bluuebunny/crossref_metadata_2025 huggingface dataset:
The hippocampus and long-term object memory in the rat
Authors: Vnek N , Rothblat LA
Published: April 2018

Animal models of amnesia have yielded many insights into the neural substrates of different types of memories. Some very important aspects of memory, however, have been ignored in research using experimental animals. For example, to examine long-term memory investigators traditionally have relied on measures of information acquisition, which stand in contrast to the measures of retention commonly used in work with humans. We have recently developed a behavioral paradigm that measures both the acquisition and long-term retention of object discriminations, and found a selective retention impairment in rats with entorhinal-hippocampal disconnection (Vnek et al., 1995). The present study was designed to determine whether direct damage to the hippocampus likewise would lead to a selective deficit in the retention of visual discriminations. Rats with aspiration lesions of the dorsal hippocampus, rats with neocortical control lesions, and normal controls were trained on three object discrimination problems and then retrained 3 weeks later to measure retention. All animals showed the same level of performance during the training (acquisition) phase of testing, but the performance of animals with dorsal hippocampal injury fell below that of controls during retraining (retention). Taken together, these and our earlier results suggest that the hippocampus and anatomically related structures are particularly important for retaining visual discriminations over long delay intervals. These findings may clarify the role of the hippocampus in nonspatial memory.
Synchronization of fast (30-40 Hz) spontaneous oscillations in intrathalamic and thalamocortical networks
Authors: Steriade M , Contreras D , Amzica F , Timofeev I
Published: April 2018

The synchronization of fast (mainly 30 to 40 Hz) oscillations in intrathalamic and thalamocortical (TC) networks of cat was studied under ketamine-xylazine anesthesia and in behaving animals by means of field potential, extra- and intracellular recordings from multiple sites in the thalamic reticular (RE) nucleus, dorsal (sensory, motor, and intralaminar) thalamic nuclei, and related neocortical areas. Far from being restricted to tonically activated behavioral states, the fast oscillations also appeared during resting sleep and deep anesthesia, when they occurred over the depolarizing component of the slow (<1 Hz) oscillation and were suppressed during the prolonged hyper- polarizations of RE, TC, and cortical neurons. The synchronization of fast rhythms among different thalamic foci was robust. Fast rhythmic cortical waves and subthreshold depolarizing potentials in TC neurons were highly coherent; however, the synchronization of the fast oscillation required recordings from reciprocally related neocortical and thalamic foci, as identified by monosynaptic responses in both directions. The short-range spatial confinement of coherent fast rhythms contrasted with the large-scale synchronization of low- frequency sleep rhythms. Transient fast rhythms, appearing over the depolarizing envelope of the slow sleep oscillation, became sustained when brain activation was elicited by stimulation of mesopontine cholinergic nuclei or during brain-active behavioral states in chronic experiments. These data demonstrate that fast rhythms are part of the background electrical activity of the brain and that desynchronization, used to designate brain-active states, is an erroneous term inasmuch as the fast oscillations are synchronized not only in intracortical but also in intrathalamic and TC networks.
Opposing actions of androgen and estrogen on in vitro firing frequency of neuronal oscillators in the electromotor system
Authors: Schaefer Je , Zakon HH
Published: April 2018

The South American knifefish (Apteronotus leptorhynchus), or brown ghost, produces a high-frequency (600–1000 Hz) sinusoidal electric organ discharge (EOD) with males discharging at higher frequencies than females. In addition, each fish has a unique EOD frequency within the frequency range of its gender. The electromotor circuit responsible for EOD production consists of a medullary pacemaker nucleus (PMN) and spinal electromotor neurons (EMNs). In vitro spinal slice recording showed that, similar to the PMN, EMNs fire spontaneously at rates near the EOD frequency of each fish. The persistence of firing 2 weeks after high spinal transaction demonstrated that spontaneous firing rate was intrinsic to the EMNs and was not dependent on presynaptic input. We confirmed that 11-ketotestosterone (11 kT) raised and 17-beta-estradiol (E2) lowered the EOD frequency of intact fish. Because electromotor cells fire spontaneously near EOD, frequency, we investigated whether these steroids affect endogenous firing rates. Steroid implants were made in normal or spinally transected fish. Two weeks later, PMNs of normal fish and EMNs of transected fish were recorded in vitro. 11 kT increased and E2 decreased the intrinsic firing rate of neurons in the PMN and the EMNS. Hormones shifted the intrinsic firing rates of EMNS, although they were synaptically isolated during the hormone exposure.
The Behavior of Optic Axons on Substrate Gradients of Retinal Basal Lamina Proteins and Merosin
Authors: Halfter Willi
Published: April 2018

To study the behavior of optic axons to continuously changing concentrations of their substrate, explants from embryonic retina were placed across gradients of retinal basal lamina proteins and merosin. The following growth patterns of axons in response to the substrate gradients were found: (1) Axons that grew up gradients, i.e., from low to high substrate concentrations, became longer and less fasciculated with increasing concentration of the substrate. On shallow basal lamina gradients, the axons also showed a directional response that resulted in guidance to higher substrate concentrations. (2) Axons that grew down gradients, i.e., from high to low substrate concentrations, became shorter and more fasciculated with decreasing concentrations of the substrate. On gradients of merosin, a significant alteration in the axonal growth direction toward higher substrate concentrations was detected. Axons heading down gradients never U turned to higher substrate concentrations. (3) Axons confronted with discontinuous substrates were confined to the borders of the substrate exclusively, whereas axons confronted with substrate gradients were able to cross into the territory beyond the substrate. (4) The growth patterns of axons on substrate gradients of basal lamina proteins and merosin were similar but not identical, indicating that axons may respond to substrate gradients dependent on its chemical composition. The present results show that substrate gradients can regulate length and fasciculation of neurites and have a limited capability to direct axons to higher substrate concentrations.
Upregulation of BDNF mRNA Expression in the Barrel Cortex of Adult Mice after Sensory Stimulation
Authors: Rocamora Nativitat , Welker Egbert , Pascual Marta , Soriano Eduardo
Published: April 2018

Upregulation of brain-derived neurotrophic factor (BDNF) mRNA expression by neuronal activity has been reported in cultured hippocampal cells and in differentin vivoexcitotoxic paradigms. The aim of the present study was to determine whether sensory stimulation of the whisker-to-barrel pathway alters BDNF mRNA expression in the cortex and, if so, to evaluate the specificity of this effect. To this end, a set of mystacial whiskers was unilaterally stimulated by mechanical deflection, and the expression of BDNF mRNA was analyzed in the barrel cortex byin situhybridization (ISH) using a35S-labeled antisense BDNF riboprobe and emulsion autoradiography. A clear-cut and specific upregulation of the BDNF mRNA expression was found at the level of the somatosensory cortex after the increased peripheral stimulation. In the barrel cortex of control mice, BDNF mRNA was present in a few cells in layers II/III and VI, whereas it was almost undetectable in layer IV. After 6 hr of whisker stimulation, increased levels of BDNF mRNA were found in layers II to VI of the contralateral barrel cortex. In layer IV, BDNF upregulation was confined to the barrels corresponding to the stimulated follicles. ISH combined with immunocytochemistry against the three calcium-binding proteins parvalbumin, calretinin, and calbindin-D28Krevealed that BDNF mRNA-expressing cells do not belong to the GABAergic cell population of the barrel cortex. The present results support a role for BDNF in activity-dependent modifications of the adult cerebral cortex.
Electrographic Seizures and New Recurrent Excitatory Circuits in the Dentate Gyrus of Hippocampal Slices from Kainate-Treated Epileptic Rats
Authors: Wuarin Jean-Pierre , Dudek F. Edward
Published: April 2018

Mossy fiber sprouting has been proposed to lead to new excitatory connections between dentate granule cells, which in turn cause electrographic seizures. We tested this hypothesis in hippocampal slices from rats made epileptic by kainate injections. The Timm’s histological method revealed intense staining of the inner molecular layer in slices from all kainate-treated rats. In bicuculline (10 μm) and 6 mm[K+]o, antidromic stimulation of the granule cells evoked bursts of population spikes superimposed on long-lasting negative shifts in all slices tested from all kainate-treated rats. Long-duration (2–47 sec), seizure-like bursts with tonic and clonic components occurred spontaneously (53%) or in response to antidromic stimulation (81%). Under identical conditions, prolonged bursts were never seen in slices from controls or from kainate-injected rats 2–4 d after treatment. Glutamate microdrops applied in the granule cell layer evoked abrupt increases in the frequency of excitatory postsynaptic potentials (EPSPs) in two thirds of the cells tested. Glutamate microstimulation was effective at several sites in the granule cell layer but ineffective in the hilus. The proportion of granule cells responding to local application of glutamate by an increase in EPSPs was higher in slices with long bursts (80% with bursts of >3 sec) than in slices with shorter bursts (33% with bursts of <3 sec). Glutamate microstimulation did not affect EPSPs in granule cells from control preparations. These results support the hypothesis that kainate-induced mossy fiber sprouting forms new excitatory connections between granule cells and can lead to increased seizure susceptibility in the dentate gyrus.
Double Transduction with GTP Cyclohydrolase I and Tyrosine Hydroxylase Is Necessary for Spontaneous Synthesis ofl-DOPA by Primary Fibroblasts
Authors: Bencsics Craig , Wachtel Stephen R. , Milstien Sheldon , Hatakeyama Kazuyuki , Becker Jill B. , Kang Un Jung
Published: April 2018

Gene transfer of tyrosine hydroxylase (TH) in animal models of Parkinson’s disease (PD), using either genetically modified cells or recombinant virus vectors, has produced partial restoration of behavioral and biochemical deficits. The limited success of this approach may be related to the availability of the cofactor, tetrahydrobiopterin (BH4), because neither the dopamine-depleted striatum nor the cells used for gene transfer possess a sufficient amount of BH4to support TH activity. To determine the role of BH4in gene therapy, fibroblast cells transduced with the gene for TH were additionally modified with the gene for GTP cyclohydrolase I, an enzyme critical for BH4synthesis. In contrast to cells transduced with only TH, doubly transduced fibroblasts spontaneously produced both BH4and 3,4-dihydroxy-l-phenylalanine. To examine further the importance of GTP cyclohydrolase I in gene therapy for PD,in vivomicrodialysis was used to assess the biochemical changes in the dopamine-denervated striatum containing grafts of genetically modified fibroblasts. Only denervated striata grafted with fibroblasts possessing both TH and GTP cyclohydrolase I genes displayed biochemical restoration. However, no significant differences from controls were observed in apomorphine-induced rotation. This is partly attributable to a limited duration of gene expressionin vivo. These differences between fibroblasts transduced with TH alone and those additionally modified with the GTP cyclohydrolase I gene indicate that BH4is critical for biochemical restoration in a rat model of PD and that GTP cyclohydrolase I is sufficient for production of BH4.
Immunocytochemical Localization of the GABACReceptor ρ Subunits in the Mammalian Retina
Authors: Enz Ralf , Brandstätter Johann Helmut , Wässle Heinz , Bormann Joachim
Published: April 2018

Polyclonal antibodies against the N terminus of the rat ρ1 subunit were generated to study the distribution of GABACreceptors in the mammalian retina. The specificity of the antibodies was tested in Western blots and transfected HEK-293 cells. No cross-reactivity with the GABAAreceptor subunits α1–3, β1–3, γ2, δ or with the glycine receptor subunits α1 and β could be detected. In contrast, the ρ1, ρ2, and ρ3 subunits were all recognized by the antibodies. In vertical sections of rat, rabbit, cat, and macaque monkey retinae, strong punctate immunoreactivity was present in the inner plexiform layer. Weaker immunoreactivity was also present in the outer plexiform layer, and cell bodies of bipolar cells were faintly labeled. Double immunostaining of vertical sections and immunostaining of dissociated rat retinae showed the punctate immunofluorescence to colocalize with bipolar cell axon terminals. The puncta possibly represent clustering of the ρ subunits at postsynaptic sites.
TheIn VivoTime Course for Elimination of Adrenalectomy-Induced Apoptotic Profiles from the Granule Cell Layer of the Rat Hippocampus
Authors: Hu Zhongting , Yuri Kazunari , Ozawa Hitoshi , Lu Haiping , Kawata Mitsuhiro
Published: April 2018

Although apoptotic cellular degeneration has been reported to be extremely rapid with the use ofin vitromodels, the time needed to clear apoptotic neurons in thein vivobrain is unknown. In this study we used a simple morphological approach to solve this problem. Four days after adrenalectomy (ADX), all of the operated rats morphologically displayed hippocampal granule cell apoptosis that was prevented completely by corticosterone replacement immediately after ADX. Therefore, we intravenously injected the rats with corticosterone 4 d after ADX and subsequently maintained them on corticosterone replacement in saline drinking water. This corticosterone replacement could protect healthy granule cells promptly and continuously against hormone-deficient apoptosis, because the normal glucocorticoid receptor immunoreactivity within the granule cell nuclei, which disappeared after ADX, was identified 1 hr after corticosterone replacement was started, and this effect persisted for several days. However, this corticosterone treatment could not prevent the irreversible apoptosis of the already degenerated granule cells at various stages of the same progressive apoptotic process. Then we successively traced the disappearance of apoptotic granule cells throughout the hippocampus at different time points by Nissl and silver staining. Given that the apoptotic cells at the earliest stage of the degenerating process when the ADX rats received corticosterone injection were the last to disappear, the period from corticosterone injection until the disappearance of the last degenerating debris of apoptotic cells was taken to represent the time course for elimination of apoptotic neuronsin vivo. We discovered that the elimination of apoptotic granule cells took 72 hr.
Neurosteroid Prolongs GABAAChannel Deactivation by Altering Kinetics of Desensitized States
Authors: Zhu Wei Jian , Vicini Stefano
Published: April 2018

Fast applications of GABA (1 mm) to nucleated and outside-out patches excised from granule neurons in cerebellar slices from developing rats evoked currents with a double exponential time course reminiscent of that of IPSCs. A neurosteroid 3α, 21dihydroxy-5α-pregnan-20-one (THDOC) remarkably increased the slow deactivation time constant and slowed down recovery from desensitization, as estimated by paired-pulse GABA applications. THDOC also reduced the amplitude of GABA currents, whereas it failed to affect the fast deactivation component and its relative contribution to peak amplitude. The effects of THDOC on slow deactivation were greater in rats younger than postnatal day 13 (P13) as compared with rats at P30–P35. THDOC failed to alter deactivation of short responses induced by a less-potent agonist taurine at saturating doses. These responses had deactivation kinetics described by a fast single exponential decay, little desensitization, and quick recovery. However, THDOC slowed deactivation if taurine responses were long enough to allow consistent desensitization, suggesting that desensitized states are required for the neurosteroid to modulate GABA responses. In outside-out patches, just as desensitized states prolonged GABA responses by producing reopening of channels activated by brief GABA pulses, THDOC increased the channel open probability by further increasing the number of late channel openings, resulting in a prolongation of the slow deactivation. Our data suggest that neurosteroid potentiates the inhibitory postsynaptic transmission via the prolongation of the slow deactivation and that the alteration of kinetics of entry and exit from desensitized states underlies the allosteric modification of GABAAreceptors by neurosteroids.
Secondary Activation of a Cation Conductance Is Responsible for NMDA Toxicity in Acutely Isolated Hippocampal Neurons
Authors: Chen Qiang X. , Perkins Katherine L. , Choi Dennis W. , Wong Robert K. S.
Published: April 2018

One of the key questions concerning glutamate toxicity is how a transient NMDA exposure can lead to a delayed death of neurons. To address this issue, we performed whole-cell recording on acutely isolated hippocampal CA1 neurons to monitor the membrane response after NMDA exposure. Transient NMDA exposure (100 μm, 10 min) induced an inward current (postexposure current;Ipe) which was associated with a Ca2+- and Na+-permeable cation conductance.Ipecontinuously increased (in the absence of NMDA) until death of the neuron occurred. Application of NMDA in the absence of extracellular calcium failed to triggerIpeand neuronal death. Postexposure suppression ofIpeprotected against NMDA toxicity. These results indicate that a cation current, which is induced by an increase in intracellular calcium concentration ([Ca2+]i) and is itself partly carried by Ca2+, links the initial NMDA exposure to neuronal death.
Identification of Endogenous Sympathetic Neuron Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP): Depolarization Regulates Production and Secretion through Induction of Multiple Propeptide Transcripts
Authors: Brandenburg Cynthia A. , May Victor , Braas Karen M.
Published: April 2018

The vasoactive intestinal peptide/pituitary adenylate cyclase-activating polypeptide (PACAP)/secretin/glucagon family of peptides displays numerous physiological roles in autonomic nervous system development and function. The regulated endogenous production and release of PACAP peptides in sympathetic neurons of the superior cervical ganglion (SCG) was investigated. The two posttranslationally processed forms of PACAP, PACAP27 and PACAP38, were identified in rat adult, neonatal, and cultured SCG neurons. PACAP38 levels were ∼5–10 fmol/adult SCG and ∼2 fmol/neonatal SCG; PACAP27 levels were comparable. The authenticity of peptide immunoreactivity in these tissues was verified by coelution with synthetic PACAP in reverse-phase HPLC analysis. Reverse transcription-PCR and sequence-specific hybridization revealed PACAP mRNA in adult, neonatal, and cultured SCG neurons;in situhybridization histochemistry and immunocytochemistry localized the PACAP peptide and proPACAP mRNA to a subset of the SCG neuronal population. Basal and stimulated release of endogenous PACAP38 from cultured sympathetic neurons was established, suggesting that these peptides may function as signaling molecules at target tissues. Chronic depolarization with 40 mmpotassium stimulated the PACAP secretory rate 10- to 20-fold, with concomitant increases in cellular PACAP peptide and mRNA levels. When examined using Northern analysis, depolarizing conditions not only stimulated the 2.2 kb form of PACAP mRNA, but also induced the expression of a shortened, 0.9 kb, transcript. Further reverse-transcription PCR analysis demonstrated that this smaller transcript was not identical to the unique testicular message. These studies identify PACAP38 and PACAP27 as regulated endogenous releasable peptides contributing to the functional diversity and phenotypic plasticity of the sympathetic nervous system.
Somatostatin Inhibits Excitatory Transmission at Rat Hippocampal Synapses via Presynaptic Receptors
Authors: Boehm Stefan , Betz Heinrich
Published: April 2018

Somatostatin is one of the major peptides in interneurons of the hippocampus. It is believed to play a role in memory formation and to reduce the susceptibility of the hippocampus to seizure-like activity. However, at the cellular level, the actions of somatostatin on hippocampal neurons are still controversial, ranging from inhibition to excitation. In the present study, we measured autaptic currents of hippocampal neurons isolated in single-neuron microcultures. Somatostatin and the analogous peptides seglitide and octreotide reduced glutamatergic, but not GABAergic, autaptic currents via pertussis toxin-sensitive G-proteins. This effect was observed whether autaptic currents were mediated by NMDA or non-NMDA glutamate receptors. Furthermore, somatostatin did not affect currents evoked by the direct application of glutamate, but reduced the frequency of spontaneously occurring excitatory autaptic currents. These results show that presynaptic somatostatin receptors of the SRIF1family inhibit glutamate release at hippocampal synapses. Somatostatin, seglitide, and octreotide also reduced the frequency of miniature excitatory postsynaptic currents in mass cultures without affecting their amplitudes. In addition, all three agonists inhibited voltage-activated Ca2+currents at neuronal somata, but failed to alter K+currents, effects that were also abolished by pertussis toxin. Thus, presynaptic somatostatin receptors in the hippocampus selectively inhibit excitatory transmission via G-proteins of the Gi/Gofamily and through at least two separate mechanisms, the modulation of Ca2+channels and an effect downstream of Ca2+entry. This presynaptic inhibition by somatostatin may provide a basis for its reportedly anticonvulsive action.
Pigment-Dispersing Hormone Shifts the Phase of the Circadian Pacemaker of the CockroachLeucophaea maderae
Authors: Petri Bernhard , Stengl Monika
Published: April 2018

An antiserum against the crustacean neuropeptide pigment-dispersing hormone stains a small set of neurons in the optic lobes of several hemimetabolous and holometabolous insects. These cells, the primary branches of which in the optic lobe lie in the accessory medulla, fulfill several criteria predicted for neurons of the circadian clock. For example, in fruit flies they expresstimelessandperiod, which are two molecular components of the circadian pacemaker.

To test whether pigment-dispersing hormone fulfills a circadian function in the cockroachLeucophaea maderae, 150 fmol of synthetic peptide was injected into the vicinity of the accessory medulla. This resulted in a stable phase-dependent resetting of the phase of the circadian locomotor activity rhythm, which depended on the amount of pigment-dispersing hormone injected. The resulting phase–response curve differs from that obtained with light pulses, suggesting that pigment-dispersing hormone-immunoreactive neurons are not part of the visual input pathway to the pacemaker but an integral part of it and/or part of a nonphotic input into the clock. A possible role of these neurons in coupling the bilaterally paired circadian pacemakers is discussed.
The Responses of Rat Trigeminal Ganglion Neurons to Capsaicin and Two Nonpungent Vanilloid Receptor Agonists, Olvanil and Glyceryl Nonamide
Authors: Liu L. , Lo Y.-C. , Chen I.-J. , Simon S. A.
Published: April 2018

Capsaicin, the pungent ingredient in hot pepper, activates and subsequently desensitizes a subset of polymodal nociceptors. Because its initial application to skin produces pain, nonpungent analogs such as olvanil and glyceryl nonivamide (GLNVA) were synthesized to enhance its clinical use. To explore how these nonpungent analogs differ from capsaicin, whole-cell patch-clamp recordings were performed on cultured rat trigeminal ganglion neurons.

In neurons held at −60 mV, capsaicin, olvanil, and GLNVA were found to activate one or two kinetically distinct inward currents. Two inward currents were also activated when extracellular Ca2+was replaced with Ba2+and also when intracellular chloride was replaced by aspartate. The reversal potentials of the rapidly and slowly activating currents were 15.3 ± 6 and −4.0 ± 2.5 mV, respectively. These data provide strong evidence for subtypes of vanilloid receptors. One difference among these agonists is that, on average, the activation kinetics of the currents evoked by 1 μmolvanil and 30 μmGLNVA are considerably slower than those evoked by 1 μmcapsaicin. Measurements of the peak current,Ip, versus agonist concentration were fit to the Hill equation to yield values of the half maximal concentrations (K1/2), and the Hill coefficients (n). For capsaicin, olvanil, and GLNVA,K1/2= 0.68, 0.59, and 27.0 μm; andn= 1.38, 1.32, and 1.24, respectively.

We propose that olvanil and GLNVA are nonpungent because they activate different subtypes of receptors and/or because of their activation kinetics (compared with capsaicin) are, on average, slower than the rate they inhibit action potentials from polymodal nociceptors.
Neurotrophins Protect Cultured Cerebellar Granule Neurons against the Early Phase of Cell Death by a TwoComponent Mechanism
Authors: Courtney Michael J. , Åkerman Karl E. O. , Coffey Eleanor T.
Published: April 2018

Cerebellar granule neurons cultured with serum develop a mature neuronal phenotype, including stimulus-coupled release of glutamate, and depend on elevated potassium for survival. We find that cells cultured with serum undergo two phases of cell death. By 6 din vitro, 30–50% of the cells present are dead; after this time the remaining cells die. Elevated potassium prevents only this later phase of death, whereas neurotrophins protect these cells against the early phase of death. Factors that bind p75NTRor TNF-R, members of the same receptor family, exhibit voltage-sensitive calcium channel-dependent protection, whereas ligands of expressed Trk receptors show additional calcium channel-independent protection. The cells express TrkB protein and show elevated c-Fos and c-Jun levels in response to BDNF. No TrkA is detected, although p75NTRprotein is expressed and NGF induces depolarization-dependent elevation of c-Jun levels. In the presence of the protein kinase C inhibitor bisindolylmaleimide, BDNF-induced survival promotion is reduced partially, whereas NGF-induced death is unmasked. Basal survival mechanisms are insensitive to inhibition of PK-C or PI-3 kinase. We conclude that BDNF promotes survival in part via its TrkB receptor, whereas there is an additional pathway promoting survival and elevating c-Jun evoked by both NGF and BDNF via a non-Trk receptor.
Implication of OTX2 in Pigment Epithelium Determination and Neural Retina Differentiation
Authors: Bovolenta Paola , Mallamaci Antonello , Briata Paola , Corte Giorgio , Boncinelli Edoardo
Published: April 2018

The expression pattern ofOtx2, a homeobox-containing gene, was analyzed from the beginning of eye morphogenesis until neural retina differentiation in chick embryos. Early on,Otx2expression was diffuse throughout the optic vesicles but became restricted to their dorsal part when the vesicles contacted the surface ectoderm. As the optic cup forms,Otx2was expressed only in the outer layer, which gives rise to the pigment epithelium. This earlyOtx2expression pattern was complementary to that of PAX2, which localizes to the ventral half of the developing eye and optic stalk.Otx2expression was always observed in the pigment epithelium at all stages analyzed but was extended to scattered cells located in the central portion of the neural retina around stage 22. The number of cells expressingOtx2transcripts increased with time, following a central to peripheral gradient. Bromodeoxyuridine labeling in combination with immunohistochemistry with anti-OTX2 antiserum and different cell-specific markers were used to determine that OTX2-positive cells are postmitotic neuroblasts undergoing differentiation into several, if not all, of the distinct cell types present in the chick retina. These data indicate thatOtx2might have a double role in eye development. First, it might be necessary for the early specification and subsequent functioning of the pigment epithelium. Later, OTX2 expression might be involved in retina neurogenesis, defining a differentiation feature common to the distinct retinal cell classes.
Presynaptic Initiation by Action Potentials of Retrograde Signals in Developing Neurons
Authors: Primi Marie-Pierre , Clarke Peter G. H.
Published: April 2018

Until recently, the only means by which electrical activity was believed to initiate retrograde signals was via postsynaptic events: modulated synthesis or release of trophic factors. We have evidence in chick embryos for a presynaptic initiation of retrograde signals from the retina to the isthmo-optic nucleus, which is known to undergo 55% neuron death between embryonic days 12 and 17 and to become laminated during this period. Intraocular injections of saxitoxin just before embryonic day 14 reduce neuron death and prevent lamination in the isthmo-optic nucleus within as few as 6 hr. We show that these rapid effects are attributable to the direct action of saxitoxin on the isthmo-optic terminals. Alternative possibilities, such as an indirect effect via the target cells, are ruled out by control experiments. Normally, action potentials may lead to a chain of second messenger events in the axon terminal that is signaled retrogradely via the transport of a long-lived second messenger.
Competition among the Axonal Projections of an Identified Neuron Contributes to the Retraction of Some of Those Projections
Authors: Gan Wen-Biao , Macagno Eduardo R.
Published: April 2018

AP neurons in the embryonic leech CNS extend lateral projections to peripheral targets through the ganglionic nerve roots and longitudinal projections toward neighboring ganglia through the connective nerves. The lateral projections grow extensively in the periphery; in contrast, the longitudinal projections achieve relatively little growth and eventually retract, the majority having essentially disappeared by the end of embryogenesis. Cutting both nerve roots, which eliminates both lateral projections, however, induces the longitudinal projections of the AP neuron to begin to grow rapidly toward adjacent ganglia within 14 hr after the axotomy. By using a laser microbeam to cut just the lateral projections of the AP cells, we further show that it is indeed the loss of its lateral projections, and not a secondary response to the cutting of other components of the root nerves, that induces the longitudinal projections of the AP cell to grow extensively. In addition, we report that reducing the outgrowth of the lateral projections by: (1) cutting only one lateral projection, or (2) ablating pioneer neurons required by the AP neuron to establish its peripheral arbor, also results in a significant increase in the growth of the longitudinal projections. Finally, we demonstrate that increasing the outgrowth of the longitudinal projections by ablating the AP cells in adjacent ganglia results in a significant reduction in the outgrowth of the lateral projections. Taken together, these results indicate, first, that the longitudinal and lateral projections usually grow at the expense of each other, and second, that normally the extensive outgrowth of its lateral projections is a necessary condition for a developing AP neuron to retract its longitudinal projections.
Glial Cell Line-Derived Neurotrophic Factor Protects against Ischemia-Induced Injury in the Cerebral Cortex
Authors: Wang Yun , Lin Shinn-Zong , Chiou Ai-Lin , Williams Lawrence R. , Hoffer Barry J.
Published: April 2018

Glial cell line-derived neurotrophic factor (GDNF), a recently described and cloned member of the transforming growth factor (TGF)-β superfamily, has been shown to have marked trophic activity on several populations of central neurons. Survival-promoting and injury protectant activityin vitroandin vivo, using several paradigms, has been demonstrated for ventral mesencephalic dopaminergic neurons and spinal cord motoneurons. In view of a proposed commonality of mechanisms, involving intracellular free radical generation, depolarization-induced Ca2+influx, and mitochondrial respiratory enzyme injury, between such GDNF-responsive paradigms and those of ischemia-induced injury, we tested the effects of GDNF on the extent of neural degeneration induced by transient middle cerebral artery (MCA) occlusion. We now report that intracerebroventricular and intraparenchymal administration of GDNF potently protects the cerebral hemispheres from damage induced by MCA occlusion. In addition, the increase in nitric oxide that accompanies MCA occlusion and subsequent reperfusion is blocked almost completely by GDNF. Thus, this protein may play an important role in the treatment of cerebrovascular occlusive disease.
Local Blockade of Sodium Channels by Tetrodotoxin Ameliorates Tissue Loss and Long-Term Functional Deficits Resulting from Experimental Spinal Cord Injury
Authors: Teng Yang Dong , Wrathall Jean R.
Published: April 2018

Although relatively little is known of the mechanisms involved in secondary axonal loss after spinal cord injury (SCI), recent data fromin vitromodels of white matter (WM) injury have implicated abnormal sodium influx as a key event. We hypothesized that blockade of sodium channels after SCI would reduce WM loss and long-term functional deficits. To test this hypothesis, a sufficient and safe dose (0.15 nmol) of the potent Na+channel blocker tetrodotoxin (TTX) was determined through a dose–response study. We microinjected TTX or vehicle (VEH) into the injury site at 15 min after a standardized contusive SCI in the rat. Behavioral tests were performed 1 d after injury and weekly thereafter. Quantitative histopathology at 8 weeks postinjury showed that TTX treatment significantly reduced tissue loss at the injury site, with greater effect on sparing of WM than gray matter. TTX did not change the pattern of chronic histopathology typical of this SCI model, but restricted its extent, tripled the area of residual WM at the epicenter, and reduced the average length of the lesions. Serotonin immunoreactivity caudal to the epicenter, a marker for descending motor control axons, was nearly threefold that of VEH controls. The increase in WM at the epicenter was significantly correlated with the decrease in functional deficits. The TTX group exhibited a significantly enhanced recovery of coordinated hindlimb functions, more normal hindlimb reflexes, and earlier establishment of a reflex bladder. The results demonstrate that Na+channels play a critical role in WM lossin vivoafter SCI.
Paradoxical Effects of External Modulation of Inhibitory Interneurons
Authors: Tsodyks Misha V. , Skaggs William E. , Sejnowski Terrence J. , McNaughton Bruce L.
Published: April 2018

The neocortex, hippocampus, and several other brain regions contain populations of excitatory principal cells with recurrent connections and strong interactions with local inhibitory interneurons. To improve our understanding of the interactions among these cell types, we modeled the dynamic behavior of this type of network, including external inputs. A surprising finding was that increasing the direct external inhibitory input to the inhibitory interneurons, without directly affecting any other part of the network, can, in some circumstances, cause the interneurons to increase their firing rates. The main prerequisite for this paradoxical response to external input is that the recurrent connections among the excitatory cells are strong enough to make the excitatory network unstable when feedback inhibition is removed. Because this requirement is met in the neocortex and several regions of the hippocampus, these observations have important implications for understanding the responses of interneurons to a variety of pharmacological and electrical manipulations. The analysis can be extended to a scenario with periodically varying external input, where it predicts a systematic relationship between the phase shift and depth of modulation for each interneuron. This prediction was tested by recording from interneurons in the CA1 region of the rat hippocampusin vivo, and the results broadly confirmed the model. These findings have further implications for the function of inhibitory and neuromodulatory circuits, which can be tested experimentally.
Neuropeptide Hierarchies and the Activation of Sequential Motor Behaviors in the Hawkmoth,Manduca sexta
Authors: Gammie Stephen C. , Truman James W.
Published: April 2018

In insects, the shedding of the old cuticle at the end of a molt involves a stereotyped sequence of distinct behaviors. Our studies on the isolated nervous system ofManduca sextashow that the peptides ecdysis-triggering hormone (ETH) and crustacean cardioactive peptide (CCAP) elicit the first two motor behaviors, the pre-ecdysis and ecdysis behaviors, respectively. Exposing isolated abdominal ganglia to ETH resulted in the generation of sustained pre-ecdysis bursts. By contrast, exposing the entire isolated CNS to ETH resulted in the sequential appearance of pre-ecdysis and ecdysis motor outputs. Previous research has shown that ETH activates neurons within the brain that then release eclosion hormone within the CNS. The latter elevates cGMP levels within and increases the excitability of a group of neurons containing CCAP. In our experiments, the ETH-induced onset of ecdysis bursts was always associated with a rise in intracellular cGMP within these CCAP neurons. We also found that CCAP immunoreactivity decreases centrally during normal ecdysis. Isolated, desheathed abdominal ganglia responded to CCAP by generating rhythmical ecdysis bursts. These ecdysis motor bursts persisted as long as CCAP was present and could be reinduced by successive application of the peptide. CCAP exposure also actively terminated pre-ecdysis bursts from the abdominal CNS, even in the continued presence of ETH. Thus, the sequential performance of the two behaviors arises from one modulator activating the first behavior and also initiating the release of the second modulator. The second modulator then turns off the first behavior while activating the second.
An Escalating Dose/Multiple High-Dose Binge Pattern of Amphetamine Administration Results in Differential Changes in the Extracellular Dopamine Response Profiles in Caudate-Putamen and Nucleus Accumbens
Authors: Kuczenski Ronald , Segal David S.
Published: April 2018

Amphetamine (AMPH)-induced psychosis is most frequently associated with a chronic high-dose “binge” or “run” pattern of stimulant abuse, generally preceded by a period of gradually escalating doses of the drug. We showed previously that animals subjected to such a regimen of AMPH administration developed, over multiple daily binges, a unique pattern of behavioral response that included a decrease in stereotypy and a pronounced increase in locomotion. Because of the involvement of mesolimbic and mesostriatal dopamine (DA) pathways in locomotion and stereotypy, respectively, we hypothesized that a persistent shift in the relative magnitude of caudate-putamen (CP) and nucleus accumbens (NAC) DA transmission may contribute to this altered behavioral profile. To test this hypothesis, we examined CP and NAC extracellular DA in response to multiple high-dose AMPH binges. Our results revealed that with multiple binges the CP DA response but not the NAC response developed a profound tolerance/tachyphylaxis to the drug-induced increase in extracellular transmitter. These differential regional response alterations seem to correspond to the shift in the relative expression of stereotypy and locomotion. We hypothesize that changes in DA synthesis, perhaps mediated by regionally specific adaptations in DA autoreceptor function, contribute to the differential extracellular transmitter response profiles, and suggest that these neurochemical changes may have important implications for the mechanisms underlying the addictive and psychotogenic properties of AMPH.
Effects of 4-Aminopyridine on Muscle and Motor Unit Force in Canine Motor Neuron Disease
Authors: Pinter M. J. , Waldeck R. F. , Cope T. C. , Cork L. C.
Published: April 2018

Hereditary Canine Spinal Muscular Atrophy (HCSMA) is an autosomal dominant disorder of motor neurons that shares features with human motor neuron disease. In animals exhibiting the accelerated phenotype (homozygotes), we demonstrated previously that many motor units exhibit functional deficits that likely reflect underlying deficits in neurotrans-mission. The drug 4-aminopyridine (4AP) blocks voltage-dependent potassium conductances and is capable of increasing neurotransmission by overcoming axonal conduction block or by increasing transmitter release. In this study, we determined whether and to what extent 4AP could enhance muscle force production in HCSMA. Systemic 4AP (1–2 mg/kg) increased nerve-evoked whole muscle twitch force and electromyograms (EMG) to a greater extent in older homozygous animals than in similarly aged, symptomless HCSMA animals or in one younger homozygous animal. The possibility that this difference was caused by the presence of failing motor units in the muscles from homozygotes was tested directly by administering 4AP while recording force produced by failing motor units. The results showed that the twitch force and EMG of failing motor units could be significantly increased by 4AP, whereas no effect was observed in a nonfailing motor unit from a symptomless, aged-matched HCSMA animal. The ability of 4AP to increase force in failing units may be related to the extent of failure. Although 4AP increased peak forces during unit tetanic activation, tetanic force failure was not eliminated. These results demonstrate that the force outputs of failing motor units in HCSMA homozygotes can be increased by 4AP. Possible sites of 4AP action are considered.
Neurotoxicity of the 22 kDa Thrombin-Cleavage Fragment of Apolipoprotein E and Related Synthetic Peptides Is Receptor-Mediated
Authors: Tolar Martin , Marques Marcos A. , Harmony Judith A. K. , Crutcher Keith A.
Published: April 2018

Potent neurotoxicity is associated with both apolipoprotein E (apoE)-related synthetic peptides and the 22 kDa N-terminal thrombin-cleavage fragment of apoE. Furthermore, the E4 isoform of the 22 kDa fragment is significantly more toxic than the same fragment derived from the E3 isoform, suggesting the possibility of a direct role of apoE-associated neurotoxicity in the pathophysiology of Alzheimer’s disease. In the present study, the potential role of cell surface receptors in mediating neurotoxicity was assessed by using a variety of agents that should block the heparin-binding and receptor-binding activity of apoE. Effective inhibitors of neurotoxicity of both the apoE peptides and the apoE fragment include heparin, heparan sulfate, sodium chlorate and heparinase, the low-density lipoprotein (LDL) receptor-related protein receptor-associated protein, and a polyclonal anti-LDL receptor-related protein antibody. These results suggest that the neurotoxicity of the 22 kDa thrombin cleavage fragment of apoE and related peptides is receptor-mediated, and that the most likely candidate receptor is a heparan sulfate proteoglycan–LDL receptor-related protein complex.
Characterization of Guanylate Kinase-Associated Protein, a Postsynaptic Density Protein at Excitatory Synapses That Interacts Directly with Postsynaptic Density-95/Synapse-Associated Protein 90
Authors: Naisbitt Scott , Kim Eunjoon , Weinberg Richard J. , Rao Anuradha , Yang Fu-Chia , Craig Ann Marie , Sheng Morgan
Published: April 2018

The structure of central synapses is poorly understood at the molecular level. A recent advance came with the identification of the postsynaptic density-95 (PSD-95)/synapse-associated protein 90 family of proteins as important mediators of the synaptic clustering of certain classes of ion channels. By yeast two-hybrid screening, a novel protein termed guanylate kinase-associated protein (GKAP) has been isolated that binds to the GK-like domain of PSD-95 (Kim et al., 1997). Here we present a detailed characterization of GKAP expression in the rat brain and report the cloning of a novel GKAP splice variant. By Northern blot, GKAP mRNAs (4, 6.5, and 8 kB) are expressed predominantly in the rat brain. Byin situhybridization, GKAP is expressed widely in neurons of cortex and hippocampus and in the Purkinje and granule cells of the cerebellum. On brain immunoblots, two prominent bands of 95 and 130 kDa are detected that correspond to products of short and long N-terminal splice variants of GKAP. Two independent GKAP antibodies label somatodendritic puncta in neocortical and hippocampal neurons in a pattern consistent with synaptic elements. Immunogold electron microscopy reveals GKAP to be predominantly postsynaptic and present at asymmetric synapses and in dendritic spines. The distribution of GKAP immunogold particles is uniform in the lateral plane of the PSD but peaks in the perpendicular axis ∼20 nm from the postsynaptic membrane. In cultured hippocampal neurons GKAP immunoreactive puncta colocalize with the AMPA receptor subunit Glu receptor 1 but not with the GABAAreceptor subunits β2 and β3. Thus GKAP is a widely expressed neuronal protein localized specifically in the PSD of glutamatergic synapses, consistent with its direct interaction with PSD-95 family proteins.
Dopamine Depresses Excitatory and Inhibitory Synaptic Transmission by Distinct Mechanisms in the Nucleus Accumbens
Authors: Nicola Saleem M. , Malenka Robert C.
Published: April 2018

The release of dopamine (DA) in the nucleus accumbens (NAc) is thought to be critical for mediating natural rewards as well as for the reinforcing actions of drugs of abuse. DA and amphetamine depress both excitatory and inhibitory synaptic transmission in the NAc by a presynaptic D1-like DA receptor. However, the mechanisms of depression of excitatory and inhibitory synaptic transmission appear to be different. DA depressed the frequency of spontaneous miniature EPSCs, but the frequency of miniature IPSCs was depressed only when spontaneous release was made dependent on Ca2+influx through voltage-dependent Ca2+channels. Furthermore, the K+channel blocker Ba2+attenuated the effects of DA on evoked IPSPs, but not on EPSPs. Thus, DA appears to depress inhibitory synaptic transmission in the NAc by reducing Ca2+influx into the presynaptic terminal, but depresses excitatory transmission by a distinct mechanism that is independent of the entry of Ca2+.