bluuebunny/crossref_metadata_2025 huggingface dataset:
Isoproterenol potentiates synaptic transmission primarily by enhancing presynaptic calcium influx via P- and/or Q-type calcium channels in the rat amygdala
Authors: Huang CC , Hsu KS , Gean PW
Published: April 2018

The effects of selective beta-adrenergic receptor agonist isoproterenol (Iso) on neuronal excitability and synaptic transmission were investigated in brain slices of rat amygdala. Iso (15 microM) produced a long-lasting enhancement of the EPSP that was not blocked by pretreatment with 20 microM D-2-amino-5-phosphonovalerate (D-APV) alone or D-APV in combination with kynuretic acid (1 mM). The sensitivity of postsynaptic neurons to the glutamate receptor agonist AMPA was unchanged by Iso pretreatment. Superfusion of Iso reversibly blocked the after-hyperpolarization (AHP) that followed a depolarizing current pulse and caused more action potential firing. Intracellular application of a selective inhibitor of the catalytic subunit of cAMP- dependent protein kinase A blocked the effect of Iso on the AHP, whereas Iso-induced potentiation was entirely normal in the same neuron. In addition, Iso decreased the magnitude of paired-pulse facilitation, which is consistent with a presynaptic mode of action. Substituting the Mg2+ for Ca2+ in the medium completely abolished the Iso-induced enhancement of the EPSP. The effect of Iso also was blocked by low concentrations of omega-agatoxin-IVA, but not by nifedipine or omega-conotoxin-GVIA. These results suggest that Iso enhances synaptic transmission in the amygdala via a presynaptic site of action: the mechanism underlying the potentiating effect likely is attributable to an increased Ca2+ influx through P- and/or Q-type Ca2+ channels.
Nimodipine accelerates axonal sprouting after surgical repair of rat facial nerve
Authors: Angelov DN , Neiss WF , Streppel M , Andermahr J , Mader K , Stennert E
Published: April 2018

Facial-facial anastomosis (FFA), i.e., suture of transected facial nerve, was performed in adult Wistar rats. For 10–112 d post-operation (DPO), half of the animals received standard food (placebo) and half received food pellets containing 1000 ppm nimodipine, a Ca2+ channel blocker. The time course of mimetic reinnervation between these two groups was compared by counting all retrogradely labeled motoneurons after injection of horseradish peroxidase (HRP) into the whiskerpad. In unoperated animals, injection of HRP labeled 1280 +/- 113 motoneurons. After FFA, this number dropped to zero, and the first HRP-labeled facial motoneurons reappeared in both placebo- and nimodipine-treated animals at 14 DPO. The treatment with nimodipine yielded two beneficial effects. (1) It accelerated axonal sprouting until 28 DPO. Whereas the number of HRP-labeled cells in the placebo group was 171 +/- 9 (mean +/- SD) at 16 DPO, 372 +/- 43 at 21 DPO, and 636 +/- 187 at 28 DPO, the number of sprouted motoneurons in nimodipine-treated rats was twice as high: 386 +/- 34 at 16 DPO, 620 +/- 28 at 21 DPO, and 756 +/- 257 at 28 DPO. (2) Nimodipine reduced the polyneuronal innervation of the target muscles. Whereas the number of HRP-labeled cells in the placebo group increased to 1430 +/- 36 at 56 DPO and 1600 +/- 31 at 112 DPO, the number of labeled motoneurons in nimodipine-treated rats remained almost within the normal range: 1315 +/- 31 at 56 DPO and 1354 +/- 33 at 112 DPO.
The onconeural antigen Nova-1 is a neuron-specific RNA-binding protein, the activity of which is inhibited by paraneoplastic antibodies
Authors: Buckanovich RJ , Yang YY , Darnell RB
Published: April 2018

Nova-1, a protein expressed in tumors and neurons, is a target antigen in a human paraneoplastic motor disorder [paraneoplastic opsoclonus- myoclonus ataxia (POMA)]. We evaluated the relationship between the function of Nova-1 and its role as a disease antigen. We show that Nova- 1 is a neuron-specific RNA-binding protein with sequence and functional similarities to FMR-1. Nova-1 mRNA is restricted to the subcortical nervous system, and the protein binds to RNA with high affinity. Nova-1 KH domains mediate this RNA binding, and point mutations within them abrogate binding. POMA disease antisera (6/6) recognize the third KH domain but not an inactive point mutant, and affinity-purified antibody blocks Nova-1 RNA binding. Thus, a cardinal feature of POMA is the production of antibodies that inhibit Nova-1-RNA interactions, suggesting such inhibition may cause the neurological disease.
Cell cycle blockers mimosine, ciclopirox, and deferoxamine prevent the death of PC12 cells and postmitotic sympathetic neurons after removal of trophic support
Authors: Farinelli SE , Greene LA
Published: April 2018

In the present study, we tested whether apoptotic neuronal death caused by withdrawal of trophic support might be prevented by agents that block cell cycle progression. We used three complementary model systems that exhibit apoptotic death: dividing PC12 cells deprived of nerve growth factor (NGF); and primary cultures of postmitotic sympathetic neurons deprived of NGF. We show that cell death in each case can be suppressed by treatment with the G1/S blockers mimosine, ciclopirox, and deferoxamine at concentrations that correlate with their abilities to block PC12 cell proliferation. In contrast, agents that block cell cycle progression in the S-, G2-, or M-phase do not prevent cell death. These observations support the hypothesis that removal of trophic support from dividing or postmitotic neuronal cells provokes their apoptotic death by causing them either to proceed through or to attempt to re-enter an uncoordinated and consequently fatal cell cycle. Moreover, the data suggest that simply blocking the cycle at any point is not protective but, rather, that it is necessary to block at specific “safe” points. This study defines a safe point in the cell cycle before the G1/S transition that is demarcated by the action of these three agents.
Dorsal spinocerebellar tract neurons in the chronic intact cat during wakefulness and sleep: analysis of spontaneous spike activity
Authors: Soja PJ , Fragoso MC , Cairns BE , Jia WG
Published: April 2018

Relatively little is known about the transmission of ascending sensory information from lumbar levels across the behavioral states of sleep and wakefulness. The present study used extracellular recording methods in chronically instrumented intact behaving cats to monitor the activity of lumbar dorsal spinocerebellar tract (DSCT) neurons within Clarke's column during the states of wakefulness, quiet sleep, and active sleep. Clarke's column DSCT neurons were identified using antidromic identification and retrograde labeling techniques. The spontaneous spike rate and interspike interval data of DSCT neurons were quantified as a function of behavioral state. During wakefulness and quiet sleep, the spike rate of DSCT neurons was stable, and interspike interval histograms (ISIH) indicated a relatively high degree of regularity in DSCT neuronal spike train patterns. In contrast, during active sleep there was a marked reduction in the ongoing spike rate in a vast majority of cells tested. The magnitude of change in ISIHs and interspike interval data during active sleep depended in part on whether the reduction in cell firing was maintained or periodic throughout active sleep. Further suppression of spontaneous activity also was observed during intense rapid-eye-movement episodes of active sleep that were associated with clustered pontogeniculo- occipital wave and muscular twitches and jerks. After re-awakening, spontaneous spike activity of Clarke's column DSCT neurons resembled that recorded during previous episodes of wakefulness. These data provide evidence that ascending proprioceptive and exteroceptive sensory transmission through Clarke's column is diminished during the behavioral state of active sleep.
Loss of the p53 tumor suppressor gene protects neurons from kainate- induced cell death
Authors: Morrison RS , Wenzel HJ , Kinoshita Y , Robbins CA , Donehower LA , Schwartzkroin PA
Published: April 2018

The tumor suppressor gene p53 recently has been associated with the induction of cell death in response to some forms of cellular damage. A possible role for p53-related modulation of neuronal viability has been suggested by the finding that p53 expression is increased in damaged neurons in models of ischemia and epilepsy. We evaluated the possibility that p53 expression (in knockout mice) is required for induction of cell damage in a model of seizure activity normally associated with well defined patterns of cell loss. Subcutaneous injection of kainic acid, a potent excitotoxin, induced comparable seizures in both wild-type mice (+/+) and mice deficient in p53 (-/-). Using a silver impregnation technique to examine neurodegeneration in animals killed 7 d after kainate injection, we found that a majority of +/+ mice exhibited extensive cell loss in the hippocampus, involving subregions CA1, CA3, the hilus, and the subiculum. Apoptotic cell death, as identified with an in situ nick end labeling technique to detect DNA fragmentation, was confirmed in CA1- but not CA3- degenerating neurons. In marked contrast, a majority of p53 -/- mice displayed no signs of cell damage; in the remaining p53 -/- mice, damage was mild to moderate and was confined almost entirely to cells in CA3b of the dorsal hippocampus. In +/+ mice, but not in -/- mice, damaged neurons also were observed in the amygdala, piriform cortex, cerebral cortex, caudate-putamen, and thalamus after kainate treatment. The pattern and extent of damage in mice heterozygous for p53 (+/-) were identical to those seen in +/+ mice, suggesting that a single copy of p53 is sufficient to confer neuronal vulnerability. These results demonstrate that p53 influences viability in multiple neuronal subtypes and brain regions after excitotoxic insult.
Localization and active transport of mRNA in axons of sympathetic neurons in culture
Authors: Olink-Coux M , Hollenbeck PJ
Published: April 2018

In neurons, the establishment and maintenance of distinct somatic, dendritic, and axonal domains has long been known to rely on regulated traffic of organelles and proteins. More recently, the local targeting of specific mRNAs has also been demonstrated, at least in dendrites, to provide a local supply of specific proteins. Here we set out to test directly for the presence of mRNA in axons of cultured chick sympathetic neurons, to examine their distribution during axonal outgrowth, to determine the reliance of this distribution on specific cytoskeletal elements, and to assess whether the axonal and somatic mRNA complements differ. Using fluorescent in situ hybridization, we found that sympathetic axons do contain poly(A+) mRNA along their length in a pattern that changes gradually as axons elongate, from an evenly dispersed punctate distribution with strong growth cone staining to a distribution focused at branch points, varicosities, and some growth cones. Selective perturbations of the cytoskeleton revealed that the presence of axonal mRNA was dependent on microtubules (MTs), but not actin filaments, indicating that mRNA transport and/or anchoring within the axon are active processes involving MTs. Finally, reverse transcription-PCR amplification of RNAs from the axonal and somatic compartments showed that beta-actin mRNA was present in both compartments, whereas mRNA encoding alpha-tubulin was restricted to the somatic compartment and entirely absent from the axons. Thus, the mRNA populations in the soma versus the axon are both quantitatively and qualitatively different, and these neurons are able to direct specific mRNAs to the axon.
Calcium dependence of large dense-cored vesicle exocytosis evoked by calcium influx in bovine adrenal chromaffin cells
Authors: Engisch KL , Nowycky MC
Published: April 2018

We used the perforated-patch technique to examine the relationship between Ca2+ entry and exocytosis of large dense-cored vesicles in bovine adrenal chromaffin cells. Exocytosis evoked by single-step depolarizations was monitored by capacitance detection. Ca2+ entry was varied by changing external calcium concentration, stepping to different test potentials, depolarizing for different durations, or applying blockers of specific calcium channel subtypes. Regardless of protocol, the amount of exocytosis was strictly related to the integral of the voltage-clamped calcium current, raised to a power of approximately 1.5. Thus, despite the complexities of transient and nonuniform changes in submembrane calcium concentration produced by voltage-gated calcium entry, the calcium dependence of large dense- cored vesicle fusion under conditions of minimal stimulation is well approximated by a simple transfer function of summed calcium entry.
Nitric oxide and carbon monoxide activate locus coeruleus neurons through a cGMP-dependent protein kinase: involvement of a nonselective cationic channel
Authors: Pineda J , Kogan JH , Aghajanian GK
Published: April 2018

Nitric oxide (NO) and carbon monoxide (CO) have been identified as two diffusible signaling messengers in the brain, capable of stimulating soluble guanylate cyclase. Locus coeruleus (LC) is rich in the alpha 1 and beta 1 subunits of soluble guanylate cyclase. Therefore, the possible role of the cGMP pathway in the regulation of LC neurons was investigated with electrophysiological techniques in rat brain slices. Bath application of various NO donors or CO-containing solutions increased the firing rate of most LC neurons. This activation was reversed by the NO scavenger hemoglobin, but not by methemoglobin. Bath or intracellular application of selective activators of cGMP-dependent protein kinase also caused increases in LC cell firing rate. The actions of NO donors and kinase activators were mutually occlusive and reversed by H8, an inhibitor of the cGMP-dependent protein kinase. Hemoglobin and H8 reduced the firing rate of LC neurons, but no change was found with inhibitors or activators of the NO synthase. In intracellular and whole-cell recordings, NO effect was associated with an inward current and an increase in the input conductance (mean reversal potential = -27 mV); these effects were abolished using a low- sodium buffer. Spontaneous EPSCs of LC cells were not modified with the NO donor administration. Taken together, these data suggest that NO and CO activate noradrenergic neurons of LC via a cGMP-dependent protein kinase and a nonselective cationic channel. It also is proposed that these effects occur at the postsynaptic level and that there may be a tonic regulation of LC neuronal firing by the cGMP pathway.
Xenopus spinal neurons express Kv2 potassium channel transcripts during embryonic development
Authors: Burger C , Ribera AB
Published: April 2018

Developmentally regulated delayed rectifier potassium currents determine the waveform of the action potential in all Xenopus embryonic primary spinal neurons. To examine this developmental program at the molecular level, we have isolated Xenopus Kv2 potassium channel genes Kv2.1 and Kv2.2. Both genes induce functional heterologous expression of delayed rectifier potassium currents. Transcripts from both Kv2 genes are present in developing embryos; however, only Kv2.2 mRNA is detectable in embryonic spinal neurons. Notably, Kv2.2 transcripts localize to ventral spinal neurons, whereas previously described Kv1.1 transcripts are found in dorsal spinal neurons. Thus, spinal neuron subtypes express distinct potassium channel genes, yet they temporally coordinate functional expression of delayed rectifier potassium currents.
Neuropeptide Y1 receptors inhibit N-type calcium currents and reduce transient calcium increases in rat dentate granule cells
Authors: McQuiston AR , Petrozzino JJ , Connor JA , Colmers WF
Published: April 2018

Neuropeptide Y (NPY) is far more abundant in the dentate gyrus than elsewhere in the hippocampal formation, but it does not alter the synaptic excitation of dentate granule cells (DGCs) as it does for pyramidal cells in areas CA1 and CA3. NPY inhibited depolarization- induced increases in intracellular Ca2+ concentrations ([Ca2+]i) in DGCs in hippocampal slices, without altering the resting [Ca2+]i. NPY inhibited Ca2+ currents (ICa) via a Y1 receptor in 84% of acutely isolated DGCs and via a Y2 receptor in 31% of the NPY-responsive cells tested. ICa inhibition was completely occluded by omega-conotoxin-GVIA but not by nimodipine. The inhibition of ICa was accompanied by a change in the time course of ICa activation in only 27% of NPY- responsive cells. Only 23% of DGCs responded to NPY when Ba2+ was substituted for extracellular Ca2+ and when [Ca2+]i was strongly buffered. Therefore, NPY inhibits an N-type ICa in DGCs, mainly via Y1 receptors. Furthermore, it seems that more than one mechanism, one of which may be sensitive to [Ca2+]i, may couple NPY receptors to the Ca2+ channels in DGCs. Because the release of dynorphin from DGCs depends in part on N-type currents, NPY receptors are poised to regulate the release of opioid peptides from DGC somata and dendrites.
NMDA receptor activation-responsive phosphoproteins in the developing optic tectum
Authors: Scheetz AJ , Constantine-Paton M
Published: April 2018

A front phosphorylation assay followed by two-dimensional gel electrophoresis was used to detect proteins in the tadpole optic tectum, the phosphorylation state of which is regulated by NMDA receptor activation. Five proteins with isoelectric points between 4 and 7 displayed marked increases in their phosphorylation state in response to application of 10 microM glutamate and 50 microM NMDA. This response was inhibited by 60 microM 2-amino-5-phosphopentanoic acid. These proteins are termed NMDA receptor activation-responsive phosphoproteins (NARPPs). Two NARPPs were identified as both in vitro and in vivo substrates for protein kinase C. Of these two NARPPs, one was located in the postsynaptic density (NARPP-50), and one was located in the nuclear fraction (NARPP-21). Phosphorylation of NARPP-21 was also induced by application of the metabotropic glutamate receptor agonist trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid (trans- ACPD) (100 microM). Phosphorylation of all NARPPs was eliminated by dantrolene, which inhibits release of calcium from intracellular stores. In adult tecta, only NARPP-21 and -50 were phosphorylation. Thus the phosphorylation state of most NARPPs is regulated differently when synaptic plasticity is low. Further characterization of NARPPs should lead to identification of second messenger systems involved in NMDA receptor signaling and developmental synaptic plasticity.
Association of beta 1 integrin with phosphotyrosine in growth cone filopodia
Authors: Wu DY , Wang LC , Mason CA , Goldberg DJ
Published: April 2018

Filopodia of growth cones are key elements in the transduction of extracellular cues that guide axon growth during development. How they are specialized to carry out this role is poorly understood. We previously had found tyrosine phosphorylated protein to be heavily concentrated at the tips of many filopodia of Aplysia growth cones in certain culturing conditions, suggesting that tyrosine phosphorylation might be involved in filopodial specialization. Immunocytochemistry was used to analyze the protein composition of the tip aggregates to determine whether there was an association of the tip phosphorylation with any important extracellular cue. beta 1 integrin, a subunit of the receptor for laminin-type neurite growth promoters, coconcentrated with phosphotyrosine at filopodial tips of both Aplysia and mouse growth cones. Several observations indicated that the association of beta 1 integrin with phosphotyrosine is close. beta 1 integrin and phosphotyrosine are known to colocalize at focal contacts, sites of adhesion of cells to the extracellular matrix, but the composition and behavior of the tip aggregates mark them as distinct structures. Also found in the tip aggregates was a member of the ezrin-radixin-moesin family of proteins, which are thought to link membrane proteins to submembranous bundles of actin filaments. Use of an inhibitor of protein-tyrosine kinases to deplete tip phosphotyrosine also caused disappearance of beta 1 integrin from the tip, suggesting a role for tyrosine phosphorylation in facilitating interaction of growth cones with certain environmental cues by fostering the aggregation of receptors in filopodia.
Histaminergic descending inputs to the mesopontine tegmentum and their role in the control of cortical activation and wakefulness in the cat
Authors: Lin JS , Hou Y , Sakai K , Jouvet M
Published: April 2018

We have demonstrated previously the importance of histaminergic neurons in arousal mechanisms. In addition to their ascending axons, these neurons also send heavy descending inputs to the mesopontine tegmentum (MPT), which plays a key role in cortical activation during wakefulness (W). This anatomical link suggests histaminergic control of the mechanisms of the MPT relevant to behavioral states. In this study, we sought to demonstrate, at the light microscopy level, hypothalamotegmental histaminergic pathways and their topographical interaction with MPT neurons in the cat and to explore further their involvement in sleep-wake control. Using immunohistochemistry of histamine (HA), either alone or together with that of choline- acetyltransferase or tyrosine hydroxylase, a large number of very fine, short and varicose HA-positive fibers and terminal-like dots were detected in the MPT, including the laterodorsal tegmental nucleus, locus coeruleus (LC), LC alpha, and peri-LC alpha. Furthermore, these fibers and terminal-like structures were found in close proximity to a great number of cholinergic or noradrenergic neurons. We also investigated the effects of microadministration of HA agonists and antagonist into the mediodorsal pontine tegmentum on the cortical electroencephalogram (EEG) power spectra and the sleep-wake cycle in freely moving cats. Microinjection of HA or 2-thiazolylethylamine (an H1-receptor agonist) caused a long-lasting suppression of cortical slow activity and an increase in quiet wakefulness (W). Paradoxical sleep, however, was less affected. The effects of HA were attenuated by systemic or in situ pretreatment with mepyramine (an H1-receptor antagonist), which when injected alone produced an increase in slow wave sleep. Microinjection of impromidine (an H2-receptor agonist) into the same area had no effect on either the cortical EEG or W. Because MPT ascending and presumed cholinergic neurons discharge tonically during cortical activation of W and because HA causes excitation of MPT cholinergic neurons via H1 receptors, we hypothesize that the histaminergic descending afferents in the MPT would promote cortical desynchronization and W, at least partially, via activation of H1 receptors situated on cholinergic neurons and that the interactions between histaminergic and cholinergic neurons constitute an important circuit in cortical activation during W.
Psychostimulants depress excitatory synaptic transmission in the nucleus accumbens via presynaptic D1-like dopamine receptors
Authors: Nicola SM , Kombian SB , Malenka RC
Published: April 2018

The effects of dopamine (DA) and the psychostimulants cocaine and amphetamine on excitatory transmission in the nucleus accumbens (NAc) were examined in rat NAc slices using both extracellular-field and whole-cell patch-clamp recording. DA, cocaine, and amphetamine reversibly reduced the excitatory synaptic responses (EPSPs/EPSCs) elicited by stimulation of prelimbic cortical afferents. DA and amphetamine increased paired-pulse facilitation, reduced the frequency of spontaneous miniature EPSCs (mEPSCs), and had no effect on mEPSC amplitude, suggesting a presynaptic mechanism for the observed reduction in excitatory synaptic transmission. The effects of DA and amphetamine were attenuated by the D1 receptor antagonist SCH23390 but not by the D2 receptor antagonist sulpiride. The broad-spectrum DA receptor agonist 6,7-ADTN mimicked the effects of DA and the psychostimulants, but neither the D1 receptor agonists SKF38393 and SKF81297 nor the D2 receptor agonist quinpirole caused a significant reduction in EPSP magnitude. SKF38393 at a higher concentration (100 microM) was effective in reducing the EPSP, however, and this reduction was sensitive to SCH23390. There was no difference in the effects of DA in cells from mutant mice lacking D1a receptors and cells from wild- type control mice. Unilaterally lesioning the dopaminergic afferents to the NAc using 6-hydroxydopamine attenuated the amphetamine-induced reduction in EPSP magnitude in slices from the lesioned hemisphere but not the control (unlesioned) hemisphere. These results indicate that DA and psychostimulants (acting indirectly by increasing endogenous extracellular DA levels) reduce excitatory synaptic transmission in the NAc by activating presynaptic DA receptors with D1-like properties.
Nitric oxide and peptide neurohormones activate cGMP synthesis in the crab stomatogastric nervous system
Authors: Scholz NL , Goy MF , Truman JW , Graubard K
Published: April 2018

In the neural circuits that comprise the crustacean stomatogastric nervous system (STNS), synaptically delivered neurotransmitters and circulating neurohormones elicit a wide range of rhythmic motor outputs. However, functional roles for second messengers in this system are poorly understood. Here we demonstrate two different signaling pathways that control the synthesis of 3′,5′-cGMP in the crab STNS. One pathway is activated by nitric oxide (NO) and is mediated by a cytoplasmic guanylate cyclase. A second pathway is stimulated by peptide-containing extracts from a crab neurohemal organ that activate a membrane-associated guanylate cyclase. Using whole-mount immunocytochemistry to localize individual cGMP-containing cells, we find that NO elevates intracellular cGMP in a small subset of STNS neurons. Immunopositive cells are found predominantly in the stomatogastric ganglion, with a few additional cells located in the oesophageal and commissural ganglia. Crab tissues differ in their sensitivities to NO and to the peptide-containing extract. The NO- mediated pathway is apparently restricted to the nervous system, whereas the peptidemediated pathway is present in every tissue tested. The results of these experiments demonstrate that multiple signaling pathways involving cGMP are present in the STNS and suggest that this second messenger may help control the metabolic and physiological status of these motor circuits.
Contributions of calcium-dependent and calcium-independent mechanisms to presynaptic inhibition at a cerebellar synapse
Authors: Dittman JS , Regehr WG
Published: April 2018

Activation of either adenosine A1 receptors or GABAB receptors inhibits many excitatory synapses in the mammalian brain. However, the extent to which different mechanisms contribute to such synaptic modulation is unclear. We examined the manner in which activation of adenosine A1 receptors and GABAB receptors modulates synaptic strength at the granule cell to Purkinje cell synapse in rat cerebellar slices. Optical determination of presynaptic calcium influx revealed that presynaptic calcium channels were modulated by 2-chloroadenosine (2CA) and baclofen, agonists of the adenosine A1 receptor and the GABAB receptor, respectively. 2CA and baclofen differentially affected three classes of calcium channels without altering the shape of the presynaptic volley, suggesting that changes in presynaptic waveform do not contribute significantly to synaptic modulation. 2CA affected neither the amplitude nor the frequency of spontaneous miniature postsynaptic currents, whereas baclofen reduced the frequency by approximately 40% without affecting the amplitude. In addition, 2CA and baclofen do not change either fiber excitability or presynaptic residual calcium. Taken together, our data indicate that activation of the adenosine A1 receptor reduces synaptic strength by modulating presynaptic calcium channels. Baclofen modulates presynaptic calcium channels as well but also affects release processes downstream from calcium entry.
Characterization of an M-like current modulated by thyrotropin- releasing hormone in normal rat lactotrophs
Authors: Sankaranarayanan S , Simasko SM
Published: April 2018

In rat pituitary lactotrophs, a component of thyrotropin-releasing hormone (TRH)-induced prolactin secretion is dependent on extracellular calcium and is associated with an increase in action-potential firing. The mechanism underlying the TRH-induced increase in firing frequency was investigated using the perforated-patch variation of the whole-cell patch-clamp technique. TRH was found to inhibit a voltage-dependent, noninactivating K+ current that was similar to M-currents originally identified in neurons. The TRH-modulated M-like current started to activate at approximately -60 mV and had a V0 of -28 mV and thus would be active under the normal resting potentials of lactotrophs (-35 to - 45 mV). Exponential fits to deactivating tail currents revealed a fast and a slow component. The deactivation rates of the M-like current and the ratio of the fast to the slow component of deactivation were found to increase with more hyperpolarized potentials. In addition, increasing the duration of command potentials led to the conversion of the fast component to the slow component of deactivation. The M-like current in lactotrophs was partially sensitive to 4-aminopyridine and tetraethylammonium. TRH inhibition of this current was associated with acceleration of deactivation rates and a depolarizing shift in the voltage of activation (V0 = -17 mV). The effect of TRH on the M-like current was lost in whole-cell voltage-clamp conditions, suggesting the requirement of an important cytosolic component that mediates the effect of TRH.
DNA damage and apoptosis in Alzheimer's disease: colocalization with c- Jun immunoreactivity, relationship to brain area, and effect of postmortem delay
Authors: Anderson AJ , Su JH , Cotman CW
Published: April 2018

Many neurons in Alzheimer's disease (AD) exhibit terminal deoxynucleotidyl transferase (TdT) labeling for DNA strand breaks with a distribution suggestive of apoptosis. We have shown previously that immunoreactivity for c-Jun is elevated in AD and found in association with neuronal pathology. In addition, cultured neurons undergoing beta- amyloid-mediated apoptosis exhibit a selective and prolonged induction of c-Jun. Consequently, we conducted double-labeling experiments to examine whether c-Jun is associated with DNA strand breaks in AD tissue; we observed a strong colocalization between these markers. As would be predicted based on the distribution of AD pathology, we also found that TdT labeling was prominent in the entorhinal cortex, but absent or at very low levels in cerebellum. Furthermore, we confirmed that postmortem delay (PMD) does not affect TdT labeling within the limits used for tissue used in this study. However, in contrast to previous studies, we report an increase in TdT labeling with more extended PMDs. Finally, gel electrophoresis of genomic DNA isolated from AD and control cases failed to reveal evidence for either an apoptotic or a necrotic mechanism of cell death in AD, possibly because of a low number of cells actually undergoing cell death at any given time. Our findings support the hypothesis that DNA damage labeled using TdT reflects neuronal vulnerability and cell loss associated with AD pathology, and that at least a portion of the cells labeled with this technique is undergoing apoptosis. Furthermore, in agreement with in vitro findings, these results suggest a relationship between the expression of c-Jun and neuronal risk and/or cell death in AD.
Effects of denervation on acetylcholine receptor clusters on frog cardiac ganglion neurons as revealed by quantitative laser scanning confocal microscopy
Authors: Horch HL , Sargent PB
Published: April 2018

We examined the effects of denervation on clusters of nicotinic acetylcholine receptors (AChRs) on autonomic neurons in the frog heart using immunofluorescence techniques and laser scanning confocal microscopy. We showed previously that normally innervated neurons have both large, brightly stained AChR clusters and small, dim AChR clusters. A majority (80%) of the large/bright AChR clusters are located at synaptic sites, whereas the small/dim clusters are distributed widely over the cell surface. Here, we use image analysis to identify these two classes of clusters on images generated from stacks of optical sections through neuronal cell bodies and to examine the effects of denervation on their number, size, and brightness (pixel intensity). Denervation reduces the number of large/ bright AChR clusters per cell to < 10% of sham-operated values and increases the number of small/dim clusters per cell by two- to threefold. These changes occur at 4 d of denervation, the earliest time examined, and are sustained for 6 weeks. The size of large/bright AChR clusters is decreased compared with sham-operated controls, and their brightness is unchanged. The size of small/dim AChR clusters is unchanged by denervation, but their brightness is increased. Denervation results in a shift in the contribution of each AChR cluster class to the total measurable AChR pool-from one dominated by large/bright clusters to one dominated by small/dim clusters. These results show that the nerve terminals on cardiac ganglion neurons appear to exert a continual and reversible influence on the organization of the postsynaptic membrane.
Clustered voltage-gated Na+ channels in Aplysia axons
Authors: Johnston WL , Dyer JR , Castellucci VF , Dunn RJ
Published: April 2018

Clustering of voltage-gated Na+ channels is critical for the fast saltatory conduction of action potentials in vertebrate myelinated axons. However, the mechanisms responsible for the generation and maintenance of Na+ channel clustering are not well understood. In this study we have raised an antibody against the cloned SCAP-1 voltage- gated Na+ channel of the marine invertebrate Aplysia californica and used it to examine Na+ channel localization in Aplysia ganglia and in cultured Aplysia sensory neurons. Our results show that there is a large cytoplasmic pool of Na+ channels in the soma of Aplysia neurons. Furthermore, we show that Na+ channels in Aplysia axons are not homogeneously distributed but, rather, are present in distinct clusters. Theoretical considerations indicate that Na+ channel clustering may enhance action potential conduction. We propose that clustered Na+ channels may be a fundamental property of many axons, and perhaps of many membranes that conduct Na(+)-dependent action potentials.
Synaptic remodeling revealed by repeated in vivo observations and electron microscopy of identified frog neuromuscular junctions
Authors: Ko CP , Chen L
Published: April 2018

This work aimed to examine the mechanism of synaptic remodeling using repeated in vivo observations, followed by electron microscopy, of identified frog neuromuscular junctions (NMJs). Our previous light microscopic studies suggested that extension of synaptic extracellular matrix (ECM) precedes, and may play a role in, nerve terminal (NT) growth during synaptic remodeling. To test this hypothesis, sartorius muscles were double labeled with a fluorescent dye, 4-(4-diethylamino- styryl)-N-methylpyridinium iodide, for NTs and rhodamine-conjugated peanut agglutinin for synaptic ECM. The double-labeled NMJs were observed in vivo with video-enhanced fluorescence microscopy. Two to three months after nerve sprouting was induced by a nerve graft, the same NMJs were restained and reexamined. After the final in vivo observations, the same NMJs were examined with semiserial thin section electron microscopy. Light microscopic observation of NMJs that showed synaptic ECM longer than the NT was confirmed with electron microscopy. At junctional branches where synaptic ECM extended beyond the NT, a Schwann cell process longer than the NT was observed in one example, whereas a Schwann cell with the same length as the NT was seen in other examples. In both cases, junctional folds were absent at the extended ECM region. In contrast, junctional folds were observed at the region vacated by a retracted NT. These results suggest that extension of synaptic ECM and Schwann cell processes may lead, and play a role in, the NT growth during the remodeling of adult synaptic connections.
An adult-like pattern of ocular dominance columns in striate cortex of newborn monkeys prior to visual experience
Authors: Horton JC , Hocking DR
Published: April 2018

In macaque monkeys, the geniculocortical afferents serving each eye segregate in layer IVc of striate cortex during early life into a pattern of alternating inputs called ocular dominance columns. It has been disputed whether visual experience is necessary for the formation of ocular dominance columns. To settle this issue, fetal monkeys were delivered prematurely by Caesarean section at embryonic day 157 (E157), 8 d before the end of normal gestation. To avoid light exposure, the Caesarean section and all subsequent feedings and procedures were done in absolute darkness, using infrared night-vision goggles. Tritiated proline was injected into the right eye 1 d after delivery (E158). One week later at postnatal age 0 (P0), the equivalent of a full-term pregnancy (E165/P0), alternate sections of unfolded and flattened visual cortex were prepared for autoradiography or cytochrome oxidase (CO). All three newborns studied at E165/P0 had well segregated ocular dominance columns organized into the characteristic mosaic present in adults. In the upper layers, a mature pattern of CO patches (also known as blobs or puffs) was visible, aligned with the ocular dominance columns in layer IVc. Every other row of patches in layers II, III was labeled by [3H]proline. In V2, a distinct system of alternating thick- pale-thin-pale CO stripes was present. These findings indicate that stimulation of the retina by light is not necessary for the development of columnar systems in the visual cortex. Ocular dominance columns, patches, and V2 stripes all are well formed before visual experience. Even the thalamic input to the patches in the upper layers of striate cortex is segregated by eye in newborns.
Fine grain of the neural representation of human spatial vision
Authors: Smallman HS , MacLeod DI , He S , Kentridge RW
Published: April 2018

It is widely held that in human spatial vision the visual scene is initially processed through visual filters, each of which is responsive to narrow ranges of image spatial frequencies. The physiological basis of these filters are thought to be cortical neurons with receptive fields of different sizes. The grain of the neural representation of spatial vision is much finer than had been supposed. Using laser interferometry, which effectively bypasses the demodulation of the optics of the eye, we measured discrimination of, and adaptation to, high spatial frequency laser interference fringe patterns. Spatial frequency discrimination was good right up to the visual resolution limit (average Weber fractions of 0.13 at 50 c/deg). Both contrast and spatial frequency matches made after adapting to extremely fine interference fringes strongly suggested that there existed even finer, relatively unadapted, filters (mechanisms with small receptive fields). The smallest cortical receptive fields processing spatial information in human vision are so small that they can possess receptive field centers hardly wider than single cone photoreceptors.
Electrophysiological and morphological properties of layers V-VI principal pyramidal cells in rat prefrontal cortex in vitro
Authors: Yang CR , Seamans JK , Gorelova N
Published: April 2018

This study examined the electrophysiological and morphological characteristics of layers V-VI pyramidal prefrontal cortex (PFC) neurons. In vitro intracellular recordings coupled with biocytin injections that preserved some of the PFC efferents to the nucleus accumbens (NAc) were made in brain slices. Four principal pyramidal cell types were identified and classified as regular spiking (RS) (19%), intrinsic bursting (IB) (64%), repetitive oscillatory bursting (ROB) (13%), and intermediate (IM) (4%) types. All PFC cells exhibited either subthreshold oscillation in membrane voltage or pacemaker-like rhythmic firing. IB neurons were demonstrated electrophysiologically and cytochemically to be PFC-->NAc neurons. In all IB and some RS neurons, a tetrodotoxin-sensitive, slowly inactivating Na+ current and a transient Ni(2+)-sensitive, low-threshold Ca2+ current mediated subthreshold inward rectification. During sustained membrane depolarization, the Na+ current was opposed by a 4-aminopyridine- sensitive, outwardly rectifying, slowly inactivating K+ current. Together, these three currents controlled the firing threshold of the PFC neurons. All IB and ROB cells also had postspike Ca(2+)-mediated depolarizing afterpotentials, postburst Ca(2+)-dependent after hyperpolarizations, and low- and high-threshold Ca2+ spikes. In addition, ROB cells had a hyperpolarizing “sag” mediated by the cationic conductance, Ih. IB and ROB neurons had extensive dendritic trees and radially ascending or tangentially projecting axon collaterals. RS and IM cells had comparatively simpler morphological profiles. These electrophysiological and morphological properties of the four principal pyramidal PFC cell types have provided valuable details for understanding further how PFC processes input and transmit outputs to regions such as the NAc.
Dopamine D1 receptor actions in layers V-VI rat prefrontal cortex neurons in vitro: modulation of dendritic-somatic signal integration
Authors: Yang CR , Seamans JK
Published: April 2018

The ionic mechanisms by which dopamine (DA) regulates the excitability of layers V-VI prefrontal cortex (PFC) output neurons (including those that project to the nucleus accumbens) were investigated in rat brain slices using in vitro intracellular recording techniques. DA or the D1 receptor agonist SKF38393, but not the D2 agonist quinpirole, reduced the first spike latency and lowered the firing threshold of the PFC neurons in response to depolarizing current pulses. This was accomplished by enhancing the duration of a tetradotoxinsensitive, slowly inactivating Na+ current and attenuating a slowly inactivating, outwardly rectifying, dendrotoxin-sensitive K+ current. Furthermore, D1 receptor stimulation attenuated high-threshold Ca2+ spike(s) (HTS) evoked primarily from the apical dendrites of these PFC neurons. Taken together, these data suggest that D1 receptor stimulation on layers V- VI pyramidal PFC neurons: (1) restricts the effects of inputs to the apical dendrites of these neurons by attenuating the dendritic HTS- mediated amplification of such inputs; and (2) potentiates the influence of local inputs from neighboring deep layers V-VI neurons by enhancing the slowly inactivating Na+ current and attenuating the slowly inactivating K+ current. By influencing the input/output characteristics of PFC-->NAc neurons, DA may play an important role in the processes through which PFC signals are translated into action.
A framework for mesencephalic dopamine systems based on predictive Hebbian learning
Authors: Montague PR , Dayan P , Sejnowski TJ
Published: April 2018

We develop a theoretical framework that shows how mesencephalic dopamine systems could distribute to their targets a signal that represents information about future expectations. In particular, we show how activity in the cerebral cortex can make predictions about future receipt of reward and how fluctuations in the activity levels of neurons in diffuse dopamine systems above and below baseline levels would represent errors in these predictions that are delivered to cortical and subcortical targets. We present a model for how such errors could be constructed in a real brain that is consistent with physiological results for a subset of dopaminergic neurons located in the ventral tegmental area and surrounding dopaminergic neurons. The theory also makes testable predictions about human choice behavior on a simple decision-making task. Furthermore, we show that, through a simple influence on synaptic plasticity, fluctuations in dopamine release can act to change the predictions in an appropriate manner.
Phosphorylation of brain sodium channels in the I--II linker modulates channel function in Xenopus oocytes
Authors: Smith RD , Goldin AL
Published: April 2018

Voltage-gated sodium channels, which initiate action potentials in mammalian brain neurons, are modulated functionally by cAMP-dependent protein kinase A (PKA), resulting in reduced sodium current amplitude. Comparing brain and muscle sodium channels, we show that only the brain channel is modulated by PKA. The brain sodium channel I-II linker is both necessary and sufficient for PKA modulation, as shown by exchanging the I-II linker regions of the two channels. PKA consensus sites in the brain channel I-II linker were eliminated by deletion and site-specific mutagenesis. The mutant channels demonstrated decreased levels of phosphorylation when metabolically labeled in oocytes with [gamma-32P]-ATP, and they did not respond with a reduction in current magnitude after PKA induction. Modulation of the brain channel by PKA phosphorylation was mimicked by adding fixed negative charges at the PKA consensus sites, suggesting that the decrease in current was a direct result of the negative charge at one or more of the PKA sites in the I-II linker.
Evidence for multiple AMPA receptor complexes in hippocampal CA1/CA2 neurons
Authors: Wenthold RJ , Petralia RS , Blahos J II , Niedzielski AS
Published: April 2018

The AMPA receptor, which is involved in most fast glutamatergic transmission in the mammalian brain and is expressed in most neurons, is made up of four subunits, GluR1–4. In situ hybridzation, immunocytochemistry studies, and single-cell PCR analyses show that the number and type of AMPA receptor subunits expressed vary among neuronal populations and that two to four subunits usually are expressed in each neuron. Neurons that express two or more subunits theoretically could produce multiple pentameric receptor complexes that differ in their subunit compositions, and these complexes could be targeted to different synaptic populations. To determine whether a single neuronal population produces multiple AMPA receptor complexes, we used a preparation of CA1/CA2 hippocampal pyramidal neurons and immunoprecipitation with subunit-specific antibodies to characterize the receptor complexes. The CA1/CA2 pyramidal neurons express high levels of GluR1–3 and receive multiple excitatory inputs, offering the possibility that distinct receptor complexes may be assembled and expressed selectively at different synaptic populations. Our results suggest the presence of two major populations of AMPA receptor complexes: those made up of GluR1 and GluR2 and those made up of GluR2 and GluR3. Very few complexes contained both GluR1 and GluR3, whereas approximately 8% of the total AMPA receptor complexes was homomeric GluR1. The integrity of the receptor complex was verified by measuring [3H]AMPA binding activity in the immunoprecipitated fractions. These results show that AMPA receptor complexes with different subunit compositions are present in CA1/CA2 pyramidal neurons and suggest an additional mechanism to regulate receptor expression in neurons.