bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Dopamine in the Nucleus Accumbens and Striatum during Sexual Behavior in the Female Rat
Authors: Becker Jill B. , Rudick Charles N. , Jenkins William J.
Published: April 2018

Dopamine in dialysate from the nucleus accumbens (NAcc) increases during sexual and feeding behavior and after administration of drugs of abuse, even those that do not directly activate dopaminergic systems (e.g., morphine or nicotine). These findings and others have led to hypotheses that propose that dopamine is rewarding, predicts that reinforcement will occur, or attributes incentive salience. Examining increases in dopamine in NAcc or striatum during sexual behavior in female rats provides a unique situation to study these relations. This is because, for the female rat, sexual behavior is associated with an increase in NAcc dopamine and conditioned place preference only under certain testing conditions. This experiment was conducted to determine what factors are important for the increase in dopamine in dialysate from NAcc and striatum during sexual behavior in female rats. The factors considered were the number of contacts by the male, the timing of contacts by the male, or the ability of the female to control contacts by the male. The results indicate that increased NAcc dopamine is dependent on the timing of copulatory stimuli, independent of whether the female rat is actively engaged in regulating this timing. For the striatum, the timing of copulatory behavior influences the magnitude of the increase in dopamine in dialysate, but other factors are also involved. We conclude that increased extracellular dopamine in the NAcc and striatum conveys qualitative or interpretive information about the rewarding value of stimuli. Sexual behavior in the female rat is proposed as a model to determine the role of dopamine in motivated behavior.
Cyclin-Dependent Kinases and P53 Pathways Are Activated Independently and Mediate Bax Activation in Neurons after DNA Damage
Authors: Morris Erick J. , Keramaris Elizabeth , Rideout Hardy J. , Slack Ruth S. , Dyson Nicholas J. , Stefanis Leonidas , Park David S.
Published: April 2018

DNA damage has been implicated as one important initiator of cell death in neuropathological conditions such as stroke. Accordingly, it is important to understand the signaling processes that control neuronal death induced by this stimulus. Previous evidence has shown that the death of embryonic cortical neurons treated with the DNA-damaging agent camptothecin is dependent on the tumor suppressor p53 and cyclin-dependent kinase (CDK) activity and that the inhibition of either pathway alone leads to enhanced and prolonged survival. We presently show that p53 and CDKs are activated independently on parallel pathways. An increase in p53 protein levels, nuclear localization, and DNA binding that result from DNA damage are not affected by the inhibition of CDK activity. Conversely, no decrease in retinoblastoma protein (pRb) phosphorylation was observed in p53-deficient neurons that were treated with camptothecin. However, either p53 deficiency or the inhibition of CDK activity alone inhibited Bax translocation, cytochromecrelease, and caspase-3-like activation. Taken together, our results indicate that p53 and CDK are activated independently and then act in concert to control Bax-mediated apoptosis.
Plasma Membrane Ca2+-ATPase Isoform 2a Is the PMCA of Hair Bundles
Authors: Dumont Rachel A. , Lins Ulysses , Filoteo Adelaida G. , Penniston John T. , Kachar Bechara , Gillespie Peter G.
Published: April 2018

Mechanoelectrical transduction channels of hair cells allow for the entry of appreciable amounts of Ca2+, which regulates adaptation and triggers the mechanical activity of hair bundles. Most Ca2+that enters transduction channels is extruded by the plasma membrane Ca2+-ATPase (PMCA), a Ca2+pump that is highly concentrated in hair bundles and may be essential for normal hair cell function. Because PMCA isozymes and splice forms are regulated differentially and have distinct biochemical properties, we determined the identity of hair bundle PMCA in frog and rat hair cells. By screening a bullfrog saccular cDNA library, we identified abundant PMCA1b and PMCA2a clones as well as rare PMCA2b and PMCA2c clones. Using immunocytochemistry and immunoprecipitation experiments, we showed in bullfrog sacculus that PMCA1b is the major isozyme of hair cell and supporting cell basolateral membranes and that PMCA2a is the only PMCA present in hair bundles. This complete segregation of PMCA1 and PMCA2 isozymes holds for rat auditory and vestibular hair cells; PMCA2a is the only PMCA isoform in hair bundles of outer hair cells and vestibular hair cells and is the predominant PMCA of hair bundles of inner hair cells. Our data suggest that hair cells control plasma membrane Ca2+-pumping activity by targeting specific PMCA isozymes to distinct subcellular locations. Because PMCA2a is the only Ca2+pump present at appreciable levels in hair bundles, the biochemical properties of this pump must account fully for the physiological features of transmembrane Ca2+pumping in bundles.
Inhibition of Mitochondrial Complex II Induces a Long-Term Potentiation of NMDA-Mediated Synaptic Excitation in the Striatum Requiring Endogenous Dopamine
Authors: Calabresi Paolo , Gubellini Paolo , Picconi Barbara , Centonze Diego , Pisani Antonio , Bonsi Paola , Greengard Paul , Hipskind Robert A. , Borrelli Emiliana , Bernardi Giorgio
Published: April 2018

Abnormal involuntary movements and cognitive impairment represent the classical clinical symptoms of Huntington's disease (HD). This genetic disorder involves degeneration of striatal spiny neurons, but not striatal large cholinergic interneurons, and corresponds to a marked decrease in the activity of mitochondrial complex II [succinate dehydrogenase (SD)] in the brains of HD patients. Here we have examined the possibility that SD inhibitors exert their toxic action by increasing glutamatergic transmission. We report that SD inhibitors such as 3-nitroproprionic acid (3-NP), but not an inhibitor of mitochondrial complex I, produce a long-term potentiation of the NMDA-mediated synaptic excitation (3-NP-LTP) in striatal spiny neurons. In contrast, these inhibitors had no effect on excitatory synaptic transmission in striatal cholinergic interneurons and pyramidal cortical neurons. 3-NP-LTP involves increased intracellular calcium and activation of the mitogen-activated protein kinase extracellular signal-regulated kinase and is critically dependent on endogenous dopamine acting via D2 receptors, whereas it is negatively regulated by D1 receptors. Thus 3-NP-LTP might play a key role in the regional and cell type-specific neuronal death observed in HD.
A Critical Role of the Strychnine-Sensitive Glycinergic System in Spontaneous Retinal Waves of the Developing Rabbit
Authors: Zhou Z. Jimmy
Published: April 2018

In the developing vertebrate retina, spontaneous electric activity occurs rhythmically in the form of propagating waves and is believed to play a critical role in activity-dependent visual system development, including the establishment of precise retinal and geniculate circuitry. To elucidate how spontaneous retinal waves encode specific developmental cues at various developmental stages, it is necessary to understand how the waves are generated and regulated. Using Ca2+imaging and patch clamp in a flat-mount perinatal rabbit retinal preparation, this study demonstrates that, in addition to the cholinergic system, a strychnine-sensitive system in the inner retina plays an obligatory and developmentally regulated role in the initiation and propagation of spontaneous retinal waves. This system, which is believed to be the glycinergic network, provided an excitatory drive during early retinal development. It then became inhibitory after postnatal day 1 (P1) to P2, an age when a number of coordinated transitions in neurotransmitter systems occurred concomitantly, and finally contributed to the complete inhibition and disappearance of spontaneous waves after P7–P9. This glycinergic contribution was notably distinct from that of the ionotropic GABAergic system, which was found to exert an inhibitory but nonessential influence on the early wave formation. Blocking glycine- and GABA-gated anion currents had opposing effects on spontaneous retinal waves between embryonic day 29 and P0, suggesting that Cl−transporters, particularlyR(+)-butylindazone-sensitive K-Cl cotransporters, may have a synapse- and/or cell type-specific distribution pattern, in addition to an age-dependent expression pattern in the inner retina. Overall, the results revealed an important reliance of spontaneous retinal waves on dynamic and coordinated interactions among multiple, nonredundant neurotransmitter systems.
Long-Lasting Enhancement of Glutamatergic Synaptic Transmission by Acetylcholine Contrasts with Response Adaptation after Exposure to Low-Level Nicotine
Authors: Girod Romain , Role Lorna W.
Published: April 2018

Attempts to mimic synaptic delivery of acetylcholine (ACh) with brief, repetitive pulses of high concentration ACh at synapses of medial habenula (MHN) and interpeduncular nucleus (IPN) neuronsin vitroelicited temporally distinct facilitation and inhibition of glutamate secretion via nicotinic and muscarinic ACh receptor-mediated pathways, respectively. ACh-induced nicotinic facilitation was sustained for up to 2 hr, whereas muscarinic inhibition was transient. Prolonged exposure to nicotine inactivated nicotinic receptors selectively, thus decreasing the relative contribution of the facilitatory versus inhibitory influences of ACh. The net effect of ACh in modulating glutamatergic transmission at MHN–IPN synapses may be determined by pre-exposure to nicotine, because the drug appears to switch the balance between the facilitatory and inhibitory actions of ACh.
Amygdala Is Critical for Stress-Induced Modulation of Hippocampal Long-Term Potentiation and Learning
Authors: Kim Jeansok J. , Lee Hongjoo J. , Han Jung-Soo , Packard Mark G.
Published: April 2018

Stress is a biologically significant factor shown to influence synaptic plasticity and memory functioning in the hippocampus. This study examined the role of the amygdala, a brain structure implicated in coordinating stress behaviors and modulating memory consolidation, in mediating stress effects on hippocampal long-term potentiation (LTP) and memory in rats. Electrolytic lesions of the amygdala effectively blocked the adverse physiological and behavioral effects of restraint and tailshock stress, without impeding the increase in corticosterone secretion to stress. Physiologically, hippocampal slices from stressed animals exhibited impaired LTP relative to slices from unstressed control animals, whereas hippocampal slices from stressed animals with amygdalar lesions exhibited normal LTP. Behaviorally, stressed animals were impaired in retention of a hippocampal-dependent hidden platform version of the Morris water maze task, and this impairment was blocked by amygdalar lesions. In a fixed location–visible platform water maze task that can be acquired by independent hippocampal and nonhippocampal memory systems, stress enhanced the use of nonhippocampal-based memory to acquire the task. These results indicate that an intact amygdala is necessary for the expression of the modulatory effects of stress on hippocampal LTP and memory.
Involvement of Human Amygdala and Orbitofrontal Cortex in Hunger-Enhanced Memory for Food Stimuli
Authors: Morris J. S. , Dolan R. J.
Published: April 2018

We used positron emission tomography to measure regional cerebral blood flow (rCBF) in 10 healthy volunteers performing a recognition memory task with food and non-food items. The biological salience of the food stimuli was manipulated by requiring subjects to fast before the experiment and eat to satiation at fixed time points during scanning. All subjects showed enhanced recognition of food stimuli (relative to non-food) in the fasting state. Satiation significantly reduced the memory advantage for food. Left amygdala rCBF covaried positively with recognition memory for food items, whereas rCBF in right anterior orbitofrontal cortex covaried with overall memory performance. Right posterior orbitofrontal rCBF covaried positively with hunger ratings during presentation of food items. Regression analysis of the neuroimaging data revealed that left amygdala and right lateral orbitofrontal rCBF covaried as a function of stimulus category (i.e., food vs non-food). These results indicate the involvement of amygdala and discrete regions of orbitofrontal cortex in the integration of perceptual (food), motivational (hunger), and cognitive (memory) processes in the human brain.
PKCγ Contributes to a Subset of the NMDA-Dependent Spinal Circuits That Underlie Injury-Induced Persistent Pain
Authors: Martin William J. , Malmberg Annika B. , Basbaum Allan I.
Published: April 2018

In previous studies we provided evidence that the γ isoform of protein kinase C (PKCγ) is an important contributor to the increased pain sensitivity that occurs after injury. Here we combined electrophysiological and behavioral approaches in wild-type and PKCγ-null mice to compare the hyperexcitability of wide dynamic range neurons in lamina V of the spinal cord dorsal horn with the behavioral hyperexcitability produced by the same injury [application of a C-fiber irritant, mustard oil (MO), to the hindpaw]. Wild-type and null mice did not differ in their response to mechanical or thermal stimuli before tissue injury, and the magnitude of the response to the MO stimuli was comparable. In wild-type mice, MO produced a dramatic and progressive enhancement of the response of lamina V neurons to innocuous mechanical and thermal stimuli. The time course of the neuronal hyperexcitability paralleled the time course of the MO-induced behavioral allodynia (nocifensive behavior in response to a previously innocuous mechanical stimulus). Neuronal hyperexcitability was also manifest in the PKCγ-null mice, but it lasted <30 min. By contrast, the behavioral allodynia produced by MO in the PKCγ-null mice, although reduced to approximately half that of the wild-type mice, persisted long after the lamina V hyperexcitability had subsided. Because the MO-induced behavioral allodynia was completely blocked by an NMDA receptor antagonist, we conclude that PKCγ mediates the transition from short- to long-term hyperexcitability of lamina V nociresponsive neurons but that the persistence of injury-induced pain must involve activity within multiple NMDA-dependent spinal cord circuits.
Caspase-9 Activation Results in Downstream Caspase-8 Activation and Bid Cleavage in 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine-Induced Parkinson's Disease
Authors: Viswanath Veena , Wu Yongqin , Boonplueang Rapee , Chen Sylvia , Stevenson Fang Feng , Yantiri Ferda , Yang Lichuan , Beal M. Flint , Andersen Julie K.
Published: April 2018

Parkinson's disease (PD) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity are both associated with dopaminergic neuron death in the substantia nigra (SN). Apoptosis has been implicated in this cell loss; however, whether or not it is a major component of disease pathology remains controversial. Caspases are a major class of proteases involved in the apoptotic process. To evaluate the role of caspases in PD, we analyzed caspase activation in MPTP-treated mice, in cultured dopaminergic cells, and in postmortem PD brain tissue. MPTP was found to elicit not only the activation of the effector caspase-3 but also the initiators caspase-8 and caspase-9, mitochondrial cytochromecrelease, and Bid cleavage in the SN of wild-type mice. These changes were attenuated in transgenic mice neuronally expressing the general caspase inhibitor protein baculoviral p35. These mice also displayed increased resistance to the cytotoxic effects of the drug. MPTP-associated toxicity in culture was found temporally to involve cytochromecrelease, activation of caspase-9, caspase-3, and caspase-8, and Bid cleavage. Caspase-9 inhibition prevented the activation of both caspase-3 and caspase-8 and also inhibited Bid cleavage, but not cytochromecrelease. Activated caspase-8 and caspase-9 were immunologically detectable within MPP+-treated mesencephalic dopaminergic neurons, dopaminergic nigral neurons from MPTP-treated mice, and autopsied Parkinsonian tissue from late-onset sporadic cases of the disease. These data demonstrate that MPTP-mediated activation of caspase-9 via cytochromecrelease results in the activation of caspase-8 and Bid cleavage, which we speculate may be involved in the amplification of caspase-mediated dopaminergic cell death. These data suggest that caspase inhibitors constitute a plausible therapeutic for PD.
Rapid Redistribution of the Postsynaptic Density Protein PSD-Zip45 (Homer 1c) and Its Differential Regulation by NMDA Receptors and Calcium Channels
Authors: Okabe Shigeo , Urushido Tomoe , Konno Daijiro , Okado Haruo , Sobue Kenji
Published: April 2018

PSD-Zip45 (Homer 1c) and PSD-95 are postsynaptic density (PSD) proteins containing distinct protein-interacting motifs. Green fluorescent protein (GFP)-tagged PSD-Zip45 and PSD-95 molecules were targeted to the PSD in hippocampal neurons. We analyzed dynamic behavior of these GFP-tagged PSD proteins by using time-lapse confocal microscopy. In contrast to the less dynamic properties of PSD-95, PSD-Zip45 showed rapid redistribution and a higher steady-state turnover rate. Differential stimulation protocols were found to alter the direction of PSD-Zip45 assembly–disassembly. Transient increases in intracellular Ca2+by voltage-dependent Ca2+channel activation induced PSD-Zip45 clustering. In contrast, NMDA receptor-dependent Ca2+influx resulted in the disassembly of PSD-Zip45 clusters. Thus, neuronal activity differentially redistributes a specific subset of PSD proteins, which are important for localization of both surface receptors and intracellular signaling complexes.
Schwann Cells Express Active Agrin and Enhance Aggregation of Acetylcholine Receptors on Muscle Fibers
Authors: Yang Jie-Fei , Cao Guan , Koirala Samir , Reddy Linga V. , Ko Chien-Ping
Published: April 2018

To explore novel roles of glial cells in synaptic function and formation, we examined the expression of agrin in frog Schwann cells and tested their role in the aggregation of acetylcholine receptors (AChRs). Using reverse transcription-PCR, we found that Schwann cells along nerve fibers in tadpoles expressed only the inactive agrin isoform B0 but began to also express active agrin isoforms B11 and B19 at approximately metamorphosis. During nerve regeneration in the adult, the expression of these active agrin isoforms in Schwann cells was upregulated, including the appearance of the most potent isoform, B8. This upregulation was induced by regenerating axons but not by nerve injury per se. In muscle cultures, the presence of adult Schwann cells enhanced the number and the total area of AChR aggregates 2.2- and 4.5-fold, respectively, and this enhancement was eliminated by heparin treatment. Furthermore, adult Schwann cells in culture expressed active agrin isoforms and produced agrin protein. Using a novel technique to selectively ablate perisynaptic Schwann cells (PSCs) at the neuromuscular junction, we found that PSCs also expressed active agrin isoforms B11 and B19, and these active isoforms were upregulated, including the appearance of B8, during reinnervation. Observationin vivoshowed that extrajunctional AChR aggregates were associated with PSC sprouts after nerve injury and subsequent reinnervation. These results suggest that, contrary to the prevailing view that only neurons express active agrin, glial cells also express active agrin and play a role in the aggregation of AChRs bothin vitroandin vivo.
Elevated Postsynaptic [Ca2+]iand L-Type Calcium Channel Activity in Aged Hippocampal Neurons: Relationship to Impaired Synaptic Plasticity
Authors: Thibault Olivier , Hadley Robert , Landfield Philip W.
Published: April 2018

Considerable evidence supports a Ca2+dysregulation hypothesis of brain aging and Alzheimer's disease. However, it is still not known whether (1) intracellular [Ca2+]iis altered in aged brain neurons during synaptically activated neuronal activity; (2) altered [Ca2+]iis directly correlated with impaired neuronal plasticity; or (3) the previously observed age-related increase in L-type voltage-sensitive Ca2+channel (L-VSCC) density in hippocampal neurons is sufficient to impair synaptic plasticity. Here, we used confocal microscopy to image [Ca2+]iin single CA1 neurons in hippocampal slices of young-adult and aged rats during repetitive synaptic activation. Simultaneously, we recorded intracellular EPSP frequency facilitation (FF), a form of short-term synaptic plasticity that is impaired with aging and inversely correlated with cognitive function. Resting [Ca2+]idid not differ clearly with age. Greater elevation of somatic [Ca2+]iand greater depression of FF developed in aged neurons during 20 sec trains of 7 Hz synaptic activation, but only if the activation triggered repetitive action potentials for several seconds. Elevated [Ca2+]iand FF also were negatively correlated in individual aged neurons. In addition, the selective L-VSCC agonist Bay K8644 increased the afterhyperpolarization and mimicked the depressive effects of aging on FF in young-adult neurons. Thus, during physiologically relevant firing patterns in aging neurons, postsynaptic Ca2+elevation is closely associated with altered neuronal plasticity. Moreover, selectively increasing postsynaptic L-VSCC activity, as occurs in aging, negatively regulated a form of short-term plasticity that enhances synaptic throughput. Together, the results elucidate novel processes that may contribute to impaired cognitive function in aging.
Early Development of Neuronal Activity in the Primate HippocampusIn Utero
Authors: Khazipov Roustem , Esclapez Monique , Caillard Olivier , Bernard Christophe , Khalilov Ilgam , Tyzio Roman , Hirsch June , Dzhala Volodymyr , Berger Brigitte , Ben-Ari Yehezkel
Published: April 2018

Morphological studies suggest that the primate hippocampus develops extensively before birth, but little is known about its functional development. Patch-clamp recordings of hippocampal neurons and reconstruction of biocytin-filled pyramidal cells were performed in slices of macaque cynomolgus fetuses delivered by cesarean section. We found that during the second half of gestation, axons and dendrites of pyramidal cells grow intensively by hundreds of micrometers per day to attain a high level of maturity near term. Synaptic currents appear around midgestation and are correlated with the level of morphological differentiation of pyramidal cells: the first synapses are GABAergic, and their emergence correlates with the growth of apical dendrite into stratum radiatum. A later occurrence of glutamatergic synaptic currents correlates with a further differentiation of the axodendritic tree and the appearance of spines. Relying on the number of dendritic spines, we estimated that hundreds of new glutamatergic synapses are established every day on a pyramidal neuron during the last third of gestation. Most of the synaptic activity is synchronized in spontaneous slow (≈0.1 Hz) network oscillations reminiscent of the giant depolarizing potentials in neonatal rodents. Epileptiform discharges can be evoked by the GABA(A) receptor antagonist bicuculline by the last third of gestation, and postsynaptic GABA(B) receptors contribute to the termination of epileptiform discharges. Comparing the results obtained in primates and rodents, we conclude that the template of early hippocampal network development is conserved across the mammalian evolution but that it is shifted toward fetal life in primate.
Control of Dorsal Raphe Serotonergic Neurons by the Medial Prefrontal Cortex: Involvement of Serotonin-1A, GABAA, and Glutamate Receptors
Authors: Celada Pau , Puig M. Victoria , Casanovas Josep M. , Guillazo Gemma , Artigas Francesc
Published: April 2018

Anatomical evidence indicates that medial prefrontal cortex (mPFC) neurons project to the dorsal raphe nucleus (DR). In this study, we functionally characterized this descending pathway in rat brain. Projection neurons in the mPFC were identified by antidromic stimulation from the DR. Electrical stimulation of the mPFC mainly inhibited the activity of DR 5-HT neurons (55 of 66). Peristimulus time histograms showed a silence of 150 ± 9 msec poststimulus (latency, 36 ± 1 msec). The administration of WAY-100635 and picrotoxinin partly reversed this inhibition, indicating the involvement of 5-HT1Aand GABAAreceptors. In rats depleted of 5-HT withp-chlorophenylalanine, the electrical stimulation of mPFC mainly activated 5-HT neurons (31 of 40). The excitations (latency, 17 ± 1 msec) were antagonized by MK-801 and NBQX. Likewise, MK-801 prevented the rise in DR 5-HT release induced by electrical stimulation of mPFC. The application of 8-OH-DPAT in mPFC significantly inhibited the firing rate of DR 5-HT neurons and, in dual-probe microdialysis experiments, reduced the 5-HT output in mPFC and DR. Furthermore, the application of WAY-100635 in mPFC significantly antagonized the reduction of 5-HT release produced by systemic 8-OH-DPAT administration in both areas. These results indicate the existence of a complex regulation of DR 5-HT neurons by mPFC afferents. The stimulus-induced excitation of some 5-HT neurons by descending excitatory fibers releases 5-HT, which inhibits the same or other DR neurons by acting on 5-HT1Aautoreceptors. Afferents from the mPFC also inhibit 5-HT neurons through the activation of GABAergic interneurons. Ascending serotonergic pathways may control the activity of this descending pathway by acting on postsynaptic 5-HT1Areceptors.
Kurtoxin, A Gating Modifier of Neuronal High- and Low-Threshold Ca Channels
Authors: Sidach Serguei S. , Mintz Isabelle M.
Published: April 2018

Studies of Ca channels expressed in oocytes have identified kurtoxin as a promising tool for functional and structural studies of low-threshold T-type Ca channels. This peptide, isolated from the venomous scorpionParabuthus transvaalicus, inhibits low-threshold α1G and α1H Ca channels expressed in oocytes with relatively high potency and high selectivity. Here we report its effects on Ca channel currents, carried by 5 mmBa2+ions, in rat central and peripheral neurons. In thalamic neurons 500 nmkurtoxin inhibited T-type Ca channel currents almost completely (90.2 ± 2.5% at −85 mV;n= 6). Its selectivity, however, was less than expected because it also reduced the composite high-threshold Ca channel current recorded in these cells (46.1 ± 6.9% at −30 mV;n= 6). In sympathetic and thalamic neurons, 250–500 nmkurtoxin partially inhibited N-type and L-type Ca channel currents, respectively. It similarly reduced the high-threshold Ca channel current that remains after a blockade of P-type, N-type, and L-type Ca channels in thalamic neurons. In contrast, kurtoxin facilitated steady-state P-type Ba currents in Purkinje neurons (by 34.9 ± 3.7%;n= 10). In all cases the kurtoxin effect was voltage-dependent and entailed a modification of channel gating. Exposure to kurtoxin slowed current activation kinetics, although its effects on deactivation varied with the channel types. Kurtoxin thus appears as a unique gating-modifier that interacts with different Ca channel types with high affinity. This unusual property and the complex gating modifications it induces may facilitate future studies of gating in voltage-dependent ion channels.
Intrinsic Firing Dynamics of Vestibular Nucleus Neurons
Authors: Sekirnjak Chris , du Lac Sascha
Published: April 2018

Individual brainstem neurons involved in vestibular reflexes respond to identical head movements with a wide range of firing responses. This diversity of firing dynamics has been commonly assumed to arise from differences in the types of vestibular nerve inputs to vestibular nucleus neurons. In this study we show that, independent of the nature of inputs, the intrinsic membrane properties of neurons in the medial vestibular nucleus substantially influence firing response dynamics. Hyperpolarizing and depolarizing inputs evoked a markedly heterogenous range of firing responses. Strong postinhibitory rebound firing (PRF) was associated with strong firing rate adaptation (FRA) and occurred preferentially in large multipolar neurons. In response to sinusoidally modulated input current, these neurons showed a pronounced phase lead with respect to neurons lacking strong PRF and FRA. A combination of the hyperpolarization-activated H current and slow potassium currents contributed to PRF, whereas FRA was predominantly mediated by slow potassium currents. An integrate-and-fire-type model, which simulated FRA and PRF, reproduced the phase lead observed in large neurons and showed that adaptation currents were primarily responsible for variations in response phase. We conclude that the heterogeneity of firing dynamics observed in response to head movements in intact animals reflects intrinsic as well as circuit properties.
Using Optical Flow to Characterize Sensory-Motor Interactions in a Segment of the Medicinal Leech
Authors: Zoccolan Davide , Torre Vincent
Published: April 2018

Activation of motoneurons innervating leech muscles causes the appearance of a two-dimensional vector field of deformations on the skin surface that can be fully characterized using a new technique (Zoccolan et al., 2001) based on the computation of the optical flow, the two-dimensional vector field describing the point displacements on the skin. These vector fields are characterized by their origin (i.e., the singular point) and by four elementary components that combine linearly: expansion (or compression), rotation, longitudinal shear, and oblique shear. All motoneurons can be classified and recognized according to the components of the deformations they elicit: longitudinal motoneurons give rise almost exclusively to longitudinal negative shear, whereas circular motoneurons give rise to both positive longitudinal shear and significant negative expansion. Oblique motoneurons induce strong oblique shear, in addition to longitudinal shear and negative expansion. Vector fields induced by the contraction of longitudinal, circular, and oblique fibers superimpose linearly. Skin deformations can therefore be attributed rather reliably to the contraction of distinct longitudinal, circular, and oblique muscle fibers. We compared the deformation patterns produced by touching the skin with those produced by intracellular stimulation of P, T, and N cells: vector fields resulting from the activation of P cells were almost identical to those produced by mechanical stimulation. Therefore, motor responses triggered by light or moderate touch are almost entirely mediated by excitation of P cells, with minor contributions from T and N cells.
Facilitation of Conditioned Fear Extinction by Systemic Administration or Intra-Amygdala Infusions of d-Cycloserine as Assessed with Fear-Potentiated Startle in Rats
Authors: Walker David L. , Ressler Kerry J. , Lu Kwok-Tung , Davis Michael
Published: April 2018

NMDA receptor antagonists block conditioned fear extinction when injected systemically and also when infused directly into the amygdala. Here we evaluate the ability ofd-cycloserine (DCS), a partial agonist at the strychnine-insensitive glycine-recognition site on the NMDA receptor complex, to facilitate conditioned fear extinction after systemic administration or intra-amygdala infusions.

Rats received 10 pairings of a 3.7 sec light and a 0.4 mA footshock (fear conditioning). Fear-potentiated startle (increased startle in the presence vs the absence of the light) was subsequently measured before and after 30, 60, or 90 presentations of the light without shock (extinction training). Thirty non-reinforced light presentations produced modest extinction, and 60 or 90 presentations produced nearly complete extinction (experiment 1). DCS injections (3.25, 15, or 30 mg/kg) before 30 non-reinforced light exposures dose-dependently enhanced extinction (experiment 2) but did not influence fear-potentiated startle in rats that did not receive extinction training (experiment 3). These effects were blocked by HA-966, an antagonist at the glycine-recognition site (experiment 4). Neither DCS nor HA-966 altered fear-potentiated startle when injected before testing (experiment 5). The effect of systemic administration was mimicked by intra-amygdala DCS (10 μg/side) infusions (experiment 6).

These results indicate that treatments that promote NMDA receptor activity after either systemic or intra-amygdala administration promote the extinction of conditioned fear.
The Age-Related Decrease in CNS Remyelination Efficiency Is Attributable to an Impairment of Both Oligodendrocyte Progenitor Recruitment and Differentiation
Authors: Sim Fraser J. , Zhao Chao , Penderis Jacques , Franklin Robin J. M.
Published: April 2018

The age-associated decrease in the efficiency of CNS remyelination has clear implications for recovery from demyelinating diseases such as multiple sclerosis (MS) that may last for several decades. Developing strategies to reverse the age-associated decline requires the identification of how the regenerative process is impaired. We addressed whether remyelination becomes slower because of an impairment of recruitment of oligodendrocyte progenitors (OPs) or, as is the case in some MS lesions, an impairment of OP differentiation into remyelinating oligodendrocytes. The OP response during remyelination of focal, toxin-induced CNS demyelination in young and old rats was compared byin situhybridization using probes to two OP-expressed mRNA species: platelet-derived growth factor-α receptor and the OP transcription factor myelin transcription factor 1 (MyT1). We found that the expression patterns for the two OP markers are very similar and reveal a delay in the colonization of the demyelinated focus with OPs in the old animals compared with the young animals. By comparing the mRNA expression pattern of MyT1 with that of the myelin proteins myelin basic protein and Gtx, we found that in the old animals there is also a delay in OP differentiation that increases with longer survival times. These results indicate that the age-associated decrease in remyelination efficiency occurs because of an impairment of OP recruitment and the subsequent differentiation of the OPs into remyelinating oligodendrocytes, and that strategies aimed at ameliorating the age-associated decline in remyelination efficiency will therefore need to promote both components of the regenerative process.
Cell Type- and Input-Specific Differences in the Number and Subtypes of Synaptic GABAAReceptors in the Hippocampus
Authors: Klausberger Thomas , Roberts J. David B. , Somogyi Peter
Published: April 2018

Networks of parvalbumin (PV)-expressing basket cells are implicated in synchronizing cortical neurons at various frequencies, through GABAAreceptor-mediated synaptic action. These cells are interconnected by GABAergic synapses and gap junctions, and converge with a different class of cholecystokinin-expressing, PV-negative basket cells onto pyramidal cells. To define the molecular specializations in the synapses of the two basket cell populations, we used quantitative electron microscopic immunogold localization of GABAAreceptors. Synapses formed by PV-positive basket cells on the somata of pyramidal cells had several-fold higher density of α1subunit-containing receptors than synapses made by PV-negative basket cells, most of which were immunonegative. The density of the β2/3subunits was similar in the two populations of synapse, indicating similar overall receptor density. Synapses interconnecting parvalbumin-expressing basket cells contained a 3.6 times higher overall density of GABAAreceptor (β2/3subunits) and 3.2 times higher density of α1subunit labeling compared with synapses formed by boutons of PV-positive basket cells on pyramidal cells. Thus, PV-positive basket cells mainly act through α1subunit-containing GABAAreceptors, but the receptor density depends on the postsynaptic cell type. These observations, together with previously reported enrichment of the α2subunit-containing receptors in synapses made by PV-negative basket cells, indicate that the number and subtypes of GABAAreceptors present in different synapse populations are regulated by both presynaptic and postsynaptic influences. The high number of GABAAreceptors in synapses on basket cells might contribute to the precisely timed phasing of basket cell activity.
Glutamate But Not Glycine Agonist Affinity for NMDA Receptors Is Influenced by Small Cations
Authors: Nahum-Levy Rinat , Tam Eyal , Shavit Sara , Benveniste Morris
Published: April 2018

NMDA receptor currents desensitize in an agonist-dependent manner when either the glutamate or glycine agonist is subsaturating. This may result from a conformational change in the NMDA receptor protein that lowers glutamate and glycine binding site affinity induced by co-agonist binding, channel opening, or ion permeation. We have used whole-cell voltage clamp of cultured hippocampal neurons with agonist paired-pulse protocols to demonstrate that glutamate and glycine dissociate 7.9- and 6.8-fold slower in the absence of their respective co-agonists than when their co-agonists are present. Paired-pulse and desensitization protocols were used to show that co-agonist binding and channel opening are sufficient to cause a reduction in glycine affinity, but extracellular sodium or magnesium binding was required in addition to conformational changes leading to channel opening to reduce glutamate binding-site affinity. Use of cesium or potassium as the major extracellular cation prevented the reduction of glutamate affinity. In addition, the use of choline-, sodium-, or cesium-based intracellular solutions did not alter desensitization characteristics, indicating that the site responsible for reduction of glutamate affinity is not in the intracellular domain. The fact that the reduction of glutamate affinity is dependent on certain small extracellular cations whereas the reduction of glycine affinity is insensitive to such cations indicates that conformational changes induced by the binding of glutamate are not completely paralleled by the conformational changes induced by glycine. Although glutamate and glycine are essential co-agonists, these data suggest that they have differential roles in the process of NMDA receptor activation.
Failure of Brain-Derived Neurotrophic Factor-Dependent Neuron Survival in Mouse Trisomy 16
Authors: Dorsey Susan G. , Bambrick Linda L. , Balice-Gordon Rita J. , Krueger Bruce K.
Published: April 2018

The neurotrophin, brain derived neurotrophic factor (BDNF), exerts multiple effects on the development and maintenance of the nervous system, including regulating synaptic plasticity and promoting neuron survival. Here we report the selective failure of BDNF-dependent survival in cultured hippocampal neurons from the trisomy 16 (Ts16) mouse, an animal model of Down syndrome. This failure is accompanied by overexpression of a truncated, kinase-deficient isoform (T1) of the BDNF receptor tyrosine receptor kinase B (trkB). Adenovirus-mediated introduction of exogenous full-length trkB into Ts16 neurons fully restored BDNF-dependent survival, whereas exogenous truncated trkB expression in normal, euploid neurons reproduced the Ts16 BDNF signaling failure. Thus, the failure of Ts16 neurons to respond to BDNF is caused by dysregulation of trkB isoform expression. Such a neurotrophin signaling defect could contribute to developmental and degenerative disorders of the nervous system.
Cdk5/p35 Regulates Neurotransmitter Release through Phosphorylation and Downregulation of P/Q-Type Voltage-Dependent Calcium Channel Activity
Authors: Tomizawa Kazuhito , Ohta Jun , Matsushita Masayuki , Moriwaki Akiyoshi , Li Sheng-Tian , Takei Kohji , Matsui Hideki
Published: April 2018

Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine/threonine kinase with close structural homology to the mitotic Cdks. The complex of Cdk5 and p35, the neuron-specific regulatory subunit of Cdk5, plays important roles in brain development, such as neuronal migration and neurite outgrowth. Moreover, Cdk5 is thought to be involved in the promotion of neurodegeneration in Alzheimer's disease.

Cdk5 is abundant in mature neurons; however, its physiological functions in the adult brain are unknown. Here we show that Cdk5/p35 regulates neurotransmitter release in the presynaptic terminal. Both Cdk5 and p35 were abundant in the synaptosomes. Roscovitine, a specific inhibitor of Cdk5 in neurons, induced neurotransmitter release from the synaptosomes in response to membrane depolarization and enhanced the EPSP slopes in rat hippocampal slices. The electrophysiological study using each specific inhibitor of the voltage-dependent calcium channels (VDCCs) and calcium imaging revealed that roscovitine enhanced Ca2+influx from the P/Q-type VDCC. Moreover, Cdk5/p25 phosphorylated the intracellular loop connecting domains II and III (LII-III) between amino acid residues 724 and 981 of isoforms cloned from rat brain of the α1Asubunit of P/Q-type Ca2+channels. The phosphorylation inhibited the interaction of LII-IIIwith SNAP-25 and synaptotagmin I, which were plasma membrane solubleN-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor (SNARE) proteins and were required for efficient neurotransmitter release. These results strongly suggest that Cdk5/p35 inhibits neurotransmitter release through the phosphorylation of P/Q-type VDCC and downregulation of the channel activity.
Descending 5-Hydroxytryptamine Raphe Inputs Repress the Expression of Serotonergic Neurons and Slow the Maturation of Inhibitory Systems in Mouse Embryonic Spinal Cord
Authors: Branchereau Pascal , Chapron Jacqueline , Meyrand Pierre
Published: April 2018

Spontaneous synchronous rhythmic activities are a common feature of immature neuronal networks. Although the mechanisms underlying such activities have been studied extensively, whether they might be controlled by modulatory information remains questionable. Here, we investigated the role of descending serotonergic (5-HT) inputs from the medulla to the spinal cord in the maturation of rhythmic activity. We found that in spinal cords maintained, as a whole, in organotypic culture without the medulla, the maturation of spontaneous activity is similar to that found in spinal cords developedin utero. Interestingly, in organotypic cultures without the medulla (i.e., devoid of descending inputs), numerous intraspinal neurons expressed 5-HT, unlike in spinal cords cultivated in the presence of the medulla or maturedin utero. We demonstrated that this 5-HT expression was specifically dependent on the absence of 5-HT fibers and was repressed by 5-HT itself via activation of 5-HT1Areceptors. Finally, to verify whether the expression of 5-HT intraspinal neurons could compensate for the lack of descending 5-HT fibers and play a role in the development of spontaneous activity, we blocked the 5-HT synthesis usingp-chlorophenylalanine methyl ester in cultures devoid of the medulla. Surprisingly, we found that this pharmacological treatment did not prevent the development of spontaneous activity but accelerated the maturation of intraspinal inhibition at the studied stages. Together, our data indicate that descending 5-HT raphe inputs (1) repress the expression of spinal serotonergic neurons and (2) slow the maturation of inhibitory systems in mouse spinal cord.
Estrogen Regulates the Development of Brain-Derived Neurotrophic Factor mRNA and Protein in the Rat Hippocampus
Authors: Solum Derek T. , Handa Robert J.
Published: April 2018

During development, estrogen has a variety of effects on morphological and electrophysiological properties of hippocampal neurons. Brain-derived neurotrophic factor (BDNF) also plays an important role in the survival and differentiation of neurons during development. We examined the effects of gonadectomy with and without estrogen replacement on the mRNA and protein of BDNF and its receptor, trkB, during early postnatal development of the rat hippocampus. We used immunocytochemistry to demonstrate that estrogen receptor α (ERα) and BDNF were localized to the same cells within the developing hippocampus. BDNF and ERα were colocalized in pyramidal cells of the CA3 subregion and to a lesser extent in CA1. To determine whether BDNF mRNA was regulated by estrogen during development, we gonadectomized male rat pups at postnatal day 0 (P0) and examined mRNA and protein levels from P0 to P25 using real-time reverse transcription-PCR and Western blot analysis. After gonadectomy, BDNF mRNA levels are significantly reduced on P7, but after treatment of gonadectomized animals with estradiol benzoate on P0, levels at all ages were similar to those in intact animals. BDNF mRNA changes after gonadectomy are accompanied by an increase in the levels of BDNF protein, which were reduced by estrogen treatment at P0. We also examined the effect of postnatal estrogen treatment on trkB. There were no significant changes in trkB mRNA or protein in gonadectomized or estrogen-replaced animals. These results suggest that a direct interaction may exist between ERα and BDNF to alter hippocampal physiology during development in the rat.
Target Interaction Regulates Distribution and Stability of Specific mRNAs
Authors: Hu Jiang-Yuan , Meng Xu , Schacher Samuel
Published: April 2018

Several factors regulate export of mRNAs from neuronal cell bodies. Usingin situhybridization and RT-PCR, we examined how target interaction influences the distribution of mRNAs expressed in sensory neurons (SNs) ofAplysiamaintained in cell culture. Interaction with a synaptic target has two effects on the distribution of mRNA encoding an SN-specific peptide, sensorin: the target affects the accumulation of sensorin mRNA at the axon hillock and the stability of sensorin mRNA exported to distal sites. Synapse formation with motor neuron L7 results in the accumulation of high levels of sensorin mRNA in the axon hillock of the SN and in SN neurites contacting L7. SNs cultured alone or in contact with motor neuron L11, with which no synapses form, show a more uniform distribution of sensorin mRNA in the cytoplasm of the SN cell body, with little expression in neurites. Contact with L7 or L11 had little or no effect on the distribution of two other mRNAs in the cytoplasm of SN cell bodies. Sensorin mRNA exported to SN neurites after 1 d in culture is more stable when the SN contacts L7 compared with SN neurites that contact L11. After removal of the SN cell body, the amounts of sensorin mRNA already exported to the neurites are greater when neurites contact L7 compared with neurites in contact with L11. The results indicate that target interaction and synapse formation regulate both the accumulations of specific mRNAs destined for export and their stability at distant sites.