Postembryonic development of the dorsal longitudinal flight muscle and its innervation in Manduca sextaDuch, Carsten; Bayline, Ronald J.; Levine, Richard B.
doi: 10.1002/(SICI)1096-9861(20000619)422:1<1::AID-CNE1>3.0.CO;2-Spmid: 10842215
The neuromuscular systems of holometabolous insects must be remodeled during metamorphosis to allow striking behavioral changes, such as the acquisition of flight. The fast contracting dorsal longitudinal flight muscle (DLM) of Manduca arises from an anlage containing both remnants of specific larval dorsal body wall muscles and extrinsic myoblasts. In the mesothorax, the DLM is innervated by five persisting larval motoneurons: one in the mesothoracic and four in the prothoracic ganglion. These motoneurons innervate two slowly contracting body wall muscles in the larva. 2 days before pupation, the DLM template fibers begin to degenerate, whereas other muscles remain intact until pupation. Correspondingly, the motor terminals retract from the template fibers while they remain on other muscle fibers until pupation. Accumulation and proliferation of putative myoblasts also starts 2 days before pupation in close spatial relationship to the retracted motor tufts around the degenerating larval template fibers. Proliferation increases through the early pupal stages, and is detected within the anlage until the ninth day after pupation. 2 days after pupation, the anlage splits into five bundles, each innervated by one motoneuron. Striations occur on the seventh day after pupation when the growing motor axons reach the attachment sites. Subsequently, the muscle grows in volume and higher‐order motor branches are formed. Within the central nervous system, there is dramatic regression of larval dendrites followed by growth of new dendrites as the persistent motoneurons assume their new role in flight behavior. Both central and peripheral remodeling follow similar time courses. J. Comp. Neurol. 422:1–17, 2000. © 2000 Wiley‐Liss, Inc.
Activity‐dependent reconfiguration of the effective dendritic field of motoneuronsKorogod, Sergey M.; Kulagina, Irina B.; Horcholle‐Bossavit, Ginette; Gogan, Paul; Tyc‐Dumont, Suzanne
doi: 10.1002/(SICI)1096-9861(20000619)422:1<18::AID-CNE2>3.0.CO;2-Apmid: N/A
A neuron in vivo receives a continuous bombardment of synaptic inputs that modify the integrative properties of dendritic arborizations by changing the specific membrane resistance (Rm). To address the mechanisms by which the synaptic background activity transforms the charge transfer effectiveness (Tx) of a dendritic arborization, the authors simulated a neuron at rest and a highly excited neuron. After in vivo identification of the motoneurons recorded and stained intracellularly, the motoneuron arborizations were reconstructed at high spatial resolution. The neuronal model was constrained by the geometric data describing the numerized arborization. The electrotonic structure and Tx were computed under different Rm values to mimic a highly excited neuron (1 kOhm.cm2) and a neuron at rest (100 kOhm.cm2). The authors found that the shape and the size of the effective dendritic fields varied in the function of Rm. In the highly excited neuron, the effective dendritic field was reduced spatially by switching off most of the distal dendritic branches, which were disconnected functionally from the somata. At rest, the entire dendritic field was highly efficient in transferring current to the somata, but there was a lack of spatial discrimination. Because the large motoneurons are more sensitive to variations in the upper range of Rm, they switch off their distal dendrites before the small motoneurons. Thus, the same anatomic structure that shrinks or expands according to the background synaptic activity can select the types of its synaptic inputs. The results of this study demonstrate that these reconfigurations of the effective dendritic field of the motoneurons are activity‐dependent and geometry‐dependent. J. Comp. Neurol. 422:18–34, 2000. © 2000 Wiley‐Liss, Inc.
Orbitofrontal sulci of the human and macaque monkey brainChiavaras, Mary M.; Petrides, Michael
doi: 10.1002/(SICI)1096-9861(20000619)422:1<35::AID-CNE3>3.0.CO;2-Epmid: N/A
The present study investigated the orbitofrontal sulci in 100 normal adult human cerebral hemispheres by using magnetic resonance images that were transformed into the standardized proportional stereotaxic space most commonly used, that of Talairach and Tournoux (Talairach and Tournoux [1988]. Co‐planar stereotaxic atlas of the human brain. New York: Thieme). The patterns formed by the individual sulci were then examined and compared with those of the less convoluted macaque monkey brain. Four sulci forming a similar sulcal pattern were identified in both species. The olfactory sulcus occupies the most medial position forming the lateral border of the gyrus rectus. Lateral to this, the medial, lateral, and transverse orbital sulci form a pattern often resembling an “H,” “X,” or “K.” These sulci divide the orbitofrontal cortex into four major gyri: the medial, lateral, anterior, and posterior orbital gyri. Three major types of sulcal pattern were identified in both species based on the arrangement of these orbital sulci. Additional sulci were observed in the human brain, creating more complex patterns. Probability maps were constructed for the four main orbitofrontal sulci of the human brain. These maps provide a statistical description of the variability of the location of the orbitofrontal sulci within the three‐dimensional coordinate system of Talairach and Tournoux (Talairach and Tournoux [1988]. Co‐planar stereotaxic atlas of the human brain. New York: Thieme). Because these maps may be directly compared with any image transformed into the same standardized space, they provide a valuable tool for identifying and describing the location of functional or structural changes in the orbitofrontal region of the human brain. J. Comp. Neurol. 422:35–54, 2000. © 2000 Wiley‐Liss, Inc.
Neuroanatomy of cells expressing clock genes in Drosophila: Transgenic manipulation of the period and timeless genes to mark the perikarya of circadian pacemaker neurons and their projectionsKaneko, Maki; Hall, Jeffrey C.
doi: 10.1002/(SICI)1096-9861(20000619)422:1<66::AID-CNE5>3.0.CO;2-2pmid: 10842219
Subsets of brain neurons expressing the clock genes period (per) and timeless (tim) are involved in the generation of circadian behavioral rhythms. However, current knowledge of projection patterns of these neurons is limited to those immunoreactive to an antibody against a crustacean neuropeptide. The GAL4‐expression system was utilized to visualize neuronal processes from all per and tim‐expressing neurons in the central nervous system. Each of two types of GAL4‐driver fusion genes, per‐gal4 or tim‐gal4, was combined in transgenic flies with marker genes—lacZ, and sequences encoding green fluorescent protein or TAU protein—under the control of the GAL4‐responsive element UAS. This allowed visualization of the cytoplasm of GAL4‐expressing cells. Thus, neurites of clock neurons in the adult brain as well as those of larvae and pupae were revealed. Among the anatomical patterns revealed by per‐gal4‐ or tim‐gal4‐driven marker expression were a previously unknown, dorsally located neuronal cluster, along with the projections of these cells and of other dorsal neurons characterized in earlier studies only by the location of their perikarya. The similarity of projections from PER‐ or TIM‐containing neurons during development to those in the adult implies that these features of mature clock neurons are established by the larval stages. Neurons that have never been identified as PER‐ or TIM‐immunoreactive were also visualized in this assay system, indicating promoter activity of the clock genes in these cells and suggesting that their products cannot accumulate to detectable levels in certain neurons. J. Comp. Neurol. 422:66–94, 2000. © 2000 Wiley‐Liss, Inc.
Olivocochlear neurons sending axon collaterals into the ventral cochlear nucleus of the ratHorváth, Miklos; Kraus, K. Suzanne; Illing, Robert‐Benjamin
doi: 10.1002/(SICI)1096-9861(20000619)422:1<95::AID-CNE6>3.0.CO;2-#pmid: N/A
The olivocochlear projection constitutes the last stage of the descending auditory system in the mammalian brain. Its neurons reside in the superior olivary complex (SOC) and project to the inner and outer hair cell receptors in the cochlea. Olivocochlear neurons were also reported to send axon collaterals into the cochlear nucleus, but controversies about their number and about species differences persist. By injecting the fluorescent retrograde axonal tracers diamidino yellow and fast blue into the cochlea and the ventral cochlear nucleus (VCN), we studied the distribution and number of olivocochlear neurons with and without axon collaterals into the VCN of the rat. We found that olivocochlear neurons residing in the lateral superior olive (LSO), the intrinsic lateral olivocochlear cells (intrinsic LOCs), do not send axon collaterals into the VCN. By contrast, a majority, and possibly all, olivocochlear neurons residing in the ventral nucleus of the trapezoid body (VNTB), the medial olivocochlear cells (MOCs), do have such axon collaterals. These cells may thus affect processing in the ascending auditory pathway at the level of the receptors and concurrently at the level of the secondary sensory neurons in the cochlear nucleus. Belonging to the lateral olivocochlear system, shell neurons reside around the LSO and form a third group of olivocochlear cells (shell LOCs). Like intrinsic LOCs, they innervate the inner hair cells, but like MOCs they do, by means of axon collaterals, project into the VCN. These findings have implications for understanding both auditory signal processing and the plasticity responses that occur following loss of cochlear function. J. Comp. Neurol. 422:95–105, 2000. © 2000 Wiley‐Liss, Inc.
Ascending spinal systems in the fish, Prionotus carolinusFinger, Thomas E.
doi: 10.1002/(SICI)1096-9861(20000619)422:1<106::AID-CNE7>3.0.CO;2-Tpmid: 10842221
The fin rays of the pectoral fin of the sea robins (teleostei) are specialized chemosensory organs heavily invested with solitary chemoreceptor cells innervated only by spinal nerves. The rostral spinal cord of these animals is marked by accessory spinal lobes which are unique enlargements of the dorsal horn of the rostral spinal segments receiving input from the fin ray nerves. Horseradish peroxidase (HRP) and 1,1`‐dioctadecyl‐3,3,3`,3`‐tetramethylindocarbocyanine perchlorate (diI) were used as anterograde and retrograde tracers to examine the connectivity of these accessory lobes and the associated ascending spinal systems in the sea robin, Prionotus carolinus. The majority of dorsal root fibers terminate within the accessory lobes at or nearby their level of entrance into the spinal cord. A few dorsal root axons turn rostrally in the dorsolateral fasciculus to terminate in the lateral funicular complex situated at the spinomedullary junction. The lateral funicular complex also receives a heavy projection from the ipsilateral accessory lobes. In addition, it contains a few large neurons that project back onto the accessory lobes. Injections of either diI or HRP into the lateral funicular complex label fibers of the medial lemniscus which crosses the midline in the caudal medulla to ascend along the ventral margin of the contralateral rhombencephalon. Within the medulla, fibers leave the medial lemniscus to terminate in the inferior olive and in the ventrolateral medullary reticular formation. Upon reaching the midbrain, the medial lemniscus turns dorsally to terminate heavily in a lateral division of the torus semicircularis, in the ventral optic tectum, and in the lateral subnucleus of the nuc. preglomerulosus of the thalamus. Lesser projections also reach the posterior periventricular portion of the posterior tubercle with a few fibers terminating along the ventral, posterior margin of the ventromedial (VM) nucleus of the thalamus. The restricted projection to the ventral tectum is noteworthy in that this part of the tectum maintains the representation of the ventral visual field, that is, the area in which the fin rays lie. A prominent spinocerebellar system is also evident. Both direct and indirect spinocerebellar fibers can be followed through the dorsolateral fasciculus, with or without relay in the lateral funicular nucleus and terminating in a restricted portion of the granule cell layer of the ipsilateral corpus cerebelli. The similarities in connectivity of the spinal cord between the sea robins and other vertebrates are striking. It is especially notable because sea robins utilize the chemosensory input from the fin rays to localize food in the environment. Thus, although these fish use their spinal chemosense as other fishes use their external taste systems, the spinal chemosense apparently relies on the medial lemniscal system to guide this chemically driven feeding behavior. J. Comp. Neurol. 422:106–122, 2000. © 2000 Wiley‐Liss, Inc.
Distribution of voltage‐gated sodium channel α‐subunit and β‐subunit mRNAs in human hippocampal formation, cortex, and cerebellumWhitaker, William R.J.; Clare, Jeffrey J.; Powell, Andrew J.; Chen, Yu Hua; Faull, Richard L.M.; Emson, Piers C.
doi: 10.1002/(SICI)1096-9861(20000619)422:1<123::AID-CNE8>3.0.CO;2-Xpmid: 10842222
The distribution of mRNAs encoding voltage‐gated sodium channel α subunits (I, II, III, and VI) and β subunits (β1 and β2) was studied in selected regions of the human brain by Northern blot and in situ hybridisation experiments. Northern blot analysis showed that all regions studied exhibited heterogenous expression of sodium channel transcripts. In situ hybridisation experiments confirmed these findings and revealed a predominantly neuronal distribution. In the parahippocampal gyrus, subtypes II and VI and the β‐subunit mRNAs exhibited robust expression in the granule cells of the dentate gyrus and pyramidal cell layer of the hippocampus. Subtypes I and III showed moderate expression in granule cells and low expression in the pyramidal cell layer. Distinct expression patterns were also observed in the cortical layers of the middle frontal gyrus and in the entorhinal cortex. In particular, all subtypes exhibited higher levels of expression in cortical layers III, V, and VI compared with layers I and II. All subtypes were expressed in the granular layer of the cerebellum, whereas specific expression of subtypes I, VI, β1, and β2 mRNAs was observed in Purkinje cells. Subtypes I, VI, and β1 mRNAs were expressed, at varying levels, in the pyramidal cells of the deep cerebellar nuclei. These data indicate that, as in rat, human brain sodium channel mRNAs have a distinct regional distribution, with individual cell types expressing different compliments of sodium channels. The differential distribution of sodium channel subtypes suggest that they have distinct roles that are likely to be of paramount importance in maintaining the functional heterogeneity of central nervous system neurons. J. Comp. Neurol. 422:123–139, 2000. © 2000 Wiley‐Liss, Inc.
Development of inhibitory circuitry in visual and auditory cortex of postnatal ferrets: Immunocytochemical localization of calbindin‐ and parvalbumin‐containing neuronsGao, Wen Jun; Wormington, Amy B.; Newman, Douglas E.; Pallas, Sarah L.
doi: 10.1002/(SICI)1096-9861(20000619)422:1<140::AID-CNE9>3.0.CO;2-0pmid: 10842223
The inhibitory neurotransmitter γ‐aminobutyric acid (GABA) is thought to play an important role in activity‐dependent stages of brain development. Previous studies have shown that different functional subclasses of cortical GABA‐containing neurons can be distinguished by antibodies to the calcium‐binding proteins parvalbumin and calbindin. Thus insight into the development of distinct subsets of inhibitory cortical circuits can be gained by studying the development of these calcium‐binding protein‐containing neurons. Previous studies in several mammalian species have suggested that calcium‐binding proteins are upregulated in sensory cortex when thalamocortical afferents arrive. In ferrets, the ingrowth of thalamic axons into cortex occurs well into postnatal development, allowing access to early stages of cortical development and calcium‐binding protein expression. We find in ferrets that both parvalbumin‐ and calbindin‐immunoreactivity are present in primary visual and primary auditory cortex long before thalamocortical synapse formation, but that there is a sharp decline in immunoreactivity by postnatal day 20. Day 20 in ferrets corresponds to postnatal day 1 in cats, and thus previous studies in postnatal cats would have missed this early pattern of calcium‐binding protein distribution. Another surprising finding is that the proportion of parvalbumin‐ and calbindin‐immunoreactive neurons peaks secondarily late in development, between P60 and adulthood. This result suggests that the parvalbumin‐ and calbindin‐containing subclasses of nonpyramidal neurons remain immature until late in the critical period for cortical plasticity, and that they are positioned to play an important role in experience‐dependent modification of cortical circuits. J. Comp. Neurol. 422:140–157, 2000. © 2000 Wiley‐Liss, Inc.