bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of selective brainstem or spinal cord lesions on treadmill locomotion evoked by stimulation of the mesencephalic or pontomedullary locomotor regions
Authors: Noga BR , Kriellaars DJ , Jordan LM
Published: March 2018

The descending pathways from the brainstem locomotor areas were investigated by utilizing reversible cooling (to block synaptic or fiber transmission) and irreversible subtotal lesions of the brainstem or spinal cord (C2-C3 level). Experiments were conducted on decerebrate cats induced to walk on a treadmill by electrical stimulation of the brainstem. Locomotion produced by stimulation of the mesencephalic locomotor region (MLR) was not abolished by caudal brainstem lesions that isolated the lateral tegmentum or by extended rostral/caudal dorsal hemisections of the spinal cord. These results demonstrate that the MLR does not require a pathway projecting through the lateral tegmentum of the brainstem or the dorsal half of the spinal cord, as previously suggested (Mori et al., 1977, 1978b; Shik and Yagodnitsyn, 1978; Shik, 1983). Rather, the results indicate that the descending pathway originating from the MLR projects through the medial reticular formation (MedRF) and the ventral half of the spinal cord. Locomotion produced by stimulation of the pontomedullary locomotor region (PLR) was blocked by reversible cooling of either the MedRF or the ventrolateral funiculus of the spinal cord. In some cases, locomotion could be produced by stimulation of the PLR following extended dorsal hemisections of the spinal cord. These results demonstrate that the PLR can also produce locomotion by activation of cells in the MedRF that project caudally through the ventral half of the spinal cord. Stimulation of the PLR could also elicit locomotion following its surgical isolation from the MedRF of the brainstem. Furthermore, lesions of the dorsal spinal cord resulted in the loss of PLR-evoked locomotion in some, but not all, cases. Thus, an alternative projection of the PLR through the dorsal half of the spinal cord (Kazennikov et al., 1980, 1983a,b; Shik, 1983) cannot be ruled out. Overall, these results demonstrate that the PLR is not an essential component of the motor pathway originating from the MLR. The organizational scheme of “brainstem locomotor regions” is discussed in the context of recent information demonstrating a link between the sensory component of the trigeminal system and locomotor pathways (Noga et al., 1988).
The segmentation of the leech nervous system is prefigured by myogenic cells at the embryonic midline expressing a muscle-specific matrix protein
Authors: Thorey IS , Zipser B
Published: March 2018

In the leech, adult muscle cells and embryonic mesodermal/myogenic cells express the cell-type-specific Laz 10–1 epitope on extracellular matrix-associated proteins. Using this muscle-specific epitope as a marker, we found the following correlations between the development of identifiable myogenic cells at the embryonic midline and the segmentation of the leech CNS into 32 reiterative ganglia. (1) During the production of mesodermal and ectodermal stem cells, cell bodies of midline myogenic cells create 32 anterior-posterior intervals along the midline of the embryonic germinal plate. The mesoblasts then rearrange themselves into 32 somites whose spacing follows the intervals between the midline myogenic cell bodies. (2) Bilateral segmental zones of myogenic differentiation originate in juxtaposition to the midline myogenic cells. (3) The first two types of muscle precursors develop from midline and adjacent bilateral myogenic cells; they are the precursors of the CNS muscles and of three groups of ventral blood sinus muscles. These two types of muscle precursors demarcate the boundaries of the territory within which neuroblasts proliferate and coalesce into segmental hemiganglionic primordia: Cell bodies of muscle precursors, like cornerstones, demarcate the anterior and posterior borders of the hemiganglionic primordia; their longitudinal processes surround the expanding hemiganglionic primordia on the medial, lateral, dorsal, and ventral aspect. The contours of muscle precursors and midline myogenic cells are sharply delineated by immunohistochemical staining of the Laz 10–1 epitopes. In contrast, undifferentiated mesoblasts are surrounded by diffuse layers of stained epitopes, which are expressed at fluctuating levels. Because elevated levels of this matrix epitope are associated with mesodermal/myogenic cells undergoing morphogenetic rearrangements, it may participate in the molecular mechanisms underlying the segmentation of the nervous system.
Synaptic physiology of horizontal connections in the cat's visual cortex
Authors: Hirsch JA , Gilbert CD
Published: March 2018

Horizontal connections are a principal component of intrinsic cortical circuitry. They arise mainly from pyramidal cells and course parallel to the brain's surface for distances as long as 8 mm, linking columns with shared orientation preference and allowing cells to integrate visual information from outside their receptive fields. We examined the synaptic physiology of the horizontal pathway in slices of the cat's striate cortex and found that activating lateral fibers produced both excitation and inhibition. We recorded the postsynaptic responses of identified pyramidal cells in layer 2 + 3 of area 17 to electrical shocks applied at three sites: in the home column of the impaled neuron either in layer 2 + 3 or 4, or at a lateral distance of 0.9–3 mm in layer 2 + 3. Within the home column, suprathreshold stimuli produced compound EPSPs with action potentials, followed by fast, GABAAergic IPSPs and a slower, GABABergic IPSP. For the distant stimulating site, the threshold response was an EPSP. Stronger shocks frequently evoked a disynaptic, GABAAergic IPSP that truncated the EPSP and could dominate the postsynaptic response. At the resting potential, the horizontally evoked EPSP was too small to elicit spikes. With depolarization of the membrane, however, it grew several hundred-fold. This amplification was blocked by N-(2,6-dimethylphenylcarbamoylmethyl)triethylammonium bromide (QX-314), but not by 2-amino-5-phosphonovalerate (APV), indicating that it was mediated by Na+ channels, rather than by NMDA receptors. We propose that the horizontal connections provide the means for stimuli outside the receptive field to modulate activity elicited within its confines. The voltage-dependent enhancement of the laterally evoked EPSP may explain why stimulating the surround by itself fails to drive cells but can facilitate their response to stimuli within the receptive field. The ability to initiate disynaptic inhibition from lateral sites shows that recruiting appropriate groups of horizontal fibers can also have a suppressive effect. Thus, the effect of horizontal input is state dependent, with the size and sign of the laterally evoked response changing according to the balance of converging inputs.
Learning-dependent neuronal activity in the premotor cortex: activity during the acquisition of conditional motor associations
Authors: Mitz AR , Godschalk M , Wise SP
Published: March 2018

It has been proposed that the premotor cortex plays a role in the selection of motor programs based on environmental context. To test this hypothesis, we recorded the activity of single neurons as monkeys learned visuomotor associations. The hypothesis predicts that task- related premotor cortical activity before learning should differ from that afterward. We found that a substantial population of premotor cortex neurons, over half of those adequately tested, showed the predicted learning-dependent changes in activity. The present findings support a role for premotor cortex in motor preparation, generally, and suggest a specific role in the selection of movements on the basis of arbitrary associations.
Spinal 5-HT3 receptor-mediated antinociception: possible release of GABA
Authors: Alhaider AA , Lei SZ , Wilcox GL
Published: March 2018

Although 5-HT is clearly involved in spinal analgesia, its mode of action remains obscure, perhaps because it has multiple and often opposing effects mediated by its multiple receptor subtypes. This investigation uses selective agonists and antagonists directed at the most recently defined class of 5-HT receptors (5-HT3 receptors) in behavioral and electrophysiological studies of nociception in the spinal cord of rodents. The results demonstrate uniformly inhibitory effects of a selective 5-HT3 agonist on responses to noxious stimuli. Intrathecally administered 2-methyl 5-HT produced dose-dependent antinociception in the tail-flick test and inhibited behaviors elicited by intrathecally administered agonists for excitatory amino acid and neurokinin receptors, namely NMDA and substance P (SP). All 20 dorsal horn neurons we examined, which projected to the brain and responded to both noxious stimuli and NMDA, were inhibited in a current-related manner by this 5-HT3 agonist applied iontophoretically. Both the behavioral and electrophysiological effects were blocked not only by the 5-HT3 antagonists zacopride and ICS 205–930, but also by antagonists to the inhibitory amino acid GABA. Therefore, 5-HT via an action at 5-HT3 receptors may evoked release of GABA, which may in turn inhibit nociceptive transmission at a site postsynaptic to terminals of primary afferent fibers. If the descending serotonergic analgesic system in humans operates similarly, understanding it may enable the development of new nonopioid, nonaddictive analgesics.
Terminal degeneration and synaptic disassembly following receptor photoablation in the retina of the fly's compound eye
Authors: Brandstatter JH , Shaw SR , Meinertzhagen IA
Published: March 2018

A long-term objective of our studies on the first optic neuropil (or lamina) underlying the fly's compound eye is to explore how afferent photoreceptor synapses disappear during normal adult experience. To increase the frequency of this loss and the chances for its detection artificially, we have examined in this study the synapses during the degeneration of their presynaptic elements, the synaptic terminals of the receptor cells. This may be reliably procured by illuminating for 12 min with strong green light eyes that have received an injection of the dye sulforhodamine 101 (Picaud et al., 1988). The lesion is local and develops rapidly. Degeneration among terminals is progressive but asynchronous. There are several different types of degeneration, most interpretable as stages in a temporal progression after illumination- induced injury. Degenerative changes include shrinkage and darkening of terminals and mitochondrial swelling. Synaptic sites are lost in a defined sequence: (1) the T-shaped presynaptic ribbon disappears first; (2) the members of what is normally a tetrad of postsynaptic elements withdraw as an ensemble from the receptor terminal's membrane, and the surrounding epithelial glial cells extend between former pre- and postsynaptic partners; and (3) the postsynaptic elements then separate from each other. In the most rapidly affected terminals, the frequencies for those synaptic sites at which both presynaptic ribbons and postsynaptic elements remain intact decline by 85%, even in the first 8 hr postillumination.
The development of afferent projections to the robust archistriatal nucleus in male zebra finches: a quantitative electron microscopic study
Authors: Herrmann K , Arnold AP
Published: March 2018

Because the projections into the robust nucleus of the archistriatum (RA) are thought to play important roles in song learning and sexual differentiation of the zebra finch (Poephila guttata), quantitative electron microscopic techniques were used to measure the development of synaptic input to the neuropil of RA in this species. Two nuclei [hyperstriatum ventrale pars caudalis (HVc) and lateral magnocellular nucleus of the anterior neostriatum (IMAN)] that send projections to RA were lesioned at each of three different ages: 25 d after hatching, 53 d, and adulthood. In tissue from RA processed for conventional electron microscopy, lesion-induced degeneration was used to identify synapses from either HVc or IMAN. Axosomatic synapses were excluded from analysis. In control (unlesioned) animals, the density of synapses in neuropil increased slightly between days 28 and 56 and remained constant thereafter. Because of a large increase in the volume of RA, the total number of synapses in neuropil of RA tripled between days 28 and 56 and decreased significantly between day 56 and adulthood. The density and total number of synapses in neuropil originating from HVc increased significantly between days 25 and 53, but did not change significantly thereafter. In contrast, the density and total number of synapses from IMAN decreased significantly between days 25 and 53 and did not change thereafter. Presynaptic terminals from IMAN were larger than those from HVc. These data demonstrate that the most rapid phase of song learning is accompanied by a major rearrangement of synaptic contacts into RA that stem from HVc and IMAN.
Expression of ion channels and mutational effects in giant Drosophila neurons differentiated from cell division-arrested embryonic neuroblasts
Authors: Saito M , Wu CF
Published: March 2018

A culture system of “giant” Drosophila neurons derived from cytokinesis- arrested embryonic neuroblasts was developed to overcome the technical difficulties usually encountered in studying small Drosophila neurons. Cytochalasin B-treated neuroblasts differentiated into giant multinucleated cells that displayed neuronal morphology and neuron- specific markers (Wu et al., 1990). Here, we report that these giant neurons express different excitability patterns and membrane channels similar to those reported in excitable tissues of Drosophila. Individual neurons exhibited distinct all-or-none or graded voltage responses upon current injection. Both current- and voltage-clamp recordings could be performed on the same neuron because of the large cell size, thus making it possible to elucidate the functional role of the individual types of channels. By using pharmacological agents and ion substitution, the following currents were identified in these giant neurons: inward Na+ and Ca2+ currents and outward voltage-activated (the A-type and delayed rectifier) and Ca(2+)-activated K+ currents. In addition, we found a tetrodotoxin (TTX)-sensitive, Na(+)-dependent outward K+ current and a persistent component of an inward Na+ current, which have not been reported in Drosophila previously. This culture system can be used to analyze the mutational perturbations in ion channels and the resultant alterations in membrane excitability. Neurons from the mutant slowpoke (slo), which is known to lack a component of the Ca(2+)-activated K+ currents in muscles, exhibited prolonged action potentials associated with defects in the Ca(2+)- activated K+ current. This abnormality appeared to be more severe in the neurites than in the soma.
Release of endogenous excitatory amino acids from ON-type bipolar cells isolated from the goldfish retina
Authors: Tachibana M , Okada T
Published: March 2018

Excitatory amino acids are presumed to be the transmitter of retinal bipolar cells. However, one of the essential criteria for the identification of the transmitter, its release from the cells upon depolarization, has not been demonstrated. This article examines the release of endogenous excitatory amino acids from bipolar cells and correlates this release with the influx of Ca2+. Bipolar cells with a large, bulblike axon terminal (ON-type cells with mixed inputs from rods and cones) were enzymatically isolated from the goldfish retina. Horizontal cells dissociated from the catfish retina were used as a probe of excitatory amino acids, because these cells can detect submicromolar concentrations of L-glutamate with high selectivity. An isolated bipolar cell was closely apposed to a dissociated horizontal cell, and each cell was voltage clamped by a patch pipette in the whole- cell clamp configuration. When the bipolar cell was depolarized from - 60 mV to a potential more positive than -40 mV using a 500-msec voltage pulse, an outward current (greater than 20 pA) was recorded from the apposed horizontal cell, which was maintained at +40 mV. The reversal potential of the current induced by the substance released from bipolar cells (Irs) was close to 0 mV and was almost identical to the responses evoked with ionophoretically applied L-glutamate. Both reversal potentials were shifted to the same, more negative value when the external Na+ was replaced with choline. Furthermore, the Irs was suppressed reversibly by the application of kynurenic acid, a glutamate antagonist. When the Ca current (ICa) of the bipolar cell was blocked by Cd2+, the Irs also disappeared. The peak amplitude of Irs was closely related to that of the ICa. We conclude that mixed rod/cone ON- type bipolar cells of the goldfish retina release an endogenous excitatory amino acid or a closely related compound in a Ca(2+)- dependent manner.
Internalization and processing of basic fibroblast growth factor by neurons and astrocytes
Authors: Walicke PA , Baird A
Published: March 2018

The fate of iodinated basic fibroblast growth factor (FGF) after its binding to cultured astrocytes and hippocampal neurons was studied. Autoradiography after light and electron microscopy establishes that, if cells are returned to 37 degrees C, the 125I-basic FGF bound internalizes into vesicles in the cytoplasm, localizes to the perinuclear cytoplasm, and is translocated to chromatin structures of the nucleus. The radiolabeled protein is long-lived, a finding confirmed by biochemical analyses. Polyacrylamide gel electrophoresis and autoradiography of both hippocampal neurons and astrocyte extracts reveal that these cells internalize 125I-basic FGF and then metabolize it to three major heparin-binding peptides with molecular weights of 15.5, 9, and 4 kDa. These peptides are initially detected 16 hr after binding to neurons and 4 hr after binding to astrocytes but are still detectable 48 and 16 hr, respectively, after initial binding (though present at lower levels). Immunoprecipitation with sequence-specific antisera to basic FGF reveals that the 15.5-kDa fragment is generated by cleavage at the carboxyl terminus, that the 9-kDa peptide contains the sequences between residues 30 and 87, and the 4-kDa peptide is a C- terminus fragment containing the sequence of basic FGF(106–120) but without basic FGF(139–146) immunoreactivity. The internalization of basic FGF is required for this processing; the treatment of cells with trypsin and 2 M NaCl at different times after binding can only prevent the metabolism of basic FGF if it is performed immediately after binding. Similarly, WGA, which inhibits basic FGF binding to its high- affinity receptor, prevents the metabolism of basic FGF. The possible significance of a metabolic pathway that is responsible for the processing of basic FGF after its internalization by cells in the CNS is discussed in light of its potential function as a neurotrophic factor.
Voltage-dependent calcium currents in Purkinje cells from rat cerebellar vermis
Authors: Regan LJ
Published: March 2018

Whole-cell patch clamp recording was used to characterize calcium currents in Purkinje cells dissociated from the cerebellar vermis of 1- 3-week postnatal rats. A subset of Purkinje cells had a low-threshold, transient current similar to the T-type current in peripheral neurons. All Purkinje cells had a high-threshold, slowly inactivating current. Only a small component of the high-threshold current was sensitive to dihydropyridine (DHP) antagonists or to the dihydropyridine agonist BAY K8644. omega-Conotoxin had very little effect on the high-threshold current. The results suggest that these Purkinje cells have at least three types of calcium channels: T-type channels (present in only a fraction of cells), DHP-sensitive L-type channels (contributing a small fraction of the high-threshold current), and a predominant type of high- threshold channel that is pharmacologically distinct from L-type and N- type channels characterized in peripheral neurons.
The site for initiation of action potential discharge over the somatodendritic axis of rat hippocampal CA1 pyramidal neurons
Authors: Turner RW , Meyers DE , Richardson TL , Barker JL
Published: March 2018

Early electrophysiological studies in the mammalian hippocampus reported that orthodromic depolarization of pyramidal cells evoked action potential discharge (presumed Na+ dependent) both at the axon hillock and at one or more sites in the dendritic arborization (Cragg and Hamlyn, 1955; Andersen, 1959, 1960; Spencer and Kandel, 1961; Andersen and Lomo, 1966). Although tetrodotoxin (TTX)-sensitive spikes have been recorded at the dendritic level (Wong et al., 1979; Benardo et al., 1982; Miyakawa and Kato, 1986; Turner et al., 1989), the site for initiation of these potentials has not yet been determined. In this study, we examine the site for initiation of Na+ spike discharge over the cell axis of rat hippocampal CA1 pyramidal neurons. Intrasomatic and intradendritic recordings were obtained from pyramidal neurons of hippocampal slices maintained in vitro. Spike discharge was evoked by alvear (antidromic) stimulation or orthodromically by stimulation of afferent inputs in stratum oriens (SO) or stratum radiatum (SR). Antidromic and orthodromic spikes were greatest in amplitude in somatic recordings and declined over the apical dendritic axis, while spike half-width was shortest at the cell body and increased with distance from stratum pyramidale. Measurements of orthodromic spike threshold revealed that the only location at which spikes discharged at a consistent membrane potential at threshold intensity (voltage threshold) was the cell body region. Finally, at threshold intensity, SR-evoked intradendritic spikes were blocked by local application of TTX in stratum pyramidale, while spike blockade at suprathreshold intensity required the diffusion of TTX into the apical dendritic region. These results indicate that, for threshold intensities of stimulation, antidromic and orthodromic spike discharge in CA1 pyramidal cells is initiated in the region of the cell body layer, subsequently conducting over the apical dendrites in a retrograde fashion. In contrast, SR-evoked orthodromic spike discharge exhibits an intensity-dependent shift in the site of origin up to 200 microns within the apical dendritic arborization.
Mineralocorticoid hormones suppress serotonin-induced hyperpolarization of rat hippocampal CA1 neurons
Authors: Joels M , Hesen W , de Kloet ER
Published: March 2018

Pyramidal neurons in the rat CA1 hippocampal area contain intracellular mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) to which the adrenal hormone corticosterone can bind with differential affinity. The pyramidal neurons also have high amounts of 5-HT1a receptors, which mediate a membrane hyperpolarization. With intracellular recording in vitro, we found that selective occupation of MRs suppresses the 5-HT-induced hyperpolarization of CA1 pyramidal neurons. The suppression of 5-HT responses was observed 1–4 hr after a brief (20-min) application of the steroids. Binding properties of the 5- HT1a receptor were not significantly affected by in vitro steroid application. Furthermore, responses to the GABAB agonist baclofen were not changed after treatment with MR ligands, implying that the K+ conductance to which both GABAB and 5-HT1a receptors are linked is also no target for the steroid action. The MR-mediated effect on 5-HT responsiveness potentially enhances cellular activity. Because activation of GRs was previously found to suppress norepinephrine- induced excitability in the same neurons, the data support the concept that cellular homeostasis in the hippocampus is under control of corticosterone via coordinative, antagonistic MR- and GR-mediated events.
The Lurcher cerebellar mutant phenotype is not expressed on a staggerer mutant background
Authors: Messer A , Eisenberg B , Plummer J
Published: March 2018

The hierarchy of the various processes responsible for the development of the complex, elaborated Purkinje cell can be examined by taking advantage of a series of spontaneous mutations that affect cerebellar development in the mouse. This study uses double mutants containing genes for two separate hereditary cerebellar mutations that have been shown to act intrinsically in Purkinje cells in order to investigate the time course and modes of action of these mutations. Lurcher mice show 100% degeneration of Purkinje cells, starting during the second postnatal week, while staggerer mice show reduced numbers of Purkinje cells in a distinctive mediolateral distribution from the time of birth, with the remainder grossly stunted. When these mutations are combined genetically, mice shown by progeny tests to harbor both staggerer and Lurcher genotypes exhibit staggerer-like behavior and overall cerebellar morphology; they also do not lose 100% of their Purkinje cells, as Lurcher mutants would otherwise do. Instead, they show a characteristic staggerer cerebellar pathology. We conclude that the intrinsic action of the staggerer gene in Purkinje cells occurs earlier in development than do effects of the Lurcher gene, and that the action of the staggerer gene prevents Purkinje cells from acquiring the characteristics required for the cytotoxic action of the Lurcher gene.
Locus coeruleus involvement in the learning of classically conditioned bradycardia
Authors: Harris GC , Fitzgerald RD
Published: March 2018

Opioid agonists are known to inhibit the activity of locus coeruleus (LC) neurons. In this study, microinjections of the mu-opioid agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO; 1.6 microM) bilaterally into the LC caused a significant impairment in the development of a heart-rate (HR) conditioned response (CR). The adverse effect of DAMGO on the HR CR could be reversed with naltrexone pretreatment. Microinjections of DAMGO into the periaqueductal gray, parabrachial nucleus, or fourth ventricle structures 1–2 mm away from the LC had no effects on the development of an HR CR. We conclude that central noradrenergic activity as mediated by the LC is critically involved in the learning and retention of conditioned cardiovascular responses.
c-fos mRNA, Fos, and Fos-related antigen induction by hypertonic saline and stress
Authors: Sharp FR , Sagar SM , Hicks K , Lowenstein D , Hisanaga K
Published: March 2018

The induction of c-fos mRNA was assessed using Northern blots and in situ hybridization in adult rats administered hypertonic saline (HS) and isotonic saline (IS). HS induced c-fos mRNA in magnocellular paraventricular nucleus (PVNm), parvocellular paraventricular nucleus (PVNp), supraoptic nucleus (SON), and lamina terminalis (LMT). This occurred within 5 min, peaked at 30n60 min, and disappeared by 180 min. Fos protein, detected using a specific monoclonal antibody, was maximal at 1–2 hr and disappeared 4–8 hr after HS administration. This confirms observations showing that the c-fos gene response is transient even in the presence of a continuing stimulus. In contrast, Fos-like immunoreactivity (FLI), detected using two polyclonal antisera, was observed in PVNm, PVNp, SON, and LMT for 1–24 hr during continuous osmotic stimulation. Moreover, FLI was observable in these structures for 7 d in rats administered HS and allowed to drink water ad libitum beginning 24 hr later. At times greater than 8 hr, FLI presumably represents Fos-related antigens (FRA), proteins immunologically and functionally related to Fos, whose expression is much more prolonged than authentic Fos following the osmotic stimulus. In addition to induction of c-fos expression in regions specifically involved in osmotic regulation, HS injections also induced c-fos in many other forebrain regions. In order to assess the induction of c-fos mRNA due to the “stress” of the injections, rats injected with isotonic saline were compared to uninjected controls. Isotonic saline injections induced c-fos mRNA in the PVNp, anterior hypothalamus, suprachiasmatic nucleus, cingulate gyrus, neocortex, ventral lateral septal nucleus, piriform cortex, hippocampal pyramidal and dentate granule neurons, paraventricular and intralaminar thalamic nuclei, bed nuclei of stria terminalis, cortical and medial amygdaloid nuclei, and other structures. In accord with other work, we interpret this pattern of c- fos expression to result from the stress of handling and injections. Since Fos and FRA probably bind to the promoters of target genes and regulate their expression, they likely mediate biochemical changes in the cells activated by the osmotic and stressful stimuli. Whereas the Fos signal is transient, FRA may act on target genes for the duration of the stimulus or longer.
Chronic testosterone treatment impairs vocal learning in male zebra finches during a restricted period of development
Authors: Korsia S , Bottjer SW
Published: March 2018

To study the effects of chronic exposure to testosterone on song behavior development, we administered various amounts of testosterone to juvenile male zebra finches during different periods of song acquisition. We report that testosterone exposure during development profoundly impairs song learning in juvenile males. The effects of the hormone do not seem to be dose related but vary according to the period of life during which testosterone is administered. Exposure to testosterone starting before day 40 and lasting until adulthood decreases the number of syllables in the birds' repertoire and increases the number of phrases per bout of singing. In addition to these changes in the “syntactical” features of song, acoustic abnormalities are also present in the song syllables of males that begin to receive testosterone during the first month of life. Administration of testosterone during only the first 3 weeks of life produces acoustic abnormalities but has no effect on repertoire size or bout structure. Birds receiving the hormone between 20 and 40 d of age develop both acoustic abnormalities and a reduced repertoire size, but their song bouts contain a normal number of song phrases. Exposure to testosterone starting on day 40 produce no behavioral abnormalities. These results indicate that normal song development requires a period of low levels of circulating testosterone and also provide support for the idea that vocal learning entails a progressive sequence of events.
Isolation and functional characterization of Schwann cells derived from adult peripheral nerve
Authors: Morrissey TK , Kleitman N , Bunge RP
Published: March 2018

To facilitate the development of autologous transplantation techniques with which to test the ability of Schwann cell (ScC) implantations to treat nervous system injury, we have developed a method for procuring large, essentially pure populations of ScCs from adult peripheral nerve. By allowing small explants of peripheral nerve trunk to undergo axonal and myelin breakdown in vitro, rather than dissociating the nerve immediately after harvest, we are able to (1) rid the explant of nearly all fibroblasts and (2) capitalize on the intrinsic ScC mitogenic response to peripheral nerve degeneration. Here, we describe a method that yields up to 98% pure ScC populations from adult rat sciatic nerve (based on cell soma and nuclear morphology, S100 staining, and behavior of dissociated cells on neurites) at cell yields of greater than 2 x 10(4) cells/mg of starting nerve weight. The purification technique was successfully applied to human tissue; human phrenic nerve yielded 98% pure ScC populations at cell yields of 2 x 10(4) cells/mg of initial nerve weight. Similar to neonatally derived ScCs, adult rat cells can be expanded in coculture with dorsal root ganglion (DRG) neurons or in isolation in the presence of glial growth factor and forskolin. Cells expanded indefinitely on DRG neurons, or up to 10 weeks on chemical mitogens, return to quiescence following removal of the mitogenic stimulus. Expanded adult-derived rat ScCs retain functional capacity, as evidenced by their ability to myelinate DRG neurites and to support regeneration of processes from embryonic rat retinal explants.
Response of facial and rubrospinal neurons to axotomy: changes in mRNA expression for cytoskeletal proteins and GAP-43
Authors: Tetzlaff W , Alexander SW , Miller FD , Bisby MA
Published: March 2018

Neurons confined within the mammalian CNS usually do not regenerate after axonal injury, while axonal regeneration is the rule in the PNS. It has been hypothesized that this may be related to differences in the microenvironment of the PNS versus CNS and to differences in the neuronal response to injury. In order to test the latter hypothesis, we compared changes in gene expression after axotomy in two populations of neurons: rat facial motoneurons and rat rubrospinal neurons. In situ hybridization with cDNA probes for the medium and light neurofilament protein revealed a reduced mRNA content in both facial and rubrospinal neurons at all times investigated (i.e., 1, 2, and 3 weeks after axotomy). On the other hand, mRNAs for actin and tubulin were increased in both neuronal populations during the first week after axotomy. While this increase was sustained in facial motoneurons for several weeks, total tubulin mRNA and actin mRNA were decreased in rubrospinal neurons at 2 and 3 weeks after axotomy, coincident with their atrophy. The developmentally regulated T alpha 1 tubulin mRNA, which was previously shown to be reexpressed in facial motoneurons after axotomy, was elevated severalfold in axotomized rubrospinal neurons, and increased levels persisted in some rubrospinal neurons as late as 7 weeks after axotomy. Similarly, the developmentally regulated GAP-43 mRNA increased in both axotomized facial and rubrospinal neurons, and increased levels were sustained in some axotomized rubrospinal neurons for at least 7 weeks. The response of rubrospinal neurons to axotomy in the cervical spinal cord is, in the first week, qualitatively similar to the response of facial motoneurons. However, by 2 weeks after axotomy there is a generalized reduction in mRNA levels for all three cytoskeletal proteins that is associated with neuronal atrophy. During this period, mRNA levels for the two specific markers of the growth state, T alpha 1 tubulin and GAP-43, remain elevated. Thus, axotomy of rubrospinal neurons appears to set in motion two independent events. First, an axotomy signal initiates a cell-body reaction similar to that of PNS neurons, including increased mRNA levels for T alpha 1 tubulin and GAP- 43. Later, a generalized cellular atrophy and decrease in mRNA levels occur without reversing the specific responses of T alpha 1 and GAP-43 to axotomy. We conclude that the failure of rubrospinal neurons to regenerate is not due to a failure to initiate gene-expression changes characteristic of regenerating peripheral neurons.
Intracellular calcium concentrations during "chemical hypoxia" and excitotoxic neuronal injury
Authors: Dubinsky JM , Rothman SM
Published: March 2018

Because hypoxic/ischemic neurodegeneration appears to be in part linked to glutamate neurotoxicity, we measured intracellular calcium (Ca2+i) levels in cultured hippocampal neurons during exposure to toxic doses of glutamate (GLU) and to an anoxic environment simulated by sodium cyanide (NaCN). Changes in Ca2+i produced by cyanide greatly exceeded those induced by GLU. The NaCN response was mimicked when oxidative metabolism was also disrupted by sodium azide, oligomycin, or dinitrophenol. Noncompetitive NMDA receptor antagonists and enzymatic GLU degradation abolished the GLU-induced Ca2+i increases and attenuated those produced by NaCN. Only NaCN-induced increases were blocked when dantrolene and ruthenium red were applied to prevent release from intracellular pools. All responses were reduced proportionally in the absence of added external calcium. These results suggest that extracellular GLU accumulation and subsequent activation of GLU receptors were involved in the NaCN response. During such metabolic compromise, however, GLU-induced elevations of Ca2+i were enormously amplified. In parallel toxicity studies, NaCN was not neurotoxic despite the large elevations in Ca2+i, indicating that a general elevation in cytoplasmic calcium does not necessarily predict neurodegeneration.
Organization of hindlimb muscle afferent projections to lumbosacral motoneurons in the chick embryo
Authors: Lee MT , O'Donovan MJ
Published: March 2018

We have examined the organization of muscle afferent projections to motoneurons in the lumbosacral spinal cord of chick embryos between stage 37, when muscle afferents first reach the motor nucleus, and stage 44, which is just before hatching. Connectivity between afferents and motoneurons was assessed by stimulating individual muscle nerves and recording the resulting motoneuron synaptic potentials intracellularly or electrotonically from other muscle nerves. Most of the recordings were made in the presence of DL-2-amino-5- phosphonovaleric acid (APV), picrotoxin, and strychnine to block long- latency excitatory and inhibitory pathways. Activation of muscle afferents evoked slow, positive potentials in muscle nerves but not in cutaneous nerves. These potentials were abolished in 0 mM Ca2+, 2mM Mn2+ solutions, indicating that they were generated by the action of chemical synapses. The muscle nerve recordings revealed a wide-spread pattern of excitatory connections between afferents and motoneurons innervating six different thigh muscles, which were not organized according to synergist-antagonist relationships. This pattern of connectivity was confirmed using intracellular recording from identified motoneurons, which allowed the latency of the responses to be determined. Short-latency potentials in motoneurons were produced by activation of homonymous afferents and the heteronymous afferents innervating the hip flexors sartorius and anterior iliotibialis. Stimulation of anterior iliotibialis afferents also resulted in some short-latency excitatory postsynaptic potentials (EPSPs) in motoneurons innervating the knee extensor femorotibialis, though other connections were of longer latency. Afferents from the adductor, a hip extensor, did not evoke short-latency EPSPs in any of these three types of motoneurons. Short-latency, but not long-latency EPSPs, persisted during repetitive stimulation at 5 Hz, suggesting that they were mediated monosynaptically. Long-latency, fatigue-sensitive potentials were maintained in the presence of APV, picrotoxin, and strychnine, suggesting that polysynaptic pathways utilize non-NMDA receptors as well as NMDA receptors. We found no difference in the pattern of inputs to femorotibialis motoneurons between stage 37–39 and near hatching at stage 44, suggesting muscle afferent projections to these motoneurons are correct at stage 37, when the afferents first reach the lateral motor column in substantial numbers.
Genetic hypothyroid mice: normal cerebellar morphology but altered glycerol-3-phosphate dehydrogenase in Bergmann glia
Authors: Sugisaki T , Noguchi T , Beamer WG , Kozak LP
Published: March 2018

The present study was undertaken to investigate the effects of thyroid deficiency on cerebellar development with mouse endocrine genetic models. Four types of mutant mice, the growth hormone- and thyroid hormone-deficient Snell dwarf mouse (dw/dw), the growth hormone- deficient little mouse (lit/lit), the primary hypothyroid mouse (hyt/hyt), and the congenital genital goiter mouse (cog/cog) were analyzed for expression of the glial enzyme marker glycerol-3-phosphate dehydrogenase (GPDH) and several other marker proteins. GPDH expression, as determined by enzyme activity and Northern blot analysis, was reduced by about 50% in the cerebellum and brainstem of the three hypothyroid mutant mice. No reduced expression was found in any region of the brain of the growth hormone-deficient lit/lit mutant. Visualization of GPDH by immunohistology showed that the immunoreactive enzyme was strikingly reduced in the Bergmann glial cells of dw/dw, hyt/hyt, and cog/cog mutant mice, particularly in the radial glial processes. To evaluate the specificity of the effect on GPDH expression, we also examined the expression of the glial cell-specific S-100 protein by immunohistology. In all mutant cerebella, both the intensity and pattern of staining of the Bergmann glial cells were indistinguishable from that of normal controls, suggesting that the Bergmann glial cells are morphologically normal in the hypothyroid mice. The morphology of the Purkinje cell neurons was similarly visualized by immunohistology using an antiserum specific for the microtubule-associated proteins. Surprisingly, the morphology of the Purkinje cell dendritic arborization also appeared unaltered in the hypothyroid mice. The results suggest that the morphological development of the mouse cerebellum is relatively unaffected by hypothyroidism.
Presynaptic calcium and serotonin-mediated enhancement of transmitter release at crayfish neuromuscular junction
Authors: Delaney K , Tank DW , Zucker RS
Published: March 2018

Fura-2 microfluorometric measurements of calcium concentrations in excitor motor nerve terminals of the first walking leg of crayfish Procambrus clarkii were made during application of serotonin (5-HT) to examine whether changes in residual calcium concentration or calcium influx are responsible for the 5-HT-induced increase in transmitter release at this synapse. Calcium concentrations and EPSPs were monitored simultaneously during 0.5-Hz and moderate-frequency (3–16 Hz) stimulation before, during, and after a 5-min application of 5-HT at concentrations between 5 and 100 microM. We did not observe a significant increase in resting calcium concentration [Ca2+]i in presynaptic terminals during or after application of 5-HT despite simultaneously recorded excitatory junction potential (EJP) enhancement. Injection of the calcium buffer EGTA to concentrations sufficient to reduce significantly the buildup of frequency-dependent facilitation during trains of action potentials did not reduce 5-HT- mediated EJP enhancement. We therefore conclude that 5-HT does not release calcium from intracellular stores to an extent sufficient to overcome calcium buffering and removal systems. Spontaneous release of transmitter quanta was increased by 5-HT to the same extent in normal and increased-osmolarity saline in the absence of measured changes in [Ca2+]i. Thus, changes in residual calcium cannot explain 5-HT-induced synaptic enhancement. Increasing the action-potential-mediated calcium influx by broadening the spike or by increasing extracellular calcium increased evoked transmitter release and increased the accumulation of calcium during trains of action potentials. However, though 5-HT produced a comparable synaptic enhancement, we found no evidence for increased calcium accumulation during trains of action potentials, suggesting that net calcium influx, buffering, and removal are not affected by 5-HT. Therefore, we conclude that 5-HT's action does not result from effects on calcium metabolism and suggest that it acts on the neurosecretory apparatus to increase the effectiveness of calcium for stimulating release. Furthermore, based on its relatively constant effects on facilitated and unfacilitated action-potential-evoked release and spontaneous transmitter release, we conclude that 5-HT actions are independent of the concentration of calcium that is driving release.
Temporal patterns of muscle activation for arm movements in three- dimensional space
Authors: Flanders M
Published: March 2018

Little is known about the patterns of muscle activation that subserve arm movement in three-dimensional space. In this study, activation patterns of seven arm muscles were related to the spatial direction of human arm movement. Twenty movement directions defined two orthogonal vertical planes in space. The arm movements were moderately paced; each movement lasted approximately 500 msec. New techniques of EMG analysis were developed to describe the temporal pattern of muscle activation. For each muscle, a principal component analysis revealed a common phasic and tonic waveform for all directions of movement, within one plane. A temporal shifting procedure based on best covariance values revealed activation delays associated with different movement directions. The results show a consistent pattern of temporal shifting of the common waveform for movements in different directions. Coupled with past results showing that activation amplitude is a function of the cosine angle of movement or force direction, the present results suggest a relatively simple control strategy for mechanically complex arm movements: neural circuits produce a common phasic and tonic activation waveform that is scaled in amplitude and delayed in time, depending on the desired movement direction.
The characterization and localization of the glutamate receptor subunit GluR1 in the rat brain
Authors: Rogers SW , Hughes TE , Hollmann M , Gasic GP , Deneris ES , Heinemann S
Published: March 2018

The cloning of cDNAs that encode functional glutamate receptors makes it possible to produce antibodies that can be used as high-affinity probes for the localization and characterization of these receptors in the mammalian brain. We have made antibodies to different regions of the first cloned member of this family, GluR1, using bacterially overproduced antigen. On Western blots, these antisera detect glycoprotein(s) of 105 kDa present in crude membranes of the hippocampus and cerebellum. The 105-kDa band is associated with postsynaptic densities, and it is observed in cultured cells upon transfection with the GluR1 cDNA. Although glutamate receptors are thought to be the most prevalent excitatory ligand-gated ion channel in the mammalian brain, immunohistochemistry reveals that the receptors recognized by these antisera are localized predominantly in neurons of the cerebellum and some structures of the limbic system, including the hippocampus, the central nucleus of the amygdala, and portions of the septum. This pattern of expression is, in general, consistent with the distribution of GluR1 mRNA as determined by in situ hybridization histochemistry. Our results suggest that glutamate excitatory circuits recognized by these antisera are predominantly found in regions of the limbic system that are reciprocally interconnected.