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Previous studies have shown that nerve growth factor (NGF) produces a selective induction of tyrosine hydroxylase (TH) in peripheral adrenergic neurons and that NGF is transported retrogradely with a high selectivity from the adrenergic nerve terminals to the perikaryon. In order to investigate the biological importance of retrograde NGF transport, the following experiments have been performed; (a) effect of NGF on TH activity in superior cervical ganglia (SCG) after unilateral injection into the anterior eye chamber and the submaxillary gland; and (b) effect of systemic injection of NGF on TH activity in SCG after blockage of retrograde axonal transport by axotomy. After unilateral injection of NGF into the anterior eye chamber and submaxillary gland of both 8-10-day-old rats and adult mice, the increase in TH activity in the SCG was considerably larger on the injected than on the non-injected side although the adrenergic neurons supplying the two organs do not account for more than 25% of the total number of adrenergic neurons in the SCG. A direct diffusion mechanism could be excluded by the fact that unilateral local injection of [125 I] produced no significant side difference in the accumulation of radioactivity in the SCG 2 after injection whereas after 14 h there was a several-fold difference between the injected and non-injected side. Moreover, the nodose ganglia which are located very close to the SCG exhibited no statistically significant difference in the accumulation of radioactivity at any time. Forty-eight hours after subcutaneous injections of 10 mg/kg of NGF the increase in TH activity of the SCG amounted to 154% on the intact side and to 92% on the axotomized side. However, these experiments do not permit decisions about the extent the axotomy, as such, impaired the response to NGF. It is concluded that the biological effect of NGF results to a considerable extent, from the moiety which reaches the cell body by retrograde transport from the nerve terminals.

In the present experiments the uptake and retrograde axonal transport of antibodies to dopamine beta-hydroxylase (DBH) in adrenergic neurons was studied. When partially purified labelled antibodies to DBH were injected unilaterally into the vicinity of the adrenergic nerve terminals in the iris, radioactive substances accumulated preferentially in the superior cervical ganglia of the injected. By SDS (sodium dodecyl sulfate) gel electrophoresis and immunoprecipitation it could be shown that the accumulated radioactivity in the superior cervical ganglion represented antibodies to DBH. This retrograde accumulation was greatly reduced by colchicine, axotomy or destruction of the adrenergic nerve terminals by 6-hydroxydopamine. The rate of retrograde transport was the same as that of nerve growth factor (NGF) and tetanus toxin in sympathetic neurons. The retrograde transport of antibodies was confined to sympathetic neurons and could not be detect in either sensory or motor neurons.

Previous investigations have shown that tetanus toxin is transported retrogradely in all peripheral neurons whereas the transport of NGF is confined to adrenergic and sensory neurons. Other macromolecules with molecular weights and general physiochemical properties similar to NGF and tetanus toxin (e.g., cytochrome C, insulin, horseradish peroxidase and bovine serum albumin) are not transported to a detectable extent if injected in comparable molar concentrations. For tetanus toxin, which is transported in all peripheral neurons, it has be assumed that it's retrograde transport depends on properties common to all neurons. In view of the relatively high ganglioside content of the neurons and the high affinity of tetanus toxin for the trisialoganglioside GT1, we studied the influence of gangliosides on the retrograde transport of tetanus toxin as compared to NGF. We included into the study cholera toxin which is known to have a high affinity for the monosialoganglioside GM1 and wheat germ agglutinatinin, a lectin with specific affinity for glycoproteins with N-acetyl-glucosamine residues. Both cholera toxin and wheat germ agglutinin were transported efficiently in all peripheral neurons. Preincubation of 125I-cholera toxin with monosialoganglioside GM1 completely blocked its retrograde axonal transport. The transport of NGF and wheat germ agglutinin was affected neither by various purified gangliosides nor by a mixture of bovine brain gangliosides. The transport of tetanus toxin was only reduced by 50% both by the trisialoganglioside GT1 and the bovine ganglioside mixture.

Nerve growth factor is retrogradely transported in sympathetic and sensory neurons throughout life. Although this transport is known to be biologically significant in sympathetic neurons, such a function was not yet known in sensory ganglia. By using the neuropeptide substance P as a biochemical marker, we show that sensory ganglia from newborn and adult rats respond in nerve growth factor and that its retrograde axonal transport is biologically relevant, as indicated by an increase in substance P and in general protein content.

In previous studies it has been shown that nerve growth factor (NGF) is taken up with a high selectivity by adrenergic nerve terminals and is transported retrogradely to the perikaryon11,22. It was the aim of the present experiments to investigate whether the sensory neurons exhibit the same high degree of selectivity for retrograde transport throughout the whole life cycle, although it is known that their dramatic response to NGF is confined to a short period of ontogenetic development. Unilateral injection of [125I]NGF into the forepaw of adult rats was followed by a preferential accumulation of radioactivity in the sensory ganglia (C6-C7) of the injected side. However, this preferential accumulation was not detectable earlier than 6 h after injection and reached a maximum (ratio between injected and non-injected side, 5:1) after 11-16 h. Transection of the plexus brachialis abolished and local administration of colchicine prior to that of [125I]NGF greatly reduced the preferential accumulation of radioactivity in the ganglia of the injected side. The rate of retrograde transport of NGF in sensory neurons was calculated to be 13 mm/h which is about 5 times faster than that in adrenergic neurons. The selectivity of this retrograde transport was demonstrated by the fact that injection of 125I-labeled bovine serum albumin and cytochrome c did not result in a preferential accumulation of radioactivity in the sensory ganglia of the injected side. Light microscopic autoradiography revealed heavily labeled cells in the sensory ganglia (C6-C7) of the injected side after administration of [125I]NGF into the forepaw. Only cells belonging to the large cell type were labeled. Prolonged (7 mug/g/day over 5 days) injection of NGF into the forepaw of 10-day-old rats did not result in a hypertropic response of the sensory neurons as far as can be judged from morphometric studies at the light microscopic level.