Developmental changes in the neurotransmitter properties of dissociated sympathetic neurons: a cytochemical study of the effects of medium

On the Road from Phenotypic Plasticity to Stem Cell Therapy

In 1981, I published a paper in the first issue of The Journal of Neuroscience with my postdoctoral mentor, Richard Bunge. At that time, the long-standing belief that each neuron expressed only one neurotransmitter, known as Dale's Principle (Dale, 1935), was being hotly debated following a report by French embryologist Nicole Le Douarin showing that neural crest cells destined for one transmitter phenotype could express characteristics of another if transplanted to alternate sites in the developing embryo (Le Douarin, 1980). In the Bunge laboratory, we were able to more directly test the question of phenotypic plasticity in the controlled environment of the tissue culture dish. Thus, in our paper, we grew autonomic catecholaminergic neurons in culture under conditions which promoted the acquisition of cholinergic traits and showed that cells did not abandon their inherited phenotype to adopt a new one but instead were capable of dual transmitter expression. In this Progressions article, I detail the path that led to these findings and how this study impacted the direction I followed for the next 40 years. This is my journey from phenotypic plasticity to the promise of a stem cell therapy.

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.

Peptidergic nerves in the eye, their source and potential pathophysiological relevance

Over the last five decades, several neuropeptides have been discovered which subsequently have been found to be highly conserved during evolution, to be widely distributed both in the central and peripheral nervous system and which act as neurotransmitters and/or neuromodulators. In the eye, the first peptide to be explored was substance P which was reported to be present in the retina but also in peripherally innervated tissues of the eye. Substance P is certainly the best characterized peptide which has been found in sensory neurons innervating the eye. Functionally, it has been shown to act trophically on corneal wound healing and to participate in the irritative response in lower mammals, a model for neurogenic inflammation, where it mediates the noncholinergic nonadrenergic contraction of the sphincter muscle. Over the last three decades, the interest has extended to investigate the presence and distribution of other neuropeptides including calcitonin gene-related peptide, vasoactive intestinal polypeptide, neuropeptide Y, pituitary adenylate cyclase-activating polypeptides, cholecystokinin, somatostatin, neuronal nitric oxide, galanin, neurokinin A or secretoneurin and important functional results have been obtained for these peptides. This review focuses on summarizing the current knowledge about neuropeptides in the eye excluding the retina and retinal pigment epithelium and to elucidate their potential functional significance.

Role for calcium/calmodulin-dependent protein kinase II in the p75-mediated regulation of sympathetic cholinergic transmission

Neurotrophins regulate sympathetic neuron cotransmission by modulating the activity-dependent release of norepinephrine and acetylcholine. Nerve growth factor promotes excitatory noradrenergic transmission, whereas brain-derived neurotrophic factor (BDNF), acting through the p75 receptor, increases inhibitory cholinergic transmission. This regulation of corelease by target-derived factors leads to the functional modulation of myocyte beat rate in neuron-myocyte cocultures. Calcium/calmodulin-dependent protein kinase II (CaMKII) has been implicated in the control of both pre- and postsynaptic mechanisms of synaptic plasticity. We demonstrate that CaMKII acts in conjunction with p75 signaling to regulate cholinergic transmission between sympathetic neurons and heart cells. Inhibition of presynaptic CaMKII prevents the BDNF-dependent shift to inhibitory neurotransmission, whereas presynaptic expression of a constitutively active CaMKII results in inhibitory neurotransmission in the absence of added BDNF, suggesting that activation of presynaptic CaMKII is both necessary and sufficient for a shift from excitatory to inhibitory transmission. Several isozymes of CaMKII are expressed in sympathetic neurons, with the delta-CaMKII being activated by BDNF and nerve growth factor. Activated CaMKII is less effective at promoting cholinergic transmission in the absence of p75 signaling, demonstrating that p75 and CaMKII act to coordinate neurotransmitter selection in sympathetic neurons.

Neurotrophic factors and their receptors in axonal regeneration and functional recovery after peripheral nerve injury

Over a half a century of research has confirmed that neurotrophic factors promote the survival and process outgrowth of isolated neurons in vitro. The mechanisms by which neurotrophic factors mediate these survival-promoting effects have also been well characterized. In vivo, peripheral neurons are critically dependent on limited amounts of neurotrophic factors during development. After peripheral nerve injury, the adult mammalian peripheral nervous system responds by making neurotrophic factors once again available, either by autocrine or paracrine sources. Three families of neurotrophic factors were compared, the neurotrophins, the GDNF family of neurotrophic factors, and the neuropoetic cytokines. Following a general overview of the mechanisms by which these neurotrophic factors mediate their effects, we reviewed the temporal pattern of expression of the neurotrophic factors and their receptors by axotomized motoneurons as well as in the distal nerve stump after peripheral nerve injury. We discussed recent experiments from our lab and others which have examined the role of neurotrophic factors in peripheral nerve injury. Although our understanding of the mechanisms by which neurotrophic factors mediate their effects in vivo are poorly understood, evidence is beginning to emerge that similar phenomena observed in vitro also apply to nerve regeneration in vivo.

Norepinephrine transporter expression in cholinergic sympathetic neurons: differential regulation of membrane and vesicular transporters

Sympathetic neurons that undergo a noradrenergic to cholinergic change in phenotype provide a useful model system to examine the developmental regulation of proteins required to synthesize, store, or remove a particular neurotransmitter. This type of change occurs in the sympathetic sweat gland innervation during development and can be induced in cultured sympathetic neurons by extracts of sweat gland-containing footpads or by leukemia inhibitory factor. Sympathetic neurons initially produce norepinephrine (NE) and contain the vesicular monoamine transporter 2 (VMAT2), which packages NE into vesicles, and the norepinephrine transporter (NET), which removes NE from the synaptic cleft to terminate signaling. We have used a variety of biochemical and molecular techniques to test whether VMAT2 and NET levels decrease in sympathetic neurons which stop producing NE and make acetylcholine. In cultured sympathetic neurons, NET protein and mRNA decreased during the switch to a cholinergic phenotype but VMAT2 mRNA and protein did not decline. NET immunoreactivity disappeared from the developing sweat gland innervation in vivo as it acquired cholinergic properties. Surprisingly, NET simultaneously appeared in sweat gland myoepithelial cells. The presence of NET in myoepithelial cells did not require sympathetic innervation. VMAT2 levels did not decrease as the sweat gland innervation became cholinergic, indicating that NE synthesis and vesicular packaging are not coupled in this system. Thus, production of NE and the transporters required for noradrenergic transmission are not coordinately regulated during cholinergic development.

Morphological and electrical characteristics of postnatal hippocampal neurons in culture: the presence of bicuculline- and strychnine-sensitive IPSPs

A modified method was developed for tissue-culturing postnatal hippocampal neurons using simple mechanical trituration for cell isolation and not including any hydrolysing enzymes, nerve growth factors or antiproliferating agents. The morphological properties of such neurons were characterized with light and interference polarizing microscopy, which revealed the appearance of growth cones from peripheral neurons and the presence of different types of neurons, including bipolar, stellate and pyramidal-like cells (i.e., pyramidal and dentate gyrus granule cells), which could be related to their putative counterparts in intact brain. The whole-cell configuration of the patch-clamp method was used for electrophysiological recordings of inhibitory synapses between these dissociated cultured neurons from the early postnatal rat hippocampus. This study indicated the presence of tetrodotoxin (TTX)-sensitive and TTX-resistant inhibitory postsynaptic potential (IPSPs) and inhibitory postsynaptic currents (IPSCs) in current-clamp and voltage clamp modes respectively. The coincident reversal potentials for IPSCs and for GABAA and glycine-evoked currents, and the sensitivity of the IPSCs to bicuculline or strychnine, indicated that these IPSCs were Cl-(-)dependent and mediated by either GABAA or glycine receptors. Inhibitory postsynaptic currents recorded under voltage-clamp conditions decayed with a time course that could be fitted by a single exponential with a value of 26 ms. An average quantal content of 2.5 was responsible for a typical GABA and glycine-activated IPSC and a single quantum for GABAergic input was inferred to activate about 160, and for glycinergic, about 200 Cl-, channels.

P19 cells differentiate into glutamatergic and glutamate-responsive neurons in vitro

The neurotransmitter L-glutamate has been associated with a number of developmental events within the central nervous system including synaptogenesis and the refinement of topographically ordered neural maps. As a model for studying such events at the molecular level, we have examined the expression of glutamate and glutamate receptors in neurons that develop from P19 cells in response to retinoids. We report here that many P19-derived neurons do contain glutamate in secretory vesicles and that this glutamate appears to function as a neurotransmitter. The neurotransmitter GABA is also present in these cultures and both glutamate and GABA appeared to co-localize in some neuronal processes. Both neurotransmitters were released from the neurons in response to membrane depolarization. These neurons also express various glutamate receptor subunits including GluR1, GluR4 and NMDAR1 as detected by immunological methods. Using whole-cell patch-clamping, we have recorded spontaneous postsynaptic potentials which increase in both amplitude and frequency with time in culture and which are sensitive to the glutamate antagonist kynurenic acid Thus, P19-derived neurons mature in culture and form electrically active neural networks involving glutamate and glutamate receptors.

Target-independent cholinergic differentiation in the rat sympathetic nervous system

Chemical coding in the sympathetic nervous system involves both noradrenergic and, for a minority of neurons, cholinergic neurotransmission. The expression of the cholinergic phenotype in the developing sympathetic nervous system was examined to determine if coding for cholinergic transmission occurs before or after innervation of peripheral target organs. The vesicular acetylcholine transporter (VAChT) and choline acetyltransferase, the products of the "cholinergic gene locus" determining the cholinergic phenotype, were expressed in principal cells of the paravertebral, but only rarely in prevertebral, sympathetic chains as early as embryonic day 14. A subpopulation of VAChT- and choline acetyltransferase-positive sympathetic ganglion cells persisted throughout development of the stellate and more caudal paravertebral ganglia into anatomically distinct cell groups, and into adulthood. The forepaw eccrine sweat glands, innervated exclusively by the stellate ganglion, received VAChT-positive nerve terminals at least as early as postembryonic day 4, coincident with the development of the sweat glands themselves. These terminals, like the VAChT-positive cell bodies of the developing stellate ganglion, have some noradrenergic traits including expression of tyrosine hydroxylase, but did not express the vesicular monoamine transporter, and are therefore not functionally noradrenergic. Development of the cholinergic phenotype in principal cells of the sympathetic paravertebral ganglia apparently occurs via receipt of instructive cues, or selection, within the sympathetic chain itself or perhaps even during migration of the cells of the neural crest from which the paravertebral ganglia arise.

Morphological and immunohistochemical properties of primary long-term cultures of adult guinea-pig ventricular cardiomyocytes with peripheral cardiac neurons

Long-term (2-12 weeks) cultures of adult guinea-pig ventricular myocytes, cocultured with neurons derived from stellate or intrinsic cardiac ganglia, retain their functional properties (Horackova et al., 1993, 1994, 1995). The present study was designed to investigate the morphological and immunochemical properties of such neurons and their associated cardiomyocytes. Cultured myocytes studied by means of phalloidin-rhodamine (for F-actin) and an antibody raised against myomes revealed parallel myofibrils with striations typical of rod-shaped cardiomyocytes, even while myocytes changed from cylindrical to flattened form as they established intercellular contacts. Microtubular networks, identified by alpha-tubulin DM1A antibody, were arrayed longitudinally in myofibrils, being especially prominent during the formation of intercellular contacts between myocytes. Histochemically identified adult peripheral autonomic neurons cultured alone or with myocytes displayed a variety of shapes. alpha-Tubulin staining was associated with the somata and neurites of various-shaped neurons whether cultured alone or with myocytes. Cultured neurons derived from stellate and intrinsic cardiac ganglia also exhibited staining for the general neuronal marker PGP 9.5 (protein gene product 9.5), and for specific markers of the following neurochemicals: tyrosine hydroxylase, acetylcholinesterase, choline acetyltransferase, neuropeptide Y, vasoactive intestinal peptide, calcitonin gene-related peptide, bradykinin, oxytocin, and NADPH-diaphorase. These data indicate that: (a) adult ventricular myocytes cocultured with intrathoracic neurons retain the structural properties of adult myocytes found in vivo; (b) intrinsic cardiac and extrinsic intrathoracic neurons cultured alone or with cardiomyocytes display morphological characteristics similar to those of neurons studied in situ; (c) intrinsic cardiac and intrathoracic extracardiac neurons cultured alone or with cardiomyocytes display a variety of morphologies (unipolar, bipolar, and multipolar), larger and more multipolar neurons being present in cultures derived from stellate versus intrinsic cardiac ganglia; (d) such cultured neurons are associated with a number of neurochemicals, more than one chemical being associated with each neuron. This model presents an excellent opportunity to study the morphology of individual peripheral extracardiac and intracardiac neurons as well as their potential to produce various neurochemicals that are known to be involved in the neuromodulation of cardiomyocyte function.

Development of neuropeptide Y immunoreactive amacrine and ganglion cells in the pre- and postnatal cat retina

In the adult cat, neuropeptide Y (NPY) immunoreactivity (IR) is found within a subgroup of gamma-type ganglion cells and a large group of regularly arrayed amacrine cells. To examine the development of these two cell groups, we charted the appearance and maturation of neuropeptide Y immunoreactivity in the pre- and post-natal cat retina. Neuropeptide Y immunoreactivity is first observed at the central retina within the ganglion cell layer on embryonic day 46, and immunoreactivity within amacrine cells of the inner plexiform layer is present by E50. The number of immunoreactive profiles reaches the adult level in the amacrine population first (around P7), while the ganglion cell population shows a protracted development, with new cells being added until the third postnatal week. NPY-immunoreactive profiles in the ganglion cell layer were confirmed to be ganglion cells by retrograde labeling in both pre- and post-natal animals. Thus, neuropeptide Y-immunoreactive ganglion cells and amacrine cells attain their mature state with very different timecourses, although both cell groups initially follow a central to peripheral pattern of development. Interestingly, NPY expression within the ganglion cell population is temporally correlated with retinal synaptogenesis in the inner plexiform layer. As in the adult cat, NPY-immunoreactive ganglion cells never show a regular distribution during development, while NPY-IR amacrine cells are always distributed regularly even at the earliest ages. The prenatal presence of a regular distribution of NPY-IR amacrine cells suggests that these cells may participate in establishing the ganglion cell mosaics that appear during postnatal development.

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.

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.

Cell migration from the olfactory neuroepithelium of neonatal and adult rodents

This study reports the presence of olfactory cell clusters in postnatal and adult animals within the lamina propria of the olfactory mucosa and the nerve fiber layer of the olfactory bulb. The results obtained from mice and rats, partially or totally unilaterally bulbectomized, have been compared with observations in intact control animals. Light microscopic observation has shown that, in bulbectomized animals, the clusters are present in both experimental and normal sides and are usually associated with olfactory axon bundles. Moreover, when compared with intact animals, differences are present in terms of number of clusters and regions from where they originate. The morphological identity of the cells of the clusters with the globose basal cell of the olfactory neuroepithelium could be demonstrated with the electron microscope. By autoradiographic means, it was possible to show that they originate from the olfactory neurogenetic matrix and migrate along olfactory axon bundles. Interestingly, the migrating cells do not express olfactory marker protein. Altogether, these observations suggest that the olfactory matrix may be capable of originating neural elements other than olfactory receptor neurons.

Cell modulation of hydrophobic tailed 16S acetylcholinesterase by intracellular calcium in rat superior cervical ganglion neurons

In primary cell cultures of rat superior cervical ganglia (SCG) the tailed asymmetric 16S molecular form of acetylcholinesterase (AChE) possesses hydrophilic (high-salt soluble, HSS) and hydrophobic (detergent extracted, DE) variants. Hydrophobic tailed acetylcholinesterase is associated with membranes through a glycolipid anchor. In the presence of tunicamycin, an antibiotic which inhibits protein glycosylation, the cellular amount of the hydrophobic DE 16S AChE is increased. Exposure of the cells to the calcium ionophore A 23187 leads to a decrease in DE 16S AChE and a correlated increase in hydrophilic HSS 16S AChE. These results suggest the existence of an endogenous processing of tailed AChE, transforming the hydrophobic variant into an hydrophilic one controlled through glycosylation and intracellular calcium.

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.

The cholinergic neuronal differentiation factor from heart cell conditioned medium is different from the cholinergic factors in sciatic nerve and spinal cord

Environmental cues play an important role in determining the transmitter phenotype of developing sympathetic neurons. Several factors have been described which can induce cholinergic function in cultured sympathetic neurons. We have compared certain biological and immunological properties of three of them, cholinergic differentiation factor (CDF), membrane-associated neurotransmitter-stimulating factor (MANS), and ciliary neurotrophic factor (CNTF), to determine whether they are different. As previously reported, all three increased acetylcholine synthesis in cultured sympathetic neurons. In addition, MANS as well as CNTF and CDF decreased catecholamine synthesis. CNTF and MANS, but not CDF, promoted the survival of embryonic chick ciliary neurons. Affinity-purified antibodies raised against a synthetic peptide corresponding to the N-terminal sequence of CDF immunoprecipitated CDF, but not MANS or CNTF. These results indicate that although CDF, MANS, and CNTF have similar effects on transmitter synthesis by cultured sympathetic neurons, CDF lacks the ciliary neurotrophic activity of MANS and CNTF. Further, CDF possesses an N-terminal epitope which is absent from both MANS and CNTF. Thus, CDF is distinct from MANS and CNTF, and at least two factors exist which can alter the transmitter phenotype of sympathetic neurons in vitro.

Peptides and vasomotor mechanisms

The multiple and diverse roles played by neuropeptide Y, vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide and other biologically active peptides in the cardiovascular system are considered. A model of the vascular neuroeffector junction is described, which illustrates the interactions of peptidergic and nonpeptidergic transmitters that are possible at pre- and postjunctional sites. The effects of peptides on specific endothelial receptors are also described, which highlights the ability of these agents to act as dual regulators of vascular tone at both adventitial and intimal surfaces, following local release from nerves, or from endothelial cells themselves. Changes in expression of vascular neuropeptides that occur during development and aging in some disease situations and following nerve lesion are discussed.

Co-localization and plasticity of transmitters in peripheral autonomic and sensory neurons

Immunohistochemical studies have shown that most peripheral autonomic and sensory ganglia are heterogeneous, consisting of several populations of neurons which can be distinguished by their content of peptide and non-peptide transmitters, and transmitter-associated enzymes. Many neurons contain several different potential transmitters, especially neuropeptides. Some neuropeptides have been localized in more than one population of autonomic and sensory neurons. However, the peptide often occurs together with a distinctive combination of additional transmitters in each neuronal class. The precise combination of transmitters found in any individual neuron is highly correlated with the peripheral target of the neuron. This indicates that immunohistochemically defined neuronal populations represent distinct functional classes of neurons. In an increasing number of cases, many of the potential transmitters contained in a particular neuron have been shown to be released from the nerve terminals, and to contribute to presynaptic or postsynaptic effects of nerve activation. Despite this association between the combination of potential transmitters contained in a neuron, and the function of the neuron, not all transmitters or transmitter-associated enzymes are expressed equally at all times in the life of a neuron: the levels of some substances change dramatically during development; some are detected only after experimental alteration of the environment of the developing or mature neurons. Taken together, these results indicate that, during development, pathway-specific information influences the differentiation of peripheral autonomic and sensory neurons. Furthermore, the expression of neuropeptides and transmitter-associated enzymes in a particular neuron appears to be under continuous regulation. These phenomena demonstrate the complexity and precision involved in development and maintenance of the peripheral autonomic and sensory nervous systems.

Plasticity in the nervous system of adult hydra. II. Conversion of ganglion cells of the body column into epidermal sensory cells of the hypostome

Due to the tissue dynamics of hydra, every neuron is constantly changing its location within the animal. At the same time specific subsets of neurons defined by morphological or immunological criteria maintain their particular spatial distributions, suggesting that neurons switch their phenotype as they change their location. A position-dependent switch in neuropeptide expression has been demonstrated. The possibility that ganglion cells of the body column are converted into epidermal sensory cells of the head was examined using a monoclonal antibody, TS33, whose binding is restricted to a subset of epidermal sensory cells of the hypostome, the apical end of the head. When animals devoid of interstitial cells, which are the nerve cell precursors, were decapitated and allowed to regenerate, they formed TS33+ epidermal sensory cells. As this latter cell type is not found in the body column, and the interstitial cell-free animals contained only epithelial cells and ganglion cells in the part of the ectoderm that formed the head during regeneration, the TS33+ epidermal sensory cells most likely arose from the TS33- ganglion cells. The observation of epidermal sensory cells labeled with both TS33 and TS26, a monoclonal antibody that binds to ganglion cells, in regenerating and normal heads provides further support. The double-labeled cells are probably in transition from a ganglion cell to an epidermal sensory cell. These results provide a second example of position-dependent changes in neuron phenotype, and suggest that the differentiated state of a neuron in hydra is only metastable with regard to phenotype.

Determination of the birth date and proliferative state of dissociated cells from fetal rat brain

The proliferative status and time of origin of dissociated cells from cerebral cortex, basal ganglia, diencephalon, mesencephalon and rhombencephalon of the fetal rat brain have been analyzed. The distributions of cells in different phases of the cell cycle after dissociation and after 7 days in culture have been determined with flow cytofluorometry. Two separate DNA indicators, propidium iodide and Hoechst 33258, have been used. Almost all of the dissociated cells recovered from the 5 brain regions, between embryonic days 15 and 20, are in G1, or growth arrest phase of the cell cycle. In contrast, only about 55% of the liver cells (same fetal age) are in G1, or growth arrest phase. The times of the last in vivo mitoses of the dissociated cells have been determined by maternal injection of [3H]thymidine and autoradiography of cultures. The majority of the cells recovered on embryonic days 16 and 17 from the 5 brain regions appeared to have undergone DNA synthesis within a period of 24 h prior to dissociation. When the fetuses were sacrificed 96 h after the injection, less than 20% of the cells were labelled, and grain density was drastically reduced. Most labelled cells survive in the serum-free culture medium for more than 7 days. Dissociated cultures of synchronized and birth-dated cells from different brain regions of fetal rat should prove particularly useful for the study of cellular development and function.

Comparison of the effects of elevated K+ ions and muscle-conditioned medium on the neurotransmitter phenotype of cultured sympathetic neurons

Neuronal depolarization and culture media conditioned by certain nonneuronal cells (CM) are known to exert opposite effects on the expression of cholinergic and noradrenergic traits in cultured rat sympathetic neurons. We have compared their effects on the developments of choline acetyltransferase (CAT), tyrosine hydroxylase (TOH), dopa decarboxylase (AADC) and acetylcholinesterase (AcChE) in these cultures. A macromolecular factor which was partially purified from CM increased CAT development in a dose-dependent manner and depressed the development of TOH and AADC by 5- to 10-fold. In the presence of intermediate concentrations of this partially purified factor, both CAT and catecholamine synthesizing enzymes developed to high levels, whereas high concentrations caused a long-lasting, but not total, impairment of TOH development. The effects of CM on both CAT and AADC activities resulted from variations in the number of immunotitratable enzyme molecules. Conversely, K+ ions (30-40 mM) depressed the development of CAT by 90% and stimulated TOH development 2.5-fold. Cultures grown with CM in high K+ medium had similar CAT and TOH activities as compared to those cultures grown without CM in low K+ medium suggesting that CM and K+ ions had antagonistic effects on the expression of these enzymes. However, K+ ions did not affect the development of AADC in these cultures. CM suppressed in a reversible manner the development of the 16 S form of AcChE. In the presence of 40 mM K+, the rate of development of AcChE was reduced. In particular, the development of 16 S AcChE was strikingly impaired, although not totally suppressed. The effect of elevated K+ ions on the percentage of 16 S AcChE was rapidly reversible. It is concluded that CM and elevated K+ ions have antagonistic effects on CAT and TOH, but not on AADC development; AcChE, in particular its asymmetric 16 S form, is regulated independently of the cholinergic/noradrenergic status of sympathetic neurons.

Long-term blockade by toxin F of nicotinic synaptic potentials in cultured sympathetic neurons

The effects of a recently identified blocker of neuronal nicotinic transmission, toxin F, were studied in cultured sympathetic neurons. Single principal neurons, dissociated from superior cervical ganglia of newborn rats, were grown on cardiac myocytes in microculture. The toxin blocked nicotinic synaptic potentials in these cultures but had no effect on muscarinic interactions. When toxin F was applied by addition to the perfusion medium, the concentration required for blocking most of the nicotinic potential was 40 nM, and the recovery from blockade was slow (t1/2 = 95 +/- 64 min). When the toxin was briefly applied by pressure ejection from a pipette, the concentration in the pipette necessary for blockade was 21 microM, and 30-60% of the response recovered within a few minutes while the remainder recovered slowly (t1/2 of the remainder = 105 +/- 82 min). One possible explanation for the difference in recovery time is that toxin F binds initially with low affinity to the nicotinic receptor but with time the toxin receptor complex converts to a high affinity state. The presence of dihydro-beta-erythroidine during perfusion of toxin F prevented the long-lasting blockade by the toxin, suggesting that toxin F and dihydro-beta-erythroidine act through a common binding site. The specificity, potency, and slow reversibility of the effects of toxin F make it useful as a probe for studying neuronal nicotinic receptors of cultured sympathetic neurons.

Differences in monoamine oxidase activity between cultured noradrenergic and cholinergic sympathetic neurons

Two types of monoamine oxidase activity (MAO-A and MAO-B) help regulate the levels of biogenic amines such as catecholamines and serotonin. Although MAO-A has greater activity toward most catecholamines than MAO-B, no direct experiments have determined the types and levels of MAO activity that are normally expressed in noradrenergic neurons. Noradrenergic neurons from neonatal rat superior cervical ganglia were isolated and cultured under conditions that permit either continued expression of the noradrenergic phenotype or promote a transition to a predominantly cholinergic phenotype. After 14-21 days in vitro, neurons from both types of cultures were assayed for the type and amount of monoamine oxidase activity using tryptamine, a common substrate for both MAO-A and MAO-B. Neurons cultured under noradrenergic conditions expressed sevenfold greater MAO activity than neurons cultured under cholinergic conditions. Essentially all MAO activity in the noradrenergic cultures was inhibited by preincubation with 10(-8)-10(-9) M clorgyline, which indicated that this activity was primarily MAO-A. Cultures grown under cholinergic conditions exhibited 6- to 10-fold lower MAO-A activity and an 8- to 10-fold lower level of catecholamine synthesis from labeled precursors compared to neurons grown under noradrenergic conditions. These results directly demonstrate that high MAO-A activity is expressed in noradrenergic neurons in vitro. The corresponding decreases in both MAO-A specific activity and catecholamine synthesis as neurons become cholinergic in vitro suggest that the expression of the noradrenergic phenotype involves the coordinate regulation of degradative as well as synthetic enzymes involved in catecholamine metabolism.

The use of a tyrosine-hydroxylase cDNA probe to study the neurotransmitter plasticity of rat sympathetic neurons in culture

We have compared quantitatively the effects of muscle-conditioned medium (CM) and elevated K+ concentration (40 mM) on the enzymatic activity of tyrosine hydroxylase (TH) and on TH-mRNA levels in primary cultures of rat sympathetic neurons. Northern blot analysis of RNA from cultured neurons with a 32P-labeled rat TH-cDNA probe was performed. The probe hybridized strongly with a single RNA species of 1.9 kb, similar in size to the TH-mRNA from PC12 pheochromocytoma cells. In agreement with earlier data both CM and a partially purified factor from CM increased choline acetyltransferase activity up to 200-fold and depressed TH activity by 2- to 7-fold in cultured sympathetic neurons. These effects were accompanied by a decrease in TH-mRNA level, which correlated with the decrease in TH activity. On the other hand, a culture medium supplemented with 40 mM KCl caused a 1.5- to 5-fold increase in TH activity, which was accompanied by an increase in TH-mRNA level of the same order of magnitude. As a working hypothesis, we suggest that CM and neuronal depolarization control the transcription of the TH gene in an antagonistic manner.

Characterization of the vesicular monoamine transporter in cultured rat sympathetic neurons: persistence upon induction of cholinergic phenotypic traits

The binding of [3H]dihydrotetrabenazine ([3H]TBZOH), a specific ligand of the reserpine-sensitive monoamine transporter in brain and adrenal medulla storage vesicles, has been measured in cultured sympathetic neurons from newborn rat in relation to their neurotransmitter phenotype. As shown previously, neurons cultured in the absence of muscle-conditioned medium displayed high activities in catecholamine synthesizing enzymes and low levels of choline acetyltransferase, and neurons cultured in conditioned medium displayed the reverse pattern (J. P. Swerts, A. Le Van Thai, A. Vigny, and M. J. Weber, Dev. Biol. 100, 1-11, 1983). The density of [3H]TBZOH binding sites as well as their subcellular distribution were identical in both types of cultures. Two other structures rich in choline acetyltransferase, the electric organ of Torpedo and the ciliary ganglion of the chick embryo did not contain measurable amounts of [3H]TBZOH binding sites, suggesting that the monoamine transporter is not an ubiquitous component of cholinergic synaptic vesicles. These data suggest that the synthesis of the monoamine transporter in sympathetic neurons is not coregulated with the syntheses of the three norpinephrine synthesizing enzymes. It is proposed that the same population of synaptic vesicles can accumulate acetylcholine or catecholamine, depending only upon which neurotransmitter synthesizing enzymes are expressed by sympathetic neurons.

Plasticity in the nervous system of adult hydra. I. The position-dependent expression of FMRFamide-like immunoreactivity

The plasticity of nerve cells expressing the neuropeptide FMRFamide was examined in adult hydra. Using a whole-mount technique with indirect immunofluorescence, the spatial pattern of neurons showing FMRFamide-like immunoreactivity (FLI) was visualized. These neurons were located in the tentacles, hypostome, and peduncle, but not in the body column or basal disc. Since every neuron in the nerve net is continuously displaced toward an extremity and eventually sloughed, the constant pattern of FLI+ neurons could arise in one of two ways. When displaced into the appropriate region, FLI- neurons are converted to FLI+ neurons, or FLI+ neurons arise by differentiation from interstitial cells. To distinguish between these two possibilities, interstitial cells, the multipotent precursors of the nerve cells, were eliminated by treatment with hydroxyurea or nitrogen mustard. Following head, or foot and peduncle, removal from these animals, the missing structures regenerated. The spatial pattern of FLI+ neurons reappeared in the newly regenerated head or peduncle. This shows FLI- neurons in the body column were converted to FLI+ when their position was changed to the head or the peduncle. When the peduncle was grafted into the body column, it was converted to basal disc or body column tissue, and FLI disappeared. The appearance and loss of FLI was always position dependent. These results indicate that the neurons in the mature nerve net can change their neuropeptide phenotype in response to changes in their position.

Cytochemical study of developing neurotransmitter properties of dissociated sympathetic neurons grown in co-culture with dissociated pineal cells

We studied the development of neurotransmitter phenotype in sympathetic neurons grown in the presence of pinealocytes, a target tissue having adrenergic but not cholinergic receptors. Neurons, dissociated from neonatal rat superior cervical ganglia, were grown in co-culture with dissociated pineal cells. Both ganglionic and pineal non-neuronal background cells were allowed to grow nearly to confluency. Electron microscopic cytochemical techniques were used to examine sets of co-cultures at weekly intervals over 5 weeks. Adrenergic vesicles were identified by their dense granular precipitate following potassium permanganate fixation. We found that the percentage of small granular vesicles, both in synaptic boutons onto other neurons and in axonal varicosities, declined very little over 5 weeks. After an initial drop from 75 to 65%, the percentage of small granular vesicles remained remarkably constant. Throughout the 5 weeks, more than 70% of the boutons and varicosities contained a predominance of small granular vesicles; fewer than 20% contained a predominance of clear vesicles. Although both somal synaptic boutons and axonal varicosities retained a predominantly adrenergic ultrastructure, at certain weeks there was a statistically significant shift in the percent distribution of adrenergic vesicles in somal boutons compared with the distribution in axonal varicosities. Because these cultures were grown under conditions known to favor an induction of acetylcholine metabolism and a suppression of catecholamine metabolism, we conclude that the maintenance of adrenergic ultrastructure over 5 weeks may be due to the presence of the pineal cells.

Neonatal treatment with nerve growth factor antiserum eliminates cholinergic sympathetic innervation of rat sweat glands

Most mammalian sympathetic neurons are noradrenergic, and their dependence upon nerve growth factor (NGF) for survival during development is well established. A minor population of sympathetic neurons, including those that innervate sweat glands, is cholinergic. To determine whether cholinergic sympathetic neurons, like their noradrenergic counterparts, require NGF during development, neonatal rats were treated with NGF-antiserum and 3 weeks later their sweat glands were examined for the presence of innervation. Acetylcholinesterase (AChE) staining and vasoactive intestinal polypeptide-like immunoreactivity (VIP-IR) which mark the mature sweat gland innervation were absent from the sweat glands of the anti-NGF treated animals. Further, when the glands were examined with the electron microscope, no axons or nerve terminals were evident. These observations indicate that the elaboration of the sweat gland plexus is NGF-dependent and suggest that at least one population of cholinergic sympathetic neurons in the rat requires NGF for survival. Our findings are consistent with the idea that during development NGF is a required trophic factor not only for noradrenergic sympathetic but also for cholinergic sympathetic neurons.

Neuronal regulation of the development of the alpha-adrenergic chronotropic response in the rat heart

During development, there are changes in the response of automatic cardiac fibers to alpha-adrenergic agonists. In neonatal rat ventricle, in vitro phenylephrine (1 X 10(-8) M) induces an increase in automatic rate from 115 +/- 12 (mean +/- SEM) to 168 +/- 10 beats/min, P less than 0.05. In contrast, in adult rat ventricle, the rate decreases from 36 +/- 8 to 12 +/- 12 beats/min, P less than 0.05. At both ages, the response is attenuated by the alpha 1-antagonist, prazosin (1 X 10(-6) M). We used cultures of neonatal rat myocytes to determine whether maturation of innervation contributes to the ontogeny of this response. All non-innervated cultures showed a positive chronotropic response to alpha-stimulation; phenylephrine (1 X 10(-8) M) increased the rate from 40 +/- 2 to 52 +/- 2 beats/min, P less than 0.05. In contrast, 60% of the myocytes innervated with sympathetic neurons showed a decrease in rate in response to phenylephrine, from 78 +/- 6 to 67 +/- 6 beats/min, P less than 0.05. The negative chronotropic effect of phenylephrine did not result from the release of acetylcholine or adenosine, or the inhibition of presynaptic norepinephrine release by phenylephrine. Furthermore, exposure to neuronal norepinephrine is not responsible for the alteration in muscle cell responsiveness. In conclusion, we have demonstrated the modulation of the myocardial response to alpha-adrenergic stimulation by the occurrence of innervation in tissue culture. This provides an explanation for the previously identified ontogenetic change in alpha-adrenergic effects on intact cardiac fibers from excitation to inhibition.

Specific cellular expression of monoamine oxidase B during early stages of quail embryogenesis

Monoamine oxidase-B (MAO-B) is one of two distinct molecular forms of MAO that in part regulate the cellular levels of biogenic amines. In order to determine whether discrete cell populations known to express aminergic properties in the vertebrate embryo also express MAO-B, the distribution of MAO-B-immunoreactive cells was examined in early developing quail embryos. Two major patterns of staining emerge. First, tissues known to express several aminergic characteristics are initially MAO-B positive at early stages of development and continue to express immunoreactivity through Zacchei stage 20, the oldest stage examined. These include cells of the sympathetic and some cranial and trunk sensory ganglia (beginning at stage 13), the pancreas (stage 14), and the brain stem raphe (stage 14). Second, other structures that contain or accumulate biogenic amines are transiently MAO-B immunopositive during early stages of development. These tissues include extraembryonic yolk sac and presumptive gut endoderm (with most intense staining between stages 8 and 13), the ventral trunk neural tube (stages 14 and 16), and the notochord (stages 8-10). MAO-B immunoreactivity disappears from these regions at different stages, and none are MAO-B positive by stage 19-20. Other structures without known aminergic properties during early development also stain; these include liver (stage 20), mesenchymal cells that surround the Wolffian duct and lung buds (stages 14 and 18), and endothelial cells surrounding the dorsal aorta (stages 14 and 20). In general, however, MAO-B appears to be distributed in embryonic tissues that can use this enzyme to regulate biogenic amine levels either transiently or during initial phenotypic expression of aminergic traits.

Rapid changes in synaptic vesicle cytochemistry after depolarization of cultured cholinergic sympathetic neurons

Sympathetic neurons taken from rat superior cervical ganglia and grown in culture acquire cholinergic function under certain conditions. These cholinergic sympathetic neurons, however, retain a number of adrenergic properties, including the enzymes involved in the synthesis of norepinephrine (NE) and the storage of measurable amounts of NE. These neurons also retain a high affinity uptake system for NE; despite this, the majority of the synaptic vesicles remain clear even after incubation in catecholamines. The present study shows, however, that if these neurons are depolarized before incubation in catecholamine, the synaptic vesicles acquire dense cores indicative of amine storage. These manipulations are successful when cholinergic function is induced with either a medium that contains human placental serum and embryo extract or with heart-conditioned medium, and when the catecholamine is either NE or 5-hydroxydopamine. In some experiments, neurons are grown at low densities and shown to have cholinergic function by electrophysiological criteria. After incubation in NE, only 6% of the synaptic vesicles have dense cores. In contrast, similar neurons depolarized (80 mM K+) before incubation in catecholamine contain 82% dense-cored vesicles. These results are confirmed in network cultures where the percentage of dense-cored vesicles is increased 2.5 to 6.5 times by depolarizing the neurons before incubation with catecholamine. In both single neurons and in network cultures, the vesicle reloading is inhibited by reducing vesicle release during depolarization with an increased Mg++/Ca++ ratio or by blocking NE uptake either at the plasma membrane (desipramine) or at the vesicle membrane (reserpine). In addition, choline appears to play a competitive role because its presence during incubation in NE or after reloading results in decreased numbers of dense-cored vesicles. We conclude that the depolarization step preceding catecholamine incubation acts to empty the vesicles of acetylcholine, thus allowing them to reload with catecholamine. These data also suggest that the same vesicles may contain both neurotransmitters simultaneously.

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

Transient expression of catecholaminergic phenotypic traits is a widespread phenomenon during embryonic development in mammals, occurring in cells of the embryonic gut mesenchyme, in ventrolateral portions of the neural tube, cells of cranial sensory and dorsal root ganglia, and in the embryonic pancreas. In the current study the manifestation of the catecholamine (CA) phenotype in these populations has been further defined. Specifically, the existence of the high-affinity uptake process for CAs in these populations has been investigated. By combining the techniques of radioautography following accumulation of [3H]norepinephrine (3H-NE) and [3H]dopamine (3H-DA) with immunohistochemical detection of tyrosine hydroxylase (T-OH), it has been possible to demonstrate simultaneously CA accumulation by T-OH-positive gut cells. Uptake of 3H-NE was first detected in T-OH-positive cells of the gut on gestational day 12.5 (E12.5). By contrast, T-OH immunoreactivity was first detected on E11.5. By E13.5 virtually every T-OH-positive cell oral to the umbilical flexure was radioautographically labeled. Uptake at E13.5 displayed Michaelis-Menten saturation kinetics, had a Vmax of 35 fmole/gut/min, a Km of 1.45 microM, was blocked by desmethylimipramine (DMI), and by incubation at 4 degrees C. On subsequent gestational days, silver grains marking areas of amine concentration were found increasingly over T-OH-negative cells. A similar pattern of uptake was found in guts which had been grown in organotypic tissue culture for the purpose of eliminating extrinsic sympathetic innervation. T-OH-positive gut cells also accumulated 3H-DA. Concentration of 3H-DA was blocked by both benztropine and DMI suggesting that accumulation had properties common to both NE and DA systems. By contrast to cells of the gut, accumulation of CAs was not a property of transiently T-OH-positive cells in other locations. Therefore, specific, high-affinity uptake and retention of CAs is an additional property of transiently catecholaminergic gut cells. Appearance of CA synthetic enzymes precedes the appearance of the CA storage process in cells of the gut. Persistence of the uptake process after the loss of detectable T-OH suggests continued viability of the population. The absence of CA accumulation by other T-OH-positive cells suggests basic molecular differences among the various populations.

Decrease of tailed, asymmetric 16S acetylcholinesterase in rat superior cervical ganglion neurons in vitro after potassium depolarization: partial antagonist action of a calcium-channel blocker

In primary cell cultures of rat superior cervical ganglia the tailed, asymmetric 16S molecular form of acetylcholinesterase (AChE) is preferentially decreased after potassium depolarization. This effect is not related to noradrenergic differentiation elicited by high potassium concentration. Moreover there is a partial antagonist action of a calcium-channel blocker, methoxyverapamil (D-600). These results suggest that membrane electrical activity exerts a regulatory control on AChE, and Ca2+ fluxes play an important role in regulatory events of AChE biosynthesis.

Non-neuronal cell conditioned medium stimulates peptidergic expression in sympathetic and sensory neurons in vitro

Regulation of peptide neurotransmitter metabolism was examined in dissociated cell cultures of neonatal rat sympathetic and sensory ganglia. Previous studies have shown that pineal gland conditioned medium (PCM) influences substance P (SP) and somatostatin (SS) metabolism in sympathetic neurons in vitro. The present study examines mechanisms mediating these effects, and compares the actions of PCM on sympathetic and sensory neurons. PCM treatment increased SP levels in a dose-dependent manner without altering SS content of sympathetic neurons cultured in the presence of ganglion non-neuronal cells. Conversely, treatment of pure sympathetic neuron cultures resulted in a dose-dependent increase in SS, while SP was virtually undetectable at all doses. By contrast, dorsal root ganglion, trigeminal ganglion, and nondose ganglion sensory neurons contained SP both in the presence and absence of ganglion non-neuronal cells. Moreover, in each of these neuronal populations treatment with PCM increased SP levels both in the presence and in the absence of ganglion non-neuronal cells. These observations suggest that ganglion non-neuronal cells are necessary for sympathetic but not sensory neuron expression of SP. Moreover, PCM apparently stimulates SP in neurons which already contain the peptide, but the factor cannot foster de novo expression of the phenotype. PCM also influenced other transmitter traits in sympathetic neurons, suggesting linkage between mechanisms regulating peptides and other transmitters. In cultures containing both sympathetic neurons and non-neuronal cells, PCM treatment increased cholineacetyltransferase (CHAC) activity as well as SP, and decreased tyrosine hydroxylase (TOH) activity. By contrast, PCM treatment of pure sympathetic neuron cultures led to parallel increases in SS and TOH activity with negligible levels of SP and CHAC. These observations suggest that in sympathetic neurons, SS may be linked with noradrenergic expression, while SP is associated with cholinergic development, although more data are required to confirm this relationship. Moreover, there may be a reciprocal relationship between SP and SS expression by sympathetic neurons analogous to previous observations regarding cholinergic-noradrenergic expression (P. H. Patterson and L. L. Y. Chun, Proc. Natl. Acad. Sci. USA 71, 3607-3610, 1974; Dev. Biol. 56, 263-280, 1977). Consequently, neurotransmitter phenotypic expression is a complex process in which the environment regulates a balance among multiple transmitters.

In vitro adrenergic and cholinergic innervation of the developing rat myocyte

We studied the development of selective adrenergic and cholinergic neuroeffector transmission in primary cultures of isolated ventricular muscle cells. Explants of either thoracolumbar sympathetic ganglia or sacrococcygeal spinal cord were added to newborn rat ventricular cultures harvested prior to the onset of in vivo autonomic innervation. Neuronal growth, migration, and the formation of neuromuscular junctions were observed with light and scanning electron microscopy. Glyoxylic acid histofluorescence, reflecting catecholamine synthesis, was found in only the sympathetic neuromuscular cultures. Choline acetyltransferase activity was detected in both spinal cord and sympathetic neuromuscular cultures, but was significantly higher in the spinal cord neuromuscular cultures. The isolated ventricular muscle cells remained at a constant spontaneous contraction frequency, regardless of the type of culture preparation. Guanethidine sulfate application produced a positive chronotropic response, blocked by propranolol, in the sympathetic neuromuscular cultures, but not in the spinal cord neuromuscular cultures. Bethanechol sulfate produced a negative chronotropic response, blocked by atropine, in the spinal cord neuromuscular cultures, but not in the sympathetic neuromuscular cultures. Isolated ventricular muscle cells in the absence of neurons failed to respond to either agent. Direct microelectrode stimulation of adrenergic or cholinergic neurons likewise respectively produced either a positive or negative ventricular muscle cell chronotropic response. These studies are the first to establish the selective production of functional cholinergic and adrenergic innervation of isolated cardiac muscle cells in vitro.

Target organ regulation of substance P in sympathetic neurons in culture

Target organ regulation of the putative, peptide neurotransmitter, substance P (SP) was examined in explants and dissociated cell cultures of the neonatal rat sympathetic superior cervical ganglion (SCG). SP levels increased dramatically in explants, rising more than 30-fold after 72 hr in culture. By contrast, peptide levels did not increase in dissociated ganglion cultures. However, SP increased almost 10-fold in cell cultures grown on a monolayer of cells derived from the pineal or salivary gland, targets of the SCG. By contrast, SP content did not increase in cultures grown on a substrate of cells derived from heart or intestine. Peptide identity in the SCG-target cocultures was authenticated by means of combined high-pressure liquid chromatography (HPLC)-radioimmunoassay. Moreover, immunohistochemical examination localized the peptide virtually exclusively to sympathetic neurons and nerve processes. Mechanisms mediating the sympathetic-target interaction were examined in SCG-pineal cocultures. The increase in peptide required interactions with living tissue, since substrates of killed target cells did not elevate SP levels. The target influences were not mediated by nerve growth factor or indoleamines, potential secretory products of pineal in culture. Veratridine treatment prevented the increase in SP in the cocultures, and tetrodotoxin blocked the veratridine effect, suggesting that sodium influx and membrane depolarization prevent SP elevation. Our observations suggest that sympathetic neuron interactions with target organs influence peptidergic expression, and that this interaction may be restricted to certain appropriate target structures.

Regulation of enzymes responsible for neurotransmitter synthesis and degradation in cultured rat sympathetic neurons. II. Regulation of 16 S acetylcholinesterase by conditioned medium

The molecular forms of acetylcholinesterase (AcChE) have been studied in primary cultures of newborn rat sympathetic neurons grown either in the absence (CM- cultures) or in the presence (CM+ cultures) of muscle conditioned medium. The cultures were treated with a mitotic poison to eliminate non-neuronal cells. CAT activity increased with time in culture 4- to 20-fold faster in CM+ than in CM- cultures. In agreement with previous experiments (J.P. Swerts, A. Le Van Thaï, A. Vigny, and M.J. Weber, 1983, Develop. Biol. 100, 1-11), AcChE activity developed at a 3-fold lower rate in CM+ than in CM- cultures. This deficit in AcChE activity in CM+ cultures resulted from a deficit in the number of enzyme molecules immunoprecipitable with an antiserum raised against rat brain AcChE. In both types of cultures, AcChE forms were separated by sucrose gradient sedimentation into three main peaks corresponding to the 16 S and 10 S forms and a mixture of the 6.5 and 4 S forms. In 3-day-old CM+ and CM- cultures, the 16 S form represented 2% of the total activity. After 12-26 days, the percentage of 16 S form raised to 15-30% in CM- cultures, but remained lower than 5% in CM+ cultures. This difference was also observed when AcChE molecular forms were analyzed in the presence of protease inhibitors. A similar result was obtained by comparing cultures grown with and without a macromolecular factor partially purified from conditioned medium. These results suggest that an inverse relationship exists between the presence of 16 S AcChE and the presence of cholinergic synapses in these cultures.

Adrenal chromaffin cells form functional cholinergic synapses in culture

Adrenomedullary cells and autonomic ganglion cells originate from the neural crest. Both cell types synthesize, store and release catecholamines; however, their structural and functional properties are distinctly different. Aloe and Levi-Montalcini have shown in vivo that when the adrenal medulla is exposed to exogenous nerve growth factor (NGF) most cells differentiate into neuronal cells substantially similar to sympathetic neurones. Experiments in vitro have also shown that neonatal as well as adult adrenal chromaffin cells and their neoplastic correlate (PC12 cells) undergo neurone-like morphologic differentiation in response to NGF. From these morphological and biochemical studies alone, however, it remains uncertain whether the functional neuronal transformation is also accompanied. We report here that the adrenal chromaffin cells in culture can differentiate into neuronal cells having functional synapses which were found to be cholinergic in nature. Furthermore, the type of synaptic vesicles in the newly formed synapses was apparently dependent upon K+ levels in the culture medium.

Development of cholinergic properties in nerve cell cultures in the presence of brain extract

Cells dissociated from cerebral hemispheres of 6-day-old chick embryos were cultured either in standard nutrient medium or in the presence of a brain extract from 8-day-old chick embryo. Morphological observations showed the development of bipolar and multipolar neurons in both culture conditions and acetylcholinesterase activity was found in all neuronal cells. Brain extract stimulated the morphological maturation of neurons, expressed by the formation of fiber bundles, fine structural maturation and development of synapses rich in clear vesicles. Furthermore, acetylcholinesterase and choline acetyltransferase activities were higher in the cultures treated with brain extract. In these cultures, the values of choline acetyltransferase activity reached a peak at 10 days and then decreased. These observations are discussed with particular reference to proliferation, maturation and degeneration of cholinergic neurons.

Regulation of enzymes responsible for neurotransmitter synthesis and degradation in cultured rat sympathetic neurons. I. Effects of muscle-conditioned medium

The enzymatic machinery for neurotransmitter synthesis and breakdown have been compared in sister cultures of newborn rat sympathetic neurons grown for 12-28 days either in the presence (CM+ cultures) or in the absence (CM- cultures) of a culture medium conditioned by rat skeletal muscle cells. Neuron numbers, total protein, and lactate dehydrogenase activities were identical in CM+ and CM- cultures. Choline acetyltransferase activity was 27- to 100-fold higher in homogenates of CM+ than CM- cultures, whereas acetylcholinesterase activity was 2.5-fold lower. The activities of tyrosine hydroxylase (TOH), DOPA decarboxylase, and dopamine beta-hydroxylase were all about twofold lower in homogenates from CM+ cultures. All these effects were also observed in homogenates of sympathetic neuron cultures grown with and without a macromolecular factor partially purified from CM (Weber, J. (1981). Biol. Chem. 256, 3447-3453.). Experiments of mixing homogenates from CM+ and CM- cultures suggested that the differences in each of the enzyme activities did not result from differences in the concentrations of hypothetical reversible enzyme activators and/or inhibitors. In addition, the deficit in TOH activity in CM+ cultures resulted from a decrease in the enzymatic Vmax with no significant variation in the apparent Km's for the substrate and the cofactor. An identical decrease in the Vmax was observed if TOH was assayed under phosphorylating or nonphosphorylating conditions, suggesting that this decrease did not result from differences in the state of enzyme phosphorylation. Immunoprecipitation curves of TOH activity by an anti-TOH antiserum were parallel when performed on homogenates from CM+ and CM- cultures, suggesting a difference in the number of enzyme molecules without detectable alteration of their kinetic properties.

Evidence for neurotransmitter plasticity in vivo: developmental changes in properties of cholinergic sympathetic neurons

We have examined the cholinergic sympathetic innervation of sweat glands in footpads of adult and developing rats. Acetylcholinesterase staining reveals a plexus of heavily stained fibers in the sweat glands of adult rats. Reaction product appears among and around bundles of axons that lie at a considerable distance from the cells of the secretory tubule. Each bundle contains 8-12 axons that possess numerous varicosities and contain small clear and large dense core vesicles. The glands of the hindpaws and their innervation develop during the first three weeks after birth. Catecholamine-containing axons were associated with the forming glands. At 7 and 10 days, intensely fluorescent fibers surrounded the tubules, and all of the axon profiles associated with the glands contained small granular vesicles (SGV) after permanganate fixation to reveal vesicular stores of norepinephrine. At 14 days the sweat gland plexus was less intensely fluorescent than at earlier ages and relatively few SGV were present. By 21 days, no endogenous catecholamine fluorescence and no SGV were detectable. However, following exposure to exogenous catecholamine, fluorescent fibers were present in the sweat glands of mature rats and they corresponded in position and density to the plexus localized with acetylcholinesterase staining. Catecholamine uptake was blocked by incubation in the cold and by desmethylimipramine and was not observed in cholinergic parasympathetic fibers in the iris or salivary glands. After intraperitoneal administration of 5-hydroxydopamine and permanganate fixation, all the axons in the sweat glands contained a few SGV. Thus, the developing sweat glands appear to be innervated by noradrenergic axons that lose their stores of endogenous catecholamines but not their capacity for uptake and storage as they elaborate an axonal plexus in the maturing glands. These observations support the hypothesis that cholinergic sympathetic neurons appear to undergo a transition from noradrenergic to cholinergic function during development in vivo similar to that previously described in cell culture.

Mechanism of uptake and retrograde axonal transport of noradrenaline in sympathetic neurons in culture: reserpine-resistant large dense-core vesicles as transport vehicles

The uptake and retrograde transport of noradrenaline (NA) within the axons of sympathetic neurons was investigated in an in vitro system. Dissociated neurons from the sympathetic ganglia of newborn rats were cultured for 3-6 wk in the absence of non-neuronal cells in a culture dish divided into three chambers. These allowed separate access to the axonal networks and to their cell bodies of origin. [3H]NA (0.5 X 10(-6) M), added to the axon chambers, was taken up by the desmethylimipramine- and cocaine-sensitive neuronal amine uptake mechanisms, and a substantial part was rapidly transported retrogradely along the axons to the nerve cell bodies. This transport was blocked by vinblastine or colchicine. In contrast with the storage of [3H]NA in the axonal varicosities, which was totally prevented by reserpine (a drug that selectively inactivates the uptake of NA into adrenergic storage vesicles), the retrograde transport of [3H]NA was only slightly diminished by reserpine pretreatment. Electron microscopic localization of the NA analogue 5-hydroxydopamine (5-OHDA) indicated that mainly large dense-core vesicles (700-1,200-A diam) are the transport compartment involved. Whereas the majority of small and large vesicles lost their amine dense-core and were resistant to this drug. It, therefore, seems that these vesicles maintained the amine uptake and storage mechanisms characteristic for adrenergic vesicles, but have lost the sensitivity of their amine carrier for reserpine. The retrograde transport of NA and 5-OHDA probably reflects the return of used synaptic vesicle membrane to the cell body in a form that is distinct from the membranous cisternae and prelysosomal structures involved in the retrograde axonal transport of extracellular tracers.