Brain‐derived neurotrophic factor stimulates neurite outgrowth in a calretinin‐enriched neuronal culture system

A calretinin enriched cell culture system which comprised approximately 40% of the total neuronal population of the E14 rat embryo was established from the region of the thalamic eminence (TE), and the effects of several neurotrophins on the neurite growth of calretinin‐immunoreactive (CR‐IR) neurons was investigated. A 4‐day treatment of BDNF significantly increased the ratio of CR‐IR to microtubule‐associated protein 2‐immunoreactive neurons at concentrations between 50 and 250 ng\ml. IGF‐I at 100 ng\ml and TGF‐ at 250 ng\ml also increased this ratio. None of the neurotrophins examined increased the number of primary neurites. BDNF did, however, increase the number of secondary neurites. BDNF‐treated primary and secondary neurites were also significantly longer than neurites from neurons in control cultures. IGF‐I elicited an increase in primary neurite length, but did not affect either number or length of secondary neurites. TGF‐α had no effect on either number or length of the primary and secondary neurites. These results indicate that the maturation and development of CR‐IR neurites is specifically affected by BDNF. It is suggested that BDNF increases the CR concentration above the threshold of detection by immunohistochemistry in cells and stimulates the sprouting of secondary CR‐IR neurites.