Early ontogeny of the vagus nerve: an analysis of the medulla oblongata and cervical spinal cord of the postnatal rat.

Retrograde transport of cholera toxin conjugated with horseradish peroxidase in the postnatal rat has revealed remarkable features of dendritic fields of vagal motor neurons in the medulla oblongata and cervical spinal cord during the period of early development (0-10 days). At birth, vagal motor neurons in the dorsal motor nucleus of the vagus, nucleus ambiguus, nucleus retroambigualis, nucleus dorsomedials and the spinal nucleus of the accessory nerve are small with relatively few, unbranched processes. The span of the dendritic tree is much smaller than that found in adult animals. By the postnatal Day 2 there are marked changes in the soma as well as in the dendritic tree of these neurons. There is dispersion of the cell bodies within the neuropil as well as an expansion of the total area of the brain stem occupied by these motor neurons and their dendritic processes which show extensive growth and branching. By postnatal Day 3 the most extensive proliferation of these neurons is seen and appears to represent the peak of dendritic growth of vagal motor neurons such that the area occupied by the dendritic tree of a single neuron is three times that seen in an adult rat. This proliferation gradually decreased during the subsequent seven days of early development (i.e. Days 4-10) so that by Day 10 the dendritic span of vagal motor neurons was reduced to about twice the adult size. This growth progressively decreased from Days 10 to 30 at which time adult levels were reached. Ultrastructural examination of these horseradish peroxidase labeled dendrites showed a positive correlation between the number of dendritic processes and the number of axo-dendritic synapses. This was accompanied by an increase in the number of identifiable synaptic junctions. These morphological complexities observed during the period of early development of vagal motor neurons indicate that the vagus nerve undergoes dramatic changes during the period of early development including the establishment of numerous synaptic contacts between vagal afferents and efferents in the brainstem. A number of these changes occur in developing dendritic fields of vagal motor neurons during the first three days of neonatal life. It is reasonable to assume that developmental abnormalities during this "critical period" could produce significant functional changes in the pattern of respiration as well as in the control of airway smooth muscle.     

Formation of GABA-Aα1 and GABA-B1 receptor-mediated inhibitory network in the ventrolateral part of the solitary tract nucleus during the early postnatal period under normal conditions and prenatal serotonin deficiency

Time course of formation of the inhibitory receptor network (GABA-Aα1 and GABA-B1) in the respiratory subnuclei (ventral and lateral) of the solitary tract (NTS) during the early postnatal period was studied on laboratory Wistar rats under normal conditions and prenatal serotonin deficiency. It was found that in normal rats the maturation of the inhibitory receptor networks in both NTS subnuclei occurs within the first three postnatal weeks. Some features of their formation were noticed. The dynamics of changes in intensity of GABA-Аα1 expression in the ventral and lateral subnuclei proceeds in a similar way. During the first postnatal week, GABA-Aα1 expression is low. In the neuropil, the network of GABA-Aα1-containing presynaptic terminals and synapses is poorly developed. Within the second week, the number of GABA-Aα1-expressing neurons increases in both subnuclei with a simultaneous rise in the density of the network of terminals and synaptic structures. By the end of the third week, the number of GABA-Aα1-expressing neurons decreases, but the network density continues to increase. GABA-B1 expression in the ventral and lateral subnuclei occurs also simultaneously, although with some distinctions. During the first postnatal week, intensity of GABA-B1 expression is weak. In the neuropil, few GABA-B1-containing terminals form a loose network with sporadic synaptic structures. During the second week, expression of the receptor increases, being particularly considerable in the ventral subnuclei. Simultaneously, the density of the presynaptic terminals increases. By the end of the third week, the number of GABA-B1-expressing neurons in the ventral subnuclei decreases, while in the lateral subnuclei remains almost intact and the network density increases. The data obtained show that prenatal serotonin deficiency leads to malformation and impaired maturation of the GABAergic inhibitory neuronal network in the ventrolateral part of NTS.     

Quantitative Autoradiography of [3H]Indalpine Binding Sites in the Rat Brain: II. Regional Distribution

The localization of binding sites for [3H]indalpine to sections of rat brain was studied by a quantitative autoradiographic technique. Binding sites for this specific neuronal 5-hydroxytryptamine (5-HT) uptake inhibitor are concentrated in areas rich in 5-HT neuronal cell bodies, fibers, and synaptic terminals. One of the most interesting features of this regional distribution is the very high density of these sites found in the dorsal raphe, substantia nigra, ventral tegmental area, and locus ceruleus. Components of the visual system also show pronounced labelling with [3H]indalpine. The finding that limbic structures are strongly labelled by this drug may be related to the antidepressant activity of indalpine. The anatomical distribution of binding sites demonstrated is consistent with the specific labelling of 5-HT neurons by [3H]indalpine and confirms previous studies carried out with another 5-HT uptake inhibitor, [3H]imipramine.     

Comparative electron microscopic study of the visual cortex neurons of the cat in postnatal ontogeny

The maturation of layers II-VI of neurons and perineuronal neuropil of the cat visual cortex (field 17) was studied from postnatal day 1 to day 21. The differentiation of large, small (associate) pyramid and stellate neurons was described. During the first postnatal week, the somata of layers II-VI of neurons undergo significant changes, the perikaryal cytoplasm increases in volume. Cell bodies of large pyramidal neurons mature by day 15. During the second postnatal week and almost till day 15, the rough endoplasmic reticulum of small pyramidal and stellate neurons undergoes proliferation; dendritic processes are branching. In stellate neurons the amount of cytoplasmic organelles increases dramatically only after the second postnatal week, and this is presumably induced by the opening of eyes on day 12. The second postnatal week is the period of greatest growth of dendritic, axonal and glial processes in perineural neuropil of layers V-VI. In the perineuronal neuropil of large pyramidal neurons (layers V-VI) there appear symmetric synapses with pyramidal cells, dendritic processes and dendritic spines. This occurs just at the time when kittens first open the eyes. From this time and during postnatal days 15-21, asymmetric synapses appear in the perineuronal neuropil of large pyramidal neurons. In the perineuronal neuropil of small pyramidal and stellate neurons. (layers II-IV), synapses reveal the mature appearance by day 15. After the opening of the eyes and up to postnatal day 21, dendritic growth and spine production occur in the perineuronal neuropil of small pyramidal and stellate neurons.     

The localization of neuronal nitric oxide synthase may influence its role in neuronal precursor proliferation and synaptic maintenance

Neuronal nitric oxide synthase (nNOS) is implicated in some developmental processes, including neuronal survival, differentiation, and precursor proliferation. To define the roles of nNOS in neuronal development, we utilized the olfactory system as a model. We hypothesized that the role of nNOS may be influenced by its localization. nNOS expression was developmentally regulated in the olfactory system. During early postnatal development, nNOS was expressed in developing neurons in the olfactory epithelium (OE), while in the adult its expression was restricted to periglomerular (PG) cells in the olfactory bulb (OB). At postnatal week 1 (P1W), loss of nNOS due to targeted gene deletion resulted in a decrease in immature neurons in the OE due to decreased proliferation of neuronal precursors. While the pool of neuronal precursors and neurogenesis normalized in the nNOS null mouse by P6W, there was an overgrowth of mitral or tufted cells dendrites and a decreased number of active synapses in the OB. Cyclic GMP (cGMP) immunostaining was reduced in the OE and in the glomeruli of the OB at early postnatal and adult ages, respectively. Our results suggest that nNOS appears necessary for neurogenesis in the OE during early postnatal development and for glomerular organization in the OB in the adult. Thus, the location of nNOS, either within cell bodies or perisynaptically, may influence its developmental role.     

Architectonics of GABAergic inhibitory network in the sensorimotor area of the rat neocortex in the early postnatal period under normal conditions and after acute perinatal hypoxia

The distribution of GABAergic interneurons as well as terminal and synaptic networks in different layers of the rat sensorimotor neocortex were studied at different stages of the postnatal period under normal conditions and after exposure to perinatal hypoxia. In control animals, the architectonics of the inhibitory network in different layers of the sensorimotor neocortex was shown to display distinctive features at different stages of the postnatal development. At early postnatal stages, a significant portion of neurons in layers II–V are immunopositive for GAD-67, indicative of a high level of GABA expression, however, GABA transmission is extremely weak, thus supporting the presence in the neuropil of only sporadic GABAergic terminals and synapses. By the juvenile age, a dramatic drop in the number of GABAergic neurons and an increase in the density of the network of GABA-immunopositive processes and synaptic structures occur in the neuropil, suggesting a considerable increase in GABA transmission. A higher level of GABA transmission is revealed in layers IV and V, persisting over the prepubertal period. Our results demonstrate that acute perinatal hypoxia affects the state of the inhibitory GABAergic network in the rat sensorimotor neocortex during the postnatal period. GABA expression and transmission were shown to change virtually in all layers.     

Postembryonic development of serotonin-immunoreactive neurons in the central nervous system of the blowfly

Summary Neurons immunoreactive with antibodies to serotonin (5-HT) were mapped in the thoracico-abdominal ganglia of the blowfly, Calliphora erythrocephala, during postembryonic development. Reconstructions from serial sections of tissue processed with a preincubation PAP-method permitted a detailed analysis of the morphological changes occurring in 5-HT-immunoreactive (5-HTi) neurons.All the 5-HTi cell bodies in the thoracico-abdominal ganglia of the 3rd instar larva, except two in the metathoracic ganglion, retain their immunochemical phenotype throughout pupal development. Hence, all the adult 5-HTi neurons in these ganglia differentiate during embryonic development. The finer processes of the larval 5-HTi neurons undergo a substantial regression during the first 24 h of pupal development, and thereafter new branches form on the primary processes of the same cell bodies. The slight change in relative position of 5-HTi cell bodies and the reorganization of the neuropil into an adult pattern occur during the first half of pupal development. The neuropil mass and extent of 5-HTi processes continue to increase during the following days and appear to be fully developed two days (80% of pupal development) before hatching.On the basis of the presented data, some of the basic processes are discussed that lead to the transformation of the larval nervous system into its adult form.     

Distribution of five peptides, three general neuroendocrine markers, and two synaptic-vesicle-associated proteins in the spinal cord and dorsal root ganglia of the adult and newborn dog: an immunocytochemical study

This study describes the immunocytochemical distribution of five neuropeptides (calcitonin gene-related peptide [CGRP], enkephalin, galanin, somatostatin, and substance P), three neuronal markers (neurofilament triplet proteins, neuron-specific enolase [NSE], and protein gene product 9.5), and two synaptic-vesicle-associated proteins (synapsin I and synaptophysin) in the spinal cord and dorsal root ganglia of adult and newborn dogs. CGRP and substance P were the only peptides detectable at birth in the spinal cord; they were present within a small number of immunoreactive fibers concentrated in laminae I-II. CGRP immunoreactivity was also observed in motoneurons and in dorsal root ganglion cells. In adult animals, all peptides under study were localized to varicose fibers forming rich plexuses within laminae I-III and, to a lesser extent, lamina X and the intermediolateral cell columns. Some dorsal root ganglion neurons were CGRP- and/or substance P-immunoreactive. The other antigens were present in the spinal cord and dorsal root ganglia of both adult and newborn animals, with the exception of NSE, which, at birth, was not detectable in spinal cord neurons. Moreover, synapsin I/synaptophysin immunoreactivity, at birth, was restricted to laminae I-II, while in adult dogs, immunostaining was observed in terminal-like elements throughout the spinal neuropil. These results suggest that in the dog spinal cord and dorsal root ganglia, peptide-containing pathways complete their development during postnatal life, together with the full expression of NSE and synapsin I/synaptophysin immunoreactivities. In adulthood, peptide distribution is similar to that described in other mammals, although a relative absence of immunoreactive cell bodies was observed in the spinal cord.     

Distribution of neuronal nitric oxide synthase-immunoreactive neurons in the cerebral cortex and hippocampus during postnatal development

Although many reports have argued a role for nitric oxide (NO) during postnatal development, there has been no combined demonstration in the cerebral cortex and hippocampus. We have investigated the distribution and morphology of neurons and fibers expressing neuronal NO synthase (nNOS) in the cerebral cortex and hippocampal formation of rats during the postnatal development, and correlated these findings with developmental events taking place in these regions. In the cerebral cortex, the nNOS-immunoreactive cells could be divided into two classes : heavily stained neurons and lightly stained neurons. For the lightly stained nNOS-positive neurons, only the cell bodies were observed, whereas for the heavily stained neurons, the cell bodies and their dendrites were visible. During the postnatal days, heavily stained neurons reached their typical morphology in the second week and appeared in all layers except for layer I. In the hippocampus, there was a transient expression of nNOS in the pyramidal cell layer at P3â€P7, and this expression disappeared during following days. The adult pattern of staining developed gradually during the postnatal period. This study suggested that these alterations might reflect a region-specific role of NO and a potential developmental role in the postnatal cerebral cortex and hippocampus     

Synaptic connections of the neurokinin 1 receptor-like immunoreactive neurons in the rat medullary dorsal horn

The synaptic connections between neurokinin 1 (NK1) receptor-like immunoreactive (LI) neurons and γ-aminobutyric acid (GABA)-, glycine (Gly)-, serotonin (5-HT)- or dopamine-β-hydroxylase (DBH, a specific marker for norepinephrinergic neuronal structures)-LI axon terminals in the rat medullary dorsal horn (MDH) were examined under electron microscope by using a pre-embedding immunohistochemical double-staining technique. NK1 receptor-LI neurons were observed principally in laminae I and III, only a few of them were found in lamina II of the MDH. GABA-, Gly-, 5-HT-, or DBH-LI axon terminals were densely encountered in laminae I and II, and sparsely in lamina III of the MDH. Some of these GABA-, Gly-, 5-HT-, or DBH-LI axon terminals were observed to make principally symmetric synapses with NK1 receptor-LI neuronal cell bodies and dendritic processes in laminae I, II and III of the MDH. The present results suggest that neurons expressing NK1 receptor within the MDH might be modulated by GABAergic and glycinergic inhibitory intrinsic neurons located in the MDH and 5-HT- or norepinephrine (NE)-containing descending fibers originated from structures in the brainstem.     

Neural expression of alpha-internexin promoter in vitro and in vivo

alpha-Internexin is a 66 kDa neuronal intermediate filament protein found most abundantly in the neurons of the nervous systems during early development. To characterize the function of mouse alpha-internexin promoter, we designed two different expression constructs driven by 0.7 kb or 1.3 kb of mouse alpha-internexin 5'-flanking sequences; one was the enhanced green fluorescent protein (EGFP) reporter for monitoring specific expression in vitro, and the other was the cre for studying the functional DNA recombinase in transgenic mice. After introducing DNA constructs into non-neuronal 3T3 fibroblasts and a neuronal Neuro2A cell line by lipofectamine transfection, we observed that the expression of EGFP with 1.3 kb mouse alpha-internexin promoter was in a neuron-dominant manner. To establish a tissue-specific pattern in the nervous system, we generated a transgenic mouse line expressing Cre DNA recombinase under the control of 1.3 kb alpha-Internexin promoter. The activity of the Cre recombinase at postnatal day 1 was examined by mating the cre transgenic mice to ROSA26 reporter (R26R) mice with knock-in Cre-mediated recombination. Analyses of postnatal day 1 (P1) newborns showed that beta-galactosidase activity was detected in the peripheral nervous system (PNS), such as cranial nerves innervating the tongue and the skin as well as spinal nerves to the body trunk. Furthermore, X-gal-labeled dorsal root ganglionic (DRG) neurons showed positive for alpha-Internexin in cell bodies but negative in their spinal nerves. The motor neurons in the spinal cord did not exhibit any beta-galactosidase activity. Therefore, the cre transgene driven by mouse alpha-internexin promoter, described here, provides a useful animal model to specifically manipulate genes in the developing nervous system.     

Alterations in Serotonin Parameters in Brain of Thiamine-Deficient Rats Are Evident Prior to the Appearance of Neurological Symptoms

Abstract: Biochemical alterations of serotoninergic parameters have been demonstrated in experimental thiamine deficiency. In addition, hypophagia and hypothermia, two physiological processes associated with changes in the serotonin [5-hydroxytryptamine (5-HT)] system, are manifest early during the progression of thiamine deficiency. The binding of selected 5-HT radioligands was therefore investigated in discrete brain regions of pyrithiamine-induced thiamine-deficient rats. Using quantitative receptor autoradiography, the binding of 8-hydroxy-2-(di- n -[³H]propylamino)tetralin, a ligand used to label the somatodendritic 5-HT_1A autoreceptor of the dorsal raphe nucleus, was found to be unaffected in this region, suggesting that the structural integrity of the 5-HT cell bodies is maintained throughout the course of pyrithiamine treatment. Increased binding of [³H]-ketanserin was observed in regions considered vulnerable as well as in some considered to be nonvulnerable during the course of thiamine deficiency. These binding changes, which appear to represent changes in the density of the postsynaptic 5-HT_2A receptor population rather than the "tetrabenazine-sensitive" vesicular monoamine transporter, are evident before the appearance of histopathologic lesions and coincide with altered tissue concentrations of 5-HT. These data suggest that 5-HT neurons, although structurally intact, are functionally affected early during the progression of thiamine deficiency. These alterations, which are likely a part of adaptive neuronal change consequent to thiamine dysfunction, may be important in the physiological manifestations and the learning deficits commonly encountered in experimental thiamine deficiency.     

4-Iodotomoxetine: a novel ligand for serotonin uptake sites.

The tomoxetine analog, R-4-iodotomoxetine, binds in vitro to a single site of rat cortical membranes with high affinity (Kd = 0.03 +/- 0.01 nM, n = 4) and can be blocked by a selective serotonin reuptake site inhibitor, paroxetine. The [125I]R-4-iodotomoxetine binding at equilibrium is saturable and is temperature- and Na(+)-dependent. The number of specific [125I]R-4-iodotomoxetine binding sites (Bmax = 356 +/- 20 fmol/mg protein) is similar to that of [3H]citalopram (329 +/- 30 fmol/mg protein), a known serotonin uptake inhibitor. The binding of [125I]R-4-iodotomoxetine is selectively inhibited by several serotonin uptake blockers, and a good correlation is demonstrated between the potency of various drugs to inhibit in vitro binding of [125I]R-4-iodotomoxetine and [3H]citalopram. In addition, lesions performed with the neurotoxin p-chloroamphetamine, which destroys monoamine neurons, including serotonergic neuronal system, result in a 90% reduction of [125I]R-4-iodotomoxetine binding when compared to sham controls. These results indicate that the binding sites labeled by [125I]R-4-iodotomoxetine are associated with the neuronal serotonin uptake sites. However, the in vivo and ex vivo results do not show regional localization corresponding to the distribution of serotonin uptake sites. The nonspecific uptake may be related to this compound's high lipophilicity (octanol-buffer partition coefficient = 1100 - 1400 at pH 7). Although the in vivo properties of [125I]R-4-iodotomoxetine make it an unlikely candidate for mapping serotonin uptake sites with SPECT, the high affinity and selectivity should make it a useful tool for in vitro studies of the serotonin uptake sites.     

Constancies in the neuronal architecture of the suboesophageal ganglion at metamorphosis in the beetleTenebrio molitor L.

Summary Topological organization of identified neurons has been characterized for the larval, pupal and imaginal suboeosphageal neuropil of the meal-worm beetleTenebrio molitor. Neuronal fate mapping allows identification of individually persisting neurons in the metamorphosing suboesophageal ganglion ofTenebrio. Analysis was performed on interneurons characterized by serotonin and CCAP (crustacean cardioactive peptide) immunohistochemistry, on motoneurons that innervate the dorsal and ventral longitudinal muscles, and on suboesophageal descending neurons. All these different populations of neurons show topologically invariant features throughout metamorphosis. Motoneurons, interneurons, and descending suboesophageal neurons of the imaginal suboeosphageal ganglion embody individually persisting larval interneurons. Impacts for a functional interpretation of the neuronal architecture of the suboesophageal ganglion are discussed.     

Presence and distribution of serotonin immunoreactivity in the cyprids of the barnacle Balanus amphitrite

In this work, the presence and distribution of serotonin in the cyprid of the barnacle Balanus amphitrite were investigated by immunohistochemical methods. Serotonin-like immuno-reactive neuronal cell bodies were detected in the central nervous system only. Various clusters of immunoreactive neuronal cell bodies are distributed in the brain (protocerebrum, deutocerebrum, optical lobes), and at least, four pairs of neuronal cell bodies were detected in the centrally positioned neuropil of the posterior ganglion. Rich plexuses of immunoreactive nerve fibers in the neuropil area were also observed. Furthermore, bundles of strongly immunoreactive nerve fibers surrounding the gut wall were localized, and immunoreactive nerve terminals in the antennules and compound eyes were observed. These data demonstrate the presence of a serotonin-like immunoreactive substance in the barnacle cyprids; furthermore, its immunolocalization in the cephalic nerve terminals allows us to postulate the involvement of this bioactive molecule in substrate recognition during the settlement process.     

Severe deficits in 5-HT2A -mediated neurotransmission in BDNF conditional mutant mice

BDNF is thought to provide critical trophic support for serotonin neurons. In order to determine postnatal effects of BDNF on the serotonin system, we examined a line of conditional mutant mice that have normal brain content of BDNF during prenatal development but later depletion of this neurotrophin in the postnatal period. These mice show a behavioral phenotype that suggests serotonin dysregulation. However, as shown here, the presynaptic serotonin system in the adult conditional mutant mice appeared surprisingly normal from histological, biochemical, and electrophysiological perspectives. By contrast, a dramatic and unexpected postsynaptic 5-HT2A deficit in the mutant mice was found. Electrophysiologically, serotonin neurons appeared near normal except, most notably, for an almost complete absence of expected 5-HT2A -mediated glutamate and GABA postsynaptic potentials normally displayed by these neurons. Further analysis showed that BDNF mutants had much reduced 5-HT2A receptor protein in dorsal raphe nucleus and a similar deficit in prefrontal cortex, a region that normally shows a high level of 5-HT2A receptor expression. Recordings in prefrontal slice showed a marked deficit in 5-HT2A -mediated excitatory postsynaptic currents, similar to that seen in the dorsal raphe. These findings suggest that postnatal levels of BDNF play a relatively limited role in maintaining presynaptic aspects of the serotonin system and a much greater role in maintaining postsynaptic 5-HT2A and possibly other receptors than previously suspected.     

Carboxypeptidase H-like immunoreactivity in the striatum of cats and monkeys

The enzyme carboxypeptidase H was detected by immunohistochemistry in the striatum of adult cats and monkeys. Specific labelling was observed in the neuropil as well as in both medium-sized and large neuronal cell bodies. The distribution of neurons and neuropil expressing immunoreactivity to carboxypeptidase H was examined in relation to the pattern of immunoreactivity to the neuropeptides enkephalin and substance P. Carboxypeptidase H-like immunoreactivity was found both in zones rich and poor in immunostaining for the two peptides, but was usually denser in those striatal areas in which substance P-positive cell bodies are clustered (striosomes). The results further suggest a role for carboxypeptidase H in the metabolism of multiple neuropeptides in vivo.     

Severe deficits in 5‐HT2A‐mediated neurotransmission in BDNF conditional mutant mice

BDNF is thought to provide critical trophic support for serotonin neurons. In order to determine postnatal effects of BDNF on the serotonin system, we examined a line of conditional mutant mice that have normal brain content of BDNF during prenatal development but later depletion of this neurotrophin in the postnatal period. These mice show a behavioral phenotype that suggests serotonin dysregulation. However, as shown here, the presynaptic serotonin system in the adult conditional mutant mice appeared surprisingly normal from histological, biochemical, and electrophysiological perspectives. By contrast, a dramatic and unexpected postsynaptic 5‐HT_2A deficit in the mutant mice was found. Electrophysiologically, serotonin neurons appeared near normal except, most notably, for an almost complete absence of expected 5‐HT_2A‐mediated glutamate and GABA postsynaptic potentials normally displayed by these neurons. Further analysis showed that BDNF mutants had much reduced 5‐HT_2A receptor protein in dorsal raphe nucleus and a similar deficit in prefrontal cortex, a region that normally shows a high level of 5‐HT_2A receptor expression. Recordings in prefrontal slice showed a marked deficit in 5‐HT_2A‐mediated excitatory postsynaptic currents, similar to that seen in the dorsal raphe. These findings suggest that postnatal levels of BDNF play a relatively limited role in maintaining presynaptic aspects of the serotonin system and a much greater role in maintaining postsynaptic 5‐HT_2A and possibly other receptors than previously suspected. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006     

The Drosophila larval visual system: high-resolution analysis of a simple visual neuropil

The task of the visual system is to translate light into neuronal encoded information. This translation of photons into neuronal signals is achieved by photoreceptor neurons (PRs), specialized sensory neurons, located in the eye. Upon perception of light the PRs will send a signal to target neurons, which represent a first station of visual processing. Increasing complexity of visual processing stems from the number of distinct PR subtypes and their various types of target neurons that are contacted. The visual system of the fruit fly larva represents a simple visual system (larval optic neuropil, LON) that consists of 12 PRs falling into two classes: blue-senstive PRs expressing Rhodopsin 5 (Rh5) and green-sensitive PRs expressing Rhodopsin 6 (Rh6). These afferents contact a small number of target neurons, including optic lobe pioneers (OLPs) and lateral clock neurons (LNs). We combine the use of genetic markers to label both PR subtypes and the distinct, identifiable sets of target neurons with a serial EM reconstruction to generate a high-resolution map of the larval optic neuropil. We find that the larval optic neuropil shows a clear bipartite organization consisting of one domain innervated by PRs and one devoid of PR axons. The topology of PR projections, in particular the relationship between Rh5 and Rh6 afferents, is maintained from the nerve entering the brain to the axon terminals. The target neurons can be subdivided according to neurotransmitter or neuropeptide they use as well as the location within the brain. We further track the larval optic neuropil through development from first larval instar to its location in the adult brain as the accessory medulla.     

SURFACE STRUCTURE OF ISOLATED NEURONS : Detachment of Nerve Terminals during Axon Regeneration

Freehand, isolated neuronal perikarya from the hypoglossal nucleus of the rabbit have been examined with light-and electron-microscopy (transmission and scanning). The surface of the cell bodies was largely covered with spherical particles which were 0.5–2 µ in diameter. Transmission electron microscopy proved that the spherical particles were synaptic nerve terminals. Crush of the hypoglossal nerve which leads to chromatolysis and swelling of the neuronal cell bodies results in a conspicuous reduction in the number of terminals attached to the surface of hypoglossal neurons. This effect was observed both for isolated neurons and in tissue sections. The effect is considered in relation to earlier reported variations in the adherence of neuropil to isolated neuronal perikarya. The functional importance of nerve ending detachment in connection with nerve injury is discussed.