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M D Gershon

Publications and source records attributed to M D Gershon.

At least 19 recordsLinked to original sources
PubMed1997

Mediation by protein kinases C and A of Go-linked slow responses of enteric neurons to 5-HT.

5-HT activates the peristaltic reflex and is the neurotransmitter of a subset of myenteric interneurons. Hyperpolarizing afterpotential (AH)/type 2 neurons respond to 5-HT with a long-lived depolarization that is caused by the inhibition of a Ca(2+)-activated K+ conductance (gKCa). This effect is mediated by a G-protein-coupled receptor, 5-HT1P. 5-HT1P agonists specifically activate G alpha o, the immunoreactivity of which was found to be highly abundant and membrane-associated in almost all enteric neurons. Responses of hyperpolarizing AH/type 2 neurons to 5-HT were inhibited by intracellular injection of GDP beta S or anti-G alpha o Fab fragments but were potentiated and prolonged by intracellular GTP gamma S. Responses to 5-HT were antagonized by pertussis toxin, downregulation of protein kinase C (PKC) and inhibitors of phosphatidylcholine phospholipase C (PC-PLC), PKC (including pseudosubstrate peptides, chelerythrine, and the alpha/beta isoform-specific inhibitor Go 6976), protein kinase A (PKA), and adenylate cyclase. Responses to 5-HT were mimicked by activators of PKC, and 5-HT induced a concentration-dependent increase in the membrane-associated PKC activity in isolated myenteric ganglia. Immunocytochemical studies suggested that the most abundant isoforms of PKC in enteric neurons are alpha and delta. These data suggest that signal transduction of the 5-HT1P-mediated slow response to 5-HT involves activation of PC-PLC by G alpha o to liberate diacylglycerol, which stimulates PKC (most likely alpha). PKC probably activates adenylate cyclase, which through cAMP, activates PKA. Activation of both PKA and PKC lead to closure of gKCa.

Adenylyl Cyclase Inhibitors↗
PubMed1997

Genes and lineages in the formation of the enteric nervous system.

The enteric nervous system is large, complex, and independent of the CNS. Its neural-crest-derived precursors migrate along defined pathways to colonize the bowel. Recent studies of the sequential actions of essential growth and transcription factors have revealed that enteric neuronal development involves a complex interaction of lineage-determined and microenvironmental elements.

Animals↗
PubMed1996

Increased expression of laminin-1 and collagen (IV) subunits in the aganglionic bowel of ls/ls, but not c-ret -/- mice.

Extracellular matrix molecules, including laminin, affect the development of enteric neurons and accumulate in the aganglionic colon of ls/ls mice. Quantitative Northern analysis revealed that mRNAs encoding the beta 1 and gamma 1 subunits of laminin and collagens alpha 1(IV) and alpha 2(IV) are increased in the colons of ls/ls mice. Transcripts of laminin alpha 1 were evaluated quantitatively with reverse transcription and the competitive polymerase chain reaction (RT-cPCR). The abundance of laminin alpha 1 transcripts was developmentally regulated, but greater in the ls/ls than the wild-type colon at each age examined. In situ hybridization revealed that transcripts in the colon encoding laminin alpha 1 and beta 1 and collagen alpha 2(IV) were initially expressed in the endoderm, but by E15, expression shifted to cells of the colonic mesenchyme (ls/ls > wild type) where crest-derived cells migrate. The expression of laminin alpha 1 was examined in the totally aganglionic intestine of E15 and newborn c-ret -/- mice, to determine whether an increase occurs when neurogenesis fails independently of the ls/ls defect. RT-cPCR revealed no difference from control in mRNA encoding laminin alpha 1 in the c-ret -/- colon in either E15 or newborn animals. The accumulation of immunohistochemically demonstrable laminin that is prominent in the newborn ls/ls colon could not be detected in that of c-ret -/- animals. These observations suggest that transcripts encoding laminin-1 and collagen (IV) are increased in the colon and surrounding pelvic mesenchyme of ls/ls mice because of an intrinsic lesion, rather than a secondary consequence of aganglionosis. The data are compatible with the hypothesis that the increased expression of laminin-1 contributes to the failure of crest-derived cells to complete their colonization of the ls/ls colon.

Animals↗
PubMed1996

In situ identification and visualization of neurons that mediate enteric and enteropancreatic reflexes.

To identify neurons participating in enteric and enteropancreatic reflexes, we validated the use of the activity-dependent markers FM1-43 and FM2-10 as "on-line" probes for the visualization of activated guinea pig enteric and pancreatic neurons. FM1-43 or FM2-10 labeling of neuronal perikarya and processes was induced by KCl (70 mM), veratridine (1.0 microM), intracellular injection of depolarizing current pulses, stimulation of afferent inputs, evoking reflexes (by inflating an intraluminal balloon, blowing puffs of N2 at, or applying glucose to, the villous surface of the duodenum), or injury; labeling was prevented by tetrodotoxin (0.5 microM). Intracellular recording and injection of Neurobiotin confirmed that FM1-43 labeled neurons that spike, but not those that exhibit only fast excitatory postsynaptic potentials. Perikarya did not label if axonal transport was blocked by colchicine. When pulses of N2 or glucose were directed at duodenal villi in vitro, labeling by FM1-43 or FM2-10 was observed in myenteric and pancreatic neurons, as well as in subsets of cells in pancreatic islets and intestinal crypts. Hexamethonium blocked the spread of label via nicotinic synapses and thus enabled primary afferent neurons to be located. Balloon distension elicited hexamethonium-resistant labeling of epithelial cells, interstitial cells, and Dogiel type II neurons in each plexus; however, in preparations stimulated with pulses of N2 or glucose, hexamethonium-resistant labeling of neurons occurred only in the submucosal plexus and not in myenteric ganglia. These observations suggest that primary afferent neurons responsible for mucosal pressure- or glucose-induced enteric and enteropancreatic reflexes are submucosal, whereas myenteric afferent neurons become activated only when the wall of the bowel is distended. The data are compatible with the possibility that primary afferent neurons are activated by a signaling molecule released from intestinal epithelial cells.

Animals↗
PubMed1996

Localization and function of a 5-HT transporter in crypt epithelia of the gastrointestinal tract.

The peristaltic reflex can be evoked in the absence of input from the CNS because the responsible neural pathways are intrinsic to the intestine. Mucosal enterochromaffin cells have been postulated to be pressure transducers, which activate the intrinsic sensory neurons that initiate the reflex by secreting 5-HT. All of the criteria necessary to establish 5-HT as this transmitter have been fulfilled previously, except that no mucosal mechanism for 5-HT inactivation was known. In the current investigation, desensitization of 5-HT receptors was demonstrated to inhibit the peristaltic reflex in the guinea pig large intestine in vitro. At low concentration (1.0 nM), the 5-HT uptake inhibitor fluoxetine potentiated the reflex, but higher concentrations blocked it, suggesting that the peristaltic reflex depends on the 5-HT transporter-mediated inactivation of 5-HT. Specific (Na+ -dependent, fluoxetine-sensitive) uptake of 3H-5-HT by intestinal crypt epithelial cells was found by radioautography. mRNA encoding the neuronal 5-HT transporter was demonstrated in the intestinal mucosa by Northern analysis and located in crypt epithelial cells as well as in myenteric neurons by in situ hybridization. cDNA encoding the 5-HT transporter was cloned from the mucosa and completely sequenced. 5-HT transporter immunoreactivity was detected in crypt epithelial cells and enteric neurons. Mucosal epithelial cells thus express a plasmalemmal 5-HT transporter identical to that of serotonergic neurons. This molecule seems to play a critical role in the peristaltic reflex.

Animals↗
PubMed1996

Acidification of serotonin-containing secretory vesicles induced by a plasma membrane calcium receptor.

Parafollicular (PF) cells secrete 5-hydroxytryptamine in response to increased extracellular Ca2+ ([Ca2+]e). This stimulus causes Cl- channels in PF secretory vesicles to open, leading to vesicle acidification. PF cells express a plasmalemmal heptahelical receptor (CaR) that binds Ca2+, Gd3+, and Ba2+. We now report that the CaR mediates vesicle acidification. Ca2+, Gd3+, and Ba2+ induced vesicle acidification, which was independent of channel-mediated Ca2+ entry. Agonist-induced vesicle acidification was blocked by pertussis toxin, inhibitors of phosphatidylinositol-phospholipase C, calmodulin, NO synthase, guanylyl cyclase, or protein kinase G. PF cells contained NO synthase immunoreactivity, and vesicles were acidified by NO donors and dibutyryl cGMP. [Ca2+]e, and Gd3+ mobilized thapsigargin-sensitive internal Ca2+ stores. [35S]G alpha i and [35S]G alpha q were immunoprecipitated from PF membranes incubated with agonists in the presence of [35S]adenosine 5'-O-(thiotriphosphate). Labeling of G alpha i but not G alpha q was antagonized by pertussis toxin. Vesicles acidified in response to activation of protein kinase C; however, protein kinase C inhibition blocked calcium channel- but not CaR-dependent acidification. We propose the following signal transduction pathway: CaR -> Gi -> phosphatidylinositol-phospholipase C -> inositol 1,4,5-trisphosphate -> [Ca2+]i -> Ca2+/calmodulin -> NO synthase -> NO -> guanylyl cyclase -> cGMP -> protein kinase G -> opens vesicular Cl- channel.

Animals↗
PubMed1996

Identification of cells that express 5-hydroxytryptamine1A receptors in the nervous systems of the bowel and pancreas.

Although serotonin (5-HT)1A receptors are known to be present on neural elements in both the bowel and the pancreas, the precise location of these receptors has not previously been determined. Earlier investigations have suggested that 5-HT1A receptors are synthesized in enteric, but not pancreatic ganglia, and that they mediate pre-and postjunctional inhibition. Wholemount in situ hybridization was used to identify cells that contain mRNA encoding 5-HT1A receptors, and immunocytochemistry was employed to locate receptor protein. mRNA encoding 5-HT1A receptors was found in the majority of neurons in both submucosal and myenteric plexuses. 5-HT1A immunoreactivity, however, was abundant only on the surfaces of a limited subset of nerve cell bodies and processes. 5-HT-immunoreactive axons were found in close proximity to sites of 5-HT1A immunoreactivity. Myenteric, but not submucosal calbindin-immunoreactive neurons (with Dogiel type II morphology) were surrounded by rings of 5-HT1A immunoreactivity. The cytoplasm of the cell bodies and dendrites of a small subset of Dogiel type I neurons was also intensely 5-HT1A immunoreactive. Most of the Dogiel type I 5-HT1A-immunoreactive myenteric neurons, and some of the type II neurons that were ringed by 5-HT1A immunoreactivity became doubly labeled following injections of the retrograde tracer, FluoroGold (FG), into the submucosal plexus. 5-HT1A-immunoreactive neurons in distant submucosal ganglia also became labeled by retrograde transport of FG. None of the 5-HT1A-immunoreactive cells were labeled by the intraluminal administration of the beta-subunit of cholera toxin, a marker for vasoactive intestinal peptide-containing secretomotor neurons. These observations suggest that some of the myenteric 5-HT1A-immunoreactive neurons project to submucosal ganglia and that the submucosal 5-HT1A-immunoreactive cells are interneurons. In addition to neurons, a subset of 5-HT-containing enterochromaffin cells expressed 5-HT1A immunoreactivity, which was co-localized with 5-HT in secretory granules. In the pancreas, 5-HT1A immunoreactivity was observed in ganglia, acinar nerves, and glucagonimmunoreactive islet cells. Serotonergic enteropancreatic axons have been found to terminate in close proximity to each of these structures, which may thus be the targets of this innervation. The abundance of 5-HT1A receptor immunoreactivity on nerves of the gut and pancreas suggests that drugs designed to interact with these receptors may have unanticipated visceral actions.

Animals↗
PubMed1996

Regional differences in the number of neurons in the myenteric plexus of the guinea pig small intestine and colon: an evaluation of markers used to count neurons.

BACKGROUND: Subsets of myenteric neurons have been identified. To determine the proportional representation of neurons in each, it is necessary to relate the number of neurons in the subset to that of the complete set. Prior estimates of total numbers of neurons, obtained with many different markers, have varied widely. METHODS: Markers were compared for counting myenteric neurons in dissected laminar preparations of guinea pig duodenum, jejunum-ileum, and colon; the effect of stretching preparations on these counts was also determined. Markers included the visualization of single-stranded nucleic acid with cuprolinic blue and the immunocytochemical demonstration of neuron specific enolase (NSE), PGP9.5, S-100, and the constitutive expression of a Fos related antigen (FRA). RESULTS: Neurons could not be counted accurately by demonstrating NSE, PGP9.5, or S-100. The number of neurons detected by demonstrating FRA was consistently less than that determined with cuprolinic blue (approximately 65%). Cuprolinic blue-derived estimates of neuron numbers were higher than most reported in the literature, but comparable to those recently obtained with "a nerve cell body" antiserum. Ganglionic area was found to be stretch independent. The rank order of neurons/cm2 and ganglionic area/ unit resting length was colon > duodenum >> jejunum-ileum; more neurons were found in the myenteric plexus of the colon (7.3 x 10(6)) than in that of the entire small intestine (6.5 x 10(6)). CONCLUSIONS: Prior studies that have obtained denominators for estimating the proportions of myenteric neuronal subsets with markers that do not reveal the entire population should be re-evaluated. The guinea pig colon contains a surprisingly large number of neurons, the physiological significance of which must be determined.

Animals↗
PubMed1996

Is nitric oxide involved in 5-HT-induced fluid secretion in the gut?

The present study was undertaken to test the hypothesis that 5-HT stimulates nitric oxide (NO) generating neurons, and that these neurons participate in the mediation of 5-HT-induced fluid secretion. 5-HT induced electrogenic Cl- secretion in guinea-pig distal colon. This response was abolished by tetrodotoxin but not by atropine. The maximum response to 5-HT (10(-5) M) was inhibited by approximately 65% (P < 0.05, n = 6) by the NO synthase inhibitor, NG-nitro-L-arginine (L-NNA, 10(-4) M). The substrate of NO synthase, L-Arg (10(-3) M) reversed the inhibition of 5-HT-induced secretions by L-NNA. 5-HT-induced diarrhea in fasted mice was reduced by atropine in vivo. NG-Nitro-L-Arg methyl ester (L-NAME, 1-32 mg/kg, i.p.) dose-dependently inhibited 5-HT (1 mg/kg)-induced diarrhea. The inhibitory effect of L-NAME was reversed by L-Arg, but not D-Arg (600 mg/kg, i.p., respectively). Taken together, these data suggest that 5-HT-induced fluid secretion in the gut is partly due to the activation of neurons that generate NO.

Animals↗
PubMed1996

Targeting of glycoprotein I (gE) of varicella-zoster virus to the trans-Golgi network by an AYRV sequence and an acidic amino acid-rich patch in the cytosolic domain of the molecule.

Previous studies suggested that varicella-zoster virus (VZV) envelope glycoproteins (gps) are selectively transported to the trans-Golgi network (TGN) and that the cytosolic domain of gpI (gE) targets it to the TGN. To identify targeting signals in the gpI cytosolic domain, intracellular protein trafficking was studied in transfected cells expressing chimeric proteins in which a full-length or mutated gpI cytosolic domain was fused to the gpI transmembrane domain and interleukin-2 receptor (tac) ectodomain. Expressed protein was visualized with antibodies to tac. A targeting sequence (AYRV) and a second, acidic amino acid-rich region of the gpI cytosolic domain (putative signal patch) were each sufficient to cause expressed protein to colocalize with TGN markers. This targeting was lost when the tyrosine of the AYRV sequence was replaced with glycine or lysine, when arginine was replaced with glutamic acid, or when valine was substituted with lysine. In contrast, tyrosine could be replaced by phenylalanine and valine could be substituted with leucine. Mutation of alanine to aspartic acid or deletion of alanine abolished TGN targeting. Exposure of transfected cells to antibodies to the tac ectodomain revealed that the TCN targeting of expressed tac-gpI chimeric proteins occurred as a result of selective retrieval from the plasmalemma. These data suggest that the AYRV sequence and a second signaling patch in the cytosolic domain of gpI are responsible for its targeting to the TGN. The observations also support the hypothesis that the TGN plays a critical role in the envelopment of VZV.

Amino Acid Sequence↗
PubMed1996

Participation of 5-HT3, 5-HT4, and nicotinic receptors in the peristaltic reflex of guinea pig distal colon.

The roles of 5-hydroxytryptamine3 (5-HT3), 5-HT4, and nicotinic receptors in the peristaltic reflex were investigated in isolated segments of guinea pig distal colon. The reflex assessed by measuring the propulsion of solid pellets, was affected neither by 5-HT3-selective antagonists (ondansetron granisetron) nor by 5-HT4-selective antagonists (SDZ-205-557, GR-113808A, SB-204070) applied individually (1.0 microM); nevertheless, the reflex was inhibited by combining these antagonists or by applying a 5-HT3/5-HT4 dual antagonist (FK-1052). Hexamethonium abolished the peristaltic reflex at 100 microM, but not at 10-32 microM. In contrast, the peristaltic reflex was inhibited when hexamethonium (32 microM was combined with either a 5-HT3- or 5-HT4-selective antagonist (1.0 microM). These observations suggest that 5-HT3, 5-HT4, and nicotinic receptors participate in the initiation and/or propagation of the peristaltic reflex. The data are consistent with the idea that these receptors are arranged in parallel in the neural pathways that mediate the peristaltic reflex in the distal colon.

Animals↗
PubMed1996

Expression and development of a functional plasmalemmal 5-hydroxytryptamine transporter by thyroid follicular cells.

5-Hydroxytryptamine (5-HT) is synthesized and secreted by thyroid parafollicular (PF) cells. As all PF granules contain 5-HT, it is released whenever PF cells secrete. Because 5-HT stimulates follicular (F) cells and can modulate their response to TSH, 5-HT has been proposed to be a paracrine PF to F cell transmitter. This role would require a thyroid mechanism to rapidly inactivate 5-HT. A 5-HT transporter (SERT) in the plasma membrane of serotonergic neurons inactivates neuronal 5-HT. We thus tested the hypothesis that this molecule is expressed in the thyroid. Messenger RNA encoding SERT was demonstrated in both the human thyroid and a rat F cell line (FRTL-5). SERT immunoreactivity was detected in rat F, but not PF, cells. Transporter-mediated uptake of [3H]5-HT by F cells arose early in development (E13 in mice) and was maintained in adult life in mice, guinea pigs, bats, and rats (FRTL-5 cells). These observations indicate that a functional SERT is expressed in the thyroid, not by the 5-HT-secreting PF cells, but by their putative F cell targets.

Aging↗
PubMed1996

Distinct subpopulations of enteric neuronal progenitors defined by time of development, sympathoadrenal lineage markers and Mash-1-dependence.

Enteric and sympathetic neurons have previously been proposed to be lineally related. We present independent lines of evidence that suggest that enteric neurons arise from at least two lineages, only one of which expresses markers in common with sympathoadrenal cells. In the rat, sympathoadrenal markers are expressed, in the same order as in sympathetic neurons, by a subset of enteric neuronal precursors, which also transiently express tyrosine hydroxylase. If this precursor pool is eliminated in vitro by complement-mediated lysis, enteric neurons continue to develop; however, none of these are serotonergic. In the mouse, the Mash-1-/- mutation, which eliminates sympathetic neurons, also prevents the development of enteric serotonergic neurons. Other enteric neuronal populations, however, including those that contain calcitonin gene related peptide are present. Enteric tyrosine hydroxylase-containing cells co-express Mash-1 and are eliminated by the Mash-1-/- mutation, consistent with the idea that in the mouse, as in the rat, these precursors generate serotonergic neurons. Serotonergic neurons are generated early in development, while calcitonin gene related peptide-containing enteric neurons are generated much later. These data suggest that enteric neurons are derived from at least two progenitor lineages. One transiently expresses sympathoadrenal markers, is Mash-1-dependent, and generates early-born enteric neurons, some of which are serotonergic. The other is Mash-1-independent, does not express sympathoadrenal markers, and generates late-born enteric neurons, some of which contain calcitonin gene related peptide.

Animals↗
PubMed1996

Myenteric ganglionic 5-hydroxytryptamine(1P) signal transmission is mediated via Go protein.

The role of G proteins in mediating the signal transduction of the guinea pig myenteric ganglionic 5-hydroxytryptamine (5-HT)1P receptors was examined. Stimulation of ganglionic membranes with 5-HT in the presence of [35S]GTPgammaS or [alpha 32P]GTP increased guanine nucleotide binding to G(alpha)o but not to G(alpha)s, G(alpha)i or G(alpha)q in a concentration-dependent fashion. Pertussis toxin pretreatment markedly reduce this 5-HT induced response. Similarly, the 5-HT1P receptor-mediated slowly developing and long-lasting depolarizing response is potentiated by GTPgammaS and is inhibited by GDPbetaS or pertussis toxin. The activation of G(alpha)o by 5-HT also was mimicked by the 5-HT1P agonist, 5-hydroxyindalpine and was blocked by the selective 5-HT1P antagonist, N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide. These data provide compelling evidence to suggest that transmembrane signaling for the 5-HT1P receptors in isolated myenteric ganglia is transduced by the trimeric Go protein.

Animals↗
PubMed1995

Infection of cells by varicella zoster virus: inhibition of viral entry by mannose 6-phosphate and heparin.

Envelope glycoproteins of varicella zoster virus (VZV) contain mannose 6-phosphate (Man6P) residues. We now report that Man6P competitively and selectively inhibits infection of cells in vitro by cell-free VZV; furthermore, dephosphorylation of VZV by exposure to alkaline phosphatase rapidly destroys infectivity. Cells are also protected from VZV in a concentration-dependent manner by heparin (ED50 = 0.23 micrograms/ml; 95% confidence limits = 0.16-0.26 microgram/ml) but not by chondroitin sulfate. Both heparin and Man6P are protective only when present about the time of inoculation. Heparin but not Man6P interferes with the attachment of VZV to cell surfaces; moreover, VZV binds to heparin-affinity columns. These data are compatible with a working hypothesis, whereby VZV attaches to cell surfaces by binding to a heparin sulfate proteoglycan. This binding stabilizes VZV, making possible a low-affinity interaction with another Man6P-dependent receptor, which is necessary for viral entry.

Alkaline Phosphatase↗
PubMed1995

Appearance of neuropeptides and NADPH-diaphorase during development of the enteropancreatic innervation.

Pancreatic ganglia are formed by neural crest-derived precursors, are innervated by enteric neurons, and contain neuropeptides. In addition, the enzyme NADPH-diaphorase is located in a subset of enteric and pancreatic neurons. The expression of neural markers (GAP-43 and NC-1), neurotransmitter-related markers (including neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), gastrin-releasing peptide (GRP), galanin (GAL), dopamine beta hydroxylase (DBH), substance P (SP), calcitonin gene-related peptide (CGRP)), and NADPH-diaphorase was studied in the fetal and neonatal rat gut and pancreas (E12-P28) in situ and in vitro. NC-1, GAP-43 and DBH-immunoreactive cells were found in the primordial stomach on day E12, and in the pancreas on day E13, along with NPY in endocrine cells. Pancreatic NPY-immunoreactive neurons were detected by day E18. CGRP was seen in the foregut at day E12 but not in the pancreas until day E14. Other neuropeptides (SP, GAL, GRP and VIP) all appeared in the foregut earlier than in the pancreas. NADPH-diaphorase activity was first found in situ in foregut neurons on day E13, and in the pancreas on day E14, but seen in explants a day earlier. These observations show that development of neurons occurs earlier in the gut than in the pancreas, and that NADPH-diaphorase activity appears earlier than the immunoreactivities of the neuropeptides.

Animals↗
PubMed1995

Expression of nicotinic acetylcholine receptors and subunit mRNA transcripts in cultures of neural crest cells.

The expression of neuronal phenotypic characteristics by neural crest-derived neurons is dependent upon both environmental cues and intrinsic properties. Neuronal nicotinic acetylcholine receptors (nAChRs) are expressed by most neural crest-derived peripheral neurons; nevertheless, the factors that influence and modulate the early expression of nAChRs on neuronal precursor cells are unknown. We used RT-PCR to analyze the temporal sequence of the appearance of transcripts encoding alpha 3, alpha 5, alpha 7, beta 2, and beta 4 nAChR subunits in cultures of quail neural crest cells. At 2 days in culture, mRNA encoding each of these nAChR subunits was detectable and, except for alpha 7, remained so through 12 days. The appearance of NAPA 73 immunoreactivity during neural crest cell migration suggested that some cells express neuronal characteristics early in development and that the expression of nAChR subunits may be cell autonomous for some neural crest-derived cells. Between 8 and 10 days in culture, a 2.0-kb transcript encoding alpha 3 subunit appears in addition to the expected 3.5-kb transcript that is present at 8 days. nAChR protein was detected immunocytochemically at 7 days and was observed in immunoblots by 9 days. Whole-cell patch clamp recordings demonstrated that functional nAChRs develop concurrently in a subset of neural crest-derived neurons. In addition, both neuronal and nonneuronal cells showed inward and delayed outward currents in response to step depolarization. The appearance of functional nAChRs on neural crest-derived cells, in vitro, occurs independently of innervation and of the components in growth medium. The data suggest that neural crest-derived cells express transcripts encoding nAChR subunits, possibly as an intrinsic property of some peripheral neurons, early in development.

Animals↗