bluuebunny/crossref_metadata_2025 huggingface dataset:
Removal of Polysialic Acid–Neural Cell Adhesion Molecule Induces Aberrant Mossy Fiber Innervation and Ectopic Synaptogenesis in the Hippocampus
Authors: Seki Tatsunori , Rutishauser Urs
Published: April 2018

The mossy fiber axons of both the developing and adult dentate gyrus express the highly polysialylated form of neural cell adhesion molecule (NCAM) as they innervate the proximal apical dendrites of pyramidal cells in the CA3 region of the hippocampus. The present study used polysialic acid (PSA)-deficient and NCAM mutant mice to evaluate the role of PSA in mossy fiber development. The results indicate that removal of PSA by either specific enzymatic degradation or mutation of the NCAM-180 isoform that carries PSA in the brain causes an aberrant and persistent innervation of the pyramidal cell layer by mossy fibers, including excessive collateral sprouting and/or defasciculation of these processes, as well as formation of ectopic mossy fiber synaptic boutons. These results are considered in terms of two possible effects of PSA removal: an increase in the number of mossy fibers that can grow into the pyramidal cell layer and an inhibition of process retraction by formation of stable junctions including synapses. As these defects on granule cells in the adult animal and PSA-positive granule cells continue to be produced in the mature brain, the present findings may be relevant to previous studies suggesting that PSA–NCAM function is required for long-term potentiation, long-term depression, and learning behaviors associated with hippocampus.
The Processing of First- and Second-Order Motion in Human Visual Cortex Assessed by Functional Magnetic Resonance Imaging (fMRI)
Authors: Smith Andrew T. , Greenlee Mark W. , Singh Krish D. , Kraemer Falk M. , Hennig Jürgen
Published: April 2018

We have examined the activity levels produced in various areas of the human occipital cortex in response to various motion stimuli using functional magnetic resonance imaging (fMRI) methods. In addition to standard luminance-defined (first-order) motion, three types of second-order motion were used. The areas examined were the motion area V5 (MT) and the following areas that were delineated using retinotopic mapping procedures: V1, V2, V3, VP, V3A, and a new area that we refer to as V3B. Area V5 is strongly activated by second-order as well as by first-order motion. This activation is highly motion-specific. Areas V1 and V2 give good responses to all motion stimuli, but the activity seems to be related primarily to the local spatial and temporal structure in the image rather than to motion processing. Area V3 and its ventral counterpart VP also respond well to all our stimuli and show a slightly greater degree of motion specificity than do V1 and V2. Unlike V1 and V2, the response in V3 and VP is significantly greater for second-order motion than for first-order motion. This trend is evident, but less marked, in V3A and V3B and absent in V5. The results are consistent with the hypothesis that first-order motion sensitivity arises in V1, that second-order motion is first represented explicitly in V3 and VP, and that V5 (and perhaps also V3A and V3B) is involved in further processing of motion information, including the integration of motion signals of the two types.
Hypothalamic Ventromedial Nuclei Amplify Circadian Rhythms: Do They Contain a Food-Entrained Endogenous Oscillator?
Authors: Choi SuJean , Wong Lai Sze , Yamat Cherrilyn , Dallman Mary F.
Published: April 2018

Several endogenous oscillators determine circadian rhythms. One, light-entrained, is in the suprachiasmatic nuclei (SCN), the others, food-entrained, are in unknown sites. To determine how the hypothalamic ventromedial nuclei (VMN) and feeding affect rhythms, we compared nocturnally active rats fed eitherad libitumor for 2 hr/d during light [restricted feeding (RF)] and either with or without colchicine-induced disruption of VMN. We measured rhythms in temperature, locomotor activity, feeding, drinking, corticosterone, and the numbers of cells expressing c-Fos in light/dark in hypothalamic nuclei, the suprachiasmatic nuclei, and two major SCN targets, the subparaventricular zone (sPVNz) and paraventricular thalamus (pvTHAL). c-Fos cells were always light > dark in SCN, whereas the VMN and sPVNz lacked light/dark differences except after RF and RF plus VMN disruption, respectively. Controls fedad libitumhad high-amplitude rhythms and, generally, c-Fos cells dark > light. In RF controls, a c-Fos pattern dark > light occurred in VMN; generally, c-Fos cell numbers increased elsewhere maintaining dark > light. By contrast, levels of corticosterone peaked before food. In rats fedad libitum, VMN with colchicine markedly reduced rhythm amplitudes, not phase. c-Fos patterns were abolished except in pvTHAL and SCN. In RF, VMN disruption blocked corticosterone and light/dark c-Fos patterns in all nuclei but produced a pattern in the sPVNz like SCN. We conclude that VMN amplify rhythmic output from the SCN, and the RF-induced rhythm in VMN enhances c-Fos activity driven by the SCN. The VMN may contain a food-entrained oscillator, and the sPVNz may integrate output from several oscillators.
Memory Modulation Across Neural Systems: Intra-Amygdala Glucose Reverses Deficits Caused by Intraseptal Morphine on a Spatial Task But Not on an Aversive Task
Authors: McNay Ewan C. , Gold Paul E.
Published: April 2018

Based largely on dissociations of the effects of different lesions on learning and memory, memories for different attributes appear to be organized in independent neural systems. Results obtained with direct injections of drugs into one brain region at a time support a similar conclusion. The present experiments investigated the effects of simultaneous pharmacological manipulation of two neural systems, the amygdala and the septohippocampal system, to examine possible interactions of memory modulation across systems. Morphine injected into the medial septum impaired memory both for avoidance training and during spontaneous alternation. When glucose was concomitantly administered to the amygdala, glucose reversed the morphine-induced deficits in memory during alternation but not for avoidance training. These results suggest that the amygdala is involved in modulation of spatial memory processes and that direct injections of memory-modulating drugs into the amygdala do not always modulate memory for aversive events. These findings are contrary to predictions from the findings of lesion studies and of studies using direct injections of drugs into single brain areas. Thus, the independence of neural systems responsible for processing different classes of memory is less clear than implied by studies using lesions or injections of drugs into single brain areas.
Binding of Serotonin to Receptors at Multiple Sites Is Required for Structural Plasticity Accompanying Long-Term Facilitation ofAplysiaSensorimotor Synapses
Authors: Sun Zhong-Yi , Schacher Samuel
Published: April 2018

Long-term changes in the efficacy ofAplysiasensorimotor synapses accompany nonassociative and associative forms of behavioral plasticity. This synapse expresses long-term facilitation either with repeated applications of 5-hydroxytryptamine (5-HT) or with a single pairing of tetanus in the sensory neuron (SN) and bath application of 5-HT. We examined whether structural changes in the SN accompany all forms of long-term synaptic enhancement and the locations at which 5-HT must bind receptors to evoke long-term functional and/or structural changes. Pairing tetanus with one application of 5-HT evoked both functional and structural changes after 24 hr only when 5-HT application was temporally paired with the tetanus and activated receptors on both the SN cell body and terminal region. Repeated application of 5-HT to the terminal region alone failed to evoke any long-term change. Repeated applications of 5-HT to the SN cell body alone evoked a change in synaptic efficacy at 24 hr but failed to increase SN varicosities. Repeated applications of 5-HT to both the SN cell body and the terminal region evoked increases in both synaptic efficacy and the number of SN varicosities at 24 hr. The results indicate that different external stimuli can evoke equivalent forms of long-term synaptic facilitation with or without structural changes in the SNs. Changes in the number of SN varicosities can accompany different forms of long-term facilitation and require the activation of 5-HT receptors at multiple sites.
Extensive Divergence and Convergence in the Thalamocortical Projection to Monkey Somatosensory Cortex
Authors: Rausell Estrella , Bickford Lincoln , Manger Paul R. , Woods Timothy M. , Jones Edward G.
Published: April 2018

This study examined the extent of thalamocortical divergence as a potential determinant of activity-dependent representational plasticity in area 3b of adult monkey somatosensory cortex. Single or paired injections of anterogradely transported tracers, of varying anteroposterior extent, were made horizontally from behind in defined parts of the body representation in the ventral posterior lateral (VPL) and/or ventral posterior medial (VPM) thalamic nuclei, and the distribution and density of labeled thalamocortical terminations were mapped in cortex. Injections of increasing size in any dimension of VPL or VPM resulted in increasing accumulation of labeled terminals within the region of projection, implying extensive convergence of individual axons. Anteroposteriorly elongated injections labeled mediolaterally extended but anteroposteriorly restricted zones in cortex. Dorsoventral placement of an injection in VPL or VPM determined anteroposterior location of labeling in cortex.

Dual injections separated mediolaterally or dorsoventrally by ∼1 mm, and in different parts of the thalamic body or head–face representation gave rise to labeled thalamocortical terminations that overlapped extensively. For injection sites at different anteroposterior levels in VPL or VPM, the area of cortical convergence was related to their extent of anteroposterior coincidence. Labeled terminations arising from injections in immediately adjacent parts of VPL and VPM did not overlap in cortex.

The extent of thalamocortical divergence and convergence revealed by these experiments is greater than that predictable from labeling of single axons and is sufficiently great to account for representational plasticity that exceeds the 1.5 mm cortical “distance limit.”
Behavioral Discrimination between Quinine and KCl Is Dependent on Input from the Seventh Cranial Nerve: Implications for the Functional Roles of the Gustatory Nerves in Rats
Authors: St. John Steven J. , Spector Alan C.
Published: April 2018

The rat glossopharyngeal nerve (GL), which innervates posterior tongue taste buds, contains several physiologically defined taste fiber types; at least one type is primarily responsive to certain alkaloids (such as quinine), and another is primarily responsive to acids and salts. In contrast, the chorda tympani (CT), which innervates anterior tongue taste buds, does not appear to contain fibers that differentially respond to quinine relative to salts and acids. It was therefore predicted that GL transection should disrupt behavioral discriminations between quinine and either acids or salts. Water-restricted rats were trained to press one of two levers if a sampled taste stimulus was quinine (0.1–1.0 mm) and the second lever if the sampled stimulus was KCl (0.1–1.0m). Sham surgery, GL transection, and sublingual and submaxillary salivary gland extirpation were found to have no effect relative to presurgical performance. Both CT transection and combined GL and CT transection caused a substantial and approximately equal decrement in discrimination performance. Removal of the gustatory branches of the seventh cranial nerve [CT and greater superficial petrosal (GSP)] nearly eliminated the discrimination of the taste stimuli, and combined transection of the CT, GL, and GSP unequivocally reduced performance to chance levels. Although these findings were not presaged by the known electrophysiology, they nonetheless compare favorably with other studies reporting little effect of GL transection on behavioral responses to quinine. These results, in the context of other discrimination studies reported in the literature, suggest that, in rats, the neural coding of taste quality depends primarily on the input of the facial nerve.
Single-Cell Correlates of a Representational Boundary in Rat Somatosensory Cortex
Authors: Hickmott Peter W. , Merzenich Michael M.
Published: April 2018

In primary somatosensory cortex (S1), the transition from one representation to the next is typically abrupt when assayed physiologically. However, the extent of anatomical projections to and within the cortex do not strictly respect these physiologically defined transitions. Physiological properties, such as synaptic strengths or intracortical inhibition, have been hypothesized to account for the functionally defined precision of these representational borders. Because these representational borders can be translocated across the cortex by manipulations or behaviors that change the activity patterns of inputs to the cortex, understanding the physiological mechanisms that delimit representations is also an important starting point for understanding cortical plasticity.

A novelin vivoandin vitropreparation has been developed to examine the cellular and synaptic mechanisms that underlie representational borders in the rat.In vivo, a short segment of the border between the forepaw–lower jaw representations in rat S1 was mapped using standard electrophysiological methods and was visibly marked using iontophoresis of pontamine sky blue dye. Slices were then obtained from this marked region and maintainedin vitro.Intracellularly recorded responses to electrical stimulation of supragranular cortex were obtained from single neurons near the border in response to stimulation within the representational zone or across the border. Both excitatory and inhibitory responses were smaller when evoked by stimuli that activated projections that crossed borders, as compared with stimuli to projections that did not. These findings indicate that intracortical network properties are contributing to the expressions of representational discontinuities in the cortex.
Identification of the Amino Terminus of Neuronal Ca2+Channel α1 Subunits α1B and α1E as an Essential Determinant of G-Protein Modulation
Authors: Page Karen M. , Cantı́ Carles , Stephens Gary J. , Berrow Nicholas S. , Dolphin Annette C.
Published: April 2018

We have examined the basis for G-protein modulation of the neuronal voltage-dependent calcium channels (VDCCs) α1E and α1B. A novel PCR product of α1E was isolated from rat brain. This contained an extended 5′ DNA sequence and was subcloned onto the previously cloned isoform rbEII, giving rise to α1Elongwhose N terminus was extended by 50 amino acids. VDCC α1 subunit constructs were co-expressed with the accessory α2-δ and β2a subunits inXenopusoocytes and mammalian (COS-7) cells. The α1Elongshowed biophysical properties similar to those of rbEII; however, when G-protein modulation of expressed α1 subunits was induced by activation of co-expressed dopamine (D2) receptors with quinpirole (100 nm) in oocytes, or by co-transfection of Gβ1γ2 subunits in COS-7 cells, α1Elong, unlike α1E(rbEII), was found to be G-protein-modulated, in terms of both a slowing of activation kinetics and a reduction in current amplitude. However, α1Elongshowed less modulation than α1B, and substitution of the α1E1–50with the corresponding region of α1B1–55produced a chimera α1bEEEE, with G-protein modulation intermediate between α1Elongand α1B. Furthermore, deletion of the N-terminal 1–55 sequence from α1B produced α1BΔN1–55, which could not be modulated, thus identifying the N-terminal domain as essential for G-protein modulation. Taken together with previous studies, these results indicate that the intracellular N terminus of α1E1–50and α1B1–55is likely to contribute to a multicomponent site, together with the intracellular I–II loop and/or the C-terminal tail, which are involved in Gβγ binding and/or in subsequent modulation of channel gating.
On the Action of the Anti-Absence Drug Ethosuximide in the Rat and Cat Thalamus
Authors: Leresche Nathalie , Parri H. Rheinallt , Erdemli Gül , Guyon Alice , Turner Jonathan P. , Williams Stephen R. , Asprodini Eftihia , Crunelli Vincenzo
Published: April 2018

The action of ethosuximide (ETX) on Na+, K+, and Ca2+currents and on tonic and burst-firing patterns was investigated in rat and cat thalamic neuronsin vitroby using patch and sharp microelectrode recordings. In thalamocortical (TC) neurons of the rat dorsal lateral geniculate nucleus (LGN), ETX (0.75–1 mm) decreased the noninactivating Na+current,INaP, by 60% but had no effect on the transient Na+current. In TC neurons of the rat and cat LGN, the whole-cell transient outward current was not affected by ETX (up to 1 mm), but the sustained outward current was decreased by 39% at 20 mV in the presence of ETX (0.25–0.5 mm): this reduction was not observed in a low Ca2+(0.5 mm) and high Mg2+(8 mm) medium or in the presence of Ni2+(1 mm) and Cd2+(100 μm). In addition, ETX (up to 1 mm) had no effect on the low-threshold Ca2+current,IT, of TC neurons of the rat ventrobasal (VB) thalamus and LGN and in neurons of the rat nucleus reticularis thalami nor on the high-threshold Ca2+current in TC neurons of the rat LGN.

Sharp microelectrode recordings in TC neurons of the rat and cat LGN and VB showed that ETX did not change the resting membrane potential but increased the apparent input resistance at potentials greater than −60 mV, resulting in an increase in tonic firing. In contrast, ETX decreased the number of action potentials in the burst evoked by a low-threshold Ca2+potential. The frequency of the remaining action potentials in a burst also was decreased, whereas the latency of the first action potential was increased. Similar effects were observed on the burst firing evoked during intrinsic δ oscillations.

These results indicate an action of ETX onINaPand on the Ca2+-activated K+current, which explains the decrease in burst firing and the increase in tonic firing, and, together with the lack of action on low- and high-threshold Ca2+currents, the results cast doubts on the hypothesis that a reduction ofITin thalamic neurons underlies the therapeutic action of this anti-absence medicine.
Localized Synaptic Actions of Neurotrophin-4
Authors: Wang Xin-hao , Berninger Benedikt , Poo Mu-ming
Published: April 2018

Neurotrophins secreted by the postsynaptic target cell may participate in activity-dependent synaptic modification during development and in the mature brain. A fundamental question of how neurotrophins can sculpt synaptic connections is whether neurotrophin-induced synaptic changes are spatially restricted to the site of neurotrophin secretion or whether they can spread to neighboring synapses. Using a model system of nerve–muscle coculture in which neurotrophin-4 (NT-4) is overexpressed in a subpopulation of postsynaptic myocytes, we demonstrated that presynaptic potentiation is restricted to synapses on myocytes overexpressing NT-4 without affecting nearby synapses formed by the same neuron on control myocytes. Likewise, postsynaptic modulation of acetylcholine channels by secreted NT-4 is spatially restricted to <60 μm from the site of NT-4 secretion. Therefore, activity-dependent secretion of neurotrophins can result in highly localized modification of neuronal connections.
Effects of Pedunculopontine Tegmental Nucleus Lesions on Responding for Intravenous Heroin under Different Schedules of Reinforcement
Authors: Olmstead Mary C. , Munn Elizabeth M. , Franklin Keith B. J. , Wise Roy A.
Published: April 2018

The pedunculopontine tegmental nucleus (PPTg) is believed to play important roles in reward and learning. We examined the effect of PPTg lesions (0.5 μl of 0.1mNMDA injected bilaterally over 10 min) on the learning of an operant response for opiate reward. In 14 adult male Long–Evans rats, bilateral lesions of the PPTg disrupted the acquisition of responding for intravenous heroin (0.1 mg/kg infused at a rate of 0.25 ml/28 sec) on a fixed ratio-1 (FR-1) schedule of reinforcement. The 12 remaining lesioned animals increased their heroin intake over the acquisition sessions but did not reach the response levels of sham-lesioned animals on the 15th and final session. The sham- and PPTg-lesioned animals that learned the FR-1 task exhibited similar patterns of responding during extinction and reacquisition sessions. When tested on a progressive ratio (PR) schedule of reinforcement, however, PPTg-lesioned animals had lower break points than sham-lesioned animals. Asymmetric lesions, which destroyed the majority of the nucleus in one hemisphere only, did not produce any behavioral deficits. Rats that were lesioned after training also did not show deficits in responding under either FR or PR schedules. These findings suggest that PPTg lesions reduce the rewarding effect of opiates but do not disrupt the ability either to learn an operant response or the response requirements of a PR schedule.
Coadministration of Galanin Antagonist M40 with a Muscarinic M1Agonist Improves Delayed Nonmatching to Position Choice Accuracy in Rats with Cholinergic Lesions
Authors: McDonald Michael P. , B. Willard Lauren , Wenk Gary L. , Crawley Jacqueline N.
Published: April 2018

The neuropeptide galanin is overexpressed in the basal forebrain in Alzheimer’s disease (AD). In rats, galanin inhibits evoked hippocampal acetylcholine release and impairs performance on several memory tasks, including delayed nonmatching to position (DNMTP). Galanin(1–13)-Pro2-(Ala-Leu)2-Ala-NH2(M40), a peptidergic galanin receptor ligand, has been shown to block galanin-induced impairment on DNMTP in rats. M40 injected alone, however, does not improve DNMTP choice accuracy deficits in rats with selective cholinergic immunotoxic lesions of the basal forebrain. The present experiments used a strategy of combining M40 with an M1cholinergic agonist in rats lesioned with the cholinergic immunotoxin192IgG-saporin. Coadministration of intraventricular M40 with intraperitoneal 3-(3-S-n-pentyl-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-methylpyridine (TZTP), an M1agonist, improved choice accuracy significantly more than a threshold dose of TZTP alone. These results suggest that a galanin antagonist may enhance the efficacy of cholinergic treatments for the cognitive deficits of AD.
Contribution of Subsaturating GABA Concentrations to IPSCs in Cultured Hippocampal Neurons
Authors: Hill Matthew W. , Reddy P. Amruta , Covey Douglas F. , Rothman Steven M.
Published: April 2018

The time course of EPSCs and IPSCs is at least partly determined by the concentration profile of neurotransmitter acting on postsynaptic receptors. Several recent reports have suggested that the peak synaptic cleft concentration of the inhibitory neurotransmitter GABA likely reaches at least 500 μm, a level that saturates the GABAAreceptor. In the course of investigating the experimental anticonvulsant 3,3-diethyl-2-pyrrolidinone (diethyl-lactam), we have observed an important contribution to IPSC decay by subsaturating concentrations of GABA. Diethyl-lactam augments currents elicited by the exogenous application of subsaturating concentrations of GABA in voltage-clamped, cultured hippocampal neurons and significantly prolongs the decay of autaptic IPSCs and miniature IPSCs in our cultures. In addition, diethyl-lactam potentiates currents in excised outside-out membrane patches elicited by the prolonged application of low concentrations of GABA. However, when patches are exposed to 1–2 msec pulses of 1 mmGABA, diethyl-lactam does not alter current decay. Tiagabine, which blocks GABA reuptake, does not prolong IPSCs, so it is unlikely that uptake inhibition accounts for the enhancement of IPSCs. EPSCs and miniature IPSC frequency are unaffected by diethyl-lactam, again consistent with a postsynaptic site of action. We propose that during an IPSC, a substantial number of postsynaptic receptors must be exposed to subsaturating concentrations of GABA. A simplified model of GABAAreceptor kinetics can account for the effects of diethyl-lactam on exogenous GABA and IPSCs if diethyl-lactam has its main effect on the monoliganded states of the GABAAreceptor.
P2Y2Nucleotide Receptors Expressed Heterologously in Sympathetic Neurons Inhibit Both N-Type Ca2+and M-Type K+Currents
Authors: Filippov Alexander K. , Webb Tania E. , Barnard Eric A. , Brown David A.
Published: April 2018

The P2Y2receptor is a uridine/adenosine triphosphate (UTP/ATP)-sensitive G-protein-linked nucleotide receptor that previously has been reported to stimulate the phosphoinositide signaling pathway. Messenger RNA for this receptor has been detected in brain tissue. We have investigated the coupling of the molecularly defined rat P2Y2receptor to neuronal N-type Ca2+channels and to M-type K+channels by heterologous expression in rat superior cervical sympathetic (SCG) neurons. After the injection of P2Y2cRNA, UTP inhibited the currents carried by both types of ion channel. As previously reported [Filippov AK, Webb TE, Barnard EA, Brown DA (1997) Inhibition by heterologously expressed P2Y2nucleotide receptors of N-type calcium currents in rat sympathetic neurones. Br J Pharmacol 121:849–851], UTP inhibited the Ca2+current (ICa(N)) by up to 64%, with an IC50of ∼0.5 μm. We now find that UTP also inhibited the K+Mcurrent (IK(M)) by up to 61%, with an IC50of ∼1.5 μm. UTP had no effect on either current in neurons not injected with P2Y2cRNA. Structure–activity relations for the inhibition ofICa(N)andIK(M)in P2Y2cRNA-injected neurons were similar, with UTP ≥ ATP > ITP ≫ GTP,UDP. However, coupling to these two channels involved different G-proteins: pretreatment withPertussistoxin (PTX) did not affect UTP-induced inhibition ofIK(M)but reduced inhibition ofICa(N)by ∼60% and abolished the voltage-dependent component of this inhibition. In unclamped neurons, UTP greatly facilitated depolarization-induced action potential discharges. Thus, the single P2Y2receptor can couple to at least two G-proteins to inhibit both Ca2+Nand K+Mchannels with near-equal facility. This implies that the P2Y2receptor may induce a broad range of effector responses in the nervous system.
Alternative RNA Splicing of the NMDA Receptor NR1 mRNA in the Neurons of the Teleost Electrosensory System
Authors: Bottai Daniele , Maler Leonard , Dunn Robert J.
Published: April 2018

The sequence for cDNA encoding the NMDA receptor subunit 1 (aptNR1) of the weakly electric fishApteronotus leptorhynchushas been determined. The deduced amino acid sequence is ∼88% identical to other vertebrate NR1 proteins, with sequence homology extending to the alternatively spliced cassettes N1 and C1. The fish and mammalian N1 and C1 splice cassettes are identical at 20 of 21 and 30 of 37 amino acid positions, respectively. We did not detect a C2 splice cassette in aptNR1 mRNA, but we did find two novel C-terminal alternative splice cassettes labeled C1′ and C1".

The relative levels of NR1 transcripts containing the N1 and C1 splice cassettes were determined by using RNase protection andin situhybridization analysis. N1-containing mRNAs are more abundant in caudal brain regions, similar to the patterns reported for mammalian brain. In contrast, the relative levels of transcripts containing the C1 splice cassette are much lower in fish than in mammals, averaging only 9% for the whole brain. The levels of C1 splicing increased in more rostral brain regions.In situhybridizations with N1- and C1-specific probes demonstrated that N1 cassette splicing occurs in most neurons but that C1 splicing is heterogeneous and is restricted to a subset of neuronal types in the electrosensory system.
Preferential Utilization of Acetate by Astrocytes Is Attributable to Transport
Authors: Waniewski Robert A. , Martin David L.
Published: April 2018

Exogenous acetate is preferentially metabolized by astrocytes in the CNS, but the biochemical basis for this selectivity is unknown. We observed that rat cortical astrocytes produce14CO2from 0.2 mm[14C]acetate at a rate of 0.43 nmol/min per milligram of protein, 18 times faster than cortical synaptosomes. Subsequent studies examined whether this was attributable to cellular differences in the transport or metabolism of acetate. The activity of acetyl-CoA synthetase, the first enzymatic step in acetate utilization, was greater in synaptosomes than in astrocytes (5.0 and 2.9 nmol/min per milligram of protein), indicating that slower metabolism in synaptosomes cannot be attributed to lack of enzymatic activity. [14C]Acetate uptake in astrocytes is rapid and time-dependent and follows saturation kinetics (Vmax, 498 nmol/min per milligram of protein;Km, 9.3 mm). Uptake is inhibited stereospecifically byl-lactate as well as by pyruvate, fluoroacetate, propionate, and α-cyano-4-hydroxycinnamate (CHC). Preloading astrocytes withl-lactate or acetate, but notd-lactate, pyruvate, or glyoxylate, transaccelerates [14C]acetate uptake. Acetate uptake by astrocytes appears to be mediated by a carrier with properties similar to that of monocarboxylate transport. In contrast, studies with synaptosomes provided no evidence for time-dependent, saturable, transaccelerated, or CHC-inhibitable uptake of [14C]acetate. The high rate of transport in astrocytes compared with synaptosomes explains the rapid incorporation of [14C]acetate into brain glutamine over glutamate. These findings provide support for the use of acetate as a marker for glial metabolism and suggest that extracellular acetate in the brain generated from acetylcholine and ethanol metabolism is accumulated first by astrocytes.
Localized Sources of Neurotrophins Initiate Axon Collateral Sprouting
Authors: Gallo Gianluca , Letourneau Paul C.
Published: April 2018

The sprouting of axon collateral branches is important in the establishment and refinement of neuronal connections during both development and regeneration. Collateral branches are initiated by the appearance of localized filopodial activity along quiescent axonal shafts. We report here that sensory neuron axonal shafts rapidly sprout filopodia at sites of contact with nerve growth factor-coated polystyrene beads. Some sprouts can extend up to at least 60 μm through multiple bead contacts. Axonal filopodial sprouts often contained microtubules and exhibited a debundling of axonal microtubules at the site of bead–axon contact. Cytochalasin treatment abolished the filopodial sprouting, but not the accumulation of actin filaments at sites of bead–axon contact. The axonal sprouting response is mediated by the trkA receptor and likely acts through a phosphoinositide-3 kinase-dependent pathway, in a manner independent of intracellular Ca2+fluctuations. These findings implicate neurotrophins as local cues that directly stimulate the formation of collateral axon branches.
Intracellular Correlates of Acquisition and Long-Term Memory of Classical Conditioning in Purkinje Cell Dendrites in Slices of Rabbit Cerebellar Lobule HVI
Authors: Schreurs Bernard G. , Gusev Pavel A. , Tomsic Daniel , Alkon Daniel L. , Shi Ting
Published: April 2018

Intradendritic recordings in Purkinje cells from a defined area in parasaggital slices of cerebellar lobule HVI, obtained after rabbits were given either paired (classical conditioning) or explicitly unpaired (control) presentations of tone and periorbital electrical stimulation, were used to assess the nature and duration of conditioning-specific changes in Purkinje cell dendritic membrane excitability. We found a strong relationship between the level of conditioning and Purkinje cell dendritic membrane excitability after initial acquisition of the conditioned response. Moreover, conditioning-specific increases in Purkinje cell excitability were still present 1 month after classical conditioning. Although dendritically recorded membrane potential, input resistance, and amplitude of somatic and dendritic spikes were not different in cells from paired or control animals, the size of a potassium channel-mediated transient hyperpolarization was significantly smaller in cells from animals that received classical conditioning. In slices of lobule HVI obtained from naive rabbits, the conditioning-related increases in membrane excitability could be mimicked by application of potassium channel antagonist tetraethylammonium chloride, iberiotoxin, or 4-aminopyridine. However, only 4-aminopyridine was able to reduce the transient hyperpolarization. The pharmacological data suggest a role for potassium channels and, possibly, channels mediating an IA-like current, in learning-specific changes in membrane excitability. The conditioning-specific increase in Purkinje cell dendritic excitability produces an afterhyperpolarization, which is hypothesized to release the cerebellar deep nuclei from inhibition, allowing conditioned responses to be elicited via the red nucleus and accessory abducens motorneurons.
Induction of Interleukin-1 Associated with Compensatory Dopaminergic Sprouting in the Denervated Striatum of Young Mice: Model of Aging and Neurodegenerative Disease
Authors: Ho Angela , Blum Mariann
Published: April 2018

Young mice challenged with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which selectively destroys the substantia nigra dopaminergic neurons in the midbrain, exhibit spontaneous recovery of dopaminergic nerve terminals. However, such recovery becomes attenuated with age. Here we report that newly sprouted fibers originate from spared dopaminergic neurons in the ventral tegmental area. We found that interleukin-1 (IL-1), an immune response-generated cytokine that can enhance dopaminergic sprouting when exogenously applied, increased dramatically in the denervated striatum of young mice (2 months) compared with middle-aged mice (8 months) after MPTP treatment. Young mice displayed a maximal 500% induction of IL-1α synthesis that remained elevated for several weeks in the dorsal and ventral striatum, whereas middle-aged mice exhibited a modest 135% induction exclusively in the dorsal striatum for a week. IL-1α immunoreactivity was localized in GFAP-immunoreactive hypertrophied astrocytes and neurons within the denervated striatum of young mice. However, no induction of IL-1α mRNA was seen in the midbrain in either age group despite glial activation. Because we have reported that IL-1 can regulate astroglia-derived dopaminergic neurotrophic factors, it was surprising that no changes were observed in acidic and basic fibroblast growth factor or glial cell line-derived neurotrophic factor mRNA levels associated with MPTP-induced plasticity of dopaminergic neurons in the striatum of young mice. Interestingly, we found that dopaminergic neurons express IL-1 receptors, thus suggesting that IL-1α could directly act as a target-derived dopaminergic neurotrophic factor to initiate or enhance the sprouting of dopaminergic axonal terminals. These findings strongly suggest that IL-1α could play an important role in MPTP-induced plasticity of dopaminergic neurons.
Biochemical and Morphometric Analyses Show that Myelination in the Insulin-like Growth Factor 1 Null Brain Is Proportionate to Its Neuronal Composition
Authors: Cheng Clara M. , Joncas George , Reinhardt Rickey R. , Farrer Robert , Quarles Richard , Janssen Jeremy , McDonald Michael P. , Crawley Jacqueline N. , Powell-Braxton Lynn , Bondy Carolyn A.
Published: April 2018

To elucidate the role of insulin-like growth factor 1 (IGF1) in the normal development of brain myelination, we used behavioral, biochemical, and histological analyses to compare the myelination of brains fromIgf1−/−and wild-type (WT) littermate mice. The studies were conducted at postnatal day 40, at which time theIgf1−/−mice weighed ∼66% less than wild-type mice. However, theIgf1−/−brain weight was only reduced by ∼34%. Formal neurological testing showed no sign of central or peripheral myelinopathy inIgf1−/−mice. Myelin composition was not significantly different, and myelin concentration, normalized to brain weight or protein, was equal inIgf1−/−and WT mice. Likewise, concentrations of myelin-specific proteins (MBP, myelin proteolipid protein, MAG, and 2′,3′-cyclic nucleotide,3′-phosphodiesterase) were not significantly different inIgf1−/−and WT mice. The myelin-associated lipids galactocerebroside and sulfatide were modestly reduced inIgf1−/−brains. Regional oligodendrocyte populations and myelin staining patterns were comparable inIgf1−/−and WT brains, with the notable exception of the olfactory system. TheIgf1−/−olfactory bulb was profoundly reduced in size and was depleted of mitral neurons and oligodendrocytes, and its efferent tracts were depleted of myelin.

In summary, this study shows that myelination of theIgf1−/−brain is proportionate to its neuronal composition. Where projection neurons are preserved despite the deletion of IGF1, as in the cerebellar system, oligodendrocytes and myelination are indistinguishable from wild type. Where projection neurons are depleted, as in the olfactory bulb, oligodendrocytes are also depleted, and myelination is reduced in proportion to the reduced projection neuron mass. These data make a strong case for the primacy of axonal factors, not including IGF1, in determining oligodendrocyte survival and myelination.
Glutamate Transporter GLT-1 Is Transiently Localized on Growing Axons of the Mouse Spinal Cord before Establishing Astrocytic Expression
Authors: Yamada Keiko , Watanabe Masahiko , Shibata Takashi , Nagashima Masabumi , Tanaka Kohichi , Inoue Yoshiro
Published: April 2018

The glutamate transporter GLT-1 is expressed in astrocytes of the mature brain and spinal cord. In the present study, we examined its expression in the developing mouse spinal cord. Byin situhybridization,35S-labeled antisense oligonucleotide probes for GLT-1 mRNA consistently labeled the mantle zone/gray matter from embryonic day 11 through the adult stage. However, immunohistochemistry with a specific antibody visualized distinct regional and cellular localizations during the time between the fetal and postnatal stages. At fetal stages, GLT-1 immunoreactivity predominated in the marginal zone/white matter, observed as tiny puncta in cross-sections and as thin fibers in longitudinal sections. The GLT-1-immunopositive structures were also labeled for neuron-specific enolase, a glycolytic enzyme specific to postmitotic neurons and endocrine cells. By electron microscopy, GLT-1 immunoreactivity was detected in axons forming frequent enlargements and was focally localized on a small portion of the axolemma, particularly that facing adjacent axons. At early postnatal stages, GLT-1 disappeared from axons in white matter tracts and, instead, appeared in astrocytic processes surrounding various neuronal elements in the gray matter. Therefore, before switching to astrocytic expression, GLT-1 is transiently expressed in neurons and localized in differentiating axons. Together with our previous finding on the localization of glutamate transporter GLAST in radial glial fibers, GLT-1 and GLAST are thus localized during development on distinct directional cellular elements along which young neurons elongate their axons or move their cell bodies, respectively.
Nerve Growth Factor Induces Process Formation in Meningeal Cells: Implications for Scar Formation in the Injured CNS
Authors: Frisén Jonas , Risling Mårten , Korhonen Laura , Zirrgiebel Ute , Johansson Clas B. , Cullheim Staffan , Lindholm Dan
Published: April 2018

Nerve growth factor (NGF) induces the differentiation and supports the survival of subpopulations of neurons in the PNS and CNS. Here we report that meningeal cells in the pia mater express immunoreactivity and mRNA for both known NGF receptors, the low-affinity receptor p75 and the tyrosine kinase receptor trkA. NGF induces rapid tyrosine phosphorylation of trkA in meningeal cellsin vitro. NGF does not stimulate proliferation of primary meningeal cells but induces process outgrowth. p75- and trkA-immunoreactive meningeal cells with long processes, resembling NGF-treated cellsin vitro, are abundant in the scar tissue that forms at spinal cord lesions in rat and cat. These data suggest that NGF, which is expressed at increased levels in the brain and spinal cord after lesions, may be involved in scar formation in the injured CNS.
Mechanisms Underlying the Early Establishment of Thalamocortical Connections in the Rat
Authors: Molnár Zoltán , Adams Richard , Blakemore Colin
Published: April 2018

We labeled axonal projections using carbocyanine dyes in the developing rat brain to study cellular interactions that might underlie the establishment of thalamocortical connectivity. By embryonic day 14 (E14), groups of neurons in the ventral diencephalon and the primitive internal capsule have established projections to the dorsal thalamus, and thalamic fibers pass in topographic order among them. Simultaneously, axons from the early-born cells in both subplate and marginal zone (i.e., the original cortical preplate) establish an ordered array that fills the intermediate zone. Thalamic axons and preplate fibers meet in the lateral part of the internal capsule (at E15 for occipital cortex and dorsolateral thalamus). Subsequently, selective labeling of corresponding thalamic and early corticofugal projections reveals thalamic fibers growing in association with early corticofugal axons, right up to the cortical subplate. A small carbocyanine crystal implanted at any point in the cortex shortly after the arrival of thalamic axons (E16 for the occipital cortex) labels a single, tight bundle containing both descending and ascending fibers, rather than two separate tracts, providing further evidence for intimate topographic association of the two axon systems. Crystals placed in a row, parasagittally or coronally along the hemisphere, reveal separate, topographically distributed, discrete fiber bundles throughout the pathway, leading to spatially ordered groups of back-labeled thalamic cells. These results indicate that the topography of thalamic axons is maintained throughout the pathway and that they reach the cortex by associating with the projections of a number of preexisting cells, including the preplate scaffold.
The Development of Topography in the Hamster Geniculo-Cortical Projection
Authors: Krug Kristine , Smith Adam L. , Thompson Ian D.
Published: April 2018

Precise point-to-point connectivity is the basis of ordered maps of the visual field. The immaturity of the newborn hamster’s visual system has allowed us to examine emerging topography in the geniculo-cortical projection well before thalamic axons have reached their cortical target, layer IV. Using anterograde transneuronal labeling with wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), we visualized the ingrowth of the whole population of geniculate fibers in the neonatal hamster. Two days after birth (P2), the bulk of the fibers is in the deep cortical layers and the subplate. At the same age, injections of paired retrograde tracers (red and green fluorescent latex microspheres) into area 17 reveal an unordered projection from the dorsal lateral geniculate nucleus (dLGN) to cortex. Individual labeled cells are found throughout the dLGN, and quantitative analysis reveals no segregation of the red and the green populations. At P6, when the pattern of geniculate back label appears ordered and essentially adult-like, geniculate fibers have reached layer IV. The role of selective cell death in this process was investigated by making a tracer injection at P2 and allowing the animals to survive to P6 or P12, when the map is mature. The results show early labeled neurons that made inappropriate connections when the projection was scattered surviving through the period of geniculate cell death. We conclude that the geniculo-cortical map develops from an initially unordered projection to the subplate and the lower cortical layers. Selective cell death appears not to contribute significantly to this process.
Growth and Fate of PSA-NCAM+ Precursors of the Postnatal Brain
Authors: Ben-Hur Tamir , Rogister Bernard , Murray Kerren , Rougon Geneviève , Dubois-Dalcq Monique
Published: April 2018

Oligodendrocyte-type 2 astrocyte (O-2A) lineage cells are derived from multipotential stem cells of the developing CNS. Precursors of O-2A progenitors express the polysialylated (PSA) form of the neural cell adhesion molecule (NCAM) and are detected in neonatal rat brain glial cultures. It is unclear how such PSA-NCAM+ “pre-progenitors” are related to neural stem cells and whether they still have the potential to differentiate along several neural lineages. Here we isolated PSA-NCAM+ pre-progenitor cells from glial cultures by immunopanning and found that most of these cells expressed nestin and PDGF-receptor-α but not O-2A antigens. PSA-NCAM+ cells synthesized transcripts for fibroblast growth factor (FGF) receptors 1, 2, and 3 and responded to FGF2 by survival and proliferation, growing into large clusters resembling neural spheres. FGF2-induced proliferation of PSA-NCAM+ pre-progenitors was significantly enhanced by thyroid hormone (T3), which on its own did not increase cell survival or mitosis. After adhesion and withdrawal of the mitogen, spheres generated mostly oligodendrocytes and astrocytes but very rarely neurons. PSA-NCAM immunopanned cells grown in epidermal growth factor (EGF) also adopted a mostly glial fate after differentiation. In contrast, PSA-NCAM-negative cells and striatal neonatal stem cells, grown in EGF or FGF2, generated the three CNS cell types. Like neural stem cells, PSA-negative cells generated more oligodendrocytes and fewer neurons when expanded in FGF2 and T3. Thus emergence of PSA-NCAM at the surface of neonatal brain precursors coincides with their restriction to a glial fate. T3 modulates these events by enhancing PSA-NCAM+ pre-progenitor growth in FGF2 and favoring an oligodendrocyte fate.
Competition for Neurotrophic Factors: Ocular Dominance Columns
Authors: Elliott Terry , Shadbolt Nigel R.
Published: April 2018

Activity-dependent competition between afferents in the primary visual cortex of many mammals is a quintessential feature of neuronal development. From both experimental and theoretical perspectives, understanding the mechanisms underlying competition is a significant challenge. Recent experimental work suggests that geniculocortical afferents might compete for retrograde neurotrophic factors. We show that a mathematically well-characterized model of retrograde neurotrophic interactions, in which the afferent uptake of neurotrophic factors is activity-dependent and in which the average level of uptake determines the complexity of the axonal arbors of afferents, permits the anatomical segregation of geniculocortical afferents into ocular dominance columns. The model induces segregation provided that the levels of neurotrophic factors available either by activity-independent release from cortical cells or by exogenous cortical infusion are not too high; otherwise segregation breaks down. We show that the model exhibits changes in ocular dominance column periodicity in response to changes in interocular image correlations and that the model predicts that changes in intraocular image correlations should also affect columnar periodicity.