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J B Furness

Publications and source records attributed to J B Furness.

At least 109 records · Page 6Linked to original sources
PubMed1995

Plurichemical transmission and chemical coding of neurons in the digestive tract.

The enteric nervous system contains neurons with well-defined functions. However, when neurons of the same function are examined in different regions or species, they are found to show subtle differences in their pharmacologies of transmission and different chemical coding. Individual enteric neurons use more than one transmitter, i.e., transmission is plurichemical. For example, enteric inhibitory neurons have three or more primary transmitters, including nitric oxide, vasoactive intestinal peptide, and possibly adenosine triphosphate and pituitary adenylyl cyclase activating peptide. Primary transmitters are highly conserved, although their relative roles vary considerably between gut regions. Multiple substances, including transmitters and their synthesizing enzymes and nontransmitters (such as neurofilament proteins), provide neurons with a chemical coding through which their functions and projections can be identified. Although equivalent neurons in different regions have the same primary transmitters, other chemical markers differ substantially. Caution must be taken in extrapolating pharmacological and neurochemical observations between species or even between regions in the one species. On the other hand, careful interregion and interspecies comparisons lead to an understanding of the features of enteric neurons that are highly conserved and can be used in valid extrapolation.

Animals↗
PubMed1995

Identification of sensory nerve cells in a peripheral organ (the intestine) of a mammal.

It is commonly believed that the cell bodies of mammalian sensory neurons are contained within spinal and cranial sensory ganglia associated with the central nervous system or within the central nervous system itself. However, strong circumstantial evidence implies that some sensory neurons are contained entirely within the gastrointestinal tract. We have investigated this possibility by using intracellular methods to record the responses of myenteric neurons in the guinea-pig small intestine to physiological stimuli applied to the neighbouring mucosa. The results show that the myenteric plexus contains a population of chemosensitive sensory neurons and that these neurons correspond to neurons with AH electrophysiological properties and Dogiel type II morphology. This is the first direct evidence that some sensory neurons are contained entirely within the peripheral nervous system.

Action Potentials↗
PubMed1995

Evidence that enteric motility reflexes can be initiated through entirely intrinsic mechanisms in the guinea-pig small intestine.

Although motility reflexes can be elicited in the intestine in vivo after all neural connections with the central nervous system are cut, or in vitro in isolated intestinal segments, it is not proven that the cell bodies of the primary sensory neurons for these reflexes are in the intestinal wall. It is feasible that the nerve cells are in dorsal root ganglia and that axon reflexes are involved in the initiation of the reflexes. We have examined reflexes in segments of guinea-pig intestine in which extrinsic denervation, 9-11 days before the intestine was removed, and isolation of the intestine in vitro were combined. The experimental segments were isolated from extrinsic inputs by severing nerves in the mesentery and those running in the gut wall that entered the segment. The effectiveness of denervation was confirmed histochemically. Ascending and descending reflexes were evoked by mucosal distortion or distension and responses were recorded by intracellular microelectrodes in the circular muscle. Reflex responses recorded after denervation were no different to those recorded from control tissue. It is concluded that, in the small intestine of the guinea-pig, cell bodies of primary sensory neurons for mucosal and probably for distension reflexes are intrinsic to the organ.

Animals↗
PubMed1995

Pharmacological evidence that nitric oxide may be a retrograde messenger in the enteric nervous system.

1. The effects of inhibition of nitric oxide synthase on neuro-neuronal and neuromuscular transmission during motility reflexes in the small intestine of the guinea-pig were examined. 2. Isolated segments of intestine were secured in a three chambered organ bath so that different parts of the reflex pathways could be independently exposed to drug-containing solutions. Reflexes were evoked by distension or compression of the mucosa in two adjacent chambers and reflex responses were recorded from the circular muscle with intracellular microelectrodes in the third chamber. Thus, the actions of drugs at connections between sensory neurones and interneurones, between interneurones and other interneurones and at motor neurones could be distinguished. 3. NG-monomethyl-L-arginine (L-NMMA; 100 microM), an inhibitor of nitric oxide synthase, did not affect the ascending excitatory reflex when added to either the central stimulation chamber or the recording chamber. 4. In contrast, L-NMMA (100 microM) enhanced the descending inhibitory reflex when added to the chamber in which stimuli were applied. This effect was prevented by prior exposure to L-arginine (100 microM), which had no effect by itself. Conduction of reflexes between the stimulus chamber and the recording chamber was unaffected by the presence of L-NMMA in an intervening chamber. 5. L-NMMA (100 microM) added to the recording chamber depressed the descending inhibitory reflex, an effect that was prevented by previous exposure to L-arginine. 6. The nitric oxide donor, sodium nitroprusside (100 microM), added to the stimulus chamber, depressed both ascending excitatory and descending inhibitory reflexes. When added to the middle chamber,sodium nitroprusside had no effect on conduction of reflexes through this chamber.7. It is deduced that nitric oxide, released from the cell bodies of descending interneurones, suppresses transmission from synaptic connections made with them by enteric sensory neurones.

Amino Acid Oxidoreductases↗
PubMed1995

Colocalization of neuropeptide Y with other neurochemical markers in the guinea-pig small intestine.

The chemical coding and projections of neurons containing neuropeptide Y (NPY) have been investigated in the myenteric plexus of the guinea-pig small intestine. Chemical coding was determined by investigating the colocalization of NPY immunoreactivity with the immunoreactivities for bombesin (BN), 5-HT, nitric oxide synthase (NOS), and somatostatin. Projections were determined by studying the consequences of nerve lesions created by myectomy and myotomy operations. NPY immunoreactivity was localized in four classes of myenteric neuron, anally projecting interneurons, neurons that projected anally and to the circular muscle, neurons projecting to the longitudinal muscle and in a small population of secretomotor neurons that projected to the mucosa. The interneurons and muscle motor neurons both had Dogiel type I morphology, whereas the secretomotor neurons had fine branching processes. Of the NPY-immunoreactive Dogiel type I neurons, 98% were also immunoreactive for NOS; conversely, 82% of NOS-immunoreactive neurons were immunoreactive for NPY. BN was also colocalized with NPY and NOS; 30% of the NPY-immunoreactive neurons were BN/NOS/NPY-immunoreactive. No nerve cells had BN and NPY immunoreactivity without NOS immunoreactivity. The presence of NPY immunoreactivity was investigated in three classes of descending interneurons that are distinguished by their reactivities for somatostatin, 5-HT and NOS. NPY immunoreactivity was never colocalized with 5-HT or somatostatin, but most NPY-immunoreactive descending interneurons whose terminals formed pericellular baskets were also reactive for BN and NOS. The average projection lengths of the NPY interneurons was 2-3 mm, in the anal direction. Evaluation of immunoreactivity for BN, NOS and NPY revealed three major populations of anally directed circular muscle motor neurons, with BN/NOS/NPY, BN/NOS and NOS/NPY immunoreactivities. Examination of simultaneous labeling after nerve lesions showed that NOS/NPY neurons had short anal projections, averaging about 2-3 mm, and neurons with BN immunoreactivity were longer, having average projections of about 5-8 mm.

Animals↗
PubMed1995

Cholinergic, somatostatin-immunoreactive interneurons in the guinea pig intestine: morphology, ultrastructure, connections and projections.

The shape, projection, ultrastructure and chemistry of interneurons that were initially identified by their immunoreactivity for somatostatin in the small intestine of the guinea pig were examined. Somatostatin immunoreactive nerve cell bodies and nerve fibres were located in the myenteric plexus. Simultaneous labelling for 2 antigens revealed that the somatostatin immunoreactive interneurons were also immunoreactive for choline acetyltransferase, but not for calbindin or neuropeptide Y. Cell shapes were determined by immunohistochemistry, ultrastructural analysis and intracellular dye filling. The neurons had large cell bodies (38 x 14 microns) which gave rise to long branched filamentous dendrites and a single axon. The projections of the somatostatin immunoreactive interneurons were determined by analysis of patterns of fibre loss and survival following degenerative section of myenteric nerve pathways and by analysis of individual neurons that were injected intracellularly with dye. The axons projected anally, sometimes after a short oral excursion, and were confined to the myenteric plexus. They gave rise to multiple varicose branches within myenteric ganglia: in the majority of cases the first branch was within 100 microns of the cell body. Synaptic inputs to the cells were examined by light and electron microscopy. All somatostatin immunoreactive neurons received numerous somatostatin immunoreactive inputs on the cell body and all filamentous processes. Ultrastructural investigation indicated that these constituted the majority of all inputs. It is concluded that cholinergic, somatostatin immunoreactive, interneurons have a unique soma morphology and form synaptically connected chains that run anally in the myenteric plexus.

Animals↗
PubMed1994

Characterization of 5-HT receptors mediating contraction and relaxation of the longitudinal muscle of guinea-pig distal colon in vitro.

A range of agonists and antagonists were used to characterize the receptors through which 5-hydroxytryptamine (5-HT) contracts and relaxes the longitudinal muscle of segments of guinea-pig distal colon, in vitro. 5-HT contracted the longitudinal muscle over the concentration range 10(-9) to 10(-4) mol/l. The 5-HT3 receptor agonist, 2-methyl-5-HT, produced concentration dependent contractions over the range 10(-6) to 10(-4) mol/l. 5-methoxytryptamine, an agonist at 5-HT4 receptors, caused contractions over a concentration range of 10(-8) to 10(-4) mol/l. The 5-HT4 antagonist, SDZ 205-557 (5 x 10(-7) mol/l) substantially suppressed the responses to low concentrations of 5-HT and to 5-methoxytryptamine, but had no effect on the responses to higher concentrations of 5-HT. In contrast, the 5-HT3 antagonist, granisetron (10(-6) mol/l), blocked the effect of 2-methyl-5-HT and substantially depressed responses to high concentrations of 5-HT, but had no effect on lower concentrations of 5-HT. Granisetron produced a small reduction in the response to 5-methoxytryptamine. Tetrodotoxin (TTX) (3 x 10(-7) mol/l) almost abolished the response to 5-methoxytryptamine and markedly suppressed the response to 2-methyl-5-HT, but the responses to 5-HT were only partially reduced. The 5-HT1 antagonist, methiothepin (10(-6) mol/l) depressed the response to 5-HT (10(-7) to 10(-4) mol/l) and blocked its TTX insensitive component. The 5-HT2 antagonist, ketanserin, in concentrations up to 10(-5) mol/l, had no effect on the contractions evoked by 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Nitric oxide synthase in the enteric nervous system of the guinea-pig: a quantitative description.

The distribution and abundance of nitric oxide synthase (NOS)-containing neurons and their terminals in the gastrointestinal tract of the guinea-pig were examined in detail using NADPH diaphorase histochemistry and NOS immunohistochemistry. NOS-containing cell bodies were found in the myenteric plexus throughout the gastrointestinal tract and in the submucous plexus of the stomach, colon and rectum. NOS-containing neurons comprised between 12% (in the duodenum) and 54% (in the esophagus) of total myenteric neurons. In the ileum, NOS neurons represented 19% of total myenteric neurons. Most of the NOS neurons throughout the gastrointestinal tract possessed lamellar dendrites and a single axon. NOS-containing terminals were abundant in the circular muscle, including that of the sphincters, but were rare in the longitudinal muscle, except for the taeniae of the caecum. The muscularis mucosae of the esophagus, stomach, colon and rectum received a medium to dense innervation by NOS terminals. Within myenteric ganglia, NOS-containing terminals were extremely sparse in the esophagus, stomach and duodenum, common in the ileum and distal colon and extremely dense in the proximal colon and rectum. The submucous plexus in the ileum and large intestine contained a sparse plexus of NOS-containing terminals. NOS terminals were not observed in the mucosa of any region. We conclude that throughout the gastrointestinal tract of the guinea-pig, NOS neurons are inhibitory motor neurons to the circular muscle; in the ileum and large intestine, NOS neurons may also function as interneurons.

Amino Acid Oxidoreductases↗
PubMed1994

Calretinin-immunoreactive neurons and their projections in the guinea-pig colon.

The distribution of nerve cells and fibres with immunoreactivity for the calcium-binding protein, calretinin, was studied in the distal colon of the guinea-pig. The projections of the neurons were determined by examining the consequences of lesioning the myenteric plexus. Calretinin-immunoreactive neurons comprised 17% of myenteric nerve cells and 6% of submucous nerve cells. Numerous calretinin-immunoreactive nerve fibres were located in the longitudinal and circular muscle, and within the ganglia of the myenteric and submucous plexuses. Occasional fibres were found in the muscularis mucosae, but they were very rare in the lamina propria of the mucosa. Lesion studies revealed that myenteric neurons innervated the underlying circular muscle and provided both ascending and descending processes that gave rise to varicose branches in myenteric ganglia. Calretinin-immunoreactive fibres also projected to the tertiary component of the myenteric plexus, and are therefore likely to be motor neurons to the longitudinal muscle. Varicose fibres that supplied the submucous ganglia appear to arise from submucous nerve cells. Arterioles of the submucous plexus were sparsely innervated by calretinin-immunoreactive fibres. The submucous plexus was the principal source of immunoreactive nerve fibres in the muscularis mucosae. This work shows that calretinin-IR reveals different neuronal populations in the large intestine to those previously reported in the small intestine.

Animals↗
PubMed1994

Projections of 5-hydroxytryptamine-immunoreactive neurons in guinea-pig distal colon.

The presence of 5-hydroxytryptamine in enteric neurons of the guinea-pig distal colon was demonstrated by immunohistochemistry and the projections of the neurons were determined. 5-Hydroxytryptamine-containing nerve cells were observed in the myenteric plexus but no reactive nerve cells were found in submucous ganglia. Varicose reactive nerve fibres were numerous in the ganglia of both the myenteric and submucous plexuses, but were infrequent in the longitudinal muscle, circular muscle, muscularis mucosae and mucosa. Reactivity also occurred in enterochromaffin cells. Lesion studies showed that the axons of myenteric neurons projected anally to provide innervation to the circular muscle and submucosa and to other more anally located myenteric ganglia. The results suggest that a major population of 5-hydroxytryptamine neurons in the colon is descending interneurons, most of which extend for 10 to 15 mm in the myenteric plexus and innervate both 5-hydroxytryptamine and non-5-hydroxytryptamine neurons.

Animals↗
PubMed1994

Charybdotoxin and iberiotoxin but not apamin abolish the slow after-hyperpolarization in myenteric plexus neurons.

Myenteric neurons of guinea-pig ileum were studied with intracellular microelectrodes. The specific toxins charybdotoxin, iberiotoxin and apamin were used to characterize the prolonged after-hyperpolarizations of AH neurons in this preparation. Charybdotoxin and iberiotoxin blocked prolonged after-hyperpolarizations in 23 of 24 AH neurons, but apamin had no effect on 5 of 5 AH neurons. Abolition of the after-hyperpolarizations was accompanied by depolarization and increases in input resistances of those AH neurons affected, but the shapes of action potentials were unchanged. The excitability of the AH neurons was enhanced as shown by an increase in the number of action potentials evoked by a 500-ms depolarizing current pulse or by a train of 15-ms depolarizing current pulses (10Hz). The other class of myenteric neurons, S neurons, was also investigated. The 19 S neurons studied fired action potentials only at the start of a 500 ms depolarization, but the toxins had no effect on this behaviour or on their other properties. Intracellular injection of Neurobiotin into the neurons studied and subsequent immunohistochemical staining to localise the calcium-binding protein, calretinin, indicated that all major classes of S neurons were included in the sample. Thus, the prolonged after-hyperpolarizations in AH neurons may be due to opening of a large-conductance (BK) calcium-dependent potassium channel, but similar channels play little or no role in regulation of the excitability of S neurons.

Animals↗
PubMed1994

Combined intracellular injection of Neurobiotin and pre-embedding immunocytochemistry using silver-intensified gold probes in myenteric neurons.

We have developed methods to examine the neurochemistry of synaptic inputs to individual myenteric neurons labeled by dye injection through intracellular recording electrodes. Myenteric neurons of the guinea-pig ileum were filled with Neurobiotin, fixed, washed in 50% ethanol, exposed to sodium cyanoborohydride, incubated in avidin-biotin-horseradish peroxidase and incubated in antisera to calretinin or calbindin. The Neurobiotin-filled cells were revealed using the diaminobenzidine (DAB) reaction. The tissue was examined at the light microscope level to determine the morphology and projections of the Neurobiotin-filled neurons, and then incubated in 1 nm gold-labeled secondary antibodies. Following osmication, the gold probes were silver-intensified and the tissue embedded flat in resin. The tissue was re-examined at the light microscope level. Neurons containing a DAB reaction product could be distinguished from neurons containing a silver-intensified gold reaction product using oblique or epipolarized illumination. Ultrathin sections were taken through the injected neurons and examined. At the ultrastructural level, Neurobiotin-filled cell bodies and their processes (labeled with DAB) were easily distinguished from the structures labeled by silver-intensified gold. Gold-labeled terminals of enteric interneurons made synapses and close contacts with Neurobiotin-filled nerve cell bodies and their processes. This technique is valuable for the neurochemical identification of synaptic inputs to morphologically and/or functionally characterized myenteric neurons and could be easily applied to other preparations, such as brain slices.

Animals↗
PubMed1994

Electrophysiological and morphological classification of myenteric neurons in the proximal colon of the guinea-pig.

Intracellular recordings were made from myenteric neurons in the proximal colon of the guinea-pig. The electrical behaviour of the neurons in response to intracellular depolarizing current pulses, and to internodal strand stimulation, was recorded. The intracellular electrode contained the intracellular marker biocytin which was injected into impaled neurons for subsequent histochemistry. Proximal colon myenteric neurons displayed electrophysiological properties similar to myenteric neurons in the small intestine, and were classified as either AH- or S-neurons. AH-neurons were characterized by the presence of a slow afterhyperpolarization following an action potential. Internodal strand stimulation evoked slow excitatory synaptic potentials in five out of six AH-neurons tested, but did not evoke fast excitatory synaptic potentials in 26 AH-neurons tested. S-neurons lacked a slow afterhyperpolarization, but internodal strand stimulation evoked fast excitatory synaptic potentials in all 113 neurons and slow excitatory synaptic potentials in seven out of 17 tested. A subpopulation of AH-neurons displayed a rhythmic oscillation in membrane potential which could be triggered by an action potential. S-neurons could be subdivided into those that fired tonically and those that fired phasically in response to long depolarizing current pulses. About 80% of the AH-neurons were immunoreactive for calbindin, as were 10% of S-neurons. A further 17% of S-neurons, but no AH neurons, were calretinin immunoreactive. Morphological analysis of filled neurons revealed eight distinct classes. Neurons electrophysiologically classified as AH typically had a large, oval soma and several long tapering processes. Processes of AH-neurons branched into many adjacent ganglia. Almost all S-neurons were uniaxonal and many axons ended in an expansion bulb in the myenteric plexus. S-neurons typically had broad, lamellar processes, or short, spiny processes. Roughly equal proportions of S-neurons had oral or anal projection. However, almost all S-neurons that were immunoreactive for calbindin or calretinin projected orally. The results indicate that myenteric neurons in the proximal colon of the guinea-pig are electrophysiologically similar to myenteric neurons in the small intestine, but there are a greater number of morphological and chemical categories.

Action Potentials↗
PubMed1994

Gastrointestinal neurotransmitters.

The enteric nervous system contains neurones that are intrinsic to the gastrointestinal tract and the axons of extrinsic neurones. More than 30 functional types of neurone are present and about 25 different possible neurotransmitters have been identified in enteric neurones. Most neurones utilize several transmitters; amongst the transmitters of an individual neurone, one is usually a primary transmitter and other substances are subsidiary transmitters or neuromodulators. The primary transmitter is the substance that has the major role in acutely changing the excitability of the innervated cell. Current evidence indicates that primary transmitters are strongly conserved; that is, the same substance will be the neurotransmitter in functionally equivalent neurones in different regions of the gastrointestinal tract and in different species. In contrast, subsidiary transmitters and neuromodulators of equivalent neurones in different regions are not necessarily the same. Only about seven of the approximately 25 enteric neurotransmitters are known to be primary transmitters. Acetylcholine is the primary transmitter of vagal and pelvic preganglionic neurones, of enteric interneurones, of one class of secretomotor neurone in the intestine and of motor neurones controlling gastric acid secretion. Acetylcholine and tachykinins are co-primary transmitters of muscle motor neurones, with acetylcholine appearing to have the greater role. Tachykinins are probably primary transmitters of enteric sensory neurones at neuroneuronal synapses. Serotonin may also be a transmitter to neurones in the enteric ganglia. Nitric oxide appears to be the usual primary transmitter of enteric inhibitory motor neurones to the muscle. ATP and vasoactive intestinal peptide are subsidiary transmitters of these neurones, although in some regions they may have a primary transmitter role. Vasoactive intestinal peptide is the primary transmitter of non-cholinergic secretomotor neurones. Gastrin releasing peptide is the primary transmitter of motor neurones to gastrin cells. Noradrenaline is the primary transmitter of sympathetic neurones that supply the intestine.

Animals↗
PubMed1994

Investigation of the role of 5-HT3 and 5-HT4 receptors in ascending and descending reflexes to the circular muscle of guinea-pig small intestine.

1. The present study was undertaken to ascertain whether 5-hydroxytryptamine (5-HT) acting at either 5-HT3 or 5-HT4 receptors plays a significant role in motility reflexes in the guinea-pig small intestine. 2. An isolated segment of small intestine was opened along its mesenteric border and pinned, mucosa uppermost, in a three chambered organ bath so that the oral, middle and anal regions of a single preparation could be separately superfused. 3. Conventional intracellular recording methods were used to monitor the responses of the circular muscle in the oral or the anal end chambers when distension was applied in either of the other two chambers or the mucosal villi were compressed in the middle chamber. Drugs were added to the middle chamber. 4. 5-HT3 receptor antagonists (tropisetron, 0.1-10 microM; granisetron, 1 microM and BRL 46470, 1 microM) depressed the ascending excitatory reflex evoked by these stimuli but had no effect on the descending inhibitory reflex. The depression of the excitatory reflex was observed whether the reflex was evoked from the chamber containing the drug or was simply conducted, via interneurones, through this chamber. 5. The 5-HT4 receptor antagonist, SDZ 205-557 (1 microM), had no significant effect on either the ascending or descending reflex pathways. However, 5-HT4 receptors were present as cisapride (0.1 microM) significantly enhanced the ascending excitation without affecting the descending inhibition. This effect of cisapride was converted to a significant depression of the ascending reflex by SDZ 205-557. 6. The results suggest that 5-HT3, but not 5-HT4, receptors play an important role in the ascending excitatory reflex and that these receptors may be on interneurones in the reflex pathway.

4-Aminobenzoic Acid↗
PubMed1994

Characterization of 5-hydroxytryptamine receptors mediating mucosal secretion in guinea-pig ileum.

1. The receptor subtypes through which 5-hydroxytryptamine (5-HT) increases electrolyte secretion across the mucosa of guinea-pig ileum were studied. 2. Flat sheep preparations of guinea-pig mucosa plus submucosa were placed in Ussing chambers and the short circuit current (ISC), an index of net electrogenic electrolyte transport across the mucosa, was measured under voltage clamp conditions. 3. Low concentrations of 5-HT (10-300 nM) evoked monophasic increases in ISC which were significantly reduced by hyoscine (100 nM), tetrodotoxin (TTX, 300 nM) and the 5-HT2 receptor antagonist, ketanserin (3-300 nM). 4. Higher concentrations of 5-HT (1-10 microM) produced biphasic responses which were reduced by hyoscine (100 nM), TTX (300 nM), ketanserin (3-300 nM) and also by the 5-HT3 receptor antagonists, granisetron (1 microM) and ICS 205-930 (100 nM). 5. 2-Methyl-5-HT (1-100 microM) and alpha-methyl-5-HT (30 nM-30 microM), agonists at 5-HT3 and 5-HT2 receptors respectively, also evoked ISC increases. These responses were reduced by hyoscine (100 nM) and abolished by TTX (300 nM) and the respective receptor antagonists, granisetron (1 microM) and ketanserin (30 nM). 6. The 5-HT4 receptor antagonist, SDZ 205-557 (300 nM) had no effect on the response to 5-HT. 7. The TTX-resistant response to 5-HT was not affected by 5-HT2,3 or 4 receptor antagonists. 8. These results indicate that 5-HT mediates secretion partly by an action on 5-HT3 receptors located on cholinergic and noncholinergic secretomotor neurones, partly by an action on higher affinity'5-HT2-like' receptors predominantly on noncholinergic neurones, and partly by a direct action on the epithelium.

Animals↗
PubMed1994

FGF2 regulates proliferation of neural crest cells, with subsequent neuronal differentiation regulated by LIF or related factors.

Two of the key early events in the development of the peripheral nervous system are the proliferation of neural crest precursor cells and their subsequent differentiation into different neural cell types. We present evidence that members of the fibroblast growth factor family, (FGF1 or FGF2) act directly on the neural crest cells in vitro to stimulate proliferation in the presence of serum. These findings correlate with in situ hybridisation analysis, which shows FGF2 mRNA is expressed in cells both in the neural tube and within newly formed sensory ganglia (dorsal root ganglia, DRG) at embryonic day 10 in the mouse, when neural crest precursors are proliferating within the DRG. This data infers an autocrine/paracrine loop for FGF regulation of proliferation. Evidence supporting this notion is provided by the finding that part of the endogenous proliferative activity in the NC cultures is related to FGF. It was also found, in early neural crest cultures, that exogenous FGF completely inhibited neuronal differentiation, probably as a direct consequence of its mitogenic activity. In order to stimulate neuronal differentiation significantly, it was necessary to remove the FGF and replace it with leukemia inhibitory factor (LIF) or related factors. Under these conditions, 50% of the cells differentiated into neurons, which developed a sensory neuron morphology and were immunoreactive for the sensory markers CGRP and substance P. These data support a model of neural crest development, whereby multipotential neural crest precursor cells are stimulated to divide by FGF and subsequent development into sensory neurons is regulated by LIF or other cytokines with a similar signalling mechanism.

Animals↗