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( cont'd )
E9 chick brain
Oculomotor nerve (III)
Ciliary ganglion
Ca-dependent potassium
current ( I k(Ca) )
Total current
Ca 2+ free current =
No calcium
5 nA
ganglion cells
(4 days in vitro)
5 ms
Iris extract
No calcium
FIGURE 8.D An extract from iris induces calcium-dependent potassium currents. A. Ciliary ganglion
neurons, which innervate the iris, were isolated from E9 chicks and placed in dissociated culture. B. When
the cultures are grown in control culture medium, one can record very little calcium-dependent potassium
current (I K(Ca) ). This is shown by recording total current and subtracting the current in Ca ++ -free media. When
an extract from the iris was added to the cultured neurons, a much larger I K(Ca) is subsequently recorded.
(Adapted from Subramony et al., 1996)
in I K[Ca] that depends on transcription (Lhuillier and
Dryer, 2000). These results suggest that retrograde signals
can affect the translation, insertion or modification of
potassium channels with a very short latency. The regula-
tion of I K[Ca] , and many other channels, is likely to depend
on several signals. For example, there is a second
isoform of TGFb that inhibits the functional expression of
I K[Ca] , and an afferent-derived signal (neuregulin-1) partic-
ipates in upregulating this channel (Cameron et al., 1999,
emerge from this section. First, neurons manufacture
many of the synaptic building blocks even before
making contact with one another. Second, intercellular
signaling induces the differentiation of newly formed
synapses from the moment of contact. Signals from glia,
extracellular matrix, and neighboring neurons all par-
ticipate in synaptogenesis. Third, synapses do not func-
tion in a mature manner for quite some time after they
are fabricated. We will discuss how their functional
properties change with development and how this
might explain some of the behavioral limitations that
young animals display (see Chapter 10).
Studies of the synapse began in earnest during the
early 1950s with the arrival of two new techniques.
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