bluuebunny/crossref_metadata_2025 huggingface dataset:
Voltage-Activated Calcium Currents in Rat Retinal Ganglion CellsIn Situ: Changes during Prenatal and Postnatal Development
Authors: Schmid Susanne , Guenther Elke
Published: April 2018

Voltage-activated calcium currents (ICa) are one way by which calcium influx into neurons is mediated. To investigate changes in kinetic properties ofICaduring neuronal development and to correlate possible kinetic changes with specific differentiation processes, theICaof retinal ganglion cells (RGCs) was recorded with the perforated patch-clamp technique in rat retinal slices and in whole mounts at different prenatal and postnatal stages.

ICadensity increased between embryonic day (E) 20 and the adult stage, paralleled by a shift in activation of the ω-conotoxin GVIA-sensitiveICatoward more negative membrane potentials. Furthermore, developmental alterations were observed inICainactivation rate during a 120 msec test pulse and in steady-state inactivation ofICa. The most striking feature inICakinetics was a transient slowing of calcium current deactivation, which peaked at postnatal day (P)3–5 and affected allICasubtypes.

Although the shift in activation and the decreased inactivation rate ofICacan be explained by differential regulation of distinct calcium channel subtypes, it is more likely that a more general alteration of the cells’ functional state was the underlying factor in alterations in steady-state inactivation and current deactivation ofICa.

Alterations in the ω-conotoxin GVIA-sensitive and the toxin-resistant currents temporarily coincide with dendritic differentiation, and it is tempting to speculate about their role in network formation in the inner retina. In contrast, alterations in steady-state inactivation and current deactivation may be involved in the regulation of RGC survival, because they occur during the period of programmed cell death in the ganglion cell layer.

In conclusion, distinct time windows of alterations in calcium channel properties were found, and this study has provided a basis for performing functional assays to clarify in detail the developmental process to which these alterations are related.
Role of Brain-Derived Neurotrophic Factor in Target Invasion in the Gustatory System
Authors: Ringstedt Thomas , Ibáñez Carlos F. , Nosrat Christopher A.
Published: April 2018

Brain-derived neurotrophic factor (BDNF) is a survival factor for different classes of neurons, including gustatory neurons. We have studied innervation and development of the gustatory system in transgenic mice overexpressingBDNFunder the control of regulatory sequences from thenestingene, an intermediate filament gene expressed in precursor cells of the developing nervous system and muscle. In transgenic mice, the number and size of gustatory papillae were decreased, circumvallate papillae had a deranged morphology, and there was also a severe loss of lingual taste buds. Paradoxically, similar deficits have been found in BDNF knock-out mice, which lack gustatory neurons. However, the number of neurons in gustatory ganglia was increased in BDNF-overproducing mice. Although gustatory fibers reached the tongue in normal numbers, the amount and density of nerve fibers in gustatory papillae were reduced in transgenic mice compared with wild-type littermates. Gustatory fibers appeared stalled at the base of the tongue, a site of ectopicBDNFexpression, where they formed abnormal branches and sprouts. Interestingly, palatal taste buds, which are innervated by gustatory neurons whose afferents do not traverse sites of ectopic BDNF expression, appeared unaffected. We suggest that lingual gustatory deficits in BDNF overexpressing mice are a consequence of the failure of their BDNF-dependent afferents to reach their targets because of the effects of ectopically expressedBDNFon fiber growth. Our findings suggest that mammalian taste buds and gustatory papillae require proper BDNF-dependent gustatory innervation for development and that the correct spatial expression ofBDNFin the tongue epithelium is crucial for appropriate target invasion and innervation.
NK-1 Receptor Immunoreactivity in Distinct Morphological Types of Lamina I Neurons of the Primate Spinal Cord
Authors: Yu X. H. , Zhang E.-T. , Craig A. D. , Shigemoto R. , Ribeiro-da-Silva A. , De Koninck Y.
Published: April 2018

In cat and monkey, lamina I cells can be classified into three basic morphological types (fusiform, pyramidal, and multipolar), and recent intracellular labeling evidence in the cat indicates that fusiform and multipolar lamina I cells are two different types of nociceptive cells, whereas pyramidal cells are innocuous thermoreceptive-specific. Because earlier observations indicated that only nociceptive dorsal horn neurons respond to substance P (SP), we examined which morphological types of lamina I neurons express receptors for SP (NK-1r).

We categorized NK-1r-immunoreactive (IR) lamina I neurons in serial horizontal sections from the cervical and lumbar enlargements of four monkeys. Consistent results were obtained by two independent teams of observers. Nearly all NK-1r-IR cells were fusiform (42%) or multipolar (43%), but only 6% were pyramidal (with 9% unclassified). We obtained similar findings in three monkeys in which we used double-labeling immunocytochemistry to identify NK-1r-IR and spinothalamic lamina I neurons retrogradely labeled with cholera toxin subunit b from the thalamus; most NK-1r-IR lamina I spinothalamic neurons were fusiform (48%) or multipolar (33%), and only 10% were pyramidal. In contrast, most (∼75%) pyramidal and some (∼25%) fusiform and multipolar lamina I spinothalamic neurons did not display NK-1r immunoreactivity.

These data indicate that most fusiform and multipolar lamina I neurons in the monkey can express NK-1r, consistent with the idea that both types are nociceptive, whereas only a small proportion of lamina I pyramidal cells express this receptor, consistent with the previous finding that they are non-nociceptive. However, these findings also indicate that not all nociceptive lamina I neurons express receptors for SP.
Distinct Subtypes of Metabotropic Glutamate Receptors Mediate Differential Actions on Excitability of Spinal Respiratory Motoneurons
Authors: Dong Xiao-Wei , Feldman Jack L.
Published: April 2018

Metabotropic glutamate receptors (mGluRs) modulate neuronal function by affecting excitability and altering synaptic transmission. We have shown that the mGluR agonist (1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid (1S,3R-ACPD) has multiple actions on phrenic motoneurons (PMNs), including reduction of inspiratory-modulated synaptic currents and an increase of neuronal excitability. We hypothesized that these actions were mediated by different mGluR subtypes. We have now identified the involvement of mGluR subtypes and their roles in modulating the excitability of PMNs and the consequent inspiratory motor output in anin vitroneonatal rat brainstem–spinal cord preparation. Activation of postsynaptic group-I mGluRs increases PMN excitability, associated with the production of an inward current and a decrease in membrane conductance, whereas activation of group-II or group-III mGluRs decreases PMN inspiratory-modulated synaptic current, probably via a presynaptic mechanism. To confirm further the distinction and the involvement of group-I and group-II/-III receptor subtypes affecting PMN excitability, we used the membrane permeable cAMP analog 8-bromo-cAMP (8-Br-cAMP) to elevate intracellular cAMP concentration to mask or occlude any effects mediated via the cAMP cascade. 8-Br-cAMP attenuated the reduction of the inspiratory-modulated activity of PMNs by both (S)-4-carboxy-3-hydroxyphenylglycine (4C3HPG) andl-(+)-2-amino-4-phosphonobutyric acid (l-AP4), agonists for group-II and group-III mGluRs, respectively, but did not affect the actions of 3,5-dihydroxyphenylglycine (DHPG), an agonist for group-I mGluRs. These three groups of mGluRs are all endogenously activated during the inspiratory phase. We conclude that three groups of mGluRs are functionally expressed in the phrenic nucleus and that their activation modulates PMN excitability via distinct mechanisms, with group-I acting at postsynaptic sites and group-II and group-III acting at presynaptic sites.
The Concentration of Synaptically Released Glutamate Outside of the Climbing Fiber–Purkinje Cell Synaptic Cleft
Authors: Dzubay Jeffrey A. , Jahr Craig E.
Published: April 2018

AMPA receptors and glutamate transporters expressed by cerebellar Bergmann glial cells are activated by neurotransmitter released from climbing fibers (Bergles et al., 1997). Based on anatomical evidence, this is most likely the result of glutamate diffusing out of the climbing fiber–Purkinje cell synaptic clefts (Palay and Chan-Palay, 1974). We used the change in the EC50of the Bergmann glia AMPA receptors produced by cyclothiazide (CTZ) to estimate the concentration of glutamate reached at the glial membrane. The decrease of the EC50gives rise to a concentration-dependent potentiation of the AMPA receptor-mediated responses (Patneau et al., 1993). By comparing the increase in amplitude of the AMPA receptor response in the Bergmann glia (840 ± 240%;n= 8) with the shift in the glutamate dose–response curve measured in excised patches (EC50, 1810 μmin control vs 304 μmin CTZ), we estimate that the extrasynaptic transmitter concentration reaches 160–190 μm. This contrasts with the concentration in the synaptic cleft, thought to rapidly rise above 1 mm, but is still high enough to activate glutamate receptors. These results indicate that the sphere of influence of synaptically released glutamate can extend beyond the synaptic cleft.
Involvement of cGMP-Dependent Protein Kinase in Adrenergic Potentiation of Transmitter Release from the Calyx-Type Presynaptic Terminal
Authors: Yawo Hiromu
Published: April 2018

I have previously reported that norepinephrine (NE) induces a sustained potentiation of transmitter release in the chick ciliary ganglion through a mechanism pharmacologically distinct from any known adrenergic receptors. Here I report that the adrenergic potentiation of transmitter release was enhanced by a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX) and by zaprinast, an inhibitor of cGMP-selective phosphodiesterase. Exogenous application of the membrane-permeable cGMP, 8-bromo-cGMP (8Br-cGMP), potentiated the quantal transmitter release, and after potentiation, the addition of NE was no longer effective. On the other hand, 8Br-cAMP neither potentiated the transmitter release nor occluded the NE-induced potentiation. The NE-induced potentiation was blocked by neither nitric oxide (NO) synthase inhibitor nor NO scavenger. The quantal transmitter release was not potentiated by NO donors, e.g., sodium nitroprusside. The NE-induced potentiation and its enhancement by IBMX was antagonized by two inhibitors of protein kinase G (PKG), Rp isomer of 8-(4-chlorophenylthio) guanosine-3′,5′-cyclic monophosphorothioate and KT5823. As with NE-induced potentiation, the effects of 8Br-cGMP on both the resting intraterminal [Ca2+] ([Ca2+]i) and the action potential-dependent increment of [Ca2+]i(ΔCa) in the presynaptic terminal were negligible. The reduction of the paired pulse ratio of EPSC is consistent with the notion that the NE- and cGMP-dependent potentiation of transmitter release was attributable mainly to an increase of the exocytotic fusion probability. These results indicate that NE binds to a novel adrenergic receptor that activates guanylyl cyclase and that accumulation of cGMP activates PKG, which may phosphorylate a target protein involved in the exocytosis of synaptic vesicles.
Functionally Antagonistic Interactions between the TrkA and p75 Neurotrophin Receptors Regulate Sympathetic Neuron Growth and Target Innervation
Authors: Kohn Judi , Aloyz Raquel S. , Toma Jean G. , Haak-Frendscho Mary , Miller Freda D.
Published: April 2018

In this report, we provide evidence that NGF and BDNF have functionally antagonistic actions on sympathetic neuron growth and target innervation, with NGF acting via TrkA to promote growth and BDNF via p75NTR to inhibit growth. Specifically, in cultured sympathetic neurons that themselves synthesize BDNF, exogenous BDNF inhibits and function-blocking BDNF antibodies enhance process outgrowth. Both exogenous and autocrine BDNF mediate this effect via p75NTR because (1) BDNF does not inhibit growth of neurons lacking p75NTR, (2) function-blocking p75NTR antibodies enhance NGF-mediated growth, and (3) p75NTR−/−sympathetic neurons grow more robustly in response to NGF than do their wild-type counterparts. To determine the physiological relevance of this functional antagonism, we examined the pineal gland, a well defined sympathetic target organ. BDNF is present in the pineal gland during target innervation, and incoming sympathetic axons are p75NTR positive. Moreover, the pineal glands of BDNF+/−and BDNF−/−mice are hyperinnervated with sympathetic fibers, and tyrosine hydroxylase (TH) levels are elevated. Increased tyrosine hydroxylase is also observed in the BDNF+/−carotid artery, another sympathetic neuron target. Thus, BDNF, made by sympathetic neurons and/or their target organs, acts via p75NTR to antagonize NGF-mediated growth and target innervation, suggesting that sympathetic target innervation is determined by the balance of positively and negatively acting neurotrophins present in developing and potentially mature targets.
Different Contributions of the Human Amygdala and Ventromedial Prefrontal Cortex to Decision-Making
Authors: Bechara Antoine , Damasio Hanna , Damasio Antonio R. , Lee Gregory P.
Published: April 2018

The somatic marker hypothesis proposes that decision-making is a process that depends on emotion. Studies have shown that damage of the ventromedial prefrontal (VMF) cortex precludes the ability to use somatic (emotional) signals that are necessary for guiding decisions in the advantageous direction. However, given the role of the amygdala in emotional processing, we asked whether amygdala damage also would interfere with decision-making. Furthermore, we asked whether there might be a difference between the roles that the amygdala and VMF cortex play in decision-making. To address these two questions, we studied a group of patients with bilateral amygdala, but not VMF, damage and a group of patients with bilateral VMF, but not amygdala, damage. We used the “gambling task” to measure decision-making performance and electrodermal activity (skin conductance responses, SCR) as an index of somatic state activation.Allpatients, those with amygdala damage as well as those with VMF damage, were (1) impaired on the gambling task and (2) unable to develop anticipatory SCRs while they pondered risky choices. However, VMF patients were able to generate SCRs when they received a reward or a punishment (play money), whereas amygdala patients failed to do so. In a Pavlovian conditioning experiment the VMF patients acquired a conditioned SCR to visual stimuli paired with an aversive loud sound, whereas amygdala patients failed to do so. The results suggest that amygdala damage is associated with impairment in decision-making and that the roles played by the amygdala and VMF in decision-making are different.
Arginine Analogs Modify Signal Detection by Neurons in the Visual Cortex
Authors: Kara Prakash , Friedlander Michael J.
Published: April 2018

Nitric oxide (NO) modulates neurotransmitter release, induction of long-term synaptic potentiation and depression, and activity levels of neurons. However, it is not known whether NO contributes to the ability of the CNS to distinguish sensory signals from background noise and/or extract sensory information with greater reliability. We addressed these questions in the visual cortex,in vivo, using electrophysiological recording and analysis of signal detection from individual neurons. This was combined with microiontophoretic application of arginine analogs that either upregulate or downregulate the brain’s endogenous NO-generating pathways or compounds that produce exogenous NO. Protocols that enhance NO levels generally increased the number of action potentials per trial evoked by visual stimuli, improved signal detection, and decreased the coefficient of variation of visually evoked responses, whereas NO-reducing protocols predominantly had complementary effects. Control experiments demonstrate that these effects are likely attributable to the specific ability of these arginine compounds to modify NO levels versus other nonspecific effects. Differential effects between neighboring cells and between single-cell receptive subfields suggest that these actions have a significant direct neural component versus exclusively operating indirectly on neurons through the central vascular actions of NO.
Localization of a Suprachiasmatic Nucleus Subregion Regulating Locomotor Rhythmicity
Authors: LeSauter J. , Silver Rae
Published: April 2018

The bilaterally symmetrical suprachiasmatic nuclei (SCN) of the hypothalamus are the loci of the mammalian clock controlling circadian rhythms. Previous studies suggested that all regions of the SCN are equipotential as circadian rhythmicity is sustained after partial ablation, as long as ∼25% of the nuclei are spared. In contrast to these results, we found that animals bearing partial lesions of the SCN that spared the subregion delimited by cells containing the calcium-binding protein calbindin-D28K(CaBP), sustained circadian locomotor rhythms. Furthermore, there was a correlation between the strength of the rhythm and the number of spared CaBP cells. Partial lesions that destroyed this region but spared other compartments of the SCN resulted in loss of rhythmicity. The next study indicates that transplants of half-SCN grafts that contain CaBP cells restore locomotor rhythms in SCN-lesioned host animals, whereas transplants containing SCN tissue but lacking cells of this subnucleus fail to restore rhythmicity. Finally, there was a correlation between the number of CaBP-positive cells in the graft and the strength of the restored rhythm. Taken together, the results indicate that pacemakers in the region of the CaBP subnucleus are necessary and sufficient for the control of locomotor rhythmicity and that the SCN is functionally heterogeneous.
Sensitization to the Effects of Tumor Necrosis Factor-α: Neuroendocrine, Central Monoamine, and Behavioral Variations
Authors: Hayley Shawn , Brebner Karen , Lacosta Susan , Merali Zul , Anisman Hymie
Published: April 2018

Consistent with the proposition that cytokines act as immunotransmitters between the immune system and the brain, systemic administration of the proinflammatory cytokine tumor necrosis factor-α (TNF-α; 1.0–4.0 μg) induced mild illness in CD-1 mice, increased plasma corticosterone concentrations, and altered central norepinephrine, dopamine, and serotonin turnover. The actions of TNF-α were subject to a time-dependent sensitization effect. After reexposure to a subeffective dose of the cytokine (1.0 μg) 14–28 d after initial treatment, marked illness was evident (reduced consumption of a palatable substance and diminished activity and social exploration), coupled with an elevation of plasma corticosterone levels. In contrast, cytokine reexposure 1–7 d after initial treatment did not elicit illness, and at the 1 d interval the corticosterone response to the cytokine was reduced. The increase of norepinephrine release within the paraventricular nucleus of the hypothalamus, as reflected by elevated accumulation of 3-methoxy-4-hydroxyphenylglycol, was augmented at the longer reexposure intervals. In contrast, within the central amygdala and the prefrontal cortex TNF-α reexposure at the 1 d interval was associated with a pronounced sensitization-like effect, which was not apparent at longer intervals. Evidently, systemic TNF-α proactively influences the response to subsequent treatment; however, the nature of the effects (i.e., the behavioral, neuroendocrine, and central transmitter alterations) vary over time after initial cytokine treatment. It is suggested that the sensitization may have important repercussions with respect to cognitive effects of TNF-α and may also be relevant to analyses of the neuroprotective or neurodestructive actions of cytokines.
Direct Evidence for Biphasic cAMP Responsive Element-Binding Protein Phosphorylation during Long-Term Potentiation in the Rat Dentate GyrusIn Vivo
Authors: Schulz Stefan , Siemer Helge , Krug Manfred , Höllt Volker
Published: April 2018

Phosphorylation of the transcription factor cAMP responsive element-binding protein (CREB) is thought to play a key role in synaptic plasticity and long-term memory. However, direct evidence for CREB phosphorylation during hippocampal long-term potentiation (LTP)in vivois sparse. Here, we show that, in the intact animal, CREB is rapidly phosphorylated in response to high-frequency stimulation but not low-frequency stimulation of the perforant pathway. CREB phosphorylation occurred in a biphasic manner, with a first peak at 30 min and a second long-lasting peak beginning 2 hr after tetanic stimulation and lasting for at least 24 hr. Only stimuli that generated nondecremental LTP promoted a sustained hyperphosphorylation of CREB but not stimuli that produced decremental LTP. CREB phosphorylation was specifically triggered in the dentate gyrus, as well as the CA1, but not the CA3, hippocampal region. Pretreatment with the NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate completely prevented activation of CREB. Together, we have resolved the spatial and temporal dynamics of CREB phosphorylation during hippocampal LTP, showing that the transcription factor CREB is specifically recruited at two distinct time points in some forms of hippocampal synaptic plasticityin vivo.
l-Proline and l-Pipecolate Induce Enkephalin-Sensitive Currents in Human Embryonic Kidney 293 Cells Transfected with the High-Affinity Mammalian Brainl-Proline Transporter
Authors: Galli Aurelio , Jayanthi Lankupalle D. , Ramsey I. Scott , Miller Joshua W. , Fremeau Robert T. , DeFelice Louis J.
Published: April 2018

The high-affinity mammalian brainl-proline transporter (PROT) belongs to the GAT1 gene family, which includes Na- and Cl-dependent plasma membrane carriers for neurotransmitters, osmolites, and metabolites. These transporters couple substrate flux to transmembrane electrochemical gradients, particularly the Na gradient. In the nervous system, transporters clear synapses and help to replenish transmitters in nerve terminals. The localization of PROT to specific excitatory terminals in rat forebrain suggests a role for this carrier in excitatory transmission (Renick et al., 1999). We investigated the voltage regulation and electrogenicity of this novel transporter, using human embryonic kidney (HEK) 293 cells stably transfected with rat PROT cDNA. In physiological solutions between −140 and −40 mV,l-proline (PRO) and its six-member ring congenerl-pipecolate (PIP) induced inward current. The current–voltage relationship and the variance of current fluctuations were similar for PRO- and PIP-induced current, and the ratio of induced variance to the mean current ranged from 20 to 60 fA. Des-Tyr-Leu-enkephalin (GGFL), a competitive peptide inhibitor of PROT, reduced the rat PROT-associated current to control levels. GGFL alone did not elicit currents, and the GGFL-sensitive substrate-induced current was absent in nontransfected cells. Finally, GGFL inhibited PROT-mediated transport only when applied to the extracellular face of PROT. These data suggest that (1) PROT uptake is electrogenic, (2) individual transporter currents are voltage-independent, and (3) GGFL is a nonsubstrate inhibitor that interacts either with an extracellular domain of PROT or in an externally accessible pore.
Depolarization-Induced Mitochondrial Ca Accumulation in Sympathetic Neurons: Spatial and Temporal Characteristics
Authors: Pivovarova Natalia B. , Hongpaisan Jarin , Andrews S. Brian , Friel David D.
Published: April 2018

Several lines of evidence suggest that neuronal mitochondria accumulate calcium when the cytosolic free Ca2+concentration ([Ca2+]i) is elevated to levels approaching ∼500 nm, but the spatial, temporal, and quantitative characteristics of net mitochondrial Ca uptake during stimulus-evoked [Ca2+]ielevations are not well understood. Here, we report direct measurements of depolarization-induced changes in intramitochondrialtotalCa concentration ([Ca]mito) obtained by x-ray microanalysis of rapidly frozen neurons from frog sympathetic ganglia. Unstimulated control cells exhibited undetectably low [Ca]mito, but high K+depolarization (50 mm, 45 sec), which elevates [Ca2+]ito ∼600 nm, increased [Ca]mitoto 13.0 ± 1.5 mmol/kg dry weight; this increase was abolished by carbonyl cyanidep-(trifluoromethoxy) phenylhydrazone (FCCP). The elevation of [Ca]mitowas a function of both depolarization strength and duration. After repolarization, [Ca]mitorecovered to prestimulation levels with a time course that paralleled the decline in [Ca2+]i. Depolarization-induced increases in [Ca]mitowere spatially heterogeneous. At the level of single mitochondria, [Ca]mitoelevations depended on proximity to the plasma membrane, consistent with predictions of a diffusion model that considers radial [Ca2+]igradients that exist early during depolarization. Within individual mitochondria, Ca was concentrated in small, discrete sites, possibly reflecting a high-capacity intramitochondrial Ca storage mechanism. These findings demonstrate thatin situCa accumulation by mitochondria, now directly identified as the structural correlate of the “FCCP-sensitive store,” is robust, reversible, graded with stimulus strength and duration, and dependent on spatial location.
Gp-41-Mediated Astrocyte Inducible Nitric Oxide Synthase mRNA Expression: Involvement of Interleukin-1β Production by Microglia
Authors: Hu Shuxian , Ali Humaira , Sheng Wen S. , Ehrlich Laura C. , Peterson Phillip K. , Chao Chun C.
Published: April 2018

Mechanisms underlying human immunodeficiency virus-1 encephalopathy are not completely known; however, recent studies suggest that the viral protein gp41 may be neurotoxic via activation of inducible nitric oxide synthase (iNOS) in glial cells. In the present study, we investigated the NO-generating activity of primary human fetal astrocytes in response to gp41 and the relationship to microglial cell production of interleukin-1 (IL-1). Gp41 failed to trigger iNOS mRNA expression in highly enriched (>99%) astrocyte or microglial cell cultures. However, gp41-treated microglia released a factor(s) that triggered iNOS mRNA expression and NO production in astrocytes. Because IL-1 receptor antagonist protein blocked gp41-induced NO production, a pivotal role was suggested for microglial cell IL-1 production in astrocyte iNOS expression. Also, gp41 induced IL-1β mRNA expression and IL-1 production in microglial cell but not astrocyte cultures. Using specific inhibitors, we found that gp41-induced IL-1β production in microglia was mediated via a signaling pathway involving protein-tyrosine kinase. These data support the hypothesis that gp41 induces astrocyte NO production indirectly by triggering upregulation of microglial cell IL-1 expression.
The Contribution of Color to Motion Processing in Macaque Middle Temporal Area
Authors: Thiele Alexander , Dobkins Karen R. , Albright Thomas D.
Published: April 2018

The chromatic properties of an image yield strong cues for object boundaries and thus hold the potential to facilitate the detection of object motion. The extent to which cortical motion detectors exploit chromatic information, however, remains a matter of debate. To address this further, we quantified the strength of chromatic input to directionally selective neurons in the middle temporal area (MT) of macaque cerebral cortex using an equivalent luminance contrast (EqLC) paradigm. This paradigm, in which two sinusoidal gratings, one heterochromatic and the other achromatic, are superimposed and moved in opposite directions, allows the sensitivity of motion detectors to heterochromatic stimuli to be quantified and expressed relative to the benchmark of sensitivity for a luminance-defined stimulus.

The results of these experiments demonstrate that the chromatic contrast in a moving red–green heterochromatic grating strongly influences directional responses in MT when the luminance contrast in that same grating is relatively low; for such stimuli, EqLC is at least 5%. When luminance contrast is added to the heterochromatic grating, however, EqLC wanes sharply and becomesnegative(−4%) when luminance contrast is sufficiently high (>17–23%). Thus, the chromatic properties of an object appear to confer little or no benefit to motion processing by MT neurons when sufficient luminance contrast concurrently exists. These data support a simple model in which chromatic motion processing in MT is almost exclusively determined by magnocellular input. Additionally, a comparison of neuronal and psychophysical data suggests that MT may not be the sole contributor to the perceptual experience elicited by motion of heterochromatic patterns, or that only a subset of MT neurons serve this function.
Presynaptic Regulation of Glutamate Release in the Ventral Tegmental Area During Morphine Withdrawal
Authors: Manzoni Olivier J. , Williams John T.
Published: April 2018

The regulation of glutamate (Glu) release from the excitatory input to dopamine cells in the ventral tegmental area (VTA) during acute withdrawal from morphine was studied in slices from animals treated for 6–7 d with morphine. EPSCs were inhibited by opioid agonists acting at μ-subtype receptors but not by selective δ- or κ-subtype agonists. The opioid inhibition was reduced by 65% with the potassium channel blocker 4-aminopyridine (4-AP; 100 μm) and a 12-lipoxygenase inhibitor, baicalein (5 μm), suggesting that opioids acted via a transduction pathway involving activation of a voltage-dependent potassium conductance by lipoxygenase metabolites as has been shown in the periaqueductal gray (Vaughan et al., 1997). During withdrawal, neither the potency nor the efficacy ofd-Ala-Met-enkephalin-Gly-ol (DAMGO) were changed; however, the blockade of μ-opioid inhibition by both 4-AP and baicalein was reduced. In addition, the potency of baclofen to depress EPSCs by GABA-B receptors and the effects of the GABA-uptake inhibitor NO-711 (10 μm) were increased in withdrawn rats. Finally, group 2 (but not group 4 or 1) metabotropic glutamate receptor-mediated presynaptic inhibition was also enhanced in morphine-withdrawn rats. These results suggest that one of the consequences of withdrawal from chronic morphine is an enhanced presynaptic inhibition of the excitatory inputs to the dopamine cells of the VTA. Inhibition of glutamate release during acute withdrawal would add to the inhibition of dopamine cells that is mediated by an augmented release of GABA (Bonci and Williams, 1997).
Striatal Preproenkephalin Gene Expression Is Upregulated in Acute but Not Chronic Parkinsonian Monkeys: Implications for the Contribution of the Indirect Striatopallidal Circuit to Parkinsonian Symptomatology
Authors: Schneider Jay S. , Decamp Emmanuel , Wade Timothy
Published: April 2018

This study examined the extent of striatal dopamine (DA) denervation and coincident expression of preproenkephalin (PPE) mRNA in monkeys made parkinsonian by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration. Some animals (n= 4) became moderately parkinsonian after receiving large doses of MPTP over short periods of time and were symptomatic for only a short period of time (1–3 months; acute parkinsonian group). Other animals became moderately parkinsonian after receiving either escalating doses of MPTP over long periods (4–6 months;n= 5) or a high dose of MPTP over a short period (<1 month;n= 1) and remained symptomatic for an extended period (>8 months; chronic parkinsonian group). Despite similar symptomatology and similar degrees of striatal DA denervation at the time of their deaths, only acute parkinsonian animals had significantly increased PPE expression in sensorimotor striatal regions. PPE expression in chronic parkinsonian animals was either not changed or significantly decreased in most striatal regions. These findings suggest that the duration and not the extent of striatal DA denervation is a critical factor in modulating changes in striatal PPE expression. Furthermore, these results question the role of increased activity in the enkephalin-containing indirect striatopallidal pathway in the expression of parkinsonian symptoms.
Activation of Presynaptic cAMP-Dependent Protein Kinase Is Required for Induction of Cerebellar Long-Term Potentiation
Authors: Linden David J. , Ahn Sohyun
Published: April 2018

Cerebellar long-term potentiation (LTP) is a persistent increase in the strength of the granule cell–Purkinje neuron synapse that occurs after brief stimulation of granule cell axons at 2–8 Hz. Previous work has indicated that cerebellar LTP induction requires presynaptic Ca influx, stimulation of Ca-sensitive adenylyl cyclase, and activation of PKA. The evidence implicating PKA has come from bath application of drugs during LTP induction, an approach that does not distinguish between PKA activation in the presynaptic or postsynaptic cell. Although bath application of PKA inhibitor drugs (KT5720, Rp-8CPT-cAMP-S) blocked LTP induction in granule cell–Purkinje neuron pairs in culture, selective application to granule cell or Purkinje neuron somata via patch pipettes did not. We hypothesized that presynaptic PKA activation is required for LTP induction but that drugs applied to the granule cell soma cannot diffuse to the terminal within this timescale. To test this hypothesis, we transfected cerebellar cultures with an expression vector encoding a peptide inhibitor of PKA [Rous sarcoma virus (RSV)-protein kinase A inhibitor (PKI)]. Transfection of RSV-PKI into presynaptic granule cells, but not postsynaptic Purkinje neurons or glial cells, blocked LTP induction produced by either synaptic stimulation or an exogenous cAMP analog. An expression vector encoding a control peptide with no PKA inhibitory activity was ineffective. These results show that induction of cerebellar LTP requires a presynaptic signaling cascade, including Ca influx, stimulation of Ca-sensitive adenylyl cyclase, and activation of PKA, and argue against a requirement for postsynaptic Ca signals or their sequelae.
Regulation of the Subcellular Distribution of m4 Muscarinic Acetylcholine Receptors in Striatal NeuronsIn Vivoby the Cholinergic Environment: Evidence for Regulation of Cell Surface Receptors by Endogenous and Exogenous Stimulation
Authors: Bernard Véronique , Levey Allan I. , Bloch Bertrand
Published: April 2018

Our aim was to determine how the cholinergic environment influences,in vivo, the membrane abundance and the intracellular trafficking of the muscarinic receptor m4 (m4R). Immunohistochemistry at light and electron microscopic level was used to detect the subcellular localization of m4R in several populations of striatal cholinoceptive neurons, including cholinergic neurons and medium spiny neurons.

(1) In control rats, in cholinergic neurons, m4R is mostly restricted to intracytoplasmic sites involved in its synthesis, especially endoplasmic reticulum. In contrast, m4R is preferentially located at the plasma membrane in cell bodies and dendritic shafts and spines of medium spiny neurons. The density of m4R was greater at the membrane of perikarya in patches (striatal areas with low acetylcholine activity) than in matrix (striatal areas with high acetylcholine activity). (2) Stimulation of muscarinic receptor with oxotremorine provokes translocation of m4R from the membrane to endosomes in perikarya and dendrites of medium spiny neurons but has no influence on the localization of m4R in the cytoplasm of cholinergic cell bodies.

Our results suggest that the intraneuronal trafficking and the abundance of membrane-bound m4Rin vivois under regulation of the cholinergic environment. The m4R subcellular compartmentalization depends on the phenotype of the cholinoceptive neuron and on its neurochemical environment. Such regulation, by modulating availability of receptor for endogenous and exogenous ligands, may play key roles in the response of target neurons.
Actin Filaments and the Opposing Actions of CaM Kinase II and Calcineurin in Regulating α7-Containing Nicotinic Receptors on Chick Ciliary Ganglion Neurons
Authors: Liu Qing-song , Berg Darwin K.
Published: April 2018

Nicotinic acetylcholine receptors containing α7 subunits have a high relative permeability to calcium and influence numerous calcium-dependent cellular events. On chick ciliary ganglion neurons the receptors are concentrated on somatic spines containing actin filaments. Using conventional whole-cell patch-clamp recording from dissociated ciliary ganglion neurons, we show that responses from α7-containing receptors undergo substantial rundown when the receptors are repeatedly challenged with nicotine. Stabilization of actin filaments with phalloidin partially prevents the rundown, whereas collapse of actin filaments with latrunculin A exacerbates it. The rundown depends on calcium influx through the receptors because it requires receptor activation and can be prevented by replacing extracellular calcium with barium or by intracellular dialysis with BAPTA. Thapsigargin and ryanodine each inhibit the rundown, demonstrating further a requirement for calcium release from internal stores. Blockade of calmodulin by calmidazolium or blockade of CaM kinase II with either KN93 or autocamtide-2-related inhibitory peptide each prevents the rundown; blockade of the phosphatase calcineurin with either cyclosporin A or deltamethrin increases the rundown. The results indicate a balance of calcium-dependent kinase and phosphatase activities in regulating the function of α7-containing receptors. Manifestation of the rundown depends in part on the loss of intracellular components via dialysis because little rundown is seen if perforated patch-clamp recording is used to monitor receptor responses even in latrunculin A-treated cells. A membrane-permeable calcineurin inhibitor, however, still decreases the nicotinic response in a calcium-dependent manner, confirming that calcium-dependent phosphoregulation of α7-containing receptors occurs in the intact cell.
The Establishment of GABAergic and Glutamatergic Synapses on CA1 Pyramidal Neurons is Sequential and Correlates with the Development of the Apical Dendrite
Authors: Tyzio Roman , Represa Alfonso , Jorquera Isabel , Ben-Ari Yehezkel , Gozlan Henri , Aniksztejn Laurent
Published: April 2018

We have performed a morphofunctional analysis of CA1 pyramidal neurons at birth to examine the sequence of formation of GABAergic and glutamatergic postsynaptic currents (PSCs) and to determine their relation to the dendritic arborization of pyramidal neurons. We report that at birth pyramidal neurons are heterogeneous. Three stages of development can be identified: (1) the majority of the neurons (80%) have small somata, an anlage of apical dendrite, and neither spontaneous nor evoked PSCs; (2) 10% of the neurons have a small apical dendrite restricted to the stratum radiatum and PSCs mediated only by GABAAreceptors; and (3) 10% of the neurons have an apical dendrite that reaches the stratum lacunosum moleculare and PSCs mediated both by GABAAand glutamate receptors. These three groups of pyramidal neurons can be differentiated by their capacitance (Cm= 17.9 ± 0.8; 30.2 ± 1.6; 43.2 ± 3.0 pF, respectively). At birth, the synaptic markers synapsin-1 and synaptophysin labeling are present in dendritic layers but not in the stratum pyramidale, suggesting that GABAergic peridendritic synapses are established before perisomatic ones. The present observations demonstrate that GABAergic and glutamatergic synapses are established sequentially with GABAergic synapses being established first most likely on the apical dendrites of the principal neurons. We propose that different sets of conditions are required for the establishment of functional GABA and glutamate synapses, the latter necessitating more developed neurons that have apical dendrites that reach the lacunosum moleculare region.
Deafening Alters Neuron Turnover within the Telencephalic Motor Pathway for Song Control in Adult Zebra Finches
Authors: Wang Niangui , Aviram Rina , Kirn John R.
Published: April 2018

In the telencephalon of adult songbirds, projection neurons are lost and replaced within the efferent pathway controlling learned vocal behavior. We examined the potential role of auditory experience in regulating the addition and long-term survival of vocal control neurons in adult male zebra finches. Deafened and control birds were injected with the cell birth marker [3H]thymidine and then killed 1 or 4 months later. At the 1 month survival time, the number of [3H]-labeled neurons present in the high vocal center (HVC) was 70% lower in deafened birds compared with controls. This was true for all [3H]-labeled HVC neurons, as well as the subset that projected to the robust nucleus of the archistriatum. Over the next 3 months, two-thirds of the [3H]-labeled HVC neurons in control birds were lost, presumably through cell death. Surprisingly, deafened birds showed no loss over this interval. The total number of HVC neurons did not differ between control and deafened birds at either survival time. Nuclear diameters of [3H]-labeled HVC neurons decreased with cell age in both control and deafened birds, a process that may relate to the eventual death and replacement of these cells. These results suggest that experience influences the addition and also the longer-term fate of neurons formed in adulthood. We propose that auditory deprivation decreases the incorporation of new neurons and prolongs their life span. Alterations in the neuronal replacement cycle may relate to the gradual deterioration in song that occurs after deafening in adult zebra finches.
Cellular Analog of Differential Classical Conditioning inAplysia: Disruption by the NMDA Receptor Antagonistdl-2-Amino-5-Phosphonovalerate
Authors: Murphy Geoffrey G. , Glanzman David L.
Published: April 2018

We previously showed that the associative enhancement ofAplysiasiphon sensorimotor synapses in a cellular analog of classical conditioning is disrupted by infusing the Ca2+chelator 1,2-bis(2-aminophenoxy)ethane-N,N-N′,N′-tetraacetic acid into the postsynaptic motor neuron before training or by training in the presence of the NMDA receptor antagonistdl-2-amino-5-phosphonovalerate (APV). Our earlier experiments with APV used a nondifferential training protocol, in which different preparations were used for associative and nonassociative training. In the present experiments we extended our investigation of the role of NMDA receptor type potentiation in learning inAplysiato differential conditioning. A cellular analog of differential conditioning was performed with a reduced preparation that consisted of the CNS plus two pedal nerves. A siphon motor neuron and two siphon sensory neurons, both of which were presynaptically connected to the motor neuron, were impaled with sharp microelectrodes. One sensorimotor synapse received paired stimulation with a conditioned stimulus (brief activation of a single sensory neuron) and an unconditioned stimulus (pedal nerve shock), whereas the other sensorimotor synapse received unpaired stimulation. Training in normal artificial seawater (ASW) resulted in significant differential enhancement of synapses that received the paired stimulation. Training in APV blocked this differential synaptic enhancement. A comparison of the present data with the data from earlier experiments that used nondifferential training is consistent with the possibility that differential training comprises competition between the presynaptic sensory neurons. Synaptic competition may contribute significantly to the associative effect of paired stimulation in the differential training paradigm.
Comparison of Cysteine String Protein (Csp) and Mutant α-SNAP Overexpression Reveals a Role for Csp in Late Steps of Membrane Fusion in Dense-Core Granule Exocytosis in Adrenal Chromaffin Cells
Authors: Graham Margaret E. , Burgoyne Robert D.
Published: April 2018

Assembly of the SNARE complex and its disassembly caused by the action of solubleN-ethylmaleimide-sensitive factor (NSF) attachment protein (SNAP) and NSF is crucial for the maintenance of vesicular traffic, including fusion of regulated exocytotic vesicles. Various other proteins may also have important roles in the processes leading to membrane fusion via interaction with the SNARE proteins, including the secretory vesicle cysteine string protein (Csp). Here we have examined the effect of overexpression of a dominant negative α-SNAP mutant or Csp on exocytosis of dense-core granules in single chromaffin cells monitored using amperometry to detect released catecholamine. Exocytosis of trans-Golgi network (TGN)-derived dense-core granules was substantially inhibited by expression of α-SNAP(L294A). The amplitude and characteristics of the individual release events were unaffected by expression of α-SNAP(L294A), consistent with an essential role for α-SNAP in early steps of priming but not in the fusion process. In contrast, Csp overexpression, which also inhibited the extent of exocytosis, also modified the kinetics of the individual release events seen as an increase in the rise time and a broadening of the residual amperometric spikes in Csp-transfected cells. These results suggest that unlike α-SNAP, Csp plays a key role in the protein interactions close to the fusion process or fusion pore opening during Ca2+-regulated exocytosis.
Molecular Cloning and Functional Expression of the Potassium-Dependent Sodium–Calcium Exchanger from Human and Chicken Retinal Cone Photoreceptors
Authors: Prinsen Clemens F. M. , Szerencsei Robert T. , Schnetkamp Paul P. M.
Published: April 2018

Light causes a rapid lowering of cytosolic free calcium in the outer segments of both retinal rod and cone photoreceptors. This light-induced lowering of calcium is caused by extrusion via a Na–Ca exchanger located in the rod and cone outer segment plasma membrane and plays a key role in the process of light adaptation. The Na–Ca exchanger in retinal rod outer segment was shown earlier to be a novel Na–Ca+K exchanger (NCKX), and its cDNA was obtained by molecular cloning from several mammalian species. On the other hand, the proper identity of the retinal cone Na–Ca exchanger, in terms of both functional characteristics (e.g., requirement for and transport of potassium) and molecular identity, has not yet been elucidated. Here, we report the molecular cloning, intraretinal localization byin situhybridization, and initial functional characterization of the chicken and human cone-specific Na–Ca exchangers. In addition we report the chicken rod-specific NCKX. We identified NCKX transcripts in both human and chicken cones and observed strong potassium-dependent Na–Ca exchange activity after heterologous expression of human and chicken cone NCKX cDNAs in cultured insect cells.In situhybridization in chicken retina showed abundant rod NCKX transcripts only in rod photoreceptors, whereas abundant cone NCKX transcripts were found in most, if not all, cone photoreceptors and also in a subpopulation of retinal ganglion cells. A detailed comparison with the previously described retinal rod and brain NCKX cDNAs is presented.