bluuebunny/crossref_metadata_2025 huggingface dataset:
Elemental composition and water content of rat optic nerve myelinated axons and glial cells: effects of in vitro anoxia and reoxygenation
Authors: LoPachin RM , Stys PK
Published: April 2018

Electron probe x-ray microanalysis was used to measure water content and concentrations (mmol/kg dry weight) of elements (Na, P, S, Cl, K, Ca, and Mg) in myelinated axons and glial cells of rat optic nerve exposed to in vitro anoxia and reoxygenation. In response to anoxia, large, medium, and small diameter fibers exhibited an early (5 min) and progressive loss of Na and K regulation which culminated (60 min) in severe depletion of respective transmembrane gradients. As axoplasmic Na levels increased during anoxic exposure, a parallel rise in Ca content was noted. For all axons, mean water content decreased progressively during the initial 10 min of anoxia and then returned toward normal values as anoxia continued. Analyses of mitochondrial areas revealed a similar pattern of elemental disruption except that Ca concentrations rose more rapidly during anoxia. Following 60 min of postanoxia reoxygenation, the majority of larger fibers displayed little evidence of recovery, whereas a subpopulation of small axons exhibited a trend toward restoration of normal elemental composition. Glial cells and myelin were only modestly affected by anoxia and subsequent reoxygenation. Thus, anoxic injury of CNS axons is associated with characteristic changes in axoplasmic distributions of Na, K, and Ca. The magnitude and temporal patterns of elemental Na and Ca disruption are consistent with reversal of Na(+)-Ca2+ exchange and subsequent Ca entry (Stys et al., 1992). During reoxygenation, elemental deregulation continues for most CNS fibers, although a subpopulation of small axons appears to be capable of recovery.
The mechanisms of generation and propagation of synchronized bursting in developing networks of cortical neurons
Authors: Maeda E , Robinson HP , Kawana A
Published: April 2018

The characteristics and mechanisms of synchronized firing in developing networks of cultured cortical neurons were studied using multisite recording through planar electrode arrays (PEAs). With maturation of the network (from 3 to 40 d after plating), the frequency and propagation velocity of bursts increased markedly (approximately from 0.01 to 0.5 Hz and from 5 to 100 mm/sec, respectively), and the sensitivity to extracellular magnesium concentration (0–10 mM) decreased. The source of spontaneous bursts, estimated from the relative delay of onset of activity between electrodes, varied randomly with each burst. Physical separation of synchronously bursting networks into several parts using an ultraviolet laser, divided synchronous bursting into different frequencies and phases in each part. Focal stimulation through the PEA was effective at multiple sites in eliciting bursts, which propagated over the network from the site of stimulation. Stimulated bursts exhibited both an absolute refractory period and a relative refractory period, in which partially propagating bursts could be elicited. Periodic electrical stimulation (at 1 to 30 sec intervals) produced slower propagation velocities and smaller numbers of spikes per burst at shorter stimulation intervals. These results suggest that the generation and propagation of spontaneous synchronous bursts in cultured cortical neurons is governed by the level of spontaneous presynaptic firing, by the degree of connectivity of the network, and by a distributed balance between excitation and recovery processes.
Multiple presynaptic metabotropic glutamate receptors modulate excitatory and inhibitory synaptic transmission in hippocampal area CA1
Authors: Gereau RW , Conn PJ
Published: April 2018

The metabotropic glutamate receptors (mGluRs) have many important roles in regulation of neuronal excitability and synaptic transmission. In hippocampal area CA1, activation of mGluRs can reduce both excitatory and inhibitory synaptic transmission. The conventional view is that the presynaptic effects are mediated by L-2-amino-4-phosphonobutyric acid (L-AP4)-sensitive, or group III mGluRs (mGluR4, mGluR6, mGluR7, mGluR8). However, some studies suggest that other mGluR subtypes may also be involved in regulation of excitatory and inhibitory synaptic transmission in area CA1. We have found that two pharmacologically distinct presynaptic receptors are involved in the depression of excitatory transmission at the Schaffer collateral--CA1 synapse. Consistent with previous studies, one receptor subtype is an L-AP4- sensitive receptor that is pharmacologically similar to mGluR4 or mGluR7. However, we have found that a second mGluR subtype, which is pharmacologically similar to mGluR1 and mGluR5 (group I mGluRs), can also reduce excitatory synaptic transmission in area CA1. Analysis of effects of agonists of these two receptors on miniature EPSCs and paired-pulse facilitation suggest that both receptors are localized presynaptically. It is also shown that the mGluR that reduces transmission at inhibitory synapses in area CA1 is presynaptically localized, is insensitive to L-AP4, and is sensitive to agonists selective for mGluR1 and mGluR5.
Saccade target selection in frontal eye field of macaque. I. Visual and premovement activation
Authors: Schall JD , Hanes DP , Thompson KG , King DJ
Published: April 2018

We investigated how the brain selects the targets for eye movements, a process in which the outcome of visual processing is converted into guided action. Macaque monkeys were trained to make a saccade to fixate a salient target presented either alone or with multiple distractors during visual search. Neural activity was recorded in the frontal eye field, a cortical area at the interface of visual processing and eye movement production. Neurons discharging after stimulus presentation and before saccade initiation were analyzed. The initial visual response of frontal eye field neurons was modulated by the presence of multiple stimuli and by whether a saccade was going to be produced, but the initial visual response did not discriminate the target of the search array from the distractors. In the latent period before saccade initiation, the activity of most visually responsive cells evolved to signal the location of the target. Target selection occurred through suppression of distractor evoked activity contingent on the location of the target relative to the receptive field. The evolution of a signal specifying the location of the salient target could be dissociated from saccade initiation in some cells and could occur even when fixation was maintained. Neural activity in the frontal eye fields may participate in or be the product of the decision process guiding eye movements.
Recovery of tail-elicited siphon-withdrawal reflex following unilateral axonal injury is associated with ipsi- and contralateral changes in gene expression in Aplysia californica
Authors: Noel F , Frost WN , Tian LM , Colicos MA , Dash PK
Published: April 2018

Behavioral, cellular and molecular changes were examined following axonal injury in the marine mollusc Aplysia californica. Unilateral nerve injury was performed by crushing the pleural-pedal connective and the peripheral pedal nerves innervating one side of the posterior body wall and the tail. The injury procedure severs the axons of the pleural sensory neurons resulting in the blockade of the tail-elicited siphon- withdrawal reflex. Partial reflex recovery is observed within 3 d and reaches 50% of the pretest value by six weeks postinjury. Retrograde staining of injured nerves combined with electrophysiological recordings from siphon motor neurons show that axons can regenerate through the crushed site and reconnect with the tail by three weeks postinjury. Moreover, the behavioral and electrophysiological measurements suggest that the contralateral sensory neurons may contribute to the early recovery of the siphon-withdrawal reflex. The levels of mRNAs coding for actin and calreticulin are elevated while the mRNAs coding for intermediate filament protein, sensorin A, FMRFamide are reduced in the ipsilateral pleural ganglia as detected by Northern blots. In the contralateral pleural ganglia, the levels of mRNAs coding for actin, sensorin A and FMRFamide are elevated. These molecular changes in both the ipsi- and contralateral sides are consistent with the hypothesis that both sides are participating in the behavioral recovery following unilateral axonal injury.
A comparison of the role of dynorphin in the hippocampal mossy fiber pathway in guinea pig and rat
Authors: Salin PA , Weisskopf MG , Nicoll RA
Published: April 2018

Several behavioral studies in rat (Gallagher, 1988) have suggested that opioids in the hippocampus could play an important role in learning and memory. However, in this species, very few reports specifically address the issue of physiological actions of opioids released by the mossy fibers which constitute the principal source of dynorphin and enkephalin in the hippocampus. In the guinea pig high frequency stimulation of mossy fibers causes a transient heterosynaptic inhibition of neighboring mossy fibers (Weisskopf et al., 1993) or perforant path synapses in the dentate (Wagner et al., 1993), which is mediated by the synaptic release of dynorphin that activates presynaptic kappa receptors. We show here that neither exogenous nor endogenous dynorphin affect mossy fiber excitatory postsynaptic potentials in the Sprague-Dawley rat, which is consistent with the finding that kappa receptor binding in the mossy fiber termination zone is dense in the guinea pig and sparse in this rat. More surprisingly, although kappa receptor binding is found in the rat dentate gyrus molecular layer and in the CA3 pyramidal cell layer, dynorphin had no action on perforant path field responses, somatic potassium currents or evoked monosynaptic inhibitory postsynaptic currents in CA3 cells. This lack of action appears to be an exception among rodents as dynorphin significantly inhibited mossy fiber responses in the hamster, mouse, and even another strain of rat, Long-Evans. Unlike the kappa mediated actions, the mu opioid receptor agonist DAMGO inhibited Sprague-Dawley mossy fiber responses, as it does in guinea pig. In contrast to other investigators, however, we found that the opioid receptor antagonist naloxone had no effect on Sprague-Dawley mossy fiber LTP.
Coupling potentials in CA1 neurons during calcium-free-induced field burst activity
Authors: Valiante TA , Perez Velazquez JL , Jahromi SS , Carlen PL
Published: April 2018

Small amplitude depolarizations (fast prepotentials, spikelets) recorded in mammalian neurons are thought to represent either dendritic action potentials or presynaptic action potentials attenuated by gap junctions. We have used whole-cell recordings in an in vitro calcium- free model of epilepsy to record spikelets from CA1 neurons of the rat hippocampus. It was found that spikelet appearance was closely correlated with the occurrence of dye coupling between pyramidal neurons, indicating that both phenomena share a common substrate. Spikelets were characterized according to waveform (amplitude and shape) and temporal occurrence. Spikelet amplitudes were found to be invariant with neuronal membrane potential, and their pattern of occurrence was indistinguishable from patterns of action potential firing in these cells. Voltage and current recordings revealed a spikelet waveform that was usually biphasic, comprised of a rapid depolarization followed by a slower hyperpolarization. Numerical differentiation of spike bursts resulted in waveforms similar to recorded spikelet sequences, while numerical integration of spikelets yielded waveforms that were indistinguishable from action potentials. Modification of spikelet waveforms by the potassium channel blocker tetraethylammonium chloride suggests that spikelets may arise from both resistive and capacitive transmission of presynaptic action potentials. Intracellular alkalinization and acidification brought about by perfusion with NH4Cl caused changes in spikelet frequency, consistent with reported alterations of field burst activity in this model of epilepsy. These results suggest that spikelets result from gap junctional communication, and may be important determinants of neuronal activity during seizure-like activity.
Excitotoxic degeneration is initiated at non-random sites in cultured rat cerebellar neurons
Authors: Bindokas VP , Miller RJ
Published: April 2018

Prolonged stimulation of cultured cerebellar neurons by kainic acid (KA) leads to death of neurons first evident from the swelling of soma and neurites. Stimulation is accompanied by increases in [Ca2+]i and [Na+]i as monitored using digital imaging microfluorimetry. “Blebs” tended to form on neurites with the highest increases in [Ca2+]i. Points of Ca2+ entry into neurites via glutamate-receptor-gated channels predicted where approximately 80% of blebs would form tens of minutes later. These sites were close to neurite intersections where there was a high likelihood of synaptic contacts and were enriched in mitochondria as revealed by rhodamine 123 staining. Ca2+, but not Na+ entry, produced a loss of mitochondrial potential. Prolonged KA, but not 50K, applications could fully dissipate the neuronal Na+ gradient. Recovery of resting [Na+]i was delayed by Ca2+ loading. We propose that blebs form at certain synaptic regions due to localized ionic fluxes and local Ca2+ overloading. Increased [Ca2+]i may hamper restoration of normal [Na+]i permitting local osmotic swelling as well as activation of Ca(2+)-dependent enzymes and other processes. Na+ may slow, block, or reverse Na/Ca exchange and enhance swelling. These conditions could not be reproduced by global changes in ion concentrations produced by Ca2+ or Na+ ionophores. The earliest stages of excitotoxicity thus appear to be manifestations of localized disruptions of ionic homeostasis mediated by Ca2+ overload and Na+ influx.
Development and regulation of dendritic stratification in retinal ganglion cells by glutamate-mediated afferent activity
Authors: Bodnarenko SR , Jeyarasasingam G , Chalupa LM
Published: April 2018

In the mature retina, the dendrites of retinal ganglion cells (RGCs) are segregated into either ON or OFF sublaminae of the inner plexiform layer (IPL), but early in development the dendritic processes of these cells are multistratified, ramifying throughout the IPL. We examined the time course of dendritic stratification in developing beta cells, the largest class of ganglion cells in the cat retina, by retrograde labeling of fixed tissue with Dil. Dendritic stratification begins in the central and peripheral retina by embryonic day 50, about 2 weeks before birth and is not fully completed until 5 months postnatally. A clear central-to-peripheral gradient in the incidence of stratified beta cells first becomes evident shortly after birth. This stratification process was effectively halted by short-term intraocular injections (4–11 d) of the glutamate analog 2-amino-4-phosphonobutyrate (APB), which hyperpolarizes rod bipolar cells and ON cone bipolar cells, thereby preventing the release of glutamate by these interneurons. APB treatment did not alter the somal sizes or the tangential extent of the dendrites of developing beta cells, nor did it cause abnormal loss of these neurons. The organization of the inner nuclear layer, containing the APB-sensitive bipolar cells, was also not compromised by such injections. When APB treatment was discontinued there was a rapid resumption of dendritic stratification resulting in a normal incidence of stratified RGCs. Thus, short-term APB treatment causes a delay rather than a permanent arrest of the stratification process.(ABSTRACT TRUNCATED AT 250 WORDS)
Differential expression of AMPA receptor subunits in NOS-positive neurons of cortex, striatum, and hippocampus
Authors: Catania MV , Tolle TR , Monyer H
Published: April 2018

AMPA receptor (AMPAR) subunits expression was studied in nitric oxide synthase (NOS)-positive neurons of the adult rat cortex, striatum, and hippocampus, by a double-labeling approach, combining nonradioactive in situ hybridization and immunocytochemistry. The majority of cortical and hippocampal NOS-immunopositive neurons were characterized by a predominant expression of GluR-A and -D mRNA and low or undetectable expression of GluR-B and -C mRNA. In the striatum, the expression profile of AMPAR subunits in NOS-positive neurons differed from that in the other two regions. This is reflected in the overall low expression of all AMPA receptor subunits and the paucity of GluR-D subunit expression that contrasts with the high expression of this subunit in NOS-positive cells in the hippocampus. Double-labeling experiments revealed a substantial correspondence between mRNA and protein levels of AMPAR subunits. Further evidence for the regional diversity of NOS- positive neurons is derived from the expression analysis of glutamate decarboxylase (GAD)-65 and -67 mRNAs. NOS-positive neurons expressed high levels of GAD-65, but not -67 in the cortex, high levels of both forms in the hippocampus, and low or undetectable levels of both mRNAs in the striatum. Despite of these differences, NOS-positive neurons share the common feature of low GluR-B subunit expression, suggesting the presence of AMPAR channels with high Ca2+ permeability, regardless of the regional location. The relative resistance of NOS-positive interneurons in neurodegenerative diseases suggests that glutamate receptor-mediated Ca2+ influx alone does not suffice to explain neuronal vulnerability, and additional factors have thus to be considered.
PDGFs protect hippocampal neurons against energy deprivation and oxidative injury: evidence for induction of antioxidant pathways
Authors: Cheng B , Mattson MP
Published: April 2018

Platelet-derived growth factors (PDGFs) and PDGF receptors are expressed in brain, where their functions are largely unknown. We tested the hypothesis that PDGFs play a role in promoting the survival of neurons exposed to metabolic and oxidative insults. Exposure of rat and mouse hippocampal cell cultures to glucose-deficient medium or the hydroxyl radical-promoting agent FeSO4 resulted in progressive neuronal loss. Pretreatment of cultures with PDGF-AA or PDGF-BB resulted in highly significant attenuation of glucose deprivation- and FeSO4- induced neuronal degeneration. In each injury paradigm the neuroprotective actions of the PDGFs were concentration dependent (3– 100 ng/ml). In the case of glucose deprivation, significant protection was seen when cells were exposed to PDGFs prior to, or up to 8 hr following, the onset of glucose deprivation. Pretreatment with PDGFs was required for protection against FeSO4-induced oxidative injury. Western blot and immunocytochemical analyses demonstrated that cultured embryonic hippocampal neurons expressed both PDGF alpha- and beta- receptors. PDGFs induced tyrosine phosphorylation of several proteins including a band at 180 kDa, the molecular weight of PDGF receptors. Induction of peroxide accumulation in neurons by FeSO4 was attenuated in cultures pretreated with PDGFs, suggesting that PDGFs enhanced cellular antioxidant mechanisms. Measurements of anti-oxidant enzyme activities in control and PDGF-treated cultures showed that both PDGF- AA and PDGF-BB increased both catalase and glutathione peroxidase activities, and PDGF-AA also increased superoxide dismutase activities. These findings suggest that PDGFs, which are widely expressed in brain and induced in response to injury, may play roles in protecting neurons against metabolic and oxidative insults.
Dynamics of central nervous 5-HT1A-receptors under psychosocial stress
Authors: Flugge G
Published: April 2018

It is well established that stress leads to changes in the serotonergic system. In order to gain a better understanding of the effects of recurrent stressful experiences on the serotonergic system, changes in the 5-HT1A-receptor system resulting from different periods of psychosocial stress (PSS) were analyzed in the present study. Male tree shrews (Tupaia belangeri) were submitted to subordination stress for 2, 10, 21, and 28 d. 5-HT1A-receptor binding was quantified by in vitro receptor autoradiography using the agonist 3H-8-OH-DPAT (3H-8-hydroxy-2- (di-n-propylamino)tetralin. PSS caused a downregulation of 3H-8-OH-DPAT binding sites in cortical areas and in the hippocampus. After 10, 21, and 28 d of PSS, the number of binding sites was reduced in layers V and VI of the posterior cingulate cortex (by 34%). After 28 d of PSS, the number of binding sites was reduced in the parietal cortex (by 18%), in the prefrontal cortex (by 16%), in the regio retrobulbaris (by 8%), and in region CA1 of the hippocampus (by 11%). In the raphe nuclei, no PSS-induced downregulation of 5-HT1A-receptors occurred. A transient increase in 3H-8-OH-DPAT binding was observed in the claustrum after 2 d of PSS (by 15%). There were also transient decreases in affinities for the radioligand probably representing receptor desensitization, for example, in the dorsal raphe nucleus after 28 d of PSS. In conclusion, the dynamic 5-HT1A-receptor changes occurring during PSS include downregulation and transient desensitization of receptors. They reflect regulatory mechanisms which probably lead to destabilization of the serotonergic system during prolonged PSS.
Basic fibroblast growth factor increases division and delays differentiation of dopamine precursors in vitro
Authors: Bouvier MM , Mytilineou C
Published: April 2018

Growth factors have been shown to be involved in the regulation of division and differentiation of neuroepithelial cells. In the present study we examined the ability of various factors to influence the development of dopamine precursors. Primary neuronal cultures were prepared from the embryonic day 12 (E12) rat ventral mesencephalon, a time and place which coincides with the beginning of the birth of the dopamine neurons of the substantia nigra pars compacta. At low plating density in serum-free medium, the dopamine precursors divide for approximately 1 d in vitro. We report here that basic fibroblast growth factor (bFGF) can expand the period of dopamine precursor division at least until day 8 in culture, which is well beyond the normal division of these cells. This increase in cell division was accompanied by a delay in differentiation as compared to untreated control cultures. Upon differentiation, the high-affinity dopamine uptake values in bFGF- treated cultures were 20 times maximal control values. Mature dopamine neurons appeared at the same time as astrocytes, which may be playing a role in inducing dopamine neuron differentiation. IGF-I, GDNF, and EGF were unable to mimic the effect of bFGF on division and differentiation of dopamine precursors. Expanding in vitro the number of dopamine precursors provides tissue that may be suitable for transplantation in patients with Parkinson's disease.
Intraneuronal delivery of protein kinase C pseudosubstrate leads to growth cone collapse
Authors: Theodore L , Derossi D , Chassaing G , Llirbat B , Kubes M , Jordan P , Chneiweiss H , Godement P , Prochiantz A
Published: April 2018

Axonal navigation during development requires that cues present in the extracellular environment be capable of modifying the structure of the cone in a dynamic way. Protein kinase C (PKC) has long been suspected to be one of the multiple molecular relays present in the terminal structure of the developing axon and involved in the transduction of extracellular signals. The latter proposal is, however, based on the use of drugs or of protocols leading to pleiotropic and often nonspecific effects. In the present study, we have taken advantage of the discovery of a peptide capable of translocating across biological membranes and to accumulate in the cytoplasm and nucleus of cells in culture, to internalize a highly specific peptidic inhibitor of PKC. We demonstrate that linking the two peptides (vector and PKC inhibitor) allows the internalization of the latter in live cells, specifically inhibits PKC and provokes a rapid modification of growth cone morphology. This set of data thus establishes that a peptidic inhibitor of PKC activity, once internalized, provokes a change in growth cone morphology, reminiscent of the collapse phenotype. In addition, the present study describes a new efficient and harmless way to introduce pharmacologically active substances in neural cells in culture.
Presynaptic glutamate levels in tonic and phasic motor axons correlate with properties of synaptic release
Authors: Shupliakov O , Atwood HL , Ottersen OP , Storm-Mathisen J , Brodin L
Published: April 2018

Synaptic glutamate release involves the accumulation of cytoplasmic glutamate in synaptic vesicles, whereafter it is released by triggered exocytosis. As glutamatergic terminals are known to be functionally diverse it was of interest to examine whether the presynaptic glutamate supply differs between individual axon terminals with distinct release properties. The glutamatergic terminals in the crustacean neuromuscular system system comprise a “phasic” type which shows fatigue of release during repetitive stimulation, and a “tonic” type which can maintain transmission for long periods. Quantitative immunogold analysis showed that the axons in a tonic nerve innervating slow muscles in the abdomen contained two times higher levels of glutamate labeling over axoplasmic matrix and over mitochondria, as compared to the corresponding elements in a phasic nerve. Similar results were obtained when adjacent phasic and tonic axons in a mixed nerve innervating leg muscles were compared. In the terminal regions of tonic and phasic axons the glutamate labeling differed correspondingly over axoplasmic matrix and mitochondria, while the synaptic vesicles showed a similar strong accumulation of labeling in both types of terminal. The level of labeling for glutamine, a glutamate precursor, was closely similar in phasic and tonic axons. The axoplasmic glutamate concentration was estimated to be in the low millimolar range, through comparison with coprocessed conjugates with known glutamate concentration. These results show that fatigue-resistant tonic axons and terminals contain higher levels of glutamate than fatiguable phasic axons, presumably representing an adaptation to the markedly different impulse activities in the two types of neuron. The axonal glutamate concentrations are in the range of the Km value for vesicular glutamate transport. Thus in tonic axons the high glutamate level appears to promote an efficient refilling of synaptic vesicles during sustained release, while in phasic axons the refilling should be slower which is compatible with an infrequent release.
Cyclic-GMP enhances light-induced excitation and induces membrane currents in Drosophila retinal photoreceptors
Authors: Bacigalupo J , Bautista DM , Brink DL , Hetzer JF , O'Day PM
Published: April 2018

Phototransduction in the Drosophila retina appears to require the phosphoinositide signaling cascade following receptor/G-protein activation. Subsequent opening of membrane cationic channels causes excitation. The biochemical events underlying channel opening and regulation of sensitivity remain largely unknown. Evidence is mounting that phototransduction in Drosophila and other invertebrate species may additionally involve the second messenger, cyclic-GMP (cGMP). We report that exogenous cGMP influenced Drosophila retinal phototransduction in two ways. In whole cell tight-seal voltage-clamp experiments, membrane permeant cGMP analog, 8-bromo-cyclic-GMP (8-Br-cGMP), induced membrane currents and dramatically enhanced light-induced currents. The currents induced by 8-Br-cGMP possessed reversal potentials similar to those induced by light. The magnitudes of cGMP-induced currents exhibited marked dependence on intensity of background illumination. Potential direct or modulatory roles of cGMP in Drosophila phototransduction are discussed.
Differential processing of semicircular canal signals in the vestibulo- ocular reflex
Authors: Angelaki DE , Hess BJ , Suzuki J
Published: April 2018

Selective semicircular canal inactivation and three-dimensional eye movement recordings have been used to investigate the spatial organization of vestibular signals in the vestibulo-ocular reflex (VOR) of rhesus monkeys. In animals with one pair of semicircular canals inactivated, afferent activity no longer codes all spatial components of head angular velocity. if it were the activation pattern of semicircular canal afferents alone that determines VOR slow phase eye velocity, the head velocity components along the sensitivity vectors of the remaining intact semicircular canals would determine the orientation of slow phase eye velocity. Thus, angular head velocity and slow phase eye velocity would not necessarily always align. Alternatively, if vestibulo-ocular signals coded absolute angular head motion in space based on both semicircular canal and otolith afferent information, one might expect a spatial transformation of the encoded head angular velocity signals such that slow phase eye velocity and angular head velocity continue to spatially align. Examination of the VOR at different frequencies between 0.01 Hz and 1 Hz revealed a frequency-specific spatial organization of vestibulo-ocular signals. Mid and high frequency vestibulo-ocular responses were determined exclusively by the orientation of the sensitivity vectors of the remaining intact semicircular canals. In contrasts, low frequency vestibulo-ocular responses were largely determined by the orientation of the head relative to gravity. These low frequency responses after selective semicircular canal inactivation could be predicted and simulated by a simple model where semicircular canal signals are spatially transformed from a head-fixed to a space-fixed (inertial) representation of angular head velocity. These findings suggest that low frequency vestibulo-ocular responses are dominated by inertial vestibular signals that detect absolute head motion in space based on both semicircular canal and otolith afferent information. Inertial vestibular signals are likely to contribute to head control and motor coordination of gaze, head and body posture.
Impaired peripheral nerve regeneration in a mutant strain of mice (Enr) with a Schwann cell defect
Authors: Rath EM , Kelly D , Bouldin TW , Popko B
Published: April 2018

Schwann cell-axon interactions in the development, maintenance, and regeneration of the normal peripheral nervous system are complex. A previously described transgene-induced insertional mutation (BPFD#36), now referred to as Enervated (Enr), results in disrupted Schwann cell- axon interactions. In this report, after a crush or transection injury to Enr peripheral nerves, we demonstrate impaired nerve regeneration. There are fewer myelinated fibers per mm2 and thinner myelin sheaths surrounding regenerating axons in the nerves of homozygous mutant mice compared to wild type mice at 28 d after crush injury to the sciatic nerve. Abnormal Schwann cell-axon interactions remain in Enr/Enr animals as evidenced by the relatively frequent ultrastructural finding of unmyelinated large diameter axons in the regenerating nerves. Additionally, nerve graft experiments indicate that the impairment in regeneration is due to a Schwann cell defect. Morphologic and morphometric findings in conjunction with molecular analysis of regenerating nerves suggest that the Enr defect causes a disruption in the ability of “early ” Schwann cells to differentiate to a more mature phenotype. In mutant homozygous and wild type nerves at 7 d after crush injury there are similar levels of mRNA for the low-affinity nerve growth factor receptor, but in the mutant homozygous regenerating nerves there is 11-fold less mRNA for glial fibrillary acidic protein, a more mature phenotypic marker of Schwann cells. This Schwann cell differentiation defect likely accounts for both the peripheral neuropathy and impaired nerve regeneration observed in Enr mice.
Early patterns of migration, morphogenesis, and intermediate filament expression of subventricular zone cells in the postnatal rat forebrain
Authors: Zerlin M , Levison SW , Goldman JE
Published: April 2018

Recent studies using retroviral labeling of subventricular zone (SVZ) progenitors in vivo in neonatal rats have directly demonstrated the generation of both astrocytes and oligodendrocytes from these progenitors. In the present study, we used a recombinant retroviral vector encoding beta-galactosidase, and analyzed brains within the first week after retroviral injection to trace the early routes that SVZ cells take as they migrate into white matter and cortex and characterized the early morphological and antigenic changes that accompanied their differentiation. SVZ cells follow specifically definable migratory routes as they colonize the cortex and subcortical white matter. Glial progenitors do not populate the cortex in a systematic, laminar fashion, as do neuroblasts. The abundance of labeled progenitors in radial arrangements and the close apposition of many immature cells to vimentin+ radial glial processes, suggest that glial progenitors migrate along radial glia. Labeled SVZ cells, which displayed a simple, unipolar or bipolar morphology, lacked detectable vimentin and nestin intermediate filaments. Similarly, beta- galactosidase-positive cells in white matter lacked these filaments. In contrast, labeled, multipolar cells in the cortex, and a few of the immature-appearing cortical cells expressed nestin and vimentin. At these early time points, GFAP was not detected in beta-galactosidase- labeled cells. Multipolar cells in cortex frequently displayed processes extending toward and contacting blood vessels. These observations suggest that the expression of nestin and vimentin occurs after progenitors emigrate from the SVZ and that filament expression and contact with blood vessels represent an early stage of astrocyte differentiation.
Differential susceptibility of human CNS-derived cell populations to TNF-dependent and independent immune-mediated injury
Authors: D'Souza S , Alinauskas K , McCrea E , Goodyer C , Antel JP
Published: April 2018

We examined whether oligodendrocytes, neurons, and astroglia derived from the human central nervous system differ in susceptibility to injury mediated by tumor necrosis factor (TNF)-alpha and by activated CD4+ T cells acting via a TNF-independent mechanism. Injury was assessed either as cell membrane-directed (lysis), measured by 51chromium (Cr) or lactate dehydrogenase (LDH) release, or nucleus- directed (apoptosis), measured by morphologic features based on propidium iodide (PI) staining and by DNA fragmentation measured by a terminal transferase (TdT)-mediated dUTP biotin nick end labeling technique (TUNEL). TNF did not induce 51Cr or LDH release in any cell targets, but did induce nuclear (66 +/- 2% of cells) and DNA (68 +/- 2% of cells) fragmentation selectively in the oligodendrocytes over 96 hr. At this time, there was no significant loss of oligodendrocyte cell number. Nuclear injury could be induced in neurons by serum deprivation and in malignant astrocytes by the combination of TNF and low serum. CD4+ T cells activated with phytohemagglutin (pha) or anti-CD3 plus interleukin-2 induced significant 51Cr and LDH release in all target cells tested; only pha-activated CD4+ T-cell cocultures showed reduced target cell numbers. Significant nuclear fragmentation was observed only for glioma cells (22 +/- 1% of cells). Differences in susceptibility to different immune effector mechanisms and in the nature of the injury response to the same effector mediator among human CNS-derived neural cells will need to be considered in design of therapeutic strategies aimed at protecting or limiting target cell injury consequent to disease or trauma.
Hippocampal lesions disrupt decrements but not increments in conditioned stimulus processing
Authors: Han JS , Gallagher M , Holland P
Published: April 2018

Studies recording hippocampal neural activity show widespread registration of events during associative learning. Recent computational models of hippocampal function have stressed its role in attentional processes specified by well-developed modern theories of associative learning. These modeling efforts are largely aimed at accounting for the behavioral outcomes of damage to the hippocampal system in terms of underlying changes in information processing. Two experiments examined the effects of neurotoxic lesions of the hippocampus on changes in attentional processing of a conditioned stimulus (CS) in appetitive Pavlovian conditioning in rats. In Experiment 1, hippocampal lesions eliminated the reduction in associability of a CS usually produced by preexposure to that cue (latent inhibition). In Experiment 2, hippocampal lesions interfered with the loss in associability of a CS normally produced when that CS consistently predicts another event. In contrast, in Experiment 2, hippocampal lesions did not prevent the enhancement of CS associability when a previously consistent predictive relation between two events was made inconsistent. This research supports previous claims that the hippocampus is involved in regulating the processing of CSs in Pavlovian conditioning, and provides new evidence for a hippocampal role in decremental, but not incremental, changes in attention.
Interleukin-1-induced long-lasting changes in hypothalamic corticotropin-releasing hormone (CRH)--neurons and hyperresponsiveness of the hypothalamus-pituitary-adrenal axis
Authors: Schmidt ED , Janszen AW , Wouterlood FG , Tilders FJ
Published: April 2018

Hypothalamic CRH neurons that control ACTH secretion from the pituitary gland have secretory terminals in the external zone of the median eminence (ZEME). These neurons can coproduce vasopressin (AVP), a neuropeptide that potentiates the ACTH releasing effects of CRH. Recently, we found increased AVP production in adult rats weeks after single exposure to a stressor, which may play a role in event-induced stress disorders. Here, we describe the long-term changes in the HPA axis of adult male rats following a single exposure to a stressor, the cytokine interleukin-1 beta (IL-1 beta). The effects on storage and release of AVP and CRH were established by quantitative immunocytochemistry, the effects on ACTH and corticosterone responses by radioimmunoassay. Single administration of IL-1 beta (5 micrograms/kg i.p.) induces a delayed (at least 4 d) and a long-lasting (at least 3 weeks) increase of vasopressin (AVP) stores in CRH terminals of the ZEME without affecting the CRH stores, and a marked increase of the fraction of CRH terminals that costore AVP. Eleven days after IL-1 beta administration, a second IL-1 beta challenge causes a marked depletion of the AVP stores in the ZEME within 2 hr, which is not seen in rats treated with vehicle 11 d earlier. This is accompanied by twofold higher ACTH and corticosterone responses, as compared to those in vehicle pretreated rats. IL-1 beta-pretreated rats also showed increased ACTH and corticosterone responses to electric footshocks. We conclude that transient activation of the HPA axis by a single administration of IL-1 beta induces a delayed and long-lasting hyperproduction, hyperstorage, and hypersecretion of AVP from hypothalamic CRH neurons that results in hyperresponsiveness of the HPA axis to subsequent stimuli.
Cholinergic basal forebrain neurons project to cortical microvessels in the rat: electron microscopic study with anterogradely transported Phaseolus vulgaris leucoagglutinin and choline acetyltransferase immunocytochemistry
Authors: Vaucher E , Hamel E
Published: April 2018

Physiological evidence indicates that central cholinergic pathways are involved in the regulation of cerebral cortical blood flow. We investigated the possible contribution of basal forebrain cholinergic neurons from the substantia innominata (SI) to the innervation of cortical microvessels. Basalo-cortical perivascular nerve terminals were detected by light and electron microscopic immunocytochemistry of anterogradely transported Phaseolus vulgaris leucoagglutinin (PHA-L) following its injection in the SI, and were compared to cortical perivascular cholinergic (immunoreactive for choline acetyltransferase (ChAT)) terminals. The basal forebrain origin of cholinergic terminals was evaluated after unilateral ibotenic acid lesion of the SI. PHA-L varicose fibers reached and surrounded microvessels in all cortical subdivisions examined. When studied at the ultrastructural level in the fronto-parietal and perirhinal cortices, perivascular PHA-L nerve terminals were located significantly closer to microvessels in the fronto-parietal than in the perirhinal cortex (respective average distance of 0.98 +/- 0.09 and 1.34 +/- 0.07 micron; p < 0.01). PHA-L and ChAT terminals in the fronto-parietal cortex compared very well in their perivascular distribution but not in the perirhinal cortex. In both cortices, perivascular PHA-L terminals were similar in size to, but engaged more frequently in synaptic contacts than their ChAT counterparts. Following SI lesion, the density of cortical ChAT terminals including those reaching microvessels decreased significantly (56 and 63%, respectively, p < 0.005) in the fronto-parietal cortex, while the cortical and perivascular denervations were much less pronounced (26%, not significant and 35%, p < 0.05, respectively) in the perirhinal cortex. These results indicate that basal forebrain neurons project preferentially to fronto-parietal cortical microvessels and further show that a significant proportion of these projections are cholinergic. In addition, the difference in distribution and/or synaptic incidence between perivascular PHA-L and ChAT terminals suggested that noncholinergic SI neurons also contribute to these neurovascular associations, and more so in the perirhinal cortex, as further indicated by the lesion studies. Such finding corroborates recent physiological evidence for a functional innervation of the cortical microvascular bed by SI neurons, a role that might be relevant to the overall pathology of Alzheimer's dementia.
Extracellular dopamine in the medial preoptic area: implications for sexual motivation and hormonal control of copulation
Authors: Hull EM , Du J , Lorrain DS , Matuszewich L
Published: April 2018

Dopamine (DA) activity in the medial preoptic area (MPOA) contributes to the control of male rat sexual behavior. We tested (1) whether extracellular DA increases during precopulatory exposure to an estrous female and during copulation, (2) whether exposure to another male increases extracellular DA, (3) whether motor activity during copulation accounts for increased DA levels, and (4) whether concurrent or recent testosterone influences DA levels or copulation in castrates. Extracellular DA and its metabolites in male rats' MPOA were measured using microdialysis. DA level increased during precopulatory exposure to the female in all animals that subsequently copulated; this included all intact animals, all testosterone-treated castrates, and 9 of 14 1- week castrates treated with oil vehicle. DA levels did not increase in any animal that subsequently failed to copulate, including the remaining 1-week, and all 2-week, vehicle-treated castrates. When the barrier was removed and the animals were allowed to copulate, levels of DA and its metabolites continued to rise in intact males and in castrates that copulated. The DA response to the estrous female could not be attributed to nonsexual social stimuli, since exposure to another male was ineffective. The DA response to copulation could not be attributed primarily to motor activity, since animals running voluntarily in a running wheel did not show significantly increased DA. These and previous data suggest that DA released in the MPOA in response to an estrous female may contribute to sexual motivation and copulatory proficiency. Testosterone may promote copulation in part through permissive actions on dopamine release.
Attention and target selection for smooth pursuit eye movements
Authors: Ferrera VP , Lisberger SG
Published: April 2018

Two rhesus monkeys were trained to track a small moving target in the presence of a moving distractor. The target and distractor were distinguished by their color. Smooth pursuit eye movements were quantified in terms of the latency of the eye movement and the open- loop eye acceleration profile. Smooth pursuit latencies for single targets were on the order of 100 msec. When the target was paired with a distractor moving in the same direction as the target, pursuit latencies decreased to roughly 85 msec. When the target was paired with a distractor moving in the opposite direction, pursuit latencies increased to roughly 150 msec. The motion of the distractor had no significant effect on the eye acceleration profile. Experiments were performed to dissociate visual search for the target from pursuit initiation by providing a spatial cue rather than the color cue. These experiments showed that visual search necessarily preceded pursuit initiation only when the distractor moved in the opposite direction relative to the target. In this case, visual search contributed about 25 msec to the overall latency of pursuit. Control experiments showed that the monkey need not attend to the distractor in order for it to influence the latency of pursuit. A network model was developed in which units that represent the motions of the target and distractor compete against one another. Attention serves to bias the outcome of this competition toward the direction of the selected target. The performance of this network exhibits a striking parallel to the effect of the distractor on smooth pursuit latency.
Protein kinase C involvement in homologous desensitization of delta- opioid receptor coupled to Gi1-phospholipase C activation in Xenopus oocytes
Authors: Ueda H , Miyamae T , Hayashi C , Watanabe S , Fukushima N , Sasaki Y , Iwamura T , Misu Y
Published: April 2018

We have developed the coexpression system of both delta-opioid receptor (DOR1) and M2-muscarinic receptor (M2) which mediate agonist-evoked currents due to common post-receptor mechanisms including Gi1 and phospholipase C (PLC) activation in Xenopus oocytes reconstituted with Gi1 alpha. The DOR1-currents by 100 nM D-Ser2-leu-enkephalin-Thr6 (DSLET) were selectively desensitized by 10 nM phorbol 12-myristate 13- acetate (PMA). The PMA-desensitization of DSLET-currents was abolished in the presence of calphostin C, a protein kinase C inhibitor, or reversed by an intracellular injection of calcineurin, a protein phosphatase 2B. When a higher concentration (3 microM) of DSLET was used, DSLET-currents were rapidly desensitized by repeated challenges of DSLET itself. However, repeated challenges of 10 microM ACh caused no influence on such DSLET- or M2-currents. The desensitization of DSLET-currents was selectively reversed by protein kinase C inhibitors. Similar results were also obtained with various delta-opioid agonists. These results suggest that protein kinase Cis involved in the homologous desensitization of delta-opioid receptors.