bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterizing the Site and Mode of Action of Dynorphin at Hippocampal Mossy Fiber Synapses in the Guinea Pig
Authors: Castillo Pablo E. , Salin Paul A. , Weisskopf Marc G. , Nicoll Roger A.
Published: April 2018

Extracellular field potential recordings from the CA3 region in guinea pig hippocampal slices were used to study the release and action of dynorphin at the mossy fiber synapse. Dynorphin A(1–17) or U69593 inhibited mossy fiber synaptic responses in preparations in which the CA3 region was surgically isolated from the rest of the hippocampus. This inhibition was completely reversed by the κ1selective antagonist nor-BNI, thus establishing the presence of functional κ1receptors in CA3. Inhibitory effects of dynorphin on mossy fiber responses were unaltered in the presence of the N- or P-type Ca2+channel blockers, ω-CgTx or ω-Aga IVA, respectively. This indicates that the action of dynorphin is independent of the particular type of Ca2+channel that mediates transmitter release at the mossy fiber terminal. Heterosynaptic inhibition of mossy fiber responses was observed in the presence of nifedipine, ω-CgTx, or ω-Aga IVA, indicating that dynorphin release does not depend specifically on L-, N-, or P-type Ca2+channels. The blockade of heterosynaptic inhibition by the membrane-permeant Ca2+chelator EGTA-AM suggests the involvement of a slow Ca2+-dependent process in dynorphin release. On the basis of a variety of experimental evidence, we propose that the time course of heterosynaptic inhibition is determined primarily by the time course of clearance of dynorphin in the extracellular space.
Protein Synthesis within Dendrites: Glycosylation of Newly Synthesized Proteins in Dendrites of Hippocampal Neurons in Culture
Authors: Torre Enrique R. , Steward Oswald
Published: April 2018

There is increasing evidence that certain mRNAs are present in dendrites and can be translated there. The present study uses two strategies to evaluate whether dendrites also possess the machinery for protein glycosylation. First, precursor labeling techniques were used in conjunction with autoradiography to visualize glycosyltransferase activities that are characteristic of the rough endoplasmic reticulum (RER) (mannose) or the Golgi apparatus (GA) (galactose and fucose) in dendrites that had been separated from their cell bodies and in intact neurons treated with brefeldin A or low temperature. Second, immunocytochemical techniques were used to define the subcellular distribution of proteins that are considered markers of the RER (ribophorin I) and GA (p58, α-mannosidase II, galactosyltransferase, and TGN38/41). Autoradiographic analysis revealed that isolated dendrites incorporated sugar precursors in a tunicamycin-sensitive and protein synthesis-dependent manner. Moreover, when intact neurons were pulse-labeled with3H-labeled sugars at low temperature or after treatment with brefeldin A, labeling was distributed over proximal and sometimes distal dendrites. Immunolabeling for RER markers was predominantly localized in cell bodies but extended for a considerable distance into dendrites of all neurons. Immunolabeling for GA markers was confined to the cell body in ∼70% of the neurons, but in 30% of the neurons, the staining extended into proximal and middle dendrites. These results indicate that the machinery for glycosylation extends well into dendrites in many neurons.
A Missense Mutation in the Sodium Channel Scn8a Is Responsible for Cerebellar Ataxia in the Mouse Mutantjolting
Authors: Kohrman David C. , Smith Marianne R. , Goldin Alan L. , Harris John , Meisler Miriam H.
Published: April 2018

The voltage-gated sodium channel Scn8a is broadly distributed in brain and spinal cord. We have identified a missense mutation in Scn8a that is associated with cerebellar ataxia in thejoltingmutant, a mild allele of the “motor endplate disease” locus. Thejoltingmutation results in substitution of Thr for an evolutionarily conserved Ala residue in the cytoplasmic S4–S5 linker of domain III. Introduction of the corresponding mutation into the rat brain IIA sodium channel shifted the voltage dependence of activation by 14 mV in the depolarizing direction, without affecting the kinetics of fast inactivation or recovery from inactivation. A shift in the threshold of the Scn8a channel could account for the reduced spontaneous activity of Purkinje cells, reduced inhibitory output from the cerebellum, and loss of motor control observed injoltingmice.
Modulation of High Voltage-Activated Calcium Channels by Somatostatin in Acutely Isolated Rat Amygdaloid Neurons
Authors: Viana Félix , Hille Bertil
Published: April 2018

We investigated actions of somatostatin (Som) on voltage-gated calcium channels in acutely isolated rat amygdaloid neurons. Somatostatin caused a dose-dependent inhibition of the high voltage-activated (HVA) Ca2+current, with little or no effect on the low voltage-activated (LVA) current. Nifedipine (2–10 μm) reduced the peak current by ∼15% without reducing inhibition of current by Som significantly, ruling out L-type channels as the target of modulation. The modulation appears to involve N- and P/Q-type calcium channels. After pretreatment with ω-conotoxin-GVIA (ω-CgTx) or ω-agatoxin-IVA, the inhibition was reduced but not abolished, whereas the combined application of both toxins nearly abolished the modulation. The Som analog BIM-23060 mimicked the effects of Som, whereas BIM-23058 had no effect, implicating Som type-2 receptors (SSTR-2). The inhibition was voltage-dependent, being minimal for small depolarizations, and was often accompanied by a slowing of the activation time course. Strong depolarizing prepulses partially relieved the inhibition and restored the time course of activation. Intracellular dialysis with GTPγS led to spontaneous inhibition and a slowing of the current like that with Som and occluded the effects of the peptide. Dialysis with GDPβS also diminished the inhibition. A short preincubation with 50 μmof the alkylating agentN-ethylmaleimide (NEM) prevented the action of somatostatin. These results suggest a role for NEM-sensitive G-proteins in the Som inhibition. Application of 8-CPT-cAMP and IBMX did not mimic or prevent the effects of Som.
Activation of Metabotropic Glutamate Receptor Subtype mGluR1 Contributes to Post-Traumatic Neuronal Injury
Authors: Mukhin Alexey , Fan Lei , Faden Alan I.
Published: April 2018

The role of phospholipase C-coupled (group I) metabotropic glutamate receptors (mGluR1 and mGluR5) in post-traumatic neuronal injury was examined using ratin vivoandin vitromodels. Traumatic injury to mixed neuronal/glial cultures induced phosphoinositide hydrolysis and caused neuronal death. Pharmacological blockade of group I receptors significantly reduced these effectsin vitroand decreased neurological deficits as well as neuronal loss produced by traumatic brain injuryin vivo.In contrast, activation of group I receptors by a specific agonistin vitroexacerbated post-traumatic neuronal death in a dose-dependent manner. Antisense oligodeoxynucleotide directed to mGluR1, but not to mGluR5, was neuroprotectivein vitro, although each oligodeoxynucleotide reduced the respective receptor-stimulated accumulation of inositol phosphates to a similar degree. Together, these findings suggest that activation of mGluR1 contributes to post-traumatic neuronal injury and that mGluR1 antagonists may have therapeutic potential in brain injury.
Flk-1, a Receptor for Vascular Endothelial Growth Factor (VEGF), Is Expressed by Retinal Progenitor Cells
Authors: Yang Xianjie , Cepko Constance L.
Published: April 2018

Throughout development of the vertebrate retina, progenitor cells are multipotential, producing a variety of distinctive cell types. Little is known of the molecular mechanisms directing the determination of cell fate. We have examined retinal progenitor cells for expression of receptor tyrosine kinases in an attempt to define receptors that could allow a progenitor to respond to its environment. We found that the receptor tyrosine kinase Flk-1, previously shown to be expressed in endothelial cells, is also expressed in neural progenitor cells of the mouse retina. Flk-1 RNA expression in the retinal progenitors commences with the onset of neuronal differentiation and persists throughout retinal neurogenesis. Flk-1 RNA and protein levels in the retina vary temporally during development, as shown byin situhybridization and Western blot analysis. Patterns of β-galactosidase expression in mice containing the lacZ gene in place of the Flk-1 gene are consistent with Flk-1 being expressed in retinal progenitors. In addition, we show that the ligand of Flk-1, vascular endothelial growth factor (VEGF), is expressed in the developing retina by differentiated cells and that a chimeric ligand of VEGF fused to alkaline phosphatase binds to proliferating retinal progenitors. Furthermore, the neural retina-derived Flk-1 protein kinase is activated by VEGFin vitro. Thus, the Flk-1 receptor protein kinase is expressed on the surface of neural progenitors in mouse retina and may play a critical role in neurogenesis as well as in vasculogenesis.
Ventromedial Preoptic Prostaglandin E2 Activates Fever-Producing Autonomic Pathways
Authors: Scammell Thomas E. , Elmquist Joel K. , Griffin John D. , Saper Clifford B.
Published: April 2018

Fever is thought to be initiated by pyrogenic cytokines inducing the production of prostaglandin E2 (PGE2) in the preoptic area (POA); PGE2 may act as a paracrine mediator that stimulates the neural pathways that raise body temperature. This essential role for prostaglandins in fever first was proposed 25 years ago, but the specific preoptic cell groups at which PGE2 acts and the pathways through which fever is produced remain poorly understood. To better define the role of preoptic PGE2 in fever, we developed a new method for combining acute brain injections with Fos immunohistochemistry. We microinjected a threshold dose of PGE2 to construct an anatomically detailed map of fever-producing preoptic sites. The most pyrogenic preoptic sites were clustered along the ventromedial aspect of the POA, surrounding and just anterior to the organum vasculosum of the lamina terminalis. We then used Fos immunohistochemistry to identify the pattern of neural activation induced by fever-producing preoptic injections of PGE2 and compared it with the Fos pattern seen after systemic immune stimulation. PGE2 fever was accompanied by Fos induction in the ventromedial POA and the parvicellular subnuclei of the paraventricular nucleus of the hypothalamus (PVH). In contrast to the Fos pattern seen after intravenous lipopolysaccharide administration, PGE2 injection did not induce Fos in the circumventricular organs or the magnocellular subnuclei of the PVH. These observations establish a potential site of PGE2 action during fever and help define candidate pathways through which fever occurs.
Aging Changes in Voltage-Gated Calcium Currents in Hippocampal CA1 Neurons
Authors: Campbell Lee W. , Hao Su-Yang , Thibault Olivier , Blalock Eric M. , Landfield Philip W.
Published: April 2018

Previous current-clamp studies in rat hippocampal slice CA1 neurons have found aging-related increases in long-lasting calcium (Ca)-dependent and Ca-mediated potentials. These changes could reflect an increase in Ca influx through voltage-gated Ca channels but also could reflect a change in potassium currents. Moreover, if altered Ca influx is involved, it is unclear whether it arises from generally increased Ca channel activity, lower threshold, or reduced inactivation. To analyze the basis for altered Ca potentials, whole-cell voltage-clamp studies of CA1 hippocampal neurons were performed in nondissociated hippocampal slices of adult (3- to 5-month-old) and aged (25- to 26-month-old) rats. An aging-related increase was found in high-threshold Ca and barium (Ba) currents, particularly in the less variable, slowly inactivating (late) current at the end of a depolarization step. Input resistance of neurons did not differ between age groups. In steady-state inactivation and repetitive-pulse protocols, inactivation of Ca and Ba currents was not reduced and, in some cases, was slightly greater in aged neurons, apparently because of larger inward current. The current blocked by nimodipine was greater in aged neurons, indicating that some of the aging increase was in L-type currents. These results indicate that whole-cell Ca currents are increased with aging in CA1 neurons, apparently attributable to greater channel activity rather than to reduced inactivation. The elevated Ca influx seems likely to play a role in impaired function and enhanced susceptibility to neurotoxic influences.
Short-Term GDNF Treatment Provides Long-Term Rescue of Lesioned Nigral Dopaminergic Neurons in a Rat Model of Parkinson’s Disease
Authors: Winkler Christian , Sauer Hansjörg , Lee Chong S. , Björklund Anders
Published: April 2018

Glial cell line-derived neurotrophic factor (GDNF) has been shown to exert neuroprotective effects on dopamine (DA) neuronsin vivo. Here we report long-term rescue of nigral DA neurons after delayed short-term GDNF administration in a rat lesion model that reproduces the slowly progressing degenerative process seen in Parkinson’s disease. GDNF injected close to the substantia nigra provided near-complete protection and persistent survival of the lesioned nigral neurons for at least 4 months after discontinuation of GDNF treatment. Long-term rescue of the nigral cells, however, was not accompanied by any significant reinnervation of the lesioned striatal target or any signs of functional recovery in either drug-induced or spontaneous motor behaviors. We conclude that not only preservation of the nigral DA neurons but also restoration of striatal DA function is necessary for functional recovery in the rat Parkinson model.
Reconstruction of the Nigrostriatal Pathway by Simultaneous Intrastriatal and Intranigral Dopaminergic Transplants
Authors: Mendez Ivar , Sadi Damaso , Hong Murray
Published: April 2018

The main strategy in experimental and clinical neural transplantation in Parkinson’s disease has been to place fetal nigral grafts not in their ontogenic site (substantia nigra) but in their target area (striatum). The reason for this ectopic placement is the apparent inability of nigral grafts placed in the ventral mesencephalon (VM) of the adult host to grow axons for long distances that are capable of reaching the ipsilateral striatum and thus restoring the nigrostriatal pathway.

The present study demonstrates for the first time that simultaneous dopaminergic transplants (double grafts) placed in the substantia nigra and ipsilateral striatum of rats bearing unilateral 6-hydroxydopamine lesions reconstruct the dopaminergic nigrostriatal pathway in the adult rat brain. Numerous tyrosine hydroxylase-immunoreactive axons were observed arising from the intranigral graft and growing rostrally along the internal capsule and medial forebrain bundle to reinnervate the ipsilateral striatum, which also had received a dopaminergic graft. These double grafts achieved not only greater striatal reinnervation than the standard intrastriatal graft but also a faster and more complete rotational recovery to amphetamine challenge 6 weeks after transplantation.

These results suggest strongly that embryonic nigral transplants implanted in the striatum are capable of promoting growth and providing guidance to axons arising from a dopaminergic graft placed homotopically in the VM, resulting in restoration of the dopaminergic nigrostriatal projection. Reconstruction of the nigrostriatal pathway by double grafts may not only achieve substantial striatal reinnervation but may also contribute to the reestablishment of dopaminergic regulation of the nigrostriatal circuitry.
Intrinsic Variability of Ocular Dominance Column Periodicity in Normal Macaque Monkeys
Authors: Horton Jonathan C. , Hocking Davina R.
Published: April 2018

Little is known about intrinsic variation from animal to animal in the periodicity of columnar systems within various regions of the mammalian cerebral cortex. To address this issue, complete mosaics of the ocular dominance columns were reconstructed from flat-mounts of the left and right striate cortex (V1) in six normal adult macaques (Macaca fascicularis). To identify the columns, we enucleated the right eye and subsequently processed striate cortex for cytochrome oxidase (CO) activity. Average column areas for the intact eye and the missing eye were nearly equal, confirming that monocular enucleation in adult macaques produces negligible column shrinkage. The contralateral eye’s columns occupied more territory than the ipsilateral eye’s columns, even in the central visual field representation (0° to 8°), where they predominated by 52 to 48%. The column mosaics showed remarkable variation in periodicity. The number of column pairs along the V1/V2 border ranged from 101 sets in one monkey to 154 sets in another. Average column width along the V1/V2 border ranged between 670 and 395 μm, a nearly twofold difference. The widest columns were found in the foveal representation. This high degree of innate variability should be taken into account when considering the effects of various sensory manipulations (e.g., strabismus, anisometropia), which have been reported to alter the periodicity of ocular dominance columns. We found pronounced intrinsic variation in the width and number of ocular dominance columns in a sample of sixM.fascicularis, indicating that the number of hypercolumns within a given cortical area can range widely among normal members of the same species.
The Role of Activity in the Development of Long-Range Horizontal Connections in Area 17 of the Ferret
Authors: Ruthazer Edward S. , Stryker Michael P.
Published: April 2018

Horizontal connections in area 17 of adult cats and ferrets link cells with similar preferred orientations by a patchy network of projections extending several millimeters across the cortex. The maturation of orientation selectivity in ferret area 17 has been demonstrated previously by quantitative single-unit recording and optical imaging to begin at approximately postnatal days (P) 32–P36. We therefore made restricted injections of cholera toxin B-subunit (CTB) or CTB-gold into ferret area 17 at a series of developmental ages and statistically quantified the degree of clustering in plots of retrogradely labeled cells in tangential sections through layer III for comparison to the published values for orientation tuning at each age. At P21, horizontal connections within area 17 lacked patchiness entirely, although clear patches of labeled cells were present in extrastriate areas. By P27, significant clustering of horizontal connections within area 17 was present. A second phase of cluster refinement was observed to occur at approximately P34–P36, coinciding with the emergence of mature orientation tuning and maps. Continuous silencing of cortical action potentials by chronic tetrodotoxin infusion from P21 resulted in a spatially random distribution of retrogradely labeled cells at P34. In contrast, bilateral enucleation from P21 did not prevent the initial development of clustered horizontal connections. We conclude, based on our findings and those of others, that the anatomical specificity of long-range horizontal connections results from an activity-dependent process that initially can use spontaneous activity in the cortical and thalamic networks to establish crude periodic connections and later uses visual cues to refine these connections.
Differential Effects of Protein Synthesis Inhibition on the Activity-Dependent Expression of BDNF Transcripts: Evidence for Immediate-Early Gene Responses from Specific Promoters
Authors: Lauterborn Julie C. , Rivera Santiago , Stinis Curtiss T. , Hayes Valerie Y. , Isackson Paul J. , Gall Christine M.
Published: April 2018

In the adult rat forebrain, brain-derived neurotrophic factor (BDNF) expression is very rapidly induced by neuronal activity, suggesting that this might occur without intervening protein synthesis. The ratBDNFgene has four differentially regulated promoter regions; each gives rise to an mRNA containing a unique 5′ exon (I–IV) and a common 3′ exon (V) that codes for mature BDNF protein. The present study used exon-specificin situhybridization and bothin vivoandin vitropreparations to determine whether activity induces BDNF as an “immediate-early gene” (IEG) from specific promoter regions and to compare the regulation of BDNF and nerve growth factor (NGF). In cultured hippocampal slices, kainic acid markedly increased pan-BDNF (exon V) and NGF mRNA content; cycloheximide attenuated the effect of kainic acid on both.In vivostimulation of a paroxysmal afterdischarge increased both pan-BDNF and NGF mRNA levels in the dentate gyrus granule cells; pretreatment with anisomycin modestly attenuated the paroxysmal afterdischarge-induced increase of both transcripts. To determine whether partial drug effects on BDNF expression reflect the differential regulation of transcript species, levels of mRNAs containing exons I–IV were evaluated. A single afterdischarge increased exon I–IV-containing mRNA levels; anisomycin significantly attenuated the increase in exon I- and II-containing mRNAs but had no effect on the increase in exon III- and IV-containing mRNAs. These data show that for mature forebrain neurons, activity induces the expression of BDNF exon III- and IV-containing transcripts as IEG responses.
D1/D5 Dopamine Receptor Activation Increases the Magnitude of Early Long-Term Potentiation at CA1 Hippocampal Synapses
Authors: Otmakhova Nonna A. , Lisman John E.
Published: April 2018

The role of the mesolimbic dopaminergic system in the reinforcement of learning suggests that dopamine should be able to modulate activity-dependent synaptic plasticity. We have examined the effect of D1/D5 agonists on early long-term potentiation (LTP) (40 min) in the CA1 region of hippocampal slices. D1/D5 agonists (+)bromo-APB, 6-chloro-PB, and dihydrexidine increased the magnitude of LTP in a synapse-specific manner (by ∼10, 15, and 20%, respectively). This D1/D5 effect was mimicked by a low dose (10 μm) of the adenylyl cyclase activator forskolin. The D1/D5 antagonist (+)SCH 23390 reduced early LTP. In catecholamine-depleted slices, LTP was smaller by ∼20-25% and could not be decreased further by D1/D5 antagonist. Under these conditions, D1/D5 agonist 6-chloro-PB and forskolin produced a larger enhancement of LTP (20–25%), restoring it to the control level. At the same dose, dideoxyforskolin did not affect early LTP. The D1/D5 agonist effect was completely blocked by the D1/D5 antagonist (+)SCH 23390. These results indicate that dopamine produces a synapse-specific enhancement of early LTP through D1/D5 receptors and cAMP.
Differential Actions of Serotonin, Mediated by 5-HT1Band 5-HT2CReceptors, on GABA-Mediated Synaptic Input to Rat Substantia Nigra Pars Reticulata NeuronsIn Vitro
Authors: Stanford Ian M. , Lacey Michael G.
Published: April 2018

The ability of serotonin to modulate GABA-mediated synaptic input to substantia nigra pars reticulata (SNr) neurons was investigated with the use of whole-cell patch-clamp recording from slices of rat midbrain. Fast evoked GABAAreceptor-mediated synaptic currents (IPSCs) were attenuated reversibly ∼60% by serotonin, which also caused an inward current with reversal potential of −25 mV. This inward current was blocked by the 5-HT2receptor antagonist ritanserin, whereas the IPSC depression was blocked by the 5-HT1Breceptor antagonist pindolol. The amplitude ratio of IPSC pairs (50 msec interpulse interval) was enhanced by serotonin (in ritanserin) and also by the GABABreceptor agonist baclofen (which also depressed the IPSC), consistent with a presynaptic site of action in both cases. In contrast, spontaneous tetrodotoxin-sensitive GABAAsynaptic currents (sIPSCs) were increased in frequency by serotonin (an action that was sensitive to ritanserin, but not pindolol) but reduced in frequency by baclofen. SNr neurons therefore receive inhibitory synaptic input mediated by GABAAreceptors from at least two distinct sources. One, probably originating from the striatum, may be depressed via presynaptic 5-HT1Band GABABreceptors. The second is likely to arise from axon collaterals of SNr neurons themselves and is facilitated by an increase in firing via postsynaptic, somatodendritic 5-HT2Creceptor activation, but it is depressed by GABABreceptor activation. Thus, serotonin can both depolarize and disinhibit SNr neurons via 5-HT2Cand 5-HT1Breceptors, respectively, but excitation may be limited by GABA released from axon collaterals.
Multipotent CNS Stem Cells Are Present in the Adult Mammalian Spinal Cord and Ventricular Neuroaxis
Authors: Weiss Samuel , Dunne Christine , Hewson Jennifer , Wohl Cheryl , Wheatley Matt , Peterson Alan C. , Reynolds Brent A.
Published: April 2018

Neural stem cells in the lateral ventricles of the adult mouse CNS participate in repopulation of forebrain structuresin vivoand are amenable toin vitroexpansion by epidermal growth factor (EGF). There have been no reports of stem cells in more caudal brain regions or in the spinal cord of adult mammals. In this study we found that although ineffective alone, EGF and basic fibroblast growth factor (bFGF) cooperated to induce the proliferation, self-renewal, and expansion of neural stem cells isolated from the adult mouse thoracic spinal cord. The proliferating stem cells, in both primary culture and secondary expanded clones, formed spheres of undifferentiated cells that were induced to differentiate into neurons, astrocytes, and oligodendrocytes. Neural stem cells, whose proliferation was dependent on EGF+bFGF, were also isolated from the lumbar/sacral segment of the spinal cord as well as the third and fourth ventricles (but not adjacent brain parenchyma). Although all of the stem cells examined were similarly multipotent and expandable, quantitative analyses demonstrated that the lateral ventricles (EGF-dependent) and lumbar/sacral spinal cord (EGF+bFGF-dependent) yielded the greatest number of these cells. Thus, the spinal cord and the entire ventricular neuroaxis of the adult mammalian CNS contain multipotent stem cells, present at variable frequency and with uniquein vitroactivation requirements.
Primary Motor and Sensory Cortex Activation during Motor Performance and Motor Imagery: A Functional Magnetic Resonance Imaging Study
Authors: Porro Carlo A. , Francescato Maria Pia , Cettolo Valentina , Diamond Mathew E. , Baraldi Patrizia , Zuiani Chiara , Bazzocchi Massimo , di Prampero Pietro E.
Published: April 2018

The intensity and spatial distribution of functional activation in the left precentral and postcentral gyri during actual motor performance (MP) and mental representation [motor imagery (MI)] of self-paced finger-to-thumb opposition movements of the dominant hand were investigated in fourteen right-handed volunteers by functional magnetic resonance imaging (fMRI) techniques. Significant increases in mean normalized fMRI signal intensities over values obtained during the control (visual imagery) tasks were found in a region including the anterior bank and crown of the central sulcus, the presumed site of the primary motor cortex, during both MP (mean percentage increase, 2.1%) and MI (0.8%). In the anterior portion of the precentral gyrus and the postcentral gyrus, mean functional activity levels were also increased during both conditions (MP, 1.7 and 1.2%; MI, 0.6 and 0.4%, respectively).

To locate activated foci during MI, MP, or both conditions, the time course of the signal intensities of pixels lying in the precentral or postcentral gyrus was plotted against single-step or double-step waveforms, where the steps of the waveform corresponded to different tasks. Pixels significantly (r> 0.7) activated during both MP and MI were identified in each region in the majority of subjects; percentage increases in signal intensity during MI were on average 30% as great as increases during MP. The pixels activated during both MP and MI appear to represent a large fraction of the whole population activated during MP. These results support the hypothesis that MI and MP involve overlapping neural networks in perirolandic cortical areas.
Multiple NPY Receptors Coexist in Pre- and Postsynaptic Sites: Inhibition of GABA Release in Isolated Self-Innervating SCN Neurons
Authors: Chen Gong , van den Pol Anthony N.
Published: April 2018

Although NPY has been shown to influence the action of many transmitters in the brain, modulation of GABA, the primary inhibitory transmitter, has not been detected with electrophysiology. Using whole-cell patch-clamp recording, we found that NPY has a large modulatory effect on GABAergic neurons of the suprachiasmatic nucleus (SCN) that act as the circadian clock in the mammalian brain. NPY, acting at both Y1- and Y2-like receptors, reduced the frequency of spontaneous miniature inhibitory postsynaptic currents while having little effect on the postsynaptic GABA receptors, suggesting a presynaptic mechanism of NPY action. In single self-innervating neurons, application of either Y1 or Y2 agonists to the same neuron significantly inhibited the evoked autaptic GABA release. The use of single-neuron microcultures has allowed the demonstration that a single peptide, NPY, has two different receptors coded for by different genes in the same axon terminal. The Y1 and Y2 agonists also inhibited whole-cell calcium currents when applied to the same neuron, indicating a coexistence of Y1- and Y2-like receptors in the postsynaptic cell body. The self-innervating cell model we use here may be applicable generally for discriminating presynaptic versus postsynaptic actions of other neurotransmitters and neuromodulators and locating their subtype receptors.
GABABReceptor-Mediated Inhibition of Tetrodotoxin-Resistant GABA Release in Rodent Hippocampal CA1 Pyramidal Cells
Authors: Jarolimek Wolfgang , Misgeld Ulrich
Published: April 2018

Tight-seal whole-cell recordings from CA1 pyramidal cells of rodent hippocampus were performed to study GABABreceptor-mediated inhibition of tetrodotoxin (TTX)-resistant IPSCs. IPSCs were recorded in the presence of TTX and glutamate receptor antagonists. (R)-(−)-baclofen reduced the frequency of TTX-resistant IPSCs by a presynaptic action. The inhibition by (R)-(−)-baclofen was concentration-dependent, was not mimicked by the less effective enantiomer (S)-(+)-baclofen, and was blocked by the GABABreceptor antagonist CGP 55845A, suggesting a specific effect on GABABreceptors. The inhibition persisted in the presence of the Ca2+channel blocker Cd2+. There was no requirement for an activation of K+conductances by (R)-(−)-baclofen, because the inhibition of TTX-resistant IPSCs persisted in Ba2+and Cd2+. Because the time courses of TTX-resistant IPSCs were not changed by (R)-(−)-baclofen, there was no evidence for a selective inhibition of quantal release from a subgroup of GABAergic terminals. (R)-(−)-baclofen reduced the frequency of TTX-resistant IPSCs in guinea pigs and Wistar rats, whereas the inhibition was much smaller in Sprague Dawley rats. In Cd2+and Ba2+, β-phorbol-12,13-dibutyrate and forskolin enhanced the frequency of TTX-resistant IPSCs. Only β-phorbol-12,13-dibutyrate reduced the inhibition by (R)-(−)-baclofen. We conclude that GABABreceptors inhibit TTX-resistant GABA release through a mechanism independent from the well known effects on Ca2+or K+channels. The inhibition of quantal GABA release can be reduced by an activator of protein kinase C.
Estrogen Induces Axonal Outgrowth in the Nucleus Retroambiguus–Lumbosacral Motoneuronal Pathway in the Adult Female Cat
Authors: VanderHorst Veronique G. J. M. , Holstege Gert
Published: April 2018

In 1995, we discovered a new pathway in the cat, which originates from the nucleus retroambiguus (NRA) and terminates in a distinct set of lumbosacral hindlimb, axial, and pelvic floor motoneuronal cell groups [VanderHorst VGJM, Holstege G (1995) Caudal medullary pathways to lumbosacral motoneuronal cell groups in the cat: evidence for direct projections possibly representing the final common pathway for lordosis. J Comp Neurol 359:457–475]. The NRA is a compact group of interneurons located laterally in the caudal medulla oblongata. Its projection to lumbosacral motoneurons is thought to represent the final common pathway for male mounting and for female receptive or lordosis behavior. However, females only display lordosis behavior when they arein estrus, which suggests that the NRA–lumbosacral pathway is only active during estrus. This raised the question of whether estrogen affects this pathway. The effect of estrogen on the NRA–lumbosacral projection was studied light microscopically, using wheat-germ agglutinin horseradish peroxidase (WGA-HRP) as a tracer. The rubrospinal pathway served as control. The density of labeled NRA fibers in their target hindlimb motoneuronal cell groups appeared abundant in estrous and very weak in nonestrous cats. Such differences were not found in the rubrospinal pathway. For electron microscopical study, the NRA projection to the semimembranosus motoneuronal cell group was selected. In this cell group, an almost ninefold increase of labeled profiles was found in estrous versus nonestrous cats. Moreover, the semimembranous motoneuronal cell group contained labeled growth cones in estrous, but not in nonestrous, cats. The present study is the first to show that estrogen induces axonal outgrowth of a precisely identified pathway in the adult mammalian central nervous system. The possible mechanisms underlying this outgrowth are discussed.
Spatiotemporal Patterns of Spindle Oscillations in Cortex and Thalamus
Authors: Contreras Diego , Destexhe Alain , Sejnowski Terrence J. , Steriade Mircea
Published: April 2018

Spindle oscillations (7–14 Hz) appear in the thalamus and cortex during early stages of sleep. They are generated by the combination of intrinsic properties and connectivity patterns of thalamic neurons and distributed to cortical territories by thalamocortical axons. The corticothalamic feedback is a major factor in producing coherent spatiotemporal maps of spindle oscillations in widespread thalamic territories. Here we have investigated the spatiotemporal patterns of spontaneously occurring and evoked spindles by means of multisite field potential and unit recordings in intact cortex and decorticated animals. We show that (1) spontaneous spindle oscillations are synchronized over large cortical areas during natural sleep and barbiturate anesthesia; (2) under barbiturate anesthesia, the cortical coherence is not disrupted by transection of intracortical synaptic linkages; (3) in intact cortex animals, spontaneously occurring barbiturate spindle sequences occur nearly simultaneously over widespread thalamic territories; (4) in the absence of cortex, the spontaneous spindle oscillations throughout the thalamus are less organized, but the local coherence (within 2–4 mm) is still maintained; and (5) spindling propagation is observed in intact cortex animals only when elicited by low intensity cortical stimulation, applied shortly before the initiation of a spontaneous spindle sequence; propagation velocities are between 1 and 3 mm/sec, measured in the anteroposterior axis of the thalamus; increasing the intensity of cortical stimulation triggers spindle oscillations, which start simultaneously in all leads. We propose that,in vivo, the coherence of spontaneous spindle oscillations in corticothalamic networks is attributable to the combined action of continuous background corticothalamic input initiating spindle sequences in several thalamic sites at the same time and divergent corticothalamic and intrathalamic connectivity.
DrosophilaSerotonin Transporters Have Voltage-Dependent Uptake Coupled to a Serotonin-Gated Ion Channel
Authors: Galli A. , Petersen C.I. , deBlaquiere M. , Blakely R.D. , DeFelice L.J.
Published: April 2018

Serotonin (5HT) transporters (SERTs) couple to existing ion gradients to transport 5HT into presynaptic terminals. In mammalian SERTs, the transport cycle is reported as electroneutral, with a translocation of zero net charge, and 5HT uptake is independent of membrane voltage. Yet mammalian SERTs exhibit 5HT-induced currents, andDrosophilaSERTs (dSERTs) show voltage-dependent uptake. Thus, the relationship between uptake and current remains controversial; furthermore, the number of 5HT molecules translocated per ion channel event is unknown. To investigate this, we have used heterologous expression of cloned dSERTs to measure 5HT flux and dSERT currents concurrently under voltage clamp, and we have used fluctuation analysis to measure the size of the elementary ionic events in the same cells. RNA-injectedXenopusoocytes accumulate 5HT, and paroxetine or desipramine inhibit this uptake. RNA-injected oocytes also display paroxetine-sensitive 5HT-induced currents and 5HT-independent leak currents. Na replacement decreases the uptake and the induced currents. 5HT-induced current and 5HT uptake both increase at negative potentials, where 5HT carries ∼5% of the induced current. Recently, several groups have reported similar phenomena for other transporters, in which transmitter-induced currents exceed the predictions of coupled transport. We now provide evidence that in dSERT, ∼500 5HT molecules are translocated per channel opening, which, at −20 mV, carries ∼10,000 electronic charges. These data support a model in which 500 SERT cycles occur for each 5HT-induced channel opening or a model in which 500 5HT molecules and 10,000 electronic charges pass through a common pore.
Arachidonic Acid Inhibits Transient Potassium Currents and Broadens Action Potentials during Electrographic Seizures in Hippocampal Pyramidal and Inhibitory Interneurons
Authors: Keros Sotirios , McBain Chris J.
Published: April 2018

The transient outward potassium current was studied in outside-out macropatches excised from the soma of CA1 pyramidal neurons and stratum (st.) oriens–alveus inhibitory interneurons in rat hippocampal slices. Arachidonic acid dose dependently decreased the charge transfer associated with the transient current, concomitant with an increase in the rate of current inactivation. Arachidonic acid (AA) did not affect the voltage dependence of steady state inactivation but did prolong the period required for complete recovery from inactivation. The effects of AA were mimicked by the nonmetabolizable analog of AA, 5,8,11,14-eicosatetraynoic acid, suggesting that metabolic products of AA were not responsible for the observed blocking action. In addition, AA blocked st. oriens–alveus–lacunosum-moleculare interneuron transient currents but not currents recorded from basket cell interneurons. In current clamp experiments, AA was without effect on the action potential waveform of CA1 pyramidal neurons under control recording conditions. In voltage-clamp experiments, the use of a test pulse paradigm, designed to mimic the action potential voltage trajectory, revealed that the transient current normally associated with a single spike deactivates too rapidly for AA to have an effect. Transient currents activated by longer duration “action potential” waveforms, however, were attenuated by AA. Consistent with this finding was the observation that AA broadened interictal spikes recorded in the elevated [K+]omodel of epilepsy. These data suggest that AA liberated from hippocampal neurons may act to block the transient current selectively in both CA1 pyramidal neurons and inhibitory interneurons and to broaden action potentials selectively under pathological conditions.
Complementary and Overlapping Expression of Glial Cell Line-Derived Neurotrophic Factor (GDNF), c-ret Proto-Oncogene, and GDNF Receptor-α Indicates Multiple Mechanisms of Trophic Actions in the Adult Rat CNS
Authors: Trupp Miles , Belluardo Natale , Funakoshi Hiroshi , Ibáñez Carlos F.
Published: April 2018

Glial cell line-derived neurotrophic factor (GDNF), the most potent trophic factor yet described for both dopaminergic neurons of the substantia nigra and spinal motorneurons, has recently been shown to signal through a multireceptor complex composed of a novel glycosylphosphatidylinositol-anchored GDNF receptor-α (GDNFR-α) and the receptor tyrosine kinase product of the c-ret proto-oncogene (RET). Despite its importance, the individual expression patterns and the relationships between domains of expression of the different components of this trophic system are not understood. We show here byin situhybridization that GDNF mRNA is expressed in the normal adult rat brain in several targets of substantia nigra neurons, including striatum, nucleus accumbens, thalamic nuclei, olfactory tubercle, hippocampus, cerebellum, and cingulate cortex as well as in the internal granular cell layer of the olfactory bulb. Within the basal ganglia we observe a pronounced segregation of regions expressing GDNF from those expressing GDNF receptors, suggesting that within these structures GDNF is functioning in its anticipated role as a target-derived trophic factor. In addition, the expression of GDNF and both GDNF receptors within the cerebellum, hippocampus, and olfactory bulb may indicate a paracrine mode of action. Importantly, we also see expression of RET mRNA in cellular populations within the cerebellum and the glomerular layer of the olfactory bulb, as well as in the subthalamic nucleus, which lack GDNFR-α expression, indicating that RET functions either independently of GDNFR-α or with GDNFR-α presented intrans. Conversely, GDNFR-α is widely expressed in many regions in which RET expression is absent, suggesting that GDNFR-α may associate with additional signaling receptors. Finally, RET and GDNFR-α show distinct patterns of regulated expression in the brain after kainic acid stimulation and in the sciatic nerve after nerve transection. Taken together these findings indicate that GDNF, RET, and GDNFR-α utilize multiple mechanisms to comprise physiologically relevant trophic circuits for different neuronal populations.
Mash1andneurogenin1Expression Patterns Define Complementary Domains of Neuroepithelium in the Developing CNS and Are Correlated with Regions Expressing Notch Ligands
Authors: Ma Qiufu , Sommer Lukas , Cserjesi Peter , Anderson David J.
Published: April 2018

Genetic studies inDrosophilaand in vertebrates have implicated basic helix-loop-helix (bHLH) genes in neuronal fate determination and cell type specification. We have compared directly the expression ofMash1andneurogenin1(ngn1), two bHLH genes that are expressed specifically at early stages of neurogenesis. In the PNS these genes are expressed in complementary autonomic and sensory lineages. In the CNSin situhybridization to serial sections and double-labeling experiments indicate thatMash1andngn1are expressed in adjacent and nonoverlapping regions of the neuroepithelium that correspond to future functionally distinct areas of the brain. We also showed that in the PNS several other bHLH genes exhibit similar lineal restriction, as dongn1andMash1, suggesting that complementary cascades of bHLH factors are involved in PNS development. Finally, we found that there is a close association between expression ofngn1andMash1and that of two Notch ligands. These observations suggest a basic plan for vertebrate neurogenesis whereby regionalization of the neuroepithelium is followed by activation of a relatively small number of bHLH genes, which are used repeatedly in complementary domains to promote neural determination and differentiation.
Failed Cell Migration and Death of Purkinje Cells and Deep Nuclear Neurons in theweaverCerebellum
Authors: Maricich Stephen M. , Soha Jill , Trenkner Ekkhert , Herrup Karl
Published: April 2018

The mouse neurological mutantweaverhas an atrophic cerebellar cortex with deficits in both Purkinje and granule cell number. Although granule cells are known to die postnatally shortly after their final cell division, the cause of the Purkinje cell deficit (cell death vs lack of production) is unknown. We report here a quantitative analysis of large cerebellar neurons of theweavermutant during postnatal development. We explored the hypothesis that the cells of the entire cerebellar anlage were affected by the mutation by including in our study the neurons of the deep cerebellar nuclei (DCN). Our analysis reveals that in homozygousweavermutants (1) the DCN are displaced laterally, display an abnormal anatomy, and suffer a 20–25% decrease in neuron number; (2) this numerical deficit is located in medial regions, similar to the localization of cortical deficits in both Purkinje and granule cells; (3) pyknotic figures are present in the juvenile DCN and in the Purkinje cell layer; and (4) the majority of cell death in these populations occurs not in medial regions where the numerical deficits are observed, but rather laterally where adult cell number is nearly normal. These results lead us to propose that the completeweaverphenotype includes a failure of the cell movements that lead to the fusion of the bilateral cerebellar anlage, and that this failure to migrate properly leaves some of the Purkinje cells and DCN neurons in a position where they are unable to make appropriate connections, leading to their death. In addition to implications for normal development, these observations suggest thatweavereffects on the cerebellum can be unified into one consolidated model in which failure of cell movement affects all major cerebellar neurons.
Transneuronal Labeling of a Nociceptive Pathway, the Spino-(Trigemino-)Parabrachio-Amygdaloid, in the Rat
Authors: Jasmin Luc , Burkey Adam R. , Card J. Patrick , Basbaum Allan I.
Published: April 2018

Transneuronal tracing of a nociceptive pathway, the spino-(trigemino)-parabrachio-amygdaloid pathway, was performed using an α-herpes virus, the Bartha strain of pseudorabies virus (PRV). Microinjection of PRV into the central nucleus of the amygdala (Ce) resulted in progressive retrograde and transneuronal infection of a multisynaptic circuit involving neurons in the brainstem and spinal cord as detected immunocytochemically. At short survival (26 hr), retrogradely labeled neurons were concentrated in the external lateral nucleus of the parabrachial complex (elPB) but were absent from both the trigeminal nucleus caudalis (TNC) and the spinal cord. At longer survivals (52 hr), labeled cells were present in lamina I of both the TNC and spinal dorsal horn. Retrograde labeling from the Ce with Fluoro-gold demonstrated that elPB neurons have long dendrites extending laterally into the terminal field of spinal and trigeminal afferents, where transneuronal passage of PRV to these afferents could occur. Even longer survivals (76 hr) resulted in a columnar pattern of cell labeling in the TNC and spinal dorsal horn that extended from lamina I into lamina II. At this longest survival, primary sensory neurons became infected. Bilateral excitotoxic lesions of the elPB blocked almost all viral passage from the Ce to superficial laminae of the TNC and spinal dorsal horn. These results demonstrate that nociceptive input to the amygdala is relayed from neurons in lamina I through the elPB. We propose that this modular arrangement of lamina I and II neurons may provide the basis for spinal processing of peripheral input to the amygdala.