bluuebunny/crossref_metadata_2025 huggingface dataset:
Ectopic α2-Adrenoceptors Couple to N-Type Ca2+Channels in Axotomized Rat Sensory Neurons
Authors: Abdulla Fuad A. , Smith Peter A.
Published: April 2018

Dorsal root ganglion (DRG) neurons from control rats or from rats in which the sciatic nerve had been sectioned were studied by whole-cell recording techniques. Noradrenaline (10–100 μm) activated β-adrenoceptors and increased L-type Ca2+channel current in control DRG cells, but this had little effect on excitability (the number of action potentials generated by a pulse of current at rheobasic strength). By contrast, in cells from nerve-damaged animals, noradrenaline activated α2-adrenoceptors, suppressed N-type Ca2+channel current, and increased excitability. In axotomized cells, it also reduced total outward current recorded at +70 mV. Because noradrenaline did not affect total outward current recorded in the presence of the Ca2+channel blocker Cd2+(0.5–1 mm), its effects on excitability may result from reduction of Ca2+-sensitive K+-conductance(s) following suppression of N-type Ca2+channel current. The strongest effects of noradrenaline were seen in small cells and in cells from animals that exhibited autotomy, a self-mutilatory behavior that can accompany peripheral nerve damage. Because many of these small DRG cells may be involved in the transmission of nociceptive information, changes in coupling between Ca2+channels and adrenoceptors may contribute to the generation of the ectopic sensory nerve activity that has been implicated in the etiology of neuropathic pain.
Calcium-Containing Organelles Display Unique Reactivity to Chemical Stimulation in Cultured Hippocampal Neurons
Authors: Korkotian Eduard , Segal Menahem
Published: April 2018

Cultured rat hippocampal neurons grown on glass coverslips for 1–3 weeks were loaded with the calcium-sensitive fluorescent dye Fluo-3 and viewed with a confocal laser scanning microscope. Large pyramidal-shaped neurons were found to contain dye-accumulating organelles in their somata, primarily around nuclei and near the base of their primary dendrites. These organelles varied in size and increased in density over weeks in culture, and were not colocalized with the endoplasmic reticulum or with mitochondria. The Fluo-3 fluorescence in these calcium-containing organelles (CCOs) was transiently quenched by exposure to Mn2+, indicating that the dye is a genuine [Ca2+] reporter and is not just a site of accumulating Fluo-3 dye. Recovery of fluorescence in the CCOs after washout of Mn2+involved activation of a thapsigargin-sensitive process.

CCOs responded to stimuli that evoke a rise of cytosolic [Ca2+] ([Ca]i) in a unique manner; perfusion of caffeine caused a prolonged rise of [Ca] in the CCOs ([Ca]C), whereas it caused only a transient rise of [Ca]i. Pulse application of caffeine also caused a faster effect on [Ca]Cthan on [Ca]i. Glutamate caused a transient rise of both [Ca]iand [Ca]C, followed by a prolonged fall of only [Ca]Cto below rest level. This fall was blocked by preincubation with thapsigargin. Ryanodine blocked the cytosolic effects of caffeine but not its effect on [C]C.

A clear distinction between CCOs and the known calcium stores was seen in digitonin-permeabilized cells; in these, remaining Fluo-3 reported changes in store calcium, i.e., caffeine caused a reduction in Fluo-3 fluorescence in permeabilized cells, whereas it still caused an increase in [Ca]C. A possible role of CCOs in regulation of release of calcium from ryanodine-sensitive stores was indicated by the observation that CCO-containing cells exhibited a larger and faster response to caffeine than cells that did not have them. We propose that CCOs constitute a unique functional compartment involved in release of calcium from calcium-sensitive stores.
Spatially Selective Auditory Responses in the Superior Colliculus of the Echolocating Bat
Authors: Valentine Doreen E. , Moss Cynthia F.
Published: April 2018

When a bat approaches a target, it continuously modifies its echolocation sounds and relies on incoming echo information to shape the characteristics of its subsequent sonar cries. In addition, acoustic information about the azimuth and elevation of a sonar target elicits orienting movements of the head and pinnae toward the sound source. This requires a common sensorimotor interface, where echo information is used to guide motor behaviors.

Using single-unit neurophysiological methods and free-field auditory stimulation, we present data on biologically relevant specializations in the superior colliculus (SC) of the bat for orientation by sonar. In the bat’s SC, two classes of spatially tuned neurons are distinguished by their sensitivity to echoes. One population shows facilitated, delay-tuned responses to pairs of sounds, simulating sonar emissions and echoes. Delay tuning, related to encoding target range, may play a role in guiding motor responses in echolocation, because the bat adjusts its emissions with changes in target distance. The delay-facilitated response depends on the direction of stimulation and on the temporal relationship between the simulated emission and echo in the sound pair, suggesting that this class of neurons represents the location of a target in three dimensions. A second population encodes the target in two dimensions, azimuth and elevation, and does not show a facilitated response to echoes delivered from any locus. Encoding of azimuth and elevation may be important for directing head aim, and this class may function in transforming auditory spatial information into signals used to guide acoustic orientation.
Representation of Accurate Temporal Information in the Electrosensory System of the African Electric Fish,Gymnarchus niloticus
Authors: Guo Yuan-Xing , Kawasaki Masashi
Published: April 2018

Differential-phase-sensitive neurons in the electrosensory lateral line lobe (ELL) of the African electric fish,Gymnarchus niloticus,are sensitive to time disparities on the order of microseconds between afferent action potentials. These action potentials fire in a phase-locked manner in response to the animal’s own wave-type electric organ discharges (EODs) (Kawasaki and Guo, 1996). The time disparity is one of the essential cues for an electrical behavior, the jamming avoidance response (JAR). To gain an insight into the accurate temporal processing in the ELL, firing time accuracy and dynamic response properties of action potentials of the phase-locked neurons (PLNs) in the ELL were examined. The temporal accuracy of the entire neuronal circuit for the JAR was also measured using behavioral responses.

Standard deviation of firing times of PLNs’ action potentials was ∼6 μsec. The PLNs represent zerocrossing times of each stimulus cycle with this accuracy even when stimulus phase was modulated at high frequencies (∼50 Hz). Distinct JAR occurred when time disparity was diminished below 1 μsec, and a marginal JAR could still be detected with a time disparity of 100 nsec. Standard deviation of the firing times of EODs was approximately several hundred nanoseconds. This stability of the EOD, however, was demonstrated to be unnecessary for the JAR. JARs occurred even when a large artificial jitter (∼60 μsec) was introduced to a stimulus that mimicked fish’s own EOD and the time disparity for JAR was diminished to 1 μsec. This immunity of JAR to the EOD jitter is explained by the insensitivity of the differential-phase-sensitive neurons in the ELL to a common phase modulation.

The JAR of the South American electric fish,Eigenmannia, also occurs in response to stimuli that generate comparably small phase differences (Rose and Heiligenberg, 1985b; Carr et al., 1986a). The present study revealed that the independently evolvedEigenmanniaandGymnarchusexhibit a comparative level of remarkable temporal accuracy.
Phencyclidine Increases Forebrain Monoamine Metabolism in Rats and Monkeys: Modulation by the Isomers of HA966
Authors: Jentsch J. David , Elsworth John D. , Redmond Jr. D. Eugene , Roth Robert H.
Published: April 2018

The noncompetitive NMDA receptor antagonist phencyclidine (PCP) has psychotomimetic properties in humans and activates the frontal cortical dopamine innervation in rats, findings that have contributed to a hyperdopaminergic hypothesis of schizophrenia. In the present studies, the effects of the enantiomers of 3-amino-1-hydroxypyrrolid-2-one (HA966) on PCP-induced changes in monoamine metabolism in the forebrain of rats and monkeys were examined, because HA966 has been shown previously to attenuate stress- or drug-induced activation of dopamine systems. In rats, PCP (10 mg/kg, i.p.) potently activated dopamine (DA) turnover in the medial prefrontal cortex (PFC) and nucleus accumbens. Serotonin utilization was also increased in PFC. Pretreatment with either R-(+)HA966 (15 mg/kg, i.p.) or S-(−)HA966 (3 mg/kg, i.p.) partially blocked PCP-induced increases in PFC DA turnover, whereas neither enantiomer altered the effect of PCP on DA turnover in the nucleus accumbens or the PCP-induced increases in serotonin turnover in PFC. PCP (0.3 mg/kg, i.m.) exerted regionally selective effects on the dopaminergic and serotonergic innervation of the monkey frontal cortex, effects blocked by pretreatment with S-(−)HA966 (3 mg/kg, i.m.). Importantly, these data demonstrate that in the primate, PCP has potent effects on dopamine transmission in the frontal cortex, a brain region thought to be dysfunctional in schizophrenia. In addition, a role for S-(−)HA966 as a modulator of cortical monoamine transmission in primates is posited.
Phosphorylation of Transcription Factor CREB in Rat Spinal Cord after Formalin-Induced Hyperalgesia: Relationship toc-fosInduction
Authors: Ji Ru-Rong , Rupp Fabio
Published: April 2018

The involvement of cAMP-responsive element-binding protein (CREB) signaling in tissue injury-induced inflammation and hyperalgesia has been characterized by measuring phosphorylation of CREB at serine-133 (CREB Ser133) using a specific antibody. In the unstimulated state, unphosphorylated CREB was observed in most nuclei of spinal neurons except for motor neurons, where only a small portion of neurons were stained. A few dorsal root ganglion (DRG) neurons were also CREB-positive. After a unilateral injection of formalin into the hindpaw, a strong and bilateral phosphorylation of CREB Ser133 was induced, as assessed by both immunohistochemistry and Western blot. PhosphoCREB (pCREB)-positive neurons were found in laminae I, II, V, and X of spinal cord on both sides. CREB phosphorylation was very rapid and reached peak levels within 10 min of formalin treatment, whereas few pCREB-positive neurons were seen in unstimulated spinal cord. The induction of pCREB was predominantly postsynaptic, because only 5% of DRG neurons were labeled after inflammation. In contrast to CREB phosphorylation, the induction of c-Fos expression reached peak levels 2 hr after formalin treatment and c-Fos induction was mainly ipsilateral. Both formalin-evoked CREB phosphorylation and c-Fos expression in the spinal cord were suppressed by pretreatment with the NMDA receptor antagonist MK-801 (3.5 mg/kg, i.p.) or halothane anesthesia.

These results suggest that CREB signaling may play a role in the long-term facilitation of spinal cord neurons after hyperalgesia. Furthermore, our results indicate that CREB phosphorylation may be necessary but not sufficient forc-fosinduction.
Differential Binding Profile and Internalization Process of Neurotensin via Neuronal and Glial Receptors
Authors: Nouel Dominique , Faure Marie-Pierre , St. Pierre Jacques-André , Alonso Richard , Quirion Rémi , Beaudet Alain
Published: April 2018

Two G-protein-coupled receptors for the tridecapeptide neurotensin (NT) have been identified and cloned in mammalian brain: a high-affinity (Kd= 0.3 nm) receptor, sensitive to the antagonist SR 48692 but insensitive to levocabastine, and a lower-affinity (Kd= 2–4 nm) receptor, sensitive to levocabastine but with poor affinity for SR 48692. Although there is good evidence that the high-affinity site is predominantly expressed in neurons, little is known of the cellular localization of the low-affinity receptor. In the present study, we identify by confocal microscopy selective levocabastine-sensitive, SR 48692-resistant binding of a fluorescent derivative of NT (fluo-NT) to a subpopulation of glial fibrillary acidic protein-immunoreactive glial cells grown in culture from the midbrain and cerebral cortex of embryonic and neonatal rats, respectively. We also demonstrate, by combining fluo-NT detection with tyrosine hydroxylase immunofluorescence, that these glial binding sites are differentially regulated from the SR 48692-sensitive NT receptor expressed in the same cultures by mesencephalic dopamine neurons. Whereas the latter undergoes rapid ligand-induced internalization followed by centripetal mobilization of ligand-receptor complexes from processes to perikarya and from perikaryal periphery to cell center, the former induces the formation of cell-surface clusters that fail to internalize. It is concluded that NT may exert its effects on both neurons and astrocytes in the CNS. Whereas NT neural signaling is exerted through high-affinity receptors and may be partly effected through internalization of receptor-ligand complexes, glial signaling is exerted through low-affinity NT receptors and appears to be transduced exclusively at the level of the plasma membrane.
Loss of Lever Press-Related Firing of Rat Striatal Forelimb Neurons after Repeated Sessions in a Lever Pressing Task
Authors: Carelli Regina M. , Wolske Martin , West Mark O.
Published: April 2018

Lateral striatal neurons that fire phasically in relation to active movement of the contralateral forelimb (determined via daily sensorimotor examination) were studied during acquisition of cued lever pressing. Rats were trained to lift the contralateral forepaw from the floor to press a lever in the presence of a tone. The tone was presented 70 times per day (session) for 18 consecutive days. All animals acquired the task, evidenced by gradual improvements across sessions and eventual asymptotic levels in tone discrimination, reaction time, and efficiency of the lever press. Forelimb neurons fired in relation to the lever press during early sessions of acquisition but not after repeated sessions on the task. This difference in firing could not be attributed to differences in forelimb movements during lever pressing or to sampling from different populations of neurons in early versus late sessions. In view of evidence that striatal damage impairs acquisition of motor skills, the change in firing suggests that the striatal activity present in early sessions may be necessary for the acquisition of, but not the automatic performance of, learned motor responses.
Effects of Interaural Intensity Difference on the Processing of Interaural Time Difference in the Owl’s Nucleus Laminaris
Authors: Viete Svenja , Peña José Luis , Konishi Masakazu
Published: April 2018

Interaural time and intensity differences (ITD and IID) are processed independently in the owl’s auditory system. This paper examines whether this independence is established in nucleus laminaris (NL), the first site of ITD processing. A plot of discharge rate against time difference (ITD curve) is sinusoidal in NL. The ITDs that produce the peaks are called the most favorable ITDs, and those that produce the troughs are called the least favorable ITDs. IID had little effect on the discharge rates of laminaris neurons for the most and least favorable ITDs. The degree of peak–trough modulation changed slightly with variation in IID. In contrast, IID in tonal stimuli affected the temporal aspect of ITD curves depending on the difference between the stimulus frequency and the neuron’s best frequency (BF). For frequencies below BF, IID caused large and systematic shifts in ITD toward the ear in which the sound was louder, whereas for frequencies above BF, IID caused small shifts in ITD toward the opposite ear. IID had little effect on ITD curves taken with BF or broadband noise. These results can be largely accounted for by the effects of frequency and intensity on the timing of impulses at the level of the cochlear nuclei. Thus, the processing of ITD by NL neurons is independent of IID for behaviorally relevant stimuli, because the timing of impulses is insensitive to sound level when the signal is broadband.
Metabotropic Glutamate Receptor Activation Modulates Kainate and Serotonin Calcium Response in Astrocytes
Authors: Haak Laurel L. , Heller H. Craig , van den Pol Anthony N.
Published: April 2018

Although metabotropic glutamate receptor (mGluR) modulation has been studied extensively in neurons, it has not been investigated in astrocytes. We studied modulation of glutamate-evoked calcium rises in primary astrocyte cultures using fura-2 ratiometric digital calcium imaging. Calcium plays a key role as a second messenger system in astrocytes, both in regulation of many subcellular processes and in long distance intercellular signaling. Suprachiasmatic nucleus (SCN) and cortical astrocytes showed striking differences in sensitivity to glutamate and to mGluR agonists, even after several weeks in culture. Kainate-evoked intracellular calcium rises were inhibited by concurrent application of the type I and II mGluR agonists quisqualate (10 μm),trans-(±)-1-amino-1,3-cyclopentanedicarboxylate (100–500 μm), and (2S-1′S-2′S)-2-(carboxycyclopropyl)glycine (L-CCG-I) (10 μm). Inhibition mediated by L-CCG-I had long-lasting effects (>45 min) in ∼30% of the SCN astrocytes tested. The inhibition could be mimicked by the L-type calcium channel blocker nimodipine (1 μm) as well as by protein kinase C (PKC) activators phorbol 12,13-dibutyrate (10 μm) and phorbol 12-myristate 13-acetate (500 nm), and blocked by the PKC inactivator (±)-1-(5-isoquinolinesulfonyl)-2-methylpiperazine (200 μm), suggesting a mechanism involving PKC modulation of L-type calcium channels. In contrast, mGluRs modulated serotonin (5HT)-evoked calcium rises through a different mechanism. The type III mGluR agonistl-2-amino-4-phosphonobutyrate consistently inhibited 5HT-evoked calcium rises, whereas in a smaller number of cells quisqualate and L-CCG-I showed both inhibitory and additive effects. Unlike the mGluR-kainate interaction, which required a pretreatment with an mGluR agonist and was insensitive to pertussis toxin (PTx), the mGluR modulation of 5HT actions was rapid and was blocked by PTx. These data suggest that glutamate, acting at several metabotropic receptors expressed by astrocytes, could modulate glial activity evoked by neurotransmitters and thereby influence the ongoing modulation of neurons by astrocytes.
Depletion and Replenishment of Vesicle Pools at a Ribbon-Type Synaptic Terminal
Authors: von Gersdorff Henrique , Matthews Gary
Published: April 2018

Synaptic depression was studied using capacitance measurements in synaptic terminals of retinal bipolar neurons. Single 250 msec depolarizations evoked saturating capacitance responses averaging ∼150 fF, whereas trains of 250 msec depolarizations produced plateau capacitance increases of ∼300 fF. Both types of stimuli were followed by pronounced synaptic depression, which recovered with a time constant of ∼8 sec after single pulses but required >20 sec for full recovery after pulse trains. Inactivation of presynaptic calcium current could not account for depression, which is attributed instead to depletion of releasable and reserve vesicle pools that are recruited and replenished at different rates. Recovery from depression was normal in the absence of fast endocytosis, suggesting that replenishment was from a reserve pool of preformed vesicles rather than from preferential recycling of recently fused vesicles. Given thein vivolight response of the class of bipolar neuron studied here, it is likely that, under at least some illumination conditions, the cells produce a fast and phasic bout of exocytosis rather than tonic release.
A Family of Activity-Dependent Neuronal Cell-Surface Chondroitin Sulfate Proteoglycans in Cat Visual Cortex
Authors: Lander Cynthia , Kind Peter , Maleski Michael , Hockfield Susan
Published: April 2018

Monoclonal antibody Cat-301 recognizes a chondroitin sulfate proteoglycan (CSPG) expressed on the extracellular surface of cell bodies and proximal dendrites of specific subsets of neurons in many areas of the mammalian CNS, including the cat visual cortex. The Cat-301 CSPG is first detected at the close of the critical period in development, a period during which the pattern of neuronal activity determines the mature synaptic circuitry and neuronal phenotype. In the cat visual cortex, dark-rearing from birth prolongs the duration of the critical period and attenuates the expression of the Cat-301 antigen, implicating the Cat-301 CSPG in the cellular mechanisms that terminate the period of synaptic plasticity. Because the Cat-301 antigen is expressed on only a limited subset of neurons, we have further examined the molecular heterogeneity among neuronal cell-surface CSPGs and have asked (1) whether other neuronal subsets carry distinct CSPGs and (2) whether the activity-dependent expression of the Cat-301 CSPG is a property generalizable to related cell-surface CSPGs. Here, we report two new monoclonal antibodies, Cat-315 and Cat-316, which together with Cat-301 define a family of at least seven related yet distinct CSPGs. These three antibodies define nonidentical subsets of neurons in the cat visual cortex. The expression of normal levels of these CSPGs is reduced by dark-rearing. Together, these data show that the family of cell-surface CSPGs is molecularly diverse, that different sets of neurons express distinct complements of cell-surface antigens, and that the regulation of CSPG expression by activity may be a general feature of neuronal cell-surface CSPGs.
Opposite Membrane Potential Changes Induced by Glucose Deprivation in Striatal Spiny Neurons and in Large Aspiny Interneurons
Authors: Calabresi Paolo , Ascone Carlos Magarinos , Centonze Diego , Pisani Antonio , Sancesario Giuseppe , D’Angelo Vincenza , Bernardi Giorgio
Published: April 2018

We have studied the electrophysiological effects of glucose deprivation on morphologically identified striatal neurons recorded from a corticostriatal slice preparation. The large majority of the recorded cells were spiny neurons and responded to aglycemia with a slow membrane depolarization coupled with a reduction of the input resistance. In voltage-clamp experiments aglycemia caused an inward current. This current was associated with a conductance increase and reversed at −40 mV. The aglycemia-induced membrane depolarization was not affected by tetrodotoxin (TTX) or 6-cyano-7-nitroquinoxaline-2,3-dione plus aminophosphonovalerate, antagonists acting respectively on AMPA and NMDA glutamate receptors. Also, the intracellular injection of bis(2-aminophenoxy)ethane-N,N,N′,N′-tetra-acetic acid, a calcium (Ca2+) chelator, and low Ca2+/high Mg2+-containing solutions failed to reduce this phenomenon. Conversely, it was reduced by lowering external sodium (Na+) concentration.

A minority of the recorded cells had the morphological characteristics of large aspiny interneurons and the electrophysiological properties of “long-lasting afterhyperpolarization (LA) cells.” These cells responded to aglycemia with a membrane hyperpolarization/outward current that was coupled with an increased conductance. This current was not altered by TTX, blockers of ATP-dependent potassium (K+) channels, and adenosine A1 receptor antagonists, whereas it was reduced by solutions containing low Ca2+/high Mg2+. This current reversed at −105 mV and was blocked by barium, suggesting the involvement of a K+conductance. We suggest that the opposite membrane responses of striatal neuronal subtypes to glucose deprivation might account for their differential neuronal vulnerability to aglycemia and ischemia.
Trophic Support of Cultured Spiral Ganglion Neurons by Depolarization Exceeds and Is Additive with that by Neurotrophins or cAMP and Requires Elevation of [Ca2+]iwithin a Set Range
Authors: Hegarty Joseph L. , Kay Alan R. , Green Steven H.
Published: April 2018

Spiral ganglion neurons (SGNs) require both pre- and postsynaptic contacts to maintain viability. BDNF, NT-3, chlorphenylthio-cAMP, and depolarization (veratridine or elevated [K+]o) all promote survival of SGNsin vitro, depolarization being the most effective. Combining different trophic stimuli increases survival in an additive manner. Neurotrophins and depolarization maintain comparable soma size and neurite extension, but SGNs are shrunken in cAMP. Elevated [K+]ohas a biphasic effect on SGN survival; survival improves as [K+]ois raised to 30 mm(30K) and falls as [K+]ois further increased; SGN survival in 80 mm[K+]o(80K) is poor relative to survival in 30K. These responses to elevated [K+]oare potentiated by an L-type channel agonist, whereas L-type Ca2+channel blockers antagonize the trophic effect of depolarization. Four hours after depolarization, steady-state [Ca2+]iis elevated in SGNs in 30K and further elevated in SGNs in 80K. At 22 hr after depolarization, by which time death of neurons in 80K has begun, elevated [Ca2+]ilevels in surviving neurons in 80K are not higher than those in neurons in 30K (∼150–450 nm), suggesting that neurons with high [Ca2+]iare preferentially lost. Veratridine causes oscillatory increases in [Ca2+]ito 250–350 nm. Thus, [Ca2+]iis predictive of cell survival; [Ca2+]ielevated to 100–500 nmin a sustained or oscillatory manner permits SGN survival independent of exogenous neurotrophic factors. Higher [Ca2+]iis associated with cell death.
Functional Expression of the Heteromeric “Olfactory” Cyclic Nucleotide-Gated Channel in the Hippocampus: A Potential Effector of Synaptic Plasticity in Brain Neurons
Authors: Bradley Jonathan , Zhang Yinong , Bakin Robert , Lester Henry A. , Ronnett Gabriele V. , Zinn Kai
Published: April 2018

Cyclic nucleotide-gated (cng) channels are important components of signaling systems mediating sensory transduction. In vertebrate photoreceptors, light activates a signaling cascade that causes a decrease in intracellular cGMP concentrations, closing retinal cng channels. Signal transduction in olfactory receptor neurons is believed to proceed via G-protein-mediated elevation of intracellular cAMP in response to odorant binding by 7-helix receptors. cAMP opens the olfactory cng channel, which is highly permeable to Ca2+. Here we demonstrate byin situhybridization and immunohistochemistry with subunit-specific antibodies that both subunits of the heteromeric rat olfactory cng channel are also widely expressed in the brain. Expression of the retinal rod cng channel, however, can be detected only in the eye. In the adult hippocampus, the olfactory cng channel is expressed on cell bodies and processes of CA1 and CA3 neurons. In cultured embryonic hippocampal neurons, the channel is localized to a subset of growth cones and processes. We recorded conductances with the electrophysiological characteristics of the heteromeric olfactory cng channel in excised inside-out patches from these cultured neurons. We also show that Ca2+influx into hippocampal neurons in response to cyclic nucleotide elevation can be detected using fura-2 imaging. Cyclic nucleotide elevation has been implicated in several mechanisms of synaptic plasticity in the hippocampus, and these mechanisms also require elevation of intracellular Ca2+. Our results suggest that the “olfactory” cng channel could regulate synaptic efficacy in brain neurons by modulating Ca2+levels in response to changes in cyclic nucleotide concentrations.
Differential Subcellular Regulation of NMDAR1 Protein and mRNA in Dendrites of Dentate Gyrus Granule Cells after Perforant Path Transection
Authors: Gazzaley Adam H. , Benson Deanna L. , Huntley George W. , Morrison John H.
Published: April 2018

Unilateral transection of the excitatory perforant path results in the acute deafferentation of a segregated zone on the distal dendrites of hippocampal dentate gyrus granule cells (i.e., outer molecular layer), followed by sprouting, reactive synaptogenesis, and a return of physiological and behavioral function. To investigate cellular mechanisms underlying NMDA receptor plasticity in response to such extensive synaptic reorganization, we quantitatively evaluated changes in intensity levels of NMDAR1 immunofluorescence and NMDAR1 mRNA hybridization within subcellular compartments of dentate gyrus granule cells 2, 5, and 9 d after perforant path lesions. There were no significant changes in either measure at 2 d postlesion. However, at 5 and 9 d postlesion, during the period of axonal sprouting and synaptogenesis, there was an increase in NMDAR1 immunolabeling that was restricted to the dendritic segments of the denervated outer molecular layer and the granule cell somata. In contrast, NMDAR1 mRNA levels at 5 and 9 d postlesion increased throughout the full extent of the molecular layer, including both denervated and nondenervated segments of granule cell dendrites. These findings reveal that NMDAR1 mRNA is one of a limited population of mRNAs that is transported into dendrites and further suggest that in response to terminal proliferation and sprouting, increased mRNA transport occurs throughout the full dendritic extent, whereas increased local protein synthesis is restricted to denervated regions of the dendrites whose afferent activity is perturbed. These results begin to elucidate the dynamic postsynaptic subcellular regulation of receptor subunits associated with synaptic plasticity after denervation.
Cell Fate Specification and Symmetrical/Asymmetrical Divisions in the Developing Cerebral Cortex
Authors: Mione Maria C. , Cavanagh John F. R. , Harris Brett , Parnavelas John G.
Published: April 2018

Two different modes of cell division are adopted by progenitor cells to generate the neurons and glia of the cerebral cortex: they either divide symmetrically to generate other progenitors or a pair of postmitotic cells or divide asymmetrically to generate both a progenitor and a postmitotic cell. In this study we used a lineage marker, the BAG retrovirus, in embryonic day 16 rats in combination with bromodeoxyuridine (BrdU) to identify patterns of cell generation in the cerebral cortex, and investigated the relationship between the phenotype of cells and the history of their lineages. The location, phenotype and birth order of clonally related cells were studied in the subsequent 3 weeks. Only pyramidal neurons and/or astrocytes formed discrete clusters in which several generations of family members were present, whereas nonpyramidal neurons were found exclusively in pairs or as single cells. Analysis of BrdU levels in these cells showed that nonpyramidal neurons were originally part of larger clones and were found dispersed in the neocortex because of tangential migration of their progenitors, dispersion of postmitotic cells, or death of clonal relatives. These results suggest that both symmetrical and asymmetrical division can be adopted by progenitor cells to generate cortical neurons and glial cells and that cell extrinsic events contribute to the isolation of nonpyramidal neurons.
Early Developmental Destruction of Terminals in the Striatal Target Induces Apoptosis in Dopamine Neurons of the Substantia Nigra
Authors: Marti Maria J. , James Christopher J. , Oo Tinmarlar F. , Kelly William J. , Burke Robert E.
Published: April 2018

Many developing neural systems with peripheral projections depend on their target for trophic support during a critical period of natural cell death. Much less is known about central systems. That dopaminergic neurons of the substantia nigra may depend on their target, the striatum, during development is suggested by the presence of a natural apoptotic cell death event in these neurons that can be augmented by an early developmental axon-sparing striatal injury. To further assess the target dependence of these neurons, we have used the selective neurotoxin 6-hydroxydopamine to lesion their terminals within the striatum during development, while sparing intrinsic striatal target neurons. This lesion results in an induction of apoptotic cell death in phenotypically defined dopaminergic neurons that appears on the third postlesion day and persists until the tenth. This inducibility of cell death is dependent on developmental age: it is most marked before postnatal day (PND) 14. As late as PND42, inducibility is still detectable but much less so. In addition, at day 42 the morphology of cell death changes and becomes nonapoptotic in some cells. We conclude that terminal injury during a critical period of postnatal development, like axon-sparing target injury, induces augmented apoptotic death in mesencephalic dopaminergic neurons. These results suggest that these neurons have a period of target dependence. Regulation of this dependence is likely to influence the mature adult number of dopaminergic neurons.
Local Homogeneity of Cell Cycle Length in Developing Mouse Cortex
Authors: Cai Li , Hayes Nancy L. , Nowakowski Richard S.
Published: April 2018

We have measured the amount of variation in the length of the cell cycle for cells in the pseudostratified ventricular epithelium (PVE) of the developing cortex of mice on embryonic day 14. Our measurements were made in three cortical regions (i.e., the neocortex, archicortex, and periarchicortex) using three different methods: the cumulative labeling method (CLM), the percent labeled mitoses (PLM) method, and a comparison of the time needed for the PLM to ascend from 0 to 100% with the time needed for the PLM to descend from 100 to 0%. These 3 different techniques provide different perspectives on the cytokinetic parameters. Theoretically, CLM gives an estimate for a maximum value of the total length of the cell cycle (TC), whereas PLM gives an estimate of a minimum value of TC. The difference between these two estimates indicates that the range for TCis ±1% of the mean TCfor periarchicortex, ±7% for neocortex, and ±8% for archicortex. This was confirmed by a lengthening of the PLM descent time in comparison with its ascent time. The sharpness of the transitions and the flatness of the plateau of the PLM curves indicate that 99% of the proliferating cells are within this narrow estimated range for TC; hence, only ∼1% deviate outside of a relatively restricted range from the average TCof the population. In the context of the possible existence within the cortical PVE of two populations with markedly dissimilar cell cycle kinetics from the mean, one such population must comprise ∼99% of the total population, and the other, if it exists, is only ∼1% of the total. This seems to be true for all three cortical regions. The narrow range of TCindicates a homogeneity in the cell cycle length for proliferating cells in three different cortical regions, despite the fact that progenitor cells of different lineages may be present. It further predicts the existence of almost synchronous interkinetic nuclear movements of the proliferating cells in the ventricular zone during early development of the cerebral cortex.
Synchrony of Clonal Cell Proliferation and Contiguity of Clonally Related Cells: Production of Mosaicism in the Ventricular Zone of Developing Mouse Neocortex
Authors: Cai Li , Hayes Nancy L. , Nowakowski Richard S.
Published: April 2018

We have analyzed clonal cell proliferation in the ventricular zone (VZ) of the early developing mouse neocortex with a replication-incompetent retrovirus encoding human placental alkaline phosphatase (AP). The retrovirus was injected into the lateral ventricles on embryonic day 11 (E11), i.e., at the onset of neuronogenesis. Three days postinjection, on E14, a total of 259 AP-labeled clones of various sizes were found in 7 fetal brains. There are approximately 7 cell cycles between E11 and E14 (Takahashi et al., 1995a), and there is a 1–2 cell cycle delay between retroviral injection and the production of a retrovirally labeled “founder” cell; thus, we estimate that the “age” of the clones was about 5–6 cell cycles. Almost one-half of the clones (48.3%) identified were pure proliferating clones containing cells only in the VZ. Another 18.5% contained both proliferating and postproliferative cells, and 33.2% contained only postproliferative cells. It was striking that over 90% of the clonally related proliferating cells occurred in clusters of two or more apparently contiguous cells, and about 73% of the proliferating cells occurred in clusters of three or more cells. Regardless of the number of cells in the clone, these clusters were tightly packed and confined to a single level of the VZ. This clustering of proliferating cells indicates that clonally related cells maintain neighbor–neighbor relationships as they undergo interkinetic nuclear migration and progress through several cell cycles, and, as a result, the ventricular zone is a mosaic of small clusters of clonally related and synchronously cycling cells. In addition, cells in the intermediate zone and the cortical plate were also frequently clustered, indicating that they became postproliferative at a similar time and that the output of the VZ is influenced by its mosaic structure.
Interconnected Parallel Circuits between Rat Nucleus Accumbens and Thalamus Revealed by Retrograde Transynaptic Transport of Pseudorabies Virus
Authors: O’Donnell Patricio , Lavı́n Antonieta , Enquist Lynn W. , Grace Anthony A. , Card J. Patrick
Published: April 2018

One of the primary outputs of the nucleus accumbens is directed to the mediodorsal thalamic nucleus (MD) via its projections to the ventral pallidum (VP), with thecoreandshellregions of the accumbens projecting to the lateral and medial aspects of the VP, respectively. In this study, the multisynaptic organization of nucleus accumbens projections was assessed using intracerebral injections of an attenuated strain of pseudorabies virus, a neurotropic α herpesvirus that replicates in synaptically linked neurons. Injection of pseudorabies virus into different regions of the MD or reticular thalamic nucleus (RTN) produced retrograde transynaptic infections that revealed multisynaptic interactions between these areas and the basal forebrain. Immunohistochemical localization of viral antigen at short postinoculation intervals confirmed that the medial MD (m-MD) receives direct projections from the medial VP, rostral RTN, and other regions previously shown to project to this region of the thalamus. At longer survival intervals, injections confined to the m-MD resulted in transynaptic infection of neurons in the accumbens shell but not in the core. Injections that also included the central segment of the MD produced retrograde infection of neurons in the lateral VP and the polymorph (pallidal) region of the olfactory tubercle (OT) and transynaptic infection of a small number of neurons in the rostral accumbens core. Injections in the lateral MD resulted in retrograde infection in the globus pallidus (GP) and in transynaptic infection in the caudate-putamen. Viral injections into the rostroventral pole of the RTN infected neurons in the medial and lateral VP and at longer postinoculation intervals, led to transynaptic infection of scattered neurons in the shell and core. Injection of virus into the intermediate RTN resulted in infection of medial VP neurons and second-order infection of neurons in the accumbens shell. Injections in the caudal RTN or the lateral MD resulted in direct retrograde labeling of cells within the GP and transynaptic infection of neurons in the caudate-putamen. These results indicate that the main output of VP neurons receiving inputs from the shell of the accumbens is heavily directed to the m-MD, whereas a small number of core neurons appear to influence the central MD via the lateral VP. Further segregation in the flow of information to the MD is apparent in the organization of VP and GP projections to subdivisions of the RTN that give rise to MD afferents. Collectively, these data provide a morphological basis for the control of the thalamocortical system by ventral striatal regions, in which parallel connections to the RTN may exert control over activity states of cortical regions.
Differential and Time-Dependent Changes in Gene Expression for Type II Calcium/Calmodulin-Dependent Protein Kinase, 67 kDa Glutamic Acid Decarboxylase, and Glutamate Receptor Subunits in Tetanus Toxin-Induced Focal Epilepsy
Authors: Liang Fengyi , Jones Edward G.
Published: April 2018

To study potential molecular mechanisms of epileptogenesis in the neocortex, the motor cortex of rats was injected with tetanus toxin (TT), and gene expression for 67 kDa glutamic acid decarboxylase (GAD-67), type II calcium/calmodulin-dependent protein kinase (CaMKII), NMDA receptor subunit 1 (NR1), and AMPA receptor subunit 2 (GluR2) was investigated byin situhybridization histochemistry. Injections of 20–35 ng TT induced recurrent seizures after a postoperative period ranging from 4 to 13 d. A majority of rats perfused 5–7 d after TT injection showed altered gene expression, but the changes varied in their areal extent, ranging from most neocortical areas on the injected side in some rats to mainly the frontoparietal cortex or the motor cortex in others. Epileptic rats perfused 14 d after TT injection showed a focus of increased GAD-67 and NR1, and of decreased α-CaMKII and GluR2 mRNA levels at the injection site. A zone of cortex surrounding the focus showed changes in α-CaMKII, GAD-67, and NR1 mRNA levels that were reciprocal to those in the focus. The results suggest that TT-induced seizure activity initially spread to a variable extent but was gradually restricted 2–3 d after seizure onset. The focus and the surround showing reciprocal changes in gene expression are thought to correspond to the electrophysiologically identified epileptic focus and inhibitory surround, respectively. The findings suggest that lateral inhibition between neighboring cortical regions will be affected and contribute to a neurochemical segregation of an epileptic focus from surrounding cortex.
Group I Metabotropic Glutamate Receptors mGluR1α and mGluR5a: Localization in Both Synaptic Layers of the Rat Retina
Authors: Koulen Peter , Kuhn Rainer , Wässle Heinz , Brandstätter Johann Helmut
Published: April 2018

We examined the distribution of the group I metabotropic glutamate receptors, mGluR1α and mGluR5a, in the adult rat retina and during postnatal development using receptor-specific antisera. In contrast to the restricted localization of group II and group III mGluRs to either the outer plexiform layer (OPL) or the inner plexiform layer (IPL), group I mGluRs are present in both synaptic layers in the rat retina. Double-labeling experiments and electron microscopy showed that in the OPL the two receptors are localized on the dendritic tips of bipolar cells postsynaptic to photoreceptor terminals. In the IPL the two mGluRs are localized on amacrine cell processes postsynaptic to bipolar cell terminals. These results suggest that group I mGluRs are involved in synaptic processing in both plexiform layers and in both the scotopic and photopic pathways in the rat retina. We propose that mGluR1α and mGluR5a play an important modulatory role in the responses of retinal neurons to inhibitory and excitatory neurotransmitters.
Intercircuit Control of Motor Pattern Modulation by Presynaptic Inhibition
Authors: Bartos Marlene , Nusbaum Michael P.
Published: April 2018

Rhythmically active neural networks can control the modulatory input that they receive via their synaptic effects onto modulatory neurons. This synaptic control of network modulation can occur presynaptically, at the axon terminals of the modulatory neuron. For example, in the crab stomatogastric ganglion (STG), a gastric mill network neuron presynaptically inhibits transmitter release from a modulatory projection neuron called modulatory commissural neuron 1. We showed previously that the gastric mill rhythm-timed presynaptic inhibition of the STG terminals of MCN1 is pivotal for enabling MCN1 to activate this rhythm. We also showed that MCN1 excites the pyloric rhythm within the STG. Here we show that, because MCN1 stimulation conjointly excites the gastric mill and pyloric rhythms, the gastric mill rhythm-timed presynaptic inhibition of MCN1 causes a rhythmic interruption in the MCN1-mediated excitation of the pyloric rhythm. Consequently, during each protraction phase of the gastric mill rhythm, presynaptic inhibition suppresses MCN1 excitation of the pyloric rhythm, thereby weakening the pyloric rhythm. During the retraction phase, presynaptic inhibition is absent and MCN1 elicits a faster, stronger, and modified pyloric rhythm. Thus, in addition to its role in enabling a neural circuit to regulate the modulatory transmission that it receives, presynaptic inhibition is also used effectively to rhythmically control the activity level of a distinct, but behaviorally related, neural circuit.
H+Permeation and pH Regulation at a Mammalian Serotonin Transporter
Authors: Cao Yongwei , Mager Sela , Lester Henry A.
Published: April 2018

The rat serotonin transporter expressed inXenopusoocytes displays an inward current in the absence of 5-HT when external pH is lowered to 6.5 or below. The new current differs from the leakage current described previously in two ways. (1) It is ∼10-fold larger at pH 5 than the leakage current at pH 7.5 and reaches 1000 H+/sec per transporter at extremes of voltage and pH with no signs of saturation. (2) It is selective for H+by reversal potential measurements. Similar H+-induced currents are also observed in several other ion-coupled transporters, including the GABA transporter, the dopamine transporter, and the Na+/glucose transporter. The high conductance and high selectivity of the H+-induced current suggest that protons may be conducted via a hydrogen-bonded chain (a “proton-wire mechanism”) formed at least partially by side chains within the transporter. In addition, pH affects other conducting states of rat serotonin transporter. Acidic pH potentiates the 5-HT-induced, transport-associated current and inhibits the hyperpolarization-activated transient current. The dose–response relationships for these two effects suggest that two H+binding sites, with pKavalues close to 5.1 and close to 6.3, govern the potentiation of the 5-HT-induced current and the inhibition of the transient current, respectively. These results are important for developing structure-function models that explain permeation properties of neurotransmitter transporters.
β43′: An Enhancer Displaying Neural-Restricted Activity Is Located in the 3′-Untranslated Exon of the Rat Nicotinic Acetylcholine Receptor β4 Gene
Authors: McDonough Jennifer , Deneris Evan
Published: April 2018

Members of a neuronal nicotinic acetylcholine receptor subunit gene cluster ordered β4, α3, α5 in the vertebrate genome are expressed in highly restricted patterns in the PNS and CNS. Nothing is known, however, about the regulatory elements that control transcription of these genes in selected neuronal cell populations. We report here a novel enhancer, designated β43′, that is positioned in the β4 3′-untranslated exon. It is composed of two nearly identical 37 bp direct repeats that are separated by 6 bp. Multimerization of the enhancer upstream of the α3 minimal promoter results in synergistic activation. Analysis in different cell types, including three neural lines and primary keratinocytes, shows that β43′ is preferentially active in the neural line PC12, which expresses all members of the cluster. Mobility shift assays reveal a cell-type-specific complex, which forms with the first repeat of the enhancer and PC12 extracts. Complexes co-migrating with the PC12 cell complex are not detected with extracts from other lines, which suggests that PC12 cells contain a differentially expressed factor that may be important for the restricted activity of β43′. The cell-type-specific activity of the β43′ enhancer suggests that it is important for regulating restricted expression patterns of one or more clustered neuronal acetylcholine receptor genes. Its location within the β4 gene may be a selective pressure for maintaining tight linkage of clustered neuronal nAchR genes.