Analysis and visualization of cell movement in the developing zebrafish brain

Detailed reconstruction of the spatiotemporal history of embryonic cells is key to understanding tissue formation processes but is often complicated by the large number of cells involved, particularly so in vertebrates. Through a combination of high-resolution time-lapse lineage tracing and antibody staining, we have analyzed the movement of mesencephalic and metencephalic cell populations in the early zebrafish embryo. To facilitate the analysis of our cell tracking data, we have created TracePilot, a software tool that allows interactive manipulation and visualization of tracking data. We demonstrate its utility by showing novel visualizations of cell movement in the developing zebrafish brain. TracePilot (http://www.mpi-cbg.de/tracepilot) is Java-based, available free of charge, and has a program structure that allows the incorporation of additional analysis tools.

Involvement of actin in the electrotonic conductivity of mixed synapses in Mauthner neurons in the goldfish

The effects of phalloidin, a preperation which highly specifically and selectively polymerizes actin and which binds to actin, on the electrotonic conductivity and structure of mixed synapses were studied in goldfish Mauthner neurons (MN). These experiments showed that paired subthreshold electrical stimulation of the afferent input in the presence of phalloidin led to increases in the amplitude of MN responses to the second stimulus by an average of 80%. In controls, this amplitude increased by only 10% and only when suprathreshold stimuli were used, while subthreshold stimuli were ineffective. We regard these results as demonstrating increases in the conductivity of mixed synapses, this being induced by polymerization of actin. At the ultrastructural level, application of phalloidin to MN and their mixed synapses induced increases in the sizes and numbers of actin-containing desmosome-like contacts, and in the numbers of fibrillar bridges in the clefts of these contacts. Use of colloidal gold as a label for phalloidin demonstrated that bridges were made of actin. The interdependent morphofunctional changes seen in mixed synapses provide grounds for suggesting a role for actin in the conduction of the electrotonic signal through mixed synapses. The structural substrate for this process may be provided by bridges in the clefts of desmosome-like contacts.

Functional circuitry involved in the regulation of whisker movements

Neuroanatomical tract-tracing methods were used to identify the oligosynaptic circuitry by which the whisker representation of the motor cortex (wMCx) influences the facial motoneurons that control whisking activity (wFMNs). Injections of the retrograde tracer cholera toxin subunit B into physiologically identified wFMNs in the lateral facial nucleus resulted in dense, bilateral labeling throughout the brainstem reticular formation and in the ambiguus nucleus as well as predominantly ipsilateral labeling in the paralemniscal, pedunculopontine tegmental, Kölliker-Fuse, and parabrachial nuclei. In addition, neurons in the following midbrain regions projected to the wFMNs: superior colliculus, red nucleus, periaqueductal gray, mesencephalon, pons, and several nuclei involved in oculomotor behaviors. Injections of the anterograde tracer biotinylated dextran amine into the wMCx revealed direct projections to the brainstem reticular formation as well as multiple brainstem and midbrain structures shown to project to the wFMNs. Regions in which retrograde labeling and anterograde labeling overlap most extensively include the brainstem parvocellular, gigantocellular, intermediate, and medullary (dorsal and ventral) reticular formations; ambiguus nucleus; and midbrain superior colliculus and deep mesencephalic nucleus. Other regions that contain less dense regions of combined anterograde and retrograde labeling include the following nuclei: the interstitial nucleus of medial longitudinal fasciculus, the pontine reticular formation, and the lateral periaqueductal gray. Premotoneurons that receive dense inputs from the wMCx are likely to be important mediators of cortical regulation of whisker movements and may be a key component in a central pattern generator involved in the generation of rhythmic whisking activity.

Distribution of an orphan G-protein coupled receptor (JP05) mRNA in the human brain

JP05, also called GPR72 or GIR, is an orphan G-protein-coupled receptor, GPCR, showing significant structural similarity to the tachykinin receptors. The anatomical distribution of JP05 mRNA was first described in the central nervous system of the mouse, and recently the human JP05 orphan receptor gene has been cloned. In the present study the distribution of JP05 mRNA was examined in the human forebrain using in situ hybridization analysis. The results revealed a wide but discrete distribution of the transcript with strongly JP05 mRNA expressing cells, presumably neurons, present in the cerebral cortex (layer II), hippocampus (pyramidal CA3 neurons and granule cells), amygdala (basal and periamygdaloid cortical nuclei), in the endopiriform nucleus, diagonal band of Broca, thalamus (nucleus reuniens, parafascicular nucleus) and hypothalamus (posterior, dorsal, and around the medial mammillary). Weaker signals were detected in the deeper cortical layers and throughout the striatum. A few positive cells were evident in the raphe but not in the substantia nigra or pontine nuclei. The results indicate significant similarities between human and mouse brain with regard to JP05 mRNA expression. The distribution patterns of JP05 mRNA in the human brain suggest involvement in control of emotions and of neuroendocrine, cognitive and motor functions.

First discrete autoradiographic distribution of aminopeptidase N in various structures of rat brain and spinal cord using the selective iodinated inhibitor [125I]RB 129

The selective and potent aminopeptidase N inhibitor [125I]RB 129 has been used for the radioautographic localization of this enzyme in rat brain, spinal cord and intestine. Brain microvessels and intestine brush-border cells were shown to present a high concentration of aminopeptidase N. Moreover, a labeling of various brain structures was observed. A very high level of binding occurred in the meninges, choroid plexus, pineal gland, paraventricular nucleus and pituitary gland. Moderate to high labeling was also observed in the cortex, caudate-putamen, subthalamic nucleus, central periaqueductal gray, thalamus, as well as in the dorsal and ventral horn of the spinal cord, which are known to contain a high concentration of enkephalins, opioid receptors and neutral endopeptidase. This co-localization confirms the physiological implication of aminopeptidase N in the inactivation of enkephalins accounting for the requirement of dual inhibition of neutral endopeptidase and aminopeptidase N to observe highly significant morphine-like effects induced by the protected endogenous opioid peptides. Aminopeptidase N was also visualized in moderate to high levels in other brain structures such as the hippocampus, nucleus accumbens, substantia nigra, hypothalamus (dorsomedial and ventromedial nuclei), raphe nucleus, pontine nucleus, inferior olive, and in high concentration in the granular layer of cerebellum. In summary, aminopeptidase N has been visualized for the first time in numerous brain areas using the selective inhibitor [125I]RB 129. This iodinated probe could allow the ex vivo and in vivo localization of aminopeptidase N in various tissues to be investigated and may also be used to evaluate quantitative changes in aminopeptidase N expression in pathological situations. Aminopeptidase N, which preferably removes NH2-terminal neutral amino acids from peptides, has probably a host of substrates. Nevertheless, a certain in vivo selectivity could be achieved by the presence of the enzyme in structures where the peptide effector and its receptors are also co-localized.

Local sonic hedgehog signaling regulates oligodendrocyte precursor appearance in multiple ventricular zone domains in the chick metencephalon

In the chick metencephalon, oligodendrocyte precursors arise in distinct domains of the ventricular zone. During development, the earliest oligodendrocyte precursors appear in the metencephalic ventral ventricular zone adjacent to the midline, consistent with their location in the spinal cord. In contrast to spinal cord, however, distinct domains in the lateral and dorsal metencephalic ventricular zone subsequently generate oligodendrocyte precursors. All oligodendrogenic domains of the metencephalon appear in close apposition to regions that transiently express sonic hedgehog (Shh). Inhibition studies demonstrate a functional requirement for Shh signaling in the early appearance of metencephalic oligodendrocyte precursors, while in vitro studies suggest a dose-dependent increase in the number of oligodendrocyte precursors in response to Shh. In purified cultures of oligodendrocyte precursors, Shh promotes cell survival and proliferation, suggesting that Shh can act directly on these cells. These data suggest that Shh may be responsible for the localized appearance of oligodendrocyte precursors throughout the CNS, irrespective of the dorso-ventral neural axis.

Calretinin expression in specific neuronal systems in the brain of an advanced teleost, the grey mullet (Chelon labrosus)

The distribution of calretinin (CR) in the brain of an "advanced" teleost, the grey mullet, was studied by using immunoblotting and immunocytochemical techniques. In immunoblots of protein extracts of rat and mullet brains, the CR antibody stained a single band of about 29 kDa. CR immunoreactivity was observed in specific neuronal populations of all brain regions. The primary olfactory system, the optic nerve fibers, and some sensory fibers of other cranial nerves exhibited strong CR immunoreactivity. In the forebrain, the CR-immunoreactive (CR-ir) populations were scarce in the telencephalon and hypophysiotrofic hypothalamus, but numerous in many specialized nuclei of the diencephalon (preglomerulosus complex, nucleus glomerulosus, anterior glomerular nucleus, nucleus diffusus) and pretectum (parvocellular and magnocellular superficial pretectal nuclei, central pretectal nucleus), which are related to sensory systems. The two main forebrain bundles, medial and lateral, contained numerous CR-ir fibers. The midbrain sensory centers (optic tectum and torus semicircularis) exhibited numerous CR-ir cells and fibers. Likewise, the secondary gustatory nucleus of the isthmus is one of the nuclei exhibiting more intense CR immunoreactivity. Characteristically, the efferent cerebellar system (eurydendroid cells and brachium conjunctivum) and some afferent cerebellar fibers were CR-ir. In the medulla oblongata, a number of reticular cells, the inferior olive, and the magnocellular octaval nucleus exhibited CR immunoreactivity. CR-ir motoneurons were also observed in the spinal cord and in the oculomotor nucleus. Together with results obtained in other vertebrates, present results suggest that neural systems using calretinin to maintain intracellular calcium concentration have been rather well conserved during vertebrate evolution.

Development of spontaneous glycinergic currents in the Mauthner neuron of the zebrafish embryo

We used whole cell and outside-out patch-clamp techniques with reticulospinal Mauthner neurons of zebrafish embryos to investigate the developmental changes in the properties of glycinergic synaptic currents in vivo from the onset of synaptogenesis. Miniature inhibitory postsynaptic currents (mIPSCs) were isolated and recorded in the presence of TTX (1 microM), kynurenic acid (1 mM), and bicuculline (10 microM) and were found to be sensitive to strychnine (1 microM). The mIPSCs were first observed in 26-29 h postfertilization (hpf) embryos at a very low frequency of approximately 0.04 Hz, which increased to approximately 0.5 Hz by 30-40 hpf, and was approximately 10 Hz in newly hatched (>50 hpf) larvae, indicating an accelerated increase in synaptic activity. At all embryonic stages, the amplitudes of the mIPSCs were variable but their means were similar ( approximately 100 pA), suggesting rapid formation of the postsynaptic matrix. The 20-80% rise times of mIPSCs in embryos were longer (0.6-1.2 ms) than in larvae (approximately 0.3 ms), likely due to slower diffusion of glycine at the younger, immature synapses. The mIPSCs decayed with biexponential (tau(off1) and tau(off2)) time courses with a half-width in 26-29 hpf embryos that was longer and more variable than in older embryos and larvae. In 26- to 29-hpf embryos, tau(off1) was approximately 15 ms and tau(off2) was approximately 60 ms, representing events of intermediate duration; but occasionally long mIPSCs were observed in some cells where tau(off1) was approximately 40 ms and tau(off2) was approximately 160 ms. In 30-40 hpf embryos, the events were faster, with tau(off1) approximately 9 ms and tau(off2) approximately 40 ms, and in larvae, events declined somewhat further to tau(off1) approximately 4 ms and tau(off2) approximately 30 ms. Point-per-point amplitude histograms of the decay of synaptic events at all stages resulted in the detection of similar single channel conductances estimated as approximately 45 pS, indicating the presence of heteromeric glycine receptors (GlyRs) from the onset of synaptogenesis. Fast-flow (1 ms) application of a saturating concentration of glycine (3-10 mM) to outside-out patches obtained at 26-29 hpf revealed GlyR currents that decayed biexponentially with time constants resembling the values found for intermediate and long mIPSCs; by 30-40 hpf, the GlyR currents resembled fast mIPSCs. These observations indicate that channel kinetics limited the mIPSC duration. Our data suggest that glycinergic mIPSCs result from the activation of a mixture of fast and slow GlyR subtypes, the properties and proportion of which determine the decay of the synaptic events in the embryos.

Autoradiographic localization of (125)I[Tyr(14)]orphanin FQ/nociceptin and (125)I[Tyr(10)]orphanin FQ/nociceptin(1-11) binding sites in rat brain

The endogenous ligand for the orphan opioid receptor, orphanin FQ/nociceptin (OFQ), has recently been characterized. The OFQ peptide sequence contains paired basic amino acids, suggesting the possibility of posttranslational processing to a peptide containing the first 11 amino acids of the OFQ peptide. This peptide has been reported in the brain and it has a unique pharmacology. In the present study, we compared the autoradiographic distribution of (125)I[Tyr(14)]OFQ and (125)I[Tyr(10)]OFQ(1-11) in coronal rat brain sections. Nonspecific binding was defined with unlabeled OFQ or OFQ(1-11), respectively. Both radioligands demonstrated high levels of specific binding (>95% of total binding), with no appreciable binding in white matter areas with either ligand. (125)I[Tyr(14)]OFQ binding was widely distributed throughout the rat brain. In contrast, (125)I[Tyr(10)]OFQ(1-11) binding was more restricted. The highest (125)I[Tyr(14)]OFQ binding levels measured in this study were found in the locus coeruleus, an area which contained very low (125)I[Tyr(10)]OFQ(1-11) binding. Both ligands labeled the cortex, hippocampus and amygdala. In the thalamus, (125)I[Tyr(14)]OFQ binding was prominent in most nuclei, whereas (125)I[Tyr(10)]OFQ(1-11) binding was restricted to the midline thalamus. (125)I[Tyr(14)]OFQ binding was heavy in the suprachiasmatic hypothalamus, and moderate in other hypothalamic nuclei. (125)I[Tyr(10)]OFQ(1-11) binding in the hypothalamus, however, was present mainly in the ventromedial hypothalamic nucleus. Lower binding levels of both ligands were found in the caudate putamen. The distinct autoradiographic patterns of these two ligands are consistent with different binding sites, which might help explain their different functional activities.

The metencephalic floor plate of chick embryos expresses two secretory glycoproteins homologous with the two glycoproteins secreted by the subcommissural organ

The nature and the function of the compounds secreted by the floor plate (FP) of the metencephalon are little known. The FP cells of the hindbrain react with antibodies (AFRU) against the glycoproteins secreted by the subcommissural organ (SCO). One of the these proteins, RF-Gly I, is a 540-kDa core glycosylated protein. The aims of the present investigation were to identify by immunoblot the AFRU-immunoreactive compound secreted by the FP of chick embryos, to establish temporal and regional patterns of this secretory activity, and to obtain information about the fate of these compounds. It was established that the SCO and FP of chick embryos secrete two AFRU-immunoreactive compounds of 540 and 230 kDa. The two compounds secreted by the FP have been designated as FP-Gly I and FP-Gly II. The expression of these proteins was circumscribed to the metencephalic FP, and occurred from HH 29 to HH 36. Within the FP cells, FP-Gly I and FP-Gly II were confined to the supranuclear and apical regions, which under the electron microscope displayed numerous cisternae of the rough endoplasmic reticulum and granules. Aggregates of AFRU-immunoreactive material appeared on the free surface of the FP. The possibility that FP-Gly I and FP-Gly II are released into the ventricle to reach distant targets is discussed.

Immunohistochemical localisation of the 5-HT2C receptor protein in the rat CNS

5-HT2C receptor mRNA has a widespread distribution in the human and rat CNS but the absence of a specific high affinity ligand has made autoradiographic localisation of the receptor difficult. By raising polyclonal antibodies against the rat 5-HT2C receptor protein this study reports the immunohistochemical distribution of this receptor in the rat CNS. A sephadex purified 5-HT2C antiserum visualised a single immunopositive band (54 kDa) in Western blots of membranes prepared from several rat brain regions and caused intense membrane immunofluorescence in HEK 293 cells transfected with h5-HT2C cDNA, which were both attenuated by incubation with the antigenic peptide sequence (200-300 microM). 5-HT2C-like immunoreactivity was located on neurones throughout the CNS. The most abundant 5-HT2C-like immunoreactive cell bodies were in the anterior olfactory nucleus, medial and intercalated amygdaloid nuclei, hippocampus layers CA1 to CA3, laterodorsal and lateral geniculate thalamic nuclei, caudate-putamen and several areas of the cortex (including piriform and frontal), consistent with this receptor being located postsynaptic to serotonergic neurones. Immunopositive neurones were also found in the dorsal raphé, suggesting that 5-HT2C receptors may be on some serotonergic neurones. The overall distribution of 5-HT2C-like immunoreactivity complements previous findings with conventional radioligands and agrees well with reported levels of 5-HT2C receptor mRNA.