Age-associated and cell-type specific changes in NGF requirement for neurite regeneration from trigeminal ganglion cells of the shrew (Suncus murinus).

Low density (20-50 cells/cm2), dissociated cultures of trigeminal ganglion (TRG) cells of the shrew, were made in a serum-free medium, and neurite growth was compared across ages of the animal and between NGF-free and NGF-rich conditions. TRG cells from newborn shrew (0-3 days old), which grew long neurites in an NGF-rich medium, failed to grow any neurites in an NGF-free medium. In contrast, TRG cells from aged shrew (16-19 months), which grew neurites without NGF, exhibited no further increment in neurite length when NGF (50-200 ng/ml) was added to the culture medium. TRG cells from adult shrew (4-5 months) were revealed to be a mixture of NGF-dependent and NGF-independent cells. The NGF-dependent cells (20% of the population) had large-sized somata of 24-32 microns diameter (L-type cells) and 2-7 long neurites enriched with arborizations. The remaining NGF-independent cells (80%) had small-sized somata (15-25 microns, S-type cells), and grew 1-3 neurites with a small number of arborizations. These findings suggest that the primary sensory neuron of the shrew has a cell-type specific critical period in the aging process with respect to the requirement of NGF for neurite promotion.