Clinical, neuropathologic and pharmacologic aspects of Huntington's disease: Correlates with a new animal model

N8WO-Psychophmmac.

F-v.

VOl

1.

13 - 30.

pp.

1977.

Per@mcm

Prees.

Printed

in

Great

Britain

CLINICAL, NEUROPATHOLOGIC AND PHARMACOLOGIC ASPECTS OF HUNTINGTON'S DISEASE: CORRELATES WITH A NEW ANIMAL MODEL J. T. COYLE, R. SCHWARCZ, J. P. BENNETT and P. CAMPOCHIARO Departments of Pharmacology and Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland, U.S.A. (Final

form,

December

1976)

Abstract Huntington's disease (HD) is a neurologic disorder inherited in an autosomal dominant fashion that is characterized by dementia and a movement disorder. The movement dysfunction appears to be due to degeneration of neurons intrinsic to the striatum resulting in a functional imbalance between the intact dopaminergic input and the paucity of cholinergic and GABA-ergic neurons in the striatum. Similar neurochemical and histologic alterations in the nigro-striatal axis can be produced in rats by stereotaxic injection of kainic acid, a rigid analogue of glutamate, into the corpus striatum. The animal model of HD resulting from the striatal kainate lesions offers opportunities for better understanding the pathophysiology of HD as well as for testing pharmacologic agents that may correct neurotransmitter imbalances of HD. The kainate induced lesion suggests testable hypotheses concerning the fundamental defect in HD.

1. 2.

3.

Keyworae : Huntington's neurotransmitter-receptors,

disease, kainic striatum.

acid,

y-aminobutyric

acid,

acetylcholine,

Introduction Huntington's vous

Disease

system

HD lies

at

symptoms

the

and Folstein,

drugs

cause tating could report, shall

the primary

between

disorder lead the

but

be reviewed

deficits clinical

developing

also

because

the

features, briefly;

with

which

occurs

unknown,

and mental

and neurologic research

elucidation

of

and a recently

that

et 'al.,

the

restricted

allows

for

symptoms.

the Hence,

interest

not

only

be-

treatments

for

this

devas-

the pathophysiology

and pharmacologic discovered

13

(McHugh

in chronic

In

in human neuropsychopharmacology.

neuropathology

mental

(Marsden

of nature

efficacious

1968);

illness

neuroleptics remains

the ner-

to anti-psychotic

experiment and basic

for

advances

dyskinesia defect

a cruel

concern

to fundamental clinical

tardive

early

affective

of HD responds

of (Bruyn,

Its

and psychiatry.

treatment

pathologic

neuronal

wide-spread

of a genuine

the

disorder

abnormalities

and biopolar

disorder

prolonged

of HD provides

HD has provoked

neurology

and resembles

Although

degenerative

and movement

of schizophrenia

The movement

receiving

neuropathology correlation

between

those

1975).

schizophrenics 1975b).

by dementia

interface

can mimic

neuroleptic

(HD) is an hereditary,

characterized

animal

treatment model

for

of HD this of HD

HD, which

14

et al.

J. 'I. Coyle

provides the

a basis

disorder,

for

will

investigating

the

pathophysiology

The onset

of HD is

around

the

dyskinesic

their

onset

ably

resulting

disorder, the

insidious

35-40

years

symptoms

the

exaggerated function

can also

tility. patients

initially

limb

although

appearance,

dysarthria,

rigid

this onset

of

the

of symptoms

of

in the the

both

have inexor-

the movement

initial

stages exhibit

patterns.

Motor

the

form,

age of

undys-

in ocular affects

predominates

of

but

extremities

Westphal disorder

below

or

progress

and disturbances

of HD, the form

become

on a quasi-intentional

in stereotypic

dysphagia

variant

patients; the

recur

some cases

symptoms

and restless take

symptoms

psychiatric

In terms

when fullblown,

that

the the

in the

15 years.

movements

character;

include

exhibiting

Oliver,

Hither

may seem fidgety

movements

the

generally,

their

progresses,

An akinetic, 10% of

but 1968).

in approximately

and awkward athetotic

and variable;

After

individual as it

Features

age (Bruyn,

may appear

in death

dulating,

mately

of

concurrently.

disease;

of

be discussed. Clinical

apparent

and pharmacotherapy

mo-

approxiin those

20 (Deuhurst

and

1970).

Mental

changes

are not.

are

an invariable

. The psychiatric

subtle

changes

exhibit

striking

havior.

manifestations

in personality

Although are relatively

than

observed

hallucinations

arerare,

frequent;

these

in schizophrenia.

aphasic

HD whereas 1975).

delusions

and apraxic

of memory, associated

disturbances

of grandeur

however,

The psychiatric

motor

are

symptoms

heralded

systematized

progress

seen

by

and of persecu-

less

into

judgement and insight. with loss of orientation generally

symptoms

Patients may later or hypomanic be-

in depression

delusions,

the

and are often

and Folstein,

in mood resulting

flagrant dementia with impairment the mental changes are not usually agnostic,

of

are protean

(McHugh

alterations

tion

concomitant

in the

a more

Notably, or the

presenile

de-

mentias. Genetics HD is

inherited

of affected complete, provided

or affected

essentially they

and racial per

in an autosomal

males

100,000.

live

groups; Genetic

all long

and Epidemiology dominant

females

individuals enough.

and its studies

will

fashion,

i.e.,

bear

gene.

bearing HD has been

prevalance indicate

in the that

the the

develop

in virtually

and U.K.

spontaneous

of

Since

gene will

identified U.S.

half

is

mutation

the

offspring

penetrance

is

symptoms all

approximately makes a

ethnic 5

Huntington's

disease:

contribution

to the

negligible 1969).

Although

significantly female children

al.,

1974;

there

clinical incidence

in adult-onset

and Chase,

may be modifier

of

HD the

more frequent in the are more susceptible

Shoulson

genes

and experimental disease

sex ratio

is

This

affect

(Stevens

l:l,

juvenile form of to this variant

1975).

that

the

aspects

15

and Parsonage,

paternal

descent

is

the disorder; in addition, by a 2:l ratio (Bird et

inheritance

pattern

the age of onset

suggests

and severity

that of

the

disorder. Neuropathology The brains (Lange the

of 8D patients

et aZ.,

1976).

caudate-putamen

On microscopic is

On gross where

analysis,

apparent

(Bruyn,

as well

as small

neurons

intrinsic

weigh

to

there

is marked loss

In

atrophy

occurs,

region.

fibers

a patchy

and focal

degeneration

of neurons

cerebral

cortex.

In contrast

to Parkinson's

cuous

lack

of neuropathologic

changes

Neuroanatomy Recent fied

the

cuit

(Fig.

in neurochemistry

relationships

among several

1).

nigra

turn).

Although in

Dopaminergic provide

the

aZ.,

1976),

this

neurotransmitter

striatum

there

is

et aZ.,

(direct

or indirect)

ons intrinsic inhibitory

currently are

over

the

striatum

influence dopamine

ergic

or due to

blockade

of

intrinsic

in disinhibition

the

receptor

types

bodies the

(Sethy

and Van Wert,

of

the

1974;

(striaof

Kitai

et

responses

adenylate

Racagni that

of

cyclase influence

local-circuit

fact

sub-

effects

an inhibitory

due to degeneration neurons.

cir-

1969;

cholinergic by the

clari

in the

postsynaptic

dopamine-receptors

cholinergic

lying

postsynaptic

exerts

rate

considerably

(Connor,

certain

firing

stimulation,

is a conspi-

caudate-putamen

by a dopamine-sensitive of

V and VI

the nigro-striatal

to the

input

In addi-

III, there

have

in

cell

that

'

nigra.

or inhibitory

evidence

of

Circuit

whether

has been demonstrated

post-synaptic neurons

debate

gliosis

perikarya. layers

substantia

their

dilitation.

reduction

Disease,

projection

The dopaminergic

1975).

to the

with

excitatory

compelling

affects

Nigro-Striatal

terminal

are mediated

(Siggins

This

is

in neuronal

neuronal

in

degeneration of the large in a near complete loss of

and neuroanatomy

neurons

a dense

there

in the

of the

developments

stantia dopamine

decrement

occur

and reactive

shows a marked

tion,

controls

changes

ventricular

neurons

strio-pallidal of the

age matched

striking

with

variant, resulting

The pallidum

and a variable

than

the most

in striatal

the Westphal

neurons

the

less

examination,

a severe

1968). striatal

significantly

et at., reduction of

by neuroleptics, Other striatal

the

neur1976). in dopaminresults local-

J. T. Coyle

16 circuit Since

neurons

utilize

GABA has been

dopaminergic

to the

release

firing from

cortico-striatal

the

GABAergic where

(Rattori

et

cortex.

at.,

(GABA) as their inhibitory

GABAergic sites

neurons they

cerebral pathway

direct

intrinsic

at presynaptic nigra

acid

to have

these

In addition, substantia

neuronal vation

suggested

terminals,

transmitter 1975).

y-aminobutyric

et ai!.

in the with

exert 1973).

Recently,

may use glutamate

cell

bodies

Spencer as its

Cortex

+

on striatal

may regulate

striatum

Huntington’s

Normal

effects

neurons

an inhibitory The striatum

neurotransmitter.

(Bartholini in the influence receives

(1976)

has

neuroand Stadler,

striatum

project

on dopaminergic a massive innershown

neurotransmitter.

Disease Cortex

Dopamine Fig. 1. Neuronal Pathways in the Nigro-Striatal Circuit. Some of the identified neuronal pathways relevant to the pathophysiology of HD are presented; the synaptic relationships among the component neurons presented in the model are compatible with experimental results but have not been The dopaminergic neurons (Dopaconclusively established. mine) with cell bodies in the substantia nigra innervate the striatum and exert an inhibitory (-) influence over These chointrinsic striatal cholinergic (Ach) neurons. linergic local circuit neurons innervate excitatory (+> post-synaptic muscarinic receptors. The striatum also receives an excitatory (+) innervation from the cerebral cortex that may be glutamatergic (?Glu). The striatum contains GABAergic (GABA) local circuit neurons as well as GABAergic perikarya that provide an inhibitory (-> proIn HD, neurons in the jection to the substantia nigra. cerebral cortex degenerate as indicated by the crosshatching. The striatal cholinergic and GABAetgic neurons undergo degeneration whereas the dopaminergic pathway remains intact.

that

the

Huntington's

disease:

clinical

and experimental

Neurochemistry Since

1973,

in the with of

several

processes

HD (Fig. glutamic

1).

decarboxylase,

in HD brains

(Table to the

addition,

the

interneurons.

in

the

slightly

The receptors lie

in neurons

in these

several

post-synaptic

of [3~]

and putamen,

to the

they

binding

et al.,

in all three SD brains.

Whereas

serotonin

receptor

(Enna

but

is

only

The neurochemical HD point

significantly

that

is

significantly

increased

alterations

striatum

and the

reduced

neurons.

Several

lines

deplete

dopamine

choreic

symptoms;

alleviate gic

the

in

either

with

L-Dopa

appears

caudate,

presumably

between

in the

in the

40 and 60%

by specific 40-50X

in the

The S-adre-

globus

binding

pallidus is unchanged

substantia

circuit

this

with

1970).

in the

pallidus.

only

nigra

of

its that

of patients

dopaminergic

striatal

support

neuroleptics

(Klawans,

levels

of HD

of intrinsic

evidence

dopamine

neurotransmitter.

GABA receptor

the unaffected

by interfering

similarly,

symptoms

neurotransmission

number of

initial nigra

approximately

the nigro-striatal

between

the

as measured

globus

reduced

is noteworthy

to an imbalance

the

are reduced

It

of striatal

substantia

receptors

reduced

receptors,

Pharmacology

with

These is

by 70% in the

synthesizes

loss

altered

releasing

LSD,

that

In

caudate-putamen,

in the

also

HD.

and [3~]

neurons

reduced.

receptors

serotonin

enzyme

Similarly,

are

neurons

nigra

pathway.

hydroxylaae,

normal

mildly

with

GABAergic

of severe

tyrosine

decrease is

1976aj. areas

but

the

in the

caudate-putamen.

acetylcholine

regions.

caudate

the

of patients

of muscarinic three

of

activity

and substantia

the

reduction

dopamine,

the

GABAergic

evidence

activity for

of patients

the neurotransmitter

of

striato-nigral

neurotransmitters

pallidus

binding nergic

in

synthesizes

degeneration

severe

are variably

for

and globus

The density

the

pathway

reduced

but

in

caudate-putamen

neuropathologic

In contrast,

caudate-putamen

putamen

the

is

alterations

the brains

reduction

acetyltransferase,

a patchy

with

in

that the

as the

of choline

in a synthesis

enzyme

there

as well

exhibits in concert

and only

the

Thus,

the biochemical

and specific

GABA in both

striatum

activity

acetylcholine,

enzyme

1).

examined

neurotransmission

a striking

as endogenous

intrinsic

is

is

17

of SD

have

synaptic

There

acid

GABA, as well

which

investigators

mediating

aspects

input

cholinergic

and GABAergic

interpretation. synthesis block

Conversely, to precipitate

Drugs or storage

dopamine potentiation choreic

dying to the that

reduce

receptors

the

also

of dopaminermovements

in

18

J. T. Coyle Table Effect of Striatal Injection on Neurochemical Parameters

et al. 1.

of Kainate and Huntington's Disease in Caudate-Putamen and Substantia Nigra Percent

Neuron-type

Striatal Kainate lesion Caudate-Putamen

GABAergic Glutamate Decarboxylase GABA GABA-Uptake GABA-Receptor

32 33 43 295

Cholinergic Choline Acetyltransferase Acetylcholine Choline Uptake Muscarinic Receptor

30 29 40 57

Dopaminergic Tyrosine Hydroxylase Dopamine Dopamine Uptake Dopamine-Sensitive

Adenylate

Serotonergic Serotonin Uptake Serotonin Receptor LSD-Receptor

Cyclase

147 87 129 15

t f A +

Dopaminergic Tyrosine

Decarboxylase

Hydroxylase

control Huntington's Disease

l&/+6*cse,g

6* 7* 7* 19*

40-55*f, g ND 74-113C'd

20-48*a’c’%h

* 5* +_ 6* + 8* 5. 3*

ND ND 46kC'd,h

+ f f f

79-loge 57-79 ND ND

11 7 13 3"

99 2 12 46 f 9* 37 + 5* Substantia

GABAergic Glutamate GABA

of

ND

1j2*c’~ 41*csd

Nigra

43 f 4* 42 f 3"

26xe,g 3g*f,g

92 -c 13

1473

Rats received a unilateral injection of 2 ug of kainic acid and were killed 10 days after lesion; the injected striatum (caudate-putamen) and ipsilateral substantia nigra were assayed for the various neurochemical parameters (Coyle and Schwarcs, 1976; Schwarcs and Coyle, 1977; Schwarcs et al., 1977). Results are presented as percent of unlesioned (for rat) or normal human (for RD) controls. The spread in values for the RD results indicate the variation between caudate and putamen as well as variations among the results of the different laboratories. The grouping of the receptors with their respective presynaptic neurons is for the sake of clarity and does not mean to imply that these are upre-synapticu receptors. References for RD studies: aAquilonius et al., 1975; bBernheimer et al., 1973; 'Rnna et al., 1976b; dEnna et al., 1976a; eMcGeer and FicGeer, 1976a; fPerry et al., 1973; gurquhart et al., 1975; hWastek et al., 1976. ND-not determined; *p < 0.01 as compared to control.

Huntington's

disease:

presymptomatic

individuals;

in Parkinsonian

patients

treated

of the

ubiquitous

Because

1972). brain,

pharmacologic

associated

with

of heuristic choline its mine,

have

bate

the

transmission It

is

its

are

thus

retard

the

stimulate

drugs

that

increase

symptoms

enzymatic

physostigKlawans

blockers

and

exacer-

GABAergic

(Shoulson

et aZ.,

neuro1976).

GABA-sminotransferase

of GABA as well

such as muscimol

of acetyl-

to enhance

inhibit

are

or retarding

1973;

receptor

stage

which

inactivation

the GABA receptor

et al.,

approaches

drugs

levels

inhibitor

(Walker

at an experimental that

are

interventions

and Deanol,

cholinergic

Pharmacologic

however,

neurotransmission

acetylcholinesterase

muscarinic

currently

in the

neuronal

as choline

et al.,

neurons

such

the

observed

(Klawans

cholinergic

cholinergic

such

as the

to reduce

of L-Dopa of

19

side-effect

nevertheless,

synthesis, such

of RD.

hypothesized,

levels

to enhance

Conversely,

symptoms

high

aspects

a frequent

distribution

Thus,

been reported 1972).

is

side-effects;

of degradation,

Rubovits,

with

strategies

troublesome

enhancing

and experimental

and dyskinesia

interest.

via

rate

clinical

as drugs

may be of

that

therapeutic

and

directly value

(Bird,

1976). Animal A major animal

impediment

model

for

understanding onal ready

they

occur

testing

order

results

axons

of extrinsic

fected.

This

ing

from

terminals

striatum

no functional

ablates

shown to have cordingly, ons intrinsic

minimal to

the

the

of neurons

creates

the the

functional

in the

total

destruction

behavioral

sequelae

must be devised striatum

while

striatum

sparing

since

would processes

the

input;

region

itself

striatum

and Marcus, arise

from

strihence, has

has been

1975).

lesion

unaflesion-

the

the

diswhereas

are

Simply

selectively that

that

striatum

between

the

the

The major

region

also

of

of

losses

neurons.

or removal (Villablanca

that

the

but

a

the movement

imbalance cells

provide

to -determine

to the

intrinsic

neur-

in RD.

that

through

of the

symptoms

defect

intrinsic

intrinsic

a more detailed

neuronal

HD is

or pass

and the depleted only

specific for

of a suitable

would

resulting

underlying

model

innervate

can occur

Notably,

a technique

loss

not

imbalances

been destroyed.

about

for

agents

and the the

lack

sequelae

of pharmacologic

reproduces

that loss

allow

such a model

imbalances

an animal

a selective neurons

selective

dopaminergic the

neurons.

variety

devising

would

importantly,

neuronal

a model . which in ?ID may offer some clues in the way of

model

the

and electrophysiologic

More

a wide the

HD

of HD has been

An animal

Finally,

hurdle

atal

disorder. in HD.

correct

for

research

neurochemical

occurring

means for

disease.

this

of the

losses

whether

in the.basic

Model

AC-

the neurextrinsic

J. T. Coyle

20 In our mate

laboratory,

analogues

in HD.

we have

to produce

Systemic

degeneration

of neurons the

of

toxic

effects

of glutamate

(Olney

of

larization kainic

acid,

interacts tered

To limit into

marker

toxic

effects

region

via

enzymes

for

the

GABAergic

neurons

(tyrosine

hydroxylase)

and Schwartz, there

is

2 ug of kainic

line the These

of

tyrosine

reduction

of in

have

rat

for

sensitivity

to deposoma whereas

analogue

of

excitatory

glutamate,

agent

effects

that

when adminis-

to the

striatum,

the

drug

placed

cannulae.

In

initial

used

of

as little

is not been

the

in the

striatum

After

(McGeer

to

by 100X.

and McGeer,

1967b).

a similar

as well

contrast

contrast,

increased

causes

terminals (in

and and cho-

In marked rather

acid,

injection

decarboxylase

toxin,

dopaminergic

decarboxylase

but

(Coyle

ug of kainic

acid

acid

confirmed

a nonspecific

effects

later.

striatum.

reduced

and terminals

toxic

as 0.5

48 hours

by 80% in the

studies,

dopaminergic

of glutamic

striatum

was in-.

acetyltransferase)

to monitor

of glutamic

reduced

sulfate,

neurons

acids

neuronal

and the

were

activities

subsequently

the markers

and GABAergic

the

hydroxylase

copper

amino

for,

action

(choline

injection

in the are

neurons;

and neuronal

decarboxylase)

acid , .the activities

observations

The injection gic

in

acetyltransferase activity

acid

striatum

the

acetyltransferase

ar-

neuroexcitatory

neurotoxic

cholinergic acid

a 20% reduction

choline

of kainic

With

the

The neuro-

1976).

intrinsic

1976).

causes

and in 1972).

containing

potent

and produces

retina

detected

mice

their

A cyclic

a stereotaxically

in the

the

of gluta-

those

to depolarize

dentrites

1972).

to

et al.,

ability

to be an extremely

(glutamic

of

Olney

with

to the

effects

to immature

and sulphur

et al.,

(Buu et aZ.,

the

similar

importance,

receptors

the

striatum glutamate

correlates

limited

shown

glutamate

systemically

fused

of

is

(Curtis

has been

with

neurotoxic

1969;

dicarboxylic

Of particular

by glutamate

the

layer

(Olney,

to glutamate

are unresponsive

rat

may be due to its

several

1972).

the

inner-nuclear

hypothalamus

related

et aZ.,

axons

in

of

of monosodium

in the

nucleus

the neurotoxicity

advantage

lesions

administration

cuate

structurally

taken

et al.

the

60-654;

as the effects

cholinerof kainic

acid). To obtain the

cholinergic gic

more detailed

striatum,

several

and GABAergic

and serotonergic

after 60-70X

information pre-

the

injection

decrement

endogenous

neurons

terminals of

2.5

on the

and post-synaptic intrinsic that

sequelae to the

innervate

ng of kainate

of

neurochemical the

(Table

in the

activity

of

glutamic

GABA and the

activity

of

the

acid

synaptosomal

kainate

for

and the were

decarboxylase, affinity

to the

dopaminer-

examined

The injection high

lesion

parameters

striatum region

1).

the

10 days

elicits the

levels

uptake

a of

Huntington's process

for

levels

of

affinity

GABA.

of

activity

significantly

affected

finity

of

unaffected from

stem cell

et al.,

(Schwartz

The receptors were

also

nylate the

is

jected

as measured

receptor

for

Neurochemical mited acid

generation. marker

the

substantia lesions,

is

kainate

late the

is

striatum

striatum

afis

for

the

but

arise

of kainate

and, localized

activity

neurons,

of

kainate in the

is

not

of its

on the

activity

in the

associated

with

ipsilateral

and Coyle, alterations similar

the

are not

ipsilateral

also

sub-

undergoes the

in activity to nigral

de-

enzymatic

in the

ipsila-

in the

dopamine-sensitive

indicating that

have

in the

6-hydroxydopamine

or dendrites.

of neurons

li-

of glutamic

somata

nigra;

of

has been demonstrated

insensitivity

terminals

lesion

hydroxylase,

reduced

in a 75% decrement

by the

affinity

GABA in the

cyclase

dopaminergic

of GABA recep-

activity

pathway

tyrosine

adenylate

are also

1977).

striatal

a 60% decrement GABAergic

results

are remarkably

from

the

in-

receptors, LSD,

is unaffected

in

et al.,

of endogenous

because

(Schwartz

GABA,

by

40% in the

The density

increase

stria-

as measured

is reduced and [3H]

of [3H]

ade-

to the

serotonergic

binding 3-fold

intrinsic

Putative striatum.

sites,

Dopamine-sensitive

Serotonin

levels

the

at postsynaptic

receptor,

striato-nigral

dopaminergic

The neurochemical striatum

is

Dopamine-sensitive not

of [3H]

resulting

the

nigra

1977a).

(Campochiaro

There

lie

on neurons

lesioned

specific

and in the

lesion

cyclase

receptor

the

GABA occurs

hence,

nigra.

do-

are not high

markers effects

lesion.

bensilate,

a significant

In contrast,

for

teral

tal

by the

region.

nigra;

acti-

terminals,

the

toxic

chblinergic

binding

40% in

decarboxylase

stantia

and Coyle,

alterations

to this

the

presumably

to be localized

specific

although r3H]

which

The muscarinic

(Schwartz

approximately lesion

dopamine

synaptosomal

innervate to

of [3H]-quinuclidinyl

by the

kainate

which

by the kainate

appears

by 85%.

striatum

tors,

neurons, affected

binding

as quantified reduced

these

which

reduced

the

the

of endogenous for

neurochemical

insensitive

high

1977). for

specific

are

levels

serotonergic

Accordingly,

terminals,

bodies,

significantly

cyclase,

tum,

lesion.

and serotonergic

brain

Similarly,

the

synaptosomal

process

striatal

21

In contrast,

the

uptake

for

the

60-70X.

control;

injection.

a marker

aspects

acetyltransferase, of

are reduced

synaptosomal

by the

choline

activity

50% above

the

kainate

of

and the

is

of

and experimental

activity

choline

serotonin,

by the

dopaminergic

for

hydroxylase

and the uptake

the

acetylcholine

process

tyrosine

pamine

clinical

Similarly,

endogenous uptake

vity

disease:

that

The striaadeny-

this

their

dopamine

cell

bodies

1977b). produced

by kainate

to those

occurring

injection in the

into

the

caudate-putamen

rat and

in

J. T. Coyle

22. nigra

of patients

presynaptic the

as well

dopaminergic the

duced is

with

neurochemical

striatum

for

dying

pathway

cholinergic in both

markers

GABAergic

remains

relatively

significantly

whereas

the

elevated

In Nissl-stained

large the

rat

in

crosis

the

of glia

the

cells.

trinsic

the

(Coyle,

adjacent

neuropil

is

neuronal

somata.

Although

post-synaptic Glial

cell

of bodies

mination

in the

derived

Histologic jection with

from

observed

acid

The kainate perikarya

than

observed

the

in

exhibit

in the

HD, negligible

injected from

typically

the

seen rigid

histologic

with

in HD and

of

the

the

but

the brain

fragments of

to from

similarities observed

in the

brains

striatum

exhibits

nearly

total

Although

or Westphal changes

form

are

similar

of the

are observed

disorder in the

the and

the

de-

specialiwith

mem-

evidence neurons

site

in with

and terof

injection,

intrastriatal

also

such neuronal to

laden

those

the

changes region.

of

of passage

certain

in HD, they

of my-

synaptic

receiving but

in-

of dendrites

compelling

axons

days of

whereas

and are

distant

number

lo-14 loss

intact

site

spares

glone-

in the

total

disappearance

provide

of

or the

Bundles

neurotoxic

the

head

caudate

remain

of rats

entire

striatum,

activity

perikarya

(Fig.

also

or nonspecific

of

only

loss

cannula but

the

injected

received

a generalized

increase

at the

is

have

is

neurons

of

survive,

acid

injection

reduced

in preparation).

phagocytic

with

the neuropathologic

HD.

neuronal vere

changes

of kainic

ences

of neurons

not

changes

fibers,

attached

kainic

are re-

nearly

tail

the

observations

that

tip

small

observations

boutons

histologic

area from

of

disorganized remain

striatum

that

a generalized

capsule

show increased

These

is

and Schwarcx,

terminal

the hypothesis

the

the the

microscopic

neuron

cells

there

receptors

the

rats

involves

affect

in

Lesion

there

of inflammatory

internal

severely

of

death, only

analysis light

presumably

fragments.

support

but

Kuhar

axons,

zation.

not

Ultrastructural

neurons

brane

does

is

Acid

1.5 mm from not

no evidence

elinated

generated

of

neuron

The nigro-striatal

striatum.

forebrain

The lesion

site,

confirms

binding

before

in the

The postsynaptic

innervating

Kainic

the

affects

but is

injection

lesion

Striatal

reduction

nigra.

unaffected.

days

striatum.

There

at

the

similar

and GABAergic

in the

kainate-lesioned

ten

loss

caudate-putamen

bus pallidus.

after

cell

is.a

cholinergic

GABA receptor

in a radius

neuronal

neurons

the

neurons

'through

acid

perikarya

This

2).

sections

of kainic

of neuronal

of

There

neurons

in the

Histology

1).

for

as the

and serotonergic

cases

an injection

DD (Table

et al.

important

indiffer-

of patients depletion losses

(Bruyn,

of

are more

the neuropathologic substantia

dying

1968). nigra

se-

changes As in although

Huntington's

disease:

clinical

and

experimental

aspects

23

Fig. 2. Histology of the Kainate-lesioned striatum. The kainate injected (2 up) striata were obtained from rats 10 days after treatment. For electronmicroscopy, the tissues were fixed with 5% glutaraldehyde, post-fixed with buffered osmium-tetroxide (1%) and embedded in Maraglas. A. Photomicrograph of Note normal rat striatum. B. Photomicrograph of kainate injected striatum. The lighter the near complete loss of neuronal perikarya and the gliosis. C. Electronmicroareas, which are internal capsule fibers, appear unaffected. graph of neuropil of kainate injected striatum. Note several apparent terminal D. Electron miboutons (b) that impinge upon degenerated dendrites (arrows). crograph of kainate injected striatum showing a group of intact myelinated adjacent to severely disrupted neuroaxons, presumably internal capsule fibers, pi1 (Coyle, Kuhar and Schwartz, in preparation).

J. T. Coyle

24

similar neurochemical alterations kainic acid lesion, the pallidurn

et al.

do occur in this region. In the striatal and cerebral cortex are spared whereas both of

these areas are significantly involved in HD. The differences from l-ID, particularly the lack of involvement of the pallidum and the cerebral cortex, reflect the limited area affected by the stereotaxic injection of kainate. Perhaps, additional injections of kainate into these other areas may offer an even better model of HD. Behavioral

Consequences of Striatal

Kainate

Lesion

Rats receiving a unilateral striatal injection of kainate undergo a gradual evolution.of behavioral symptoms. During the initial hours after injection, the rats exhibit episodic dystonic posturing toward the side contralateral to injection with occasional tonic-clonic movement of the contralateral extremities; the axial torsion and retrocollis resembles that seen in the hereditary torsion dystonia (Eldridge and Fahn, 1976). As these symptoms recede, the animals develop spontaneous contralateral rotatory behavior that lasts for 24-36 hours. The animals then lapse into a per.iod of hypoactivity and aphagia lasting an additional 24-36 hours. This is followed by spontaneous rotatory activity the ipsilateral side of 2-3 days of duration. Subsequently, ipsilateral

toward rota-

tory behavior can be precipitated by administration of indirectly acting dopamine-receptor agonists. The fact that the kainate-lesioned rats do exhibit rotatory behavior instead of choreaform movements is not surprising since rodents do not develop motor symptoms analogous to primates with pharmacologically or surgically induced nigro-striatal dysfunction (Marsden et al., 1975a). The behavior of the rats in the chronic state after unilateral kainate lesion of the striatum resemble that of rats which have a unilateral ablation of the dopaminergic nigro-striatal.pathway on the same side (Ungerstedt, 1971). Although the dopaminergic nigro-striatal pathway is intact in the kainate lesioned striatum, the similar behavior of the kainate lesioned and the "Parkinsonian" rats is not unexpected because of the severe degeneration of striatal efferents after the kainate injection. alogy of the rat

This behavioral response adds further support for the anstriatal kainate lesion to the Westphal or rigid variant of HD.

Associated

Neurochemical

Changes of Striatal

An advantage of having an animal model is that cal and electrophysiologic intrinsic to the striatum

Kainate

Lesion

the dynamics of the neurochemi-

alterations resulting from degeneration of neurons can be examined. Degeneration of neurons upon which

Huntington's

disease:

clinical

and experimental

aspects

25

the dopaminergic terminals synapse in the striatum as well as the loss of the GADAergic inhibitory input to the nigra would presumably affect the neurochemical economy of the nigro-striatal dopaminergic pathway. And, indeed, this appears to be the case; for, tyrosine hydroxylase, the initial and rate-limiting enzyme in synthesis pathway for catecholamines, undergoes a prolonged activation after lesion of zyme exhibits a assayed in vitro in vivo. These

the striatum with kainate (Schwartz and Coyle, 1977a). The en4-fold enhancement of affinity for its pteridine cofactor when and an accelerated conversion of L-tyrosine to L-DOPA occurs alterations are not simply dependent upon impulse flow since

acute transection of the dopaminergic axons does not result in the reversal of the activation of tyrosine hydroxylase (Schwartz and Coyle, in preparation). In addition, in the kainate-lesioned striatum there is a marked increase in the specific receptor-binding of r3D] GABA. Kinetic studies reveal that this increased binding reflects a 3-fold increase in the affinity of the receptor site for [3H] GAbAwithout any change in the total number of receptor sites. These receptor alterations are compatible with the denervation supersensitivity of GABAreceptors in the lesioned striatum dies represent only two of the possible cidate the neurochemical, neuroanatomic generation

of striatal

(Campochiaro et al., 1977). These stuones that could be done to further eluand electrophysiologic sequelae of de-

neurons. Table 2.

Effect

of GADA-T Inhibitor on GABAlevels Striatum S. Nigra GABA: nmoles/mg 2.2 t 0.2-t 10.5 zk 0.3t Control 4.4 2 0.4*t Kainate Lesion of Striatum 0.7 f 0.2*t Kainate Lesion of Striatum 4.1 2 0.2* 15.2 f 1.2 treated with KMI-71.645 Rats received a unilateral injection of kainic acid (2 ug) 12 days The rats were then injected (i.p.) with prior to the experiment. KMI-71.645. (100 mg/kg) or an equivalent volume of diluent and were sacrificed 4 hr later. The GADAlevels of the kainate injected striata and ipsilateral nigras and of the contralateral uninjected striata and nigras of diluent treated animals (control) were measured. @MI-71.645 was kindly donated by Merril International). *Differs from control, p'd 0.01; tDiffers from m-71.645 treated, p < 0.01.

J. T. Coyle

26

Pharmacology The primary

importance

tors

the

opportunity

ther

they

correct

ment

of Parkinsonian

sulted to bear

studies,

(y-acetylynic lized

the

with

y-acetylynic

kainate the dence

symptoms

only

in the

striatum,

in

the

of our

evidence

it

affected of

It the

is

fallacy

of

produces

to 'those

observed to is

glutamate

results of jor

its

seaweed toxic

in sufficient

hypothesize in chronic,

the brain

Amino acid

specifically

glutermatergic

amounts

excessive innervation

acids

normally

can produce

an abnormality

lesions

(Van Harreveld

from

of

by HD. the

in

present

Notably,

cerebral

of

by stria-

similar

with kainate

may pro-

of HD.

Although

the

HD, it

is

by humans, receptors

receptors striatum and has

it

for

brain

to that

neuronal the

the

the

and Fifkova,

cortex

1977).

dying

in the

similar

GABA

be produced

synthesized

glutamate

the

strikingly

of

evi

the

in HD

lesion

defect

in glutamatergic

stimulation

affected

must

not

the

et al.,

effects

by overstimulation

of

of HD in light

Defect

pathophysiologic

of

supersensiti-

Primary

of

the

to pharma-

increments

of patients

and is probably

effect

glutamate.

and homocysteic

when injected one might

from

exerts

neurotransmitter

the underlying

in spite

symptoms

toxicity

GABA in

In view

alterations of

treatment

to ameliorate

the kainate

and histologic axis

of

(Campochiaro

similar

the mechanism

degradation

possible

range.

reduce

of

In

catabo-

Acute

dopamine-receptor

on the

case

the

thus,

is

are necessary

will

that the

the nigro-striatal

into

derived

apparently

in

that

normal

that

levels

2); it

much smaller

Lesion

to conclude

speculate

some insight

kainate

Kainate

retard

(Table

the

re-

be brought

striatum.

enzyme

in the

supersensitivity

neurochemical in

that

and nigra

Nevertheless,

reasonable vide

logic

of

has

might

striatum.

regions,

to the

possible

of the

same cause.

tum which

is

a GABA-receptor

Implications

nigra

because

striatum

the

lesioned

in dopamine

Disease

dopamine,

treat-

of a "suicide-substrate"

increases

GABA levels

whe-

Since

for

presumably

these

investiga-

to determine

strategies

effects

3-fold

allows

and GASA in the

in the

in both

increases

of Parkinson's

levels

the

enzyme would in

precursor

similar

and ipsilateral

their

modest

the

it

agents

GABA-transferase,

effects

neurons

increase

that

vity

striatum

of GABAergic

cologically

its

GABA results

lesioned

loss

for

that

abnormalities.

acetylcholine

examined

of this

enhance

HD is

pharmacologic

L-DOPA,

of

we have

GABA; inhibition

for

improvement,

deficits

Lesion

and behavioral

with

GABA; RMI 71.645)

of GABA and thus

model

various

symptomatic

to correct

preliminary

testing

neurochemical patients

in dramatic

the Kainate

of an animal

of the

of

et al.

the

such as

of kainate

1971).

Thus,

function

that

in

the

regions

receives the

highest

a ma-

Huntington's brain

concentration

veral

mechanisms

these

include:

of

als,

2) excessive receptors

cess

for

sive

stimulation

firing

symptomatic

exhibit

phase

1973).

generalized hypothesis."

1975);

and abnormalities

of

since

CSF and brain

glutamate

of

generalized lular

and Lewis,

neuronal

energy

1973).

action

in HD that

excesthat

the

pre-

affects

verification

membrane

innervated

needs

about

is

conceivable

of that

a gradual

de-

and proThe quite

of neurotoxicity

the hypothesis

a

or cel-

occurring

is undoubtedly before

gluta-

and water,

terminals.

the mechanism

to be obtained

sodium

normally

there

attractive,

that stimulation

characteristics

to the

in

and depletion

by glutamatergic

although

et al.,

been reported

preclude of

is

signifi-

Gortz

Excessive

of NA+-K+ ATPase

vulnerable

information

analogues

do not

It

and recep-

exhibit 1973;

influxes

(Perry

"glutamate

have

in HD.

1970).

nervous

fundamental

of the

however,

as a consequence,

hypothesis",

a more

and Stein,

in large

makes neurons

Much additional

experimental

These,

and Quastel,

of neurons

receptor and its

involves

are normal

and function

activation

of glutamate;

levels

degeneration

results

(Okamoto defect

degeneration

glutamate

pro-

in SD is

central

of HD patients

(Menkes

structure

receptors

metabolism

gressive culative.

uptake

during

in the

suggest

fibroblasts

the neuronal

stores

polarizing "glutamate

that defect

on the basis

culture

potassium,

cellular

energy

the

in tissue

mediate

studies

be posited

in liver

intraneuronal

cellular

several

might

growth

(Bolt

glutamate

loss

metabolism

For example,

abnormal

receptors

terminof gluta-

affinity

dysfunction

in glutamate

than

cantly

mate

neuronal

defect

Furthermore,

defect

HD patients

high

primary

Se-

of HD.

of HD patients

et al.,

of such

in nerve

3) supersensitivity

an hypothesis

as the

1976).

stimulation;

of glutamate

presynaptic

of

receptors

symptoms

is no obvious

system

limitation

glutamate

27

et at.,

(Simon

neurons,

in the

aspects

glutamate-receptor

of synthesis

glutamatergic

A major of

receptors

enhance rate

of

and experimental

glutamate

specifically

or 4) an impairment

do not

There

apparent

might

glutamate.

patients

clinical

1) an elevated

mate

tor

disease:

speof

merits

in human material. Acknowledgements

We acknowledge cipated Victoria

in

these

Rhodes.

and MD-26654

the

excellent

experiments

technical and the

assistance secretarial

J.T.C.

receives

research

and a Basil

O'Connor

Grant

support from

of Robert assistance from

the March

Zaczek of Carol

USPHS Grants of Dimes.

who partiKenyon DA+0266

and

J. T. Coyle

28

In&tie8 Dr. Johns

Joseph

and reprint

requests

T. Coyle,

Department

Hopkins

725 North Baltimore,

Wolfe

University

School

should

et al.

be addressed

to:

of Pharmacology of Medicine

Street

M&yland

21205

U.S.A. References

AQUILONIUS, S. -M., ECKERNAS, S. -A. and SUNDWALL, A. (1975). Regional distribution of choline acetyltransferase in the human brain: changes in Huntington's chorea. J. Neural. Neurosurg. Psych&t. 38: 669-677. BARTHOLINI, G. and STADLER, H. (1975). Cholinergic zd GABAergic influences on the dopamine release in extrapyramidal centers. In: Chemical Tools in Catechotamine Research II, Almegren, O., Carlsson, A. and Engel, J. (eds.), pp. 235-241. North-Holland Publ., Amsterdam. BERNHEIMER, H., BIRKMAYER, W., HORNYKIEWICZ, O., JELLINGER, K. and SEITELBERGERGER, F. Brain dopamine and syndromes of Parkinson and Hunting(1973). ton. J. NeuroZ. Sci. 20: 415-455. BIRD, E. D. (1976). Bio%mical.studies on y-aminobutyric acid metabolism in Huntington's chorea. In: Biochemistry and Neurology, Bradford, H. F. and Marsden, C. D. (eds.), pp. 83-92, Academic Press, New York. BIRD, E. D., CARO, A. J. and PILLING, A sex related factor in J. B. (1974). the inheritance of Huntington's chorea. Ann. Hum. Genet., Land. 37: 255-260, BOLT, J. M. W. and LEWIS, G. P. (1973). Huntington's Chorea: a stay of liver function and histology. Ql. J. Med. 42: 151-174. BRUYN, G. W. (1968). Huntington's chorea: hztorical, clinical and laboratory synopsis. In: Ha&book of Clinical Neurology 2: 298-378, NorthHolland, Amsterdam. BUU, N. T., PUIL, E. and VAN GELDER, N. M. (1976). Receptors for amino acids in excitable tissues. Gen. Pharmac. 7: 5-14. Characteristics and CAMPOCHIARO, P., SCHWARCZ, R. and COYLE,-J. T. (1977). localization of the sodium independent [3H] GABA receptor site in rat striatum. L?rain Res., submitted. CONNOR, J. D. (1970). Caudate nucleus neurons: correlation of the effects of substantia nigra stimulation with iontophoretic dopamine. J. Physiol (Lord.) 208: 691-703. COYLE, J. T. and SCHWARCZ, R. (1976). Lesion of striatal neurons with kainic acid provides a model for Huntington's chorea. Nature -263: 244-246. CURTIS, D. R., DUGGAN, A. W., FELIX, D., JOHNSTON, G. A. R., TREBECES, A. K. and WATKINS, J. C. (1972). Excitation of mammalian central neurons by acidic amino acids. Brain Res. 41: 283-301. DEWHURST, K. and OLIVER, J. 71970). Huntington's disease of young people. Eur. Neural. 3: 278-289. ELDRIDGE, R. and-FAHN, S. (1976). Raven Press, New York. Dystonia. ENNA, S. J., BENNETT, J. P., BYLUND, D. B., SNYDER, S. H., BIRD, E. D. and IVERSEN, L. L. (1976a). Alterations of brain neurotransmitter receptor binding in Huntington's chorea. Brain Res. 115: 531-537. ENNA, S. J., BIRD, E. D., BENNETT, J. P., BYLUND, D. B.,,YAMAMURA, H. I., IVERSEN, L. L. and SNYDER, S. H. changes in (1976b). Huntington's chorea: neurotransmitter receptors in the brain. N. Engl. J. Med. 294: 1305-1309. GORTZ, I., ROBERTS, E. and COMINGS, D. E. (1975). Fibroblastan Huntington's disease. N. Engl. J. Med. -293: 1225-1227.

Huntington's

disease:

clinical

and experimental

aspects

29

HATTORI, T., McGEER, P. L., FIBIGER, H. C. and McGEER, E. G. (1973). On the source of GABA-containing terminals in the substantia nigra: electron microscopic, autoradiographic and biochemical studies. Brain Res. 54: 103-114. KITAI, S. T., SUGIMORI, M. and KOCSIO, J. D. (1976). ExcitatoryTature of dopamine in the nigro-caudate pathway. ExpZ. Brain Res. 24: 351-363. KLAWANS, 8. L. (1970). A pharmacologic analysis of Hunting%'s chorea. Cur. Neural. 4: 148-163. KLAWANS, H.-L., PAULSON, G. W., RINGEL, S. P. and BARBEAU, A. (1972): Use of L-DOPA in the detection of presymptomatic Huntington's chorea. N. EngZ. J. Med. -286: 332-334. KLAWANS, H. L. and RUBOVITS, R. (1972). Central cholinergic-anticholinergic antagonism in Huntington's chorea. Neurologql 22: 107-116. LANGE, H., THORNER, G., HOPF, A. and SCHRODER, K.P. (1976). Morphometric studies of the neuropathological changes in choreatic diseases. J. Neurolog. Sci. 28: 401-425. MARSDEN,T. D., DUVOISIN, R. C., JENNER, P., PARKER, J. D., PYCOCK, C. and TARSY, D. (1975a). Relationship between animal models and clinical Parkinsonism. Ad. Neural. 9: 165-175. MARSDEN, C. D., TARSY, DT and BALDESSARINI, R. J. (1975b). Spontaneous and drug-induced movement disorders in psychotic patients. In: Psychiatric Aspects of Neeurologic Disease, Benson, D. F. and Blumer, D. (eds.), pp. 219265, Grune & Stratton, New York. McGEER, E. G. and McGEER, P. L. (1976a). Duplication of biochemical changes of Huntington's chorea by intrastriatal injection of glutamic and kainic acids. Nature 263: 517-519. McGEER, P. L. and McGEER, E. G. (1976b). Enzymes associated with the metabolism of catecholamines, acetylcholine and GABA in human controls and patients with Parkinson's disease and Huntington's chorea. J. Neurochem. 26: 65-76. MCHUGH, P. R. and FOLSTEIN, M. F. (1975). Psychiatric syndromes of Huntington's chorea: a clinical and phenomenologic study. In: Psychiatric Aspects of NeuroZogic Disease, Benson, D. F. and Blume, D. (eds.), pp. 267-686, Grune & Stratton, New York. MENKES, J. H. and STEIN, N. (1973). Fibroblast cultures in Huntington's disease. N. EngZ. J. Med. 288: 856-857. OKAMOTO, K. and QUASTEL, J. H. (1970). Water uptake and energy metabolism in brain slices from the rat. Biochem. J. 120: 25-36. OLNEY, J. W. (1969). Glutamate-induced rezal degeneration in neonatal mice. Electron microscopy of the evolving lesion. J. Neuropath. ExpZ. NeuroZ. -28: 455-474. OLNEY, J. W., HO, 0. L. and RHEE, V. (1972). Cytotoxic effects of acidic and sulphur-containing amino acids on the infernt mouse central nervous system. Expl. Brain Res. 14: 61-76. PERRY, T. J., HANSENYS. and KLOSTER, M. (1973). Huntington's chorea-deficiency of y-aminobutyric acid in brain. N. Engl. J. Med. 288: 337-342. RACAGNI, G., CHENEY, D. L., TRABUCCHI, M. and COSTA, E. (197K In V&o actions of clozapine and haloperidol on the turnover rate of acetylcholine in 323-332. rat striatum. J. Pharmac. ,Expl. Ther. -196: SCHWARCZ, R., BENNETT, J. P. and COYLE, J. T. (1977). Loss of striatal serotonin synaptic receptor binding induced by kainic acid lesions: correlations with Huntington's disease. J. Neuxochem., in press. SCHARCZ, R. and COYLE, J. T. (1977a). Striatal lesions with kainic acid: neurochemical characteristics. Brain Res., in press. SCHWARCZ, R. and COYLE, J. T. (1977b). Neurochemical sequelae of kainate injections in corpus striatum and substantia nigra of the rat. Life Sci., in press.

J.

30

T. Coyle

et al.

Modifications of striatal acetyl(1974). Res. receptor agonists and antagonists. Common. Chem. Pathol. Phamnac. 8: 13-28. SHODLSON, I. and CHASE, T. N. (1975). Huntington's disease. Ann. Rev. Med. 26: 419-426. Huntington's disease: SH?itLSON, I., KARTZINEL, R. and CHASE, T. (1976). Neurology treatment with dipropylacetic acid and ganaaa-aminobutyric acid. 26: 61-63. (1975). Electrophysiologic SISINS, G. R., HOFFER, B. J. and DNGERSTEDT, V. evidence for involvement of cyclic adenosine monophosphate in dopamine reLife Sci. 15: 779-792. sponses of caudate neurons. (1976). Binding of [3H] kainic SIMON, J. R., CONTRERA, J. F. and KDHAR, MTJ. acid, an analogue of L-glutamate to brain membrane. J. Neurochem. -26: 141-147. SPENCER, H. J. (1976). Antagonism of cortical excitation of striatal neurons by glutamic acid diethyl ester: evidence for glutamic acid as an excitatory transmitter in rat striatum. Brain Res. 102: 91-101. STEVENS, D. and PARSONAGE, M. (1969). Mutazn in Huntington's chorea. J. Neural. Neurosurg. Psych&t. 32: 140-143. DNGERSTEDT, U. (1971). PostsynGtic supersensitivity after 6-hydroxydopamine Actu Physiol. Stand. induced degeneration of nigro-striatal dopamine system. fS-qpZ.) 367: 69-93. DRQDHART, N.,PERRY, T. L., HANSEN, S. and KENNEDY, J. (1975). GABA content and glutamic acid decarboxylase activity in brain of Huntington's chorea patients and control subjects. J. Neuxochem. 24: 1071-1075. VAN HARREVELD, A. and FIFKOVA, E. (1971). Lightand electronmicroscopic changes in central nervous tissue after electrophoretic injection of glutamate. Ezp. Mol. Path. 15: 61-81. Effects of caudate nuclei reVILLABLANCA, J. R. and MARES, R. J. (1975). moval in cats. Comparison with effects of frontal cortex ablation. In: Brain Mechanisms in Mental Retardation, Buchwald, N. A. and Brazier, A. B. (eds.), pp. 273-311, Academic Press, New York. WALKER, J. E., HOCHN, M., SEARS, E. and LEWIS, J. (1973). Dimethyl aminoethanol in Huntington's chorea. Lancet 1: 1512-1513. WASTEK, G. J., STERN, L. Z., JOHNSON, P. C.-and YAMAMDRA, H. I. (1976). Huntington's disease. Regional alteration in muscarinic cholinergic receptor binding in human brain. Life Sci. -19: 1033-1040.

SETHY, V. B. and VAN WRRT, M. l-l. choline

concentration

by dopamine