t:RYOBIOLOGY
Absence
16, 179-183
( 1979)
of Evidence for a Hibernation “Trigger” of Richardson’s Ground Squirrel B. ABBOTT& Department
of Zoology,
L. C. H. WANG,
Unioersity
of Alberta,
In 1969 Dawe and Spurrier ( 1) presented the first evidence for a blood-borne “trigger” for mammalian hibernation. This was done by injecting blood from hibernating 13lined ground squirrels (Spermophilus tridecemlineatus) into summer-active animals of the same species, and apparently inducing summer hibernation. Subsequent studies have demonstrated several features of this “trigger” mechanism. First, blood serum dialyzate from hibernating 1Slined ground squirrels containing molecules of less than 10,000 MW was found to be effective in inducing summer hibernation (2, 3). Secondly, this “trigger” substance can be preserved cryogenically (4). Thirdly, blood serum dialyzate from other hibernating rodents will induce hibernation in the 13-lined ground squirrels (4, 10). In addition, serum containing this “trigger” substance will also induce hibernation in 6-week-old 13-lined ground squirrels (3). Recent attempts to characterize this “trigger” (7) indicate that the substance is contained in an albumin fraction of the blood serum. Experiments which demonstrated hibernation induction property of blood from hibernating arctic ground squirrels (Spermophilus undulatus; 10) and woodchucks ( Marmota monax; 4, lo), indicate that this “trigger” substance may be common to many rodent hibernators. However, Galster Received September ber 20, 1978.
19, 1978;
accepted
in Blood
Dialyzate
J. D. GLASS
AND
Edmonton,
Alberta
T6G
2E9
(5) found no indication of a similar substance when summer-active arctic ground squirrels were injected with cryogenically preserved blood from woodchucks in deep hibernation. In this study, we describe our search for a comparable “trigger” substance for the induction of hibernation in another hibernating species, the Richardson’s ground squirrel, Spermophilus richardsonii. MATERIALS
AND
METHODS
A. Animals All animals were live-trapped approximately 10 miles southwest of Edmonton, Alberta. They were maintained individually at 22°C with a 12L:12D photoperiod and were fed Vitamite cubes (Northwest Feeds, Ltd., Edmonton) and water ad Z&turn. Animals were weighed weekly to aid in the determination of their endogenous phase of hibernation ( 8). Typically, ground squirrels gain weight rapidly to a peak and plateau or begin to lose weight immediately prior to the onset of hibernation (8; Wang, unpublished). Using this criterion we selected animals in their hibernating phase as donors and they were placed in a cold (6°C) and dark walk-in environmental chamber to induce hibernation. Most donor animals had been in captivity for more than 2 years, and their hibernation cycles were out of phase, as they were hibernating in summer. Each donor was in a hibernation bout for at least 5 days prior to blood collection. Ground
Novem-
179 OOll-2240/79/020179-05$02.00/0 Copyrighl Q 1979 by Academic Press, Inc. All rights of reproduction in any form reserved.
180
ABBOTTS,
WANG,
squirrels which showed no weight gain were thought to be in their nonhibernating phase and were selected as recipients for “trigger” in the first three trials conducted in May, June, and August, 1977, respectively. In trial 4, which was conducted in August, 1977, freshly captured young of the year were used. The recipients for “trigger” were maintained at 22°C and a 12L: 12D photoperiod for at least 4 weeks prior to the initiation of the experiments. B. Blood Collection and Dialysate Preparation The procedures for blood collection and preparation of the dialyzate followed those described by Dawe and his colIeagues (1, 2, 3, 4, 10). Briefly, blood was rapidly collected (within 90 set of initial disturbance) by decapitation in trials 1, 2, and 3 and in trial 4 by opening the chest and withdrawing blood directly from the heart into a heparinized syringe. Blood was left to stand for 10 min and centrifuged to obtain the serum (or plasma). The serum was then decanted and dialyzed 1:4 against physiological saline for 30 min using dialysis tubing (Fisher Scientific Co.) with a SO00MW cutoff. Dialysis tubing with a cutoff of 12,000 to 14,006 MW was used in trial 4. In trial 4 we divided the blood into two samples. One was treated with Bacitracin ( Sigma Chemical Co. ) to a final concentration of approximately 0.49 mM, while the other sample was left untreated. Bacitracin has been shown (6) to inhibit peptidase activity. From the work of Swan and Schatte (11) on an anti-metabolic peptide from the brain of a hibernating animal and the size limitations reported by Dawe and Spurrier (3), we reasoned that the bloodborne trigger could be a peptide. Thus, by using Bacitracin we could increase the activity of the “trigger” by slowing its degradation. All procedures were carried out in a cold room (6 2 l.O’C) with cold instruments, except the injection of the dialyzate
AND GLASS
which was made at room temperature (22°C). C. Administration of Hibernating Serum Dialyzate In trials 1, 2, and 3, 1.0 ml of dialyzate or physiological saline was injected into each recipient via cardiac puncture (n = 7) or saphenous venipuncture (n = 20). In trial 4, all recipients were injected with 0.5 to 1.0 ml dialyzate, dialyzate + Bacitracin or physiological saline via saphenous venipuncture. Not all attempts at venipuncture were equally successful; generally, the rate of successwas about 60 to 70%. D. Experimental Protocol In trials 1, 2, and 3, animals were placed in a cold (6 f l.O”C), dark room immediately following injection. All animals were supplied with Vitamite cubes and water ad libitum and supplied with cotton wool in addition to the normal wood shaving bedding. In trial 4, animals were again placed immediately in a cold, dark room with cotton wool but their feeding regimes were modified. Animals in Group D (receiving dialyzate), Group B (receiving Bacitracin-treated dialyzate), and Group S (receiving saline) were given Vitamite cubes ad libitum and sunflower seedsdaily. Water bottles were removed and lettuce was supplied daily as a water source in an attempt to keep the bedding dry and thus more conducive to hibernation. Group N, which did not receive any injection, was maintained on Vitamite cubes and water ad libitum to serve as a control for the fortified food regime. In all trials, the bedding was changed weekly or when soiled. In addition, animals were weighed weekly in trial 4. Daily inspection for behavioral changes (nest building) and bouts of hibernation, which were monitored via the sawdust technique, were made. At the onset of week 4 in trials 1, 2, and 3 and week 6 and week 12 in trial 4, food
ABSENCE
OF
HIBERNATION
181
“TRIGGER”
5OOr
W-M S-C zoo-
I Capt wt
I
I Inj wt
I I
I 2
I 3
I 4
I 5
/ 6
I 7
I 8
Group D Group B GroupC Group N I 9
I 10
I 11
I 12
Week FIG. 1. Weekly weights (in grams) of animals in trial 4. Mean weight Bars indicate SE. Animals were maintained individually in a cold (6 chamber. Observations were made daily for hibernation. Weights were week. Animals were deprived of food for 7 days at the onset of week D: dialysate; Group B: dialysate + Bacitracin; Group S: saline; Group D, B, and S received sunflower seeds as supplements, Group N did not.)
withdrawn for 7 days as food deprivation facilitates the induction of hibernation in this species (Wang, unpublished). was
RESULTS
that
hibernated
at
shown. walk-in of each (Group Groups
All but four animals (21 out of 25) in trial 4 exhibited bouts of hibernation during the winter. DISCUSSION
It can be seen in Table 1 that none of the trials 1, 2, or 3 showed any evidence for the effectiveness of blood dialyzate in inducing summer hibernation. There was no difference in nest-building behavior among the experimental groups (Table 1). Table 2 shows the results of trial 4. No incidence of hibernation was seen until week 6 when animals were deprived of food. Those animals
of each group is * l.O”C), dark taken at the end 6 and week 12. N: no injection;
this
time
were
in
neither of the dialyzate injected groups. Furthermore, no difference was found between the weights of the saline and dialyzate injected groups (Fig. 1). Those animals which were maintained on Vitamite cubes only (Group N) were slightly lower in body weight, but paralleled the changes seen in the other groups.
Studies in which blood from woodchucks (4), arctic ground squirrels and arctic marmots (10) induced hibernation in 13-lined ground squirrels suggest that this “trigger” phenomenon may be widespread among hibernating species. The results obtained in this study, however, do not support this. In no instance did the injection of hibernating serum dialyzate induce summer hibernation in the Richardson’s ground squirrel. Furthermore, Galster (5) reported no evidence for a hibernation inducing substance in blood from hibernating eastern marmots and arctic ground squirrels, using arctic ground squirrels as recipients. It is important to note that the 1Slined ground squirrel was the recipient in all studies which have shown evidence for “trigger”
182
ABBOTT&
WANG,
AND
TABLE
1
GLASS
Occurrences of Hibernation and Nest Building in Trials 1,2, and 3. Animals in a Cold (6 & l”C), Dark Walk-in Environmental Chamber. Observations 4 Weeks. Food Was Withdrawn at the End of Week 3 Saline
Trial
1
May
1977
Dialyaate
Hib
Nest bldg
10
-a
-a -
-
2 1977
Hib
Neat bldg
-a
-
for
injected
Y
-a
17 1)
-
4 9
-
-
-
-
-
-
-
T4 T5 T6 T7
-
-
7 z 11
-
-
-
s3 14; 29 5 3
-
47 26
-
-
-
Tl T2 T3
Trial 3 August 1977
Individually Out Daily
Animal
-
8 13
Trial June
injected
Animal
114 1~6
Were Maintained Were Carried
b
b
Q Absence. b Presence.
(1, 2, 3, 4, 7, 9, 10). We suggest, therefore, that the ability to exhibit “trigger” induced hibernation may be a phenomenon peculiar to the 1Slined ground squirrel. Experiments involving the testing of blood preparations which induce hibernation in the 13-lined ground squirrel on other hibernat-
ing species should be undertaken this apparent conflict. SUMMARY
In order to examine evidence for a bloodborne “trigger” for mammalian hibernation, serum dialyzate from hibernating Richard-
TABLE Occurrence Dark Walk-in at the Onset That Week
2
of Hibernation in Trial 4. Animals Were Maintained Individually Environmental Chamber. Observations Were Made Daily. Animals of Week 6 and Week 12. Number Indicates the Number of Animals
Group
D B s N Group Group Group Group
(n (n (n (n
= = = =
to resolve
in a Cold (6 f l”C), Were Deprived of Food That Hibernated during
Week
8) 8) 9) 10)
1
2
3
4
5
6
7
8
9
10
11
12
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 2 2
0 0 2 1
0 0 1 0
0 0 2 0
0 0 2 0
0 0 2 0
1 1 5 3
D : dialyzate, enriched food regime. B : dialyzate + Bacitracin, enriched S : saline, enriched food regime. N : no injection, normal food regime.
food
regime.
ABSENCE
OF
HIBERNATION
son’s ground squirrels (Spermophilus richardsonii) was injected into summer-active ground squirrels of the same species. Four independent trials involving 52 animals were performed. In all trials, no effect of the dialyzate was seen on nest building, weight gain or loss, or on occurrence of hibernation. ACKNOWLEDGMENTS This Council
“TRIGGER”
6.
7.
study was supported by a National Research of Canada Grant A6455 to L. Wang. REFERENCES
1. Dawe, A. R., and Spurrier, W. A. Hibernation induced in ground squirrels by blood transfusions. Science 163,298 ( 1969). 2. Dawe, A. R., and Spurrier, W. A. The bloodborne “trigger” for natural mammalian hibernation in the 13-lined ground squirrel and the woodchuck. Cryobiology, 9,163-172 (1972). 3. Dawe, A. R., and Spurrier, W. A. Summer hibernation of infant (g-week old) I3-lined ground squirrels, Citellus tridecemlineatus. Cryobiology 11, 3343 ( 1974). 4. Dawe, A. R., Spurrier, W. A., and Armour, J. A. Summer hibernation induced from cryogenically preserved blood “trigger.” Science 168,497498 ( 1970). 5. Galster, W. A. Failure to initiate hibernation
8.
9.
10.
11.
183
with blood from the hibernating arctic ground squirrel, Cite&s undulatus, and Eastern woodchuck, Marmota monar. J. Therm. Biol. 3, 93 (1978). McKelvy, F., LeBlanc, P., Landes, C., Perric, S., Grimm-Jorgensen, Y., and Kordon, C. The use of Bacitracin as an inhibitor of the degradation of thyrotropin releasing factor and lutenizing hormone releasing factor. Biochem. Biophys. Res. Commun. 73, 507515 (1976). Oeltgen, P. R., Spurrier W. A., and Bergman, L. Chemical characterization of a hibemating inducing trigger(s) in the plasma of hibernating woodchucks and ground squirrels. J. Therm. Biol. 3, 94 (1978). Pengelley, E. T., and Fisher, K. C. The effect of temperature and photoperiod on the yearly hibernating behavior of captive golden-mantled ground squirrels ( Citellus lateralis tescorum). Can. J. 2001. 41, 11031120 (1963). Rosser, S. R., and Bruce, D. S. Induction of summer hibernation in the 1%lined ground squirrel, Cite&s tridecemlineatus. Cryobiology 15,113-116 (1978). Spurrier, W. A., Folk, G. E., and Dawe, A. R. Induction of hibernation in the 13-lined ground squirrel shown by comparative serum transfusions from arctic mammals. Cryobiology 13,368-374 ( 1976). Swan, H., and Schatte, C. Antimetabolic extract from the brain of the hibernating ground squirrel, Cite&s tridecemlineatus. Science 195, 84-85 ( 1977).
Absence
16, 179-183
( 1979)
of Evidence for a Hibernation “Trigger” of Richardson’s Ground Squirrel B. ABBOTT& Department
of Zoology,
L. C. H. WANG,
Unioersity
of Alberta,
In 1969 Dawe and Spurrier ( 1) presented the first evidence for a blood-borne “trigger” for mammalian hibernation. This was done by injecting blood from hibernating 13lined ground squirrels (Spermophilus tridecemlineatus) into summer-active animals of the same species, and apparently inducing summer hibernation. Subsequent studies have demonstrated several features of this “trigger” mechanism. First, blood serum dialyzate from hibernating 1Slined ground squirrels containing molecules of less than 10,000 MW was found to be effective in inducing summer hibernation (2, 3). Secondly, this “trigger” substance can be preserved cryogenically (4). Thirdly, blood serum dialyzate from other hibernating rodents will induce hibernation in the 13-lined ground squirrels (4, 10). In addition, serum containing this “trigger” substance will also induce hibernation in 6-week-old 13-lined ground squirrels (3). Recent attempts to characterize this “trigger” (7) indicate that the substance is contained in an albumin fraction of the blood serum. Experiments which demonstrated hibernation induction property of blood from hibernating arctic ground squirrels (Spermophilus undulatus; 10) and woodchucks ( Marmota monax; 4, lo), indicate that this “trigger” substance may be common to many rodent hibernators. However, Galster Received September ber 20, 1978.
19, 1978;
accepted
in Blood
Dialyzate
J. D. GLASS
AND
Edmonton,
Alberta
T6G
2E9
(5) found no indication of a similar substance when summer-active arctic ground squirrels were injected with cryogenically preserved blood from woodchucks in deep hibernation. In this study, we describe our search for a comparable “trigger” substance for the induction of hibernation in another hibernating species, the Richardson’s ground squirrel, Spermophilus richardsonii. MATERIALS
AND
METHODS
A. Animals All animals were live-trapped approximately 10 miles southwest of Edmonton, Alberta. They were maintained individually at 22°C with a 12L:12D photoperiod and were fed Vitamite cubes (Northwest Feeds, Ltd., Edmonton) and water ad Z&turn. Animals were weighed weekly to aid in the determination of their endogenous phase of hibernation ( 8). Typically, ground squirrels gain weight rapidly to a peak and plateau or begin to lose weight immediately prior to the onset of hibernation (8; Wang, unpublished). Using this criterion we selected animals in their hibernating phase as donors and they were placed in a cold (6°C) and dark walk-in environmental chamber to induce hibernation. Most donor animals had been in captivity for more than 2 years, and their hibernation cycles were out of phase, as they were hibernating in summer. Each donor was in a hibernation bout for at least 5 days prior to blood collection. Ground
Novem-
179 OOll-2240/79/020179-05$02.00/0 Copyrighl Q 1979 by Academic Press, Inc. All rights of reproduction in any form reserved.
180
ABBOTTS,
WANG,
squirrels which showed no weight gain were thought to be in their nonhibernating phase and were selected as recipients for “trigger” in the first three trials conducted in May, June, and August, 1977, respectively. In trial 4, which was conducted in August, 1977, freshly captured young of the year were used. The recipients for “trigger” were maintained at 22°C and a 12L: 12D photoperiod for at least 4 weeks prior to the initiation of the experiments. B. Blood Collection and Dialysate Preparation The procedures for blood collection and preparation of the dialyzate followed those described by Dawe and his colIeagues (1, 2, 3, 4, 10). Briefly, blood was rapidly collected (within 90 set of initial disturbance) by decapitation in trials 1, 2, and 3 and in trial 4 by opening the chest and withdrawing blood directly from the heart into a heparinized syringe. Blood was left to stand for 10 min and centrifuged to obtain the serum (or plasma). The serum was then decanted and dialyzed 1:4 against physiological saline for 30 min using dialysis tubing (Fisher Scientific Co.) with a SO00MW cutoff. Dialysis tubing with a cutoff of 12,000 to 14,006 MW was used in trial 4. In trial 4 we divided the blood into two samples. One was treated with Bacitracin ( Sigma Chemical Co. ) to a final concentration of approximately 0.49 mM, while the other sample was left untreated. Bacitracin has been shown (6) to inhibit peptidase activity. From the work of Swan and Schatte (11) on an anti-metabolic peptide from the brain of a hibernating animal and the size limitations reported by Dawe and Spurrier (3), we reasoned that the bloodborne trigger could be a peptide. Thus, by using Bacitracin we could increase the activity of the “trigger” by slowing its degradation. All procedures were carried out in a cold room (6 2 l.O’C) with cold instruments, except the injection of the dialyzate
AND GLASS
which was made at room temperature (22°C). C. Administration of Hibernating Serum Dialyzate In trials 1, 2, and 3, 1.0 ml of dialyzate or physiological saline was injected into each recipient via cardiac puncture (n = 7) or saphenous venipuncture (n = 20). In trial 4, all recipients were injected with 0.5 to 1.0 ml dialyzate, dialyzate + Bacitracin or physiological saline via saphenous venipuncture. Not all attempts at venipuncture were equally successful; generally, the rate of successwas about 60 to 70%. D. Experimental Protocol In trials 1, 2, and 3, animals were placed in a cold (6 f l.O”C), dark room immediately following injection. All animals were supplied with Vitamite cubes and water ad libitum and supplied with cotton wool in addition to the normal wood shaving bedding. In trial 4, animals were again placed immediately in a cold, dark room with cotton wool but their feeding regimes were modified. Animals in Group D (receiving dialyzate), Group B (receiving Bacitracin-treated dialyzate), and Group S (receiving saline) were given Vitamite cubes ad libitum and sunflower seedsdaily. Water bottles were removed and lettuce was supplied daily as a water source in an attempt to keep the bedding dry and thus more conducive to hibernation. Group N, which did not receive any injection, was maintained on Vitamite cubes and water ad libitum to serve as a control for the fortified food regime. In all trials, the bedding was changed weekly or when soiled. In addition, animals were weighed weekly in trial 4. Daily inspection for behavioral changes (nest building) and bouts of hibernation, which were monitored via the sawdust technique, were made. At the onset of week 4 in trials 1, 2, and 3 and week 6 and week 12 in trial 4, food
ABSENCE
OF
HIBERNATION
181
“TRIGGER”
5OOr
W-M S-C zoo-
I Capt wt
I
I Inj wt
I I
I 2
I 3
I 4
I 5
/ 6
I 7
I 8
Group D Group B GroupC Group N I 9
I 10
I 11
I 12
Week FIG. 1. Weekly weights (in grams) of animals in trial 4. Mean weight Bars indicate SE. Animals were maintained individually in a cold (6 chamber. Observations were made daily for hibernation. Weights were week. Animals were deprived of food for 7 days at the onset of week D: dialysate; Group B: dialysate + Bacitracin; Group S: saline; Group D, B, and S received sunflower seeds as supplements, Group N did not.)
withdrawn for 7 days as food deprivation facilitates the induction of hibernation in this species (Wang, unpublished). was
RESULTS
that
hibernated
at
shown. walk-in of each (Group Groups
All but four animals (21 out of 25) in trial 4 exhibited bouts of hibernation during the winter. DISCUSSION
It can be seen in Table 1 that none of the trials 1, 2, or 3 showed any evidence for the effectiveness of blood dialyzate in inducing summer hibernation. There was no difference in nest-building behavior among the experimental groups (Table 1). Table 2 shows the results of trial 4. No incidence of hibernation was seen until week 6 when animals were deprived of food. Those animals
of each group is * l.O”C), dark taken at the end 6 and week 12. N: no injection;
this
time
were
in
neither of the dialyzate injected groups. Furthermore, no difference was found between the weights of the saline and dialyzate injected groups (Fig. 1). Those animals which were maintained on Vitamite cubes only (Group N) were slightly lower in body weight, but paralleled the changes seen in the other groups.
Studies in which blood from woodchucks (4), arctic ground squirrels and arctic marmots (10) induced hibernation in 13-lined ground squirrels suggest that this “trigger” phenomenon may be widespread among hibernating species. The results obtained in this study, however, do not support this. In no instance did the injection of hibernating serum dialyzate induce summer hibernation in the Richardson’s ground squirrel. Furthermore, Galster (5) reported no evidence for a hibernation inducing substance in blood from hibernating eastern marmots and arctic ground squirrels, using arctic ground squirrels as recipients. It is important to note that the 1Slined ground squirrel was the recipient in all studies which have shown evidence for “trigger”
182
ABBOTT&
WANG,
AND
TABLE
1
GLASS
Occurrences of Hibernation and Nest Building in Trials 1,2, and 3. Animals in a Cold (6 & l”C), Dark Walk-in Environmental Chamber. Observations 4 Weeks. Food Was Withdrawn at the End of Week 3 Saline
Trial
1
May
1977
Dialyaate
Hib
Nest bldg
10
-a
-a -
-
2 1977
Hib
Neat bldg
-a
-
for
injected
Y
-a
17 1)
-
4 9
-
-
-
-
-
-
-
T4 T5 T6 T7
-
-
7 z 11
-
-
-
s3 14; 29 5 3
-
47 26
-
-
-
Tl T2 T3
Trial 3 August 1977
Individually Out Daily
Animal
-
8 13
Trial June
injected
Animal
114 1~6
Were Maintained Were Carried
b
b
Q Absence. b Presence.
(1, 2, 3, 4, 7, 9, 10). We suggest, therefore, that the ability to exhibit “trigger” induced hibernation may be a phenomenon peculiar to the 1Slined ground squirrel. Experiments involving the testing of blood preparations which induce hibernation in the 13-lined ground squirrel on other hibernat-
ing species should be undertaken this apparent conflict. SUMMARY
In order to examine evidence for a bloodborne “trigger” for mammalian hibernation, serum dialyzate from hibernating Richard-
TABLE Occurrence Dark Walk-in at the Onset That Week
2
of Hibernation in Trial 4. Animals Were Maintained Individually Environmental Chamber. Observations Were Made Daily. Animals of Week 6 and Week 12. Number Indicates the Number of Animals
Group
D B s N Group Group Group Group
(n (n (n (n
= = = =
to resolve
in a Cold (6 f l”C), Were Deprived of Food That Hibernated during
Week
8) 8) 9) 10)
1
2
3
4
5
6
7
8
9
10
11
12
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 2 2
0 0 2 1
0 0 1 0
0 0 2 0
0 0 2 0
0 0 2 0
1 1 5 3
D : dialyzate, enriched food regime. B : dialyzate + Bacitracin, enriched S : saline, enriched food regime. N : no injection, normal food regime.
food
regime.
ABSENCE
OF
HIBERNATION
son’s ground squirrels (Spermophilus richardsonii) was injected into summer-active ground squirrels of the same species. Four independent trials involving 52 animals were performed. In all trials, no effect of the dialyzate was seen on nest building, weight gain or loss, or on occurrence of hibernation. ACKNOWLEDGMENTS This Council
“TRIGGER”
6.
7.
study was supported by a National Research of Canada Grant A6455 to L. Wang. REFERENCES
1. Dawe, A. R., and Spurrier, W. A. Hibernation induced in ground squirrels by blood transfusions. Science 163,298 ( 1969). 2. Dawe, A. R., and Spurrier, W. A. The bloodborne “trigger” for natural mammalian hibernation in the 13-lined ground squirrel and the woodchuck. Cryobiology, 9,163-172 (1972). 3. Dawe, A. R., and Spurrier, W. A. Summer hibernation of infant (g-week old) I3-lined ground squirrels, Citellus tridecemlineatus. Cryobiology 11, 3343 ( 1974). 4. Dawe, A. R., Spurrier, W. A., and Armour, J. A. Summer hibernation induced from cryogenically preserved blood “trigger.” Science 168,497498 ( 1970). 5. Galster, W. A. Failure to initiate hibernation
8.
9.
10.
11.
183
with blood from the hibernating arctic ground squirrel, Cite&s undulatus, and Eastern woodchuck, Marmota monar. J. Therm. Biol. 3, 93 (1978). McKelvy, F., LeBlanc, P., Landes, C., Perric, S., Grimm-Jorgensen, Y., and Kordon, C. The use of Bacitracin as an inhibitor of the degradation of thyrotropin releasing factor and lutenizing hormone releasing factor. Biochem. Biophys. Res. Commun. 73, 507515 (1976). Oeltgen, P. R., Spurrier W. A., and Bergman, L. Chemical characterization of a hibemating inducing trigger(s) in the plasma of hibernating woodchucks and ground squirrels. J. Therm. Biol. 3, 94 (1978). Pengelley, E. T., and Fisher, K. C. The effect of temperature and photoperiod on the yearly hibernating behavior of captive golden-mantled ground squirrels ( Citellus lateralis tescorum). Can. J. 2001. 41, 11031120 (1963). Rosser, S. R., and Bruce, D. S. Induction of summer hibernation in the 1%lined ground squirrel, Cite&s tridecemlineatus. Cryobiology 15,113-116 (1978). Spurrier, W. A., Folk, G. E., and Dawe, A. R. Induction of hibernation in the 13-lined ground squirrel shown by comparative serum transfusions from arctic mammals. Cryobiology 13,368-374 ( 1976). Swan, H., and Schatte, C. Antimetabolic extract from the brain of the hibernating ground squirrel, Cite&s tridecemlineatus. Science 195, 84-85 ( 1977).
