Presence and disappearance of nerve growth factor receptors on sensory neurons in culture

The age-dependent presence of nerve growth factor (NGF) receptors on neurites of sensory neurons of dorsal root ganglia removed from chicks of different embryonic ages and subsequently kept in culture with NGF and/or brain extract has been investigated by autoradiography. Most of the neurons removed at embryonic Day 10 (E10), (82–95%) can be labeled with iodinated NGF, irrespective of whether they are selected for survival by means of NGF, brain extract, or both. However, when neurons are isolated from E16 chicks and maintained in culture with brain extract, only about 28% of the neurons have NGF receptors at reduced density. This percentage is higher than that expected if the number of neurons surviving with NGF would be exactly correlated with the number of neurons displaying NGF receptors: at E16 only about 5% of the neurons survive with NGF alone. In order to determine if the decrease in the number of neurons displaying NGF receptors also occurs in vitro, E10 neurons were cultured for various periods of time either with NGF or brain extract. Most of the neurons grown with NGF do not lose their NGF receptors. In contrast, the majority of the neurons grown in the presence of brain extract lose their receptors: after 6 days in culture, only about 25% of the neurons can be labeled with NGF. It is concluded that in vitro, a maturation with regard to the NGF receptor occurs in the presence of brain extract similar to that observed in vivo.