bluuebunny/crossref_metadata_2025 huggingface dataset:
Neuroprotective Effects of Creatine and Cyclocreatine in Animal Models of Huntington’s Disease
Authors: Matthews Russell T. , Yang Lichuan , Jenkins Bruce G. , Ferrante Robert J. , Rosen Bruce R. , Kaddurah-Daouk Rima , Beal M. Flint
Published: April 2018

The gene defect in Huntington’s disease (HD) may result in an impairment of energy metabolism. Malonate and 3-nitropropionic acid (3-NP) are inhibitors of succinate dehydrogenase that produce energy depletion and lesions that closely resemble those of HD. Oral supplementation with creatine or cyclocreatine, which are substrates for the enzyme creatine kinase, may increase phosphocreatine (PCr) or phosphocyclocreatine (PCCr) levels and ATP generation and thereby may exert neuroprotective effects. We found that oral supplementation with either creatine or cyclocreatine produced significant protection against malonate lesions, and that creatine but not cyclocreatine supplementation significantly protected against 3-NP neurotoxicity. Creatine and cyclocreatine increased brain concentrations of PCr and PCCr, respectively, and creatine protected against depletions of PCr and ATP produced by 3-NP. Creatine supplementation protected against 3-NP induced increases in striatal lactate concentrationsin vivoas assessed by1H magnetic resonance spectroscopy. Creatine and cyclocreatine protected against malonate-induced increases in the conversion of salicylate to 2,3- and 2,5-dihydroxybenzoic acid, biochemical markers of hydroxyl radical generation. Creatine administration protected against 3-NP-induced increases in 3-nitrotyrosine concentrations, a marker of peroxynitrite-mediated oxidative injury. Oral supplementation with creatine or cyclocreatine results in neuroprotective effectsin vivo, which may represent a novel therapeutic strategy for HD and other neurodegenerative diseases.
Blockade and Recovery of Spontaneous Rhythmic Activity after Application of Neurotransmitter Antagonists to Spinal Networks of the Chick Embryo
Authors: Chub Nikolai , O’Donovan Michael J.
Published: April 2018

We studied the regulation of spontaneous activity in the embryonic (day 10–11) chick spinal cord. After bath application ofeitheran excitatory amino acid (AP-5 or CNQX) and a nicotinic cholinergic (DHβE or mecamylamine) antagonist,orglycine and GABA receptor (bicuculline, 2-hydroxysaclofen, and strychnine) antagonists, spontaneous activity was blocked for a period (30–90 min) but then reappeared in the presence of the drugs. The efficacy of the antagonists was assessed by their continued ability to block spinal reflex pathways during the reappearance of spontaneous activity. Spontaneous activity ceased over the 4–5 hour monitoring period when both sets of antagonists were applied together.

After application of glycine and GABA receptor antagonists, the frequency of occurrence of spontaneous episodes slowed and became highly variable. By contrast, during glutamatergic and nicotinic cholinergic blockade, the frequency of occurrence of spontaneous episodes initially slowed and then recovered to stabilize near the predrug level of activity. Whole-cell recordings made from ventral spinal neurons revealed that this recovery was accompanied by an increase in the amplitude of spontaneously occurring synaptic events.

We also measured changes in the apparent equilibrium potential of the rhythmic, synaptic drive of ventral spinal neurons using voltage or discontinuous current clamp. After excitatory blockade, the apparent equilibrium potential of the rhythmic synaptic drive shifted ∼10 mV more negative to approximately −30 mV. In the presence of bicuculline, the apparent equilibrium potential of the synaptic drive shifted toward the glutamate equilibrium potential.

Considered with other evidence, these findings suggest that spontaneous rhythmic output is a general property of developing spinal networks, and that GABA and glycinergic networks alter their function to compensate for the blockade of excitatory transmission.
Platelet-Activating Factor Receptor Stimulation Disrupts Neuronal MigrationIn Vitro
Authors: Bix Gregory J. , Clark Gary D.
Published: April 2018

LIS-1is a gene whose hemi-deletion causes the human neuronal migration disorder Miller–Dieker lissencephaly. It encodes a subunit of a brain platelet-activating factor (PAF) acetylhydrolase, an enzyme that inactivates PAF by hydrolyzing the acetyl moiety in thesn2position of this phospholipid. Because PAF receptor activation has been shown to affect the developing neuronal cytoskeleton, we have hypothesized that a role for PAF in neurodevelopment is that of a modulator of neuroblast movement (a cytoskeletal function) and that an aberrant regulation of PAF could lead to an early arrest in migration. This report examines the effects of the nonhydrolyzable PAF receptor agonist methyl carbamyl PAF (mc-PAF) on the unidirectionalin vitromigration of granule cells from cerebellar cell reaggregates on a laminin substrate. Bath treatment with mc-PAF yields a dose-dependent decrease in granule cell migration compared with controls. This effect can be blocked by the simultaneous bath application of BN 52021 andtrans-BTD, PAF receptor-specific antagonists. Although mc-PAF minimally inhibited neurite growth, its primary effect was on somal movement along preextended neurites. These experiments suggest that the stimulation of neuronal PAF receptors could be one crucial step for the regulation of neuroblast migration and that disturbed PAF catabolism during neurodevelopment could contribute to the neuronal migration defects observed in Miller–Dieker lissencephaly.
Brain Dopamine Neurotoxicity in Baboons Treated with Doses of Methamphetamine Comparable to Those Recreationally Abused by Humans: Evidence from [11C]WIN-35,428 Positron Emission Tomography Studies and DirectIn VitroDeterminations
Authors: Villemagne Victor , Yuan Jie , Wong Dean F. , Dannals Robert F. , Hatzidimitriou George , Mathews William B. , Ravert Hayden T. , Musachio J. , McCann Una D. , Ricaurte George A.
Published: April 2018

The present study sought to determine whether doses of methamphetamine in the range of those used recreationally by humans produce brain dopamine (DA) neurotoxicity in baboons and to ascertain whether positron emission tomography (PET) imaging with the DA transporter (DAT) ligand [11C]WIN-35,428 ([11C]2β-carbomethoxy-3β-(4-fluorophenyl)-tropane) could be used to detect methamphetamine-induced DAT loss in living primates. Baboons were treated with saline (n= 3) or one of three doses of methamphetamine [0.5 mg/kg (n= 2); 1 mg/kg (n= 2); and 2 mg/kg (n= 3)], each of which was given intramuscularly four times at 2 hr intervals. PET studies were performed before and 2–3 weeks after methamphetamine treatment. After the final PET studies, animals were killed for direct neurochemical determination of brain DA axonal markers. PET-derived binding potential values, used to index striatal DAT density, were significantly decreased after methamphetamine, with larger decreases occurring after higher methamphetamine doses. Reductions in striatal DAT documented by PET were associated with decreases in DA, dihydroxyphenylacetic acid, and specific [3H]WIN-35,428 and [3H]DTBZ binding determinedin vitro. Decreases in DAT detected with PET were highly correlated with decreases in specific [3H]WIN-35,428 binding determinedin vitroin the caudate of the same animal (r= 0.77;p= 0.042). These results indicate that methamphetamine, at doses used by some humans, produces long-term reductions in brain DA axonal markers in baboons, and that it is possible to detect methamphetamine-induced DAT loss in living nonhuman primates by means of PET.
Postnatal Development of Phase-Locked High-Fidelity Synaptic Transmission in the Medial Nucleus of the Trapezoid Body of the Rat
Authors: Chuhma Nao , Ohmori Harunori
Published: April 2018

Synaptic transmission in the medial nucleus of the trapezoid body of rats was analyzed in postnatal days 4–13 (P4–P13) by applying the whole-cell patch-recording technique to brain slices. In P4–P6 animals, evoked EPSCs fluctuated extensively in amplitude and occurred in marked asynchrony, followed by spontaneous EPSCs. With development of animals, the evoked EPSCs increased in amplitude, and the rise time became faster. In addition, the synaptic transmission became phase-locked. The coefficient of variation (CV) of EPSC amplitude decreased with development (0.32 ± 0.03 for P4–P5 and 0.05 ± 0.01 for P9–P11). The amplitude of miniature EPSCs did not change throughout the postnatal days investigated (−30.2 ± 0.3 pA at −70 mV). The CV was dependent on extracellular Ca2+concentration ([Ca2+]o) and was reduced with the increase of [Ca2+]o, and this [Ca2+]odependence was shifted toward lower [Ca2+]owith development. Direct patch recording of the presynaptic terminals demonstrated an increase in Ca2+currents during these postnatal days. The phase-locked high-fidelity transmission in this synapse is achieved with development likely through the increase of Ca2+currents and Ca2+sensitivity of transmitter release mechanisms in the presynaptic terminal.
Plasma Membrane Ca2+-ATPase Extrudes Ca2+from Hair Cell Stereocilia
Authors: Yamoah Ebenezer N. , Lumpkin Ellen A. , Dumont Rachel A. , Smith Peter J. S. , Hudspeth A. J. , Gillespie Peter G.
Published: April 2018

Mechanically sensitive hair cells of the auditory and vestibular systems use Ca2+to control adaptation of mechanical transduction, to effect frequency tuning, to trigger neurotransmitter release, and to mediate efferent synaptic signaling. To determine the role that pumps play in regulation of Ca2+in the hair bundle, the organelle responsible for mechanoelectrical transduction, we localized and quantified the plasma membrane Ca2+-ATPase (PMCA) of the bundle. We found that each hair bundle contains ∼106PMCA molecules or ∼2000 per square micrometer of bundle membrane and that PMCA is the principal calmodulin binding protein of the bundle. Consistent with biochemical estimates of PMCA density, we measured with extracellular Ca2+-selective electrodes a substantial Ca2+efflux from bundles. The number of bundle Ca2+pumps and magnitude of resting Ca2+efflux suggested that PMCA should generate a substantial membrane current as bundles expel Ca2+. Measurement of whole-cell currents revealed a transduction-dependent outward current that was consistent with the activity of PMCA. Finally, dialysis of hair cells with PMCA inhibitors led to a large increase in the concentration of Ca2+in bundles, which suggests that PMCA plays a major role in regulating bundle Ca2+concentration. Our data further indicate that PMCA could elevate the extracellular Ca2+concentration close to hair bundles above the low level found in bulk endolymph.
Fetal Spinal Cord Transplants Support Growth of Supraspinal and Segmental Projections after Cervical Spinal Cord Hemisection in the Neonatal Rat
Authors: Diener Pamela S. , Bregman Barbara S.
Published: April 2018

Cervical spinal cord injury at birth permanently disrupts forelimb function in goal-directed reaching. Transplants of fetal spinal cord tissue permit the development of skilled forelimb use and associated postural adjustments (Diener and Bregman, 1998, companion article). The aim of this study was to determine whether transplants of fetal spinal cord tissue support the remodeling of supraspinal and segmental pathways that may underlie recovery of postural reflexes and forelimb movements. Although brainstem-spinal and segmental projections to the cervical spinal cord are present at birth, skilled forelimb reaching has not yet developed. Three-day-old rats received a cervical spinal cord overhemisection with or without transplantation of fetal spinal cord tissue (embryonic day 14); unoperated pups served as normal controls. Neuroanatomical tracing techniques were used to examine the organization of CNS pathways that may influence target-directed reaching. In animals with hemisections only, corticospinal, brainstem-spinal, and dorsal root projections within the spinal cord were decreased in number and extent. In contrast, animals receiving hemisections plus transplants exhibited growth of these projections throughout the transplant and over long distances within the host spinal cord caudal to the transplant. Raphespinal axons were apposed to numerous propriospinal neurons in control and transplant animals; these associations were greatly reduced in the lesion-only animals. These observations suggest that after neonatal cervical spinal cord injury, embryonic transplants support axonal growth of CNS pathways and specifically supraspinal input to propriospinal neurons. We suggest that after neonatal spinal injury in the rat, the transplant-mediated reestablishment of supraspinal input to spinal circuitry is the mechanism underlying the development of target-directed reaching and associated postural adjustments.
Role of Synaptic Inhibition in Processing of Dynamic Binaural Level Stimuli
Authors: Sanes Dan H. , Malone Brian J. , Semple Malcolm N.
Published: April 2018

We have recently discovered a paradoxical aftereffect associated with inhibition in the gerbil auditory midbrain. Single neurons in the inferior colliculus (IC) were assessed for sensitivity to a virtual motion stimulus produced by modulating the interaural level difference (ILD), a major cue for sound localization. The class of neuron studied was predominantly excited by contralateral stimulation and inhibited by ipsilateral stimulation. Sound pressure level was modulated trapezoidally at the ipsilateral “inhibitory” ear, whereas the contralateral “excitatory” level remained constant. When the inhibitory stimulus was decreased within a range of sound levels that maintained suppression under static conditions, an unexpected discharge was often elicited, apparently because of an aftereffect of synaptic inhibition. In contrast, when the inhibitory stimulus was increased within a range of sound levels that produced only modest suppression under static conditions, neuronal discharge was often profoundly suppressed. In many cases the “conditioned enhancement” or “conditioned suppression” persisted for several seconds after the modulation of ILD, and such conditioned responses were influenced by the modulation depth and rate. To test the effect of inhibition in the IC directly, glycine and GABA were pulsed from a glass recording pipette during a constant monaural excitatory stimulus. The acoustically elicited discharge rate was potentiated markedly if preceded immediately by the brief (0.5–10 sec) application of inhibitory transmitter. Collectively, these results revealed unusually long-lasting effects of inhibition that may establish a new range of acoustic cues to which the neuron responds best. This may have broad implications for processing ensuing auditory stimuli.
Sodium Current in Rat and Cat Thalamocortical Neurons: Role of a Non-Inactivating Component in Tonic and Burst Firing
Authors: Parri H. Rheinallt , Crunelli Vincenzo
Published: April 2018

The properties of the Na+current present in thalamocortical neurons of the dorsal lateral geniculate nucleus were investigated in dissociated neonate rat and cat neurons and in neurons from slices of neonate and adult rats using patch and sharp electrode recordings.

The steady-state activation and inactivation of the transient Na+current (INa) was well fitted with a Boltzmann curve (voltage of half-maximal activation and inactivation,V1/2, −29.84 mV and −70.04 mV, respectively). Steady-state activation and inactivation curves showed a small region of overlap, indicating the occurrence of aINawindow current.INadecay could be fitted with a single exponential function, consistent with the presence of only one channel type.

Voltage ramp and step protocols showed the presence of a noninactivating component of the Na+current (INaP) that activated at potentials more negative (V1/2= −56.93 mV) than those ofINa. The maximal amplitude ofINaPwas ∼2.5% ofINa, thus significantly greater than the calculated contribution (0.2%) of theINawindow component. Comparison of results from dissociated neurons and neurons in slices suggested a dendritic as well as a somatic localization ofINaP. Inclusion of papain in the patch electrode removed the fast inactivation ofINaand induced a current with voltage-dependence (V1/2= −56.92) and activation parameters similar to those ofINaP.

Current-clamp recordings with sharp electrodes showed thatINaPcontributed to depolarizations evoked from potentials of approximately −60 mV and unexpectedly to the amplitude and latency of low-threshold Ca2+potentials, suggesting that this noninactivating component of the Na+channel population plays an important role in the integrative properties of thalamocortical neurons during both tonic and burst-firing patterns.
Nitric Oxide and Superoxide Contribute to Motor Neuron Apoptosis Induced by Trophic Factor Deprivation
Authors: Estévez Alvaro G. , Spear Nathan , Manuel S. Machelle , Radi Rafael , Henderson Christopher E. , Barbeito Luis , Beckman Joseph S.
Published: April 2018

Primary cultures of rat embryonic motor neurons deprived of brain-derived neurotrophic factor (BDNF) induce neuronal nitric oxide synthase (NOS) within 18 hr. Subsequently, >60% of the neurons undergo apoptosis between 18 and 24 hr after plating. Nitro-l-arginine and nitro-l-arginine methyl ester (l-NAME) prevented motor neuron death induced by trophic factor deprivation. Exogenous generation of nitric oxide at concentrations lower than 100 nmovercame the protection byl-NAME. Manganese tetrakis (4-benzoyl acid) porphyrin, a cell-permeant superoxide scavenger, also prevented nitric oxide-dependent motor neuron death. Motor neurons cultured without trophic support rapidly became immunoreactive for nitrotyrosine when compared with motor neurons incubated with BDNF,l-NAME, or manganese TBAP. Our results suggest that peroxynitrite, a strong oxidant formed by the reaction of NO and superoxide, plays an important role in the induction of apoptosis in motor neurons deprived of trophic factors and that BDNF supports motor neuron survival in part by preventing neuronal NOS expression.
A Role for L-Type Calcium Channels in Developmental Regulation of Transmitter Phenotype in Primary Sensory Neurons
Authors: Brosenitsch Teresa A. , Salgado-Commissariat Delanthi , Kunze Diana L. , Katz David M.
Published: April 2018

To examine the influence of activity-dependent cues on differentiation of primary afferent neurons, we investigated the short- and long-term effects of depolarization and calcium influx on expression of transmitter traits in sensory ganglion cell cultures. We focused on expression of tyrosine hydroxylase (TH), a marker for dopaminergic neurons, in developing petrosal ganglion (PG), nodose ganglion, and dorsal root ganglion neurons grown in the presence or absence of depolarizing concentrations of KCl. Exposure to 40 mmKCl increased the proportion of TH-immunoreactive neurons in all three ganglia in a developmentally regulated manner that corresponded to the temporal pattern of dopaminergic expressionin vivo. PG neurons, for example, were most responsive to elevated KCl on embryonic day 16.5 (E16.5), the age at which the dopaminergic phenotype is first detectablein vivo. However, KCl was relatively ineffective at increasing TH expression in neonatal PG, indicating a critical period for induction of this phenotype by depolarization. Detailed analysis of TH induction in PG neurons demonstrated that, although N-type calcium channels carried the majority of the high voltage-activated calcium current, only L-type calcium channel blockade inhibited the effect of elevated KCl. Further studies revealed that after removal of high KCl, neurons remained sensitized to subsequent stimulation for >1 week. Specifically, cultures exposed to KCl beginning on E16.5 (the conditioning stimulus), then returned to control medium, and subsequently re-exposed to elevated KCl after 9 d (the test stimulus) contained fourfold more TH-positive neurons than did cultures exposed to the test stimulus alone. Moreover, blockade of L-type calcium channels during the conditioning stimulus completely abolished long-term potentiation of the TH response to elevated KCl. These findings demonstrate a novel role for L-type calcium channels in activity-dependent plasticity of transmitter expression in sensory neurons and indicate that exposure to depolarizing stimuli during early development may alter neuronal response properties at later ages.
Interrelationships between Somatostatin sst2A Receptors and Somatostatin-Containing Axons in Rat Brain: Evidence for Regulation of Cell Surface Receptors by Endogenous Somatostatin
Authors: Dournaud Pascal , Boudin Hélène , Schonbrunn Agnes , Tannenbaum Gloria S. , Beaudet Alain
Published: April 2018

Using an antipeptide antibody, we reported previously on the distribution of the somatostatin sst2A receptor subtype in rat brain. Depending on the region, immunolabeled receptors were either confined to neuronal perikarya and dendrites or distributed diffusely in tissue. To investigate the functional significance of these distribution patterns, we examined the regional and cellular relationships between somatostatin axons and sst2A receptors in the rat CNS, using double-labeling immunocytochemistry. Light and confocal microscopy revealed a significant correlation (p< 0.02) between the distribution of somatodendritic sst2A receptor immunoreactivity and that of somatostatin terminal fields, both quantitatively and qualitatively. Furthermore, in regions of somatodendritic labeling, a subpopulation of sst2A-immunoreactive cells was also immunopositive for somatostatin, suggesting that a subset of sst2A receptors consists of autoreceptors. By contrast, in regions displaying diffuse sst2A labeling only moderate to low densities of somatostatin terminals were observed, and no significant relationship was found between terminal density and receptor immunoreactivity. At the electron microscopic level, areas expressing somatodendritic sst2A labeling were found by immunogold cytochemistry to display low proportions of membrane-associated, as compared with intracellular, receptors. Conversely, in regions displaying diffuse sst2A receptor labeling, receptors were predominantly associated with neuronal plasma membranes, a finding consistent with the high density of sst2 binding sites previously visualized in these areas by autoradiography. Double-labeling studies demonstrated that in the former but not in the latter regions, sst2A-immunoreactive somata and dendrites were heavily contacted by somatostatin axon terminals. Taken together, these results suggest that the low incidence of membrane-associated receptors observed in regions of somatodendritic sst2A labeling may be caused by downregulation of cell surface receptors by endogenous somatostatin, possibly through ligand-induced receptor internalization.
Endbulb Synapses in the Anteroventral Cochlear Nucleus Express a Specific Subset of AMPA-Type Glutamate Receptor Subunits
Authors: Wang Ya-Xian , Wenthold Robert J. , Ottersen Ole P. , Petralia Ronald S.
Published: April 2018

The anteroventral cochlear nucleus (AVCN) acts as the first relay center in the conduction of auditory information from the ear to the brain, and it probably performs a crucial role in sound localization. Auditory nerve input to the principal neurons of the AVCN, the spherical bushy cells, appears to be mediated by an excitatory amino acid such as glutamate, which acts at a specialized, large synaptic ending called an endbulb of Held. Presumably, endbulb synapses contain some specific combination of glutamate receptors to facilitate rapid neurotransmission of auditory signals. AMPA glutamate receptor composition at the endbulb synapses was examined with both light and electron microscope immunocytochemistry. Electron microscope localization of AMPA receptors was examined with two techniques, preembedding immunoperoxidase and postembedding immunogold, which provide maximum sensitivity and greatest accuracy, respectively. Dense and frequent labeling was seen with the AMPA receptor subunit antibodies GluR2/3 and GluR4, which were colocalized at the endbulb synapses. In contrast, immunolabeling with antibody to GluR2 was low. These data indicate that the major glutamate receptor at this synapse is an AMPA receptor made up mainly of GluR3 and GluR4 subunits. Receptors composed of these subunits display properties, such as calcium permeability and rapid desensitization, that facilitate their specialized functions in auditory information processing.
Optical Mapping of Neural Responses in the Embryonic Rat Brainstem with Reference to the Early Functional Organization of Vagal Nuclei
Authors: Sato Katsushige , Momose-Sato Yoko , Hirota Akihiko , Sakai Tetsuro , Kamino Kohtaro
Published: April 2018

We examined the functional organization of the vagal nuclei of the rat embryo during morphogenesis, using multiple-site optical recording with a voltage-sensitive dye. Slice preparations with vagus nerve fibers were dissected from 13- to 16-d-old embryonic (E13–E16) rat brainstems, and they were stained with the dye. Electrical activity in response to vagal stimulation was recorded optically from many sites. In the E13–E14 preparations, two types of spike-like optical signals were recorded: one was a narrow signal (type I), and the other was a broader signal (type II). Comparison with the morphology revealed by DiI labeling suggests that the type I signal response area corresponds to the nucleus of the tractus solitarius, and the type II signal response area corresponds to the dorsal motor nucleus of the vagus nerve. In the E15–E16 preparations, type I signals were followed by a slow signal related to glutamate-mediated excitatory postsynaptic potentials, suggesting that synaptic function is organized in the nucleus of the tractus solitarius by the 15-d-old embryonic stage. In the E14 preparation, a small, slow signal was evoked only in Mg2+-free solution, implying that postsynaptic function related to NMDA receptors emerges, in latent form, at the 14-d-old embryonic stage. In the E15 and E16 preparations, although the nucleus ambiguus is identified morphologically, no neural response-related optical signal was observed there, indicating that the embryonic organization of morphology and physiological function is not necessarily temporally coincident. We have mapped the dynamic spatiotemporal patterns of the evoked optical signals and have outlined the early phase of the functional organization of the cranial nuclei related to the vagus.
Widespread Elimination of Naturally Occurring Neuronal Death inBax-Deficient Mice
Authors: White Fletcher A. , Keller-Peck Cynthia R. , Knudson C. Michael , Korsmeyer Stanley J. , Snider William D.
Published: April 2018

The proapoptotic molecule BAX is required for death of sympathetic and motor neurons in the setting of trophic factor deprivation. Furthermore, adultBax−/−mice have more motor neurons than do their wild-type counterparts. These findings raise the possibility that BAX regulates naturally occurring cell death during development in many neuronal populations. To test this idea, we assessed apoptosis using TUNEL labeling in several well-studied neural systems during embryonic and early postnatal development inBax−/−mice. Remarkably, naturally occurring cell death is virtually eliminated between embryonic day 11.5 (E11.5) and postnatal day 1 (PN1) in most peripheral ganglia, in motor pools in the spinal cord, and in the trigeminal brainstem nuclear complex. Additionally, reduction, although not elimination, of cell death was noted throughout the developing cerebellum, in some layers of the retina, and in the hippocampus. Saving of cells was verified by axon counts of dorsal and ventral roots, as well as facial and optic nerves that revealed 24–35% increases in axon number. Interestingly, many of the supernumerary axons had very small cross-sectional areas, suggesting that the associated neurons are not normal. We conclude that BAX is a critical mediator of naturally occurring death of peripheral and CNS neurons during embryonic life. However, rescue from naturally occurring cell death does not imply that the neurons will develop normal functional capabilities.
The Pharmacology and Roles of two K+Channels in Motor Pattern Generation in theXenopusEmbryo
Authors: Kuenzi Frederick M. , Dale Nicholas
Published: April 2018

The spinal neurons of theXenopusembryo that participate in the swimming motor pattern possess two kinetically distinct sets of potassium currents: the fastIKfand sodium-dependentIKNa, which together constitute ∼80% of the outward current; and the slowIKs, which constitutes the remainder. To study their respective roles in cell excitability and the swimming pattern, we have characterized their pharmacological properties. Catechol selectively blocked the fast potassium currents (IC50, ∼10 μm). The block was voltage-dependent, with partial unblocking occurring at positive voltages. α-Dendrotoxin and dendrotoxin-I selectively blocked the slow potassium current. Catechol and the dendrotoxins had different effects on membrane excitability: catechol caused spike broadening but had little effect on repetitive firing, whereas both dendrotoxins markedly increased repetitive firing without affecting spike width. By applying these agents to the whole embryo, we tested the role of the fast and slow currents in motor pattern generation. Catechol had little effect on fictive swimming, suggesting that the fast K+currents are not critical to circuit operation. However, dendrotoxin disrupted swimming early in the episode and increased the duration of ventral root bursts. The slow K+current, which is a minor component of the total outward current, thus appears to play an important role in motor pattern generation.
Changes in the Properties of Gap Junctions during Neuronal Differentiation of Hippocampal Progenitor Cells
Authors: Rozental Renato , Morales Mildred , Mehler Mark F. , Urban Marcia , Kremer Marion , Dermietzel Rolf , Kessler John A. , Spray David C.
Published: April 2018

The cellular mechanisms that regulate progenitor cell lineage elaboration and maturation during embryonic development of the mammalian brain are poorly understood. Conditionally immortalized mouse hippocampal multipotent progenitor cells (MK31 cells) were found to be strongly coupled by gap junctions comprising connexin 43 (Cx43) during early neuronal ontogeny; the presence of this Cx type was confirmed by electrophysiological, molecular biological, and immunocytochemical assays. However, as progenitor cells underwent intermediate stages of neuronal differentiation under the influence of interleukin 7 (IL-7) alone or terminal differentiation after composite exposure to basic fibroblast growth factor, IL-7, and transforming growth factor α, coupling strength and the level of Cx43 expression declined. An additional population of junctional channels with distinct properties was detected at an intermediate stage of neuronal differentiation. Reverse transcription-PCR assays detected mRNA encoding Cx40 in IL-7-treated cells and Cx33 after both treatment conditions. Because functional channels in exogenous expression systems are not formed by pairing Cx40 with Cx43 or by pairing Cx33 with itself or additional connexins, these experimental observations raise the possibility that the progressive loss of coupling during differentiation of neural progenitor cells may involve downregulation of Cx43 coupled with potentiation of expression of Cx33 and Cx40. Furthermore, continued expression of Cx43 in differentiating neuroblasts could mediate intercellular communication between neuronal precursor cells and astrocytes by direct signaling via homotypic gap junction channels.
Spatial Firing of Hippocampal Place Cells in Blind Rats
Authors: Save Etienne , Cressant Arnaud , Thinus-Blanc Catherine , Poucet Bruno
Published: April 2018

The rat hippocampus contains cells that are characterized by location-specific firing. Previous work has shown that the angular position of hippocampal place cell firing fields is accurately controlled by the position of visual cues, suggesting that vision plays a important role in triggering place cell activity. However, a role for other types of information has also been suggested because place cell activity can be recorded while animals are moving in the darkness. In this study, we asked whether place fields can get established in rats that have never seen their environment. We studied place cell activity in early blind rats and found that these rats had place cells very similar to those recorded from sighted rats. This result suggests that early vision is not necessary for normal firing of hippocampal place cells. Dynamic, motion-related information in conjunction with stimulus recognition seems to be sufficient.
Contributions of the Dopaminergic System to Voluntary and Automatic Orienting of Visuospatial Attention
Authors: Yamaguchi Shuhei , Kobayashi Shotai
Published: April 2018

Visuospatial attention can be directed by voluntary or involuntary control independent of eye movement. The involvement of cortical and subcortical neural structures in this covert orienting mechanism has been studied using neuroimaging and electrophysiological techniques. This study was designed to investigate the role of the dopaminergic system in both voluntary and automatic orienting mechanisms of visuospatial attention. We recorded event-related evoked potentials (ERPs) and reaction time (RT) during a cued priming task in both patients with idiopathic Parkinson’s disease (PD) and control subjects. Voluntary and automatic shifts in attention were studied by using central and peripheral cues, respectively. In the experiment using a central cue, the RT data showed that when the cue–target interval was long, PD patients’ responses were delayed, and cue validity effects were reduced, whereas in the peripheral cue experiment the validity effects persisted across all trials. The ERPs demonstrated reduced sustained negativities preceding the imperative targets in both the central and peripheral cue experiments in PD patients. Furthermore, during the long cue–target interval in the central cue experiment, PD patients showed reduced attention shift-related negativities (ARNs) at the anterior scalp sites, whereas ARNs were generated widely in the peripheral cue experiment. The ERP findings were consistent with the RT data. These findings suggest that the dopaminergic system may contribute to voluntary and sustained control of visuospatial attention as well as to the neural system for response preparation, whereas automatic control of visuospatial attention is relatively independent of the dopamine system.
Presynaptic GABABAutoreceptor Modulation of P/Q-Type Calcium Channels and GABA Release in Rat Suprachiasmatic Nucleus Neurons
Authors: Chen Gong , van den Pol Anthony N.
Published: April 2018

GABA is the primary transmitter released by neurons of the suprachiasmatic nucleus (SCN), the circadian clock in the brain. Whereas GABABreceptor agonists exert a significant effect on circadian rhythms, the underlying mechanism by which GABABreceptors act in the SCN has remained a mystery. We found no GABABreceptor-mediated effect on slow potassium conductance, membrane potential, or input resistance in SCN neuronsin vitrousing whole-cell patch-clamp recording. In contrast, the GABABreceptor agonist baclofen (1–100 μm) exerted a large and dose-dependent inhibition (up to 100%) of evoked IPSCs. Baclofen reduced the frequency of spontaneous IPSCs but showed little effect on the frequency or amplitude of miniature IPSCs in the presence of tetrodotoxin. The activation of GABABreceptors did not modulate postsynaptic GABAAreceptor responses. The depression of GABA release by GABABautoreceptors appeared to be mediated primarily through a modulation of presynaptic calcium channels. The baclofen inhibition of both calcium currents and evoked IPSCs was greatly reduced (up to 100%) by the P/Q-type calcium channel blocker agatoxin IVB, suggesting that P/Q-type calcium channels are the major targets involved in the modulation of GABA release. To a lesser degree, N-type calcium channels were also involved. The inhibition of GABA release by baclofen was abolished by a pretreatment with pertussis toxin (PTX), whereas the inhibition of whole-cell calcium currents by baclofen was only partially depressed by PTX, suggesting that G-protein mechanisms involved in GABABreceptor modulation at the soma and axon terminal may not be identical. We conclude that GABABreceptor activation exerts a strong presynaptic inhibition of GABA release in SCN neurons, primarily by modulating P/Q-type calcium channels at axon terminals.
Mechanisms of Amphetamine Action Revealed in Mice Lacking the Dopamine Transporter
Authors: Jones Sara R. , Gainetdinov Raul R. , Wightman R. Mark , Caron Marc G.
Published: April 2018

Amphetamine (AMPH) inhibits uptake and causes release of dopamine (DA) from presynaptic terminals. AMPH can act on both vesicular storage of DA and directly on the dopamine transporter (DAT). To assess the relative importance of these two processes, we have examined the releasing actions of AMPH in mice with a genetic deletion of the DAT. The sequence of actions of AMPH has been determined by following the real time changes of DA in the extracellular fluid of intact tissue with fast scan cyclic voltammetry. In striatal slices from wild-type mice, AMPH causes a gradual (∼30 min) increase in extracellular DA, with a concomitant disappearance of the pool of DA available for depolarization-evoked release. Conversely, in slices from mice lacking the DAT, although a similar disappearance of electrically stimulated DA release occurs, extracellular DA does not increase. Similarly, microdialysis measurements of DA after AMPH in freely moving animals show no change in mice lacking the DAT, whereas it increases 10-fold in wild-type mice. In contrast, redistribution of DA from vesicles to the cytoplasm by the use of a reserpine-like compound, Ro4–1284, does not increase extracellular DA in slices from wild-type animals; however, subsequent addition of AMPH induces rapid (<5 min) release of DA. Thus, the DAT is required for the releasing action, but not the vesicle-depleting action, of AMPH on DA neurons, and the latter represents the rate-limiting step in the effects of AMPH. Furthermore, these findings suggest that in the absence of pharmacological manipulation, such as the use of amphetamine, endogenous cytoplasmic DA normally does not reach sufficient concentrations to reverse the DAT.
Ectopic Cell Cycle Proteins Predict the Sites of Neuronal Cell Death in Alzheimer’s Disease Brain
Authors: Busser Jonathan , Geldmacher David S. , Herrup Karl
Published: April 2018

Alzheimer’s disease (AD) is a major dementing illness characterized by regional concentrations of senile plaques, neurofibrillary tangles, and extensive neuronal cell death. Although cell and synaptic loss is most directly linked to the severity of symptoms, the mechanisms leading to the neuronal death remain unclear. Based on evidence linking neuronal death during development to unexpected reappearance of cell cycle events, we investigated the brains of 12 neuropathologically verified cases of Alzheimer’s disease and eight age-matched, disease-free controls for the presence of cell cycle proteins. Aberrant expression of cyclin D, cdk4, proliferating cell nuclear antigen, and cyclin B1 were identified in the hippocampus, subiculum, locus coeruleus, and dorsal raphe nuclei, but not inferotemporal cortex or cerebellum of AD cases. With only one exception, control subjects showed no significant expression of cell cycle markers in any of the six regions. We propose that disregulation of various components of the cell cycle is a significant contributor to regionally specific neuronal death in AD.
Protein Kinase C Disrupts Cannabinoid Actions by Phosphorylation of the CB1 Cannabinoid Receptor
Authors: Garcia D. E. , Brown S. , Hille B. , Mackie K.
Published: April 2018

We have found that phosphorylation of a G-protein-coupled receptor by protein kinase C (PKC) disrupts modulation of ion channels by the receptor. In AtT-20 cells transfected with rat cannabinoid receptor (CB1), the activation of an inwardly rectifying potassium current (Kircurrent) and depression of P/Q-type calcium channels by cannabinoids were prevented by stimulation of protein kinase C by 100 nmphorbol 12-myristate 13-acetate (PMA). In contrast, activation of Kircurrent by somatostatin was unaffected, and inhibition of calcium channels was only modestly attenuated. The possibility that PKC acted by phosphorylating CB1 receptors was confirmed by demonstrating that PKC phosphorylated a single serine (S317) of a fusion protein incorporating the third intracellular loop of CB1. Mutating this serine to alanine did not affect the ability of CB1 to modulate currents, but it eliminated disruption by PMA, demonstrating that PKC can disrupt ion channel modulation by receptor phosphorylation.
A Neuronal Sec1 Homolog Regulates Neurotransmitter Release at the Squid Giant Synapse
Authors: Dresbach T. , Burns M. E. , O’Connor V. , DeBello W. M. , Betz H. , Augustine G. J.
Published: April 2018

Sec1-related proteins are essential for membrane fusion at distinct stages of the constitutive and regulated secretory pathways in eukaryotic cells. Studies of neuronal isoforms of the Sec1 protein family have yielded evidence for both positive and negative regulatory functions of these proteins in neurotransmitter release. Here, we have identified a squid neuronal homolog (s-Sec1) of Sec1 proteins and examined its function in neurotransmitter release at the squid giant synapse. Microinjection of s-Sec1 into the presynaptic terminal of the giant synapse inhibited evoked neurotransmitter release, but this effect was prevented by coinjecting the cytoplasmic domain of squid syntaxin (s-syntaxin), one of the binding partners of s-Sec1. A 24 amino acid peptide fragment of s-Sec1, which inhibited the binding of s-Sec1 to s-syntaxinin vitro, completely blocked release, suggesting an essential function of the s-Sec1/s-syntaxin interaction in transmitter release. Electron microscopy showed that injection of s-Sec1 did not change the spatial distribution of synaptic vesicles at presynaptic release sites (“active zones”), whereas the inhibitory peptide increased the number of docked vesicles. These distinct morphological effects lead us to conclude that Sec1 proteins function at different stages of synaptic vesicle exocytosis, and that an interaction of s-Sec1 with syntaxin—at a stage blocked by the peptide—is necessary for docked vesicles to fuse.
Development of a Sexually Dimorphic Projection from the Bed Nuclei of the Stria Terminalis to the Anteroventral Periventricular Nucleus in the Rat
Authors: Hutton Leslie A. , Gu Guibao , Simerly Richard B.
Published: April 2018

The principal nucleus of the bed nuclei of the stria terminalis (BSTp) is larger in male rats and conveys olfactory information relevant for reproduction to the hypothalamus. In males, the BSTp provides a massive projection to the anteroventral periventricular nucleus of the preoptic region (AVPV), which in contrast to most sexually dimorphic nuclei contains more neurons in female rats. Injections of the anterograde tracerPhaseolus vulgarisleucoagglutinin into the BSTp of adult female rats failed to demonstrate the strong projection to the AVPV observed previously in males. The ontogeny of this robust sex difference was examined by using the axonal marker DiI. The projection from the BSTp to the AVPV is established between postnatal day 9 (P9) and P10 in male rats and seems to be maintained during the juvenile period. Although labeled fibers extended from the BSTp toward the preoptic region in both male and female neonates, a similar connection with the AVPV was not apparent in female rats at any of the ages studied, and the density of labeled axons in the AVPV of P10 males was 20-fold greater than that of P10 females. A projection from the BSTp to the medial preoptic nucleus was also weaker in females but was much more substantial than that to the AVPV. These findings suggest that a sex- and region-specific activity influences the development of the projection from the BSTp to the AVPV, producing a sexually dimorphic architecture in pathways that convey olfactory information to the hypothalamus.
Pharmacological Specialization of Learned Auditory Responses in the Inferior Colliculus of the Barn Owl
Authors: Feldman Daniel E. , Knudsen Eric I.
Published: April 2018

Neural tuning for interaural time difference (ITD) in the optic tectum of the owl is calibrated by experience-dependent plasticity occurring in the external nucleus of the inferior colliculus (ICX). When juvenile owls are subjected to a sustained lateral displacement of the visual field by wearing prismatic spectacles, the ITD tuning of ICX neurons becomes systematically altered; ICX neurons acquire novel auditory responses, termed “learned responses,” to ITD values outside their normal, pre-existing tuning range. In this study, we compared the glutamatergic pharmacology of learned responses with that of normal responses expressed by the same ICX neurons. Measurements were made in the ICX using iontophoretic application of glutamate receptor antagonists. We found that in early stages of ITD tuning adjustment, soon after learned responses had been induced by experience-dependent processes, the NMDA receptor antagonistd,l-2-amino-5-phosphonopentanoic acid (AP-5) preferentially blocked the expression of learned responses of many ICX neurons compared with that of normal responses of the same neurons. In contrast, the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) blocked learned and normal responses equally. After long periods of prism experience, preferential blockade of learned responses by AP-5 was no longer observed. These results indicate that NMDA receptors play a preferential role in the expression of learned responses soon after these responses have been induced by experience-dependent processes, whereas later in development or with additional prism experience (we cannot distinguish which), the differential NMDA receptor-mediated component of these responses disappears. This pharmacological progression resembles the changes that occur during maturation of glutamatergic synaptic currents during early development.