Selective expression of high-affinity uptake of catecholamines by transiently catecholaminergic cells of the rat embryo: studies in vivo and in vitro

Evaluating the mouse neural precursor line, SN4741, as a suitable proxy for midbrain dopaminergic neurons

To overcome the ethical and technical limitations of in vivo human disease models, the broader scientific community frequently employs model organism-derived cell lines to investigate disease mechanisms, pathways, and therapeutic strategies. Despite the widespread use of certain in vitro models, many still lack contemporary genomic analysis supporting their use as a proxy for the affected human cells and tissues. Consequently, it is imperative to determine how accurately and effectively any proposed biological surrogate may reflect the biological processes it is assumed to model. One such cellular surrogate of human disease is the established mouse neural precursor cell line, SN4741, which has been used to elucidate mechanisms of neurotoxicity in Parkinson disease for over 25 years. Here, we are using a combination of classic and contemporary genomic techniques - karyotyping, RT-qPCR, single cell RNA-seq, bulk RNA-seq, and ATAC-seq - to characterize the transcriptional landscape, chromatin landscape, and genomic architecture of this cell line, and evaluate its suitability as a proxy for midbrain dopaminergic neurons in the study of Parkinson disease. We find that SN4741 cells possess an unstable triploidy and consistently exhibits low expression of dopaminergic neuron markers across assays, even when the cell line is shifted to the non-permissive temperature that drives differentiation. The transcriptional signatures of SN4741 cells suggest that they are maintained in an undifferentiated state at the permissive temperature and differentiate into immature neurons at the non-permissive temperature; however, they may not be dopaminergic neuron precursors, as previously suggested. Additionally, the chromatin landscapes of SN4741 cells, in both the differentiated and undifferentiated states, are not concordant with the open chromatin profiles of ex vivo, mouse E15.5 forebrain- or midbrain-derived dopaminergic neurons. Overall, our data suggest that SN4741 cells may reflect early aspects of neuronal differentiation but are likely not a suitable proxy for dopaminergic neurons as previously thought. The implications of this study extend broadly, illuminating the need for robust biological and genomic rationale underpinning the use of in vitro models of molecular processes.

Evaluating the mouse neural precursor line, SN4741, as a suitable proxy for midbrain dopaminergic neurons

To overcome the ethical and technical limitations of in vivo human disease models, the broader scientific community frequently employs model organism-derived cell lines to investigate of disease mechanisms, pathways, and therapeutic strategies. Despite the widespread use of certain in vitro models, many still lack contemporary genomic analysis supporting their use as a proxy for the affected human cells and tissues. Consequently, it is imperative to determine how accurately and effectively any proposed biological surrogate may reflect the biological processes it is assumed to model. One such cellular surrogate of human disease is the established mouse neural precursor cell line, SN4741, which has been used to elucidate mechanisms of neurotoxicity in Parkinson disease for over 25 years. Here, we are using a combination of classic and contemporary genomic techniques - karyotyping, RT-qPCR, single cell RNA-seq, bulk RNA-seq, and ATAC-seq - to characterize the transcriptional landscape, chromatin landscape, and genomic architecture of this cell line, and evaluate its suitability as a proxy for midbrain dopaminergic neurons in the study of Parkinson disease. We find that SN4741 cells possess an unstable triploidy and consistently exhibits low expression of dopaminergic neuron markers across assays, even when the cell line is shifted to the non-permissive temperature that drives differentiation. The transcriptional signatures of SN4741 cells suggest that they are maintained in an undifferentiated state at the permissive temperature and differentiate into immature neurons at the non-permissive temperature; however, they may not be dopaminergic neuron precursors, as previously suggested. Additionally, the chromatin landscapes of SN4741 cells, in both the differentiated and undifferentiated states, are not concordant with the open chromatin profiles of ex vivo , mouse E15.5 forebrain- or midbrain-derived dopaminergic neurons. Overall, our data suggest that SN4741 cells may reflect early aspects of neuronal differentiation but are likely not a suitable a proxy for dopaminergic neurons as previously thought. The implications of this study extend broadly, illuminating the need for robust biological and genomic rationale underpinning the use of in vitro models of molecular processes.

Evaluating the mouse neural precursor line, SN4741, as a suitable proxy for midbrain dopaminergic neurons

To overcome the ethical and technical limitations of in vivo human disease models, the broader scientific community frequently employs model organism-derived cell lines to investigate of disease mechanisms, pathways, and therapeutic strategies. Despite the widespread use of certain in vitro models, many still lack contemporary genomic analysis supporting their use as a proxy for the affected human cells and tissues. Consequently, it is imperative to determine how accurately and effectively any proposed biological surrogate may reflect the biological processes it is assumed to model. One such cellular surrogate of human disease is the established mouse neural precursor cell line, SN4741, which has been used to elucidate mechanisms of neurotoxicity in Parkinson disease for over 25 years. Here, we are using a combination of classic and contemporary genomic techniques - karyotyping, RT-qPCR, single cell RNA-seq, bulk RNA-seq, and ATAC-seq - to characterize the transcriptional landscape, chromatin landscape, and genomic architecture of this cell line, and evaluate its suitability as a proxy for midbrain dopaminergic neurons in the study of Parkinson disease. We find that SN4741 cells possess an unstable triploidy and consistently exhibits low expression of dopaminergic neuron markers across assays, even when the cell line is shifted to the non-permissive temperature that drives differentiation. The transcriptional signatures of SN4741 cells suggest that they are maintained in an undifferentiated state at the permissive temperature and differentiate into immature neurons at the non-permissive temperature; however, they may not be dopaminergic neuron precursors, as previously suggested. Additionally, the chromatin landscapes of SN4741 cells, in both the differentiated and undifferentiated states, are not concordant with the open chromatin profiles of ex vivo , mouse E15.5 forebrain- or midbrain-derived dopaminergic neurons. Overall, our data suggest that SN4741 cells may reflect early aspects of neuronal differentiation but are likely not a suitable a proxy for dopaminergic neurons as previously thought. The implications of this study extend broadly, illuminating the need for robust biological and genomic rationale underpinning the use of in vitro models of molecular processes.

SGLT2 Inhibitor-Induced Sympathoexcitation in White Adipose Tissue: A Novel Mechanism for Beiging

Recent preclinical data show that sodium glucose cotransporter 2 (SGLT2) inhibitors are able to reduce weight gain and induce beiging in white adipose tissue (WAT). We have previously shown that in neurogenic hypertensive Schlager (BPH/2J) mice, treatment with the SGLT2 inhibitor, Dapagliflozin, reduced blood pressure and prevented weight gain. Here we show that chemical sympathetic denervation achieved by systemic administration of 6-hydroxy-dopamine (6-OHDA) reduces body weight and the heightened sympathetic nervous system (SNS) innervation in WAT. Furthermore, we demonstrate that 2 weeks of Dapagliflozin treatment increases SNS innervation in WAT of hypertensive mice. This increase is accompanied by a non-significant elevation in mRNA levels of the Ucp1 and Pgc-1α genes, which are markers of beiging. No significant difference in the mRNA levels of the inflammatory mediators Il-6 and Tnf-α were detected in WAT of Dapagliflozin treated mice. These findings suggest that SGLT-2 inhibitor-associated prevention of weight gain may be mediated, at least in part, by inducing the beiging of WAT.

Three types of tyrosine hydroxylase-positive CNS neurons distinguished by dopa decarboxylase and VMAT2 co-expression

1. We investigate here for the first time in primate brain the combinatorial expression of the three major functionally relevant proteins for catecholaminergic neurotransmission tyrosine hydroxylase (TH), aromatic acid acid decarboxylase (AADC), and the brain-specific isoform of the vesicular monoamine transporter, VMAT2, using highly specific antibodies and immunofluorescence with confocal microscopy to visualize combinatorial expression of these proteins. 2. In addition to classical TH, AADC, and VMAT2-copositive catecholaminergic neurons, two unique kinds of TH-positive neurons were identified based on co-expression of AADC and VMAT2. 3. TH and AADC co-positive, but VMAT2-negative neurons, are termed "nonexocytotic catecholaminergic TH neurons." These were found in striatum, olfactory bulb, cerebral cortex, area postrema, nucleus tractus solitarius, and in the dorsal motor nucleus of the vagus. 4. TH-positive neurons expressing neither AADC nor VMAT2 are termed "dopaergic TH neurons." We identified these neurons in supraoptic, paraventricular and periventricular hypothalamic nuclei, thalamic paraventicular nucleus, habenula, parabrachial nucleus, cerebral cortex and spinal cord. We were unable to identify any dopaergic (TH-positive, AADC-negative) neurons that expressed VMAT2, suggesting that regulatory mechanisms exist for shutting off VMAT2 expression in neurons that fail to biosynthesize its substrates. 5. In several cases, the corresponding TH phenotypes were identified in the adult rat, suggesting that this rodent is an appropriate experimental model for further investigation of these TH-positive neuronal cell groups in the adult central nervous system. Thus, no examples of TH and VMAT2 co-positive neurons lacking AADC expression were found in rodent adult nervous system. 6. In conclusion, the adult mammalian nervous system contains in addition to classical catecholaminergic neurons, cells that can synthesize dopamine, but cannot transport and store it in synaptic vesicles, and neurons that can synthesize only L-dopa and lack VMAT2 expression. The presence of these additional populations of TH-positive neurons in the adult primate CNS has implications for functional catecholamine neurotransmission, its derangement in disease and drug abuse, and its rescue by gene therapeutic maneuvers in neurodegenerative diseases such as Parkinson's disease.

Retrograde Axonal Transport of Dopamine Beta Hydroxylase Antibodies by Neurons in the Trigeminal Ganglion

In this study we describe a population of neurons in the adult rat trigeminal ganglion (TG) that express dopamine beta-hydroxylase (DBH) and tyrosine hydroxylase (TH), and transport anti-DBH from their terminals. We have used NGF and NT3 labeled with biotin and anti-p75NTR labeled with FITC to examine the transport of neurotrophins and their receptors by these cells. In both the superior cervical ganglion (SCG) and the TG all neurons that transported anti-DBH transported NGF. While 100% of the DBH positive neurons in the TG also transported NT3, approximately 25% of these neurons in the SCG failed to transport NT3. In the SCG virtually all the neurons transported anti-p75NTR with the neurotrophins while in the TG more than 25% of these neurons failed to transport anti-p75NTR with the neurotrophins. These findings suggest that DBH positive neurons in the TG depend upon target-derived NGF and NT3 for their noradrenergic phenotype.

Fate of transient catecholaminergic cell types revealed by site-specific recombination in transgenic mice

Catecholamine-producing cell types are generated from specified neuronal lineages during vertebrate development. The catecholaminergic phenotype is also expressed transiently in some cell types in non-catecholaminergic tissues, including the sensory ganglia, enteric ganglia, and ventral portions of the neural tube during embryonic development. The fate of the transient catecholaminergic cell types at later developmental stages, however, has not been elucidated. We developed a Cre-loxP-mediated recombination system under the control of the dopamine beta-hydroxylase (DBH) promoter, which drives gene expression in typical noradrenergic and adrenergic cell groups as well as in transient catecholaminergic cell types. Expression of Cre recombinase in transgenic mice resulted in an efficient recombination in noradrenergic and adrenergic cell groups at the adult stage. The recombination was also induced in the cranial nerve/spinal cord motor neurons and sensory/enteric ganglion neurons. Analysis of recombination patterns in transgenic mouse embryos showed the occurrence of recombination during prenatal development in both cell types exhibiting the typical and transient catecholaminergic phenotypes. Because the DBH gene promoter is expressed transiently in the ventral neural tube and sensory ganglion during embryonic development, our results provide evidence that the cell types showing a transient catecholaminergic phenotype in these tissues are destined to become mature motor neurons or sensory ganglion neurons during subsequent differentiation.

Regulation by neurotransmitter receptors of serotonergic or catecholaminergic neuronal cell differentiation

The murine F9-derived 1C11 clone exhibits a stable epithelial morphology, expresses nestin, an early neuroectodermal marker, and expresses genes involved in neuroectodermal cell fate. Upon appropriate induction, 100% of 1C11 precursor cells develop neurite extensions and acquire neuronal markers (N-CAM, synaptophysin, gammagamma-enolase, and neurofilament) as well as the general functions of either serotonergic (1C11*(/5HT)) (5HT, 5-hydroxytryptamine) or noradrenergic (1C11**(/NE)) (NE, norepinephrine) neurons. The two programs are shown to be mutually exclusive. 1C11 thus behaves as a neuroepithelial cell line with a dual bioaminergic fate. 1C11*(/5HT) cells implement a functional 5-HT transporter and thereby a complete serotonergic phenotype within 4 days, whereas 5-HT(1B/D), 5-HT(2B), and 5-HT(2A) receptors are sequentially induced. The accurate time schedule of catecholaminergic differentiation was defined. Catecholamine synthesis, storage, and catabolism are acquired within 4 days; the noradrenergic phenotype is complete at day 12 and includes a functional norepinephrine transporter and an alpha(1D)-adrenoreceptor (day 8). The time-dependent onset of neurotransmitter-associated functions proper to either program is similar to in vivo observations. Along each pathway, the selective induction of serotonergic or adrenergic receptors is shown to be an essential part of the differentiation program, since they promote an autoregulation of the corresponding phenotype.

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.

Evidence for NOS-containing renal neuronal somata transiently expressing a catecholaminergic phenotype during development in the rat

Transiently catecholaminergic cells (TC-cells) expressing tyrosine hydroxylase (TH) have been shown in a variety of tissues during embryonic life. To investigate the possible relationship of nitric oxide synthase (NOS)-containing renal neuronal somata (RNS) and the TC-cells, we examined serial 100 microm slices of whole kidneys for TH-immunofluorescence and NADPH-d histochemistry during prenatal and postnatal development. The number of TH-cells increased during the prenatal period, peaked at birth and were very rare by PD21. A subpopulation of TH-immunoreactive RNS displayed NADPH-d activity. By PD21 the TH-positive RNS had practically disappeared while the number of NADPH-d positive RNS was markedly increased. These results suggest that kidneys possess transient catecholaminergic cells which display NOS-activity and that NOS expression may be the end-point in the differentiation of the RNS.

CRE and TRE sequences of the rat tyrosine hydroxylase promoter are required for TH basal expression in adult mice but not in the embryo

Tyrosine hydroxylase (TH), the rate-limiting enzyme in the biosynthesis of catecholamine neurotransmitters, is expressed in a restricted number of areas, and subject to numerous regulations during development and in adulthood. Two transcription factor binding sites present in the proximal region of the TH gene, the TPA-responsive element (TRE) and the c-AMP responsive element (CRE), have been shown to play important roles in TH gene regulation in vitro. In order to elucidate in vivo the role of these two sites, we produced transgenic mice bearing a 5.3-kb fragment from the 5' flanking sequence of the TH gene with mutations in either the CRE-or TRE-sites. Using the intact 5.3-kb fragment fused to two different reporter genes (HSV1-tk and lacZ), we show that this promoter fragment is able to specifically direct expression in catecholaminergic tissues both in adult mice and embryos. Interestingly, the CRE- and TRE-mutated transgenes were not expressed in adult mice, contrary to the situation in embryos where they were specifically expressed in catecholaminergic regions. These results demonstrate that the CRE and TRE play an essential role in basal TH expression in adult tissues in vivo. Moreover, they suggest that distinct transcription factors are involved in TH regulation in developing and adult tissues. In support of this, gel mobility shift experiments revealed a complex present only in embryonic tissues. Taken together, these data highlight the diversity of the mechanisms underlying the establishment and maintenance of the catecholaminergic phenotype.

Early ontogeny of catecholaminergic cell lineage in brain and peripheral neurons monitored by tyrosine hydroxylase-lacZ transgene

As the first and rate limiting enzyme in the biosynthetic pathway for catecholamine (CA) neurotransmitters, tyrosine hydroxylase (TH) is a specific phenotypic marker for CA cells in the central and peripheral nervous systems of adult animals. During embryogenesis, TH expression appears permanently within cells destined to be CA-secreting during adult life, and transiently in several cell types that will not express TH in adulthood. In this study, we examined the early ontogeny of TH expression in transgenic mouse embryos by following the expression of a lacZ reporter, driven by the tissue-specific promoter of the rat TH gene. The lacZ reporter product, beta-galactosidase (beta-gal), visualized by X-gal staining, first became apparent in primordia of sensory ganglia serving the glossopharyngeal (IX) and vagal (X) cranial nerves at embryonic day (E)9.0. Between E9.5 and E10.5, beta-gal expression extended to the remaining cranial sensory ganglia serving the trigeminal (V) and facial (VII) nerves, dorsal root ganglia, ventrolateral neural tube and sympathetic ganglion primordia. During that same period, the first beta-gal expression in the embryonic brain also appeared within distinct regions, such as the ventral prosencephalon, the ventral and dorsolateral mesencephalon and the rostral and caudal rhombencephalon. The level of beta-gal expression in all these tissues decreased at E13.5, but a distinct adult pattern of beta-gal expression started to emerge in the substantia nigra and ventral tegmental area in the central nervous system and the adrenal medulla in the periphery. Our findings indicate that the proximal 9.0 kb of the 5' promoter region of the rat TH gene encodes sufficient information to direct development of the appropriate catecholaminergic lineage cells in the central and most peripheral nervous systems during embryogenesis.

Plasticity in the myenteric plexus of the rat ileum after long-term sympathectomy

To investigate the effect of chronic sympathectomy on the innervation of a tissue with an extensive intrinsic component, 1-week-old rat pups were treated with 50 mg/kg guanethidine for 3 weeks, a treatment shown to produce complete and long-lasting sympathectomy, and the ileum examined. Changes in the levels of noradrenaline, neuropeptide Y, calcitonin gene-related peptide, substance P and vasoactive intestinal polypeptide in the external muscle layers containing the myenteric plexus of the ileum were determined between 6 and 20 weeks of age. After sympathectomy, noradrenaline levels were initially depleted (3% of age-matched controls at 6 weeks, P < 0.001, and 18% of age-matched controls at 12 weeks, P < 0.001), but were not significantly reduced at 20 weeks (67% of age-matched controls). Such increases in noradrenaline content with time after sympathectomy did not occur in the mesenteric vein (levels in 20-week-old sympathectomized rats were 2% of the control values (P < 0.001). In the myenteric plexus, catecholamine fluorescent nerve fibers were seen in the 12-week-old sympathectomized rats, although tyrosine hydroxylase-immunoreactivity was absent. Guanethidine sympathectomy had no effect on the neuropeptide levels in 6-week-old rat ileum but there was a selective increase at 20 weeks; the levels of calcitonin gene-related peptide and substance P were increased (X3, P < 0.001 and X1.6, P < 0.05, respectively) while vasoactive intestinal polypeptide and neuropeptide Y levels were unchanged. Short-term sympathectomy (destruction of sympathetic nerve terminals by acute 6-hydroxydopamine treatment) had no affect on noradrenaline or peptide levels in this tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Interferon-gamma promotes cholinergic differentiation of embryonic septal nuclei and adjacent basal forebrain

In cultured rat embryonic septal nuclei with adjacent basal forebrain, murine interferon-gamma (IFN gamma) produces a striking increase in choline acetyltransferase (ChAT) activity and mRNA. The effect of IFN gamma on cholinergic differentiation is more potent in E14 cultures than in older cultures. IFN gamma does not cause a change in the affinity of ChAT for choline, nor does it affect cell proliferation. Whereas IFN gamma doubles neuronal cell number, the cholinergic cell number increases more than 7-fold. Ameboid microglia respond to IFN gamma with the translocation of p91 to the nucleus. The action of IFN gamma is not mediated by NGF or bFGF. The enhancement of cholinergic expression that occurs with increased cell density may be partly attributable to an endogenous IFN gamma-like molecule, since antibodies to IFN gamma offset the effects of increased cell density.

The stability of endogenous tyrosine hydroxylase protein in PC-12 cells differs from that expressed in mouse fibroblasts by gene transfer

Previous studies have used recombinant retroviruses encoding the tyrosine hydroxylase (TH) gene to transduce various cell lines, including fibroblasts (NIH-3T3), a pituitary tumor cell line (AtT20), and a pancreatic endocrine line (RIN). These genetically modified cells, synthesizing either 3,4-dihydroxyphenylalanine, dopamine, or both, are potential donors for treatment of Parkinson's disease. However, the levels of TH protein in such transduced cells have been low and heterogeneous. Using several modified versions of retrovirus vectors encoding TH, we demonstrated that protein stability is an important factor governing levels of TH in NIH-3T3 fibroblasts. Whereas low levels of TH protein were observed in infected NIH-3T3 cells, high levels of a TH-beta gal fusion protein were found. This difference was due to a significantly longer half-life of the TH-beta gal fusion protein relative to TH alone. However, the TH-beta gal fusion protein was found to be enzymatically inactive. We also found that the half-life of the endogenous TH protein in PC-12 cells is sevenfold longer than the TH protein in transduced fibroblasts, implying that a cell-type specific regulator or mechanism may stabilize TH in catecholaminergic cells.

Behavior of embryonic chick heart cells in culture. 1. Cellular responses to insulin-transferrin-selenium

Muscle cell-enriched primary cell cultures were prepared from 8-day embryonic chick heart ventricles (74% of these cells showed positive staining with anti-cardiac myosin antibody). To determine if ITS (a commercial mixture of insulin, transferrin, and selenium) affects these cardiac muscle cells, immunostaining and autoradiography were performed to determine the Muscle Cell Labeling Index (MLI). MLI represents the proportion of cardiac myosin-positive cells that specifically incorporated [3H]thymidine. The MLI for ITS-treated cells was 52%. Controls in Serum-free Nutrient Medium (SFNM) had a MLI of 27%. Combinations of growth signals also were tested. Whereas 5% Fetal Bovine Serum (FBS) was optimal for stimulation of [3H]thymidine incorporation, 10 and 20% FBS elicited an inhibitory effect. Addition of ITS enhanced the stimulatory effect of FBS and relieved some of the inhibitory effect. TGF-beta also was shown to have inhibitory effect on [3H]thymidine incorporation in these heart cells, but the inhibitory effect was not seen when it was added with ITS. Staining with anti-cardiac myosin antibody revealed that when the cells were cultured with ITS for 6 or 10 days, the percentages of muscle cells were 65 and 59%, whereas the percentages of muscle cells of controls in SFNM dropped to 44 and 31% respectively. Additional experiments showed that cell number increased in the presence of 5% FBS. In contrast, although ITS stimulated DNA synthesis, it did not immediately stimulate complete cell division. The percentage of muscle cells remained around 74% in the presence of 5% FBS, whereas it fell slightly (to 65%) in SFNM. This study showed that cardiac muscle cells from 8-day embryos in culture were responsive to ITS, FBS and TGF-beta and that ITS may be permissive for continued expression of differentiation of embryonic cardiac muscle cells.

Cell fate determination in the peripheral nervous system: the sympathoadrenal progenitor

Studies of postnatal chromaffin cells, sympathetic neurons and Small Intensely Fluorescent (SIF) cells have suggested that these cells develop from a common progenitor, the sympathoadrenal (SA) progenitor, whose fate is determined by the relative levels of nerve growth factor (NGF) and glucocorticoid (GC) in its environment (Unsicker et al., 1978, Proc. Natl. Acad. Sci. USA 75:3498-3502; Doupe et al., 1985a, J. Neurosci. 5:2119-2142). Recent studies have identified such a bipotential SA progenitor in the rat embryo. Surprisingly, this progenitor is initially unresponsive to NGF; neuronal differentiation is instead promoted by fibroblast growth factor (FGF). However, FGF appears to promote NGF responsiveness, suggesting that neuronal differentiation involves a relay or cascade of growth factor action. Furthermore, chromaffin cell differentiation appears to involve two sequential, GC-dependent events: the inhibition of neuronal differentiation and the induction of epinephrine synthesis. The former event is a prerequisite to the latter. Thus both the chromaffin and neuronal pathways of differentiation follow a series of dependent events, involving changes in the responsiveness of SA progenitors to environmental factors. Such changes correlate with changes in antigenic marker expression that can be observed in vivo. In addition to choosing between neuronal and endocrine fates, SA progenitors must also express an appropriate neurotransmitter phenotype. For example, sympathetic neurons can become either noradrenergic or cholinergic. This cholinergic potential is already present in uncommitted SA progenitors, as evidenced by their ability to synthesize acetylcholine. Recent studies suggest that these cells may have yet other developmental capacities, including the ability to synthesize serotonin. This capacity is consistent with the hypothesis that SA progenitors are closely related to progenitors of enteric neurons, an idea supported by recent observations using novel antigenic markers. The SA progenitor may be, therefore, a "master" neuroendocrine progenitor for the peripheral nervous system.

Development of tyrosine hydroxylase-, dopamine- and dopamine β-hydroxylase-immunoreactive neurons in a teleost, the three-spined stickleback

The development of catecholaminergic neuronal systems in the brain of a teleost, the three-spined stickleback, was studied through embryonic to early larval stages by immunocytochemistry using specific antibodies against dopamine, tyrosine hydroxylase and dopamine beta-hydroxylase. By analysing the spatiotemporal patterns of development for the catecholaminergic nuclei, possible homologies with nuclei in amniote brains have been identified. The noradrenergic neurons in the isthmus region of the rostral rhombencephalon originate in the same manner as the A4-A7 + subcoeruleus group in mammals. Their developmental characteristics show the largest similarities with the subcoeruleus group of birds and mammals, although some features are shared with developing A6 (locus coeruleus) neurons. Catecholaminergic neurons never appear during development in the ventral mesencephalon of the three-spined stickleback. A group of large dopaminergic neurons that accompany the cerebrospinal fluid (CSF)-contacting neurons follows the border between the hypothalamus and the ventral thalamus into the caudal hypothalamus, where they are continuous with the dopaminergic neurons in the posterior tuberculum. They are thus topologically comparable with the dopaminergic neurons of the zona incerta in mammals. The dopaminergic CSF-contacting neurons that line the median, lateral and posterior recesses of the third ventricle do not contain tyrosine hydroxylase-immunoreactivity at any developmental stage. This indicates that they take up and accumulate exogenous dopamine or L-dihydroxyphenylalanine, and do not synthesize dopamine from tyrosine at any developmental stage. Tyrosine hydroxylase-immunoreactive neurons appear in the pineal organ on the day of hatching (120 h post-fertilization). They were still observed in 240-h-old larvae, but are absent in the pineal organ of adult sticklebacks. The initial appearance and subsequent differentiation of catecholaminergic neurons in the stickleback embryo follow essentially the same spatial and temporal pattern as in amphibian, avian and mammalian embryos. This observation supports the hypothesis that morphologically, topologically and chemically similar monoaminergic neurons in different vertebrate classes are homologous.

Characterization of the norepinephrine uptake system and the role of norepinephrine in the expression of the adrenergic phenotype by quail neural crest cells in clonal culture

This study investigates the role norepinephrine (NE) may play in regulating the differentiation of quail neural crest cells into sympatho-adrenal cells. Cues originating from the embryonic microenvironment are thought to play an important role during development. It is conceivable that NE has a positive regulatory function because adrenergic expression by quail neural crest cells in clonal culture can be inhibited by NE uptake inhibitors such as desipramine (DMI). This possibility is further supported by the notion that in the avian embryo presumptive adrenergic neural crest cells are likely to encounter catecholamines shortly after they have acquired the NE uptake mechanism. Our present data indicate that neural crest cells in clonal culture express a high affinity NE uptake system that can be inhibited by desipramine. As in the embryo, it appears before noticeable levels of catecholamines are accumulated by neural crest cells, as judged by formaldehyde-induced catecholamine fluorescence (FIF). A comparison of the time course of appearance of different adrenergic markers suggests that immunoreactivity against the biosynthetic enzyme tyrosine hydroxylase (TH) may appear first, and that it is followed very closely by the appearance of detectable levels of dopamine-beta-hydroxylase (DBH) and the NE uptake mechanism. Accumulation of catecholamines (FIF) is observed last. Addition of exogenous NE leads to an increase in adrenergic expression in vitro as judged by an increase in the number of colonies containing FIF-positive cells as well as cells expressing the biosynthetic enzymes TH and DBH. This suggests that exogenous NE can play a positive regulatory role in the differentiation of quail neural crest cells into sympathoadrenal cells.

Evidence that enteric neurons may derive from the sympathoadrenal lineage

The first neurons that differentiate in the embryonic foregut of mammals transiently express catecholamine biosynthetic enzymes and accumulate catecholamine. Since this transmitter is found predominantly in cells of the sympatho-adrenal (SA) lineage, it has been suggested that enteric and sympathetic neurons may derive from the same progenitor. Enteric neurons would then lose the catecholamine phenotype during further development, as the two lineages diverge. We have further investigated this possibility using the SA1 monoclonal antibody that binds selectively to SA progenitor cells in the embryonic rat. We find that SA1 binds to the tyrosine hydroxylase+, neurofilament+, and SCG10+ cells of the Embryonic Day 14.5 (E14.5) rat foregut. We also find that a marker for later neuronal differentiation in the SA lineage, B2, also appears in the myenteric plexus concomitant with the loss of SA1 staining. Thus, at least some enteric neuronal precursors may exhibit the SA1----B2 antigenic switch previously observed in developing sympathetic neurons at E14.5. SA1 staining in the foregut partially overlaps with staining for neuropeptide Y, vasoactive intestinal polypeptide, and serotonin. These results support the hypothesis that enteric and sympathetic neurons derive from a common progenitor and that as the markers for the SA lineage are down-regulated, the many types of enteric neurons begin to differentiate.

Some neuronal cell populations express human dopamine beta-hydroxylase-lacZ transgenes transiently during embryonic development

The 5' flanking region from the human dopamine beta-hydroxylase gene directs expression of bacterial beta-galactosidase reporter genes to a subset of adult neurons and adrenal chromaffin cells of transgenic mice. In this paper, we examine the spatial and temporal patterns of expression of these transgenes during embryogenesis. Expression begins at embryonic day 9 in the developing central and peripheral nervous systems and persists in cell populations in which expression is observed in adult transgenic mice. However, transient embryonic expression occurs in presumptive neuroblasts in developing sensory ganglia and ventrolateral neural tube that are destined to synthesize neurotransmitters other than catecholamines. These observations support the concept that some cells fated to become "non-catecholaminergic" neurons exhibit transient catecholaminergic features during their differentiation.

Transiently catecholaminergic (TC) cells in the bowel of the fetal rat: precursors of noncatecholaminergic enteric neurons

Experiments were done to study the fate of transient catecholaminergic (TC) cells that develop in the rodent gut during ontogeny. When they are first detected, at Day E11 in rats, TC cells are distributed along the vagal pathway, in advance of the descending fibers of the vagus nerves, and in the foregut. The early TC cells coexpress the immunoreactivities of several neural markers, including 150-kDa neurofilament protein, peripherin, microtubule associated protein (MAP) 5, and growth-associated protein (GAP)-43, with those of the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH). All cells in the fetal rat bowel at Day E11 that express neural markers also express TH immunoreactivity. The primitive TC cells also express the immunoreactivities of neural cell adhesion molecule (N-CAM), neuropeptide Y (NPY), and nerve growth factor (NGF) receptor (and NGF receptor mRNA). By Day E12 TC cells are found along the vagal pathway and throughout the entire preumbilical bowel. At this age TC cells acquire additional characteristics, including MAP 2 and synaptophysin immunoreactivities and acetylcholinesterase activity, which indicate that they continue to mature as neurons. In addition, TC cells of the rat are immunostained at Day E12 by the NC-1 monoclonal antibody, which in rats labels multiple cell types including migrating cells of neural crest origin. Despite their neural properties, at least some TC cells divide and therefore are neural precursors and not terminally differentiated neurons. At Day E10 TH mRNA-containing cells were not detected by in situ hybridization; however, by Day E11 TH mRNA was detected in sympathetic ganglia and in scattered cells in the mesenchyme of the foregut and vagal pathway. At this age, the number of enteric and vagal cells containing TH mRNA is about 30% less than the number of cells containing TH immunoreactivity in adjacent sections. The ratio of TH mRNA-containing cells to TH-immunoreactive vagal and enteric cells is even less at Day E12, especially in more caudal regions of the preumbilical bowel. A similar decline in the ratio of TH mRNA-containing to TH-immunoreactive cells was not observed in sympathetic ganglia. After Day E12 TH mRNA cannot be detected in enteric or vagal cells by in situ hybridization; nevertheless, TH immunoreactivity continues to be present through Day E14. DBH, NPY, and NGF receptor immunoreactivities are expressed by TH-immunoreactive transitional cells in the fetal rat gut after TH mRNA is no longer detectable.(ABSTRACT TRUNCATED AT 400 WORDS)

Target regulation of neurotransmitter phenotype

Studies of sympathetic neurons developing in cell culture revealed a surprising degree of transmitter plasticity and established the role of environmental factors in determining transmitter choice. The sympathetic neurons that innervate sweat glands undergo a change in neurotransmitter phenotype from noradrenergic to cholinergic during normal development similar to that observed in culture. Cross-innervation experiments indicate that the target sweat glands induce the switch and thereby specify the phenotype of the neurons that innervate them. Thus, both the transmitter plasticity and the role of environmental influences initially elucidated in culture are part of the developmental repertoire of sympathetic neurons in vivo. Further, these findings extend considerably our understanding of the role that targets may play during development; targets may not only determine how many neurons survive but also what their properties will be.

Inhibition of the adrenergic phenotype in cultured neural crest cells by norepinephrine uptake inhibitors

Tricyclic antidepressants in combination with in vitro clonal analysis of quail neural crest cells were used to examine the role the norepinephrine uptake mechanism might play in the development of adrenergic neural crest derivatives. Norepinephrine (NE) uptake inhibitors blocked expression of the adrenergic phenotype by neural crest cells. The degree of inhibition of phenotypic expression correlated with the potency and specificity of the uptake inhibitors. The drugs acted during the early phase of in vitro development, i.e., several days before overt expression of the adrenergic phenotype in clonal culture. They were nontoxic, and a chronic exposure of the cells to NE uptake inhibitors was necessary to cause an effect. These observations suggest that norepinephrine and possibly related neurotransmitters play a direct or indirect role in the expression of the adrenergic phenotype by neural crest cells and that tricyclic antidepressants may affect neurogenesis during sensitive stages of embryonic development. The data may reflect in vivo mechanisms, since there are neurotransmitters present in the migratory pathway of presumptive sympathetic neurons and the norepinephrine uptake system is expressed in the embryo by these cells before they synthesize and accumulate catecholamines.

Transient catecholaminergic (TC) cells in the vagus nerves and bowel of fetal mice: relationship to the development of enteric neurons

Catecholaminergic cells are transiently present during development of the fetal murine bowel. These transient catecholaminergic (TC) cells appear at Day E10, but by Day E13 can no longer be detected. In order to evaluate the hypothesis that these cells are the precursors of enteric neurons, we investigated the possibilities that TC cells coexpress neuronal and catecholaminergic markers, that they can be found along the presumed path followed by crest-derived cells migrating to the gut, and that they are proliferating. TC cells were identified immunocytochemically using polyclonal or monoclonal antibodies to tyrosine hydroxylase (TH). At Day E9.5, TH-immunoreactive cells were observed to be present along the wall of the primordial esophagus in lines that extended from the developing nodose ganglia down to the boundary of the stomach. At Day E9.5, TC cells were absent from the remaining foregut. These lines of esophageal TH-immunoreactive cells became continuous with similar cells in the wall of the stomach and duodenum on Day E10. Coincident expression of neurofilament immunoreactivity was seen in all of the esophageal TH-immunoreactive cells present at Day E9.5, as well as in the entire set of esophageal and lower enteric TH-immunoreactive cells present at Day E10 (or later); moreover, at Days E9.5 and E10, all of the neurofilament-immunoreactive cells in the esophagus, stomach, or duodenum were also TH-immunoreactive. In contrast, neurofilament immunoreactivity was not expressed by the endodermally derived pancreatic duct and islet cells, which were also TH-immunoreactive; nor could expression of neurofilament immunoreactivity be detected in the TH-immunoreactive cells of the nodose ganglia. It was not until Day E11 that neurofilament-immunoreactive cells, which did not coexpress TH immunoreactivity (the definitive phenotype of enteric neurons) began to appear in the gut. Vagal axons reached as far distally as the nodose ganglion on Day E9.5, the esophagogastric junction on Day E10, and did not enter the stomach until Day E11. When the vagus nerves reached their level, the TH-immunoreactive cells in the wall of the esophagus came to lie among the nerve fibers. TH-immunoreactive cells are thus present on the pathway ultimately followed by the vagus nerves, but they develop before vagal fibers reach their level. The vagal TH-immunoreactive cells, therefore, are probably not initially migrating on vagal fibers, but appear instead to be overtaken by the descending vagus nerves.(ABSTRACT TRUNCATED AT 400 WORDS)

Differentiation of noradrenergic traits in the principal neurons and small intensely fluorescent cells of the parasympathetic sphenopalatine ganglion of the rat

Catecholamine synthetic enzymes are found in many cranial parasympathetic principal neurons, and in the small intensely fluorescent (SIF) cells that populate parasympathetic as well as sympathetic ganglia. While there is evidence that the acquisition of noradrenergic properties in sympathetic neuron precursors depends on factors that these cells encounter in the trunk environment, the mechanisms that direct the development of noradrenergic traits in cranial parasympathetic neurons and SIF cells are not understood. The present study examines the time course of appearance of tyrosine hydroxylase (TH) immunoreactivity in the principal neurons and SIF cells of the rat sphenopalatine ganglion. We show that the sphenopalatine ganglion of normal adult rats contains both a small population of TH-immunoreactive principal neurons and many SIF cells. The TH-immunoreactive principal neurons do not synthesize or store detectable catecholamines, even though the majority of sphenopalatine ganglion neurons do contain 1-amino acid decarboxylase catalytic activity. Sphenopalatine ganglion principal neurons do not accumulate detectable levels of exogenous catecholamines. This observation suggests that they lack a high affinity norepinephrine uptake system. In contrast to what has been observed previously for sympathetic neurons, the appearance of TH immunoreactivity in sphenopalatine neurons is not temporally correlated with the cessation of neural crest cell migration. The first TH-immunoreactive neurons do not appear in the sphenopalatine ganglion until Embryonic Day 16.5, 2 days after the ganglion has condensed and process outgrowth has begun. The number of sphenopalatine neurons that express TH immunoreactivity increases dramatically between Embryonic Day 18.5 and Postnatal Day 1, but then decreases. In fact, the percentage of sphenopalatine neurons that express TH immunoreactivity is almost fivefold higher in newborn than in adult rats. SIF cells cannot be definitively identified in the sphenopalatine ganglion until after Embryonic Day 18.5. The time course of appearance of TH immunoreactivity in sphenopalatine ganglion cells raises the possibility that TH expression is stimulated in these cells by factors encountered either at their condensation site or at their target, such as glucocorticoids or nerve growth factor. The relatively late appearance of SIF cells in the sphenopalatine ganglion argues against the hypothesis that SIF cells are the precursors of all autonomic neurons.

Insulin growth factors regulate the mitotic cycle in cultured rat sympathetic neuroblasts

While neuronal mitosis is uniquely restricted to early development, the underlying regulation remains to be defined. We have now developed a dissociated, embryonic sympathetic neuron culture system that uses fully defined medium in which cells enter the mitotic cycle. The cultured cells expressed two neuronal traits, tyrosine hydroxylase [L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.2] and the neuron-specific 160-kDa neurofilament subunit protein, but were devoid of glial fibrillary acidic protein, a marker for non-myelin-forming Schwann cells in ganglia. Approximately one-third of the tyrosine hydroxylase-positive cells synthesized DNA in culture, specifically incorporating [3H]thymidine into their nuclei. We used this system to define factors regulating the mitotic cycle in sympathetic neuroblasts. Members of the insulin family of growth factors, including insulin and insulin-like growth factors I and II, regulated DNA synthesis in the presumptive neuroblasts. Insulin more than doubled the proportion of tyrosine hydroxylase-positive cells entering the mitotic cycle, as indicated by autoradiography of [3H]thymidine incorporation into nuclei. Scintillation spectrometry was an even more sensitive index of DNA synthesis, revealing a 4-fold insulin stimulation with an ED50 of 100 ng/ml. Insulin-like growth factor I was 100-fold more potent than insulin, whereas insulin-like growth factor II was less potent, suggesting that insulin growth factor type I receptors mediated the mitogenic responses. In contrast, the trophic protein nerve growth factor exhibited no mitogenic effect, suggesting that the mitogenic action of insulin growth factors is highly specific. Our observations are discussed in the context of the detection of insulin growth factors and receptors in the developing brain.

Evidence for neurotransmitter plasticity in vivo. II. Immunocytochemical studies of rat sweat gland innervation during development

Previous studies of the cholinergic sympathetic innervation of rat sweat glands provide evidence for a change in neurotransmitter phenotype from noradrenergic to cholinergic during development. To define further the developmental history of cholinergic sympathetic neurons, we have used immunocytochemical techniques to examine developing and mature sweat gland innervation for the presence of the catecholamine synthetic enzymes tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) and for two neuropeptides present in the mature cholinergic innervation, vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP). In 7-day old animals, intensely TH- and DBH-immunoreactive axons were closely associated with the forming glands. The intensity of both the TH and DBH immunofluorescence decreased as the glands and their innervation developed. Neither TH-IR nor DBH-IR disappeared entirely; faint immunoreactivity for both enzymes was reproducibly detected in mature animals. In contrast to noradrenergic properties, the expression of peptide immunoreactivities appeared relatively late. No VIP-IR or CGRP-IR was detectable in the sweat gland innervation at 4 or 7 days. In some glands VIP-IR first appeared in axons at 10 days, and was evident in all glands by 14 days. CGRP-IR was detectable only after 14 days. In addition to VIP-IR and CGRP-IR, we examined the sweat gland innervation for several neuropeptides which have been described in noradrenergic sympathetic neurons including neuropeptide Y, somatostatin, substance P, and leu- and met-enkephalin; these peptides were not evident in either developing or mature sweat gland axons. Our observations provide further evidence for the early expression and subsequent modulation of noradrenergic properties in a population of cholinergic sympathetic neurons in vivo. In addition, the asynchronous appearance during development of the two neuropeptide immunoreactivities raises the possibility that the expression of peptide phenotypes may be controlled independently.

Differentiation of catecholaminergic cells in cultures of embryonic avian sensory ganglia

From the results of previous studies in which developing peripheral ganglia from quail embryos were transplanted into younger chicken embryo hosts, we concluded that spinal and cranial sensory ganglia contain dormant precursors with autonomic potentialities. Here we describe the differentiation of these precursors in vitro, from dorsal root and nodose ganglion cell suspensions. Dorsal root ganglia were removed from quail embryos at 9 to 15 days of incubation, dissociated to single cells, and grown in tissue culture. The differentiation of cells with autonomic features was followed by monitoring properties associated with the adrenergic phenotype (absent from quail sensory ganglia during normal embryonic development). Provided that the medium was supplemented with chicken embryo extract, numerous cells displaying tyrosine hydroxylase immunoreactivity could be detected from day 4 onward. They possessed long, multiple processes but appeared morphologically distinct from primary sensory neurons. The catalytic activity of tyrosine hydroxylase and of other enzymes required for catecholamine production was demonstrated in the cultures by glyoxylic acid-induced histofluorescence and by radiochemical measurement of the conversion of exogenous tyrosine to norepinephrine. A large proportion of tyrosine hydroxylase-positive cells were found to incorporate [3H]thymidine before and after differentiating. In contrast, recognizable sensory neurons never exhibited adrenergic properties and did not divide. Qualitatively similar results were obtained with cultures of dissociated nodose ganglia. These findings lend further weight to the assumption that latent autonomic precursors are included in the non-neuronal compartment of sensory ganglia.

Partial expression of catecholaminergic traits in cholinergic chick ciliary ganglia: studies in vivo and in vitro

We have previously demonstrated that at embryonic Day (E) 8, some cells of the chick ciliary ganglion (CG) contain the catecholaminergic (CA) enzyme tyrosine hydroxylase (TH), but not phenylethanolamine-N-methyltransferase (PNMT); and that in culture essentially all cells express both enzymes. In the present study, we sought to determine, first, whether the expression of adrenergic traits in the CG in vivo is transient or permanent in the CG. To do so, CGs were removed from E5 to postnatal Day 5, fixed, and processed for the immunocytochemical localization of the CA enzymes: TH, L-amino acid decarboxylase (AADC), and PNMT. At all stages examined, some CG neurons expressed TH immunoreactivity (TH-IR) and all contained AADC-IR. However, none stained with PNMT antibodies, indicating that these cells stably express some, but not all, of the CA enzymes. Second, we examined whether CG neurons in culture expressed other CA markers. CG neurons did not contain detectable levels of TH enzyme activity nor did they transport and store exogenously supplied monoamines. These results indicate that some but not all traits necessary for adrenergic function are present in CG neurons in vitro. Third, we sought to establish whether CA expression in CG neurons is affected by modification in culture conditions. Cultures of CG neurons continued to express TH-IR even when grown in the presence of either 50% HCM or 20 mM KCl for 5 days. Finally, the expression of the cholinergic enzyme, choline acetyltransferase (CAT) was assessed in CG cultures by biochemical assay. CAT activity increased five-fold between 5 and 17 days in vitro, irrespective of the presence of TH-IR in 100% of the CG neurons of sister cultures. These data suggest that at least a subpopulation of CG neurons express both TH and CAT in culture. We conclude that the postmitotic neurons of the CG are able to express some but not all of the traits characteristic of a CA phenotype while maintaining cholinergic expression. These findings suggest that (1) the appearance of the full complement of adrenergic properties is not coordinated and may be regulated by different environmental cues and (2) parasympathetic neurons can express both adrenergic and cholinergic traits simultaneously.