Isoelectric focusing of the chick eye ciliary neuronotrophic factor

Ciliary neurotrophic factor stimulates neurite outgrowth from spinal cord neurons

Ciliary neurotrophic factor (CNTF) has been shown to promote the survival of motoneurons, but its effects on axonal outgrowth have not been examined in detail. Since nerve growth factor (NGF) promotes the outgrowth of neurites within the same populations of neurons that depend on NGF for survival, we investigated whether CNTF would stimulate neurite outgrowth from motoneurons in addition to enhancing their survival. We found that CNTF is a powerful promoter of neurite outgrowth from cultured chick embryo ventral spinal cord neurons. An effect of CNTF on neurite outgrowth was detectable within 7 hours, and at a concentration of 10 ng/ml, CNTF enhanced neurite length by about 3- to 4-fold within 48 hours. The neurite growth-promoting effect of CNTF does not appear to be a consequence of its survival-promoting effect. To determine whether the effect of CNTF on spinal cord neurons was specific for motoneurons, we analyzed cell survival and neurite outgrowth for motoneurons labeled with diI, as well as for neurons taken from the dorsal half of the spinal cord, which lacks motoneurons. We found that the effect of CNTF was about the same for motoneurons as it was for neurons from the dorsal spinal cord. The responsiveness of a variety of spinal cord neurons to CNTF may broaden the appeal of CNTF as a candidate for the treatment of spinal cord injury or disease.

Involvement of ras p21 in neurotrophin-induced response of sensory, but not sympathetic neurons

Little is known about the signal transduction mechanisms involved in the response to neurotrophins and other neurotrophic factors in neurons, beyond the activation of the tyrosine kinase activity of the neurotrophin receptors belonging to the trk family. We have previously shown that the introduction of the oncogene product ras p21 into the cytoplasm of chick embryonic neurons can reproduce the survival and neurite-outgrowth promoting effects of the neurotrophins nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), and of ciliary neurotrophic factor (CNTF). To assess the potential signal-transducing role of endogenous ras p21, we introduced function-blocking anti-ras antibodies or their Fab fragments into cultured chick embryonic neurons. The BDNF-induced neurite outgrowth in E12 nodose ganglion neurons was reduced to below control levels, and the NGF-induced survival of E9 dorsal root ganglion (DRG) neurons was inhibited in a specific and dose-dependent fashion. Both effects could be reversed by saturating the epitope-binding sites with biologically inactive ras p21 before microinjection. Surprisingly, ras p21 did not promote the survival of NGF-dependent E12 chick sympathetic neurons, and the NGF-induced survival in these cells was not inhibited by the Fab-fragments. The survival effect of CNTF on ras-responsive ciliary neurons could not be blocked by anti-ras Fab fragments. These results indicate an involvement of ras p21 in the signal transduction of neurotrophic factors in sensory, but not sympathetic or ciliary neurons, pointing to the existence of different signaling pathways not only in CNTF-responsive, but also in neurotrophin-responsive neuronal populations.

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.

ras p21 protein promotes survival and fiber outgrowth of cultured embryonic neurons

Although evidence obtained with the PC12 cell line has suggested a role for the ras oncogene proteins in the signal transduction of nerve growth factor-mediated fiber outgrowth, little is known about the signal transduction mechanisms involved in the neuronal response to neurotrophic factors in nontransformed cells. We report here that the oncogene protein T24-ras, when introduced into the cytoplasm of freshly dissociated chick embryonic neurons, promotes the in vitro survival and neurite outgrowth of nerve growth factor-responsive dorsal root ganglion neurons, brain-derived neurotrophic factor-responsive nodose ganglion neurons, and ciliary neuronotrophic factor-responsive ciliary ganglion neurons. The proto-oncogene product c-Ha-ras also promotes neuronal survival, albeit less strongly. No effect could be observed with truncated counterparts of T24-ras and c-Ha-ras lacking the 23 C-terminal amino acids including the membrane-anchoring, palmityl-accepting cysteine. These results suggest a generalized involvement of ras or ras-like proteins in the intracellular signal transduction pathway for neurotrophic factors.

Specific neurotrophic interactions between cortical and subcortical visual structures in developing rat: in vitro studies

We investigated the influence of different subcortical structures on the survival of specific populations of occipital cortex neurons developing in vitro. Explants of embryonic day 14-15 (E14-15) rat cortex were cultured for 5 days with explants of either diencephalon or optic tectum or another occipital cortex explant. Stereological analysis of the explants revealed that after 5 days in vitro (5 DIV) all the cortical explants contained equal proportions of healthy neurons, glia, neuropil, and degenerating profiles, regardless of the culturing conditions. In order to determine if different neuronal populations survived preferentially in the cortical explants as a result of the presence of potential target or afferent structures, we used HRP filling and 3H-thymidine labeling techniques. Specific differences in the morphology of the cells and their time of origin are found in the cortical explants. In the cortical explants cocultured with diencephalon (Cx + D) the cortical cells that survive tend to be round with small cross-sectional areas and have few neurites. These cells are generated late in the culturing period. The surviving cortical neurons in the cortex plus tectum (Cx + T) cultures are larger--many with a pyramidal-shaped soma and several neurites. These cells are generated earlier in vitro. The cortex cultured with other cortex (Cx + Cx) gives values intermediate to the Cx + D and Cx + T cultures. The results of these experiments suggest that there are diffusible trophic factors that arise from subcortical structures that selectively support the survival of neuron populations in the developing neocortex.

Purification of adult rat sciatic nerve ciliary neuronotrophic factor

The ciliary neuronotrophic factor (CNTF), a protein required for the survival of cultured avian embryonic parasympathetic ciliary ganglionic neurons, was recently purified from extracts of selected chick intraocular tissues. Here we report the purification of a mammalian CNTF activity from extracts of adult rat sciatic nerve using a fractionation procedure similar to that employed for isolating chick eye CNTF. About 2 micrograms of CNTF protein can be obtained from each 1.5 g batch of nerve tissue. Like the chick CNTF, the mammalian factor displays trophic activity for dorsal root and sympathetic as well as ciliary ganglionic neurons. The nerve CNTF activity differs from its chick counterpart in molecular weight and chromatographic behavior on ion-exchange columns. Unlike purified nerve growth factor (NGF), nerve CNTF activity is insensitive to anti-NGF antibodies and is unable to support the survival of 8-day chick embryo dorsal root ganglion neurons.

Neuronotrophic factors: effects on central cholinergic regeneration in vivo

To determine if neurotrophic factors (NTFs) which either support the survival (CNTF) or promote neuritic outgrowth (PNPF) of peripheral cholinergic neurons in vitro affect central cholinergic regeneration in vivo, NTFs were administered intracerebrally to rats after injury to septohippocampal fibers. Choline acetyltransferase activity within intrahippocampal iris implants was used as an index of cholinergic innervation. CNTF stimulated cholinergic sprouting while PNPF was ineffective under our experimental conditions, suggesting that the effects of other NTFs in vivo may be mediated by enhanced neuronal survival after injury rather than increased axonal sprouting.

Purification of the chick eye ciliary neuronotrophic factor

Dissociated 8-day chick embryo ciliary ganglionic neurons will not survive for even 24 h in culture without the addition of specific supplements. One such supplement is a protein termed the ciliary neuronotrophic factor (CNTF) which is present at very high concentrations within intraocular tissues that contain the same muscle cells innervated by ciliary ganglionic neurons in vivo. We describe here the purification of chick eye CNTF by a 2 1/2-day procedure involving the processing of intraocular tissue extract sequentially through DE52 ion-exchange chromatography, membrane ultrafiltration-concentration, sucrose density gradient ultracentrifugation, and preparative sodium dodecyl sulfate-polyacrylamide gradient electrophoresis. An aqueous extract of the tissue from 300 eyes will yield about 10-20 micrograms of biologically active, electrophoretically pure CNTF with a specific activity of 7.5 X 10(6) trophic units/mg protein. Purified CNTF has an Mr of 20,400 daltons and an isoelectric point of about 5, as determined by analytical gel electrophoresis. In addition to supporting the survival of ciliary ganglion neurons, purified CNTF also supports the 24-h survival of cultured neurons from certain chick and rodent sensory and sympathetic ganglia. CNTF differs from mouse submaxillary nerve growth factor (NGF) in molecular weight, isoelectric point, inability to be inactivated by antibodies to NGF, ability to support the in vitro survival of the ciliary ganglion neurons, and inability to support that of 8-day chick embryo dorsal root ganglionic neurons. Thus, CNTF represents the first purified neuronotrophic factor which addresses parasympathetic cholinergic neurons.

Chemically defined requirements for the survival of cultured 8-day chick embryo ciliary ganglion neurons

We have previously demonstrated that both peripheral and central neurons from embryonic chick and newborn mouse can be maintained in a serum-free defined culture medium containing the appropriate neuronotrophic agent and the N1 supplement consisting of insulin, transferrin, putrescine, progesterone and selenite. In the present studies we have examined the short-term survival requirements of 8-day embryonic chick ciliary ganglion (CG) neurons. By comparing CG neuronal survival in our standard culture medium, Eagle's Basal Medium (EBM), with several other commercially available basal media, we have established that CG neurons also have specific requirements for pyruvate, serine and iron (Fe3+), in addition to their trophic factor (Ciliary Neuronotrophic Factor, CNTF) and the N1 supplement. The data suggest the existence of 3 subsets of CG neurons differing in their essential needs, namely: (1) those supported by glucose in the absence of pyruvate, (2) those requiring exogenous pyruvate but not serine or Fe3+, and (3) those which need pyruvate, serine and Fe3+. The minimal effective concentration of pyruvate could be decreased by a factor of 50 in the concurrent presence of serine and Fe3+. Serine was also a limiting element in the survival of some of these CG neurons. The Fe3+ concentration required by the same neurons was considerably diminished with the availability of transferrin, perhaps reflecting an increased Fe3+ transmembrane transport efficiency. Insulin was found to be the only N1 ingredient required for the survival of CG neurons. Insulin was a constant requirement for all 3 subsets of CG neurons, even when cultured in the total absence of glucose (but presence of pyruvate).