bluuebunny/crossref_metadata_2025 huggingface dataset:
c-fosExpression in Brainstem Premotor Interneurons during Cholinergically Induced Active Sleep in the Cat
Authors: Morales Francisco R. , Sampogna Sharon , Yamuy Jack , Chase Michael H.
Published: April 2018

The present study was undertaken to identify trigeminal premotor interneurons that become activated during carbachol-induced active sleep (c-AS). Their identification is a critical step in determining the neural circuits responsible for the atonia of active sleep. Accordingly, the retrograde tracer cholera toxin subunit B (CTb) was injected into the trigeminal motor nuclei complex to label trigeminal interneurons. To identify retrograde-labeled activated neurons, immunocytochemical techniques, designed to label the Fos protein, were used. Double-labeled (i.e., CTb+, Fos+) neurons were found exclusively in the ventral portion of the medullary reticular formation, medial to the facial motor nucleus and lateral to the inferior olive. This region, which encompasses the ventral portion of the nucleus reticularis gigantocellularis and the nucleus magnocellularis, corresponds to the rostral portion of the classic inhibitory region of Magoun and Rhines (1946). This region contained a mean of 606 ± 41.5 ipsilateral and 90 ± 32.0 contralateral, CTb-labeled neurons. These cells were of medium-size with an average soma diameter of 20–35 μm. Approximately 55% of the retrogradely labeled cells expressedc-fosduring a prolonged episode of c-AS. We propose that these neurons are the interneurons responsible for the nonreciprocal postsynaptic inhibition of trigeminal motoneurons that occurs during active sleep.
Dopamine D4 Receptor-Knock-Out Mice Exhibit Reduced Exploration of Novel Stimuli
Authors: Dulawa Stephanie C. , Grandy David K. , Low Malcolm J. , Paulus Martin P. , Geyer Mark A.
Published: April 2018

The involvement of dopamine neurotransmission in behavioral responses to novelty is suggested by reports that reward is related to increased dopamine activity, that dopamine modulates exploratory behavior in animals, and that Parkinson's disease patients report diminished responses to novelty. Some studies have reported that polymorphisms of the human dopamine D4 receptor (D4R) gene are associated with personality inventory measures of the trait called “novelty-seeking”. To explore a potential role for the D4R in behavioral responses to novelty, we evaluated D4R-knock-out (D4R−/−) and wild-type (D4R+/+) mice in three approach–avoidance paradigms: the open field, emergence, and novel object tests. These three paradigms differ in the degree to which they elicit approach, or exploratory behavior, and avoidance, or anxiety-related behavior. Thus, we used these three tests to determine whether the D4R primarily influences the exploratory or the anxious component of responses to approach–avoidance conflicts. D4R−/− mice were significantly less behaviorally responsive to novelty than D4R+/+ mice in all three tests. The largest phenotypic differences were observed in the novel object test, which maximizes approach behavior, and the smallest phenotypic differences were found in the open field test, which maximizes avoidance behavior. Hence, D4R−/− mice exhibit reductions in behavioral responses to novelty, reflecting a decrease in novelty-related exploration.
Spinal Opioid Analgesia: How Critical Is the Regulation of Substance P Signaling?
Authors: Trafton Jodie A. , Abbadie Catherine , Marchand Serge , Mantyh Patrick W. , Basbaum Allan I.
Published: April 2018

Although opioids can reduce stimulus-evoked efflux of Substance P (SP) from nociceptive primary afferents, the consequences of this reduction on spinal cord nociceptive processing has not been studied. Rather than assaying SP release, in the present study we examined the effect of opioids on two postsynaptic measures of SP release, Fos expression and neurokinin-1 (NK-1) receptor internalization, in the rat. The functional significance of the latter was first established inin vitrostudies that showed that SP-induced Ca2+mobilization is highly correlated with the magnitude of SP-induced NK-1 receptor internalization in dorsal horn neurons. Using anin vivoanalysis, we found that morphine had little effect on noxious stimulus-evoked internalization of the NK-1 receptor in lamina I neurons. However, internalization was reduced when we coadministered morphine with a dose of an NK-1 receptor antagonist that by itself was without effect. Thus, although opioids may modulate SP release, the residual release is sufficient to exert maximal effects on the target NK-1 receptors. Morphine significantly reduced noxious stimulus-induced Fos expression in lamina I, but the Fos inhibition was less pronounced in neurons that expressed the NK-1 receptor. Taken together, these results suggest that opioid analgesia predominantly involves postsynaptic inhibitory mechanisms and/or presynaptic control of non-SP-containing primary afferent nociceptors.
Dual Responses of CNS Mitochondria to Elevated Calcium
Authors: Brustovetsky Nickolay , Dubinsky Janet M.
Published: April 2018

Isolated brain mitochondria were examined for their responses to calcium challenges under varying conditions. Mitochondrial membrane potential was monitored by following the distribution of tetraphenylphosphonium ions in the mitochondrial suspension, mitochondrial swelling by observing absorbance changes, calcium accumulation by an external calcium electrode, and oxygen consumption with an oxygen electrode. Both the extent and rate of calcium-induced mitochondrial swelling and depolarization varied greatly depending on the energy source provided to the mitochondria. When energized with succinate plus glutamate, after a calcium challenge, CNS mitochondria depolarized transiently, accumulated substantial calcium, and increased in volume, characteristic of a mitochondrial permeability transition. When energized with 3 mmsuccinate, CNS mitochondria maintained a sustained calcium-induced depolarization without appreciable swelling and were slow to accumulate calcium. Maximal oxygen consumption was also restricted under these conditions, preventing the electron transport chain from compensating for this increased proton permeability. In 3 mmsuccinate, cyclosporin A and ADP plus oligomycin restored potential and calcium uptake. This low conductance permeability was not effected by bongkrekic acid or carboxyatractylate, suggesting that the adenine nucleotide translocator was not directly involved. Fura-2FF measurements of [Ca2+]isuggest that in cultured hippocampal neurons glutamate-induced increases reached tens of micromolar levels, approaching those used with mitochondria. We propose that in the restricted substrate environment, Ca2+activated a low-conductance permeability pathway responsible for the sustained mitochondrial depolarization.
AMPA Receptor Calcium Permeability, GluR2 Expression, and Selective Motoneuron Vulnerability
Authors: Vandenberghe Wim , Robberecht Wim , Brorson James R.
Published: April 2018

AMPA receptor-mediated excitotoxicity is proposed to play a major pathogenic role in the selective motoneuron death of amyotrophic lateral sclerosis. Motoneurons have been shown in various models to be more susceptible to AMPA receptor-mediated injury than other spinal neurons. It has been hypothesized that this selective vulnerability of motoneurons is caused by the expression of highly Ca2+-permeable AMPA receptors and a complete or relative lack of the AMPA receptor subunit Glu receptor 2 (GluR2). The aim of this study was to quantify the relative Ca2+permeability of AMPA receptors and the fractional expression of GluR2 in motoneurons by combining whole-cell patch-clamp electrophysiology and single-cell RT-PCR and to compare these properties with those of dorsal horn neurons. Spinal motoneurons and dorsal horn neurons were isolated from embryonic rats and cultured on spinal astrocytes. As in previous studies, motoneurons were significantly more vulnerable to AMPA and kainate than dorsal horn neurons. However, all motoneurons expressed GluR2 mRNA (∼40% of total AMPA receptor subunit mRNA), and their AMPA receptors had intermediate whole-cell relative Ca2+permeability (PCa2+/PCs+∼ 0.4). AMPA receptor PCa2+/PCs+and the relative abundance of GluR2 varied more widely in dorsal horn neurons than in motoneurons, but the mean values did not differ significantly between the two cell populations. GluR2 was virtually completely edited at the Q/R site both in motoneurons and dorsal horn neurons. These results indicate that the selective vulnerability of motoneurons to AMPA receptor agonists is not determined solely by whole-cell relative Ca2+permeability of AMPA receptors.
Ribozyme-Mediated Inhibition of Caspase-3 Protects Cerebellar Granule Cells from Apoptosis Induced by Serum–Potassium Deprivation
Authors: Eldadah Basil A. , Ren Renée F. , Faden Alan I.
Published: April 2018

Apoptosis is an important mechanism of physiological and pathological cell death. It is regulated by several gene products, including caspases and the bcl-2-like proteins, whose roles have been demonstrated in numerous systems. One of these is a model of cerebellar granule cells (CGCs) in which apoptosis is induced by acute removal of serum and depolarizing concentrations of potassium. Previous work by several authors showed that benzyloxycarbonyl-DEVD-fluoromethylketone, a somewhat selective caspase inhibitor, significantly protected CGCs from apoptosis; however, because this molecule targets multiple caspases, it is not known whether a single caspase is primarily responsible for effecting cell death in this model. We attempted to answer this question by cotransfecting CGCs with green fluorescent protein reporter and a hammerhead ribozyme directed against caspase-3 mRNA. Maximal protection by this ribozyme was observed after 24 hr of deprivation, at which time apoptosis was 18 ± 0.7% compared with 32 ± 2% in control cells. Significant protection was also observed with human inhibitor of apoptosis (IAP)-like protein–X-linked IAP, a specific inhibitor of caspase-3, -7, and -9, and with p35, a general caspase inhibitor. Overexpression of bcl-2 produced almost complete protection from apoptosis after 24 hr of serum–K+deprivation (5 ± 2 vs 44 ± 2% in control cells). These results confirm that caspases play an important role in CGC apoptosis and indicate that caspase-3 itself is a significant mediator of this process.
Intraneuronal Aggregate Formation and Cell Death after Viral Expression of Expanded Polyglutamine Tracts in the Adult Rat Brain
Authors: Senut Marie-Claude , Suhr Steven T. , Kaspar Brian , Gage Fred H.
Published: April 2018

Expanded polyglutamine (polyQ) tracts have been linked to a new class of human disease characterized by psychiatric/motor syndromes associated with specific patterns of neurodegeneration. We have used a direct viral approach to locally express expanded polyglutamine tracts fused to the green fluorescent protein (97Q-GFP) in the adult rat brain. We show that intrastriatal expression of 97Q-GFP causes the rapid formation of fibrillar, cytoplasmic, and ubiquitinated nuclear aggregates in neurons. 97Q-GFP expression also results in a specific temporal pattern of cell death in the striatum. Co-infection studies suggest that high level 97Q-GFP-expressing cells die during the first month, whereas low level 97Q-GFP-expressing neurons persist for up to 6 months after infection. These data indicate that cumulative expression of polyQ repeats throughout the life of the animal is not required to induce neuronal death, but rather acute overexpression of polyQ is toxic to adult neuronsin vivo.
Mast Cells Migrate from Blood to Brain
Authors: Silverman Ann-Judith , Sutherland Anne K. , Wilhelm Marta , Silver Rae
Published: April 2018

It is well established that mast cells (MCs) occur within the CNS of many species. Furthermore, their numbers can increase rapidly in adults in response to altered physiological conditions. In this study we found that early postpartum rats had significantly more mast cells in the thalamus than virgin controls. Evidence from semithin sections from these females suggested that mast cells were transiting across the medium-sized blood vessels. We hypothesized that the increases in mast cell number were caused by their migration into the neural parenchyma. To this end, we purified rat peritoneal mast cells, labeled them with the vital dyes PKH26 or CellTracker Green, and injected them into host animals. One hour after injection, dye-filled cells, containing either histamine or serotonin (mediators stored in mast cells), were located close to thalamic blood vessels. Injected cells represented ∼2–20% of the total mast cell population in this brain region. Scanning confocal microscopy confirmed that the biogenic amine and the vital dye occurred in the same cell. To determine whether the donor mast cells were within the blood–brain barrier, we studied the localization of dye-marked donor cells and either Factor VIII, a component of endothelial basal laminae, or glial fibrillary acidic protein, the intermediate filament found in astrocytes. Serial section reconstructions of confocal images demonstrated that the mast cells were deep to the basal lamina, in nests of glial processes. This is the first demonstration that mast cells can rapidly penetrate brain blood vessels, and this may account for the rapid increases in mast cell populations after physiological manipulations.
Exacerbated Responses to Oxidative Stress by an Na+Load in Isolated Nerve Terminals: the Role of ATP Depletion and Rise of [Ca2+]i
Authors: Chinopoulos Christos , Tretter Laszlo , Rozsa Adrienn , Adam-Vizi Vera
Published: April 2018

We have explored the consequences of a [Na+]iload and oxidative stress in isolated nerve terminals. The Na+load was achieved by veratridine (5–40 μm), which allows Na+entry via a voltage-operated Na+channel, and oxidative stress was induced by hydrogen peroxide (0.1–0.5 mm). Remarkably, neither the [Na+]iload nor exposure to H2O2had any major effect on [Ca2+]i, mitochondrial membrane potential (Δψm), or ATP level. However, the combination of an Na+load and oxidative stress caused ATP depletion, a collapse of Δψm, and a progressive deregulation of [Ca2+]iand [Na+]ihomeostasis. The decrease in the ATP level was unrelated to an increase in [Ca2+]iand paralleled the rise in [Na+]i. The loss of Δψm was prevented in the absence of Ca2+but unaltered in the presence of cyclosporin A. We conclude that the increased ATP consumption by the Na,K–ATPase that results from a modest [Na+]iload places an additional demand on mitochondria metabolically compromised by an oxidative stress, which are unable to produce a sufficient amount of ATP to fuel the ATP-driven ion pumps. This results in a deregulation of [Na+]iand [Ca2+]i, and as a result of the latter, collapse of Δψm. The vicious cycle generated in the combined presence of Na+load and oxidative stress could be an important factor in the neuronal injury produced by ischemia or excitotoxicity, in which the oxidative insult is superimposed on a disturbed Na+homeostasis.
Functional GluR6 Kainate Receptors in the Striatum: Indirect Downregulation of Synaptic Transmission
Authors: Chergui Karima , Bouron Alexandre , Normand Elisabeth , Mulle Christophe
Published: April 2018

Kainate receptors (KARs) are abundantly expressed in the basal ganglia, but their function in synaptic transmission has not been established. In the present study, we show that the GluR6 subunit of KARs is expressed in both substance P- and enkephalin-containing GABAergic projection neurons of the mouse striatum. Using whole-cell voltage-clamp recordings in brain slices, we demonstrate the presence of functional KARs in the dorsal striatum activated by low concentrations of the AMPA/KAR agonist domoate in wild-type but not GluR6-deficient mice. Despite the abundance of KARs, we found no evidence for synaptic activation of these receptors after single or repetitive stimulation of glutamatergic afferents. Domoate induces a transient increase in the frequency of spontaneous IPSCs of small amplitude and a sustained depression of large IPSCs evoked by minimal electrical stimulation within the striatum in wild-type mice but not in GluR6-deficient mice. This depressant effect is inhibited in presence of adenosine A2Areceptor antagonists, ZM-241385 and SCH-58261. These data strongly suggest that, in striatal neurons, KARs depress GABAergic synaptic transmission indirectly via release of adenosine acting on A2Areceptors.
Curvature of Visual Space Under Vertical Eye Rotation: Implications for Spatial Vision and Visuomotor Control
Authors: Crawford J. Douglas , Henriques Denise Y. P. , Vilis Tutis
Published: April 2018

Most models of spatial vision and visuomotor control reconstruct visual space by adding a vector representing the site of retinal stimulation to another vector representing gaze angle. However, this scheme fails to account for the curvatures in retinal projection produced by rotatory displacements in eye orientation. In particular, our simulations demonstrate that even simple vertical eye rotation changes the curvature of horizontal retinal projections with respect to eye-fixed retinal landmarks. We confirmed the existence of such curvatures by measuring target direction in eye coordinates in which the retinotopic representation of horizontally displaced targets curved obliquely as a function of vertical eye orientation. We then asked subjects to point (open loop) toward briefly flashed targets at various points along these lines of curvature. The vector-addition model predicted errors in pointing trajectory as a function of eye orientation. In contrast, with only minor exceptions, actual subjects showed no such errors, showing a complete neural compensation for the eye position-dependent geometry of retinal curvatures. Rather than bolstering the traditional model with additional corrective mechanisms for these nonlinear effects, we suggest that the complete geometry of retinal projection can be decoded through a single multiplicative comparison with three-dimensional eye orientation. Moreover, because the visuomotor transformation for pointing involves specific parietal and frontal cortical processes, our experiment implicates specific regions of cortex in such nonlinear transformations.
Muscarinic Inhibition of Calcium Current and M Current in Gαq-Deficient Mice
Authors: Haley Jane E. , Delmas Patrick , Offermanns Stefan , Abogadie Fe C. , Simon Melvin I. , Buckley Noel J. , Brown David A.
Published: April 2018

Activation of M1muscarinic acetylcholine receptors (M1mAChR) inhibits M-type potassium currents (IK(M)) and N-type calcium currents (ICa) in mammalian sympathetic ganglia. Previous antisense experiments suggested that, in rat superior cervical ganglion (SCG) neurons, both effects were partly mediated by the G-protein Gαq(Delmas et al., 1998a; Haley et al., 1998a), but did not eliminate a contribution by other pertussis toxin (PTX)-insensitive G-proteins. We have tested this further using mice deficient in the Gαqgene.

PTX-insensitive M1mAChR inhibition ofICawas strongly reduced in Gαq−/− mouse SCG neurons and was fully restored by acute overexpression of Gαq. In contrast, M1mAChR inhibition ofIK(M)persisted in Gαq−/− mouse SCG cells. However, unlike rat SCG neurons, muscarinic inhibition ofIK(M)was partly PTX-sensitive. Residual (PTX-insensitive)IK(M)inhibition was slightly reduced in Gαq−/− neurons, and the remaining response was then suppressed by anti-Gαq/11antibodies.

Bradykinin (BK) also inhibitsIK(M)in rat SCG neurons via a PTX-insensitive G-protein (Gqand/or G11; Jones et al., 1995). In mouse SCG neurons,IK(M)inhibition by BK was fully PTX-resistant. It was unchanged in Gαq−/− mice but was abolished by anti-Gαq/11antibody.

We conclude that, in mouse SCG neurons (1) M1mAChR inhibition ofICais mediated principally by Gq, (2) M1mAChR inhibition ofIK(M)is mediated partly by Gq, more substantially by G11, and partly by a PTX-sensitive G-protein(s), and (3) BK-induced inhibition ofIK(M)is mediated wholly by G11.
Inhibition of Activity-Dependent Arc Protein Expression in the Rat Hippocampus Impairs the Maintenance of Long-Term Potentiation and the Consolidation of Long-Term Memory
Authors: Guzowski John F. , Lyford Gregory L. , Stevenson Gail D. , Houston Frank P. , McGaugh James L. , Worley Paul F. , Barnes Carol A.
Published: April 2018

It is widely believed that the brain processes information and stores memories by modifying and stabilizing synaptic connections between neurons. In experimental models of synaptic plasticity, such as long-term potentiation (LTP), the stabilization of changes in synaptic strength requires rapidde novoRNA and protein synthesis. Candidate genes, which could underlie activity-dependent plasticity, have been identified on the basis of their rapid induction in brain neurons. Immediate-early genes (IEGs) are induced in hippocampal neurons by high-frequency electrical stimulation that induces LTP and by behavioral training that results in long-term memory (LTM) formation. Here, we investigated the role of the IEGArc(also termed Arg3.1) in hippocampal plasticity. Arc protein is known to be enriched in dendrites of hippocampal neurons where it associates with cytoskeletal proteins (Lyford et al., 1995).Arcis also notable in that its mRNA and protein accumulate in dendrites at sites of recent synaptic activity (Steward et al., 1998). We used intrahippocampal infusions of antisense oligodeoxynucleotides to inhibit Arc protein expression and examined the effect of this treatment on both LTP and spatial learning. Our studies show that disruption of Arc protein expression impairs the maintenance phase of LTP without affecting its induction and impairs consolidation of LTM for spatial water task training without affecting task acquisition or short-term memory. Thus,Arcappears to play a fundamental role in the stabilization of activity-dependent hippocampal plasticity.
High-Level Neuronal Expression of Aβ1–42in Wild-Type Human Amyloid Protein Precursor Transgenic Mice: Synaptotoxicity without Plaque Formation
Authors: Mucke Lennart , Masliah Eliezer , Yu Gui-Qiu , Mallory Margaret , Rockenstein Edward M. , Tatsuno Gwen , Hu Kang , Kholodenko Dora , Johnson-Wood Kelly , McConlogue Lisa
Published: April 2018

Amyloid plaques are a neuropathological hallmark of Alzheimer's disease (AD), but their relationship to neurodegeneration and dementia remains controversial. In contrast, there is a good correlation in AD between cognitive decline and loss of synaptophysin-immunoreactive (SYN-IR) presynaptic terminals in specific brain regions. We used expression-matched transgenic mouse lines to compare the effects of different human amyloid protein precursors (hAPP) and their products on plaque formation and SYN-IR presynaptic terminals. Four distinct minigenes were generated encoding wild-type hAPP or hAPP carrying mutations that alter the production of amyloidogenic Aβ peptides. The platelet-derived growth factor β chain promoter was used to express these constructs in neurons. hAPP mutations associated with familial AD (FAD) increased cerebral Aβ1–42levels, whereas an experimental mutation of the β-secretase cleavage site (671M→I) eliminated production of human Aβ. High levels of Aβ1–42resulted in age-dependent formation of amyloid plaques in FAD-mutant hAPP mice but not in expression-matched wild-type hAPP mice. Yet, significant decreases in the density of SYN-IR presynaptic terminals were found in both groups of mice. Across mice from different transgenic lines, the density of SYN-IR presynaptic terminals correlated inversely with Aβ levels but not with hAPP levels or plaque load. We conclude that Aβ is synaptotoxic even in the absence of plaques and that high levels of Aβ1–42are insufficient to induce plaque formation in mice expressing wild-type hAPP. Our results support the emerging view that plaque-independent Aβ toxicity plays an important role in the development of synaptic deficits in AD and related conditions.
The Small GTP-Binding Protein TC10 Promotes Nerve Elongation in Neuronal Cells, and Its Expression Is induced during Nerve Regeneration in Rats
Authors: Tanabe Katsuhisa , Tachibana Taro , Yamashita Toshihide , Che Yong Ho , Yoneda Yoshihiro , Ochi Takahiro , Tohyama Masaya , Yoshikawa Hideki , Kiyama Hiroshi
Published: April 2018

We have made a rat cDNA library using nerve-transected hypoglossal nuclei. Using this library, we performed expressed-sequence tag analysis coupled within situhybridization to identify genes whose expression is altered in response to nerve injury. In this gene screening, a member of Rho family GTPases, TC10, which had not yet been characterized in neuronal cells, was identified. TC10 mRNA expression was very low in normal motor neurons; however, axotomy induced its expression dramatically. Other family members such as RhoA, Rac1, and Cdc42 were moderately expressed in normal motor neurons and showed slight upregulation after axotomy. The expression level of TC10 mRNA was low in the embryonic brain and gradually increased with development. However, the expression of TC10 mRNA in the adult brain was lower and more restricted than that of RhoA, Rac1, and Cdc42. Cultured dorsal root ganglia exhibited dramatic neurite extension secondary to adenovirus-mediated expression of TC10. It can be concluded that although TC10 expression is lower in developing and mature motor neurons compared with other Rho family members, TC10 expression is induced by nerve injury to play a crucial role in nerve regeneration, particularly neurite elongation, in cooperation with other family members.
The Development of Abnormal Axon Trajectories after Rotation of One Eye inXenopus
Authors: Guo Yujin , Udin Susan B.
Published: April 2018

The targeting of isthmotectal axons in theXenopusbinocular pathway is guided by both activity-dependent cues and activity-independent cues. Abnormal visual activity induced by unilateral eye rotation overrides activity-independent cues and causes isthmotectal axons to arborize at new locations during a critical period of development that ends ∼3 months postmetamorphosis (PM). Horseradish peroxidase staining of isthmotectal axons reveals that they normally run rostrocaudally in the tectum; in contrast, those axons in animals with early eye rotation have circuitous trajectories. In this paper, by studying the trajectories and branching patterns of isthmotectal axons at different times after eye rotation, we aimed to investigate when and how activity cues determine the projection pattern of isthmotectal axons. As suggested by electrophysiological recording, isthmotectal axons initially grow normally and make arbors according to activity-independent cues despite the presence of abnormal visual input. Our findings demonstrate that the development of abnormal trajectories starts by 2 weeks PM in response to eye rotation and is a protracted process. It begins in the tectal regions in which the initial connections of isthmotectal axons are first formed according to activity-independent cues. At transitional stages (5 and 10 weeks), axons with arbors at two different locations are observed, with locations corresponding to the old and new termination sites, respectively. Later, at 10 weeks of age, the fainter horseradish peroxidase staining in arbors at old termination sites suggests that the older arbors are undergoing withdrawal.
Leukemia Inhibitory Factor Requires Concurrent p75LNTRSignaling to Induce Apoptosis of Cultured Sympathetic Neurons
Authors: Savitz Sean I. , Kessler John A.
Published: April 2018

Apoptosis may result either from positive induction by ligand binding to a plasma membrane receptor or from negative induction attributable to loss of a suppressor signal. For example, apoptosis of developing sympathetic neurons may be induced in culture either by exposure to leukemia inhibitory factor (LIF) or by deprivation of nerve growth factor. This study compared the cell death pathways activated in sympathetic neurons by these two different stimuli. Both types of cell death were developmentally regulated; both were maximal in the immediate postnatal period and disappeared over the next 2 weeks. Both types of cell death were reduced by genetic deletion of Bax or by virally mediated overexpression of Bcl-2. Similarly both were reduced by inhibition of caspase activity or by inhibition of Nedd-2 synthesis with antisense oligonucleotides. Finally, both involved activation of c-Jun N-terminal kinase (JNK) signaling. Nedd-2 expression by sympathetic neurons declined in parallel with the developmental loss of LIF-mediated cell death, suggesting that downregulation of the caspase during development may underlie the loss of cytokine-mediated apoptosis. Treatment of sympathetic neurons with an antibody that blocks the function of the low-affinity neurotrophin receptor (p75LNTR) prevented LIF-induced cell death. Similarly genetic deletion of p75LNTRprevented apoptosis after LIF treatment. These observations suggest that concurrent p75LNTRsignaling is necessary for LIF-induced cell death and that cytokine-mediated cell death and growth factor deprivation appear to activate the same intracellular pathways involving JNK signaling.
Cellular Mechanisms of Long-Lasting Adaptation in Visual Cortical NeuronsIn Vitro
Authors: Sanchez-Vives Maria V. , Nowak Lionel G. , McCormick David A.
Published: April 2018

The cellular mechanisms of spike-frequency adaptation during prolonged discharges and of the slow afterhyperpolarization (AHP) that follows, as occurin vivowith contrast adaptation, were investigated with intracellular recordings of cortical neurons in slices of ferret primary visual cortex. Intracellular injection of 2 Hz sinusoidal or constant currents for 20 sec resulted in a slow (τ = 1–10 sec) spike-frequency adaptation, the degree of which varied widely among neurons. Reducing either [Ca2+]oor [Na+]oreduced the rate of spike-frequency adaptation. After the prolonged discharge was a slow (12–75 sec) AHP that was associated with an increase in membrane conductance and a rightward shift in the discharge frequency versus injected current relationship. The reversal potential of the slow AHP was sensitive to changes in [K+]o, indicating that it was mediated by a K+current. Blockade of transmembrane Ca2+conductances did not reduce the slow AHP. In contrast, reductions of [Na+]oreduced the slow AHP, even in the presence of pronounced Ca2+spikes. We suggest that the activation of Na+-activated and Ca2+-activated K+currents plays an important role in prolonged spike-frequency adaptation and therefore may contribute to contrast adaptation and other forms of adaptation in the visual systemin vivo.
Medial Frontal Cortex Mediates Perceptual Attentional Set Shifting in the Rat
Authors: Birrell Jennifer M. , Brown Verity J.
Published: April 2018

If rodents do not display the behavioral complexity that is subserved in primates by prefrontal cortex, then evolution of prefrontal cortex in the rat should be doubted. Primate prefrontal cortex has been shown to mediate shifts in attention between perceptual dimensions of complex stimuli. This study examined the possibility that medial frontal cortex of the rat is involved in the shifting of perceptual attentional set. We trained rats to perform an attentional set-shifting task that is formally the same as a task used in monkeys and humans. Rats were trained to dig in bowls for a food reward. The bowls were presented in pairs, only one of which was baited. The rat had to select the bowl in which to dig by its odor, the medium that filled the bowl, or the texture that covered its surface. In a single session, rats performed a series of discriminations, including reversals, an intradimensional shift, and an extradimensional shift.

Bilateral lesions by injection of ibotenic acid in medial frontal cortex resulted in impairment in neither initial acquisition nor reversal learning. We report here the same selective impairment in shifting of attentional set in the rat as seen in primates with lesions of prefrontal cortex. We conclude that medial frontal cortex of the rat has functional similarity to primate lateral prefrontal cortex.
Syntaxin Modulation of Slow Inactivation of N-Type Calcium Channels
Authors: Degtiar Vadim E. , Scheller Richard H. , Tsien Richard W.
Published: April 2018

Syntaxin, a membrane protein vital in triggering vesicle fusion, interacts with voltage-gated N- and P/Q-type Ca2+channels. This biochemical association is proposed to colocalize Ca2+channels and presynaptic release sites, thus supporting rapid and efficient initiation of neurotransmitter release. The syntaxin channel interaction may also support a novel signaling function, to modulate Ca2+channels according to the state of the associated release machinery (Bezprozvanny et al., 1995;Wiser et al., 1996; see also Mastrogiacomo et al., 1994). Here we report that syntaxin 1A (syn1A) coexpressed with N-type channels inXenopusoocytes greatly promoted slow inactivation gating, but had little or no effect on the onset of and recovery from fast inactivation. Accordingly, the effectiveness of syntaxin depended strongly on voltage protocol. Slow inactivation was found for N-type channels even in the absence of syntaxin and could be distinguished from fast inactivation on the basis of its slow kinetics, distinct voltage dependence (voltage-independent at potentials higher than the level of half-inactivation), and temperature independence (Q10, ∼0.8). Trains of action potential-like stimuli were more effective than steady depolarizations in stabilizing the slowly inactivated condition. Agents that stimulate protein kinase C decreased the inhibitory effect of syntaxin on N-type channels. Application of BoNtC1 to cleave syntaxin sharply attenuated the modulatory effects on Ca2+channel gating, consistent with structural analysis of syntaxin modulation, supporting use of this toxin to test for the impact of syntaxin on Ca2+influx in nerve terminals.
Extensive Sprouting of Sensory Afferents and Hyperalgesia Induced by Conditional Expression of Nerve Growth Factor in the Adult Spinal Cord
Authors: Romero Mario I. , Rangappa Nagarathnamma , Li Li , Lightfoot Ellis , Garry Mary G. , Smith George M.
Published: April 2018

Genetic transfer of growth-promoting molecules was proposed as a potential strategy to modify the nonpermissive nature of the adult CNS to induce axonal regeneration. To evaluate whether overexpression of neurotrophins or cellular adhesion molecules would effect axonal plasticity, adenoviruses encoding fibroblast growth factor-2 (FGF-2/Adts), nerve growth factor (NGF/Adts), neurotrophin-3, and the cell adhesion molecules N-cadherin and L1 were injected into the dorsal horn of the adult spinal cord. Transgene expression was primarily localized to astrocytes in the dorsal horn and motor neurons within the ventral horn. Overexpression of these factors, with the exception of NGF/Adts, failed to increase axonal sprouting. Eight days after NGF/Adts injections, axonal sprouting within the dorsal horn was apparent, and after 4 weeks, extensive spouting was observed throughout the entire dorsal horn, extending into the ventral horn and the white matter of the lateral funiculus. These axons were identified primarily as a subpopulation of nociceptive fibers expressing calcitonin gene-related peptide and substance-P. Behavioral analysis revealed thermal hyperalgesia and perturbation of accurate paw placement on grid-walking tasks for both FGF-2- and NGF-treated animals. These results indicate that the administration of growth-promoting molecules can induce robust axonal plasticity of normal adult primary sensory neurons into areas of transgene expression, causing significant alterations in behavioral responses. This observation also indicates that gene transfer protocols that aim to reconstruct diseased or injured pathways should also be designed to prevent the sprouting of the normal circuitry from adjacent unaffected neurons.
Inhibition of the cAMP Pathway Decreases Early Long-Term Potentiation at CA1 Hippocampal Synapses
Authors: Otmakhova Nonna A. , Otmakhov Nikolai , Mortenson Lindsay H. , Lisman John E.
Published: April 2018

Long-term potentiation (LTP) has several different phases, and there is general agreement that the late phase of LTP requires the activation of adenylyl cyclase (AC) and cAMP-dependent protein kinase (PKA). In contrast, several studies indicate that the early LTP is not affected by interfering with the cAMP pathway. We have further tested the role of the cAMP pathway in early LTP using several types of inhibitors. Bath application of the PKA inhibitor H89 suppressed the early LTP induced by a single tetanus. Similarly, the LTP induced by a pairing protocol was decreased by postsynaptic intracellular perfusion of the peptide PKA inhibitor PKI(6–22) amide. The decrease of LTP produced by these inhibitors was evident immediately after induction. These results indicate that PKA is important in early LTP, that its locus of action is postsynaptic, and that it does not act merely by enhancing the depolarization required for LTP induction. The failure of some other inhibitors of the cAMP pathway to affect the early phase of LTP might be attributable to the saturation of some step in the cAMP pathway during a tetanus. In agreement with this hypothesis we found that application of the AC inhibitor SQ 22536 by itself did not affect the early phase of LTP, but did produce a reduction if the cAMP pathway was already attenuated by the PKA inhibitor H89. Our analysis of the results of genetic modifications of the cAMP pathway, especially the work on AC knock-outs, indicates that the genetic data are generally consistent with the pharmacological results showing the importance of this pathway in early LTP.
Regulation of the On Bipolar Cell mGluR6 Pathway by Ca2+
Authors: Nawy Scott
Published: April 2018

Glutamate produces a hyperpolarizing synaptic potential in On bipolar cells by binding to the metabotropic glutamate receptor mGluR6, leading to closure of a cation channel. Here it is demonstrated that this cation channel is regulated by intracellular Ca2+. Glutamate-evoked currents were recorded from On bipolar cells in light-adapted salamander retinal slices in the presence of 2 mmexternal Ca2+. When glutamate was applied almost continuously, interrupted only briefly to measure the size of the response, the glutamate response remained robust. However, currents elicited by intermittent and brief applications of glutamate exhibited time-dependent run down. Run down of the glutamate response was also voltage dependent, because it was accelerated by membrane hyperpolarization. Run down was triggered, at least in part, by a rise in intracellular Ca2+; measured as a function of time or voltage, it was attenuated by intracellular buffering of Ca2+with BAPTA or by omitting Ca2+from the bathing solution. Current–voltage measurements demonstrated that Ca2+induced run down of the glutamate response by downregulating cation channel function, rather than by preventing closure of the channel by glutamate and mGluR6. A major source of the Ca2+that mediated this inhibition is the cation channel itself, which was found to be permeable to Ca2+, accounting for the use dependence of the run down. These results suggest that Ca2+influx through the cation channel during background illumination could provide a signal to close the cation channel and repolarize the membrane toward its dark potential, an adaptive mechanism for coping with changes in ambient light.
Regulation of Phosphorylation of the GluR1 AMPA Receptor in the Neostriatum by Dopamine and PsychostimulantsIn Vivo
Authors: Snyder Gretchen L. , Allen Patrick B. , Fienberg Allen A. , Valle Carmina G. , Huganir Richard L. , Nairn Angus C. , Greengard Paul
Published: April 2018

The activation of cAMP-dependent protein kinase regulates the physiological activity of AMPA-type glutamate receptors. In this study, phosphorylation of the AMPA receptor subunit GluR1 at Ser845was increased in neostriatal slices by activation of D1-type dopamine receptors and by inhibitors of protein phosphatase 1/protein phosphatase 2A. In contrast, Ser831, a residue which, when phosphorylated by protein kinase C or calcium/calmodulin-dependent kinase II, increases AMPA receptor channel conductance, was unaffected by either D1 or D2 receptor agonists in neostriatal slices. The phosphorylation of Ser845, but not Ser831, was strongly increased in neostriatumin vivoin response to the psychostimulants cocaine and methamphetamine. The effects of dopamine and psychostimulants on the phosphorylation of GluR1 were attenuated in dopamine and cAMP-regulated phosphoproteinMr32 kDa (DARPP-32) knock-out mice. These results identify DARPP-32 and AMPA-type glutamate receptors as likely essential cellular effectors for psychostimulant actions.
Phosphorylated Syntaxin 1 Is Localized to Discrete Domains Along a Subset of Axons
Authors: Foletti Davide L. , Lin Richard , Finley Michael A. F. , Scheller Richard H.
Published: April 2018

Syntaxin 1 is a SNARE protein that plays a central role in synaptic vesicle (SV) exocytosis. We generated an antibody that specifically recognizes a casein kinase II-mediated phosphorylation on serine-14 of syntaxin 1. In this report we show that this phosphorylation occursin vivoand is developmentally regulated in the rat brain, rising to a level of 40% of the total syntaxin in adult animals. Phosphorylated syntaxin is preferentially associated with SNAP-25 and localizes to discrete domains of the axonal plasma membrane that do not colocalize with pools of synaptic vesicles. These phosphosyntaxin domains may define fusion sites for a novel class of vesicles outside classical active zones.
In UteroCocaine-Induced Dysfunction of Dopamine D1Receptor Signaling And Abnormal Differentiation of Cerebral Cortical Neurons
Authors: Jones Liesl B. , Stanwood Gregg D. , Reinoso Blesilda S. , Washington Ricardo A. , Wang Hoau-Yan , Friedman Eitan , Levitt Pat
Published: April 2018

Monoamines modulate neuronal differentiation, and alteration of monoamine neurotransmission during development produces specific changes in neuronal structure, function, and pattern formation. We have previously observed that prenatal exposure to cocaine in a clinically relevant animal model produces increased length of pyramidal neuron dendrites in the anterior cingulate cortex (ACC) postnatally. We now report that cocaine administered intravenously to pregnant rabbits at gestational stages preceding and during cortical histogenesis results in the early onset of hypertrophic dendritic outgrowth in the embryonic ACC. Confocal microscopy of DiI-labeled neurons revealed that the atypical, tortuous dendritic profiles seen postnatally in ACC-cocaine neurons already are apparentin utero. No defects in neuronal growth were observed in visual cortex (VC), a region lacking prominent dopamine innervation. In striking correlation with ourin vivoresults,in vitroexperiments revealed a significant enhancement of spontaneous process outgrowth of ACC neurons isolated from cocaine-exposed fetuses but no changes in neurons derived from visual cortex. The onset of modified growthin vivois paralleled by reduced D1Areceptor coupling to its G-protein. These data suggest that the dynamic growth of neurons can be regulated by early neurotransmitter signaling in a selective fashion. Prenatal onset of defects in dopamine receptor signaling contributes to abnormal circuit formation and may underlie specific cognitive and behavioral dysfunction.
Abnormal Phrenic Motoneuron Activity and Morphology in Neonatal Monoamine Oxidase A-Deficient Transgenic Mice: Possible Role of a Serotonin Excess
Authors: Bou-Flores Céline , Lajard Anne-Marie , Monteau Roger , De Maeyer Edward , Seif Isabelle , Lanoir Jeanne , Hilaire Gérard
Published: April 2018

In rodent neonates, the neurotransmitter serotonin (5-HT) modulates the activity of both the medullary respiratory rhythm generator and the cervical phrenic motoneurons. To determine whether 5-HT also contributes to the maturation of the respiratory network, experiments were conductedin vitroon the brainstem–spinal cord preparation of neonatal mice originating from the control strain (C3H) and the monoamine oxidase A-deficient strain, which has a brain perinatal 5-HT excess (Tg8). At birth, the Tg8 respiratory network is unable to generate a respiratory pattern as stable as that produced by the C3H network, and the modulation by 5-HT of the network activity present in C3H neonates is lacking in Tg8 neonates. In addition, the morphology of the phrenic motoneurons is altered in Tg8 neonates; the motoneuron dendritic tree loses the C3H bipolar aspect but exhibits an increased number of spines and varicosities. These abnormalities were prevented in Tg8 neonates by treating pregnant Tg8 dams with the 5-HT synthesis inhibitorp-chlorophenylalanine or a 5-HT2Areceptor antagonist but were induced in wild-type neonates by treating C3H dams with a 5-HT2Areceptor agonist. We conclude that 5-HT contributes, probably via 5-HT2Areceptors, to the normal maturation of the respiratory network but alters it when present in excess. Disorders affecting 5-HT metabolism during gestation may therefore have deleterious effects on newborns.
Long-Term rAAV-Mediated Gene Transfer of GDNF in the Rat Parkinson's Model: Intrastriatal But Not Intranigral Transduction Promotes Functional Regeneration in the Lesioned Nigrostriatal System
Authors: Kirik Deniz , Rosenblad Carl , Björklund Anders , Mandel Ronald J.
Published: April 2018

Previous studies have used recombinant adeno-associated viral (rAAV) vectors to deliver glial cell line-derived neurotrophic factor (GDNF) in the substantia nigra to protect the nigral dopamine (DA) neurons from 6-hydroxydopamine-induced damage. However, no regeneration or functional recovery was observed in these experiments. Here, we have used an rAAV-GDNF vector to express GDNF long-term (6 months) in either the nigral DA neurons themselves, in the striatal target cells, or in both of these structures. The results demonstrate that both nigral and striatal transduction provide significant protection of nigral DA neurons against the toxin-induced degeneration. However, only the rats receiving rAAV-GDNF in the striatum displayed behavioral recovery, accompanied by significant reinnervation of the lesioned striatum, which developed gradually over the first 4–5 months after the lesion. GDNF transgene expression was maintained at high levels throughout this period. These results provide evidence that rAAV is a highly efficient vector system for long-term expression of therapeutic proteins in the nigrostriatal system.
Modeling LGN Responses during Free-Viewing: A Possible Role of Microscopic Eye Movements in the Refinement of Cortical Orientation Selectivity
Authors: Rucci Michele , Edelman Gerald M. , Wray Jonathan
Published: April 2018

Neural activity appears to be essential for the normal development of the orientation-selective responses of cortical cells. It has been proposed that the correlated activity of LGN cells is a crucial component for shaping the receptive fields of cortical simple cells into adjacent, oriented subregions alternately receiving ON- and OFF-center excitatory geniculate inputs. After eye opening, the spatiotemporal structure of neural activity in the early stages of the visual pathway depends not only on the characteristics of the environment, but also on the way the environment is scanned. In this study, we use computational modeling to investigate how eye movements might affect the refinement of orientation tuning in the presence of a Hebbian scheme of synaptic plasticity. Visual input consisting of natural scenes scanned by varying types of eye movements was used to activate a spatiotemporal model of LGN cells. In the presence of different types of movement, significantly different patterns of activity were found in the LGN. Specific patterns of correlation required for the development of segregated cortical receptive field subregions were observed in the case of micromovements, but were not seen in the case of saccades or static presentation of natural visual input. These results suggest an important role for the eye movements occurring during fixation in the refinement of orientation selectivity.