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PubMed1984

Somatic and visceral primary afferents in the lower thoracic dorsal root ganglia of the cat.

Anterograde transport of horseradish peroxidase (HRP) through somatic and visceral nerves was used to estimate the proportions of somatic and visceral dorsal root ganglion (DRG) cells of the lower thoracic ganglia of the cat. A concentrated solution of HRP was applied for at least 5 hours to the central end of the right greater splanchnic nerve and of the left T9-intercostal nerve of adult cats. Some animals remained under chloralose anaesthesia for the duration of the HRP transport time (up to 53 hours) whereas longer HRP application and transport times (4-5 days) were allowed in animals that recovered from barbiturate anaesthesia. Visceral DRG cells were found in approximately equal numbers in all ganglia examined (T7-T11). Population estimates were obtained for the T8 and T9 ganglia where visceral DRG cells were found to be 6.2% (T8) and 5.2% (T9) of the total cell population. In contrast, somatic DRG cells were found in large numbers in the ganglia examined (T8 and T9) where they amounted to over 90% of the cell population. Measurement of cross-sectional areas and estimates of cell diameters of the DRG cells showed greater proportions of large somatic cells (diameter greater than 40 micron) than of large visceral cells. Similar distributions of cell size were found for both somatic and visceral DRG cells with diameters less than 40 micron. These results show that the proportion of visceral afferent fibres in the dorsal roots that mediate the spinal cord projection of the splanchnic nerve is very small. Since viscerosomatic convergence in the thoracic spinal cord is very extensive, the present results suggest considerable divergence of the visceral afferent input to the central nervous system.

Animals↗
PubMed1987

Ultrastructure and distribution of substance P-immunoreactive sensory collaterals in the guinea pig prevertebral sympathetic ganglia.

A light and electron microscopic study has been made of the substance P-immunoreactive networks formed by sensory nerve fibres in the prevertebral sympathetic ganglia of the guinea pig to seek confirmation that these networks arise from collateral branches of sensory fibres passing through the ganglia and to explore the synaptic and other specialized relationships established by these networks. Slices from coeliac-superior mesenteric and inferior mesenteric ganglia of young adult males, perfusion-fixed by paraformaldehyde, were immunostained with a monoclonal antibody to substance P, and the immunolabelling was visualized by a peroxidase reaction. Immunolabelled fibres passing through the ganglia were seen by light microscopy to give off varicose collaterals that ramified in the ganglionic neuropil. Electron microscopy showed that the parent fibres were almost exclusively unmyelinated. Many collaterals ran directly beneath the basal lamina bordering the intraganglionic tissue spaces, and the varicosities either remained superficially exposed under the basal lamina or sank deeper into the supporting Schwann cells, becoming apposed to dendrites of the ganglionic neurones, upon which they formed synapses, or to other nerve terminals. The incidence of these specific associations was quantified, singly and in combination. Synapses could be situated at the same level as unlabelled synapses on the same dendrite, and exposed varicosities could lie within 0.5 micron of exposed, postsynaptic dendrites. These observations confirm a collateral, synaptic nature for the networks and suggest additional nonsynaptic modes of release and sites of transmitter action. They are consistent with the hypothesis that the system serves a nocifensor function of axon reflex type.

Animals↗
PubMed1988

Spinal origins of preganglionic B and C neurons that innervate paravertebral sympathetic ganglia nine and ten of the bullfrog.

These experiments were designed to characterize the distribution, morphology, and number of spinal preganglionic neurons that selectively innervate the B- and C-type sympathetic neurons in paravertebral ganglia 9 and 10 of the bullfrog. For this purpose, horseradish peroxidase (HRP) was applied to the anterior end of the sectioned sympathetic chain between ganglia 8 and 9. Subsequent retrograde axonal transport of the HRP labeled ipsilateral spinal neurons whose cell bodies form a column having rostral and caudal boundaries that are, respectively, just caudal to the level of spinal nerve 4 and midway between the entry zones of spinal nerves 7 and 8. In all segments, the labeled preganglionic somata were found in the lateral half of the spinal gray and slightly dorsal to the central canal; a position analogous to that of the intermediolateral cell column in mammals. Most labeled preganglionic neurons were multipolar in shape, and the cell bodies lying between spinal nerves 4 and 5 were, on average, larger than those found between spinal nerves 7 and 8. In transverse sections that were cut near spinal nerve 5, the axons of preganglionic neurons could be seen to exit the cord through ventral roots. Counts of labeled preganglionic neurons indicate that an average +/- S.D. of 338 +/- 89 cells innervate ganglia 9 and 10. Selective labeling of preganglionic B neurons, by cutting spinal nerves 7 and 8 central to their rami communicantes at the time of HRP application, revealed an average +/- S.D. of 137 +/- 31 cells that lie exclusively between spinal nerves 4 and 6. By contrast, selective labeling of preganglionic C neurons, by cutting the sympathetic chain rostral to ganglion 7 at the time of HRP application, revealed an average +/- S.D. of 187 +/- 77 cells in an adjacent portion of the preganglionic column that is bounded by spinal nerve 6 and by a point midway between spinal nerves 7 and 8. These results thus demonstrate a clear segmental segregation between the preganglionic B and C neurons that innervate ganglia 9 and 10.

Animals↗
PubMed1989

Lumbar dorsal root ganglia of the cat: a quantitative study of peptide immunoreactivity and cell size.

The purpose of the present study was to quantify the extent to which several peptides and serotonin coexist with substance P or somatostatin in selected lumbar dorsal root ganglia of the cat. The technique for the simultaneous visualization of two antigens by immunofluorescence was used to investigate the coexistence of neuropeptides in the lumbar dorsal root ganglia of colchicine-treated cats. Perikarya immunoreactive for calcitonin gene-related peptide, galanin, leu-enkephalin, somatostatin, and substance P were visualized in both the lumbar 5 and 6 dorsal root ganglia. In contrast, no immunoreactivity was observed for adipokinetic hormone, bombesin, dynorphin A, met-enkephalin, oxytocin, tyrosine hydroxylase, thyrotropin-releasing hormone, vasopressin, vasoactive intestinal peptide, or serotonin in either ganglion examined. Substance P coexisted with calcitonin-gene-related peptide, somatostatin, and leu-enkephalin. Somatostatin was colocalized with calcitonin gene-related peptide, leu-enkephalin, and substance P but coexisted with galanin minimally. The cell area of immunoreactive perikarya was also examined. Data concerning the cross-sectional area of immunoreactive cells indicated that somatostatin-immunoreactive perikarya were generally the largest population observed (up to approximately 6,000 microns2). Somatostatin and calcitonin gene-related peptide, as well as substance P and calcitonin gene-related peptide, coexisted in populations of cell bodies that had a smaller size (less than 2,000 microns2). These results suggest that certain peptides which coexist in the dorsal root ganglia may provide histochemical markers for functional groups of primary afferent neurons.

Afferent Pathways↗
PubMed1990

Connections of the subthalamic nucleus with ventral striatopallidal parts of the basal ganglia in the rat.

The present study was undertaken to establish the precise anatomical relationship of the subthalamic nucleus (STh) with limbic lobe-afferented parts of the basal ganglia in the rat. The anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L), injected in the STh, the globus pallidus, the ventral pallidum, the ventral striatum, and the parafascicular thalamic nucleus, and the retrograde tracers Fluoro-Gold (FG) and cholera toxin B (CTb), injected in the globus pallidus, the ventral pallidum, the ventral striatum, and the ventral mesencephalon, were used for this purpose. The results of these tracing experiments confirm the general notion of reciprocal connections between the STh and pallidal areas. Thus the dorsomedial part of the STh is connected with the subcommisural ventral pallidum, whereas a more ventral and lateral part of the medial STh is related to the medial globus pallidus. The lateral hypothalamic area, directly adjacent to the STh, containing neurons with a morphology quite similar to those in the STh, projects to parts of the ventral pallidum related to the olfactory tubercle. The reciprocal projection from this pallidal area to subthalamic regions appears to be very sparse. The medial STh sends strong projections to the medial part of the entopeduncular nucleus and the adjacent lateral hypothalamic area. Sparser projections from the medial STh reach the rostral and medial part of the caudate-putamen and the nucleus accumbens. The nucleus accumbens sends a very sparse projection back to the medial STh. The projections of the medial STh to the ventral mesencephalon appear also to be topographically organized. The lateral hypothalamus and a few cells in the most medial part of the STh project to the ventral tegmental area, whereas progressively more lateral parts of the ventral mesencephalon, in particular the substantia nigra, receive input from successively more lateral and caudal parts of the STh. In addition, a number of STh fibers reach the midbrain extrapyramidal area. The lateral part of the parafascicular thalamic nucleus projects to the lateral part of the STh, whereas parafascicular neurons medial to the fasciculus retroflexus project to the dorsomedial portion of the STh. The medial part of the STh and the adjacent lateral hypothalamus are intimately connected with limbic parts of the basal ganglia in a way similar and parallel to the connections of the lateral STh with motor-related parts of the basal ganglia. These findings suggest a role for the STh in nonmotor functions of the basal ganglia.

Animals↗
PubMed1991

Distribution of vasoactive intestinal peptide- and substance P-containing nerves originating from neurons of airway ganglia in cat bronchi.

This study examined the possibility that vasoactive intestinal peptide (VIP)- and substance P (SP)-containing nerve fibers in bronchial smooth muscle, glands, epithelium, and blood vessels originate from neurons of airway ganglia. Explants of airway walls were maintained in culture with the expectation that nerve fibers from neurons of airway ganglia would remain viable, whereas fibers originating from neurons not present in the airway walls would degenerate. Airways were dissected and placed into culture dishes containing CMRL 1066 medium for 3, 5, and 7 days. In controls (noncultured), VIP- and SP-like immunoreactivity was observed in nerve fibers associated with bronchial smooth muscle, glands, and blood vessel walls and in nerve cell bodies of airway ganglia. Nerve fibers containing SP were also observed within the bronchial epithelium. After 3, 5, and 7 days in culture, VIP- and SP-containing fibers were identified in all of the same locations except in the airway epithelium where SP-containing fibers could not be demonstrated. VIP and SP were frequently colocalized in the same nerve fibers of bronchial smooth muscle and glands in controls and cultured airways. There were no statistically significant differences in nerve fiber density for either VIP- or SP-containing fibers in bronchial smooth muscle between controlled and cultured airways. VIP concentrations in cultured airways were significantly less than in controls. The results suggest that a large proportion of VIP- and SP-containing nerve fibers supplying bronchial smooth muscle, glands, and blood vessels in the airways originate from neurons of airway ganglia.

Animals↗
PubMed1991

Comparative aspects of the basal ganglia-tectal pathways in reptiles.

To determine how the basal ganglia in reptiles may influence visuomotor behavior, the connections from the basal ganglia to the tectum of the midbrain were studied in several species of reptiles. Immunohistochemical studies by means of antibodies against Leu-enkephalin (LENK) as well as experimental hodological studies with anterograde (PHA-L) and retrograde (HRP, Fluorogold, Cholera toxin) tracers were carried out. The results indicate that within the class of Reptilia, two different patterns occur: one in which information from the basal ganglia is relayed to the tectum via the substantia nigra as well as via a pretectal, enkephalinergic cell group, and another one in which only the ventral route, via the substantia nigra, is present. The former pattern is found in turtles, crocodiles, and the lacertid lizards Podarcis and Gallotia, and the latter pattern in the gekkonid lizards Gekko and Eublepharis, in Varanus, and in the snakes Python and Thamnophis. The presence or absence of the pretectal relay center is reflected in the laminar distribution of LENK immunoreactivity in the tectum. The apparent lack of a pretectal relay in nocturnal gekkonids and in snakes underlines the hypothesis (Reiner et al., '84: T.I.N.S. 7:320-325) that a de-emphasis of visual-basal ganglia mechanisms has occurred during the evolution of ancestral reptiles to modern mammals.

Animals↗
PubMed1994

Parvalbumin-containing GABAergic neurons in the basal ganglia output system of the rat.

The output of the basal ganglia is directed through the entopeduncular nucleus (EPN) and the substantia nigra pars reticulata (SNR) and pars lateralis (SNL), which provide a gamma-aminobutyric acidergic (GABAergic) projection to various nuclei of the thalamus and brainstem. Although many neurons within the SNR and EPN have been described as modality specific, the morphological and neurochemical similarities preclude their precise identification. In the present study, the immunocytochemical localization of parvalbumin, a calcium-binding protein, is used in combination with axonal tracing to verify neuronal heterogeneity within the SNR, SNL, and EPN. The results reveal that the majority of neurons in all three centers contain parvalbumin. The parvalbumin-containing neurons are distributed in the caudal two-thirds of the EPN, the rostral part of the SNL, and the lateral two-thirds of the entire rostrocaudal extent of the SNR, the areas involved in sensorimotor function of the basal ganglia. Moreover, the nigrothalamic, nigrocollicular, and EPN-thalamic neurons possess parvalbumin immunoreactivity, whereas the EPN-habenular neurons are devoid of parvalbumin immunoreactivity. The results indicate a neurochemical heterogeneity within the GABAergic output neurons of the basal ganglia and suggest that the parvalbumin-containing neurons of the SNR, SNL, and EPN are the tonically active output neurons that form a major link in the disinhibitory neuronal circuit of the basal ganglia, especially that concerned with sensorimotor function.

Animals↗
PubMed2005

Identification of a novel type II classical cadherin: rat cadherin19 is expressed in the cranial ganglia and Schwann cell precursors during development.

To identify a novel type II classical cadherin, we searched the genome database and found rat cadherin19 (cad19) with high similarity to human cadherin19. We also found nucleotide sequences corresponding to rat cad19 in mouse and chicken genomes. In situ hybridization of rat cad19 revealed that rat cad19 mRNA was initially expressed in cephalic neural crest cells, and then in the cranial ganglia, migrating trunk neural crest cells, the nascent dorsal root ganglia, and the sympathetic ganglia. Expression of cad19 overlapped with that of neural crest markers, including Sox10 and AP-2, but cad19 expression was confined to subpopulations of the neural crest-derived cells, those typically observed in the satellite glia at the periphery of the ganglia and Schwann cell precursors along the peripheral nerves. cad19 mRNA was not detected in cells expressing Phox2b, an epibranchial placode-derived neurons, nor in those expressing neuronal markers such as Hu protein. These observations suggest that cad19 is expressed in neural crest-derived, non-neuronal cells. Although the expression of cad19 mRNA persisted in Schwann cell precursors at E14.5, it was no longer detected in maturing Schwann cells at later stages. These results suggest that cad19 is an evolutionarily conserved cadherin and may be involved in the early development of Schwann cells in the peripheral nervous system.

Amino Acid Sequence↗
PubMed1990

Comparison of demyelination and neural degeneration in spiral and Scarpa's ganglia of C57BL/6 mice.

Spiral and Scarpa's (vestibular) ganglia of female C57BL/6 mice, ranging in age from 1.5 to 32 months, were examined by light and electron microscopy. The spiral ganglia of C57BL/6 mice undergo sweeping neuronal losses. Based on cytological characteristics that repeat themselves in both young and old mice, we divided perikaryal demyelination and degeneration of spiral ganglia into four arbitary stages: 1) incipient demyelination, myelin sheaths begin to loosen and unravel; 2) contact, the partially demyelinated perikarya abut as the extracellular matrix disappear; 3) clumping, clusters of naked perikarya clump together, cytoplasmic processes surround the exterior of the clump; and 4) resorption, the clumps gradually disintegrate, leaving at completion large, fluid-filled spaces and few cellular remnants. In Scarpa's ganglia, a small number of neurons demyelinate and clump, but none degenerate or undergo resorption.

Animals↗
PubMed2006

Distribution of FMRFamide-like immunoreactivity in the alimentary tract and hindgut ganglia of the barnacle Balanus amphitrite (Cirripedia, Crustacea).

In this study, the presence and distribution of FMRFamide-like immunoreactivity in the alimentary tract of barnacle Balanus amphitrite were investigated. A net of nerve fibers strongly immunoreactive to FMRFamide-like molecules was localized in the posterior midgut and hindgut. Positive varicose nerve terminals were also localized close to the circular muscle cells and, in the hindgut, close to the radial muscular fibers. Besides this nerve fibers network, one pair of contralateral ganglia was localized in the hindgut, each of them constituted by two strongly FMRFamide-labeled neurons and one nonlabeled neuron. Their immunoreactive axons directed toward the hindgut and posterior midgut suggest an involvement of FMRFamide-like substances in adult B. amphitrite gut motility. The hindgut associated ganglia of barnacles seem to correspond to the terminal abdominal ganglia of the other crustaceans. Since they are the only residual gut ganglia in the barnacle's reduced nervous system, we can hypothesize that gut motility needs a nervous system regulation partially independent of the central nervous system.

Animals↗
PubMed2002

Functional anatomy of the basal ganglia.

Four organizational levels of the basal ganglia that could be particularly determinant in terms of functional properties are reviewed: (1) macroscopic anatomy, which is characterized by a dramatic decrease of cerebral tissue volume from the cerebral cortex to the deepest portions of the basal ganglia; (2) connectivity, which consists of both complex loops and a partition into three territories, sensorimotor, associative, and limbic (which process motor, cognitive, and emotional information, respectively); (3) neuronal morphology, characterized by a dramatic numeric and geometric convergence of striatal neurons onto pallidonigral neurons; and (4) dopaminergic innervation of the basal ganglia, which is organized as a dual system that is supposed to have opposite effects on the activity of the system. Current models of the basal ganglia are discussed.

Animals↗
PubMed2001

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.

Abdomen↗
PubMed1984

Activation by dopamine of patterned motor output from the buccal ganglia of Helisoma trivolvis.

The buccal ganglia of the snail, Helisoma trivolvis, contain an intrinsic system of dopamine-containing neurons (Trimble, Barker, and Bullard, 1983). Dopamine, when bath applied to the isolated buccal ganglia, activates patterned motor output in a dose-dependent fashion. Haloperidol blocks the activating effect of dopamine, but the similar activation evoked by serotonin is not blocked by haloperidol. We suggest that there are two separate mechanisms for activating patterned motor output from the buccal ganglia. One is serotonergic, emanating from identified cerebral ganglion cells (Granzow and Kater, 1977), while the other is dopaminergic, involving neurons intrinsic to the buccal ganglia.

Animals↗
PubMed1988

Fibronectin-like immunoreactivity in Helisoma buccal ganglia: evidence that an endogenous fibronectin-like molecule promotes neurite outgrowth.

We examined the distribution of fibronectin-like (FNL) immunoreactivity associated with intact buccal ganglia, cell-cultured buccal ganglia neurons and nonneuronal cells, and brain-conditioned medium from the snail Helisoma. In addition, the possible roles of fibronectin in the regulation of neurite outgrowth were studied. Immunofluorescent staining for FNL antigens revealed intense staining in patches and fibrous arrays over the connective tissue sheaths of buccal ganglia and nerve trunks. Within the ganglia, heavy staining was seen surrounding neurons and in track-like arrangements. In cell cultures, specific staining was associated with nonneuronal cell surfaces and to a lesser degree with the surface of identified neurons. In addition, a noncellular, substrate-bound component of brain-conditioned medium displayed FNL immunoreactivity. Since cultured Helisoma neurons require a substrate-associated, brain-derived conditioning factor (CF) in order to elaborate neurites with motile growth cones, we tested whether the FNL immunoreactive substance might act as a neuritotropic agent. Fibronectin antiserum suppressed, in a dose-dependent manner, the CF-induced sprouting of identified neurons in isolated cell culture. When added at increasing concentrations to neurons already growing in response to CF, fibronectin antiserum exerted a biphasic effect on neurite elongation; outgrowth was accelerated at low, but inhibited at high, antiserum concentrations. In contrast, growth cone structures associated with motility (filopodia and lamellipodia) were progressively reduced by increasing levels of antiserum. A short peptide derived from fibronectin's cell-binding domain (Arg-Gly-Asp-Ser) also greatly reduced neurite outgrowth. The combined results of this study indicate an abundance of FNL immunoreactive molecules within the CNS of Helisoma, their probable production by nonneuronal cells, and their function as a substrate-associated component of CF which promotes growth cone filopodial and lamellipodial activity.

Animals↗
PubMed1994

Characterization and localization of D1 dopamine receptors in the sexually dimorphic vocal control nucleus, area X, and the basal ganglia of European starlings.

D1 dopamine receptors were pharmacologically characterized and localized by quantitative autoradiography in the basal ganglia of male and female European starlings (Sturnus vulgaris). The D1 selective antagonist SCH 23390 was used to label this receptor subtype. Starlings are songbirds and possess a neural circuit implicated in the learning and production of song. This circuit includes a sexually dimorphic nucleus, area X, that is a subregion of the parolfactory lobe of the basal ganglia and is known from work on zebra finches to receive dopaminergic input from the area ventralis of Tsai. We focused our investigation on the D1-like receptor subtype because they are abundant in the basal ganglia. Competition studies indicate that a variety of dopaminergic ligands compete with [3H] SCH 23390 for the binding site in an order of potency characteristic of a D1-like receptor. Autoradiographic studies of the basal ganglia revealed high D1 receptor densities in the avian homologues of the caudate-putamen and relatively low-receptor densities were observed in the avian homologue of the globus pallidus. In male starlings, area X could be reliably discerned on the autoradiograms by the higher density of D1 receptors compared to the surrounding parolfactory lobe (LPO). This was also true for females, though not as reliably as in males. When we compared the mean D1 receptor density in area X for males and females we did not find a significant sex difference. However, we also analyzed the data by comparing sex differences in the degree to which area X has a higher receptor density in comparison with the surrounding LPO. When we normalized D1 receptor density in area X relative to the LPO, we did find a significant sex difference. This sex difference in relative receptor density represents another neural sex difference in the song circuit that may mediate sex differences in the learning and production of song in starlings and other songbirds.

Animals↗
PubMed1995

Agrin mRNA variants are differentially regulated in developing chick embryo spinal cord and sensory ganglia.

Agrin is a synapse-organizing protein synthesized and externalized by motor neurons in the spinal cord, which organizes the postsynaptic apparatus of the developing neuromuscular junction. Agrin mRNA in the nervous system consists of several alternatively spliced variants. Splicing of agrin gene transcripts at the major site of variability results in four variants: encoding 8 (B8) or 11 (B11) amino acid inserts, both (B19), or predominant variant (B0) without inserts. The insert-containing variants are neuron specific and encode agrin proteins with greater synapse-organizing activity than the B0 variant. Here, we report the localization and developmental regulation of agrin mRNA variants in chick embryo spinal cord and dorsal root ganglia. In situ hybridization using antisense oligodeoxynucleotide (ODN) probes specific for the B8 and B11 sequences shows that the neuron-specific variants are concentrated in ventrolateral cells of the chick embryo spinal cord, presumably motor neurons, beginning at embryonic day 4 (E4). By E14, the insert-containing mRNAs are found almost exclusively in presumptive motor neurons. These variants are also found in dorsal root ganglia and sympathetic ganglia, but not in non-neural tissues. Analysis by polymerase chain reaction showed that the B11 and B19 mRNA variants appeared in spinal cord at E4, whereas the B8 variant was first seen at E14. During development, B11 decreased and disappeared by E20, whereas B8 increased from E14 to E20. A similar time course was seen in dorsal root ganglia. The greatest acetylcholine receptor-aggregating activity in the spinal cord was seen from E6 to E10, coincident with the highest proportion of B11-containing transcripts and with the peak of synaptogenesis in limb muscles. These data provide the first evidence linking appearance of the neuron-specific agrin mRNA variants with expression of the functional protein. The B11 and B19 variants appeared in E2 (stage 15) neural tubes cultured for 2 days with or without notochord and trunk tissues, indicating that there is no peripheral signal required to induce these agrin mRNA variants in developing motor neurons.

Agrin↗
PubMed2002

Neurogenin1 defines zebrafish cranial sensory ganglia precursors.

Cells delaminate from epithelial placodes to form sensory ganglia in the vertebrate head. We describe the formation of cranial neurogenic placodes in the zebrafish, Danio rerio, using bHLH transcription factors as molecular markers. A single neurogenin gene, neurogenin1 (ngn1), is required for the development of all zebrafish cranial ganglia, which contrasts with other described vertebrates. Expression of ngn1 delineates zebrafish ganglionic placodes, including trigeminal, lateral line, and epibranchial placodes. In addition, ngn1 is expressed in a subset of cells within the otic vesicle that will delaminate to form the octaval (statoacoustic) ganglion. The trigeminal placode is the first to differentiate, and forms just lateral and adjacent to the neural crest. Expression of ngn1 is transient and prefigures expression of a related bHLH transcription factor, neuroD. Interfering with ngn1 function using a specific antisense morpholino oligonucleotide blocks differentiation of all cranial ganglia but not associated glial cells. Lateral line sensory neuromasts develop independently of ngn1 function, suggesting that two derivatives of lateral line placodes, ganglia and migrating primordia, are under separate genetic control.

Animals↗