Beta-nerve growth factor in developing mouse cerebral cortical synaptosomes: measurement by competitive radioimmunoassay and bioassay.

The existence of beta-nerve growth factor (beta NGF) in mouse cerebral cortical synaptosomal extracts was assessed using a newly developed radioimmunoassay and by bioassay. Displacement curves of labeled beta NGF in the radioimmunoassay by synaptosomal extracts were parallel to the beta NGF standard curves. In contrast, both mitochondrial and nonsynaptosomal extracts produced displacement curves in the beta NGF radioimmunoassay which were nonparallel to standard beta NGF. Intraventricular injections of purified beta NGF in amounts 5 and 100 ng/mouse (six to 120 times that of whole brain beta NGF concentrations) did not alter the endogenous synaptosomal beta NGF concentrations. Synaptosomal extracts contained beta NGF in relatively higher concentrations than the extracts of whole brain or cerebral cortex. Synaptosomal beta NGF levels undergo a developmental change. The beta NGF concentrations were highest in synaptosomal extracts of 12-day-old mouse cerebral cortex (the youngest age studied), and levels decreased with increasing age. Synaptosomal extracts of 12-day-old mouse cerebral cortex produced neurite outgrowth in the pheochromocytoma cell line 12 bioassay system and this response was completely inhibited by beta NGF antibodies. In the pheochromocytoma cell line 12 cell bioassay, synaptosomal extracts also caused cell-cell aggregation which was unaffected by beta NGF antibodies. These results provide evidence for the existence of beta NGF in relatively high concentration in nerve terminals of mouse cerebral cortex.