bluuebunny/crossref_metadata_2025 huggingface dataset:
Afferents to the midline thalamus issue collaterals to the nucleus tractus solitarii: an anatomical basis for thalamic and visceral reflex integration
Authors: Otake K , Reis DJ , Ruggiero DA
Published: April 2018

The goal of this study was to establish a structural basis for thalamic and visceral integration. We sought to define neural networks that convey visceral or integrated environmental stimuli to the diffuse thalamocortical relay system and that link periodic changes in forebrain and visceral reflex function. Our experiments were designed to determine whether afferents to the midline-intralaminar thalamic nuclei (MIT) issue collaterals to the general viscerosensory division of the nucleus tractus solitarii (NTS). Experiments were performed on anesthetized male Sprague-Dawley rats. Two tracers, FluoroGold and rhodamine latex microbeads, were stereotaxically centered on the MIT and NTS, respectively, in each animal. Subsets of midline thalamic afferents were identified that issue collaterals to the solitary complex. In the cerebral cortex, dually labeled soma were detected in layer V of the insular and infralimbic areas. In the subcortical forebrain, the lateral septal nucleus, anterolateral area of the bed nuclei of stria terminalis, medial preoptic nucleus, medial and central amygdaloid nuclei, caudal lateral hypothalamic area, supramammillary nucleus, and parvicellular division of the paraventricular hypothalamic nucleus constitute other newly identified sources of collateral projection. In the midbrain and pons, collateral projection cells were observed in the periaqueductal gray, dorsal raphe nucleus, mesencephalic reticular formation, laterodorsal tegmental nucleus, lateral and medial parabrachial nuclei, and noradrenergic A5 area. In the lateral parabrachial nucleus, dually labeled neurons were detected in the dorsal-lateral division. In the medulla, collaterals are derived from cells in the rostral and caudal ventrolateral reticular formation and parapyramidal area. Dually labeled cells were also found in the cerebellar fastigial nucleus. Collaterals may coordinate changes in visceral reflex excitability and thalamocortical rhythms during phases of sleep-wake cycle and behavioral expression.
Opioids inhibit endothelin-mediated DNA synthesis, phosphoinositide turnover, and Ca2+ mobilization in rat C6 glioma cells
Authors: Barg J , Belcheva MM , Zimlichman R , Levy R , Saya D , McHale RJ , Johnson FE , Coscia CJ , Vogel Z
Published: April 2018

Opioid agonists inhibit DNA synthesis in C6 rat glioma cells that express opioid receptors, induced by desipramine (DMI). This inhibition was not observed in cells that were not treated with DMI, and thus did not express opioid-binding sites. Endothelin, a known mitogen, increased thymidine incorporation dose dependently (up to 1.7-fold) in DMI-treated C6 cells. This increase was reversed by an anti-idiotypic antibody to opioid receptors, Ab2AOR, which has opioid agonist properties. The opioid antagonist naltrexone blocked the inhibition caused by Ab2AOR. Endothelin also stimulated phosphoinositide (PI) turnover and this effect was inhibited by morphine (50%) or by Ab2AOR (72%) in DMI-treated but not in DMI-untreated C6 cells. These actions of morphine and Ab2AOR were reversed by naltrexone. The inhibition of PI turnover and of thymidine incorporation by Ab2AOR or morphine was insensitive to pertussis toxin (PTX). Since PI turnover is known to induce Ca2+ mobilization, it was of interest to examine the effects of the applied opioids on intracellular Ca2+ concentrations. Endothelin increased the concentration of cytosolic free Ca2+ in the cells while Ab2AOR, morphine, and beta-endorphin reversed the endothelin-induced Ca2+ mobilization in DMI-treated but not in DMI-untreated C6 cells. The effect of these agonists was also blocked by naltrexone. The results indicate that glial cells can be a target of an opioid receptor- mediated antimitogenic action and that an abatement in PI turnover and Ca2+ mobilization may be associated with this mechanism.
Mu- and kappa-opioid receptors selectively reduce the same transient components of high-threshold calcium current in rat dorsal root ganglion sensory neurons
Authors: Moises HC , Rusin KI , Macdonald RL
Published: April 2018

Whole-cell patch-clamp recordings were used to examine the regulation of voltage-dependent calcium channels by mu- and kappa-opioid receptors in acutely isolated rat dorsal root ganglion (DRG) sensory neurons. Agonists selective for either mu- (Tyr-Pro-NMePhe-D-Pro-NH2, PLO17) or kappa-opioid receptors (dynorphin A, U69,593) inhibited high-threshold calcium currents in a reversible and naloxone-sensitive manner, whereas administration of D-Pen2,5-enkephalin, a delta-selective agonist, was without effect. However, none of the opioids reduced low-threshold T- type currents. The inhibitory effects of PLO17 were blocked by the irreversible mu-opioid antagonist beta-funaltrexamine but not the kappa- opioid antagonist nor-binaltorphimine, while responses to kappa-opioid agonists showed the opposite pattern of antagonist sensitivity. In addition, many cells responded to both PLO17 and dynorphin A (or U69,593), and in these neurons the inhibitory response to one agonist was occluded when tested in the presence of the other. These data suggest that mu- and kappa-opioid receptors are coexpressed on at least some DRG neurons and appear to be functionally coupled to a common pool of calcium channels. Both rapidly inactivating (transient) and sustained components of high-threshold current, arising from pharmacologically distinct types of calcium channels, were identified in our neurons. Activation of mu-opioid receptors selectively reduced the transient component of currents evoked at +10 mV from Vh = -80 mV, while sparing the sustained component. The transient component was irreversibly blocked by the N-type channel antagonist omega-conotoxin GVIA (omega-CgTx), and in one-half of the neurons there was a concomitant loss of the response to PLO17. In the remaining neurons, PLO17 continued to reduce a small fraction of omega-CgTx-insensitive current and subsequent administration of the L-type channel blocker nifedipine in saturating concentrations failed to reduce the opioid- induced inhibitory effect. These data demonstrate that mu-opioid receptors are negatively coupled to several pharmacologically distinct types of calcium channels in DRG sensory neurons, one that was blocked by omega-CgTx and thus likely to be N-type, and a second that was resistant to blockade by N- and L-type channel blockers.
Induction and habituation of immediate early gene expression in rat brain by acute and repeated restraint stress
Authors: Melia KR , Ryabinin AE , Schroeder R , Bloom FE , Wilson MC
Published: April 2018

Acute exposure to stress leads to activation of the pituitary-adrenal axis (PA-axis) while repeated exposure to a homotypic stressor generally results in habituation of this response. Previous studies suggested that such habituation is largely due to changes in afferents of the PA-axis. To examine where within these afferents habituation occurs, we studied the effect of acute and repeated exposure to 2 hr restraint stress on expression of c-fos mRNA, as a marker of altered neuronal activity, in brain regions previously shown to influence the activity of the PA-axis. Acute restraint stress increased expression of c-fos mRNA in cortex, hippocampus, hypothalamus, septum, and brainstem. In contrast, the effect of restraint stress on c-fos expression in the aforementioned brain regions was much smaller in animals restrained once daily for 4 d, and nonexistent in animals restrained once daily for 9 d. A similar pattern of induction and habituation of jun-B, but not zif-268, c-jun, or jun-D mRNA expression, was observed in the cortex of animals exposed to acute versus repeated restraint stress. The habituation of c-fos responses was stressor specific: exposure of restraint-adapted animals to a novel (20 min swim) stress produced an increase in levels of c-fos mRNA in every examined brain region comparable to that seen in animals exposed to this stressor for the first time. Adrenalectomy did not alter the pattern of c-fos expression induced by acute and repeated restraint stress. Therefore, activation and habituation of these c-fos responses are independent of changes in circulating levels of corticosterone.
Filopodia initiate choices made by sensory neuron growth cones at laminin/fibronectin borders in vitro
Authors: Gomez TM , Letourneau PC
Published: April 2018

Localized expression of environmental cues is thought to provide directional information to migrating neuronal growth cones by enhancing or suppressing axon outgrowth over limited regions. To investigate how such a mechanism may function in vivo, we observed growth cones of embryonic chick dorsal root ganglion neurons at a substratum border between the extracellular matrix components laminin and fibronectin in vitro using time-lapse phase-contrast and interference reflection microscopy. We found that patterns of laminin and fibronectin could locally promote or suppress the direction of growth cone migration. While migrating on either laminin or fibronectin, at least 79% of growth cones changed their rate and/or direction of outgrowth upon contact with the alternative substratum, in a manner suggesting that growth cones were selecting one substratum over the other. Complex changes in growth cone behavior were initiated by filopodial contact with the alternate substratum, suggesting that filopodia were providing intracellular signals to the growth cone. Using interference reflection microscopy, we have found that selection of a substratum is independent of the degree of close contact to the substratum. We conclude that spatially localized ECM components can direct axon outgrowth by mechanisms based on intracellular signaling through growth cone filopodia.
The astrocytic response to afferent activity blockade in chick nucleus magnocellularis is independent of synaptic activation, age, and neuronal survival
Authors: Canady KS , Hyson RL , Rubel EW
Published: April 2018

Astrocytes in nucleus magnocellularis (NM) of the chick respond to afferent activity blockade with increased immunoreactivity for glial fibrillary acidic protein (GFAP). NM neurons respond to the same manipulations with reduced protein synthesis, ribosomal dissociation, and subsequent death of a subset of these neurons. In the present study, we sought to evaluate the relationship between these neuronal and glial responses and to determine if similar activity-dependent mechanisms mediate them. We first examined the anatomical relationship between NM neurons and astrocytic processes by electron microscopy and GFAP immunostaining. Both methods showed that NM neurons deprived of activity for 6 hr were apposed by more glial processes than active NM neurons. However, we found no preferential positioning of GFAP- immunoreactive processes near neurons of the dying or surviving populations, and there were no differences in glial process apposition to dying versus surviving neurons at the EM level. To determine whether the astrocytic response is similar to the neuronal response in age dependence, GFAP immunoreactivity was analyzed in adult chickens following unilateral afferent activity blockade. Unlike the neuronal response to activity blockade, the astrocytic response is equally strong in adult animals. These results imply an independence of the neuronal and astrocytic responses to activity blockade, raising the possibility that these two cell types may be responding to different activity-related signals. This possibility was tested using an in vitro slice preparation. Unilateral stimulation of NM was provided in three ways: orthodromically, antidromically, and orthodromically in a low- calcium medium. The regulation of astrocytic GFAP immunoreactivity by these manipulations of activity was then analyzed. The results of these experiments show that, unlike neuronal protein synthesis, astrocytic GFAP immunoreactivity can be suppressed by either presynaptic or postsynaptic neuronal activity. Therefore, the astrocytes and neurons are regulated by different activity-dependent signals and, by the present measures, their responses to activity blockade appear independent of one another.
Activity-dependent enhancement of synaptic transmission in hippocampal slices treated with the phosphatase inhibitor calyculin A
Authors: Herron CE , Malenka RC
Published: April 2018

The role of protein phosphatases in regulating synaptic transmission in the CA1 region of the hippocampus was examined using slices pretreated with calyculin A, a specific inhibitor of protein phosphatases 1 and 2A. Stimulation of afferents at 1 Hz (but not 0.1 Hz) for periods of 5– 10 min caused a long-lasting enhancement of synaptic transmission. The increase in synaptic responses was not due to a change in fiber excitability, as there was a shift to the left in the input-output curve following the synaptic enhancement. The enhancement was observed only in the input that received the 1 Hz stimulation and not in an independent control pathway, indicating that the increase in synaptic strength is input specific and limited to repetitively activated synapses. Applying 1 Hz stimulation when synaptic transmission was blocked by replacing extracellular Ca2+ with Mg2+ prevented or significantly reduced any change in synaptic efficacy after reperfusion with normal Ca(2+)-containing medium. In contrast, 1 Hz stimulation given when synaptic transmission was blocked by non-NMDA and NMDA glutamate receptor antagonists still caused a synaptic enhancement following washout of the antagonists. The enhancement of synaptic transmission also was not blocked by loading CA1 cells with the calcium chelator BAPTA. Thus, influx of Ca2+ into presynaptic elements is required for the synaptic enhancement elicited by 1 Hz stimulation in calyculin A-treated hippocampal slices. Consistent with the activation of processes that cause an increase in transmitter release, the magnitude of paired-pulse facilitation decreased following the synaptic enhancement, and the NMDA receptor-mediated component of the synaptic response was increased by 1 Hz stimulation. These results suggest that when protein phosphatases are inhibited by calyculin A, prolonged periods of 1 Hz stimulation lead to activation of presynaptic Ca(2+)- dependent protein kinases, resulting in a persistent increase in evoked transmitter release. They also indicate that the activity of presynaptic protein phosphatases is critically important for limiting increases in synaptic strength following repetitive afferent activity.
Glutamate in thalamic fibers terminating in layer IV of primary sensory cortex
Authors: Kharazia VN , Weinberg RJ
Published: April 2018

Biochemical and pharmacological experiments support glutamate (Glu) as a thalamocortical transmitter, but do not distinguish direct from indirect effects (via excitation of glutamergic corticocortical fibers); anatomical studies to date have yielded variable results. We identified thalamocortical terminals in layer IV of primary somatic sensory, auditory, and visual cortex by injecting WGA-HRP in the corresponding thalamic sensory relay nuclei of rats. Terminals from each thalamic nucleus were similar, containing abundant mitochondria and loosely packed clear vesicles; they made asymmetric synaptic contacts mainly with dendritic spines. After tracer injections into nearby regions of cortex, most terminals also made asymmetric contacts mainly onto spines, but these corticocortical terminals were smaller, containing sparse mitochondria and densely packed clear vesicles. GABAergic terminals (identified by postembedding immunogold staining) made symmetric synapses mainly onto dendritic shafts; those terminating near thalamocortical terminals were also large and contained abundant mitochondria. To determine whether Glu is enriched in thalamocortical terminals, we performed postembedding double-labeling immunocytochemistry for Glu and GABA, using different gold particle sizes. The density of particles coding for Glu was significantly enriched over identified thalamocortical terminals, in comparison to nearby dendrites, astrocytes, and GABAergic terminals, and this enrichment was similar for all three sensory areas. The degree of enrichment in thalamocortical terminals, but not in GABAergic terminals, was linearly related to vesicle density. We conclude that Glu is likely to be a neurotransmitter for thalamocortical relay neurons.
Axon-glia interactions regulate ECM patterning in the postnatal rat olfactory bulb
Authors: Gonzalez ML , Silver J
Published: April 2018

It has been suggested that an inhibitory ECM containing chondroitin-6- sulfate proteoglycan (C-6S-PG) and tenascin (TN), which appears homogeneously in the core of the OB following afferent fiber arrival, helps position ingrowing olfactory axons in the prospective glomerular layer (GL) (Gonzalez and Silver, 1992; Gonzalez et al., 1993). Later, a similar ECM associated with astrocytes envelopes axonal glomeruli in rings, suggesting that axons may control the precise ECM patterning. The question remains whether formation of the matrix ring pattern around each axonal glomerulus is an intrinsic property of the matrix- producing cells or a response to developing axons. To determine if the organization of glial associated matrix in the OB was dependent on the presence of axons, we studied the effect of unilateral injection of a neurotoxin into the olfactory epithelium of postnatal rats. Using olfactory marker protein (OMP), beta-tubulin (TUJ1) antibodies, and Nissl staining, we found that at 5 and 10 d following neurotoxin administration the number of glomeruli decreased by an average of 77.0% in the injected side. At the same time, we observed that the TN/C-6S-PG rings and periglomerular cells were present only around the remaining small number of glomeruli. Elsewhere, ECM expression and the periglomerular cell configuration were more disorganized in the GL. The pattern of glial fibrillary acidic protein (GFAP) did not change significantly. We found that OMP staining, beta-tubulin immunoreactivity, and periglomerular cells reformed in a glomerular- like pattern as the olfactory axons reformed by 20 d. As the glomeruli- shaped collection of axon terminals reappeared, TN/C-6S-PG immunoreactivity also reoccurred in rings around the new axon bundles. Again, at this later stage, the expression of GFAP was similar in both sides. In our previous study (Gonzalez et al., 1993), we suggested that the initial gross positioning of glomeruli may be controlled by the overall positioning of TN/C-6S-PG. In the present study, we suggest that the formation of TN/C-6S-PG in the precise ring pattern around glomeruli appears to be dependent upon the presence of bundled olfactory axons. Various mechanisms are discussed that may explain the dynamic change in ECM expression that occurs inside the glomerulus after the neurotoxin treatment.
Reduction of perineal evoked excitatory postsynaptic potentials in cat lumbar and sacral motoneurons during micturition
Authors: Fedirchuk B , Downie JW , Shefchyk SJ
Published: April 2018

These experiments were undertaken to examine whether both premotoneuronal mechanisms and direct actions on motoneurons could contribute to suppression of excitatory perineal reflex pathways during micturition. Intracellular recordings were obtained from motoneurons innervating the external urethral sphincter (EUS), external anal sphincter (EAS), and selected hindlimb muscles in decerebrate male cats. The peak amplitudes of EPSPs evoked by electrical stimulation of peripheral cutaneous afferents were measured during micturition. In the EUS, EAS, and hindlimb motoneurons examined, EPSPs produced by stimulation of perineal afferents (superficial perineal or sensory pudendal nerves) were reduced in amplitude during micturition. The sample of PSPs evoked by stimulation of hindlimb cutaneous nerves recorded in hindlimb motoneurons revealed that these PSPs could also be reduced. In contrast, no changes were seen in monosynaptic EPSPs evoked by muscle afferent stimulation. The present study demonstrates that during micturition there is a strong suppression of perineal reflexes to both sphincter and hindlimb motoneurons. Since reduced EUS activity is required for efficient micturition, suppression of the strong excitatory perineal input to EUS motoneurons likely contributes to decreased EUS activity during the bladder contraction. It appears that the micturition circuitry utilizes both premotoneuronal mechanisms and direct motoneuronal inhibition to achieve this reflex suppression. The function of the micturition-related reduction of perineal reflexes to hindlimb or EAS motoneurons is not known at this time and further investigations are required to elucidate the interaction between micturition circuitry and hindlimb cutaneous pathways.
Neuropeptide degradation produces functional inactivation in the crustacean nervous system
Authors: Coleman MJ , Konstant PH , Rothman BS , Nusbaum MP
Published: April 2018

The pentapeptide proctolin (Proct.; Arg-Tyr-Leu-Pro-Thr) is a modulatory transmitter found throughout the crustacean nervous system. No information is available in this system, however, as to how the actions of this peptide are terminated. To study this issue in the crab Cancer borealis, we incubated exogenous proctolin (10(-5) M) with either the thoracic ganglion (TG) or with conditioned saline (CS) that had been preincubated with the TG. We removed aliquots at standard time points for analysis by reverse-phase high-performance liquid chromatography (HPLC). We found that over time the proctolin peak became progressively smaller, while three novel peaks appeared and increased in size. Comigration experiments using HPLC indicated that the major novel peak was Proct. (Tyr-Leu-Pro-Thr), while one of the two minor peaks was Proct. (Leu-Pro-Thr). The other minor peak appeared to be Proct. (Arg-Tyr), based on similar HPLC retention time to synthetic Proct. The reduction in the proctolin peak and the increase in the Proct. peak was prevented by co-incubation of proctolin with any one of several aminopeptidase inhibitors (10(-4) M). Proct. and Proct. appeared to result from a diaminopeptidase-mediated cleavage of proctolin. We tested whether N-terminal cleavage functionally inactivated proctolin by coapplying proctolin (10(-8) M) and individual aminopeptidase inhibitors (10(-5) M) to the isolated stomatogastric ganglion (STG). We found that these inhibitors significantly enhanced the proctolin excitation of the pyloric rhythm. Furthermore, application of synthetic Proct. to the STG had no effect unless high concentrations (> 10(-6) M) were used, and neither Proct. nor Proct. (10(-4) M) influenced the pyloric rhythm. Our results indicate that proctolin is enzymatically degraded and thereby biologically inactivated in the crab nervous system, primarily by extracellularly located aminopeptidase activity.
Monoclonal autoantibodies promote central nervous system repair in an animal model of multiple sclerosis
Authors: Miller DJ , Sanborn KS , Katzmann JA , Rodriguez M
Published: April 2018

Susceptible strains of mice infected intracerebrally with Theiler's murine encephalomyelitis virus develop a chronic, progressive, immune- mediated CNS demyelinating disease similar both pathologically and clinically to multiple sclerosis. Previous reports indicated that polyclonal immunoglobulins from mice injected with homogenized spinal cord promote CNS remyelination when given to SJL/J mice chronically infected with Theiler's virus. To explore further both the mechanism(s) and potential therapeutic usefulness of antibodies in the treatment of CNS demyelinating diseases, we made a panel of monoclonal antibodies derived from splenocytes of SJL/J mice injected with homogenized spinal cord, and screened them for their autoantigen-binding capability. Monoclonal IgM autoantibodies from two clones, designated SCH94.03 and SCH94.32, promoted fourfold more CNS remyelination than controls when given to chronically infected SJL/J mice. CNS remyelination, assessed morphologically by the presence of abnormally thin myelin sheaths relative to axonal diameter, correlated with the absence of clinical disease progression. In titration experiments, treatment with SCH94.03 and remyelination had a positive dose-response relationship, and as little as 10 micrograms of antibody promoted remyelination. Both SCH94.03 and SCH94.32 showed multiorgan autoreactivity, and recognized both surface and cytoplasmic determinants on glial cells. We propose that this model provides a unique system to elucidate the mechanism(s) and test the reparative potential of autoantibodies in the treatment of CNS injury.
GABAB receptors modulate an omega-conotoxin-sensitive calcium current that is required for synaptic transmission in the Xenopus embryo spinal cord
Authors: Wall MJ , Dale N
Published: April 2018

Activation of GABAB receptors in the Xenopus embryo, a simple vertebrate, causes presynaptic inhibition of transmitter release from glycinergic spinal neurons and an increase in action potential threshold. To investigate the underlying mechanisms of GABAB receptor action, we have made whole-cell voltage-clamp recordings from acutely isolated Xenopus embryo spinal neurons. The GABAB receptor agonist baclofen caused a reversible reduction in the amplitude of Ca2+ currents. This reduction of Ca2+ currents appeared to be voltage dependent as it was removed at very positive potentials. Since the specific GABAB antagonists CGP35348, phaclofen, and 2-hydroxysaclofen all blocked the reduction in Ca2+ currents, we concluded that the modulation of the Ca2+ current was mediated by GABAB receptors. We have investigated the pharmacological identity of the Ca2+ current modulated by baclofen using the selective blocker omega-conotoxin, fraction GVIA (omega-CgTX). omega-CgTX selectively blocked voltage-gated Ca2+ currents without affecting the voltage-gated Na+ current. omega-CgTX substantially occluded the action of baclofen, suggesting that GABAB receptors modulate an omega-CgTX-sensitive Ca2+ current. Since GABAB receptors mediate presynaptic inhibition, we have studied the involvement of the omega-CgTX-sensitive Ca2+ current in synaptic transmission in the intact spinal cord. Inhibitory interneuron axons were stimulated to evoke monosynaptic IPSPs in motoneurons, and recorded intracellularly. Since omega-CgTX blocked inhibitory transmission, we concluded that the omega-CgTX-sensitive Ca2+ current plays an essential role in transmitter release. If modulation of this current were to occur in nerve terminals, it could contribute to the GABAB receptor-mediated presynaptic inhibition of transmitter release.(ABSTRACT TRUNCATED AT 250 WORDS)
Territorial organization of direction-selective ganglion cells in rabbit retina
Authors: Vaney DI
Published: April 2018

The On-Off direction-selective (DS) ganglion cells in the rabbit retina comprise four discrete subtypes that orthogonally code the direction of image motion. This study examined the dendritic relationships between different subtypes of On-Off DS cells, which were identified by their distinctive type 1 bistratified (BiS1) morphology following the intracellular injection of a biotinylated tracer or Lucifer yellow under direct microscopic control. The dendrites of BiS1 cells that had closely spaced somata, which presumably comprised subtypes of On-Off DS cells with different preferred directions, were not randomly superimposed but were fasciculated into loose bundles. By contrast, tracer coupling revealed that neighboring On-Off DS cells of one subtype were highly territorial, providing complete coverage of the retina with minimal overlap. This mirrors, on a larger scale, the territorial organization within the dendritic tree of individual DS cells, suggesting that similar interactions shape both the branching pattern and the spatial extent of these neurons. Moreover, the dendrites at the edge of the dendritic field often formed tip-to-shaft or tip-to-tip contacts with dendrites from coupled cells, thus appearing to form closed dendritic loops that may be equivalent to those found within the dendritic tree. Consequently, the dendrites of one subtype are distributed uniformly and economically across the retina. The resulting plexus forms a strikingly regular scaffold on which the presynaptic interneurons generate direction selectivity.
Selective increase of NMDA-sensitive glutamate binding in the striatum of Parkinson's disease, Alzheimer's disease, and mixed Parkinson's disease/Alzheimer's disease patients: an autoradiographic study
Authors: Ulas J , Weihmuller FB , Brunner LC , Joyce JN , Marshall JF , Cotman CW
Published: April 2018

Parkinson's disease (PD) and Alzheimer's disease (AD) may share certain abnormalities since a subset of PD patients suffer from dementia, and some AD individuals show extrapyramidal symptoms. In vitro quantitative autoradiography was used to examine different subtypes of excitatory amino acid (EAA) receptors (NMDA, KA, and AMPA) and dopamine transporter sites in the striatum (caudate, putamen) and nucleus accumbens (NAc) from idiopathic PD, pure AD, and mixed PD/AD patients. PD and AD groups, and to a lesser extent the PD/AD groups, showed substantially increased binding to NMDA receptors in the striatum and NAc. No statistically significant changes in binding to KA and AMPA receptors were found in any patient group. 3H-mazindol binding to dopamine transporter sites was significantly decreased in the striatum and NAc of PD and PD/AD patients, but only in the putamen and NAc of AD patients. The data indicate that (1) the majority of striatal EAA receptors are not located on dopaminergic nigrostriatal nerve terminals, and (2) elevated binding to striatal NMDA receptors correlates with binding to dopamine transporter sites in PD patients, but not in AD and PD/AD individuals. Thus, the mechanisms of NMDA receptor changes in the striatum of AD and PD patients may be different. However, it is postulated that increased binding to NMDA receptors in Parkinson and Alzheimer striatum occurs in response to an insult(s) within the striatothalamocortical circuits and that this may contribute to the clinical similarities described for subsets of PD and AD patients.
Calcium imaging of rhythmic network activity in the developing spinal cord of the chick embryo
Authors: O'Donovan M , Ho S , Yee W
Published: April 2018

Video-rate imaging of spinal neurons loaded with calcium-sensitive dyes was used to investigate the calcium dynamics and cellular organization of spontaneously active rhythm-generating networks in the spinal cord of E9-E12 chick embryos. Spinal neurons were loaded with bath-applied fura-2am. Motoneurons were also loaded by retrograde labeling with dextran-conjugated, calcium-sensitive dyes. Dye-filled motoneurons exhibited large fluorescent changes during antidromic stimulation of motor nerves, and an increase in the 340/380 fura fluorescence ratio that is indicative of increased intracellular free calcium. Rhythmic fluorescence changes in phase with motoneuron electrical activity were recorded from motoneurons and interneurons during episodes of evoked or spontaneous rhythmic motor activity. Fluorescent responses were present in the cytosol and in the perinuclear region, during antidromic stimulation and network-driven rhythmic activity. Optically active cells were mapped during rhythmic activity, revealing a widespread distribution in the transverse and horizontal planes of the spinal cord with the highest proportion in the ventrolateral part of the cord. Fluorescent signals were synchronized in different regions of the cord and were similar in time course in the lateral motor column and in the intermediate region. In the dorsal region the rhythm was less pronounced and the signal decayed after a large initial transient. Video-rate fluorescent measurements from individual cells confirmed that fluorescent signals were synchronized in interneurons and in motoneurons although the time course of the signal could vary between cells. Some of the interneurons exhibited tonic elevations of fluorescence for the duration of the episode whereas others were rhythmically active in phase with motoneurons. At the onset of each cycle of rhythmic activity the earliest fluorescent change occurred ventrolaterally, in and around the lateral motor column, from which it spread to the rest of the cord. The results suggest that neurons in the ventrolateral part of the spinal cord are important for rhythmogenesis and that axons traveling in the ventrolateral white matter may be involved in the rhythmic excitation of motoneurons and interneurons. The widespread synchrony of the rhythmic calcium transients may reflect the existence of extensive excitatory interconnections between spinal neurons. The network-driven calcium elevations in the cytosol and the perinuclear region may be important in mediating activity-dependent effects on the development of spinal neurons and networks.
DLX-2, MASH-1, and MAP-2 expression and bromodeoxyuridine incorporation define molecularly distinct cell populations in the embryonic mouse forebrain
Authors: Porteus MH , Bulfone A , Liu JK , Puelles L , Lo LC , Rubenstein JL
Published: April 2018

Recently, the Dlx family of homeobox genes have been identified as candidates for regulating patterning and differentiation of the forebrain. We have made a polyclonal antiserum to the protein product of the Dlx-2 gene. Using this antiserum, we have characterized the spatial and temporal pattern of DLX-2 protein expression during murine development and in the adult mouse brain. These studies demonstrate that, like the mRNA from the Dlx-2 gene, DLX-2 protein is expressed in mouse embryonic forebrain, limbs, tail, genital tubercle, and branchial arches. Within the embryonic forebrain, DLX-2 protein is expressed within specific transverse and longitudinal domains. Analysis of expression within the wall of the forebrain shows that DLX-2 is expressed in proliferative regions including the ventricular and subventricular zones. DLX-2 is expressed in the same cells as MASH-1, a marker of relatively undifferentiated cells, but in a reciprocal fashion to MAP-2, a marker of terminal neuronal differentiation. A number of DLX-2-expressing cells, but not all, can be labeled with bromodeoxyuridine (BrdU). Using the patterns of DLX-2, MASH-1, MAP-2 expression, and bromodeoxyuridine incorporation, we identify four molecularly distinct populations of cells that may correspond to different stages of neuronal differentiation in the mouse basal forebrain, in which DLX-2 is expressed at the transition from proliferation to terminal differentiation.
MN20, a D2 cyclin found in brain, is implicated in neural differentiation
Authors: Ross ME , Risken M
Published: April 2018

Cyclins are regulatory proteins that promote the progression of dividing cells through the cell cycle. D-type cyclins are important mediators of the transition from G1 into S phase of the cell cycle and are thought to be widely expressed in mitotically active tissues (Matsushime et al., 1991b; Inaba et al., 1992; Xiong et al., 1992). We report the isolation of a cDNA clone, MN20, which represents a D2 cyclin message form whose expression pattern is highly restricted to brain. MN20 is not ubiquitous, but rather it is expressed only in restricted neuronal precursor populations, for example, in proliferating granule neuroblasts of the cerebellum but not hippocampus. Strikingly, MN20 expression is also found in postmitotic neuronal precursor cells of the embryonic cerebral cortex, but not in the dividing cortical neuroblasts. These observations suggest that the D2 cyclin gene serves regionally specific functions in neuronal differentiation, some of which may be distinct from the promotion of cell cycle progression and which act at the interface between mitosis and the assumption of mature neuronal morphology.
Regional modulation of neurofilament organization by myelination in normal axons
Authors: Hsieh ST , Kidd GJ , Crawford TO , Xu Z , Lin WM , Trapp BD , Cleveland DW , Griffin JW
Published: April 2018

Previous studies in the hypomyelinating mouse mutant Trembler have suggested that demyelinating axons are smaller in caliber compared to normal axons, and that there are differences in the organization of axonal neurofilaments. In the normal PNS, however, the relationship between neurofilament organization and myelination has not been investigated extensively. In normal axons, only the initial segments, the nodes of Ranvier (approximately 1 micron), and the terminals are not covered by myelin. We took advantage of an unusual feature of the primary sensory neurons in the dorsal root ganglion, the relatively long nonmyelinated stem process (up to several hundred micrometers), to determine if the presence of myelination correlates with differences in cytoskeletal organization and neurofilament phosphorylation. Axonal caliber and neurofilament numbers were substantially greater in the myelinated internodes than in the stem process or nodes of Ranvier. Neurofilament spacing, assessed by measuring the nearest-neighbor neurofilament distance, was 25–50% less in the stem processes and nodes of Ranvier than in the myelinated internodes. In the myelinated internodes, neurofilaments had greater immunoreactivity for phosphorylated epitopes than those in the stem process. These findings indicate that interactions with Schwann cells modulate neurofilament phosphorylation within the ensheathed axonal segments, and that increased phosphorylation within myelinated internodes leads to greater interfilament spacing. Lastly, the myelinated internodes had three fold more neurofilaments, but the same number of microtubules. Both the increased neurofilament spacing and the increase in neurofilament numbers in myelinated internodes contribute to a greater axonal caliber in the myelinated internodes.
Expression of neuropeptide Y and neuropeptide Y (Y1) receptor mRNA in rat spinal cord and dorsal root ganglia following peripheral tissue inflammation
Authors: Ji RR , Zhang X , Wiesenfeld-Hallin Z , Hokfelt T
Published: April 2018

By using in situ hybridization histochemistry and immunohistochemistry, neuropeptide Y (NPY) and NPY (Y1) receptor mRNA as well as NPY-like immunoreactivity were examined in the lumbar spinal cord (L4-L5) and in dorsal root ganglia (DRG, L5) in rats injected with complete Freund's adjuvant (CFA) into the hindpaw. A rapid and marked increase in NPY mRNA expression was observed in ipsilateral dorsal horn neurons 6 hr after inoculation as compared to the contralateral side. This was mainly found in the medial part of spinal lamina II. The peak level (88% increase) was reached at 3 d. In adjacent sections of the spinal cord, 96% and 33% increases were found in the number of dynorphin and enkephalin mRNA-positive neurons, respectively. Unilateral inflammation also induced a moderate increase in NPY-like immunoreactivity and the number of NPY-immunoreactive neurons in the medial part of the ipsilateral spinal dorsal horn. In addition, a marked elevation in the expression of c-Fos-like protein was observed in ipsilateral spinal neurons in laminae I, II, and V. However, no NPY mRNA-positive or NPY- immunoreactive neurons were found in the ipsilateral and contralateral DRGs in rats receiving CFA injection. Furthermore, a marked upregulation of NPY (Y1) receptor mRNA expression was detected in the ipsilateral spinal dorsal horn 1 d and 3 d after inoculation. These Y1 receptor mRNA-positive cells were mainly distributed in the medial laminae II and III. Numerous Y1 mRNA-positive, small neuron profiles were found bilaterally in the DRGs in CFA-treated rats. CFA evoked a 34% increase in the number of Y1 mRNA-positive neurons in ipsilateral DRGs as compared to contralateral DRGs. The distinct upregulation of NPY and NPY (Y1) receptor in response to peripheral inflammation suggests an involvement of NPY in the response to inflammation and in nociception.
A role for oligodendrocytes in the stabilization of optic axon numbers
Authors: Colello RJ , Schwab ME
Published: April 2018

Differentiated oligodendrocytes express neurite growth inhibitory proteins at a time when these cells are involved in the myelination of recently formed fiber pathways. As the process of myelination follows the completion of neurite outgrowth and is concurrent with the stabilization of fiber numbers in a pathway, we set out to determine whether myelination and fiber tract stability could be causally related. Myelin formation was prevented in the rat retinofugal pathway by x-irradiating the optic nerves during oligodendrocyte proliferation. Electron microscopic and immunohistochemical analysis of irradiated optic nerves at P15 showed that oligodendrocytes and myelin were virtually absent. Optic fiber numbers were determined at 2 weeks of age throughout the length of normal and x-irradiated nerves. In some cases, normal or irradiation-treated pups were intraocularly injected with FGF 5 d prior to the fiber count in order to promote neurite outgrowth. Axon counts showed that the total fiber number in a myelin-free optic nerve was 10–30% higher than that of a myelinated nerve. Further, fiber numbers fluctuated by as much as 20% along the length of a myelin-free nerve but were relatively constant throughout the length of a myelinated nerve. Treatment of myelinated nerves with fibroblast growth factor (FGF) had no effect on either total fiber numbers or fiber number fluctuation. Conversely, fiber numbers in myelin-free/FGF- treated optic nerves were as much as 40% higher than in normals. Furthermore, total fiber numbers along the length of these nerves fluctuated by up to 34%. These results indicate that, in the absence of myelination, optic fibers are able to form sprouts.(ABSTRACT TRUNCATED AT 250 WORDS)
Age-dependent long-term potentiation of inhibitory synaptic transmission in rat visual cortex
Authors: Komatsu Y
Published: April 2018

Long-term potentiation (LTP) of inhibitory synaptic transmission in rat visual cortex was investigated using intracellular recording in slice preparations. The inhibitory postsynaptic potential (IPSP) of layer V cells evoked monosynaptically by layer IV stimulation was recorded while excitatory postsynaptic potentials (EPSPs) were blocked by adding NMDA and non-NMDA receptor antagonists to the perfusate. Separate presynaptic fiber groups were activated by two stimulating electrodes placed in layer IV. One electrode was used to test the effect of conditioning stimulation; the other served as a control. Trains of high- frequency stimulation (50 Hz, 1 sec) were applied at an interval of 10 sec as a conditioning stimulation. The LTP of IPSP induced by the conditioning stimulation had properties similar to those known for LTP of EPSP in hippocampal CA1: (1) it was specific to the conditioned pathway; (2) repetitive application of the conditioning stimulation saturated the LTP; (3) LTP was induced by conditioning stimulation at intensities higher than a threshold; (4) weak conditioning stimulation to one pathway, which alone failed to induce LTP, induced associative LTP when strong conditioning stimulation was simultaneously applied to the other pathway; (5) weak conditioning stimulation sometimes induced short-term potentiation. In contrast to these similarities, LTP of IPSP was induced by a wider range of stimulus frequencies than that capable of generating LTP of EPSPs in CA1. It was induced not only by a brief high-frequency stimulation but also by an intermediate-frequency (2 Hz) stimulation continued for 5 min. In addition, the LTP induction was not dependent on postsynaptic membrane potential. Finally, the LTP of IPSP was more easily induced in developing than in mature rats. This age dependence suggests that LTP of IPSPs may contribute to the improvement of response selectivity of visual cortical cells through visual experience during postnatal development.
Functional consequences of compartmentalization of synaptic input
Authors: Coleman MJ , Nusbaum MP
Published: April 2018

Intra-axonal recordings of stomatogastric nerve axon 1 (SNAX1) indicate that there are synaptic inputs onto the SNAX1 terminals in the stomatogastric ganglion (STG) of the crab Cancer borealis (Nusbaum et al., 1992b). To determine whether this synaptic input only influenced SNAX1 activity within the STG, we identified the SNAX1 soma in the commissural ganglion (CoG). We found that this neuron has a neuropilar arborization in the CoG and also receives synaptic inputs in this ganglion. Based on its soma location, we have renamed this neuron modulatory commissural neuron 1 (MCN1). While intracellular stimulation of MCN1soma and MCN1SNAX has the same excitatory effects on the STG motor patterns, MCN1 receives distinct synaptic inputs in the STG and CoG. Moreover, the synaptic input that MCN1 receives within the STG compartmentalizes its activity. Specifically, the lateral gastric (LG) neuron synaptically inhibits MCN1SNAX-initiated activity within the STG (Nusbaum et al., 1992b), and while LG did not inhibit MCN1soma- initiated activity in the CoG, it did inhibit these MCN1 impulses when they arrived in the STG. As a result, during MCN1soma-elicited gastric mill rhythms, MCN1soma is continually active in the CoG but its effects are rhythmically inhibited in the STG by LG neuron impulse bursts. One functional consequence of this local control of MCN1 within the STG is that the LG neuron thereby controls the timing of the impulse bursts in other gastric mill neurons. Thus, local synaptic input can functionally compartmentalize the activity of a neuron with arbors in distinct regions of the nervous system.
Speech motor coordination and control: evidence from lip, jaw, and laryngeal movements
Authors: Gracco VL , Lofqvist A
Published: April 2018

The movements of the lower lip, jaw, and larynx during speech were examined for two different speech actions involving oral closing for /p/ and oral constriction for /f/. The initial analysis focused on the manner in which the different speech articulators were coordinated to achieve sound production. It was found that the lip, jaw, and laryngeal movements were highly constrained in their relative timing apparently to facilitate their coordination. Differences were noted in the degree to which speech articulator timing covaried dependent on the functional characteristics of the action. Movements associated with coordinating multiple articulators for a single sound were more highly constrained in their relative timing than were movements associated with sequencing of individual sounds. The kinematic patterns for the different articulators were found to vary in a number of systematic ways depending on the identity of the sound being produced, the phonetic context surrounding the target sound, and whether one versus two consonants were produced in sequence. The results are consistent with an underlying organization reflecting the construct of the phoneme. It is suggested that vocal tract actions for the sounds of the language are stored in memory as motor programs and sequenced together into larger meaningful units during speaking. Speech articulator motion for the different vowel sounds was found to be influenced by the identity of the following consonant, suggesting that speech movements are modified in chunks larger than the individual phonetic segments. It appears that speech production is a hierarchical process with multiple levels of organization transforming cognitive intent into coherent and perceptually identifiable sound sequences.