J. gen. Virol (1989), 70, 827-835. Printed in Great Britain
827
Key words: scrapie/glucose tolerance~obesity
Scrapie-induced Alterations in Glucose Tolerance in Mice
By R I C H A R D I. C A R P , * Y O N G S. K I M AND S H A R O N M. C A L L A H A N
New York State Office of Mental Retardation and Developmental Disabilities,
Institute for Basic Research in Development Disabilities, 1050 Forest Hill Road, Staten Island,
New York 10314, U.S.A.
(Accepted 19 December)
SUMMARY
Certain scrapie strains cause obesity in several strains of mice. The potential
association between obesity and altered glucose tolerance was assessed by monitoring
body weight and glucose tolerance throughout the incubation period in scrapie strainmouse strain combinations that do and do not produce obesity. Virtually all obese mice
showed reduced glucose tolerance as shown by significantly higher blood glucose levels
2 h after a glucose overload. Mice injected with a scrapie strain that did not cause
obesity showed normal tolerance. The scrapie infectivity titre of the pancreas of obese
mice clinically affected with scrapie was very low. Adrenalectomy prevented both the
increase in weight and aberrant glucose tolerance but had no other effect on the course
of the disease. Following increasing dilution of the inoculum, the increase in body
weight and the development of aberrant glucose tolerance reached an end-point that
was similar to that of scrapie infectivity. The system described provides an inducible
model of obesity with altered glucose tolerance.
INTRODUCTION
Of the group of human and animal diseases caused by unconventional agents, most
experimental work has been done with scrapie, which is a natural disease of sheep and goats
(Fraser, 1983; Carp et al., 1985a). The scrapie agent has been passaged in small laboratory
animals, such as mice and hamsters, in which the course of the disease is controlled by certain
genetic characteristics of both the host and the agent (Dickinson & Fraser, 1979; Fraser, 1979).
Although the nature of this group of infectious agents remains unknown, the precision of the
interaction between agent and host has permitted insights into the pathogenesis, genetics and
characteristics of the disease (Dickinson & Fraser, 1979; Carp et al., 1985b).
The initial signs used to diagnose clinical scrapie disease include incoordination, weakness
and in some cases a brief period of hyperexcitability. Subsequent signs include a loss of weight,
progressive loss of motor capability and activity, a hunched stance, paresis and paralysis
followed by death. Changes in the host that do not involve direct action of the agent on motor
functions have received little attention in studies on scrapie or the other unconventional
diseases. During scrapie infection, studies have been made of food and water intake, increases
in body weight prior to the onset of motor changes (Outram, 1972; Carp et al., 1984) and
behavioural changes measured in terms of emergence times (Heitzman & Corp, 1968) and
defaecation scores (Savage & Field, 1965). Changes were also seen in open-field and Y-maze
exploration scores (McFarland et al., 1980) and in apomorphine-induced circling behaviour
after unilateral stereotaxic injection of the nigrostriatal system (Gorde et al., 1982). Our recent
studies which focused on the obesity seen before motor changes in certain scrapie strain-mouse
strain combinations (Carp et al., 1984; Carp & Callahan, 1984) have established the importance
of the genetic characteristics of host and agent, the role of the hypothalamus (Kim et al., 1987 a)
and more recently the function of the adrenal gland in the weight increase (Kim et al., 1988).
The increase in weight of animals in these studies was caused by an accumulation of fat and
not an increased growth rate (Carp et al., 1984). This suggested that alterations in glucose
0000-8592 © 1989 SGM
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R.I.
CARP, Y. S. KIM AND S. M. CALLAHAN
m e t a b o l i s m m i g h t a c c o m p a n y o b e s i t y a n d led to t h e series o f s t u d i e s r e p o r t e d i n t h i s p a p e r , i n
w h i c h we e x a m i n e d glucose t o l e r a n c e c h a n g e s a n d t h e i r r e l a t i o n to i n c r e a s e d w e i g h t g a i n .
METHODS
Mice. Female weanling C57BL/6J and SJL/J mice (Jackson Laboratories) were housed in animal colony rooms
with controlled temperature, humidity and light cycle (12 h on, 12 h off). The IM/Dk mouse strain was kindly
provided by Dr Alan Dickinson (AFRC and MRC Neuropathogenesis Unit, Edinburgh, U.K.) and has been
maintained in our animal colony as an inbred strain by random brother-sister matings for the past 10 years. All
mice were given rodent food and water or 0-9 ~ NaC1 (for mice that were adrenalectomized) freely. Mice were earpunched for identification and weighed just before injection. Subsequently, mice were weighed in the early
afternoon of the same day of the week, with the schedule being either every week or every other week for the short
incubation scrapie models and either every other week or once per month for long incubation models.
Scrapie strains and isolates. The ME7, 22L and 22A scrapie strains were also obtained from Dr Alan Dickinson.
A recently established line, termed C602, was derived from a Suffolk sheep affected by scrapie. The line was used
after four or five mouse-to-mouse passages in C57BL mice. For all scrapie strains and lines the material to be used
for injection was prepared by passage using intracerebral (i.c.) injection of 0.03 ml of 1 ~ (w/v) brain homogenates
from mice affected by scrapie. C57BL mice were used for passaging strains ME7 and 22L and line C602. For the
22A scrapie strain, the IM mouse strain was used for passaging.
Preparation of material for injection. Brain material for injection was homogenized in phosphate-buffered saline
(PBS). Homogenates (10~ w/v) were prepared by 20 strokes of a hand-operated Ten-Broeck homogenizer.
Normal brain homogenate was prepared from C57BL mice injected with normal mouse brain (NMB)
homogenate. Homogenates (both normal and scrapie-affected) were stored at - 70°C, thawed and then diluted to
an appropriate concentration in PBS just before injection.
Injection. Stereotaxic microinjections were carried out under general anaesthesia [sodium pentobarbital, 70
mg/kg intraperitoneal (i.p.)] after mounting the mice on a stereotaxic instrument (Stoelting). The choice of the
right side for injection was made arbitrarily, since no cerebral dominance has been established in small rodents.
The coordinates used for the hypothalamus were A-I.8, L+0.5, H+5.2 (Slotnik & Leonard, 1975). Using a 30gauge stainless steel needle, 5 ~tl of a 1 ~ brain homogenate was injected. In preliminary experiments, carbon
particles were included in the inoculum and after stereotaxic injection these particles were shown to be localized in
the area designated by the coordinates. For routine i.c. injections, 0.03 ml of the appropriate dilution was used,
whereas for the i.p. route, 0.2 ml was injected.
Analysis of clinical symptoms. Mice were monitored weekly for typical motor signs of scrapie starting at 70 days
post-injection (p.i.) for short incubation models and starting at 175 days p.i. for long incubation period models.
Clinical disease was assessed by observing the activity levels of mice and their competence on an apparatus
consisting of a series of parallel bars (3 mm in diameter) placed 7 mm apart (Carp et al., 1984). With the agentmouse strain combinations used, the initial clinical findings are a reduction in activity and in the ability of the
mice to traverse the parallel bars. The incubation period was the point at which mice had shown typical motor
signs for the third consecutive week. Incubation periods are expressed as mean + standard error (s.E.).
Adrenalectomy. For adrenalectomy, mice were anaesthetized with sodium pentobarbital (70 mg/kg) and then
adrenalectomized by the lumbar approach (Debons et al., 1982). Mock-operated mice were exposed to the same
operative procedure, except for removal of the glands. Mice were adrenalectomized and mock-operated 2 to 3
weeks before injection.
Glucose tolerance test. Samples (50 to 200 ktl) were obtained via retro-orbital (right orbit) bleeding at least 1 h
before glucose loading. Heparinized micro-hematocrit tubes (Monoject) were used. The glucose loading was a
standard dose of 2 mg/g body weight injected i.p. A post-glucose blood sample (from the left orbit) was obtained
2 h after overload. Mice were bled repeatedly with intervals as short as 13 days; no difficulties were encountered
because of the multiple bleedings. In initial experiments, plasma glucose levels were determined by a colorimetric
enzymic method (Sigma). In subsequent experiments, whole blood glucose was measured photometrically using
the Glucoscan 2000 Blood Glucose Meter (Lifescan).
RESULTS
Glucose tolerance test (GTT) analyses in short incubation models injected i.p.
T h e M E 7 s t r a i n c a u s e s a w e i g h t i n c r e a s e i n S J L m i c e a f t e r i n j e c t i o n e i t h e r i.c. or
s t e r e o t a x i c a l l y i n t o t h e h y p o t h a l a m u s ( C a r p et al., 1984; C a r p & C a l l a h a n , 1984, K i m et al.,
1987a). I n t h e p r e s e n t study, S J L m i c e w e r e i n j e c t e d i.p. w i t h M E 7 or N M B a n d b o d y w e i g h t s
w e r e m o n i t o r e d . M E 7 - i n j e c t e d m i c e s h o w e d s i g n i f i c a n t l y i n c r e a s e d w e i g h t a t 196 a n d 210 d a y s
p.i. ( T a b l e 1). T h e i n c u b a t i o n p e r i o d for t h i s c o m b i n a t i o n w a s 223 _+ 1 days. A f t e r e s t a b l i s h i n g
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Scrapie alterations in glucose tolerance
829
Table 1. The effect of ME7 on the weight of SJL mice after i.p. injection
Weight (g)* after
injection with
A
t
Days pA.
154
168
183
196
210
NMB
26-8 +
27.3 +
27.7 +
28.1 +
28.2 +
ME7
1
1
1
1
1
27-8 + 1
29-5 ___1
30.2 __+1
31.4 + If
32.7 + 1~
*Weight + s.~. where n is 11 to 18.
t Significant difference from NMB: P < 0-05.
~:Significant difference from NMB: P < 0.01.
Table 2. Weight and GTT values of SJL mice injected with ME7 by the i.p. route
Glucose vflue (mg/d~
A
t
Experiment
Mouse
Days p.i.
Weight (g)
Preoverload
1
1
2
3
4
5
6
6
6
6
6
2
2
2
152
152
152
152
152
197
205
210
216
223
152
183
205
39.3
44.8
30.6
34.2
39.7
71.9
71.7
71.0
60.0
49.1
44-8
50.3
30.4
182
197
171
180
216
197
182
130
94
47
197
192
80
Posb
overload
Scrapie-positive
(day p.i.)
302*
339*
268
211
260
288*
375*
313"
621"
656*
339*
225
600*
182
189
201
189
187
189
* Values at least 3 S.D. above normal [average values for 39 SJL mice injected with NMB were 154 + 25 (mean
+ S.D.) and 173 + 35 (mean + s.D.) for the pre- and post-overload samples, respectively].
that SJL mice injected i.p. with ME7 show an increase in body weight, glucose tolerance was
assessed in five mice before the onset of typical motor signs (Table 2, experiment 1). Glucose
values after loading were all high and for two mice the values exceeded 3 S.D. above normal.
Most SJL mice injected i.p., i.c. or stereotaxically in the hypothalamus with ME7 attained body
weights between 28 and 40 g. However, a n u m b e r of mice became enormous; the glucose values
and weight for two of the i.p. injected mice during a series of repeated tests are shown in Table 2.
The pre-glucose values for mouse 6 changed from slightly hyperglycaemic shortly after signs of
incoordination began to markedly hypoglycaemic as the mouse lost weight during the
progression of clinical disease. The post-overload values increased markedly over the same time
period. Mouse 2 showed very high pre-overload values the first two times it was tested and
markedly aberrant post-overload values at the first and third tests. Two mice injected i.c. with
ME7 that attained body weights of 82.4 and 67.6 g were tested sequentially and showed very
high post-overload glucose values and a progressive decrease in pre-overload values (data not
shown).
GTT analysis in a short incubation model using mice injected stereotaxically
in the hypothalamus
Previous studies showed that the body weight of SJL mice increased after either i.c. or
stereotaxic injection with the 22L scrapie strain (Carp et al., 1984; K i m et al., 1987a). These
findings led to questions concerning a possible relationship between increased weight and
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R. I. CARP, Y. S, KIM AND S. M. CALLAHAN
830
60
56
31
52I
30
48
29
.E 28
~
44
27
40[-
"=
26
0
=l
25
>. 36['-
24
23
340
(b)
O
-- ,~ 300
26o
> 220
180
140 50 60 70 80 90 100 110 120130
Time (days p.i.)
0
70
140 210 280 350
Time (days p.i.)
Fig. 1
420
Fig. 2
Fig. 1. Weight (a) and glucose level 2 h after glucose overload (b) of SJL mice injected stereotaxically in
the hypothalamus with the 22L scrapie strain. Data points are averages of five or six mice, with s.l~.
indicated. Open symbols represent values for mice injected with NMB; closed symbols represent mice
injected with 22L.
Fig. 2. Weight ( + s.~.) of C57BL mice injected with NMB ( 0 ) or with the C602 line at a concentration
of 5~ (A) or 0.01~ ( I ) .
altered glucose metabolism. In the present study, SJL mice were injected stereotaxically in the
hypothalamus with 22L or with N M B . Glucose tolerance and weight were assessed on one set
(normal and 22L) at 50, 64, 112 and 128 days and on another set at 79, 93, 106 and 119 days (Fig.
1). Five or six scrapie-injected mice and five or six controls were used in each group. There were
significant (P < 0-02) differences in weight between the scrapie-infected and normal groups at
93, 106, 112 and 119 days p.i. and significant (P < 0.01) differences in glucose tolerance at 106,
112 and 119 days p.i. The difference in G T T values at 64 days p.i. was at the 0.05 level of
significance. The scrapie incubation period was 117 days so that the final time point (day 128)
was approximately 3 weeks after the initial signs of clinical scrapie. A t this point some 22Linjected mice had begun to lose weight whereas others were still gaining weight; this led to an
increase in the variance of the mean weight value. The post-overload glucose values also show a
m a r k e d increase in variance which was probably related to the variation observed in body
weight.
Scrapie infectivity in the pancreas
A n assessment of the infectivity level in the pancreas of SJL mice injected by the
hypothalamic route with ME7 showed an extremely low titre. The sample was taken after the
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Scrapie alterations in glucose tolerance
R
m
q
(,9) t
I
I
I
I
I
I
I
I
I
292
t
,A,
..z 284 •~.............................-----¢
i
277 ....................................
l
152[ ~
I
24
J
28
f
I
32
I
I
I
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I
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36
40
44
Body weight (g)
i
i
48
i
l l l l l l l l l l
52 320
280 240 200
160 120
Post-overload glucoselevel (mg/dl)
Fig. 3. Weight(a) and glucoselevel 2 h after glucoseoverload(b) of C57BLmice injected i.c. with NMB
(hatched), the 22A scrapie strain (unshaded) or the C602 line (shaded). The inocula were 1~ brain
homogenates. Data points are averages of the results from eight to 12 mice for the C602 and NMB
groups and three to 12 mice for the 22A group. Bars indicate S.E. Days p.i. are not plotted to scale.
onset of motor signs of disease and the titre was equal to or less than 2-6 x 102 LD 5o/g which is
between 105- and 106- fold less than that seen in brain. Similar low infectivity titres for pancreas
were obtained in a second experiment in which ME7 had been injected by the i.c. route.
Analysis of obesity and GTT in long incubation models injected i.c.
During a series of mouse-to-mouse passages of brain homogenates prepared from five scrapieaffected Suffolk sheep, some of the lines caused marked increases in weight before the onset of
motor signs of disease. In general, incubation periods became shorter during repeated passages,
but for a number of lines incubation periods remained in the range of 285 to 360 days (after
injection with a 1~ brain homogenate) even by the fifth passage. Sequential weight data for
C602, one of these lines, are shown for the fifth mouse passage in Fig. 2. In this experiment
C57BL mice were injected i.c. with either a 5 ~ homogenate of NMB or C602 or a 0.01~
homogenate of C602. Compared to the NMB group, mice injected with the 5 ~ homogenate of
C602 showed significantly higher body weight at 154 days p.i. and the significant difference
persisted until the end of the clinical phase. The incubation period was 286 + 8 days. For mice
injected with 0.01 ~ homogenate of C602, the weight increase was significant from 280 days p.i.
onward, and the incubation period was 364 + 4 days. The peak weights reached by groups of
mice injected with 5 ~ and 0.01 ~ homogenates were 55-3 and 58.0 g, respectively. These values
were almost twice those of control mice, for which average weights were between 30 and 35 g
during this period.
The next question was whether the mice that became obese in the long incubation model also
developed aberrant GTT results. C57BL mice were injected by the i.c. route with a 1~o
homogenate of the fifth mouse-to-mouse passage of C602 (Fig. 3). Additional C57BL mice were
injected with the 22A scrapie strain or with NMB homogenate, each as a 1~ homogenate. Mice
were monitored periodically for body weight and glucose tolerance. Values for weight were
significantly different between the C602 and NMB groups at 254, 284 and 292 days p.i. with P
values of < 0.001, < 0.001 and < 0.01, respectively (Fig. 3a). The post-overload glucose values
for the C602-injected group were significantly higher than those for N M B injected mice at 254,
277, 284 and 292 days p.i., with P values of < 0.02, < 0-01, < 0.001 and < 0.01, respectively
(Fig. 3b). The incubation period for the C602 isolate (1 ~ homogenate) was 284 + 5 days. It has
been reported that the 22A scrapie strain causes a reduction in body weight before the onset of
motor changes (Outram, 1972). In the present study, the weight of 22A-injected mice was
significantly lower than that of controls at 254, 277 and 292 days p.i. with an incubation period
of 368 + 0 days. The post-overload glucose values of 22A-injected mice tended to be lower than
controls but the difference was significant only at 292 days p.i. (P < 0.05).
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R. I. CARP, Y. S. KIM AND S. M. CALLAHAN
Table 3. Weight and post-glucose overload values of C57BL mice injected i.c. with high dilutions
of homogenate of the fifih passage of the C602 line
Day p.i.
A
f
h
374
397
h
Scrapie
designation
Negative (NMB)
Positivet
Negative:[:
~k
Concentration
of
homogenate
(~)
Weight
(g +S.E.)
Glucose
(mg/dl + s.E.)
Weight
(g ±S.E.)
Glucose
(mg/dl ± S.E.)
1
0-001 to 0-0000l
0-0001 to 0-00001
38.9 + 1"
45-6±3
32.9 + 3
166 ± 9*
214+31
147 + 18
38.9 ± 1"
44.2+3
39.6 ± 4
166 ± 9*
216±44
145 ± 12
* Values were pooled from samples taken at 309, 326, 374 and 397 days p.i.
t Mice were positive for clinical scrapie at the time of testing or became positive within 4 months.
2~Mice were negative for clinical scrapie at the time of testing and remained negative throughoutthe rest of the
experiment.
Correlation between infectivity and the induction of obesity and aberrant GTT
All previous studies with the long incubation model had been done with comparatively
concentrated inoculum (5 ~ to 0.01 ~) and the question arose concerning the capacity of more
dilute inocula to induce obesity and altered GTT. In an experiment in which C602 was diluted in
order to determine its infectivity end-point we assessed both weight and GTT results at various
dilutions of the C602 inoculum. In the final three dilutions (representing 0.001, 0-0001 and
0.00001 ~ concentrations of the original homogenate), 19 animals developed scrapie and 13 did
not. The 19 mice listed as scrapie-positive either had typical motor signs of scrapie at the time
they were tested (day 374 or day 393) or developed scrapie within the next 4 months. As shown in
Table 3 those mice at the end-point which developed clinical scrapie had higher total body
weight and showed aberrant GTT results compared to mice that did not develop scrapie.
The effect of adrenalectomy on the induction of obesity and aberrant GTT in a long
incubation model of scrapie
In a previous study we showed that adrenalectomy prevented the increase in body weight in
both SJL mice injected i.c. with ME7 and in C57BL mice injected in the hypothalamus with
ME7 (Kim et al., 1988). In the present study, adrenalectomy prevented the weight increase
induced by line C602 (Fig. 4a). Mock-operated mice injected with the C602 homogenate showed
a significant weight increase compared to mock-operated mice injected with NMB from day 229
on and a significant increase in weight compared to the C602-injected, adrenalectomized mice
from day 196 to the end of the experiment. Blood glucose values 2 h after a glucose overload were
significantly greater in the C602 mock-operated group compared to the NMB group only at the
last two time points (Fig. 4b). Post-glucose overload values for adrenalectomized mice injected
with the C602 line were significantly lower than the mock- operated group injected with C602 at
all time points from day 164 to day257. The final samples (day 285) were taken when some of the
C602-injected, adrenalectomized mice were showing motor signs of scrapie disease and there
was a rise in the average post-overload glucose value. There was also marked variability in the
GTT values as shown by the very large S.E. value. The incubation periods for the mockoperated and adrenalectomized mice were 284 + 2 and 281 + 2 days, respectively.
DISCUSSION
The current studies describe a previously unreported capacity of certain scrapie strains to
induce aberrant glucose tolerance. A number of findings suggest a general association between
obesity and glucose intolerance. The change in GTT results and obesity were seen before the
onset of motor changes after i.p. and non-stereotaxic i.c. injection and after stereotaxic injection
in the hypothalamus; both changes were seen in both short and long incubation period models.
In a titration assay for infectivity, there was close agreement between the endpoints of
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Scr~alteratmnsmglucoseto&rance
I
48 (a)
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
833
I
I
I I I I I
- -
44
Yz 40
36
o 32
28
24
300
260
o
~ 220
180
9 N 140
o
~"
100
50
70
90 110 130 150 170 190 210 230 250 270 290
Time (days p.i.)
Fig. 4. Weight (a) and post-overloadglucosevalues (b) in C57BL mice injected i.c. with either the C602
line or NMB. Beforeinjection (2 to 3 weeks),mice were either adrenalectomizedor mock-operated.The
four groups were: mock-operated C602 CA); mock-operated NMB (Zk); adrenalectomized C602 (O);
adrenalectomized NMB (0). Bars show s.E.
infectivity, obesity and altered G T T results (Table 3). In mice that did not become obese, such as
C57BL mice injected with 22L or 139A (data not shown)'or with 22A (Fig. 3), glucose tolerance
was not impaired. Finally, adrenalectomy prevented both the increase in body weight and
hyperglycaemia (Fig. 4). In other mouse model systems obesity and diabetes can occur together
or each can occur separately (Coleman, 1978; Craighead, 1981).
In previous studies the role of genetic control of obesity was emphasized (Carp et al., 1984;
Kim et al., 1987 a). The linkage between obesity and altered G T T observed in the present study
would mean that the latter is also under genetic control. Direct evidence of the influence of
scrapie agent genetics on glucose tolerance is shown by comparing the effects of 22A and C602
in C57BL mice (Fig. 3).
The remarkable obesity associated with the long incubation C602 scrapie line in which
infected animals attain weights nearly twice that of NMB-injected controls provides a model
system which may prove useful for the study of secondary effects of obesity and glucose
intolerance. Infected mice maintain their increased weight for as long as 17 weeks and exhibit
glucose intolerance for at least 5 weeks before the onset of the typical motor changes associated
with scrapie. The extent and duration of these changes could lead to a variety of related effects
such as peripheral neuropathy, kidney damage, aberrant cholesterol metabolism and circulatory
problems (Keys et al., 1972; Brown & Asbury, 1984).
The hypothalamus plays a role in scrapie-induced obesity in mice (Kim et al., 1987a, 1988).
The effect is probably mediated through the hypothalamic-pituitary-adrenal axis. If we assume
that aberrant glucose tolerance is secondary to obesity, then the G T T alteration would also be
the result of changes in the hypothalamic-pituitary-adrenal axis. The fact that the level of
scrapie infectivity is extremely low in the pancreas of clinically affected mice showing aberrant
G T T results suggests, but does not prove, that a direct effect of scrapie agent on the pancreas is
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R . I . CARP, Y. S. KIM AND S. M. CALLAHAN
unlikely. For example, it is possible that abortive infection of pancreatic cells led to their
dysfunction and the resultant G T T changes or that the scrapie titre had been high at some point
during the preclinical phase of disease at which time the pertinent pancreatic cells had been
permanently damaged. In a previous study that demonstrated probable neuroendocrine
involvement in experimental scrapie, histopathological changes in ovaries occurred in the
absence of high scrapie titres in the affected organ (Sturman, 1972).
The fact that some scrapie strain-mouse strain combinations show obesity and altered G T T
results whereas others do not can be explained on the basis of scrapie strain-specific targeting of
cells, a concept developed in Kimberlin & Walker's (1983) theory of clinical target areas. In this
theory clinical disease results from scrapie infection of specific brain areas. In support of this
theory, stereotaxic injection of different areas of the brain resulted in different incubation
periods (Kim et al., 1987b). The area of brain that gave the shortest incubation period differed
with different scrapie strains, From the findings on genetic control of scrapie-induced obesity
and altered glucose tolerance in the present study, it appears that there is also scrapie strainspecific targeting of cells involved in control of neuroendocrine functions.
In histological studies of scrapie-infected sheep brain, Beck et al. (1964) demonstrated severe
bilateral symmetrical degeneration in the hyopthalamo-neurohypophysial system with loss of
cell bodies in the supraoptic nuclei and the paraventricular nuclei. Similar lesions were also
present in the cerebellum, especially in the flocculo-nodular lobe, and in its afferent motor
system, to which motor dysfunction may be attributed. On the basis of these findings, they
suggested that scrapie in sheep could yield either motor or 'metabolic and autonomic'
disturbance or, in some instances, a combination of both. In a subsequent study, using
immunofluorescence histochemical techniques, Parry & Livett (1976) found an abnormal
distribution of neurophysin and neurosecretory material in the proximal and distal portion of the
hypothalamo--neurohypophysial system of scrapie-positive sheep. They also found increased
levels of neurophysin in the adenohypophysis of these animals. This finding suggested to the
authors that vasopressin might accompany the neurophysin and cause release of adrenocortico
trophic hormone. This provides a possible explanation for the adrenal cortical hypertrophy that
had been noted previously (Beck et al., 1964).
In the presefit study the fact that the induction of changes in a neuroendocrine system
occurred in a controlled and highly reproducible manner opens new directions for scrapie
research. It seems unlikely that scrapie-induced changes in neuroendocrine systems will yield
only aberrant glucose tolerance, obesity, adrenal hypertrophy (Carp et al., 1984; Kim et al.,
1988) and ovarian pathology (Sturman, 1972). Rather, it seems probable that a variety of
neuroendocrine systems will show changes and that the system affected and the types of changes
will depend on the scrapie strain-host combination.
The authors wish to thank Jennifer Parese and Adele Monaco for their excellent assistance in preparation of the
manuscript. The authors are also grateful to Richard Kascsak and Richard Rubenstein for their review of the
manuscript. This work was supported in part by N I H Grant No. NS21349 entitled 'Characterization of scrapieassociated fibrils'.
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