bluuebunny/crossref_metadata_2025 huggingface dataset:
Phasic Firing Time Locked to Cocaine Self-Infusion and Locomotion: Dissociable Firing Patterns of Single Nucleus Accumbens Neurons in the Rat
Authors: Peoples Laura L. , Gee Fred , Bibi Racquel , West Mark O.
Published: April 2018

The activity of single nucleus accumbens (NAcc) neurons of rats was extracellularly recorded during intravenous cocaine self-administration sessions (0.7 mg/kg per infusion, fixed ratio 1). We reported previously that NAcc neurons showed a change, usually a decrease, in firing rate during the first 1 min after the cocaine-reinforced lever press. This postpress change was followed by aprogressive reversalof that change, which began within the first 2 min after the press and was not complete until the last 1 min before the next lever press (termed the change + progressive reversal firing pattern). In the present study we documented a regular pattern of locomotion that occurred in parallel with the change + progressive reversal firing pattern. This observation suggested that discharges time locked to locomotion may determine the change + progressive reversal firing pattern. However, 55% of the neurons failed to show firing time locked to locomotion that could have contributed to the change + progressive reversal firing pattern. Moreover, for all neurons, the change + progressive reversal firing pattern was apparent even if the calculation of firing rate excluded all periods of locomotion. The present data showed that the change + progressive reversal firing pattern is not solely attributable to phasic changes in firing time locked to the execution of locomotion. The change + progressive reversal firing pattern closely mirrors changes in drug level and dopamine overflow observed by previous researchers and may thus be a component of the neurophysiological mechanism by which drug level regulates drug-taking behavior during an ongoing self-administration session.
The Cellular and Subcellular Localization of Huntingtin-Associated Protein 1 (HAP1): Comparison with Huntingtin in Rat and Human
Authors: Gutekunst Claire-Anne , Li Shi-Hua , Yi Hong , Ferrante Robert J. , Li Xiao-Jiang , Hersch Steven M.
Published: April 2018

The cellular and subcellular distribution of HAP1 was examined in rat brain by light and electron microscopic immunocytochemistry and subcellular fractionation. HAP1 localization was also determined in human postmortem tissue from control and Huntington’s disease (HD) cases by light microscopic immunocytochemistry. At the cellular level, the heterogeneity of HAP1 expression was similar to that of huntingtin; however, HAP1 immunoreactivity was more widespread. The subcellular distribution of HAP1 was examined using immunogold electron microscopy. Like huntingtin, HAP1 is a cytoplasmic protein that associates with microtubules and many types of membranous organelles, including mitochondria, endoplasmic reticulum, tubulovesicles, endosomal and lysosomal organelles, and synaptic vesicles. A quantitative comparison of the organelle associations of HAP1 and huntingtin showed them to be almost identical. Within HAP1-immunoreactive neurons in rat and human brain, populations of large and small immunoreactive puncta were visible by light microscopy. The large puncta, which were especially evident in the ventral forebrain, were intensely HAP1 immunoreactive. Electron microscopic analysis revealed them to be a type of nucleolus-like body, which has been named a stigmoid body, that may play a role in protein synthesis. The small puncta, less intensely labeled, were primarily mitochondria. These results indicate that the localization of HAP1 and huntingtin is more similar than previously appreciated and provide further evidence that HAP1 and huntingtin have localizations consistent with roles in intracellular transport. Our data also suggest, however, that HAP1 is not present in the abnormal intranuclear and neuritic aggregates containing the N-terminal fragment of mutant huntingtin that are found in HD brains.
Amino Acid Residues that Control pH Modulation of Transport-Associated Current in Mammalian Serotonin Transporters
Authors: Cao Yongwei , Li Ming , Mager Sela , Lester Henry A.
Published: April 2018

The rat and human serotonin transporters (rSERT and hSERT, respectively) were expressed inXenopusoocytes and studied using site-directed mutagenesis, electrophysiological recordings, and [3H]5-HT uptake measurements. rSERT, but not hSERT, displayed increased transport-associated current at low pH. Chimeras and point mutations showed that, of the 52 nonidentical residues, a single residue at position 490 (threonine in rSERT and lysine in hSERT) governs this difference. Furthermore, potentiation required the glutamate residue at position 493. Cysteine substitution and alkylation experiments showed that residue 493 is extracellular. Cysteine at 493 increased, whereas aspartate decreased, the net charge movement per transported 5-HT molecule. The mutations at this region did not significantly affect other aspects of SERT function, including agonist-independent leakage current, voltage-dependent transient current, and H+current. This region may therefore be part of an external gate required for rSERT function. The data and analyses show that, in the absence of detailed structural information, a gate–lumen–gate scheme is useful for interpreting results from mutations that alter functional properties of neurotransmitter transporters.
Postsynaptic Mechanisms Underlying Responsiveness of Amygdaloid Neurons to Nociceptin/Orphanin FQ
Authors: Meis Susanne , Pape Hans-Christian
Published: April 2018

Effects of nociceptin/orphanin FQ (N/OFQ), the endogenous ligand of the opioid-like orphan receptor (ORL), were investigated in the rat lateral (AL) and central (ACe) amygdalain vitro. Approximately 98% of presumed projection neurons in the AL responded to N/OFQ with an increase in inwardly rectifying potassium conductance, resulting in an impairment in cell excitability. Half-maximal effects were obtained at 30.6 nm; the Hill coefficient was 0.63. In the ACe, 31% of the cells displayed responses similar to that in the AL, 44% were nonresponsive, and 25% responded with a small potassium current with a linear current–voltage relationship. Responses to N/OFQ were reduced by 100 μmBa2+, were insensitive to 10 μmnaloxone, and were blocked by a selective ORL antagonist, [Phe1ψ(CH2-NH)Gly2]NC(1–13)NH2(IC50= 760 nm). Involvement of G-proteins was indicated by irreversible effects and blockade of action of N/OFQ during intracellular presence of GTP-γ-S (100 μm) and GDP-β-S (2 mm), respectively, and prevention of responses after incubation in pertussis toxin (500 ng/ml). These mechanisms may contribute to the role of N/OFQ in the reduction of fear responsiveness and stress that have recently been suggested on the basis of histochemical and behavioral studies.
Multiple Limbic Regions Mediate the Disruption of Prepulse Inhibition Produced in Rats by the Noncompetitive NMDA Antagonist Dizocilpine
Authors: Bakshi Vaishali P. , Geyer Mark A.
Published: April 2018

Prepulse inhibition (PPI), a phenomenon in which a weak prestimulus decreases the startle response to an intense stimulus, provides an operational measure of sensorimotor gating (a process by which an organism filters sensory information) and is diminished in schizophrenia and schizotypal patients. The psychotomimetic phencyclidine and its potent congener dizocilpine are noncompetitive antagonists of the NMDA receptor complex, and they disrupt PPI in rodents, mimicking the clinically observed PPI deficit. The neuroanatomical substrates mediating the PPI-disruptive effects of noncompetitive NMDA antagonists are unknown. The present study sought to identify brain regions subserving the disruption of PPI produced by noncompetitive NMDA antagonists in rats. PPI was measured in startle chambers immediately after bilateral infusion of dizocilpine (0, 0.25, 1.25, and 6.25 μg/0.5 μl/side) into one of six brain regions: amygdala, dorsal hippocampus, medial prefrontal cortex, nucleus accumbens, ventral hippocampus, and dorsomedial thalamus. Dizocilpine significantly decreased PPI after infusion into the amygdala or dorsal hippocampus. A trend toward PPI disruption was observed with administration into medial prefrontal cortex. In contrast, no change in PPI was produced by dizocilpine infusion into nucleus accumbens, ventral hippocampus, or dorsomedial thalamus. Startle reactivity was increased by dizocilpine infusion into amygdala, dorsal hippocampus, nucleus accumbens, and dorsomedial thalamus, but not medial prefrontal cortex. These findings indicate that multiple limbic forebrain regions mediate the ability of noncompetitive NMDA antagonists to disrupt PPI and that the PPI-disruptive and the startle-increasing effects of dizocilpine are mediated by different central sites.
The Visuo-Motor Pathway in the Local Circuit of the Rat Superior Colliculus
Authors: Isa Tadashi , Endo Toshiaki , Saito Yasuhiko
Published: April 2018

Intrinsic circuit of the superior colliculus (SC), in particular the pathway from the optic tract (OT) to neurons in the intermediate layer (SGI), was investigated by whole-cell patch-clamp recording in slice preparations obtained from 17- to 24-d-old rats. Stimulation of the OT induced monosynaptic EPSPs in neurons in the superficial gray layer (SGS) and the optic layer (SO), and disynaptic or polysynaptic EPSPs in a majority of SGI neurons. Stimulation of the SGS induced monosynaptic or oligosynaptic EPSPs in the SGI neurons. Both the monosynaptic EPSPs induced in the SGS/SO neurons by stimulation of the OT and those induced in the SGI neurons by stimulation of the SGS were mediated by AMPA- and NMDA-type glutamate receptors. Thus, we have clarified the existence of the glutamatergic excitatory pathway from the OT to the SGI neurons via SGS and SO neurons. The EPSPs in the SGI neurons induced by stimulation of the OT or SGS were remarkably enhanced by bicuculline, suggesting that the signal transmission in this pathway is under strong suppression by the GABAergic system.
Medial Forebrain Bundle Lesions Fail to Structurally and Functionally Disconnect the Ventral Tegmental Area from Many Ipsilateral Forebrain Nuclei: Implications for the Neural Substrate of Brain Stimulation Reward
Authors: Simmons Janine M. , Ackermann Robert F. , Gallistel C. R.
Published: April 2018

Lesions in the medial forebrain bundle rostral to a stimulating electrode have variable effects on the rewarding efficacy of self-stimulation. We attempted to account for this variability by measuring the anatomical and functional effects of electrolytic lesions at the level of the lateral hypothalamus (LH) and by correlating these effects to postlesion changes in threshold pulse frequency (pps) for self-stimulation in the ventral tegmental area (VTA). We implanted True Blue in the VTA and compared cell labeling patterns in forebrain regions of intact and lesioned animals. We also compared stimulation-induced regional [14C]deoxyglucose (DG) accumulation patterns in the forebrains of intact and lesioned animals. As expected, postlesion threshold shifts varied: threshold pps remained the same or decreased in eight animals, increased by small but significant amounts in three rats, and increased substantially in six subjects. Unexpectedly, LH lesions did not anatomically or functionally disconnect all forebrain nuclei from the VTA. Most septal and preoptic regions contained equivalent levels of True Blue label in intact and lesioned animals. In both intact and lesioned groups, VTA stimulation increased metabolic activity in the fundus of the striatum (FS), the nucleus of the diagonal band, and the medial preoptic area. On the other hand, True Blue labeling demonstrated anatomical disconnection of the accumbens, FS, substantia innominata/magnocellular preoptic nucleus (SI/MA), and bed nucleus of the stria terminalis. [14C]DG autoradiography indicated functional disconnection of the lateral preoptic area and SI/MA. Correlations between patterns of True Blue labeling or [14C]deoxyglucose accumulation and postlesion shifts in threshold pulse frequency were weak and generally negative. These direct measures of connectivity concord with the behavioral measures in suggesting a diffuse net-like connection between forebrain nuclei and the VTA.
Contributions of Pathway and Neuron to Preferential Motor Reinnervation
Authors: Brushart Thomas M. , Gerber Jonathan , Kessens Philip , Chen You-Gang , Royall Richard M.
Published: April 2018

Motor axons regenerating after transection of mixed nerve preferentially reinnervate distal muscle branches, a process termed preferential motor reinnervation (PMR). Motor axon collaterals appear to enter both cutaneous and muscle Schwann cell tubes on a random basis. Double-labeling studies suggest that PMR is generated by pruning collaterals from cutaneous pathways while maintaining those in motor pathways (the “pruning hypothesis”). If all collaterals projecting to muscle are saved, then stimulation of regenerative sprouting should increase specificity by increasing the number of motoneurons with at least one collateral in a muscle pathway. In the current experiments, collateral sprouting is stimulated by crushing the nerve proximal to the repair site before suture, a maneuver that also conditions the neuron and predegenerates the distal pathway. Control experiments are performed to separate these effects from those of collateral generation.

Experiments were performed on the rat femoral nerve and evaluated by exposing its terminal cutaneous and muscle branches to HRP or Fluoro-Gold. Crush proximal to the repair site increased motor axon collaterals at least fivefold and significantly increased the percentage of correctly projecting motoneurons, consistent with the pruning hypothesis. Conditioning the nerve with distal crushes before repair had no effect on specificity. A graft model was used to separate the effects of collateral generation and distal stump predegeneration. Previous crush of the proximal femoral nerve significantly increased the specificity of fresh graft reinnervation. Stimulation of regenerative collateral sprouting thus increased PMR, confirming the pruning hypothesis. However, this effect was overshadowed by the dramatic specificity with which predegenerated grafts were reinnervated by fresh uncrushed proximal axons. These unexpected effects of predegeneration on specificity could involve a variety of possible mechanisms and warrant further study because of their mechanistic and clinical implications.
Developmentally Regulated Spontaneous Activity in the Embryonic Chick Retina
Authors: Wong Wai T. , Sanes Joshua R. , Wong Rachel O. L.
Published: April 2018

Even before birth and the onset of sensory experience, neural activity plays an important role in shaping the vertebrate nervous system. In the embryonic chick visual system, activity in the retina before vision has been implicated in the refinement of retinotopic maps, the elimination of transient projections, and the survival of a full complement of neurons. In this study, we report the detection of a physiological substrate for these phenomena: waves of spontaneous activity in the ganglion cell layer of the embryonic chick retina. The activity is robust and highly patterned, taking the form of large amplitude, rhythmic, and wide-ranging waves of excitation that propagate across the retina. Activity waves are most prominent and organized between embryonic days 13–18, coinciding with the developmental period during which retinal axons refine their connections in their targets. The spatial and temporal features of the patterns observed are consistent with the role of activity patterns in shaping eye-specific projections and retinotopic maps but inconsistent with the hypothesis that they specify lamina-specific projections in the tectum. Antagonists of glutamatergic and glycinergic transmission and of gap junctional communication suppress spontaneous activity, whereas antagonists to GABAergic transmission potentiate it. Based on these results, we propose that spontaneous activity in the ganglion cells is regulated by chemical inputs from both bipolar and amacrine cells and by gap junctional coupling involving ganglion cells.
Expression of Ciliary Tektins in Brain and Sensory Development
Authors: Norrander Jan , Larsson Magnus , Ståhl Stefan , Höög Christer , Linck Richard
Published: April 2018

Many types of neural tissues and sensory cells possess either motile or primary cilia. We report the first mammalian (murine testis) cDNA for tektin, a protein unique to cilia, flagella, and centrioles, which we have used to identify related proteins and genes in sensory tissues. Comparison with the sequence database reveals that tektins are a gene family, spanning evolution fromCaenorhabditis elegans(in which they correlate with touch receptor cilia) andDrosophila melanogaster, toMus musculusandHomo sapiens(in which they are found in brain, retina, melanocytes, and at least 13 other tissues). The peptide sequence RPNVELCRD, or a variant of it, is a prominent feature of tektins and is likely to form a functionally important protein domain. Using the cDNA as a probe, we determined the onset, relative levels, and locations of tektin expression in mouse for several adult tissues and embryonic stages by Northern blot analysis andin situhybridization. Tektin expression is significant in adult brain and in the choroid plexus, the forming retina (primitive ependymal zone corresponding to early differentiating photoreceptor cells), and olfactory receptor neurons of stage embryonic day 14 embryos. There is a striking correlation of tektin expression with the known presence of either motile or primary cilia. The evolutionary conservation of tektins and their association with tubulin in cilia and centriole formation make them important and useful molecular targets for the study of neural development.
A Transient Population of Neurons Pioneers the Olfactory Pathway in the Zebrafish
Authors: Whitlock Kathleen E. , Westerfield Monte
Published: April 2018

Mechanisms guiding the first axons from the olfactory placode of the peripheral nervous system (PNS) to the olfactory bulb in the vertebrate CNS are unknown. We analyzed the initial outgrowth of axons from the olfactory placode in zebrafish and found a precocious transient class of pioneer neurons that prefigure the primary olfactory pathway before outgrowth of olfactory sensory axons or expression of olfactory receptor genes. Not only are the pioneers antigenically, morphologically, and spatially distinct from olfactory sensory neurons, they are also developmentally distinct; via fate mapping, we show that they arise from a more anterior region of the lateral neural plate than do the first sensory neurons. After the axons of the sensory neurons grow into the CNS, the pioneer neurons undergo apoptotic cell death. When we ablated the pioneers before axonogenesis, the following sensory axons showed severe misrouting. We propose that the pioneers provide the first necessary connection from the PNS to the CNS and that they establish an axonal scaffold for the later-arriving olfactory sensory neurons.
Neural Learning Rules for the Vestibulo-Ocular Reflex
Authors: Raymond Jennifer L. , Lisberger Stephen G.
Published: April 2018

Mechanisms for the induction of motor learning in the vestibulo-ocular reflex (VOR) were evaluated by recording the patterns of neural activity elicited in the cerebellum by a range of stimuli that induce learning. Patterns of climbing-fiber, vestibular, and Purkinje cell simple-spike signals were examined during sinusoidal head movement paired with visual image movement at stimulus frequencies from 0.5 to 10 Hz. A comparison of simple-spike and vestibular signals contained the information required to guide learning only at low stimulus frequencies, and a comparison of climbing-fiber and simple-spike signals contained the information required to guide learning only at high stimulus frequencies. Learning could be guided by comparison of climbing-fiber and vestibular signals at all stimulus frequencies tested, but only if climbing fiber responses were compared with the vestibular signals present 100 msec earlier. Computational analysis demonstrated that this conclusion is valid even if there is a broad range of vestibular signals at the site of plasticity. Simulations also indicated that the comparison of vestibular and climbing-fiber signals across the 100 msec delay must be implemented by a subcellular “eligibility” trace rather than by neural circuits that delay the vestibular inputs to the site of plasticity. The results suggest two alternative accounts of learning in the VOR. Either there are multiple mechanisms of learning that use different combinations of neural signals to drive plasticity, or there is a single mechanism tuned to climbing-fiber activity that follows activity in vestibular pathways by ∼100 msec.
A Memory for Extracellular Ca2+by Speeding Recovery of P2X Receptors from Desensitization
Authors: Cook S. P. , Rodland K. D. , McCleskey E. W.
Published: April 2018

Nerve endings of nociceptors (pain-sensing neurons) express an unusual subtype of ATP-gated ion channel, the P2X3 receptor, that rapidly desensitizes (<100 msec) and slowly recovers (>20 min). Here we show that Ca2+, or certain other polyvalent cations, binds to an extracellular site on rat sensory neurons and can increase current through P2X3 channels more than 10-fold. Importantly, Ca2+facilitates P2X3 current to precisely the same level whether a transient Ca2+change occurred just before or several minutes before activating the channels with ATP. This memory for past changes in Ca2+is integrative in that a 90 sec Ca2+stimulus delivered just before an ATP application has the same effect as an earlier series of three, separated 30 sec Ca2+stimuli. These diverse phenomena are explained by a single mechanism: Ca2+speeds recovery of P2X channels from desensitization. Recovery follows an exponential growth curve that depends on the duration, but not the timing, of changes in recovery rate. Modulation of desensitization underlies a well described short-term memory in bacteria, and it might be similarly used in the nervous system.
Neurotrimin Mediates Bifunctional Effects on Neurite Outgrowth via Homophilic and Heterophilic Interactions
Authors: Gil Orlando D. , Zanazzi George , Struyk Arie F. , Salzer James L.
Published: April 2018

Neurotrimin (Ntm) together with the limbic system-associated membrane protein (LAMP) and the opioid-binding cell adhesion molecule (OBCAM) comprise the IgLON family of neural cell adhesion molecules. These glycosylphosphatidylinositol (GPI)-anchored proteins are expressed in distinct neuronal systems. In the case of Ntm, its expression pattern suggests a role in the development of thalamocortical and pontocerebellar projections (Struyk et al., 1995). We have now characterized Ntm’s function in cell adhesion and in neurite outgrowth. Cross-linking studies of transfected cells show that Ntm forms noncovalent homodimers and multimers at the cell surface. Ntm mediates homophilic adhesion, as evidenced by the reaggregation of the transfected cells and the specific binding of an Ntm-Fc chimera to these cells. Consistent with these results, Ntm-Fc binds to neurons that express Ntm at high levels, e.g., dorsal root ganglion (DRG) and hippocampal neurons. It does not bind to DRG neurons treated with phosphatidylinositol-specific phospholipase C (PI-PLC) or to sympathetic neurons that do not express Ntm or other members of the IgLON family at significant levels. Ntm promotes the outgrowth of DRG neurons, even after PI-PLC treatment, suggesting that its effects on outgrowth are mediated by heterophilic interactions. Of particular note, both membrane-bound and soluble Ntm inhibit the outgrowth of sympathetic neurons. These results strongly suggest that Ntm, and other members of the IgLON family, regulate the development of neuronal projections via attractive and repulsive mechanisms that are cell type specific and are mediated by homophilic and heterophilic interactions.
The Functional Influence of Burst and Tonic Firing Mode on Synaptic Interactions in the Thalamus
Authors: Kim Uhnoh , McCormick David A.
Published: April 2018

Thalamocortical and perigeniculate (PGN) neurons can generate action potentials either as Ca2+spike–mediated high-frequency bursts or as tonic trains. Using dual intracellular recordingsin vitroin monosynaptically connected pairs of PGN and dorsal lateral geniculate nucleus (LGNd) neurons, we found that the functional effect of synaptic transmission between these cell types was strongly influenced by the membrane potential and hence the firing mode of both the pre- and postsynaptic neurons. Activation of single action potentials or low-frequency spike trains in PGN or thalamocortical neurons resulted in the generation of PSPs that were 0.5–2.0 mV in amplitude. In contrast, the generation of Ca2+spike-mediated bursts of action potentials in the presynaptic cell increased these PSPs to an average of 4.4 mV for the IPSP and 3.0 mV for the EPSP barrage, because of temporal summation and/or facilitation. If the postsynaptic neuron was at a resting membrane potential (e.g., −65 mV), these PSP barrages could result in the activation of a low-threshold Ca2+spike and burst of action potentials. These results demonstrate that the burst firing mode of action potential generation is a particularly effective means by which perigeniculate and thalamocortical neurons may influence one another. We propose that the activation of burst discharges in these cell types is essential for the generation of some forms of synchronized rhythmic oscillations of sleep and of epileptic seizures.
Synaptic Integration in Striate Cortical Simple Cells
Authors: Hirsch Judith A. , Alonso José-Manuel , Reid R. Clay , Martinez Luis M.
Published: April 2018

Simple cells in the visual cortex respond to the precise position of oriented contours (Hubel and Wiesel, 1962). This sensitivity reflects the structure of the simple receptive field, which exhibits two sorts of antagonism betweenonandoffinputs. First, simple receptive fields are divided into adjacentonandoffsubregions; second, within each subregion, stimuli of the reverse contrast evoke responses of the opposite sign: push–pull (Hubel and Wiesel, 1962;Palmer and Davis, 1981; Jones and Palmer, 1987; Ferster, 1988). We have made whole-cell patch recordings from cat area 17 during visual stimulation to examine the generation and integration of excitation (push) and suppression (pull) in the simple receptive field. The temporal structure of the push reflected the pattern of thalamic inputs, as judged by comparing the intracellular cortical responses to extracellular recordings made in the lateral geniculate nucleus. Two mechanisms have been advanced to account for the pull–withdrawal of thalamic drive and active, intracortical inhibition (Hubel and Wiesel, 1962; Heggelund, 1986; Ferster, 1988). Our results suggest that intracortical inhibition is the dominant, and perhaps sole, mechanism of suppression. The inhibitory influences operated within a wide dynamic range. When inhibition was strong, the membrane conductance could be doubled or tripled. Furthermore, if a stimulus confined to one subregion was enlarged so that it extended into the next, the sign of response often changed from depolarizing to hyperpolarizing. In other instances, the inhibition modulated neuronal output subtly, by elevating spike threshold or altering firing rate at a given membrane voltage.
Relationships between the Prefrontal Cortex and the Basal Ganglia in the Rat: Physiology of the Corticosubthalamic Circuits
Authors: Maurice Nicolas , Deniau Jean-Michel , Glowinski Jacques , Thierry Anne-Marie
Published: April 2018

The prelimbic–medial orbital areas (PL/MO) of the prefrontal cortex are connected to the medial part of the subthalamic nucleus (STN) through a direct projection and an indirect circuit that involves the core of the nucleus accumbens (NAcc) and the ventral pallidum (VP). In the present study, the influence of the PL/MO on the discharge of STN cells has been characterized. The major pattern of the responses observed after stimulation of PL/MO consisted of two excitatory peaks often separated by a brief inhibitory period. The early excitation was most likely to be caused by the activation of direct cortical inputs because its latency matches the conduction time of the prefrontal STN projections. The late excitation resulted from the activation of the indirect PL/MO–STN pathway that operates through a disinhibitory process. Indeed, the late excitation was no longer observed after acute blockade of the glutamatergic corticostriatal transmission by CNQX application into the NAcc. A similar effect was obtained after the blockade of the GABAergic striatopallidal transmission by bicuculline application into the VP. Finally, the brief inhibition that followed the early excitation was likely to result from the activation of a feedback inhibitory loop through VP because this inhibition was no longer observed after the blockade of STN inputs by CNQX application into the VP. This study further indicates the implication of STN in prefrontal basal ganglia circuits and underlines that in addition to a direct excitatory input, medial STN receives an indirect excitatory influence from PL/MO through an NAcc–VP–STN disinhibitory circuit.
Single-Cell RT-PCR and Functional Characterization of Ca2+Channels in Motoneurons of the Rat Facial Nucleus
Authors: Plant T. D. , Schirra C. , Katz E. , Uchitel O. D. , Konnerth A.
Published: April 2018

Voltage-dependent Ca2+channels are a major pathway for Ca2+entry in neurons. We have studied the electrophysiological, pharmacological, and molecular properties of voltage-gated Ca2+channels in motoneurons of the rat facial nucleus in slices of the brainstem. Most facial motoneurons express both low voltage-activated (LVA) and high voltage-activated (HVA) Ca2+channel currents. The HVA current is composed of a number of pharmacologically separable components, including 30% of N-type and ∼5% of L-type. Despite the dominating role of P-type Ca2+channels in transmitter release at facial motoneuron terminals described in previous studies, these channels were not present in the cell body. Remarkably, most of the HVA current was carried through a new type of Ca2+channel that is resistant to toxin and dihydropyridine block but distinct from the R-type currents described in other neurons.

Using reverse transcription followed by PCR amplification (RT-PCR) with a powerful set of primers designed to amplify all HVA subtypes of the α1-subunit, we identified a highly heterogeneous expression pattern of Ca2+channel α1-subunit mRNA in individual neurons consistent with the Ca2+current components found in the cell bodies and axon terminals. We detected mRNA for α1Ain 86% of neurons, α1Bin 59%, α1Cin 18%, α1Din 18%, and α1Ein 59%. Either α1Aor α1BmRNAs (or both) were present in all neurons, together with various other α1-subunit mRNAs. The most frequently occurring combination was α1Awith α1Band α1E. Taken together, these results demonstrate that the Ca2+channel pattern found in facial motoneurons is highly distinct from that found in other brainstem motoneurons.
Alzheimer Amyloid Protein Precursor in the Rat Hippocampus: Transport and Processing through the Perforant Path
Authors: Buxbaum Joseph D. , Thinakaran Gopal , Koliatsos Vassilis , O’Callahan James , Slunt Hilda H. , Price Donald L. , Sisodia Sangram S.
Published: April 2018

Amyloid deposition is a neuropathological hallmark of Alzheimer’s disease. The principal component of amyloid deposits is β amyloid peptide (Aβ), a peptide derived by proteolytic processing of the amyloid precursor protein (APP). APP is axonally transported by the fast anterograde component. Several studies have indicated that Aβ deposits occur in proximity to neuritic and synaptic profiles. Taken together, these latter observations have suggested that APP, axonally transported to nerve terminals, may be processed to Aβ at those sites. To examine the fate of APP in the CNS, we injected [35S]methionine into the rat entorhinal cortex and examined the trafficking and processing ofde novosynthesized APP in the perforant pathway and at presynaptic sites in the hippocampal formation. We report that both full-length and processed APP accumulate at presynaptic terminals of entorhinal neurons. Finally, we demonstrate that at these synaptic sites, C-terminal fragments of APP containing the entire Aβ domain accumulate, suggesting that these species may represent the penultimate precursors of synaptic Aβ.
Ca2+/Calcineurin-Inhibited Adenylyl Cyclase, Highly Abundant in Forebrain Regions, Is Important for Learning and Memory
Authors: Antoni F. A. , Palkovits M. , Simpson J. , Smith S. M. , Leitch A. L. , Rosie R. , Fink G. , Paterson J. M.
Published: April 2018

Activation of cAMP synthesis by intracellular Ca2+is thought to be the main mode of cAMP generation in the brain. Accordingly, the Ca2+-activated adenylyl cyclases I and VIII are expressed prominently in forebrain neurons. The present study shows that the novel adenylyl cyclase type IX is inhibited by Ca2+and that this effect is blocked selectively by inhibitors of calcineurin such as FK506 and cyclosporin A. Moreover, adenylyl cyclase IX is inhibited by the same range of intracellular free Ca2+concentrations that stimulate adenylyl cyclase I. Adenylyl cyclase IX is expressed prominently in the forebrain. Substantial arrays of neurons positive for AC9 mRNA were found in the olfactory lobe, in limbic and neocortical areas, in the striatum, and in the cerebellar system. These data show that the initiation of the cAMP signal by adenylyl cyclase may be controlled by Ca2+/calcineurin and thus provide evidence for a novel mode of tuning the cAMP signal by protein phosphorylation/dephosphorylation cascades.
Glial Cell Line-Derived Neurotrophic Factor Requires Transforming Growth Factor-β for Exerting Its Full Neurotrophic Potential on Peripheral and CNS Neurons
Authors: Krieglstein Kerstin , Henheik Prisca , Farkas Lilla , Jaszai Jozsef , Galter Dagmar , Krohn Knut , Unsicker Klaus
Published: April 2018

Numerous studies have suggested that glial cell line-derived neurotrophic factor (GDNF) is a potent neurotrophic molecule. We show now on a variety of cultured neurons including peripheral autonomic, sensory, and CNS dopaminergic neurons that GDNF is not trophically active unless supplemented with TGF-β. Immunoneutralization of endogenous TGF-β provided by serum or TGF-β-secreting cells, as e.g., neurons, in culture abolishes the neurotrophic effect of GDNF. The dose–response relationship required for the synergistic effect of GDNF and TGF-β identifies 60 pg/ml of either factor combined with 2 ng/ml of the other factor as the EC50. GDNF/TGF-β signaling employs activation of phosphatidylinositol-3 (PI-3) kinase as an intermediate step as shown by the effect of the specific PI-3 kinase inhibitor wortmannin. The synergistic action of GDNF and TGF-β involves protection of glycosylphosphatidylinositol (GPI)-linked receptors as shown by the restoration of their trophic effects after phosphatidylinositol-specific phospholipase C-mediated hydrolysis of GPI-anchored GDNF family receptor α. The biological significance of the trophic synergism of GDNF and TGF-β is underscored by colocalization of the receptors for TGF-β and GDNF on all investigated GDNF-responsive neuron populationsin vivo. Moreover, thein vivorelevance of the TGF-β/GDNF synergism is highlighted by the co-storage of TGF-β and GDNF in secretory vesicles of a model neuron, the chromaffin cell, and their activity-dependent release. Our results broaden the definition of a neurotrophic factor by incorporating the possibility that two factors that lack a neurotrophic activity when acting separately become neurotrophic when acting in concert. Moreover, our data may have a substantial impact on the treatment of neurodegenerative diseases.
Correlation-Based Development of Ocularly Matched Orientation and Ocular Dominance Maps: Determination of Required Input Activities
Authors: Erwin Ed , Miller Kenneth D.
Published: April 2018

We extend previous models for separate development of ocular dominance and orientation selectivity in cortical layer 4 by exploring conditions permitting combined organization of both properties. These conditions are expressed in terms of functions describing the degree of correlation in the firing of two inputs from the lateral geniculate nucleus (LGN), as a function of their retinotopic separation and their “type” (ON center or OFF center and left eye or right eye).

The development of ocular dominance requires that the correlations of an input with other inputs of the same eye be stronger than or equal to its correlations with inputs of the opposite eye and strictly stronger at small retinotopic separations. This must be true after summing correlations with inputs of both center types. The development of orientation-selective simple cells requires that (1) an input’s correlations with other inputs of the same center type be stronger than its correlations with inputs of the opposite center type at small retinotopic separation; and (2) this relationship reverse at larger retinotopic separations within an arbor radius (the radius over which LGN cells can project to a common cortical point). This must be true after summing correlations with inputs serving both eyes.

For orientations to become matched in the two eyes, correlated activity within the receptive fields must be maximized by specific between-eye alignments of ON and OFF subregions. Thus the correlations between the eyes must differ depending on center type, and this difference must vary with retinotopic separation within an arbor radius.

These principles are satisfied by a wide class of correlation functions. Combined development of ocularly matched orientation maps and ocular dominance maps can be achieved either simultaneously or sequentially. In the latter case, the model can produce a correlation between the locations of orientation map singularities and local ocular dominance peaks similar to that observed physiologically.

The model’s main prediction is that the above correlations should exist among inputs to cortical layer 4 simple cells before vision. In addition, mature simple cells are predicted to have certain relationships between the locations of the ON and OFF subregions of the left and right eyes’ receptive fields.
Neurogenesis and Commitment of Corticospinal Neurons inreeler
Authors: Polleux Franck , Dehay Colette , Kennedy Henry
Published: April 2018

In the homozygous (but not the heterozygous)reelermutant, disruption of neuron migration leads to a major perturbation of the cortical environment that in turn could modify (1) the specification of neuronal fate and (2) the proliferation dynamics of cortical precursors. To investigate these issues, tritiated thymidine injections during cortical neurogenesis were coupled with postnatal injections of a retrograde tracer in the spinal cord to accurately measure the neurogenesis of corticospinal neurons in the heterozygous and homozygous mutant. The homozygousreelershows (1) strict conservation of area-specific timetables of corticospinal neuron generation; (2) neurons with the appropriate birthdates show an enhanced probability of projecting to the spinal cord; (3) during early stages of corticogenesis, there is a reduced rate of neuron production followed at later stages by an increased rate of neuron production; and (4) these changes in the rate of neuron production were shown to be at least partially attributable to changes in the proportions of differentiative divisions. Taken together, our results show that in the developing cortex, the neurogenesis and specification of a given neuronal phenotype are partially controlled by the postmigratory compartment. On the other hand, neither areal identity nor the chronology of production of layer-specific neuronal phenotype seems to depend on the integrity of the cellular environment.
Brainstem Application of Melanocortin Receptor Ligands Produces Long-Lasting Effects on Feeding and Body Weight
Authors: Grill Harvey J. , Ginsberg Abigail B. , Seeley Randy J. , Kaplan Joel M.
Published: April 2018

Recent evidence suggests that the central melanocortin (MC) system is a prominent contributor to food intake and body weight control. MC receptor (MC-R) populations in the arcuate and paraventricular nuclei are considered probable sites of action mediating the orexigenic effects of systemically or intracerebroventricularly administered ligands. Yet, the highest MC4-R density in the brain is found in the dorsal motor nucleus of the vagus nerve, situated subjacent to the commissural nucleus of the solitary tract, a site of pro-opiomelanocortin mRNA expression. We evaluated the contribution of the caudal brainstem MC system by (1) performing respective dose–response analyses for an MC-R agonist (MTII) and antagonist (SHU9119) delivered to the fourth ventricle, (2) comparing, in the same rats, the fourth intracerebroventricular dose–response profiles to those obtained with lateral intracerebroventricular delivery, and (3) delivering an effective dose of MTII or SHU9119 to rats before a 24 hr period of food deprivation. Fourth intracerebroventricular agonist treatment yielded a dose-dependent reduction of short-term (2 and 4 hr) and longer-term (24 hr) food intake and body weight. Fourth intracerebroventricular antagonist treatment produced the opposite pattern of results: dose-related increases in food intake and corresponding increases in body weight change for the 24–96 hr observation period. Comparable dose–response functions for food intake and body weight were observed when these compounds were delivered to the lateral ventricle. Results from deprived rats (no effect of MTII or SHU9119 on weight loss) support the impression derived from the dose–response analyses that the body weight change that follows MC treatments is secondary to their respective effects on food intake. Results support the relevance of the brainstem MC-R complement to the control of feeding.
Synaptic Physiology and Ultrastructure incomatoseMutants Define anIn VivoRole for NSF in Neurotransmitter Release
Authors: Kawasaki Fumiko , Mattiuz Annette M. , Ordway Richard W.
Published: April 2018

N-Ethylmaleimide–sensitive fusion protein (NSF) is a cytosolic protein thought to play a key role in vesicular transport in all eukaryotic cells. Although NSF was proposed to function in the trafficking of synaptic vesicles responsible for neurotransmitter release, only recently havein vivoexperiments begun to reveal a specific function for NSF in this process. Our previous work showed that mutations in aDrosophilaNSF gene, dNSF1, are responsible for the temperature-sensitive paralytic phenotype incomatose(comt) mutants. In this study, we perform electrophysiological and ultrastructural analyses in three differentcomtalleles to investigate the function of dNSF1 at native synapsesin vivo. Electrophysiological analysis of postsynaptic potentials and currents at adult neuromuscular synapses revealed that in the absence of repetitive stimulation,comtsynapses exhibit wild-type neurotransmitter release at restrictive (paralytic) temperatures. In contrast, repetitive stimulation at restrictive temperatures revealed a progressive, activity-dependent reduction in neurotransmitter release incomtbut not in wild type. These results indicate that dNSF1 does not participate directly in the fusion of vesicles with the target membrane but rather functions in maintaining the pool of readily releasable vesicles competent for fast calcium-triggered fusion. To define dNSF1 function further, we used transmission electron microscopy to examine the distribution of vesicles within synaptic terminals, and observed a marked accumulation of docked vesicles at restrictive temperatures incomt. Together, the results reported here define a role for dNSF1 in the priming of docked synaptic vesicles for calcium-triggered fusion.
NSF Function in Neurotransmitter Release Involves Rearrangement of the SNARE Complex Downstream of Synaptic Vesicle Docking
Authors: Tolar Leigh Anna , Pallanck Leo
Published: April 2018

The SNARE hypothesis has been proposed to explain both constitutive and regulated vesicular transport in eukaryotic cells, including release of neurotransmitter at synapses. According to this model, a vesicle targeting/docking complex consisting primarily of vesicle- and target-membrane proteins, known as SNAREs, serves as a receptor for the cytosolicN-ethylmaleimide-sensitive fusion protein (NSF). NSF-dependent hydrolysis of ATP disassembles the SNARE complex in a step postulated to initiate membrane fusion. While features of this model remain tenable, recent studies have challenged fundamental aspects of the SNARE hypothesis, indicating that further analysis of these components is needed to fully understand their roles in neurotransmitter release. We have addressed this issue by using the temperature-sensitiveDrosophilaNSF mutantcomatose(comt) to study the function of NSF in neurotransmitter releasein vivo. Synaptic electrophysiology and ultrastructure incomtmutants have recently defined a role for NSF after docking in the priming of synaptic vesicles for fast calcium-triggered fusion. Here we report that an SDS-resistant neural SNARE complex, composed of the SNARE polypeptides syntaxin, n-synaptobrevin, and SNAP-25, accumulates incomtmutants at restrictive temperature. Subcellular fractionation experiments indicate that these SNARE complexes are distributed predominantly in fractions containing plasma membrane and docked synaptic vesicles. Together with the electrophysiological and ultrastructural analyses ofcomtmutants, these results indicate that NSF functions to disassemble or otherwise rearrange a SNARE complex after vesicle docking and that this rearrangement is required to maintain the readily releasable pool of synaptic vesicles.
Enhanced Opioid Efficacy in Opioid Dependence Is Caused by an Altered Signal Transduction Pathway
Authors: Ingram Susan L. , Vaughan Christopher W. , Bagley Elena E. , Connor Mark , Christie MacDonald J.
Published: April 2018

Chronic morphine administration induces adaptations in neurons resulting in opioid tolerance and dependence. Functional studies have implicated a role for the periaqueductal gray area (PAG) in the expression of many signs of opioid withdrawal, but the cellular mechanisms are not fully understood. This study describes an increased efficacy, rather than tolerance, of opioid agonists at μ-receptors on GABAergic (but not glutamatergic) nerve terminals in PAG after chronic morphine treatment. Opioid withdrawal enhanced the amplitudes of electrically evoked inhibitory synaptic currents mediated by GABAAreceptors and increased the frequency of spontaneous miniature GABAergic synaptic currents. These effects were not blocked by 4-aminopyridine or dendrotoxin, although both Kv channel blockers abolish acute opioid presynaptic inhibition of GABA release in PAG. Instead, the withdrawal-induced increases were blocked by protein kinase A inhibitors and occluded by metabolically stable cAMP analogs, which do not prevent acute opioid actions. These findings indicate that opioid dependence induces efficacious coupling of μ-receptors to presynaptic inhibition in GABAergic nerve terminals via adenylyl cyclase- and protein kinase A-dependent processes in PAG. The potential role of these adaptations in expression of withdrawal behavior was supported by inhibition of enhanced GABAergic synaptic transmission by the α2adrenoceptor agonist clonidine. These findings provide a cellular mechanism that is consistent with other studies demonstrating attenuated opioid withdrawal behavior after injections of protein kinase A inhibitors into PAG and suggest a general mechanism whereby opioid withdrawal may enhance synaptic neurotransmission.