Pc12

15-20 ^ma

0.5-1 ^m

< 30 ^m/day

B35 neuroblastoma

10-20 ^m

0.5-1 ^m'

30 ^m/day

These values are intended to help distinguish between particularly fast- or slow-moving growth cones in choosing a culture system.

"Because these neurons can develop significantly elongated cell bodies, diameters are approximate or listed as length x width. bGrowth rates for axons in culture vary widely with culture conditions, substrata, and time in culture. ^Different classes of neurons in these cultures can be distinguished by their diameters; ciliary neurons average 23 ^m in diameter whereas choroid neurons average 13 ^m in diameter. dA rough net rate for pulsatile growth averaged over 1-2 days. ePurkinje neurons start out at about 8 ^m in diameter when plated and mature to larger sizes by 21 days in culture. fOn a highly adhesive substrate, growth rates are low, but increase > 10-fold on laminin. gThe primary explanted axon has a large diameter and forms a large growth cone that is not motile. hIn a presence of a Helisoma brain extract, small motile growth cones sprout from the soma and axon tip. 'Differentiated with dibutryyl cyclic AMP. 1 The rate of growth is faster in the region of another neuron or guidepost cell and slower when extending along the epithelium.

very large growth cones such as Aplysia (Schaefer et al., 2002) and Heliosoma (Chapter 9) have proven useful for light microscope studies. A variety of smaller vertebrate neurons, both central and peripheral, have been used to study protrusive activity, including rodent sensory (Lewis and Bridgman, 1992) and cortical (Boukhelifa et al., 2001) neurons, and chick sympathetic (Dailey and Bridgman, 1989) and spinal motor (Brown et al., 2000) neurons. Because growth cones of some central neurons advance with characteristics different than those of peripheral neurons in culture, rat hippocampal neurons have been useful subjects despite their small size (Ruthel and Banker, 1999).

3. Development of Cell Polarity

Several kinds of neurons can be induced to differentiate into their completely polarized form in culture, producing both an axon and dendrites. These include

Table III

Developmental Properties of Cultured Neurons

Table III

Developmental Properties of Cultured Neurons

Name

No. of cells available

Minimum density of culturesa

Maximum time in culture4

Chick sensory (DRG)

104 per ganglion

10,000/cm2

1-5 days

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