bluuebunny/crossref_metadata_2025 huggingface dataset:
Production and survival of projection neurons in a forebrain vocal center of adult male canaries
Authors: Kirn JR , Alvarez-Buylla A , Nottebohm F
Published: March 2018

Neurons are produced in the adult canary telencephalon. Many of these cells are incorporated into the high vocal center (nucleus HVC), which participates in the control of learned song. In the present work, 3H- thymidine and fluorogold were employed to follow the differentiation and survival of HVC neurons born in adulthood. We found that many HVC neurons born in September grow long axons to the robust nucleus of the archistriatum (nucleus RA) and thus become part of the efferent pathway for song control. Many of these new neurons have already established their connections with RA by 30 d after their birth. By 240 d, 75–80% of the September-born HVC neurons project to RA. Most of these new projection neurons survive at least 8 months. The longevity of HVC neurons born in September suggests that these cells remain part of the vocal control circuit long enough to participate in the yearly renewal of the song repertoire.
Characterization of phospholipase A2 (PLA2) activity in gerbil brain: enhanced activities of cytosolic, mitochondrial, and microsomal forms after ischemia and reperfusion
Authors: Rordorf G , Uemura Y , Bonventre JV
Published: March 2018

Brain phospholipase A2 (PLA2) activity has not been well characterized. Given the importance of this enzymatic activity for a variety of cellular functions in the brain, we characterized the subcellular distribution of PLA2 activity in gerbil brain and evaluated how PLA2 activity was altered by ischemia and reperfusion. Cytosolic, mitochondrial, and microsomal fractions were prepared by differential centrifugation of forebrain homogenates. PLA2 activities of each fraction were assayed by measuring release of arachidonic acid (AA) from exogenous 14C-AA-phosphatidylcholine (PC), - phosphatidylethanolamine (PE), and -phosphatidylinositol (PI). Two forms of PLA2 were present in the cytosolic fraction: a high-molecular- weight form, active against PC and PE, and a smaller form with an Mr of approximately 14 kDa, active against PE. In the mitochondrial and microsomal fractions, a single form (Mr approximately 14 kDa) was dominant, active against both PC and PE. The role of PLA2 activation in ischemic brain injury remains controversial. PLA2 enzymatic activity was characterized in gerbil brain after 10 min of common carotid occlusion, followed by 10 min of reperfusion. Ischemic/reperfused brains had significantly higher PLA2 specific activities in each subcellular fraction. Ischemia and reperfusion did not change the gel- filtration elution patterns of PLA2 activity of the various forms of the enzyme. Cytosolic, mitochondrial, and microsomal activities were optimal at a pH of approximately 8.5. Cytosolic PLA2 activity was enhanced when Ca2+ concentration [( Ca2+]) was increased over the physiological range (10(-7) to 10(-6) M). Mitochondrial and microsomal PLA2 activities were also [Ca2+] dependent.
Anterior and posterior association cortex contributions to the somatosensory P300
Authors: Yamaguchi S , Knight RT
Published: March 2018

A P300 (P3)-evoked response is generated in a variety of mammalian species upon detection of significant environmental events. The P3 component has been proposed to index a neural system involved in attention and memory capacity. We investigated the contribution of anterior and posterior association cortex to somatosensory P3 generation. Somatosensory event-related potentials (ERPs) were recorded in controls (n = 10) and patients with unilateral lesions in temporal- parietal junction (n = 8), lateral parietal cortex (n = 8), or dorsolateral frontal cortex (n = 10). Subjects pressed a button to mechanical taps of the fifth finger (targets; p = 0.12), randomly interposed in sequences of taps to the second (standards; p = 0.76) and the third or fourth finger (tactile novels; p = 0.06). Occasional shock stimuli were delivered to the wrist (shock novels; p = 0.06). The scalp- recorded P3 was differentially affected by anterior and posterior association cortex lesions. Subjects with temporal-parietal lesions showed markedly reduced P3s to all types of stimuli at all scalp locations. The reductions were largest at the parietal electrode site over the lesioned hemisphere. Parietal patients had normal P3s for all stimulus types except for contralateral shock novels, which generated reduced P3s. Frontal lesions had reductions of the novelty P3 over frontal sites with minimal changes in the target P3. The data support the existence of multiple intracranial P3 sources. The data further indicate that association cortex in the temporal-parietal junction is critical for generating the scalp-recorded target and novelty P3s, whereas dorsolateral frontal cortex contributes preferentially to novelty P3 generation. The N2 component was reduced by parietal and frontal lesions in patients who had intact target P3s, suggesting that different neural systems underlie N2 and P3 generation.
Early postnatal hyperthyroidism alters hippocampal circuitry and improves radial-maze learning in adult mice
Authors: Schwegler H , Crusio WE , Lipp HP , Brust I , Mueller GG
Published: March 2018

Inbred mice show strain-specific differences in the hippocampal mossy fiber projection. These differences are most pronounced in the portion of the projection that forms synaptic connections with the basal dendrites of the CA3 pyramidal neurons [intra- and infrapyramidal mossy fiber (IIP-MF) projection]. We have previously demonstrated that the extent of the IIP-MF subfield is positively correlated with the capacity to perform a spatial radial-maze task and that an experimentally induced enlargement of the IIP-MFs, by means of postnatal thyroxine treatment, predicted the ability of adult two-way avoidance learning. In the present study, we tested whether this treatment would also influence radial-maze performance. Forty-five male mouse pups from the inbred strain DBA/2 (chosen because of scanty IIP- MF projection and poor radial-maze learning) were divided into three groups that received daily injections of either 2 micrograms L- thyroxine, an alkaline vehicle solution, or physiological saline. Treatment lasted from postnatal days 0 to 11. At the age of 3 months, these animals were tested in an eight-arm radial maze. The extent of their IIP-MF projections was measured by means of planimetry on Timm- stained sections. Thyroxine-treated animals made significantly fewer errors and had larger IIP-MF projections as compared to both control groups. Within each group, the individual variability of the IIP-MF projection was significantly and positively correlated with performance. We conclude that experimentally modified IIP-MF projections mediate processes underlying spatial working memory. It would appear that the hippocampal circuitry alterations induced by postnatal hyperthyroidism can counteract a hereditary lack of talent, albeit only partially and in selected populations.
Regulation of acetylcholine receptors on chick ciliary ganglion neurons by components from the synaptic target tissue
Authors: Halvorsen SW , Schmid HA , McEachern AE , Berg DK
Published: March 2018

Chick ciliary ganglion neurons have nicotinic acetylcholine receptors (AChRs) that mediate synaptic transmission through the ganglion. A soluble component of about 50 kDa from embryonic eye tissue, the synaptic target of the ganglion, increases the development of ACh sensitivity by the neurons 10-fold over a 1-week period in culture. The increased sensitivity does not arise from a change in agonist affinity or esterase activity. Both the basal ACh response obtained in the absence of the 50-kDa component and the elevated responses obtained with it can be inhibited by neuronal bungarotoxin (nBgt) but not by alpha-bungarotoxin (alpha Bgt). Increases of less than twofold are observed for the binding of anti-AChR monoclonal antibody 35 (mAb 35), nBgt, and alpha Bgt to the neurons under these conditions. Extract fractions containing the 50-kDa component also enable the neurons to enhance their ACh responses through a cAMP-dependent mechanism. Either the 50-kDa fraction induces the appearance of a new type of AChR regulated by cAMP, or it alters the function of existing AChRs. The 50- kDa fraction produces no change in neuronal growth but can increase GABA responses sixfold, indicating that its effects are not confined to AChRs. It is not clear whether a single molecular species is responsible for the diverse regulatory effects or whether several types of active components are present in the fraction. The component which enhances ACh sensitivity is trypsin-sensitive and heat-labile, as expected for a protein. The component may be widely distributed since the 50-kDa fraction from a number of tissues can increase the ACh response. The fraction from eye tissue, however, has a specific activity 5–10 times greater than that of the liver fraction. A wide distribution would suggest multiple targets and roles for the component during development.
Cloning and characterization of Ca(2+)-dependent and Ca(2+)-independent PKCs expressed in Aplysia sensory cells
Authors: Kruger KE , Sossin WS , Sacktor TC , Bergold PJ , Beushausen S , Schwartz JH
Published: March 2018

We isolated cDNA clones from an Aplysia sensory-cell library encoding two isoforms of protein kinase C (PKC). Several isozyme-specific regions are conserved in the Aplysia kinases, notably the variable regions V5 in the Ca(2+)-dependent PKC (Apl I) and V1 in the Ca(2+)- independent PKC (Apl II). Neuronal proteins with the properties expected of these two isoforms can be identified with antibodies raised against peptides synthesized from the amino acid sequences deduced from the clones. Sacktor and Schwartz (1990) measured the proportion of kinase activity that can be translocated to membrane in Aplysia sensory neurons and ganglia by stimuli that produce the presynaptic facilitation underlying behavioral sensitization. Much less Apl I and Apl II are translocated, suggesting that still other isoforms of PKC exist in these cells.
Selective and divided attention during visual discriminations of shape, color, and speed: functional anatomy by positron emission tomography
Authors: Corbetta M , Miezin FM , Dobmeyer S , Shulman GL , Petersen SE
Published: March 2018

Positron emission tomography (PET) was used to identify the neural systems involved in discriminating the shape, color, and speed of a visual stimulus under conditions of selective and divided attention. Psychophysical evidence indicated that the sensitivity for discriminating subtle stimulus changes in a same-different matching task was higher when subjects selectively attended to one attribute than when they divided attention among the attributes. PET measurements of brain activity indicated that modulations of extrastriate visual activity were primarily produced by task conditions of selective attention. Attention to speed activated a region in the left inferior parietal lobule. Attention to color activated a region in the collateral sulcus and dorsolateral occipital cortex, while attention to shape activated collateral sulcus (similarly to color), fusiform and parahippocampal gyri, and temporal cortex along the superior temporal sulcus. Outside the visual system, selective and divided attention activated nonoverlapping sets of brain regions. Selective conditions activated globus pallidus, caudate nucleus, lateral orbitofrontal cortex, posterior thalamus/colliculus, and insular-premotor regions, while the divided condition activated the anterior cingulate and dorsolateral prefrontal cortex. The results in the visual system demonstrate that selective attention to different features modulates activity in distinct regions of extrastriate cortex that appear to be specialized for processing the selected feature. The disjoint pattern of activations in extravisual brain regions during selective- and divided-attention conditions also suggests that preceptual judgements involve different neural systems, depending on attentional strategies.
Biochemical studies of stimulus convergence during classical conditioning in Aplysia: dual regulation of adenylate cyclase by Ca2+/calmodulin and transmitter
Authors: Abrams TW , Karl KA , Kandel ER
Published: March 2018

Activity-dependent facilitation is a mechanism of associative synaptic plasticity that contributes to classical conditioning in Aplysia. Previous studies of activity-dependent facilitation in the mechanosensory neurons of Aplysia suggested that the Ca2+ influx during paired spike activity enhances the transmitter-stimulated, cAMP- dependent, presynaptic facilitation in these cells. Moreover, paired activity was found to potentiate the activation of the adenylate cyclase by transmitter. It was therefore proposed that the Ca2+/calmodulin-sensitive cyclase may serve as a site of interaction between the inputs from the conditioned and unconditioned stimuli. These studies were carried out to test whether a Ca2+/calmodulin- sensitive adenylate cyclase in the Aplysia CNS has the properties necessary to mediate such an associative interaction. Three lines of evidence indicate that the same cyclase molecules that are sensitive to Ca2+/calmodulin are also stimulated by receptor to facilitatory transmitter via the stimulatory G-protein, Gs: First, calmodulin inhibitors reduced stimulation of the cyclase by facilitatory transmitter. When membranes had been preexposed to one of these inhibitors, trifluoperazine, the addition of exogenous calmodulin partially reversed the inhibition. Second, when Gs had been activated by GTP gamma S, so that it persistently activated the catalytic unit of the cyclase, stimulation of the cyclase by Ca2+ was greatly amplified, suggesting that the two inputs interact in activating a common population of the enzyme. Third, solubilized cyclase activity that bound to calmodulin-Sepharose in a Ca(2+)-dependent manner was stimulated by Gs, which had been partially purified from Aplysia CNS, as well as by Ca2+/calmodulin. Having demonstrated dual activation of the cyclase, we have explored the dependence of cyclase activation on the temporal pattern of Ca2+ and transmitter addition. Optimal activation required that a pulse of Ca2+ temporally overlap the addition of facilitatory transmitter. These several results suggested that the dually regulated adenylate cyclase might underlie the temporal requirements for effective classical conditioning in this system.
The postsynaptic inhibitory control of lumbar motoneurons during the atonia of active sleep: effect of strychnine on motoneuron properties
Authors: Soja PJ , Lopez-Rodriguez F , Morales FR , Chase MH
Published: March 2018

The present study examined the effects of strychnine on the tonic hyperpolarization and the changes in membrane properties of lumbar motoneurons that occur during active sleep. To carry out these studies, intracellular recordings from lumbar motoneurons were combined with the juxtacellular microiontophoretic application of strychnine in chronic, undrugged, normally respiring cats. During active sleep, compared to quiet sleep, motoneurons that were not exposed to strychnine exhibited tonic hyperpolarization, a decrease in cell excitability, and an increase in membrane conductance; they were also bombarded by high- frequency, large-amplitude IPSPs. In conjunction with the juxtacellular application of strychnine, there was a marked reduction in the degree of hyperpolarization during active sleep; motoneuron excitability was no longer suppressed, and there was a reduction in the increase in membrane conductance. In addition, the large-amplitude IPSPs were blocked. These results identify glycine as the neurotransmitter responsible for the state-dependent changes in membrane properties and the hyperpolarization of motoneurons that takes place during active sleep.
Low-threshold transient calcium current in rat hippocampal lacunosum- moleculare interneurons: kinetics and modulation by neurotransmitters
Authors: Fraser DD , MacVicar BA
Published: March 2018

Interneurons from the CA1 lacunosum-moleculare (L-M) region were isolated by trypsin-hyaluronidase treatment and mechanical trituration of the L-M. Interneurons isolated in this manner were multipolar with several dendritic processes and could be distinguished from CA1 pyramidal neurons. The properties of a low-threshold transient (LTT) Ca2+ current were investigated using whole-cell voltage-clamp techniques. The activation threshold of the LTT Ca2+ current was -60 mV, and the peak current, 100 +/- 9 pA (mean +/- SEM; n = 15), was observed at -30 mV. Ca2+ was the predominant charge carrier because the current was not affected by tetrodotoxin and was abolished in Ca(2+)- free external solution. Steady state inactivation was observed when the holding potential was positive to -100 mV, and the current was half- inactivated at -84 mV. Complete inactivation occurred at a holding potential of -60 mV. The time-to-peak of the current was highly voltage dependent and ranged from 10 msec at -60 mV to 4 msec at 0 mV. The time constant of inactivation was also voltage dependent and ranged from 27 msec at -60 mV to 12 msec at greater than -30 mV. Recovery from inactivation to 90% of maximum current occurred within 200 msec. L-M interneurons receive synaptic inputs from the septum that release ACh or GABA and from the raphe nuclei that release 5-HT. Carbachol, a nonhydrolyzable cholinergic agonist, and 5-HT quickly and reversibly increased the amplitude of the LTT Ca2+ current. Carbachol's actions were blocked by atropine, indicating that this effect was mediated by muscarinic receptors.
A comparative study of the behavioral deficits following lesions of various parts of the zebra finch song system: implications for vocal learning
Authors: Scharff C , Nottebohm F
Published: March 2018

Song production in song birds is controlled by an efferent pathway. Appended to this pathway is a “recursive loop” that is necessary for song acquisition but not for the production of learned song. Since zebra finches learn their song by imitating external models, we speculated that the importance of the recursive loop for learning might derive from its processing of auditory feedback during song acquisition. This hypothesis was tested by comparing the effects on song in birds deafened early in life and birds with early lesions in either of two nuclei--Area X and the lateral magnocellular nucleus of the anterior neostriatum (LMAN). These nuclei are part of the recursive loop. The three treatments affected song development differently, as reflected by various parameters of the adult song of these birds. Whereas LMAN lesions resulted in songs with monotonous repetitions of a single note complex, songs of Area X-lesioned birds consisted of rambling series of unusually long and variable notes. Furthermore, whereas song of LMAN lesioned birds stabilized early, song stability as seen in intact birds was never achieved in Area X-lesioned birds. Early deafness also resulted in poorly structured and unstable song. We conclude that Area X and LMAN contribute differently to song acquisition: the song variability that is typical of vocal development persists following early deafness or lesions of Area X but ends abruptly following removal of LMAN. Apparently, LMAN plays a crucial role in fostering the kinds of circuit plasticity necessary for learning.
Pontomedullary glutamate receptors mediating locomotion and muscle tone suppression
Authors: Lai YY , Siegel JM
Published: March 2018

Microinjection of NMDA and non-NMDA agonists into the same sites in pontomedullary motor “inhibitory” areas of decerebrate animals produced opposite effects on muscle tone. Microinjection of non-NMDA agonists into peri-locus coeruleus alpha (peri-LC alpha) and nucleus magnocellularis (NMC) suppressed muscle tone, while injection of NMDA agonists at the same sites increased muscle tone and produced locomotion. The latency, duration, and magnitude of muscle tone change after both NMDA and non-NMDA agonist injections were dose dependent. Increased muscle tone and locomotor effects were blocked by NMDA antagonists, and muscle tone suppression effects were blocked by non- NMDA antagonists. We conclude that pontomedullary non-NMDA receptors mediate muscle tone suppression, and that NMDA receptors mediate locomotion and muscle tone facilitation. Activation of both NMDA and non-NMDA pontomedullary receptors by glutamate release in REM sleep can explain the combination of motor activation and loss of muscle tone that characterizes this state. In the waking animal, the co- localization of these mechanisms may facilitate the coordination of locomotion with postural adjustments.
Isolation of the progenitor cells of the sympathoadrenal lineage from embryonic sympathetic ganglia with the SA monoclonal antibodies
Authors: Carnahan JF , Patterson PH
Published: March 2018

Our previous articles in this series described the production of five monoclonal antibodies (SA1-5) that bind to adrenal chromaffin cells and to cells in embryonic sympathetic ganglia and adrenal primordia (Carnahan and Patterson, 1991), and the downregulation of the sympathoadrenal (SA) antigens in vivo as neuronal markers begin to be expressed (Anderson et al., 1991). These results support the hypothesis that sympathetic neurons and adrenal chromaffin cells are derived from a common embryonic progenitor that displays both neuron- and chromaffin cell-specific markers. We have taken advantage of the fact that at least some of the SA antigens are expressed on the cell surface to isolate SA+ cells from embryonic day 14.5 rat superior cervical, sympathetic ganglia by fluorescence-activated cell sorting. This population of cells is significantly enriched in the expression of markers (tyrosine hydroxylase and neurofilament) found in the putative progenitors in situ. Growth in glucocorticoid maintains the expression of the SA antigens in the sorted cells and induces the chromaffin cell marker enzyme phenylethanolamine N-methyl transferase. In contrast, growth of the sorted cells in basic fibroblast growth factor, NGF, and insulin results in the rapid loss of SA 1 expression and the outgrowth of neurites. The ability to manipulate the fate of the SA+ cells in vitro confirms the suggestion from the in vivo observations that the SA+ cells in the ganglia are at least bipotential progenitors, capable of differentiating along the chromaffin or neuronal pathways.
A study of the mechanism of Ca2+ current inhibition produced by serotonin in rat dorsal raphe neurons
Authors: Penington NJ , Kelly JS , Fox AP
Published: March 2018

Calcium currents and their modulation by 5-HT were studied using both whole-cell and single-channel patch-clamp techniques in acutely isolated adult rat dorsal raphe neurons. Evidence for three types of Ca channels (T, N, L) was obtained in both whole-cell and single-channel experiments. Approximately 4% of the total high-threshold Ca current (L- type) was sensitive to dihydropyridines (DHPs) while approximately 40% of the Ca current (N-type) was sensitive to omega-conotoxin (omega- CgTx). About 56% of the whole-cell current was insensitive to either DHPs or omega-CgTx and may thus represent a different kind of Ca current. 5-HT reduced raphe neuron Ca currents by approximately 50%, while slowing activation. 5-HT inhibited both omega-CgTx-sensitive and - insensitive Ca current. Inhibition by 5-HT was voltage dependent; prepulses to +80 mV lasting for 20 msec almost completely abolished the 5-HT-mediated inhibition. The voltage dependence of the response to 5- HT suggested that trains of action potentials might overcome the inhibition due to 5-HT. Trains of brief depolarizations were used to simulate action potentials; only about 5% of the 5-HT-induced inhibition was relieved by the trains. These results suggest that while large depolarizations could restore the Ca current inhibited by 5-HT, physiological stimuli, such as trains of action potentials, could not. The action of 5-HT was made irreversible by inclusion of GTP-gamma-S in the patch pipette, suggesting a G-protein mediation of the response to 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)
Intracellular analysis in vivo of different barosensitive bulbospinal neurons in the rat rostral ventrolateral medulla
Authors: Granata AR , Kitai ST
Published: March 2018

Neurons located in the rostral ventrolateral medulla (RVLM) with projections to the intermediolateral column (IML) in the spinal cord were electrophysiologically characterized and anatomically identified using an intracellular recording technique in vivo. A group of spontaneously active neurons was antidromically activated by electrical stimulation of the IML in the thoracic spinal cord (T2-T3 level). The axonal conduction velocities ranged from 1.5 m/sec to 11.0 m/sec; mean value, 5.5 +/- 2.6 m/sec (+/- SD). The firing pattern and changes in membrane potential in relation to the cardiac cycle were investigated in these bulbospinal neurons. A first group discharged action potentials with higher frequency at the end of the diastolic/beginning of the systolic period. The average of the neuronal membrane potentials demonstrated depolarizing potentials at the end of the diastolic/beginning of the systolic period. These depolarizing potentials increased in magnitude when the neurons were hyperpolarized. Therefore, they were characterized as EPSPs. The baroreceptor reflex activation produced by the increase in systemic arterial pressure following intravenous injection of phenylephrine elicited hyperpolarization, a decrease in the rate of discharge, and an increase in the membrane input resistance, suggesting that a disfacilitatory effect was produced by the activation of baroreceptor inputs on these bulbospinal neurons. Conversely, the inactivation of the baroreceptor reflex by intravenous injection of sodium nitroprusside produced depolarization and an increase in the firing rate. These neurons were characterized as baroreceptor-sensitive type I neurons. A second group of bulbospinal neuron in the RVLM was differentiated from the first group because it demonstrated a decrease in the frequency of discharge at the end of the diastolic/beginning of the systolic period. The average of the membrane potentials showed hyperpolarizing potentials that decreased in magnitude when the neuron was hyperpolarized. These hyperpolarizing potentials occurred at the end of the diastolic/beginning of the systolic period and were reversed in polarity after intracellular injections of chloride ions for several minutes. Therefore, these potentials were characterized as chloride- dependent IPSPs locked to the cardiac cycle. In some of these neurons, the electrical stimulation of the IML produced, in addition to the antidromic action potential, a monosynaptic EPSP with a shorter latency. Based on these unique characteristics, these neurons were defined as barosensitive type II neurons. During constant baroreceptor inactivation achieved by the hypotension produced by intravenous infusions of sodium nitroprusside, the pattern of discharge of barosensitive type II neurons became very regular, and the IPSPs locked to the cardiac cycle were absent.(ABSTRACT TRUNCATED AT 400 WORDS)
The NMDA receptor antagonist D-2-amino-5-phosphonopentanoate (D-AP5) impairs spatial learning and LTP in vivo at intracerebral concentrations comparable to those that block LTP in vitro
Authors: Davis S , Butcher SP , Morris RG
Published: March 2018

This series of experiments investigated whether the NMDA receptor antagonist D-2-amino-5-phosphonopentanoate (D-AP5) could induce impairments of spatial learning across a dose range comparable to its impairment of hippocampal long-term potentiation (LTP) in vivo. Estimations of the extracellular concentration of D-AP5 in hippocampus using microdialysis were also made to compare whether these impairments occur at concentrations similar to those required to impair LTP in the in vitro hippocampal slice. Rats were chronically infused with D-AP5 into the lateral ventricle at a range of concentrations (0–50 mM) via osmotic minipumps. They were first trained to find and escape onto a hidden platform in an open-field water maze task. After the behavioral learning, they were anesthetized with urethane and an attempt was made to evoke and monitor hippocampal LTP. Extracellular samples of D-AP5 in hippocampus were then taken using microdialysis, and finally, the animals were killed and tissue samples dissected. The microdialysis and tissue samples were analyzed for D-AP5 content using HPLC with fluorescence detection. The results established, first, that D-AP5 impairs spatial learning in a linear dose-dependent manner, highly correlated with its corresponding impairment of hippocampal LTP in vivo. No concentration of D-AP5 was observed to block LTP without affecting learning. Second, the microdialysis estimates indicated that, subject to certain assumptions, D-AP5 causes these impairments at extracellular concentrations comparable to those that impair LTP in vitro. Third, comparison of the whole tissue and microdialysis samples revealed a concentration ratio of approximately 30:1, indicating that 97% of the intracerebral D-AP5 is inaccessible to the dialysis probes. Infusion of 20 mM EGTA was found to cause a sevenfold increase in D-AP5 in the dialysis perfusates, suggesting that at least part of the inaccessible D-AP5 is trapped by a calcium-dependent mechanism. Two further behavioral control studies indicated that the D-AP5-induced impairment of spatial learning is unlikely to be secondary to a drug- induced motor disturbance, and that the performance of the D-AP5 group whose concentration was just sufficient to block hippocampal LTP completely was statistically indistinguishable from that of a group of rats with bilateral hippocampal lesions induced by ibotenic acid. Taken together, these findings offer support for the hypothesis that activation of NMDA receptors is necessary for certain kinds of learning.
Glutamate uptake disguises neurotoxic potency of glutamate agonists in cerebral cortex in dissociated cell culture
Authors: Rosenberg PA , Amin S , Leitner M
Published: March 2018

The pharmacological properties of glutamate agonists were compared in astrocyte-rich and astrocyte-poor cultures derived from embryonic rat cerebral cortex. The object of this investigation was to determine the extent to which glutamate uptake might influence the receptor-mediated neurotoxic actions of these compounds. In astrocyte-rich cultures, using 30 min exposures, we observed that the potencies of the poorly transported agonists NMDA (35 microM) and D-glutamate (89 microM) were higher than that of L-glutamate (205 microM). In astrocyte-poor cultures, L-glutamate was much more potent, with an EC50 of 5 +/- 4 microM (3–12 microM), for a 30 min exposure, whereas the potencies of NMDA and D-glutamate were essentially unchanged. L- and D-aspartate were also more effective in astrocyte-poor cultures, again with EC50 values of approximately 6–10 microM, as compared with 130 and 108 microM, respectively, in astrocyte-rich cultures. In other experiments, blocking sodium-dependent glutamate uptake in astrocyte-rich cultures, by using a sodium-free medium, made glutamate as potent an agonist as in astrocyte-poor cultures. Finally, we directly assessed the glutamate uptake system in astrocyte-rich and astrocyte-poor cultures and found that uptake was reduced approximately 25-fold in the astrocyte-poor cultures. These results show that in the presence of abundant astrocytes the neurotoxic potencies of L-glutamate, L-aspartate, and D- aspartate are substantially under-estimated.
Electrical activity increases growth cone calcium but fails to inhibit neurite outgrowth from rat sympathetic neurons
Authors: Garyantes TK , Regehr WG
Published: March 2018

Previous studies have shown that the growth of axons from both mouse dorsal root ganglion neurons and Helisoma neurons is arrested when the cells are electrically stimulated (Cohan and Kater, 1986; Fields et al., 1990a). Furthermore, in the case of Helisoma neurons, this arrest has been attributed to a rise in the calcium concentration in the growth cones (Cohan et al., 1987). To test the generality of these results, we examined the response of cultured rat superior cervical ganglion (SCG) neurons to electrical stimulation and changes in cytoplasmic calcium. Suprathreshold electrical stimulation of SCG neurons at 10 Hz by extracellular patch electrodes for periods of up to 1 hr had no measurable effect on their rate of growth. In agreement with previous studies, electrical stimulation was accompanied by a rise in the internal calcium concentration: when measured by the fluorescence of fura-2, growth cone calcium levels rose from about 100 nM to greater than 500 nM and then settled to a plateau value of about 350 nM. Despite this increase, however, growth of SCG neurons' processes continued. Our results show that electrical activity is not a universal signal for neurons to stop growing and that a rise in internal calcium does not always arrest the migration of growth cones.
Identification and stimulation by serotonin of intrinsic sensory neurons of the submucosal plexus of the guinea pig gut: activity- induced expression of Fos immunoreactivity
Authors: Kirchgessner AL , Tamir H , Gershon MD
Published: March 2018

The bowel is the only organ of the body in which neural reflexes can be elicited in the absence of input from the brain or spinal cord. This activity is mediated by the enteric nervous system (ENS), which contains primary afferent neurons. Experiments were carried out to locate the primary afferent neurons of the ENS. Two types of stimulation were used to activate neurons in the wall of the gut in vitro: exposure of the mucosa to cholera toxin or delivery of pressure to the mucosal surface with puffs of N2 from a micropipette. Neurons that became active in response to these stimuli were identified by demonstrating the intranuclear immunoreactivity of Fos, the product of the c-fos protooncogene. No Fos immunoreactivity could be detected in the absence of stimulation; however, application of cholera toxin and puffs of N2 each induced the appearance of Fos immunoreactivity in neurons in both the submucosal and myenteric plexuses. With either stimulus, the induction of Fos immunoreactivity was antagonized by TTX and therefore depended on neuronal activity. The appearance of Fos immunoreactivity could also be prevented by the 5-HT1P receptor antagonist N-acetyl-5-hydroxytryptophyl-5-hydroxytryptophan amide. In contrast, the stimulus-induced expression of Fos immunoreactivity was inhibited, but not abolished, by hexamethonium, which limited the spread of activation within the submucosal plexus and completely prevented expression of Fos immunoreactivity by myenteric neurons in response to mucosal puffs of N2. FluoroGold was injected into single ganglia of the myenteric plexus in order to identify submucosal neurons with myenteric projections. Submucosal neurons in which Fos immunoreactivity was induced by the stimuli were doubly labeled by FluoroGold. A subset of the submucosal, but not myenteric, neurons that expressed Fos immunoreactivity was doubly labeled by antibodies to calbindin. Submucosal calbindin-immunoreactive neurons were found to contain substance P immunoreactivity and could also be immunostained by anti-idiotypic antibodies that react with 5-HT1P receptors. A subset of dynorphin1–8-immunoreactive submucosal neurons (which are known to costore vasoactive intestinal peptide and to be secretomotor in function) expressed nuclear Fos immunoreactivity in response to cholera toxin, but not puffs of N2. These data suggest that intrinsic primary afferent neurons are located in the submucosal plexus, project to the myenteric plexus, and are activated by 5-HT acting on the 5-HT1P receptor subtype. These neurons are probably cholinergic and costore calbindin and substance P.
F3/F11 cell surface molecule expression in the developing mouse cerebellum is polarized at synaptic sites and within granule cells
Authors: Faivre-Sarrailh C , Gennarini G , Goridis C , Rougon G
Published: March 2018

The distribution of the F3/F11 neuronal cell surface molecule was investigated in the developing and adult mouse cerebellum by immunocytochemistry at the light and electron microscopic levels. F3/F11 was confined to subsets of neuronal types, since the Purkinje cell body and dendritic arborization as well as the stellate cells were not immunoreactive. In the young developing cerebellum, the granule cell axons strongly express F3/F11 as soon as they begin to grow, consistent with a functional role in promoting directional outgrowth of neuronal processes. In 10-d-old and adult cerebella, the granule cell bodies and dendrites were not immunoreactive whereas the parallel fibers, which are the granule cell axons, were labeled including in their presynaptic varicosities. By contrast, dendrites, cell bodies, and axons of Golgi cells were labeled by anti-F3 antibodies. Hence, F3/F11 can either be expressed throughout the cell or be polarized to the axons. This raises the question of how segregation of the glypiated F3/F11 molecule between different subcellular compartments depending on the type of neuron is achieved. F3/F11 was found to be present at three types of synaptic sites, suggesting that it might play a role in the formation and maintenance of synapses. However, in each type of synpase, F3/F11 was present at only the pre- or postsynaptic site, never at both: the parallel fiber varicosities contained F3/F11 whereas the postsynaptic compartment in contact, that is, the Purkinje cell dendritic spines, did not. The granule cell dendrites were unlabeled while the mossy fiber terminals contacting them were immunoreactive, and finally, the Golgi cell dendrites and dendritic spines were labeled while the presynaptic compartment contacting them was not. If F3/F11 functions as an adhesion molecule in vivo as indicated by in vitro assays, F3/F11-mediated adhesion is likely to be heterophilic.
Distinct spatial and temporal expression patterns of K+ channel mRNAs from different subfamilies
Authors: Drewe JA , Verma S , Frech G , Joho RH
Published: March 2018

Different types of K+ channels play important roles in many aspects of excitability. The isolation of cDNA clones from Drosophila, Aplysia, Xenopus, and mammals points to a large multigene family with several distinct members encoding K+ channels with unique electrophysiological and pharmacological properties. Given the pivotal role K+ channels play in the fine tuning of electrical properties of excitable tissues, we studied the spatial and temporal basis of K+ channel diversity. We report the isolation of two putative K+ channels that define two new subfamilies based upon amino acid sequence similarities with other known K+ channels. Northern blot and in situ hybridization studies revealed differences in the spatial and temporal expression patterns for these two new clones along with mRNAs from other K+ channel subfamilies. Two of the K+ channels studied are predominantly expressed in the brain. One of the “brain-specific” K+ channels is first expressed after about 2 weeks of postnatal cerebellar development and remains at levels about 10-fold higher in the cerebellum than in the rest of the brain.
Development of axonal arbors of layer 4 spiny neurons in cat striate cortex
Authors: Callaway EM , Katz LC
Published: March 2018

Spiny neurons in layer 4 of cat striate cortex are the primary recipients of geniculocortical afferents and provide crucial links to other cortical layers for processing visual information. Using intracellular staining, we examined the development of the local axonal projections of these neurons to determine (1) whether the laminar specificity of their projections emerged specifically or was sculpted from transient exuberant projections and (2) whether the emergence of excitatory connections from layer 4 to layer 2/3 could contribute to the activity-dependent development of clustered horizontal connections of layer 2/3 pyramidal neurons. Differences in the extent of projections to infragranular (layers 5 and 6, which receive sparse projections) versus superficial layers (layers 2/3 and 4, which receive extensive projections) developed specifically from the outset. By postnatal day 15 (P15) projections to infragranular layers matured and were indistinguishable from those in the oldest animal studied (P33). In contrast, projections to superficial layers continued to increase in complexity after P15. Projections within layer 4, which were the most elaborate at all ages studied, reached maturity at about P20, while those to layer 2/3 continued to increase in complexity through P33. No evidence for exuberant projections to any of these cortical layers was observed. At very early postnatal ages (P5) projections to the subplate region were evident. These disappeared by P8-P11, suggesting the presence of transient connections from layer 4 spiny neurons to subplate neurons. Binocular deprivation did not prevent the emergence of projections from layer 4 spiny neurons into layer 2/3 or development of normal laminar differences in projection density. Connections from layer 4 to layer 2/3 emerged after horizontal connections in layer 2/3 were crudely clustered, but in synchrony with the later refinement of clusters. Collaterals from layer 4 cells first crossed into layer 3 at P11, but were extremely short (extending only 50–200 microns beyond the laminar boundary) and uncommon (only 4 of 19 cells). Since by P8 horizontal projections of layer 2/3 pyramidal neurons are already crudely clustered, the emergence of crude clustering is probably independent of layer 4 to layer 2/3 excitatory projections. The proportion of cells projecting to layer 2/3 and the complexity of their arbors both increased in the subsequent weeks, closely matching the timing of both the refinement of crudely clustered horizontal connections and the emergence of visual responsiveness in layer 2/3.(ABSTRACT TRUNCATED AT 400 WORDS)
Activation and desensitization of AMPA/kainate receptors by novel derivatives of willardiine
Authors: Patneau DK , Mayer ML , Jane DE , Watkins JC
Published: March 2018

Willardiine [(S)-1-(2-amino-2-carboxyethyl)pyrimidine-2,4-dione] is a naturally occurring heterocyclic excitatory amino acid present in the seeds of Acacia and Mimosa. A series of 5-substituted willardiines were synthesized in single enantiomeric forms and tested for activity at AMPA/kainate receptors, using whole-cell recording from mouse embryonic hippocampal neurons. The (S)- but not (R)-isomers of willardiine and 5- bromowillardiine were potent agonists, producing rapidly but incompletely desensitizing responses. At equilibrium, (S)-5- fluorowillardiine (EC50, 1.5 microM) was seven times more potent than (R,S)-AMPA (EC50, 11 microM) and 30 times more potent than willardiine (EC50, 45 microM); the potency sequence was fluoro greater than nitro greater than chloro approximately bromo greater than iodo greater than willardiine. Willardiines produce strikingly different degrees of desensitization: at saturating doses the equilibrium response to the weakly desensitizing agonist (S)-5-iodowillardiine was similar in amplitude to the response to kainate and 10 times larger than the response to the strongly desensitizing agonist (S)-willardiine. The desensitization sequence was fluoro greater than willardiine greater than nitro approximately chloro greater than bromo greater than iodo greater than kainate. Cross-desensitization experiments confirm that willardiines bind to the same receptors activated by kainate and AMPA, and show that both the rapidly desensitizing and equilibrium responses to willardiines are mediated by the same receptor: (S)-5- iodowillardiine blocked activation of the rapidly desensitizing response evoked by (S)-willardiine and (S)-5-fluorowillardiine, while the latter agonists blocked the equilibrium response to (S)-5- iodowillardiine. A slowly decaying inward tail current was recorded after a brief application of (S)-5-fluorowillardiine but not (S)- willardiine, consistent with a model in which willardiines bind with different affinity to desensitized receptors, such that following removal of agonist, receptors trapped in the desensitized state can return to the open state before dissociation of agonist terminates receptor activation. Willardiines are the first compounds characterized in which simple changes in molecular structure are associated with marked differences in the ability of agonists to produce desensitization of AMPA/kainate receptors.
Differential effects of haloperidol and clozapine on neurotensin gene transcription in rat neostriatum
Authors: Merchant KM , Dobner PR , Dorsa DM
Published: March 2018

A single dose of typical neuroleptic, haloperidol, has been demonstrated to increase the expression of neurotensin/neuromedin N (NT/N) mRNA in the dorsolateral striatum within 1 hr of its administration (Merchant et al., 1991). The present study further investigated neuroleptic-induced regulation of NT/N gene transcription. Levels of NT/N mRNA were examined at various times following a single dose of haloperidol (1 mg/kg, i.p.) or the atypical antipsychotic clozapine (20, 30, or 40 mg/kg, i.p.) by in situ hybridization histochemistry and quantitative solution hybridization. In the dorsolateral striatum, the two drugs had strikingly different effects; haloperidol rapidly (within 30 min) increased the expression of mature NT/N mRNA while virtually no increase was observed in response to nontoxic doses of clozapine at any of the time points examined. Following haloperidol, maximal induction occurred at 7 hr, at which time NT/N mRNA levels were an order of magnitude higher than basal levels. By 20 hr after haloperidol, there was a significant decline in striatal NT/N mRNA levels. In situ hybridization analysis using an intron-derived probe revealed that haloperidol-induced increases in mature NT/N mRNA levels in the striatum were preceded by a transient increase in intron-containing NT/N gene transcripts. These data strongly indicate that acute haloperidol treatment results in transient transcriptional activation of NT/N gene, although a concomitant effect on the stability of NT/N primary transcripts cannot be ruled out. In contrast to their differential effects in the dorsolateral striatum, a single dose of both haloperidol and clozapine induced a small but significant increase in NT/N mRNA expression in the shell sector of the nucleus accumbens. These results raise the possibility that NT neurons in the nucleus accumbens may, at least in part, mediate the antipsychotic effects of classical neuroleptics, whereas NT cells in the dorsolateral region of the striatum may be involved in mediating other effects of typical neuroleptics such as extrapyramidal motor symptoms.
The microphysiology of peripheral taste organs
Authors: Roper SD
Published: March 2018

Recent studies on how peripheral taste organs function have revealed a number of intriguing membrane mechanisms underlying taste transduction. The story is still evolving, but certain generalities can now be stated confidently. For example, there is no one single chemosensory membrane transduction event. Instead, the different taste qualities--sweet, sour, salty, bitter--are subserved by different mechanisms. Furthermore, chemical and electrical synaptic processing in the taste bud is likely to modulate the output of the taste organs and may contribute to how different taste qualities are discriminated. Synapses occur between adjacent cells in the taste organ as well as between receptor cells and sensory fibers. The preponderance of data indicates that biogenic amines are present in taste buds and exert some form of neuromodulatory control, if not frank neurotransmission, in peripheral taste organs. Current research in the microphysiology of taste buds includes extending and refining our understanding of how the apical, chemosensitive regions of receptor cells respond to taste stimuli, identifying what synaptic transmitters exist in taste organs, and exploring synaptic mechanisms in taste buds.