bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulation of TTX-RINaby PKC and PKA and Their Role in PGE2-Induced Sensitization of Rat Sensory NeuronsIn Vitro
Authors: Gold Michael S. , Levine Jon D. , Correa Ana M.
Published: April 2018

A tetrodotoxin-resistant voltage-gated Na+current (TTX-RINa) appears to be the current primarily responsible for action potential generation in the cell body and terminals of nociceptive afferents. Although other voltage-gated Na+currents are modulated by the activation of protein kinase C (PKC), protein kinase A (PKA), or both, the second messenger pathways involved in the modulation of TTX-RINaare still being defined. We have examined the modulation of TTX-RINain isolated sensory neurons with whole-cell voltage-clamp recording. Activation of either PKC or PKA increased TTX-RINa. PKA activation also produced a leftward shift in the conductance–voltage relationship of TTX-RINaand an increase in the rates of current activation, deactivation, and inactivation. Inhibitors of PKC decreased TTX-RINa, whereas inhibitors of PKA had no effect on the current. Investigating the interaction between PKC and PKA revealed that although inhibitors of PKA had little effect on PKC-induced modulation of TTX-RINa, inhibitors of PKC significantly attenuated PKA-induced modulation of the current. Finally, although PGE2-induced modulation of TTX-RINawas more similar to PKA-induced modulation of the current than to PKC-induced modulation, PGE2-induced effects were inhibited by inhibitors of both PKC and PKA. Thus, although TTX-RINais a common target for cellular processes involving the activation of either PKA or PKC, PKC activity is necessary to enable subsequent PKA-mediated modulation of TTX-RINa.
Chronic Interleukin-6 Alters NMDA Receptor-Mediated Membrane Responses and Enhances Neurotoxicity in Developing CNS Neurons
Authors: Qiu Zhihua , Sweeney Dan D. , Netzeband Jeffrey G. , Gruol Donna L.
Published: April 2018

Recent studies show that the cytokine interleukin-6 (IL-6) is expressed at elevated levels in the CNS in several disease states and contributes to the neuropathological process. The mechanisms through which IL-6 exerts its CNS effects are primarily unknown. We have investigated the pathophysiological effects of IL-6 on developing CNS neurons using a culture model system and a chronic treatment paradigm. Here, we show, using current- and voltage-clamp recordings, that chronic IL-6 treatment of developing cerebellar granule neurons increases the membrane and current response to NMDA and that these effects are the primary mechanism through which IL-6 produces an enhanced calcium signal to NMDA. We also show that calcium influx through voltage-sensitive calcium channels contributes to the enhanced calcium signal to NMDA in the IL-6-treated neurons in a developmentally regulated manner and that the membrane depolarization to NMDA is more sensitive to the NMDA receptor antagonist ifenprodil in the IL-6-treated neurons compared with control neurons at a late developmental stage, consistent with a larger proportion of NMDA receptors containing the NMDAR2B subunit in the IL-6-treated neurons. Additional studies show that IL-6 treatment reduces the number of granule neurons in culture and enhances neurotoxicity involving NMDA receptors. These results support a pathological role for IL-6 in the CNS and indicate that NMDA receptor-mediated functions are likely to play a critical role in neuropathological changes observed in CNS diseases associated with elevated CNS levels of IL-6.
D1Receptor in Interneurons of Macaque Prefrontal Cortex: Distribution and Subcellular Localization
Authors: Muly E. Chris , Szigeti Klara , Goldman-Rakic Patricia S.
Published: April 2018

Working memory performance is influenced by dopamine activation of D1 family dopamine receptors in the prefrontal cortex; working memory performance is maximal at moderate stimulation of D1 family receptors and is reduced by either higher or lower levels of D1 stimulation. The neuronal mechanisms that underlie this complex relationship are not yet understood. Previous work from this laboratory has demonstrated that the D1 family receptors, D1and D5, are located in different compartments of pyramidal cells. Here we use an antibody specific to the D1receptor and double-label immunohistochemistry at the light and electron microscopic level to demonstrate that D1-like immunoreactivity (D1-LIR) is also present in interneurons. D1receptor is prevalent in parvalbumin-containing interneurons and is less common in calretinin-containing interneurons. At the ultrastructural level, D1-LIR is found associated with the Golgi apparatus and endoplasmic reticulum in the soma, with the membranes of vesicles in proximal dendrites, and with the plasma membrane on distal dendrites, where it is often located near asymmetric synapses. In addition, D1-LIR is also seen in presynaptic axon terminals, which give rise to symmetric synapses onto dendritic shafts and soma. These results raise the possibility that the circuit basis of working memory in the prefrontal cortex involves a D1-mediated inhibitory component.
Neurotransmitter Coupling through Gap Junctions in the Retina
Authors: Vaney David I. , Nelson J. Charles , Pow David V.
Published: April 2018

Although all bipolar cells in the retina probably use the excitatory transmitter glutamate, approximately half of the cone bipolar cells also contain elevated levels of the inhibitory transmitter glycine. Some types of cone bipolar cells make heterologous gap junctions with rod amacrine cells, which contain elevated levels of glycine, leading to the hypothesis that the bipolar cells obtain their glycine from amacrine cells. Experimental support for this hypothesis is now provided by three independent lines of evidence. First, the glycine transporter GLYT1 is expressed by the glycine-containing amacrine cells but not by the glycine-containing bipolar cells, suggesting that only the amacrine cells are functionally glycinergic. Second, the gap-junction blocker carbenoxolone greatly reduces exogenous3H-glycine accumulation into the bipolar cells but not the amacrine cells. Moreover, when the endogenous glycine stores in both cell classes are depleted by incubating the retina with a glycine-uptake inhibitor, carbenoxolone blocks the subsequent glycine replenishment of the bipolar cells but not the amacrine cells. Third, intracellular injection of rod amacrine cells with the gap-junction permeant tracer Neurobiotin secondarily labels a heterogenous population of cone bipolar cells, all of which show glycine immunoreactivity. Taken together, these findings indicate that the elevated glycine in cone bipolar cells is not derived by high-affinity uptake orde novosynthesis but is obtained by neurotransmitter coupling through gap junctions with glycinergic amacrine cells. Thus transmitter content may be an unreliable indicator of transmitter function for neurons that make heterologous gap junctions.
Psychostimulant-Induced Fos Protein Expression in the Thalamic Paraventricular Nucleus
Authors: Deutch Ariel Y. , Bubser Michael , Young Cheryl D.
Published: April 2018

Lesions of glutamatergic afferents to the nucleus accumbens have been reported to block psychostimulant-induced behavioral sensitization. However, thalamic glutamatergic projections to the nucleus accumbens have received little attention in the context of psychostimulant actions. We examined the effects of acute amphetamine and cocaine administration on expression of Fos protein in the thalamic paraventricular nucleus (PVT), which provides glutamatergic inputs to the nucleus accumbens and also receives dopaminergic afferents. Immunoblot and immunohistochemical studies revealed that both psychostimulants dose-dependently increased PVT Fos expression. PVT neurons retrogradely labeled from the nucleus accumbens were among the PVT cells that showed a Fos response to amphetamine. D2family dopamine agonists, including low doses of the D3-preferring agonist 7-OH-DPAT, increased the numbers of Fos-like-immunoreactive neurons in the PVT. Conversely, the effects of cocaine and amphetamine on PVT Fos expression were blocked by pretreatment with the dopamine D2/3antagonist raclopride. Because PVT neurons express D3but not other dopamine receptor transcripts, it appears that psychostimulants induce Fos in PVT neurons through a D3dopamine receptor. We suggest that the PVT may be an important part of an extended circuit subserving both the arousing properties and reinforcing aspects of psychostimulants.
An Oscillatory Short-Term Memory Buffer Model Can Account for Data on the Sternberg Task
Authors: Jensen Ole , Lisman John E.
Published: April 2018

A limited number (7 ± 2) of items can be held in human short-term memory (STM). We have previously suggested that observed dual (theta and gamma) oscillations could underlie a multiplexing mechanism that enables a single network to actively store up to seven memories. Here we have asked whether models of this kind can account for the data on the Sternberg task, the most quantitative measurements of memory search available. We have found several variants of the oscillatory search model that account for the quantitative dependence of the reaction time distribution on the number of items (S) held in STM. The models differ on the issues of (1) whether theta frequency varies with S and (2) whether the phase of ongoing oscillations is reset by the probe. Using these models the frequencies of dual oscillations can be derived from psychophysical data. The derived values (fθ= 6–10  Hz ; fγ= 45–60  Hz) are in reasonable agreement with experimental values. The exhaustive nature of the serial search that has been inferred from psychophysical measurements can be plausibly explained by these oscillatory models. One argument against exhaustive serial search has been the existence of serial position effects. We find that these effects can be explained by short-term repetition priming in the context of serial scanning models. Our results strengthen the case for serial processing and point to experiments that discriminate between variants of the serial scanning process.
Rhythmic Properties of the Hamster Suprachiasmatic NucleusIn Vivo
Authors: Yamazaki Shin , Kerbeshian Marie C. , Hocker Craig G. , Block Gene D. , Menaker Michael
Published: April 2018

We recorded multiple unit neural activity [multiunit activity (MUA)] from inside and outside of the suprachiasmatic nucleus (SCN) in freely moving male golden hamsters housed in running-wheel cages under both light/dark cycles and constant darkness. The circadian period of MUA in the SCN matched the period of locomotor activity; it was ∼24 hr in wild-type and 20 hr in homozygoustaumutant hamsters. The peak of MUA in the SCN always occurred in the middle of the day or, in constant darkness, the subjective day. There were circadian rhythms of MUA outside of the SCN in the ventrolateral thalamic nucleus, the caudate putamen, the accumbens nucleus, the medial septum, the lateral septum, the ventromedial hypothalamic nucleus, the medial preoptic region, and the stria medullaris. These rhythms were out-of-phase with the electrical rhythm in the SCN but in-phase with the rhythm of locomotor activity, peaking during the night or subjective night. In addition to circadian rhythms, there were significant ultradian rhythms present; one, with a period of ∼80 min, was in antiphase between the SCN and other brain areas, and another, with a period of ∼14 min, was in-phase between the SCN and other brain areas. The periods of these ultradian rhythms were not significantly different in wild-type andtaumutant hamsters. Of particular interest was the unique phase relationship between the MUA of the bed nucleus of the stria terminalis (BNST) and the SCN; in these two areas both circadian and ultradian components were always in-phase. This suggests that the BNST is strongly coupled to the SCN and may be one of its major output pathways. In addition to circadian and ultradian rhythms of MUA, neural activity both within and outside the SCN was acutely affected by locomotor activity. Whenever a hamster ran on its wheel, MUA in the SCN and the BNST was suppressed, and MUA in other areas was enhanced.
A Persistent Activity-Dependent Facilitation in Chromaffin Cells Is Caused by Ca2+Activation of Protein Kinase C
Authors: Smith Corey
Published: April 2018

Activity-dependent facilitation was studied in bovine adrenal chromaffin cells. Stimulation with a train of depolarizations caused subsequent triggered exocytotic activity to be significantly enhanced. After the facilitating stimulus train, the readily releasable vesicle pool (RRP) size was estimated from capacitance jumps in response to paired depolarizations and found to be elevated for a period of at least 10 min. The time dependency of onset and degree of facilitation could be well fitted assuming protein kinase C (PKC)-dependent and independent Ca2+-mediated processes. Both processes increase the recruitment of vesicles from the reserve pool to the RRP, resulting in an greater number of releasable vesicles. The data suggest that cell activity can act as a trigger to increase cytosolic Ca2+to a level sufficient to cause an increase in the number of readily releasable secretory vesicles, with the more persistent component of the evoked facilitation being mediated through activity-dependent activation of PKC.
Subthalamic Nucleus Neurons Switch from Single-Spike Activity to Burst-Firing Mode
Authors: Beurrier Corinne , Congar Patrice , Bioulac Bernard , Hammond Constance
Published: April 2018

The modification of the discharge pattern of subthalamic nucleus (STN) neurons from single-spike activity to mixed burst-firing mode is one of the characteristics of parkinsonism in rat and primates. However, the mechanism of this process is not yet understood. Intrinsic firing patterns of STN neurons were examined in rat brain slices with intracellular and patch-clamp techniques. Almost half of the STN neurons that spontaneously discharged in the single-spike mode had the intrinsic property of switching to pure or mixed burst-firing mode when the membrane was hyperpolarized from −41.3 ± 1.0 mV (range, −35 to −50 mV;n= 15) to −51.0 ± 1.0 mV (range, −42 to −60 mV;n= 20). This switch was greatly facilitated by activation of metabotropic glutamate receptors with 1S,3R-ACPD. Recurrent membrane oscillations underlying burst-firing mode were endogenous and Ca2+-dependent because they were largely reduced by nifedipine (3 μm), Ni2+(40 μm), and BAPTA-AM (10–50 μm) at any potential tested, whereas TTX (1 μm) had no effect. In contrast, simultaneous application of TEA (1 mm) and apamin (0.2 μm) prolonged burst duration. Moreover, in response to intracellular stimulation at hyperpolarized potentials, a plateau potential with a voltage and ionic basis similar to those of spontaneous bursts was recorded in 82% of the tested STN neurons, all of which displayed a low-threshold Ni2+-sensitive spike. We propose that recurrent membrane oscillations during bursts result from the sequential activation of T/R- and L-type Ca2+currents, a Ca2+-activated inward current, and Ca2+-activated K+currents.
Differential Binding of Tropane-Based Photoaffinity Ligands on the Dopamine Transporter
Authors: Vaughan Roxanne A. , Agoston Gregory E. , Lever John R. , Newman Amy Hauck
Published: April 2018

Benztropine and its analogs are tropane ring–containing dopamine uptake inhibitors that produce behavioral effects markedly different from cocaine and other dopamine transporter blockers. We investigated the benztropine binding site on dopamine transporters by covalently attaching a benztropine-based photoaffinity ligand, [125I]N-[n-butyl-4-(4‴-azido-3‴-iodophenyl)]-4′,4"-difluoro-3α-(diphenylmethoxy)tropane ([125I]GA II 34), to the protein, followed by proteolytic and immunological peptide mapping. The maps were compared with those obtained for dopamine transporters photoaffinity labeled with a GBR 12935 analog, [125I]1-[2-(diphenylmethoxy)ethyl]-4-[2-(4-azido-3-iodophenyl)ethyl]piperazine ([125I]DEEP), and a cocaine analog, [125I]3β-(p-chlorophenyl)tropane-2β-carboxylic acid, 4′-azido-3′-iodophenylethyl ester ([125I]RTI 82), which have been shown previously to interact with different regions of the primary sequence of the protein. [125I]GA II 34 became incorporated in a membrane-bound, 14 kDa fragment predicted to contain transmembrane domains 1 and 2. This is the same region of the protein that binds [125I]DEEP, whereas the binding site for [125I]RTI 82 occurs closer to the C terminal in a domain containing transmembrane helices 4–7. Thus, although benztropine and cocaine both contain tropane rings, their binding sites are distinct, suggesting that dopamine transport inhibition may occur by different mechanisms. These results support previously derived structure–activity relationships suggesting that benztropine and cocaine analogs bind to different domains on the dopamine transporter. These differing molecular interactions may lead to the distinctive behavioral profiles of these compounds in animal models of drug abuse and indicate promise for the development of benztropine-based molecules for cocaine substitution therapies.
Calcium Channel Types with Distinct Presynaptic Localization Couple Differentially to Transmitter Release in Single Calyx-Type Synapses
Authors: Wu Ling-Gang , Westenbroek Ruth E. , Borst J. Gerard G. , Catterall William A. , Sakmann Bert
Published: April 2018

We studied how Ca2+influx through different subtypes of Ca2+channels couples to release at a calyx-type terminal in the rat medial nucleus of the trapezoid body by simultaneously measuring the presynaptic Ca2+influx evoked by a single action potential and the EPSC. Application of subtype-specific toxins showed that Ca2+channels of the P/Q-, N-, and R-type controlled glutamate release at a single terminal. The Ca2+influx through the P/Q-type channels triggered release more effectively than Ca2+influx through N- or R-type channels. We investigated mechanisms that contributed to these differences in effectiveness. Electrophysiological experiments suggested that individual release sites were controlled by all three subtypes of Ca2+channels. Immunocytochemical staining indicated, however, that a substantial fraction of N- and R-type channels was located distant from release sites. Although these distant channels contributed to the Ca2+influx into the terminal, they may not contribute to release. Taken together, the results suggest that the Ca2+influx into the calyx via N- and R-type channels triggers release less effectively than that via P/Q-type because a substantial fraction of the N- and R-type channels in the calyx is localized distant from release sites.
Reciprocal Changes in the Firing Probability of Lateral and Central Medial Amygdala Neurons
Authors: Collins Dawn R. , Paré Denis
Published: April 2018

The amygdala is essential for classical fear conditioning. According to the current model of auditory fear conditioning, the lateral nucleus is the input station of the amygdala for conditioned auditory stimuli, whereas the central nucleus is the output station for conditioned fear responses. Yet, the lateral nucleus does not project to the central medial nucleus, where most brainstem projections of the amygdala originate. The available evidence suggests that the basal nuclei could transmit information from the lateral to the central medial nucleus. However, interposed between the basolateral complex and the central nucleus are clusters of GABAergic cells, the intercalated neurons, which receive inputs from the lateral and basal nuclei and contribute a massive projection to the central medial nucleus. Because it is impossible to predict the consequences of these connections, we correlated the spontaneous and auditory-evoked activity of multiple simultaneously recorded neurons of the lateral, basal, and central nuclei. The spontaneous activity of lateral and basolateral neurons was positively correlated to that of central lateral cells but negatively correlated to that of central medial neurons. In response to auditory stimuli, the firing probability of lateral and central medial neurons oscillated in phase opposition, initially being excited and inhibited, respectively. In light of previous anatomical findings, we propose that the lateral nucleus exerts two indirect actions on central medial neurons: an excitation via the basal nuclei and an inhibition via intercalated neurons.
Metabotropic Glutamate Receptor Subtype 7 Ablation Causes Deficit in Fear Response and Conditioned Taste Aversion
Authors: Masugi Miwako , Yokoi Mineto , Shigemoto Ryuichi , Muguruma Keiko , Watanabe Yasuyoshi , Sansig Gilles , van der Putten Herman , Nakanishi Shigetada
Published: April 2018

Metabotropic glutamate receptors (mGluRs) consist of eight different subtypes and exert their effects on second messengers and ion channels via G-proteins. The function of individual mGluR subtypes in the CNS, however, largely remains to be clarified. We examined the fear response of freezing after electric shock in wild-type and mGluR7−/−knockout littermates. Wild-type mice displayed freezing immediately after and 1 d after footshock. In comparison, mGluR7−/−knockout mice showed significantly reduced levels in both immediate postshock and delayed freezing responses. However, the knockout mice exhibited no abnormalities in pain sensitivity and locomotor activity. To further examine amygdala-dependent behavior, we performed conditioned taste aversion (CTA) experiments. In wild-type mice, the administration of saccharin followed by intraperitoneal injection of the malaise-inducing agent LiCl resulted in an association between saccharin and LiCl. This association caused strong CTA toward saccharin. In contrast, mGluR7−/−knockout mice failed to associate between the taste and the negative reinforcer in CTA experiments. Again, the knockout mice showed no abnormalities in taste preference and in the sensitivity to LiCl toxicity. These results indicate that mGluR7 deficiency causes an impairment of two distinct amygdala-dependent behavioral paradigms. Immunohistochemical and immunoelectron-microscopic analyses showed that mGluR7 is highly expressed in amygdala and preferentially localized at the presynaptic axon terminals of glutamatergic neurons. Together, these findings strongly suggest that mGluR7 is involved in neural processes subserving amygdala-dependent averse responses.
Expression of a Novel Protocadherin, OL-Protocadherin, in a Subset of Functional Systems of the Developing Mouse Brain
Authors: Hirano Shinji , Yan Qiong , Suzuki Shintaro T.
Published: April 2018

We cloned a novel protocadherin cDNA, which we named OL-protocadherin (OL-pc), from mouse brain cDNA libraries. Its cytoplasmic region showed no similarities to other protocadherins, indicating that it belongs to a novel subfamily of protocadherins. Experiments using transfectants showed that OL-pc is a homophilic cell–cell adhesion molecule. The molecular mass of OL-pc was 140 kDa in the brain. Expression of OL-pc mRNA was specific to the nervous system, changing over time from the embryonic stage to the adult stage. The OL-pc expression seemed to be restricted to a subset of functionally related brain nuclei and regions such as the nuclei in the main olfactory system, the limbic system, and the olivocortical projection. There were at least two distinct patterns of distribution for the OL-pc protein. First, it was localized in particular brain nuclei or compartments, such as the stripes of the developing cerebellum. Second, it was found at the synapse in regions such as the glomeruli of the olfactory bulb. In addition, the OL-pc protein seemed not to be detected or was detected only weakly in some regions, such as hippocampus in which the mRNA was expressed at high levels. These results indicate that the expression of OL-pc is developmentally regulated in a subset of the functional systems and that it may be involved in the formation of the neural network by segregation of the brain nuclei and mediation of the axonal connections.
Synaptic Interaction between Hypocretin (Orexin) and Neuropeptide Y Cells in the Rodent and Primate Hypothalamus: A Novel Circuit Implicated in Metabolic and Endocrine Regulations
Authors: Horvath Tamas L. , Diano Sabrina , van den Pol Anthony N.
Published: April 2018

Hypocretin (orexin) has recently been shown to increase feeding when injected into the brain. Using both rat and primate brains, we tested the hypothesis that a mechanism of hypocretin action might be related to synaptic regulation of the neuropeptide Y (NPY) system. Hypocretin-immunoreactive terminals originating from the lateral hypothalamus make direct synaptic contact with neurons of the arcuate nucleus that not only express NPY but also contain leptin receptors. In addition, hypocretin-containing neurons also express leptin receptor immunoreactivity. This suggests a potential mechanism of action for hypocretin in the central regulation of metabolic and endocrine processes. The excitatory actions of hypocretin could increase NPY release, resulting in enhanced feeding behavior and altered endocrine regulation, whereas leptin, released from adipose tissue as an indicator of fat stores, would have the opposite effect on the same neurons, leading to a decrease in NPY and NPY-mediated hypothalamic functions. On the other hand, the innervation of hypocretin cells by NPY boutons raises the possibility that NPY may exert an effect on hypothalamic functions, at least in part, via mediation or feedback action on these lateral hypothalamic cells. Our data indicate that a direct interaction between leptin, hypocretin, and NPY exists in the hypothalamus that may contribute to the central regulation of metabolic and endocrine processes in both rodents and primates.
Integrin Subunit Gene Expression Is Regionally Differentiated in Adult Brain
Authors: Pinkstaff Jason K. , Detterich Jon , Lynch Gary , Gall Christine
Published: April 2018

Integrins are a diverse family of heterodimeric (αβ) adhesion receptors recently shown to be concentrated within synapses and involved in the consolidation of long-term potentiation. Whether neuronal types or anatomical systems in the adult rat brain are coded by integrin type was studied in the present experiments by mapping the relative densities of mRNAs for nine α and four β subunits. Expression patterns were markedly different and in some regions complementary. General results and areas of notable labeling were as follows: α1—limited neuronal expression, neocortical layer V, hippocampal CA3; α3 and α5—diffuse neuronal and glial labeling, Purkinje cells, hippocampal stratum pyramidale, locus coeruleus (α3); α4— discrete limbic regions, olfactory cortical layer II, hippocampal CA2; α6—most prominently neuronal, neocortical subplate, endopiriform, subiculum; α7—discrete, all neocortical layers, hippocampal granule cells and CA3, cerebellar granule and Purkinje cells, all efferent cranial nerve nuclei; α8—discrete neuronal, deep cortex, hippocampal CA1, basolateral amygdala, striatum; αV—all cortical layers, striatum, Purkinje cells; β4—dentate gyrus granule cells; β5—broadly distributed, neocortex, medial amygdala, cerebellar granule and Purkinje cells, efferent cranial nerve nuclei; α2, β2, and β3—mRNAs not detected. These results establish that brain subfields express different balances of integrin subunits and thus different integrin receptors. Such variations will determine which matrix proteins are recognized by neurons and the types of intraneuronal signaling generated by matrix binding. They also could generate important differences in synaptic plasticity across brain systems.
Central Peptidergic Neurons Are Hyperactive during Collateral Sprouting and Inhibition of Activity Suppresses Sprouting
Authors: Watt John A. , Moffet Christopher W. , Zhou Xinrong , Short Sonja , Herman James P. , Paden Charles M.
Published: April 2018

Little is known regarding the effect of chronic changes in neuronal activity on the extent of collateral sprouting by identified CNS neurons. We have investigated the relationship between activity and sprouting in oxytocin (OT) and vasopressin (VP) neurons of the hypothalamic magnocellular neurosecretory system (MNS). Uninjured MNS neurons undergo a robust collateral-sprouting response that restores the axon population of the neural lobe (NL) after a lesion of the contralateral MNS (Watt and Paden, 1991). Simultaneously, lesioned rats develop chronic urinary hyperosmolality indicative of heightened neurosecretory activity. We therefore tested the hypothesis that sprouting MNS neurons are hyperactive by measuring changes in cell and nuclear diameters, OT and VP mRNA pools, and axonal cytochrome oxidase activity (COX). Each of these measures was significantly elevated during the period of most rapid axonal growth between 1 and 4 weeks after the lesion, confirming that both OT and VP neurons are hyperactive while undergoing collateral sprouting. In a second study the hypothesis that chronic inhibition of neuronal activity would interfere with the sprouting response was tested. Chronic hyponatremia (CH) was induced 3 d before the hypothalamic lesion and sustained for 4 weeks to suppress neurosecretory activity. CH abolished the lesion-induced increases in OT and VP mRNA pools and virtually eliminated measurable COX activity in MNS terminals. Counts of the total number of axon profiles in the NL revealed that CH also prevented axonal sprouting from occurring. These results are consistent with the hypothesis that increased neuronal activity is required for denervation-induced collateral sprouting to occur in the MNS.
Somatic Recording of GABAergic Autoreceptor Current in Cerebellar Stellate and Basket Cells
Authors: Pouzat Christophe , Marty Alain
Published: April 2018

Patch-clamp recordings were performed from stellate and basket cells in rat cerebellar slices. Under somatic voltage clamp, short depolarizing pulses were applied to elicit action potentials in the axon. After the action potential, a bicuculline- and Cd2+-sensitive current transient was observed. A similar response was obtained when eliciting axonal firing by extracellular stimulation. With an isotonic internal Cl−solution, the peak amplitude of this current varied linearly with the holding potential, yielding an extrapolated reversal potential of −20 to 0 mV. Unlike synaptic or autaptic GABAergic currents obtained in the same preparation, the current transient had a slow rise-time and a low variability between trials. This current was blocked when 10 mmBAPTA was included in the recording solution. In some experiments, the current transient elicited axonal action potentials. The current transient was reliably observed in animals aged 12–15 d, with a mean amplitude of 82 pA at −70 mV, but was small and rare in the age group 29–49 d. Numerical simulations could account for all properties of the current transient by assuming that an action potential activates a distributed GABAergic conductance in the axon. The actual conductance is probably restricted to release sites, with an estimated mean presynaptic current response of 10 pA per site (−70 mV, age 12–15 d). We conclude that in developing rats, stellate and basket cell axons have a high density of GABAergic autoreceptors and that a sizable fraction of the corresponding current can be measured from the soma.
Competitive Mechanisms Subserve Attention in Macaque Areas V2 and V4
Authors: Reynolds John H. , Chelazzi Leonardo , Desimone Robert
Published: April 2018

It is well established that attention modulates visual processing in extrastriate cortex. However, the underlying neural mechanisms are unknown. A consistent observation is that attention has its greatest impact on neuronal responses when multiple stimuli appear together within a cell’s receptive field. One way to explain this is to assume that multiple stimuli activate competing populations of neurons and that attention biases this competition in favor of the attended stimulus. In the absence of competing stimuli, there is no competition to be resolved. Accordingly, attention has a more limited effect on the neuronal response to a single stimulus. To test this interpretation, we measured the responses of neurons in macaque areas V2 and V4 using a behavioral paradigm that allowed us to isolate automatic sensory processing mechanisms from attentional effects. First, we measured each cell’s response to a single stimulus presented alone inside the receptive field or paired with a second receptive field stimulus, while the monkey attended to a location outside the receptive field. Adding the second stimulus typically caused the neuron’s response to move toward the response that was elicited by the second stimulus alone. Then, we directed the monkey’s attention to one element of the pair. This drove the neuron’s response toward the response elicited when the attended stimulus appeared alone. These findings are consistent with the idea that attention biases competitive interactions among neurons, causing them to respond primarily to the attended stimulus. A quantitative neural model of attention is proposed to account for these results.
Cellular Sites for Dynorphin Activation of κ-Opioid Receptors in the Rat Nucleus Accumbens Shell
Authors: Svingos Adena L. , Colago Eric E. O. , Pickel Virginia M.
Published: April 2018

The nucleus accumbens (Acb) is prominently involved in the aversive behavioral aspects of κ-opioid receptor (KOR) agonists, including its endogenous ligand dynorphin (Dyn). We examined the ultrastructural immunoperoxidase localization of KOR and immunogold labeling of Dyn to determine the major cellular sites for KOR activation in this region. Of 851 KOR-labeled structures sampled from a total area of 10,457 μm2, 63% were small axons and morphologically heterogenous axon terminals, 31% of which apposed Dyn-labeled terminals or also contained Dyn. Sixty-eight percent of the KOR-containing axon terminals formed punctate-symmetric or appositional contacts with unlabeled dendrites and spines, many of which received convergent input from terminals that formed asymmetric synapses. Excitatory-type terminals that formed asymmetric synapses with dendritic spines comprised 21% of the KOR-immunoreactive profiles. Dendritic spines within the neuropil were the major nonaxonal structures that contained KOR immunoreactivity. These spines also received excitatory-type synapses from unlabeled terminals and were apposed by Dyn-containing terminals. These results provide ultrastructural evidence that in the Acb shell (AcbSh), KOR agonists play a primary role in regulating the presynaptic release of Dyn and other neuromodulators that influence the output of spiny neurons via changes in the presynaptic release of or the postsynaptic responses to excitatory amino acids. The cellular distribution of KOR complements those described previously for the reward-associated μ- and δ-opioid receptors in the Acb shell.
Metrifonate Increases Neuronal Excitability in CA1 Pyramidal Neurons from Both Young and Aging Rabbit Hippocampus
Authors: Oh M. Matthew , Power John M. , Thompson Lucien T. , Moriearty Pamela L. , Disterhoft John F.
Published: April 2018

The effects of metrifonate, a second generation cholinesterase inhibitor, were examined on CA1 pyramidal neurons from hippocampal slices of young and aging rabbits using current-clamp, intracellular recording techniques. Bath perfusion of metrifonate (10–200 μm) dose-dependently decreased both postburst afterhyperpolarization (AHP) and spike frequency adaptation (accommodation) in neurons from young and aging rabbits (AHP:p< 0.002, young;p< 0.050, aging; accommodation:p< 0.024, young;p< 0.001, aging). These reductions were mediated by muscarinic cholinergic transmission, because they were blocked by addition of atropine (1 μm) to the perfusate. The effects of chronic metrifonate treatment (12 mg/kg for 3 weeks) on CA1 neurons of aging rabbits were also examinedex vivo. Neurons from aging rabbits chronically treated with metrifonate had significantly reduced spike frequency accommodation, compared with vehicle-treated rabbits. Chronic metrifonate treatment did not result in a desensitization to metrifonateex vivo, because bath perfusion of metrifonate (50 μm) significantly decreased the AHP and accommodation in neurons from both chronically metrifonate- and vehicle-treated aging rabbits. We propose that the facilitating effect of chronic metrifonate treatment on acquisition of hippocampus-dependent tasks such as trace eyeblink conditioning by aging subjects may be caused by this increased excitability of CA1 pyramidal neurons.
Major Changes in the Brain Histamine System of the Ground SquirrelCitellus lateralisduring Hibernation
Authors: Sallmen Tina , Beckman Alexander L. , Stanton Toni L. , Eriksson Krister S. , Tarhanen Juhani , Tuomisto Leena , Panula Pertti
Published: April 2018

Hibernation in mammals such as the rodent hibernatorCitellus lateralisis a physiological state in which CNS activity is endogenously maintained at a very low, but functionally responsive, level. The neurotransmitter histamine is involved in the regulation of diurnal rhythms and body temperature in nonhibernators and, therefore, could likely play an important role in maintaining the hibernating state. In this study, we show that histamine neuronal systems undergo major changes during hibernation that are consistent with such a role. Immunohistochemical mapping of histaminergic fibers in the brains of hibernating and nonhibernating golden-mantled ground squirrels (C. lateralis) showed a clear increase in fiber density during the hibernating state. The tissue levels of histamine and its first metabolitetele-methylhistamine were also elevated throughout the brain of hibernating animals, suggesting an increase in histamine turnover during hibernation, which occurs without an increase in histidine decarboxylase mRNA expression. This hibernation-related apparent augmentation of histaminergic neurotransmission was particularly evident in the hypothalamus and hippocampus, areas of importance to the control of the hibernating state, in whichtele-methylhistamine levels were increased more than threefold. These changes in the histamine neuronal system differ from those reported for the metabolic pattern in other monoaminergic systems during hibernation, which generally indicate a decrease in turnover. Our results suggest that the influence of histamine neuronal systems may be important in controlling CNS activity during hibernation.
GABAergic Excitatory Synapses and Electrical Coupling Sustain Prolonged Discharges in the Prey Capture Neural Network ofClione limacina
Authors: Norekian Tigran P.
Published: April 2018

Afterdischarges represent a prominent characteristic of the neural network that controls prey capture reactions in the carnivorous molluscClione limacina. Their main functional implication is transformation of a brief sensory input from a prey into a lasting prey capture response. The present study, which focuses on the neuronal mechanisms of afterdischarges, demonstrates that a single pair of interneurons [cerebral A interneuron (Cr-Aint)] is responsible for afterdischarge generation in the network. Cr-Aint neurons are electrically coupled to all other neurons in the network and produce slow excitatory synaptic inputs to them. This excitatory transmission is found to be GABAergic, which is demonstrated by the use of GABA antagonists, uptake inhibitors, and double-labeling experiments showing that Cr-Aint neurons are GABA-immunoreactive. The Cr-Aint neurons organize three different pathways in the prey capture network, which provide positive feedback necessary for sustaining prolonged spike activity. The first pathway includes electrical coupling and slow chemical transmission from the Cr-Aint neurons to all other neurons in the network. The second feedback is based on excitatory reciprocal connections between contralateral interneurons. Recurrent excitation via the contralateral cell can sustain prolonged interneuron firing, which then drives the activity of all other cells in the network. The third positive feedback is represented by prominent afterdepolarizing potentials after individual spikes in the Cr-Aint neurons. Afterdepolarizations apparently represent recurrent GABAergic excitatory inputs. It is suggested here that these afterdepolarizing potentials are produced by GABAergic excitatory autapses.
Cloning and Expression of a Novel Member of the Low Voltage-Activated T-Type Calcium Channel Family
Authors: Lee Jung-Ha , Daud Asif N. , Cribbs Leanne L. , Lacerda Antonio E. , Pereverzev Alexei , Klöckner Udo , Schneider Toni , Perez-Reyes Edward
Published: April 2018

Low voltage-activated Ca2+channels play important roles in pacing neuronal firing and producing network oscillations, such as those that occur during sleep and epilepsy. Here we describe the cloning and expression of the third member of the T-type family, α1I or CavT.3, from rat brain. Northern analysis indicated that it is predominantly expressed in brain. Expression of the cloned channel in eitherXenopusoocytes or stably transfected human embryonic kidney-293 cells revealed novel gating properties. We compared these electrophysiological properties to those of the cloned T-type channels α1G and α1H and to the high voltage-activated channels formed by α1Eβ3. The α1I channels opened after small depolarizations of the membrane similar to α1G and α1H but at more depolarized potentials. The kinetics of activation and inactivation were dramatically slower, which allows the channel to act as a Ca2+injector. In oocytes, the kinetics were even slower, suggesting that components of the expression system modulate its gating properties. Steady-state inactivation occurred at higher potentials than any of the other T channels, endowing the channel with a substantial window current. The α1I channel could still be classified as T-type by virtue of its criss-crossing kinetics, its slow deactivation (tail current), and its small (11 pS) conductance in 110 mmBa2+solutions. Based on its brain distribution and novel gating properties, we suggest that α1I plays important roles in determining the electroresponsiveness of neurons, and hence, may be a novel drug target.
Mechanisms of Calcium Influx into Hippocampal Spines: Heterogeneity among Spines, Coincidence Detection by NMDA Receptors, and Optical Quantal Analysis
Authors: Yuste Rafael , Majewska Ania , Cash Sydney S. , Denk Winfried
Published: April 2018

Dendritic spines receive most excitatory inputs in the vertebrate brain, but their function is still poorly understood. Using two-photon calcium imaging of CA1 pyramidal neurons in rat hippocampal slices, we investigated the mechanisms by which calcium enters into individual spines in the stratum radiatum. We find three different pathways for calcium influx: high-threshold voltage-sensitive calcium channels, NMDA receptors, and an APV-resistant influx consistent with calcium-permeable AMPA or kainate receptors. These pathways vary among different populations of spines and are engaged under different stimulation conditions, with peak calcium concentrations reaching >10 μm. Furthermore, as a result of the biophysical properties of the NMDA receptor, the calcium dynamics of spines are exquisitely sensitive to the temporal coincidence of the input and output of the neuron. Our results confirm that individual spines are chemical compartments that can perform coincidence detection. Finally, we demonstrate that functional studies and optical quantal analysis of single, identified synapses is feasible in mammalian CNS neurons in brain slices.
GABA- and Glutamate-Activated Channels in Green Fluorescent Protein-Tagged Gonadotropin-Releasing Hormone Neurons in Transgenic Mice
Authors: Spergel Daniel J. , Krüth Ulrich , Hanley Daniel F. , Sprengel Rolf , Seeburg Peter H.
Published: April 2018

Mice were generated expressing green fluorescent protein (GFP) under the control of the gonadotropin-releasing hormone (GnRH) promoter. Green fluorescence was observed in, and restricted to, GnRH-immunopositive neuronal somata in the olfactory bulb, ganglion terminale, septal nuclei, diagonal band of Broca (DBB), preoptic area (POA), and caudal hypothalamus, as well as GnRH neuronal dendrites and axons, including axon terminals in the median eminence and organum vasculosum of the lamina terminalis (OVLT). Whole-cell recordings from GFP-expressing GnRH neurons in the OVLT–POA–DBB region revealed a firing pattern among GFP-expressing GnRH neurons distinct from that of nonfluorescent neurons. Nucleated patches of GFP-expressing GnRH neurons exhibited pronounced responses to fast application of GABA and smaller responses tol-glutamate and AMPA. One-fifth of the nucleated patches responded to NMDA. The GABA-A, AMPA, and NMDA receptor channels on GnRH neurons mediating these responses may play a role in the modulation of GnRH secretory oscillations.
Differential Sorting of Nerve Growth Factor and Brain-Derived Neurotrophic Factor in Hippocampal Neurons
Authors: Mowla S. Javad , Pareek Sangeeta , Farhadi Hooman F. , Petrecca Kevin , Fawcett James P. , Seidah Nabil G. , Morris Stephen J. , Sossin Wayne S. , Murphy Richard A.
Published: April 2018

Nerve growth factor (NGF) is released through the constitutive secretory pathway from cells in peripheral tissues and nerves where it can act as a target-derived survival factor. In contrast, brain-derived neurotrophic factor (BDNF) appears to be processed in the regulated secretory pathway of brain neurons and secreted in an activity-dependent manner to play a role in synaptic plasticity. To determine whether sorting differences are intrinsic to the neurotrophins or reflect differences between cell types, we compared NGF and BDNF processing in cultured hippocampal neurons using a Vaccinia virus expression system. Three independent criteria (retention or release from cells after pulse–chase labeling, depolarization-dependent release, and immunocytochemical localization) suggest that the bulk of newly synthesized NGF is sorted into the constitutive pathway, whereas BDNF is primarily sorted into the regulated secretory pathway. Similar results occurred with AtT 20 cells, including those transfected with cDNAs encoding neurotrophin precursor–green fluorescent protein fusions. The NGF precursor, but not the BDNF precursor, is efficiently cleaved by the endoprotease furin in thetrans-Golgi network (TGN). Blocking furin activity in AtT 20 cells with α1-PDX as well as increasing the expression of NGF precursor partially directed NGF into the regulated secretory pathway. Therefore, neurotrophins can be sorted into either the constitutive or regulated secretory pathways, and sorting may be regulated by the efficiency of furin cleavage in the TGN. This mechanism may explain how neuron-generated neurotrophins can act both as survival factors and as neuropeptides.
Specification of Distinct Dopaminergic Neural Pathways: Roles of the Eph Family Receptor EphB1 and Ligand Ephrin-B2
Authors: Yue Yong , Widmer David A. J. , Halladay Alycia K. , Cerretti Douglas Pat , Wagner George C. , Dreyer Jean-Luc , Zhou Renping
Published: April 2018

Dopaminergic neurons in the substantia nigra and ventral tegmental area project to the caudate putamen and nucleus accumbens/olfactory tubercle, respectively, constituting mesostriatal and mesolimbic pathways. The molecular signals that confer target specificity of different dopaminergic neurons are not known. We now report that EphB1 and ephrin-B2, a receptor and ligand of the Eph family, are candidate guidance molecules for the development of these distinct pathways. EphB1 and ephrin-B2 are expressed in complementary patterns in the midbrain dopaminergic neurons and their targets, and the ligand specifically inhibits the growth of neurites and induces the cell loss of substantia nigra, but not ventral tegmental, dopaminergic neurons. These studies suggest that the ligand–receptor pair may contribute to the establishment of distinct neural pathways by selectively inhibiting the neurite outgrowth and cell survival of mistargeted neurons. In addition, we show that ephrin-B2 expression is upregulated by cocaine and amphetamine in adult mice, suggesting that ephrin-B2/EphB1 interaction may play a role in drug-induced plasticity in adults as well.