Page 324 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

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producing cells into the striatum has been tried Hemiballism. After destruction of the sub-
with the aim of increasing local dopamine thalamic nucleus (by ischemia or tumor) sud-
concentration. The symptoms of Parkinson’s den flinging movements occur. They are
disease can also be improved by inhibiting thought to be due to decreased stimulation of
cholinergic neurons in the striatum. These neu- inhibitory GABAergic neurons in the internal
rons stimulate those striatal neurons that are part of the pallidum and substantia nigra
normally inhibited by dopamine. (p.r.). It leads to disinhibition of neurons in
Systems subthalamic nucleus or the internal part of the thalamus. treatment with neuroleptics,
Glutamate antagonists and lesions of the
Tardive dyskinesia (dystonia) is caused by
longer-term
the pallidum can also cause disinhibition of
which displace dopamine from receptors
the thalamus, and thus an improvement in
Neuromuscular and Sensory have also been made to delay the apoptotic (→ p. 352). They cause sensitization of those
the clinical picture of the disease. Attempts
(→ D2). These drugs are used as antipsychotics
neurons that express increased numbers of do-
death of the nigrostriatal neurons by means of
pamine receptors in the subsynaptic mem-
antioxidatively-acting drugs and of growth
factors.
brane. The activity of the subthalamic nucleus
is suppressed via disinhibition of neurons in
the external part of the pallidum. Nonactiva-
Hyperkinesias
tion of the subthalamic nucleus and increased
ease of the basal ganglia. It is largely a disease
tivity of neurons in the internal part of the pal-
lidum and in substantia nigra (p.r.). This re-
of the striatum.
10 Chorea is the most common hyperkinetic dis- inhibition by striate neurons decrease the ac-
The inherited variant of the disease (Hun-
sults in disinhibition of the thalamus and in-
tington’s chorea; → C1) becomes manifest in voluntary movements. In addition to the in-
the fourth or fifth decade of life and leads to creased expression of receptors, apoptosis of
an irreversible progressive destruction of stria- those neurons that are normally inhibited by
tal neurons. The responsible gene is on the dopamine is also important.
short arm of chromosome 4. It is thought that Lesions of the striatum and pallidum addi-
the genetic defect results in the cellular in- tionally lead to athetosis, a hyperkinesia
crease of a protein (huntingtin) that is difficult marked by excruciatingly slow, screw-like
to break down. Cell death is accelerated by the movements. Lesions in the pallidum and thala-
effect of the excitatory neurotransmitter gluta- mus cause dystonia (prolonged torsions and
mate, which stimulates neurons by activating twists; also regarded as proximal athetosis).
calcium-permeable ionic channels. The cell is
2+
damaged by excessive entry of Ca .
In Sydenham’s chorea, contrary to Hunting-
ton’s chorea there is largely reversible damage
to the striatal neurons (→ C2). It is caused by
the deposition of immunocomplexes in the
course of rheumatic fever, and it occurs mainly
in children.
In rare cases the striatal neurons have been
damaged by ischemia (atherosclerosis), tumor,
or inflammation (encephalitis).
The result of the destruction of striatal neu-
rons is chiefly an increased inhibition of neu-
rons in the subthalamic nucleus that normally
activate inhibitory neurons in the substantia
nigra (p.r.). This leads to disinhibition of cells
in the thalamus, resulting in sudden, erratic,
314 and involuntary movements that are normally
suppressed by the basal ganglia.
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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