bluuebunny/crossref_metadata_2025 huggingface dataset:
An evaluation of the nitric oxide/cGMP/cGMP-dependent protein kinase cascade in the induction of cerebellar long-term depression in culture
Authors: Linden DJ , Dawson TM , Dawson VL
Published: April 2018

Cerebellar long-term depression (LTD) is a model system of information storage in which a persistent attenuation of the parallel fiber- Purkinje neuron (PN) synapse is induced by conjunctive stimulation of parallel fiber and climbing fiber inputs at low frequency. As some studies have suggested that release of the gaseous second messenger, nitric oxide (NO), in the molecular layer and the consequent activation of soluble guanylate cyclase and cGMP-dependent protein kinase (PKG) in the PN, is necessary for LTD induction, we have further examined this hypothesis using a cell culture protocol. In cerebellar cultures made from transgenic mice in which the gene for neuronal nitric oxide synthase (nNOS) has been rendered null, LTD induced by glutamate/depolarization conjunctive stimulation was indistinguishable from that in cultures from wild-type mice in terms of amplitude, rate of onset, and duration. Bath application of cGMP analogs produced a large (80%), transient attenuation of glutamate-gated inward currents. However, application of an activator of soluble guanylate cyclase or an inhibitor of type V cGMP-phosphodiesterase did not mimic the effect of cGMP analogs, and inclusion of cGMP analogs in the patch pipette did not give rise to a slowly developing attenuation, suggesting that these compounds exert their effects at the cell surface. Free Ca was measured in the distal dendritic arbor of single PNs by fura-2 microfluorimetry.
Pattern recognition of amino acid signatures in retinal neurons
Authors: Marc RE , Murry RF , Basinger SF
Published: April 2018

Pattern recognition of amino acid signals partitions the cells of the goldfish retina into nine statistically unique biochemical theme classes and permits a first-order chemical mapping of virtually all cellular space. Photoreceptors, bipolar cells, and ganglion cells display a set of unique, nominally glutamatergic type E1, E1+E2, and E4 signatures, respectively. All horizontal cells are assignable to a GABAergic gamma 2 class or a non-GABAergic class with a glutamate-rich E3 signature. The amacrine cell layer is largely a mixture of (1) a taurine-dominated T1 Muller's cell signature and (2) GABAergic gamma 1, glycinergic G1, and dual glycinergic/GABAergic G gamma 1 amacrine cell signatures. Several major conclusions emerge from this work. (1) Glutamatergic, GABAergic, and glycinergic neural signatures and glial signatures account for over 99% of the cellular space in the retina. (2) All known neurons in the goldfish retina are associated with a set of conventional nonpeptide neurotransmitters. (3) Multiple forms of metabolic profiles are associated with a single nominal neurotransmitter category. (4) Glutamate and aspartate contents exhibit overlapping distributions and are not adequate univariate probes for identifying cell classes. (5) Signatures can serve as quantitative measures of cell state.
Characterization of a forebrain gaze field in the archistriatum of the barn owl: microstimulation and anatomical connections
Authors: Knudsen EI , Cohen YE , Masino T
Published: April 2018

We present evidence that the archistriatum in the forebrain of the barn owl participates in gaze control, that it can mediate gaze changes independently of the optic tectum (OT), and that it projects in parallel to both the OT and to saccade-generating circuitry in the brainstem tegmentum. These properties are similar to those of the frontal eye fields (FEF) in the prefrontal cortex of primates. The forebrain was surveyed for sites where electrical microstimulation would induce head saccades. Head (and eye) saccades were elicited from the anterior 70% of the archistriatum, a region that we refer to as the archistriatal gaze fields (AGF). At single stimulation sites in the AGF, saccade amplitude tended to vary as a function of stimulation parameters (current strength, pulse frequency, and train duration) and starting head position. In contrast, saccade direction was largely independent of these parameters. Saccade direction did vary over a wide range of primarily contraversive directions with the site of stimulation in the AGF. Using anatomical pathway tracing techniques, we found that the archistriatum projects strongly and in parallel to the deep layers of the OT and to nuclei in the midline brainstem tegmentum. Previous work has shown that electrical microstimulation of either of these brainstem regions evokes saccadic movements of the head and/or eyes (du Lac and Knudsen, 1990; Masino and Knudsen, 1992b). Inactivation of the OT with lidocaine reduced the size but did not eliminate (or change the direction of) the saccades evoked by AGF stimulation. The direct anatomical pathway from the archistriatum to the midline tegmental nuclei can account for saccades that persist following OT inactivation. The similarities between the AGF in barn owls and the FEF in primates suggest that the same general plan of anatomical and functional organization supports the contribution of the forebrain to gaze control in a wide variety of species.
Dopaminergic correlates of motivated behavior: importance of drive
Authors: Wilson C , Nomikos GG , Collu M , Fibiger HC
Published: April 2018

In vivo brain microdialysis was used to monitor changes in dopamine (DA) release in the nucleus accumbens (NAc) during anticipatory and consummatory components of feeding behavior. During 10 daily training sessions, rats were first confined to one compartment of a testing chamber for 10 minutes. During this period (anticipatory phase) they were prevented from gaining access to a highly palatable liquid meal by a wire mesh screen. The screen was then removed and the animals were permitted to consume the meal for 20 min (consummatory phase). On removal of the screen, the latency to begin drinking decreased and the amount consumed increased as a function of days of training, both measures reaching asymptotic levels by day 7. Trained animals were implanted with dialysis probes in the NAc on day 10, and on day 12 DA release was monitored during the feeding session. Compared to controls, trained animals failed to show significantly greater increases in accumbal DA release during the anticipatory phase, all groups showing small (approximately 10%) increases on being placed in the test chamber. In contrast, compared to controls, DA release increased significantly in the NAc during consumption of the palatable meal. The magnitude of this increase was significantly enhanced (30% vs 71% peak increase) in animals that were 20 hr food deprived at the time of testing. The latter animals also showed a statistically significant increase (24%) in DA release during the anticipatory phase. A subsequent experiment in which consumption of the palatable liquid was limited to 5 ml in deprived and nondeprived animals indicated that only part of the deprivation-induced potentiation of accumbal DA release could be attributed to the larger volume consumed by the deprived animals. That is, the same volume and rate of consumption of a small amount of the liquid diet produced a significantly greater increase in accumbal DA release in deprived than in nondeprived animals (42% vs 23% peak increase). Feeding-induced increases in accumbal DA release were not due to postingestional factors as direct injections of the liquid diet into the stomach by gavage failed to produce this effect. The results of these experiments indicate (1) that consummatory rather than anticipatory aspects of feeding are robustly associated with increases in DA release in the NAc, and (2) that motivational state can influence the magnitude of the neurochemical events that are associated with goal- directed behaviors.
Lactate released by Muller glial cells is metabolized by photoreceptors from mammalian retina
Authors: Poitry-Yamate CL , Poitry S , Tsacopoulos M
Published: April 2018

The nature of fuel molecules trafficking between mammalian glial cells and neurons was explored using acute retinal cell preparations of solitary Muller glial cells, Muller cells still attached to photoreceptors (the “cell complex”), and solitary photoreceptors. 14C- Molecules in the cell complex, Muller cells, and respective baths were quantitated following 30 min incubation in bicarbonate-buffered Ringer's solution carrying 5 mM 14C(U)-glucose, and substrate preference by solitary photoreceptors was assessed by measuring 14CO2 production. Muller cells alone metabolized 14C-glucose predominantly to carbohydrate intermediates, while the presence of photoreceptors raised proportionately the amount of radiolabeling in amino acids. 14C-Lactate was the major carbohydrate found in the bath. However, in the presence of photoreceptors, its amount was 70% less than that for Muller cells alone. This decrease matched the expected production of 14CO2 by photoreceptor oxidative metabolism and was antagonized by the addition of unlabeled lactate. Moreover, while solitary photoreceptors consumed both exogenous 14C-lactate and 14C-glucose, lactate was a better substrate for their oxidative metabolism. In the cell complex, the metabolism of amino acids increased and illumination affected primarily glutamate and glutamine production: the specific activity of glutamate changed in parallel with that of lactate, and that of glutamine increased by eightfold in darkness. These results demonstrate transfer of lactate from Muller cells to photoreceptors and underscore a photoreceptor-dependent modulation of lactate and amino acid metabolism. We propose that net production and release of lactate by Muller cells serves to maintain their glycolysis elevated and to fuel mitochondrial oxidative metabolism and glutamate resynthesis in photoreceptors.
Response of monkey MST neurons to optic flow stimuli with shifted centers of motion
Authors: Duffy CJ , Wurtz RH
Published: April 2018

Neurons in the dorsal region of the medial superior temporal area (MSTd) have previously been shown to respond to the expanding radial motion that occurs as an observer moves through the environment. In previous experiments, MSTd neurons were tested with radial and circular motion centered in the visual field. However, different directions of observer motion, relative to the direction of gaze, are accompanied by visual motion centered at different locations in the visual field. The present experiments investigated whether neurons that respond to radial and circular motion might respond differently when the center of motion was shifted to different regions of the visual field. About 90% of the 245 neurons studied responded differently when the center of motion was shifted away from the center of the field. The centers of motion preferred by each neuron were limited to one area of the visual field. All parts of the visual field were represented in the sample, with greater numbers of neurons preferring centers of motion closer to the center of the field. We hypothesize that each of the MSTd neurons has a center of motion field with a gradient of preferred centers of motion, and that there is an orderly arrangement of MSTd neurons with each region of the visual field being represented by a set of neurons. This arrangement creates the potential for graded responses from individual neurons for different directions of heading as an observer moves through the environment.
Electron microscopic analysis of D1 and D2 dopamine receptor proteins in the dorsal striatum and their synaptic relationships with motor corticostriatal afferents
Authors: Hersch SM , Ciliax BJ , Gutekunst CA , Rees HD , Heilman CJ , Yung KK , Bolam JP , Ince E , Yi H , Levey AI
Published: April 2018

The precise localization of D1 and D2 dopamine receptors within striatal neurons and circuits is crucial information for further understanding dopamine pharmacology. We have used subtype specific polyclonal and monoclonal antibodies against D1 and D2 dopamine receptors to determine their cellular and subcellular distributions, their colocalization, and their differential connectivity with motor cortical afferents labeled either by lesion-induced degeneration or by anterograde transport of biotinylated dextrans. D1 and D2 are primarily expressed in medium-sized neurons and spiny dendrites. Axon terminals containing D1 were rare whereas D2-immunoreactive axon terminals forming symmetrical synapses with dendrites and spines were common. In 2 microns sections, D1 was localized to 53% of neurons, and D2 to 48% of neurons, while mixing D1 and D2 antibodies labeled 78%. By electron microscopy, D1 was localized to 43% of dendrites and 38% of spines while D2 was localized to 38% of dendrites and 48% of spines. Combining D1 and D2 antibodies resulted in the labeling of 88.5% of dendrites and 92.6% of spines. Using different chromogens for D1 and D2, colocalization was not observed. Ipsilateral motor corticostriatal afferents were primarily axospinous and significantly more synapsed with D1 than D2-positive spines (65% vs 47%). Contralateral motor corticostriatal afferents were frequently axodendritic and no difference in their frequency of synapses with D1 and D2 dendrites and spines was observed. These findings demonstrate differential patterns of expression of D1 and D2 receptors in striatal neurons and axon terminals and their differential involvement in motor corticostriatal circuits.
A novel RING-H2 motif protein downregulated by axotomy: its characteristic localization at the postsynaptic density of axosomatic synapse
Authors: Nakayama M , Miyake T , Gahara Y , Ohara O , Kitamura T
Published: April 2018

Axonal injury and its repair are common and basic neuropathological processes in the CNS, and are composed of a complex of events in a molecular term. In order to get a comprehensive understanding of these processes, we isolated several known and unknown genes which were up-or downregulated in the facial nucleus after transection of the facial nerve by a subtractive/differential screening. Among them, we focus on one downregulated gene, named Neurodap1, because this gene encodes a novel protein carrying the RING-H2 sequence motif categorized in the zinc finger family. Immunoelectron microscopic analysis revealed that the protein encoded by Neurodap1, Neurodap1, was distributed mainly on the cytoplasmic side of the membranes constituting endoplasmic reticulum and Golgi apparatus, supporting the notion of a previously postulated function of RING-H2 motif proteins, that is, involvement in the protein sorting machinery. More interestingly, Neurodap1 was also bound to the postsynaptic density (PSD) region of axosomatic synapses. This fact suggests that Neurodap1 is associated with a specific system sorting proteins to PSD. Therefore, Neurodap1, a newly identified protein as an axotomy-suppressed gene product, might play a significant role in synaptic communication and plasticity through the control of the formation of PSD for maintaining vital functions of nerve cells.
Dynamics of learning and recall at excitatory recurrent synapses and cholinergic modulation in rat hippocampal region CA3
Authors: Hasselmo ME , Schnell E , Barkai E
Published: April 2018

Hippocampal region CA3 contains strong recurrent excitation mediated by synapses of the longitudinal association fibers. These recurrent excitatory connections may play a dominant role in determining the information processing characteristics of this region. However, they result in feedback dynamics that may cause both runaway excitatory activity and runaway synaptic modification. Previous models of recurrent excitation have prevented unbounded activity using biologically unrealistic techniques. Here, the activation of feedback inhibition is shown to prevent unbounded activity, allowing stable activity states during recall and learning. In the model, cholinergic suppression of synaptic transmission at excitatory feedback synapses is shown to determine the extent to which activity depends upon new features of the afferent input versus components of previously stored representations. Experimental work in brain slice preparations of region CA3 demonstrates the cholinergic suppression of synaptic transmission in stratum radiatum, which contains synapses of the longitudinal association fibers.
Peripheral benzodiazepine receptors are colocalized with activated microglia following transient global forebrain ischemia in the rat
Authors: Stephenson DT , Schober DA , Smalstig EB , Mincy RE , Gehlert DR , Clemens JA
Published: April 2018

In mammalian brain the expression of peripheral benzodiazepine receptors (PBRs) can be markedly induced following different types of neuronal injury. PBRs are believed to be expressed on non-neuronal cells in the brain, yet the specific cell type that expresses these receptors following CNS insult has not been defined. In the present study, we investigated the effects of transient global forebrain ischemia on PBRs by autoradiographic localization of 3H-PK11195 binding. The distribution of PBRs was compared to glial fibrillary acidic protein (GFAP) as a marker for astrocytes and OX42 as a marker for microglia. Five to 6 d following four-vessel occlusion (4-VO), an increase in PBRs was seen in the CA1 region of all 15 brains examined. In brains from rats subjected to 4-VO, microglia were selectively activated in stratum pyramidale of the CA1 layer. In contrast, astrocytes appeared to be activated in multiple hippocampal cell layers including stratum radiatum and stratum oriens. Activated astrocytes were also found in regions that did not exhibit increased 3H-PK11195 binding. In some brains, selected regions of secondary lesion, specifically necrotic thalamic nuclei and the isocortex were found to be strongly immunoreactive for OX42 but lacked GFAP immunoreactive cells. In adjacent sections, these same regions displayed high densities of 3H-PK1195 binding. These observations lend further support to the application of 3H-PK11195 binding as a marker of neuronal injury in the brain. Furthermore, the data strongly suggest that activated microglia rather than astrocytes express PBRs following ischemic insults.
Trans-synaptic regulation of NMDA receptor RNAs during optic nerve regeneration
Authors: Hieber VC , Goldman D
Published: April 2018

A goldfish NMDA receptor (NMDAR) cDNA was used to analyze NMDAR RNA expression during optic nerve regeneration. Following crush of the optic nerve, NMDAR RNA levels initially decrease and then increase in retinal ganglion cells. This latter increase corresponds with the time when ganglion cell axons are forming stable connections with their targets in the optic tectum. NMDAR RNA stability assays indicate that the increase in this RNA is largely a result of increased NMDAR gene expression. This increase requires return of electrical activity in the regenerating axons, interaction between ganglion cell axons and their targets in the optic tectum, and functional NMDARs in the postsynaptic tectal cells. These requirements for induction of presynaptic NMDAR RNA are similar to those proposed for synapse stabilization during development and regeneration of the visual system and during long-term potentiation (LTP) in the hippocampus.
NMDA receptor subunit mRNA expression by projection neurons and interneurons in rat striatum
Authors: Landwehrmeyer GB , Standaert DG , Testa CM , Penney JB , Young AB
Published: April 2018

N-Methyl-D-aspartate (NMDA) receptors are enriched in the neostriatum and are thought to mediate several actions of glutamate including neuronal excitability, long-term synaptic plasticity, and excitotoxic injury. NMDA receptors are assembled from several subunits (NMDAR1, NMDAR2A-D) encoded by five genes; alternative splicing gives rise to eight isoforms of subunit NMDAR1. We studied the expression of NMDA receptor subunits in neurochemically identified striatal neurons of adult rats by in situ hybridization histochemistry using a double- labeling technique. Enkephalin-positive projection neurons, somatostatin-positive interneurons, and cholinergic interneurons each have distinct NMDA receptor subunit phenotypes. Both populations of striatal interneurons examined express lower levels of NMDAR1 and NMDAR2B subunit mRNA than enkephalin-positive neurons. The three striatal cell populations differ also in the presence of markers for alternatively spliced regions of NMDAR1, suggesting that interneurons preferentially express NMDAR1 splice forms lacking one (cholinergic neurons) or both (somatostatin-positive neurons) alternatively spliced carboxy-terminal regions. In addition, somatostatin- and cholinergic-, but not enkephalin-positive neurons express NMDAR2D mRNA. Thus, these striatal cell populations express different NMDAR-subunit mRNA phenotypes and therefore are likely to display NMDA channels with distinct pharmacological and physiological properties. Differences in NMDA receptor expression may contribute to the relative resistance of striatal interneurons to the neurotoxic effect of NMDA receptor agonists.
Neurotransmitter receptors of starburst amacrine cells in rabbit retinal slices
Authors: Zhou ZJ , Fain GL
Published: April 2018

The receptor pharmacology of cholinergic (“starburst”) amacrine cells was studied in a newly developed rabbit retinal slice preparation with whole-cell patch clamp. Displaced starburst cells were labeled with the fluorescent dye 4,6-diamidino-2-phenylindole (DAPI), and their dendritic morphology was identified in the slice with Lucifer yellow. Under conditions in which synaptic transmission was blocked by Cd2+, starburst cells responded vigorously to the bath-applied neurotransmitters GABA, glycine, and glutamate. The response to GABA consisted of an inward current and an increase in noise, which could be mimicked by the GABAA agonists muscimol and trans-4-aminocrotonic acid (TACA), but not by the GABAB agonist baclofen or the GABAC agonist cis- 4-aminocrotonic acid (CACA). The GABA-evoked currents were reversibly inhibited by bicuculline and picrotoxin and had a reversal potential close to the chloride equilibrium potential. Noise analysis of GABA- activated whole-cell currents yielded elementary conductance estimates of 12.5 pS. Glycine (30–200 microM) also activated a Cl- conductance in starburst cells, which could be completely blocked by strychnine. The non-NMDA agonists kainate (KA, 30–100 microM) and alpha-amino-3-hydroxy- 5-methylisoxazole-4-propionic acid (AMPA, 60 microM) evoked robust responses, which were reversibly blocked by 6-cyano-7-nitroquinoxaline- 2,3-dione (CNQX), and which reversed near the equilibrium potential for cations. NMDA coapplied with glycine in salines free of Cd2+ and Mg2+ elicited small but detectable responses. The I/V relation of the NMDA- evoked response showed a characteristic “J”-shaped region in a saline containing 1 mM Mg2+ and 0 Cd2+, indicating that NMDA receptors were present directly on starburst cells. This was consistent with our finding that whole-cell currents evoked by KA and NMDA had different noise characteristics. These results place new constraints on models of starburst cell function and suggest that GABA-mediated inhibition of the starburst cell itself may play an important role in directional selectivity in the retina.
Prostaglandins facilitate peptide release from rat sensory neurons by activating the adenosine 3',5'-cyclic monophosphate transduction cascade
Authors: Hingtgen CM , Waite KJ , Vasko MR
Published: April 2018

Prostaglandins sensitize sensory neurons to activation by mechanical, thermal and chemical stimuli. This sensitization also results in an increase in the stimulus-evoked release of the neuroactive peptides, substance P and calcitonin gene-related peptide from sensory neurons. The cellular transduction cascade underlying the prostaglandin-induced augmentation of peptide release is not known. Therefore, we examined whether the sensitizing action of prostaglandins on peptide release from sensory neurons grown in culture is mediated by the second messenger, adenosine 3′, 5′ cyclic monophosphate (cAMP). Prostaglandin E2 and carba prostacyclin (a stable analog of prostaglandin I2) significantly increase the content of cAMP-like immunoreactive substance (icAMP) in the sensory neuron cultures at concentrations that also augment the bradykinin- or capsaicin-evoked release of peptides. Furthermore, pretreating sensory neurons with agents that increase intracellular cAMP mimics the sensitizing action of prostaglandins. Exposing cultures to either forskolin (0.1–10 microM), cholera toxin (1.5 micrograms), or 8-bromo-cAMP (100 microM) results in a significant enhancement of the bradykinin- or capsaicin-stimulated release of both substance P-like and calcitonin gene-related peptide-like immunoreactive substances. Pretreating sensory neurons with the adenylyl cyclase inhibitor, 9-tetrahydro-2-furyl adenine (5 mM), abolishes the prostaglandin-induced increases in icAMP content and attenuates the prostaglandin E2 or carba prostacyclin enhancement of the evoked release of calcitonin gene-related peptide-like immunoreactive substance. These results demonstrate that the cAMP transduction cascade mediates the sensitizing actions of prostaglandins on peptide release from sensory neurons.
Rod photoreceptor neurite sprouting in retinitis pigmentosa
Authors: Li ZY , Kljavin IJ , Milam AH
Published: April 2018

In animal models for retinitis pigmentosa (RP), rod photoreceptors show abnormal distribution of rhodopsin prior to undergoing cell death. To elucidate the steps in degeneration of human photoreceptors, immunocytochemistry was performed on donor retinas from 15 RP patients and five normal subjects. Rhodopsin immunolabeling in the normal retinas was restricted to the rod outer segments. In the RP retinas, rhodopsin was present in shortened rod outer segments and in the surface membranes of the rod inner segments and somata. In regions of photoreceptor death, the surviving rods had sprouted rhodopsin-positive neurites that were closely associated with gliotic Muller cell processes and extended to the inner limiting membrane. Rods and cones in the RP maculas did not form neurites, but the axons of peripheral cones were abnormally elongated and branched. Double immunofluorescence labeling showed that the rod neurites bypassed the horizontal and rod bipolar cells that are normally postsynaptic to rod axons. To our knowledge, this is the first report of rod neurite sprouting in vivo. We were unable to find neurites on degenerate rods in old rds mice, an animal model for RP. The rod neurites in the human RP retinas resemble the long, branched processes formed by rods cultured on Muller cells or purified N-CAM. Neurite growth by surviving rods in the RP retinas may be a response to neurotrophic factor upregulation, loss of inhibitory factors, or changes in molecules associated with reactive Muller cells. Such changes in the retinal microenvironment may impede functional integration of transplanted photoreceptors. The contributions of the rhodopsin-positive rod neurites and abnormal cone axons to the functional abnormalities observed in RP are unknown.
Increase of extracellular corticotropin-releasing factor-like immunoreactivity levels in the amygdala of awake rats during restraint stress and ethanol withdrawal as measured by microdialysis
Authors: Pich EM , Lorang M , Yeganeh M , Rodriguez de Fonseca F , Raber J , Koob GF , Weiss F
Published: April 2018

Previous research has suggested a role for corticotropin-releasing factor (CRF) in the anxiogenic effects of stressful stimuli and ethanol withdrawal. This hypothesis was explored in a series of experiments using intracranial microdialysis to monitor CRF-like immunoreactivity (CRF-IR) in the extracellular compartment of the rat amygdala. The synaptic origin of CRF-IR release in the amygdala was determined in vitro by assessing the Ca2+ dependency of 4-aminopyridine stimulated CRF-IR release from tissue preparations of rat amygdala. In vivo experiments were performed in awake rats after the placement of microdialysis probes in the amygdala. In the first experiment, transient restraint stress (20 min) produced an increase of CRF-IR release (basal levels, 1.19 +/- 0.15 fmol/50 microliters; stress levels, 4.54 +/- 1.33 fmol/50 microliters; p < 0.05) that returned to basal values within 1 hr. When 4-aminopyridine (5 mM) was added to the perfusion medium, it consistently increased CRF-IR release (4.83 +/- 0.92 fmol/50 microliters, p < 0.05). In the second experiment, CRF-IR release was measured during ethanol withdrawal in rats previously maintained for 2–3 weeks on a liquid diet containing ethanol (8.5%). Basal CRF-IR levels were 2.10 +/- 0.43 fmol/50 microliters in ethanol exposed rats and 1.30 +/- 0.19 fmol/50 microliters in control rats. During withdrawal, a progressive increase of CRF-IR levels over time was observed, reaching peak values at 10–12 hr after the onset of withdrawal (10.65 +/- 0.49 fmol/50 microliters vs 1.15 +/- 0.30 fmol/50 microliters of control rats, p < 0.01).
An emergent model of orientation selectivity in cat visual cortical simple cells
Authors: Somers DC , Nelson SB , Sur M
Published: April 2018

It is well known that visual cortical neurons respond vigorously to a limited range of stimulus orientations, while their primary afferent inputs, neurons in the lateral geniculate nucleus (LGN), respond well to all orientations. Mechanisms based on intracortical inhibition and/or converging thalamocortical afferents have previously been suggested to underlie the generation of cortical orientation selectivity; however, these models conflict with experimental data. Here, a 1:4 scale model of a 1700 microns by 200 microms region of layer IV of cat primary visual cortex (area 17) is presented to demonstrate that local intracortical excitation may provide the dominant source of orientation-selective input. In agreement with experiment, model cortical cells exhibit sharp orientation selectivity despite receiving strong iso-orientation inhibition, weak cross- orientation inhibition, no shunting inhibition, and weakly tuned thalamocortical excitation. Sharp tuning is provided by recurrent cortical excitation. As this tuning signal arises from the same pool of neurons that it excites, orientation selectivity in the model is shown to be an emergent property of the cortical feedback circuitry. In the model, as in experiment, sharpness of orientation tuning is independent of stimulus contrast and persists with silencing of ON-type subfields. The model also provides a unified account of intracellular and extracellular inhibitory blockade experiments that had previously appeared to conflict over the role of inhibition. It is suggested that intracortical inhibition acts nonspecifically and indirectly to maintain the selectivity of individual neurons by balancing strong intracortical excitation at the columnar level.
Reorganization of ascending 5-HT axon projections in animals previously exposed to the recreational drug (+/-)3,4-methylenedioxymethamphetamine (MDMA, "ecstasy")
Authors: Fischer C , Hatzidimitriou G , Wlos J , Katz J , Ricaurte G
Published: April 2018

The recreational drug (+/)3,4-methylenedioxymethamphetamine (MDMA, “ecstasy”) is a methamphetamine derivative that selectively destroys central 5-HT axons and axon terminals in animals and, possibly, humans. The fate of 5-HT neurons following MDMA injury is uncertain. In particular, while it is known that central 5-HT axons can undergo regenerative sprouting after MDMA injury, it has not been determined whether they reestablish the original innervation pattern. To address this question, the present studies examined 5-HT innervation patterns in animals lesioned with MDMA 12–18 months previously. Both rodents (rats) and nonhuman primates (squirrel monkeys) were examined, since there is indication that serotonergic recovery after MDMA injury may be species dependent. 5-HT axon projections were studied neurochemically, autoradiographically and immunocytochemically. In both rodents and nonhuman primates previously lesioned with MDMA, substantial serotonergic axonal sprouting was observed. However, in a few rats and in most squirrel monkeys, the reinnervation pattern was highly abnormal: distant targets (e.g., dorsal neocortex) remained denervated, while some proximal targets (e.g., amygdala, hypothalamus) were reinnervated or hyperinnervated. Although the specific determinants of axonal recovery after MDMA injury remain to be identified, it appears that axons which initially sustain more severe damage, are longer, or are more highly arborized have low probability of recovering. The observation that some brain regions remain denervated, while others are reinnervated or hyperinnervated suggests that, under some circumstances, MDMA injury can lead to a lasting reorganization of ascending 5-HT axon projections. Such lasting changes in brain innervation, documented here in MDMA-treated animals, may have implications for humans using MDMA recreationally.
Thalamocortical projections have a K+ channel that is phosphorylated and modulated by cAMP-dependent protein kinase
Authors: Moreno H , Kentros C , Bueno E , Weiser M , Hernandez A , Vega-Saenz de Miera E , Ponce A , Thornhill W , Rudy B
Published: April 2018

The finding that some K+ channel mRNAs are restricted to certain populations of neurons in the CNS suggests that there are K+ channels tailored to certain neuronal circuits. One such example are the transcripts from the KV3.2 gene, the majority of which are expressed in thalamic relay neurons. To gain insights into the specific roles of KV3.2 subunits, site specific antibodies were raised to determine their localization in thalamic relay neurons. Immunohistochemical and focal lesioning studies demonstrate that KV3.2 proteins are localized to the terminal fields of thalamocortical projections. It is also shown that KV3.2 channels expressed in vitro are strongly inhibited through phosphorylation by cAMP-dependent protein kinase (PKA). Channels containing KV3.1 subunits, which otherwise exhibit nearly identical electrophysiological properties in heterologous expression systems but have a different and less restricted pattern of expression in the CNS, are not affected by PKA. Therefore, this modulation might be associated with the specific roles of KV3.2 subunits. Furthermore, we demonstrate that KV3.2 proteins can be phosphorylated in situ by intrinsic PKA. KV3.2 subunits display properties and have a localization consistent with a role in the regulation of the efficacy of the thalamocortical synapse, and could thereby participate in the neurotransmitter-mediated control of functional states of the thalamocortical system associated with global states of awareness.
The leech homeobox gene Lox4 may determine segmental differentiation of identified neurons
Authors: Wong VY , Aisemberg GO , Gan WB , Macagno ER
Published: April 2018

We cloned and characterized a new leech homeobox gene, Lox4, a homolog of the Drosophila genes Ultrabithorax and abdominal-A. Lox4 has a complex and dynamic pattern of expression within a series of segmentally homologous neurons. These include a pair of specialized motor neurons of one segmental ganglion, the rostral penile evertors (RPEs), and their segmental homologs in other midbody ganglia. During gangliogenesis, Lox4 was expressed within this series of neurons in three different temporal patterns: (1) it was never expressed in the RPE homologs of ganglia 1–3; (2) it was expressed in the RPEs during gangliogenesis, but was turned off when these neurons started to differentiate after gangliogenesis; and (3) it was expressed in the RPE homologs of segments 4–5 and 7–21 during gangliogenesis and the subsequent period of axonogenesis. We found that these neurons have three distinct peripheral axonal morphologies that correlate with the three temporal patterns of expression. Our results suggest that the homeobox gene Lox4 may determine neuronal identities within this series of segmental homologs.
Transient memory impairment in monkeys with bilateral lesions of the entorhinal cortex
Authors: Leonard BW , Amaral DG , Squire LR , Zola-Morgan S
Published: April 2018

Performance on five behavioral tasks was assessed post-operatively in Macaca fascicularis monkeys prepared with bilateral lesions of the entorhinal cortex (E group). Three of the tasks were also readministered 9–14 months after surgery. Initial learning of the delayed nonmatching-to-sample (DNMS) task was impaired in the E animals relative to unoperated control monkeys. On the delay portion of DNMS, the performance of E animals was nearly at control levels at short delays (up to 60 sec) but was impaired at 10 min and 40 min retention intervals. On the retest of DNMS, the E animals performed normally at all retention intervals. The E animals were unimpaired on the four other memory tasks. Neuroanatomical studies revealed a significant transverse expansion of the terminal field of the perirhinal cortical projection in the CA1 region of the hippocampus. Compared to unlesioned, anatomical control monkeys, the transverse length of the perirhinal terminal field in CA1 increased approximately 70% in the E monkeys. Although this was a striking morphological alteration, it is not known whether the sprouting of this projection influenced the behavioral recovery. The results of these studies suggest that the entorhinal cortex may normally participate in the learning and performance of tasks that are dependent on the medial temporal lobe memory system. However, recovery of normal DNMS performance demonstrates that the entorhinal cortex is not, by itself, essential for learning and performance of such tasks.
Ligand-induced growth cone collapse: amplification and blockade by variant GAP-43 peptides
Authors: Igarashi M , Li WW , Sudo Y , Fishman MC
Published: April 2018

Growth cones are powerful amplifiers for signals from the microenvironment. Their collapse can be triggered by cell surface components of myelin and brain membranes, as well as by soluble ligands, including neurotransmitters. GAP-43 is a protein concentrated on the inner surface of the growth cone membrane. Assayed in isolation, it interacts with the heterotrimeric protein, G(o), and in oocytes it amplifies the effects of ligand-triggered G protein activation. We wished to examine whether GAP-43 serves to amplify signals at the growth cone. The G(o) stimulating region of GAP-43 is encoded in the 10 amino acids (MLCCMRRT-KQ) of the first exon. We examined the effect of this peptide upon chick dorsal root ganglion growth cone collapse and neurite retraction triggered by brain membranes or myelin, as well as by serotonin. We find that application of the GAP-43 1–10 peptide amplifies the effects of all three ligands. The amplification is greater when GAP-43 1–10 is injected intracellularly. Peptides with amino acid substitutions for the two cysteine residues manifest parallel changes in growth cone collapse and G(o) stimulation. In particular, tyrosine or methionine substitutions cause the peptide to inhibit G(o) and to block induced growth cone collapse. The GAP-43 peptides therefore regulate the sensitivity of growth cones to extrinsic signals. The modified peptides serve as a starting point for the design of reagents to enhance CNS regeneration.
Pre- and postsynaptic determinants of EPSC waveform at cerebellar climbing fiber and parallel fiber to Purkinje cell synapses
Authors: Takahashi M , Kovalchuk Y , Attwell D
Published: April 2018

Excitatory postsynaptic currents (EPSCs) at the parallel fiber and climbing fiber to Purkinje cell synapses were studied by whole-cell clamping Purkinje cells in cerebellar slices. Reducing glutamate release with adenosine or GABA decreased the amplitude of the EPSCs, with a larger suppression being produced at the parallel fiber synapse. Reducing glutamate release also speeded the decay of the EPSCs, and this effect was not a series resistance artefact since postsynaptic reduction of the current with CNQX did not speed the EPSC decay. Blocking glutamate uptake slowed the decay of the EPSCs. At the climbing fiber synapse, adenosine had little suppressive effect on the smaller EPSC evoked by the second of a pair of stimuli. Blocking desensitization of postsynaptic AMPA receptors prolonged the EPSC decay, preferentially increased the size of the second EPSC, and resulted in adenosine having a similar suppressive effect on the first and second EPSC. These data suggest that, at these synapses, the fall of glutamate concentration in the synaptic cleft overlaps with the decay of the EPSC, and that the EPSC size and duration are controlled by the amount of glutamate released, the rate of glutamate uptake, and desensitization.
Functional differentiation of adult neural circuits from a single embryonic network
Authors: Casasnovas B , Meyrand P
Published: April 2018

The stomatogastric nervous system (STNS) of adult lobsters and crabs generates a number of different rhythmic motor patterns which control different regional movements of the foregut. Since these output patterns are generated by discrete neural networks that, in the adult, are well characterized in terms of synaptic and cellular properties, this system constitutes an ideal model for exploring the mechanisms underlying the ontogeny of neural network organization. The foregut and its rhythmic motor patterns were studied in in vitro STNS nerve-muscle preparations of the embryo and different larval stages of the lobster Homarus gammarus. The development of Homarus comprises a long embryonic stage in ovo followed by three pelagic larval stages prior to the onset of benthic life. During these stages the foregut itself develops slowly from a simple ectodermal invagination that occurs in the embryo. During successive larval stages it progressively acquires all the specialized structures and shape of the adult foregut. In contrast, the STNS is morphologically recognizable at early embryonic stages. In all recorded stages the STNS spontaneously expresses rhythmic motor activity. During development, this activity is progressively restructured, beginning with a single rhythmic motor pattern in the embryo where all the stomodeal muscles are strongly coordinated. In subsequent stages, however, this single pattern is progressively subdivided to give rise eventually to the three discrete rhythmic motor patterns characteristic of the adult STNS. Our data suggest that rather than a dismantling of redundant embryonic and larval neural networks, the different adult networks emerge as a progressive partitioning of discrete circuits from a single embryonic network.
Postnatal development of synchronized network oscillations in the ferret dorsal lateral geniculate and perigeniculate nuclei
Authors: McCormick DA , Trent F , Ramoa AS
Published: April 2018

Extracellular and intracellular recordings from slices of ferret dorsal lateral geniculate nucleus (LGNd) at postnatal ages P10–53 were performed to examine the postnatal development of spindle waves and the ability of block of GABAA receptors to alter these spindle waves into a slower, synchronous oscillation. As in prior studies in the adult, intracellular and extracellular recordings at ages P33–53 revealed robust spindle waves to be present in both the LGNd and perigeniculate nucleus (PGN). Intracellular recordings from thalamocortical relay cells in the A-laminae of the LGNd revealed that these cells received repetitive inhibitory postsynaptic potentials (IPSPs) at 6–9 Hz during the generation of spindle waves, and generated rebound low threshold Ca2+ spikes and bursts of 2–6 action potentials following each second or third IPSP. Intracellular recordings from the GABAergic neurons of the PGN at P33–53 revealed barrages of EPSPs that activated low threshold Ca2+ spikes and high frequency burst discharges of 2–10 action potentials during spindle wave generation. In contrast, full spindle waves were absent at ages prior to approximately P22 and spindle waves between the ages of P26 and approximately P30 were relatively weak and associated with only one or two action potentials per burst in both PGN neurons and LGNd relay cells. Bath application of the GABAA antagonist bicuculline methiodide at P41–53 resulted in a conversion of normal spindle waves into a marked 2–4 Hz oscillation in which the action potential firing of both thalamocortical relay and PGN neurons was greatly increased. In contrast, block of GABAA receptors prior to age P39 did not result in the generation of the slowed, 2–4 Hz network oscillation. Investigation of the electrophysiological properties of PGN neurons revealed that the postnatal development of spindle waves and bicuculline-induced slow oscillations were associated with an increase in the ability of PGN neurons to generate high frequency bursts of action potentials, suggesting that these changes in electrophysiological properties may contribute to the late development of synchronized oscillations in the ferret LGNd.
BDNF enhances the differentiation but not the survival of CNS stem cell- derived neuronal precursors
Authors: Ahmed S , Reynolds BA , Weiss S
Published: April 2018

We have previously reported the isolation of an EGF-responsive precursor from the embryonic and adult mouse striatum. This precursor exhibits self renewal and the ability to produce a sphere of undifferentiated cells which can be induced to differentiate into neurons and glia. RT-PCR analysis of these spheres of undifferentiated cells revealed the expression of mRNA for the trkB neurotrophin receptor, both with and without the catalytic domain, and little or no expression of trkA or trkC. We examined the actions of BDNF on the fate of EGF-generated neural precursors. Ten days after a one-time exposure to BDNF, single EGF-generated spheres showed a twofold increase in neuron number and a marked enhancement in neurite outgrowth. Examination of neuronal nuclei with immunochemical probes for c-fos and bromodeoxyuridine revealed that the actions of BDNF were directly upon neuronal cells and did not involve division of neuronal precursors. The twofold increase in neuronal number due to BDNF, observed after 10 d in vitro, was significantly reduced after 21 d in vitro and was not apparent at 27 d in vitro. Quantitative analyses revealed that while repeated application of BDNF did not prevent the loss of neuron number over time, it did result in a significant increase in neurite numbers. Moreover, delayed addition of BDNF mimicked the increase in neuronal numbers seen when BDNF was present throughout. These BDNF actions did not appear to involve the enhancement of a novel neuronal phenotype, with all effects being due to increase in the numbers and neurite outgrowth of neurons that colocalize GABA and substance P. These findings suggest that BDNF markedly enhances the antigenic and morphologic differentiation of EGF-generated neuronal precursors. BDNF alone does not appear to act as a survival factor for neuronal precursors nor is it sufficient for preventing their death over time.