Distribution of nerve growth factor in chick embryo sympathetic neurons in vitro

An improved procedure for the immunohistochemical localization of nerve growth factor-like immunoreactivity

Nerve growth factor (NGF) is a survival factor required by a number of neuronal populations including most post-ganglionic sympathetic neurones. NGF has been detected and quantified in many tissues but there is little information regarding its cellular localization. Although it has been argued that histological detection has proven difficult due to the low levels of NGF present, other factors may contribute to prevent its identification. In the present study, we report a method for the histological detection of NGF-like immunoreactivity in the rat superior cervical ganglia (SCG). Adult Wistar-Kyoto rats were perfused briefly with either a high or low pH buffer prior to fixation and routine immunohistochemistry. Polyclonal antibodies to native mouse NGF used in the present study recognized mouse NGF but not recombinant human neurotrophin 3 (rhNT3) or brain-derived neurotrophic factor (rhBDNF) by immunoblot analysis. NGF-like immunoreactivity was localized to most sympathetic neurones. Immunoreactivity was detected in the cytoplasm with dense labelling around nuclei. No stain was seen in sections incubated with normal sheep IgG or from animals perfused with phosphate buffer (pH 7.4) prior to fixation. In addition, axotomy resulted in the disappearance of NGF immunoreactivity which was confirmed by biochemical quantification. Finally, no NGF immunoreactivity was found in neurones of rats treated systemically with NGF antiserum 3 days earlier. Possible mechanisms underlying the improvement of NGF immunohistochemistry by pH manipulation before fixation are discussed.

Production and transport of endogenous trophic activity in a peripheral nerve following target removal

High concentrations of trophic factor for sympathetic neurones were found in the discrete nerve which innervates the expansor secundariorum muscle of the chicken wing. Mouse nerve growth factor (NGF) was additive with nerve extract in allowing survival of sympathetic neurones. Antiserum to NGF, while inhibiting outgrowth in response to NGF, only partially blocked survival promoted by the nerve extract. In these characteristics, the nerve extract resembled the previously characterized activity of its target organ. However, after surgical removal of the muscle there was no decrease in the concentration of trophic factors in the nerve 7 days later. Likewise sectioning, crushing or removing a piece of nerve 1 cm from the muscle had little effect on trophic levels after muscle removal. Retrograde transport of the activity occurred in the nerve even in the absence of the muscle. Distal to ligatures placed on the nerve stump 24 h earlier, 60% of the trophic activity was inhibited by an antiserum to mouse NGF suggesting that a chicken form of the molecule is present and transported. In culture, cells of the nerve sheath produced trophic factors, and the rate of production increased greatly during the first 24 h of incubation. Two conclusions are made: the major source of trophic activity in the nerve is Schwann cells and at least two molecules are present, one of which is a chicken form of NGF.

Receptor binding activities of biotinylated derivatives of beta-nerve growth factor

beta-nerve growth factor (NGF) was modified by biotinylation via carboxyl group substitution (C-bio-NGF) using biotin hydrazide and the coupling reagent 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide, under reaction conditions that yielded an average of 3 biotin additions per NGF subunit. NGF was also biotinylated through amino group substitution, using N-hydroxysuccinimidyl biotin, to produce derivatives with ratios of one, two, and four biotin moieties per NGF subunit (N-bio-NGF). The various biotinylated NGF derivatives were compared with native NGF for their capacity to compete with 125I-NGF for binding to NGF receptors on rat pheochromocytoma (PC12) cells at 4 degrees C. On the basis of such radioreceptor assays, C-bio-NGF was as effective as native NGF in binding to NGF receptors. C-bio-NGF was also as effective as native NGF in promoting neurite outgrowth from PC12 cells. In contrast, N-bio-NGF containing one biotin per NGF subunit was only 28% as active in binding as native NGF. Increasing the biotin:NGF ratio to 2 to 4 further decreased receptor binding to 13% and 6%, respectively, as compared to native NGF. Once bound to cells, C-bio-NGF had the capacity to mediate the specific binding of 125I-streptavidin to PC12 cells. This binding of streptavidin was prevented by excess native NGF and by antiserum to NGF, but not by RNase A, insulin, cytochrome c, or nonimmune serum. In addition, a variant PC12 line lacking functional NGF receptors was not labeled by 125I-streptavidin after prior incubation with C-bio-NGF.

Ultrastructural studies on the intracellular fate of 125I-nerve growth factor in cultured rat sympathetic neurons

Primary cell cultures of sympathetic neurons from rat were exposed to 125I-nerve growth factor (NGF) and the fate of the NGF in the cell was followed using electron microscopic autoradiography. The intracellular localization of NGF was determined in the cell bodies and in the proximal neurites of neurons that had been grown in three-chamber dishes, following 5 or 24 hr of retrograde transport of NGF from the distal portions of the neurites. Label in the proximal neurites was predominantly associated with lysosomes and multivesicular bodies (MVBs), and at 5 hr elongated tubular elements were especially heavily labeled. Most of the label in the cell bodies was concentrated in lysosomes and MVBs. Lysosomes accounted for the largest fraction (45-60%) of the grains in the cell body, with a labeling density (LD = % grains/% area) of 3-5, while MVBs accounted for 5-10% of the grains with an LD of 5-20. We observed no evidence of nuclear labeling after 5 or 24 hr of retrograde transport. Mass cultures of neurons were incubated for 22 hr with NGF in the presence of the lysosomal inhibitors chloroquine (CQ, 0.05 mM) or methylamine (MA, 10 mM). In both agents the lysosomes were swollen with membranous material but still sequestered NGF, especially in CQ where the lysosomes were associated with almost 65% of the grains and had an LD of 6. CQ and MA had different effects on the morphology of the MVBs: in CQ they were few in number and compact while in MA they were numerous and appeared swollen and vacuolated. We observed no evidence for the nuclear accumulation of NGF even in the presence of the lysosomotropic agents.

Characteristics of the association of nerve growth factor with primary cultures of rat sympathetic neurons

Long-term primary cultures of rat sympathetic neurons require NGF for survival and development. The kinetics of the interaction of 125I-NGF with sympathetic neuron cultures suggests the presence of diffusional barriers preventing a determination of true dissociation and association rate constants. Although the observed rate constants do not accurately reflect the microscopic interaction of NGF with receptor, the ratio of the observed rate constants does provide a good estimate of the KD. This value (1 X 10(-9)M) agrees with earlier steady state measurements of the KD. The association of 125I-NGF with neuronal cultures is temperature-dependent with internalization and retrograde transport occurring at 37 degrees C. The retrograde transport of 125I-NGF in compartmentalized neuronal cultures is concentration dependent and saturates at about 100 ng/ml (4 X 10(-9)M). The amount of 125I-NGF accumulated by retrograde transport appears to be increased subsequent to a period of NGF-starvation. The increase in uptake does not appear to be due to an increase in NGF receptor number since the number of binding sites is not greatly increased upon NGF starvation.