New synapses associated with the granule-containing cells of rat sympathetic ganglia

The synapses of the rat superior cervical sympathetic ganglion were studied with both conventional and ultrastructural histochemical methods. Besides the cholinergic synapses polarized from preganglionic fibers to sympathetic ganglion neurons, two morphologically and functionally different types of synapses were observed in relation to the small granule-containing (catecholamine-containing) cells of the rat superior cervical ganglion. The first type is an efferent adrenergic synapse polarized from granule-containing cells to the dendrites of the sympathetic ganglion neurons. This type of synapse might mediate the inhibitory effects (slow inhibitory postsynaptic potentials) induced by catecholamines on the sympathetic neurons. The second type is a reciprocal type of synapse between the granule-containing cells and the cholinergic preganglionic fibers. Through such synapses, these cells could exert a modulating effect on the excitatory preganglionic fibers. Therefore, we propose that these cells, through their multiple synaptic connections, exhibit a local modulatory feedback system in the rat sympathetic ganglia and may serve as interneurons between the preganglionic and postganglionic sympathetic neurons.     

Properties of descending dorsal unpaired median (DUM) neurons of the locust suboesophageal ganglion

A group of six dorsal unpaired median (DUM) neurons of the suboesophageal ganglion (SOG) of locusts was studied with neuroanatomical and electrophysiological techniques. The neurons are located posteriorly in the SOG and have axons that descend into the ganglia of the ventral nerve cord, some as far as the terminal abdominal ganglion. Within thoracic ganglia the neurons have profuse dendritic ramifications in many neuropiles, including ventral sensory neuropiles. Based on their projection patterns three different morphological types of neurons can be distinguished. These neurons receive excitatory inputs through sensory pathways that ascend from the thoracic ganglia and are activated by limb movements. They may be involved in the modulation of synaptic transmission in thoracic ganglia.     

Characterization of cardiac innervation in the nudibranch, Archidoris montereyensis

The heart of the nudibranch mollusc Archidoris montereyensis is regulated by a small number of powerful effector neurons located in the right pleural and visceral ganglia. Two identifiable neurons in the pleural ganglion, a heart excitor (PlHE) and a heart inhibitor (PlHI), are especially important regulators of cardiac function in that low levels of spontaneous activity in either cell significantly alters the amplitude and rate of heart contractions. These neurons have extensive dendritic arbors within the right pleural ganglion and branching axonal processes within the visceral ganglion. The visceral ganglion also contains a heart excitor neuron (VHE) and at least two heart inhibitor neurons (VHI cells), but their influence on cardiac activity is weaker than that of the pleural ganglion cells. All of these heart effector cells appear to be motor neurons with axons that terminate predominantly in the atrio-ventricular valve region of the heart via the pericardial nerve. The simplicity and strength of these neuronal connections to the heart of Archidoris make this a favorable preparation for studies of cardiac regulation.     

Single neurone responses to tactile stimulation of the heart in the snail,Helix pomatia L.

Summary The electrical activity of the heart nerve and of single neurons in the suboesophageal ganglia were recorded during tactile stimulation of the heart. 15 neurons were identified which responded to heart stimulation by inhibiting or accelerating activity. Cells influenced by heart afferents are scattered in the visceral and in the right and left parietal ganglia.In most of the cases both decrease and increase of cell activity are caused by synaptic potentials, in some cases, however, the neuron is assumed to have a sensory character.The activity of three neurons influenced by heart stimulation was conducted into the heart nerve. These cells are central neurons of a heart-CNS-heart reflex.Some of the neurons located in the right parietal and visceral ganglia have no connection with the mechanoreceptors of the heart. Since their spikes propagate into the heart nerve, they probably take part in the extracardial regulation of heart activity.One of the neurons located in the visceral ganglion (cell V12) sends its axon into the heart nerve. The response of this neuron to heart stimulation was an increase in activity and an inhibition of the heart rate. This is an inhibitory neuron of the extracardial heart regulatory system.     

Influence of the pteropod mollusk pedal ganglia locomoter system on anatomically isolated neurons

It was established during experiments on pedal ganglia generating locomotor rhythm isolated fromClione limacina, a pteropod mollusk, that this rhythm was irregular in 30% of preparations; i.e., the locomotor generator worked in bursts which alternated with periods of regular activity. Locomotor bursts were produced by excitation in command neurons located within the pedal ganglia. Single neurons were extracted from the ganglia in these preparations generating locomotor bursts by means of an intracellular microelectrode; their somata were then placed in their original sites amongst the ganglia cells. A total of 35 neurons were isolated showing changed activity during bursts. Nine of these cells renewed their erratic activity (linked to locomotor bursts) following reinsertion into the ganglion. Neurons which had initially shown an excitatory pattern during bursts continued to be excited; the same was true for inhibitory types. These observations indicate that the command neurons governing generator operation can act on target cells when morphological contact with them has been suppressed.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow; M. V. Lomonosov State University. Moscow. Translated from Neirofiziologiya, Vol. 18, No. 6, pp. 756–763, November–December, 1986.     

Identification of two cardioacceleratory neurons in the isopod crustacean, Ligia exotica and their effects on cardiac ganglion cells

We identified two pairs of cardioacceleratory (CA1, CA2) neurons in the central nervous system of the isopod Ligiaexotica and examined their effects on the cardiac ganglion (CG). CA1 neurons had cell bodies in the 2nd thoracic ganglion and had arborizations in the subesophageal ganglion and the 1st and 2nd thoracic ganglia. CA2 neurons had cell bodies in the 3rd thoracic ganglion and had arborizations in the 2nd, 3rd and 4th thoracic ganglia. They sent axons to the heart through the ipsilateral 3rd roots of the ganglia where their cell bodies were located. Repetitive stimulation of the CA1 axon rapidly increased the burst frequency of the CG, and that of CA2 rather slowly. The increased burst rate caused by the CA1 stimulation was significantly higher than that caused by CA2. Overall depolarization of a quiescent CG cell produced by the CA1 stimulation was significantly larger in amplitude than that produced by CA2. Facilitation was obviously seen in the excitatory post-synaptic potentials evoked by the CA1 stimulation. These results show that the synaptic properties of CA1 and CA2 neurons are different, suggesting that they have different functional roles in heart regulation. Accepted: 19 July 1997     

Parasympathetic control of the heart. I. An interventriculo-septal ganglion is the major source of the vagal intracardiac innervation of the ventricles.

The locations, projections, and functions of the intracardiac ganglia are incompletely understood. Immunocytochemical labeling with the general neuronal marker protein gene product 9.5 (PGP 9.5) was used to determine the distribution of intracardiac neurons throughout the cat atria and ventricles. Fluorescence microscopy was used to determine the number of neurons within these ganglia. There are eight regions of the cat heart that contain intracardiac ganglia. The numbers of neurons found within these intracardiac ganglia vary dramatically. The total number of neurons found in the heart (6,274 +/- 1,061) is almost evenly divided between the atria and the ventricles. The largest ganglion is found in the interventricular septum (IVS). Retrogradely labeled fluorescent tracer studies indicated that the vagal intracardiac innervation of the anterior surface of the right ventricle originates predominantly in the IVS ganglion. A cranioventricular (CV) ganglion was retrogradely labeled from the anterior surface of the left ventricle but not from the anterior surface of the right ventricle. These new neuroanatomic data support the prior physiological hypothesis that the CV ganglion in the cat exerts a negative inotropic effect on the left ventricle. A total of three separate intracardiac ganglia innervate the left ventricle, i.e., the CV, IVS, and a second left ventricular (LV2) ganglion. However, the IVS ganglion provides the major source of innervation to both the left and right ventricles. This dual innervation pattern may help to coordinate or segregate vagal effects on left and right ventricular performance.     

The ultrastructure of the cardiac ganglion of the desert scorpion,Paruroctonus mesaensis (Scorpionida: Vaejovidae)

Light and electron microscopy of the pacemaker ganglion of the scorpion heart indicate that it is about 15 mm long and 50 μm in diameter and extends along the dorsal midline of the heart. The largest cell bodies (30–45 μm in diameter) occur in clusters along the length of the ganglion. The ganglion appears to be innervated with fibers from the subesophageal and first three abdominal ganglia. The cardiac ganglion is surrounded by a neurilemma and a membranous sheath. The latter is apparently derived from connective tissue cells seen outside the ganglion. Nerve fibers other than those in the neuropil areas are usually surrounded by membrane and cytoplasm of glial cells. Often there are several layers of glial membrane, forming a loose myelin. The cardiac nerves to the heart muscle are also surrounded by a neurilemma, and the axons are surrounded by glia. The motor nerves contain lucent vesicles 60–100 nm and opaque granules 120–180 nm in diameter. In the cardiac ganglion, some nerve cell bodies have complex invaginations of glial processes forming a peripheral trophospongium. In the neuropil areas, nerve cell processes are often in close apposition. The septilaminar configuration typical of gap junctions is common, with gap distances of 1–4 nm. In tissues stained with lanthanum phosphate during fixation, we found gaps with unstained connections (1–2 nm diameter) between nerve-nerve and glial-nerve cell processes. Annular or double-membrane vesicles in various stages of formation were also seen in some nerve fibers in ganglia stained with lanthanum phosphate. Nerve endings with electron-lucent vesicles 40–60 nm in diameter are abundant in the cardiac ganglion, suggesting that these contain the excitatory transmitter of intrinsic neurons of the ganglion. Less abundant are fibers with membrane-limited opaque granules, circular or oblong in shape and as much as 330 nm in their longest dimension. Also seen were some nerve endings with both vesicles and granules.     

Input to the lateral habenula from the basal ganglia is excitatory, aversive, and suppressed by serotonin

The lateral habenula (LHb) has recently been identified as a key regulator of the reward system by driving inhibition onto dopaminergic neurons. However, the nature and potential modulation of the major input to the LHb originating from the basal ganglia are poorly understood. Although the output of the basal ganglia is thought to be primarily inhibitory, here we show that transmission from the basal ganglia to the LHb is excitatory, glutamatergic, and suppressed by serotonin. Behaviorally, activation of this pathway is aversive, consistent with its role as an "antireward" signal. Our demonstration of an excitatory projection from the basal ganglia to the LHb explains how LHb-projecting basal ganglia neurons can have similar encoding properties as LHb neurons themselves. Our results also provide a link between antireward excitatory synapses and serotonin,?a neuromodulator implicated in depression.     

Inhibition and facilitation in parasympathetic ganglia of the urinary bladder

Neurons in vesical parasympathetic ganglia receive excitatory and inhibitory inputs from both divisions of the autonomic nervous system. Sacral parasympathetic pathways (cholinergic) provide the major excitatory input to these ganglia via activation of nicotinic receptors. Parasympathetic pathways also activate muscarinic inhibitory and excitatory receptors, which may exert a modulatory influence on transmission. Cholinergic transmission is relatively inefficient when preganglionic nerves are stimulated at low frequencies (< 1 Hz). However, excitatory postsynaptic potentials (EPSPs) and postganglionic firing markedly increase during repetitive stimulation at frequencies of 1-10 Hz. It is concluded that enhanced transmitter release accounts for the temporal facilitation and that vesical ganglia function as "high pass filters" that amplify the parasympathetic excitatory input to the detrusor muscle during micturition. Transmission in vesical ganglia is also sensitive to adrenergic inhibitory and facilitatory synaptic mechanisms elicited by efferent pathways in the hypogastric nerves. The effects of exogenous norepinephrine indicate that adrenergic inhibition is mediated by alpha receptors and reflects primarily a presynaptic depression of transmitter release although postsynaptic adrenergic hyperpolarizing and depolarizing effects have also been noted. Adrenergic facilitation is mediated by beta receptors as well as unidentified receptors. Norepinephrine also can inhibit or excite spontaneously active neurons in vesical ganglia. The existence of inhibitory and facilitatory synaptic mechanisms in vesical ganglia provides the basis for a complex ganglionic modulation of the central autonomic outflow to the bladder.     

Amine modulation of the neurogenic Limulus heart

(1) The biogenic amines octopamine (OCT), dopamine (DA), epinephrine (E), and norepinephrine (NE) cause dose-dependent increases in both the rate and amplitude of contractions of the isolated Limulus heart-cardiac ganglion. Their relative ability to produce this excitation is OCT greater than DA approximately the same as E greater than NE. (2) The excitatory effects of all these amines are antagonized by the alpha-adrenergic blocker phentolamine and the dopaminergic antagonist haloperidol. The beta-adrenergic antagonist dichloroisoproterenol slightly reduces amine excitation, but is also a partial agonist. The beta-adrenergic antagonist propanolol, the alpha-blocker phenoxybenzamine, and the serotonin antagonist metergoline are ineffective. (3) In addition to their excitatory effects, DA and, to a lesser extent, NE initially reduce contraction rate and amplitude. (4) The transient inhibition is eliminated selectively by metergoline and is unaffected by the other antagonists. (5) The amines all increase the frequency of cardiac ganglion electrical bursting activity, whether ganglia are isolated or attached to cardiac muscle. Dopamine and NE also transiently inhibit the cardiac ganglion. (6) The amines do not alter myocardial resting tension, contractility, or membrane potential. (7) These amines appear to exert their modulatory effects on Limulus heart by altering the properties of the neurons which comprise its cardiac ganglion.     

Localization of ovulation hormone-like neuropeptide in the central nervous system of the snail Lymnaea stagnalis by means of immunocytochemistry and in situ hybridization

Summary The caudo-dorsal cells (CDC) in the cerebral ganglia of the pond snail Lymnaea stagnalis synthesize the 36-amino acid ovulation hormone (CDCH). We have used immuno-cytochemistry and in situ hybridization to reveal the localization of neurons and axons containing CDCH-like material.A monoclonal antibody to a fragment of CDCH and a cDNA probe encoding CDCH reacted with the CDC-system, with specific cell groups in the cerebral and pleural ganglia, and with individually occurring neurons throughout the central nervous system. The cells in the pleural ganglia, which were found in about 50% of the preparations studied, are considered as ectopic CDC. They are morphologically similar to CDC in their somal dimensions and axonal organization. By means of immuno-electron microscopy it was shown that these neurons contain secretory vesicles that are similar to those of the CDC. The neurons of the bilateral groups occurring in the cerebral ganglia in addition to the CDC are smaller and more intensely stained than the CDC. Axons of these small neurons probably have varicosities located on the CDC axons in the neuropil of the cerebral ganglion, indicating synaptic contacts. Two major axon tracts could be followed from (or toward) the neuropil of the cerebral ganglion. One tract runs from the cerebral gangion via the pleural and parietal ganglia to the visceral ganglion, giving off branches to most nerves emanating from these ganglia. The other tract could be traced through the cerebro-pedal connective to the pedal ganglia. Only in the right pedal ganglion was extensive axonal branching observed. The nerves emanating from this ganglion contained many more immunoreactive axons than those from the left pedal ganglion. A polyclonal antibody raised against the synthetic fragment of CDCH stained, in addition to the neurons and axons revealed with the monoclonal antibody and the cDNA probe, three other major groups of neurons. Two are located in the cerebral ganglion, the other in the left pedal ganglion.The present findings suggest the presence of a system of neurons that contain CDCH or CDCH-like peptides. The role this system may play in the control of egg-laying and egg-laying behaviour is discussed.     

Pigment-dispersing factor in the locust abdominal ganglia may have roles as circulating neurohormone and central neuromodulator

Pigment-dispersing factor (PDF) is a neuropeptide that has been indicated as a likely output signal from the circadian clock neurons in the brain of Drosophila. In addition to these brain neurons, there are PDF-immunoreactive (PDFI) neurons in the abdominal ganglia of Drosophila and other insects; the function of these neurons is not known. We have analyzed PDFI neurons in the abdominal ganglia of the locust Locusta migratoria. These PDFI neurons can first be detected at about 45% embryonic development and have an adult appearance at about 80%. In each of the abdominal ganglia (A3-A7) there is one pair of lateral PDFI neurons and in each of the A5-A7 ganglia there is additionally a pair of median neurons. The lateral neurons supply varicose branches to neurohemal areas of the lateral heart nerves and perisympathetic organs, whereas the median cells form processes in the terminal abdominal ganglion and supply terminals on the hindgut. Because PDF does not influence hindgut contractility, it is possible that also these median neurons release PDF into the circulation. Release from one or both the PDFI neuron types was confirmed by measurements of PDF-immunoreactivity in hemolymph by enzyme immunoassay. PDF applied to the terminal abdominal ganglion triggers firing of action potentials in motoneurons with axons in the genital nerves of males and the 8th ventral nerve of females. Because this action is blocked in calcium-free saline, it is likely that PDF acts via interneurons. Thus, PDF seems to have a modulatory role in central neuronal circuits of the terminal abdominal ganglion that control muscles of genital organs.     

Synaptic dimorphism in Onychophoran cephalic ganglia

The taxonomic location of the Onychophora has been controversial because of their phenotypic and genotypic characteristics, related to both annelids and arthropods. We analyzed the ultrastructure of the neurons and their synapses in the cephalic ganglion of a poorly known invertebrate, the velvet worm Peripatus sedgwicki, from the mountainous region of El Valle, Mérida, Venezuela. Cephalic ganglia were dissected, fixed and processed for transmission electron microscopy. The animal has a high degree of neurobiological development, as evidenced by the presence of asymmetric (excitatory) and symmetric (inhibitory) synapses, as well as the existence of glial cell processes in a wide neuropile zone. The postsynaptic terminals were seen to contain subsynaptic cisterns formed by membranes of smooth endoplasmic reticulum beneath the postsynaptic density, whereas the presynaptic terminal showed numerous electron transparent synaptic vesicles. From the neurophylogenetic perspectives, the ultrastructural characteristics of the central nervous tissue of the Onychophora show important evolutionary acquirements, such as the presence of both excitatory and inhibitory synapses, indicating functional synaptic transmission, and the appearance of mature glial cells.     

Properties of the serotonergic cerebral ganglion neurons of the gastropod mollusc, Philine aperta

The characteristics of a pair of identified neurons found in the cerebral ganglia of the gastropod mollusc Philine aperta have been examined. Because they appear to contain serotonin, and since they probably also use serotonin as a neurotransmitter, these neurons were named the serotonergic cerebral neurons (SCNs). Each SCN sent an axon out of the ipsilateral cerebro-buccal connective to the buccal ganglia. The SCNs also had extensive projections to all the ipsilateral, and most of the contralateral, buccal nerve trunks. Stimulating the SCNs produced the hyperpolarization of a pair of identified buccal ganglion mechano-sensory neurons (the S-cells), and had an excitatory action on the electrical activity of acinar cells of the salivary glands. A comparison of the properties of the Philine SCNs with those of similar serotonin-containing cerebral ganglion neurons in other gastropod molluscs provides evidence of homology with these neurons.     

Effects of synthetic bag cell and atrial gland peptides on identified nerve cells in Aplysia

We have examined the effects of peptides on the neuroendocrine bag cells, the R2 neuron and the left upper quadrant (LUQ) neurons of the abdominal ganglion of Aplysia californica. Peptides include those extracted from the atrial gland, a reproductive organ; those released by an afterdischarge of the bag cells; and 2 synthetic peptides: the amidated 9-amino acid C-terminal portion of atrial gland peptides A/B/ERH (B26-34), and the 8-amino acid alpha-bag cell peptide (alpha-BCP1-8). Peptides were applied by superfusion, arterial perfusion, pressure ejection from micropipettes, or by inducing a bag cell afterdischarge. Both alpha-BCP1-8 and B26-34 are able to produce a bag cell afterdischarge when applied to the abdominal ganglion but are not as effectively able to trigger the bag cells when applied selectively to the ganglia of the head ring. Peptides released by the bag cells inhibit R2 and LUQ neurons; whereas atrial gland extract mildly excites LUQ neurons and powerfully excites R2. The inhibitory effect of the LUQ cells and R2 following an afterdischarge of the bag cells is mimicked by alpha-BCP1-8. The excitatory effect of the atrial gland extract cannot be duplicated with B26-34. Rather, instead of having an excitatory effect on R2 and LUQ cells, B26-34 seems to mimick alpha-BCP1-8 and inhibit these neurons. Both peptides produce a membrane conductance increase in R2 and LUQ cells.     

Origin and clonal relationship of common inhibitory motoneurons CI1 and CI3 in the locust CNS

In the primordial thoracic ganglia of locust embryos, the bromodeoxiuridine (BrdU) technique for labelling proliferating cells and their progeny was combined with intracellular dye injection to investigate the origin and the clonal relationship of common inhibitory motoneurons. Common inhibitors 1 (CI₁) and 3 (CI₃) were found to be siblings, that is, they are produced by the division of one ganglion mother cell. This ganglion mother cell results from the first division of neuroblast 5–5, at about 30% of embryonic development. A large portion, at least, of the ganglion mother cells produced by subsequent divisions of neuroblast 5–5 give rise to interneurons with contralaterally ascending or descending axons and GABA-like immunoreactivity. Thus, CI₁ and CI₃ are more closely related to putative inhibitory interneurons than they are to other, that is, excitatory, motoneurons. Consistent with this, the CI somata are associated with cell bodies of putative inhibitory interneurons rather than with clusters of excitatory motoneuron somata. These results elicit speculations regarding the evolutionary origin of inhibitory motoneurons. 1994 John Wiley & Sons, Inc.     

Control of leech swimming activity by the cephalic ganglia

We investigated the role played by the cephalic nervous system in the control of swimming activity in the leech, Hirudo medicinalis, by comparing swimming activity in isolated leech nerve cords that included the head ganglia (supra- and subesophageal ganglia) with swimming activity in nerve cords from which these ganglia were removed. We found that the presence of these cephalic ganglia had an inhibitory influence on the reliability with which stimulation of peripheral (DP) nerves and intracellular stimulation of swim-initiating neurons initiated and maintained swimming activity. In addition, swimming activity recorded from both oscillator and motor neurons in preparations that included head ganglia frequently exhibited irregular bursting patterns consisting of missed, weak, or sustained bursts. Removal of the two head ganglia as well as the first segmental ganglion eliminated this irregular activity pattern. We also identified a pair of rhythmically active interneurons, SRN1, in the subesophageal ganglion that, when depolarized, could reset the swimming rhythm. Thus the cephalic ganglia and first segmental ganglion of the leech nerve cord are capable of exerting a tonic inhibitory influence as well as a modulatory effect on swimming activity in the segmental nerve cord.     

Segmental peptidergic innervation of abdominal targets in larval and adult dipteran insects revealed with an antiserum against leucokinin I

Summary An antiserum against the cockroach neuropeptide leucokinin I (LKI) was used to study peptidergic neurons and their innervation patterns in larvae and adults of three species of higher dipteran insects, the flies Drosophila melanogaster, Calliphora vomitoria, and Phormia terraenovae, as well as larvae of a primitive dipteran insect, the crane fly Phalacrocera replicata. In the larvae of the higher dipteran flies, the antiserum revealed three pairs of cells in the brain, three pairs of ventro-medial cells in the subesophageal ganglion, and seven pairs of ventro-lateral cells in the abdominal ganglia. Each of these 14 abdominal leucokinin-immunoreactive (LKIR) neurons innervates a single muscle of the abdominal body wall (muscle 8), which is known to degenerate shortly after adult emergence. Conventional electron microscopy demonstrates that this muscle is innervated by at least one axon containing clear vesicles and two axons containing dense-cored vesicles. Electronmicroscopical immunocytochemistry shows that the LKIR axon is one of these two axons with dense-cored vesicles and that it forms terminals on the sarcolemma of its target muscle. The abdominal LKIR neurons appear to survive metamorphosis. In the adult fly, the efferent abdominal LKIR neurons innervate the spiracles, the heart, and neurohemal regions of the abdominal wall. In the crane fly larva, dorso-medial and ventrolateral LKIR cell bodies are located in both thoracic and abdominal ganglia of the ventral nerve cord. As in the larvae of the other flies, the abdominal ventrolateral LKIR neurons form efferent axons. However, in the crane fly larva there are two pairs of efferent LKIR neurons in each of the abdominal ganglia and their peripheral targets include neurohemal regions of the dorsal transverse nerves. An additional difference is that in the crane fly, a caudal pair of LKIR axons originating from the penultimate pair of dorso-median LKIR cells in the terminal ganglion innervate the hindgut.     

Pax3-expressing trigeminal placode cells can localize to trunk neural crest sites but are committed to a cutaneous sensory neuron fate

The cutaneous sensory neurons of the ophthalmic lobe of the trigeminal ganglion are derived from two embryonic cell populations, the neural crest and the paired ophthalmic trigeminal (opV) placodes. Pax3 is the earliest known marker of opV placode ectoderm in the chick. Pax3 is also expressed transiently by neural crest cells as they emigrate from the neural tube, and it is reexpressed in neural crest cells as they condense to form dorsal root ganglia and certain cranial ganglia, including the trigeminal ganglion. Here, we examined whether Pax3+ opV placode-derived cells behave like Pax3+ neural crest cells when they are grafted into the trunk. Pax3+ quail opV ectoderm cells associate with host neural crest migratory streams and form Pax3+ neurons that populate the dorsal root and sympathetic ganglia and several ectopic sites, including the ventral root. Pax3 expression is subsequently downregulated, and at E8, all opV ectoderm-derived neurons in all locations are large in diameter, and virtually all express TrkB. At least some of these neurons project to the lateral region of the dorsal horn, and peripheral quail neurites are seen in the dermis, suggesting that they are cutaneous sensory neurons. Hence, although they are able to incorporate into neural crest-derived ganglia in the trunk, Pax3+ opV ectoderm cells are committed to forming cutaneous sensory neurons, their normal fate in the trigeminal ganglion. In contrast, Pax3 is not expressed in neural crest-derived neurons in the dorsal root and trigeminal ganglia at any stage, suggesting either that Pax3 is expressed in glial cells or that it is completely downregulated before neuronal differentiation. Since Pax3 is maintained in opV placode-derived neurons for some considerable time after neuronal differentiation, these data suggest that Pax3 may play different roles in opV placode cells and neural crest cells.