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A
P7
P21
Noradrenergic
Cholinergic
B
Transplanted foot pad tissue (cholinergic target)
Thorax (adrenergic target)
Noradrenergic
Cholinergic
Noradrenergic
Transplanted parotid gland tissue
(noradrenergic target)
Sweat gland tissue
Foot pad tissue (cholinergic target)
Cholinergic
Noradrenergic
Cholinergic
FIGURE 4.16 Control of transmitter phenotype by sweat glands in the footpad. A. A noradrenergic
neuron begins to innervate developing sweat glands. As it does so, it switches and becomes cholinergic. B.
Neurons that innervate hair follicles are noradrenergic, yet when a piece of footpad containing sweat glands
is transplanted into hairy skin, the local neurons that innervate the transplanted sweat glands become cholin-
ergic. Conversely, when a piece of parotid gland tissue, which is normally innervated by adrenergic neurons,
is transplanted to the footpad, the local neurons that innervate it are noradrenergic. (After Landis, 1992)
by all migrating neural crest cells, so cells are sensitive
to Nrg-1 as soon as they arrive at their destination
but only the late cells to migrate in, those that do so
after many neurons are already differentiating, see
substantial amounts of Nrg-1. This is one reason
why glial cells differentiate later than neurons.
Another, as in the retina, has to do which Notch. Notch
activation drives glial determination in crest-derived
cells. As neurons begin to differentiate, they express
Delta, which through Notch activation turns off
proneural gene activity in neighboring cells, and thus
forces them down a non-neural pathway (Morrison,
2001).
C OMPETENCE AND HISTOGENES IS
The cells of the cerebral cortex are generated near
the ventricular surface of the closed neural tube. As
described in Chapter 3, the cell divisions of cortical
neuroblasts give rise to postmitotic neurons that
 
 
 
 
 
 
 
 
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