bluuebunny/crossref_metadata_2025 huggingface dataset:
Proprioceptive Input to Feeding Motor Programs inAplysia
Authors: Evans Colin G. , Cropper Elizabeth C.
Published: April 2018

Although central pattern generators (CPGs) can produce rhythmic activity in isolation, it is now generally accepted that under physiological conditions information from the external and internal environment is incorporated into CPG-induced motor programs. Experimentally advantageous invertebrate preparations may be particularly useful for studies that seek to characterize the cellular mechanisms that make this possible. In these experiments, we study sensorimotor integration in the feeding circuitry of the molluscAplysia. We show that a premotor neuron with plateau properties, B51, is important for generating the radula closing/retraction phase of ingestive motor programs. When B51 is depolarized in semi-intact preparations, radula closing/retractions are enhanced. When B51 is hyperpolarized, radula closing/retractions are reduced in size. In addition to being important as a premotor interneuron, B51 is also a sensory neuron that is activated when the feeding apparatus, the radula, rotates backward. The number of centripetal spikes in B51 is increased if the resistance to backward rotation is increased. Thus, B51 is a proprioceptor that is likely to be part of a feedback loop that insures that food will be moved into the buccal cavity when difficulty is encountered. Our data suggest, therefore, thatAplysiaare able to adjust feeding motor programs to accommodate the specific qualities of the food ingested because at least one of the neurons that generates the basic ingestive motor program also serves as an on-line monitor of the success of radula movements.
Duodenal Sensory Neurons Project to Sphincter of Oddi Ganglia in Guinea Pig
Authors: Kennedy Audra L. , Mawe Gary M.
Published: April 2018

Retrograde labeling of duodenum–sphincter of Oddi (SO) preparationsin vitrowith the carbocyanine dye DiI revealed that duodenal neurons project to the SO. The duodenum–SO-projecting neurons were immunoreactive (IR) for choline acetyltransferase but not nitric oxide synthase or calretinin, indicating that this is a cholinergic projection and that this pathway is distinct from the circuitry involved in the ascending limb of the peristaltic reflex. Approximately 20% of the duodenum–SO projection neurons were IR for calbindin. Calbindin-IR nerves within SO ganglia degenerated when the SO was maintained in organ culture alone, but persisted when the SO was cultured with the duodenum intact. Therefore, SO ganglia are a target of the calbindin-positive duodenum–SO projection. Because calbindin is a marker of intrinsic sensory neurons that have processes that pass to the mucosa, these neurons are in position to detect the release of a compound from the mucosa and signal its release to SO ganglia. When applied to retrogradely labeled neurons, cholecystokinin (CCK) elicited a prolonged depolarization, indicating that duodenum–SO-projecting neurons could be capable of detecting CCK released from the mucosa. It is proposed that the role of the intrinsic sensory neurons that project to the SO may be to signal the postprandial release of CCK, thus providing an instruction to decrease SO resistance and facilitate the flow of bile into the duodenum.
Synaptic Potentials Mediated via α-Bungarotoxin-Sensitive Nicotinic Acetylcholine Receptors in Rat Hippocampal Interneurons
Authors: Frazier Charles J. , Buhler Amber V. , Weiner Jeffrey L. , Dunwiddie Thomas V.
Published: April 2018

Exogenous application of acetylcholine elicits inward currents in hippocampal interneurons that are mediated via α-bungarotoxin-sensitive nicotinic acetylcholine receptors, but synaptic responses mediated via such receptors have never been reported in mammalian brain. In the present study, EPSCs were evoked in hippocampal interneurons in rat brain slices by electrical stimulation and were recorded by using whole-cell voltage-clamp techniques. Nicotinic EPSCs were isolated pharmacologically, using antagonists to block other known types of ligand-gated ion channels, and then were tested with either α-bungarotoxin or methyllycaconitine, which are selective antagonists for nicotinic acetylcholine receptors that contain the α7 receptor subunit. Each antagonist proved highly effective at reducing the remaining synaptic current. Evoked α7-mediated nicotinic EPSCs also were desensitized by superfusion with 1 μmnicotine, had extrapolated reversal potentials near 0 mV, and showed strong inward rectification at positive potentials. In several interneurons, methyllycaconitine-sensitive spontaneous EPSCs also were observed that exhibited a biphasic decay rate very similar to that of the α7-mediated evoked response. These studies provide the first demonstration of a functional cholinergic synapse in the mammalian brain, in which the primary postsynaptic receptors are α-bungarotoxin-sensitive nicotinic acetylcholine receptors.
Three-Dimensional Structure and Composition of CA3→CA1 Axons in Rat Hippocampal Slices: Implications for Presynaptic Connectivity and Compartmentalization
Authors: Shepherd Gordon M. G. , Harris Kristen M.
Published: April 2018

Physiological studies of CA3→CA1 synaptic transmission and plasticity have revealed both pre- and postsynaptic effects. Understanding the extent to which individual presynaptic axonal boutons could provide local compartments for control of synaptic efficacy and microconnectivity requires knowledge of their three-dimensional morphology and composition. In hippocampal slices, serial electron microscopy was used to examine a nearly homogeneous population of CA3→CA1 axons in the middle of stratum radiatum of area CA1. The locations of postsynaptic densities (PSDs), vesicles, and mitochondria were determined along 75 axon segments (9.1 ± 2.0 μm in length). Synapses, defined by the colocalization of PSDs and vesicles, occurred on average at 2.7 μm intervals along the axons. Most varicosities (68%) had one PSD, 19% had 2–4 PSDs, and 13% had none. Synaptic vesicles occurred in 90% of the varicosities. One-half (53%) of the varicositieslackedmitochondria, raising questions about their regulation of ATP and Ca2+, and 8% of varicosities containedonlymitochondria. Eleven axons were reconstructed fully. The varicosities were oblong and varied greatly in both length (1.1 ± 0.7 μm) and volume (0.13 ± 0.14 μm3), whereas the intervaricosity shafts were narrow, tubular, and similar in diameter (0.17 ± 0.04 μm) but variable in length (1.4 ± 1.2 μm). The narrow axonal shafts resemble dendritic spine necks and thus could promote biochemical compartmentalization of individual axonal varicosities. The findings raise the intriguing possibility of localized differences in metabolism and connectivity among different axons, varicosities, and synapses.
Reduced Striatal Dopamine Transporter Density in Abstinent Methamphetamine and Methcathinone Users: Evidence from Positron Emission Tomography Studies with [11C]WIN-35,428
Authors: McCann Una D. , Wong Dean F. , Yokoi Fuji , Villemagne Victor , Dannals Robert F. , Ricaurte George A.
Published: April 2018

Methamphetamine and methcathinone are psychostimulant drugs with high potential for abuse. In animals, methamphetamine and related drugs are known to damage brain dopamine (DA) neurons, and this damage has recently been shown to be detectable in living nonhuman primates by means of positron emission tomography (PET) with [11C]WIN-35,428, a DA transporter (DAT) ligand. The present studies determined whether living humans with a history of methamphetamine or methcathinone abuse showed evidence of lasting decrements in brain DAT density. PET studies were performed in 10 control subjects, six abstinent methamphetamine users, four abstinent methcathinone users, and three patients with Parkinson’s disease (PD). On average, subjects had abstained from amphetamine use for ∼3 years. Before PET studies, all subjects underwent urine and blood toxicology screens to rule out recent drug use. Compared with controls, abstinent methamphetamine and methcathinone users had significant decreases in DAT density in the caudate nucleus (−23 and −24%, respectively) and putamen (−25 and −16%, respectively). Larger decreases in DAT density were evident in patients with PD (47 and 68% in caudate and putamen, respectively). Neither methamphetamine nor methcathinone users showed clinical signs of parkinsonism. Persistent reductions of DAT density in methamphetamine and methcathinone users are suggestive of loss of DAT or loss of DA terminals and raise the possibility that as these individuals age, they may be at increased risk for the development of parkinsonism or neuropsychiatric conditions in which brain DA neurons have been implicated.
Nicotine Selectively Enhances NMDA Receptor-Mediated Synaptic Transmission during Postnatal Development in Sensory Neocortex
Authors: Aramakis V. Bess , Metherate Raju
Published: April 2018

The neurotransmitters acetylcholine (ACh) and glutamate have been separately implicated in synaptic plasticity during development of sensory neocortex. Here we show that these neurotransmitters can, in fact, act synergistically via their actions at nicotinic ACh receptors (nAChRs) and NMDA receptors, respectively. To determine how activation of nAChRs modifies glutamatergic EPSPs, we made whole-cell recordings from visualized pyramidal neurons in slices of rat auditory cortex. Pulsed (pressure) ejection of nicotine onto apical dendrites selectively enhanced EPSPs mediated by NMDA receptors without affecting AMPA/kainate (AMPA/KA) receptor-mediated EPSPs. The enhancement occurred during a transient, postnatal period of heightened cholinergic function [neurons tested on postnatal day 8–16 (P8–16)], and not in the mature cortex (>P19). Three related findings indicated the mechanism of action: (1) The specific α7 nAChR antagonist methyllycaconitine citrate (MLA) blocked the effect of nicotine; (2) pulsed nicotine did not enhance postsynaptic depolarizations induced by iontophoretically applied NMDA; and (3) bath exposure to nicotine for several minutes produced apparent nAChR desensitization and precluded enhancement of EPSPs by pulsed nicotine. Together, the data suggest that nicotine acts at rapidly desensitizing, presynaptic α7 nAChRs to increase glutamate release onto postsynaptic NMDA receptors. The synergistic actions mediated by α7 nAChRs and NMDA receptors may contribute to experience-dependent synaptic plasticity in sensory neocortex during early postnatal life.
Decreased Odor Avoidance after Electric Shock inDrosophilaMutants Biases Learning and Memory Tests
Authors: Préat Thomas
Published: April 2018

TheDrosophilamutantsamnesiac,dunce(dnc), andrutabagawere isolated after associative conditioning tests, during which animals were trained to associate the presence of an odor with that of electric shocks (ES). In the absence of conditioning, the odor avoidance (OA) of these mutants was shown to be normal, indicating that their poor associative conditioning performance was attributable to specific learning or memory deficits. However, I show that the OA of the mutants is greatly decreased after their exposure to ES. This effect can last for hours. These results strongly suggest that part of the defect displayed by these mutants in associative conditioning tests does not correspond to a learning or memory deficit but might arise from abnormal sensitivity to stressful stimuli. I looked at the OA after ES of two previously characterizeddncmutants.Df(1)N79fspecifically decreases Dnc expression in the mushroom bodies, leading to a normal level of learning but decreased memory.Df(1)N79fmutants displayed a normal OA after ES.Df(1)N64j15affects the entire brain expression of Dnc, leading to decreased learning and memory.Df(1)N64j15animals showed a strong decrease of their OA after ES. Thus, the lack of Dnc “general” expression is most likely responsible for the OA defect, which would be responsible for the apparent learning defect after conditioning. In contrast, the Dnc phosphodiesterase accumulated in the mushroom bodies would be involved specifically in memory formation.
Continuous and Transient Vesicle Cycling at a Ribbon Synapse
Authors: Rouze Ned C. , Schwartz Eric A.
Published: April 2018

Optical methods were used to study the Ca2+dependence of vesicle cycling in bipolar cells isolated from goldfish retinas. Uniformly raising the Ca2+concentration to between 0.8 and 20 μmproduced a continuous vesicle cycle of balanced exocytosis and endocytosis with a maximum rate equivalent to the turnover of the entire surface membrane of a terminal every 2 min (or ∼900 vesicles sec−1). Increasing the Ca2+concentration above 20 μminhibited continuous vesicle cycling. In contrast, influx of Ca2+through voltage-gated channels produced a transient burst of exocytosis that increased the surface area of a terminal by a maximum of 12% (equivalent to the addition of 13,000 vesicles). Endocytosis was delayed until after Ca2+influx stopped and the average Ca2+concentration in the terminal declined. Hence, a single terminal has mechanisms for both continuous and transient vesicle cycling.
Cytoskeletal Assembly and ATP Release Regulate Astrocytic Calcium Signaling
Authors: Cotrina Maria Luisa , Lin Jane H.-C. , Nedergaard Maiken
Published: April 2018

We have studied the role of actin fiber assembly on calcium signaling in astrocytes. We found that (1) after astrocytes have been placed in culture, it takes several hours for organization of the definitive actin cytoskeleton. Actin organization and the number of cells engaged in calcium signaling increased in parallel. (2) Disruption of the actin cytoskeleton attenuated the calcium wave propagation; cytochalasin D treatment reduced the number of astrocytes engaged in calcium signaling. (3) Propagation of calcium waves depends on cytoskeletal function; inhibition of myosin light chain kinase suppressed wave activity. (4) Astrocytic calcium signaling is mediated by release of ATP and purinergic receptor stimulation, because agents that interfere with this cascade attenuated or reduced calcium signaling. Because purinergic receptors are fully functional shortly after plating and not affected by cytochalasin D, these observations indicate that cytoskeleton organization is a prerequisite for interastrocytic calcium signaling mediated by release of ATP.
Establishment of Patterned Thalamocortical Connections Does Not Require Nitric Oxide Synthase
Authors: Finney Eva M. , Shatz Carla J.
Published: April 2018

Subplate neurons are early-generated neurons that project into the overlying neocortex and are required for the formation of ocular dominance columns. A subset of subplate neurons express nitric oxide synthase (NOS) and produce nitric oxide (NO), a neuronal messenger thought to be involved in adult hippocampal synaptic plasticity and also in the establishment of certain specific connections during visual system development. Here, we examine whether the NOS-containing subplate neurons are involved in ocular dominance column formation in the ferret visual system. Ocular dominance columns form in ferrets between postnatal day 35 (P35) and P60. NOS expression in the visual subplate is low at birth, increases to a maximum at the onset of ocular dominance column formation, and falls thereafter. Nevertheless, blockade of NOS with daily injections of nitroarginine from P14 to P56 fails to prevent the formation of ocular dominance columns, although NOS activity is reduced by >98%. To test further a requirement for NOS in the patterning of connections during CNS development, we examined the cortical barrels in the somatosensory system of mice carrying targeted disruptions of NOS that also received injections of nitroarginine; cortical barrels formed normally in these animals. In addition, barrel field plasticity induced by whisker ablation at birth was normal in nitroarginine-injected NOS knock-out mice. Thus, despite the dynamic regulation of NOS in subplate neurons, NO is unlikely to be essential for the patterning of thalamocortical connections either in visual or somatosensory systems.
Anesthetics Eliminate Somatosensory-Evoked Discharges of Neurons in the Somatotopically Organized Sensorimotor Striatum of the Rat
Authors: West Mark O.
Published: April 2018

The somatotopic organization of the lateral striatum has been demonstrated by anatomical studies of corticostriatal projections from somatosensory and motor cortices and by single-cell recordings in awake animals. The functional organization in the rat, characterized thus far in the freely moving rat preparation, could be mapped more precisely if a stereotaxic, and possibly an anesthetized, preparation could be used. Because striatal discharges evoked by innocuous somatosensory stimulation are used in mapping, this study tested whether such discharges can be observed during anesthesia, encouraged by responsiveness during anesthesia in somatosensory cortical layers projecting to the striatum. Electrode tracks through lateral striatum of anesthetized rats (pentobarbital or ketamine) revealed spontaneously discharging neurons but no discharges evoked by somatosensory examination (passive manipulation and cutaneous stimulation of 14 body parts). Similar tracks in chronically implanted rats showed evoked firing at numerous sites during wakefulness but not during anesthesia (pentobarbital or urethane). Comparisons of the activity of individual neurons between wakefulness and anesthesia showed that pentobarbital, ketamine, chloral hydrate, urethane, or metofane eliminated evoked firing and suppressed spontaneous firing. Recovery time was greater for neural than for behavioral measures. Thus, mapping as proposed is ruled out, and more importantly, the data show that somatotopically organized lateral striatal neurons stop discharging in response to natural stimulation during anesthesia. Available data indicate they do not reach threshold in response to depolarizations produced by glutamatergic corticostriatal synaptic transmission projected from the somatosensory cortex. These data and demonstrations of anesthetic-induced imbalances in most striatal neurotransmitters emphasize that many results regarding striatal physiology and pharmacology during anesthesia cannot be extrapolated to behavioral conditions, thus indicating the need for more empirical testing in conscious animals.
A Ca2+/Calmodulin-Dependent Protein Kinase ModulatesDrosophilaPhotoreceptor K+Currents: A Role in Shaping the Photoreceptor Potential
Authors: Peretz Asher , Abitbol Ilane , Sobko Alexander , Wu Chun-Fang , Attali Bernard
Published: April 2018

Light activation ofDrosophilaphotoreceptors leads to the generation of a depolarizing receptor potential via opening of transient receptor potential and transient receptor potential-like cationic channels. Counteracting the light-activated depolarizing current are two voltage-gated K+conductances,IAandIK, that are expressed in these sensory neurons. Here we show thatDrosophilaphotoreceptorsIAandIKare regulated by calcium–calmodulin (Ca2+/calmodulin) via a Ca2+/calmodulin-dependent protein kinase (CaM kinase), withIKbeing far more sensitive thanIA. Inhibition of Ca2+/calmodulin byN-(6 aminohexyl)-5-chloro-1-naphthalenesulfonamide or trifluoperazine markedly reduced the K+current amplitudes. Likewise, inhibition of CaM kinases by KN-93 potently depressedIKand accelerated its C-type inactivation kinetics. The effect of KN-93 was specific because its structurally related but functionally inactive analog KN-92 was totally ineffective. InDrosophilaphotoreceptor mutantShKS133, which allows isolation ofIK, we demonstrate by current-clamp recording that inhibition ofIKby quinidine or tetraethylammonium increased the amplitude of the photoreceptor potential, depressed light adaptation, and slowed down the termination of the light response. Similar results were obtained when CaM kinases were blocked by KN-93. These findings place photoreceptor K+channels as an additional target for Ca2+/calmodulin and suggest thatIKis well suited to act in concert with other components of the signaling machinery to sharpen light response termination and fine tune photoreceptor sensitivity during light adaptation.
G-Protein β-Subunit Specificity in the Fast Membrane-Delimited Inhibition of Ca2+Channels
Authors: Garcı́a David E. , Li Bin , Garcı́a-Ferreiro Rafael E. , Hernández-Ochoa Erick O. , Yan Kang , Gautam Narasimhan , Catterall William A. , Mackie Ken , Hille Bertil
Published: April 2018

We investigated which subtypes of G-protein β subunits participate in voltage-dependent modulation of N-type calcium channels. Calcium currents were recorded from cultured rat superior cervical ganglion neurons injected intranuclearly with DNA encoding five different G-protein β subunits. Gβ1and Gβ2strongly mimicked the fast voltage-dependent inhibition of calcium channels produced by many G-protein-coupled receptors. The Gβ5subunit produced much weaker effects than Gβ1and Gβ2, whereas Gβ3and Gβ4were nearly inactive in these electrophysiological studies. The specificity implied by these results was confirmed and extended using the yeast two-hybrid system to test for protein–protein interactions. Here, Gβ1or Gβ2coupled to the GAL4-activation domain interacted strongly with a channel sequence corresponding to the intracellular loop connecting domains I and II of a α1subunit of the class B calcium channel fused to the GAL4 DNA-binding domain. In this assay, the Gβ5subunit interacted weakly, and Gβ3and Gβ4failed to interact. Together, these results suggest that Gβ1and/or Gβ2subunits account for most of the voltage-dependent inhibition of N-type calcium channels and that the linker between domains I and II of the calcium channel α1subunit is a principal receptor for this inhibition.
Depolarization Stimulates Initial Calcitonin Gene-Related Peptide Expression by Embryonic Sensory NeuronsIn Vitro
Authors: Ai Xingbin , MacPhedran Sally E. , Hall Alison K.
Published: April 2018

The neuropeptide calcitonin gene-related peptide (CGRP) is expressed by one-third of adult rat lumbar dorsal root ganglion (DRG) neurons, many of which mediate pain sensation or cause vasodilation. The factors that regulate the developmental expression of CGRP are poorly understood. Embryonic DRG neurons initially lack CGRP. When these neurons were stimulated in culture by serum or persistent 50 mmKCl application, the same percentage of CGRP-immunoreactive (CGRP-IR) neurons developedin vitroas was seen in the adult DRGin vivo. The addition of the L-type calcium channel blockers, 5 μmnifedipine or 10 μmverapamil, dramatically decreased the proportion of CGRP-IR neurons that developed, although the N-type calcium channel blocker, 2.5 μmω-conotoxin, was less effective. By contrast, the sodium channel blocker 1 μmtetrodotoxin had no effect on CGRP expression after depolarization. Fura-2 ratiometric imaging demonstrated that mean intracellular free calcium levels increased from 70 to 135 nmwith chronic depolarization, and the addition of nifedipine inhibited that increase. Only a subpopulation of neurons had elevated calcium concentrations during chronic depolarization, and they were correlated with CGRP expression. Key signal transduction pathways were tested pharmacologically for their role in CGRP expression after depolarization; the addition of the CaM kinase inhibitor KN-62 reduced the proportion of CGRP-IR neurons to basal levels. By contrast, protein kinase A and protein kinase C were not implicated in the depolarization-induced CGRP increases. These data suggest that depolarization and the subsequent Ca2+-based signal transduction mechanisms play important roles in thede novoexpression of CGRP by specific embryonic DRG neurons.
Dexamethasone Induces Hypertrophy of Developing Medial Septum Cholinergic Neurons: Potential Role of Nerve Growth Factor
Authors: Shi Bitao , Rabin Stuart J. , Brandoli Cinzia , Mocchetti Italo
Published: April 2018

Glucocorticoid hormones influence neuronal plasticity during development; however little is known about the mechanisms of this trophic activity. Because glucocorticoids increase nerve growth factor (NGF) synthesis in selected brain areas and NGF plays a role in the development of basal forebrain cholinergic neurons, we tested the hypothesis that glucocorticoids may foster maturation of the cholinergic phenotype during postnatal development via the induction of NGF biosynthesis. The synthetic glucocorticoid dexamethasone (DEX) was injected systemically (0.5 mg/kg, s.c.) once a day for 1 week in 7-d-old (P7) rats. DEX elicited an increase in NGF mRNA and protein levels in the cerebral cortex and hippocampus as well as specific NGF responses, such as TrkA tyrosine phosphorylation in the septum, choline acetyltransferase (ChAT) and p75 neurotrophin receptor (p75NTR) immunoreactivity, and a relative number of cholinergic neurons in the medial septum. To examine whether the effect of DEX is age-related, we treated 1- and 14-d-old rats with DEX for 1 week. DEX increased NGF expression in rats treated from P1 to P8 but not in those treated from P14 to P21. The age-related increased expression of NGF correlated with the induction of ChAT immunoreactivity in the medial septum. Moreover, in the spinal cord, neither NGF nor ChAT levels were increased by DEX, suggesting that the glucocorticoid-mediated changes seen in the basal forebrain are associated with specific NGF responses. Our data suggest that by increasing NGF levels, glucocorticoids may play a role in the maturation of postnatal cholinergic neurons.
Signals from the Superficial Layers of the Superior Colliculus Enable the Development of the Auditory Space Map in the Deeper Layers
Authors: King Andrew J. , Schnupp Jan W. H. , Thompson Ian D.
Published: April 2018

We have examined whether the superficial layers of the superior colliculus (SC) provide the source of visual signals that guide the development of the auditory space map in the deeper layers. Anatomical tracing experiments with fluorescent microspheres revealed that a retinotopic map is present in the newborn ferret SC. Aspiration of the caudal region of the superficial layers of the right SC on postnatal day 0 did not cause a reorganization of this projection. Consequently, recordings made when the animals were mature showed that visual units in the remaining superficial layers in rostral SC had receptive fields that spanned a restricted region of anterior space. Auditory units recorded beneath the remaining superficial layers were tuned to corresponding anterior locations. Both the superficial layer visual map and the deeper layer auditory map were normal in the left, unoperated SC. The majority of auditory units recorded throughout the deeper layers ventral to the superficial layer lesion were also tuned to single sound directions. In this region of the SC, however, we observed much greater scatter in the distribution of preferred sound directions and a significant increase in the proportion of units with spatially ambiguous responses. The auditory representation was degraded, although many of these units were also visually responsive. Equivalent lesions of the superficial layers made in adult ferrets did not alter the topographic order in the auditory representation, suggesting that visual activity in these layers may be involved in aligning the different sensory maps in the developing SC.
Membrane-Associated Molecules Guide Limbic and Nonlimbic Thalamocortical Projections
Authors: Mann Fanny , Zhukareva Victoria , Pimenta Aurea , Levitt Pat , Bolz Jürgen
Published: April 2018

Membrane-associated signals expressed in restricted domains of the developing cerebral cortex may mediate axon target recognition during the establishment of thalamocortical projections, which form in a highly precise manner during development. To test this hypothesis, we first analyzed the outgrowth of thalamic explants from limbic and nonlimbic nuclei on membrane substrates prepared from limbic cortex and neocortex. The results show that different thalamic fiber populations are able to discriminate between membrane substrates prepared from target and nontarget cortical regions. A candidate molecule that could mediate selective choice in the thalamocortical system is the limbic system-associated membrane protein (LAMP), which is an early marker of cortical and subcortical limbic regions (Pimenta et al., 1995) that can promote outgrowth of limbic axons. Limbic thalamic and cortical axons showed preferences for recombinant LAMP (rLAMP) in a stripe assay. Incubation of cortical membranes with an antibody against LAMP prevented the ability of limbic thalamic fibers to distinguish between membranes from limbic cortex and neocortex. Strikingly, nonlimbic thalamic fibers also responded to LAMP, but in contrast to limbic thalamic fibers, rLAMP inhibited branch formation and acted as a repulsive axonal guidance signal for nonlimbic thalamic axons. The present studies indicate that LAMP fulfills a role as a selective guidance cue in the developing thalamocortical system.
TheLymnaeaCardioexcitatory Peptide (LyCEP) Receptor: A G-Protein–Coupled Receptor for a Novel Member of the RFamide Neuropeptide Family
Authors: Tensen Cornelis P. , Cox Kingsley J. A. , Smit August B. , van der Schors Roel C. , Meyerhof Wolfgang , Richter Dietmar , Planta Rudi J. , Hermann Petra M. , van Minnen Jan , Geraerts Wijnand P. M. , Knol Jaco C. , Burke Julian F. , Vreugdenhil Erno , van Heerikhuizen Harm
Published: April 2018

A novel G-protein–coupled receptor (GRL106) resembling neuropeptide Y and tachykinin receptors was cloned from the molluscLymnaea stagnalis. Application of a peptide extract from theLymnaeabrain toXenopusoocytes expressing GRL106 activated a calcium-dependent chloride channel. Using this response as a bioassay, we purified the ligand for GRL106,Lymnaeacardioexcitatory peptide (LyCEP), an RFamide-type decapeptide (TPHWRPQGRF-NH2) displaying significant similarity to theAchatinacardioexcitatory peptide (ACEP-1) as well as to the recently identified family of mammalian prolactin-releasing peptides. In theLymnaeabrain, the cells that produce egg-laying hormone are the predominant site of GRL106 gene expression and appear to be innervated by LyCEP-containing fibers. Indeed, LyCEP application transiently hyperpolarizes isolated egg-laying hormone cells. In theLymnaeapericardium, LyCEP-containing fibers end blindly at the pericardial lumen, and the heart is stimulated by LyCEPin vitro. These data confirm that LyCEP is an RFamide ligand for GRL106.
Cell Production and Cell Death in the Generation of Variation in Neuron Number
Authors: Strom Richelle C. , Williams Robert W.
Published: April 2018

Retinal ganglion cell numbers in adult mice vary from 40,000 to 80,000. Much of this variation and the prominent bimodality of strain averages are generated by allelic variants at the neuron number control 1 (Nnc1) locus on chromosome 11. TheNnc1locus may modulate either ganglion cell production or the severity of ganglion cell death. Here we have determined what the relative contributions of these two processes are to variation in adult cell number by estimating total ganglion cell production in 10 strains of mice (A/J, BALB/cJ, BXD32, C57BL/6J, CAST/Ei, CARL/ChGo, CE/J, C3H/HeSnJ, DBA/2J, and LP/J). These strains have adult populations that range from 45,000 to 76,000 (data available athttp://qtl.ml.org). We estimated cell production by counting ganglion cell axons after ganglion cell neurogenesis but before the onset of significant cell death. Total cell production ranges from 131,000 to 224,000, and most of the variation in adult ganglion cell number is explained by this significant variation in cell production. In contrast, the percentage of cell death is relatively uniform in most strains (∼69% cell loss). The exceptions are BXD32, a strain that has an extremely high adult cell population, andMus caroli(CARL/ChGo), a wild southeast Asian species that is distantly related to laboratory strains. In BXD32 andM. caroli, ∼62% of the population dies. Our analysis indicates that substitutions of single alleles at theNnc1locus are responsible for production differences of ∼8000 ganglion cells.
Long-Term Antidepressant Treatments Result in a Tonic Activation of Forebrain 5-HT1AReceptors
Authors: Haddjeri Nasser , Blier Pierre , de Montigny Claude
Published: April 2018

We report here the first direct functional evidence of an increase in the tonic activation of postsynaptic 5-HT1Areceptors by antidepressant treatments. Because 5-HT1Areceptor activation hyperpolarizes and inhibits CA3pyramidal neurons in the dorsal hippocampus, we determined, usingin vivoextracellular recording, whether the selective 5-HT1Areceptor antagonist WAY 100635 could disinhibit these neurons. Unexpectedly, no disinhibition could be detected in controls. However, after long-term treatment with the tricyclic antidepressant imipramine, the selective 5-HT reuptake inhibitor paroxetine, the reversible monoamine oxidase-A inhibitor befloxatone, the α2-adrenergic antagonist mirtazapine, or the 5-HT1Areceptor agonist gepirone or multiple electroconvulsive shock (ECS) administration, WAY 100635 markedly increased (60–200%) the firing activity of CA3pyramidal neurons. Such a disinhibition was absent in rats treated with the nonantidepressant drug chlorpromazine, in rats receiving only one ECS, or in rats receiving multiple ECSs in combination with an intrahippocampal pertussis toxin treatment to inactivate Gi/o-coupled 5-HT1Areceptors. These data indicate that such antidepressant treatments, acting on entirely different primary targets, might alleviate depression by enhancing the tonic activation of forebrain postsynaptic 5-HT1Areceptors.
Temporal and Binaural Properties in Dorsal Cochlear Nucleus and Its Output Tract
Authors: Joris Philip X. , Smith Philip H.
Published: April 2018

The dorsal cochlear nucleus (DCN) is one of three nuclei at the terminal zone of the auditory nerve. Axons of its projection neurons course via the dorsal acoustic stria (DAS) to the inferior colliculus (IC), where their signals are integrated with inputs from various other sources. The DCN presumably conveys sensitivity to spectral features, and it has been hypothesized that it plays a role in sound localization based on pinna cues. To account for its remarkable spectral properties, a DCN circuit scheme was developed in which three inputs converge onto projection neurons: auditory nerve fibers, inhibitory interneurons, and wide-band inhibitors, which possibly consist of Onset-chopper (Oc) cells. We studied temporal and binaural properties in DCN and DAS and examined whether the temporal properties are consistent with the model circuit.

Interneurons (type II) and projection (types III and IV) neurons differed from Occells by their longer latencies and temporally nonlinear responses to amplitude-modulated tones. They also showed evidence of early inhibition to clicks. All projection neurons examined were inhibited by stimulation of the contralateral ear, particularly by broadband noise, and this inhibition also had short latency. Because Occells had short-latency responses and were well driven by broadband stimuli, we propose that they provide short-latency inhibition to DCN for both ipsilateral and contralateral stimuli. These results indicate more complex temporal behavior in DCN than has previously been emphasized, but they are consistent with the recently described nonlinear behavior to spectral manipulations and with the connectivity scheme deduced from such manipulations.
Effects of Transforming Growth Factor-β (Isoforms 1–3) on Amyloid-β Deposition, Inflammation, and Cell Targeting in Organotypic Hippocampal Slice Cultures
Authors: Harris-White Marni E. , Chu Teresa , Balverde Zerlinde , Sigel Jason J. , Flanders Kathleen C. , Frautschy Sally A.
Published: April 2018

The transforming growth factor-β (TGF-β) family consists of three isoforms and is part of a larger family of cytokines regulating differentiation, development, and tissue repair. Previous work from our laboratory has shown that TGF-β1 can increase amyloid-β protein (Aβ) immunoreactive (Aβir) plaque-like deposits in rat brain. The aim of the current study was to evaluate all three isoforms of TGF-β for their ability to affect the deposition and neurotoxicity of Aβ in an organotypic, hippocampal slice culture model of Aβ deposition. Slice cultures were treated with Aβ either with or without one of the TGF-β isoforms. All three isoforms can increase Aβ accumulation (over Aβ treatment alone) within the slice culture, as determined by ELISA. However, there are striking differences in the pattern of Aβir among the three isoforms of TGF-β. Isoforms 1 and 3 produced a cellular pattern of Aβ staining that colocalizes with GS lectin staining (microglia). TGF-β2 produces dramatic Aβ staining of pyramidal neurons in layers CA1–CA2. In addition to cellular Aβ staining, plaque-like deposits are increased by all of the TGF-βs. Although no gross toxicity was observed, morphological neurodegenerative changes were seen in the CA1 region when the slices were treated with Aβ plus TGF-β2. Our results demonstrate important functional differences among the TGF-β isoforms in their ability to alter the cellular distribution and degradation of Aβ. These changes may be relevant to the pathology of Alzheimer’s disease (AD).
Synaptic Modifications in Cultured Hippocampal Neurons: Dependence on Spike Timing, Synaptic Strength, and Postsynaptic Cell Type
Authors: Bi Guo-qiang , Poo Mu-ming
Published: April 2018

In cultures of dissociated rat hippocampal neurons, persistent potentiation and depression of glutamatergic synapses were induced by correlated spiking of presynaptic and postsynaptic neurons. The relative timing between the presynaptic and postsynaptic spiking determined the direction and the extent of synaptic changes. Repetitive postsynaptic spiking within a time window of 20 msec after presynaptic activation resulted in long-term potentiation (LTP), whereas postsynaptic spiking within a window of 20 msec before the repetitive presynaptic activation led to long-term depression (LTD). Significant LTP occurred only at synapses with relatively low initial strength, whereas the extent of LTD did not show obvious dependence on the initial synaptic strength. Both LTP and LTD depended on the activation of NMDA receptors and were absent in cases in which the postsynaptic neurons were GABAergic in nature. Blockade of L-type calcium channels with nimodipine abolished the induction of LTD and reduced the extent of LTP. These results underscore the importance of precise spike timing, synaptic strength, and postsynaptic cell type in the activity-induced modification of central synapses and suggest that Hebb’s rule may need to incorporate a quantitative consideration of spike timing that reflects the narrow and asymmetric window for the induction of synaptic modification.
Suppression of Ethanol-Reinforced Behavior by Naltrexone Is Associated with Attenuation of the Ethanol-Induced Increase in Dialysate Dopamine Levels in the Nucleus Accumbens
Authors: Gonzales Rueben A. , Weiss Friedbert
Published: April 2018

The opiate antagonist naltrexone suppresses ethanol-reinforced behavior in animals and decreases ethanol intake in humans. However, the mechanisms underlying these actions are not well understood. Experiments were designed to test the hypothesis that naltrexone attenuates the rewarding properties of ethanol by interfering with ethanol-induced stimulation of dopamine activity in the nucleus accumbens (NAcc). Simultaneous measures of the effects of naltrexone on dialysate dopamine levels in the NAcc and on operant responding for oral ethanol were used. Male Wistar rats were trained to self-administer ethanol (10–15%, w/v) in 0.2% (w/v) saccharin during daily 30 min sessions and were surgically prepared for intracranial microdialysis. Experiments began after reliable self-administration was established. Rats were injected with naltrexone (0.25 mg/kg, s.c.) or saline and 10 min later were placed inside the operant chamber for a 20 min waiting period with no ethanol available, followed by 30 min of access to ethanol. A transient rise in dialysate dopamine levels was observed during the waiting period, and this effect was not altered by naltrexone. Ethanol self-administration reliably increased dopamine levels in controls. Naltrexone significantly suppressed ethanol self-administration and prevented ethanol-induced increases in dialysate dopamine levels. Subsequent dose–effect analyses established that the latter effect was not merely a function of reduced ethanol intake but that naltrexone attenuated the efficacy of ethanol to elevate dialysate dopamine levels. These results suggest that suppression of ethanol self-administration by opiate antagonists is the result of interference with dopamine-dependent aspects of ethanol reinforcement, although possible additional effects via nondopaminergic mechanisms cannot be eliminated as a factor in opiate antagonist-induced reduction of ethanol intake.
Synthesis of the Antioxidant Glutathione in Neurons: Supply by Astrocytes of CysGly as Precursor for Neuronal Glutathione
Authors: Dringen Ralf , Pfeiffer Brigitte , Hamprecht Bernd
Published: April 2018

Deficiency of the antioxidant glutathione in brain appears to be connected with several diseases characterized by neuronal loss. To study neuronal glutathione metabolism and metabolic interactions between neurons and astrocytes in this respect, neuron-rich primary cultures and transient cocultures of neurons and astroglial cells were used. Coincubation of neurons with astroglial cells resulted within 24 hr of incubation in a neuronal glutathione content twice that of neurons incubated in the absence of astroglial cells. In cultured neurons, the availability of cysteine limited the cellular level of glutathione. During a 4 hr incubation in a minimal medium lacking all amino acids except cysteine, the amount of neuronal glutathione was doubled. Besides cysteine, also the dipeptides CysGly and γGluCys were able to serve as glutathione precursors and caused a concentration-dependent increase in glutathione content. Concentrations giving half-maximal effects were 5, 5, and 200 μmfor cysteine, CysGly, and γGluCys, respectively. In the transient cocultures, the astroglia-mediated increase in neuronal glutathione was suppressed by acivicin, an inhibitor of the astroglial ectoenzyme γ-glutamyl transpeptidase, which generates CysGly from glutathione. These data suggest the following metabolic interaction in glutathione metabolism of brain cells: the ectoenzyme γ-glutamyl transpeptidase uses as substrate the glutathione released by astrocytes to generate the dipeptide CysGly that is subsequently used by neurons as precursor for glutathione synthesis.
On the Mechanism of the γ → β Frequency Shift in Neuronal Oscillations Induced in Rat Hippocampal Slices by Tetanic Stimulation
Authors: Traub Roger D. , Whittington Miles A. , Buhl Eberhard H. , Jefferys John G. R. , Faulkner Howard J.
Published: April 2018

Tetanic stimulation of the CA1 region of rat hippocampal slices can induce γ frequency population oscillations (30–100 Hz) after a latency of 50–150 msec that are synchronized to within 1–2 msec when simultaneous stimuli are delivered to two sites 2 mm or more apart. When tetanic stimuli, twice-threshold for eliciting γ oscillations, are used, new phenomena occur. (1) After a period of γ, there is a switch to β frequencies (10–25 Hz); (2) during the switch, pyramidal cell spike afterhyperpolarizations (AHPs) increase and rhythmic EPSPs occur in pyramidal cells; and (3) after an episode of single-site, twice-threshold-induced γ/β oscillations, simultaneous two-site threshold stimuli induce γ oscillations that are locally synchronized, butno longer are capable of long-range synchrony. We studied the cellular mechanisms of the γ/β switch with electrophysiological techniques and computer simulations. Our model predicts that the observed increases in both pyramidal cell AHPs and in pyramidal/pyramidal cell EPSPs are necessary and sufficient for the β switch to occur. Firing patterns generated by the model, both for pyramidal cells and for interneurons, resemble experimental records. A one-site twice-threshold stimulus might lead to an inability of the two sites to synchronize at γ frequencies, after subsequent two-site stimulation, via this mechanism. If depression is induced at synapses coupling pyramidal cells at one site to interneurons at the other site, then two-site stimulation cannot produce interneuron doublets; hence, as shown previously, the two sites will be unable to synchronize. This mechanism works in simulations, and we provide experimental evidence that synaptic depression and loss of doublets occur after a sufficiently strong local tetanus to one site. We suggest that long-range excitatory connections onto interneurons determine whether different pyramidal cell “assemblies” can synchronize at γ frequencies, whereas excitatory connections onto pyramidal cells determine whether such assemblies can synchronize at β frequencies.
Interaural Intensity Difference Processing in Auditory Midbrain Neurons: Effects of a Transient Early Inhibitory Input
Authors: Oswald Jeffrey P. , Klug Achim , Park Thomas J.
Published: April 2018

Interaural intensity differences (IIDs) are important cues that animals use to localize high-frequency sounds. Neurons sensitive to IIDs are excited by stimulation of one ear and inhibited by stimulation of the other ear, such that the response magnitude of the cell depends on the relative strengths of the two inputs, which in turn depends on the sound intensities at the ears. In the auditory midbrain nucleus, the inferior colliculus (IC), many IID-sensitive neurons have response functions that decline steeply from maximum to zero spikes as a function of IID. However, there are also many neurons with much more shallow response functions that do not decline to zero spikes. We present evidence from single-unit recordings in the Free-tailed bat’s IC that this partially inhibited response pattern is a result of the inhibitory input to these cells being very brief (∼2 msec). Of the cells sampled, 54 of 137 (40%) achieved partial inhibition when tested with 60 msec tones, and the inhibition to these 54 cells occurred primarily during the first few milliseconds of the excitatory response. Consequently, the initial component of the response was highly sensitive to IIDs, whereas the later component was primarily insensitive to IIDs. Each of the 54 “partially inhibited” cells was able to reach complete inhibition with very short stimuli, such as simulated bat echolocation calls that invoked only the initial, IID-sensitive component. Local application of inhibitory transmitter antagonists disabled the short inhibitory input, indicating that this response pattern is created within the IC.
Inducible Genetic Suppression of Neuronal Excitability
Authors: Johns David C. , Marx Ruth , Mains Richard E. , O’Rourke Brian , Marbán Eduardo
Published: April 2018

Graded, reversible suppression of neuronal excitability represents a logical goal of therapy for epilepsy and intractable pain. To achieve such suppression, we have developed the means to transfer “electrical silencing” genes into neurons with sensitive control of transgene expression. An ecdysone-inducible promoter drives the expression of inwardly rectifying potassium channels in polycistronic adenoviral vectors. Infection of superior cervical ganglion neurons did not affect normal electrical activity but suppressed excitability after the induction of gene expression. These experiments demonstrate the feasibility of controlled ion channel expression after somatic gene transfer into neurons and serve as the prototype for a novel generalizable approach to modulate excitability.