bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased expression of neuronal nitric oxide synthase (NOS) in visceral neurons after nerve injury
Authors: Vizzard MA , Erdman SL , de Groat WC
Published: April 2018

The distribution of nitric oxide synthase immunoreactivity (NOS-IR) and the changes in this distribution after peripheral axotomy were examined in lumbosacral afferent and preganglionic neurons (PGNs) innervating the pelvic viscera of the male rat. The visceral neurons in L6-S1 and L1-L2 dorsal root ganglia (DRG) and in the spinal cord were identified by retrograde axonal transport following injection of Fluorogold (FG) into the major pelvic ganglion (MPG). Axotomy was performed by removing the MPG on one side 2–4 weeks prior to sacrificing the animals. A differential distribution of NOS-IR was detected in DRG cells at different segmental levels of control animals. Significantly greater numbers of NOS-IR cells were present in thoracic (T8, T10, T12; 30–44 cell profiles/section) and rostral lumbar DRGs (L1-L2; 3–15 NOS-IR cell profiles/section) compared to caudal lumbosacral (L5-S1) DRGs (0.2–0.7 cell profiles/section). A significant increase in the number of NOS-IR cells was detected in the L6-S1 DRG (p < or = 0.001; 11 NOS-IR cell profiles/section) but not in the L2 or L5 DRG ipsilateral to axotomy. In these ganglia, an average of 37.0 +/- 4.0% (L6) and 20.6 +/- 2.2% (S1), respectively, of FG-labeled pelvic afferent neurons were NOS-IR compared to 1.1 +/- 0.5% (L6) and 2.5 +/- 1.4% (S1) contralateral to the axotomy. Following axotomy, a significantly greater percentage of dye-labeled pelvic visceral afferents in the L1 and L2 DRG also exhibited NOS-IR in comparison to the contralateral side. Following axotomy, NOS-IR fibers were detected along the lateral edge of the dorsal horn extending from Lissauer's tract to the region of the sacral parasympathetic nucleus (SPN) on the ipsilateral side of the L6 and S1 spinal segments. These NOS-IR fibers were not detected in adjacent spinal segments (L4, L5, or S2). Axotomy also changed the numbers of NADPH-d-positive and NOS-IR cells in the region of the SPN in the L6 spinal segment. Contralateral to the axotomy 38.3 +/- 4.0% of PGNs in the L6 spinal segment were colabeled with NOS-IR; however, ipsilateral to axotomy, a significantly greater percentage (61.0 +/- 3.0%; p < or = 0.01) of PGNs exhibited NOS-IR. Axotomy did not alter the distribution of PGNs in the S1 segment exhibiting NOS-IR. These results indicate that NOS-IR in visceral afferent and PGNs is plastic and can be upregulated by peripheral nerve injury.
Expression of m1-m4 muscarinic acetylcholine receptor proteins in rat hippocampus and regulation by cholinergic innervation
Authors: Levey AI , Edmunds SM , Koliatsos V , Wiley RG , Heilman CJ
Published: April 2018

A family of muscarinic ACh receptor genes are expressed in hippocampus, but little is known about the localization of the encoded proteins and their regulation by cholinergic innervation. Subtype-specific antibodies were used to localize m1-m4 proteins in the hippocampal formation by immunocytochemistry and to determine the alterations in the subtypes following deafferentation. Each of the receptors is differentially localized in Ammon's horn and dentate gyrus, with highly complementary distributions. m1 is widely expressed in somata and dendrites of pyramidal neurons and granule cells in dentate gyrus. m2 immunoreactivity is expressed mostly in nonpyramidal neurons, and in several discrete bands of fibers and puncta surrounding pyramidal neurons and other layers. m3 is enriched in pyramidal neurons, the neuropil in stratum lacunosum-moleculare and the outer third of the molecular layer of dentate gyrus. m4 is enriched in nonpyramidal neurons, in fiber pathways (alveus, fimbria, and hippocampal commissure), and in the inner third of the molecular layer. Fimbria- fornix lesions decreased ipsilateral m2- and m4-immunoreactive axons in the fimbria, with no apparent changes in the distribution of any of the receptors in hippocampus. 192-IgG immunotoxin lesions of the cholinergic septohippocampal projections, which spare noncholinergic projections, produced a small decrease in m2-immunoreactive fibers in the fimbria with no other major changes in the distribution of subtypes. Immunoprecipitation studies at 3–28 d following fimbria- fornix lesions revealed a 25% loss of m2 at 3 d in hippocampus, and upregulation of both m1 (20–29% at 7–14 d) and m4 (44% at 28 d). Thus, the vast majority of muscarinic receptor subtypes are intrinsic to the hippocampal formation and/or nonseptal hippocampal afferents. A subset of m2 and m4 are presynaptically localized, with m2 in cholinergic axons and m2 and m4 possibly in noncholinergic axons that comprise the septohippocampal pathway. The unique laminar and regional distributions of m1-m4 in the hippocampus reflect differential cellular and subcellular distributions of the subtypes and/or selective association of receptor subtypes with certain afferent and intrinsic connections. These results indicate that each subtype likely has a different role in cholinergic modulation of excitatory and inhibitory hippocampal circuits.
Fast, local signal transduction between the mu opioid receptor and Ca2+ channels
Authors: Wilding TJ , Womack MD , McCleskey EW
Published: April 2018

We used patch-clamp methods to describe signal transduction between the mu opioid receptor, the binding site for morphine, and high-threshold Ca2+ channels in dorsal root ganglion (DRG) sensory neurons from adult rats. Opioid signaling persists in excised membrane patches, and an activated opioid receptor can only inhibit nearby Ca2+ channels; thus, no readily diffusible second-messenger molecule mediates between the mu receptor and Ca2+ channels. Inhibition of Ca2+ channels begins several hundred msec after application of opioid and it is maximal by 5 sec; this is faster than typical phosphorylation cascades. Blockade of the known serine-threonine kinases and phosphatases does not affect this opioid signaling and, as shown previously by Seward et al. (1991) and Moises et al. (1994a), pertussis toxin eliminates virtually all of the effect. Inhibited channels can open, but their half-activation voltage is unphysiologically positive. The link between the mu receptor and Ca2+ channels is clearly unlike the protein kinase C-dependent paths that couple mu receptors to NMDA channels in dorsal horn neurons (Chen and Huang, 1991) and alpha-adrenergic receptors to Ca2+ channels in DRG neurons (Diverse-Pierluissi and Dunlap, 1993). The rapid kinetics and tight localization of the signaling path are properties expected if receptor and channel are linked directly by a G-protein, but these properties do not constitute proof of such a pathway.
Individual variation and lateral asymmetry of the rat primary somatosensory cortex
Authors: Riddle DR , Purves D
Published: April 2018

We have evaluated the interindividual variability and lateral symmetry of a major cortical area by comparing the primary somatosensory cortex (S1) of adult rats. Our choice of the rat was dictated by the accuracy with which one can measure S1 and its component representations in the rodent brain; the importance of such measurements lies in understanding the rules that govern the allocation of cortical space and, ultimately, the consequences of differential allocation for behavior. With respect to interindividual differences, the major somatic representations in S1 are surprisingly variable in size. The area of the whiskerpad representation, for example, ranged from 3.72 to 6.84 mm2 in a sample of 53 rats; other components of S1 showed comparable differences among animals. With respect to lateral symmetry, the average area of each major representation was similar for the right and left hemispheres; thus, we found no consistent bias in the size of S1 or its elements in the sample as a whole. Within individual animals, however, the sizes of the major somatic representations were often quite different in the two hemispheres. The magnitude of the lateral differences averaged 7.9 +/- 0.8% (mean +/- SEM) for the whisker pad representation, 11.6 +/- 1.3% for the upper lip, 15.4 +/- 1.6% for the furry buccal pad, 13.9 +/- 1.4% for the lower jaw, and 13.3 +/- 1.2% for the forepaw. These results show that the amount of cortical space allocated to corresponding functions in individual rats--or in the two hemispheres of a particular rat--are often different. Such variations are likely to be reflected in somatosensory performance.
Kainic acid-induced neuronal death is associated with DNA damage and a unique immediate-early gene response in c-fos-lacZ transgenic rats
Authors: Kasof GM , Mandelzys A , Maika SD , Hammer RE , Curran T , Morgan JI
Published: April 2018

Previously, we established that persistent upregulation of c-fos expression preceded kainic acid (KA)-induced neuronal death in mice. To discriminate between events that are products of the seizures elicited by KA and those that are specifically associated with its neurotoxic actions, we have examined the expression of cellular immediate-early genes (cIEGs) following KA or pentylenetetrazol (PTZ) treatment in c- fos-lacZ transgenic rats. While both chemoconvulsants elicit seizures, only KA causes selective neuronal death. Following treatment of transgenic rats with KA there was a protracted expression of Fos-lacZ that lasted for 2–3 d. In contrast, PTZ elicited a transient increase in the transgene product that lasted about 6 hr. Normally, Fos and Fos- lacZ were detected only in neuronal nuclei. However, 6 hr following kainic acid (but not PTZ) administration, beta-galactosidase activity appeared in the cytoplasm of neurons within vulnerable regions (as determined by the terminal transferase biotinylated-UTP nick end labeling (TUNEL) procedure). Like c-fos, transcripts for other cIEGs were elevated for longer periods in the KA-treated rat hippocampus. In addition, fra-1 and fra-2 were only induced in the KA-treated rat. These changes in mRNA levels were paralleled by a sustained increase in AP-1 DNA binding activity. Thus, quantitative and qualitative changes in AP-1 DNA binding complexes accompany neurotoxic cell death that are not observed following seizures.
Bilateral control of hindlimb scratching in the spinal turtle: contralateral spinal circuitry contributes to the normal ipsilateral motor pattern of fictive rostral scratching
Authors: Stein PS , Victor JC , Field EC , Currie SN
Published: April 2018

In a spinal turtle, unilateral stimulation in the rostral scratch receptive field elicited rhythmic fictive rostral scratching in ipsilateral hindlimb motor neurons; contralateral hip motor activity was also rhythmic and out-of-phase with ipsilateral hip motor activity. When left and right rostral scratch receptive fields were stimulated simultaneously, bilateral rhythmic fictive rostral scratching was produced; left hindlimb scratching was out-of-phase with right hindlimb scratching. Thus, spinal circuits coordinate interlimb phase during bilateral fictive scratching. We examined the contributions of contralateral spinal circuitry to the normal pattern of right hindlimb fictive rostral scratching by removing the left halves of the D7 segment and the hindlimb enlargement (D8-S2 segments). After left- hemicord removal, stimulation in the right rostral scratch receptive field usually elicited a variation of rostral scratching with rhythmic right hip flexor activity and no right hip extensor activity; thus, right hip flexor rhythm generation does not require left hindlimb enlargement circuitry. Normal right hindlimb rostral scratching with rhythmic alternation between hip flexor and extensor activities was rarely observed; thus, contralateral spinal circuitry contributes to the production of normal ipsilateral fictive rostral scratching. After left-hemicord removal, stimulation in the left rostral scratch receptive field elicited rhythmic right hip extensor activity; thus, contralateral spinal circuitry can generate a hip extensor rhythm during ipsilateral rostral scratch receptive field stimulation. Our observations and those of Berkowitz and Stein (1994a,b) support the concept that an ipsilateral hindlimb's normal rostral scratch motor pattern is generated by a modular central pattern generator that is bilaterally distributed in the spinal cord.
Growth cones are actively influenced by substrate-bound adhesion molecules
Authors: Burden-Gulley SM , Payne HR , Lemmon V
Published: April 2018

As axons advance to appropriate target tissues during development, their growth cones encounter a variety of cell adhesion molecules (CAMs) and extracellular matrix molecules (ECM molecules). Purified CAMs and ECM molecules influence neurite outgrowth in vitro and are thought to have a similar function in vivo. For example, when retinal ganglion cell (RGC) neurons are grown on different CAM and ECM molecule substrates in vitro, their growth cones display distinctive morphologies (Payne et al., 1992). Similarly, RGC growth cones in vivo have distinctive shapes at different points in the pathway from the eye to the tectum, suggesting the presence of localized cues that determine growth cone behaviors such as pathway selection at choice points. In this report, time-lapse video microscopy was utilized to examine dynamic transformations of RGC growth cones as they progressed from L1/8D9, N-cadherin, or laminin onto a different substrate. Contact made by the leading edge of a growth cone with a new substrate resulted in a rapid and dramatic alteration in growth cone morphology. In some cases, the changes encompassed the entire growth cone including those regions not in direct contact with the new substrate. In addition, the growth cones displayed a variety of behavioral responses that were dependent upon the order of substrate contact. These studies demonstrate that growth cones are actively affected by the substrate, and suggest that abrupt changes in the molecular composition of the growth cone environment are influential during axonal pathfinding.
Neuroblast long-term cell cultures from human fetal olfactory epithelium respond to odors
Authors: Vannelli GB , Ensoli F , Zonefrati R , Kubota Y , Arcangeli A , Becchetti A , Camici G , Barni T , Thiele CJ , Balboni GC
Published: April 2018

Primary cell cultures from human fetal olfactory neuroepithelium have been isolated, cloned, and propagated in continuous in vitro culture for approximately 1 year. The two clones we report here synthesize both neuronal proteins and olfactory-specific markers as well as the putative olfactory neurotransmitter, carnosine. In addition, patchclamp experiments reveal that these cells are electrically excitable. Following exposure to a panel of aromatic chemicals one of the cell cultures shows a specific increase in intracellular cAMP, indicating that some degree of functional maturity is expressed in vitro. The results suggest that these cells originate from the “stem cell” compartment that gives rise to mature olfactory receptor neurons. These long-term cell cultures represent models that will be useful in studying the mechanism(s) of olfaction and the regulation of olfactory neurogenesis and differentiation.
The optic tract and tectal ablation influence the composition of neurofilaments in regenerating optic axons of Xenopus laevis
Authors: Zhao Y , Szaro BG
Published: April 2018

Neurofilaments have been proposed to regulate axonal stability and diameter through changes in number and subunit composition. We have found that pathway and target innervation directly influence the molecular composition of neurofilaments within regenerating optic axons of Xenopus laevis. Immunocytochemistry was used to examine neurofilaments within two abnormal visual pathways. The first was an aberrant, transient retinoretinal projection, which formed when some axons entered the contralateral optic nerve at the chiasm. The second was formed by regenerating axons deprived of their normal targets by surgical ablation of both optic tecta. Distal to an orbital nerve crush, the neurofilament proteins NF-L, NF-M, NF-H, and XNIF disappear from degenerating fibers. In normally regenerating axons, these neurofilament proteins emerge in a progression reminiscent of development. In the aberrant retinoretinal projection, levels of XNIF, NF-L, and -M remained lower than in normally regenerating axons, whereas NF-H and a phosphorylated form of NF-M were undetectable for at least 35 d after nerve crush. Normally, these two latter forms reappear between 15 and 21 d after surgery. Thus, this transient, incorrect axonal projection expressed neurofilaments in a very different pattern from correctly regenerating axons. In tecta-ablated frogs, staining of phosphorylation independent epitopes of XNIF, NF-L, and -M increased normally after axons entered the tract, but that of NF-H and phosphorylated NF-M remained low for at least 42 d after axotomy. Thus, separate parts of the visual pathway influence the complexity of neurofilaments.
Disconnection of intracortical synaptic linkages disrupts synchronization of a slow oscillation
Authors: Amzica F , Steriade M
Published: April 2018

The intracortical synaptic linkages underlying the synchronization of a recently described slow (< 1 Hz) oscillation (Steriade et al., 1993b,c) were investigated in anesthetized cats by means of multisite extra- and intracellular recordings, including dual impalements, from rostral and caudal sites in the association cortical suprasylvian and marginal gyri, before and after reversible lidocaine inactivation or transections in the middle suprasylvian gyrus. Stimulus-evoked responses revealed that the rostral and caudal suprasylvian foci are reciprocally connected, with a preference for posterior-to-anterior responses. Lidocaine infusion between the stimulating and recording sites disrupted the intracortical synaptic linkage, while leaving unaffected the responses at the sites close to the stimulating electrodes. The high coherence between slowly oscillating field potentials and intracellular activities recorded from anterior and posterior suprasylvian foci was lost after reversible inactivation or transections in the middle suprasylvian gyrus, whereas the synchrony between adjacent foci within the anterior or posterior areas was preserved. Two to four hours after inactivation or transection the synchrony between all channels was totally or partially recovered. We introduced the synchrony coefficient (SyCo) and calculated the SyCo for closely located and distant sites. Lidocaine infusion or transection did not affect the SyCo between leads placed on the same site, but significantly (60%) decreased the SyCo between channels separated by the functionally inactivated or transected sector. Our results demonstrate that pathways within or beneath the suprasylvian gyrus sustain the synchronization of the slow oscillation between cortical sites. As the loss of long-range coherence was not permanent, intergyral paths and/or corticothalamocortical loops may exert compensatory functions after the disconnection of intrasuprasylvian synaptic linkages.
Dopamine modulates GABAc receptors mediating inhibition of calcium entry into and transmitter release from bipolar cell terminals in tiger salamander retina
Authors: Wellis DP , Werblin FS
Published: April 2018

Using optical recording techniques, we directly monitored pre- and postsynaptic calcium dynamics at bipolar cell terminals while inhibiting synaptic release with applied GABA and modulating inhibition with dopamine. To monitor pre-synaptic activity, individual bipolar cells in the retinal slice were filled with either fura-2 or fluo-3 through a patch electrode. Calcium entry into bipolar terminals, elicited by depolarization from -60 mV to 0 mV, was reduced to 36% of control in the presence of 200 microM bath-applied GABA. Further addition of 100 microM dopamine to the bath relieved the GABAergic inhibition and nearly doubled the calcium entry. Yet dopamine alone had no apparent direct effect upon calcium entry. The relief from GABAergic inhibition could be reproduced with SKF-38393, a dopamine D1 receptor agonist, and with forskolin, an adenylyl cyclase activator, suggesting that dopamine acts through a cAMP second-messenger pathway. To monitor transmitter release from bipolar cells, slices were loaded with fura- 2AM, a membrane permeable form of the dye. Puffs of 110 mM KCl at bipolar dendrites depolarized bipolar cells and elicited calcium signals that could be monitored both at bipolar terminals and in postsynaptic cells. Consistent with the results above, GABA inhibited calcium entry at bipolar terminals and also reduced transmitter release, measured as a decrease in calcium entry in amacrine and ganglion cells. The addition of dopamine relieved this inhibition and increased transmitter release. Our results show the spatiotemporal correlation between the GABAergic inhibition of calcium entry at bipolar terminals, the resulting reduction in postsynaptic activity, and the relief of this inhibition with dopamine.
Neuromuscular metamorphosis in the moth Manduca sexta: hormonal regulation of synapses loss and remodeling
Authors: Truman JW , Reiss SE
Published: April 2018

The motor system of the moth Manduca sexta is completely remodeled during the pupal-adult transformation (PAT). It is stable until the formation of the pupal stage (0% PAT), but larval motor end plates become disrupted by 5% PAT and are lost by 10% PAT, at the time that the muscle has begun to degenerate. Most of the axonal arbor is retracted by 15% with the first signs of adult sprouts appearing by 20% PAT, coinciding with proliferative activity in the remains of the larval muscle. Extensive growth of the axonal arbor begins after 30% PAT, with an initial phase of rapid longitudinal growth (35–50% PAT) and then the production of short transverse branches that then form sprays of end plates (50–70% PAT). Growth and maturation of the end plates occupies the remainder of metamorphosis. Neuromuscular metamorphosis was interfered with by systemic or local treatment with a mimic of the insect juvenile hormone. The results of these treatments suggest that some aspects of the removal of larval axonal branches requires cues from the target. For the sprouting response, the rapid longitudinal growth over the muscle appears to be due to ecdysteroids acting directly on the cell body of the motoneuron. By contrast, the subsequent production and maintenance of transverse sprouts and the corresponding end plates may be an indirect response to stimulation of muscle growth and differentiation by ecdysteroids.
Olfactory marker protein mRNA is found in axons of olfactory receptor neurons
Authors: Wensley CH , Stone DM , Baker H , Kauer JS , Margolis FL , Chikaraishi DM
Published: April 2018

The separation between the cell bodies of olfactory receptor neurons in the nasal cavity and their axon terminals in the olfactory bulb make them attractive for studying axonal transport. Although high molecular weight RNAs are generally believed to be excluded from axons of mature neurons, we demonstrate here that mRNA for olfactory marker protein (OMP), an abundant cytoplasmic protein selectively expressed in mature receptor cells, is present in rodent olfactory receptor axons. OMP RNA was detected by in situ hybridization at the light microscope level in axons and in terminals. By nuclease protection, the level of OMP RNA in the olfactory bulb was 5–10% of that in the olfactory epithelium where the cell bodies reside. In contrast to axonally transported vasopressin and oxytocin mRNAs, which are deficient in their 3′ polyA tails, axonal OMP RNA fractionated as polyA+. OMP RNA was lost from axons and terminals after deafferentation, suggesting that OMP RNA was synthesized in receptor cell bodies in the epithelium and was transported into axons and terminals in the olfactory bulb. RNA for G(olf), a G-protein highly expressed in dendrites of mature olfactory receptor neurons, was not detected in the olfactory bulb. We hypothesize that the immature nature of the cytoskeleton and, specifically, the lack of tightly bundled microtubules allows transport of particular mRNAs in olfactory receptor axons.
The orbital and medial prefrontal circuit through the primate basal ganglia
Authors: Haber SN , Kunishio K , Mizobuchi M , Lynd-Balta E
Published: April 2018

The ventral striatum is considered an interface between limbic and motor systems. We followed the orbital and medial prefrontal circuit through the monkey basal ganglia by analyzing the projection from this cortical area to the ventral striatum and the representation of orbitofrontal cortex via the striatum, in the globus pallidus and substantia nigra. Following injections of Lucifer yellow and horse radish peroxidase into the medial ventral striatum, there is a very densely labeled distribution of cells in areas 13a and 13b, primarily in layers V and VI, and in medial prefrontal areas 32 and 25. Injections into the shell of the nucleus accumbens labeled primarily areas 25 and 32. The reaction product in the globus pallidus and the substantia nigra supports previous studies demonstrating that efferent projections from the ventral striatum are represented topographically in the ventral pallidum and nontopographically in the substantia nigra, pars compacta. Tritiated amino acid or PHA-L tracer injections into orbitofrontal cortex produce dense patches of terminal labeling along the medial edge of the caudate nucleus and the dorsal part of the nucleus accumbens. These results demonstrate that the orbital prefrontal cortex projects primarily to the medial edge of the ventral striatum and to the core of the nucleus accumbens. The arrangement of terminals in the globus pallidus and substantia nigra show two different patterns. Thus, the orbital and medial prefrontal cortex is represented in a confined region of the globus pallidus but throughout an extensive area of the dorsal substantia nigra. Terminals are extensive throughout the region of the dopaminergic neurons, suggesting that this input may influence a wide area of both the striatum and frontal cortex.
Tactile resolution: peripheral neural mechanisms underlying the human capacity to determine positions of objects contacting the fingerpad
Authors: Wheat HE , Goodwin AW , Browning AS
Published: April 2018

We measured the ability of humans to discriminate the positions of spherical objects passively contacting the fingerpad. The discrimination threshold averaged 0.55 mm for a moderately curved sphere (radius 5.80 mm) and decreased to 0.38 mm for a more curved sphere (radius 1.92 mm); since the receptor density is about 1 per mm2, these values are substantially smaller than those predicted by the sampling theorem (referred to as hyperacuity). To elucidate the underlying neural mechanisms, responses to the same spheres and random sequences of stimuli were recorded from single Merkel afferents (SAIs) and Meissner afferents (RAs) in anesthetized monkeys. For multiple applications of identical stimuli, coefficients of variation of responses were around 3%. Profiles of responses across the SAI population were “hill-shaped.” A change in position of the stimulus on the skin resulted in a matching shift of the profile, evident over the whole profile for the more curved sphere but ony at the skirts for the less curved sphere. The shift in response profiles, relative to the standard deviations, increased as the change in position increased, and was more reliable for the more curved sphere. Responses were measured over four time frames: 0.2, 0.3, 0.5, and 1.0 sec. Although responses increased with an increase in integration time, so, too, did their standard deviations, so that signal-to-noise ratios or the resolution in the SAI population was bout the same at 0.2 sec as at 1.0 sec. Only half the RAs responded; responses were small, but signalled reliable information about the position of the stimulus.
Fear and the human amygdala
Authors: Adolphs R , Tranel D , Damasio H , Damasio AR
Published: April 2018

We have previously reported that bilateral amygdala damage in humans compromises the recognition of fear in facial expressions while leaving intact recognition of face identity (Adolphs et al., 1994). The present study aims at examining questions motivated by this finding. We addressed the possibility that unilateral amygdala damage might be sufficient to impair recognition of emotional expressions. We also obtained further data on our subject with bilateral amygdala damage, in order to elucidate possible mechanisms that could account for the impaired recognition of expressions of fear. The results show that bilateral, but not unilateral, damage to the human amygdala impairs the processing of fearful facial expressions. This impairment appears to result from an insensitivity to the intensity of fear expressed by faces. We also confirmed a double dissociation between the recognition of facial expressions of fear, and the recognition of identity of a face: these two processes can be impaired independently, lending support to the idea that they are subserved in part by anatomically separate neural systems. Based on our data, and on what is known about the amygdala's connectivity, we propose that the amygdala is required to link visual representations of facial expressions, on the one hand, with representations that constitute the concept of fear, on the other. Preliminary data suggest the amygdala's role extends to both recognition and recall of fearful facial expressions.
Blocking Ca(2+)-dependent synaptic release delays motoneuron differentiation in the rat spinal cord
Authors: Xie H , Ziskind-Conhaim L
Published: April 2018

Development of motoneuron electrical properties and excitability was studied in spinal cord explants of rat embryos cultured for 1–3 weeks. The morphological organization of the spinal cord and synaptic inputs onto motoneurons were maintained in organ culture. The rate of differentiation of motoneuron resting potential and increase in membrane excitability was similar in vitro and in vivo, suggesting that these properties were regulated by cellular signals or extracellular differentiation-promoting factors that were preserved in culture. However, maturation of input resistance, action potential threshold and action potential maximum rate of rise was slower than in vivo. Culturing spinal cord explants with their dorsal root ganglia attached did not facilitate motoneuron differentiation. The role of newly formed synaptic pathways in regulating the changes in motoneuron electrical properties was studied in the presence of blockers of synaptic transmission. Motoneuron differentiation was delayed in spinal cords cultured in the presence of TTX, indicating that electrical activity influenced the time course of their development. However, blocking synaptic transmission with antagonists of glutamate, glycine, and GABAA receptors did not affect the rate of motoneuron differentiation, suggesting that maturation of motoneuron phenotype was independent of activation of these transmitter-gated channels. Incubating spinal cords in medium containing high-K+, which increased the frequency of spontaneous potentials, reversed the inhibitory effect of TTX. Similar to TTX action, motoneuron development was retarded when synaptic release was chronically blocked with either tetanus toxin or omega- conotoxin, a Ca2+ channel blocker. These findings suggested that electrical activity in spinal cord explants modulated motoneuron differentiation via Ca(2+)-dependent synaptic release of neurotransmitters or neurotrophic factors.
Activity of the beta 3 nicotinic receptor promoter is a marker of neuron fate determination during retina development
Authors: Matter JM , Matter-Sadzinski L , Ballivet M
Published: April 2018

We have previously shown that transcription of the beta 3 nicotinic receptor gene within the chick CNS is regulated by a promoter 143 base pairs (bp) in length. Here, we demonstrate that in the developing visual system this promoter is active in a subset of retinal cells, the majority of which are ganglion cells. Because the beta 3 promoter is activated very early during retina development, it can provide a marker of ganglion cell induction and differentiation. Transfection of neuroretina explants enabled us to detect activity of the beta 3 promoter in premigratory cells localized on the ventricular side of the retina. Double-labeling experiments showed that activation of the beta 3 promoter takes place before the last S-phase, suggesting that this particular phenotypic trait is determined when precursor cells are still proliferating. The beta 3 phenotype is induced in about one-tenth of the total pool of retinal progenitor cells and is stable upon changing the cellular environment. Our study suggests that at the very early stages of retina neurogenesis, some lineage restrictions have already occurred in the population of retinal progenitor cells.
Intrinsic neuromodulation in the Tritonia swim CPG: the serotonergic dorsal swim interneurons act presynaptically to enhance transmitter release from interneuron C2
Authors: Katz PS , Frost WN
Published: April 2018

Heterosynaptic enhancement of transmitter release is potentially very important for neuronal computation, yet, to our knowledge, no prior study has shown that stimulation of one neuron directly enhances release from an interneuron. Here, we demonstrate that in the marine mollusk Tritonia diomedea, the serotonergic dorsal swim interneurons (DSIs) heterosynaptically increase the amount of transmitter released from another interneuron, C2. Stimulation of a single DSI at physiological firing frequencies increases the size of synaptic potentials evoked by C2. This increase in synaptic efficacy is correlated with an increase in homosynaptic paired-pulse facilitation by C2. Thus, it is likely to be due to an enhancement of transmitter release from C2, rather than a postsynaptic action on the followers of C2. This is further supported by the fact that DSI stimulation enhances the strengths of all chemical synapses made by C2 within the swim network, regardless of their sign. Furthermore, DSI enhances the amplitude of C2 synaptic potentials recorded in neurons that DSI itself does not synapse with. Finally, DSI differentially modulates different synaptic inputs to the same postsynaptic target; while increasing C2- evoked EPSPs it simultaneously decreases the size of EPSPs evoked by other DSIs. The heterosynaptic facilitation of C2 synaptic potentials by DSI is not caused by a simple depolarization of C2, but may be a direct action on the transmitter release mechanism. This neuromodulatory effect, which is intrinsic to the circuitry of the central pattern generator for escape swimming in Tritonia, may be important for self-reconfiguration of the swim motor network.
Induction of a serotonergic and neuronal phenotype in thyroid C-cells
Authors: Clark MS , Lanigan TM , Page NM , Russo AF
Published: April 2018

We have investigated whether rat thyroid C-cells can acquire a phenotype similar to serotonergic neurons. C-cells are neural crest derived endocrine cells with some intrinsic neuronal and serotonergic properties. A relatively simple isolation scheme yielded cultures of about 50% initial purity, as measured by fluorescence activated cell sorting. These enriched C-cells could extend neurites up to 550 microns on a laminin-containing substratum in the presence of NGF. The cultured C-cells expressed neurofilaments and this expression was enhanced by NGF treatment. The C-cells also expressed two markers of the sympathoadrenal neural crest lineage, the mammalian achaete scute homolog-1 (MASH-1) transcription factor, and the B2 cell surface antigen. Interestingly, MASH-1 was not detectable after the C-cells were placed in culture, which is consistent with neuronal differentiation, since MASH-1 is only expressed in neuronal progenitors prior to differentiation. We then demonstrated that C-cells possess the fundamental features of serotonergic neurons: synthesis and secretion, uptake, and feedback control. The enriched C-cells, as well as the CA77 C-cell line, showed 5-HT immunostaining, expression of tryptophan hydroxylase mRNA, 5-HT1B autoreceptor mRNA, and 5-HT transporter mRNA and activity. NGF greatly induced 5-HT transporter activity as determined by sensitivity to sertraline, a selective 5-HT reuptake inhibitor. Based on these results, we propose that thyroid C-cells are derived from a vagal sympathoadrenal progenitor, similar to serotonergic enteric neurons, and can undergo neuronal transdifferentiation. Hence, these cells should provide suitable and convenient models for molecular and cellular studies on serotonergic neurons.
Desensitizing glutamate receptors shape excitatory synaptic inputs to tiger salamander retinal ganglion cells
Authors: Lukasiewicz PD , Lawrence JE , Valentino TL
Published: April 2018

AMPA/kainate (KA) receptors mediate a component of ganglion cell excitatory postsynaptic currents (EPSCs). We investigated whether desensitization at these receptors contribute to the shape of transient EPSCs in ON-OFF ganglion cells. Whole-cell, voltage-clamp recordings were made from ganglion cells in the retinal slice or in isolation. EPSCs were evoked by either stimulating the slice with light or puffing K+ at the outer plexiform layer (OPL). The AMPA/KA receptor-mediated component of the EPSCs was isolated by including NMDA receptor antagonists in the bath. Strychnine and picrotoxin blocked inhibitory inputs. In isolated ganglion cells, cyclothiazide (10 microM), which blocks desensitization in non-NMDA receptors, enhanced both the amplitude and the duration of currents evoked by puffs of AMPA or glutamate. EPSCs evoked by K(+)-puffs in the OPL were also enhanced by cyclothiazide (30 microM). When AMPA/KA receptors were blocked with NBQX (10 microM), no enhancement of the EPSCs by cyclothiazide was observed, indicating that cyclothiazide did not act presynaptically. Cyclothiazide also enhanced the amplitude and duration of both the ON and OFF light-evoked (L-) EPSCs recorded in ON-OFF ganglion cells. Current-voltage relationships showed the enhancement was not voltage dependent. When control and enhanced responses where normalized, it was observed that the rate of desensitization of both the ON and OFF L- EPSCs was decreased by cyclothiazide. Cyclothiazide selectively enhanced the AMPA/KA receptor-mediated component of ganglion cells EPSCs, suggesting that desensitization of AMPA/KA receptors shape transient L-EPSCs.
Cysteine string protein immunoreactivity in the nervous system and adrenal gland of rat
Authors: Kohan SA , Pescatori M , Brecha NC , Mastrogiacomo A , Umbach JA , Gundersen CB
Published: April 2018

Cysteine string proteins (csps) are a recently discovered class of cysteine-rich proteins. They have been shown to associate preferentially with synaptic vesicle fractions of Torpedo electric organ or rat brain where they have been implicated in events associated with transmitter secretion. However, to date there has been no information concerning the distribution of csps in rat tissues. We investigated the localization of csps in the rat retina and CNS using immunohistochemistry with affinity purified anti-csp antibodies. Specific csp immunoreactivity having a punctate appearance is present throughout the neuraxis. Csp immunoreactivity is particularly abundant in synapse-rich regions including those of the retina, main olfactory bulb, hippocampal formation, and cerebellum. White matter tracts are devoid of csp immunoreactivity. Neuromuscular junctions show strong csp immunoreactivity. This localization of csp immunoreactivity is compatible with a role for csps in presynaptic events at a wide variety of synapses. Immunohistochemical analysis of a non-neuronal, secretory tissue, the adrenal gland, reveals prominent csp immunoreactivity in the chromaffin cells of the adrenal medulla. However, csp immunoreactivity is not detected in adrenal cortical regions. These findings are confirmed and extended by immunoblot and Northern analyses which identify a 35 kDa and a 5 kb product, respectively, in extracts of adrenal. The presence of csps in the adrenal medulla suggests that these proteins may also participate in secretion-related events in certain non-neuronal cells.
Preferential neuronal loss in layer III of the medial entorhinal cortex in rat models of temporal lobe epilepsy
Authors: Du F , Eid T , Lothman EW , Kohler C , Schwarcz R
Published: April 2018

We recently described a pronounced neuronal loss in layer III of the entorhinal cortex (EC) in patients with intractable temporal lobe epilepsy (Du et al., 1993a). To explore the pathophysiology underlying this distinct neuropathology, we examined the EC in three established rat models of epilepsy using Nissl staining and parvalbumin immunohistochemistry. Adult male rats were either electrically stimulated in the ventral hippocampus for 90 min or injected with kainic acid or lithium/pilocarpine. Animals were observed for behavioral changes for up to 6 hr and were killed 24 hr or 4 weeks after the experimental treatments. At 24 hr, all animals that had exhibited a bout of acute status epilepticus showed a consistent pattern of neuronal loss in the EC in Nissl-stained sections. Neurodegeneration was most pronounced in layer III of the medial Ec at all dorsoventral levels. A few surviving neurons were frequently present in the lesioned area. An identical pattern of nerve cell loss was also seen in the EC of rats killed 4 weeks following the treatments. This lesion was completely prevented by an injection of diazepam and pentobarbital, given 1 hr after kainic acid administration. Immunohistochemistry demonstrated a relative resistance of parvalbumin-positive neurons in layer III of the medial EC. Taken together, these experiments indicate that prolonged seizures cause a preferential neuronal loss in layer III of the medial EC and that this lesion may be related to a pathological elevation of intracellular calcium ion concentrations.
Immunochemical identification and subcellular distribution of the alpha 1A subunits of brain calcium channels
Authors: Westenbroek RE , Sakurai T , Elliott EM , Hell JW , Starr TV , Snutch TP , Catterall WA
Published: April 2018

A site-directed anti-peptide antibody (anti-CNA1) directed against the alpha 1 subunit of class A calcium channels (alpha 1A) recognized a protein of approximately 190-200 kDa in immunoblot and immunoprecipitation analyses of rat brain glycoproteins. Calcium channels recognized by anti-CNA1 were distributed throughout the brain with a high concentration in the cerebellum. Calcium channels having alpha 1A subunits were concentrated in presynaptic terminals making synapses on cell bodies and on dendritic shafts and spines of many classes of neurons and were especially prominent in the synapses of the parallel fibers of cerebellar granule cells on Purkinje neurons where their localization in presynaptic terminals was confirmed by double labeling with the synaptic membrane protein syntaxin or the microinjected postsynaptic marker Neurobiotin. They were present in lower density in the surface membrane of dendrites of most major classes of neurons. There was substantial labeling of Purkinje cell bodies, but less intense staining of the cell bodies of hippocampal pyramidal neurons, layer V pyramidal neurons in the dorsal cortex, and most other classes of neurons in the forebrain and cerebellum. Scattered cell bodies elsewhere in the brain were labeled at low levels. These results define a unique pattern of localization of class A calcium channels in the cell bodies, dendrites, and presynaptic terminals of most central neurons. Compared to class B N-type calcium channels, class A calcium channels are concentrated in a larger number of presynaptic nerve terminals implying a more prominent role in neurotransmitter release at many central synapses.
Glutamate-gated inhibitory currents of central pattern generator neurons in the lobster stomatogastric ganglion
Authors: Cleland TA , Selverston AI
Published: April 2018

Inhibitory glutamatergic neurotransmission is an elemental “building block#x201D; of the oscillatory networks within the crustacean stomatogastric ganglion (STG). This study constitutes the initial characterization of glutamatergic currents in isolated STG neurons in primary culture. Superfusion of 1 mM L-glutamate evoked a current response in 45 of 65 neurons examined. The evoked current incorporated two kinetically distinct components in variable proportion: a fast desensitizing component and a slower component. The current was mediated by an outwardly rectifying conductance increase and reversed at -48.8 +/- 5.3 mV. Reducing the external chloride concentration by 50% deflected the glutamate equilibrium potential (Eglu) by +14 mV, while increasing external potassium threefold shifted Eglu by up to +6 mV. Ibotenic acid fully activated both components of the glutamate response. Saturating concentrations of glutamate completely occluded neuronal responses to ibotenic acid, indicating that ibotenic acid was activating the same receptor(s) as glutamate. Millimolar concentrations of quisqualic acid, kainate, AMPA, and NMDA each failed to evoke any response. Picrotoxin (10(-4)M) completely blocked the glutamate response. Niflumic acid (100 microM) blocked > 80% of the desensitizing component and congruent to 50% of the sustained component. Reduction or elimination of extracellular calcium did not abolish the response. This study extends the ionic and pharmacological analysis of glutamatergic conductances in STG neurons. The currents described are consistent with glutamatergic inhibitory synaptic and agonist-evoked responses previously described in situ. We discuss their pharmacology, ionic mechanisms, and functional significance.
Restricted eating with weight loss selectively decreases extracellular dopamine in the nucleus accumbens and alters dopamine response to amphetamine, morphine, and food intake
Authors: Pothos EN , Creese I , Hoebel BG
Published: April 2018

Weight loss is known to alter food intake and drug self-administration, but the neural basis of this is unknown. Therefore, we studied effects of weight loss on neurochemistry of a brain mechanism involved in behavior reinforcement. In rats reduced 20-30% below normal weight, basal extracellular dopamine (DA) in the nucleus accumbens (NAC) decreased up to 50% (p < 0.01), as measured by in vivo microdialysis. No such change was observed in dorsal striatum (STR) or medial prefrontal cortex. In underweight rats, systemic amphetamine (1.5 mg/kg i.p.) transiently restored extracellular DA, but only to basal normal levels. Morphine (20 mg/kg i.p.) or a meal also increased DA, but the percent increase was significantly smaller in underweight than normal weight animals. Amphetamine infused locally by reverse dialysis in the NAC increased extracellular DA more in underweight animals than controls, suggesting that DA had accumulated in the presynaptic terminals. This was confirmed by finding significantly more DA in homogenized NAC micropunches of underweight rats. Receptor counts in micropunches and quantitative receptor autoradiography showed 3H- SCH23390 and 3H-spiperone D1- and D2-type binding in the NAC, STR, frontal cortex and hypothalamus did not change significantly. Locomotor activity was depressed suggesting that low DA release in the NAC may be related to energy conservation during weight loss. Low extracellular DA may also underlie the increase in food and drug intake typically observed in underweight animals and humans when they attempt to restore extracellular DA levels by natural or artificial means.