bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonobligate Role of Early or Sustained Expression of Immediate-Early Gene Proteins c-Fos, c-Jun, and Zif/268 in Hippocampal Mossy Fiber Sprouting
Authors: Nahm Walter K. , Noebels Jeffrey L.
Published: April 2018

Axon sprouting in dentate granule cells is an important model of structural plasticity in the hippocampus. Although the process can be triggered by deafferentation, intense activation of glutamate receptors, and other convulsant stimuli, the specific molecular steps required to initiate and sustain mossy fiber (MF) reorganization are unknown. The cellular immediate early genes (IEGs)c-fos,c-jun, andzif/268are major candidates for the initial steps of this plasticity, because they encode transcription factors that may trigger cascades of activity-dependent neuronal gene expression and are strongly induced in all experimental models of MF sprouting. The mutant mouse stargazer offers an important opportunity to test the specific role of IEGs, because it displays generalized nonconvulsive epilepsy and intense MF sprouting in the absence of regional cell injury. Here we report that stargazer mice show no detectable elevations in c-Fos, c-Jun, or Zif/268 immediate early gene proteins (IEGPs) before or during MF growth. Experimental results in stargazer, including (1) a strong IEGP response to kainate-induced convulsive seizures, (2) no IEGP response after prolongation of spike-wave synchronization, (3) no IEGP increase at the developmental onset of seizures or after prolonged seizure suppression, and (4) unaltered levels of the intracellular Ca2+-buffering proteins calbindin-D28kor parvalbumin, exclude the possibility that absence of an IEGP response in stargazer is either gene-linked or suppressed by known refractory mechanisms. These data demonstrate that increased levels of these IEGPs are not an obligatory step in MF-reactive sprouting and differentiate the early downstream molecular cascades of two major seizure types.
Functional Streams and Local Connections of Layer 4C Neurons in Primary Visual Cortex of the Macaque Monkey
Authors: Yabuta N. Harumi , Callaway Edward M.
Published: April 2018

The primate visual system is composed of multiple, functionally specialized cortical areas. The functional diversity among areas is thought to reflect different contributions from early parallel visual pathways to the area V1 neurons providing input to “higher” cortical areas. The M pathway is believed to provide information about motion and contrast, via layer 4B of V1, to dorsal visual areas. The P pathway is believed to provide information about shape and color, via layer 2/3 of V1, to ventral visual areas, with specialized contributions from cytochrome-oxidase (CO) blob versus interblob neurons. However, the detailed anatomical relationships between the M and P pathways and the neurons in V1 that provide input to higher extrastriate cortical areas are poorly understood. To study these relationships, spiny stellate neurons in the M- and P-recipient layers of V1, 4Cα and 4Cβ, respectively, were intracellularly labeled, and their axonal and dendritic arbors were reconstructed. We find that neurons with dendrites in upper layer 4Cα project axons to layer 4B and CO blobs in layer 2/3, thus relaying M input to these regions. Other neurons in lower layer 4Cα provide M input to interblobs. These cells have either (1) dendrites restricted to lower layer 4Cα and axons specifically targeting layer 2/3 interblobs, or (2) dendrites in lower 4Cα and 4Cβ and axons targeting blobs and interblobs. P-recipient layer 4Cβ neurons have dense axonal arbors in both blobs and interblobs but not layer 4B. Quantitative analyses reveal that 4Cα cells provide approximately five times more synapses than 4Cβ cells to layer 4B, whereas 4Cβ cells provide five times more synapses than 4Cα cells to layer 2/3. These observations imply that M input is dominant in layer 4B. In layer 2/3, both blobs and interblobs receive M and P input, but the P input is dominant, and M input to interblobs derives exclusively from a subpopulation of M afferents that targets lower 4Cα, not from afferents targeting only upper 4Cα (cf. Blasdel and Lund, 1983). We speculate that the M and P pathways to interblobs are “X-like” linear systems, whereas blobs also receive nonlinear “Y-like” M input.
Survival of Purified Rat PhotoreceptorsIn VitroIs Stimulated Directly by Fibroblast Growth Factor-2
Authors: Fontaine Valérie , Kinkl Norbert , Sahel José , Dreyfus Henri , Hicks David
Published: April 2018

Basic fibroblast growth factor (FGF-2) influences the differentiation and survival of retinal photoreceptorsin vivoandin vitro, but it is not known whether it acts directly on photoreceptor FGF receptors or indirectly through activation of surrounding cells. To clarify the effects of FGF-2 on photoreceptor survival, we developed a purified photoreceptor culture system. The outer nuclear layers of postnatal day 5–15 rat retinas were isolated by vibratome sectioning, and the photoreceptor fractions obtained were enzymatically dissociated. Photoreceptors were maintained in monolayer culture for 1 week in a chemically defined medium. Immunocytochemical labeling showed that >99.5% of cells were photoreceptors, and glial contamination represented ∼0.2%. Photoreceptors from postnatal day 5–9 retinas survived for at least 24 hrin vitro, whereas cells from postnatal day 10–15 retinas died rapidly. Subsequent studies performed with postnatal day 5 photoreceptors showed that their survival was increased in a dose-dependent manner after the addition of FGF-2. In control cultures, 36% of originally seeded photoreceptors were alive after 5 din vitro, and in the presence of 20 ng/ml FGF-2 this number was doubled to 62%. This increase was not caused by proliferation of photoreceptor precursors. Denaturing or blocking FGF-2 prevented enhancement of survival. Conversely, only 25.5% of photoreceptors survived in the presence of epidermal growth factor (EGF). FGF- and EGF-receptor mRNA and proteins were detected in purified photoreceptorsin vitro, and addition of FGF-2 or EGF led to tyrosine phosphorylation of photoreceptor proteins. These data support a direct mechanism of action for FGF-2 stimulation of photoreceptor survival.
Axotomy Reduces the Effect of Analgesic Opioids Yet Increases the Effect of Nociceptin on Dorsal Root Ganglion Neurons
Authors: Abdulla Fuad A. , Smith Peter A.
Published: April 2018

There is some doubt as to the effectiveness of opioids in the management of neuropathic pain. We therefore examined the actions of morphine and the opioid-like peptide nociceptin (both 1 μ) on dorsal root ganglion (DRG) neurons that were isolated from control or from nerve-injured rats. Both substances reduced ω-conotoxin (CTX) GVIA-sensitive, N-type Ca2+channel current and small persistent nifedipine/ CTX-insensitive (non-N, non-L type) current. Nifedipine-sensitive L-type current was unaffected. The effect of nociceptin was antagonized by naloxone benzoylhydrazone (nalbzoh) but not by naloxone. Sciatic nerve section (axotomy) profoundlyreducedthe effects of morphine and the μ-receptor agonistd-ala2,N-Me-Phe4,Gly-ol5enkephalin (DAMGO). The effect of the κ-agonist [(+)-(5α,7α,8β)-N-methyl-N-(7-(1-pyrrolidinyl)-1-oxaspiro(4,5)dec-8-yl)-benzeneacetamide] (U69593) was unchanged, whereas the effect of nociceptin wasincreased. All agonists produced their strongest effects on the small, putative nociceptive cells and their weakest effects on the largest cells. The δ-receptor agonist, enkephalind-pen2,5(DPDPE), was without effect on control or on axotomized cells. These and other data suggest that the functional downregulation of μ-opioid receptors on sensory nerves contributes to the poor efficacy of opioids in neuropathic pain. Also, the increased effectiveness of nociceptin after axotomy supports the hypothesis that its actions are mediated via a “non-opioid” receptor. Pronounced suppression of Ca2+channel current in axotomized DRG neurons by nociceptin led to a reduction in Ca2+-dependent K+conductance and a marked increase in excitability. Despite this, the spinal administration of nociceptin or agonists that activate ORL1(opioid-like orphan receptor) may prove to be of clinical interest in the management of neuropathic pain.
The Vesicular GABA Transporter, VGAT, Localizes to Synaptic Vesicles in Sets of Glycinergic as Well as GABAergic Neurons
Authors: Chaudhry Farrukh A. , Reimer Richard J. , Bellocchio Elizabeth E. , Danbolt Niels C. , Osen Kirsten K. , Edwards Robert H. , Storm-Mathisen Jon
Published: April 2018

A transporter thought to mediate accumulation of GABA into synaptic vesicles has recently been cloned (McIntire et al., 1997). This vesicular GABA transporter (VGAT), the first vesicular amino acid transporter to be molecularly identified, differs in structure from previously cloned vesicular neurotransmitter transporters and defines a novel gene family. Here we use antibodies specific for N- and C-terminal epitopes of VGAT to localize the protein in the rat CNS. VGAT is highly concentrated in the nerve endings of GABAergic neurons in the brain and spinal cord but also in glycinergic nerve endings. In contrast, hippocampal mossy fiber boutons, which although glutamatergic are known to contain GABA, lack VGAT immunoreactivity. Post-embedding immunogold quantification shows that the protein specifically associates with synaptic vesicles. Triple labeling for VGAT, GABA, and glycine in the lateral oliva superior revealed a higher expression of VGAT in nerve endings rich in GABA, with or without glycine, than in others rich in glycine only. Although the great majority of nerve terminals containing GABA or glycine are immunopositive for VGAT, subpopulations of nerve endings rich in GABA or glycine appear to lack the protein. Additional vesicular transporters or alternative modes of release may therefore contribute to the inhibitory neurotransmission mediated by these two amino acids.
Pituitary Adenylate Cyclase-Activating Polypeptide Expression and Modulation of Neuronal Excitability in Guinea Pig Cardiac Ganglia
Authors: Braas Karen M. , May Victor , Harakall Susan A. , Hardwick Jean C. , Parsons Rodney L.
Published: April 2018

Cardiac output is regulated by the coordinate interactions of stimulatory sympathetic and inhibitory parasympathetic signals. Intracardiac parasympathetic ganglia are integrative centers of cardiac regulation, and modulation of the parasympathetic drive on the heart is accomplished by altering intrinsic cardiac ganglion neuron excitability. The pituitary adenylate cyclase-activating polypeptide (PACAP)/vasoactive intestinal peptide (VIP) family of peptides modulates cardiac function, and in guinea pig heart, PACAP appears to act directly on intrinsic parasympathetic cardiac ganglia neurons through PACAP-selective receptors. A multidisciplinary project tested whether cardiac PACAP peptides act through PACAP-selective receptors as excitatory neuromodulators amplifying the parasympathetic inhibition from guinea pig cardiac ganglia. Thein vivosources of regulatory PACAP peptides were localized immunocytochemically to neuronal fibers and a subpopulation of intrinsic postganglionic cardiac neurons. RT-PCR confirmed that cardiac ganglia expressed proPACAP transcripts and have PACAP peptide biosynthetic capabilities. Messenger RNA encoding PACAP-selective PAC1 receptor isoforms were also present in cardiac ganglia. Alternative splicing of PAC1 receptor transcripts produced predominant expression of thevery shortvariant with neither HIP nor HOP cassettes; lower levels of the PAC1HOP2 receptor mRNA were present. Almost all of the parasympathetic neurons expressed membrane-associated PAC1 receptor proteins, localized immunocytochemically, which correlated with the population of cells that responded physiologically to PACAP peptides. PACAP depolarized cardiac ganglia neurons and increased neuronal membrane excitability. The rank order of peptide potency on membrane excitability in response to depolarizing currents was PACAP27>PACAP38>VIP. The PACAP-induced increase in excitability was not a function of membrane depolarization nor was it caused by alterations in action potential configuration. These results support roles for PACAP peptides as integrative modulators amplifying, through PACAP-selective receptors, the parasympathetic cardiac ganglia inhibition of cardiac output.
Activation of CNS Circuits Producing a Neurogenic Cystitis: Evidence for Centrally Induced Peripheral Inflammation
Authors: Jasmin Luc , Janni Gabriella , Manz Herbert J. , Rabkin Samuel D.
Published: April 2018

We present a model of neurogenic cystitis induced by viral infection of specific neuronal circuits of the rat CNS. Retrograde infection by pseudorabies virus (PRV) of neuronal populationsneighboringthose that innervate the bladder consistently led to a localized immune response in the CNS and bladder inflammation. Infection of bladder circuits themselves or of circuits distant from these rarely produced cystitis. Absence of virus in bladder and urine ruled out an infectious cystitis. Total denervation of the bladder, selective C-fiber deafferentation, or bladder sympathectomy prevented cystitis without affecting the CNS disease, indicating a neurogenic component to the inflammation. The integrity of central bladder-related circuits is necessary for the appearance of bladder inflammation, because only CNS lesions affecting bladder circuits, i.e., bilateral dorsolateral or ventrolateral funiculectomy, as well as bilateral lesions of Barrington’s nucleus/locus coeruleus area, prevented bladder inflammation. The close proximity in the CNS of noninfected visceral circuits to infected somatic neurons would thus permit a bystander effect, leading to activation of the sensory and autonomic circuits innervating the bladder and resulting in a neurogenic inflammation localized to the bladder. The present study indicates that CNS dysfunction can bring about a peripheral inflammation.
Indications for GABA-Immunoreactive Axo-Axonic Contacts on the Intraspinal Arborization of a Ib Fiber in Cat: A Confocal Microscope Study
Authors: Lamotte d’Incamps Boris , Destombes Josette , Thiesson Danièle , Hellio Raymond , Lasserre Xavier , Kouchtir-Devanne Nezha , Jami Léna , Zytnicki Daniel
Published: April 2018

Confocal microscopy was used to detect GABA-immunoreactive axo-axonic appositions, indicating possible synaptic contacts, on Ib fiber terminals in the lumbosacral spinal cord. A Ib fiber from posterior biceps-semitendinosus muscles was labeled by intra-axonal ejection of tetramethylrhodamine dextran (red), and serial sections of S1–L7 spinal cord segments were processed for GABA immunocytochemistry revealed by fluorescein isothiocynate (green). Appositions between GABA-immunoreactive structures and the labeled fiber appeared as yellow spots because of the presence of both fluorochromes in small volumes (0.3 * 0.3 * 0.5 μm3) of tissue. These spots were identified as probable axo-axonic contacts when: (1) they were observed in two to four serial confocal planes, indicating that they did not occur by chance; and (2) their sizes, shapes, and locations were similar to those of axo-axonic contacts found on Ia terminals, known to bear presynaptic boutons, and resembled the axo-axonic synapses described in electron microscope studies of Ib boutons in Clarke’s column. A total of 59 presumed axo-axonic contacts was observed on two Ib collaterals, representing an estimated 20% of the total complement. In a three-dimensional reconstruction of one collateral, they were mostly located in terminal positions, and some branches bore more contacts than others. Such differential distribution could not result from chance appositions between GABAergic structures and Ib arborization and further supported the identification of axo-axonic contacts. Segmental Ib collaterals bear axo-axonic synapses that might ensure differential funneling of information toward different targets.
The Connection from Cortical Area V1 to V5: A Light and Electron Microscopic Study
Authors: Anderson John C. , Binzegger Tom , Martin Kevan A. C. , Rockland K. S.
Published: April 2018

Area V5 (middle temporal) in the superior temporal sulcus of macaque receives a direct projection from the primary visual cortex (V1). By injecting anterograde tracers (biotinylated dextran andPhaseolus vulgarislectin) into V1, we have examined the synaptic boutons that they form in V5 in the electron microscope. Nearly 80% of the target cells in V5 were spiny (excitatory). The boutons formed asymmetric (Gray’s type 1) synapses with spines (54%), dendrites (33%), and somata (13%). All somatic targets and some (26%) of the target dendritic shafts showed features characteristic of smooth (inhibitory) cells. Each bouton formed, on average, 1.7 synapses. The larger boutons formed multiple synapses with the same neuron and completely enveloped the entire spine head. On most dendritic shafts and all somata the postsynaptic densityen facewas disk-shaped but in about half the cases the reconstructed postsynaptic densities of synapses on spines appeared as complete or partial annuli. Even in the zones of densest innervation only 3% of the asymmetric synapses were formed by the labeled boutons. Although the V1 projection forms only a small minority of synapses in V5, its affect could be considerably amplified by local circuits in V5, in a way analogous to the amplification of the small thalamic input to area V1.
Extraocular Motor Unit and Whole-Muscle Responses in the Lateral Rectus Muscle of the Squirrel Monkey
Authors: Goldberg Stephen J. , Meredith M. Alex , Shall Mary S.
Published: April 2018

Because primate studies provide data for the current experimental models of the human oculomotor system, we investigated the relationship of lateral rectus muscle motoneuron firing to muscle unit contractile characteristics in the squirrel monkey. Also examined was the correlation of whole-muscle contractile force with the degree of evoked eye displacement. A force transducer was used to record lateral rectus whole-muscle or muscle unit contraction in response to abducens whole-nerve stimulation or stimulation of single abducens motoneurons or axons. Horizontal eye displacement was recorded using a magnetic search coil.

(1) Motor units could be categorized based on contraction speed (fusion frequency) and fatigue. (2) The kt value (change in motoneuronal firing necessary to increase motor unit force by 1.0 mg) of the units correlated with maximum tetanic tension. (3) There was some tendency for maximum tetanic tension of this unit population to separate into three groups. (4) At a constant frequency of 100 Hz, 95% of the motor units demonstrated significantly different force levels dependent on immediately previous stimulation history (hysteresis). (5) A mean force change of 0.32 gm/° and a mean frequency change of 4.7 Hz/° of eye displacement were observed in response to whole-nerve stimulation.

These quantitative data provide the first contractile measures of primate extraocular motor units. Models of eye movement dynamics may need to consider the nonlinear transformations observed between stimulation rate and muscle tension as well as the probability that as few as two to three motor units can deviate the eye 1°.
Selective Neuronal Expression of Green Fluorescent Protein with Cytomegalovirus Promoter Reveals Entire Neuronal Arbor in Transgenic Mice
Authors: van den Pol Anthony N. , Ghosh Prabhat K.
Published: April 2018

In simple nervous systems, identified groups of neurons can be studied in depth. To allow the same advantage in the mammalian brain, we have generated green fluorescent protein (GFP) transgenic mice in which only a few types of neurons are strongly labeled with a fluorescent molecule, which the neurons synthesize internally, allowing the cells, their dendrites, filopodia, and axons to be identified in both living and fixed CNS, in slices and culture. The same neurons, with GFP expression controlled by part of the major immediate early promoter of human cytomegalovirus (CMV), show GFP beginning early in development, from one generation to the next, allowing cellular and physiological studies of axonal and dendritic growth, fate mapping, anatomical connections, and synapse formation in identified neurons. The human CMV promoter sequence we used was different from that used in previous work with other reporter genes and gave a dramatically different pattern of expression. Two transgenic lines with the same CMV promoter show similar anatomical patterns of expression in the present study. Strong GFP labeling was found in a subpopulation of mossy fibers that innervated parasagittal bands in the cerebellar cortex and olfactory axons that projected into the olfactory bulb, subsets of motoneurons and dorsal root ganglion cells, granule but not mitral cells of the olfactory bulb, and a group of neurons in the hypothalamic suprachiasmatic nucleus. A novel type of neuron was strongly labeled in the olfactory bulb external plexiform layer. In normal brains, CMV does not constitute a threat, but in the developing brain, CMV can cause debilitating neurodegeneration and death; studies using the CMV promoter aid in understanding the affinity of CMV that has been suggested for specific brain regions.
Modulation of Synaptic GABAAReceptor Function by PKA and PKC in Adult Hippocampal Neurons
Authors: Poisbeau Pierrick , Cheney Michael C. , Browning Michael D. , Mody Istvan
Published: April 2018

Several protein kinases are known to phosphorylate Ser/Thr residues of certain GABAAreceptor subunits. Yet, the effect of phosphorylation on GABAAreceptor function in neurons remains controversial, and the functional consequences of phosphorylating synaptic GABAAreceptors of adult CNS neurons are poorly understood. We used whole-cell patch-clamp recordings of GABAAreceptor-mediated miniature IPSCs (mIPSCs) in CA1 pyramidal neurons and dentate gyrus granule cells (GCs) of adult rat hippocampal slices to determine the effects of cAMP-dependent protein kinase (PKA) and Ca2+/phospholipiddependent protein kinase (PKC) activation on the function of synaptic GABAAreceptors. The mIPSCs recorded in CA1 pyramidal cells and in GCs were differentially affected by PKA and PKC. In pyramidal cells, PKA reduced mIPSC amplitudes and enhanced the fraction of events decaying with a double exponential, whereas PKC was without effect. In contrast, in GCs PKA was ineffective, but PKC increased the peak amplitude of mIPSCs and also favored double exponential decays. Intracellular perfusion of the phosphatase inhibitor microcystin revealed that synaptic GABAAreceptors of pyramidal cells, but not those of GCs, are continually phosphorylated by PKA and conversely, dephosphorylated, most likely by phosphatase 1 or 2A. This differential, brain region-specific phosphorylation of GABAAreceptors may produce a wide dynamic range of inhibitory synaptic strength in these two regions of the hippocampal formation.
A Pair of Reciprocally Inhibitory Histaminergic Sensory Neurons Are Activated within the Same Phase of Ingestive Motor Programs inAplysia
Authors: Evans Colin G. , Alexeeva Vera , Rybak Jurgen , Karhunen Tuula , Weiss Klaudiusz R. , Cropper Elizabeth C.
Published: April 2018

Previous studies have shown that each buccal ganglion inAplysiacontains two B52 neurons, one in each hemiganglion. We now show that there are two B52 neurons in a single buccal hemiganglion and four cells in an animal. We also show that the B52 neurons are histamine-immunoreactive and use reverse phase HPLC to show that the histamine-immunoreactive substance is authentic histamine. Previous studies have shown that the B52 neurons make numerous inhibitory synaptic connections with neurons active during the radula closing/retraction phase of ingestive motor programs. A computational model of theAplysiafeeding central pattern generator has, therefore, suggested that the B52 neurons play a role in terminating closing/retraction. Consistent with this idea we show that both B52 neurons fire at the beginning of radula opening/protraction. We also show that both B52 neurons are sensory neurons. They are depolarized when a flap of connective tissue adjacent to the buccal commissural arch is stretched. During ingestive feeding this is likely to occur at the peak of closing/retraction as opening/protraction begins. In the course of this study we compare the two ipsilateral B52 neurons and show that these cells are virtually indistinguishable; e.g., they use a common neurotransmitter, make the same synaptic connections, and are both sensory as well as premotor neurons. Nevertheless we show that the B52 neurons are reciprocally inhibitory. Our results, therefore, strikingly confirm theoretical predictions made by others that neurons that inhibit each other will not necessarily participate in antagonistic phases of behavior.
A Novel Pineal Night-Specific ATPase Encoded by the Wilson Disease Gene
Authors: Borjigin Jimo , Payne Aimee S. , Deng Jie , Li Xiaodong , Wang Michael M. , Ovodenko Boris , Gitlin Jonathan D. , Snyder Solomon H.
Published: April 2018

We have identified a pineal night-specific ATPase (PINA), a novel splice variant of the ATP7B gene disrupted in Wilson disease (WD). PINA expression exhibits a dramatic diurnal rhythm in both pineal gland and retina with 100-fold greater expression at night than at day. PINA is expressed in pinealocytes and a subset of photoreceptors in adult rats and is transiently expressed in the retinal pigment epithelium and the ciliary body during retinal development. Nocturnal pineal expression of PINA is under the control of a suprachiasmatic nucleus clock mediated by superior cervical ganglion innervation of the pineal.In vitro, PINA expression in pineal cells can be stimulated by agents activating the cAMP signal transduction pathway. PINA is able to restore copper transport activity inSaccharomyces cerevisiaedeficient in the homologous copper-transporting ATPase CCC2, suggesting that this protein may function as a copper transporter in rat pinealocytes. These studies suggest a potential role of rhythmic copper metabolism in pineal and/or retina circadian function.
Temporally Graded Retrograde Amnesia of Contextual Fear after Hippocampal Damage in Rats: Within-Subjects Examination
Authors: Anagnostaras Stephan G. , Maren Stephen , Fanselow Michael S.
Published: April 2018

We have shown previously that electrolytic lesions of the dorsal hippocampus (DH) produce a severe deficit in contextual fear if made 1 d, but not 28 d, after fear conditioning (Kim and Fanselow, 1992). As such, the hippocampus seems to play a time-limited role in the consolidation of contextual fear conditioning. Here, we examine retrograde amnesia of contextual fear produced by DH lesions in a within-subjects design. Unlike our previous reports, rats had both a remote and recent memory at the time of the lesion. Rats were given 10 tone–shock pairings in one context (remote memory) and 10 tone–shock pairings in a distinct context (with a different tone) 50 d later (recent memory), followed by DH or sham lesions 1 d later. Relative to controls, DH-lesioned rats exhibited no deficit in remote contextual fear, but recent contextual fear memory was severely impaired. They also did not exhibit deficits in tone freezing. This highly specific deficit in recent contextual memory demonstrated in a within-subjects design favors mnemonic over performance accounts of hippocampal involvement in fear. These findings also provide further support for a time-limited role of the hippocampus in memory storage.
Activation of Human D3 Dopamine Receptor Inhibits P/Q-Type Calcium Channels and Secretory Activity in AtT-20 Cells
Authors: Kuzhikandathil Eldo V. , Oxford Gerry S.
Published: April 2018

The D3 dopamine receptor is postulated to play an important role in the regulation of neurotransmitter secretion at both pre- and postsynaptic terminals. However, this hypothesis and the underlying mechanisms remain untested because of the lack of D3-selective ligands, paucity of appropriate model secretory systems, and the weak and inconsistent coupling of D3 receptors to classical signal transduction pathways. The absence of ligands that selectively discriminate between D3 and D2 receptorsin vivoprecludes the study of D3 receptor function in the brain and necessitates the use of heterologous expression systems. In this report we demonstrate that activation of the human D3 dopamine receptor expressed in the AtT-20 neuroendocrine cell line causes robust inhibition of P/Q-type calcium channels via pertussis toxin-sensitive G-proteins. In addition, using the vesicle trafficking dye FM1–43, we show that D3 receptor activation significantly inhibits spontaneous secretory activity in these cells. Our results not only support the hypothesis that the D3 receptor can regulate secretory activity but also provide insight into the underlying signaling mechanisms. We propose a functional model in which the D3 receptor tightly regulates neurotransmitter release at a synapse by only allowing the propagation of spikes above a certain frequency or burst-duration threshold.
Spatial- and Task-Dependent Neuronal Responses during Real and Virtual Translocation in the Monkey Hippocampal Formation
Authors: Matsumura Nobuhisa , Nishijo Hisao , Tamura Ryoi , Eifuku Satoshi , Endo Shunro , Ono Taketoshi
Published: April 2018

Neuropsychological data in humans demonstrated a pivotal role of the medial temporal lobe, including the hippocampal formation (HF) and the parahippocampal gyrus (PH), in allocentric (environment-centered) spatial learning and memory. In the present study, the functional significance of the monkey HF and PH neurons in allocentric spatial processing was analyzed during performance of the spatial tasks. In the tasks, the monkey either freely moved to one of four reward areas in the experimental field by driving a cab that the monkey rode (real translocation task) or freely moved a pointer to one of four reward areas on the monitor (virtual translocation task) by manipulating a joystick. Of 389 neurons recorded from the monkey HF and PH, 166 had place fields that displayed increased activity in a specific area in the experimental field and/or on the monitor (location-differential neurons). More HF and PH neurons responded in the real translocation task. These neurons had low mean spontaneous firing rates (0.96 spikes/sec), similar to those of rodent HF place cells. The remaining nonresponsive neurons had significantly higher mean firing rates (8.39 spikes/sec), similar to interneurons or θ cells in the rodent HF. Furthermore, most location-differential neurons showed different responses in different tasks. These results suggest that the HF and PH are crucial in allocentric information processing and, moreover, that the HF can encode different reference frames that are context or task-dependent. This may be the neural basis of episodic memory.
Specific Alteration of Spontaneous GABAergic Inhibition in Cerebellar Purkinje Cells in Mice Lacking the Potassium Channel Kv1.1
Authors: Zhang Chuan-Li , Messing Albee , Chiu Shing Yan
Published: April 2018

In the cerebellum, the basket cell innervation on Purkinje cells provides a major GABAergic inhibitory control of the single efferent output from the cerebellum. The Shaker-type K channel Kv1.1 is localized at the axon arborization preceding the terminal of the basket cells and is therefore a potential candidate for regulating the GABAergic inhibition. In this study, we directly assess this role of Kv1.1 by electrophysiological analysis of Kv1.1 null mutant mice. Whole-cell patch-clamp recordings of spontaneous IPSCs (sIPSCs) were made from Purkinje cells in thin cerebellar slices from postnatal day (P)10–15 Kv1.1-null mutants using wild-type littermates as controls. The null mutation confers a very specific change in the sIPSC: the frequency increases about twofold, without accompanying changes in the mean and variance of its amplitude distribution. The frequency and amplitude of the miniature IPSCs (mIPSCs) are unaffected. Spontaneous firing rate of the basket cells is unaltered. Evoked IPSC does not show multiple activity in the mutants. Motor skills tests show that Kv1.1 null mice display a compromised ability to maintain balance on a thin stationary rod. We conclude that the Kv1.1 null mutation results in a persistent elevation of the tonic inhibitory tone on the cerebellum Purkinje cell efferent and that this is not fully compensated for by residual Shaker-type channels. We further suggest that the increase in inhibitory tone in the mutants might underlie the behavioral deficits. At the cellular level, we propose that Kv1.1 deletion enhances excitability of the basket cells by selectively enhancing the likelihood of action potential propagation past axonal branch points.
A Mitogen-Activated Protein Kinase Cascade in the CA1/CA2 Subfield of the Dorsal Hippocampus Is Essential for Long-Term Spatial Memory
Authors: Blum Sonja , Moore Anthony N. , Adams Frank , Dash Pramod K.
Published: April 2018

Behavioral, biophysical, and pharmacological studies have implicated the hippocampus in the formation and storage of spatial memory. However, the molecular mechanisms underlying long-term spatial memory are poorly understood. In this study, we show that mitogen-activated protein kinase (MAPK, also called ERK) is activated in the dorsal, but not the ventral, hippocampus of rats after training in a spatial memory task, the Morris water maze. The activation was expressed as enhanced phosphorylation of MAPK in the pyramidal neurons of the CA1/CA2 subfield. In contrast, no increase in the percentage of phospho-MAPK-positive cells was detected in either the CA3 subfield or the dentate gyrus. The enhanced phosphorylation was observed only after multiple training trials but not after a single trial or after multiple trials in which the location of the target platform was randomly changed between each trial. Inhibition of the MAPK/ERK cascade in dorsal hippocampi did not impair acquisition, but blocked the formation of long-term spatial memory. In contrast, intrahippocampal infusion of SB203580, a specific inhibitor of the stress-activated MAPK (p38 MAPK), did not interfere with memory storage. These results demonstrate a MAPK-mediated cellular event in the CA1/CA2 subfields of the dorsal hippocampus that is critical for long-term spatial memory.
κ- and μ-Opioids Reverse the Somatostatin Inhibition of Ca2+Currents in Ciliary and Dorsal Root Ganglion Neurons
Authors: Polo-Parada Luis , Pilar Guillermo
Published: April 2018

Neuromodulators, including transmitters and peptides, modify neuronal excitability. In most neurons, multiple neuromodulator receptors are present on a single cell. Previous work has demonstrated either occlusive or additive effects when two neuromodulators that target the same ion channel are applied together. In this study, we characterize the modulation of Ca2+and K+channels in embryonic chick ciliary ganglion neurons by somatostatin (Som) and opioids, including the effects of these neuromodulators when applied in combination. We report a modulation of calcium current by κ- or μ-opioids that can prevent Som effects when applied before Som and can replace Som effects when applied after Som. We term these effects demodulation because they do not have the characteristics of simple occlusion but rather represent a dominant effect of opioid-mediated modulation of calcium channels over Som-mediated modulation. These opioid effects persist in the presence of kinase and phosphatase inhibitors, as well as after alteration of the intracellular Ca2+concentration. Furthermore, they are present in both whole-cell and perforated-patch recording configurations. These effects of opioids on Som-mediated modulation do not seem to be mediated by a general uncoupling of Som receptors from G-protein–coupled signaling systems because K+current modulation by Som can persist in the presence of opioids. Demodulation by opioids was also observed in dorsal root ganglion neurons on the modulation of calcium current by GABA and norepinephrine (NE). In both preparations, this demodulatory interaction occurred between voltage-independent (opioids) and voltage-dependent (Som, GABA, and NE) modulatory pathways.
Selective Excitation of Subtypes of Neocortical Interneurons by Nicotinic Receptors
Authors: Porter James T. , Cauli Bruno , Tsuzuki Keisuke , Lambolez Bertrand , Rossier Jean , Audinat Etienne
Published: April 2018

The cellular mechanisms by which neuronal nicotinic cholinergic receptors influence many aspects of physiology and pathology in the neocortex remain primarily unknown. Whole-cell recordings and single-cell reverse transcription (RT)-PCR were combined to analyze the effect of nicotinic receptor agonists on different types of neurons in acute slices of rat neocortex. Nicotinic receptor agonists had no effect on pyramidal neurons and on most types of interneurons, including parvalbumin-expressing fast spiking interneurons and somatostatin-expressing interneurons, but selectively excited a subpopulation of interneurons coexpressing the neuropeptides vasoactive intestinal peptide (VIP) and cholecystokinin. This excitation persisted in the presence of glutamate, GABA, and muscarinic receptor antagonists and in the presence of tetrodotoxin and low extracellular calcium, suggesting that the depolarization was mediated through the direct activation of postsynaptic nicotinic receptors. The responses were blocked by the nicotinic receptor antagonists dihydro-β-erythroidine and mecamylamine and persisted in the presence of the α7 selective nicotinic receptor antagonist methyllycaconitine, suggesting that the involved nicotinic receptors lacked the α7 subunit. Single-cell RT-PCR analysis indicated that the majority of the interneurons that responded to nicotinic stimulation coexpressed the α4, α5, and β2 nicotinic receptor subunits. Therefore, these results provide a role for non-α7 nicotinic receptors in the selective excitation of a subpopulation of neocortical interneurons. Because the neocortical interneurons expressing VIP have been proposed previously to regulate regional cortical blood flow and metabolism, these results also provide a cellular basis for the neuronal regulation of cortical blood flow mediated by acetylcholine.
Autoregulatory Sequences are Revealed by Complex Stability Screening of the Mousebrn-3.0Locus
Authors: Trieu May , Rhee Jerry M. , Fedtsova Natalia , Turner Eric E.
Published: April 2018

The POU-IV or Brn-3 class of transcription factors exhibit conserved structure, DNA-binding properties, and expression in specific subclasses of neurons across widely diverged species. In the mouse CNS, Brn-3.0 expression characterizes specific neurons from neurogenesis through the life of the cell. This irreversible activation of expression suggests positive autoregulation. To search forcis-acting elements that could mediate autoregulation we used a novel method, complex stability screening, which we applied to rapidly identify functional Brn-3.0 recognition sites within a large genomic region encompassing the mousebrn-3.0locus. This method is based on the observation that the kinetic stability of Brn-3.0 complexes with specific DNA sequences, as measured by their dissociation half-lives, is highly correlated with the ability of those sequences to mediate transcriptional activation by Brn-3.0. The principal Brn-3.0 autoregulatory region lies ∼5 kb upstream from the Brn-3.0 transcription start site and contains multiple Brn-3.0-binding sites that strongly resemble the optimal binding site for this protein class. This region also mediates transactivation by the closely related protein Brn-3.2, suggesting a regulatory cascade of POU proteins in specific neurons in which Brn-3.2 expression precedes Brn-3.0.
The Performance of Synapses That Convey Discrete Graded Potentials in an Insect Visual Pathway
Authors: Simmons Peter J.
Published: April 2018

Synapses from nonspiking neurons transmit small graded changes in potential, but variability in their postsynaptic potential amplitudes has not been extensively studied. At synapses where the presynaptic signal is an all-or-none spike, the probabilistic manner of neurotransmitter release causes variation in the amplitudes of postsynaptic potentials. I have measured the reliability of the operation of synapses that convey small graded potentials between pairs of identified large, second-order neurons in the locust ocellar system. IPSPs are mediated by small rebound spikes, which are graded in amplitude, in the presynaptic neuron. A transfer curve plotting amplitudes of spikes against amplitudes of IPSPs has a characteristic S shape with a linear central portion where IPSP amplitude is between −0.2 and −0.6 as large as spike amplitude but shows appreciable scatter. Approximately half of the scatter is attributable to background noise, most of which originates in photoreceptors and persists in darkness. The remaining noise is intrinsic to the synapse itself and is usually 0.3–0.7 mV in amplitude. It limits the resolution with which two spike amplitudes can be distinguished from one another to ∼2 mV and, because the linear part of the transfer curve occupies ∼10 mV in spike amplitudes, limits the number of discrete signal levels that can be conveyed across the synapse to approximately five. The amplitude of the noise is constant throughout the synaptic operating range, which means it is unlikely that presynaptic membrane potential controls transmitter release by setting a single probability level for quantal release.
Activity-Dependent Intracellular Acidification Correlates with the Duration of Seizure Activity
Authors: Xiong Zhi-Qi , Saggau Peter , Stringer Janet L.
Published: April 2018

Synchronized neuronal activity (seizures) can appear in the presence or absence of synaptic transmission. Mechanisms of seizure initiation in each of these conditions have been studied, but relatively few studies have addressed seizure termination. In particular, how are seizures terminated in the absence of synaptic activity where there is no loss of excitatory drive or augmentation of inhibitory inputs? We have studied dynamic activity-dependent changes of intracellular pH in the absence of synaptic transmission using the fluorescent pH indicator carboxylseminaphthorhodafluo-1. During epileptiform activity we observed intracellular acidification, whereas between seizures the intracellular pH recovered. Experimental conditions that shortened the epileptiform discharge correlated with more rapid intracellular acidification. On the other hand, experimental manipulation of intracellular pH altered the duration of the seizure discharge, with acidification resulting in early termination of the epileptiform activity. These data show a direct relationship between the level of intracellular acidification and the duration of the seizures, suggesting that an intracellular pH-dependent process can terminate nonsynaptic neuronal synchronization.
Ca2+-Evoked Serotonin Secretion by Parafollicular Cells: Roles in Signal Transduction of Phosphatidylinositol 3′-kinase, and the γ and ζ Isoforms of Protein Kinase C
Authors: Liu Kuo-peing , Hsiung Shu-chi , Adlersberg Mella , Sacktor Todd , Gershon Michael D. , Tamir Hadassah
Published: April 2018

Parafollicular (PF) cells secrete 5-HT in response to stimulation of a G-protein-coupled Ca2+receptor (CaR) by increased extracellular Ca2+(↑[Ca2+]e). We tested the hypothesis that protein kinase C (PKC) participates in stimulus–secretion coupling. Immunoblots from membrane and cytosolic fractions of isolated PF cells revealed conventional (α, βI, and γ), novel (δ and ε), and atypical (ι/λ and ζ) PKCs. Only PKCγ was found to have been translocated to the membrane fraction when secretion of 5-HT was evoked by ↑[Ca2+]eor phorbol esters. Although phorbol downregulation caused PKCγ to disappear, secretion was only partially inhibited. A similar reduction of ↑[Ca2+]e-evoked secretion was produced by inhibitors of conventional and/or novel PKCs (Gö6976, calphostin C, and pseudoA), and these compounds did not inhibit secretion at all when applied to phorbol-downregulated cells. In contrast, the phorbol downregulation-resistant component of secretion was abolished by pseudoZ, which inhibits the atypical PKCζ. Stimulation of PF cells with ↑[Ca2+]eincreased the activity of immunoprecipitated PKCζ (but not PKCι/λ), and the activity of this PKCζ was inhibited by pseudoZ. PF cells were found to express regulatory (p85) and catalytic (p110α and p110β) subunits of phosphatidylinositol 3′-kinase (PI3′-kinase). ↑[Ca2+]eincreased the activity of immunoprecipitated PI3′-kinase; moreover, PI3′-kinase inhibitors (wortmannin and LY294002) antagonized secretion. We suggest that PKC isoforms mediate secretion of 5-HT by PF cells in response to stimulation of the CaR. PKC involvement can be accounted for by PKCγ and an isoform sensitive to inhibition by pseudoZ, probably PKCζ, which is activated via PI3′-kinase.
Paradoxical Actions of the Serotonin Precursor 5-hydroxytryptophan on the Activity of Identified Serotonergic Neurons in a Simple Motor Circuit
Authors: Fickbohm David J. , Katz Paul S.
Published: April 2018

Neurotransmitter synthesis is regulated by a variety of factors, yet the effect of altering transmitter content on the operation of neuronal circuits has been relatively unexplored. We used electrophysiological, electrochemical, and immunohistochemical techniques to investigate the effects of augmenting the serotonin (5-HT) content of identified serotonergic neurons embedded in a simple motor circuit. The dorsal swim interneurons (DSIs) are serotonergic neurons intrinsic to the central pattern generator (CPG) for swimming in the molluscTritonia diomedea. As expected, treatment with the serotonin precursor 5-hydroxytryptophan (5-HTP) increased the intensity of serotonin immunolabeling and enhanced the potency of synaptic and modulatory actions elicited by the DSIs. It also greatly enhanced the ability of the DSIs to evoke rhythmic CPG activity. After 5-HTP treatment, microvoltammetric measurements indicated an increase in a putative 5-HT electrochemical signal during swim CPG activation. Paradoxically, the spiking activity of the serotonergic neurons decreased to a single burst at the onset of the rhythmic motor program, whereas the overall duration of the episode remained about the same. 5-HTP treatment gradually reduced the rhythmicity of the CPG output. Thus, more serotonin did not result in a more robust swim motor program, suggesting that serotonin synthesis must be kept within certain limits for the circuit to function correctly and indicating that altering neurotransmitter synthesis can have serious consequences for the output of neural networks.
Extraction of Sensory Parameters from a Neural Map by Primary Sensory Interneurons
Authors: Jacobs Gwen A. , Theunissen Frederic E.
Published: April 2018

We examine the anatomical basis for the representation of stimulus parameters within a neural map and examine the extraction of these parameters by sensory interneurons (INs) in the cricket cercal sensory system. The extraction of air current direction by these sensory interneurons can be understood largely in terms of the anatomy of the system. There are two critical anatomical constraints. (1) The arborizations of afferents with similar directional tuning properties are located near each other within the neural map. Therefore, a continuous variation in stimulus direction causes a continuous variation in the spatial pattern of activation. (2) The restriction of the synaptic connections of an interneuron to a unique set of afferents results from the unique anatomy of that interneuron: its dendritic arbors are located within restricted regions of the afferent map containing afferents with a limited subset of directional sensitivities. The functional organization of the set of four interneurons studied here is equivalent to a Cartesian coordinate system for computing the stimulus direction vector. For any air current stimulus direction, the firing rates of the active interneurons could be decoded as Cartesian coordinates by neurons at successive processing stages. The implications of this Cartesian coordinate system are discussed with respect to optimal coding strategies and developmental constraints on the cellular implementation of this coding scheme.