bluuebunny/crossref_metadata_2025 huggingface dataset:
A Single Exposure to Amphetamine Is Sufficient to Induce Long-Term Behavioral, Neuroendocrine, and Neurochemical Sensitization in Rats
Authors: Vanderschuren Louk J. M. J. , Schmidt E. Donné , De Vries Taco J. , Van Moorsel Caroline A. P. , Tilders Fred J.H. , Schoffelmeer Anton N. M.
Published: April 2018

Repeated treatment with psychostimulant drugs causes long-lasting behavioral sensitization and associated neuroadaptations. Although sensitization induced by a single psychostimulant exposure has also been reported, information on the behavioral and neurochemical consequences of a single psychostimulant exposure is sparse. Therefore, to evaluate whether behavioral sensitization evoked by single and repeated psychostimulant pretreatment regimens represent the same neurobiological phenomenon, the time-dependent expression of behavioral, neurochemical, and neuroendocrine sensitization after a single exposure to amphetamine was investigated in rats. A single exposure to amphetamine (5 mg/kg, i.p.) caused context-independent sensitization of the locomotor effects of amphetamine, which intensified over time. Thus, sensitization to amphetamine was marginal at 3 d after treatment and more evident after 1 week, whereas 3 weeks after treatment, profound sensitization, as well as cross-sensitization, to cocaine was observed. Amphetamine pretreatment caused an increase in the electrically evoked release of [3H]dopamine from nucleus accumbens, caudate putamen, and medial prefrontal cortex slices and of [14C]acetylcholine from accumbens and caudate slices. The hyperreactivity of dopaminergic nerve terminals appeared to parallel the development of locomotor sensitization, i.e., whereas hyperreactivity of accumbens dopaminergic terminals increased between 3 d and 3 weeks after treatment, the hyperreactivity of medial prefrontal dopaminergic terminals decreased. Pre-exposure to amphetamine also sensitized the hypothalamus–pituitary–adrenal axis response to amphetamine at 1 and 3 weeks, but not at 3 d after treatment. Because these data closely resemble those reported previously for repeated amphetamine pretreatment, it is concluded that a single exposure to amphetamine is sufficient to induce long-term behavioral, neurochemical, and neuroendocrine sensitization in rats.
Synaptic Basis of Cortical Persistent Activity: the Importance of NMDA Receptors to Working Memory
Authors: Wang Xiao-Jing
Published: April 2018

Delay-period activity of prefrontal cortical cells, the neural hallmark of working memory, is generally assumed to be sustained by reverberating synaptic excitation in the prefrontal cortical circuit. Previous model studies of working memory emphasized the high efficacy of recurrent synapses, but did not investigate the role of temporal synaptic dynamics. In this theoretical work, I show that biophysical properties of cortical synaptic transmission are important to the generation and stabilization of a network persistent state. This is especially the case when negative feedback mechanisms (such as spike-frequency adaptation, feedback shunting inhibition, and short-term depression of recurrent excitatory synapses) are included so that the neural firing rates are controlled within a physiological range (10–50 Hz), in spite of the exuberant recurrent excitation. Moreover, it is found that, to achieve a stable persistent state, recurrent excitatory synapses must be dominated by a slow component. If neuronal firings are asynchronous, the synaptic decay time constant needs to be comparable to that of the negative feedback; whereas in the case of partially synchronous dynamics, it needs to be comparable to a typical interspike interval (or oscillation period). Slow synaptic current kinetics also leads to the saturation of synaptic drive at high firing frequencies that contributes to rate control in a persistent state. For these reasons the slow NMDA receptor-mediated synaptic transmission is likely required for sustaining persistent network activity at low firing rates. This result suggests a critical role of the NMDA receptor channels in normal working memory function of the prefrontal cortex.
Amygdala Neurons Mediate Acquisition But Not Maintenance of Instrumental Avoidance Behavior in Rabbits
Authors: Poremba Amy , Gabriel Michael
Published: April 2018

Whereas the amygdala is generally understood to be involved in aversively motivated learning, the specific associative function of the amygdala remains controversial. This study addressed the amygdalar role in mediation of discriminative instrumental avoidance learning of rabbits. Bilateral microinjection of the GABA receptor agonist muscimol centered in the basolateral nucleus of the amygdala was given to inactivate amygdalar neurons at each of three stages of acquisition. The absence of behavioral learning in rabbits trained immediately after amygdalar inactivation confirmed previous results with electrolytic lesions. The absence of savings during training after muscimol had become ineffective indicated an amygdalar role in the establishment of acquisition-relevant neural plasticity, not simply in the expression of the learned response. A time-limited role of the amygdala in instrumental avoidance learning was indicated by the finding that intra-amygdalar muscimol failed to disrupt performance of the well-established avoidance response. The passage of time alone (with no training trials) was sufficient to reduce amygdalar involvement in response performance. These results and demonstrations that other limbic system areas make time-limited contributions to learning indicate that the amygdala is part of a larger intermediate memory system that supports learning and performance before habit consolidation.
Mice Deficient in Cellular Glutathione Peroxidase Show Increased Vulnerability to Malonate, 3-Nitropropionic Acid, and 1-Methyl-4-Phenyl-1,2,5,6-Tetrahydropyridine
Authors: Klivenyi Peter , Andreassen Ole A. , Ferrante Robert J. , Dedeoglu Alpaslan , Mueller Gerald , Lancelot Eric , Bogdanov Mikhail , Andersen Julie K. , Jiang Dongmei , Beal M. Flint
Published: April 2018

Glutathione peroxidase (GSHPx) is a critical intracellular enzyme involved in detoxification of hydrogen peroxide (H2O2) to water. In the present study we examined the susceptibility of mice with a disruption of the glutathione peroxidase gene to the neurotoxic effects of malonate, 3-nitropropionic acid (3-NP), and 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP). Glutathione peroxidase knock-out mice showed no evidence of neuropathological or behavioral abnormalities at 2–3 months of age. Intrastriatal injections of malonate resulted in a significant twofold increase in lesion volume in homozygote GSHPx knock-out mice as compared to both heterozygote GSHPx knock-out and wild-type control mice. Malonate-induced increases in conversion of salicylate to 2,3- and 2,5-dihydroxybenzoic acid, an index of hydroxyl radical generation, were greater in homozygote GSHPx knock-out mice as compared with both heterozygote GSHPx knock-out and wild-type control mice. Administration of MPTP resulted in significantly greater depletions of dopamine, 3,4-dihydroxybenzoic acid, and homovanillic acid in GSHPx knock-out mice than those seen in wild-type control mice. Striatal 3-nitrotyrosine (3-NT) concentrations after MPTP were significantly increased in GSHPx knock-out mice as compared with wild-type control mice. Systemic 3-NP administration resulted in significantly greater striatal damage and increases in 3-NT in GSHPx knock-out mice as compared to wild-type control mice. The present results indicate that a knock-out of GSHPx may be adequately compensated under nonstressed conditions, but that after administration of mitochondrial toxins GSHPx plays an important role in detoxifying increases in oxygen radicals.
Distinct Roles of Synaptic and Extrasynaptic NMDA Receptors in Excitotoxicity
Authors: Sattler Rita , Xiong Zhigang , Lu Wei-Yang , MacDonald John F. , Tymianski Michael
Published: April 2018

Excitatory synaptic activity governs excitotoxicity and modulates the distribution of NMDA receptors (NMDARs) among synaptic and extrasynaptic sites of central neurons. We investigated whether NMDAR localization was functionally linked to excitotoxicity by perturbing F-actin, a cytoskeletal protein that participates in targeting synaptic NMDARs in dendritic spines. Depolymerizing F-actin did not affect NMDA-evoked whole-cell currents. However, the number of dendritic NMDAR clusters and the NMDAR-mediated component of miniature spontaneous EPSCs were reduced, whereas the number of AMPA receptor clusters and AMPA receptor-mediated component of EPSCs was unchanged. This selective perturbation of synaptically activated NMDARs had no effect on neuronal death or the accumulation of45Ca2+evoked by applying exogenous NMDA orl-glutamate, which reach both synaptic and extrasynaptic receptors. However, it increased survival and decreased45Ca2+accumulation in neurons exposed to oxygen glucose deprivation, which causes excitotoxicity by glutamate release at synapses. Thus, synaptically and extrasynaptically activated NMDARs are equally capable of excitotoxicity. However, their relative contributions vary with the location of extracellular excitotoxin accumulation, a factor governed by the mechanism of extracellular neurotransmitter accumulation, not the synaptic activation of NMDARs.
Neuronal Inwardly Rectifying K+Channels Differentially Couple to PDZ Proteins of the PSD-95/SAP90 Family
Authors: Nehring Ralf B. , Wischmeyer Erhard , Döring Frank , Veh Rüdiger W. , Sheng Morgan , Karschin Andreas
Published: April 2018

Several signaling proteins clustered at the postsynaptic density specialization in neurons harbor a conserved C-terminal PDZ domain recognition sequence (X-S/T-X-V/I) that mediates binding to members of the PSD-95/SAP90 protein family. This motif is also present in the C termini of some inwardly rectifying K+(Kir) channels. Constitutively active Kir2 channels as well as G protein-gated Kir3 channels, which are fundamental for neuronal excitability, were analyzed as candidates for binding to PSD-95/SAP90 family members. Therefore C termini of Kir2.1(+), Kir2.3(+), Kir2.4(−), Kir3.1(−), Kir3.2(+), Kir3.3(+) and Kir3.4(−) subunits (+, motif present; −, motif absent) were used as baits in the yeast two-hybrid assay to screen forin vivointeraction with PDZ domains 1–3 of PSD-95/SAP90. In contrast to Kir2.1 and Kir2.3, all Kir3 fragments failed to bind PSD-95 in this assay, which was supported by the lack of coimmunoprecipitation and colocalization of the entire proteins in mammalian cells. A detailed analysis of interaction domains demonstrated that the C-terminal motif in Kir3 channels is insufficient for binding PDZ domains. Kir2.1 and Kir2.3 subunits on the other hand coprecipitate with PSD-95. When coexpressed in a bicistronic internal ribosome entry site expression vector in HEK-293 cells macroscopic and elementary current analysis revealed that PSD-95 suppressed the activity of Kir2.3 channels by >50%. This inhibitory action of PSD-95, which predominantly affects the single-channel conductance, is likely attributable to a molecular association with additional internal interaction sites in the Kir2.3 protein.
α1ESubunits Form the Pore of Three Cerebellar R-Type Calcium Channels with Different Pharmacological and Permeation Properties
Authors: Tottene Angelita , Volsen Stephen , Pietrobon Daniela
Published: April 2018

R-type Ca2+channels cooperate with P/Q- and N-type channels to control neurotransmitter release at central synapses. The leading candidate as pore-forming subunit of R-type channels is the α1Esubunit. However, R-type Ca2+currents with permeation and/or pharmacological properties different from those of recombinant Ca2+channels containing α1Esubunits have been described, and therefore the molecular nature of R-type Ca2+channels remains not completely settled. Here, we show that the R-type Ca2+current of rat cerebellar granule cells consists of two components inhibited with different affinity by the α1Eselective antagonist SNX482 (IC50values of 6 and 81 nm) and a third component resistant to SNX482. The SNX482-sensitive R-type current shows the unique permeation properties of recombinant α1Echannels; it is larger with Ca2+than with Ba2+as charge carrier, and it is highly sensitive to Ni2+block and has a voltage-dependence of activation consistent with that of G2 channels with unitary conductance of 15 pS. On the other hand, the SNX482-resistant R-type current shows permeation properties similar to those of recombinant α1Aand α1Bchannels; it is larger with Ba2+than with Ca2+as charge carrier,and it has a low sensitivity to Ni2+block and a voltage-dependence of activation consistent with that of G3 channels with unitary conductance of 20 pS. Gene-specific knock-down by antisense oligonucleotides demonstrates that the different cerebellar R-type channels are all encoded by the α1Egene, suggesting the existence of α1Eisoforms with different pore properties.
Ninjurin2, a Novel Homophilic Adhesion Molecule, Is Expressed in Mature Sensory and Enteric Neurons and Promotes Neurite Outgrowth
Authors: Araki Toshiyuki , Milbrandt Jeffrey
Published: April 2018

A large number of cell adhesion molecules mediate cell-to-cell and cell-to-extracellular matrix interaction during development, differentiation and regeneration of the peripheral nervous system. Here, we report the identification of a novel cell surface adhesion molecule, ninjurin2 (for nerve injury induced protein 2). Ninjurin2 is a homolog of a homophilic cellular adhesion molecule, ninjurin1, that was previously isolated as a gene induced in Schwann cells after nerve injury. Ninjurin1 and 2 share conserved hydrophobic regions for their transmembrane domains; however, they do not contain comparable adhesion motifs nor do they interact with each other. In the peripheral nervous system, ninjurin2 is expressed constitutively in mature sensory and enteric neurons but not in glial cells or in autonomic ganglia. Ninjurin2 is upregulated in Schwann cells surrounding the distal segment of injured nerve with a time course similar to that of ninjurin1, neural CAM, and L1. Ninjurin2 promotes neurite outgrowth from primary cultured dorsal root ganglion neurons, presumably via homophilic cellular interactions. Ninjurin2 is also highly expressed in hematopoietic and lymphatic tissues. Finally, the ninjurin2 gene is located on human chromosome 12p13 in which several disorders of unknown etiology have been mapped, including inflammatory bowel disease and acrocallosal syndrome.
The Urokinase Plasminogen Activator Receptor (UPAR) Is Preferentially Induced by Nerve Growth Factor in PC12 Pheochromocytoma Cells and Is Required for NGF-Driven Differentiation
Authors: Farias-Eisner Robin , Vician Linda , Silver Abigail , Reddy Srinivasa , Rabbani Shafaat A. , Herschman Harvey R.
Published: April 2018

Nerve growth factor (NGF)-driven differentiation of PC12 pheochromocytoma cells is a well studied model used both to identify molecular, biochemical, and physiological correlates of neurotrophin-driven neuronal differentiation and to determine the causal nature of specific events in this differentiation process. Although epidermal growth factor (EGF) elicits many of the same early biochemical and molecular changes in PC12 cells observed in response to NGF, EGF does not induce molecular or morphological differentiation of PC12 cells. The identification of genes whose expression is differentially regulated by NGF versus EGF in PC12 cells has, therefore, been considered a source of potential insight into the molecular specificity of neurotrophin-driven neuronal differentiation. A “second generation” representational difference analysis procedure now identifies the urokinase plasminogen activator receptor (UPAR) as a gene that is much more extensively induced by NGF than by EGF in PC12 cells. Both an antisense oligonucleotide for the UPAR mRNA and an antibody directed against UPAR protein block NGF-induced morphological and biochemical differentiation of PC12 cells; NGF-induced UPAR expression is required for subsequent NGF-driven differentiation.
Proteasome Inhibitors Induce Cytochrome c–Caspase-3-Like Protease-Mediated Apoptosis in Cultured Cortical Neurons
Authors: Qiu Jian Hua , Asai Akio , Chi Shunji , Saito Nobuhito , Hamada Hirofumi , Kirino Takaaki
Published: April 2018

The ubiquitin–proteasome protein degradation pathway is crucial in controlling intracellular levels of a variety of short-lived proteins and maintaining cellular growth and metabolism. In a previous study, we showed the accumulation of conjugated ubiquitin in CA1 neurons of the gerbil after 5 min of forebrain ischemia (Morimoto et al., 1996; Ide et al., 1999). The accumulation of conjugated ubiquitin may reflect proteasome malfunction. In the present study, we investigated the effects of proteasome inhibitors on primary neuronal cultures to determine whether proteasomal malfunction induces neuronal death. When carbobenzoxy-Leu-Leu-Leu-aldehyde or lactacystin, two different types of proteasome inhibitors, were separately used to suppress proteasome activity, we observed induction of apoptotic neuronal cell death in both cases. During the apoptotic process, mitochondrial membrane potential was disrupted, cytochrome-c was released from mitochondria into the cytosol, and caspase-3-like proteases were activated. Apoptosis was inhibited by pretreatment with acetyl-aspartyl-glutamyl-valyl-aspart-1-aldehyde or overexpression of Bcl-x/L. These results demonstrated that suppression of proteasome function induces neuronal apoptosis via the release of cytochrome c from mitochondria and activation of caspase-3-like proteases.
Evidence that Brain-Derived Neurotrophic Factor from Presynaptic Nerve Terminals Regulates the Phenotype of Calbindin-Containing Neurons in the Lateral Septum
Authors: Fawcett James P. , Alonso-Vanegas Mario A. , Morris Stephen J. , Miller Freda D. , Sadikot Abbas F. , Murphy Richard A.
Published: April 2018

Brain-derived neurotrophic factor (BDNF) is transported anterogradely in neurons of the CNS and can be released by activity-dependent mechanisms to regulate synaptic plasticity. However, few neural networks have been identified in which the production, transport, and effects of BDNF on postsynaptic neurons can be analyzed in detail. In this study, we have identified such a network. BDNF has been colocalized by immunocytochemistry with tyrosine hydroxylase (TH) in nerve fibers and nerve terminals within the lateral septum of rats. BDNF-containing nerve fibers terminate on a population of calbindin-containing neurons in lateral septum that contain TrkB, the high-affinity receptor for BDNF. Overexpression of BDNF in noradrenergic neurons increased levels of calbindin in septum, as well as in whole-brain lysates. Septal levels of calbindin and BDNF partially decreased after unilateral lesions of the medial forebrain bundle (MFB), induced with 6-hydroxydopamine, a treatment that abolished TH staining. These data suggest that BDNF is anterogradely transported within the MFB in catecholaminergic neurons arising from brainstem nuclei. To determine whether BDNF affects the production of calbindin in lateral septal neurons directly, we tested the effects of BDNF on cultures of septal neurons from embryonic day 16–17 rats. BDNF promoted the expression of calbindin, as well as the arborization of calbindin-containing neurons, but BDNF had no effect on cell division or survival. Together, these results suggest that BDNF, anterogradely transported in catecholaminergic neurons, regulates calbindin expression within the lateral septum.
Segregation of On and Off Bipolar Cell Axonal Arbors in the Absence of Retinal Ganglion Cells
Authors: Günhan-Agar Emine , Kahn Dianna , Chalupa Leo M.
Published: April 2018

Retinal cells that respond selectively to light onset or offset are segregated into On and Off pathways. Here, we describe the development of cone bipolar cells whose axonal arbors at maturity synapse onto ganglion cell dendrites confined to On and Off strata of the inner plexiform layer (IPL). In particular, we sought to determine whether the formation of this segregated pattern is dependent on the presence of ganglion cells. Developing bipolar cells were visualized using an antibody against recoverin, the calcium binding protein that labels On and Off cone bipolar cells in the adult rat retina. Recoverin-positive cells were apparent in the ventricular zone on the day of birth [postnatal day 0 (P0)], before bipolar cells begin to migrate to the inner nuclear layer. Two distinct strata were first apparent in the IPL at P8, with the Off pathway maturing earlier than the On pathway. There was no indication of exuberant bipolar cell projections. Throughout development, there were also a small number of recoverin-positive cells of unknown origin in the ganglion cell layer.

To assess whether the formation of On and Off cone bipolar cell projections is dependent on the presence of ganglion cells, these target neurons were eliminated by unilateral section of the optic nerve. This was done on the day of birth, resulting in a total loss of ganglion cells 5–6 d before bipolar cell axons innervate the IPL. In retinas with optic nerve sections, On and Off cone bipolar cells were present, albeit at a lower than normal density, and the axonal arbors of these interneurons were organized into two distinct strata. This indicates that ganglion cells are not essential for the formation of segregated On and Off bipolar cell inputs. These results lend support to the hypothesis that specific ingrowth patterns of bipolar cell terminal arbors could regulate the formation of stratified retinal ganglion cell dendrites.
Neuronal Correlates for Preparatory Set Associated with Pro-Saccades and Anti-Saccades in the Primate Frontal Eye Field
Authors: Everling Stefan , Munoz Douglas P.
Published: April 2018

Diversity in behavioral responses to sensory stimuli has been attributed to variations in preparatory set. Variability in oculomotor responses toward identical visual stimuli has been well documented, but the neuronal processes underlying this variability are poorly understood. Here, we report evidence for set-related activity for saccadic eye movements in single neurons in the frontal eye field (FEF) in monkeys trained on a task in which they either had to look toward a visual stimulus (pro-saccade) or away from the stimulus (anti-saccade) depending on a previous instruction. A portion of FEF neurons were identified as neurons projecting directly to the superior colliculus (SC) with antidromic activation techniques. Saccade-related neurons in the FEF had lower prestimulus and stimulus-related activity on anti-saccade trials compared with pro-saccade trials. The level of prestimulus activity correlated with saccadic reaction times, express saccade occurrence, and errors in the anti-saccade task. In addition, saccade-related activity in the FEF was higher for pro-saccades than for anti-saccades. These results demonstrate that the direct descending pathway from the FEF to the SC carries preparatory set-related activity for pro-saccades and anti-saccades. The results also provide insights into the neuronal basis of variations in saccadic reaction times and in the control of the prepotent response to glance to a flashed stimulus.
Long-Term Depression and Depotentiation in the Sensorimotor Cortex of the Freely Moving Rat
Authors: Froc David J. , Chapman C. Andrew , Trepel Christopher , Racine Ronald J.
Published: April 2018

Activity-dependent reductions in synaptic efficacy are central components of recent models of cortical learning and memory. Here, we have examined long-term synaptic depression (LTD) and the reversal of long-term potentiation (depotentiation) of field potentials evoked in sensorimotor cortex by stimulation of the white matter in the adult, freely moving rat. Prolonged, low-frequency stimulation (1 Hz for 15 min) was used to induce either depotentiation or LTD. LTD was expressed as a reduction in the amplitude of both monosynaptic and polysynaptic field potential components. Both LTD and depotentiation were reliably induced by stimulation of the ipsilateral white matter. Stimulation of the contralateral neocortex induced only a depotentiation effect, which decayed more rapidly than that induced by ipsilateral stimulation (hours vs days). Although ipsilateral LTD was effectively induced by a single session of low-frequency stimulation, multiple sessions of stimulation, either massed or spaced, induced LTD effects that were larger in magnitude and longer lasting. Previously, we showed that the induction of long-term potentiation in the neocortex of chronic preparations required multiple, spaced stimulation sessions to reach asymptotic levels. Here, we report that LTD also required multiple stimulation sessions to reach asymptotic levels, but massed and spaced patterns of low-frequency stimulation were equally effective.
Impaired Recognition Memory in Monkeys after Damage Limited to the Hippocampal Region
Authors: Zola Stuart M. , Squire Larry R. , Teng Edmond , Stefanacci Lisa , Buffalo Elizabeth A. , Clark Robert E.
Published: April 2018

Monkeys with lesions limited to the hippocampal region (the hippocampus proper, the dentate gyrus, and the subiculum) were impaired on two tasks of recognition memory: delayed nonmatching to sample and the visual paired-comparison task. Recognition memory was impaired in five different groups of monkeys, whether the lesions were made by an ischemic procedure, by radio frequency, or by ibotenic acid. The finding that the hippocampal region is essential for normal recognition memory performance is considered in the context of current ideas about the role of the hippocampus in declarative memory.
Medial Frontal Cortex in Action Monitoring
Authors: Luu Phan , Flaisch Tobias , Tucker Don M.
Published: April 2018

Effective behavior requires continuous action monitoring. Electrophysiological studies in both monkeys and humans have shown activity in the medial frontal cortex that reflects dynamic control and monitoring of behavioral acts. In humans, the centromedial frontal cortex shows an electrical response within 100 msec of an error, the error-related negativity (ERN). The ERN occurs only when subjects are aware of making an error, suggesting that a critical factor may be self-monitoring of the action process. In the present study, we examined late responses in a deadline reaction time task, in which the subject becomes increasingly aware of making an error as the response becomes increasingly late. We found evidence of response conflict before errors defined by late responses but not before errors defined by incorrect responses. The results also show a linear increase in the amplitude of the ERN with increasingly late responses. These data suggest that frontal networks provide dynamic representations that monitor and evaluate the unfolding action plan.
Changes in Activating Protein 1 (AP-1) Composition Correspond with the Biphasic Profile of Nerve Growth Factor mRNA Expression in Rat Hippocampus after Hilus Lesion-Induced Seizures
Authors: Elliott Robert C. , Gall Christine M.
Published: April 2018

In adult brain, nerve growth factor (NGF) gene expression is generally upregulated by neuronal activity. However, a single episode of hilus lesion (HL)-induced limbic seizures stimulates a biphasic increase in NGF mRNA expression with peaks at 4–6 and 24 hr after lesion and an intervening return to control levels at 10–12 hr after lesion.In vitrostudies suggest that NGF transcription is regulated via an activating protein 1 (AP-1) binding site in the first intron of the NGF gene. To examine the relationship between seizure-induced AP-1 binding and NGF gene expression in this paradigm, NGF mRNA levels and AP-1 binding were examined after HL seizures. Furthermore, to gain insight into the functional composition of the AP-1 complex, supershift analysis was performed to characterize which Fos and Jun family members are included in the AP-1-binding complex at the different time points analyzed. Solution hybridization analysis verified the biphasic increase in NGF mRNA content of the dentate gyrus after HL seizures. After an initial increase, AP-1 binding slowly declined in a stepwise manner that encompassed, but did not correspond with, the two phases of NGF mRNA expression. However, supershift analyses demonstrated that the relative contributions of JunD and JunB to the AP-1 complex exhibited positive and negative correlations, respectively, with the phases of increased NGF expression after HL. These results suggest that AP-1 complexes containing JunD promote NGF transactivation and that transient changes in the relative contributions of JunD and JunB to AP-1 binding underlie the biphasic increase in NGF gene expression induced by HL seizures.
Regulation of Kinetic Properties of GluR2 AMPA Receptor Channels by Alternative Splicing
Authors: Koike Maki , Tsukada Shota , Tsuzuki Keisuke , Kijima Hiromasa , Ozawa Seiji
Published: April 2018

The four subunits of the AMPA-type glutamate receptor (GluR1–GluR4 or GluR-A–GluR-D) exist in two distinct forms, flip and flop, generated by alternative splicing of a 115 bp region. The GluR2 subunit plays a key role in determining the functional properties of the AMPA receptor channel. In this study, we examined the differences in kinetic properties between the flip and flop splice variants of the GluR2 subunit expressed inXenopusoocytes using fast agonist application techniques. Glutamate was applied to outside-out patches from oocytes with piezo-driven double-barreled application pipettes. Because homomeric receptor channels composed of the edited form of GluR2 (GluR2R) produce no appreciable current responses, we expressed the unedited form of GluR2 (GluR2Q) in oocytes, which produced large current responses sufficient for analysis of the kinetic properties. The time constant for desensitization during application of 1 mmglutamate was 5.89 ± 0.17 msec (n= 50) in flip and 1.18 ± 0.05 msec (n= 37) in flop. The deactivation time constant was 0.62 ± 0.06 msec (n= 10) in flip and 0.54 ± 0.05 msec (n= 10) in flop. The steady-state nondesensitizing current was 6.8 ± 0.4% (n= 53) of the peak current in flip, whereas it was almost negligible in flop, being only 1.1 ± 0.1% (n= 36). The slower desensitization kinetics and larger steady-state current responses in the flip variant were also observed in heteromeric receptors assembled from GluR2Q/GluR2R. Thus, desensitization occurred much more prominently in the flop variant in the recombinant GluR2 receptor channels.
TheFlatheadMutation Causes CNS-Specific Developmental Abnormalities and Apoptosis
Authors: Roberts Melanie R. , Bittman Kevin , Li Wei-Wei , French Richard , Mitchell Bartley , LoTurco Joseph J. , D'Mello Santosh R.
Published: April 2018

We describe a new mutation,flathead(fh), that arose spontaneously in an inbred colony of Wistar rats. The mutation is autosomal recessive, and the behavioral phenotype offh/fhrats includes spontaneous seizures, tremor, impaired coordination, and premature death. A striking feature of thefhmutation is a dramatic reduction in brain size (40% of normal at birth). In contrast, no abnormalities are evident in the peripheral nervous system or in other tissues outside of the CNS. Although bromodeoxyuridine incorporation assays indicate that the rate of cell proliferation in thefh/fhcortex is similar to that of unaffected animals,in situterminal deoxynucleotidyl transferase-mediated dUTP-biotin end-labeling assays reveal a dramatic increase in apoptotic cell death beginning after embryonic day 16 (E16). At E18 there is a 20-fold increase in cell death in the ventricular zone offh/fhneocortex, and at postnatal day 1 (P1), the number of apoptotic cells is still two times that of normal. However, by P8 the extent of cell death infh/fhis comparable to that of unaffected littermates, indicating that the reduction in brain growth is caused by abnormally high apoptosis during a discrete developmental period. Late-developing structures such as the cerebellum, neocortex, hippocampus, and retina are most severely affected by thefhmutation. Within these structures, later-generated neuronal populations are selectively depleted. Together, these results suggest that theflatheadgene is essential for a developmental event required for the generation and maturation of late-born cell populations in the brain.
Spectral-Temporal Receptive Fields of Nonlinear Auditory Neurons Obtained Using Natural Sounds
Authors: Theunissen Frédéric E. , Sen Kamal , Doupe Allison J.
Published: April 2018

The stimulus–response function of many visual and auditory neurons has been described by a spatial-temporal receptive field (STRF), a linear model that for mathematical reasons has until recently been estimated with the reverse correlation method, using simple stimulus ensembles such as white noise. Such stimuli, however, often do not effectively activate high-level sensory neurons, which may be optimized to analyze natural sounds and images. We show that it is possible to overcome the simple-stimulus limitation and then use this approach to calculate the STRFs of avian auditory forebrain neurons from an ensemble of birdsongs. We find that in many cases the STRFs derived using natural sounds are strikingly different from the STRFs that we obtained using an ensemble of random tone pips. When we compare these two models by assessing their predictions of neural response to the actual data, we find that the STRFs obtained from natural sounds are superior. Our results show that the STRF model is an incomplete description of response properties of nonlinear auditory neurons, but that linear receptive fields are still useful models for understanding higher level sensory processing, as long as the STRFs are estimated from the responses to relevant complex stimuli.
Functional Specificity of Callosal Connections in Tree Shrew Striate Cortex
Authors: Bosking William H. , Kretz Robert , Pucak Michele L. , Fitzpatrick David
Published: April 2018

Although callosal connections have been shown to link extensive regions of primary visual cortex, the distribution of these connections with respect to the map of visual space and the map of orientation preference remains unclear. Here we combine optical imaging of intrinsic signals with injection of fluorescent microspheres to assess the functional specificity of callosal connections in the tree shrew. By imaging both hemispheres simultaneously while presenting a series of spatially restricted stimuli, we find that a substantial region of visual space is represented bilaterally. Each hemisphere includes a representation of the ipsilateral visual field that is highly compressed relative to that of the contralateral visual field and is most extensive in the lower visual field, where ∼30οof central visual space are represented bilaterally. Callosal connections extend throughout the region of bilateral representation but terminate in a spatially restricted manner that links visuotopically corresponding sites in the two hemispheres. In contrast, callosal connections appear to terminate without regard for the map of orientation preference, showing little sign of the orientation-specific modular and axial specificity that is characteristic of long-range horizontal connections. By coordinating the activity in the two hemispheres in a way that preserves nearest neighbor relationships, callosal connections may best be viewed as elements of local circuits that operate within a single bilateral representation of visual space.
Response Characteristics of an Identified, Sexually Dimorphic Olfactory Glomerulus
Authors: King Jane Roche , Christensen Thomas A. , Hildebrand John G.
Published: April 2018

Partitioning of synaptic neuropil into glomeruli is a common feature of primary olfactory centers in most animal species. The functional significance of glomeruli, however, is not yet well understood. The present study is part of our effort to test the hypothesis that each glomerulus is a functional unit dedicated to processing information about a particular odorant or attribute of odor molecules and that the glomerular array constitutes a map of “odor space.” We investigated the physiological and morphological features of uniglomerular projection neurons (PNs) associated with an identified glomerulus in each antennal lobe of the female sphinx moth,Manduca sexta.This “lateral large female glomerulus” (latLFG) is sexually dimorphic and therefore may play a female-specific role, such as processing of information about one or more odorants important for orientation of a female to host plants for oviposition. Together with the medial LFG (medLFG), the latLFG resides outside the array of spheroidal ordinary glomeruli, near the entrance of the antennal (olfactory) nerve. Each LFG is innervated by four to five PNs. Using intracellular recording and staining, we examined the responses of latLFG-PNs to odorants that represent major classes of volatiles released by host plants ofM. sexta. All latLFG-PNs were excited when the ipsilateral antenna was stimulated with low concentrations of the monoterpenoid linalool. Dose–response analysis showed that neither other monoterpenoids nor representatives of other classes of host plant volatiles were similarly stimulatory to latLFG-PNs. These findings are consistent with the idea that each glomerulus has a characteristic, limited molecular receptive range.
Role of cAMP Cascade in Synaptic Stability and Plasticity: Ultrastructural and Physiological Analyses of Individual Synaptic Boutons inDrosophilaMemory Mutants
Authors: Renger John J. , Ueda Atsushi , Atwood Harold L. , Govind C. K. , Wu Chun-Fang
Published: April 2018

Mutations of the genesrutabaga(rut) anddunce(dnc) affect the synthesis and degradation of cAMP, respectively, and disrupt learning inDrosophila. Combined ultrastructural analysis and focal electrophysiological recording in the larval neuromuscular junction revealed a loss of stability and fine tuning of synaptic structure and function in both mutants. Increased ratios of docked/undocked vesicles and poorly defined synaptic specializations characterizeddncsynapses. In contrast,rutboutons possessed fewer, although larger, synapses with lower proportions of docked vesicles. At reduced Ca2+levels, decreased quantal content coupled with an increase in failure rate was seen inrutboutons and reduced pair-pulse facilitation were found in bothrutanddncmutants. At physiological Ca2+levels, strong enhancement, instead of depression, in evoked release was observed in somedncandrutboutons during 10 Hz tetanus. Furthermore, increased variability of synaptic transmission, including fluctuation and asynchronicity of evoked release, paralleled an increase in synapse size variation in bothdncandrutboutons, which might impose problems for effective signal processing in the nervous system. Pharmacological and genetic studies indicated broader ranges of physiological alteration bydncandrutmutations than either the acute effects of cAMP analogs or the available mutations that affect cAMP-dependent protein kinase (PKA) activity. This is consistent with previous reports of more severe learning defects indncandrutmutations than these PKA mutants and allows identification of the phenotypes involving long-term developmental regulation and those conferred by PKA.
Functional Consequences of Reduction in NMDA Receptor Glycine Affinity in Mice Carrying Targeted Point Mutations in the Glycine Binding Site
Authors: Kew James N. C. , Koester Anja , Moreau Jean-Luc , Jenck Francois , Ouagazzal Abdel-Mouttalib , Mutel Vincent , Richards J. Grayson , Trube Gerhard , Fischer Guenther , Montkowski Alexandra , Hundt Wolfgang , Reinscheid Rainer K. , Pauly-Evers Meike , Kemp John A. , Bluethmann Horst
Published: April 2018

We have used site-directed mutagenesis in conjunction with homologous recombination to generate two mouse lines carrying point mutations in the glycine binding site of the NMDAR1 subunit (Grin1). Glycine concentration–response curves from acutely dissociated hippocampal neurons revealed a 5- and 86-fold reduction in receptor glycine affinity in mice carryingGrin1D481NandGrin1K483Qmutations, respectively, whereas receptor glutamate affinity remained unaffected. Homozygous mutantGrin1D481Nanimals are viable and fertile and appear to develop normally. However, homozygous mutantGrin1K483Qanimals are significantly lighter at birth, do not feed, and die within a few days. No gross abnormalities in CNS anatomy were detected in eitherGrin1D481NorGrin1K483Qmice. Interestingly,in situhybridization and Western blot analysis revealed changes in the expression levels of NMDA receptor subunits inGrin1D481Nmice relative to wild type that may represent a compensatory response to the reduction in receptor glycine affinity.Grin1D481Nmice exhibited deficits in hippocampal theta burst-induced long-term potentiation (LTP) and spatial learning and also a reduction in sensitivity to NMDA-induced seizures relative to wild-type controls, consistent with a reduced activation of NMDA receptors. Mutant mice exhibited normal prepulse inhibition but showed increased startle reactivity. Preliminary analysis indicated that the mice exhibit a decreased natural aversion to an exposed environment. The lethal phenotype ofGrin1K483Qanimals confirms the critical role of NMDA receptor activation in neonatal survival. A milder reduction in receptor glycine affinity results in an impairment of LTP and spatial learning and alterations in anxiety-related behavior, providing further evidence for the role of NMDA receptor activation in these processes.
Neurotrophin-3 Sorts to the Constitutive Secretory Pathway of Hippocampal Neurons and Is Diverted to the Regulated Secretory Pathway by Coexpression with Brain-Derived Neurotrophic Factor
Authors: Farhadi Hooman F. , Mowla S. Javad , Petrecca Kevin , Morris Stephen J. , Seidah Nabil G. , Murphy Richard A.
Published: April 2018

Hippocampal neurons release nerve growth factor (NGF) through the constitutive secretory pathway, thus allowing the protein to be continuously available for promoting nerve cell survival. In contrast, hippocampal neurons use the regulated secretory pathway to process brain-derived neurotrophic factor (BDNF), which alters synaptic activity when released acutely from dense-core vesicles. Thus, understanding how neurons sort and deliver neurotrophins may provide clues to their functions in brain. In this study, we monitored the processing and delivery of neurotrophin-3 (NT-3). Pulse–chase studies, immunocytochemistry, and secretagogue-induced release experiments were performed on cultured hippocampal neurons and AtT-20 cells infected with vaccinia viruses encoding the NT-3 precursor (pro-NT-3). Results show that most newly synthesized NT-3 is released through the constitutive secretory pathway as a result of furin-mediated endoproteolytic cleavage of pro-NT-3 in thetrans-Golgi network. Pro-NT-3 can also be diverted into the regulated secretory pathway when cells are treated with α1-PDX, a selective inhibitor of furin-like enzymes, or when pro-NT-3 expression is increased by transient transfection methods. In cells coinfected with viruses coding for pro-NT-3 and pro-BDNF, NT-3 is sorted into the regulated pathway, stored in secretory granules, and released in response to extracellular cues together with BDNF, apparently as a result of heterodimerization, as suggested by coimmunoprecipitation data. Taken together, these data show that sorting of the NT-3 precursor can occur in both the constitutive and regulated secretory pathways, which is consistent with NT-3 having both survival-promoting and synapse-altering functions.
A MAP Kinase-Signaling Pathway Mediates Neurite Outgrowth on L1 and Requires Src-Dependent Endocytosis
Authors: Schmid Ralf-Steffen , Pruitt Wendy M. , Maness Patricia F.
Published: April 2018

The neural cell adhesion molecule L1 mediates the axon outgrowth, adhesion, and fasciculation necessary for proper development of synaptic connections. Mutations of human L1 cause an X-linked mental retardation syndrome termed CRASH (corpus callosum hypoplasia, retardation, aphasia, spastic paraplegia, and hydrocephalus), and L1 knock-out mice display defects in neuronal process extension resembling the CRASH phenotype. Little is known about the biochemical or cellular mechanism by which L1 performs neuronal functions. Here it is demonstrated that clustering of L1 with antibodies or L1 protein in rodent B35 neuroblastoma and cerebellar neuron cultures induced the phosphorylation/activation of the mitogen-activated protein kinases (MAPKs) and extracellular signal-regulated kinases 1 and 2. MAPK activation was essential for L1-dependent neurite outgrowth, because chemical inhibitors [2-(2′-amino-3′-methoxyphenyl)-oxanaphthalen-4-one and 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene] of the MAPK kinase MEK strongly suppressed neurite outgrowth by cerebellar neurons on L1. The nonreceptor tyrosine kinase pp60c-srcwas required for L1-triggered MAPK phosphorylation, as shown insrc-minus cerebellar neurons and by expression of the kinase-inactive mutant Src(K295M) in B35 neuroblastoma cells. Phosphatidylinositol 3-kinase (PI3-kinase) and the small GTPase p21racwere identified as signaling intermediates to MAPK by phosphoinositide and Rac–GTP assays and expression of inhibitory mutants. Antibody-induced endocytosis of L1, visualized by immunofluorescence staining and confocal microscopy of B35 cells, was blocked by expression of kinase-inactive Src(K295M) and dominant-negative dynamin(K44A) but not by inhibitors of MEK or PI3-kinase. Dynamin(K44A) also inhibited L1 antibody-triggered MAPK phosphorylation. This study supports a model in which pp60c-srcregulates dynamin-mediated endocytosis of L1 as an essential step in MAPK-dependent neurite outgrowth on an L1 substrate.
Role and Origin of the GABAergic Innervation of Dorsal Raphe Serotonergic Neurons
Authors: Gervasoni Damien , Peyron Christelle , Rampon Claire , Barbagli Bruno , Chouvet Guy , Urbain Nadia , Fort Patrice , Luppi Pierre-Hervé
Published: April 2018

Extracellular electrophysiological recordings in freely moving cats have shown that serotonergic neurons from the dorsal raphe nucleus (DRN) fire tonically during wakefulness, decrease their activity during slow wave sleep (SWS), and are nearly quiescent during paradoxical sleep (PS). The mechanisms at the origin of the modulation of activity of these neurons are still unknown. Here, we show in the unanesthetized rat that the iontophoretic application of the GABAAantagonist bicuculline on dorsal raphe serotonergic neurons induces a tonic discharge during SWS and PS and an increase of discharge rate during quiet waking. These data strongly suggest that an increase of a GABAergic inhibitory tone present during wakefulness is responsible for the decrease of activity of the dorsal raphe serotonergic cells during slow wave and paradoxical sleep. In addition, by combining retrograde tracing with cholera toxin B subunit and glutamic acid decarboxylase immunohistochemistry, we demonstrate that the GABAergic innervation of the dorsal raphe nucleus arises from multiple distant sources and not only from interneurons as classically accepted. Among these afferents, GABAergic neurons located in the lateral preoptic area and the pontine ventral periaqueductal gray including the DRN itself could be responsible for the reduction of activity of the serotonergic neurons of the dorsal raphe nucleus during slow wave and paradoxical sleep, respectively.