bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Threshold Ca2+Currents in Dendritic Recordings from Purkinje Cells in Rat Cerebellar Slice Cultures
Authors: Mouginot Didier , Bossu Jean-Louis , Gähwiler Beat H.
Published: April 2018

Voltage-dependent Ca2+conductances were investigated in Purkinje cells in rat cerebellar slice cultures using the whole-cell and cell-attached configurations of the patch-clamp technique. In the presence of 0.5 mmCa2+in the extracellular solution, the inward current activated with a threshold of −55 ± 1.5 mV and reached a maximal amplitude of 2.3 ± 0.4 nA at −31 ± 2 mV. Decay kinetics revealed three distinct components: a fast (24.6 ± 2 msec time constant), a slow (304 ± 46 msec time constant), and a nondecaying component. Rundown of the slow and sustained components of the current, or application of antagonists for the P/Q-type Ca2+channels, allowed isolation of the fast-inactivating Ca2+current, which had a threshold for activation of −60 mV and reached a maximal amplitude of 0.7 nA at a membrane potential of −33 mV. Both activation and steady-state inactivation of this fast-inactivating Ca2+current were described with Boltzmann equations, with half-activation and inactivation at −51 mV and −86 mV, respectively. This Ca2+current was nifedipine-insensitive, but its amplitude was reduced reversibly by bath-application of NiCl2and amiloride, thus allowing its identification as a T-type Ca2+current. Channels with a conductance of 7 pS giving rise to a fast T-type ensemble current (insensitive to ω-Aga-IVA) were localized with a high density on the dendritic membrane. Channel activity responsible for the ensemble current sensitive to ω-Aga-IVA was detected with 10 mmBa2+as the charge carrier. These channels were distributed with a high density on dendritic membranes and in rare cases were also seen in somatic membrane patches.
Conservation of Topology, But Not Conformation, of the Proteolipid Proteins of the Myelin Sheath
Authors: Gow Alexander , Gragerov Alexander , Gard Anthony , Colman David R. , Lazzarini Robert A.
Published: April 2018

The proteolipid protein gene products DM-20 and PLP are adhesive intrinsic membrane proteins that make up ≥50% of the protein in myelin and serve to stabilize compact myelin sheaths at the extracellular surfaces of apposed membrane lamellae. To identify which domains of DM-20 and PLP are positioned topologically in the extracellular space to participate in adhesion, we engineered N-glycosylation consensus sites into the hydrophilic segments and determined the extent of glycosylation. In addition, we assessed the presence of two translocation stop-transfer signals and, finally, mapped the extracellular and cytoplasmic dispositions of four antibody epitopes. We find that the topologies of DM-20 and PLP are identical, with both proteins possessing four transmembrane domains and N and C termini exposed to the cytoplasm. Consistent with this notion, DM-20 and PLP contain within their N- and C-terminal halves independent stop-transfer signals for insertion into the bilayer of the rough endoplasmic reticulum duringde novosynthesis. Surprisingly, the conformation (as opposed to topology) of DM-20 and PLP may differ, which has been inferred from the divergent effects that many missense mutations have on the intracellular trafficking of these two isoforms. The 35 amino acid cytoplasmic peptide in PLP, which distinguishes this protein from DM-20, imparts a sensitivity to mutations in extracellular domains. This peptide may normally function during myelinogenesis to detect conformational changes originating across the bilayer from extracellular PLP interactionsin transand trigger intracellular events such as membrane compaction in the cytoplasmic compartment.
Growth Factor-Induced Transcription of GluR1 Increases Functional AMPA Receptor Density in Glial Progenitor Cells
Authors: Chew Li-Jin , Fleck Mark W. , Wright Paul , Scherer Steven E. , Mayer Mark L. , Gallo Vittorio
Published: April 2018

We analyzed the effects of two growth factors that regulate oligodendrocyte progenitor (O-2A) development on the expression of glutamate receptor (GluR) subunits in cortical O-2A cells. In the absence of growth factors, GluR1 was the AMPA subunit mRNA expressed at the lowest relative level. Basic fibroblast growth factor (bFGF) caused an increase in GluR1 and GluR3 steady-state mRNA levels. Platelet-derived growth factor (PDGF) did not modify the mRNA levels for any of the AMPA subunits but selectively potentiated the effects of bFGF on GluR1 mRNA (4.5-fold increase). The kainate-preferring subunits GluR7, KA1, and KA2 mRNAs were increased by bFGF, but these effects were not modified by cotreatment with PDGF. Nuclear run-on assays demonstrated that PDGF+bFGF selectively increased the rate of GluR1 gene transcription (2.5-fold over control). Western blot analysis showed that GluR1 protein levels were increased selectively (sixfold over control) by PDGF+bFGF. Functional expression was assessed by rapid application of AMPA to cultured cells. AMPA receptor current densities (pA/pF) were increased nearly fivefold in cells treated with PDGF+bFGF, as compared with untreated cells. Further, AMPA receptor channels in cells treated with PDGF+bFGF were more sensitive to voltage-dependent block by intracellular polyamines, as expected from the robust and selective enhancement of GluR1 expression. Our combined molecular and electrophysiological findings indicate that AMPA receptor function can be regulated by growth factor-induced changes in the rate of gene transcription.
Actin Plays a Role in Both Changes in Cell Shape and Gene- Expression Associated with Schwann Cell Myelination
Authors: Fernandez-Valle Cristina , Gorman Douglas , Gomez Anna M. , Bunge Mary Bartlett
Published: April 2018

Schwann cell (SC) differentiation into a myelinating cell requires concurrent interactions with basal lamina and an axon destined for myelination. As SCs differentiate, they undergo progressive morphological changes and initiate myelin-specific gene expression. We find that disrupting actin polymerization with cytochalasin D (CD) inhibits myelination of SC/neuron co-cultures. Basal lamina is present, neurons are healthy, and the inhibition is reversible. Electron microscopic analysis reveals that actin plays a role at two stages of SC differentiation. At 0.75–1.0 μg/ml CD, SCs do not differentiate and appear as “rounded” cells in contact with axons. This morphology is consistent with disruption of actin filaments and cell shape changes. However, at 0.25 μg/ml CD, SCs partially differentiate; they elongate and segregate axons but generally fail to form one-to-one relationships and spiral around the axon.In situhybridizations reveal that SCs in CD-treated cultures do not express mRNAs encoding the myelin-specific proteins 2′,3′-cyclic nucleotide phosphodiesterase (CNP), myelin-associated glycoprotein (MAG), and P0. Our results suggest that at the lower CD dose, SCs commence differentiation as evidenced by changes in cell shape but are unable to elaborate myelin lamellae because of a lack of myelin-specific mRNAs. We propose that F-actin influences myelin-specific gene expression in SCs.
An Electrophysiological Study of the Postnatal Development of the Corticospinal System in the Macaque Monkey
Authors: Olivier Etienne , Edgley Steve A. , Armand Jean , Lemon Roger N.
Published: April 2018

Postnatal development of the corticospinal system was investigated in 13 macaques using noninvasive transcranial magnetic stimulation (TMS) of the motor cortex and direct electrical stimulation of corticospinal axons in the medullary pyramid and spinal cord. The latency of antidromic corticospinal volleys evoked from the pyramid and recorded from the motor cortex decreased dramatically during the first postnatal months. Our data predict that conduction velocity (CV) of the fastest corticospinal neurons over their cranial course would reach adult values at ∼11 months. The CV of corticospinal neurons in the spinal cord increased with age but with a slower time course. In the neonate, the fastest spinal CV was estimated at 7.8 m/sec, ∼10 times slower than in adults (mean 80.0 m/sec). Our data predict that full myelination of corticospinal axons in the spinal cord would not occur until ∼36 months. No short-latency EMG responses were elicited in arm and hand muscles by TMS until 3 months of age; TMS thresholds were high initially and then fell progressively with age. When corrected for body size, relative latencies of EMG responses showed an exponential decrease during the first postnatal months.

Our data are consistent with the hypothesis that fine finger movements are not observed before functional CM connections are well established and that rapid changes in the physiological properties of the corticospinal system coincide with the period in which precision grip is known to mature (3–6 months). However, corticospinal development continues long after simple measures of dexterity indicate functional maturity, and these changes may contribute to the improved speed and coordination of skilled hand tasks.
Maturation of Neuronal Form and Function in a Mouse Thalamo-Cortical Circuit
Authors: Warren Richard A. , Jones Edward G.
Published: April 2018

Postnatal development of physiological properties underlying slow intrathalamic oscillations was studied by whole-cell recording from synaptically coupled neurons of the reticular nucleus (RTN) and ventral posterior nucleus (VPN) of mouse brain slicesin vitroand compared with the morphological development of dye-injected cells. Between postnatal days 3 and 11 (P3–P11), progressive changes in RTN and VPN neurons included shortening of the membrane time constant, decreasing input resistance, and lowering of the resting membrane potential (RMP). Low-threshold Ca2+spikes (LTS) were present from P3, but their capacity to sustain multispike bursts was limited before P11. Synaptic responses were evoked in RTN and VPN neurons by electrical stimulation of the internal capsule from P3. Younger RTN neurons responded with a single spike, but their capacity to fire bursts gradually improved as the RMP reached levels below the LTS activation potential. Concomitantly, as the reversal potential of the inhibitory postsynaptic potential in VPN neurons became more negative, its capacity to deinactivate the LTS increased, and rebound bursts that could maintain oscillations were produced; sustained oscillations became the typical response to internal capsule stimulation at P12. The functional maturation of the intrathalamic circuitry, particularly between P10 and P14, occurs in parallel with the morphological maturation (size, dendritic growth, and dendritic field structure) of individual RTN and VPN neurons, as studied by confocal microscopy. Maturation of RTN cells led that of VPN cells by 2–3 d. The appearance of intrathalamic oscillations is probably correlated with the appearance of slow-wave sleep in postnatal animals.
Human Brain Language Areas Identified by Functional Magnetic Resonance Imaging
Authors: Binder Jeffrey R. , Frost Julie A. , Hammeke Thomas A. , Cox Robert W. , Rao Stephen M. , Prieto Thomas
Published: April 2018

Functional magnetic resonance imaging (FMRI) was used to identify candidate language processing areas in the intact human brain. Language was defined broadly to include both phonological and lexical–semantic functions and to exclude sensory, motor, and general executive functions. The language activation task required phonetic and semantic analysis of aurally presented words and was compared with a control task involving perceptual analysis of nonlinguistic sounds. Functional maps of the entire brain were obtained from 30 right-handed subjects. These maps were averaged in standard stereotaxic space to produce a robust “average activation map” that proved reliable in a split-half analysis. As predicted from classical models of language organization based on lesion data, cortical activation associated with language processing was strongly lateralized to the left cerebral hemisphere and involved a network of regions in the frontal, temporal, and parietal lobes. Less consistent with classical models were (1) the existence of left hemisphere temporoparietal language areas outside the traditional “Wernicke area,” namely, in the middle temporal, inferior temporal, fusiform, and angular gyri; (2) extensive left prefrontal language areas outside the classical “Broca area”; and (3) clear participation of these left frontal areas in a task emphasizing “receptive” language functions. Although partly in conflict with the classical model of language localization, these findings are generally compatible with reported lesion data and provide additional support for ongoing efforts to refine and extend the classical model.
Electrophysiological and Immunocytochemical Evidence for a cGMP-Mediated Inhibition of Subfornical Organ Neurons by Nitric Oxide
Authors: Rauch Matthias , Schmid Herbert A. , deVente Jan , Simon Eckhart
Published: April 2018

The activation of neurons in the subfornical organ (SFO) by angiotensin II (AngII) is well established and is widely regarded as the basis for the AngII-induced increase in water intake. Application of the nitric oxide (NO) donor sodium nitroprusside (SNP) led to an inhibition of the spontaneous electrical activity in 96% of the neurons sensitive for SNP (n= 50). In addition, the firing rate in 60% of the neurons inhibited by SNP decreased in response to superfusion with the natural substrate of the NO synthase (NOS)l-arginine whereas 70% increased their frequency after application of the NOS blockerNG-monomethyl-l-arginine (l-NMMA;n= 10). The inhibitory effect of SNP could be mimicked by application of membrane-permeable 8-Br-cGMP. The presence of nNOS, the neuronal isoform of NOS, was demonstrated immunocytochemically and using the NADPH–diaphorase technique on SFO slices. Using a highly selective antibody against cGMP in formaldehyde-fixed tissue, the NO donors SNP, 3-morpholinosydnonimine (SIN-1), andS-nitroso-N-acetyl-dl-penicillamine (SNAP) caused a strong increase in cGMP formation when applied under the same conditions as used for the electrophysiological recordings. These electrophysiological results suggest an important role for NO in SFO-mediated responses and offer a plausible explanation for thein vivo-observed opposite effects of AngII and NO on water intake.
Regulation of a Putative Neurotransmitter Effect of Corticotropin-Releasing Factor: Effects of Adrenalectomy
Authors: Pavcovich Luis A. , Valentino Rita J.
Published: April 2018

This study tested the hypothesis that endogenous glucocorticoids regulate a putative neurotransmitter function of corticotropin-releasing factor (CRF) in the locus coeruleus (LC). LC spontaneous discharge and activation by intracerebroventricularly administered CRF, hypotensive challenge, sciatic nerve stimulation, and carbachol were compared in adrenalectomized and sham-operated halothane-anesthetized rats. LC spontaneous discharge was higher in adrenalectomized versus sham-operated rats. Intracoerulear microinfusion of a CRF antagonist decreased LC discharge rates of adrenalectomized rats to rates comparable with those observed in sham-operated rats but had no effect in sham-operated rats. The CRF dose–response curve was shifted in a complex manner in adrenalectomized rats, suggesting that a proportion of CRF receptors were occupied before CRF administration, and low doses of CRF were additive. Higher doses of CRF produced effects that were greater than predicted by simple additivity. Hypotensive challenge increased LC discharge rates of adrenalectomized rats by a magnitude greater than that predicted on the basis of additivity. In contrast, LC responses to carbachol and sciatic nerve stimulation were similar in both groups. The results suggest that adrenalectomy enhances tonic and stress-induced CRF release within the LC and also alters postsynaptic sensitivity of LC neurons to CRF. Because adrenalectomy also alters release of neurohormone CRF, the present study suggests that CRF actions as a neurohormone and as a neurotransmitter in the LC may be co-regulated. Such parallel regulation may underlie the coexistence of neuroendocrine and noradrenergic dysfunctions in stress-related psychiatric disorders.
Anatomic Organization of the Basilar Pontine Projections from Prefrontal Cortices in Rhesus Monkey
Authors: Schmahmann Jeremy D. , Pandya Deepak N.
Published: April 2018

In our ongoing attempt to determine the anatomic substrates that could support a cerebellar contribution to cognitive processing, we investigated the prefrontal cortical projections to the basilar pons. A detailed understanding of these pathways is needed, because the prefrontal cortex is critical for a number of complex cognitive operations, and the corticopontine projection is the obligatory first step in the corticopontocerebellar circuit. Prefrontopontine connections were studied using the autoradiographic technique in rhesus monkey. The pontine projections were most prominent and occupied the greatest rostrocaudal extent of the pons when derived from the dorsolateral prefrontal convexity, including areas 8Ad, 9/46d, and 10. Lesser pontine projections were observed from the medial prefrontal convexity and area 45B in the inferior limb of the arcuate sulcus. In contrast, ventral prefrontal and orbitofrontal cortices did not demonstrate pontine projections. The prefrontopontine terminations were located preferentially in the paramedian nucleus and in the medial parts of the peripeduncular nucleus, but each cortical area appeared to have a unique complement of pontine nuclei with which it is connected. The existence of these corticopontine pathways from prefrontal areas concerned with multiple domains of higher-order processing is consistent with the hypothesis that the cerebellum is an essential node in the distributed corticosubcortical neural circuits subserving cognitive operations.
Adult Mammalian Sensory and Motor Neurons: Roles of Endogenous Neurotrophins and Rescue by Exogenous Neurotrophins after Axotomy
Authors: Munson John B. , Shelton David L. , McMahon Stephen B.
Published: April 2018

We have tested the ability of neurotrophins to reverse axotomy-induced changes in adult motor and sensory neurons, using the physiological measure of conduction velocity. Five weeks after axotomy, sensory and motor conduction velocities were greatly reduced. NT-3 at 60 μg/d, pumped directly onto the cut nerve stump, largely prevented the change in sensory fibers. Lower doses were less effective, and NT-4/5 was without effect. In contrast, both NT-3 and NT-4/5 were effective at rescuing motoneurons, with similar dose dependencies. This amelioration of physiological deficits in adult mammalian neurons suggests possible therapeutic application of neurotrophins. We have also studied the physiological effects of neurotrophin deprivation on intact peripheral neurons. After 2 weeks of sequestration of trkB ligands (BDNF and NT-4/5), motor, but not sensory, neuron conduction was significantly slowed. Sequestration of NT-3 was found to affect both motor and sensory fiber velocities but more modestly and only with higher doses of sequestering agent. These data therefore suggest that peripherally produced neurotrophins are necessary for the maintenance of normal functional properties of peripheral neurons.
Changes in Hippocampal Circuitry after Pilocarpine-Induced Seizures as Revealed by Opioid Receptor Distribution and Activation
Authors: Bausch Suzanne B. , Chavkin Charles
Published: April 2018

The pilocarpine model of temporal lobe epilepsy was used to study the time-dependent changes in dentate gyrus circuitry after seizures. Seizures caused a decrease in μ- and δ-opioid receptor immunoreactive (MOR-IR and DOR-IR, respectively) neurons in the hilus and MOR-IR neurons in the granule cell layer. Additionally, diffuse DOR-IR, MOR-IR, and GABA immunoreactivities (GABA-IR) were increased in the inner molecular layer. Using thein vitrohippocampal slice preparation to study the physiological consequences of the anatomical changes, we found that the disinhibitory effects of the μ-opioid receptor agonist [D-Ala2,MePhe4,Gly-(ol)5]-enkephalin (DAMGO) and the GABAAreceptor antagonist bicuculline were greatly depressed 5–13 d after pilocarpine injection but returned to control levels within 6 weeks. The amplitudes of monosynaptic evoked IPSCs and the effects of DAMGO on this parameter were also slightly decreased 5–13 d after pilocarpine injection but significantly increased at 6 weeks. DAMGO significantly decreased the mean amplitude of spontaneous IPSCs (sIPSCs) at 6 weeks after pilocarpine injection but not in controls. The δ-opioid receptor agonist [d-Pen2,5]-enkephalin (DPDPE) principally inhibited excitatory transmission in saline-treated animals without affecting either sIPSCs or evoked IPSCs. The DPDPE-induced inhibition of excitatory transmission became more pronounced at 6 weeks after pilocarpine injection. These results illustrate the anatomical reorganization and functional changes in dentate gyrus circuitry evident in an animal model of temporal lobe epilepsy and provide evidence of compensatory changes after trauma to the hippocampal formation.
Requirement of Receptor Internalization for Opioid Stimulation of Mitogen-Activated Protein Kinase: Biochemical and Immunofluorescence Confocal Microscopic Evidence
Authors: Ignatova Elena G. , Belcheva Mariana M. , Bohn Laura M. , Neuman Mark C. , Coscia Carmine J.
Published: April 2018

Previously, we implicated the opioid receptor (OR), Gβγsubunits, and Ras in the opioid activation of extracellular signal-regulated protein kinase (ERK), a member of the mitogen-activated protein (MAP) kinase family involved in mitogenic signaling. We now report that OR endocytosis also plays a role in the opioid stimulation of ERK activity. COS-7 and HEK-293 cells were cotransfected with the cDNA of δ-, μ-, or κ-OR, dynamin wild-type (DWT), or the dominant suppressor mutant dynamin K44A, which blocks receptor endocytosis. The activation of ERK by opioid agonists in the presence of DWTwas detected. In contrast, parallel ectopic coexpression of the K44A mutant with OR, followed by agonist treatment, resulted in a time-dependent attenuation of ERK activation. Immunofluorescence confocal microscopy of δ-OR and DWT-cotransfected COS-7 cells revealed that agonist exposure for 10 min resulted in an ablation of cell surface δ-OR immunoreactivity (IR) and an intensification of cytoplasmic (presumably endosomal) staining as seen in the absence of overexpressed DWT. After 1 hr of δ-agonist exposure the cells displayed substantial internalization of δ-OR IR. If the cells were cotransfected with δ-OR and dynamin mutant K44A, OR IR was retained on the cell surface even after 1 hr of δ-agonist treatment. Parallel immunofluorescence confocal microscopy, using an anti-ERK antibody, showed that agonist-induced time-dependent ERK IR trafficking into perinuclear and nuclear loci was impaired in the internalization-defective cells. Thus, both biochemical and immunofluorescence confocal microscopic evidence supports the hypothesis that the opioid activation of ERK requires receptor internalization in transfected mammalian cells.
Citron Binds to PSD-95 at Glutamatergic Synapses on Inhibitory Neurons in the Hippocampus
Authors: Zhang Wandong , Vazquez Luis , Apperson Michelle , Kennedy Mary B.
Published: April 2018

Synaptic NMDA-type glutamate receptors are anchored to the second of three PDZ (PSD-95/Discs large/ZO-1) domains in the postsynaptic density (PSD) protein PSD-95. Here, we report that citron, a protein target for the activated form of the small GTP-binding protein Rho, preferentially binds the third PDZ domain of PSD-95. In GABAergic neurons from the hippocampus, citron forms a complex with PSD-95 and is concentrated at the postsynaptic side of glutamatergic synapses. Citron is expressed only at low levels in glutamatergic neurons in the hippocampus and is not detectable at synapses onto these neurons. In contrast to citron, p135 SynGAP, an abundant synaptic Ras GTPase-activating protein that can bind to all three PDZ domains of PSD-95, and Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) are concentrated postsynaptically at glutamatergic synapses on glutamatergic neurons. CaM kinase II is not expressed and p135 SynGAP is expressed in less than half of hippocampal GABAergic neurons.

Segregation of citron into inhibitory neurons does not occur in other brain regions. For example, citron is expressed at high levels in most thalamic neurons, which are primarily glutamatergic and contain CaM kinase II. In several other brain regions, citron is present in a subset of neurons that can be either GABAergic or glutamatergic and can sometimes express CaM kinase II. Thus, in the hippocampus, signal transduction complexes associated with postsynaptic NMDA receptors are different in glutamatergic and GABAergic neurons and are specialized in a way that is specific to the hippocampus.
Citron, a Rho-Target, Interacts with PSD-95/SAP-90 at Glutamatergic Synapses in the Thalamus
Authors: Furuyashiki Tomoyuki , Fujisawa Kazuko , Fujita Akiko , Madaule Pascal , Uchino Shigeo , Mishina Masayoshi , Bito Haruhiko , Narumiya Shuh
Published: April 2018

Proteins of the membrane-associated guanylate kinase family play an important role in the anchoring and clustering of neurotransmitter receptors in the postsynaptic density (PSD) at many central synapses. However, relatively little is known about how these multifunctional scaffold proteins might provide a privileged site for activity- and cell type-dependent specification of the postsynaptic signaling machinery. Rho signaling pathway has classically been implicated in mechanisms of axonal outgrowth, dendrogenesis, and cell migration during neural development, but its contribution remains unclear at the synapses in the mature CNS. Here, we present evidence that Citron, a Rho-effector in the brain, is enriched in the PSD fraction and interacts with PSD-95/synapse-associated protein (SAP)-90 bothin vivoandin vitro. Citron colocalization with PSD-95 occurred, not exclusively but certainly, at glutamatergic synapses in a limited set of neurons, such as the thalamic excitatory neurons; Citron expression, however, could not be detected in the principal neurons of the hippocampus and the cerebellum in the adult mouse brain. In a heterologous system, Citron was shown to form a heteromeric complex not only with PSD-95 but also with NMDA receptors. Thus, Citron–PSD-95/SAP-90 interaction may provide a region- and cell type-specific link between the Rho signaling cascade and the synaptic NMDA receptor complex.
NMDA Receptor-Mediated Refinement of a Transient Retinotectal Projection during Development Requires Nitric Oxide
Authors: Ernst Alan F. , Wu Hope H. , El-Fakahany Esam E. , McLoon Steven C.
Published: April 2018

A transient ipsilateral retinotectal projection is normally eliminated during embryonic development of the chick visual system. Administration of the NMDA receptor antagonist 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) during the developmental period in which this projection normally disappears prevented its complete elimination. Previous studies showed that tectal cells express nitric oxide synthase during development, and blocking synthesis of nitric oxide also prevented elimination of the ipsilateral retinotectal projection. The effect of NMDA receptor blockade on nitric oxide synthase activity in tectal cells was assessed biochemically in chick embryos. Increasing concentrations of MK-801 resulted in a dose-dependent decrease in nitric oxide synthase activity. This result suggests that NMDA receptor activation can regulate nitric oxide synthase activity in the tectum. The degree of rescue of the ipsilateral retinotectal projection was compared in embryos treated either with MK-801 or with an inhibitor of nitric oxide synthesis,Nω-nitro-l-arginine (l-NoArg). At comparable levels of inhibition of nitric oxide synthesis, no significant difference was observed in the degree of rescue mediated by NMDA receptor blockade or nitric oxide synthesis blockade. These results suggest that NMDA receptor-mediated elimination of the ipsilateral retinotectal projection is completely mediated via nitric oxide.
Neuronal Degeneration in Canine Narcolepsy
Authors: Siegel J. M. , Nienhuis R. , Gulyani S. , Ouyang S. , Wu M. F. , Mignot E. , Switzer R. C. , McMurry G. , Cornford M.
Published: April 2018

Narcolepsy is a lifelong illness characterized by persistent sleepiness, hypnagogic hallucinations, and episodes of motor paralysis called cataplexy. We have tested the hypothesis that a transient neurodegenerative process is linked to symptom onset. Using the amino-cupric silver stain on brain sections from canine narcoleptics, we found elevated levels of axonal degeneration in the amygdala, basal forebrain (including the nucleus of the diagonal band, substantia innominata, and preoptic region), entopeduncular nucleus, and medial septal region. Reactive neuronal somata, an indicator of neuronal pathology, were found in the ventral amygdala. Axonal degeneration was maximal at 2–4 months of age. The number of reactive cells was maximal at 1 month of age. These degenerative changes precede or coincide with symptom onset. The forebrain degeneration that we have observed can explain the major symptoms of narcolepsy.
Oscillatory Coupling of Hippocampal Pyramidal Cells and Interneurons in the Behaving Rat
Authors: Csicsvari Jozsef , Hirase Hajime , Czurkó András , Mamiya Akira , Buzsáki György
Published: April 2018

We examined whether excitation and inhibition are balanced in hippocampal cortical networks. Extracellular field and single-unit activity were recorded by multiple tetrodes and multisite silicon probes to reveal the timing of the activity of hippocampal CA1 pyramidal cells and classes of interneurons during theta waves and sharp wave burst (SPW)-associated field ripples. The somatic and dendritic inhibition of pyramidal cells was deduced from the activity of interneurons in the pyramidal layer [int(p)] and in the alveus and st. oriens [int(a/o)], respectively. Int(p) and int(a/o) discharged an average of 60 and 20° before the population discharge of pyramidal cells during the theta cycle, respectively. SPW ripples were associated with a 2.5-fold net increase of excitation. The discharge frequency of int(a/o) increased, decreased (“anti-SPW” cells), or did not change (“SPW-independent” cells) during SPW, suggesting that not all interneurons are innervated by pyramidal cells. Int(p) either fired together with (unimodal cells) or both before and after (bimodal cells) the pyramidal cell burst. During fast-ripple oscillation, the activity of interneurons in both the int(p) and int(a/o) groups lagged the maximum discharge probability of pyramidal neurons by 1–2 msec. Network state changes, as reflected by field activity, covaried with changes in the spike train dynamics of single cells and their interactions. Summed activity of parallel-recorded interneurons, but not of pyramidal cells, reliably predicted theta cycles, whereas the reverse was true for the ripple cycles of SPWs. We suggest that network-driven excitability changes provide temporal windows of opportunity for single pyramidal cells to suppress, enable, or facilitate selective synaptic inputs.
The Mammalian Staufen Protein Localizes to the Somatodendritic Domain of Cultured Hippocampal Neurons: Implications for Its Involvement in mRNA Transport
Authors: Kiebler Michael A. , Hemraj Indradeo , Verkade Paul , Köhrmann Martin , Fortes Puri , Marión Rosa M. , Ortı́n Juan , Dotti Carlos G.
Published: April 2018

In hippocampal neurons, certain mRNAs have been found in dendrites (Steward, 1997), and their localization and translation have been implicated in synaptic plasticity (Martin et al., 1997). One attractive candidate to achieve transport of mRNAs into dendrites is Staufen (Stau), a double-stranded RNA-binding protein, which plays a pivotal role in mRNA transport, localization, and translation inDrosophila(St. Johnston, 1995). Using antibodies raised against a peptide located in the RNA-binding domain IIa and a polyclonal antibody raised against a recently cloned human Staufen homolog, we identify a 65 kDa rat homolog in cultured rat hippocampal neurons. In agreement with the exclusive somatodendritic localization of mRNAs in these cells, we find that Staufen is restricted to the same domain. By immunoelectron microscopy, we show enrichment of the mammalian homolog of Stau (mStau) in the vicinity of smooth endoplasmic reticulum and microtubules near synaptic contacts. Finally, the association of the mStau with neuronal mRNAs is suggested by the colocalization with ribonucleoprotein particles specifically in distal dendrites known to contain mRNA, ribosomes, and translation factors (Knowles et al., 1996). These results suggest a role for mStau in the polarized transport and localization of mRNAs in mammalian neurons.
Developmental Dissociation of Serotonin-Induced Spike Broadening and Synaptic Facilitation inAplysiaSensory Neurons
Authors: Stark Laura L. , Carew Thomas J.
Published: April 2018

In sensory neurons (SNs) of adultAplysia, serotonin (5-HT)-induced spike broadening has long been implicated as important for synaptic facilitation [spike duration–dependent (SDD) facilitation], particularly at nondepressed synapses. At depressed synapses, spike broadening has less impact on synaptic facilitation; under these conditions, 5-HT induces a spike duration–independent (SDI) form of facilitation (Byrne and Kandel, 1996). It has been difficult to dissociate clearly the cellular mechanisms underlying these two forms of facilitation. However, the observation that a major form of spike broadening emerges late in juvenile development (Marcus and Carew, 1998) provides a unique opportunity to examine the relationship between spike broadening and synaptic facilitation in juvenileAplysia. We have identified three forms of synaptic plasticity in juvenileAplysia: homosynaptic depression, SDD facilitation, and SDI facilitation. We show that homosynaptic depression is fully developed in the juvenile and that 5-HT reliably induces synaptic facilitation at depressed synapses. However, in nondepressed synapses, 5-HT–induced facilitation is not reliable. Further analysis revealed that the relationship between spike broadening and synaptic facilitation for nondepressed synapses is the inverse of that in adults. Surprisingly, in juveniles, minor spike broadening induced by 5-HT results in significant synaptic facilitation, whereas major spike broadening, when it occurs, does not. These results suggest a model in which juvenile synapses predominantly use SDI facilitation, and with the emergence of major spike broadening, a developmentally transient inhibitory process emerges. This inhibitory process seems to be independent of major spike broadening induced by 5-HT because directly broadening the spike with 4-aminopyridine induces adult-like SDD synaptic facilitation. Finally, in the adult, the inhibitory process is either lost or masked, and SDD facilitation predominates at nondepressed synapses.
High-Frequency Auditory Feedback Is Not Required for Adult Song Maintenance in Bengalese Finches
Authors: Woolley Sarah M. N. , Rubel Edwin W
Published: April 2018

Male Bengalese finches do not normally change their vocal patterns in adulthood; song is stereotyped and stable over time. Adult song maintenance requires auditory feedback. If adults are deafened, song will degrade within 1 week. We tested whether feedback of all sound frequencies is required for song maintenance. The avian basilar papilla is tonotopically organized; hair cells in the basal region encode high frequencies, and low frequencies are encoded in progressively apical regions. We restricted the spectral range of feedback available to a bird by killing either auditory hair cells encoding higher frequencies or those encoding both high and low frequencies and documented resultant changes in song. Birds were treated with either Amikacin alone to kill high-frequency hair cells or Amikacin and sound exposure to target hair cells across the entire papilla. During treatment, song was recorded from all birds weekly. After treatment and song recording, evoked-potential audiograms were evaluated on each bird, and papillas were evaluated by scanning electron microscopy. Results showed that hair cell damage over 46–63% of the basal papilla and the corresponding high-frequency hearing loss had no effect on song structure. In birds with hair cell damage extending further into the apical region of the papilla and corresponding low-frequency and high-frequency hearing loss, song degradation occurred within 1 week of beginning treatment and was comparable with degradation after surgical deafening. We conclude that either low-frequency spectral cues or temporal cues via feedback of the song amplitude envelope are sufficient for song maintenance in adult Bengalese finches.
Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP), a Neuron-Derived Peptide Regulating Glial Glutamate Transport and Metabolism
Authors: Figiel Maciej , Engele Jürgen
Published: April 2018

In the brain, glutamatergic neurotransmission is terminated predominantly by the rapid uptake of synaptically released glutamate into astrocytes through the Na+-dependent glutamate transporters GLT-1 and GLAST and its subsequent conversion into glutamine by the enzyme glutamine synthetase (GS). To date, several factors have been identified that rapidly alter glial glutamate uptake by post-translational modification of glutamate transporters. The only condition known to affect the expression of glial glutamate transporters and GS is the coculturing of glia with neurons. We now demonstrate that neurons regulate glial glutamate turnover via pituitary adenylate cyclase-activating polypeptide (PACAP). In the cerebral cortex PACAP is synthesized by neurons and acts on the subpopulation of astroglia involved in glutamate turnover. Exposure of astroglia to PACAP increased the maximal velocity of [3H]glutamate uptake by promoting the expression of GLT-1, GLAST, and GS. Moreover, the stimulatory effects of neuron-conditioned medium on glial glutamate transporter expression were attenuated in the presence of PACAP-inactivating antibodies or the PACAP receptor antagonist PACAP 6-38. In contrast to PACAP, vasoactive intestinal peptide promoted glutamate transporter expression only at distinctly higher concentrations, suggesting that PACAP exerts its effects on glial glutamate turnover via PAC1 receptors. Although PAC1 receptor-dependent activation of protein kinase A (PKA) was sufficient to promote the expression of GLAST, the activation of both PKA and protein kinase C (PKC) was required to promote GLT-1 expression optimally. Given the existence of various PAC1 receptor isoforms that activate PKA and PKC to different levels, these findings point to a complex mechanism by which PACAP regulates glial glutamate transport and metabolism. Disturbances of these regulatory mechanisms could represent a major cause for glutamate-associated neurological and psychiatric disorders.
Vasoactive Intestinal Peptide and Pituitary Adenylyl Cyclase-Activating Polypeptide Inhibit Tumor Necrosis Factor-α Production in Injured Spinal Cord and in Activated Microglia via a cAMP-Dependent Pathway
Authors: Kim Woong-Ki , Kan Yanqing , Ganea Doina , Hart Ronald P. , Gozes Illana , Jonakait G. Miller
Published: April 2018

Tumor necrosis factor-α (TNF-α) production accompanies CNS insults of all kinds. Because the neuropeptide vasoactive intestinal peptide (VIP) and the structurally related peptide pituitary adenylyl cyclase-activating polypeptide (PACAP) have potent anti-inflammatory effects in the periphery, we investigated whether these effects extend to the CNS. TNF-α mRNA was induced within 2 hr after rat spinal cord transection, and its upregulation was suppressed by a synthetic VIP receptor agonist. Cultured rat microglia were used to examine the mechanisms underlying this inhibition because microglia are the likely source of TNF-α in injured CNS. In culture, increases in TNF-α mRNA resulting from lipopolysaccharide (LPS) stimulation were reduced significantly by 10−7mVIP and completely eliminated by PACAP at the same concentration. TNF-α protein levels were reduced 90% by VIP or PACAP at 10−7m. An antagonist of VPAC1receptors blocked the action of VIP and PACAP, and a PAC1antagonist blocked the action of PACAP. A direct demonstration of VIP binding on microglia and the existence of mRNAs for VPAC1and PAC1(but not VPAC2) receptors argue for a receptor-mediated effect. The action of VIP is cAMP-mediated because (1) activation of cAMP by forskolin mimics the action; (2) PKA inhibition by H89 reverses the neuropeptide-induced inhibition; and (3) the lipophilic neuropeptide mimic, stearyl-norleucine17VIP (SNV), which does not use a cAMP-mediated pathway, fails to duplicate the inhibition. We conclude that VIP and PACAP inhibit the production of TNF-α from activated microglia by a cAMP-dependent pathway.
Wind Direction Coding in the Cockroach Escape Response: Winner Does Not Take All
Authors: Levi Rafael , Camhi Jeffrey M.
Published: April 2018

Cockroaches respond to the approach of a predator by turning away and then running. Three bilateral pairs of giant interneurons are involved in determining the direction of the sensory stimulus and setting the turn direction. Each of these six interneurons has a different directional response to wind stimuli. We have tested whether these six cells use a winner-take-all mechanism to perform this directional determination: that is, each of these cells suppressing the motor response that each of the other cells promotes. Such a mechanism is found in similar behaviors of some other animals. By adding spikes to identified giant interneurons through intracellular stimulation during the sensory-induced behavior and analyzing the resulting directional leg movements, we find that a winner-take-all is not used in this system. Rather, directional determination appears to be based on collaborative calculation of direction by the giant interneurons as a group.
Effect of Lesions of the Ventrolateral Preoptic Nucleus on NREM and REM Sleep
Authors: Lu Jun , Greco Mary Ann , Shiromani Priyattam , Saper Clifford B.
Published: April 2018

Neurons in the ventrolateral preoptic nucleus (VLPO) in rats show c-fos activation after sleep and provide GABAergic innervation of the major monoamine arousal systems, suggesting that they may be a necessary part of the brain circuitry that produces sleep. We examined the effects on sleep behavior in rats of cell-specific damage to the VLPO by microinjection of ibotenic acid. Severe lesions of the central cell cluster of the VLPO (∼80–90% cell loss bilaterally) caused a 60–70% decrease in delta power and a 50–60% decrease in nonrapid-eye-movement (NREM) sleep time (p< 0.001). The number of remaining Fos-immunoreactive neurons in the VLPO cell cluster was linearly related to NREM sleep time (r= 0.77;p< 0.001) and total electroencephalogram delta power (r= 0.79;p< 0.001) but not to rapid-eye-movement (REM) sleep (r= 0.35;p> 0.10). Lesions in the region containing scattered VLPO neurons medial or dorsal to the cell cluster caused smaller changes in NREM sleep time (24.5 or 15%, respectively) but were more closely associated with loss of REM sleep (r= 0.74;p< 0.01). The insomnia caused by bilateral VLPO lesions persisted for at least 3 weeks. Lesions of the VLPO caused no change in mean body temperature or its circadian variation; after small lesions of the ventromedial preoptic nucleus, body temperature showed normal circadian variation but a wider temperature range, and sleep behavior was not affected. These experiments delineate distinct preoptic sites with primary effects on the regulation of NREM sleep, REM sleep, and body temperature.
Glucocorticoid Negative Feedback Selectively Targets Vasopressin Transcription in Parvocellular Neurosecretory Neurons
Authors: Kovács Krisztina J. , Földes Anna , Sawchenko Paul E.
Published: April 2018

To identify molecular targets of corticosteroid negative feedback effects on neurosecretory neurons comprising the central limb of the hypothalamo–pituitary–adrenal (HPA) axis, we monitored ether stress effects on corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) heteronuclear RNA (hnRNA) expression in rats that were intact or adrenalectomized (ADX) and replaced with corticosterone (B) at constant levels ranging from nil to peak stress concentrations. Under basal conditions, relative levels of both primary transcripts varied inversely as a function of plasma B titers. In response to stress, the kinetics of CRF hnRNA responses of intact and ADX rats replaced with low B were similar, peaking at 5 min after stress. By contrast, intact rats showed a delayed AVP hnRNA response (peak at 2 hr), the timing of which was markedly advanced in ADX/low B-replaced animals (peak at 5–30 min). Transcription factors implicated in these responses responded similarly. Manipulation of B status did not affect the early (5–15 min) phosphorylation of transcription factor cAMP-response element-binding protein (CREB) but accelerated maximal Fos induction from 2 hr after stress (intact) to 1 hr (ADX). Assays of binding by proteins in hypothalamic extracts of similarly manipulated rats toward consensus CRE and AP-1 response elements supported a role for the stress-induced plasma B increment in antagonizing AP-1, but not CRE, binding. These findings suggest that glucocorticoid negative feedback at the transcriptional levels is exerted selectively on AVP gene expression through a mechanism that likely involves glucocorticoid receptor interactions with immediate-early gene products.
Contrasting Effects on Discrimination Learning after Hippocampal Lesions and Conjoint Hippocampal–Caudate Lesions in Monkeys
Authors: Teng Edmond , Stefanacci Lisa , Squire Larry R. , Zola Stuart M.
Published: April 2018

Eighteen monkeys with lesions of the hippocampal region (the hippocampus proper, the dentate gyrus, and the subiculum) made by an ischemic procedure, radio frequency, or ibotenic acid were tested on a simple, two-choice object discrimination learning task that has been shown to be sensitive to large lesions of the medial temporal lobe. The monkeys were also tested on two other discrimination tasks (pattern discrimination and eight-pair concurrent discrimination) that can be learned normally by monkeys with large medial temporal lobe lesions. All of the lesion groups were impaired at learning the simple object discrimination task. Seven of the monkeys who had sustained damage to the hippocampal region also sustained damage to the tail of the caudate nucleus. These seven monkeys, but not the other 11 monkeys with hippocampal lesions, were impaired on pattern discrimination and concurrent discrimination learning. The results suggest that the hippocampal region is important for learning easy, two-choice discriminations, whereas the caudate nucleus is necessary for the normal learning of more difficult, gradually acquired discrimination tasks. The findings support the distinction between declarative memory, which depends on the hippocampus and related medial temporal lobe structures, and habit learning, which depends on the caudate nucleus.