bluuebunny/crossref_metadata_2025 huggingface dataset:
Cellular and Synaptic Modulation Underlying Substance P-Mediated Plasticity of the Lamprey Locomotor Network
Authors: Parker David , Grillner Sten
Published: April 2018

The tachykinin substance P modulates the lamprey locomotor network by increasing the frequency of NMDA-evoked ventral root bursts and by making the burst activity more regular. These effects can last in excess of 24 hr. In this paper, the effects of substance P on the synaptic and cellular properties of motor neurons and identified network interneurons have been examined.

Substance P potentiated the amplitude of monosynaptic glutamatergic inputs from excitatory interneurons and reticulospinal axons. The amplitude and frequency of miniature EPSPs was increased, suggesting that the synaptic modulation was mediated presynaptically and postsynaptically. The postsynaptic modulation was caused by a specific effect of substance P on the NMDA component of the synaptic input, whereas the presynaptic component was calcium-independent. Substance P did not affect monosynaptic glycinergic inputs from lateral interneurons, crossed inhibitory interneurons, or ipsilateral segmental interneurons or postsynaptic GABAAor GABABresponses, suggesting that it has little effect on inhibitory synaptic transmission.

At the cellular level, substance P increased synaptic inputs, resulting in membrane potential oscillations in motor neurons, crossed caudal interneurons, lateral interneurons, and excitatory interneurons. The spiking in response to depolarizing current pulses was increased in motor neurons, lateral interneurons, and excitatory interneurons, but usually was reduced in crossed inhibitory interneurons. Substance P reduced the calcium-dependent afterhyperpolarization after an action potential in motor neurons and lateral interneurons, but did not affect this conductance in excitatory or crossed inhibitory interneurons.

The relevance of these cellular and synaptic changes to the modulation of the locomotor network is discussed.
Amygdalar NMDA Receptors are Critical for New Fear Learning in Previously Fear-Conditioned Rats
Authors: Lee Hongjoo , Kim Jeansok J.
Published: April 2018

NMDA receptors in the amygdala seem to be critical for fear conditioning in naive rats. Recent spatial-learning studies suggest that previous learning protected animals from the amnesic effect of NMDA antagonists on new learning (of a similar behavioral task). Therefore, the present study examined whether blocking of NMDA receptors in the basolateral nucleus of the amygdala (BLA) prevents new fear learning in previously fear-conditioned rats, as measured by freezing behavior. Intra-BLA infusions of the NMDA receptor antagonistdl-2-amino-5-phosphonovaleric acid (APV) completely blocked fear conditioning to a tone stimulus in animals that had previously been fear-conditioned to a light stimulus. Similar results were obtained with intra-BLA infusions of APV before contextual fear conditioning in rats that had been fear-conditioned to a different context. Additional experiments showed that intra-BLA APV infusions substantially interfere with the expression and extinction of conditioned fear to tone, light, and context stimuli. Together, these results indicate that NMDA receptors in the BLA are crucial for the encoding of new fear memories (i.e., the formation of specific conditioned stimulus–unconditioned stimulus association), the expression of conditioned fear responses, and the extinction of acquired fear.
cAMP-Dependent Long-Term Potentiation of Nitric Oxide Release from Cerebellar Parallel Fibers in Rats
Authors: Kimura Shinji , Uchiyama Seiji , Takahashi Hideaki E. , Shibuki Katsuei
Published: April 2018

Nitric Oxide (NO) is released from parallel fibers (PFs) after PF stimulation. NO–cGMP signaling is essential for long-term depression (LTD) in cerebellar PF–Purkinje cell synapses, which also exhibit presynaptic long-term potentiation (LTP) after tetanic PF stimulation. This LTP is dependent on cAMP but not NO–cGMP signaling. In this study, we analyzed long-term changes of NO release from PFs in rat cerebellar slices using electrochemical NO probes. Repetitive PF stimulation at 10 Hz for 2 sec elicited a transient increase in NO concentration (2.2 ± 0.1 nm; mean ± SEM;n= 116). This NO release exhibited long-term potentiation (LTPNO) by 36 ± 3% (n= 15) after tetanic PF stimulation. Induction of LTPNOwas not affected by Glu receptor antagonists. NO release from PFs was also potentiated byl-Arg (ARG) (100 μm), forskolin (50 μm), and 8-bromo-cAMP (Br-cAMP) (1 mm) but not by 1,9-dideoxyforskolin (50 μm), a biologically inactive analog of forskolin. The potentiation induced by forskolin was significantly suppressed by H89 (10 μm), a blocker of cAMP-dependent protein kinase. The potentiation induced by forskolin, but not that induced by Arg, interfered with LTPNO. H89 (10 μm) and KT5720 (1 μm), another blocker of cAMP-dependent protein kinase, but not KT5823 (300 nm), a blocker of cGMP-dependent protein kinase, significantly suppressed LTPNO. These data indicate that neural NO release is under activity-dependent control, just as synaptic transmitter release is. LTPNOmight play a role in cross talk between presynaptic and postsynaptic plasticity by facilitating NO–cGMP-dependent postsynaptic LTD after induction of cAMP-dependent presynaptic LTP and LTPNO.
Purification from Bovine Serum of a Survival-Promoting Factor for Cultured Central Neurons and Its Identification as Selenoprotein-P
Authors: Yan Jun , Barrett John N.
Published: April 2018

We purified from bovine serum a glycoprotein that promotes the survival of rat embryonic neurons cultured from septum and other brain regions. A 40,000-fold purification was achieved by using a combination of ammonium sulfate precipitation, Zn2+affinity chromatography, Cibacron blue 3-GA dye affinity chromatography, ABx ion exchange chromatography, and preparative PAGE. The active protein had an apparent molecular weight of 50–60 kDa. The concentration required for half-maximal survival (EC50) was 12 ng/ml (∼200 pm) for the final fraction. Amino acid sequencing after cyanogen bromide cleavage yielded two sequences that are homologous to regions of deduced sequence of the selenoprotein-P (SPP) family in bovine, rat, and human. Antibodies against a synthetic peptide within the bovine SPP sequence immunoprecipitated and inhibited the survival-promoting activity of a partially purified serum fraction. The purified protein supported neuronal survival more effectively than inorganic selenium. These results suggest that SPP or an SPP-like protein contributes to the neuronal survival-promoting activity of serum.
Ciliary Neurotrophic Factor Receptor α in Spinal Motoneurons is Regulated by Gonadal Hormones
Authors: Forger Nancy G. , Wagner Christine K. , Contois Michael , Bengston Lynn , MacLennan A. John
Published: April 2018

Ciliary neurotrophic factor receptor α (CNTFRα) is the ligand-binding component of the CNTF receptor. CNTFRα expression is essential for the normal development of spinal motoneurons and is required for the development of a sex difference in motoneuron number in androgen-sensitive perineal motoneurons. We used immunocytochemistry to examine the expression and hormone regulation of CNTFRα protein in the spinal nucleus of the bulbocavernosus (SNB), dorsolateral nucleus and retrodorsolateral nucleus of the lower lumbar spinal cord of adult rats. CNTFRα immunoreactivity (CNTFRα-IR) was observed in the somata and dendrites of virtually all motoneurons. In all three motor pools, the intensity of motoneuron soma labeling was greatest among gonadally intact males and was reduced in females and gonadectomized males. The density of CNTFRα-IR in neuropil also tended to be highest in intact males. Short-term (2 d) testosterone propionate treatment reversed the decline in the density of soma labeling in the SNB of castrated males but did not reverse any other effects of castration. Long-term hormone treatment, achieved by implanting males with testosterone capsules at the time of gonadectomy, prevented the decline in soma labeling in all motor pools and partially prevented the decline in neuropil label caused by castration. We conclude that expression of CNTFRα protein is androgen-regulated in spinal motoneurons.
Differences in Ca2+Channels Governing Generation of Miniature and Evoked Excitatory Synaptic Currents in Spinal Laminae I and II
Authors: Bao Juping , Li Jing James , Perl Edward R.
Published: April 2018

Many neurons of spinal laminae I and II, a region concerned with pain and other somatosensory mechanisms, display frequent miniature “spontaneous” EPSCs (mEPSCs). In a number of instances, mEPSCs occur often enough to influence neuronal excitability. To compare generation of mEPSCs to EPSCs evoked by dorsal root stimulation (DR-EPSCs), various agents affecting neuronal activity and Ca2+channels were applied toin vitroslice preparations of rodent spinal cord during tight-seal, whole-cell, voltage-clamp recordings from laminae I and II neurons. The AMPA/kainate glutamate receptor antagonist CNQX (10–20 μm) regularly abolished DR-EPSCs. In many neurons CNQX also eliminated mEPSCs; however, in a number of cases a proportion of the mEPSCs were resistant to CNQX suggesting that in these instances different mediators or receptors were also involved. Cd2+(10–50 μm) blocked evoked EPSCs without suppressing mEPSC occurrence. In contrast, Ni2+(≤100 μm), a low-threshold Ca2+channel antagonist, markedly decreased mEPSC frequency while leaving evoked monosynaptic EPSCs little changed. Selective organic antagonists of high-threshold (HVA) Ca2+channels, nimodipine, ω-Conotoxin GVIA, and Agatoxin IVA partially suppressed DR-EPSCs, however, they had little or no effect on mEPSC frequency. La3+and mibefradil, agents interfering with low-threshold Ca2+channels, regularly decreased mEPSC frequency with little effect on fast-evoked EPSCs. Increased [K+]o(5–10 mm) in the superfusion, producing modest depolarizations, consistently increased mEPSC frequency; an increase suppressed by mibefradil but not by HVA Ca2+channel antagonists. Together these observations indicate that different Ca2+channels are important for evoked EPSCs and mEPSCs in spinal laminae I and II and implicate a low-threshold type of Ca2+channel in generation of mEPSCs.
The Steroid Hormone 20-Hydroxyecdysone Enhances Neurite Growth ofDrosophilaMushroom Body Neurons Isolated during Metamorphosis
Authors: Kraft Robert , Levine Richard B. , Restifo Linda L.
Published: April 2018

Mushroom bodies (MBs) are symmetrically paired neuropils in the insect brain that are of critical importance for associative olfactory learning and memory. InDrosophila melanogaster, the MB intrinsic neurons (Kenyon cells) undergo extensive reorganization at the onset of metamorphosis. A phase of rapid axonal degeneration without cell death is followed by axonal regeneration. This re-elaboration occurs as levels of the steroid hormone 20-hydroxyecdysone (20E) are rising during the pupal stage. Based on the known role of 20E in directing many features of CNS remodeling during insect metamorphosis, we hypothesized that the outgrowth of MB axonal processes is promoted by 20E. Using a GAL4 enhancer trap line (201Y) that drives MB-restricted reporter gene expression, we identified Kenyon cells in primary cultures dissociated from early pupal CNS. Paired cultures derived from single brains isolated before the 20E pupal peak were incubated in medium with or without 20E for 2–4 d. Morphometric analysis demonstrated that MB neurons exposed to 20E had significantly greater total neurite length and branch number compared with that of MB neurons grown without hormone. The relationship between branch number and total neurite length remained constant regardless of hormone treatmentin vitro, suggesting that 20E enhances the rate of outgrowth from pupal MB neurons in a proportionate manner and does not selectively increase neuritic branching. These results implicate 20E in enhancing axonal outgrowth of Kenyon cells to support MB remodeling during metamorphosis.
Odorant-Induced and Sniff-Induced Activation in the Cerebellum of the Human
Authors: Sobel Noam , Prabhakaran Vivek , Hartley Catherine A. , Desmond John E. , Zhao Zuo , Glover Gary H. , Gabrieli John D.E. , Sullivan Edith V.
Published: April 2018

Functional magnetic resonance imaging was used to test whether odorants induce activation in the cerebellum of the human. The odorants vanillin and propionic acid both induced significant activation, primarily in the posterior lateral hemispheres. Activation was concentration-dependent, greater after stimulation with higher concentration odorants. By contrast, the action of sniffing nonodorized air induced significant activation in the anterior cerebellum, primarily in the central lobule. These findings demonstrate that the cerebellum plays a role in human olfaction. A hypothesis is proposed whereby the cerebellum maintains a feedback mechanism that regulates sniff volume in relation to odor concentration.
Light Responsiveness of the Suprachiasmatic Nucleus: Long-Term Multiunit and Single-Unit Recordings in Freely Moving Rats
Authors: Meijer Johanna H. , Watanabe Kazuto , Schaap Jeroen , Albus Henk , Détári László
Published: April 2018

The suprachiasmatic nuclei (SCN) of the hypothalamus contain a pacemaker that generates circadian rhythms in many functions. Light is the most important stimulus that synchronizes the circadian pacemaker to the environmental cycle. In this paper we have characterized the baseline neuronal firing patterns of the SCN as well as their response to light in freely moving rats. Multiunit and single-unit recordings showed that SCN neurons increase discharge during daytime and decrease discharge at night. Discharge levels of individual neurons that were followed throughout the circadian cycle appeared in phase with the population and were characterized by low discharge rates (often below 1 Hz), with a twofold increase during the day. The effect of light on the multiunit response was dependent on the duration of light exposure and on light intensity, with light thresholds of ∼0.1 lux. The light response level showed a strong dependency on time of day, with large responsiveness at night and low responsiveness during day. At both phases of the circadian cycle, the response level could be raised by an increase in light intensity. Single-unit measurements revealed that the time-dependent light response of SCN neurons was present also at the level of single units. The results show that the basic light response characteristics that were observed at the multiunit level result from an integrated response of similarly behaving single units. Research at the single-unit level is therefore a useful approach for investigating the basic principles of photic entrainment.
Caspase-2 (Nedd-2) Processing and Death of Trophic Factor-Deprived PC12 Cells and Sympathetic Neurons Occur Independently of Caspase-3 (CPP32)-Like Activity
Authors: Stefanis Leonidas , Troy Carol M. , Qi Haiqing , Shelanski Michael L. , Greene Lloyd A.
Published: April 2018

We have previously shown that caspase-2 (Nedd-2) is required for apoptosis induced by withdrawal of trophic support from PC12 cells and sympathetic neurons. Here, we examine the relationship of caspase-2 processing and cell death to induction of caspase-3 (CPP32)-like activity in PC12 cells. Caspase-2 processing, at a site tentatively identified as D333, led to the formation of an N-terminal 37 kDa product. This processing correlated temporally with induction of caspase-3-like activity. Agents previously shown to inhibit caspase-3-like activation, such as bcl-2 and the Cdk inhibitor flavopiridol, also acted upstream of caspase-2 processing. The general caspase inhibitors BAF and zVAD-FMK inhibited N-terminal caspase-2 processing. In contrast, the more selective caspase inhibitor DEVD-FMK inhibited the induction of caspase-3-like activity but did not affect caspase-2 processing or significantly suppress death in PC12 cells or sympathetic neurons. This indicates that caspase-3-like activity is not required for either caspase-2 processing or apoptosis in this paradigm. An antisense oligonucleotide to caspase-2 inhibited cell death but did not affect caspase-3-like activity, indicating that caspase-2 is not upstream of this activity and that activation of caspase-3-like caspases is not sufficient for death. Thus, in our paradigm, caspase-2 processing and caspase-3-like activity are induced independently of each other. Moreover, although death requires caspase-2, caspase-3-like activity is neither necessary nor sufficient for death.
Long-Term Desensitization of Nicotinic Acetylcholine Receptors Is Regulated via Protein Kinase A-Mediated Phosphorylation
Authors: Paradiso Ken , Brehm Paul
Published: April 2018

During prolonged application of transmitter, ligand-gated ion channels enter a nonconducting desensitized state. Studies onTorpedoelectroplax nicotinic acetylcholine (ACh) receptors have shown that entry into the desensitized state is accelerated by protein kinase A-dependent (PKA) receptor phosphorylation. To examine the effects of phosphorylation on desensitization of muscle-type ACh receptors, we expressed the frog embryonic receptor type inXenopusoocytes. Treatment of embryonic muscle ACh receptors with 8-Br cAMP had no measurable effect on the rate of entry into a desensitized state, but it greatly accelerated the recovery from desensitization. Three complementary approaches to reduce the levels of receptor phosphorylation provided additional evidence for a role of PKA-dependent phosphorylation in rescuing receptors from long-term desensitization. Inactivation of the endogenous PKA activity by coexpression of an inhibitor protein, treatment of receptors with phosphatase, and removal of phosphorylation sites by site-specific subunit mutation all resulted in slowed recovery. Our findings point to the existence of two distinct desensitized states: one requiring several seconds for full recovery and a second state from which recovery requires minutes. Receptors lacking PKA phosphorylation sites exhibit a pronounced increase in the slowly recovering component of desensitization, suggesting that receptor phosphorylation speeds overall recovery by reducing the entry into a deep desensitized state. This newly described effect of phosphorylation on ACh receptor function may serve as an important modulator of postsynaptic receptor sensitivity.
Intraocular Gene Transfer of Ciliary Neurotrophic Factor Prevents Death and Increases Responsiveness of Rod Photoreceptors in theretinal degeneration slowmouse
Authors: Cayouette Michel , Behn Darren , Sendtner Michael , Lachapelle Pierre , Gravel Claude
Published: April 2018

Several mutations causing both photoreceptor degeneration and malfunction have been identified in humans and animals. Although intraocular injection of trophic factors has been shown to reduce photoreceptor death in a few conditions of rapid photoreceptor loss, it is unclear whether long-term beneficial changes in functional properties of affected photoreceptors can be obtained by treatment with these factors. Therds/rdsmouse is a spontaneous mutant bearing a null mutation in therds/peripheringene, which is linked to many forms of dominant retinal degenerations in humans. Here, we report that intraocular adenovirus-mediated gene transfer of ciliary neurotrophic factor (CNTF) in this mutant reduces photoreceptor loss, causes a significant increase in the length of photoreceptor segments, and results in a redistribution and an increase in the retinal content of the photopigment rhodopsin. These effects are accompanied by a significant increase in the amplitude of the a- and b-waves of the scotopic electroretinogram. These results suggest that continuous administration of CNTF could potentially be useful for the treatment of some forms of retinal degeneration.
Heterotopic Neurogenesis in a Rat with Cortical Heterotopia
Authors: Lee Kevin S. , Collins Jennifer L. , Anzivino Matthew J. , Frankel Eric A. , Schottler Frank
Published: April 2018

Early cellular development was studied in the neocortex of the tish rat. This neurological mutant is seizure-prone and displays cortical heterotopia similar to those observed in certain epileptic patients. The present study demonstrates that a single cortical preplate is formed in a typical superficial position of the developing tish neocortex. In contrast, two cortical plates are formed: one in a normotopic position and a second in a heterotopic position in the intermediate zone. As the normotopic cortical plate is formed, it characteristically separates the subplate cells from the superficial Cajal-Retzius cells. In contrast, the heterotopic cortical plate is not intercalated between the preplate cells because of its deeper position in the developing cortex. Cellular proliferation occurs in two zones of the developing tish cortex. One proliferative zone is located in a typical position in the ventricular/subventricular zone. A second proliferative zone is located in a heterotopic position in the superficial intermediate zone, i.e., between the two cortical plates. This misplaced proliferative zone may contribute cells to both the normotopic and heterotopic cortical plates. Taken together, these findings indicate that misplaced cortical plate cells, but not preplate cells, comprise the heterotopia of the tish cortex. Heterotopic neurogenesis is an early developmental event that is initiated before the migration of most cortical plate cells. It is concluded that misplaced cellular proliferation, in addition to disturbed neuronal migration, can play a key role in the formation of large cortical heterotopia.
κ-Opioid Regulation of Neuronal Activity in the Rat Supraoptic NucleusIn Vivo
Authors: Brown Colin H. , Ludwig Mike , Leng Gareth
Published: April 2018

We investigated the influence of endogenous κ-opioids on the activity of supraoptic neuronsin vivo. Administration of the κ-antagonistnor-binaltorphimine (200 μg/kg, i.v.), increased the activity of phasic (vasopressin), but not continuously active (oxytocin), supraoptic neurons by increasing burst duration (by 69 ± 24%) and decreasing the interburst interval (by 19 ± 11%). Similarly, retrodialysis ofnor-binaltorphimine onto the supraoptic nucleus increased the burst duration (119 ± 57% increase) of vasopressin cells but did not alter the firing rate of oxytocin cells (4 ± 8% decrease). Thus, an endogenous κ-agonist modulates vasopressin cell activity by an action within the supraoptic nucleus. To eliminate κ-agonist actions within the supraoptic nucleus, we infused the κ-agonist U50,488H (2.5 μg/hr at 0.5 μg/hr) into one supraoptic nucleus over 5 d to locally downregulate κ-receptor function. Such infusions reduced the spontaneous activity of vasopressin but not oxytocin cells and reduced the proportion of cells displaying spontaneous phasic activity from 26% in vehicle-infused nuclei to 3% in U50,488H-infused nuclei; this treatment also prevented acute inhibition of both vasopressin and oxytocin cells by U50,488H (1000 μg/kg, i.v.), confirming functional κ-receptor downregulation. In U50,488H-infused supraoptic nuclei, vasopressin cell firing rate was increased bynor-binaltorphimine (100 and 200 μg/kg, i.v.) but not to beyond that found in vehicle-treated nuclei, indicating that these cells were not U50,488H-dependent. Thus, normally functioning κ-opioid mechanisms on vasopressin cells are essential for the expression of phasic firing.
Reexpression of Myogenic Proteins in Mature Electric Organ after Removal of Neural Input
Authors: Unguez Graciela A. , Zakon Harold H.
Published: April 2018

The electric organ (EO) of the weakly electric fishSternopygus macrurusderives from striated myofibers that fuse and suppress many muscle properties. Mature electrocytes are larger than muscle fibers, do not contain sarcomeres, or express myosin heavy chain (MHC) or tropomyosin. Furthermore, electrocytes express keratin, a protein not expressed in muscle. InS. macrurusthe EO is driven continuously at frequencies higher than those of the intermittently active skeletal muscle. The extent to which differences in EO and muscle phenotype are accounted for by activity patterns, or innervation per se, was determined by assessing the expression of MHC, tropomyosin, and keratin 2 and 5 weeks after the elimination of (1) activity patterns by spinal transection or (2) all synaptic input by denervation.

Immunohistochemical analyses showed no changes in muscle fiber phenotypes after either experimental treatment. In contrast, the keratin-positive electrocytes revealed an upregulation of MHC and tropomyosin. Nearly one-third of all electrocytes expressed MHC (35%) and tropomyosin (25%) 2 weeks after spinal transection, whereas approximately two-thirds (61%) expressed MHC 2 weeks after denervation. After 5 weeks of denervation or spinal transection, all electrocytes contained MHC and tropomyosin. Newly formed sarcomere clusters also were observed in denervated electrocytes. The MHC expressed in electrocytes corresponded to that present in a select population of muscle fibers, i.e., type II fibers. Thus, the elimination of electrical activity or all synaptic input resulted in a partial reversal of the electrocyte phenotype to an earlier developmental stage of its myogenic lineage.
Antisense Ablation of Type I Metabotropic Glutamate Receptor mGluR1Inhibits Spinal Nociceptive Transmission
Authors: Young Marie R. , Blackburn-Munro Gordon , Dickinson Tracey , Johnson Melanie J. , Anderson Heather , Nakalembe Immaculate , Fleetwood-Walker Susan M.
Published: April 2018

Electrophysiological and behavioral studies point to a role of group I metabotropic glutamate receptors (mGluR1and mGluR5) in mediating spinal nociceptive responses in rats. However, antagonists with a high degree of specificity for each of these sites are not yet available. We, therefore, examined the effects of antisense deletion of spinal mGluR1expression in assays of behavioral analgesia and of electrophysiological responses of dorsal horn neurons. Rats treated with an mGluR1antisense oligonucleotide reagent, delivered continuously to the intrathecal space of the lumbar spinal cord, developed marked analgesia as measured by an increase in the latency to tail-flick (55°C) over a period of 4–7 d. This correlated with a selective reduction in mGluR1, but not mGluR5, immunoreactivity in the superficial dorsal horn compared with untreated control rats, in parallel with a significant reduction in the proportion of neurons activated by the mGluR group I agonist 3,5-dihydroxyphenylglycine (DHPG), whereas the proportion of cells excited by the mGluR5agonist,trans-azetidine-2,4-dicarboxylic acid (t-ADA) remained unaffected. In contrast, rats treated with mGluR1sense or mismatch probes showed none of these changes compared with untreated, control rats. Furthermore, multireceptive dorsal horn neurons in mGluR1antisense-treated rats were strongly excited by innocuous stimuli to their peripheral receptive fields, but showed severe reductions in their sustained excitatory responses to the selective C-fiber activator mustard oil and in responses to DHPG.
A Dopamine/D1 Receptor/Protein Kinase A/Dopamine- and cAMP-Regulated Phosphoprotein (Mr32 kDa)/Protein Phosphatase-1 Pathway Regulates Dephosphorylation of the NMDA Receptor
Authors: Snyder Gretchen L. , Fienberg Allen A. , Huganir Richard L. , Greengard Paul
Published: April 2018

We have investigated the mechanism by which activation of dopamine (DA) receptors regulates the glutamate sensitivity of medium spiny neurons of the nucleus accumbens. Our results demonstrate that DA regulates the phosphorylation state of the NR1 subunit of NMDA-type glutamate receptors. The effect of DA was mimicked by SKF82526, a D1-type DA receptor agonist, and by forskolin, an activator of cAMP-dependent protein kinase (PKA), and was blocked by H-89, a PKA inhibitor. These data indicate that DA increases NR1 phosphorylation through a PKA-dependent pathway. DA-induced phosphorylation of NR1 was blocked in mice bearing a targeted deletion of the gene for dopamine- and cAMP-regulated phosphoprotein ofMr32 kDa (DARPP-32), a phosphoprotein that is a potent and selective inhibitor of protein phosphatase-1, indicating that the effect of PKA is mediated, in part, by regulation of the DARPP-32/protein phosphatase-1 cascade. In support of this interpretation, NR1 phosphorylation was increased by calyculin A, a protein phosphatase-1/2A inhibitor. A model is proposed in which the ability of DA to regulate NMDA receptor sensitivity is attributable to a synergistic action involving increased phosphorylation and decreased dephosphorylation of the NR1 subunit of the NMDA receptor.
Postsynaptic Ca2+Influx Mediated by Three Different Pathways during Synaptic Transmission at a Calyx-Type Synapse
Authors: Bollmann Johann H. , Helmchen Fritjof , Borst J. Gerard G. , Sakmann Bert
Published: April 2018

Whole-cell recordings and Ca2+flux measurements were made at a giant calyx-type synapse in rat brainstem slices to determine the contribution of glutamate receptor (GluR) channels and voltage-dependent Ca2+channels (VDCCs) to postsynaptic Ca2+influx during synaptic transmission. A single presynaptic action potential (AP) evoked an EPSP, followed by a single AP. The EPSP–AP sequence caused a postsynaptic Ca2+influx of ∼3.0 pC, primarily through VDCCs (∼70%) and NMDA-type (up to 30%) channels but also through AMPA-type (<5%) GluR channels. At −80 mV, the fractional Ca2+current (Pf) mediated by AMPA receptor (AMPAR) and NMDA receptor (NMDAR) channels was 1.3 and 11–12%, respectively. Simulations of the time course of Ca2+influx through GluR channels suggested that the small contribution of AMPAR channels occurred only during the first few milliseconds of an EPSP, whereas influx through NMDAR channels dominated later. The NMDAR-mediated Ca2+influx was localized in regions covered by the presynaptic terminal, whereas the Ca2+influx mediated by VDCCs was more homogeneously distributed. Because of the temporal and spatial differences, calcium ions entering through the three different pathways are likely to activate different intracellular targets in the postsynaptic cell.
Dopamine Modulates the Responsivity of Mediodorsal Thalamic Cells RecordedIn Vitro
Authors: Lavin A. , Grace A. A.
Published: April 2018

The mediodorsal thalamic nucleus (MD) receives convergent inputs from subcortical limbic structures that overlap with a dopaminergic (DA) innervation. In this study, we describe the effects of DA agonists on the basal and evoked electrophysiological activity of identified thalamic cells of rats recordedin vitro. Administration of the D1 agonist SFK 38393 (10 μm) did not produce a clear effect on the physiological properties of the thalamic cells recorded. In contrast, bath administration of the D2 agonist quinpirole (10 μm) resulted in an enhancement of membrane excitability, facilitation of the occurrence of low-threshold spikes (LTSs), and changes in the resting membrane potential of the thalamic cells tested. The quinpirole-mediated responses were reversed by administration of the D2 antagonist haloperidol. Results from experiments performed with different [K+] and K+channel blockers suggest that the effects of quinpirole are mediated at least in part by changes in K+conductances. The results from this study suggest that DA can modulate the excitability of thalamic cells and in turn may influence the way that the thalamocortical system integrates information.
Anatomic Evidence of a Three-Dimensional Mosaic Pattern of Tonotopic Organization in the Ventral Complex of the Lateral Lemniscus in Cat
Authors: Malmierca Manuel S. , Leergaard Trygve B. , Bajo Victoria M. , Bjaalie Jan G. , Merchán Miguel A.
Published: April 2018

The ventral complex of the lateral lemniscus (VCLL, i.e., the ventral and intermediate nuclei) is composed of cells embedded in the fibers of the lateral lemniscus. These cells are involved in the processing of monaural information and receive input from the collaterals of the fibers ascending to the inferior colliculus. Whereas tonotopic organization is a feature of all other nuclei of the auditory system, this functional principle is debated in the VCLL. We have made focal injections of the tracer biotinylated dextran amine into different frequency band representations of the inferior colliculus in cat. Retrogradely labeled cells and terminal fibers (collaterals of efferent local axons and other ascending lemniscal fibers) were found in the ipsilateral VCLL. The spatial distribution of the labeling was analyzed using three-dimensional (3-D) reconstruction and computer graphical visualization techniques. A complex topographic organization was found. In all cases, labeled fibers and cells were distributed in multiple clusters throughout the dorsoventral extent of the VCLL. The shape, size, and location of the labeled clusters suggest an interdigitation of clusters assigned to different frequency-band representations. But an overall mediolateral distribution gradient was observed, with high frequencies represented medially and lower frequencies progressively more laterally.

We conclude that the clusters may represent discontinuous frequency-band compartments as a counterpart to the continuous laminar compartments in the remaining auditory nuclei. The 3-D orderly mosaic pattern indicates that the VCLL preserves the spectral decomposition originated in the cochlea in a way that facilitates across-frequency integration.
Noradrenergic Excitation of Magnocellular Neurons in the Rat Hypothalamic Paraventricular Nucleus via Intranuclear Glutamatergic Circuits
Authors: Daftary Shabrine S. , Boudaba Cherif , Szabó Kriszta , Tasker Jeffrey G.
Published: April 2018

Noradrenergic projections to the hypothalamus play a critical role in the afferent control of oxytocin and vasopressin release. Recent evidence for intrahypothalamic glutamatergic circuits prompted us to test the hypothesis that the excitatory effect of noradrenergic inputs on oxytocin and vasopressin release is mediated in part by local glutamatergic interneurons. The voltage response to norepinephrine (30–300 μm) was tested with whole-cell recordings in putative magnocellular neurons of the paraventricular nucleus (PVN) in hypothalamic slices (400 μm). Norepinephrine elicited an α1receptor-mediated direct depolarization in 23% of the magnocellular neurons tested; however, the most prominent response, seen in 42% of the magnocellular neurons, was an α1receptor-mediated increase in the frequency of EPSPs. The norepinephrine-induced increase in EPSPs was blocked by tetrodotoxin and by ionotropic glutamate receptor antagonists, suggesting that norepinephrine excited presynaptic glutamate neurons to cause an increase in spike-mediated transmitter release. The increase in EPSPs also was observed in a surgically isolated PVN preparation (64% of cells) and with microdrop applications of norepinephrine (1 mm, 33% of cells) and glutamate (0.5–1 mm, 28%) in the PVN, indicating that the norepinephrine-sensitive presynaptic glutamate neurons are located within the PVN. Biocytin injection and subsequent immunohistochemical labeling revealed that both oxytocin and vasopressin neurons responded to norepinephrine. Our data indicate that magnocellular neurons of the PVN receive excitatory inputs from intranuclear glutamatergic neurons that express α1-adrenoreceptors. These glutamatergic interneurons may serve as an excitatory relay in the afferent noradrenergic control of oxytocin and vasopressin release under certain physiological conditions.
ATP Released from Astrocytes Mediates Glial Calcium Waves
Authors: Guthrie Peter B. , Knappenberger Joshua , Segal Menahem , Bennett Michael V. L. , Charles Andrew C. , Kater S. B.
Published: April 2018

Calcium waves represent a widespread form of intercellular communication. Although they have been thought for a long time to require gap junctions, we recently demonstrated that mouse cortical astrocytes use an extracellular messenger for calcium wave propagation. The present experiments identify ATP as a major extracellular messenger in this system. Medium collected from astrocyte cultures during (but not before) calcium wave stimulation contains ATP. The excitatory effects of medium samples and of ATP are blocked by purinergic receptor antagonists and by pretreatment with apyrase; these same purinergic receptor antagonists block propagation of electrically evoked calcium waves. ATP, applied at the concentration measured in medium samples, evokes responses that are qualitatively and quantitatively similar to those evoked by those medium samples. These data implicate ATP as an important transmitter between CNS astrocytes.
Effect of Zolpidem on Miniature IPSCs and Occupancy of Postsynaptic GABAAReceptors in Central Synapses
Authors: Perrais David , Ropert Nicole
Published: April 2018

GABAA-mediated miniature IPSCs (mIPSCs) were recorded from layer V pyramidal neurons of the visual cortex using whole-cell patch-clamp recording in rat brain slices. At room temperature, the benzodiazepine site agonist zolpidem enhanced both the amplitude (to 138 ± 26% of control value at 10 μm) and the duration (163 ± 14%) of mIPSCs. The enhancement of mIPSC amplitude was not caused by an increase of the single-channel conductance of the postsynaptic receptors, as determined by peak-scaled non-stationary fluctuation analysis of mIPSCs. The effect of zolpidem on fast, synaptic-like (1 msec duration) applications of GABA to outside-out patches was also investigated. The EC50for fast GABA applications was 310 μm. In patches, zolpidem enhanced the amplitude of currents elicited by subsaturating GABA applications (100–300 μm) but not by saturating applications (10 mm). The increase of mIPSC amplitude by zolpidem provides evidence that the GABAAreceptors are not saturated during miniature synaptic transmission in the recorded cells. By comparing the facilitation induced by 1 μmzolpidem on outside-out patches and mIPSCs, we estimated the concentration of GABA seen by the postsynaptic GABAAreceptors to be ∼300 μmafter single vesicle release. We have estimated a similar degree of receptor occupancy at room and physiological temperature. However, at 35°C, zolpidem did not enhance the amplitude of mIPSCs or of subsaturating GABA applications on patches, implying that, in these neurons, zolpidem cannot be used to probe the degree of receptor occupancy at physiological temperature.
Chronic Antidepressant Administration Increases the Expression of cAMP-Specific Phosphodiesterase 4A and 4B Isoforms
Authors: Takahashi Michihiro , Terwilliger Rose , Lane Caryl , Mezes Peter S. , Conti Marco , Duman Ronald S.
Published: April 2018

The influence of chronic antidepressant administration on expression of the three major phosphodiesterase (PDE) 4 subtypes found in brain (PDE4A, PDE4B, and PDE4D) was examined. The treatments tested included representatives of four major classes of antidepressants: selective reuptake inhibitors of serotonin (sertraline and fluoxetine) or norepinephrine (desipramine), a monoamine oxidase inhibitor (tranylcypromine), and electroconvulsive seizure. Expression of PDE4A and PDE4B, but not PDE4D, mRNA and immunoreactivity were significantly increased in rat frontal cortex by chronic administration of each of the four classes of antidepressants. We also found that antidepressant administration significantly increased the expression of PDE4B mRNA in the nucleus accumbens, a brain region thought to mediate pleasure and reward that could also contribute to the anhedonia often observed in depressed patients. In contrast, expression of PDE4A and PDE4B were not influenced by short-term treatment (1 or 7 d) and were not influenced by chronic administration of nonantidepressant psychotropic drugs (cocaine or haloperidol), demonstrating the time dependence and pharmacological specificity of these effects. Upregulation of PDE4A and PDE4B may represent a compensatory response to antidepressant treatment and activation of the cAMP system. The possibility that targeted inhibition of these PDE4 subtypes may produce an antidepressant effect is discussed.
Neuronal Acetylcholine Receptors with α7 Subunits Are Concentrated on Somatic Spines for Synaptic Signaling in Embryonic Chick Ciliary Ganglia
Authors: Shoop Richard D. , Martone Maryann E. , Yamada Naoko , Ellisman Mark H. , Berg Darwin K.
Published: April 2018

Nicotinic acetylcholine receptors containing α7 subunits are widely distributed in the vertebrate nervous system. In the chick ciliary ganglion such receptors generate large synaptic currents but appear to be excluded from postsynaptic densities on the cells. We show here that α7-containing receptors are concentrated on somatic spines in close proximity to putative sites of presynaptic transmitter release. Intermediate voltage electron microscopy on thick sections, together with tomographic reconstruction, permitted three-dimensional analysis of finger-like projections emanating from cell bodies. The projections were identified as spines based on their morphology, cytoskeletal content, and proximity to presynaptic elements. Bothin situand after ganglionic dissociation, the spines were grouped on the cell surface and tightly folded into mats. Immunogold labeling of receptors containing α7 subunits showed them to be preferentially concentrated on the somatic spines. Postsynaptic densities were presentin vivoboth on the soma near spines and occasionally on the spines themselves. Synaptic vesicle-filled projections from the presynaptic calyx were interdigitated among the spines. Moreover, the synaptic vesicles often abutted the membrane and sometimes included Ω profiles as if caught in an exocytotic event, even when no postsynaptic densities were juxtaposed on the spine. The results suggest several mechanisms for delivering transmitter to α7-containing receptors, and they support new ideas about synaptic signaling via spines. They also indicate that neurons must have specific mechanisms for targeting α7-containing receptors to desired locations.
Polysialic Acid Facilitates Migration of Luteinizing Hormone-Releasing Hormone Neurons on Vomeronasal Axons
Authors: Yoshida Keiko , Rutishauser Urs , Crandall James E. , Schwarting Gerald A.
Published: April 2018

Luteinizing hormone-releasing hormone (LHRH) neurons migrate from the olfactory placode to the forebrain in association with vomeronasal nerves (VNN) that express the polysialic acid-rich form of the neural cell adhesion molecule (PSA-NCAM). Two approaches were used to investigate the role of PSA-NCAM: injection of mouse embryos with endoneuraminidase N, followed by the analysis of LHRH cell positions, and examination of LHRH cell positions in mutant mice deficient in the expression of NCAM or the NCAM-180 isoform, which carries nearly all PSA in the brain. The enzymatic removal of PSA at embryonic day 12 significantly inhibited the migration of nearly half of the LHRH neuron population, without affecting the VNN tract itself. Surprisingly, the absence of NCAM or NCAM-180 did not produce this effect. However, a shift in the route of migration, resulting in an excess number of LHRH cells in the accessory olfactory bulb, was observed in the NCAM-180 mutant. Furthermore, it was found that PSA expressed by the proximal VNN and its distal branch leading to the accessory bulb, but not the branch leading to the forebrain, was associated with the NCAM-140 isoform and thus was retained in the NCAM-180 mutant. These results provide two types of evidence that PSA-NCAM plays a role in LHRH cell migration: promotion of cell movement along the VNN tract that is sensitive to acute (enzymatic), but not chronic (genetic), removal of PSA-NCAM, and a preference of a subset of migrating LHRH cells for a PSA-positive axon branch over a PSA-negative branch in the NCAM-180 mutant.
Peripheral Inflammation Facilitates Aβ Fiber-Mediated Synaptic Input to the Substantia Gelatinosa of the Adult Rat Spinal Cord
Authors: Baba Hiroshi , Doubell Timothy P. , Woolf Clifford J.
Published: April 2018

Whole-cell patch-clamp recordings were made from substantia gelatinosa (SG) neurons in thick adult rat transverse spinal cord slices with attached dorsal roots to study changes in fast synaptic transmission induced by peripheral inflammation. In slices from naive rats, primary afferent stimulation at Aβ fiber intensity elicited polysynaptic EPSCs in only 14 of 57 (25%) SG neurons. In contrast, Aβ fiber stimulation evoked polysynaptic EPSCs in 39 of 62 (63%) SG neurons recorded in slices from rats inflamed by an intraplantar injection of complete Freund’s adjuvant (CFA) 48 hr earlier (p< 0.001). Although the peripheral inflammation had no significant effect on the threshold and conduction velocities of Aβ, Aδ, and C fibers recorded in dorsal roots, the mean threshold intensity for eliciting EPSCs was significantly lower in cells recorded from rats with inflammation (naive: 33.2 ± 15.1 μA,n= 57; inflamed: 22.8 ± 11.3 μA,n= 62,p< 0.001), and the mean latency of EPSCs elicited by Aβ fiber stimulation in CFA-treated rats was significantly shorter than that recorded from naive rats (3.3 ± 1.8 msec,n= 36 vs 6.0 ± 3.5 msec,n= 12;p= 0.010). Aβ fiber stimulation evoked polysynaptic IPSCs in 4 of 25 (16%) cells recorded from naive rat preparations and 14 of 26 (54%) SG neurons from CFA-treated rats (p< 0.001). The mean threshold intensity for IPSCs was also significantly lower in CFA-treated rats (naive: 32.5 ± 15.7 μA,n= 25; inflamed: 21.9 ± 9.9 μA,n= 26,p= 0.013). The facilitation of Aβ fiber-mediated input into the substantia gelatinosa after peripheral inflammation may contribute to altered sensory processing.
Characterization of G-Protein-Gated K+Channels Composed of Kir3.2 Subunits in Dopaminergic Neurons of the Substantia Nigra
Authors: Inanobe Atsushi , Yoshimoto Yukiko , Horio Yoshiyuki , Morishige Ken-Ichiro , Hibino Hiroshi , Matsumoto Shigeto , Tokunaga Yoshimitsu , Maeda Toshihiro , Hata Yutaka , Takai Yoshimi , Kurachi Yoshihisa
Published: April 2018

G-protein-gated K+(KG) channels generate slow inhibitory postsynaptic potentials in the brain. Current opinion suggests that neuronal KGchannels are heterotetramers of Kir3.1 and Kir3.2. In substantia nigra (SN), however, mRNA of Kir3.1 does not express, whereas that of Kir3.2 clearly does. Therefore, we have characterized the KGchannels containing Kir3.2 subunits in SN using biochemical and immunological techniques. We found that they were composed of only Kir3.2 subunits and did not contain significant amounts of either Kir3.1 or Kir3.3. Furthermore, at least some of the KGchannels in SN were assemblies of the splicing variants Kir3.2a and Kir3.2c. The channels were localized specifically at the postsynaptic membrane on the dendrites of dopaminergic neurons. Kir3.2c, but not Kir3.2a, could bind a PDZ domain-containing protein, PSD-95. The heterologously expressed KGchannels composed of Kir3.2a plus Kir3.2c or Kir3.2a alone were activated by G-protein stimulation, but expression of Kir3.2c alone was not. This study reveals that the Kir3.2 splicing variants play distinct roles in the control of function and localization of some of the KGchannels in dopaminergic neurons of SN.