Twenty-five years of progress: the view from NIMH and NINDS

As directors of two NIH institutes supporting neuroscience research, we explore the gap between 25 years of stunning progress in fundamental neuroscience and the persistent needs of those with brain disorders. We conclude that closing this gap will require a more detailed comprehension of brain function, a rethinking of how we approach translational science, a focus on human neurobiology, and a continuing commitment to build a diverse, innovative neuroscience workforce. In contrast to many other areas of medicine, we lack basic knowledge about our organ of interest. The next phase of progress on brain disorders will require a significantly deeper understanding of fundamental neurobiology.

Research priorities. The NIH BRAIN Initiative

The NIH BRAIN Initiative will build on recent successes in neuroscience to create and apply new tools for understanding brain activity.

The NIH toolbox: setting a standard for biomedical research

This special issue of Neurology(®) marks the unveiling of a multi-year effort to develop the NIH Toolbox for Assessment of Neurological and Behavioral Function (NIH Toolbox). Constructed based on state-of-the-art psychometric research and novel testing methods, this approach to functional neurologic measurement is as innovative in concept as it is in design. This initiative and the resulting set of instruments, supported through the NIH Blueprint for Neuroscience Research (NIH Blueprint) and built by a development team of more than 250 scientists from almost 100 academic institutions, promises to provide long overdue economies of scale and efficiency to the clinical research enterprise. The NIH Toolbox achieves that end by providing psychometrically sound, cutting-edge, adaptable measures that enable uniformity of measurement, data sharing, and integration of findings in the research setting.

A call for transparent reporting to optimize the predictive value of preclinical research

The US National Institute of Neurological Disorders and Stroke convened major stakeholders in June 2012 to discuss how to improve the methodological reporting of animal studies in grant applications and publications. The main workshop recommendation is that at a minimum studies should report on sample-size estimation, whether and how animals were randomized, whether investigators were blind to the treatment, and the handling of data. We recognize that achieving a meaningful improvement in the quality of reporting will require a concerted effort by investigators, reviewers, funding agencies and journal editors. Requiring better reporting of animal studies will raise awareness of the importance of rigorous study design to accelerate scientific progress.

The distribution of spindle microtubules during mitosis in cultured human cells

WI-38 and HeLa cells in mitosis have been selected from fixed monolayer cultures and serially sectioned for electron microscopy. Sections perpendicular to the spindle axis permit counting of the number of microtubules at each position on the spindle axis and hence the preparation of tubule distribution profiles. Errors intrinsic to this method are discussed. The changes in the tubule distributions from one mitotic stage to another provide evidence concerning the behavior of the spindle tubules during mitosis. The ratio of the number of tubules passing the chromosomes on the metaphase plate to the maximum number in each half spindle is about 1/2. This ratio changes little in early anaphase, and then decreases in late anaphase at about the same time that a zone of increased tubule number develops at the middle of the interzone. The region where the stem bodies form contains about 3/2 the number of tubules seen elsewhere in the interzone. This ratio is almost constant as the mid-body forms in telophase and then increases to 2/1 in early interphase before the final stages of cytokinesis occur.

Adrenergic-cholinergic dual function in cultured sympathetic neurons of the rat

Sympathetic principal neurons, dissociated from the superior cervical ganglia of newborn rats and put into culture, exhibit plasticity with respect to the choice between noradrenaline (norepinephrine) and acetylcholine as transmitter. The neurons shift from an initial, immature adrenergic state to a cholinergic state in certain culture conditions, e.g in co-culture with a variety of non-neuronal cells or after exposure to a medium conditioned by such cells. To study the transition directly, we have grown single neurons in "microcultures" with cardiac myocytes, which provide a sensitive assay for the transmitters secreted by the neurons. We have shown previously that during the transition from adrenergic to cholinergic status such neurons secrete both transmitters and have terminals of mixed fine structure (dual function). We describe here experiments in which identified neurons were serially assayed over periods of 9-45 days. Partial transitions were observed, always in the direction adrenergic to cholinergic function, and one complete transition was observed from apparently purely adrenergic function to dual function and then to apparently purely cholinergic function. We also report observation of adrenergic-cholinergic dual function, in preliminary single and serial assays, in sympathetic principal neurons from the superior cervical ganglia of adult rats.

The 3rd Judith Hoyer Lecture in epilepsy, December 2, 2005 opening remarks

On December 2, 2005, Dr. Jeffrey L. Noebels presented the third lecture in a series highlighting the promise of epilepsy research. Opening remarks were provided by Dr. Story C. Landis, Director of the National Institute of Neurological Disorders and Stroke, and by Representative Steny Hoyer (D-MD). The lecture series is held in memory of Mrs. Judith Hoyer, an active member of the Board of Directors of the Epilepsy Foundation (EF) and the late wife of Rep. Hoyer. Mrs. Hoyer spent her life both helping families to cope with epilepsy and promoting research into a cure and a better quality of life for those with the disorder. The purpose of the lecture is to raise awareness of epilepsy among researchers and the public and provide intellectual stimulation that will encourage continuing progress toward finding a cure for epilepsy.

Response to: "Rescuing the NIH before it is too late"

We, the directors of the 27 NIH institutes and centers, wanted to respond to the points made by Andrew Marks in his recent editorial. While we appreciate that the scientific community has concerns, the current initiatives and directions of the NIH have been developed through planning processes that reflect openness and continued constituency input, all aimed at assessing scientific opportunities and addressing public health needs.

Developmental expression of the high affinity choline transporter in cholinergic sympathetic neurons

Choline uptake by the high affinity choline transporter (CHT) is the rate-limiting step in acetylcholine synthesis. Induction of CHT is therefore a critical step in cholinergic differentiation, and we examined the developmental expression of CHT in cholinergic sympathetic neurons that innervate rodent sweat glands. During postnatal development the earliest sympathetic axons in the rear footpads are noradrenergic, containing intense tyrosine hydroxylase immunoreactivity and lacking CHT-immunoreactivity (CHT-IR). By postnatal day 7 (P7) in mouse, and P10 in rat, weak CHT-IR appeared in axons associated with the sweat gland anlagen. CHT staining intensity increased during the following weeks in conjunction with plexus arborization and gland maturation. The pattern of CHT-immunoreactivity (CHT-IR) in the sweat gland innervation was similar to staining for the vesicular acetylcholine transporter and vasoactive intestinal peptide. Immunoblots of tissue from sympathectomized rats confirmed that most of the CHT in footpad was contained in sympathetic neurons. Although CHT expression has been reported in noradrenergic sympathetic neurons of the superior cervical ganglion, these data indicate that in the sympathetic neurons projecting to sweat glands CHT is present at detectable levels only after association with the glands.

Induction of cholinergic function in cultured sympathetic neurons by periosteal cells: cellular mechanisms

Periosteum, the connective tissue surrounding bone, alters the transmitter properties of its sympathetic innervation during development in vivo and after transplantation. Initial noradrenergic properties are downregulated and the innervation acquires cholinergic and peptidergic properties. To elucidate the cellular mechanisms responsible, sympathetic neurons were cultured with primary periosteal cells or osteoblast cell lines. Both primary cells and an immature osteoblast cell line, MC3T3-E1, induced choline acetyltransferase (ChAT) activity. In contrast, lines representing marrow stromal cells or mature osteoblasts did not increase ChAT. Growth of periosteal cells with sympathetic neurons in transwell cultures that prevent direct contact between the neurons and periosteal cells or addition of periosteal cell-conditioned medium to neuron cultures induced ChAT, indicating that periosteal cells release a soluble cholinergic inducing factor. Antibodies against LIFRbeta, a receptor subunit shared by neuropoietic cytokines, prevented ChAT induction in periosteal cell/neuron cocultures, suggesting that a member of this family is responsible. ChAT activity was increased in neurons grown with periosteal cells or conditioned medium from mice lacking either leukemia inhibitory factor (LIF) or LIF and ciliary neurotrophic factor (CNTF). These results provide evidence that periosteal cells influence sympathetic neuron phenotype by releasing a soluble cholinergic factor that is neither LIF nor CNTF but signals via LIFRbeta.

Catecholamines are required for the acquisition of secretory responsiveness by sweat glands

The sympathetic innervation of sweat glands undergoes a developmental change in transmitter phenotype from catecholaminergic to cholinergic. Acetylcholine elicits sweating and is necessary for development and maintenance of secretory responsiveness, the ability of glands to produce sweat after nerve stimulation or agonist administration. To determine whether catecholamines play a role in the development or function of this system, we examined the onset of secretory responsiveness in two transgenic mouse lines, one albino and the other pigmented, that lack tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis. Although both lines lack TH, their catecholamine levels differ because tyrosinase in pigmented mice serves as an alternative source for catecholamine synthesis (Rios et al., 1999). At postnatal day 21 (P21), 28 glands on average are active in interdigital hind footpads of albino TH wild-type mice. In contrast, fewer than one gland is active in albino TH null mice, which lack catecholamines in gland innervation. Treatment of albino TH null mice with DOPA, a catecholamine precursor, from P11 to P21 increases the number of active glands to 14. Pigmented TH null mice, which have faint catecholamine fluorescence in the developing gland innervation, possess 12 active glands at P21, indicating that catecholamines made via tyrosinase, albeit reduced from wild-type levels, support development of responsiveness. Gland formation and the appearance of cholinergic markers occur normally in albino TH null mice, suggesting that catecholamines act directly on gland cells to trigger their final differentiation and to induce responsiveness. Thus, catecholamines, like acetylcholine, are essential for the development of secretory responsiveness.

Absence of cholinergic sympathetic innervation from limb muscle vasculature in rats and mice

Although the existence of cholinergic sympathetic vasodilatory innervation in limb muscle vasculature is well established for some species, previous pharmacological studies have failed to reveal the presence of such innervation in rats. Recently, Schafer and colleagues [Schafer, M.K., Eiden, L.E., Weihe, E., 1998. Cholinergic neurons and terminal fields revealed by immunohistochemistry for the vesicular acetylcholine transporter. II. The peripheral nervous system. Neuroscience 84(2), 361-376] reported that vesicular acetylcholine transporter immunoreactivity (VAChT-IR), a marker for cholinergic terminals, is present in the innervation of the microvasculature of rat hindlimb skeletal muscle and concluded that rats possess cholinergic sympathetic innervation of limb muscle vasculature. Because of our interest in identifying targets of cholinergic sympathetic neurons, we have analyzed the transmitter properties of the innervation of muscle vessels in rat and mouse limbs. We found that the innervation of vasculature in muscle is noradrenergic, exhibiting robust catecholamine histofluorescence and immunoreactivity for tyrosine hydroxylase (TH) and the peptide transmitters, neuropeptide Y (NPY) and occasionally vasoactive intestinal peptide (VIP). In contrast, cholinergic phenotypic markers,VAChT-IR and acetylcholinesterase (AChE) activity, are absent. Neuron cell bodies in sympathetic ganglia, retrogradely labeled with injections of tracer into limb muscles, also lacked VAChT but contained TH-IR. The innervation of large extramuscular feed arteries in hindlimbs was also devoid of cholinergic markers, as were the cell bodies of sympathetic neurons innervating extramuscular femoral arteries. These results, like those of previous physiological studies, provide no evidence for the presence of cholinergic sympathetic innervation of muscle vasculature in rats or mice.

Developmental changes in the transmitter properties of sympathetic neurons that innervate the periosteum

During the development of sweat gland innervation, interactions with the target tissue induce a change from noradrenergic to cholinergic and peptidergic properties. To determine whether the change in neurotransmitter properties that occurs in the sweat gland innervation occurs more generally in sympathetic neurons, we identified a new target of cholinergic sympathetic neurons in rat, the periosteum, which is the connective tissue covering of bone, and characterized the development of periosteal innervation of the sternum. During development, sympathetic axons grow from thoracic sympathetic ganglia along rib periosteum to reach the sternum. All sympathetic axons displayed catecholaminergic properties when they reached the sternum, but these properties subsequently disappeared. Many axons lacked detectable immunoreactivities for vesicular acetylcholine transporter and vasoactive intestinal peptide when they reached the sternum and acquired them after arrival. To determine whether periosteum could direct changes in the neurotransmitter properties of sympathetic neurons that innervate it, we transplanted periosteum to the hairy skin, a noradrenergic sympathetic target. We found that the sympathetic innervation of the transplant underwent a noradrenergic to cholinergic and peptidergic change. These results suggest that periosteum, in addition to sweat glands, regulates the neurotransmitter properties of the sympathetic neurons that innervate it.

The p75 neurotrophin receptor influences NT-3 responsiveness of sympathetic neurons in vivo

To determine the role of the p75 neurotrophin receptor (p75NTR) in sympathetic neuron development, we crossed transgenic mice with mutations in p75NTR, nerve growth factor (NGF) and neurotrophin-3 (NT-3). Neuron number is normal in sympathetic ganglia of adult p75NTR-/- mice. Mice heterozygous for a NGF deletion (NGF+/-) have 50% fewer sympathetic neurons. In the absence of p75NTR (p75NTR-/- NGF+/-), however, neuron number is restored to wild-type levels. When NT-3 levels are reduced (p75NTR-/- NGF+/- NT3 +/-), neuron number decreases compared to p75NTR-/- NGF+/- NT3+/+. Thus, without p75NTR, NT3 substitutes for NGF, suggesting that p75 alters the neurotrophin specificity of TrkA in vivo.

Cellular and molecular determinants of sympathetic neuron development

The development of the sympathetic nervous system can be divided into three overlapping stages. First, the precursors of sympathetic neurons arise from undifferentiated neural crest cells that migrate ventrally, aggregate adjacent to the dorsal aorta, and ultimately differentiate into catecholaminergic neurons. Second, cell number is refined during a period of cell death when neurotrophic factors determine the number of neuronal precursors and neurons that survive. The final stage of sympathetic development is the establishment and maturation of synaptic connections, which for sympathetic neurons can include alterations in neurotransmitter phenotype. Considerable progress has been made recently in elucidating the cellular and molecular mechanisms that direct each of these developmental decisions. We review the current understanding of each of these, focusing primarily on events in the peripheral nervous system of rodents.

Development of muscarinic receptors and regulation of secretory responsiveness in rodent sweat glands

Sweat glands are innervated by sympathetic neurons which undergo a change in transmitter phenotype from noradrenergic to cholinergic during development. As soon as the glands begin to differentiate, M3 muscarinic receptor mRNA and binding sites are detectable. Receptor expression appears in the absence of innervation and is maintained after denervation. While receptor expression is not regulated by innervation, secretory responsiveness is. Muscarinic blockade during development or in adult animals results in the loss of responsiveness and its reappearance requires several days. Cholinergic muscarinic activation is most likely to regulate one or more steps in the signalling cascade that are downstream of calcium mobilization. The anterograde regulation of sweat gland responsiveness is one facet of the reciprocal interactions are required to establish a functional synapse in this system.

Target-dependent development of the vesicular acetylcholine transporter in rodent sweat gland innervation

Descriptive studies have delineated a developmental change in neurotransmitter phenotype from noradrenergic to cholinergic in the sympathetic innervation of sweat glands in rodent footpads. Transplantation and culture experiments provide evidence that interactions with the target tissue induce this change. Recent studies with an antiserum that recognizes the vesicular acetylcholine transporter (VAChT) suggest, however, that the development of cholinergic function in sympathetic neurons, including those that innervate sweat glands, occurs prior to and does not require target contact. To clarify these apparently contradictory findings, we directly compared the appearance of VAChT immunoreactivity in the sympathetic neurons that innervate sweat glands with the time that axons contact this target. We find that VAChT immunoreactivity is not detectable in either the axons or cell bodies of sweat gland neurons until several days after target innervation. Before and during VAChT acquisition, the developing sweat gland innervation contains vesicular stores of catecholamines. An analysis of mutant mice that lack sweat glands was undertaken to determine whether VAChT expression requires target interactions and revealed that VAChT does not appear in the absence of glands. These findings, together with previous studies, confirm the target dependence of cholinergic function in the sympathetic neurons that innervate sweat glands.

Overexpression of nerve growth factor in epidermis disrupts the distribution and properties of sympathetic innervation in footpads

Sympathetic and sensory neurons form distinct axonal arborizations in several peripheral targets. The developmental mechanisms responsible for partitioning sympathetic and sensory axons between potential target tissues are poorly understood. We have used rodent footpads to study this process because three populations of peripheral axons innervate topographically segregated targets in the footpad; cholinergic sympathetic axons innervate sweat glands, noradrenergic sympathetic axons innervate blood vessels, and sensory axons form a plexus at the epidermal/dermal junction. To examine how nerve growth factor (NGF), a trophic and survival factor for sympathetic and some sensory neurons, may contribute to the generation of the patterned distribution of axons among targets, we studied transgenic mice (K14-NGF mice) in which NGF expression was significantly increased in the epidermis. Whereas the temporal sequence in which sensory and sympathetic fibers arrived in the footpad was not affected, the normal partitioning of axons between target tissues was disrupted. The two sympathetic targets in footpads, sweat glands, and blood vessels lacked substantial innervation and instead a dense plexus of catecholaminergic sympathetic fibers was found commingled with sensory fibers in the dermis. Those sympathetic fibers present in sweat glands expressed an abnormal dual catecholaminergic/cholinergic phenotype. Our findings indicate that overexpression of NGF in skin interferes with the segregation of sensory and sympathetic axonal arbors and suggests a role for target-derived NGF in the establishment of distinct axonal territories. Our data also suggest that by determining where axon arbors form, NGF can indirectly influence the phenotypic properties of sympathetic neurons.

A sweat gland-derived differentiation activity acts through known cytokine signaling pathways

The sympathetic innervation of sweat glands undergoes a target-induced noradrenergic to cholinergic/peptidergic switch during development. Similar changes are induced in cultured sympathetic neurons by sweat gland cells or by one of the following cytokines: leukemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF), or cardiotrophin-1 (CT-1). None of these is the sweat gland-derived differentiation activity. LIF, CNTF, and CT-1 act through the known receptors LIF receptor beta (LIFRbeta) and gp130 and well defined signaling pathways including receptor phosphorylation and STAT3 activation. Therefore, to determine whether the gland-derived differentiation activity was a member of the LIF/CNTF cytokine family, we tested whether it acted via these same receptors and signal cascades. Blockade of LIFRbeta inhibited the sweat gland differentiation activity in neuron/gland co-cultures, and extracts of gland-containing footpads stimulated tyrosine phosphorylation of LIFRbeta and gp130. An inhibitor (CGX) of molecules that bind the CNTFRalpha, which is required for CNTF signaling, did not affect the gland-derived differentiation activity. Soluble footpad extracts induced the same changes in NBFL neuroblastoma cells as LIF and CNTF, including increased vasoactive intestinal peptide mRNA, STAT3 dimerization, and DNA binding, and stimulation of transcription from the vasoactive intestinal peptide cytokine-responsive element. Thus, the sweat gland-derived differentiation activity uses the same signaling pathway as the neuropoietic cytokines, and is likely to be a family member.

CNTF and LIF are not required for the target-directed acquisition of cholinergic and peptidergic properties by sympathetic neurons in vivo

During development, the sympathetic innervation of two targets, sweat glands and periosteum, changes the neurotransmitters it expresses from noradrenaline to acetylcholine and vasoactive intestinal peptide (VIP). The target-derived molecules that induce, these changes have not been identified. Neuropoietic cytokines, including ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF), induce the same phenotypic changes in sympathetic neurons in vitro as sweat glands and periosteum do in vivo, raising the possibility that one of these factors mediates induction of cholinergic traits and VIP by these target tissues. Because CNTF and LIF have overlapping functions and signalling pathways, they could act interchangeably or in concert to influence neurotransmitter expression. To determine whether CNTF or CNTF and LIF together are responsible for the induction of cholinergic and peptidergic function in vivo, we analyzed the neurotransmitter properties of sweat gland innervation in mice lacking CNTF or CNTF and LIF. We find that, as in wild-type mice, gland innervation in mice lacking one or both molecules appropriately expresses cholinergic properties and VIP immunoreactivity. Furthermore, footpads of mice lacking one or both genes contain choline acetyltransferase activity comparable to that of wild-type mice, and CNTF- or CNTF/LIF-deficient mice possess the normal complement of active sweat glands. We analyzed the innervation of a second, recently identified cholinergic sympathetic target, the periosteum, which is the connective tissue surrounding bone. Periosteal innervation of mice lacking CNTF, LIF, or both, like that of wild-type mice, is immunoreactive for the vesicular acetylcholine transporter, a recently identified cholinergic marker, and VIP. These results provide evidence that neither CNTF, LIF, nor a combination of the two are required for the developmental change from noradrenergic to cholinergic function that occurs in sympathetic innervation of sweat glands and periosteum.

Signals triggering the induction of leukemia inhibitory factor in sympathetic superior cervical ganglia and their nerve trunks after axonal injury

Leukemia inhibitory factor (LIF) plays an important role in regulating neuropeptide expression in sympathetic and sensory neurons after axonal transection. By 2 h after axotomy, LIF mRNA increased in nonneuronal cells in sympathetic ganglia and peripheral nerve. In addition, within 1 h of explanting sympathetic ganglia or segments of sympathetic nerve trunks, a protein factor(s) that was able to induce LIF mRNA both in sympathetic cultures and in intact ganglia in vivo was released. This factor(s) appeared to be present in sympathetic ganglia and their nerve trunks under normal conditions and to be activated and/or released after axonal injury. Since the factor(s) has a molecular weight(s) greater than 66 kDa, and no other proteins of such high molecular weight have been previously identified with LIF-inducing activity, it appears to be a novel inducer of LIF.

Differential regulation of adrenergic receptor development by sympathetic innervation

Rat sweat glands provide an interesting model system for a developmental study of adrenergic receptor expression because their sympathetic innervation undergoes a switch from a nonadrenergic to cholinergic and peptidergic phenotype. alpha 1B, alpha 2B, and beta 2 receptors are expressed in rat footpads; alpha 1 and beta 2 receptors are localized specifically to sweat glands, and alpha 2 receptors also are expressed in other tissues. alpha 1 and, to a lesser extent, beta 2 receptors decrease during development, whereas alpha 2 levels remain relatively constant. Decreased receptor expression is accompanied by the loss of alpha 1-stimulated inositol phosphate accumulation, but no change in beta-stimulated cAMP production. The number of alpha 1 and beta 2 receptors decreases after P21, when the sympathetic innervation no longer produces catecholamines. Neonatal sympathectomy causes a partial failure of alpha 1 downregulation, but has no effect on beta 2 or alpha 2 receptor levels. Therefore, at least two distinct mechanisms regulate development of adrenergic receptors in sweat glands. Innervation-independent processes control developmental expression of alpha 1, beta 2, and alpha 2 receptors, and an additional, innervation-dependent mechanism influences expression of alpha 1 receptors. Denervation at postnatal day 20, when the sympathetic innervation is cholinergic and peptidergic, results in retention of alpha 1 receptors, but cholinergic blockade begun at P20 does not. These results indicate that regulation of receptor expression in sweat glands is complex, and suggest that the innervation-dependent factors that decrease alpha 1 levels during development act through a nonadrenergic, noncholinergic mechanism.

The development of cholinergic sympathetic neurons: a role for neuropoietic cytokines?

The sympathetic neurons that innervate eccrine sweat glands undergo a phenotypic switch from noradrenergic to cholinergic and peptidergic. The changes in neurotransmitter choice are retrogradely specified by interactions with the target tissue that are mediated by a secreted differentiation factor. Production of the target-derived differentiation factor requires noradrenergic innervation. The switch from noradrenergic to cholinergic and peptidergic is reproduced in culture when neonatal sympathetic neurons are treated with members of the neuropoietic cytokine family, leukemia inhibitory factor (LIF) or ciliary neurotrophic factor (CNTF), suggesting that these cytokines might be responsible for the target-induced change in neurotransmitter properties. Analysis of transgenic mice that lack either LIF or CNTF or both, however, does not support their candidacy: the transmitter properties of the sweat gland innervation is indistinguishable from that of wild-type mice. It seems likely that another and novel member of the, family is responsible.

Cardiotrophin-1 is not the sweat gland-derived differentiation factor

Sympathetic neurons innervating sweat glands undergo a target-directed switch in neurotransmitter properties. Although the factor responsible for inducing this switch has not been identified, it appears to be a member of the neuropoietic cytokine family. Cardiotrophin-1 (CT-1), a new family member, was analyzed to determine whether it was a relevant factor. CT-1 induced choline acetyl-transferase and vasoactive intestinal peptide in cultured sympathetic neurons, and RT/PCR amplified CT-1 mRNA from footpad total RNA. The differentiation activity of CT-1 was blocked by CT-1 antiserum. The activity in sweat gland extracts and cultures was not, however, suggesting that CT-1 is not the sweat gland-derived factor.

Sympathetic axons pathfind successfully in the absence of target

To determine whether sympathetic axons require the presence of a peripheral target to grow to the correct destination, we examined the developing footpad innervation in tabby mutant mice which lack sweat glands. Despite the absence of sweat glands, noradrenergic sympathetic axons are transiently present in the presumptive target area and avoid the more distal epidermal/dermal domain occupied by sensory axons. Since sympathetic axon pathfinding was not dependent upon the target tissue, we compared the subsequent development of sweat gland axons in tabby footpads with that in control footpads. In wild-type mice, the gland-associated axonal plexus expands considerably as the secretory tubule enlarges and coils. This expansion, however, does not occur in tabby mice. The sweat gland innervation of wild-type mice loses catecholamines and acquires AChE activity and vasoactive intestinal peptide immunoreactivity. In tabby mutant mice, catecholaminergic fibers remain in the glandless footpads for 2 weeks and fail to acquire AChE or vasoactive intestinal peptide. In contrast to the altered development of gland innervation in tabby, the development of the innervation of footpad blood vessels was unaffected. Our observations indicate that the target is not required to direct sympathetic axons to the presumptive gland region of the footpad. In the absence of the target tissue, however, gland-targeted sympathetic axons retain an immature morphology and transmitter phenotype and then disappear.

The role of acetylcholine in regulating secretory responsiveness in rat sweat glands

While retrograde regulation of neuronal development by target-derived factors in the autonomic nervous system is well established, the importance of anterograde influences on target development is unclear. Previous studies suggest that sympathetic innervation of sweat glands plays a critical role in the acquisition and maintenance of their secretory function. To define the signal(s) responsible, we disrupted muscarinic cholinergic transmission in developing and adult rats. Treatment of young rats with the nonselective antagonist, atropine, or an antagonist selective for the glandular muscarinic subtype, 4-DAMP, delayed the development of secretory responsiveness. Treatment of adult animals with atropine caused its loss. Further, following denervation, treatment with the muscarinic agonist, pilocarpine, largely preserved responsiveness while untreated animals lost function. Thus, acetylcholine, whose presence in sweat gland innervation is retrogradely specified by developmental interactions with the target tissue, in turn plays an important role in inducing and maintaining target tissue responsiveness through muscarinic receptor activation.

Production of sweat gland cholinergic differentiation factor depends on innervation

Sympathetic neurons innervating sweat glands undergo a target-directed developmental switch in neurotransmitter properties. Using cultured sympathetic neurons as a bioassay for cholinergic differentiation factors, we and others found that extracts containing soluble proteins from developing and adult footpads caused the same changes in transmitter properties in sympathetic neurons in vitro that the target does in vivo. In the present studies, using footpads from Tabby mutant mice that lack sweat glands, we found that the presence of sweat glands is correlated with the presence of cholinergic differentiation activity in footpad extracts. We examined the conditions necessary for secretion of differentiation activity from primary cultures of sweat gland cells. Surprisingly, sweat gland cells cultured alone do not produce or secrete cholinergic differentiation activity. When grown in the presence of sympathetic neurons, however, gland cells induce cholinergic function, increase vasoactive intestinal peptide content, and reduce catecholamine production in the neurons. Medium conditioned by sweat gland/neuron cocultures has a similar effect on the transmitter properties of cultured sympathetic neurons, indicating that the target influence on phenotype is mediated by a secreted factor(s). The innervation-dependence of cholinergic differentiation factor production provides evidence that reciprocal interactions between neurons and sweat glands are necessary for acquisition of the mature transmitter phenotype.

Disruption of target interactions prevents the development of enkephalin immunoreactivity in sympathetic neurons

We compared the development of enkephalin (Enk) expression in normal rats and rats in which target contact was transiently disrupted with 6-hydroxydopamine (6-OHDA). During the first 3 postnatal weeks, there was a striking increase in Enk immunoreactivity (-IR) in superior cervical ganglia (SCG) assayed by radioimmunoassay (RIA). This increase was correlated with the appearance of Enk-IR in postganglionic neurons. In the caudal region of the SCG, the proportion of Enk-IR neurons and their immunoreactivity increased until one-third of the neurons possessed Enk-IR between postnatal days (P) 14 and 21. After P21, the number of Enk-IR neurons and their immunofluorescence decreased. By 6 weeks, only occasional neurons possessed moderate Enk-IR. The increases in Enk-IR were correlated with increased ganglionic proenkephalin A mRNA detected by in situ hybridization. The decrease in IR after P21 was not, however, paralleled by a comparable decrease in proenkephalin A mRNA. To determine whether interactions between SCG neurons and their target tissues influence Enk expression, we disrupted them by treating neonatal rats with a single dose of 6-OHDA at P0. This treatment transiently reduced sympathetic fiber density in the submandibular gland, one target of Enk-IR neurons, over 90%. Two weeks later, the fiber density in glands of treated animals was not different from control. Following 6-OHDA, the concentration of Enk-IR in SCG extracts and the number of Enk-IR neurons and their immunofluorescence intensity failed to increase. SCG from treated rats also contained fewer neurons with proenkephalin A mRNA. In contrast, the content of neuropeptide Y (NPY) and the proportion of NPY-IR neurons were not decreased by 6-OHDA treatment. Our results indicate that the developmental history of Enk expression differs from that of other neuropeptides in rat sympathetic ganglia, suggesting that distinct mechanisms regulate the expression of individual neuropeptides. Further, they provide evidence that target contact during a critical period is important for the induction of Enk.

Innervation of footpads of normal and mutant mice lacking sweat glands

Footpads of normal adult mice are innervated by sympathetic and sensory fibers. The sympathetic fibers associated with sweat glands contain acetylcholinesterase and immunoreactivity for vasoactive intestinal peptide. Although catecholamine histofluorescence is absent, the gland innervation exhibits immunoreactivity for tyrosine hydroxylase. A distinct population of sympathetic fibers, which possess catecholamines and neuropeptide Y as well as tyrosinehydroxylase immunoreactivity, innervates blood vessels. Sensory fibers containing immunoreactivity for substance P and calcitonin gene-related peptide course beneath the epidermis and some form endings in it. Treatment of neonatal mice with the adrenergic neurotoxin, 6-hydroxydopamine, results in loss of sympathetic innervation of sweat glands and blood vessels, permits growth of sensory axons into sweat glands, but does not alter the peptidergic sensory innervation of the dermis and epidermis. Three mouse mutations, Tabby (Ta), crinkled (cr), and downless (dl), disrupt the interactions between the mesenchyme and epidermis that are required for normal development of specific epidermal derivatives, including sweat glands. The sympathetic innervation of blood vessels and sensory innervation of footpad skin of the three mutant mice that lack sweat glands is indistinguishable from normal. The sympathetic fibers that normally innervate sweat glands, however, are not present. These results indicate that in the absence of their normal target, the sympathetic fibers that innervate sweat glands are lacking. Furthermore, they suggest that, although sensory fibers may sprout into sympathetic targets in the footpad, the domains occupied by sensory fibers are not normally accessible to sympathetic axons.

Coordinate regulation of choline acetyltransferase, tyrosine hydroxylase, and neuropeptide mRNAs by ciliary neurotrophic factor and leukemia inhibitory factor in cultured sympathetic neurons

The neurotransmitter phenotype switch that occurs in cultures of rat superior cervical ganglion neurons after treatment with leukemia inhibitory factor or ciliary neurotrophic factor is a useful model permitting investigation of the mechanisms of cytokine-mediated differentiation. Recently the actions of leukemia inhibitory factor and ciliary neurotrophic factor have been linked through their interactions with related receptor complexes. Here we compare the effects of these two cytokines on gene expression in sympathetic neuronal cultures and begin to investigate their mechanisms. We report that, as has been shown for leukemia inhibitory factor, ciliary neurotrophic factor regulates peptides and classical transmitters in these cultures at the mRNA level. In addition, we find that the induction of substance P mRNA by these cytokines is rapid, dependent on protein synthesis, and occurs in 40-50% of superior cervical ganglion neurons in dissociated culture.

The appearance of NPY and VIP in sympathetic neuroblasts and subsequent alterations in their expression

Mature sympathetic neurons contain one or more neuropeptides in addition to a classical neurotransmitter. We compared the development of two peptides, neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP), in rat superior cervical (SCG) and stellate ganglia. NPY immunoreactivity (-IR) was first detected at embryonic day (E) 12.5. It was of similar immunofluorescence intensity in almost all tyrosine hydroxylase (TH)-IR cells. In contrast, VIP-IR, of variable fluorescence intensity, appeared at E14.5 in a subset of TH-IR cells in the stellate ganglion but not in SCG. Both peptides were present in bromodeoxyuridine-labeled neuronal precursors as well as neurons. The intensity of NPY immunofluorescence increased until E16.5. Subsequently, while it continued to increase in some neurons, the intensity decreased in others so that at birth approximately 55% of SCG and stellate neurons were NPY-IR. Developmental changes in NPY concentration, determined by radioimmunoassay, were similar in both ganglia, increasing between E14.5 and E16.5 and then decreasing 60% between E16.5 and birth. VIP expression differed from that of NPY. The proportion of VIP-IR cells began to decrease the day after VIP-IR was first detected. Although VIP-IR was present in one-third of E14.5 TH-IR stellate cells, at birth only 2% were VIP-IR. VIP-IR, measured by radioimmunoassay, was uniformly severalfold more concentrated in the stellate than SCG, and its concentration decreased throughout embryonic development, 40% between E14.5 and E16.5 and 95% by birth. In situ hybridization revealed detectable mRNA for both NPY and VIP at E14.5 in stellate ganglion and mRNA for NPY, but not VIP, in SCG. Initially, ganglionic neuropeptide mRNA appeared uniformly distributed but became heterogeneous. Our data indicate that features of the diverse peptidergic phenotypes expressed by sympathetic neurons are present when peptides are first detected while others arise subsequently. The final acquisition of peptidergic phenotypic diversity is complex, entailing both early induction in many cells and subsequent restriction to specific subpopulations.

Noradrenergic regulation of cholinergic differentiation

When the sympathetic nerves that innervate rat sweat glands reach their targets, they are induced to switch from using norepinephrine as their neurotransmitter to acetylcholine. Catecholamines (such as norepinephrine) released by nerves growing to the sweat gland induce this phenotypic conversion by stimulating production of a cholinergic differentiation factor [sweat gland factor (SGF)] by gland cells. Here, culture of gland cells with sympathetic, but not sensory, neurons induced SGF production. Blockage of alpha 1- or beta-adrenergic receptors prevented acquisition of the cholinergic phenotype in sympathetic neurons co-cultured with sweat glands, and sweat glands from sympathectomized animals lacked SGF. Thus, reciprocal instructive interactions, mediated in part by small molecule neurotransmitters, direct the development of this synapse.

Regulation of vasoactive intestinal peptide expression in sympathetic neurons in culture and after axotomy: the role of cholinergic differentiation factor/leukemia inhibitory factor

Vasoactive intestinal peptide (VIP) expression increases in sympathetic neurons when they are grown in dissociated cell or explant cultures and when they are axotomized in vivo. In dissociated cell culture, the magnitude of the VIP increase was reduced when nonneuronal cells were removed and medium conditioned by ganglionic nonneuronal cells increased VIP in neuron-enriched cultures. Antiserum against cholinergic differentiation factor (also leukemia inhibitory factor; CDF/LIF), but not against ciliary neurotrophic factor, immunoprecipitated this activity. Medium conditioned by sympathetic ganglion explants also contained a VIP-stimulatory molecule that was immunoprecipitated by CDF/LIF antiserum, and CDF/LIF antiserum partially blocked VIP induction in explants. CDF/LIF mRNA was increased in dissociated cell cultures, in ganglion explants and in vivo after axotomy. Our results suggest that CDF/LIF released from ganglionic nonneuronal cells plays an important role in regulating VIP after axotomy.

Leukemia inhibitory factor mediates an injury response but not a target-directed developmental transmitter switch in sympathetic neurons

Leukemia inhibitory factor (LIF; also known as cholinergic differentiation factor) is a multifunctional cytokine that affects neurons, as well as many other cell types. To examine its neuronal functions in vivo, we have used LIF-deficient mice. In culture, LIF alters the transmitter phenotype of sympathetic neurons, inducing cholinergic function, reducing noradrenergic function, and altering neuropeptide expression. In vivo, a noradrenergic to cholinergic switch occurs in the developing sweat gland innervation, and changes in neuropeptide phenotype occur in axotomized adult ganglia. We find that the gland innervation of LIF-deficient mice is indistinguishable from normal. In contrast, neuropeptide induction in ganglia cultured as explants or axotomized in situ is significantly suppressed in LIF-deficient mice. Thus, LIF plays a role in transmitter changes induced by axotomy but not by developmental interactions with sweat glands.

Modulation of the enkephalinergic phenotype of rat sympathetic neurons by hormonal and transsynaptic mechanisms

Most sympathetic neurons contain one or more neuropeptides in addition to catecholamines. Although the regulation of catecholamines has been studied extensively, comparatively little is known about the regulation of neuropeptides. Since glucocorticoids and preganglionic innervation regulate catecholaminergic properties in chromaffin cells, we examined the effects of these factors on a co-localized neuropeptide, leucine enkephalin (L-Enk), in adult rat sympathetic neurons in vivo. Lowered serum glucocorticoid levels as a consequence of bilateral adrenalectomy resulted in a reduction of ganglionic L-Enk content that was reversed by exposure of adrenalectomized animals to the synthetic glucocorticoid, dexamethasone. Surgical denervation of the SCG eliminated L-Enk-IR preganglionic fibers and caused a dramatic increase in the number of L-Enk-IR neurons. Inhibition of the enkephalinergic component of the preganglionic innervation by chronic exposure to the opiate receptor antagonist naloxone increases the number of L-Enk-IR cell bodies and total ganglionic L-Enk content. None of the experimental manipulations noticeably altered the number or distribution of NPY-IR neurons, suggesting that the effects of glucocorticoids and the innervation on ganglionic L-Enk levels were specific and not simply an alteration of the biosynthetic state of the cells. These results demonstrate that circulating glucocorticoids and the preganglionic innervation regulate L-Enk levels in sympathetic neurons. Since both glucocorticoid levels and preganglionic activity are known to be altered by stressful stimuli, acute regulation of sympathetic L-Enk levels may constitute an important component of the autonomic response to stress.

SA-1 antigen expression in small intensely fluorescent cells is associated with proliferation

Sympathetic neurons, chromaffin cells, and small, intensely fluorescent (SIF) cells are thought to derive from a common sympathoadrenal precursor cell. Sympathoadrenal precursor cells and adrenal chromaffin cells have been shown to react with an antibody, SA-1; we now report that, like sympathoadrenal precursors, SIF cells during their proliferative phase transiently possess this epitope. Precursors and SIF cells were identified in double-label studies of the superior cervical ganglion (SCG) using SA-1 and an antibody that identifies a noradrenergic trait, tyrosine hydroxylase (TH). At E16 when the earliest SIF precursors were detected and at birth, while postmitotic principal neurons had lost SA-1 reactivity, many SIF cells expressed both TH and SA-1. As development proceeded, the proportion of SIF cells expressing only TH increased. In addition, some small SIF-like cells possessed only SA-1 reactivity at birth. Some SIF cells at P7 possessed SA-1, but it was absent at P10 and in the adult. Bromodeoxyuridine (BrdU) was used to identify proliferating SIF cells, and SA-1+ expression was correlated with the period of SIF cell proliferation. At late embryogenesis, the proportion of SA-1+ SIF cells that possessed BrdU was relatively large (17% at E20), and decreased as SIF cell division ceased (6% at P1). Our results indicate that SA-1 is present on SIF cells when these cells are capable of cell division. In addition, mature SIF cells lack SA-1 and are therefore antigenically distinct from the sympathoadrenal precursor. These data suggest that the expression of SA-1 is correlated with the ability of sympathoadrenal cells to proliferate, in the SCG early during embryogenesis, chromaffin cells both during embryogenesis and in the adult, and SIF cells during their transient period of division in the SCG.

Regulation of substance P is similar to that of vasoactive intestinal peptide after axotomy or explantation of the rat superior cervical ganglion

The regulation of the expression of substance P (SP) in the rat superior cervical ganglion was compared to that of vasoactive intestinal peptide (VIP) in vivo after axotomy and in vitro after explantation. Previous studies have demonstrated that both neuropeptides increase after explantation, depolarization, and decentralization; however, whereas VIP expression increases after postganglionic axotomy, SP expression reportedly does not. To compare the effect of axotomy on these two peptides directly, the content of both was determined in individual ganglia at various times after surgery. The level of VIP-like immunoreactivity (IR) is increased at 2 days, reaches a peak at 6 days, and then declines by 14 days to approximately half its peak value. The level of SP-IR also increases 2 days after axotomy, but returns to control values by day 6. The increase in SP-IR is accompanied by an increase in beta-preprotachykinin mRNA, suggesting that the elevation in SP content is due, at least in part, to enhanced peptide synthesis. Immunocytochemical localization of SP-IR revealed the presence of immunoreactive principal neurons in axotomized, but not in sham-operated ganglia. Similarities in the regulation of these two neuropeptides were also investigated in organ culture by examining the effects of dexamethasone and interleukin-1 beta on VIP content, since the former has been shown to prevent the increase in SP in culture, while the latter has been found to enhance this increase (Kessler, Adler, Bell, et al., 1983, Neuroscience 9:309-321; Freidin and Kessler, 1991, Proc. Natl. Acad. Sci. USA 88:3200-3203; Hart, Shadiack, and Jonakait, 1991, J. Neurosci. Res. 29:282-291). As with SP expression, dexamethasone reduces the increase in VIP expression, while interleukin-1 beta increases it. Thus, both in vivo and in vitro, similar changes in VIP and SP expression are observed following a number of experimental manipulations, suggesting that expression of the two peptides is regulated by qualitatively similar mechanisms in sympathetic neurons.

Cell interactions that determine sympathetic neuron transmitter phenotype and the neurokines that mediate them

The transmitter properties of both developing and mature sympathetic neurons are plastic and can be modulated by a number of environmental cues. Cell culture studies demonstrate that noradrenergic neurons can be induced to become cholinergic and that the expression of neuropeptides can be altered. Similar changes in transmitter phenotype occur in vivo. During development, noradrenergic neurons that innervate eccrine sweat glands acquire cholinergic and peptidergic function. This change is dependent upon interactions with the target tissue. Following injury of sympathetic neurons in developing and adult animals, striking alterations take place in peptide expression. Ciliary neurotrophic factor and cholinergic differentiation factor/leukemia inhibitory factor, members of a family that includes several hematopoietic cytokines, induce cholinergic function and modulate neuropeptide expression in cultured sympathetic neurons. Studies in progress provide evidence that members of this new cytokine family influence the transmitter phenotype of sympathetic neurons not only in vitro but also in vivo.

Ciliary neurotrophic factor coordinately activates transcription of neuropeptide genes in a neuroblastoma cell line

Differentiation factors have been identified that influence the phenotype of sympathetic neurons by altering expression of classical neurotransmitters and neuropeptides. Investigation of the molecular mechanisms through which such factors act would be facilitated by the availability of a neuronal cell line that responds to these factors in a fashion similar to sympathetic neurons. We have identified a human neuroblastoma cell line, NBFL, that responds to the differentiation factor ciliary neurotrophic factor (CNTF) by coordinately inducing multiple neuropeptide genes as do sympathetic neurons. Treatment of NBFL cells with CNTF increases vasoactive intestinal polypeptide (VIP), somatostatin, and calcitonin gene-related peptide (CGRP) mRNAs but does not change other neurotransmitter properties. The induction of VIP mRNA by CNTF in NBFL cells is dose dependent, rapid, sustained, and independent of new protein synthesis. Genomic 5' flanking sequences located within a 1.59-kilobase region of the human VIP gene and distinct from the previously defined cAMP-responsive element subserve transcriptional activation by CNTF. Further examination of NBFL cells should permit the elucidation of the molecular mechanisms by which CNTF and other differentiation factors coordinately activate neuropeptide gene transcription to influence neuronal differentiation. Similar mechanisms may mediate the effect of CNTF on neuronal survival.

Multiple cholinergic differentiation factors are present in footpad extracts: comparison with known cholinergic factors

Sweat glands in rat footpads contain a neuronal differentiation activity that switches the phenotype of sympathetic neurons from noradrenergic to cholinergic during normal development in vivo. Extracts of developing and adult sweat glands induce changes in neurotransmitter properties in cultured sympathetic neurons that mimic those observed in vivo. We have characterized further the factors present in the extract and compared their properties to those of known cholinergic factors. When assayed on cultured rat sympathetic neurons, the major activities in footpad extracts from postnatal day 21 rat pups that induce choline acetyltransferase (ChAT) and vasoactive intestinal peptide (VIP) and reduce catecholamines and neuropeptide Y (NPY) are associated with a soluble protein of 22–26 × 10(3) M(r) and a pI of 5.0. These properties are similar to those of ciliary neurotrophic factor (CNTF). Moreover, the purified fraction from footpads has ciliary neurotrophic activity. Antibodies to CNTF that immunoprecipitate all differentiation activity from sciatic nerve extracts, a rich source of CNTF, immunoprecipitate 80% of the cholinergic activity in the footpad extracts, 50% of the VIP and 20% of the NPY activities. Neither CNTF protein nor CNTF mRNA, however, can be detected in immunoblot and northern analysis of footpads even though both CNTF protein and mRNA are evident in sciatic nerve. CNTF-immunoreactivity is associated with a sparse plexus of sensory fibers in the footpad but not with sweat glands or the Schwann cells associated with them. In addition, in situ hybridization studies with oligonucleotide probes failed to reveal CNTF mRNA in sweat glands. Comparison of the sweat gland differentiation activity with the cholinergic differentiation factor from heart cells (CDF; also known as leukemia inhibitory factor or LIF) suggests that most of the cholinergic activity in foot pads is biochemically distinct from CDF/LIF. Further, antibodies that block the activity of CDF/LIF purified from heart-cell-conditioned medium do not block the ChAT-inducing activity present in footpad extracts of postnatal day 8 animals. A differentiation factor isolated from skeletal muscle did not induce cholinergic properties in sympathetic neuron cultures and therefore is unlikely to be the cholinergic differentiation factor produced by sweat glands. Taken together, our data suggest that there are at least two differentiation molecules present in the extracts and that the major cholinergic activity obtained from footpads is related to, but distinct from, CNTF. The second factor remains to be characterized. In addition, CNTF associated with sensory fibers may make a minor contribution to the cholinergic inducing activity present in the extract.

Membrane-associated neurotransmitter stimulating factor is very similar to ciliary neurotrophic factor

Membrane-associated neurotransmitter stimulating factor (MANS) can modulate sympathetic neurotransmitter expression and promote ciliary neuron survival in cell culture. Previous studies have shown that its biological effects and biochemical properties are similar to those of ciliary neurotrophic factor (CNTF). In addition, CNTF is present in spinal cord, the source of MANS. These observations raised the possibility that MANS preparations contain CNTF. We find that partially purified MANS fractions contain a 24-kD protein that is recognized in Western blots by an antiserum generated against recombinant rat CNTF (rCNTF). This antiserum immunoprecipitates virtually all the cholinergic-inducing and the ciliary neurotrophic activities present in MANS preparations. When iodinated rCNTF is incubated with spinal cord membranes, a significant proportion of the labeled CNTF segregates with the membrane pellet. The membrane-associated exogenous CNTF can be eluted from the membrane fraction by treatment with high-salt solutions, similar to that used to solubilize MANS from spinal cord membranes. Our data suggest that a substantial portion of the cholinergic differentiation and ciliary neurotrophic activities present in MANS preparations can be attributed to CNTF or a CNTF-like molecule.

Oncostatin M regulates VIP expression in a human neuroblastoma cell line

Oncostatin-M (OM), a recently described glycoprotein cytokine, is structurally and functionally related to cholinergic differentiation factor/leukemia inhibitory factor (CDF/LIF) and ciliary neurotrophic factor (CNTF). To determine whether OM, like CDF/LIF and CNTF, possesses trophic or differentiative functions for neurons we examined the effects of recombinant human OM on ciliary neuron survival and neurotransmitter expression in sympathetic neurons. Like CDF/LIF, but in contrast to CNTF, OM had no effect on ciliary neuronal survival at any concentration tested. OM produced small but reproducible increases in choline acetyl transferase (ChAT) activity and vasoactive intestinal peptide (VIP) levels in rat sympathetic neuron cultures, but this effect was significantly less than that of CNTF or CDF/LIF. To determine if human OM would elicit a more robust response from human cells, we utilized a human neuroblastoma cell line, NBFL, that responds to CNTF and CDF/LIF by altering vasoactive intestinal peptide (VIP) levels. OM specifically elevated VIP and c-fos mRNA levels in NBFL cells and was as potent as CDF/LIF in this assay. Our data provides evidence that OM acts on neurons and identifies a neural cell line responsive to OM, CNTF, CDF/LIF.