寡運動によるマウス腓腹筋の組織学的変化

Japanese Physical Therapy Association

JapanesePhysicalTherapyAssociation

me\twzaeeag16ts

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1

_53N9ff

_0989ij)

Effectof

Hindlimb

Suspension

Gastrocnemius

Muscle

on

Young

and

Adult

in

Mouse*

Nobuhide

HAIDA

andKatsuhiko

TACHINO*"

ABSTRACT

The

purpose

of

this

study

was

to

determine

the

effect

ef

hypokinesiafhypodynamia

(H/H)

on

anthropometric,

histochemical

and

histologic

characteristics of medial

_{gastrocnemius}

niuscles

(MG)

in

adult versus

immatuTe

mice.

Hindlimb

suspension

for

two

weeks was used

te

_produce

atrophy

in

two

_groups

of mice, ages

4

and

I2

weeks, with non-suspended

animals

serving' as controls.

Young

HfH

mice exhibited marked

decreases

in

body

weight and muscle weight.

H/H

reduced

the

diameter

of

both

type

I

and

type

2

fibers,

increased

the

_percentage

ef

type

I

fibers,

and

de-creased the

_percentage

of

type

₂

fibeTs

in

_young

MG.

For

all measuTements

_young

mice were more affected

than

adult micc.

The

greater

effgct

on

_young

mice

suggests

that

most of

the

atrophy occurTing

with

HrH

was

due

to

developmental

aTrest,

Key

words:

Hypoklnesia!Hypodynamia,

Gastrocnemius,

Atrophy

Introduction

Djsuse

atrophy may

be

produced

in

animals

by:

₍₁₎

isolution

of

the

lumbo-sacral

cord or

the

peripheral

innervation,

(2)

limb

immobilization

(joint

fixation

by

casting,

joint

_pinning

and

bracing),

₍₃₎

muscle

tenotomy,

(4>

_prolonged

gen-eral

anesthesia,

(5)

small

cage

restraint,

(6)

space

fiight

hypokinesia,

and

(7)

hindclimb

suspension

hypokinesiafhypodynamia

_(HIH).

HfH

_produced

by

hindlimb

suspension

differs

from

other models of

disuse

atrophy

in

that

the

hindlimb

muscles

are

free

to

undergo

a

full

Tange

of voluntary

isotonic

contractions.

Despite

freedom

of

move-ment,

hindlimb

muscles

in

the

suspended animal

have

reduced

mechanical

Ioading

(hypodynamia)

and

decreased

metor

activity

(hypokinesia).

HIH

*

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_ig

_y

_{v-rwFlvamaotswa\UtJErflt}

**

_lkmff,pt,

_scwrnex

:

siFIJit\Kml"immraft\gve\tsra

#*;F-･･･Departmtint-o'f

Physi･cal･Therapy,

School

of

Allied

Medical

Profes$lons,

Kanazawa

University

(Receiyed

12

October

1987)

suspension results

in

the

muscles

becoming

virtu-ally electrically

silent

as

measured

by

electro-myography.

However,

all

activities

are not

in-hibited

in

normal

_young,

active animalsZ}-3).

AIthough

several

studies

regarding

_the

effect

of

HfH

on

skeletal

muscle

have

been

reported,

most

previous

investigations

have

been

carried

out

in

young

immature

rodents

in

the

age

range

of

three

to

seven

weeks.

One

o,f

the

major

unresolved

probleips

in

those

studies was

the

use

of

_growing

animals

in

which

the

induced

atrophy might

be

due

to

developmental

arrest rather

than

to

a wasting

away

of

tissu'e.

The

objectives

of

this

study

were:

(a)

t.o

evalu-ate

the

effect of

HIH

on

_{gastrocnemius}

muscles

of

mice

with

anthropornetric,

histologic

and

histo-chemical

measurements,

and

(b)

to

compare

ef-fects

of

HfH

on

_}'oung

and adult aninials.

Methods

'

'Rodents

used

for

thifi

s.tudy

were

4

nc*taza#

strain,

Forty

male mice, age

4

or

I2

weeks,

ware randomly

divided

into

two

_group$,

HIH

apd

control

(CON).

HfH

was

induced

by

using a modified

Morey

method4),

The

hindquarters

were su$pended

for

a

_period

o{1

two

weeks,

using

body

haTness

and

swivel

in

a

slight

head-down

tilt

that

barely

_prevented

the

hindlimb

from

contacting

any

supportive

surface.

Access

to

feod

and

watcr was

_permitted

by

use of

the

forelimbs

on

a

_grid

surfaced

floony,

Laboratory

Rat

Chow

and water were available ad

libitum.

AEter

two

ureeks

of

suspension,

at

age

6

or

14

weeks,

the

mice

_were

sacrificed

by

cervical

dis-location,

Gastrocnemius

muscles were rapidly

excised

and

weighed,

)Veights

were

expressed

as absolute

(mg)

and relative

(mg/body

weight)

value.

Medial

_{gastrecnemius}

(MG)

samples

were

frozen

in

isopentane

cooled

to

freezing

_point

with

liquid

nitrogen.

Tissue

was

then

sectiolled

at

10um

in

a cr>,ostat at

-200C,

For

staining, myosin

ATPase

at

_pH

IO.3

and

4,6,

and

Hema-toxylin

and

Eosin5}

were used.

Staining

for

Table

1

Anthropometric

ee16#ag

1

_e

measurements

m>rosin

AT'I'ase

identified

fast

twitch,

type

2

fibers

_(alkali

stable) and

slow

twitch,

type

1

fibers

(acid

stable).

The

fiber

aTeas

and

the

_proportions

of

type

l

and

type

2

fibers

were

obtained

with

a

semi-automatic morphometric s>rstem

(Cosmozone

98,

Nilion

Kohgaku).

C}ualitative

analysls of

the

morpholegylpathology

of

the

muscles

wus

per-formed

using

a

modified

Dubowitz's

method6).

Stuclent's

t-test

ivas used

to

examine

the

effect

of age,

HIH,

and

fiber

_types

on

the

histochemical

measurement.

Significance

was accepted at

_p<

O.05.

Results

Anthropometric

measurements:

Suspension

sig-nificantly Teduced

the

body

vreight

of

the

6

week

old

mice

(22.]

±

O.8g

for

the

CON,

I5,8

±

O.7g

for

the

NIH),

but

did

not affect

the

14

week old mice

(2S,2

±

1.2

g

for

tlie

CON,

22.8

±

O.8

g

for

the

Hi'H).

There

were

marked

decreases

in

tlie

young

muscle weight and muscle

weightfbody

weight.

Older

m.ice

were

less

affected

(Tab]e

1),

'

of

young

and

adult

mice

6

weeks

Age

_(weeks)

Centrol(n=10)Suspension

(n=10)

14.weeks

Control

Suspension

(n=IO)

(n=10)

Body

weight

(g)

Muscle

wet weight

(mg)

Muscle

weight!Animal

weight

22.1

±

O.8

100.2

±

3,3

4.53

±

O.11

15.8

±

Q,7*

62.5

±

2.7*

3.79

±

,

O.13

23,2

±

1.2

143.9

±

,

4.5

6.20

±

O.14

22,8

±

O.8

119,O

±

8.4

5.01

±

O.19

ValuesControlare

means ±

S.E.

vs.

suspension,

*P<O.05

Table

2

Fiber

size, and

fiber

typecomposltlonin

control and suspended muscles

6

weeks

Suspension

(n=:1O)

14

Control(n

==

1O)

weeks

Age

_(weeks)

_{Control(n=:10)}

Suspension

(n=10)

Fiber

size

type

1

type

2

Fiber

type

type

1

type

2

(ptrnE)

composition

(%)

1,041

±

100

975

±

114

13.6

±

O.9

86.4

±

1.0

566

±

50*

548

±

39*

19.3

±

2.4*

81.7;2.2

1,310

±

249

1,161

±

244

13,O

±

O,7

87.0

±

,

O.7

785

±

86*

979

±

150*

16.7

±

2.9

83.3

±

2.9

ValuesControlare

means ±

S.E,

Japanese Physical Therapy Association

JapanesePhysicalTherapy Association

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''giii//I/1111///i/l/i:{"t'

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suspension on

_{gastrocnemius}

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60

40

20

14week

old"HIH

./eXX

/o/oxl

×

_.

× _.

x.

×

_.

Fig.

1Sections

of

_{gastrocllemius}

muscles

stained

for

myosin

ATPase

at

_pH

9.4

from

eont-rol

(A),

6

week old musele

(B)

and

14week

eld muscle

(C)

with suspension.

In

this

pre-paration,

Type

1

fibers

are appeared

_pale,

and

Type

2

fibers

are

dark

(Type

2B)

or

intermediate

(Type

2A),

×

115.

Histochemical

characteristics:

Representative

histochemical

data

are shown

in

Fig.

1.

Figure

1,

A-C,

was stained

for

myosin

alkali-ATPase.

In

contrast

to

_Fig.

IA,

which was

from

a control

MG

and

shows

normal

fiber

size,

Figs.

IB

and

Fig.

2

Distribution

lations

sented

ATPase

IC,

were

from

H/H

muscles, and show

reductiori

of

the

_diameter

of

both

type

1

and

type

2

fibers.

Fiber

atrophy

was

_greater

at

6

than

at

14

weeks

oE

age

(Table

2).

Type

I

fiber

size

decreased

46%

and

41%,

and

type

2

fiber

size

decreased

44%

and

I6%,

respectively,

for

the

6

and

I4

week

rnice,

There

was

also a significant

increase

in

the

_percentage

of

t}rpe

1

fibers

_(from

13.6%

to

l9,39{,)

in

the

_young

MG

with a

_parallel

decrease

in

2

fibers

from

suspension.

HIH

did

not

signifi-cantly

alter

the

fiber

type

distribution

in

old

MG.

Fig.

2

$1iows

the

distribution

ef

type

1

and

type

₂

fibers

in

MG.

From

these

data

suspended

_young

mice show

greater

atrophy

of

both

fiber

types

than

CON

er

old

mice.

Histopathological

evaluation:

Figure

8A

shows

a

section of a

MG

from

a

CON

mouse.

Figure

8B

4

8

12

16

20

×

lo2

Fiber

size

(gem2)

of

type

1

and

type

2

fiber

popu-from

_{gastrocnemius}

museles are

pre-as a

function

of

fiber

slze.

Myosin

staining

identified

fiber

type.

6

_pt\ffza*

Table

3

Incidence

of

fiiber

abnormalities

_in

centrol

and suspended

rnuscles

6

weeks

14

weeks

Age

(weeks)

_control

SuEPen'

_control

SU.SPen"

ston slon

(n=10)

(n=10)

(n=tlO)

(n=10)

Internal

nuclei

Necrosis

Phagocytosis

Basophilia

Fiber

splitting

Inflamrnation

Fibresis

oooooo3 54215310 oooooo2 o111119

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t

es

s

wa

ew

X

ss

ee

g,ee

ew

ueg/

ee

,

ee

1ee

ee

ss

ee

es

lee

tw

///

_,ge,

ts

/ee

la

li

,

/ha

Slli

'

ee

y

/

boew'

/

ee

ma

,

ges

ee

ee

_es

Fig.

3

Sections

of

_{gastrocnemius}

muscles

stained

for

hematoxylin

and eosin

from

control

mouse

(A).

Fig.

3B.

shows muscle

fibers

with

internal

nuclei(arrows) _,and

_greater

liferation

of

the

_perimysial

connective

tissue

than

in

Fig.

3A.

×

175.

gives

evidence of

internal

nuclei and an

increase

of connective

tissue.

As

can

be

seen

in

Table

3,

suspension

resulted

in

the

occurrence of several

histopathological

changes

in

both

age

groups.

The$e

consisted

of

the

appearance or

increase

in

ng16kse

1

_e

internal

nuclei,

_{phagocytosis,}

fibrosis,

and

fiber

necrosis and splitting.

There

was no

evidence

of

neuropathic

change,

In

CON

mice

there

were

a]so

a

few

fiber

abnormalities

but

only

in

the

6

week

old

MG.

Discussion

Mice

used

in

this

study

were

6

and

14

weeks of

age

at

the

termination

of a

two

week suspension

period.

H!H

had

marked

effects

on

the

6

week,

but

yery

little

effect

on

the

14

week

eld

mice,

Comparison

with

tlie

other studies reported using

older

rodents

is

diracult

since

different

_periods

of

suspension

were

used.

XMith

three

or moTe

weeks

of

HIH,

muscle

atTophy

clearly

occurred

in

adult

rats2),T}.

LeBlanc

et

al.S}

found

the

same

degree

of

atrophy

in

rodents

ranging

in

age

from

13

to

29

weeks with

two

weeks

of

suspen-sion,

but

McNulty

et

al.9)

reported

results

similar

to

ours

in

i7

week

eld

rats

with

HIH

_periods

as

long

as

four

weeks.

A

major criticism ol

the

HfH

model

has

been

the

use

of

_young

_growing

animals

since

atrophy can

be

due

to

the

result of

developmental

arrest

as

well

as

to

a

decrease

in

bize

or

Iobs

oi

weightie),

Although

sexual

maturity

occurrs

in

the

rat

and mouse

between

seven

and

eight

weeks

of

ageii),i2), muscle

_growth

and

development

con-tinue

for

relatively

a

long

_period.

In

the

129

strain

of

mice,

muscle

weight

increases

up

to

21

weeks

depending

upon sex

alld

muscle

typc.

Fiber

diameter

increases

in

a

curvilinear

manner

through

28

weeks

of

age

but

with

most

of

the

growth

occurr;ng

by

10

weeks

in

the

MGiL')ni4}.

There

is

a unimoclal

distTibution

consisting almost completely

of

small

iibersi3}.

Significant

histo-diemical

fiber

type

clianges

appear

to

cease atteT

8

weeksi-).

In

this

study,

CON

mice

1iad

changes similar

to

most of

those

reported

in

the

IiLerature.

INJhile

age

had

no

effect

on

body

weight

or

muscle

weight,

there

was

a

fiber

size

difference

Japanese Physical Therapy Association

JapanesePhysicalTherapy Association

Hindlimb

suspenSion

on

o

£

_growth

during

suspension while

the

l4

week

old mice were at

least

approaching

full

maturity.

Therefore,

it

appears

that

atrophy

occurring

with

HfH

in

6

week old mice

was

_primarily

due

to

the

result of

developmental

arrest,

Such

a

distinction

is

important

since

a

reduc-tion

in

_protein

content

and synthesis capacity

,and!or

a

more

rapid

_protein

degradation

has

been

reported

to

occur

with

HIHi5)'i9).

Loss

of

'muscle

mass

in

disuse

is

due,

at

least

in

_part,

to

loss

of

muscle

_{protein20),2i),}

and

slower

_protein

synthesis and

faster

_protein

degradation

or con-current

changes

of

l)oth

_processes

can

decrease

the

deposition

of

muscle

_protein22?.

Since

rates of

both

_protein

synthesis and

degTadation

are

significantly

_greater

in

_growing

than

in

adult

skeletal

muscle23),

the

sig'nifiFance

of

these

clianges

with

HIH

in

_growing

-animals

needs

clarification,

Furthermore,

the

factors

that

stimu-late

muscle

_growth

in

immature

animals

might

be

affected

by

H/H

or

limb

immobilization

of

growing

muscle23).

'

.

H!H

resulted

in

a significant reduction

in

the

sizes

of

type

1

and

type

2

fibers,

an

increase

in

the

_percentage

of

the

type

1

fibers

with

a'

_parallel

decrease

in

the

type

2

fibers

as

compaTed

to

the

CON

on

_young

mice.

This

_greater

influence

en

slow

twitch

fibers

is

coincident

with

the

trans-formation

of

a

_prop'ortion

o,f

the

type

l

fibers

into

type

2,

and

accompanied

both

by

a selective

decline

in

the

slow

twitch

component of myosin without'a

,change,

in

fast

twitch

rnyosin

and

a

shift

in

fiber

type

distribution

as

indicated

by

exantination

QE

myosin

ATPase

stained

muscles.

H/H

studies2d)-26)

have'shown

_greater

atrophy of antigr4vity,

Ioad

bearing

muscles such as

the

MC

ankle

_planter

flexors.

7the

MG.is

gffected

more

in

non-weight-bearing

conditi'ons

than

muscles used

for

ankle

dorsal

fiexion,

such

as

tibialis

anterior.

Atrophy

of

the

MG

with

HIH

may

indicate

that

it

is

normally used as an

anti-gravity

muscle

in

normal

locomotion

in

the

gastrocnemius

muscle

7

rodent.

'

In

contrast

to

other

animal

models

of

disuse,

HfH

does

not Testrict

the

hindlimb

muscles

from

full

range

of

voluntary

isotonic

contractions.

foVhile

virtually

electrical

silent

as

measured

by

single

unit

and

whole

muscle

electromyography,

such contractions are observed

to

occur

threugh-out

suspensioni).

However,

these

contractions

do

not

_prevent

loss

of

muscle

mass,

suggesting

that

skeletal

muscle

requires

a

frequent

motor-neuron

recruitment

_pattern

associated with

_postural

rnaintenance

and

body

weight support.

The

de-creases

in

muscle

activity

and

removal

of

load

bearing

tnight

directly

cause

changes

in

fiber

type

distributiQn

which

would

then

result

in

a

change

in

neural

activity2),3);iO),i5),

The

alter-native

is

that

the

decre4sed

muscle

activity

leads

to

a

change

in

the

frequency

of

impulse

activity

which

then

_produceS

the

atrophy.

Suspension

resulted

in

several

histopathological

abnormalities,

consisting

_primarily

of

internal

nuclei,

fibrosis,

necrotic

fibers

and

fiber

splitting.

These

abnormalities are rnore characteristic of a

myopathy

than

of a neuropathy.

Templeton

et al.27} observed abnorrnalities

that

he

con-sidered

su,gge$tive

of

denervation,

but

we

did

not

find

any

evidence

of small angular

fibers,

_pyknotic

nuclear

clumps,

taTget

fibers

or

_group

atrophy.

One

might even consider a

_possibility

that

isotonic

contractions

;vithout

a

load

may

be

harmful

to

the

structural

iritegrity

of

muscle.

'

_.

Severgl

co.nclusions can

be

drawn

from

this

study.

Most

of

the

atrophy occurring with

HXH

in

_young

rnice

was

_primarily

due

to

the

Tesult

of

deve]oprnental

arrest.

Suspension

resuited

in

a'e-treased

size of

both

type-I

and

type

2

fibers

in

both

age

_grQups.

The

significant changes

in

fiber

,type

composition,

an

increase

in

the

_percentage

of

the･type

1

fibers

with

a

_parallel

decrease

in

the

type

2

fibers

as

compared

to

the

CON

in

youiig

mice,

demonstrates

the

_potential

for

fiber

ab-8

_g\rstal

normalities

by

HfH

were more

characteristic

of a myopathy

than

of a neuropathy.

Acknowledgement

The

authors

thank

Dr,

W.

M,

Fowler,

Depart-ment

of

Physical

Medicine

and

Rehabilitation,

University

of

California

at

Davis,

for

his

advice.

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1)

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K.,

_Kowalchuk,

N.

et al,:

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tlte

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Exp,

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85:

30-40,

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G,C.B.,

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AJ.:

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3)

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K.E,,

Dettbarn,

SV,D.

et ab:

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cal characteiistics of rat

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E.R.:

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C.,

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M.

et al.:

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tation

te

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Mech,

Ageing

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SS:

1-9,

1985,

8>

LeBlanc,

A,C.,

MaTsh,

C,,

et al.:

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58:

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9)

McNulty,

A,L,,

Otto,

A,J.

et al.;

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18,

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Boeth,

F,W.,

Gollnick,

P.D.:

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415-420,

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Il)

Farris,

E.J,,

Grithth,

_J.Q,:

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8.

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?hiladelphia,

l949.

12>

Taylor,

R,G.,

Fowler,

_W.M,

et al.:

ContTactile

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18)

Rowe,

R.W.D.,

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MusLIe

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five

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sexes of mice.

I.

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J.

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I04:

519-580,

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ee16tsce

1

lik'

14>

N'ViTti,

P.,

Loermans,

H.M.

et aL:,

Postnatal

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and

differentiation

of muscle

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I,

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histochemical

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109-I26,

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15)

Feil,

_R.D.,

_Gladden,

_J,M,,

et al,:

_,

Fatigue

and

traction

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fast

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iii

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rats,

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58:

65-69,

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16)

Fitts,

R,H.,

Metzger,

D.A.

et al,:

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a compari$on of

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60:

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1986.

17>

HowaTd,

G.,

Steffen,

_J.M.,

et

al.:

Evaluation

of

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synthesis regulation

in

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attophy.

Fed,

Proc.

45:

fi45,

1986.

IS)

Musacchia,

XJ,,

Steffcn,

_J,M,,

ei al,:

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hypokinesia!

h}'podynamia,

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Space

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Med,

54-:

IOI5-1020,

l988.

19)

Thomason,

D,B.

Herrick,

R.E.

et aL:

Activity

induced

recovery of slow myosin expTession

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rodent

hindiimb

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]L(ed,

Sci.

Sports

Exerc.

18,

Suppl.:

s-5,

1986.

20)

Federov,

I.V,,

Shurova,

I.F.;

Content

of

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in

thc

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of animal

during

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Kosm,

Biel.

Aviakosm

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7:

17-21,

l97S,

2i)

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D.F.:

Tlie

influence

of activity on

musclc size and

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tutnover,

J.

Physiol.

(London>

264:

28S-296.

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22)

Goldberg,

A,L,,

Goodman,

H.M,:

Relationship

tween

cortisone and muscle work

in

determining

muscle size.

J.

Physio].

_<Lendon>

200:

667-675,

1969.

23)

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F.W.:

Effect'

o £

limb

immobilizution

on

skeletal

muscle,

J.

Appl.

Physiol.

i)2:

11IS-III8,

1982.

24)

_Jaspers,

S,R.,

Tischler,

M.E.:

Atrophy

and

_growth

failure

o £ rat

hindilmb

muscles

{n

tail-cast

pension.

J,

Appl,

Phlrsiel,

Respirat.

Environ,

ExeTcise.

PhysioL

57:

1472-I479.

I985,

25)

Fowler,

W.M.,

Haida,

N,

et ai,:

Effect

of

kinesia

on muscle contractility and

histology

of

normal and

dystrophic

mice.

Arch.

Phys,

Med,

Rehabil,

67:

627,

1986.

26>

Musacchia,

XJ.,

_Joseph,

M,

et al,:

Suspension

restTaint:

Induced

hypokinesia

and antiorthostasis

as a simulation of ssreightlessness,

?hysiologist

24:

S21-S22,

1981.

27>

Templcton,

G,H.,

?adalino,

_J.

et al.:

Influence

of

suspension

h)'pokinesia

on rat soleus muscle.

J.

Appl.

Physiol.

Respirat.

Environ.

Etercise.

Physiol,

Japanese Physical Therapy Association

Japanese _{Physioal 　Therapy 　Assooiation}

Hindlimb

　

suspension

　

on

　

gastrocnemius

　nluscle

．

9

〈

要 　 旨

〉

寡 運 動

に

よ

る マ ウ ス

腓

腹

筋

の

組 織 学 的 変 化

　 　 　 灰

田

儒 英 　立 野 勝 彦

金 沢 大 学 医 療 技 術 短 期 大 学 部 理 学 療 法 学 科

　

寡 運 動

（

Hypoklnesia ／Hypodynamia

）

に よ る

若

齢

及 び

成 熟

マ _ウス の

腓

腹筋

の

萎

縮

の

_差

異

につ い て

検 索 す

ること

を

目

的

と した

。

4

週

齢

（

若齢群）

，

12

週 齢

（

成 熟

群

）

のマ _ウス

40

匹 を そ れ ぞ れ 実験 群

と

対 照 群

に

分 け

，

実験群

に

_対

して は

Morey

等

の

tail

　suspension モ

デ

ル を

用

いて

_後

_肢

を

無

荷

重状態

と した。

2

週 間

の

寡運動

後

，

即 ち

6

及 び

14

週

齢

でマ _{ゥ ス}を

_{屠 殺}

し ，

体

重

を

測

定

した。 その

後

腓

腹筋

を

採

取

し， 湿

重 量

を

計

測

後

，

凍

結

切 片 を作 成

し

．Myosin

　

ATPase ，

ヘ マ _キシ リソ

・

エ _オジン

_{染 色}

を

実

施

し

．

組 織 化 学 的

．

組織 学 的 検 索 を行

なっ た

。

寡 運動

に よ り

．

若齢 群

は

対 照 群

に

比

べ

休 量

は

減 少

し た が

，

成 熱 群

で は

変 化

は

認

め

られ な

か っ た

。

腓

腹 筋

の

湿 重 量

は

若 齢 群

，

成 熟 群 と も

に

低 下 す

る

も

の の

，

前 者

の

方

が

大

で

あ

っ た

。

細 胞 径

は

若 齢 群

で は タ イ プ

1

，

2

線 維

と

も

に

著

し

く減 少

し

，

かつ タイ プ

1

線 維

の

構 成比 率

が

増 加

した

。一

方 成 熟 群

の

細 胞 径

は

，

タイ プ

1 線

維

の

方

がタ イ プ

_{2 線}

維

よ り

著

明に

減

少

した。

筋線

維

構

成 比

率

の

変

化

は

見

ら れ なか っ た。 へ v ト キ シ リ ン

・

エ オジ ソ

染 色

の

結 果

，

若齢

群

には

．

中

心

核

，

_{細 胞}

の

壊

死 や

結

_合

織

の

増

殖 像

が

認

め られ

，

1nyopathic _な

変 化

を

示

し

た

。

若 齢 群

に

見 られ

る

著

しい

筋 萎 縮

は

寡 運 動

に

伴 う成 長

の

一

時 的 停 滞

の

為

と

推 測

さ

れ

る

。