bluuebunny/crossref_metadata_2025 huggingface dataset:
NG2 Is a Major Chondroitin Sulfate Proteoglycan Produced after Spinal Cord Injury and Is Expressed by Macrophages and Oligodendrocyte Progenitors
Authors: Jones Leonard L. , Yamaguchi Yu , Stallcup William B. , Tuszynski Mark H.
Published: April 2018

Several extracellular matrix (ECM) molecules have been identified as potent inhibitors of neurite outgrowthin vitroand are believed to limit axonal growth after CNS injury. Recent studies have shown that different members of the chondroitin sulfate proteoglycan (CSPG) class of putatively inhibitory ECM molecules are expressed after a number of CNS injuries. The purpose of this study was to evaluate the relative amounts of individual CSPGs expressed after spinal cord injury (SCI) and identify their cells of origin. Evaluation of total soluble CSPGs 2 weeks after dorsal column lesion in the rat demonstrated that NG2 is highly upregulated and is a major CSPG species. Immunocytochemical analysis further demonstrated that NG2 expression is upregulated within 24 hr of injury, peaks at 1 week, and remains elevated for at least an additional 7 weeks. NG2 expression results from a multicellular response to injury, including both reactive macrophages and oligodendrocyte progenitors; astrocytes were not identified as a major source of NG2. Immunocytochemical analysis of other CSPG family members 7 d after injury showed moderate upregulation of versican, brevican, and neurocan, and downregulation of phosphacan. Axonal tracing experiments demonstrated dense NG2 labeling adjacent to the forward processes of transected corticospinal tract axons in a spatial profile that could restrict axonal growth. Thus, NG2 is a major component of this putatively inhibitory class of ECM molecules expressed at sites of SCI and may restrict axonal regeneration.
Long-Term Consequences of Switching Handedness: A Positron Emission Tomography Study on Handwriting in “Converted” Left-Handers
Authors: Siebner Hartwig R. , Limmer Claus , Peinemann Alexander , Drzezga Alexander , Bloem Bastiaan R. , Schwaiger Markus , Conrad Bastian
Published: April 2018

Until some decades ago, left-handed children who attended German schools were forced to learn to write with their right hand. To explore the long-term consequences of switching handedness, we studied the functional neuroanatomy of handwriting in 11 adult “converted” left-handers and 11 age-matched right-handers. All participants had used exclusively their right hand for writing since early childhood. Using [15O]H2O positron emission tomography, changes in normalized regional cerebral blood flow (rCBF) were assessed while participants repetitively wrote a stereotyped word with their right hand. The kinematics of handwriting did not differ between converted left-handers and right-handers. In innate right-handers, handwriting caused a preponderant left-hemispheric activation of parietal and premotor association areas. In contrast, converted left-handers demonstrated a more bilateral activation pattern with distinct activation foci in the right lateral premotor, parietal, and temporal cortex. Moreover, foci in the right rostral supplementary motor area and the right inferior parietal lobule demonstrated a positive linear relationship between the degree of “left-handedness” and normalized rCBF during right-hand writing. Functional activity in the primary sensorimotor cortex was not affected by handedness. Our findings provide evidence for persisting differences in the functional neuroanatomy of handwriting between right-handers and converted left-handers, despite decades of right-hand writing. Right-hemispheric activation in converted left-handers may reflect suppression of unwanted left-hand movements. Alternatively, this activity may represent persistent left-handedness and, as such, demonstrate a hemispheric asymmetry of hand movement representations in cortical motor association areas in relation to the direction and degree of handedness.
Development of Response Timing and Direction Selectivity in Cat Visual Thalamus and Cortex
Authors: Saul Alan B. , Feidler Jordan C.
Published: April 2018

Single-unit recordings were made in the dorsal lateral geniculate nucleus (LGN) and visual cortex of kittens that were 4–13 weeks of age. Responses to visual stimuli were analyzed to determine the relationship between two related facets of the behaviors of the cells: direction selectivity (DS) and timing. DS depends on timing differences within the receptive field. Cortical DS was present at all ages, but its temporal frequency tuning changed. In kittens, DS was more common at high (∼4 Hz) than low (∼1 Hz) temporal frequencies. This is in contrast to adults, in which DS is tuned to low frequencies, more common at 1 Hz than at 4 Hz (Saul and Humphrey, 1992a). In adult cats, the LGN provides the cortex with a wide range of timings that are also observable in cortical receptive fields (Saul and Humphrey, 1990,1992b; Alonso et al., 2001). In kittens, LGN and cortical timing were immature. Most cells showed long-latency sustained responses. At low temporal frequencies, the variance in timing was small, but at higher frequencies, all timings were well represented. The timing data thus matched the temporal frequency tuning of DS. Kittens show DS at high temporal frequencies because of the abundance of inputs with different timing at high frequencies. As cells in the LGN mature, more low-frequency timing differences become available to the cortex, allowing DS at low frequencies to become possible for more cortical cells.
Transplantation of Olfactory Ensheathing Cells into Spinal Cord Lesions Restores Breathing and Climbing
Authors: Li Ying , Decherchi Patrick , Raisman Geoffrey
Published: April 2018

One of the most devastating effects of damage to the upper spinal cord is the loss of the ability to breathe; patients suffering these injuries can be kept alive only with assisted ventilation. No known method for repairing these injuries exists. We report here the return of supraspinal control of breathing and major improvements in climbing after the application of a novel endogenous matrix transfer method. This method permits efficient transfer and retention of cultured adult rat olfactory ensheathing cells when transplanted into large lesions that destroy all tracts on one side at the upper cervical level of the adult rat spinal cord. This demonstrates that transplantation can produce simultaneous repair of two independent spinal functions.
Functional Autaptic Neurotransmission in Fast-Spiking Interneurons: A Novel Form of Feedback Inhibition in the Neocortex
Authors: Bacci Alberto , Huguenard John R. , Prince David A.
Published: April 2018

Autapses are synapses made by a neuron onto itself. Although morphological evidence for existence of autapses has been reported in several brain areas, it is not known whether such self-innervation in the neocortex is functional and robust. Here we report that GABAergic autaptic activity is present in fast-spiking, but not in low-threshold spiking, interneurons of layer V in neocortical slices. Recordings made with the perforated-patch technique, in which physiological intracellular chloride homeostasis was unperturbed, demonstrated that autaptic activity has significant inhibitory effects on repetitive firing and increased the current threshold for evoking action potentials. These results show that autapses are not rudimentary nonfunctional structures, but rather they provide a novel and powerful form of feedback inhibitory synaptic transmission in one class of cortical interneurons.
Dynamics of Gray Matter Loss in Alzheimer's Disease
Authors: Thompson Paul M. , Hayashi Kiralee M. , de Zubicaray Greig , Janke Andrew L. , Rose Stephen E. , Semple James , Herman David , Hong Michael S. , Dittmer Stephanie S. , Doddrell David M. , Toga Arthur W.
Published: April 2018

We detected and mapped a dynamically spreading wave of gray matter loss in the brains of patients with Alzheimer's disease (AD). The loss pattern was visualized in four dimensions as it spread over time from temporal and limbic cortices into frontal and occipital brain regions, sparing sensorimotor cortices. The shifting deficits were asymmetric (left hemisphere > right hemisphere) and correlated with progressively declining cognitive status (p< 0.0006). Novel brain mapping methods allowed us to visualize dynamic patterns of atrophy in 52 high-resolution magnetic resonance image scans of 12 patients with AD (age 68.4 ± 1.9 years) and 14 elderly matched controls (age 71.4 ± 0.9 years) scanned longitudinally (two scans; interscan interval 2.1 ± 0.4 years). A cortical pattern matching technique encoded changes in brain shape and tissue distribution across subjects and time. Cortical atrophy occurred in a well defined sequence as the disease progressed, mirroring the sequence of neurofibrillary tangle accumulation observed in cross sections at autopsy. Advancing deficits were visualized as dynamic maps that change over time. Frontal regions, spared early in the disease, showed pervasive deficits later (>15% loss). The maps distinguished different phases of AD and differentiated AD from normal aging. Local gray matter loss rates (5.3 ± 2.3% per year in AD v 0.9 ± 0.9% per year in controls) were faster in the left hemisphere (p< 0.029) than the right. Transient barriers to disease progression appeared at limbic/frontal boundaries. This degenerative sequence, observedin vivoas it developed, provides the first quantitative, dynamic visualization of cortical atrophic rates in normal elderly populations and in those with dementia.
Neuronal Cell Death Is Preceded by Cell Cycle Events at All Stages of Alzheimer's Disease
Authors: Yang Yan , Mufson Elliott J. , Herrup Karl
Published: April 2018

Cell cycle events play a major role in the loss of neurons in advanced Alzheimer's disease (AD). It is currently unknown, however, whether the same is true for the neuronal losses in early disease stages. To explore this issue we analyzed brain autopsy material from individuals clinically categorized with mild cognitive impairment (MCI), many if not most of whom will progress to AD. Immunocytochemistry for three cell cycle-related proteins, proliferating cell nuclear antigen, cyclin D, and cyclin B, was performed on sections from hippocampus, basal nucleus of Meynert, and entorhinal cortex. The results obtained from MCI cases were compared with material from individuals diagnosed with AD and those without cognitive impairment. In both hippocampus and basal nucleus, there was a significant percentage of cell cycle immunopositive neurons in the MCI cases. These percentages were similar to those found in the AD cases but significantly higher than non-cognitively impaired controls. In entorhinal cortex, the density of cell cycle-positive neurons was greater in MCI than in AD. However, we observed large variations in the percentages of immunopositive neurons from individual to individual. These findings lend support to the hypothesis that both the mechanism of cell loss (a cell cycle-induced death) and the rate of cell loss (a slow atrophy over several months) are identical at all stages of the AD disease process. The implication of the findings for human clinical trials is discussed.
Upstream Stimulatory Factors Are Mediators of Ca2+-Responsive Transcription in Neurons
Authors: Chen Wen G. , West Anne E. , Tao Xu , Corfas Gabriel , Szentirmay Marilyn N. , Sawadogo Michèle , Vinson Charles , Greenberg Michael E.
Published: April 2018

To identify molecular mechanisms that control activity-dependent gene expression in the CNS, we have characterized the factors that mediate activity-dependent transcription ofBDNFpromoter III. We report the identification of a Ca2+-responsive E-box element, CaRE2, withinBDNFpromoter III that binds upstream stimulatory factors 1 and 2 (USF1/2) and show that USFs are required for the activation of CaRE2-dependent transcription fromBDNFpromoter III. We find that the transcriptional activity of the USFs is regulated by Ca2+-activated signaling pathways in neurons and that the USFs bind to the promoters of a number of neuronal activity-regulated genesin vivo. These results suggest a new function for the USFs in the regulation of activity-dependent transcription in neurons.
Different Circuits for ON and OFF Retinal Ganglion Cells Cause Different Contrast Sensitivities
Authors: Zaghloul Kareem A. , Boahen Kwabena , Demb Jonathan B.
Published: April 2018

The theory of “parallel pathways” predicts that, except for a sign reversal, ON and OFF ganglion cells are driven by a similar presynaptic circuit. To test this hypothesis, we measured synaptic inputs to ON and OFF cells as reflected in the subthreshold membrane potential. We made intracellular recordings from brisk-transient (Y) cells in thein vitroguinea pig retina and show that ON and OFF cells in fact express significant asymmetries in their synaptic inputs. An ON cell receives relatively linear input that modulates a single excitatory conductance; whereas an OFF cell receives rectified input that modulates both inhibitory and excitatory conductances. The ON pathway, blocked byl-AP-4, tonically inhibits an OFF cell at mean luminance and phasically inhibits an OFF cell during a light increment. Our results suggest that basal glutamate release is high at ON but not OFF bipolar terminals, and inhibition between pathways is unidirectional: ON → OFF. These circuit asymmetries explain asymmetric contrast sensitivity observed in spiking behavior.
Selective Expression of a Persistent Tetrodotoxin-Resistant Na+Current and NaV1.9 Subunit in Myenteric Sensory Neurons
Authors: Rugiero François , Mistry Mohini , Sage Dominique , Black Joel A. , Waxman Stephen G. , Crest Marcel , Clerc Nadine , Delmas Patrick , Gola Maurice
Published: April 2018

Voltage-gated Na+currents play critical roles in shaping electrogenesis in neurons. Here, we have identified a TTX-resistant Na+current (TTX-RINa) in duodenum myenteric neurons of guinea pig and rat and have sought evidence regarding the molecular identity of the channel producing this current from the expression of Na+channel α subunits and the biophysical and pharmacological properties of TTX-RINa. Whole-cell patch-clamp recording fromin situneurons revealed the presence of a voltage-gated Na+current that was highly resistant to TTX (IC50, ∼200 μm) and selectively distributed in myenteric sensory neurons but not in interneurons and motor neurons. TTX-RINaactivated slowly in response to depolarization and exhibited a threshold for activation at –50 mV. V1/2values of activation and steady-state inactivation were –32 and –31 mV in the absence of fluoride, respectively, which, as predicted from the window current, generated persistent currents. TTX-RINaalso had prominent ultraslow inactivation, which turns off 50% of the conductance at rest (–60 mV). Substituting CsF for CsCl in the intracellular solution shifted the voltage-dependent parameters of TTX-RINaleftward by ∼20 mV. Under these conditions, TTX-RINahad voltage-dependent properties similar to those reported previously for NaN/NaV1.9 in dorsal root ganglion neurons. Consistent with this, reverse transcription-PCR, single-cell profiling, and immunostaining experiments indicated that NaV1.9 transcripts and subunits, but not NaV1.8, were expressed in the enteric nervous system and restricted to myenteric sensory neurons. TTX-RINamay play an important role in regulating subthreshold electrogenesis and boosting synaptic stimuli, thereby conferring distinct integrative properties to myenteric sensory neurons.
Spontaneous Seizures and Loss of Axo-Axonic and Axo-Somatic Inhibition Induced by Repeated Brief Seizures in Kindled Rats
Authors: Sayin Umit , Osting Susan , Hagen Joshua , Rutecki Paul , Sutula Thomas
Published: April 2018

Repeated brief seizures evoked by kindling progressively increase seizure susceptibility and eventually induce spontaneous seizures. Previous studies have demonstrated that the initial seizures evoked by kindling increase paired-pulse inhibition at 15–25 msec interpulse intervals in the dentate gyrus and also induce apoptosis, progressive neuronal loss, mossy fiber sprouting, and neurogenesis, which could potentially alter the balance of excitation and/or inhibition and modify functional properties of hippocampal circuits. In these experiments, paired-pulse inhibition in the dentate gyrus was reduced or lost after ∼90–100 evoked seizures in association with emergence of spontaneous seizures. Evoked IPSCs examined by single electrode voltage-clamp methods in granule cells from kindled rats experiencing spontaneous seizures demonstrated altered kinetics (reductions of ∼48% in 10–90% decay time, ∼40% in τ, and ∼65% in charge transfer) and confirmed that decreased inhibition contributed to the reduced paired-pulse inhibition. The loss of inhibition was accompanied by loss of subclasses of inhibitory interneurons labeled by cholecystokinin and the neuronal GABA transporter GAT-1, which project axo-somatic and axo-axonic GABAergic inhibitory terminals to granule cells and axon initial segments. Seizure-induced loss of interneurons providing axo-somatic and axo-axonic inhibition may regulate spike output to pyramidal neurons in CA3 and could play an important role in generation of spontaneous seizures. The sequence of progressive cellular alterations induced by repeated seizures, particularly loss of GABAergic interneurons providing axo-somatic and axo-axonic inhibition, may be important in the development of intractable epilepsy.
TUC-4b, a Novel TUC Family Variant, Regulates Neurite Outgrowth and Associates with Vesicles in the Growth Cone
Authors: Quinn Christopher C. , Chen Esteban , Kinjo Tashi G. , Kelly Gail , Bell Alexander W. , Elliott Robert C. , McPherson Peter S. , Hockfield Susan
Published: April 2018

The TUC (TOAD-64/Ulip/CRMP) proteins are homologs of UNC-33, a protein that is required for axon extension and guidance inCaenorhabditis elegans. The TUC proteins are expressed in newly born neurons in the developing nervous system and have been implicated in semaphorin signaling and neuronal polarity. Here, we identify several new variants of the TUC family, each of which is expressed during distinct periods of neural development. We cloned and characterized TUC-4b, a variant of TUC-4a that includes a unique N-terminal extension. The functional relevance of this N-terminal domain is demonstrated by the finding that overexpression of TUC-4b, but not TUC-4a, results in increased neurite length and branching. Furthermore, whereas TUC-4a is expressed throughout life, TUC-4b is expressed exclusively during embryonic development. TUC-4b is localized to SV2 (synaptic vesicle protein 2)-positive vesicles in the central domain of the growth cone, suggesting a potential role in growth cone vesicle transport. Furthermore, TUC-4b interacts with the SH3A (Src homology 3A) domain of intersectin, an endocytic–exocytic adaptor protein. Together, these data suggest that TUC-4b can regulate neurite extension and branching through a mechanism that may involve membrane transport in the growth cone.
Developmental Loss of Synchronous Spontaneous Activity in the Mouse Retina Is Independent of Visual Experience
Authors: Demas Jay , Eglen Stephen J. , Wong Rachel O. L.
Published: April 2018

In the immature retina, correlated spontaneous activity in the form of propagating waves is thought to be necessary for the refinement of connections between the retina and its targets. The continued presence of this activity in the mature retina would interfere with the transmission of information about the visual scene. The mechanisms responsible for the disappearance of retinal waves are not well understood, but one hypothesis is that visual experience is important. To test this hypothesis, we monitored the developmental changes in spontaneous retinal activity of both normal mice and mice reared in the dark. Using multi-electrode array recordings, we found that retinal waves in normally reared mice are present at postnatal day (P) 9 and begin to break down shortly after eye opening, around P15. By P21, waves have disappeared, and synchronous firing is comparable with that observed in the adult (6 weeks). In mice raised in the dark, we found a similar time course for the disappearance of waves. However, at P15, dark-reared retinas occasionally showed abnormally long periods of relative inactivity, not seen in controls. Apart from this quiescence, we found no striking differences between the patterns of spontaneous retinal activity from normal and dark-reared mice. We therefore suggest that visual experience is not required for the loss of synchronous spontaneous activity.
Freewheel Running Prevents Learned Helplessness/Behavioral Depression: Role of Dorsal Raphe Serotonergic Neurons
Authors: Greenwood Benjamin N. , Foley Teresa E. , Day Heidi E. W. , Campisi Jay , Hammack Sayamwong H. , Campeau Serge , Maier Steven F. , Fleshner Monika
Published: April 2018

Serotonin (5-HT) neurons in the dorsal raphe nucleus (DRN) are implicated in mediating learned helplessness (LH) behaviors, such as poor escape responding and expression of exaggerated conditioned fear, induced by acute exposure to uncontrollable stress. DRN 5-HT neurons are hyperactive during uncontrollable stress, resulting in desensitization of 5-HT type 1A (5-HT1A) inhibitory autoreceptors in the DRN. 5-HT1A autoreceptor downregulation is thought to induce transient sensitization of DRN 5-HT neurons, resulting in excessive 5-HT activity in brain areas that control the expression of learned helplessness behaviors. Habitual physical activity has antidepressant/anxiolytic properties and results in dramatic alterations in physiological stress responses, but the neurochemical mediators of these effects are unknown. The current study determined the effects of 6 weeks of voluntary freewheel running on LH behaviors, uncontrollable stress-induced activity of DRN 5-HT neurons, and basal expression of DRN 5-HT1A autoreceptor mRNA. Freewheel running prevented the shuttle box escape deficit and the exaggerated conditioned fear that is induced by uncontrollable tail shock in sedentary rats. Furthermore, double c-Fos/5-HT immunohistochemistry revealed that physical activity attenuated tail shock-induced activity of 5-HT neurons in the rostral–mid DRN. Six weeks of freewheel running also resulted in a basal increase in 5-HT1A inhibitory autoreceptor mRNA in the rostral–mid DRN. Results suggest that freewheel running prevents behavioral depression/LH and attenuates DRN 5-HT neural activity during uncontrollable stress. An increase in 5-HT1A inhibitory autoreceptor expression may contribute to the attenuation of DRN 5-HT activity and the prevention of LH in physically active rats.
Altered Expression and Uptake Activity of Spinal Glutamate Transporters after Nerve Injury Contribute to the Pathogenesis of Neuropathic Pain in Rats
Authors: Sung Backil , Lim Grewo , Mao Jianren
Published: April 2018

The central glutamatergic system has been implicated in the pathogenesis of neuropathic pain, and a highly active central glutamate transporter (GT) system regulates the uptake of endogenous glutamate. Here we demonstrate that both the expression and uptake activity of spinal GTs changed after chronic constriction nerve injury (CCI) and contributed to neuropathic pain behaviors in rats. CCI induced an initial GT upregulation up to at least postoperative day 5 primarily within the ipsilateral spinal cord dorsal horn, which was followed by a GT downregulation when examined on postoperative days 7 and 14 by Western blot and immunohistochemistry. Intrathecal administration of the tyrosine kinase receptor inhibitor K252a and the mitogen-activated protein kinase inhibitor PD98059 for postoperative days 1–4 reduced and nearly abolished the initial GT upregulation in CCI rats, respectively. Prevention of the CCI-induced GT upregulation by PD98059 resulted in exacerbated thermal hyperalgesia and mechanical allodynia reversible by the noncompetitive NMDA receptor antagonist MK-801, indicating that the initial GT upregulation hampered the development of neuropathic pain behaviors. Moreover, CCI significantly reduced glutamate uptake activity of spinal GTs when examined on postoperative day 5, which was prevented by riluzole (a positive GT activity regulator) given intrathecally twice a day for postoperative days 1–4. Consistently, riluzole attenuated and gradually reversed neuropathic pain behaviors when the 4 d riluzole treatment was given for postoperative days 1–4 and 5–8, respectively. These results indicate that changes in the expression and glutamate uptake activity of spinal GTs may play a critical role in both the induction and maintenance of neuropathic pain after nerve injury via the regulation of regional glutamate homeostasis, a new mechanism relevant to the pathogenesis of neuropathic pain.
Transmission Security for Single Kinesthetic Afferent Fibers of Joint Origin and Their Target Cuneate Neurons in the Cat
Authors: Coleman Gordon T. , Zhang Hong-Qi , Rowe Mark J.
Published: April 2018

Transmission between single identified, kinesthetic afferent fibers of joint origin and their central target neurons of the cuneate nucleus was examined in anesthetized cats by means of paired electrophysiological recording. Fifty-three wrist joint afferent–cuneate neuron pairs were isolated in which the single joint afferent fiber exerted suprathreshold excitatory actions on the target cuneate neuron. For each pair, the minimum kinesthetic input, a single spike, was sufficient to generate cuneate spike output, often amplified as a pair or burst of spikes, particularly at input rates up to 50–100 impulses per second. The high security was confirmed quantitatively by construction of stimulus–response relationships and calculation of transmission security measures in response to both static and dynamic vibrokinesthetic disturbances applied to the joint capsule. Graded stimulus–response relationships demonstrated that the output for this synaptic connection between single joint afferents and cuneate neurons could provide a sensitive indicator of the strength of joint capsule stimuli. The transmission security measures, calculated as the proportion of joint afferent spikes that generated cuneate spike output, were high (>85–90%) even at afferent fiber discharge rates up to 100–200 impulses per second. Furthermore, tight phase locking in the cuneate responses to vibratory stimulation of the joint capsule demonstrated that the synaptic linkage preserved, with a high level of fidelity, the temporal information about dynamic kinesthetic perturbations that affected the joint. The present study establishes that single kinesthetic afferents of joint origin display a capacity similar to that of tactile afferent fibers for exerting potent synaptic actions on central target neurons of the major ascending kinesthetic sensory pathway.
Circadian and Photic Regulation of Phosphorylation of ERK1/2 and Elk-1 in the Suprachiasmatic Nuclei of the Syrian Hamster
Authors: Coogan Andrew N. , Piggins Hugh D.
Published: April 2018

In this study we investigated the circadian and photic regulation of phosphorylation of the extracellular signal-related kinase (ERK) 1/2, and the transcription factor Elk-1 in the suprachiasmatic nuclei of the Syrian hamster. We report that levels of phosphorylated ERK (P-ERK) are rhythmic, peaking during the mid subjective day, whereas phosphorylated Elk-1 (P-Elk-1) shows no distinct rhythm. Light pulses during the subjective night rapidly, but transiently, induce P-ERK, whereas P-Elk-1 is also induced, albeit with a slower time course. Application of the ERK pathway inhibitor U0126 attenuates photic induction of both P-ERK and P-Elk-1 and phase advances of wheel-running behavior. The NMDA receptor channel blocker, MK-801, also significantly attenuates photic induction of P-ERK and P-Elk-1. Taken together, these results indicate a role of the ERK cascade in the regulation of free-running circadian rhythms and of photic-resetting of these rhythms and suggest that in the mammalian suprachiasmatic nuclei, Elk-1 represents a novel molecular component of the photic-induction pathway.
The α-Latrotoxin Mutant LTXN4CEnhances Spontaneous and Evoked Transmitter Release in CA3 Pyramidal Neurons
Authors: Capogna Marco , Volynski Kirill E. , Emptage Nigel J. , Ushkaryov Yuri A.
Published: April 2018

α-Latrotoxin (LTX) stimulates vesicular exocytosis by at least two mechanisms that include (1) receptor binding–stimulation and (2) membrane pore formation. Here, we use the toxin mutant LTXN4Cto selectively study the receptor-mediated actions of LTX. LTXN4Cbinds to both LTX receptors (latrophilin and neurexin) and greatly enhances the frequency of spontaneous and miniature EPSCs recorded from CA3 pyramidal neurons in hippocampal slice cultures. The effect of LTXN4Cis reversible and is not attenuated by La3+that is known to block LTX pores. On the other hand, LTXN4Caction, which requires extracellular Ca2+, is inhibited by thapsigargin, a drug depleting intracellular Ca2+stores, by 2-aminoethoxydiphenyl borate, a blocker of inositol(1,4,5)-trisphosphate-induced Ca2+release, and by U73122, a phospholipase C inhibitor. Furthermore, measurements using a fluorescent Ca2+indicator directly demonstrate that LTXN4Cincreases presynaptic, but not dendritic, free Ca2+concentration; this Ca2+rise is blocked by thapsigargin, suggesting, together with electrophysiological data, that the receptor-mediated action of LTXN4Cinvolves mobilization of Ca2+from intracellular stores. Finally, in contrast to wild-type LTX, which inhibits evoked synaptic transmission probably attributable to pore formation, LTXN4Cactually potentiates synaptic currents elicited by electrical stimulation of afferent fibers. We suggest that the mutant LTXN4C, lacking the ionophore-like activity of wild-type LTX, activates a presynaptic receptor and stimulates Ca2+release from intracellular stores, leading to the enhancement of synaptic vesicle exocytosis.
Lighting up the Senses: FM1-43 Loading of Sensory Cells through Nonselective Ion Channels
Authors: Meyers Jason R. , MacDonald Richard B. , Duggan Anne , Lenzi David , Standaert David G. , Corwin Jeffrey T. , Corey David P.
Published: April 2018

We describe a novel mechanism for vital fluorescent dye entry into sensory cells and neurons: permeation through ion channels. In addition to the slow conventional uptake of styryl dyes by endocytosis, small styryl dyes such as FM1-43 rapidly and specifically label hair cells in the inner ear by entering through open mechanotransduction channels. This labeling can be blocked by pharmacological or mechanical closing of the channels. This phenomenon is not limited to hair cell transduction channels, because human embryonic kidney 293T cells expressing the vanilloid receptor (TRPV1) or a purinergic receptor (P2X2) rapidly take up FM1-43 when those receptor channels are opened and not when they are pharmacologically blocked. This channel permeation mechanism can also be used to label many sensory cell typesin vivo. A single subcutaneous injection of FM1-43 (3 mg/kg body weight) in mice brightly labels hair cells, Merkel cells, muscle spindles, taste buds, enteric neurons, and primary sensory neurons within the cranial and dorsal root ganglia, persisting for several weeks. The pattern of labeling is specific; nonsensory cells and neurons remain unlabeled. The labeling of the sensory neurons requires dye entry through the sensory terminal, consistent with permeation through the sensory channels. This suggests that organic cationic dyes are able to pass through a number of different sensory channels. The bright and specific labeling with styryl dyes provides a novel way to study sensory cells and neuronsin vivoandin vitro,and it offers new opportunities for visually assaying sensory channel function.
Evidence for Protein Tyrosine Phosphatase, Tyrosine Kinase, and G-Protein Regulation of the Parallel Fiber Metabotropic Slow EPSC of Rat Cerebellar Purkinje Neurons
Authors: Canepari Marco , Ogden David
Published: April 2018

The slow EPSP (sEPSP) or slow EPSC (sEPSC) at parallel fiber to Purkinje neuron synapses is attributable to a nonselective cation channel coupled to activation of metabotropic type 1 glutamate receptors (mGluR1s). Photorelease ofl-glutamate in 1 msec from 4-methoxy-7-nitroindolinyl-or 7-nitroindolinyl-caged glutamate in cerebellar slices was used to isolate and study postsynaptic mechanisms coupling mGluR1 to the cation channel.l-Glutamate immediately activated a glutamate transporter current, followed by the slow mGluR1-activated conductance. Inhibitors of kinases, phosphatases, and G-proteins were tested on the peak glutamate-evoked currents. No effects of the inhibitors were seen on the initial glutamate transporter currents. In contrast, the later mGluR1 currents were either unaffected or enhanced by the protein tyrosine kinase (PTK) inhibitors PP1, K252a, and staurosporine were diminished or blocked by phosphatase inhibitors but were unaffected by inhibitors of serine–threonine kinases PKA, PKC, or PKG. The selectivesrc-PTK inhibitor PP1 (10 μmintracellularly) potentiated submaximal mGluR1 currents evoked by lowl-glutamate concentrations but had no effect on maximal responses (80 or 160 μm l-glutamate).l-Glutamate-evoked mGluR1 currents and parallel fiber sEPSCs were reversibly and completely inhibited by protein tyrosine phosphatase (PTP) inhibitor bpV(phen) (50–200 μm) and by nonselective phosphatase inhibitor orthovanadate (0.5 or 1 mm). mGluR1 currents were completely inhibited by GDPβS applied intracellularly (5 mm). The results confirm a role for a GTPase postsynaptically, show that tyrosine phosphorylation inhibits mGluR1 coupling to the channel, and show that PTPs increase activation by tyrosine dephosphorylation most likely upstream of the sEPSP cation channel.
Inhibition of Calpains Prevents Neuronal and Behavioral Deficits in an MPTP Mouse Model of Parkinson's Disease
Authors: Crocker Stephen J. , Smith Patrice D. , Jackson-Lewis Vernice , Lamba Wiplore R. , Hayley Shawn P. , Grimm Erich , Callaghan Steve M. , Slack Ruth S. , Melloni Edon , Przedborski Serge , Robertson George S. , Anisman Hymie , Merali Zul , Park David S.
Published: April 2018

The molecular mechanisms mediating degeneration of midbrain dopamine neurons in Parkinson's disease (PD) are poorly understood. Here, we provide evidence to support a role for the involvement of the calcium-dependent proteases, calpains, in the loss of dopamine neurons in a mouse model of PD. We show that administration ofN-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) evokes an increase in calpain-mediated proteolysis in nigral dopamine neuronsin vivo. Inhibition of calpain proteolysis using either a calpain inhibitor (MDL-28170) or adenovirus-mediated overexpression of the endogenous calpain inhibitor protein, calpastatin, significantly attenuated MPTP-induced loss of nigral dopamine neurons. Commensurate with this neuroprotection, MPTP-induced locomotor deficits were abolished, and markers of striatal postsynaptic activity were normalized in calpain inhibitor-treated mice. However, behavioral improvements in MPTP-treated, calpain inhibited mice did not correlate with restored levels of striatal dopamine. These results suggest that protection against nigral neuron degeneration in PD may be sufficient to facilitate normalized locomotor activity without necessitating striatal reinnervation. Immunohistochemical analyses of postmortem midbrain tissues from human PD cases also displayed evidence of increased calpain-related proteolytic activity that was not evident in age-matched control subjects. Taken together, our findings provide a potentially novel correlation between calpain proteolytic activity in an MPTP model of PD and the etiology of neuronal loss in PD in humans.
Synapse Number and Synaptic Efficacy Are Regulated by Presynaptic cAMP and Protein Kinase A
Authors: Munno David W. , Prince David J. , Syed Naweed I.
Published: April 2018

The mechanisms by which neurons regulate the number and strength of synapses during development and synaptic plasticity have not yet been defined fully. This lack of fundamental knowledge in the fields of neurodevelopment and synaptic plasticity can be attributed, in part, to compensatory mechanisms by which neurons accommodate for the loss of function in their synaptic partners. This is generally achieved either by scaling up neuronal transmitter release capabilities or by enhancing the postsynaptic responsiveness. Here, we demonstrate that regulation of synaptic strength and number between identifiedLymnaeaneurons visceral dorsal 4 (VD4, the presynaptic cell) and left pedal dorsal 1 (LPeD1, the postsynaptic cell) requires presynaptic activation of a cAMP-PKA-dependent signal. Experimental activation of the cAMP-PKA pathway resulted in reduced synaptic efficacy, whereas inhibition of the cAMP-PKA cascade permitted hyperinnervation and an overall enhancement of synaptic strength. Because synaptic transmission between VD4 and LPeD1 does not require a cAMP-PKA pathway, our data show that these messengers may play a novel role in regulating the synaptic efficacy during early synaptogenesis and plasticity.
Histological and Electrical Properties of Rat Dorsal Root Ganglion Neurons Innervating the Lower Urinary Tract
Authors: Yoshimura Naoki , Seki Satoshi , Erickson Kristin A. , Erickson Vickie L. , Chancellor Michael B. , Groat William C. de
Published: April 2018

We investigated whether primary afferent neurons innervating different regions of the lower urinary tract have different histochemical and electrophysiological properties. Neurons in rat L6–S1 DRG were identified by axonal transport of a fluorescent dye. Neurofilament-negative C-fiber cells comprise ∼70% of bladder and proximal urethral afferent neurons that send axons through the pelvic nerves, but comprise a smaller proportion (51%) of distal urethral neurons that send axons through the pudendal nerves. Isolectin-B4 (IB4) binding was detected in a higher percentage (49%) of C-fiber neurons innervating the distal urethra than in those innervating the bladder or proximal urethra (18–22%). Neurofilament-positive A-fiber neurons innervating the distal urethra had a larger average somal size than neurons innervating the bladder or proximal urethra. In patch-clamp recordings, the majority (70%) of bladder and proximal urethral neurons were sensitive to capsaicin and exhibited TTX-resistant, high-threshold action potentials, whereas a smaller proportion (53%) of distal urethral neurons exhibited TTX-resistant spikes. T-type Ca2+currents were observed in 47% of distal urethral neurons with TTX-sensitive spikes, but not in TTX-sensitive bladder or proximal urethral neurons. In summary, afferent neurons innervating bladder or proximal urethra differ from those innervating distal urethra. The latter, which more closely resemble cutaneous afferent neurons, consist of a smaller number of C-fiber neurons containing a higher percentage of IB4-positive cells and a more diverse population of A-fiber neurons, some of which exhibit T-type Ca2+channels. These differences may be related to different functions of respective target organs in the lower urinary tract.
Variable Dopamine Release Probability and Short-Term Plasticity between Functional Domains of the Primate Striatum
Authors: Cragg Stephanie J.
Published: April 2018

Release of the neuromodulator dopamine (DA) is critical to the control of locomotion, motivation, and reward. However, the probability of DA release is not well understood. Current understanding of neurotransmitter release probability in the CNS is limited to the conventional synaptic amino acid transmitters (e.g., glutamate and GABA). These fast neurotransmitters are released with a repertoire of probabilities according to synapse type, and these probabilities show activity-dependent plasticity according to synapse use. Synapses for neuromodulators such as DA, however, are designed for signaling that diverges temporally and spatially from that for fast neurotransmitters: DA receptors are exclusively metabotropic and at sites that extend to extrasynaptic locations and neighboring synapses.

In this study, the release probability of DA was explored in real time in limbicversus motor-associated functional domains of the striatum of a primate (marmoset;Callithrix jacchus) using fast-scan voltammetry at a carbon-fiber microelectrode. We show that the probability of axonal DA release varies with striatal domain. Furthermore, release probability exhibits a short-term, activity-dependent plasticity that ranges from depression to facilitation in motor-through limbic-associated regions, respectively. Rapid plasticity does not result from metabotropic D2-like DA receptor activation or ionotropic GABAAreceptor effects but is dependent on Ca2+availability.

These data reveal that rapid dynamics in DA release probability will participate in the transmission of the patterns and frequencies encoded by DA neuron action potential discharge. Furthermore, the regional variation in these features indicates that limbic-versus motor-associated DA neurons are permitted to generate diverse DA signals in response to a given firing pattern.
Brain-Derived Neurotrophic Factor Protection of Cortical Neurons from Serum Withdrawal-Induced Apoptosis Is Inhibited by cAMP
Authors: Poser Steven , Impey Soren , Xia Zhengui , Storm Daniel R.
Published: April 2018

Programmed cell death plays an important role both during the development of the CNS and in its homeostasis throughout adulthood. A complex balance between cell death- and survival-inducing signals determines the fate of individual neurons. Intracellular cAMP is thought to regulate neuronal survival, and previous studies have shown that the survival of retinal ganglion cells by brain-derived neurotrophic factor (BDNF) is dependent on cAMP. Here we report the surprising observation that cAMP attenuates the ability of BDNF to rescue cortical neurons from apoptosis after serum deprivation, a process mediated via the phosphatidylinositol 3 (PI3)-kinase signal transduction cascade. Depolarization by KCl, which increases cAMP in cortical neurons, also attenuates BDNF protection against serum withdrawal. Our data indicate that cAMP antagonizes neurotrophin protection from serum withdrawal by inhibiting the PI3-kinase signal transduction cascade. This study indicates that cAMP may inhibit some forms of neurotrophin-mediated neuronal survival and suggests that a number of PI3-kinase-regulated processes in neurons may be inhibited by cAMP.
Amyloid Precursor Protein Associates with a Nicastrin-Dependent Docking Site on the Presenilin 1–γ-Secretase Complex in Cells Demonstrated by Fluorescence Lifetime Imaging
Authors: Berezovska Oksana , Ramdya Pavan , Skoch Jesse , Wolfe Michael S. , Bacskai Brian J. , Hyman Bradley T.
Published: April 2018

γ-Secretase cleavage is the final enzymatic step generating β-amyloid via intramembranous cleavage of the amyloid precursor protein (APP). Presenilin (PS), initially identified as a gene in which mutations account for the vast majority of early-onset autosomal dominant Alzheimer's disease, is a major component of γ-secretase. Enzymatic activity also depends on nicastrin, Aph-1, and Pen-2. We propose a model in which γ-secretase components assemble, interact with substrates initially at a docking site, and then cleave and release substrates. To test this model, we developed a novel morphological technique on the basis of advanced fluorescence microscopy methods, fluorescence lifetime imaging microscopy (FLIM). FLIM allows us to examine protein–protein “proximity” in intact cells. We show that, although the strongest colocalization of APP and PS1 is in the perinuclear area, the strongest interactions detected by FLIM are at or near the cell surface. We also found that APP–PS1 interactions occur even whenγ-secretase inhibitors or “dominant-negative” PS1 mutations are used to block γ-secretase activity. Finally, using nicastrin RNA interference, we demonstrate that nicastrin is critical for APP association with PS1. We interpret these results to suggest that there is a noncatalytic docking site closely associated with PS1–γ-secretase.
Functional Organization of Human Intraparietal and Frontal Cortex for Attending, Looking, and Pointing
Authors: Astafiev Serguei V. , Shulman Gordon L. , Stanley Christine M. , Snyder Abraham Z. , Van Essen David C. , Corbetta Maurizio
Published: April 2018

We studied the functional organization of human posterior parietal and frontal cortex using functional magnetic resonance imaging (fMRI) to map preparatory signals for attending, looking, and pointing to a peripheral visual location. The human frontal eye field and two separate regions in the intraparietal sulcus were similarly recruited in all conditions, suggesting an attentional role that generalizes across response effectors. However, the preparation of a pointing movement selectively activated a different group of regions, suggesting a stronger role in motor planning. These regions were lateralized to the left hemisphere, activated by preparation of movements of either hand, and included the inferior and superior parietal lobule, precuneus, and posterior superior temporal sulcus, plus the dorsal premotor and anterior cingulate cortex anteriorly. Surface-based registration of macaque cortical areas onto the map of fMRI responses suggests a relatively good spatial correspondence between human and macaque parietal areas. In contrast, large interspecies differences were noted in the topography of frontal areas.
Early Odor Preference Learning in the Rat: Bidirectional Effects of cAMP Response Element-Binding Protein (CREB) and Mutant CREB Support a Causal Role for Phosphorylated CREB
Authors: Yuan Qi , Harley Carolyn W. , Darby-King Andrea , Neve Rachael L. , McLean John H.
Published: April 2018

Early odor preference learning in rats is associated with increases of phosphorylated CREB (pCREB) in mitral cells of the olfactory bulb. In the present study, herpes simplex virus expressing CREB (HSV-CREB) and dominant-negative mutant CREB (HSV-mCREB) have been injected into the bulb to assess a causal role for CREB and pCREB in this model. Odor paired with stroking or with the β-adrenoceptor agonist isoproterenol produces odor approach 24 hr later. Isoproterenol-induced learning exhibits an inverted U curve dose-dependent learning relationship with both low and high doses failing to produce learning. pCREB increases have only been seen at the learning effective dose.

In the present study, injection of an HSV vector expressing mutant CREB into the olfactory bulb prevented learning induced by stroking. Control HSV expressing LacZ was without effect. Expression of mutant CREB shifted the dose–learning curve for isoproterenol to the right such that a higher dose was required to induce learning. Expression of CREB shifted the dose-learning curve for isoproterenol to the left, with a lower dose now producing learning. As expected from this shift, CREB overexpression interfered with learning induced by stroking.

When learning occurred, with either CREB or mutant CREB, pCREB was observed to be elevated relative to the nonlearning LacZ control groups. Unexpectedly, with odor plus stroking in the nonlearning CREB group, the level of pCREB was also higher than with odor plus stroking in LacZ controls that did learn.

The data demonstrate a causal role for CREB and pCREB in early mammalian odor preference learning, reinforcing CREB as a “universal” memory molecule. They support evidence that CREB overexpression can be deleterious and suggest the hypothesis of an optimal pCREB window for learning.