bluuebunny/crossref_metadata_2025 huggingface dataset:
The EchidnaTachyglossus aculeatusCombines REM and Non-REM Aspects in a Single Sleep State: Implications for the Evolution of Sleep
Authors: Siegel J. M. , Manger P. R. , Nienhuis R. , Fahringer H. M. , Pettigrew J. D.
Published: April 2018

Placental and marsupial mammals exist in three states of consciousness: waking, non-REM sleep, and REM sleep. We now report that the echidnaTachyglossus aculeatus, a representative of the earliest branch of mammalian evolution (the monotremes), does not have the pattern of neuronal activity of either of the sleep states seen in nonmonotreme mammals. Echidna sleep was characterized by increased brainstem unit discharge variability, as in REM sleep. However, the discharge rate decreased and the EEG was synchronized, as in nonREM sleep. Our results suggest that REM and non-REM sleep evolved as a differentiation of a single, phylogenetically older sleep state. We hypothesize that the physiological changes that occur during postnatal sleep development parallel certain aspects of the changes that have occurred during the evolution of sleep–waking states in mammals.
Mesencephalic Substrate of Reward: Axonal Connections
Authors: Boye Sandra M. , Rompré Pierre-Paul
Published: April 2018

The behavioral version of the collision technique was used to study the existence of axonal linkage between reward-relevant sites in the ventral tegmental area (VTA) and posterior mesencephalon (PM) in six rats trained to self-administer trains of electrical brain stimulation. The combined use of fixed and moveable stimulation electrodes allowed us to carry out collision tests at a total of 46 different combinations of VTA-PM sites, and collision-like effects were observed at 24 of these. Stimulation of the VTA and the most caudal PM sites generally resulted in collision curves that were characterized by a single increase in paired-pulse effectiveness (E-values), whereas recovery in those collision curves obtained from stimulation of the VTA and more rostral PM sites was generally slower, and often characterized by a double rise. Despite little variability in interelectrode distances (1.0–3.8 mm), collision intervals varied widely, ranging from 1.5 to 7.3 msec. Recovery from refractoriness (initial 25%) was also estimated and ranged from 0.7 to 1.0 msec, resulting in conduction-time estimates of 0.7–6.3 msec. The lack of correspondence between interelectrode distances and conduction times suggests the presence of axonal branching. Results of this study constitute the first behavioral evidence of a reward-relevant axonal link between the VTA and the PM. In addition, the finding that in one animal the anterior electrode was located within the posterior portion of the lateral hypothalamus (LH) suggests that the reward-relevant axonal bundle linking the LH and VTA may extend as far back as the caudal regions of the PM.
Selective Effects of Nerve Growth Factor on Spatial Recent Memory as Assessed by a Delayed Nonmatching-to-Position Task in the Water Maze
Authors: Markowska Alicja L. , Price Donald , Koliatsos Vassilis E.
Published: April 2018

Nerve growth factor (NGF) ameliorates age-related deficits in certain types of memory in rats. Although the effects of NGF on reference memory are well documented, the influence of NGF on recent memory is less well understood. The issue of recent memory is of primary importance in the design of therapies for cognitive disorders, because this type of memory is impaired in elderly humans and is severely affected early in the course of Alzheimer’s disease (AD). The present study was designed to evaluate the effects of NGF on recent memory in a task that used escape from water as the motivating stimulus and used the same design as forced-choice recognition tasks given to humans. Fischer-344 rats, 4 months old (4MO) or 23 months old (23MO), were pretested in a new spatial recent memory task designed for the Morris water maze, a delayed nonmatching-to-position task, and infused intraventricularly with recombinant human NGF or vehicle. After 2 weeks of NGF infusion, no substantial changes in behavior were observed in either age group. However, NGF treatment extended over 4 weeks improved considerably the choice accuracy of 23MO rats to a level similar to the performance of 4MO rats. These results, together with our previous work (Markowska et al., 1994), indicate that the effects of NGF on spatial recent memory are more intense than on spatial reference memory. NGF suppressed the body weight gain in 4MO rats but did not affect 23MO rats. In 23MO rats, NGF mildly counteracted age-related deficits in inhibitory avoidance, but did not have an effect in young rats.
Predominant Expression of Platelet-Activating Factor Receptor in the Rat Brain Microglia
Authors: Mori Mikiro , Aihara Makoto , Kume Kazuhiko , Hamanoue Makoto , Kohsaka Shinichi , Shimizu Takao
Published: April 2018

Cellular localization of platelet-activating factor (PAF) receptor in the rat brain was determined by (1)in situhybridization, (2) Northern blot analysis in primary cell cultures of neurons, microglia, astrocytes, and fibroblasts, and (3) Ca2+imaging in hippocampal culture.In situhybridization revealed that the PAF receptor mRNA is expressed intensely in microglia and moderately in neurons. Northern blot analysis revealed that PAF receptor mRNA is the most abundant in microglia. In primary hippocampal cultures, PAF elevated intracellular Ca2+concentration in microglia and also in neurons, but to a lesser extent. These results suggest predominant presence of PAF receptor in microglia. Cultured microglia also expressed cPLA2mRNA the most intensely. PAF-activated microglia released arachidonic acid in a Ca2+-dependent manner and without conversion to its derivatives. We propose that microglia as well as neurons contribute to PAF-related events in the CNS by releasing arachidonic acid.
A Novel Type of Programmed Neuronal Death in the Cervical Spinal Cord of the Chick Embryo
Authors: Yaginuma Hiroyuki , Tomita Misako , Takashita Noriko , McKay Sharen E. , Cardwell Chareba , Yin Qin-Wei , Oppenheim Ronald W.
Published: April 2018

We examined the massive early cell death that occurs in the ventral horn of the cervical spinal cord of the chick embryo between embryonic days 4 and 5 (E4 and E5). Studies with immunohistochemistry,in situhybridization, and retrograde-tracing methods revealed that many dying cells express Islet proteins andLim-3mRNA (motoneuron markers) and send their axons to the somatic region of the embryo before cell death. Together, these data strongly suggest that the dying cells are somatic motoneurons. Cervical motoneurons die by apoptosis and can be rescued by treatment with cycloheximide and actinomycin D. Counts of motoneuron numbers between E3.5 and E10 revealed that, in addition to cell death between E4 and E5, motoneuron death also occurs between E6 and E10 in the cervical cord. Studies with [3H]thymidine autoradiography and morphological techniques revealed that in the early cell-death phase (E4–E5), genesis of motoneurons, axonal elongation, and innervation of muscles is still ongoing. However, studies with [3H]thymidine autoradiography also revealed that the cells dying between E4 and E5 become postmitotic before E3.5. Increased size of peripheral targets, treatment with neuromuscular blockade, and treatment with partially purified muscle or brain extracts and defined neurotrophic agents, such as NGF, BDNF, neurotrophin-3, CNTF, bFGF, PDGF, S100-β, activin, cholinergic differentiation factor/leukemia inhibitory factor, bone morphogenetic protein-2, IGF-I, interleukin-6, and TGF-β1, were all ineffective in rescuing motoneurons dying between E4 and E5. By contrast, motoneurons that undergo programmed cell death atlaterstages (E6–E10) in the cervical cord are target-dependent and respond to activity blockade and trophic factors. Experimental approaches revealed that early cell death also occurs in a notochord-induced ectopic supernumerary motoneuron column in the cervical cord. Transplantation of the cervical neural tube to other segmental regions failed to alter the early death of motoneurons, whereas transplantation of other segments to the cervical region failed toinduceearly motoneuron death. These results suggest that the mechanisms that regulate motoneuron death in the cervical spinal cord between E4 and E5 are independent of interactions with targets. Rather, this novel type of cell death seems to be determined by signals that either are cell-autonomous or are derived from other cellswithinthe cervical neural tube.
Inhibition of the NT-3 Receptor TrkC, Early in Chick Embryogenesis, Results in Severe Reductions in Multiple Neuronal Subpopulations in the Dorsal Root Ganglia
Authors: Lefcort Frances , Clary Douglas O. , Rusoff Anne C. , Reichardt Louis F.
Published: April 2018

To assess functions of neurotrophins at defined times in development, we have prepared antibodies to the extracellular domains of each of the trk receptors. Here, antibodies to trkC, the major receptor for NT-3, are used to examine trkC expression and function during the formation and maturation of the chick dorsal root ganglion (DRG). Our results show that in the immature DRG, the majority of cells express trkC, and inhibition of trkC activation results in reductions in neuronal numbers before the period of target-mediated cell death, the time when neurotrophins previously have been shown to regulate survival. Furthermore, blockade of trkCin ovoinduced reductions in subpopulations of DRG neurons known to be dependent on NGF, in addition to those dependent on NT-3 during the target-regulated cell death period. An early function for NT-3 on immature DRG neurons is supported further by data presented here that demonstrate that whereas BDNF and NGF can support a subset of immature DRG neuronsin vitro, activation of the trkC receptor either by NT-3 binding or via antibody-mediated cross-linking induces the most robust survival response. When all three neurotrophins are combined, the number of surviving neurons does not exceed that supported by NT-3 alone. Together, these data are consistent with coexpression of more than one trk receptor family member on immature sensory neurons, and they demonstrate that inhibition of trkC activation has surprisingly early and pleiotrophic effects on the development of spinal sensory ganglia.
Brain-Derived Neurotrophic Factor and Neurotrophin-4/5 Stimulate Growth of Axonal Branches from Regenerating Retinal Ganglion Cells
Authors: Sawai Hajime , Clarke David B. , Kittlerova Paula , Bray Garth M. , Aguayo Albert J.
Published: April 2018

To investigate the influences of growth factors on axonal regeneration in the mammalian CNS, we used intracellular tracers to quantitate the effects of brain-derived neurotrophic factor (BDNF), neurotrophin (NT)-4/5, or NT-3 on individual retinal ganglion cell (RGC) axons in the retinas of adult rats after optic nerve transection. A single injection of BDNF or the prolonged administration of NT-4/5 by mini-pump increased axon branch median lengths by eightfold but had no effect on the number of branches formed by the RGC axons. NT-3 did not significantly influence axonal regrowth. These specificin vivoeffects of BDNF and NT-4/5 on axonal regeneration from injured RGCs may be used to promote growth and expand the abnormally small terminal arbors observed when RGCs regrow into their CNS targets.
Maternal Glucocorticoid Secretion Mediates Long-Term Effects of Prenatal Stress
Authors: Barbazanges Arnaud , Piazza Pier Vincenzo , Le Moal Michel , Maccari Stefania
Published: April 2018

There is growing evidence that stressors occurring during pregnancy can impair biological and behavioral adaptation to stress in the adult offspring. Mechanisms by which stress in the pregnant rat can influence development of the offspring are still unknown. In the present study, we investigated the involvement of maternal corticosterone secretion during pregnancy on the hypothalamo–pituitary–adrenal axis activity of adult offspring. We investigated stress-induced corticosterone secretion and hippocampal type I and type II corticosteroid receptors in male adult rats submitted to prenatal stress born to either mothers with intact corticosterone secretion or mothers in which stress-induced corticosterone secretion was blocked by adrenalectomy with substitutive corticosterone therapy. Repeated restraint during the last week of pregnancy was used as prenatal stressor. Furthermore, the specific role of an injection of corticosterone before the restraint stress on adrenalectomized mothers with substitutive corticosterone treatment was also studied. We report here that blockade of the mother’s stress-induced glucocorticoid secretion suppresses the prolonged stress-induced corticosteroid response and the decrease in type I hippocampal corticosteroid receptors usually observed in prenatally stressed adults. Conversely, corticosterone administered during stress, to mothers in which corticosterone secretion is blocked, reinstates the effects of prenatal stress. These results suggest for the first time that stress-induced increases in maternal glucocorticoids may be a mechanism by which prenatal stress impairs the development of the adult offspring’s glucocorticoid response.
Modulation of a Neural Network by Physiological Levels of Oxygen in Lobster Stomatogastric Ganglion
Authors: Massabuau Jean-Charles , Meyrand Pierre
Published: April 2018

Although a large body of literature has been devoted to the role of O2in the CNS, how neural networks function during long-term exposures to low but physiological O2partial pressure (Po2) has never been studied. We addressed this issue in crustaceans, where arterial blood Po2is set in the 1–3 kPa range, a level that is similar to the most frequently measured tissue Po2in the vertebrate CNS. We demonstrate that over its physiological range, O2can reversibly modify the activity of the pyloric network in the lobsterHomarus gammarus. This network is composed of 12 identified neurons that spontaneously generate a triphasic rhythmic motor outputin vitroas well asin vivo. When Po2decreased from 20 to 1 kPa, the pyloric cycle period increased by 30–40%, and the neuronal pattern was modified. These effects were all dose- and state-dependent. Specifically, we found that the single lateral pyloric (LP) neuron was responsible for the O2-mediated changes. At low Po2, the LP burst duration increased without change in its intraburst firing frequency. Because LP inhibits the pyloric pacemaker neurons, the increased LP burst duration delayed the onset of each rhythmic pacemaker burst, thereby reducing significantly the cycling frequency. When we deleted LP, the network was no longer O2-sensitive.

In conclusion, we propose that (1) O2has specific neuromodulator-like actions in the CNS and that (2) the physiological role of this reduction of activity and energy expenditure could be a key adaptation for tolerating low but physiological Po2in sensitive neural networks.
Long-Term Potentiation in Distinct Subtypes of Hippocampal Nonpyramidal Neurons
Authors: Maccaferri Gianmaria , McBain Chris J.
Published: April 2018

We have investigated NMDA receptor-dependent long-term potentiation (LTP) in distinct subtypes of nonpyramidal neurons of the CA1 hippocampus using induction protocols that permitted the differentiation between a direct form of LTP and plasticity resulting simply from the “passive propagation” of LTP occurring on CA1 pyramidal neurons. Two types of stratum (st.) oriens/alveus interneurons received passive propagation of synaptic potentiation via the recurrent collaterals of CA1 pyramidal cells, but neither subtype possessed direct plasticity. In st. radiatum, two distinct classes of cells were observed: st. radiatum interneurons that showed neither direct nor propagated forms of synaptic plasticity, and “giant cells” for which EPSPs were robustly potentiated after a pairing protocol. This potentiation is similar to the LTP described in pyramidal cells, and its induction requires NMDA receptor activation. Thus, a large heterogeneity of synaptic plasticity exists in morphologically distinct neurons and suggests that complex changes in the CA1 network properties will occur after the induction of LTP.
Retroviral Misexpression ofengrailedGenes in the Chick Optic Tectum Perturbs the Topographic Targeting of Retinal Axons
Authors: Friedman Glenn C. , O’Leary Dennis D. M.
Published: April 2018

We have investigated the role of the homeodomain transcription factor genesEn-1andEn-2, homologs of theDrosophilasegment polarity geneengrailed, in regulating the development of the retinotopic map in the chick optic tectum. The En proteins are distributed in a gradient along the rostral–caudal axis of the developing tectum, with highest amounts found caudally. Previous evidence suggests that En-1 and En-2 may regulate the polarity of the rostral–caudal axis of the tectum and the subsequent topographic mapping of retinal axons. We have tested this hypothesis by using a recombinant replication-competent retrovirus to overexpress theEn-1orEn-2genes in the developing tectum. Anterograde labeling with the axon tracer DiI was used to analyze the topographic mapping of retinal axons after the time that the retinotectal projection is normally topographically organized. Overexpression of eitherEn-1orEn-2perturbed the topographic targeting of retinal axons. InEn-infected tecta, nasal retinal axons form an abnormally diffuse projection with numerous aberrant axons, branches, and arbors found at topographically incorrect locations, colocalized with domains of viral infection. In contrast, temporal axons did not form a diffuse projection or discrete aberrant arbors; however, many temporal axons were stunted and ended aberrantly rostral to their appropriate TZ, or in other cases either did not enter the tectum or formed a dense termination at its extreme rostral edge. These findings indicate that En-1 and En-2 are involved in regulating the development of the retinotopic map in the tectum. Furthermore, they support the hypothesis thatEngenes regulate the polarity of the rostral–caudal axis of the tectum, most likely by controlling the expression of retinal axon guidance molecules.
Structure, Functional Expression, and Cerebral Localization of the Levocabastine-Sensitive Neurotensin/Neuromedin N Receptor from Mouse Brain
Authors: Mazella Jean , Botto Jean-Marie , Guillemare Eric , Coppola Thierry , Sarret Philippe , Vincent Jean-Pierre
Published: April 2018

This work describes the cloning and expression of the levocabastine-sensitive neurotensin (NT) receptor from mouse brain. The receptor protein comprises 417 amino acids and bears the characteristics of G-protein-coupled receptors. This new NT receptor (NTR) type is 39% homologous to, but pharmacologically distinct from, the only other NTR cloned to date from the rat brain and the human HT29 cell line. When the receptor is expressed inXenopus laevisoocytes, the H1 antihistaminic drug levocabastine, like NT and neuromedin N, triggers an inward current. The pharmacological properties of this receptor correspond to those of the low-affinity, levocabastine-sensitive NT binding site described initially in membranes prepared from rat and mouse brain. It is expressed maximally in the cerebellum, hippocampus, piriform cortex, and neocortex of adult mouse brain.
Enhanced Fast Synaptic Transmission and a Delayed Depolarization Induced by Transient Potassium Current Blockade in Rat Hippocampal Slice as Studied by Optical Recording
Authors: Barish Michael E. , Ichikawa Michinori , Tominaga Takashi , Matsumoto Gen , Iijima Toshio
Published: April 2018

In hippocampal neurons, a slowly inactivating aminopyridine-sensitive transient potassium current, D-current, influences the time course of action potential repolarization and therefore activity-dependent Ca2+entry. We used high-speed optical recording techniques to study the effects of selectively inhibiting D-current with 4-AP (40 μm) on transmission at the Schaffer collateral (CA3)-CA1 synapse in rat hippocampal slices stained with the voltage-sensitive dye RH-155. We observed that addition of 4-AP to the bathing solution resulted in (1) augmentation of a fast component of the optical signal corresponding to the postsynaptic EPSP and action potential, and (2) the appearance of a delayed depolarization of CA1 neurons and other adjacent cells. 4-AP appeared to alter the presynaptic action potential and the dynamics of synaptic transmission to both reduce the sensitivity of the postsynaptic EPSP and action potential to ω-toxin calcium channel blockers (ω-conotoxin GVIA and ω-agatoxin IVA) and the Ca2+-dependent potassium channel blocker charybdotoxin, and to increase sensitivity to the dihydropyridine nifedipine, the NMDA receptor blocker aminophosphonopentanoic acid, and the intracellular Ca2+release inhibitor thapsigargin. The delayed depolarization induced by 4-AP was inhibited in hyperosmotic extracellular solution, suggesting that enhanced transmitter release resulted in increased accumulation of K+in the extracellular space. Because 4-AP is a convulsant at concentrations similar to those used here, we suggest that the 4-AP-targeted channel(s) carrying D-current may contribute to the hyperexcitability associated with epilepsy.
Development of an Identified Spinal Commissural Interneuron Population in an Amniote: Neurons of the Avian Hofmann Nuclei
Authors: Eide Anne Lill , Glover Joel C.
Published: April 2018

The commissural interneurons of the Hofmann nuclei (HN) of the avian spinal cord (The axonal projections of the Hofmann nuclei in the spinal cord of the late stage chicken embryo, Anat Embryol (Berl), A. L. Eide, 1996, Vol 193, pp 543–557) provide a unique opportunity to describe the development of an identified spinal commissural axon projection and its terminal collaterals in an amniote vertebrate. Here, we use the lipophilic tracer DiI to label these and other commissural projections anterogradely and retrogradely from the time the HN neurons are born. [3H]thymidine birthdating shows that the final mitoses of HN neurons occur at stages 21–24 [developmental day (d) 4]. By direct comparison, this follows the generation of motoneurons and of large, dorsally located commissural interneurons. The first HN neurons reach the ventrolateral margin of the spinal cord by d6 by a radial migration through the ventral horn. Radial migration occurs after the extension of HN axons across the midline. Thus, HN neurons are determined to be commissural interneurons before attaining their definitive locations. The HN neurons subsequently aggregate into segmentally iterated clusters at the ventrolateral margin of the spinal cord by d8. Also by d8 their longitudinal axons attain mature extent in the ventral funiculus of the contralateral side and begin to sprout collaterals. The collaterals are directed predominantly toward the medial aspect of the ventral horn at all stages, forming by d12 a dense thicket of terminals that thins out over several segments to each side of the HN of origin. The initial direction of collateral outgrowth is largely appropriate for the mature termination pattern of the HN. Terminal arbors, however, are less focused at early developmental stages than at later stages.
Modulatory Actions of Dopamine on NMDA Receptor-Mediated Responses Are Reduced in D1A-Deficient Mutant Mice
Authors: Levine Michael S. , Altemus Katharine L. , Cepeda Carlos , Cromwell Howard C. , Crawford Cynthia , Ariano Marjorie A. , Drago John , Sibley David R. , Westphal Heiner
Published: April 2018

The role of D1dopamine (DA) receptors in mediating the ability of DA to modulate responses attributable to activation of NMDA receptors was examined in mice lacking D1Adopamine receptors. Specifically, experiments were designed to test the hypothesis that the ability of DA to potentiate responses mediated by activation of NMDA receptors was attributable to activation of D1receptors. Based on this hypothesis, we would predict that in the D1Amutant mouse, either DA would not induce enhancement of NMDA-mediated responses, or the enhancement would be severely attenuated. The results provided evidence to support the hypothesis. In mutant mice, DA and D1receptor agonists did not potentiate responses mediated by activation of NMDA receptors. In contrast, in control mice, both DA and D1receptor agonists markedly potentiated responses mediated by activation of NMDA receptors. The effects of DA in attenuating responses mediated by activation of non-NMDA receptors also were altered in the mutant, suggesting that this action of DA may require coupling or interactions between D1and D2receptors. The present studies also provided an opportunity to assess some of the basic electrophysiological and morphological properties of neostriatal neurons in mice lacking D1ADA receptors. Resting membrane potential, action potential parameters, input resistance, excitability, somatic size, dendritic extent, and estimates of spine density in mutants and controls were similar, suggesting that these basic neurophysiological and structural properties have not been changed by the loss of the D1ADA receptor.
Cholinergic Stimulation of AP-1 and NFκB Transcription Factors Is Differentially Sensitive to Oxidative Stress in SH-SY5Y Neuroblastoma: Relationship to Phosphoinositide Hydrolysis
Authors: Li Xiaohua , Song Ling , Jope Richard S.
Published: April 2018

Oxidative stress appears to contribute to neuronal dysfunction in a number of neurodegenerative conditions, notably including Alzheimer’s disease, in which cholinergic receptor-linked signal transduction activity is severely impaired. To test whether oxidative stress could contribute to deficits in cholinergic signaling, responses to carbachol were measured in human neuroblastoma SH-SY5Y cells exposed to H2O2. DNA binding activities of two transcription factors that are respondent to oxidative conditions, AP-1 and NFκB, were measured in nuclear extracts. H2O2and carbachol individually induced dose- and time-dependent increases in AP-1 and NFκB. In contrast, when given together, H2O2concentration dependently (30–300 μm) inhibited the increase after carbachol in AP-1. Carbachol’s stimulation of NFκB was not inhibited except with a high concentration (300 μm) of H2O2, which was associated with impaired activation of protein kinase C. Lower concentrations of H2O2(30–300 μm) inhibited carbachol-induced [3H]phosphoinositide hydrolysis, and this inhibition correlated (r = 0.95) with the inhibition of carbachol-induced AP-1. Activation of [3H]phosphoinositide hydrolysis by the calcium ionophore ionomycin was unaffected by H2O2, indicating that phospholipase C and phosphoinositides were impervious to this treatment. In contrast, activation with NaF of G-proteins coupled to phospholipase C was concentration dependently inhibited by H2O2, indicating impaired G-protein function. These effects of H2O2are similar to signaling impairments reported in Alzheimer’s disease brain, which involve deficits in receptor- and G-protein-stimulated phosphoinositide hydrolysis, but not phospholipase C activity. Thus, these findings indicate that oxidative stress may contribute to impaired phosphoinositide signaling in neurological disorders in which oxidative stress occurs, and that oxidative stress can differentially influence transcription factors activated by cholinergic stimulation.
Microtubule Assembly in Growing Dendrites
Authors: Wang Jun , Yu Wenqian , Baas Peter W. , Black Mark M.
Published: April 2018

Dendritic microtubules (MTs) are nonuniform with respect to polarity orientation, with roughly equal proportions having a plus-end-distal or minus-end-distal orientation. In the present studies, we have microinjected biotin-labeled tubulin (Bt–tub) into cultured sympathetic neurons extending dendrites to explore the contribution of MT assembly to the elaboration and maintenance of the dendritic MT array. Within minutes of injecting Bt–tub, an enormous number of MTs were seen emanating from a point source in the cell body. Over time, this pattern changed such that by 120 min after injection, biotinylated MTs no longer emanated from a discrete site, but were distributed over a broad region that extended from the cell body into the dendrites. The observation that biotinylated MTs emanate from a point source in the soma at relatively short times after injection, but not at longer times, suggests that they undergo a redistribution subsequent to their initial nucleation rather than a simple radial expansion from the somal nucleation site. Bt–tub assembly also occurred in dendrites but, unlike in the cell body, assembly was dispersed throughout the dendrite rather than emanating from a discrete site. Immunoelectron microscopic analyses revealed that assembly in dendrites reflected the addition of Bt–tub onto the ends of both plus-end-distal and minus-end-distal MTs that existed in the cell at the time of injection. The time course of Bt–tub appearance in dendritic MTs suggested an average half-life of ∼76 min for these MTs. We discuss these observations in the context of a model for generating the MT array of dendrites that combines both MT transport and MT assembly.
Consequences of Trisomy 16 for Mouse Brain Development: Corticogenesis in a Model of Down Syndrome
Authors: Haydar Tarik F. , Blue Mary E. , Molliver Mark E. , Krueger Bruce K. , Yarowsky Paul J.
Published: April 2018

We have studied abnormalities in the tangential and radial expansion of the cerebral cortex during fetal development in the trisomy 16 (Ts16) mouse, a model for human trisomy 21 (Down syndrome). Slowed tangential expansion of the neuroepithelium in Ts16 resulted in a reduction of final telencephalic size and is predicted to decrease the number of radial cortical units in the mature brain. In addition, radial growth of the Ts16 cortex was delayed at the time of peak cortical neurogenesis in normal mice, but by embryonic day 18 the cortex reached normal thickness. Because mouse chromosome 16 shares many genes with human chromosome 21, abnormalities in Ts16 brain development may parallel abnormalities in trisomy 21.
Neurotrophin Effects on Survival and Expression of Cholinergic Properties in Cultured Rat Septal Neurons under Normal and Stress Conditions
Authors: Nonner Doris , Barrett Ellen F. , Barrett John N.
Published: April 2018

These studies tested the hypothesis that survival-promoting effects of neurotrophins on basal forebrain cholinergic neurons are enhanced under stress. Septal neurons from embryonic day 14–15 rats exposed for 10–14 d to neurotrophin [nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or neurotrophin-4 (NT-4), each at 100 ng/ml] showed a two- to threefold increase in choline acetyltransferase (ChAT) activity, with little evidence of synergistic interactions. Neurotrophins produced no significant increase in the survival of total or acetylcholinesterase (AChE)-positive neurons at moderate plating density (1200–1600 cells/mm2). However, with very low plating densities (2–28 cells/mm2) BDNF, NT-3, and NT-4 (but not NGF) increased total neuronal survival, and BDNF increased survival of AChE-positive neurons.

NGF and BDNF enhanced ChAT activity and survival of cholinergic neurons after a 24 hr hypoglycemic stress, even when added 1 hr after stress onset. All four tested neurotrophins increased total neuronal survival after hypoglycemic stress. These results suggest that neurotrophins are important for preservation of central cholinergic function under stress conditions, with different neurotrophins protecting against different stresses. The stress-associated survival-promoting effects of neurotrophins were not limited to the cholinergic subpopulation.
Cloning and Functional Expression of aDrosophilaMetabotropic Glutamate Receptor Expressed in the Embryonic CNS
Authors: Parmentier Marie-Laure , Pin Jean-Philippe , Bockaert Joël , Grau Yves
Published: April 2018

The excitatory neurotransmitter glutamate plays important roles in the mammalian brain, ranging from synaptic plasticity to memory. To mediate these functions, glutamate activates two types of receptors: ligand-gated channels and metabotropic receptors coupled to G-proteins. Both families of glutamate receptors share no sequence homology and possess original structural features compared with other ligand-gated channels and G-protein-coupled receptors, respectively. Glutamate-gated receptor-channel subunits have already been characterized in invertebrates. Here we report the cloning and functional characterization of an invertebrate metabotropic glutamate receptor (DmGluRA) isolated fromDrosophila melanogaster. This receptor displays 45 and 43% amino acid sequence identity with its mammalian homologs mGluR3 and mGluR2, respectively. Moreover, its pharmacology and transduction mechanisms are surprisingly similar to those of mGluR2 and mGluR3. DmGluRA is expressed in the CNS of the late embryo. These results indicate that the original structural features of both glutamate receptor types are conserved from insects to mammals and suggest that the functions of these receptors have been highly conserved during evolution.
A Murine Neural-Specific Homolog Corrects Cholinergic Defects inCaenorhabditis elegans unc-18Mutants
Authors: Gengyo-Ando Keiko , Kitayama Hitoshi , Mukaida Masahiro , Ikawa Yoji
Published: April 2018

Caenorhabditis elegansUNC-18 protein, homologous to yeast Sec1p, is important in neurotransmitter release, because theunc-18mutation leads to severe paralysis and presynaptic acetylcholine (ACh) accumulation. To examine the functional conservation in mammals, we tried to isolateunc-18isoforms from mouse and human brain cDNA libraries and obtained two classes of isoforms—neural genes and ubiquitous genes. Neural genes were identical to Munc-18 (also known as n-Sec1 or rbSec1), identified in rat and bovine brains as a syntaxin-binding protein. According to “Munc-18” terminology, we call the neural genes Munc-18-1 and the ubiquitous genes Munc-18-3. These mammalian isoforms exhibit 58% (Munc-18-1) and 42–43% (Munc-18-3) amino acid sequence identity with UNC-18. Next, we constructed transgenicunc-18mutants to test biological activity of mouse Munc-18-1 and Munc-18-3 under the control ofC. elegans unc-18promoter. Munc-18-1 compensates for severe locomotion disability and cholinergic defects, e.g., abnormal sensitivities to cholinesterase inhibitors and cholinergic receptor agonists inunc-18mutants, but Munc-18-3 fails. These data suggest that Munc-18-1 andC. elegans unc-18may play positive roles in ACh release and that the molecular mechanism of neuronal regulated secretion has been partially conserved from nematodes to mammals.
A SNARE Complex Containing Syntaxin 3 Is Present in Ribbon Synapses of the Retina
Authors: Morgans Catherine W. , Brandstätter Johann H. , Kellerman Joseph , Betz Heinrich , Wässle Heinz
Published: April 2018

In contrast to conventional synapses, which release neurotransmitter transiently, ribbon synapses formed by photoreceptors and bipolar cells of the retina release neurotransmitter continuously and modulate the rate in response to light. Both modes of release are mediated by synaptic vesicles but probably differ in the regulation of docking and fusion of synaptic vesicles with the plasma membrane. We have found that syntaxin 1, an essential component of the core fusion complex in conventional synapses, is absent from ribbon synapses of the retina, raising the possibility that these synapses contain a different type of syntaxin or syntaxin-like protein. By immunoprecipitating syntaxin 1-depleted retina and brain extracts with a SNAP-25 antibody and microsequencing the precipitated proteins, syntaxin 3 was detected in retina complexed with SNAP-25, synaptobrevin, and complexin. Using an anti-syntaxin 3 antiserum, syntaxin 3 was demonstrated to be present at high levels in retina compared to brain. Immunofluorescent staining of rat retina sections confirmed that syntaxin 3 is expressed by photoreceptor and bipolar cells in the retina. Thus, in the retina, expression of syntaxin 3 is correlated with ribbon synapses and may play a role in the tonic release of neurotransmitter.
Characterization of Densin-180, a New Brain-Specific Synaptic Protein of theO-Sialoglycoprotein Family
Authors: Apperson Michelle L. , Moon Il Soo , Kennedy Mary B.
Published: April 2018

We purified an abundant protein of apparent molecular mass 180 kDa from the postsynaptic density fraction of rat forebrain and obtained amino acid sequences of three tryptic peptides generated from the protein. The sequences were used to design a strategy for cloning the cDNA encoding the protein by polymerase chain reaction. The open reading frame of the cDNA encodes a novel protein of predicted molecular mass 167 kDa. We have named the protein densin-180. Antibodies raised against the predicted amino and carboxyl sequences of densin-180 recognize a 180 kDa band on immunoblots that is enriched in the postsynaptic density fraction. Immunocytochemical localization of densin-180 in dissociated hippocampal neuronal cultures shows that the protein is highly concentrated at synapses along dendrites. The message encoding densin-180 is brain specific and is more abundant in forebrain than in cerebellum. The sequence of densin-180 contains 17 leucine-rich repeats, a sialomucin domain, an apparent transmembrane domain, and a PDZ domain. This arrangement of domains is similar to that of several adhesion molecules, in particular GPIbα, which mediates binding of platelets to von Willebrand factor. We propose that densin-180 participates in specific adhesion between presynaptic and postsynaptic membranes at glutamatergic synapses.
Restricted Expression of the Actin-Regulatory Protein, Tropomyosin, Defines Distinct Boundaries, Evaginating Neuroepithelium, and Choroid Plexus Forerunners during Early CNS Development
Authors: Nicholson-Flynn Kelley , Hitchcock-DeGregori Sarah E. , Levitt Pat
Published: April 2018

In the hindbrain, rhombomeres represent morphological units that develop characteristic, segment-specific structures. Similar segments, known as prosomeres, have been proposed to exist in the forebrain. The neuroepithelial cells of the sharp boundary regions that form the borders between many segments often exhibit distinct shapes, reflecting unique cytoskeletal organization. The present investigation examined the expression of one family of actin-binding, regulatory proteins, the tropomyosins (TM), in boundaries. We found that high molecular weight TMs selectively concentrate in boundary cells and other neuroepithelial zones that exhibit unique cell shapes and movements. Specific TM expression is found at hindbrain boundaries as early as embryonic day 10 in the rat, whereas rhombomeres themselves were TM-negative. Highly restricted TM localization also defined some prosomere boundaries in the early forebrain, particularly those exhibiting unique cell shapes. Furthermore, several regions of the neuroepithelium that evaginate are TM-immunoreactive, including tuberal and preoptic neuroepithelium. Most striking, a subpopulation of neuroepithelial cells in the medial telencephalic wall expresses TM, apparently marking the neuroepithelial region that gives rise to the choroid plexus at least 2 d before its formation. This suggests that the medial cerebral wall is not entirely dedicated to generating cells that comprise allocortex. TM expression in the choroid plexus is maintained through initial evagination and appearance in all ventricles. The spatially restricted expression of TMs implicates that this actin-binding protein is involved in the dynamic regulation of cell shape or motility associated with boundary formation and morphogenesis of the neuroepithelium during critical stages of brain development.
Selective Innervation of Fast and Slow Muscle Regions during Early Chick Neuromuscular Development
Authors: Rafuse Victor F. , Milner Louise D. , Landmesser Lynn T.
Published: April 2018

The electrical properties of adult motoneurons are well matched to the contractile properties of the fast or slow muscle fibers that they innervate. How this precise matching occurs developmentally is not known. To investigate whether motoneurons exhibit selectivity in innervating discrete muscle regions, containing either fast or slow muscle fibers during early neuromuscular development, we caused embryonic chick hindlimb muscles to become innervated by segmentally inappropriate motoneurons. We used thein vitrospinal cord–hindlimb preparation to identify electrophysiologically the pools of foreign motoneurons innervating the posterior iliotibialis (pITIB), an all-fast muscle, and the iliofibularis (IFIB), a partitioned muscle containing discrete fast and slow regions. The results showed that the pITIB and the fast region of the IFIB were exclusively innervated by motoneurons that normally supply fast muscles. In contrast, the slow region of the IFIB was always innervated by motoneuron pools that normally supply slow muscles. Some experimental IFIB muscles lacked a fast region and were innervated solely by “slow” motoneurons. In addition, the intramuscular nerve branching patterns were always appropriate to the fast–slow nature of the muscle (region) innervated. The selective innervation was found early in the motoneuron death period, and we found no evidence that motoneurons grew into appropriate muscle regions, but failed to form functional contacts. Together, these results support the hypothesis that different classes of motoneurons exhibit molecular differences that allow them to project selectively to, and innervate, muscle fibers of the appropriate type during early neuromuscular development.
Hierarchical Organization of Auditory Temporal Context Sensitivity
Authors: Lewicki Michael S. , Arthur Benjamin J.
Published: April 2018

Some of the most complex auditory neurons known are contained in the songbird forebrain nucleus HVc. These neurons are highly sensitive to auditory temporal context: they respond strongly to the bird’s own song, but respond weakly or not at all when the sequence of the song syllables is altered. It is not known whether this property arisesde novoin HVc or whether it is relayed from the properties of neurons in afferent nuclei. To address this issue, we recorded from neurons in both HVc and its afferent nuclei, collectively called field L. Experimental tests were designed to determine the degree of auditory context sensitivity in field L and HVc. Tests were also performed to compare the responses to individual syllables and syllable combinations to see whether these responses could account for the response seen to the entire song.

Our results show a substantial increase in the auditory temporal context sensitivity between field L and HVc. Most field L neurons respond equally well both to normal song and to temporally manipulated versions of the same song. A few field L neurons show sensitivity to local temporal structure, such as the sequence of syllable pairs. In contrast, HVc neurons are highly dependent on the song’s local and global temporal structure. This shows that HVc neurons can integrate auditory context over periods much longer than neurons in field L and suggests that additional mechanisms are required to explain the marked sensitivity of HVc neurons to the temporal structure of the bird’s own song.
Enhancement of Behavioral and Electroencephalographic Indices of Waking following Stimulation of Noradrenergic β-Receptors within the Medial Septal Region of the Basal Forebrain
Authors: Berridge Craig W. , Foote Stephen L.
Published: April 2018

Previous studies in halothane-anesthetized rat documented potent electroencephalographic (EEG) modulatory actions of the locus coeruleus (LC) noradrenergic system, with LC neuronal activity causally related to the maintenance of EEG activity patterns associated with enhanced arousal/alertness. Recent studies, also in halothane-anesthetized rat, demonstrated that the region of the basal forebrain encompassing the medial septum/vertical limb of the diagonal band of Broca (MS) is a site at which noradrenergic efferents act to influence EEG state via actions at β-receptors.

These and other observations are consistent with the hypothesis that the LC noradrenergic system participates in the modulation of behavioral state. However, the degree to which this system modulates EEG state in the absence of anesthesia and to what extent such actions are accompanied by behavioral modulatory actions remain to be determined. The current studies examined whether small infusions of isoproterenol (ISO), a β-adrenergic agonist, into MS alter behavioral, EEG, and electromyographic (EMG) measures of sleep and waking in the resting, undisturbed rat.

These infusions resulted in a significant increase in time spent awake, defined by both behavioral and EEG/EMG measures, and in the nearly complete suppression of REM sleep. EEG/EMG responses either coincided with or preceded behavioral responses by 10–320 sec. The pattern of behavioral responses observed following MS–ISO infusions was qualitatively similar to that associated with normal waking. Infusions of vehicle into MS or ISO into sites adjacent to MS did not elicit consistent alterations in behavioral state. These results suggest that the LC noradrenergic system exerts potent behavioral and EEG-activating effects via actions of norepinephrine at β-receptors located within MS.
Modulation of Forebrain Electroencephalographic Activity in Halothane-Anesthetized Rat via Actions of Noradrenergic β-Receptors within the Medial Septal Region
Authors: Berridge Craig W. , Bolen Sarah J. , Manley Michael S. , Foote Stephen L.
Published: April 2018

The locus coeruleus (LC)–noradrenergic system modulates forebrain electroencephalographic (EEG) activity in halothane-anesthetized rat. For example, unilateral enhancement of LC neuronal activity increases cortical EEG (ECoG) and hippocampal EEG (HEEG) indices of arousal bilaterally (Berridge and Foote, 1991). Conversely, bilateral suppression of LC discharge activity increases EEG measures of sedation (Berridge et al., 1993b). The EEG-activating effects of LC stimulation appear to involve noradrenergic β-receptors (Berridge and Foote, 1991).

Two candidate sites at which LC efferents could influence ECoG and HEEG are the medial septum/vertical limb of the diagonal band of Broca (MS) and the substantia innominata/nucleus basalis of Meynert (SI). To determine whether norepinephrine mediates such actions within either of these regions, the EEG effects of small infusions of a β-agonist or antagonist into MS or SI were examined in halothane-anesthetized rat. Unilateral infusions (150 nl) of the β-agonist isoproterenol (ISO) (3.75 μg, 17 nmol) into MS, but not SI (150–450 nl), elicited robust bilateral activation of ECoG and HEEG. Infusions of glutamate (0.5 μg, 3.0 nmol) into either MS or SI elicited bilateral ECoG and HEEG activation. Neither vehicle infusions into MS nor infusions of ISO into regions adjacent to MS altered forebrain EEG activity. Bilateral, but not unilateral, MS infusions of the β-antagonist timolol (3.75 μg, 8.7 nmol) decreased EEG indices of arousal in the lightly anesthetized preparation. Power spectral analyses provided quantitative confirmation of these qualitative observations.

These results indicate that under these experimental conditions, noradrenergic efferents, presumably arising from LC, modulate forebrain EEG state via actions at β-receptors located within MS. The results presented in the accompanying report extend these observations to the unanesthetized preparation and incorporate additional measures of behavioral state.