 68. Niirnberger, F. The neuroendocrine system in hibernating mammals: Present knowledge and open questions. Cell Tissue Res. 281:391-412;1995. 69. Niirnberger, F.; Lee, T.F.; Jourdan, M.L.; Wang, L.C.H. Seasonal changes in methionine-enkephalin immunoreactivity in the brain of hibernator, Spermophilus columbiunus. Brain Res. 547:115-121;1996. 70. Oeltgen, P.R.; Blouin, R.A.; Spurrier, W. A.; Myers, R.D. Hibernation “trigger” alters renal function in the primate. Physiol. Behav. 34:79-81;1985. 71. Oeltgen, P.R.; Nilekani, S.P.; Nuchols, P.A.; Spurrier, W.A.; Su, T.-P. Further studies on opioids and hibernation: Delta opioid receptor ligand selectively induced hibernation in summer-active ground squirrels. Life Sci. 43:1565-1574;1988. 72. Oeltgen, P.R.; Nilekani, S.P.; Nuchols, P.A.; Spurrier, W.A.; Su, T.-P.; Chien, S.; Proffitt, G.E.; Mahony, C. Identiiication of the opioid receptor l&and(s) involved in summer-induced and natural winter hibernation. In: Malan, A.; Canguilhem, B. (eds). Living in the Cold II. London, Paris: Colluque INSERM/John Libbey Eurotext Ltd.; 1989:97-104. 73. Oeltgen, P.R.; Spurrier, W.A. Characterization of a hibemation induction trigger. In: Musacchia, X.J.; Janski, L. (eds). Survival in the Cold: Hibernation and Other Adaptations. New York: Elsevier/North Holland; 1981:139-157. 74. Oeltgen, P.R.; Spurrier, W.A.; Bergman, L.C. Chemical characterization of a hibernation inducing trigger in plasma of hibernating woodchucks and ground squirrels. J. Therm. Biol. 3:94-102;1978. 75. Oeltgen, P.R.; Walsh, J.W.; Hamann, S.R.; Randall, D.C.; Spurrier, W.A.; Myers, R.D. Hibernation “trigger”: Opioidlike inhibitory action of brain function of the monkey. Pharmacol. Biochem. Behav. 17:1271-1274;1982. 76. Oeltgen, P.R.; Welborn, J.R.; Nuchols, P.A.; Spurrier, W.A.; Bruce, D.S.; Su, T.-P. Opioids and hibernation II. Effects of kappa opioid U69593 on induction of hibernation in summer active ground squirrels by “Hibernation Induction Trigger” (HIT). Life Sci. 41:2115-2120;1978. 77. Riveau, G.; MaSek, K.; Parant, M.; Chedid, L. Central pyro-

Hibernation

78.

79. 80.

81.

82.

83.

84.

85. 86.

87.

88.

89.

Triggers

and Cryogens

genie activity of muramyldipeptide. J. Exp. Med. 152:869; 1980. Rivier, C.; Vale, W.; Ling, N.; Brown, M.; Guillemin, R. Stimulation in vitro of the secretion of prolactin and growth hormone by pendorphin. Endocrinology 100:238-242;1977. Rothwell, N.J. Cytokines and thermogenesis. Int. J. Obesity 17(Suppl. 3):S98-S101;1993. Ruit, K.A.; Bruce, D.S.; Chiang, P.P.; Oeltgen, P.R.; Welborn, J.R.; Nilekani, S.P. Summer hibernation in ground squirrels (Citellw tridecemlinentw) induced by injection of whole or fractionated plasma from hibernating black bears (Ursus americanus). J. Thermal Biol. 12:135-138;1987. South, F.E.; Hartner, W.C.; Luecke, R.H. Response to preoptic temperature manipulation on the awake and hibernating marmot. Am. J. Physiol. 229:150-160;1975. Spurrier, W.A.; Folk, G.E., Jr.; Dawe, A.R. Induction of sum, mer hibernation in the 13-lined ground squirrel shown by comparative serum transfusions from arctic mammals. Cryobi, ology 13:368-374;1976. Stanton, T.L.; Daley, J.C., III; Salzman, SK. Prolongation of hibernation bout duration by continuous intracerebroventricular infusion of melatonin in hibernating ground squirrels. Brain Res. 413:350-355;1987. Steinlechner, S.; Heldmaier, G.; Weber, C.; Ruf, T. Role of photoperiod: Pineal gland interaction in torpor control. In: Heller, H.C.; Musacchia, X.J.; Wang, L.C.H. (eds). Living in the Cold: Physiological and Biochemical Adaptations. New York: Elsevier; 1986:301-307. Swan, H. Kamongo and anabolone. Arch. Surg. 87:715;1963. Swan, H. Neuroendocrine aspects of hibernation. In: Musacchia, X.J.; Janski, L. (eds). Survival in the Cold: Hibernation and Other Adaptations. New York: Elsevier/North Holland; 1981:121-138. Swan, H.; Becker, P.; Schatte, C. Physiologic effects of brain extracts from hibernating and non-hibernating rodents on isolated perfused rat heart. Comp. Biochem. Physiol. 68C:175179;1981. Swan, H.; Jenkins, D.; Knox, K. Metabolic torpor in Protopterus uethiopicus: An antimetabolic extract from the brain. Am. Nat. 103:247-258;1969. Swan, H.; Schatte, C. Anti-metabolic extract from the brain of the hibernating ground squirrel, Citellus tridecemlineatus. Science 195:84-85;1977.

1133

90. Takamatsu, N.; Kojima, M.; Kondo, N.; Shiba, T. Gene structures of the chipmunk and tree squirrel HP-25 genes. In: Geiser, F.; Hulbert, A.J.; Nicol, S.C. (eds). Adaptations to the Cold: Tenth International Hibernation Symposium. Armidale: University of New England Press; 1996. 91. Vybiral, S.; Cernq, L.; Janskg, L. Mode of ACTH antipyretic action. Brain Res. Bull. 21:557-562;1988. 92. Wang, L.C.H. Hibernation and the endocrines. In: Lyman, C.; Willis, J.S.; Malan, A.; Wang, L.C.H. (eds). Hibernation and Torpor in Mammals and Birds. New York: Academic Press; 1982:206-236. 93. Wang, L.C.H.; Belke, D.; Jourdan, M.L.; Lee, T.F.; Westly, J.; Niirnberger, F. The “hibernation induction trigger”: Specificity and validity of bioassay using the 13-lined ground squirrel. Cryobiology 25:355-362;1988. 94. Wang, L.C.H.; Lee, T.F.; Jourdan, M.L. Seasonal difference in thermoregulatory responses tu opiates in a mammalian hibernator. Pharm. Biochem. Behav. 26:565-571;1987. 95. Wang, L.C.H. Is endogenous opioid involved in hibernation? In: Carey, C., et al. (eds). Life in the Cold: Ecological, Physiological and Molecular Mechanisms. Proceedings of the Ninth International Hibernation Symposium. Boulder, CO: Westview Press; 1993. 96. Wendt, C.F. Uber Wirkungen eines extraktes aus dem braunen Fettgewebe des Winterschlafenden Igels. Z. Physiol. Chem. 249:182;1937. 97. Yehuda, S.; Kastin, A.J.; Coy, D.H. Thermoregulatory and locomotor effects of DSIP: Paradoxical interactions with damphetamine. Pharmacol. Biochem. Behav. 13:895-900; 1980. 98. Ziganshin, R.H.; Mikhaleva, 1.1.; Ivanov, V.T.; Kokoz, Y.M.; Korystova, A.F.; Mavlyutova, D.A.; Emelyanova, T.G. Biologically active peptides isolated from the hrain of hibernating ground squirrels and cold adapted Yakutian horses. In: Geiser, F.; Hulbert, A.J.; Nicol, S.C. (eds). Adaptations to the Cold: Tenth International Hibernation Symposium. Armidale: University of New England Press; 1996. 99. Zirm, K.L. Ein Beitrag zur Kenntnis der naturlichen Winterschlafes und seines regulierenden Wirkstoffes. II. Z. Naturforsch. 166:536-538;1956,