Page 322 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Diseases of the Basal Ganglia
The basal ganglia are made up of: the substantia nigra (p.c.) must have been de-
– the corpus striatum (consisting of the cau- stroyed.
date nucleus and the putamen); The loss of cells in the substantia nigra (p.c.)
– the inner and outer globus pallidus (palli- decreases the corresponding dopaminergic in-
dum, consisting of an internal and an exter- nervation of the striatum (→ B1). This leads,
Systems – the subthalamic nucleus; and first of all, to disinhibition of glutamatergic
nal part);
neurons in the subthalamic nucleus and thus
to an increased activation in the internal part
– the substantia nigra (pars reticulata [p.r.]
and pars compacta [p.c.]).
of the pallidum and of the pars reticulata of
Neuromuscular and Sensory in conjunction with the cerebellum, motor cor- gic activation of the striatal neurons ceases. It
the substantia nigra. Secondly, the dopaminer-
Their function is mainly to control movement
tex, corticospinal tracts, and motor nuclei in
normally directly inhibits neurons in the sub-
stantia nigra (p.r.) and the internal part of the
the brain stem.
pallidum. Together these processes ultimately
Striatal neurons are activated, via gluta-
lead to excessive inhibition of the thalamus
mate, by neurons of the cortex. The internal in-
(GABA transmitter).
terconnections of the basal ganglia (→ A) are
mainly provided by the inhibitory transmitter
Inhibition of the thalamus suppresses vol-
culty initiating movement or can do so only as
basal ganglia have an inhibitory effect on the
thalamus via GABAergic neurons in the inner
a reaction to external stimuli (hypokinesia).
10 γ-aminobutyric acid (GABA). Ultimately the untary movement (→ B2). Patients have diffi-
pallidum and the substantia nigra (p.r.). These
Muscle tone is greatly increased (rigor). In ad-
neurons are activated via glutamate from the dition, resting tremor (4–8 per second) is
neurons of the subthalamic nucleus. Finally, common, with alternating movements espe-
the striatal neurons are partly activated and cially of the hands and fingers (a movement
partly inhibited by dopamine from the sub- similar to that used when counting money).
stantia nigra (p.c.), and also activated via Hypokinesia typically forces the patient to
cholinergic neurons. An imbalance between adopt a moderately bent posture with slightly
inhibitory and activating influences has a angled arms and legs. It also leads to a rather
harmful effect on motor functions: too strong rigid facial expression, micrographia, and soft,
an inhibition of the thalamic nuclei has a hy- monotone, and indistinct speech. Finally, other
pokinetic, too little has a hyperkinetic effect. disturbances occur, for example, increased sal-
ivation, depression, and dementia. These are
caused by additional lesions (death of neurons
Parkinson’s Disease
in the nucleus of the median raphe, of the lo-
Parkinson’s disease is a disease of the substan- cus coeruleus, or of the vagus nerve).
tia nigra (p.c.) which via dopaminergic tracts In treating Parkinson’s disease (→ B3) the
influences GABAergic cells in the corpus stria- attempt is made to increase the dopamine for-
tum. The cause is frequently a hereditary dispo- mation of the nigrostriatal neurons by admin-
sition that in middle to old age leads to degen- istering L-dopa, a precursor of dopamine
eration of dopaminergic neurons in the sub- (which cannot itself pass the blood–brain bar-
stantia nigra (→ B1). Further causes are trau- rier). Amphetamines can stimulate the release
ma (e.g., in boxers), inflammation (encephali- of dopamine as well as inhibit the reuptake of
tis), impaired circulation (atherosclerosis), tu- dopamine in the nerve endings. This also in-
mors and poisoning (especially by CO, manga- creases the synaptic concentration of dopa-
nese, and 1-methyl-4-phenyl-1,2,3,6-tetrahy- mine. Finally, dopamine breakdown can be de-
dropyridine [MPTP], which was once used as a layed by inhibitors of monoaminooxidase
substitute for heroin). The cell destruction (MAO inhibitor) or the effect of dopamine can
probably occurs partly by apoptosis; superox- be imitated by dopamine-like drugs.
312 ides are thought to play a causal role. For In addition to increasing dopamine forma-
symptoms to occur, over 70% of neurons in tion or its effect, transplantation of dopamine-
"
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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