Survival and morphology of auditory neurons in dissociated cultures of newborn mouse spiral ganglion.

We have systematically characterized neuronal survival and growth in cultures derived from newborn/postnatal day 1 mouse cochlea. Dissociated cultures of the cochlear spiral ganglion provide an experimental environment in which to examine molecular mechanisms of survival, development and physiology of auditory neurons. To relate survival to the total number of neurons present in the source tissue, three cochleas from different newborn CD-1 mice were embedded in Araldite resin and serially sectioned at 5 mum thickness. All neurons were counted. To avoid overcounting, each section served as a lookup section for the next, giving 8240+/-423 (S.D.) neurons per ganglion. Cultures maintained in the presence of adjacent non-neural tissue, brain-derived neurotrophic factor, neurotrophin 3, leukemia inhibitory factor (LIF) and 10% fetal bovine serum returned the best overall survival (30%) at 42 h post-plating. Best overall survival required the continuous presence of a serum component(s) larger than 100,000 MW. Plating efficiency (number of neurons that attach to the well after 4 h) was similar in the presence or absence of LIF. Inclusion of LIF maintained 100% survival of plated neurons over 42 h of culture; without LIF, a large fraction of the neurons did not survive. LIF appeared to maintain survival by preferentially preserving a population of bipolar neurons, while having little effect on the number of monopolar neurons. This work provides quantitative measures of survival and morphology of auditory neurons in vitro. The results support the idea that survival of spiral ganglion neurons in vivo may depend on interactions with adjacent, non-neural tissue and raise the possibility that maintenance of bipolar morphology after hair cell damage may require biochemical mechanisms in addition to those induced by neurotrophins.