bluuebunny/crossref_metadata_2025 huggingface dataset:
A calcitonin gene-related peptide receptor antagonist prevents the development of tolerance to spinal morphine analgesia
Authors: Menard DP , van Rossum D , Kar S , St Pierre S , Sutak M , Jhamandas K , Quirion R
Published: April 2018

Tolerance to morphine analgesia is believed to result from a neuronal adaptation produced by continuous drug administration, although the precise mechanisms involved have yet to be established. Recently, we reported selective alterations in rat spinal calcitonin gene-related peptide (CGRP) markers in morphine-tolerant animals. In fact, increases in CGRP-like immunostaining and decrements in specific [125]hCGRP binding in the superficial laminae of the dorsal horn were correlated with the development of tolerance to the spinal antinociceptive action of morphine. Other spinally located peptides such as substance P, galanin, and neuropeptide Y were unaffected. Thus, the major goal of the present study was to investigate whether the development of tolerance to spinally infused morphine could be modulated by the blockade of dorsal horn CGRP receptors using the potent CGRP antagonist hCGRP(8–37). Indeed, cotreatments with hCGRP(8–37) prevented, in a dose- dependent manner, the development of tolerance to morphine-induced analgesia in both the rat tail-flick/tail-immersion and paw-pressure tests. Moreover, alterations in spinal CGRP markers seen in morphine- tolerant animals were not observed after a coadministration of morphine and hCGRP(8–37). These results demonstrate the existence of specific interaction between CGRP and the development of tolerance to the spinal antinociceptive effects of morphine. They also suggest that CGRP receptor antagonists could become useful adjuncts in the treatment of pain and tolerance to the antinociceptive effects of morphine.
Localization and function of a 5-HT transporter in crypt epithelia of the gastrointestinal tract
Authors: Wade PR , Chen J , Jaffe B , Kassem IS , Blakely RD , Gershon MD
Published: April 2018

The peristaltic reflex can be evoked in the absence of input from the CNS because the responsible neural pathways are intrinsic to the intestine. Mucosal enterochromaffin cells have been postulated to be pressure transducers, which activate the intrinsic sensory neurons that initiate the reflex by secreting 5-HT. All of the criteria necessary to establish 5-HT as this transmitter have been fulfilled previously, except that no mucosal mechanism for 5-HT inactivation was known. In the current investigation, desensitization of 5-HT receptors was demonstrated to inhibit the peristaltic reflex in the guinea pig large intestine in vitro. At low concentration (1.0 nM), the 5-HT uptake inhibitor fluoxetine potentiated the reflex, but higher concentrations blocked it, suggesting that the peristaltic reflex depends on the 5-HT transporter-mediated inactivation of 5-HT. Specific (Na+ -dependent, fluoxetine-sensitive) uptake of 3H-5-HT by intestinal crypt epithelial cells was found by radioautography. mRNA encoding the neuronal 5-HT transporter was demonstrated in the intestinal mucosa by Northern analysis and located in crypt epithelial cells as well as in myenteric neurons by in situ hybridization. cDNA encoding the 5-HT transporter was cloned from the mucosa and completely sequenced. 5-HT transporter immunoreactivity was detected in crypt epithelial cells and enteric neurons. Mucosal epithelial cells thus express a plasmalemmal 5-HT transporter identical to that of serotonergic neurons. This molecule seems to play a critical role in the peristaltic reflex.
The origins of two-state spontaneous membrane potential fluctuations of neostriatal spiny neurons
Authors: Wilson CJ , Kawaguchi Y
Published: April 2018

In vivo intracellular recordings of spontaneous activity of neostriatal spiny cells revealed two-state behavior, i.e., characteristic shifts of membrane potential between two preferred levels. The more polarized level, called the Down state, varied among neurons from -61 to -94 mV. The more depolarized level, called the Up state, varied among neurons form -71 to -40 mV. For any one neuron, the membrane potential in the Up and Down states was constant over the period of observation (from 15 min to 4 hr), and the cells spent little time in transition between states. The level of membrane potential noise was higher in the Up state than in the Down state. Spontaneous membrane potential fluctuations were not abolished by experimental alteration of the membrane potential, but the time spent in each state was altered when intracellular current was used to vary the baseline membrane potential. Neither the sodium nor the calcium action potential that could be evoked by depolarization of spiny neurons was required for the occurrence of spontaneous shifts of membrane potential. Blockade of these action potentials using intracellular injection of QX314 and D890, respectively, altered neither the incidence of the membrane potential shifts nor the preferred membrane potential in either state. In contrast, antagonism of voltage-dependent potassium channels with intracellular cesium altered membrane potential shifts. In the presence of QX314 and D890, intracellular injection of cesium caused little or no change in the Down state and a large depolarizing shift in the Up state (to about -20 mV). Under these circumstances, the neuron responded to current in a nearly linear manner, and membrane conductance was found to be increased in the Up state, attributable to a membrane conductance with the same reversal potential as that of the synaptic potential evoked by cortical stimulation. These results indicate that the event underlying the Up state is a maintained barrage of synaptic excitation, but that the membrane potential achieved during the Up state in neostriatal spiny neurons is determined by dendritic potassium channels that clamp the membrane potential at a level determined by their voltage sensitivity. Neostriatal spiny neurons ordinarily receive enormously powerful excitation, which would drive the cells to saturation, and probably destroy them, if it were not for these potassium currents.
D1 dopamine receptor activation is necessary for the induction of sensitization by amphetamine in the ventral tegmental area
Authors: Vezina P
Published: April 2018

Repeated intermittent exposure to amphetamine produces long-term enhancements in the ability of this drug to produce locomotion and increase extracellular dopamine (DA) in the nucleus accumbens (NAcc). Three experiments were conducted to evaluate the role played by D1 DA receptors in the production of these changes in response to amphetamine. Rats were preexposed to amphetamine, alone or with a DA receptor antagonist, and tested for sensitization 1–3 weeks after the last drug injection. On the test for sensitization, locomotor (experiments 1 and 2) and NAcc DA (experiment 3) responses of the animals to a systemic amphetamine injection were assessed. In the first experiment, systemic injections of the D1 DA receptor antagonist SCH23390, but not other DA receptor antagonists with greater affinity for D2 DA and 5-HT2 receptors, blocked the development of locomotor sensitization produced by systemic injections of amphetamine. In the second experiment, locomotor sensitization induced by infusion of amphetamine into the ventral tegmental area (VTA) was blocked when these injections were preceded by systemic injections of SCH23390. Finally, in experiment three, co-injecting SCH23390, but not its inactive enantiomer, with amphetamine into the VTA during preexposure prevented sensitization of the NAcc DA response to this drug. These results indicate that while D2 DA receptor activation is not necessary for the induction of locomotor sensitization to amphetamine, D1 DA receptors located in the VTA play a critical role in the development of sensitized locomotor and NAcc DA response to this drug.
Inositol 1,4,5-Trisphosphate-Gated Calcium Transport through Plasma Membranes in Nerve Terminals
Authors: Ueda Hiroshi , Tamura Shigeki , Fukushima Nobuyuki , Katada Toshiaki , Ui Michio , Satoh Masamichi
Published: April 2018

We developed new biochemical approaches to demonstrate the presence of inositol 1,4,5-trisphosphate (InsP3)-gated calcium channels in presynaptic plasma membranes (SPM) and their involvement in the presynaptic receptor-mediated Ca2+influx into nerve terminals. In perfusion experiments using SPM vesicles preloaded with45Ca2+, InsP3elicited the release of45Ca2+into perfusates in a saturable manner. The InsP3-evoked45Ca2+release from resealed SPM vesicles was more potent than that from resealed vesicles using any other subcellular fractions. Here we also report the involvement of InsP3-gated mechanisms in the presynaptic receptor-mediated Ca2+influx into synaptosomes (nerve terminals) by use of such resealed vesicles reconstituted with purified Gi1.
Differential Expression of the p75 Nerve Growth Factor Receptor in Glia and Neurons of the Rat Dorsal Root Ganglia after Peripheral Nerve Transection
Authors: Zhou Xin-Fu , Rush Robert A. , McLachlan Elspeth M.
Published: April 2018

Sympathetic nerve terminals on blood vessels within the dorsal root ganglia sprout after sciatic nerve lesions in the rat. The mechanism underlying this phenomenon is not clear, but might be predicted to involve nerve growth factor or its homologs because these factors are known to trigger collateral sprouting of undamaged sympathetic noradrenergic terminals. We have found that sciatic nerve lesions lead to a decreased expression of neuronal p75, the low-affinity receptor for the neurotrophins, but an increased expression of glial p75 in ipsilateral dorsal root ganglia. Intriguingly, the increased expression of p75 was found primarily in association with glia surrounding large-diameter neurons, which are those associated with the noradrenergic sprouts. A smaller but significant glial response was also found in contralateral ganglia. The glial response in ipsilateral ganglia could be mimicked by ventral, but not dorsal, root transection. The dorsal root lesion-induced glial responses in contralateral ganglia were greater than those induced by ventral root or sciatic nerve lesions. Combined lesions of dorsal root and either ventral root or sciatic nerve did not prevent the glial responses of ipsilateral ganglia, suggesting that a peripheral signal is involved. Colocalization studies indicate that tyrosine hydroxylase-immunoreactive nerve sprouts were associated with p75-immunoreactive glial cells. Thus, increased glial synthesis of p75 might provide an explanation for the abnormal growth of sympathetic fibers in dorsal root ganglia after peripheral nerve injury.
Regulation of α7Nicotinic Acetylcholine Receptors in the Developing Rat Somatosensory Cortex by Thalamocortical Afferents
Authors: Broide Ron S. , Robertson Richard T. , Leslie Frances M.
Published: April 2018

Distributions of α7nicotinic acetylcholine receptor (nAChR) mRNA and [125I]α-bungarotoxin (α-BTX) binding sites in the developing rat somatosensory cortex were characterized in relation to acetylcholinesterase (AChE) histochemical staining of thalamocortical terminals to investigate the role of this receptor in cortical development. Using quantitativein situhybridization and receptor autoradiography, elevated levels of mRNA and binding-site expression were first detected at postnatal day 1 (P1) in deep and superficial layers, just beneath the AChE-stained thalamocortical terminals. Onset of expression occurred ∼1 d after ingrowth of AChE-stained thalamocortical afferents. By P5, mRNA and binding-site expression exhibited a disjunctive, barrel-like pattern in layer IV and, more clearly, in layer VI. The mRNA and binding-site expressions peaked at ∼1 week postnatal and then declined to adult levels. Unilateral electrolytic or cytochemical lesions placed in the thalamic ventrobasal complex at P0 (just as thalamocortical afferents are innervating the cortex) and at P6 (when the somatotopic map is well established) resulted in a marked reduction of α7nAChR mRNA and [125I]α-BTX binding-site levels in layers IV and VI, indicating their regulation by thalamocortical afferents. With P6 lesions, this reduction was observed as early as 6 hr postlesion. These results suggest that α7nAChRs are localized primarily on cortical cells in rat somatosensory cortex and provide further evidence for thalamocortical influence on cortical ontogeny. These data also suggest a role for cholinergic systems during a critical period of cortical synaptogenesis.
Retrograde Transport of Neurotrophins from the Eye to the Brain in Chick Embryos: Roles of the p75NTRand trkB Receptors
Authors: von Bartheld Christopher S. , Williams Reg , Lefcort Frances , Clary Douglas O. , Reichardt Louis F. , Bothwell Mark
Published: April 2018

The receptors involved in retrograde transport of neurotrophins from the retina to the isthmo-optic nucleus (ION) of chick embryos were characterized using antibodies to the p75 neurotrophin receptor and trkB receptors. Survival of neurons in the ION has been shown previously to be regulated by target-derived trophic factors with survival promoted or inhibited by ocular injection of brain-derived neurotrophic factor (BDNF) or nerve growth factor (NGF), respectively. In the present paper, we show that during the period of target dependence, these neurons express trkB and p75 neurotrophin receptor but not trkA or trkC mRNAs. We also show that BDNF and NT-3 were transported efficiently at low doses, whereas NGF was transported significantly only at higher doses. The transport of BDNF and NT-3 was reduced by high concentrations of NGF or by antibodies to either trkB or the p75 neurotrophin receptor. Thus both receptors help mediate retrograde transport of these neurotrophins. Ocular injection of the comparatively specific trk inhibitor K252a did not reduce transport of exogenous BDNF, but did induce significant neuronal death in the ION, which could not be prevented by co-injection of BDNF. Thus, transport of BDNF alone does not generate a trophic signal at the cell body when axonal trkB is inactivated. In summary, our results indicate that both p75 neurotrophin and trkB receptors can mediate internalization and retrograde transport of BDNF, but activation of trkB seems to be essential for the survival-promoting actions of this neurotrophin.
Possible Role of Protein Kinase C in the Sensitization of Primate Spinothalamic Tract Neurons
Authors: Lin Qing , Peng Yuan Bo , Willis William D.
Published: April 2018

The responsiveness of spinal cord nociceptive neurons to innocuous mechanical stimuli can be increased by the release of excitatory amino acids (EAAs) and peptides attributable to an injury-induced barrage of impulses. This sensitization of spinal dorsal horn neurons can also result from administration of phorbol ester by microdialysis, presumably by direct activation of protein kinase C (PKC). This study was designed to examine the effects of central sensitization of spinothalamic tract (STT) neurons produced by intradermal injection of capsaicin on the descending inhibition driven from the periaqueductal gray (PAG) and the possible role of PKC in this process in anesthetized monkeys. Sensitization of responses of STT cells to mechanical stimuli was induced by intradermal injection of capsaicin. PAG inhibition was significantly attenuated when sensitization of responses to mechanical stimuli occurred. However, perfusion of the spinal cord with NPC15437 (a selective PKC inhibitor) by microdialysis could prevent the sensitization of the responses to mechanical stimuli and the reduction in PAG inhibition of these responses induced by capsaicin injection. Results similar to those produced by capsaicin injection were observed when a PKC activator, phorbol ester (12-O-tetradecanoylphorbol-13-acetate), was infused within the dorsal horn by microdialysis. An inactive phorbol ester (4α-phorbol 12,13-didecanoate) had no effect. These results provide evidence that the activation of PKC contributes to the development of central sensitization in dorsal horn neurons produced by chemical stimulation with capsaicin. Attenuation of the effectiveness of PAG inhibition takes place when the sensitization of dorsal horn cells develops, and PKC may play a significant role in this process.
Evolution of Directional Preferences in the Supplementary Eye Field during Acquisition of Conditional Oculomotor Associations
Authors: Chen Longtang L. , Wise Steven P.
Published: April 2018

We assessed the preferred directions (PDs) of supplementary eye field (SEF) neurons during conditional visuomotor learning. Monkeys learned to select one of four saccadic eye movements in response to a foveal instruction stimulus (IS). ISs were either familiar or novel. Each familiar IS reliably evoked one saccade: 7° left, right, up, or down from the central fixation point. Novel ISs initially triggered virtually random responses among those four possibilities, but the monkeys ultimately learned to select the instructed saccade. As reported previously, activity rates on novel IS trials significantly changed during learning. Some of these cells (learning-dependent) also have significant modulation on familiar IS trials, but others (learning-selective) lack such activity. Of the former, the familiar IS activity can be either directionally selective or omnidirectional. For most neurons, PDs were apparent during all phases of learning, but they were rarely constant. Only infrequently did a neuron’s PD for novel ISs closely match that for familiar ISs throughout the learning process. In directional learning-dependent cells, the PD usually reoriented near the end of learning to resemble that for familiar IS trials. In omnidirectional cells, initially evident PDs dissipated with learning, even as the cell became more strongly modulated. Learning-selective cells typically began with significant PDs, but became unmodulated as learning progressed. Our findings show a pervasive lability in SEF PDs that may reflect a flexible and rapid remapping between inputs and responses within the premotor cortical network.
Somatostatin in the Pontine Reticular Formation Modulates Fear Potentiation of the Acoustic Startle Response: An Anatomical, Electrophysiological, and Behavioral Study
Authors: Fendt Markus , Koch Michael , Schnitzler Hans-Ulrich
Published: April 2018

The amplitude of the acoustic startle response (ASR) in rats is increased in the presence of a cue that has previously been paired with an aversive stimulus such as a footshock. This phenomenon is called fear-potentiated startle and is a model to study the neuronal and neurochemical mechanisms of the acquisition and expression of fear. The present study investigated the role in fear-potentiated startle of somatostatin in the caudal pontine reticular nucleus (PnC) by a combination of anatomical, electrophysiological, and behavioral methods. The PnC is an essential part of the primary startle circuit and is also the recipient of modulatory influences. First, we showed that the central gray (CG), which is involved in fear conditioning, is the main source of somatostatinergic input to the PnC. In the second experiment, we iontophoretically applied the somatostatin receptor agonist sandostatin on PnC neurons and extracellularly recorded the activity of PnC neurons. Sandostatin had no effect on tone-evoked or spontaneous activity, but markedly attenuated the increase of neuronal activity seen after the administration of glutamate. In our third experiment, we injected different doses of sandostatin into the PnC of awake rats. Sandostatin blocked fear potentiation of the ASR but had no effect on the baseline ASR amplitude. The present study indicates that the somatostatinergic projection from the CG to the PnC is important for the modulation of fear-potentiated startle. We present a possible neural circuitry for the expression of fear-potentiated startle based on these data and previous findings.
Rewarding Actions of Phencyclidine and Related Drugs in Nucleus Accumbens Shell and Frontal Cortex
Authors: Carlezon, William A. , Wise Roy A.
Published: April 2018

Rats learned to lever-press when such behavior was reinforced by microinjections of phencyclidine (PCP) directly into the ventromedial (shell) region of nucleus accumbens, indicating that the drug has direct rewarding actions in that region. Separate groups of rats learned to lever-press when reinforced with microinjections of dizocilpine (MK-801) or 3-((±)2-carboxypiperazin-4yl)propyl-1-phosphate (CPP), drugs known to block NMDA receptor function but not dopamine uptake, into the same region. Each drug was ineffective or markedly less effective when injected at a slightly more dorsal and lateral site in the core of nucleus accumbens. Self-administration of PCP, MK-801, or CPP directly into nucleus accumbens was not altered by co-infusion of a dose of the dopamine antagonist sulpiride that effectively blocked intracranial self-administration of the dopamine uptake inhibitor nomifensine, suggesting that the rewarding actions of the NMDA receptor antagonists are not dopamine-dependent. Rats also developed lever-pressing habits when PCP, MK-801, and CPP were each microinjected directly into frontal cortex, a region previously associated with the rewarding actions of cocaine but not nomifensine. Thus nucleus accumbens and frontal cortex are each potential substrates for the rewarding properties of PCP and related drugs, and the ability of these drugs to disrupt NMDA receptor function seems sufficient to account for their rewarding actions. When considered with independent evidence, the present results suggest a model of drug reward within which the critical event is inhibition of medium spiny neurons in nucleus accumbens.
Regulation of Neuromodulatory Actions of Angiotensin II in the Brain Neurons by the Ras-Dependent Mitogen-Activated Protein Kinase Pathway
Authors: Yang Hong , Lu Di , Yu Kan , Raizada Mohan K.
Published: April 2018

Angiotensin II (Ang II) stimulates norepinephrine transporter (NET) and tyrosine hydroxylase (TH) in the neurons, but the signal transduction mechanism of this neuromodulation is not understood. Treatment of neuronal cultures of hypothalamus-brainstem with Ang II resulted in a time- and dose-dependent activation of Ras, Raf-1, and mitogen-activated protein kinase. This activation was mediated by the interaction of Ang II with the AT1receptor subtype and was associated with the redistribution of AT1receptor with Ras and Raf-1 on the neuronal membrane. Treatment with antisense oligonucleotide (AON) to mitogen-activated protein kinase decreased mitogen-activated protein kinase immunoreactivity by 70% and attenuated Ang II stimulation of c-fos, NET, and TH mRNA levels. This demonstrates that induction of these genes requires mitogen-activated protein kinase activation by Ang II. In contrast, AON to mitogen-activated protein kinase failed to inhibit Ang II stimulation of plasminogen activator inhibitor-1 mRNA levels. These results suggest that AT1receptors are coupled to a Ras-Raf-1 mitogen-activated protein kinase signal transduction pathway that is responsible for stimulation of NET and TH, two neuromodulatory actions of Ang II in the brain.
Cholinergic-Dependent Plateau Potential in Hippocampal CA1 Pyramidal Neurons
Authors: Fraser Douglas D. , MacVicar Brian A.
Published: April 2018

Cholinergic stimulation of the hippocampal formation results in excitation and/or seizure. We report here, using whole-cell patch-clamp techniques in the hippocampal slice (34–35°C), a cholinergic-dependent slow afterdepolarization (sADP) and long-lasting plateau potential (PP). In the presence of 20 μmcarbachol, action potential firing evoked by weak intracellular current injection elicited an sADP that lasted several seconds. Increased spike firing evoked by stronger depolarizing stimuli resulted in long-duration PPs maintained close to −20 mV. Removal of either Na+or Ca2+from the external media, intracellular Ca2+([Ca2+]i) chelation with 10 mmbis(2-aminophenoxy)ethane-N,N,N′,N′-tetra-acetic acid, or the addition of 100 μmCd2+to the perfusate abolished both the sADP and PP. The sADP was depressed and the PP was abolished by either 10 μmnimodipine or 1 μmω-conotoxin, whereas 1.2 μmtetrodotoxin was ineffective. The involvement of a Na+/Ca2+exchanger was minimal because both the sADP and PP persisted after equimolar substitution of 50 mmLi+for Na+in the external media or reduction of the bath temperature to 25°C. Finally, in the absence of carbachol the sADP and PP could not be evoked when K+channels were suppressed, suggesting that depression of K+conductances alone was not sufficient to unmask the conductance. Based on these data, we propose that a Ca2+-activated nonselective cation conductance was directly enhanced by muscarinic stimulation. The sADP, therefore, represents activation of this conductance by residual [Ca2+]i, whereas the PP represents a novel regenerative event involving the interplay between high-voltage-activated Ca2+channels and the Ca2+-activated nonselective cation conductance. This latter mechanism may contribute significantly to ictal depolarizations observed during cholinergic-induced seizures.
Ultrastructural Localization of the Vesicular Monoamine Transporter-2 in Midbrain Dopaminergic Neurons: Potential Sites for Somatodendritic Storage and Release of Dopamine
Authors: Nirenberg Melissa J. , Chan June , Liu Yongjian , Edwards Robert H. , Pickel Virginia M.
Published: April 2018

Midbrain dopaminergic neurons are known to release dopamine from somata and/or dendrites located in the substantia nigra (SN) and the ventral tegmental area (VTA). There is considerable controversy, however, about the subcellular sites for somatodendritic dopamine storage in these regions. In the present study, we used dual-labeling electron microscopic immunocytochemistry to localize the vesicular monoamine transporter-2 (VMAT2), a novel marker for sites of intracellular monoamine storage, within identified dopaminergic (tyrosine hydroxylase-containing) neurons in the rat SN and VTA. In dopaminergic perikarya, immunogold labeling for VMAT2 was localized to the Golgi apparatus, tubulovesicles that resembled smooth endoplasmic reticulum (SER), and the limiting membranes of multivesicular bodies. In dopaminergic dendrites, VMAT2 was extensively localized to tubulovesicles that resembled saccules of SER, and less frequently localized to isolated small synaptic vesicles (SSVs) or large dense-core vesicles (DCVs). In rare cases, VMAT2-immunoreactive SSVs were clustered within the cytoplasm of an SN or a VTA dendrite. Dopaminergic dendrites in the VTA contained a significantly higher number of immunogold particles for VMAT2 per unit area than those in the SN. Together, these observations support the proposal that dopamine is stored in and may be released from dendritic SSVs and DCVs, but suggest that the SER is the major site of dopamine storage within midbrain dopaminergic neurons. In addition, they provide new evidence that dopaminergic dendrites in the VTA may have greater potential for reserpine-sensitive storage and release of dopamine than those in the SN.
Multiple Subtypes of Voltage-Gated Calcium Channel Mediate Transmitter Release from Parasympathetic Neurons in the Mouse Bladder
Authors: Waterman Sally A.
Published: April 2018

Multiple subtypes of voltage-gated calcium channels are coupled to transmitter release from central neurons; however, only N-type channels have been shown to play a role in autonomic neurons. The aim of the present study was to investigate potential roles for other channel subtypes in transmitter release from parasympathetic neurons in the mouse bladder using calcium channel toxins alone and in combination. Transmitter release was measured indirectly by recording the contraction of bladder dome strips in response to electrical stimulation of the neurons by single pulses or trains of 20 pulses at 1–50 Hz. ω-Conotoxin-GVIA (GVIA) and ω-conotoxin-MVIIC (MVIIC) inhibited contractions in a concentration-dependent manner, with IC50values of ∼30 and 200 nm, respectively, at low stimulation frequencies. ω-Agatoxin-IVA (agatoxin) alone did not have any significant effect up to 300 nm. Cumulative addition of the toxins demonstrated that 300 nmagatoxin had a significant effect after N-type channels were blocked with 100 nmGVIA. MVIIC (3 μm) reduced the contraction amplitude further. Testing the toxins on the cholinergic or purinergic component of the contraction separately showed that acetylcholine release depends primarily on N-type channels and, to a lesser extent, on P- and Q-type channels, whereas ATP release involves predominantly P- and Q-type channels. In conclusion, parasympathetic neurons in the mouse bladder, like central neurons, use multiple calcium channel subtypes. Furthermore, the release of the two main transmitters in these neurons has differing dependencies on the calcium channel subtypes.
Protection of Retinal Ganglion Cells from Natural and Axotomy-Induced Cell Death in Neonatal Transgenic Mice Overexpressing bcl-2
Authors: Bonfanti Lidia , Strettoi Enrica , Chierzi Sabrina , Cenni Maria Cristina , Liu Xiu-Huai , Martinou Jean-Claude , Maffei Lamberto , Rabacchi Sylvia A.
Published: April 2018

Approximately half of the retinal ganglion cells (RGCs) present in the rodent retina at birth normally die during early development. Overexpression of the proto-oncogene bcl-2 recently has been shown to rescue some neuronal populations from natural cell death and from degeneration induced by axotomy of nerves within the peripheral nervous system. Here we studyin vivothe role of the overexpression of bcl-2 in the natural cell death of RGCs and in the degenerative process induced in these cells by transection of the optic nerve. We find that in newborn bcl-2 transgenic mice, the number of RGCs undergoing natural cell death is considerably lower than in wild-type pups. Consistently, a vast majority (90%) of the ganglion cells found in the retina of neonatal transgenics are maintained in adulthood, whereas only 40% survive in wild-type mice.

After transection of the optic nerve, the number of degenerating ganglion cells, determined by counting pyknotic nuclei or nuclei with fragmented DNA, is substantially reduced in transgenic mice. In wild-type animals, almost 50% of ganglion cells degenerate in the 24 hr after the lesion, whereas almost the entire ganglion cell population survives axotomy in transgenic mice. Therefore, overexpression of bcl-2 is effective in preventing degeneration of this neuronal population, raising the possibility that ganglion cells are dependent on the endogenous expression of bcl-2 for survival. The remarkable rescue capacity of bcl-2 overexpression in these neurons makes it an interesting model for studying natural cell death and responses to injury in the CNS.
Dual Action of a Carbohydrate Epitope on Afferent and Efferent Axons in Cortical Development
Authors: Henke-Fahle Sigrid , Mann Fanny , Götz Magdalena , Wild Karen , Bolz Jürgen
Published: April 2018

During development of the mammalian cerebral cortex, ingrowing afferents from the thalamus take a path that is different from that of axons leaving the cortical plate. Thalamic axons arrive at the cortex at the time before their target cells of layer 4 are generated in the ventricular zone, but they invade the cortex only shortly before these cells have migrated to their final position in the cortex. Growth-promoting molecules are upregulated in the developing cortical plate during this period. To identify such molecules, we have generated monoclonal antibodies against membrane preparations from rat postnatal cortex. In Western blots, one antibody (mAb 10) recognized a carbohydrate epitope of a glycoprotein with an apparent molecular weight extending from 180 to 370 kDa. Immunohistochemical staining revealed that the staining pattern of mAb 10 at embryonic stages delineates the pathway of thalamocortical axons, with only very faint labeling of the corticofugal pathway.In vitroassays in combination with time-lapse imaging indicated that mAb 10 has opposite effects on the growth of thalamic and cortical axons. The growth speed and axonal elongation of thalamic fibers on postnatal cortical membranes preincubated with mAb 10 was reduced compared with untreated cortical membranes. In contrast, cortical axons grew faster and stopped their growth less frequently after addition of mAb 10 to a cortical membrane substrate. Taken together, these results suggest that a carbohydrate moiety of a membrane-associated glycoprotein plays a role in the segregation of afferent and efferent cortical axons in the white matter. Moreover, the epitope recognized by mAb 10 might also contribute to regulation of the timing of the thalamocortical innervation at later developmental stages.
Linear Systems Analysis of Functional Magnetic Resonance Imaging in Human V1
Authors: Boynton Geoffrey M. , Engel Stephen A. , Glover Gary H. , Heeger David J.
Published: April 2018

The linear transform model of functional magnetic resonance imaging (fMRI) hypothesizes that fMRI responses are proportional to local average neural activity averaged over a period of time. This work reports results from three empirical tests that support this hypothesis. First, fMRI responses in human primary visual cortex (V1) depend separably on stimulus timing and stimulus contrast. Second, responses to long-duration stimuli can be predicted from responses to shorter duration stimuli. Third, the noise in the fMRI data is independent of stimulus contrast and temporal period. Although these tests can not prove the correctness of the linear transform model, they might have been used to reject the model. Because the linear transform model is consistent with our data, we proceeded to estimate the temporal fMRI impulse–response function and the underlying (presumably neural) contrast–response function of human V1.
Amphetamine and Dopamine-Induced Immediate Early Gene Expression in Striatal Neurons Depends on Postsynaptic NMDA Receptors and Calcium
Authors: Konradi Christine , Leveque Jean-Christophe , Hyman Steven E.
Published: April 2018

Amphetamine and cocaine induce the expression of both immediate early genes (IEGs) and neuropeptide genes in rat striatum. Despite the demonstrated dependence of these effects on D1dopamine receptors, which activate the cyclic AMP pathway, there are several reports that amphetamine and cocaine-induced IEG expression can be inhibited in striatumin vivoby NMDA receptor antagonists. We find thatin vivo,the NMDA receptor antagonist MK-801 inhibits amphetamine induction ofc-fosacutely and also prevents downregulation of IEG expression with chronic amphetamine administration. Such observations raise the question of whether dopamine/glutamate interactions occur at the level of corticostriatal and mesostriatal circuitry or within striatal neurons. Therefore, we studied dissociated striatal cultures in which midbrain and cortical presynaptic inputs are removed. In these cultures, we find that dopamine- or forskolin-mediated IEG induction requires Ca2+entry via NMDA receptors but not via L-type Ca2+channels. Moreover, blockade of NMDA receptors diminishes the ability of dopamine to induce phosphorylation of the cyclic AMP responsive element binding protein CREB. Although these results do not rule out a role for circuit-level dopamine/glutamate interactions, they demonstrate a requirement at the cellular level for interactions between the cyclic AMP and NMDA receptor pathways in dopamine-regulated gene expression in striatal neurons.
Kainic Acid-Induced Seizures Enhance Dentate Gyrus Inhibition by Downregulation of GABABReceptors
Authors: Haas Kurt Z. , Sperber Ellen F. , Moshé Solomon L. , Stanton Patric K.
Published: April 2018

Seizures cause a persistent enhancement in dentate synaptic inhibition concurrent with, and possibly compensatory for, seizure-induced hippocampal hyperexcitability. To study this phenomenon, we evoked status epilepticus in rats with systemic kainic acid (KA), and 2 weeks later assessed granule cell inhibition with paired-pulse stimulation of the perforant path (PP)in vitro. Controls demonstrated three components of paired-pulse inhibition: early inhibition (10–30 msec), intermediate facilitation (30–120 msec), and late inhibition (120 msec to 120 sec). After seizures, inhibition in all components was enhanced significantly. The GABAAantagonist bicuculline blocked only early enhanced inhibition, demonstrating that both GABAAand GABABpostsynaptic receptors contribute to seizure-induced enhanced inhibition. In controls, the GABABantagonist CGP 35348 increased both GABAAand GABABresponses in granule cells, suggesting that CGP 35348 acts presynaptically, blocking receptors that suppress GABA release. In contrast, slices from KA-treated rats were markedly less sensitive to CGP 35348. To test the hypothesis that GABABreceptors regulating GABA release are downregulated after seizures, we measured paired-pulse suppression of recurrent IPSPs, or disinhibition, using mossy fiber stimuli. Early disinhibition (< 200 msec) was reduced after seizures, whereas late disinhibition remained intact. CGP 35348 blocked the early component of disinhibition in controls and, to a lesser extent, reduced disinhibition in KA slices. However, paired monosynaptic IPSPs recorded intracellularly showed no difference in disinhibition between groups. Our findings indicate that seizure-induced enhancement in dentate inhibition is caused, at least in part, by reduced GABABfunction in the polysynaptic recurrent inhibitory circuit, resulting in reduced disinhibition and heightened GABA release.
Cerebral Representation of One’s Own Past: Neural Networks Involved in Autobiographical Memory
Authors: Fink Gereon R. , Markowitsch Hans J. , Reinkemeier Mechthild , Bruckbauer Thomas , Kessler Josef , Heiss Wolf-Dieter
Published: April 2018

We studied the functional anatomy of affect-laden autobiographical memory in normal volunteers. Using H215O positron emission tomography (PET), we measured changes in relative regional cerebral blood flow (rCBF). Four rCBF measurements were obtained during three conditions: REST, i.e., subjects lay at rest (for control); IMPERSONAL, i.e., subjects listened to sentences containing episodic information taken from an autobiography of a person they did not know, but which had been presented to them before PET scanning (nonautobiographical episodic memory ecphory); and PERSONAL, i.e., subjects listened to sentences containing information taken from their own past (autobiographical episodic memory ecphory).

Comparing IMPERSONAL with REST (nonautobiographical episodic memory ecphory) resulted in relative rCBF increases symmetrically in both temporal lobes including the temporal poles and medial and superior temporal gyri. The same loci, however, with a stronger lateralization to the right hemisphere were activated in the comparison PERSONAL to REST (autobiographical episodic memory ecphory). In addition, the right temporomesial, right dorsal prefrontal, right posterior cingulate areas, and the left cerebellum were activated. A comparison of PERSONAL and IMPERSONAL (autobiographical vs nonautobiographical episodic memory ecphory) demonstrated a preponderantly right hemispheric activation including primarily right temporomesial and temporolateral cortex, right posterior cingulate areas, right insula, and right prefrontal areas. The right temporomesial activation included hippocampus, parahippocampus, and amygdala.

These results suggest that a right hemispheric network of temporal, together with posterior, cingulate, and prefrontal, areas is engaged in the ecphory of affect-laden autobiographical information.
Induction of Hebbian and Non-Hebbian Mossy Fiber Long-Term Potentiation by Distinct Patterns of High-Frequency Stimulation
Authors: Urban Nathaniel N. , Barrionuevo German
Published: April 2018

The synapse made by hippocampal mossy fibers onto pyramidal neurons of hippocampal area CA3 displays a form of long-term potentiation (LTP) that is independent of the activation of NMDA receptors. Considerable controversy exists as to whether the induction of mossy fiber LTP requires postsynaptic activation and, thus, whether mossy fiber LTP is Hebbian or non-Hebbian. Here we report the induction of both Hebbian and non-Hebbian forms of long-term potentiation at the mossy fiber–CA3 synapse inin vitroslice preparation. These two forms of potentiation can be induced selectively by different induction conditions. Sustained presynaptic activation is sufficient to induce the non-Hebbian form of mossy fiber LTP, whereas brief presynaptic activation coincident with postsynaptic depolarization is required to induce the Hebbian form. We suggest that non-Hebbian forms of plasticity may play an important role in dynamically regulating the thresholds for inducing Hebbian forms of plasticity.
Phenotypic Alteration of a Human BK (hSlo) Channel byhSloβSubunit Coexpression: Changes in Blocker Sensitivity, Activation/Relaxation and Inactivation Kinetics, and Protein Kinase A Modulation
Authors: Dworetzky Steven I. , Boissard Christopher G. , Lum-Ragan Janet T. , McKay M. Craig , Post-Munson Debra J. , Trojnacki Joanne T. , Chang Chia-Ping , Gribkoff Valentin K.
Published: April 2018

A human homolog of the large-conductance calcium-activated potassium (BK) channel β subunit (hSloβ) was cloned, and its effects on a human BK channel (hSlo) phenotype are reported. Coexpression ofhSloandhSloβ, in both oocytes and human embryonic kidney 293 cells, resulted in increased Ca2+sensitivity, marked slowing of BK channel activation and relaxation, and a significant reduction in slow inactivation. In addition, coexpression changed the pharmacology of the BK channel phenotype:hSlo-mediated currents in oocytes were more sensitive to the peptide toxin iberiotoxin than werehSlo + hSloβ currents, and the potency of blockade by the alkaloid BK blocker tetrandrine was much greater onhSlo + hSloβ-mediated currents compared withhSlocurrents alone. No significant differences in the response to charybdotoxin or the BK channel opener NS1619 were observed. Modulation of BK channel activity by phosphorylation was also affected by the presence of thehSloβ subunit. Application of cAMP-dependent protein kinase increasedPOPENofhSlochannels, but decreasedPOPENof mosthSlo + hSloβ channels. Taken together, these altered characteristics may explain some of the wide diversity of BK channel phenotypes observed in native tissues.
Visual Motion-Detection Circuits in Flies: Parallel Direction- and Non-Direction-Sensitive Pathways between the Medulla and Lobula Plate
Authors: Douglass John K. , Strausfeld Nicholas J.
Published: April 2018

The neural circuitry of motion processing in insects, as in primates, involves the segregation of different types of visual information into parallel retinotopic pathways that subsequently are reunited at higher levels. In insects, achromatic, motion-sensitive pathways to the lobula plate are separated from color-processing pathways to the lobula. Further parallel subdivisions of the retinotopic pathways to the lobula plate have been suggested from anatomical observations. Here, we provide direct physiological evidence that the two most prominent of these latter pathways are, indeed, functionally distinct: recordings from the retinotopic pathway defined by small-field bushy T-cells (T4) demonstrate only weak directional selectivity to motion, in striking contrast with previously demonstrated strong directional selectivity in the second, T5-cell, pathway. Additional intracellular recordings and anatomical descriptions have been obtained from other identified neurons that may be crucial in early motion detection and processing: a deep medulla amacrine cell that seems well suited to provide the lateral interactions among retinotopic elements required for motion detection; a unique class of Y-cells that provide small-field, directionally selective feedback from the lobula plate to the medulla; and a new heterolateral lobula plate tangential cell that collates directional, motion-sensitive inputs. These results add important new elements to the set of identified neurons that process motion information. The results suggest specific hypotheses regarding the neuronal substrates for motion-processing circuitry and corroborate behavioral studies in bees that predict distinct pathways for directional and nondirectional motion.
Involvement of a Phorbol Ester-Insensitive Protein Kinase C in the α2-Adrenergic Inhibition of Voltage-Gated Calcium Current in Chick Sympathetic Neurons
Authors: Boehm Stefan , Huck Sigismund , Freissmuth Michael
Published: April 2018

α2-Adrenoceptors regulate the efficacy at the sympatho-effector junction by means of a feedback inhibition of transmitter release. In chick sympathetic neurons, the mechanism involves an inhibition of N-type calcium channels, and we now present evidence that this effect involves an atypical, phorbol ester-insensitive protein kinase C (PKC). The inhibition of voltage-gated Ca2+currents by the specific α2-adrenergic agonist UK 14,304 was significantly attenuated when the PKC inhibitors PKCI(19–36), staurosporine, or calphostin C were included in the internal solution used to fill the patch pipettes, or if staurosporine or calphostin C were applied extracellularly; however, phorbol esters as classical activators of PKC or oleoylacetylglycerol did not mimic the effect of UK 14,304, and chronic exposure to 4-β-phorbol dibutyrate (PDBu) did not attenuate it, even though PKCα and -ε isozymes were translocated to plasma membranes by PDBu. The atypical isozyme PKCζ was translocated by 100 μmarachidonic acid (AA), but not by PDBu; 100 μmAA and linoleic acid inhibited voltage-activated Ca2+currents, and this effect was attenuated when PKCI(19–36) was added to the patch pipette solution. Our observations indicate that classical, new, and atypical PKC isozymes are present in chick sympathetic neurons and that an atypical, phorbol ester-insensitive PKC is involved in the inhibition of voltage-activated calcium currents by α2-adrenoceptor activation.
Selective G-Protein Regulation of Neuronal Calcium Channels
Authors: Toth Peter T. , Shekter Lee R. , Hui Ma Gloria , Philipson Louis H. , Miller Richard J.
Published: April 2018

We examined the properties and regulation of Ca channels resulting from the expression of human α1Band α1Esubunits stably expressed in HEK293 cells. The ancillary subunits β1Band α2/δ were also stably expressed in these cell lines. Ca currents in α1B-expressing cells had the properties of N-type currents. Ca currents in cells expressing α1Eexhibited a novel profile that was similar to the properties of the “R type” Ca current. Introduction of GTP-γ-S into α1Bcells greatly enhanced the extent of prepulse facilitation of the Ca current, whereas it had only a very small effect in α1E-expressing cells. Activation of somatostatin receptors endogenous to HEK293 cells or κ opioid receptors, expressed in the cells after transfection, inhibited Ca currents in α1B-expressing cells. This inhibition was blocked by pertussis toxin and was partially relieved by a depolarizing prepulse. In contrast, no inhibitory effects were noted in cells expressing α1Echannels under the same circumstances. HEK293 cells normally contained G-proteins from all of the four major families. Inhibition of Ca currents by κ agonists in α1B-expressing cells was enhanced slightly by the cotransfection of several G-protein α subunits. κ agonists, however, had no effect in α1E-containing cells, even after overexpression of different G-protein α-subunits. In summary, these results demonstrate that there is a large difference in the susceptibility of α1B- and α1E-based Ca channels to regulation by G-proteins. This is so despite the fact that the two types of Ca channels show substantial similarities in their primary sequences.