126
UNIT 2
Basic Tissues
Central Nervous System
Figure 7-9A.
Spinal cord.
Myelin stain,
3
7
In this section through an upper thoracic level of the
spinal
cord
(Fig. 7-4), the
white matter
(± ber pathways) has been
stained dark brown with a myelin stain. The
gray matter
is a region of densely packed neuron cell bodies, and this
stain has consequently left the gray matter in the center of
the cord relatively unaffected. The
anterior horn
of the gray
matter contains motor neurons that innervate muscle ± bers;
the
posterior horn
contains interneurons in both sensory
and motor pathways. The white matter consists of nerve
± bers carrying sensory information from receptors in skin
and muscles up to the brain (e.g., the
gracile fasciculus
) or
nerve ± bers carrying motor information down from the
brain to interneurons and motor neurons in the gray matter
of the spinal cord (e.g., the
corticospinal tract
). The
red rect-
angle
indicates the position of the tissue in Figure 7-9B that
has been stained with a Nissl stain for neuron cell bodies.
White matter
(axons)
Gray matter
(neuron cell bodies)
Posterior
Gracile
fasciculus
Posterior
horn
Anterior
horn
Corticospinal
tract
Anterior
A
Gray matter
Glia cell nuclei
Capillary
Axon
White matter
Neuron cell bodies
B
Figure 7-9B.
Spinal cord.
Nissl stain,
3
136
Nissl stains
, such as
thionin
or
cresyl violet
, react with
nucleic acids
(RNA, DNA) and, therefore, stain the
rough
endoplasmic reticulum
,
nuclei
, and
nucleoli
of neurons.
This renders the neuron cell bodies visible, along with the
nuclei of glial cells
and nuclei of epithelial cells in blood
vessels. The large cell bodies in this section belong to motor
neurons in the anterior horn of the
spinal cord
(
red rect-
angle
in Fig. 7-9A). Also visible are the nuclei of glial cells
(
astrocytes
and
oligodendrocytes
) in the
gray matter
on
the left side of the picture and in the
white matter
on the
right side of the picture (
small arrows
). It is important
to keep in mind when looking at myelin-stained sections
such as in Figure 7-9A that the light-colored areas, where
nothing seems to be stained, are in fact ± lled with neuron
cell bodies similar to the ones illustrated here.
C
Figure 7-9C.
Neurons in the reticular formation of
the brainstem.
NADPH histochemical stain,
3
68
Neurons
use a wide variety of
neurotransmitters
. In
addition to stains that react with structural components
of a nerve cell, it is possible to use
histochemical reac-
tions
to visualize the presence of particular neurotrans-
mitters. This photomicrograph illustrates an example of
such a reaction, in which only those neurons that generate
the neurotransmitter
nitric oxide (NO)
are visualized. In
this case, an enzyme necessary for the synthesis of NO,
NADPH
diaphorase
, was labeled using a blue chroma-
gen (colored substance). The neurons are colored in their
entirety because NO is a novel neurotransmitter that is not
bound in vesicles as are most neurotransmitters, but rather
is synthesized everywhere in the cell and leaks through the
cell membrane when it is released. It often functions to
modulate the action of other neurotransmitters.
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