bluuebunny/crossref_metadata_2025 huggingface dataset:
Dopamine Release and Uptake Dynamics within Nonhuman Primate StriatumIn Vitro
Authors: Cragg Stephanie J. , Hille Christopher J. , Greenfield Susan A.
Published: April 2018

The putamen of the human striatum is a heterogeneous nucleus that contains the primary site of loss of dopamine (DA) in Parkinson's disease (PD). Furthermore, different functional domains of the putamen are heterogeneously susceptible to DA loss, and yet the dynamic regulation of extracellular DA concentration ([DA]o) and comparison between domains has not been explored in the primate brain. In these studies, DA was measured in real time using fast-scan cyclic voltammetry at a carbon-fiber microelectrodein vitroin striatal sections from the common marmoset (Callithrix jacchus). [DA]oreleased by a single stimulus pulse varied threefold along a ventromedial–dorsolateral axis. DA uptake was via the DA transporter (GBR12909 sensitive, desipramine insensitive). On the basis of data modeling with simulations of Michaelis–Menten kinetics, rate maximum,Vmax, varied with region: both [DA]oandVmaxwere greatest in regions most vulnerable in PD. These differences were reflected in part by regional variation in DA content. [DA]o,Vmax, and regional variation were two- to threefold greater than in rodent caudatoputamen.

In addition, steady-state [DA]oat physiological firing rates in primate striatum was controlled by depolarization frequency, uptake, and presynaptic autoreceptors. Furthermore, regulation of [DA]oby these mechanisms differed significantly between limbic- and motor-associated domains.

These data indicate interspecies heterogeneity in striatal DA dynamics that must be considered when extrapolating behavioral and drug responses from rodent to the primate brain. Moreover, the heterogeneity demonstrated within the primate putamen in the availability and dynamic regulation of DA may be central to understanding DA function in health, cocaine abuse, and disease.
Developmental Changes in Eye-Blink Conditioning and Neuronal Activity in the Inferior Olive
Authors: Nicholson Daniel A. , Freeman John H.
Published: April 2018

Neuronal activity was recorded in the dorsal accessory inferior olive in infant rats during classical conditioning of the eye-blink response. The percentage and amplitude of eye-blink conditioned responses (CRs) increased as a function of age. The magnitude of the neuronal response to the unconditioned stimulus (US) decreased with age. There were also age-specific modifications of US-elicited inferior olive neuronal activity during paired trials in which a conditioned eye-blink response was performed. The results indicate that the development of the conditioned eye-blink response may depend on dynamic interactions between multiple developmental processes within the eye-blink circuitry. Differences in the functional maturity of olivo-cerebellar pathways may limit the induction of plasticity in the cerebellum and thereby limit the development of eye-blink conditioned responses.
Neurobeachin: A Protein Kinase A-Anchoring,beige/Chediak-Higashi Protein Homolog Implicated in Neuronal Membrane Traffic
Authors: Wang Xiaolu , Herberg Friedrich W. , Laue Michael M. , Wüllner Christiane , Hu Bin , Petrasch-Parwez Elisabeth , Kilimann Manfred W.
Published: April 2018

We describe the identification and initial characterization of neurobeachin, a neuron-specific multidomain protein of 327 kDa with a high-affinity binding site (Kd, 10 nm) for the type II regulatory subunit of protein kinase A (PKA RII). Neurobeachin is peripherally associated with pleomorphic tubulovesicular endomembranes near thetranssides of Golgi stacks and throughout the cell body and cell processes. It is also found in a subpopulation of synapses, where it is concentrated at the postsynaptic plasma membrane. In live cells, perinuclear neurobeachin is dispersed by brefeldin A (BFA) within 1 min, and in permeabilized cells a recruitment of neurobeachin from cytosol to Golgi-near membranes is stimulated by GTPγS and prevented by brefeldin A. Spots of neurobeachin recruitment are close to but distinct from recruitment sites of COP-I, AP-1, and AP-3 coat proteins involved in vesicle budding. These observations indicate that neurobeachin binding to membranes close to thetrans-Golgi requires an ADP-ribosylation factor-like GTPase, possibly in association with a novel type of protein coat. A neurobeachin isoform that does not bind RII, beige-like protein (BGL), is expressed in many tissues. Neurobeachin, BGL, and ∼10 other mammalian gene products share a characteristic C-terminal BEACH-WD40 sequence module, which is also present in gene products of invertebrates, plants, protozoans, and yeasts, thus defining a new protein family. The prototype member of this family of BEACH domain proteins, lysosomal trafficking regulator (LYST), is deficient in genetic defects of protein sorting in lysosome biogenesis (thebeigemouse and Chediak-Higashi syndrome). Neurobeachin's subcellular localization, its coat protein-like membrane recruitment, and its sequence similarity to LYST suggest an involvement in neuronal post-Golgi membrane traffic, one of its functions being to recruit protein kinase A to the membranes with which it associates.
Phase Shifting the Retinal Circadian Clock:xPer2mRNA Induction by Light and Dopamine
Authors: Steenhard Brooke M. , Besharse Joseph C.
Published: April 2018

A circadian clock is located in the retinal photoreceptors of the African clawed frogXenopus laevis. These photoreceptor clocks are thought to govern a wide variety of output rhythms, including melatonin release and gene expression. Both light and dopamine phase shift the retinal clock in a phase-dependent manner. Two homologs of theDrosophila periodgene have been cloned inXenopus, and one of these (xPer2) is acutely regulated by light. Light and dopamine inducexPer2mRNA in a similar manner. In addition, the increase ofxPer2mRNA in response to light and dopamine is the same at all times of day tested. In contrast,xPer1mRNA exhibits circadian oscillations but is relatively insensitive to phase-shifting treatments of light or dopamine. Our data suggest thatxPer2functions as the molecular link between the light/dark cycle and the circadian clock.
GABA Spillover from Single Inhibitory Axons Suppresses Low-Frequency Excitatory Transmission at the Cerebellar Glomerulus
Authors: Mitchell Simon J. , Silver R. Angus
Published: April 2018

GABA type B receptors (GABAB-Rs) are present on excitatory terminals throughout the CNS, but surprisingly little is known about their role in modulating neurotransmission under physiological conditions. We have investigated activation of GABAB-Rs on excitatory terminals within the cerebellar glomerulus, a structure where glutamatergic excitatory and GABAergic inhibitory terminals are in close apposition and make axodendritic synapses onto granule cells. Application of the GABAB-R agonist baclofen depressed evoked mossy fiber EPSCs by 54% at 1 Hz. The amplitude of miniature EPSCs recorded in tetrodotoxin was unchanged in the presence of baclofen, but the frequency was significantly reduced, indicating a purely presynaptic action of baclofen under our recording conditions. At physiological temperature (37°C) presynaptic GABAB-Rs were not tonically activated by spontaneous GABA release from Golgi cells, which fire at ∼8 Hz in slices at this temperature. However, tonic activation could be induced by blocking GABA uptake or by lowering temperature. GABAB-Rs were activated at physiological temperature when Golgi cell firing was increased above the basal level by stimulating a single inhibitory Golgi cell input at 50 Hz, suppressing the mossy fiber-evoked EPSC by 24% at 1 Hz. Furthermore, glutamate release was selectively inhibited at low-frequency mossy fiber inputs (<10 Hz) during Golgi cell stimulation. Our findings suggest that GABA spillover in the glomerulus modulates sensory input to the cerebellar cortex.
Dendritic and Axonal Targeting of Type 5 Metabotropic Glutamate Receptor Is Regulated by Homer1 Proteins and Neuronal Excitation
Authors: Ango Fabrice , Pin Jean-Philippe , Tu Jian Chen , Xiao Bo , Worley Paul F. , Bockaert Joel , Fagni Laurent
Published: April 2018

The physiological actions of neurotransmitter receptors are intimately linked to their proper neuronal compartment localization. Here we studied the effect of the metabotropic glutamate receptor (mGluR)-interacting proteins, Homer1a, b, and c, in the targeting of mGluR5 in neurons. We found that mGluR5 was exclusively localized in cell bodies when transfected alone in cultured cerebellar granule cells. In contrast, mGluR5 was found also in dendrites when coexpressed with Homer1b or Homer1c, and in both dendrites and axons when cotransfected with Homer1a. In dendrites, cotransfected mGluR5 and Homer1b/c formed clusters that colocalized with the synaptic marker synaptophysin. Interestingly when transfected alone, the Homer proteins were also translocated to neurites but did not form such clusters. Depolarization of the neurons with a mixture of ionotropic glutamate receptor agonists, NMDA and kainate, or potassium channel blockers, tetraethylammonium and 4-aminopyridine, induced transient expression of endogenous Homer1a and persistent neuritic localization of transfected mGluR5 even long after degradation of Homer1a. These results suggest that Homer1a/b/c proteins are involved in the targeting of mGluR5 to dendritic synaptic sites and/or axons and that this effect can be regulated by neuronal activity. Because the activity-dependent effect of endogenous Homer1a was also long-lasting, the axonal targeting of mGluR5 by this protein is likely to play an important role in synaptic plasticity.
Exacerbation of Noise-Induced Hearing Loss in Mice Lacking the Glutamate Transporter GLAST
Authors: Hakuba Nobuhiro , Koga Kenichiro , Gyo Kiyofumi , Usami Shin-ichi , Tanaka Kohichi
Published: April 2018

Acoustic overstimulation is one of the major causes of hearing loss. Glutamate is the most likely candidate neurotransmitter for afferent synapses in the peripheral auditory system, so it was proposed that glutamate excitotoxicity may be involved in noise trauma. However, there has been no direct evidence that noise trauma is caused by excessive release of glutamate from the inner hair cells (IHCs) during sound exposure because studies have been hampered by powerful glutamate uptake systems in the cochlea. GLAST is a glutamate transporter highly expressed in the cochlea. Here we show that after acoustic overstimulation, GLAST-deficient mice show increased accumulation of glutamate in perilymphs, resulting in exacerbation of hearing loss. These results suggest that GLAST plays an important role in keeping the concentration of glutamate in the perilymph at a nontoxic level during acoustic overstimulation. These findings also provide further support for the hypothesis that IHCs use glutamate as a neurotransmitter.
The Agrin/MuSK Signaling Pathway Is Spatially Segregated from the Neuregulin/ErbB Receptor Signaling Pathway at the Neuromuscular Junction
Authors: Trinidad Jonathan C. , Fischbach Gerald D. , Cohen Jonathan B.
Published: April 2018

The neuregulin/erbB receptor and agrin/MuSK pathways are critical for communication between the nerve, muscle, and Schwann cell that establishes the precise topological arrangement at the vertebrate neuromuscular junction (NMJ). ErbB2, erbB3, and erbB4 as well as neuregulin, agrin, and MuSK are known to be concentrated at the NMJ. Here we have examined NMJs from gastrocnemius muscle of adult rat using immunofluorescence confocal microscopy to characterize in detail the distribution of these proteins relative to the distribution of acetylcholine receptors (AChRs). We have determined that erbB2 and erbB4 are enriched in the depths of the secondary junctional folds on the postsynaptic muscle membrane. In contrast, erbB3 at the NMJ was concentrated at presynaptic terminal Schwann cells. This distribution strongly argues that erbB2/erbB4 heterodimers are the functional postsynaptic neuregulin receptors of the NMJ. Neuregulin was localized to the axon terminal, secondary folds, and terminal Schwann cells, where it was in a position to signal through erbB receptors. MuSK was concentrated in the postsynaptic primary gutter region where it was codistributed with AChRs. Agrin was present at the axon terminal and in the basal lamina associated with the primary gutter region, but not in the secondary junctional folds. The differential distributions of the neuregulin and agrin signaling pathways argue against neuregulin and erbB receptors being localized to the NMJ via direct interactions with either agrin or MuSK.
Human Cortical Muscle Coherence Is Directly Related to Specific Motor Parameters
Authors: Kilner James M. , Baker Stuart N. , Salenius Stephan , Hari Riitta , Lemon Roger N.
Published: April 2018

Cortical oscillations have been the target of many recent investigations, because it has been proposed that they could function to solve the “binding” problem. In the motor cortex, oscillatory activity has been reported at a variety of frequencies between ∼4 and ∼60 Hz. Previous research has shown that 15–30 Hz oscillatory activity in the primary motor cortex is coherent or phase locked to activity in contralateral hand and forearm muscles during isometric contractions. However, the function of this oscillatory activity remains unclear. Is it simply an epiphenomenon or is it related to specific motor parameters? In this study, we investigated task-dependent modulation in coherence between motor cortex and hand muscles during precision grip tasks. Twelve right-handed subjects used index finger and thumb to grip two levers that were under robotic control. Each lever was fitted with a sensitive force gauge. Subjects received visual feedback of lever force levels and were instructed to keep them within target boxes throughout each trial. Surface EMGs were recorded from four hand and forearm muscles, and magnetoencephalography (MEG) was recorded using a 306 channel neuromagnetometer. All subjects showed significant levels of coherence (0.086–0.599) between MEG and muscle in the 15–30 Hz range. Coherence was significantly smaller when the task was performed under an isometric condition (levers fixed) compared with a compliant condition in which subjects moved the levers against a spring-like load. Furthermore, there was a positive, significant relationship between the level of coherence and the degree of lever compliance. These results argue in favor of coherence between cortex and muscle being related to specific parameters of hand motor function.
Impaired Recognition Memory in Rats after Damage to the Hippocampus
Authors: Clark Robert E. , Zola Stuart M. , Squire Larry R.
Published: April 2018

Rats with radio-frequency or ibotenic acid lesions of the hippocampus and rats with radio-frequency lesions of the fornix were tested on the visual paired comparison task (VPC), a test of recognition memory. Memory was assessed at five different delay intervals ranging from 10 sec to 24 hr. All operated groups performed normally at the shorter delays (10 sec and 1 min). Across longer delays, the two groups with hippocampal damage were impaired. Rats with fornix lesions performed well on the VPC task but were impaired on a spatial task (spontaneous alternation). The results show that the hippocampus is essential for normal recognition memory. Moreover, fornix lesions need not mimic the effects of direct damage to hippocampal tissue. The findings are discussed in the context of the contribution of the hippocampus to recognition memory.
Enhanced Vulnerability to Cocaine Self-Administration Is Associated with Elevated Impulse Activity of Midbrain Dopamine Neurons
Authors: Marinelli Michela , White Francis J.
Published: April 2018

Individual differences in responding to a novel environment predict behavioral and neurochemical responses to psychostimulant drugs. Rats with a high locomotor response to a novel environment (HRs) exhibit enhanced self-administration (SA) behavior, sensitization, and basal or drug-induced dopamine release in the nucleus accumbens compared with rats with a low response to the novel context (LRs). In this study, we determined whether such differences in vulnerability to drug addiction might be related to differences in dopamine (DA) neuron activity. Rats were divided into HRs and LRs according to their response to a novel environment and then tested for acquisition of cocaine SA. HRs rapidly acquired cocaine SA (175 μg/kg per infusion), whereas LRs did not. Differences in cocaine SA were not caused by differences in exploratory behavior or sampling because these behaviors did not differ in HRs and LRs self-administering a saline solution. In a separate experiment, we used extracellular single-unit recordings and found that HRs exhibit higher basal firing rates and bursting activity of DA neurons in the ventral tegmental area and, to a lesser extent, in the substantia nigra pars compacta. The greater activity of midbrain DA cells in HRs was accompanied by reduced sensitivity to the inhibitory effects of a DA D2-class receptor agonist, indicating possible subsensitivity of impulse-regulating DA autoreceptors. These results demonstrate that differences in the basal activity of DA neurons may be critically involved in determining individual vulnerability to drugs of abuse.
The Cerebellum-Specific Munc13 Isoform Munc13-3 Regulates Cerebellar Synaptic Transmission and Motor Learning in Mice
Authors: Augustin Iris , Korte Stefan , Rickmann Michael , Kretzschmar Hans A. , Südhof Thomas C. , Herms Jochen W. , Brose Nils
Published: April 2018

Munc13 proteins form a family of three, primarily brain-specific phorbol ester receptors (Munc13-1/2/3) in mammals. Munc13-1 is a component of presynaptic active zones in which it acts as an essential synaptic vesicle priming protein. In contrast to Munc13-1, which is present in most neurons throughout the rat and mouse CNS, Munc13-3 is almost exclusively expressed in the cerebellum. Munc13-3 mRNA is present in granule and Purkinje cells but absent from glia cells. Munc13-3 protein is localized to the synaptic neuropil of the cerebellar molecular layer but is not found in Purkinje cell dendrites, suggesting that Munc13-3, like Munc13-1, is a presynaptic protein at parallel fiber–Purkinje cell synapses. To examine the role of Munc13-3 in cerebellar physiology, we generated Munc13-3-deficient mutant mice. Munc13-3 deletion mutants exhibit increased paired-pulse facilitation at parallel fiber–Purkinje cell synapses. In addition, mutant mice display normal spontaneous motor activity but have an impaired ability to learn complex motor tasks. Our data demonstrate that Munc13-3 regulates synaptic transmission at parallel fiber–Purkinje cell synapses. We propose that Munc13-3 acts at a similar step of the synaptic vesicle cycle as does Munc13-1, albeit with less efficiency. In view of the present data and the well established vesicle priming function of Munc13-1, it is likely that Munc13-3-loss leads to a reduction in release probability at parallel fiber–Purkinje cell synapses by interfering with vesicle priming. This, in turn, would lead to increases in paired-pulse facilitation and could contribute to the observed deficit in motor learning.
Nerve Growth Factor, But Not Epidermal Growth Factor, Increases Fra-2 Expression and Alters Fra-2/JunD Binding to AP-1 and CREB Binding Elements in Pheochromocytoma (PC12) Cells
Authors: Boss Valerie , Roback John D. , Young Andrew N. , Roback Linda J. , Weisenhorn Daniela M. Vogt , Medina-Flores Rafael , Wainer Bruce H.
Published: April 2018

In pheochromocytoma (PC12) cells nerve growth factor (NGF) and epidermal growth factor (EGF) activate similar receptor tyrosine kinase signaling pathways but evoke strikingly different biological outcomes: NGF induces differentiation and EGF acts as a mitogen. A novel approach was developed for identifying transcription factor activities associated with NGF-activated, but not EGF-activated, signaling, using random oligonucleotide clones from a DNA recognition library to isolate specific DNA binding proteins from PC12 nuclear extracts. A protein complex from NGF-treated, but not EGF-treated, cells was identified that exhibits increased mobility and DNA binding activity in gel mobility shift assays. The binding complex was identified in supershift assays as Fra-2/JunD. The clones used as probes contain either AP-1 or cAMP response element binding (CREB) recognition elements. Time course experiments revealed further differences in NGF and EGF signaling in PC12 cells. NGF elicits a more delayed and sustained ERK phosphorylation than EGF, consistent with previous reports. Both growth factors transiently inducec-fos, but NGF evokes a greater response than EGF. NGF specifically increases Fra-1 and Fra-2 levels at 4 and 24 hr. The latter is represented in Western blots by bands in the 40–46 kDa range. NGF, but not EGF, enhances the upper bands, corresponding to phosphorylated Fra-2. These findings suggest that prolonged alterations in Fra-2 and subsequent increases in Fra-2/JunD binding to AP-1 and CREB response elements common among many gene promoters could serve to trigger broadly an NGF-specific program of gene expression.
Blockade of NGF-Induced Neurite Outgrowth by a Dominant-Negative Inhibitor of the Egr Family of Transcription Regulatory Factors
Authors: Levkovitz Yechiel , O'Donovan Kevin J. , Baraban Jay M.
Published: April 2018

Although it is well established that members of the Egr family of transcription regulatory factors are induced in many neuronal plasticity paradigms, it is still unclear what role, if any, they play in this process. Because NGF stimulation of pheochromocytoma 12 cells elicits a robust induction of Egr family members, we have investigated their role in mediating long-term effects elicited by NGF in these cells by using the Egr zinc finger DNA-binding domain as a selective antagonist of Egr family-mediated transcription. We report that expression of this Egr inhibitor construct suppresses neurite outgrowth elicited by NGF but not by dibutyryl cAMP. To check that this Egr inhibitor construct does not act by blocking the MEK/ERK pathway, which is known to mediate NGF-induced neurite outgrowth, we confirmed that the Egr inhibitor construct does not block NGF activation of Elk1-mediated transcription, a response that is dependent on this pathway. Conversely, inhibition of MEK does not impair Egr family-mediated transcription. Thus, we conclude (1) that induction of Egr family members and activation of the MEK/ERK pathway by NGF are mediated by separate signaling pathways and (2) that both are required to trigger neurite outgrowth induced by NGF.
TheRpe65Leu450Met Variation Increases Retinal Resistance Against Light-Induced Degeneration by Slowing Rhodopsin Regeneration
Authors: Wenzel Andreas , Remé Charlotte E. , Williams Theodore P. , Hafezi Farhad , Grimm Christian
Published: April 2018

Excessive light can cause retinal degeneration and may be an environmental cofactor accelerating retinal dystrophies and age-related diseases. In rodent models, the light damage susceptibility (LDS) of the retina is determined genetically. In two mouse strains, with different degrees of LDS, a Leu450Met variation in the pigment epithelial protein RPE65 was shown recently to cosegregate with low LDS. Because light damage is rhodopsin-mediated, and RPE65 is essential for the regeneration of rhodopsin in the visual cycle, we analyzed this variation regarding rhodopsin metabolism and LDS in four mouse strains. We found that, in contrast to previous assertions, LDS does not correlate with the maximal retinal content of rhodopsin present after dark adaptation. Instead, LDS correlated positively with the kinetics of rhodopsin regeneration, which determine rhodopsin availability during light exposure. Light damage occurred after absorption of a threshold dose of photons and thus fast regeneration, as observed in those two strains having Leu at position 450 of RPE65, was correlated with the occurrence of photoreceptor apoptosis after short exposure. In contrast, mice with the Leu450Met variation ofRpe65regenerated rhodopsin with slow kinetics and showed an increased resistance to light-induced retinal degeneration. In these mice, RPE65 protein levels were reduced by a post-transcriptional mechanism. F1hybrid mice, carrying one normal and one variantRpe65gene, had intermediate levels of the corresponding protein and showed intermediate rhodopsin regeneration kinetics and an intermediate LDS. Thus, none of the two variants ofRpe65had a dominant effect.
Cholinergic Modulation of Excitatory Synaptic Transmission in the CA3 Area of the Hippocampus
Authors: Vogt Kaspar E. , Regehr Wade G.
Published: April 2018

Cholinergic innervation of the hippocampus has been implicated in memory formation and retrieval. Here we study cholinergic modulation of excitatory transmission in the CA3 area of the rat hippocampus. We used a combination of optical measurements of presynaptic calcium and electrophysiological measurements of synaptic currents to study associational–commissural (A/C) and mossy fiber (MF) synapses in brain slices. Direct synaptic modulation mediated by ACh receptors is only evident at the A/C synapse, where synaptic inhibition primarily reflects presynaptic calcium channel inhibition mediated by muscarinic receptors. MF synapses can, however, be indirectly modulated by muscarinic receptor activation. Muscarine elevates the firing rate of inhibitory cells, which increases GABA release and inhibits MF synapses by activating presynaptic GABABreceptors. Muscarine also depolarizes dentate granule cells and elevates their rate of firing. This leads to synaptic enhancement when combined with the use-dependent facilitation of MF synapses. In addition we were unable to evoke an increase in presynaptic calcium levels in MF boutons with local application of nicotinic receptor agonists. This finding does not support a leading hypothesis for MF modulation in which activation of presynaptic nicotinic receptors enhances transmission directly by elevating presynaptic calcium levels. However, indirect synaptic modulation could arise from nicotinic excitation of inhibitory neurons. Thus, to understand cholinergic modulation within the CA3 region, it is necessary to take into account secondary actions on synapses arising from other chemical messengers released by other cell types and to consider effects on firing patterns of presynaptic cells, which in turn influence release via use-dependent synaptic plasticity.
Presynaptic Role of cGMP-Dependent Protein Kinase during Long-Lasting Potentiation
Authors: Arancio Ottavio , Antonova Irina , Gambaryan Stepan , Lohmann Suzanne M. , Wood Jason S. , Lawrence David S. , Hawkins Robert D.
Published: April 2018

Previous research has suggested that cGMP-dependent protein kinases (cGKs) may play a role in long-term potentiation in hippocampus, but their site of action has been unknown. We examined this question at synapses between pairs of hippocampal neurons in dissociated cell culture. Injection of a specific peptide inhibitor of cGK into the presynaptic but not the postsynaptic neuron blocked long-lasting potentiation induced by tetanic stimulation of the presynaptic neuron. As controls, injection of a scrambled peptide or a peptide inhibitor of cAMP-dependent protein kinase into either neuron did not block potentiation. Conversely, injection of the α isozyme of cGK type I into the presynaptic but not the postsynaptic neuron produced activity-dependent potentiation that did not require NMDA receptor activation. Evidence from Western blots, reverse transcription-PCR, activity assays, and immunocytochemistry indicates that endogenous cGK type I is present in the neurons, including presynaptic terminals. These results support the idea that cGK plays an important presynaptic role during the induction of long-lasting potentiation in hippocampal neurons.
Bcl-XL–Caspase-9 Interactions in the Developing Nervous System: Evidence for Multiple Death Pathways
Authors: Zaidi Aliya U. , D'Sa-Eipper Cleta , Brenner Jennifer , Kuida Keisuke , Zheng Timothy S. , Flavell Richard A. , Rakic Pasko , Roth Kevin A.
Published: April 2018

Programmed cell death is critical for normal nervous system development and is regulated by Bcl-2 and Caspase family members. Targeted disruption ofbcl-xL, an antiapoptoticbcl-2gene family member, causes massive death of immature neurons in the developing nervous system whereas disruption ofcaspase-9, a proapoptoticcaspasegene family member, leads to decreased neuronal apoptosis and neurodevelopmental abnormalities. To determine whether Bcl-XLand Caspase-9 interact in an obligate pathway of neuronal apoptosis,bcl-x/caspase-9double homozygous mutants were generated. The increased apoptosis of immature neurons observed in Bcl-XL-deficient embryos was completely prevented by concomitant Caspase-9 deficiency. In contrast,bcl-x−/−/caspase-9−/−embryonic mice exhibited an expanded ventricular zone and neuronal malformations identical to that observed in mice lacking only Caspase-9. These results indicate both epistatic and independent actions of Bcl-XLand Caspase-9 in neuronal programmed cell death.

To examine Bcl-2 and Caspase family-dependent apoptotic pathways in telencephalic neurons, we compared the effects of cytosine arabinoside (AraC), a known neuronal apoptosis inducer, on wild-type, Bcl-XL-, Bax-, Caspase-9-, Caspase-3-, and p53-deficient telencephalic neuronsin vitro. AraC caused extensive apoptosis of wild-type and Bcl-XL-deficient neurons. p53- and Bax-deficient neurons showed marked protection from AraC-induced death, whereas Caspase-9- and Caspase-3-deficient neurons showed minimal or no protection, respectively. These findings contrast with our previous investigation of AraC-induced apoptosis of telencephalic neural precursor cells in which death was completely blocked by p53 or Caspase-9 deficiency but not Bax deficiency. In total, these results indicate a transition from Caspase-9- to Bax- and Bcl-XL-mediated neuronal apoptosis.
Experience-Dependent Changes in Extracellular Spike Amplitude May Reflect Regulation of Dendritic Action Potential Back-Propagation in Rat Hippocampal Pyramidal Cells
Authors: Quirk Michael C. , Blum Kenneth I. , Wilson Matthew A.
Published: April 2018

Activity-dependent attenuations in extracellular spike amplitude have been shown to correlate with a decrease in the effectiveness with which somatic action potentials back-propagate into the dendritic arbor of hippocampal pyramidal cells. In this paper we demonstrate that activity-dependent attenuations in amplitude occur during behavior and that the amount of attenuation is reduced with an animal's experience in an environment. The observed reductions are caused by an animal's experience within a specific environmental context, are dependent on functional NMDA receptors, and are accompanied by an increase in the effective coupling of pyramidal cells and interneurons. These results provide an important step in linking togetherin vivostudies within vitrodata and suggest that mechanisms of plasticity engaged during behavior may be sufficient to alter the biophysical and integrative properties of hippocampal pyramidal cells.
Enhanced Cortical Extracellular Levels of Cholecystokinin-Like Material in a Model of Anticipation of Social Defeat in the Rat
Authors: Becker Chrystel , Thiébot Marie-Hélène , Touitou Yvan , Hamon Michel , Cesselin François , Benoliel Jean-Jacques
Published: April 2018

The involvement of cholecystokinin (CCK) in the mechanisms of stress and/or anxiety was assessed byin vivomicrodialysis in rats subjected to a social stress paradigm. During the initial 30 min period of each conditioning session, a male Sprague Dawley rat (intruder) was placed in a protective cage inside the cage of a male Tryon Maze Dull rat (resident), allowing unrestricted visual, olfactory, and auditory contacts but precluding close physical contact between them. During the following 15 min period, both the protective cage and the resident were removed (nondefeated intruders) or only the protective cage was removed allowing the resident to attack the intruder (defeated rats). This procedure was repeated once daily for 4 d. On the fifth day, a guide cannula was implanted into the prefrontal cortex of intruders. During a single 30 min test session, performed 4 d later, intruders were subjected to only the 30 min protected confrontation to the resident. Anxiety-like behavior (immobility, ultrasonic vocalizations, and defensive postures), associated with an increase (approximately +100% above baseline) in cortical outflow of CCK-like material (CCKLM), were observed in defeated intruders. Pretreatment with diazepam (5 mg/kg, i.p.), but not buspirone (0.5–2 mg/kg, i.p.), prevented both the anxiety-related behavior and CCKLM overflow. The selective CCK-B receptor antagonist CI-988 (2 mg/kg, i.p.) reduced the anxiety-like behavior without affecting the increase in CCKLM outflow. These data indicate that anticipation of social defeat induces a marked activation of cortical CCKergic neurons associated with anxiety-related behaviors in rats.
Amygdalar Efferents Initiate Auditory Thalamic Discriminative Training-Induced Neuronal Activity
Authors: Poremba Amy , Gabriel Michael
Published: April 2018

It is well known that neurons of the medial geniculate (MG) nucleus of the thalamus send axonal projections to the amygdala. It has been proposed that these projections supply information that supports amygdalar associative processes underlying acquisition of acoustically cued conditioning and learning. Here we demonstrate the reverse direction of influence. Temporary inactivation of the amygdala using the GABAAreceptor agonist muscimol just before the onset of discriminative avoidance conditioning permanently blocked the development of training-induced discriminative neuronal activity in the MG nucleus of rabbits. No discriminative activity developed when the amygdala was inactivated or during later training to criterion without muscimol. Thus, amygdalar processing at the outset of training is necessary for the development of training-induced discriminative activity of neurons in the MG nucleus.
Retrograde Amnesia for Spatial Memory Induced by NMDA Receptor-Mediated Long-Term Potentiation
Authors: Brun Vegard Heimly , Ytterbø Kristin , Morris Richard G. M. , Moser May-Britt , Moser Edvard I.
Published: April 2018

If information is stored as distributed patterns of synaptic weights in the hippocampal formation, retention should be vulnerable to electrically induced long-term potentiation (LTP) of hippocampal synapses after learning. This prediction was tested by training animals in a spatial water maze task and then delivering bursts of high-frequency (HF) or control stimulation to the perforant path in the angular bundle. High-frequency stimulation induced LTP in the dentate gyrus and probably also at other hippocampal termination sites. Retention in a later probe test was disrupted. When the competitive NMDA receptor antagonist 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) was administered before the high-frequency stimulation, water maze retention was unimpaired. CPP administration blocked the induction of LTP. Thus, high-frequency stimulation of hippocampal afferents disrupts memory retention only when it induces a change in the spatial pattern of synaptic weights. The NMDA receptor dependency of this retrograde amnesia is consistent with the synaptic plasticity and memory hypothesis.
Age-Dependent Changes in Brain, CSF, and Plasma Amyloid β Protein in the Tg2576 Transgenic Mouse Model of Alzheimer's Disease
Authors: Kawarabayashi Takeshi , Younkin Linda H. , Saido Takaomi C. , Shoji Mikio , Ashe Karen Hsiao , Younkin Steven G.
Published: April 2018

The accumulation of amyloid β protein (Aβ) in the Tg2576 mouse model of Alzheimer's disease (AD) was evaluated by ELISA, immunoblotting, and immunocytochemistry. Changes in Aβ begin at 6–7 months as SDS-insoluble forms of Aβ42 and Aβ40 that require formic acid for solubilization appear. From 6 to 10 months, these insoluble forms increase exponentially. As insoluble Aβ appears, SDS-soluble Aβ decreases slightly, suggesting that it may be converting to an insoluble form. Our data indicate that it is full-length unmodified Aβ that accumulates initially in Tg2576 brain. SDS-resistant Aβ oligomers and most Aβ species that are N-terminally truncated or modified develop only in older Tg2576 mice, in which they are present at levels far lower than in human AD brain. Between 6 and 10 months, when SDS-insoluble Aβ42 and Aβ40 are easily detected in every animal, histopathology is minimal because only isolated Aβ cores can be identified. By 12 months, diffuse plaques are evident. From 12 to 23 months, diffuse plaques, neuritic plaques with amyloid cores, and biochemically extracted Aβ42 and Aβ40 increase to levels like those observed in AD brains. Coincident with the marked deposition of Aβ in brain, there is a decrease in CSF Aβ and a substantial, highly significant decrease in plasma Aβ. If a similar decline occurs in human plasma, it is possible that measurement of plasma Aβ may be useful as a premorbid biomarker for AD.
Serotonin Activates S6 Kinase in a Rapamycin-Sensitive Manner inAplysiaSynaptosomes
Authors: Khan Asad , Pepio Antonio M. , Sossin Wayne S.
Published: April 2018

The identification of tags that can specifically mark activated synapses is important for understanding how long-term synaptic changes can be restricted to specific synapses. The maintenance of synapse-specific facilitation inAplysiasensory to motor neuron cultures can be blocked by inhibitors of translation and by the drug rapamycin, which specifically blocks a signaling pathway that regulates phosphorylation of translational regulators. One important target of rapamycin is the phosphorylation and subsequent activation of S6 kinase. To test whether S6 kinase is the target for the ability of rapamycin to block synapse-specific facilitation inAplysia, we clonedAplysiaS6 kinase, its substrate S6, and the S6 kinase kinase phosphoinositide-dependent kinase 1 (PDK-1). Serotonin, which induces synapse-specific facilitation, increased phosphorylation ofAplysiaS6 kinase at threonine 399 in a rapamycin-sensitive manner inAplysiasynaptosomes. The phosphorylation of threonine 399 by 5-HT was independent of phosphoinositide-3 kinase, dependent on PKA and PKC, and occluded by the phosphatase inhibitor calyculin-A. 5-HT also increased S6 kinase activity and led to increased phosphorylation of S6 in synaptosomes. 5-HT increased levels of S6 in synaptosomes because of a rapamycin-sensitive increase in translation–stabilization of S6.AplysiaPDK-1 bound to and phosphorylatedAplysiaS6 kinase but only modulated phosphorylation of threonine 399 indirectly. These results suggest a mechanism by which the levels of translation factors can be increased specifically at activated synapses generating a long-lasting synaptic tag.
Calcium Channel Isoforms Underlying Synaptic Transmission at EmbryonicXenopusNeuromuscular Junctions
Authors: Thaler Christopher , Li Weiyan , Brehm Paul
Published: April 2018

Studies on the amphibian neuromuscular junction have indicated that N-type calcium channels are the sole mediators of stimulus-evoked neurotransmitter release. We show, via both presynaptic and postsynaptic voltage-clamp measurements, that dihydropyridine (DHP)-sensitive calcium channels also contribute to stimulus-evoked release at developingXenopusneuromuscular junctions. Whereas inhibition of postsynaptic responses by ω-conotoxin (ω-Ctx) GVIA has been taken previously as evidence that only N-type channels mediate transmitter release, we find that both N-type and DHP-sensitive calcium currents are sensitive to this toxin. The unusual sensitivity of DHP-sensitive calcium channels to ω-Ctx GVIA in presynaptic terminals raises the possibility that this channel type may have escaped detection in previous physiological studies on adult frog neuromuscular junctions. Alternatively, the additional channel isoforms may be present only during early development, when they may serve to strengthen collectively presynaptic release during critical periods of synaptogenesis.
Densin-180 Forms a Ternary Complex with the α-Subunit of Ca2+/Calmodulin-Dependent Protein Kinase II and α-Actinin
Authors: Walikonis Randall S. , Oguni Asako , Khorosheva Eugenia M. , Jeng Chung-Jiuan , Asuncion Franklin J. , Kennedy Mary B.
Published: April 2018

Densin-180 is a transmembrane protein that is tightly associated with the postsynaptic density in CNS neurons and is postulated to function as a synaptic adhesion molecule. Here we report the identification of the α-subunit of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and α-actinin-4 as potential binding partners for the densin-180 intracellular segment. We demonstrate by yeast two-hybrid and biochemical assays that the intracellular portion of densin-180, the α-subunit of CaMKII (CaMKIIα), and α-actinin interact with each other at distinct binding sites and can form a ternary complex stabilized by multiple interactions. Densin-180 binds specifically to the association domain of CaMKIIα and does not bind with high affinity to holoenzymes of CaMKII that contain β-subunit. The PDZ (PSD-95, DIg, Z0-1) domain of densin contributes to its binding to α-actinin. A distinct domain of α-actinin interacts with the kinase domains of both α- and β-subunits of CaMKII. Autophosphorylation of CaMKII increases its affinity for densin-180 from an EC50of >1 μm to an EC50of <75–150 nM. In contrast, phosphorylation of densin-180 by CaMKII at serine-1397 only slightly decreases its affinity for CaMKII. The specific interaction of densin-180 with holoenzymes of CaMKII containing only α-subunit and the increased affinity of CaMKII for densin-180 after autophosphorylation suggest that densin-180 may be involved in localization of activated CaMKII synthesized in dendrites.
Coordination of the Bladder Detrusor and the External Urethral Sphincter in a Rat Model of Spinal Cord Injury: Effect of Injury Severity
Authors: Pikov Victor , Wrathall Jean R.
Published: April 2018

Recovery of urinary tract function after spinal cord injury (SCI) is important in its own right and may also serve as a model for studying mechanisms of functional recovery after injury in the CNS. Normal micturition requires coordinated activation of smooth muscle of the bladder (detrusor) and striated muscle of the external urethral sphincter (EUS) that is controlled by spinal and supraspinal circuitry. We used a clinically relevant rat model of thoracic spinal cord contusion injury to examine the effect of varying the degree of residual supraspinal connections on chronic detrusor–EUS coordination. Urodynamic evaluation at 8 weeks after SCI showed that detrusor contractions of the bladder recovered similarly in groups of rats injured with a 10 gm weight dropped 12.5, 25, or 50 mm onto the spinal cord. In contrast, the degree of coordinated activation of the EUS varied with the severity of initial injury and the degree of preservation of white matter at the injury site. The 12.5 mm SCI resulted in the sparing of 20% of the white matter at the injury site and complete recovery of detrusor–EUS coordination. In more severely injured rats, the chronic recovery of detrusor–EUS coordination was very incomplete and correlated to decreased innervation of lower motoneurons by descending control pathways and their increased levels of mRNA for glutamate receptor subunits NR2A and GluR2. These results show that the extent of recovery of detrusor–EUS coordination depends on injury severity and the degree of residual connections with brainstem control centers.
Brain-Derived Neurotrophic Factor and Glial Cell Line-Derived Neurotrophic Factor Are Required Simultaneously for Survival of Dopaminergic Primary Sensory NeuronsIn Vivo
Authors: Erickson Jeffery T. , Brosenitsch Teresa A. , Katz David M.
Published: April 2018

Null mutations affecting members of the transforming growth factor-β and neurotrophin families result in overlapping patterns of neuronal cell death. This is particularly striking in the cranial sensory nodose-petrosal ganglion complex (NPG), in which loss of either glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or neurotrophin-4 (NT-4) results in a 30–50% reduction in neuronal survival. It is unknown, however, whether GDNF and any single neurotrophin support survival of the same cells, and if so, whether they are required simultaneously or sequentially during development. To approach these issues we defined survival requirements of nodose and petrosal neurons for GDNFin vitroand inbdnf,gdnf, andbdnf/gdnfnull mutant mice, as well as the distribution of GDNF in NPG target tissues. Our analyses focused on the total population of ganglion cells as well as the subset of NPG neurons that are dopaminergic. Neuron losses inbdnf/gdnfdouble mutants are not additive of the losses in singlebdnforgdnfnull mutants, indicating that many cells, including dopaminergic neurons, require both GDNF and BDNF for survivalin vivo. Moreover, both factors are required during the same period of development, between embryonic day (E) 15.5 and E17.5. In addition, GDNF, like BDNF is expressed in target tissues at the time of initial target innervation and coincident with GDNF dependence of the innervating neurons. Together, these findings demonstrate that both GDNF and BDNF can act as target-derived trophic factors and are required simultaneously for survival of some primary sensory neurons.
Distinct Localization of P2X Receptors at Excitatory Postsynaptic Specializations
Authors: Rubio Maria E. , Soto Florentina
Published: April 2018

ATP mediates fast excitatory synaptic transmission in some regions of the central nervous system through activation of P2X receptors. Nonetheless, the functional significance of ATP-mediated neurotransmission is not yet understood. Using postembedding immunocytochemistry, we describe the distribution of P2X2, P2X4, and P2X6subunits in cerebellum and in the CA1 region of the hippocampus. Dendritic spines of cerebellar Purkinje cells showed immunogold labeling for all three subunits when apposed to parallel fiber (PF) terminals. In contrast, no immunogold labeling was observed on dendritic spines or cell bodies receiving inputs from climbing fibers and basket cells, respectively. In CA1 pyramidal cells, postsynaptic membranes apposed to terminals of Schaffer collaterals were immunogold-labeled for P2X2, P2X4, and P2X6subunits. Immunolabeling was also observed perisynaptically and intracellularly in relation to membranes of the endoplasmic reticulum. The analysis of the tangential distribution of gold particles showed that they were preferentially located at the peripheral portion of the postsynaptic specialization of both parallel fiber and Schaffer collateral synapses. By double imunogold labeling using antibodies for P2X receptor subunits and GluR2/3 subunits of the AMPA glutamate receptors, we show that synapses expressing P2X receptors are also glutamatergic. The present study shows for the first time qualitatively and quantitatively the precise localization of P2X receptors in brain. Moreover, our data indicate that P2X receptors may play a significant role at glutamatergic synapses.