A survival factor for sympathetic neurons from avian smooth muscle

A ciliary neuronotrophic factor from peripheral nerve and smooth muscle which is not retrogradely transported

We have found that a CNTF-like molecule which supports ciliary and sympathetic neurons is not retrogradely transported in either sympathetic or parasympathetic nerves. The factor has an apparent Mr of 21 kDa, a pI of 4.9, and is present in peripheral nerves and smooth muscle of the chick. Our experiments indicate that CNTF-like activity does not accumulate on the distal side of ligated chick expansor nerves. In contrast, there is a clear accumulation of NGF. The activity further differs from NGF in that it is not removed from a smooth muscle of the chick wing by innervating sympathetic fibers. Transection of these fibers does not lead to an accumulation of ciliary activity in the expansor secundariorum muscle, suggesting that neurons do not actively deplete the muscle of factor by retrograde transport. Finally, recombinant CNTF or semi-purified preparations of CNTF-like activity labelled with 125I were not transported to the ciliary ganglion of chicks following injection of biologically active material into the eye. Our results suggest either that endogenous CNTF does not act as a survival factor in vivo, or that retrograde transport is not a property inherent to all neuronotrophic molecules.

Chicken NGF and non-NGF trophic factor synthesis and release by sciatic nerves in vitro

The time course of production and release of nerve growth factor (NGF) and non-NGF neuronotrophic factors for sympathetic neurons by chicken and rat sciatic nerves in culture was examined. These tissues actively synthesize and release neuronotrophic activity as metabolically poisoning nerves with azide dramatically reduced the amount of trophic activity released into the culture medium. The sustained release of this activity also was shown to be dependent on the presence of low-molecular-weight dialysable molecules present in foetal calf serum and amniotic fluid from day 11 chicken embryos. Affinity-purified antimouse NGF antibodies were used to show that sciatic nerves in culture release both NGF and non-NGF trophic factors. These antibodies inhibited all bioactivity of both mouse NGF and of a partially purified preparation of chicken NGF. Immunoblot studies confirm that the antibodies recognize both rodent and avian NGF. Excess antibody inhibited only about 50% of the trophic activity in media conditioned over rat or chicken nerves for the first 24 hr. Relatively similar amounts of this non-NGF trophic activity were released throughout 6 days in culture, and this trophic activity kept sympathetic neurons alive in culture in the absence of NGF for more than 4 days. NGF levels were quantified with a two-site enzyme-linked immunoassay and found to parallel changes in NGF bioactivity. Rat nerves released increasing amounts of NGF with time in culture. Whole chicken sciatic nerves, however, released decreasing amounts of NGF with time in culture, but when these nerves were desheathed by removal of the epineurium and attached tissue, the pattern of NGF release was similar to that observed in the smaller rat sciatic nerves. These studies therefore characterize antibodies recognizing chicken NGF, demonstrate that peripheral nerve tissue synthesize trophic factors other than NGF, and identify factors that influence NGF synthesis.

Endogenous chicken nerve growth factor from sheath cells is transported in regenerating nerve

We report the presence of endogenous nerve growth factor (NGF) in chicken peripheral nerve. The molecule has been detected with antibodies to mouse salivary gland NGF, using immunohistochemical and immunoelectrophoretic techniques. Previous studies have shown that these antibodies inhibit the survival activity of extracts of chicken peripheral nerve. The NGF accumulated distal, but not proximal, to a ligature placed on a peripheral sympathetic nerve demonstrating that it was retrogradely transported. This transport was detected in intact nerve fibers as well as in nerves from which the peripheral target had been ablated 6 hr or 7 days previously. The results indicate that avian NGF is present in adult chicken peripheral nerves and that this molecule shares antigenic determinants with the mouse molecule. The results further demonstrate that regenerating neurons retrogradely transport NGF supplied by cells within the peripheral nerve (presumably Schwann). The possibility that these cells also provide NGF to intact neurons is discussed.

Sympathetic neuronotrophic activity in the pulp of the cat canine tooth

Extracts of these dental pulps from adult cats contained a non-dialysable agent or agents which could support neurone survival and neurite development for at least three days in neurone-enriched cultures of sympathetic ganglion cells from 11-day chick embryos. The neurone survival-promoting activity differed from nerve growth factor (NGF) in that: (1) anti-mouse NGF serum did not inhibit it; (2) nearly all ganglionic neurones survived in optimum concentrations of pulp extract, whereas only about 35 per cent were supported by NGF; and (3) cell bodies of NGF-supported neurones were markedly larger than in neurones supported by pulp extracts. The neuronotrophic activity in individual dental pulps was highly variable among different cats, but similar between mandibular canines from the same animal. Smaller pulps had higher concentrations of trophic activity than larger ones. Gingival tissue and the anterior belly of the disgastric muscle contained little neuronotrophic activity.

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.

Nerve growth factor immunohistochemistry and biological activity in the rat iris

Nerve growth factor (NGF) production in the cultured rat iris was examined using immunohistochemistry and bioassay of irides and conditioned media. NGF immunoreactivity increased steadily with days in culture so that the intensity of staining was maximal after 6 days of culture. The localization was shown to be sensitive to the presence of cross-linking fixatives such as formaldehyde and glutaraldehyde and this effect was only partially alleviated by the use of very high concentrations of antibodies. NGF immunoreactivity was localized in Schwann cells and possibly nerve axons, but with no antigen detectable in smooth muscle fibres. Media conditioned over irides initially supported a high percentage of dissociated sympathetic neurons, but the number supported decreased with time in culture until day 4. Moreover, the use of antibodies to NGF allowed the detection of at least two types of neuronotropic activity, NGF accounting for at least 94% of the total trophic activity present after 4 days of culture. These findings provide support for the proposal that Schwann cells produce NGF and question the accepted hypothesis that the molecule is produced by smooth muscle fibres as a peripheral maintenance factor for sympathetic and sensory nerves. The results also suggest that two survival factors may be involved in the regulation of sympathetic function.

Increase in neuronotrophic activity during the period of smooth muscle innervation

The expansor secundariorum is a unique smooth muscle of the avian wing that receives a dense sympathetic innervation and contains high concentrations of survival factors for sympathetic neurons. In the present study it has been possible to simultaneously examine the appearance of the neuronotrophic activity and the arrival of nerve fibres during the period of innervation. The results show that catecholamine containing nerve fibres can first be detected within the muscle on the fourteenth day of incubation (stage 40) followed by a rapid increase in the density of fibres during the next few days until the adult pattern is reached shortly before hatch. Biochemical estimation of the innervation process by measurement of dopamine beta-hydroxylase activity was supported by the histochemical findings. Estimation of neuronotrophic activity revealed that muscle from stage 40 embryos contains only low levels of activity which increases rapidly as innervation proceeds and further, that this increase in neuronotrophic activity was directly correlated with the dopamine beta-hydroxylase activities. Possible mechanisms regulating this dramatic increase in the specific activity of trophic factors are discussed.

Regulation of sympathetic trophic factors in smooth muscle

The level and nature of trophic activity present in the chicken expansor secundariorum muscle has been shown to be altered by denervation. This muscle receives a dense, sympathetic innervation and contains high concentrations of trophic factors, which were found to be immunologically and functionally distinct from mouse Nerve Growth Factor. In young birds, denervation increased the number of neurons which could be supported by muscle extract. This difference was apparent with regard to E8 to E16 sympathetic neurons. Innervated but not denervated extract was additive with NGF in promoting neurite outgrowth. In contrast, when extracts of denervated and innervated muscle from mature birds were examined, no difference was seen in the number of neurons supported by each extract. However when the denervated and innervated extracts from mature birds were combined more neurons were supported than by a saturating dose of either extract alone. Furthermore, muscle from mature birds responded to denervation only between 2 and 9 days, whereas in young birds the effect was apparent for at least 3 weeks. Analysis of intact, control muscles during the first 8 weeks posthatch demonstrated that the number of neurons that could be supported by the individual extracts varied with the age of the bird. It is concluded that denervation does not in all instances lead to an increase in trophic activity, but does produce a change in the nature of the activity present, such that a different neuronal subpopulation may be supported.(ABSTRACT TRUNCATED AT 250 WORDS)

Tenotomy decreases sympathetic neuronal survival factors in avian smooth muscle

The expansor secundariorum of the chicken wing has a high concentration of survival factor activity for sympathetic neurons. The effect of tenotomy on this activity has been examined in newly hatched and older birds. Survival factor activity was assayed with dissociated embryonic neurons and found to be decreased after tenotomy to low levels in the newly hatched but not the older birds. No change in dopamine beta-hydroxylase concentration was detected, suggesting that tenotomy does not significantly alter impulse activity in the sympathetic innervation. The results are compared with findings after tenotomy in skeletal muscles and contrasted with increased survival factor activity produced by denervation of the expansor secundariorum.

Neurite-promoting factors from a sympathetically innervated target tissue

Previous studies have demonstrated that various cell types can produce and secrete polyornithine-attachable neurite promoting factors when cultured. This study describes an endogenous source of polyornithine-attachable neurite promoting factors. The active material extracted from an avian smooth muscle, the expansor secundariorum, is able to enhance neurite outgrowth from embryonic chick sympathetic neurons when applied to a polyornithine substrate. Unlike other polyornithine attachable factors, the material is also able to support the neurons for at least 72 hr in the absence of any added survival factors. Partial purification of the active material was achieved by affinity chromatography on polyornithine-Sepharose. The findings support the proposal that neurite promoting factors may have a definite physiological role in addition to their well established in vitro activity.

Production of nerve growth-stimulating factor(s) from chick embryo heart cells. Use of Cytodex 3 microcarriers and serum-free media

Medium conditioned by embryonic chick heart cells is known to support extensive neurite outgrowth from autonomic and sensory neurons. In the present report we describe the use of microcarrier cell culture with serum-free media to scale up the production of the nerve growth-stimulating factors. A growth medium composed of DME /F10 supplemented with insulin, transferrin, human serum albumin and fibronectin in combination with a low molecular weight (MW) fraction of fetal calf serum (FCS) or a mixture of FGF, dexamethasone, calmodulin and thrombin supported the heart cell proliferation at a rate similar to that of medium with 10% FCS. Furthermore, the level of successively accumulated nerve growth activity measured in a bioassay with sympathetic ganglia proved to be nearly equivalent to what was obtained when cells were grown in medium containing serum. The results confirm the potential of microcarrier cell culture in serum-free media for the production and subsequent recovery of a specific cell product.