Neuronotrophic activity in brain wounds of the developing rat. Correlation with implant survival in the wound cavity

Molecular and cellular aspects of nerve regeneration

Injury of an axon leads to at least four independent events, summarized in Figure 1: first, deprivation of the nerve cell body from target-derived or mediated substances, which leads to a derepressed or a permissive state; second, disruption of anterograde transport, with a resultant accumulation of anterogradely transported molecules; third, environmental response with possible consequent changes in constituents of the extracellular matrix and substances secreted from the surrounding cells; and fourth, appearance of growth inhibitors and modified protease activity. It seems that the first three of these events are obligatory, but not sufficient, i.e., they lead to a growth state only if the cell body is able to respond to the injury-induced signals from the environment (a and b). The regenerative state is characterized by alterations in protein synthesis and axonal transport and by sprouting activity. The subsequent elongation of the growing fibers depends on a continuous supply of appropriate growth factors. These factors are presumably anchored to the appropriate extracellular matrix that serves as a substratum for elongating fibers. It should be mentioned that the proliferating nonneuronal cells have a conducive effect on regeneration by forming a scaffold for the growing fibers. Accordingly, the lack of regeneration may stem from a deficiency in the ability of glial cells to provide the appropriate soluble components or from insufficient formation of extracellular matrix. In this respect, one may consider regeneration of an injured axon as a process which involves regeneration of both the nonneuronal cells and the supported axons. The regeneration of glial cells may fulfill the rules which are applied to regeneration of any other proliferating tissue. Furthermore, the processes of regeneration in the axon and the glial cells are mutually dependent. Perhaps the triggering factors provided by the nonneuronal cells affect the nonneuronal cells themselves by modulating their postlesion gliosis and thereby inducing their appropriate activation. In such a case, regeneration of nonneuronal cells may resemble an autocrine type of regulation that exists also during ontogeny. The growth regulation is shifted back to the paracrine type upon neuronal maturation or cessation of axonal growth. When the elongating fibers reach the vicinity of the target organ, they are under the influence of the target-derived factors, which guide the fibers and eventually cease their elongation.

Denervation of serotonergic fibers in the hippocampus induced a trophic factor which enhances the maturation of transplanted serotonergic neurons but not norepinephrine neurons

The trophic effects of specific denervation on the growth and survival of fetal serotonergic (5-HT) or norepinephrinergic (NE) neurons grafted into the hippocampus were assessed by means of two transplantation paradigms. In the first, fetal raphe cells (containing 5-HT neurons) were transplanted into the control hippocampus. In the second, the transplantation was performed 2 weeks after the specific removal of 5-HT afferents to the hippocampus with 5,7-dihydroxytryptamine (5,7-DHT). We found that a month after transplantation, the number of 5-HT immunoreactive neurons was not significantly different between the two experimental paradigms. However, transplanted raphe neurons had 400% more 5-HT synaptosomal high-affinity uptake and 380% higher content of 5-HT in the hippocampus with prior 5,7-DHT lesion than in control hippocampus. Furthermore, immunocytochemistry showed that the transplanted 5-HT neurons had denser processes and varicosities in the hippocampus with lesion than in control hippocampus. The somatic area of the neurons with these denser processes and varicosities was 42% larger than that of control group. A greater 5-HT level could be achieved if transplanted neurons in the control hippocampus were treated with the supernatant extracted from the hippocampus with 5,7-DHT lesion. In contrast, the NE level of the implanted fetal locus ceruleus (containing NE neurons) was not significantly higher in the 5-HT denervated hippocampus than in control hippocampus a month after transplantation. These results suggest that 5-HT denervation in the hippocampus induces a trophic substance which promotes the maturation rather than survival of 5-HT neurons but not NE neurons.

Continuous infusion of nerve growth factor prevents basal forebrain neuronal death after fimbria fornix transection

Neurons in the rat medial septum (MS) and vertical limb of the diagonal band of Broca (VDB) undergo a rapid and severe cell death after transection of their dorsal projection to the hippocampus by aspiration of the ipsilateral fimbria fornix and supracallosal striae. By 2 weeks posttransection, the extent of neuronal loss was 50% of the total neurons and 70% of the cholinergic neurons in the MS and 30% of the total neurons and 40% of the cholinergic neurons in the VDB. We hypothesized that (i) the death was due to the loss of a hippocampus-derived neuronotrophic factor, and (ii) exogenous nerve growth factor (NGF) might provide trophic support to the MS/VDB cholinergic neurons, in light of recent reports that the septal diagonal band cholinergic neurons are responsive to NGF and that NGF is present and produced in the hippocampus. In the present study, we attempted to prevent the transection-induced neuronal death by continuous infusion of exogenous 7S NGF (1 microgram/wk) through an intraventricular cannula device. We report here that NGF treatment significantly reduces both the total neuronal and cholinergic neuronal death found 2 weeks after fimbria fornix transection; there was a sparing of 50% of the neurons in the MS and essentially 100% of those in the VDB that otherwise would have died. We conclude that NGF also has a protective effect on noncholinergic neurons since calculations indicate that 80% of the NGF-affected neurons are noncholinergic.

Long-term effects of nerve growth factor and neural transplants on behavior of rats with medial septal lesions

The present experiment investigated the interaction between exogenous nerve growth factor (NGF) and intrahippocampal septal grafts on the behavior of rats after a medial septum lesion. Young female rats received a bilateral injection of a fetal septal cell suspension into the dorsal hippocampus either immediately (immediate grafts) or 8 days after the lesion (delayed grafts). For delayed grafts, a higher concentration of endogenous neurotrophic factors can be assumed to be present in the deafferentated host tissue at the time of transplantation. One group of rats with lesions received NGF with the immediate grafts, another group received NGF alone. A sham-operated group and 3 groups with lesions (and given either immediate or delayed intrahippocampal saline injections, or no other treatment) constituted controls. The animals were tested for spontaneous alternation and for performance in a radial 8-arm maze, 1, 5 and 9 months postoperatively. Medial septal lesions reduced spontaneous alternation but, 9 months after surgery, recovery was observed in both lesion-control rats and in rats with delayed grafts (but not with immediate grafts). In the radial maze task, lesions produced a persistent impairment, although both immediate and delayed grafts reduced this deficit several months after surgery (more markedly and rapidly in the case of delayed grafts). NGF, however, increased the maze learning deficit especially 5 months postoperatively. These latter results are in contrast to findings of earlier studies showing transient beneficial effects of NGF administration. It is suggested that the effects of NGF in the present study might be due to an enhanced sprouting of sympathetic fibers into the hippocampal formation.

Lack of ingrowth of retinal axons into the visually deafferented superior colliculus in young rats: a horseradish peroxidase study

Suction lesions of the brachium of the left superior colliculus (SC) and pretectal region were made in 6-11-day-old hooded rats. Central retinal projections were examined 15-261 days later by injecting the right eye of each rat with horseradish peroxidase. Retinal fibres were found to have regrown either within glial and connective tissue membranes which formed over the lesion cavity or across the surface of the lesion itself. The axons sometimes grew up the rostral face of the remaining SC to reach the superficial tectal layers; however, there was no significant penetration into the SC neuropil.

Acetylcholine-rich neuronal grafts in the forebrain of rats: effects of environmental enrichment, neonatal noradrenaline depletion, host transplantation site and regional source of embryonic donor cells on graft size and acetylcholinesterase-positive fibre outgrowth

The importance of several factors influencing the survival of cholinergic-rich embryonic tissue transplanted to the adult rat forebrain and the extent of acetylcholinesterase-positive fibre innervation of the host brain was investigated in 3 experiments. In the first two experiments, embryonic ventral forebrain tissue was grafted to the neocortex of rats in which the intrinsic cortical cholinergic innervation had been removed by nucleus basalis lesions. Housing the host rats in an enriched environment produced a temporary enhancement of fibre outgrowth 4 weeks after transplantation, but this was not maintained after 10 weeks. Fibre outgrowth was greater when the grafts were transplanted to the noradrenaline-depleted neocortex than to the intact neocortex. Neither environmental enrichment nor noradrenaline depletion influenced graft survival or size. In the third experiment, the embryonic donor tissue was dissected to separate regions containing precursors of the nucleus basalis cholinergic cells from regions containing precursors of the septal cholinergic cells, and transplanted to either the neocortex following nucleus basalis lesions or to the hippocampus following fimbria-fornix lesions. Nucleus basalis grafts showed greater growth in size than septal grafts, and grafts placed into the hippocampus showed greater growth in size than grafts placed into the neocortex. More interestingly, the extent of fibre outgrowth depended on the appropriateness of the donor tissue to the host transplantation site: nucleus basalis tissue showed greater acetylcholinesterase-positive outgrowth than septal tissue in the neocortex, whereas septal tissue showed greater outgrowth than nucleus basalis tissue in the hippocampus.

Neonatal striatal grafts prevent lethal syndrome produced by bilateral intrastriatal injection of kainic acid

It is reported that unilateral grafts of neonatal striatal tissue protect the recipient from the lethal aphagia and adipsia produced by bilateral intrastriatal injection of 10 nmol of kainic acid in rats. It is shown that neither adult striatum nor neonatal tissue from other sites have the same lifesaving effect and that the salutary effect of the graft is dependent upon graft survival. Grafts from a histoincompatible donor are apparently rejected, leading to the death of the recipient. Cyclosporine inhibits rejection thereby enabling recipient survival. It is postulated that the graft exerts a neurohumoral influence that protects the striatum from the toxic effect of kainate.

Characterization of choline acetyltransferase-sustaining and survival-promoting activities for parasympathetic neurons in pig lung

A total of 49 tissues from six animal species were screened for substances that would sustain choline acetyltransferase (ChAT) in parasympathetic ciliary neurons in culture. Among these, lungs from several species, particularly pig, contained relatively high concentrations of ChAT-sustaining activity. The bioassay used was one in which embryonic chicken ciliary ganglia were cultured as explants for 3 days with KCl and lung extract. KCl, in the presence of lung extract, sustained high concentrations of choline acetyltransferase activity, but did not maintain enzymatic activity in the absence of lung extract. These effects were dependent on the embryonic age of the ciliary ganglia. Lung extract and KCl would not maintain choline acetyltransferase activity in parasympathetic neurons taken from chickens older than embryonic day 12. In addition to ChAT-sustaining activity, pig lung also contains survival-promoting activity for parasympathetic neurons but not for other neuronal types, including sympathetic or sensory neurons of neural crest or placodal origin. This is a more specific target spectrum than previously reported ciliary survival-promoting factors that have been purified or partially purified and indicates that survival-promoting activities in pig lung are different than those previously observed. Because of the large quantitites that can be obtained, we suggest that pig lung is a preparatively feasible source for possibly novel ciliary neuron ChAT-sustaining and survival-promoting activities for parasympathetic neurons.

A neurotrophic factor derived from goldfish brain: characterization and purification

Previous studies carried out in our laboratory have demonstrated that goldfish brain contains substances that promote neurite extension from regenerating retinae in culture. Fractionation of the brain extract by molecular sieving chromatography revealed the presence of several molecular species, including two peaks that have neurotrophic activity, representing low-molecular-weight substances. One peak was eluted (P-a) with an apparent molecular weight of about 13 kDa and was designated substratum neurite extension factor (SNEF) because it retained its neurotrophic activity when adsorbed onto the substratum. This recovered Sephadex fraction (P-a) when applied in vivo intraocularly caused an earlier capacity of the corresponding retinae to sprout in vitro. Thus, at 3 and 5 days after injury the neuritic growth indices from the factor-treated retinae were of 0.9 +/- 0.2 and 2.8 +/- 0.5, respectively, as compared with indices of 0.3 +/- 0.1 and 0.9 +/- 0.2, respectively, in retinae of injured but nontreated nerves. The factor was further purified by two steps of HPLC (ion exchange followed by reversed phase). The results showed that it is an acidic glycoprotein with an apparent molecular weight of 10 kDa.

Septal deafferentation enhances the neurotrophic effects of rat hippocampus on cultured neural cells from the central nervous system

Neurotrophic effects (NTEs) of various brain regions of 4-week-old rats were examined in primary culture of rat embryonic cerebral hemispheres. Extracts of the hippocampus, brainstem and septal nucleus highly enhanced the survivability of neuronal cells and the division of non-neuronal cells by 9 days. The septohippocampal tract (fimbria fornix) was cut and the effect on the neurotrophic activity in the hippocampus was examined. The NTEs of hippocampal extracts remained unchanged 3 days after septal deafferentation, was significantly increased by 7 days, peaked at 14 days and returned to the basal level by 21 days.

Modulation of the nicotinic alpha-bungarotoxin site in chromaffin cells in culture by a factor(s) endogenous to neuronal tissue

An endogenous factor(s) which affects the in vitro binding of (alpha-BGT) to rat brain membranes has previously been found in brain supernatant. This fraction, as well as a partially purified preparation of this material from bovine brain, is here shown to affect the binding of alpha-BGT to chromaffin cell membranes. To study possible long term effects, the supernatant extract was added to adrenal medullary chromaffin cells in culture. The cells were incubated for several days and at the end of this time, the medium bathing the cells, which contained the endogenous factor(s), was removed and alpha-BGT binding to the cells measured. Binding to control cultures had shown that alpha-BGT bound to the chromaffin cells in a saturable manner, with high affinity (Kd = 1.5 nM) and the specificity of a nicotinic receptor ligand. After incubation of the cells with supernatant factor, a marked decline in the number of alpha-BGT binding sites was observed with no change in affinity. This does not appear to be due to a detrimental effect on the cells as cell number did not appear to be decreased in the cultures preincubated with the supernatant extract and the DNA and protein content were similar in the control and treated cultures. The possibility that there was some non-specific detrimental effect to the chromaffin cell membrane was considered; however, the stimulated release of noradrenaline from the cells was not affected by treatment of the cultures in the presence of the supernatant fractions. In addition, tyrosine hydroxylase activity was significantly increased in the treated cultures. D-Tubo-curarine, an antagonist at the acetylcholine receptor, caused an increase in alpha-BGT binding after 7 days of treatment, while the agonist nicotine and choline had no effect. These results suggest that in brain supernatant there may exist an endogenous factor(s), which may function in the regulation of the nicotinic-like alpha-BGT receptors in neuronal cell.

Transamination of glutamate to tricarboxylic acid-cycle intermediates in cultured neurons correlates with the ability of oxo acids to support neuronal survival in vitro

Cultures of central-nervous-system neurons at low densities require for their survival exogenous pyruvate, alpha-oxoglutarate or oxaloacetate, even in the presence of high glucose concentrations. Most other alpha-oxo acids support cell survival only in the presence of alpha-amino acids which transaminate to alpha-oxoglutarate, oxaloacetate or pyruvate. The alpha-oxo acids therefore operate as acceptors of amino groups from appropriate donors to generate tricarboxylic acid-cycle-relevant substrates, and these alpha-oxo acids provide for neuronal support only insofar as they make it possible for exogenously supplied alpha-amino acid precursors to generate intracellularly one of the three critical metabolites. To examine more closely the relationship between transamination activity and neuronal survival, we measured 14CO2 production from [14C]glutamate in the presence of appropriate alpha-oxo acid partners by using 8-day-embryonic chick forebrain, dorsal-root-ganglion and ciliary-ganglion neurons. Neuronal survival was measured concurrently in monolayer neuronal cultures maintained with the corresponding amino acid/oxo acid pairs. Forebrain and ganglionic cell suspensions both produced 14CO2 from [14C]glutamate, which accurately correlated with 24 h neuronal survival. Concentrations of glutamate or alpha-oxo acid which provide for maximal neuronal survival also produced maximal amounts of 14CO2. The same ability to generate CO2 from glutamate (in the presence of the appropriate alpha-oxo acids) can ensure neuronal survival in 24 h cultures and therefore must meet energy or other metabolic needs of those neurons which glucose itself is unable to satisfy.

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.

Hippocampal neurotrophic factor: characterization and response to denervation

The rat hippocampus contains an acidic macromolecular neurotrophic factor (NTF) which supports the survival of cultured chick ciliary ganglion cells. Hippocampal NTF increases approximately 2-fold from birth to adulthood with no further change with aging. Disruption of extrinsic inputs to the hippocampus from the entorhinal cortex, locus coeruleus or contralateral hippocampus, but not from the septum, results in an increase in the concentration of NTF in the hippocampus. Destruction of intrinsic hippocampal neurons by kainic acid treatment is accompanied by a large increase in hippocampal NTF, a result consistent with a glial origin for the factor. This conclusion is supported by the finding that a lesion-induced rise in NTF can be suppressed by administration of methotrexate, an inhibitor of gliosis.

Enhanced graft survival in the hippocampus following selective denervation

The trophic effects of denervation on the survival of fetal cholinergic neuronal cell suspensions grafted to the hippocampal formation of the rat were assessed in the present study. Young adult female rats were injected with cell suspensions of neurons obtained from the fetal basal forebrain region into the hippocampal formation simultaneously with (or without) a fimbria-fornix transection, which removes the hippocampal cholinergic afferents. Four to six months later, one group of grafted animals was evaluated histochemically for: transplant volume; number of acetylcholinesterase-positive cells, and size of acetylcholinesterase-positive cells in the graft. A parallel study was conducted to determine the total number and size of the acetylcholinesterase-positive cells in the septal-diagonal band-substantia innominata complex of the adult rat, to match with the cell survival and growth in the grafts. A second group of grafted rats was taken in parallel for biochemical analysis of choline acetyltransferase activity in the grafted hippocampus. The transplant volume in the rats with fimbria-fornix transection was greater than twice the volume seen in animals without fimbria-fornix lesion. In addition, the number of acetylcholinesterase-positive cells in the transplant was twice as great in the denervated animals as in the non-denervated ones. However, the number of acetylcholinesterase-positive cells per mm3 of graft volume did not differ between the two groups, suggesting that the trophic effect of the denervation was not specific for the cholinergic neurons, but affected the entire grafted tissue. The hippocampal choline acetyltransferase activity of the animals that received the fimbria-fornix lesion simultaneously with transplantation was about three times higher than that of the rats that received grafts but no simultaneous fimbria-fornix transection. A control experiment with animals that received an aspirative lesion of the retrosplenial cortex, transecting the perforant path input, revealed no enhancing effect of hippocampal choline acetyltransferase activity over non-lesioned grafted animals. Thus, the denervation-enhancing effects of the fimbria-fornix lesion appear to be selective and not the result of a general wound-induced mechanism. These results strongly support the contention that neurotrophic factors are released as a result of denervation in the adult hippocampal formation, and that these neurotrophic factors can support survival and growth of central cholinergic neurons. However, the factors involved do not appear to be specific for the cholinergic neurons, but rather have their trophic effects on many types of cells.

Central nervous system axonal regeneration into sciatic nerve grafts: physiological properties of the grafts and histologic findings in the neuraxis

Autologous nerve grafts were implanted extraspinally between the medulla and the ipsilateral cervical spinal cord in adult rats. Four to eight months after implantation, electrical stimulation of the grafts evoked EMG activity in a variety of head and neck muscles in 8/10 rats. In 5/10 rats, electrical stimulation of the graft during inspiration potentiated or inhibited EMG activity in each of the diaphragms. After the recordings were completed, the grafts were cut and their ends soaked in horseradish peroxidase (HRP). The average count of HRP-labeled neurons, both in the spinal cord and brain stem, was 969 (252 to 1961). Most labeled neurons were located within +/- 2 mm of the implant sites, with labeling seen in neurons as far as 9 mm away. In the brain stem, 20 different nuclei were labeled. Among them were the reticular formation, raphe complex, cranial nerve nuclei, the subceruleus, ventrolateral pontine tegmentum regions, and contralateral red nucleus. These results in adult rats showed that (i) CNS axons elongating within peripheral nerve grafts were able to conduct action potentials and maintain functional synapses on CNS neurons; (ii) newly growing neurons were situated in close proximity to the nerve graft; and (iii) many different kinds of central neurons, including monoaminergic and descending spinal tract neurons, can elongate their axons into peripheral nerve grafts.

Acetylcholine-rich transplants in the hippocampus: influence of intrinsic growth factors and application of nerve growth factor on choline acetyltransferase activity

Three groups of rats received either unilateral fimbria-fornix lesions by aspiration through the overlying cingulate cortex (group I), a fimbria-fornix lesion followed by an intrahippocampal transplant of acetylcholine (ACh)-rich embryonic septal tissue (group II), or a similar septal transplant placed into the intact hippocampus, in the absence of the denervating lesion (group III). The 3 groups were subdivided into equal subgroups receiving 6 intrahippocampal injections of nerve growth factor (NGF) at 4-day intervals, control injections of cytochrome c, or no injections. On the 28th day all animals were sacrificed and the majority taken for biochemical analysis of hippocampal choline acetyltransferase (ChAT). The animals with intact hippocampi (group III) were given a denervating fimbria-fornix lesion 3 days prior to sacrifice in order to reveal graft-derived ChAT activity from intrinsic ChAT activity. The fimbria-fornix lesions (group I) depleted hippocampal ChAT activity to 15-20% of normal, which was not influenced by NGF injections. The ACh-rich grafts placed in the denervated hippocampus (group II) restored hippocampal ChAT activity to approximately 60% of the normal level, and this was promoted to approximately 84% of NGF, but not cytochrome c, injections into the hippocampus. Grafts placed into the intact hippocampus (group III) did not raise ChAT activity above the lesion-alone level, and this was not influenced by NGF injections. Acetylcholinesterase (AChE) histochemistry showed no difference in outgrowth from the grafts in the denervated hippocampus with or without NGF injections. The results are interpreted, in agreement with observations in tissue culture, as indicating that NGF enhances ChAT activity in grafted neurons, rather than promoting survival and growth per se.

Initial growth of transplanted E11 fetal cortex and spinal cord in adult rat spinal cord

Fetal CNS (cortex and spinal cord) transplants survive and grow in the spinal cord of adult rats. The present experiments study the initial stages (10 days) to determine the developmental pattern of early (E11) fetal cortex and spinal cord transplants implanted into the T6 spinal cord of adult rats (n = 50). Controls were age-matched fetuses or pups from the donor females and surgical and vehicle controls (n = 20). E11 fetal cortex (0.5 X 1.0 mm pieces of neuroepithelium) or spinal cord (1.0 mm) were dissected from caesarean delivered fetuses from time pregnant Sprague-Dawley rats. The fetal tissue was pressure-injected between the dorsal horn and dorsal column of the host. Hosts were prepared for light and electron microscopy 1, 3, 7 and 10 days postimplantation (DPI). At 1 DPI, ovoid, ventriculated multiple neuroepithelia formed in an implantation-induced cyst in the host spinal cord. The inner layer of cells lining the ventricle of the ovoid neuroepithelia was actively dividing. The nuclei of the cells differentiated as they reached the surface of the neuroepithelium. This pattern was repeated at 3-10 DPI. At 7-10 DPI, differentiated neurons and neuroglia surrounded actively dividing neuroepithelia. These cells comprised the bulk of the transplant in the cyst. Transplanted mesenchymal cells formed pockets of cartilage in the implanted spinal cord. Although transplanted CNS consisted of only neuroepithelial cells, they differentiated into neurons that were typical for cortex or spinal cord. These data indicate that the transplanted E11 fetal tissue formed neuroepithelia which established the pattern of growth for these transplants.

The control of glial populations in brain: changes in astrocyte mitogenic and morphogenic factors in response to injury

Injury to rat brain induces a 3-10-fold increase in the activity of factors capable of stimulating astrocyte DNA synthesis and cell division in vitro. Maximum mitogenic activity was reached 10-15 days post-lesion in both the tissue surrounding the wound and in the gelfoam filling the wound cavity. Factors capable of transforming the astrocyte morphology from polygonal-flat to fibrous-like (morphogens) could also be observed in brain tissue and showed increased activity beginning at 10 days postlesion. On the other hand, morphogenic activity was very low or absent in gelfoam extracts until 15 days postlesion. Both mitogenic and morphogenic factors were nondiffusible and were partly temperature and trypsin sensitive, i.e. they had the properties of protein-like substances, but seemed different from both epidermal and fibroblast growth factors. As judged by their filtration behavior on Amicon membranes, the molecular weight of mitogens and morphogens ranged from lower than 30,000 to greater than 100,000. Inhibitors of both mitogenic and morphogenic activities with molecular weight lower than 30,000 seemed to be also present in the brain extracts. The factors described here can account for the processes of astrocytosis and astrogliosis observed in vivo in response to CNS injury.

Parasympathetic neurotrophic activity in the rat iris: determination after different denervations

The iris of the adult rat contains one or several neurotrophic factors that enhance the survival of dissociated parasympathetic neurons (from the embryonic chick ciliary ganglion) in culture. To assay survival activity, iris homogenates were serially diluted with culture medium and the percentage of neurons surviving for 2 days in a collagen matrix in culture determined. The extract induced survival curves that were similar for denervated and normal irides. Similarly no differences in fibre outgrowth from cultured whole ciliary ganglia were found. The results suggest that the apparent level of parasympathetic growth factor(s) is not under strict control of the innervation of the iris.

Specific replacements of pyruvate for trophic support of central and peripheral nervous system neurons

When embryonic central nervous system neurons are seeded at low densities with Eagle's basal medium supplemented with the serum substitute N1, glucose, and glutamine, neuronal survival for even 24 h requires the additional supply of exogenous pyruvate--and so does the survival of many peripheral nervous system neurons. Pyruvate can be replaced by alpha-ketoglutarate or oxaloacetate, but not by Krebs cycle substrates that are not keto acids. Most other alpha-keto acids tested (though not beta- or gamma-keto acids) also mimic pyruvate. The apparent equivalence to pyruvate of all these compounds includes identical ED50 values (300 microM for embryonic avian fore-brain neurons, 30-40 microM for rat hippocampal neurons), and also identical susceptibilities to the pyruvate-sparing effects of other low-molecular-weight agents present in Dulbecco's modified Eagle's medium or in astroglia conditioned medium. The substitute alpha-keto acids, however--unlike pyruvate, alpha-ketoglutarate, or oxaloacetate--support cell survival only in the presence of alpha-amino acids that transaminate to alpha-ketoglutarate, oxaloacetate, or pyruvate. The alpha-keto acids, therefore, operate as acceptors of amino groups from appropriate donors to generate Krebs cycle-relevant substrates. Consistent with this view, [14C]glutamate did not generate appreciable 14CO2 unless accompanied by a suitable alpha-keto acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Replacement of damaged cortical projections by homotypic transplants of entorhinal cortex

The extent to which transplants of embryonic cortical tissue can be used to replace damaged cortical projections has been examined. Embryonic entorhinal cortex was implanted into the entorhinal region of young adult rats that had previously received a lesion through the angular bundle. Projections between transplant and host were examined by using WGA-HRP and the fluorescent dye Fast Blue. Implants selectively innervated areas of the host hippocampus and amygdala which normally receive entorhinal afferents. Implants were innervated by cells in the host diagonal band and, in one case, by cells in the contralateral entorhinal and/or presubicular cortex. In most cases, host fibers were differentially distributed within transplants, possibly reflecting an ability of host fibers to recognize and selectively innervate their appropriate targets even though the cellular organization of the implant is different from that present during normal development. These data suggest that homotypic implants of embryonic entorhinal cortex can, in some ways, replace severed cortical projections and may eventually be able to reconstitute normal cortical circuitry.

Central nervous system-directed neuronotrophic activity present in red blood cells

A new neuronotrophic factor has been identified in extracts of vertebrate red blood cells. The factor supports the survival in culture of neurons from vertebrate central nervous systems, and does not support the survival of several peripheral ganglionic neurons. The active molecule appears to be a slightly acidic protein of 30,000-100,000 daltons.

Dorsal root innervation of spinal cord neurons after dorsal root implantation into the spinal cord of adult rats

In an attempt to enhance spinal cord reinnervation by dorsal root neurons in the adult rat, the root was cut and implanted into the cord. Wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected into the dorsal root ganglion in order to look for regrowth in the spinal cord. Instead of regenerated dorsal root axons, there was an occurrence of HRP-labelled spinal cord neurons in the vicinity of the implanted dorsal root. In control animals, which had been subjected to dorsal root crush, no labelled neurons or terminals were observed in the spinal cord.

Promoting functional plasticity in the damaged nervous system

Damage to the central and peripheral nervous system often produces lasting functional deficits. A major focus of neuroscience research has been to enhance functional restitution of the damaged nervous system and thereby produce recovery of behavioral or physiological processes. Promising procedures include surgical, physical, and chemical manipulations to reduce scar formation and minimize the disruption of support elements, administration of growth-stimulating substances, tissue grafts to bridge gaps in fiber pathways, and embryonic brain tissue grafts to provide new cells with the potential to generate fiber systems. Two elements are required for functional nervous system repair: (i) neurons with the capacity to extend processes must be present, and (ii) the regenerating neurites must find a continuous, unbroken pathway to appropriate targets through a supportive milieu.

Axonal regeneration through a peripheral nerve implanted into a brain cavity

A cavity was prepared in the rat parietal cortex by suction, filled with gel foam and left for 3 weeks during which time it became highly vascularised. Into this 3-week-old capillary bed a 5 mm length of autologous common peroneal nerve was implanted. Animals were killed at various time intervals up to 7 months after implantation of the nerve segment. The ultrastructural features of the vascular bed before and after implantation of the nerve segment were compared. In the absence of a peripheral nerve implant no axons were found within the cavity. However, at 5 weeks after implantation numerous axon-like profiles and capillaries containing fenestrations were observed within the implant. Eight weeks after implantation of the peripheral nerve both myelinated and non-myelinated axons were observed within the implant and in the surrounding capillary bed. No obvious increase in the number of axons was observed with increasing time periods. To investigate the origin of the axons within the vascular bed and/or implant the fluorochrome true blue was injected into the cavity 7 months after implantation of the nerve. Three days later selected areas of the brain, the trigeminal, superior cervical and otic ganglia were examined for retrogradely labelled fluorescent cells. Labelled cells were found adjacent to the cavity and in the ipsilateral trigeminal and superior cervical ganglia. The significance of these results in relation to the enhancement of axonal regeneration from the damaged central nervous system (CNS) is discussed.

Development of mouse spinal cord in tissue culture: IV. Effects of embryonic extracts on neuron formation and migration

Possible influences upon patterns of neurogenesis expressed in vitro were examined quantitatively by the use of microfragment cultures of embryonic day 10 mouse neural tube. Crude extracts were prepared either from whole embryos (day 13 or 15 of gestation) or from embryonic brains (day 18 of gestation) and added to the culture medium for the first 10 days of culturing. Neuronal outgrowth zones surrounding individual microfragments were reduced in area (indicating restricted neuronal migration) and in number of neurons present (indicating restricted production of neurons) following treatment with either of the extracts. The severity of reductions observed were related to the developmental age of embryonic tissue used for preparing the extract, as greatest reduction resulted from addition of embryonic day 18 brain extracts and to concentration employed, higher doses further restricting neuronal outgrowth. By increasing the concentrations of extract the proportional number of large-sized neurons forming the outgrowth zones became greater relative to the small neuron contribution, indicating an enhanced survival for this neuronal population. The formation and migration of astroglial precursor cells was not affected by the addition of any of the extracts. The number of neurons remaining within the original portions of neural tube microfragments was not significantly altered following culturing in the presence of embryonic extract. This suggested that the reduction in neuron number in the outgrowth zone actually reflected a decreased neuron production and was not simply the result of a retention of neurons within the remaining portion of the microfragment. The results suggest the presence of substances within mouse embryos that have regulatory effects on aspects of development of the central nervous system. Indications are that survival and maturation of postmitotic neuroblasts are promoted in vitro while the formation of additional neuronal progenitor cells may be partially inhibited by the addition of embryonic mouse extracts to the medium. We propose that an endogenous negative feedback mechanism may be involved in the coordination of patterns of neurogenesis.

Cytoarchitectonics of substantia nigra grafts: a light and electron microscopic study of immunocytochemically identified dopaminergic neurons and fibrous astrocytes

Maturation of dopaminergic (DA) neurons and astroglia was studied in transplants of the substantia nigra grown for up to 7 months in the brain of rats. The investigation had three specific aims. The first was to observe effects of different transplant positions on the longevity of DA neurons. Second, the grafts were examined for changes of synaptic interactions and associations between DA neurons and astroglia. Third, an answer was sought to the question whether transplanted DA neurons migrate into the adjacent host brain. The grafts were taken from the ventral mesencephalon of rat embryos of different ages (day 14 to 18 of gestation) and placed into the cerebral cortex, tectum, cerebellum, or ventricles of newborn host animals. Following different times of survival the immunocytochemical localization of tyrosine hydroxylase (TH) and of glia filament protein (GFA) in the transplants were observed. In all of the transplantation sites, except for one, neurons of different morphologies that contained TH were found in the grafts. The cerebellar white matter of the host brain failed to support the long-term survival of DA neurons. The overall structure of mature substantia nigra grafts had some resemblance to intact substantia nigra (SN). On the ultrastructural level, it was found that morphological expression of some immature features of DA neurons, such as glial sheaths, somatic spines, and lack of oligodendroglia, persisted in mature grafts. Specific associations of DA neurons and astroglia in the grafts suggested that the cytoarchitectonic appearance of a given brain region may be related to the existence of particular neuron glia relationships. In contrast to intact SN, transplants revealed deficiencies in unlabeled pleomorphic boutons and contained some TH-immunoreactive terminals. Migration of DA neurons and their processes into the adjacent host brain was rarely observed.

Enhancement of central cholinergic sprouting by prior injury: correlation with endogenous trophic content of hippocampus

Injury to neural tissue elicits the release of neurotrophic substances which support the survival of cultured cholinergic neurons. The aim of the present report was to determine the effect of prior hippocampal injury on the sprouting of mature intrinsic cholinergic septal afferents in vivo. Levels of choline acetyltransferase (CAT) in intrahippocampal iris implants were used as an index of cholinergic regeneration. The results show that prelesioning the hippocampus 1 week prior to insertion of the iris increased CAT levels of implants left for 8 days in situ. Levels of iris CAT were correlated with the trophic content of the surrounding hippocampal tissue. These observations suggest that endogenous trophic factors released as a consequence of neural injury facilitate cholinergic sprouting in vivo.

Effect of GM1 ganglioside treatment on the recovery of dopaminergic nigro-striatal neurons after different types of lesion

The effect of GM1 ganglioside treatment on the recovery of biochemical and behavioral parameters which define the activity of nigro-striatal dopaminergic systems has been investigated in rats after different types of lesion. GM1 favours the recovery of tyrosine-hydroxylase activity, of the number and affinity of 3H-N-n-propyl-norapomorphine binding sites in the striatum of the lesioned side and reduces the apomorphine-induced rotational behavior after mechanical (i.e. unilateral hemitransection) but not after chemical (i.e. 6-OHDA injected in the substantia nigra) lesion. The source of regrowing dopaminergic nerve terminals in the striatum after hemitransection is mainly a response of intact remaining axons of the ipsilateral side. Moreover the contralateral nigro-striatal systems seems to play, through intrathalamic connections, an important role in regulating the GM1-induced increase of the tyrosine-hydroxylase activity.

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.

The survival of brain transplants is enhanced by extracts from injured brain

Fragments of rat embryo corpus striatum implanted into wound cavities in the cortex of neonatal rat hosts showed very poor survival when transplantation was performed immediately after the cavity was made. Consistent survival of the transplants was made possible by supplying the implant with extracts from the injured brain of neonatal rats. These extracts also supported in vitro survival of embryonic striatal neurons, suggesting that transplanted cells benefit from injury-induced neuronotrophic factors.

Cell biology of synaptic plasticity

The nervous system of mammals retains throughout the animals' life-span the ability to modify the number, nature, and level of activity of its synapses. Synaptic plasticity is most evident after injury to the nervous system, and the cellular and molecular mechanisms that make it possible are beginning to be understood. Transplantation of brain tissue provides a powerful approach for studying mechanisms of synaptic plasticity. In turn, understanding the response of the central nervous system to injury can be used to optimize transplant survival and integration with the host brain.

Postnatal development of the serotonin innervation of the hippocampus and dentate gyrus following raphe implants

Serotoninergic (5-HT) neurons derived from the embryonic raphe nuclear area (brainstem, embryonic days (E 16-18) were implanted into the entorhinal cortex of 6-day-old (P6) neonatal rat recipients which had received a fimbria lesion and entorhinal cortex ablation on P3. The hippocampus, dentate gyrus, and the raphe implant area were examined with 5-HT immunohistochemistry 7, 14, 21, 30, and 60 days after implantation. The pattern of 5-HT reinnervation was compared to that of normal and lesioned animals, and to previous studies in which rats received septal or striatal implants. In the hippocampus adjacent to the implant 5-HT-immunoreactive fibers were first observed by 7 days postimplantation and increased in density and in their septotemporal and dorsoventral extent with increasing time postimplantation. Moderately dense fiber networks were diffusely distributed in the hippocampus and dentate gyrus at 30 and 60 days postimplant. Little, if any, indication of lamination was present. Retrogradely labeled neurons (the majority of which contained 5-HT immunoreactivity) were observed in the raphe implant following injections of Fast Blue into the hippocampal formation. A few retrogradely labeled cells did not contain 5-HT, methionine-enkephalin (ME), or substance P (SP) immunoreactivity, although ME- and SP- immunoreactive neurons were observed in the implants. The lamination patterns and the increased density of 5-HT-immunoreactive fibers following a raphe implant into the entorhinal cortex clearly differ from the normal 5-HT pattern and from the patterns of lamination following a striatal or septal implant.

Use of central neuronal cultures for the detection of neuronotrophic agents

Neuronotrophic factors, a class of macromolecules thought to be present within the neuronal environment are required to support the survival in vitro of peripheral neurons. In the present study we have established bioassay culture systems suitable for the identification of similar agents for intrinsic neurons of the central nervous system. The striatum, hippocampus and septum of 18 day fetal rats were dissociated and plated in a serum-free medium on a neurite conducive substratum which allows an easy recognition of neurons under phase contrast microscopy. These cultures contain predominantly neurons as assessed by tetanus toxin labelling, a well recognized neuronal marker. Seeding the cell suspensions at decreasing densities yields after 24 h a density dependent survival of the neuronal population. Thus a low seeding density could be chosen where survival of these neurons required an exogenous source of trophic factors. Survival of central neurons was promoted by several conditioned media derived from rodent glial cell cultures, both primary (astroglia, Schwann) and clonal (C6 glioma, Schwannoma). Serial dilutions of these media allowed the titration of their respective neuronotrophic activities. In addition, conditioned media derived from the central neuronal cultures themselves, when seeded at a high density, were also able to support the survival of low density seeded central neurons.

Neuronotrophic activities in cerebrospinal fluid of head trauma patients

Neuronotrophic factors (NTFs) are agents required for neurons to survive in tissue culture. In this study, we investigated the presence of NTFs in cerebrospinal fluid (CSF) of patients with central nervous system (CNS) injury. Cerebrospinal fluid was collected from 15 patients with acute CNS lesions in whom ventricular catheters had been placed to monitor and to facilitate the control of intracranial pressure. Neuronotrophic activity within the CSF was assayed using cultures of neurons derived from fetal rat hippocampus and embryonic chick cerebral cortex. Cerebrospinal fluid from all 15 patients contained NTFs which supported the survival of rat hippocampal neurons. Survival of chick cortex neurons was supported by eight of nine CSF samples. In the 11 patients from whom consecutive CSF samples were available, NTF activity assayed in rat hippocampal cultures tended to decrease during the first several days after CNS injury. In CSF collected from three patients by lumbar puncture for diagnosis of "nontraumatic" conditions, no NTFs were detectable. NTFs supporting hippocampal neurons were also detected in extracts of blood clot obtained from normal volunteers. Neuronotrophic activity in the CSF was heat sensitive, nondialyzable, and macromolecular, suggesting its association with a protein(s). These observations suggested that (i) NTFs are detectable in human CSF after CNS injury, (ii) NTFs appear in response to the injury itself, and (iii) at least some human NTFs can support the survival in culture of nonhuman CNS neurons.

Enhancing the self-repairing potential of the CNS after injury

Embryonic CNS tissues can now be successfully transplanted into most regions of the CNS in neonate, adult, or aged host animals. The transplants generally project to their correct target areas in the host brain. However, transplants appear to receive only partial innervation by host fibers. Replacement of lost host neurons by transplants has proven to be functionally most successful in the cases of neurosecretory, monoaminergic, or cholinergic neurons. Their success probably depends on their ability to deliver the proper neurotransmitter (and perhaps trophic factors) close to their targets rather than on their capacity to reestablish all lost connections. Efforts to achieve complete integration of the transplants will probably require interventive strategies to guide the natural repair response of CNS tissue. Survival and outgrowth of the transplants can be promoted by taking advantage of the natural increase of neurotrophic factors in response to injury. Neurotrophic factors and substrate guidance factors, once purified and completely characterized, promise to be powerful new therapeutic agents for enhancing the survival and regrowth of the injured CNS.

Laminin promotes neuritic regeneration from cultured peripheral and central neurons

The ability of axons to grow through tissue in vivo during development or regeneration may be regulated by the availability of specific neurite-promoting macromolecules located within the extracellular matrix. We have used tissue culture methods to examine the relative ability of various extracellular matrix components to elicit neurite outgrowth from dissociated chick embryo parasympathetic (ciliary ganglion) neurons in serum-free monolayer culture. Purified laminin from both mouse and rat sources, as well as a partially purified polyornithine-binding neurite promoting factor (PNPF-1) from rat Schwannoma cells all stimulate neurite production from these neurons. Laminin and PNPF-1 are also potent stimulators of neurite growth from cultured neurons obtained from other peripheral as well as central neural tissues, specifically avian sympathetic and sensory ganglia and spinal cord, optic tectum, neural retina, and telencephalon, as well as from sensory ganglia of the neonatal mouse and hippocampal, septal, and striatal tissues of the fetal rat. A quantitative in vitro bioassay method using ciliary neurons was used to (a) measure and compare the specific neurite-promoting activities of these agents, (b) confirm that during the purification of laminin, the neurite-promoting activity co-purifies with the laminin protein, and (c) compare the influences of antilaminin antibodies on the neurite-promoting activity of laminin and PNPF-1. We conclude that laminin and PNPF-1 are distinct macromolecules capable of expressing their neurite-promoting activities even when presented in nanogram amounts. This neurite-promoting bioassay currently represents the most sensitive test for the biological activity of laminin.

Endogenous and exogenous factors support neuronal survival and choline acetyltransferase activity in embryonic spinal cord cultures

Dissociated 4-day (stage 23) chick embryo lumbar cord cells were cultured at low or high cell densities for 1 or 5 days in the presence or absence of added spinal neuronotrophic factor (supplied as RN22 Schwannoma conditioned medium, RCM). In low density, 1-day cultures neuronal survival was dependent on added RCM whereas by 5 days no neurons survived, even in the presence of RCM. In high density 1-day cultures a substantial neuronal population could survive even without added RCM and a large proportion of this neuronal population would survive for 5 days. When conditioned media from high density lumbar cord cultures was supplied to low density unsupplemented cultures, a similar level of 5-day neuronal survival resulted. However, no neurons survived in RCM-supplemented 5-day high density cultures, indicating the presence in RCM of a material toxic for the neurons. Both the RCM and the high density lumbar culture-conditioned medium supported considerable choline acetyltransferase activity indicating the presence within these cultures of motoneurons.