bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective Histamine Uptake Rescues Photo- and Mechanoreceptor Function of Histidine Decarboxylase-DeficientDrosophilaMutant
Authors: Melzig Jörg , Burg Martin , Gruhn Matthias , Pak William L. , Buchner Erich
Published: April 2018

In insects, histamine is found both in the peripheral nervous system (PNS) and in the CNS and is known to function as a fast neurotransmitter in photoreceptors that have been shown to express selectively thehdcgene. This gene codes for histidine decarboxylase (HDC), the enzyme for histamine synthesis. Fast neurotransmission requires the efficient removal of the transmitter from the synaptic cleft. Here we identify inDrosophilaphoto- and mechanoreceptors a histamine uptake mechanism that can restore the function of these receptors in mutants unable to synthesize histamine. When apparent null mutants for thehdcgene imbibe aqueous histamine solution or are genetically “rescued” by a transgene ubiquitously expressing histidine decarboxylase under heat-shock control, sufficient amounts of histamine selectively accumulate in photo- and mechanoreceptors to generate near-normal electrical responses in second-order visual interneurons and qualitatively to restore wild-type visual and mechanosensory behavior. This strongly supports the proposal that histamine functions as a fast neurotransmitter also in a certain class of mechanoreceptors. A set of CNS-intrinsic neurons that in the wild type contain high concentrations of histamine apparently lacks this uptake mechanism. We therefore speculate that histamine of intrinsic neurons may function as a neuromodulator rather than as a fast transmitter.
The Nitric Oxide–cGMP Pathway May Mediate Communication between Sensory Afferents and Projection Neurons in the Antennal Lobe ofManduca Sexta
Authors: Nighorn Alan , Gibson Nicholas J. , Rivers David M. , Hildebrand John G. , Morton David B.
Published: April 2018

The nitric oxide (NO)–cGMP signaling system is thought to play important roles in the function of the olfactory system in both vertebrates and invertebrates. One way of studying the role of NO in the nervous system is to study the distribution and properties of NO synthase (NOS), as well as the soluble guanylyl cyclases (sGCs), which are the best characterized targets of NO. We study NOS and sGC in the relatively simple and well characterized insect olfactory system of the hawkmoth,Manduca sexta. We have clonedManduca sextanitric oxide synthase (MsNOS) and two sGCs (MsGCα1 and MsGCβ1), characterized their basic biochemical properties, and studied their expression in the olfactory system. The sequences of theManducagenes are highly similar to their mammalian homologs and show similar biochemical properties when expressed in COS-7 cells. In particular, we find that MsGC functions as an obligate heterodimer that is stimulated significantly by NO. We also find that MsNOS has a Ca2+-sensitive NO-producing activity similar to that of mammalian neuronal NOS. Northern andin situhybridization analyses show that MsNOS and the MsGCs are expressed in a complementary pattern, with MsNOS expressed at high levels in the antennae and the MsGCs expressed at high levels in a subset of antennal lobe neurons. The expression patterns of these genes suggest that the NO–sGC signaling system may play a role in mediating communication between olfactory receptor neurons and projection neurons in the glomeruli of the antennal lobe.
Activity of the δ-Opioid Receptor Is Partially Reduced, Whereas Activity of the κ-Receptor Is Maintained in Mice Lacking the μ-Receptor
Authors: Matthes H. W. D. , Smadja C. , Valverde O. , Vonesch J.-L. , Foutz A. S. , Boudinot E. , Denavit-Saubié M. , Severini C. , Negri L. , Roques B. P. , Maldonado R. , Kieffer B. L.
Published: April 2018

Previous pharmacological studies have indicated the possible existence of functional interactions between μ-, δ- and κ-opioid receptors in the CNS. We have investigated this issue using a genetic approach. Here we describein vitroandin vivofunctional activity of δ- and κ-opioid receptors in mice lacking the μ-opioid receptor (MOR). Measurements of agonist-induced [35S]GTPγS binding and adenylyl cyclase inhibition showed that functional coupling of δ- and κ-receptors to G-proteins is preserved in the brain of mutant mice. In the mouse vas deferens bioassay, deltorphin II and cyclic[d-penicillamine2,d-penicillamine5] enkephalin exhibited similar potency to inhibit smooth muscle contraction in both wild-type and MOR −/− mice. δ-Analgesia induced by deltorphin II was slightly diminished in mutant mice, when the tail flick test was used. Deltorphin II strongly reduced the respiratory frequency in wild-type mice but not in MOR −/− mice. Analgesic and respiratory responses produced by the selective κ-agonist U-50,488H were unchanged in MOR-deficient mice. In conclusion, the preservation of δ- and κ-receptor signaling properties in mice lacking μ-receptors provides no evidence for opioid receptor cross-talk at the cellular level. Intact antinociceptive and respiratory responses to the κ-agonist further suggest that the κ-receptor mainly acts independently from the μ-receptorin vivo. Reduced δ-analgesia and the absence of δ-respiratory depression in MOR-deficient mice together indicate that functional interactions may take place between μ-receptors and central δ-receptors in specific neuronal pathways.
Predicting the Consequences of Our Own Actions: The Role of Sensorimotor Context Estimation
Authors: Blakemore Sarah J. , Goodbody Susan J. , Wolpert Daniel M.
Published: April 2018

During self-generated movement it is postulated that an efference copy of the descending motor command, in conjunction with an internal model of both the motor system and environment, enables us to predict the consequences of our own actions (von Helmholtz, 1867; Sperry, 1950;von Holst, 1954; Wolpert, 1997). Such a prediction is evident in the precise anticipatory modulation of grip force seen when one hand pushes on an object gripped in the other hand (Johansson and Westling, 1984;Flanagan and Wing, 1993). Here we show that self-generation is not in itself sufficient for such a prediction. We used two robots to simulate virtual objects held in one hand and acted on by the other. Precise predictive grip force modulation of the restraining hand was highly dependent on the sensory feedback to the hand producing the load. The results show that predictive modulation requires not only that the movement is self-generated, but also that the efference copy and sensory feedback are consistent with a specific context; in this case, the manipulation of a single object. We propose a novel computational mechanism whereby the CNS uses multiple internal models, each corresponding to a different sensorimotor context, to estimate the probability that the motor system is acting within each context.
Modulation of Neuronal Activity in Superior Colliculus by Changes in Target Probability
Authors: Basso Michele A. , Wurtz Robert H.
Published: April 2018

Complex visual scenes require that a target for an impending saccadic eye movement be selected from a larger number of possible targets. We investigated whether changing the probability that a visual stimulus would be selected as the target for a saccade altered activity of monkey superior colliculus (SC) neurons in two experiments. First, we changed the number of possible targets on each trial. Second, we kept the visual display constant and presented a single saccade target repeatedly so that target probability was established over time. Buildup neurons in the SC, those with delay period activity, showed a consistent reduction in activity as the probability of the saccade decreased, independent of the visual stimulus configuration. Other SC neurons, fixation and burst, were largely unaffected by the changes in saccade target probability. Because we had monkeys making saccades to many locations within the visual field, we could examine activity associated with saccades outside of the movement field of neurons. We found the activity of buildup neurons to be similar across the SC, before the target was identified, and reduced when the number of possible targets increased. The results of our experiments are consistent with a role for this activity in establishing a motor set. We found, consistent with this interpretation, that the activity of these neurons was predictive of the latency of a saccadic eye movement and not other saccade parameters such as end point or peak velocity.
Distributed Encoding and Retrieval of Spatial Memory in the Hippocampus
Authors: Moser May-Britt , Moser Edvard I.
Published: April 2018

To determine whether memory is processed in a localized or distributed manner by the hippocampus, we inactivated small regions of the structure in pretrained rats before a retention test. Ibotenic acid-induced lesions removing 40% of the hippocampal tissue disrupted retrieval of spatial memory in a water maze but failed to affect new learning or retrieval of a task that was acquired postoperatively. Partial inactivation of the hippocampus by local intrahippocampal 5-aminomethyl-3-hydroxyisoxazole muscimol infusion also impaired retrieval but not new learning. This impairment was temporary; infusions had no effect on retrieval of predrug performance when the test was conducted 48 hr after the infusion. Systematic variation of the volume of dorsal and ventral hippocampal lesions showed that successful retrieval required the integrity of the entire dorsal 70% of the hippocampus. Our data suggest that although spatial tasks can be acquired with local ensembles of hippocampal neurons when other parts of the hippocampus are inactivated, spatial memory is normally both encoded and retrieved by a widely distributed hippocampal network.
Inflammatory Mediators Sensitize Acutely Axotomized Nerve Fibers to Mechanical Stimulation in the Rat
Authors: Michaelis Martin , Vogel Carola , Blenk Karl-Heinz , Arnarson Adalsteinn , Jänig Wilfrid
Published: April 2018

Many axotomized myelinated as well as unmyelinated cutaneous nerve fibers are sensitive to mechanical stimuli applied to the cut nerve end within a few hours after nerve lesion. Here we investigated the influence of inflammatory mediators on this ectopic mechanosensitivity after cutting and ligating the sural nerve in anesthetized rats. Neural activity was recorded from single axons in filaments teased from the sural or sciatic nerve proximally to the lesion site 2–33 hr after axotomy. Using calibrated von Frey hairs (1.0–128.5 mN), 30 sec trains of phasic stimuli were applied to the cut nerve end immediately before and after local application of a mixture of inflammatory mediators [inflammatory soup (IS), consisting of bradykinin, 5-HT, prostaglandin E2, histamine (all 10 μm), and K+7 mm, pH 7.0] for 2 min. Before as well as after IS application, von Frey thresholds were significantly lower in myelinated (A) fibers than in unmyelinated (C) fibers. IS application enhanced the ectopic mechanical excitability, as expressed in reduced von Frey thresholds and increased response magnitudes, of most severed mechanosensitive C fibers (77%) and some mechanosensitive A fibers (46%). The sensitization lasted for 10–40 min after a 2 min IS application. Additionally, among axotomized nerve fibers unresponsive to probing of the nerve lesion site before IS application, 1 of 63 (1.6%) A and 3 of 106 (2.8%) C fibers became mechanosensitive immediately after IS application. The results indicate that after axotomy, inflammatory processes augment touch-evoked ectopic activity in lesioned sensory nerve fibers. Because many affected afferents are presumably of nociceptive function, their enhanced neural barrage may contribute to neuropathic pain states.
Dendritic Hyperpolarization-Activated Currents Modify the Integrative Properties of Hippocampal CA1 Pyramidal Neurons
Authors: Magee Jeffrey C.
Published: April 2018

Step hyperpolarizations evoked slowly activating, noninactivating, and slowly deactivating inward currents from membrane patches recorded in the cell-attached patch configuration from the soma and apical dendrites of hippocampal CA1 pyramidal neurons. The density of these hyperpolarization-activated currents (Ih) increased over sixfold from soma to distal dendrites. Activation curves demonstrate that a significant fraction ofIhchannels is active near rest and that the range is hyperpolarized relatively more in the distal dendrites.Ihactivation and deactivation kinetics are voltage-and temperature-dependent, with time constants of activation and deactivation decreasing with hyperpolarization and depolarization, respectively.Ihdemonstrated a mixed Na+–K+conductance and was sensitive to low concentrations of external CsCl. Dual whole-cell recordings revealed regional differences in input resistance (Rin) and membrane polarization rates (τmem) across the somatodendritic axis that are attributable to the spatial gradient ofIhchannels. As a result of these membrane effects the propagation of subthreshold voltage transients is directionally specific. The elevated dendriticIhdensity decreases EPSP amplitude and duration and reduces the time window over which temporal summation takes place. The backpropagation of action potentials into the dendritic arborization was impacted only slightly by dendriticIh, with the most consistent effect being a decrease in dendritic action potential duration and an increase in afterhyperpolarization. Overall,Ihacts to dampen dendritic excitability, but its largest impact is on the subthreshold range of membrane potentials where the integration of inhibitory and excitatory synaptic inputs takes place.
Cloning and Expression of Two Related Connexins from the Perch Retina Define a Distinct Subgroup of the Connexin Family
Authors: O’Brien John , Bruzzone Roberto , White Thomas W. , Al-Ubaidi Muayyad R. , Ripps Harris
Published: April 2018

We have cloned cDNAs for two closely related connexins (Cx), Cx35 and Cx34.7, from a perch retinal cDNA library. Sequencing of PCR products from genomic DNA revealed that both connexins have an intron 71 bp after the translation initiation site; in Cx35, the intron is 900 bp in length, whereas in Cx34.7 it is ∼20 kb. Southern blots of genomic DNA suggest that the two connexins represent independent single copy genes. In Northern blots, Cx35 and Cx34.7 transcripts were detected in retina and brain; Cx34.7 also showed a weak signal in smooth muscle (gut) RNA. Antibodies against Cx35 labeled a 30 kDa band on a Western blot of retinal membranes, and in histological sections, the pattern of antibody recognition was consistent with labeling of bipolar cells and unidentified processes in the inner plexiform and nerve fiber layers. When expressed inXenopusoocytes, Cx35 and Cx34.7 formed homotypic gap junctions, but the junctional conductance between paired oocytes expressing Cx35 was 10-fold greater than that recorded for gap junctional channels formed by Cx34.7. The homotypic gap-junctional channels were closed in a voltage-dependent manner but with relatively weak voltage sensitivity. Heterotypic gap junctions formed by Cx35 and Cx34.7 displayed junctional conductances similar to those of Cx34.7 homotypic pairs and showed a slightly asymmetric current–voltage relationship; the side expressing Cx35 exhibited a higher sensitivity to transjunctional potentials. An analysis of the sequence and gene structure of the connexin family revealed that perch Cx35 and Cx34.7, skate Cx35, and mouse Cx36 constitute a novel γ subgroup.
Macroscopic and Microscopic Properties of a Cloned Glutamate Transporter/Chloride Channel
Authors: Wadiche Jacques I. , Kavanaugh Michael P.
Published: April 2018

The behavior of a Cl−channel associated with a glutamate transporter was studied using intracellular and patch recording techniques inXenopusoocytes injected with human EAAT1 cRNA. Channels could be activated by application of glutamate to either face of excised membrane patches. The channel exhibited strong selectivity for amphipathic anions and had a minimum pore diameter of ∼5Å. Glutamate flux exhibited a much greater temperature dependence than Cl−flux. Stationary and nonstationary noise analysis was consistent with a sub-femtosiemen Cl−conductance and a maximum channelPo≪ 1. The glutamate binding rate was similar to estimates for receptor binding. After glutamate binding, channels activated rapidly followed by a relaxation phase. Differences in the macroscopic kinetics of channels activated by concentration jumps ofl-glutamate ord-aspartate were correlated with differences in uptake kinetics, indicating a close correspondence of channel gating to state transitions in the transporter cycle.
Whole-Cell and Single-Channel Analysis of P-Type Calcium Currents in Cerebellar Purkinje Cells of Leaner Mutant Mice
Authors: Dove Leonard S. , Abbott Louise C. , Griffith William H.
Published: April 2018

The leaner (tgla) mutation in mice results in severe ataxia and an overt neurodegeneration of the cerebellum. Positional cloning has revealed that the tglamutation occurs in a gene encoding the voltage-activated calcium channel α1Asubunit. The α1Asubunit is highly expressed in the cerebellum and is thought to be the pore-forming subunit of P- and Q-type calcium channels. In this study we used both whole-cell and single-channel patch-clamp recordings to examine the functional consequences of the tglamutation on P-type calcium currents. High-voltage-activated (HVA) calcium currents were recorded from acutely dissociated cerebellar Purkinje cells of homozygous leaner (tgla/tgla) and age-matched wild-type (+/+) mice. In whole cell recordings, we observed a marked reduction of peak current density in tgla/tglaPurkinje cells (−35.0 ± 1.8 pA/pF) relative to that in +/+ (−103.1 ± 5.9 pA/pF). The reduced whole-cell current in tgla/tglacells was accompanied by little to no alteration in the voltage dependence of channel gating. In both genotypes, HVA currents were predominantly of the ω-agatoxin-IVA–sensitive P-type. Cell-attached patch-clamp recordings revealed no differences in single-channel conductance between the two genotypes and confirmed the presence of three distinct conductance levels (9, 13–14, and 17–18 pS) in cerebellar Purkinje cells. Analysis of patch open-probability (NPo) revealed a threefold reduction in the open-probability of channels in tgla/tglapatches (0.04 ± 0.01) relative to that in +/+ (0.13 ± 0.02), which may account for the reduced whole-cell current in tgla/tglaPurkinje cells. These results suggest that the tglamutation can alter native P-type calcium channels at the single-channel level and that these alterations may contribute to the neuropathology of the leaner phenotype.
Glutamate Receptor Activity Is Required for Normal Development of Tectal Cell DendritesIn Vivo
Authors: Rajan Indrani , Cline Hollis T.
Published: April 2018

Glutamatergic retinotectal inputs mediated principally by NMDA receptors can be recorded from optic tectal neurons early during their morphological development inXenopustadpoles. As tectal cell dendrites elaborate, retinotectal synaptic responses acquire an AMPA receptor-mediated synaptic component, in addition to the NMDA component. Here, we tested whether glutamatergic activity was required for the elaboration of dendritic arbors inXenopusoptic tectal neurons.In vivotime-lapse imaging of single DiI-labeled neurons shows that the NMDA receptor antagonist APV (100 μm) blocked the early development of the tectal cell dendritic arbor, whereas the AMPA receptor antagonist CNQX (20 μm) or the sodium channel blocker TTX (1 μm) did not. The decreased dendritic development is attributable to failure to add new branches and extend preexisting branches. These observations indicate that NMDA-type glutamatergic activity promotes the initial development of the dendritic arbor. At later stages of tectal neuron development when AMPA receptor-mediated synaptic transmission is strong, both APV and CNQX decrease dendritic arbor branch length, consistent with a role for glutamatergic synaptic transmission in maintaining dendritic arbor structure. These results indicate that AMPA and NMDA receptors can differentially influence dendritic growth at different stages of neuronal development, in correlation with changes in the relative contribution of the receptor subtype to synaptic transmission.
Genetic Analysis on the Role of Integrin during Axon Guidance inDrosophila
Authors: Hoang Bao , Chiba Akira
Published: April 2018

Heterodimeric cell surface receptor integrin is widely expressed in the nervous system, but its specific role during axon development has not been directly testedin vivo. We show that theDrosophilanervous system expresses low levels of positron-specific (PS) integrin subunits αPS1, αPS2, and βPS during embryonic axogenesis. Furthermore, certain subsets of neurons express higher levels of integrin mRNAs than do the rest. Null mutations in either the αPS1 or αPS2 subunit gene cause widespread axon pathfinding errors that can be rescued by supplying the wild-type integrin subunit to the mutant nervous system. In contrast, misexpressing either the αPS1 or αPS2 integrin subunit in all neurons leads to no obvious axon pathfinding errors. We propose that integrin does not itself serve as either a “clutch” constituting molecule or a specific growth cone “receptor,” as proposed previously, but rather as part of a molecular network that cooperatively guarantees accurate axon guidance.
Fibroblast Growth Factor 2 (FGF-2) Promotes Acquisition of Epidermal Growth Factor (EGF) Responsiveness in Mouse Striatal Precursor Cells: Identification of Neural Precursors Responding to both EGF and FGF-2
Authors: Ciccolini Francesca , Svendsen Clive N.
Published: April 2018

Epidermal growth factor (EGF) and fibroblast growth factor 2 (FGF-2) induce the proliferation of neural precursor cells isolated from specific regions of the embryonic and adult brain. However, the lineage relationship between the EGF- and FGF-2-responsive cells is unknown. In this study we used phosphorylation of the transcription factor cAMP response element-binding protein as a functional readout to identify cells responding to EGF and FGF-2. In primary cultures of mouse embryonic day 14 (E14) striatum, maintainedin vitrofor 24 hr, 12% of the cells responded to FGF-2, whereas no response to EGF could be detected. Seventy-five percent of these FGF-2-responsive cells were β tubulin III (TuJ1)-positive neurons, and 25% expressed nestin, a marker for neuroepithelial precursors. After growth factor treatment for 6 d, a population of nestin-positive cells responding to both EGF and FGF-2 were identified. The 6-d-old cultures also contained a small number of TuJ1-positive cells that responded to FGF-2 only. Priming of striatal cells for 24 hr with FGF-2 but not with EGF was sufficient to induce the appearance of EGF- and FGF-2 responsive cells after only 2 din vitro. Thus, neural precursor cells from the mouse E14 striatum initially responding to FGF-2 only acquire EGF responsiveness later duringin vitrodevelopment. At this stage EGF and FGF-2 act on the same cells. The acquisition of EGF responsiveness is promoted by FGF-2.
Development of Survival Responsiveness to Brain-Derived Neurotrophic Factor, Neurotrophin 3 and Neurotrophin 4/5, But Not to Nerve Growth Factor, in Cultured Motoneurons from Chick Embryo Spinal Cord
Authors: Becker Elena , Soler Rosa M. , Yuste Vı́ctor J. , Giné Eva , Sanz-Rodrı́guez César , Egea Joaquim , Martı́n-Zanca Dionisio , Comella Joan X.
Published: April 2018

During embryonic development, most neuronal populations undergo a process usually referred to as naturally occurring neuronal death. For motoneurons (MTNs) of the lumbar spinal cord of chick embryos, this process takes place in a well defined period of time, between embryonic days 6 and 10 (E6–E10). Neurotrophins (NTs) are the best characterized family of neurotrophic factors and exert their effects through activation of their specific Trk receptors.In vitroandin vivostudies have demonstrated that rodent motoneurons survive in response to BDNF, NT3, and NT4/5. In contrast, the trophic dependencies of chicken motoneurons have been difficult to elucidate, and various apparently conflicting reports have been published. In the present study, we describe how freshly isolated motoneurons from E5.5 chick embryos did not respond to any neurotrophinin vitro. Yet, because motoneurons were maintained alive in culture in the presence of muscle extract, they developed a delayed specific survival response to BDNF, NT3, and NT4/5 that is clearly dose-dependent, reaching saturation at doses of 100 pg/ml. This trophic response correlated with increasing expression of the corresponding functional receptors TrkB and TrkC. Moreover, TrkB receptor is able to become autophosphorylated and to activate classical intracellular signaling pathways such as the extracellular signal-regulated protein kinase when it is stimulated with its cognate ligand BDNF. Therefore, our results reconcile the reported differences betweenin vivoandin vitrostudies on the ability of chicken MTNs to respond to some members of the neurotrophin family of trophic factors.
Brain-Derived Neurotrophic Factor and Basic Fibroblast Growth Factor Downregulate NMDA Receptor Function in Cerebellar Granule Cells
Authors: Brandoli Cinzia , Sanna Angela , De Bernardi Maria A. , Follesa Paolo , Brooker Gary , Mocchetti Italo
Published: April 2018

Evidence has accumulated to suggest that the NMDA glutamate receptor subtype plays an important role in neuronal degeneration evoked by hypoxia, ischemia, or trauma. Cerebellar granule cells in culture are vulnerable to NMDA-induced neuronal excitotoxicity. In these cells, brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (FGF2) prevent the excitotoxic effect of NMDA. However, little is known about the molecular mechanisms underlying the protective properties of these trophic factors. Using cultured rat cerebellar granule cells, we investigated whether BDNF and FGF2 prevent NMDA toxicity by downregulating NMDA receptor function. Western blot and RNase protection analyses were used to determine the expression of the various NMDA receptor subunits (NR1, NR2A, NR2B, and NR2C) after BDNF or FGF2 treatment. FGF2 and BDNF elicited a time-dependent decrease in the expression of NR2A and NR2C subunits. Because NMDA receptor activation leads to increased intracellular Ca2+concentration ([Ca2+]i), we studied the effect of the BDNF- and FGF2-induced reduction in NR2A and NR2C synthesis on the NMDA-evoked Ca2+responses by single-cell fura-2 fluorescence ratio imaging. BDNF and FGF2 reduced the NMDA-mediated [Ca2+]iincrease with a time dependency that correlates with their ability to decrease NR2A and NR2C subunit expression, suggesting that these trophic factors also induce a functional downregulation of the NMDA receptor. Because sustained [Ca2+]iis believed to be causally related to neuronal injury, we suggest that BDNF and FGF2 may protect cerebellar granule cells against excitotoxicity by altering the NMDA receptor–Ca2+signaling via a downregulation of NMDA receptor subunit expression.
Electrophysiological Characterization of GABAergic Neurons in the Ventral Tegmental Area
Authors: Steffensen Scott C. , Svingos Adena L. , Pickel Virginia M. , Henriksen Steven J.
Published: April 2018

GABAergic neurons in the ventral tegmental area (VTA) play a primary role in local inhibition of mesocorticolimbic dopamine (DA) neurons but are not physiologically or anatomically well characterized. We usedin vivoextracellular and intracellular recordings in the rat VTA to identify a homogeneous population of neurons that were distinguished from DA neurons by their rapid-firing, nonbursting activity (19.1 ± 1.4 Hz), short-duration action potentials (310 ± 10 μsec), EPSP-dependent spontaneous spikes, and lack of spike accommodation to depolarizing current pulses. These non-DA neurons were activated both antidromically and orthodromically by stimulation of the internal capsule (IC; conduction velocity, 2.4 ± 0.2 m/sec; refractory period, 0.6 ± 0.1 msec) and were inhibited by stimulation of the nucleus accumbens septi (NAcc). Their firing rate was moderately reduced, and their IC-driven activity was suppressed by microelectrophoretic application or systemic administration of NMDA receptor antagonists. VTA non-DA neurons were recorded intracellularly and showed relatively depolarized resting membrane potentials (−61.9 ± 1.8 mV) and small action potentials (68.3 ± 2.1 mV). They were injected with neurobiotin and shown by light microscopic immunocytochemistry to be multipolar cells and by electron microscopy to contain GABA but not the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH). Neurobiotin-filled dendrites containing GABA received asymmetric excitatory-type synapses from unlabeled terminals and symmetric synapses from terminals that also contained GABA. These findings indicate that VTA non-DA neurons are GABAergic, project to the cortex, and are controlled, in part, by a physiologically relevant NMDA receptor-mediated input from cortical structures and by GABAergic inhibition.
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyride Neurotoxicity Is Attenuated in Mice Overexpressing Bcl-2
Authors: Yang Lichuan , Matthews Russell T. , Schulz Jörg B. , Klockgether Thomas , Liao Andrew W. , Martinou Jean-Claude , Penney John B. , Hyman Bradley T. , Beal M. Flint
Published: April 2018

The proto-oncogene Bcl-2 rescues cells from a wide variety of insults. Recent evidence suggests that Bcl-2 protects against free radicals and that it increases mitochondrial calcium-buffering capacity. The neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyride (MPTP) is thought to involve both mitochondrial dysfunction and free radical generation. We therefore investigated MPTP neurotoxicity in both Bcl-2 overexpressing mice and littermate controls. MPTP-induced depletion of dopamine and loss of [3H]mazindol binding were significantly attenuated in Bcl-2 overexpressing mice. Protection was more profound with an acute dosing regimen than with daily MPTP administration over 5 d. 1-Methyl-4-phenylpyridinium (MPP+) levels after MPTP administration were similar in Bcl-2 overexpressing mice and littermates. Bcl-2 blocked MPP+-induced activation of caspases. MPTP-induced increases in free 3-nitrotyrosine levels were blocked in Bcl-2 overexpressing mice. These results indicate that Bcl-2 overexpression protects against MPTP neurotoxicity by mechanisms that may involve both antioxidant activity and inhibition of apoptotic pathways.
Activity-Dependent Modulation of Glutamate Receptors by Polyamines
Authors: Bowie Derek , Lange G. David , Mayer Mark L.
Published: April 2018

The mechanisms by which polyamines block AMPA and kainate receptors are not well understood, but it has been generally assumed that they act as open-channel blockers. Consistent with this, voltage-jump relaxation analysis of GluR6 equilibrium responses to domoate could be well fit, assuming that spermine, spermidine, and philanthotoxin are weakly permeable open-channel blockers. Analysis of rate constants for binding and dissociation of polyamines indicated that the voltage dependence of block arose primarily from changes inkoffrather thankon. Experiments with changes in Na concentration further indicate that the voltage dependence of polyamine block was governed by ion flux via open channels. However, responses to 1 msec applications ofl-Glu revealed slow voltage-dependent rise-times, suggesting that polyamines additionally bind to closed states. A kinetic model, which included closed-channel block, reproduced these observations but required that polyamines accelerate channel closure either through an allosteric mechanism or by emptying the pore of permeant ions. Simulations with this model reveal that polyamine block confers novel activity-dependent regulation on calcium-permeable AMPA and kainate receptor responses.
Two Distinct Nicotinic Receptors, One Pharmacologically Similar to the Vertebrate α7-Containing Receptor, Mediate Cl Currents inAplysiaNeurons
Authors: Kehoe JacSue , McIntosh J. Michael
Published: April 2018

Ionotropic, nicotinic receptors have previously been shown to mediate both inhibitory (Cl-dependent) and excitatory (cationic) cholinergic responses inAplysianeurons. We have used fast perfusion methods of agonist and antagonist application to reevaluate the effects on these receptors of a wide variety of cholinergic compounds, including a number of recently isolated and/or synthesized α toxins [α-conotoxin (αCTx)] fromConussnails. These toxins have been shown in previous studies to discriminate between the many types of nicotinic receptors now known to be expressed in vertebrate muscle, neuroendocrine, and neuronal cells. One of these toxins (αCTx ImI from the worm-eating snailConus imperialis) revealed that two kinetically and pharmacologically distinct elements underlie the ACh-induced Cl-dependent response inAplysianeurons: one element is a rapidly desensitizing current that is blocked by the toxin; the other is a slowly desensitizing current that is unaffected by the toxin. The two kinetically defined elements were also found to be differentially sensitive to different agonists. Finally, the proportion of the rapidly desensitizing element to the sustained element was found to be cell-specific. These observations led to the conclusion that two distinct nicotinic receptors mediate Cl currents inAplysianeurons. The receptor mediating the rapidly desensitizing Cl-dependent response shows a strong pharmacological resemblance to the vertebrate α-bungarotoxin-sensitive, α7-containing receptor, which is permeable to calcium and mediates a rapidly desensitizing excitatory response.
Induction of NF-κB Activity during Haloperidol-Induced Oxidative Toxicity in Clonal Hippocampal Cells: Suppression of NF-κB and Neuroprotection by Antioxidants
Authors: Post Anke , Holsboer Florian , Behl Christian
Published: April 2018

Haloperidol (HP), a dopamine receptor antagonist, is cytotoxic to mouse clonal hippocampal HT22 cells in a concentration-dependent manner and causes cell death by oxidative stress. The addition of HP to HT22 cells led to an increase in intracellular peroxides and a time-dependent drop in the intracellular glutathione levels. HP-induced oxidative cell death was prevented by the pineal hormone melatonin, its precursorN-acetyl serotonin, and most effectively by vitamin E (α-tocopherol). These antioxidants inhibited the intracellular peroxide accumulation and stabilized the glutathione content of HT22 cells after the challenge with HP. At the molecular level, HP specifically induced the DNA binding activity and the transcriptional activity of the redox-sensitive transcription factor NF-κB. This enhanced NF-κB activity could be blocked by the neuroprotective antioxidants. The specific suppression of NF-κB by its inhibitor IκBα partially protected the cells against HP, indicating that the activation of NF-κB may be involved in HP-induced oxidative cell deathin vitro.
Axonal Injury Alters Alternative Splicing of the Retinal NR1 Receptor: the Preferential Expression of the NR1b Isoforms Is Crucial for Retinal Ganglion Cell Survival
Authors: Kreutz Michael R. , Böckers Tobias M. , Bockmann Jürgen , Seidenbecher Constanze I. , Kracht Bettina , Vorwerk Christian K. , Weise Jens , Sabel Bernhard A.
Published: April 2018

Cellular-specific splicing of the retinal NMDAR1 receptor (NR1) and expression of NMDAR2 receptor (NR2) subunits in response to optic nerve injury was investigated byin situhybridization in adult rats. A controlled optic nerve crush led to a clear alteration in the expression of alternatively spliced NR1 variants in the retinal ganglion cell layer (GCL). The NR1–2b and NR1–4b isoforms were preferentially expressed between 2 d and 1 week after injury, whereas expression for all other isoforms remained either unchanged or decreased to barely detectable levels within 4 weeks. Cellular silver grain density for NR2 subunits also declined in the GCL after trauma. To directly test the hypothesis that NR1b expression is crucial for cell survival after axonal trauma, we administered intraocularly an antisense oligonucleotide against the NR1b isoform 2 and 3 d after injury. This led to a drastic loss of retrogradely labeled retinal ganglion cells (RGCs). Antisense targeting clearly reduced retinal NR1 protein levels, as judged by Western blot analysis, but had no effect on the cell number in control retinas. These findings point toward injury-specific changes in alternative splicing of the NR1 receptor, which are crucial for the survival of RGCs after partial axonal trauma. We therefore propose that this reflects an adaptive, rather than a pathogenic, cellular response to neurotrauma.
Spine Loss and Other Persistent Alterations of Hippocampal Pyramidal Cell Dendrites in a Model of Early-Onset Epilepsy
Authors: Jiang Minghui , Lee Chong L. , Smith Karen L. , Swann John W.
Published: April 2018

To explore the anatomical substrates for network hyperexcitability in adult rats that become chronically epileptic after recurrent seizures in infancy, the dendritic and axonal arbors of biocytin-filled hippocampal pyramidal cells were reconstructed. On postnatal day 10, tetanus toxin was unilaterally injected into the hippocampus and produced brief but recurrent seizures for 1 week. Later, hippocampal slices taken from these rats exhibited synchronized network bursts in area CA3C. Both the apical and basilar dendritic arbors of CA3Cpyramidal cells were markedly abnormal in these epileptic rats. There was a considerable reduction in the density of dendrite spines, although the extent of this loss could vary among dendritic segments. Spine density on terminal segments of the basilar and apical dendrites was reduced on average by 35 and 20%, respectively. In addition, the diameters of these same dendritic segments were markedly reduced. Dendritic spine loss has previously been suggested to indicate a partial deafferentation of epileptic neurons, but this interpretation is difficult to reconcile with the critical role recurrent excitatory synaptic transmission plays in the generation of synchronized network burst. In this study, axonal arbors of CA3Cpyramidal cells exhibited normal branching patterns, branching complexity, and varicosity density. This suggests that if deafferentation occurs, synapses other than recurrent excitatory ones are lost. The morphological abnormalities reported here would be expected to significantly alter electrical signaling within dendrites that may contribute importantly to seizures and other behavioral sequelae of early-onset epilepsy.
Patterns of Status Epilepticus-Induced Neuronal Injury during Development and Long-Term Consequences
Authors: Sankar Raman , Shin Don H. , Liu Hantao , Mazarati Andrey , Pereira de Vasconcelos Anne , Wasterlain Claude G.
Published: April 2018

The lithium–pilocarpine model of status epilepticus (SE) was used to study the type and distribution of seizure-induced neuronal injury in the rat and its consequences during development. Cell death was evaluated in hematoxylin- and eosin-stained sections and by electron microscopy. Damage to the CA1 neurons was maximal in the 2- and 3-week-old pups and decreased as a function of age. On the other hand, damage to the hilar and CA3 neurons was minimal in the 2-week-old rat pups but reached an adult-like pattern in the 3-week-old animals, and damage to amygdalar neurons increased progressively with age. The 3-week-old animals also demonstrated vulnerability of the dentate granule cells. To evaluate neuronal apoptosis, we used terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) stain, confocal fluorescence microscopy of ethidium bromide-stained sections, electron microscopy, and DNA electrophoresis. Neurons displaying all of those features of apoptotic death in response to SE were seen in the CA1 region of the 2-week-old pups and in the hilar border of the dentate granule cells of the 3-week-old animals. Some (3/11) of the animals that underwent SE at 2 weeks of age and most of the animals that underwent SE at 3 or 4 weeks of age (8/11 and 6/8, respectively) developed spontaneous seizures later in life; the latter showed SE-induced synaptic reorganization as demonstrated by Timm methodology. These results provide strong evidence for the vulnerability of the immature brain to seizure-induced damage, which bears features of both necrotic and apoptotic death and contributes to synaptic reorganization and the development of chronic epilepsy.
Directional Tuning of Single Motor Units
Authors: Herrmann Uta , Flanders Martha
Published: April 2018

The directional activity of whole muscles has been shown to be broadly and often multimodally tuned, raising the question of how this tuning is subserved at the level of single motor units (SMUs). Previously defined rules of SMU activation would predict that units of the same muscle (or at least of the same neuromuscular compartment) are activated homogeneously with activity peaks in the same “best” direction(s). In the present study, the best directions of SMUs in human biceps (both heads) and deltoid (anterior, medial, and posterior portions) were determined by measuring the firing rate and threshold force of units for recruitment during isometric force ramps in many different directions. For all muscles studied, neighboring motor units could have significantly different best directions, suggesting that each muscle receives multiple directional commands. Furthermore, 17% of the units sampled clearly had a second-best direction, consistent with a convergence of different directional commands onto the same motoneuron. The best directions of the units changed gradually with location in the muscle. Best directions did not cluster into separate groups, thus, not supporting the existence of clearly distinguished neuromuscular compartments. Instead, the results reveal a more gradually distributed activation of the biceps and deltoid motoneuron pools. A model is proposed in which the central control mechanism optimizes the fulfillment of the continuously changing directional force requirements of a movement by gradually recruiting and derecruiting those units ideally suited for the production of the required force vector at any given time.
Short-Term Memory for Reaching to Visual Targets: Psychophysical Evidence for Body-Centered Reference Frames
Authors: McIntyre J. , Stratta F. , Lacquaniti F.
Published: April 2018

Pointing to a remembered visual target involves the transformation of visual information into an appropriate motor output, with a passage through short-term memory storage. In an attempt to identify the reference frames used to represent the target position during the memory period, we measured errors in pointing to remembered three-dimensional (3D) targets.

Subjects pointed after a fixed delay to remembered targets distributed within a 22 mm radius volume. Conditions varied in terms of lighting (dim light or total darkness), delay duration (0.5, 5.0, and 8.0 sec), effector hand (left or right), and workspace location. Pointing errors were quantified by 3D constant and variable errors and by a novel measure of local distortion in the mapping from target to endpoint positions.

The orientation of variable errors differed significantly between light and dark conditions. Increasing the memory delay in darkness evoked a reorientation of variable errors, whereas in the light, the viewer-centered variability changed only in magnitude. Local distortion measurements revealed an anisotropic contraction of endpoint positions toward an “average” response along an axis that points between the eyes and the effector arm. This local contraction was present in both lighting conditions. The magnitude of the contraction remained constant for the two memory delays in the light but increased significantly for the longer delays in darkness. These data argue for the separate storage of distance and direction information within short-term memory, in a reference frame tied to the eyes and the effector arm.
TrkB Signaling Modulates Spine Density and Morphology Independent of Dendrite Structure in Cultured Neonatal Purkinje Cells
Authors: Shimada Atsuyoshi , Mason Carol A. , Morrison Mary E.
Published: April 2018

Neurotrophins cooperate with neural activity to modulate CNS neuronal survival and dendritic differentiation. In a previous study, we demonstrated that a critical balance of neurotrophin and neural activity is required for Purkinje cell survival in cocultures of purified granule and Purkinje cells (Morrison and Mason, 1998). Here we investigate whether TrkB signaling regulates dendrite and spine development of Purkinje cells. BDNF treatment of purified Purkinje cells cultured alone did not elicit formation of mature dendrites or spines. In cocultures of granule and Purkinje cells, however, continuous treatment with BDNF over a 2 week postnatal culture period increased the density of Purkinje cell dendritic spines relative to controls without causing a shift in the proportions of headed and filopodia-like spines. The increase in spine number was blocked by adding TrkB-IgG to the medium together with BDNF. Although BDNF alone did not consistently modify the morphology of dendritic spines, treatment with TrkB-IgG alone yielded spines with longer necks than those in control cultures. None of these treatments altered Purkinje cell dendritic complexity. These analyses reveal a role for TrkB signaling in modulating spine development, consistent with recently reported effects of neurotrophins on synaptic function. Moreover, spine development can be uncoupled from dendrite outgrowth in this reductionist system of purified presynaptic and postsynaptic neurons.
Defining Affinity with the GABAAReceptor
Authors: Jones Mathew V. , Sahara Yoshinori , Dzubay Jeffrey A. , Westbrook Gary L.
Published: April 2018

At nicotinic and glutamatergic synapses, the duration of the postsynaptic response depends on the affinity of the receptor for transmitter (Colquhoun et al., 1977; Pan et al., 1993). Affinity is often thought to be determined by the ligand unbinding rate, whereas the binding rate is assumed to be diffusion-limited. In this view, the receptor selects for those ligands that form a stable complex on binding, but binding is uniformly fast and does not itself affect selectivity. We tested these assumptions for the GABAAreceptor by dissecting the contributions of microscopic binding and unbinding kinetics for agonists of equal efficacy but of widely differing affinities. Agonist pulses applied to outside-out patches of cultured rat hippocampal neurons revealed that agonist unbinding rates could not account for affinity if diffusion-limited binding was assumed. However, direct measurement of the instantaneous competition between agonists and a competitive antagonist revealed that binding rates were orders of magnitude slower than expected for free diffusion, being more steeply correlated with affinity than were the unbinding rates. The deviation from diffusion-limited binding indicates that a ligand-specific energy barrier between the unbound and bound states determines GABAAreceptor selectivity. This barrier and our kinetic observations can be quantitatively modeled by requiring the participation of movable elements within a flexible GABA binding site.