bluuebunny/crossref_metadata_2025 huggingface dataset:
A novel GABA receptor modulates synaptic transmission from bipolar to ganglion and amacrine cells in the tiger salamander retina
Authors: Lukasiewicz PD , Werblin FS
Published: April 2018

We investigated the mechanisms underlying the modulation of transmitter release from bipolar cells. Three currents, measured under whole-cell patch clamp in the tiger salamander retinal slice, were used to identify the sites of modulation and to establish their pharmacological profile. (1) A light-elicited inhibitory current was measured in bipolar cells that could be blocked by picrotoxin. This input probably arrives via GABAergic amacrine cells since there is high GABA sensitivity at the bipolar cell terminals and little GABA sensitivity at the dendrites. (2) Voltage-gated barium currents were elicited by depolarizing voltage ramps in bipolar cells. These currents most likely flowed through the calcium channels that are associated with transmitter release at the bipolar terminal. Bath-applied GABA suppressed the barium currents. (3) Puffs of potassium at bipolar dendrites depolarized bipolar cells and elicited an excitatory synaptic current measured in amacrine and ganglion cells. The excitatory synaptic currents, which reflect bipolar cell transmitter release, were also blocked by bath-applied GABA. For all three currents, the effects of GABA could be reversed by picrotoxin, but not by bicuculline or SR95531. The pharmacological profile of the receptors mediating GABA suppression of the barium currents and of excitatory synaptic transmission is characteristic of GABAC receptors (Cutting et al., 1991; Polenzani et al., 1991; Shimada et al., 1992). GABA receptors at bipolar terminals gate a chloride conductance, and most were found to have the pharmacological properties of GABAC receptors (Lukasiewicz et al., 1994). By contrast, the GABA receptors on ganglion cells have been found to be the GABAA subtype (Lukasiewicz and Werblin, 1990; Lukasiewicz et al., 1994). These results suggest that GABA acts presynaptically at GABAC receptors at the bipolar cell terminals. The GABAC receptors open chloride channels that can modulate the release of excitatory transmitter. In some experiments, bicuculline or SR95531 reversed a component of the GABA suppression of synaptic transmission. This indicates that GABAA receptors may also play a role in modulating transmission between bipolar and ganglion cells.
Electrophysiological and pharmacological evidence for the role of the nucleus accumbens in cocaine self-administration in freely moving rats
Authors: Chang JY , Sawyer SF , Lee RS , Woodward DJ
Published: April 2018

The goal of this study was to clarify the role of the nucleus accumbens septi (NAS) in the expression of cocaine self-administration behaviors. Rats were trained in a continuous reinforcement schedule to press a lever to activate a pump that provided an intravenous injection of cocaine. Once the rats were trained, neuronal activity in the NAS was monitored during cocaine self-administration with chronic recording techniques using permanently implanted microwires. In the NAS, 19% of 181 neurons exhibited either increased or decreased firing rates seconds prior to lever pressing (termed “anticipatory responses”), and 48% had altered, predominantly decreased, firing rates for a few minutes after lever pressing (“postcocaine responses”). Two-thirds of the neurons with anticipatory responses had postcocaine responses. Neurons with either of these response patterns were localized histologically to both core and shell regions of the NAS, with no statistically significant differences in the proportion of response types in either area. Analysis of videotaped cocaine self- administration behaviors revealed that anticipatory responses were specifically associated either with the animal orienting toward and pressing the lever or only with movements directly related to pressing the lever. Anticipatory-like phasic spike activity was not observed during similar movements unrelated to lever pressing. In some animals, D1 (SCH 23390) or D2 (pimozide) receptor antagonists were injected systemically prior to or during self-administration sessions to assess the effects of dopamine receptor blockade on anticipatory and postcocaine responses. Each antagonist, given separately, often produced extinction of lever pressing. Both antagonists blocked the post-cocaine inhibitory response of neurons that had anticipatory responses. Neither antagonist modified anticipatory unit responses, nor did they affect postcocaine inhibitory responses in neurons that did not exhibit anticipatory responses. Taken together, these results suggest that the role of the NAS in cocaine self-administration may consist of two different mechanisms: (1) An initiation or trigger mechanism, as represented by the anticipatory neuronal responses, in which the NAS participates in triggering or mediating the goal-directed behaviors (e.g., lever pressing) that lead to the acquisition of the reinforcing agent (e.g., cocaine).(ABSTRACT TRUNCATED AT 400 WORDS)
Expression of a calmodulin-dependent phosphodiesterase isoform (PDE1B1) correlates with brain regions having extensive dopaminergic innervation
Authors: Polli JW , Kincaid RL
Published: April 2018

Cyclic nucleotide-dependent protein phosphorylation plays a central role in neuronal signal transduction. Neurotransmitter-elicited increases in cAMP/cGMP brought about by activation of adenylyl and guanylyl cyclases are downregulated by multiple phosphodiesterase (PDE) enzymes. In brain, the calmodulin (CaM)-dependent isozymes are the major degradative activities and represent a unique point of intersection between the cyclic nucleotide- and calcium (Ca2+)-mediated second messenger systems. Here we describe the distribution of the PDE1B1 (63 kDa) CaM-dependent PDE in mouse brain. An anti-peptide antiserum to this isoform immunoprecipitated approximately 30–40% of cytosolic PDE activity, whereas antiserum to PDE1A2 (61 kDa isoform) removed 60–70%, demonstrating that these isoforms are the major CaM- dependent PDEs in brain. Quantification of PDE1B1 immunoreactivity on immunoblots indicated that striatum contains 3–17-fold higher levels of PDE1B1 than other brain regions, with lowest immunoreactivity in cerebellum. In situ hybridization demonstrated high levels of PDE1B1 mRNA in the caudate-putamen, nucleus accumbens, and olfactory tubercle. Moderate mRNA levels were observed in dentate gyrus, cerebral cortex, medial thalamic nuclei, and brainstem, whereas negligible mRNA was detectable in the globus pallidus, islands of Calleja, substantia nigra, and ventral tegmental area. Immunocytochemistry confirmed that the majority of PDE1B1 protein was localized to the caudate-putamen, nucleus accumbens, and olfactory tubercle. Within the caudate-putamen, PDE1B1 immunoreactivity was ubiquitous, while PDE1A2 immunostaining was restricted to a minor subset of striatal neurons. The expression of PDE1B1 protein and mRNA correlate strongly with areas of the brain that are richest in dopaminergic innervation; indeed, there are strikingly similar distributions for PDE1B1 and D1 dopamine receptor mRNAs. Since D1 receptor binding activates adenylyl cyclase, and striatal neurons lack CaM-sensitive forms of cyclase, the high amount of this PDE implies an important physiological role for Ca(2+)-regulated attenuation of cAMP-dependent signaling pathways following dopaminergic stimulation.
Brain-derived neurotrophic factor and neurotrophin-3 activate striatal dopamine and serotonin metabolism and related behaviors: interactions with amphetamine
Authors: Martin-Iverson MT , Todd KG , Altar CA
Published: April 2018

To investigate behavioral and neurochemical effects of neurotrophic factors in vivo, rats received continuous 14 d infusions of either brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or vehicle unilaterally into the substantia nigra. BDNF and NT-3 decreased body weights, an effect that was sustained over the infusion period. BDNF elevated daytime and nocturnal locomotion compared with infusions of vehicle or NT-3. At 2 weeks, a systemic injection of amphetamine (1.5 mg/kg, s.c.) increased the frequencies and durations of rotations contraversive to the side of BDNF and NT-3 infusions. Both factors attenuated amphetamine-induced locomotion without affecting amphetamine- induced stereotyped behaviors such as sniffing, head movements, and snout contact with cage surfaces. Only BDNF induced backward walking, and this response was augmented by amphetamine. BDNF, but not NT-3, increased dopamine turnover in the striatum ipsilateral to the infusion relative to the contralateral striatum. Both trophic factors decreased dopamine turnover in the infused substantia nigra relative to the contralateral hemisphere and increased 5-HT turnover in the striatum of both sides. Contraversive rotations were positively correlated with dopamine content decreases and 5-HT turnover increases in the striatum ipsilateral to the infused substantia nigra. Backward walking was positively correlated with increased dopamine and 5-HT turnover in the striatum of the infused hemisphere. Supranigral infusions of BDNF and NT-3 alter circadian rhythms, spontaneous motor activity, body weights, and amphetamine-induced behaviors including locomotion and contraversive rotations. These behavioral effects of the neurotrophins are consistent with a concomitant activation of dopamine and 5-HT systems in vivo.
Complete and selective cholinergic denervation of rat neocortex and hippocampus but not amygdala by an immunotoxin against the p75 NGF receptor
Authors: Heckers S , Ohtake T , Wiley RG , Lappi DA , Geula C , Mesulam MM
Published: April 2018

The immunotoxin 192 IgG-saporin, produced by coupling the ribosome- inactivating protein saporin to the monoclonal 192 IgG antibody against the low-affinity p75 NGF receptor (NGFr), was injected into the cerebral ventricle, septal area, and substantia innominata of adult rats. Injections into the cerebral ventricle induced a complete loss of NGFr-positive basal forebrain neurons and their axons. Extensive loss of cholinergic neurons was found in the septum, diagonal band, and magnocellular preoptic nucleus but not in the nucleus basalis- substantia innominata complex, where many cholinergic, presumably NGFr- negative, neurons remained intact. Cholinergic fibers were completely lost in the neocortex and hippocampus, showed some preservation in allocortical areas, and showed only minor loss in the amygdala. The NGFr-positive cholinergic basal forebrain neurons progressively degenerated during the first 5 d and did not recover after 180 d. The effect of intraventricular 192 IgG-saporin injections on NGFr-positive basal forebrain neurons could be blocked by simultaneous intraventricular injection of colchicine. Intraparenchymal injections into the septal area or substantia innominata damaged cholinergic neurons mainly around the injection sites and reduced their respective cortical and hippocampal projections. Noncholinergic septal neurons containing parvalbumin and noncholinergic neurons containing calbindin- D28k or NADPHd, which were adjacent to cholinergic nucleus basalis- substantia innominata neurons, were not affected by 192 IgG-saporin. The ChAT immunoreactivity in cortical interneurons, habenula, and brainstem was unchanged. Dopaminergic and noradrenergic cortical afferents remained intact. 192 IgG-saporin damaged two neuronal groups outside the basal forebrain that express the p75 NGF receptor: NGFr- positive cerebellar Purkinje cells after intraventricular injection and cholinergic striatal interneurons after injections into the substantia innominata. These results indicate that the immunotoxin 192 IgG-saporin induces a complete and selective lesion of NGFr-positive cholinergic basal forebrain neurons projecting to hippocampus and neocortex.
Physiological properties of vestibular primary afferents that mediate motor learning and normal performance of the vestibulo-ocular reflex in monkeys
Authors: Bronte-Stewart HM , Lisberger SG
Published: April 2018

We have used electrical stimulation of the vestibular apparatus to reveal parallels between the physiological responses of the vestibular afferents activated at different currents and the properties of the evoked eye movements before and after magnifying spectacles had been used to cause motor learning in the vestibulo-ocular reflex (VOR). Stimulation with the lowest currents caused little or no eye motion, but activated all the afferents with irregular spontaneous discharge, low sensitivities to head velocity, and highly phasic responses during rapid head turns. Stimulation with moderate currents caused substantial eye motion that was weakly affected by motor learning; these currents activated afferents with a wide range of physiological properties, including many that had intermediate discharge regularity, high sensitivity to head velocity, and clear phasic responses during rapid head turns. Stimulation at still higher currents caused still larger eye movements that were strongly altered by motor learning; these currents activated primarily afferents that had regular spontaneous discharge, lower sensitivities to head velocity, and tonic responses during rapid head turns. Stimulation at the highest currents did not cause any further increment in the amplitude of the evoked eye movement, but activated the afferents with the most regular spontaneous discharge and the lowest sensitivities to head velocity. The data imply that the VOR pathways receive substantial vestibular inputs from afferents with a middle range of thresholds for electrical stimulation. These afferents have a wide range of physiological properties, including a large group that shows substantial phasic responses during rapid head turns. The data also suggest that only a subset of these afferents, primarily those with more regular spontaneous discharge, project into the VOR pathways that are modified in association with motor learning.
Differential regulation of calcium/calmodulin-dependent protein kinase II and p42 MAP kinase activity by synaptic transmission
Authors: Murphy TH , Blatter LA , Bhat RV , Fiore RS , Wier WG , Baraban JM
Published: April 2018

Calcium/calmodulin-dependent protein kinase II (CaMK) and p42 mitogen- activated protein kinase (MAPK) are enriched in neurons and possess the capacity to become persistently active, or autonomous, following removal of the activating stimulus. Since persistent kinase activation may be a mechanism for information storage, we have used primary cultures of cortical neurons to investigate whether kinase autonomy can be triggered by bursts of spontaneous synaptic activity. We and others have found that both these kinases respond to synaptic stimulation, but differ markedly in their kinetics of activation and inactivation, as well as in their sensitivity to NMDA receptor blockade. While 90% of maximal CaMK activation was observed after only 10 sec of synaptic bursting, MAPK activity was unaffected at this early time and rose to only 30% of maximal after 2 min of stimulation. Following blockade of synaptic stimulation, CaMK activity decreased by 50% in 10–30 sec, while MAPK activity decayed by 50% within 6–10 min. Although MAPK exhibited relatively slow activation, short periods of synaptic activity could trigger the MAPK activation process, which persisted in the absence of synaptic stimulation. Comparison of the effect of NMDA receptor blockade on synaptic activation of these kinases revealed that CaMK activity is preferentially suppressed. As previous immunocytochemical studies indicate that CaMK is concentrated in dendritic processes in the vicinity of synapses, we measured synaptic calcium transients in fine dendritic processes (approximately 1 microns diameter) to assess their sensitivity to NMDA receptor blockade. Calcium transients in these fine processes were reduced by up to 90% by NMDA receptor blockade, possibly accounting for the profound sensitivity of CaMK to this treatment. The sharp contrast between the regulation of CaMK and MAPK by synaptic activity indicates that they may mediate neuronal responses to different patterns of afferent stimulation. The relatively slow activation and inactivation of MAPK suggests that it may be able to integrate information from multiple, infrequent bursts of synaptic activity.
Both N- and C-terminal regions contribute to the assembly and functional expression of homo- and heteromultimeric voltage-gated K+ channels
Authors: Hopkins WF , Demas V , Tempel BL
Published: April 2018

The functional diversity of voltage-gated K+ channels may be partially determined by the mechanisms that permit or limit the assembly of molecularly diverse K+ channel subunits. To determine possible amino acid sequence domains required for subunit assembly and expression, we have constructed 15 N- and C-terminal interstitial or truncation deletion mutations in mKv1.1 (MBK1), a mouse Shaker-like K+ channel. We injected Xenopus oocytes with cRNA encoding each of these mutants and coinjected each mutant cRNA with cRNA for wild-type mKv1.3, another mouse Shaker-like K+ channel that can form heteromultimers with mKv1.1. We found that the last five amino acids of the C-terminus of mKv1.1 contribute to functional expression by (1) rescuing the function of mutants with a large truncation of the C-terminus (delta 424–495), and (2) contributing to the slow inactivation kinetics (time constant of 2– 3 sec) of wild-type mKv1.1 whole-cell K+ currents. All C-terminal deletion mutants were able to express at least as heteromultimers with mKv1.3, suggesting that the C-terminus is not required for channel assembly. In contrast, nine different interstitial or truncation mutants in which part of a highly conserved, large (80–99 amino acid residues) domain within the N-terminus had been deleted were unable to express either homomultimers or heteromultimers. The relatively small sizes and nonoverlapping distributions of the interstitial deletions enable us to suggest that the structural integrity of this entire N- terminal domain is required for subunit assembly and functional expression of this and probably other Shaker-like K+ channel proteins.
Glutamate receptor gene expression in spinal cord of arthritic rats
Authors: Pellegrini-Giampietro DE , Fan S , Ault B , Miller BE , Zukin RS
Published: April 2018

Injury to peripheral tissue leads to hyperalgesia that appears to be partly mediated by functional changes at the level of the spinal cord. Glutamate receptors are thought to play a role in acute and short-term (minutes to hours) spinal cord nociceptive responses and may be involved in prolonged or chronic pain (hours to days). We used in situ hybridization to examine AMPA/kainate (GluR1, GluR2, and GluR3) and NMDA (NR1) receptor gene expression in spinal cord following induction of prolonged inflammation by a unilateral intraarticular injection of lipopolysaccharide (LPS; 10 micrograms) into the hindpaw. In control rats, GluR1 expression was prominent throughout the layers of the gray matter of the spinal cord. Microscopic examination revealed labeling of neuronal cell somata in all major nuclei. GluR2 was abundant in substantia gelatinosa and motor nuclei; emulsion-dipped sections exhibited intense labeling over densely packed neurons in the superficial laminae of dorsal horn and individual motoneurons of ventral horn. GluR3 and NR1 were expressed at low levels throughout spinal cord gray matter. One day after LPS injection, when joint swelling was maximal, GluR1 expression was bilaterally decreased by 25% in the substantia gelatinosa at the level of the lumbar cord. In contrast, no significant change was apparent in GluR2, GluR3, or NR1 expression in any nucleus of the cord. At 72 hr after injection, when joint diameter approached control values, all four transcripts were expressed at near control levels. These findings provide evidence for a specific decrease in GluR1 expression in the cord in response to joint inflammation.
Correlation of nitric oxide synthase expression with changing patterns of axonal projections in the developing visual system
Authors: Williams CV , Nordquist D , McLoon SC
Published: April 2018

A precise pattern of connections between the retina and central visual nuclei in the brain is established during development. Activity- dependent presynaptic mechanisms and NMDA receptor-mediated postsynaptic mechanisms are thought to play important roles in this developmental process. A model proposed for production of the newly described neurotransmitter, nitric oxide, involves presynaptic activity and activation of postsynaptic NMDA receptors. If present in the developing visual system, nitric oxide could represent a form of retrograde communication from postsynaptic to presynaptic cells that mediates the formation of the proper pattern of connections. This study used the diaphorase histochemical technique to detect the presence of nitric oxide synthase (NOS), the enzyme responsible for the production of nitric oxide, in the developing chick optic tectum. Results from this study showed that NOS is present in the developing tectum and that its expression coincides temporally with innervation by retinal axons. NOS expression reaches a peak at the time that refinement of the initial pattern of connections is occurring. WGA/HRP labeling of retinal axons confirmed that processes of NOS-positive cells in the tectum extend well into the area of the ingrowing retinal axons. Histochemical results from eyeless chick embryos indicate that NOS expression is dependent on the presence of retinal axons, which suggests that retinal axons synapse on cells that express nitric oxide. Northern blot analysis using a cDNA probe to NOS from rat brain verified the histochemical results. These results are consistent with nitric oxide having a role in development of the proper pattern of connections in the chick retinotectal system.
Paired pulse depression in cultured hippocampal neurons is due to a presynaptic mechanism independent of GABAB autoreceptor activation
Authors: Wilcox KS , Dichter MA
Published: April 2018

Most rapid synaptic inhibition in the vertebrate forebrain is mediated by GABA acting via GABAA and GABAB postsynaptic receptors. GABAergic neurotransmission exhibits frequency-dependent modulation; sequential inhibitory post-synaptic currents (IPSCs) evoked with interstimulus intervals between 25 msec and 4 sec routinely result in the attenuation of the amplitude of the second IPSC. This form of synaptic plasticity is known as paired pulse depression (PPD). The mechanism of PPD is presently unknown and the experiments performed in this study were designed to determine directly the location of the mechanism of PPD in hippocampal neurons maintained in low-density tissue culture. Evoked IPSCs were recorded between pairs of cultured neurons grown in relative isolation that were simultaneously being recorded with the whole-cell, patch-clamp technique. It was therefore possible to measure miniature IPSCs (mIPSCs) originating from the same synapses that were being stimulated to evoke release. PPD occurred routinely in this system, but the amplitudes of mIPSCs following IPSCs were unchanged. These results indicate that a presynaptic mechanism mediates PPD. The inability of GABAB receptor antagonists to block PPD revealed that this form of presynaptic plasticity was not due to autoinhibition of transmitter release via activation of presynaptic GABAB receptors. However, manipulations that significantly lowered the probability of release of neurotransmitter during the first action potential of a trial (e.g., lower calcium or baclofen) prevented the development of PPD. These results indicate that, under baseline conditions, the quantal content for IPSCs is relatively large for a single action potential, but the quantal content rapidly decreases, such that subsequent action potentials consistently result in much smaller IPSCs for periods as long as 4 sec.
Comparative localization of two forms of glutamic acid decarboxylase and their mRNAs in rat brain supports the concept of functional differences between the forms
Authors: Esclapez M , Tillakaratne NJ , Kaufman DL , Tobin AJ , Houser CR
Published: April 2018

Two isoforms of glutamic acid decarboxylase (GAD67 and GAD65) and their mRNAs were localized in the rat brain by immunohistochemistry and nonradioactive in situ hybridization methods with digoxigenin-labeled cRNA probes. In most brain regions, both GAD isoforms were present in neuronal cell bodies as well as axon terminals. A few populations of neurons, such as those in the reticular nucleus of the thalamus, exhibited similar cell body labeling for both GADs. However, in many brain regions, the cell bodies that were immunoreactive for GAD67 were often more numerous than those that were immunoreactive for GAD65. In contrast, the density (quantity) of GAD65-immunoreactive axon terminals was higher than that of GAD67-immunoreactive terminals. Strong parallels were observed between the intensity of immunohistochemical labeling of cell bodies and the levels of mRNA labeling for both GAD isoforms. Many groups of GAD-containing cell bodies were distinctly labeled for GAD67, and these same groups of neurons were heavily labeled for GAD67 mRNA. Such neurons included Purkinje cells of the cerebellar cortex, nonpyramidal cells in the cerebral cortex, and neurons of the reticular nucleus of the thalamus. Similar parallels in labeling were observed for GAD65 and its mRNA. Distinct cell body labeling for the protein and associated high levels of GAD65 mRNA were found in neurons of the reticular nucleus of the thalamus and periglomerular cells in the olfactory bulb. However, many cell bodies were not readily labeled for GAD65 with immunohistochemical methods. Such absence or weakness of cell body labeling for the protein was associated with low or moderate levels of GAD65 mRNA. Even though light cell body staining was frequently observed for GAD65 and its mRNA, strong axon terminal labeling for GAD65 was present. Thus, in the deep cerebellar nuclei to which the Purkinje cells of the cerebellar cortex project, strong terminal labeling was observed for both GAD isoforms even though only light cell body labeling of the Purkinje cells was obtained for GAD65 and its mRNA. The findings suggest that the two isoforms of GAD are present in most classes of GABA neurons but that they are not similarly distributed within the neurons. GAD67 is present in readily detectable amounts in many GAD-containing cell bodies whereas GAD65 is particularly prominent in many axon terminals. In addition, neurons that express either form of GAD mRNA also express the corresponding protein. Levels of labeling for the GAD mRNAs suggest that, under normal conditions, the synthesis of GAD65 is frequently lower than that of GAD67.(ABSTRACT TRUNCATED AT 400 WORDS)
Topographic reorganization in the striate cortex of the adult cat and monkey is cortically mediated
Authors: Darian-Smith C , Gilbert CD
Published: April 2018

In primary sensory and motor cortex of adult animals, alteration of input from the periphery leads to changes in cortical topography. These changes can be attributed to processes that are intrinsic to the cortex, or can be inherited from alterations occurring at stages of sensory processing that are antecedent to the primary sensory cortical areas. In the visual system, focal binocular retinal lesions initially silence an area of cortex that represents the region of retina destroyed, but over a period of months this area recovers visually driven activity. The retinotopic map in the recovered area is altered, shifting its representation to the portion of retina immediately surrounding the lesion. This effectively shrinks the representation of the lesioned area of retina, and expands the representation of the lesion surround. To determine the loci along the visual pathway at which the reorganization takes place, we compared the course of topographic alterations in the primary visual cortex and dorsal lateral geniculate nucleus (LGN) of cats and monkeys. At a time when the cortical reorganization is complete, the silent area of LGN persists, indicating that changes in cortical topography are due to alterations that are intrinsic to the cortex. To explore the participation of thalamocortical afferents in the reorganization, we injected a series of retrogradely transported fluorescent tracers into reorganized and surrounding cortex of each animal. Our results show that the thalamocortical arbors do not extend beyond their normal lateral territory and that this physical dimension is insufficient to account for the reorganization. We suggest that the long-range intrinsic horizontal connections are a likely source of visual input into the reorganized cortical area.
Place cells, head direction cells, and the learning of landmark stability
Authors: Knierim JJ , Kudrimoti HS , McNaughton BL
Published: April 2018

Previous studies have shown that hippocampal place fields are controlled by the salient sensory cues in the environment, in that rotation of the cues causes an equal rotation of the place fields. We trained rats to forage for food pellets in a gray cylinder with a single salient directional cue, a white card covering 90 degrees of the cylinder wall. Half of the rats were disoriented before being placed in the cylinder, in order to disrupt their internal sense of direction. The other half were not disoriented before being placed in the cylinder; for these rats, there was presumably a consistent relationship between the cue card and their internal direction sense. We subsequently recorded hippocampal place cells and thalamic head direction cells from both groups of rats as they moved in the cylinder; between some sessions the cylinder and cue card were rotated to a new direction. All rats were disoriented before recording. Under these conditions, the cue card had much weaker control over the place fields and head direction cells in the rats that had been disoriented during training than in the rats that had not been disoriented. For the former group, the place fields often rotated relative to the cue card or completely changed their firing properties between sessions. In all recording sessions, the head direction cells and place cells were strongly coupled. It appears that the strength of cue control over place cells and head direction cells depends on the rat's learned perception of the stability of the cues.
A sex difference in synaptic efficacy at the laryngeal neuromuscular junction of Xenopus laevis
Authors: Tobias ML , Kelley DB , Ellisman M
Published: April 2018

Under physiological conditions, the response of Xenopus laevis laryngeal muscle fibers to nerve stimulation is sexually differentiated; subthreshold potentials are common in males and rare in females. This sex difference in muscle fiber response is correlated with sex differences in vocal behavior. Quantal analyses at male and female laryngeal synapses were performed to determine if there is a sex difference in synaptic strength. Quantal content at laryngeal synapses is significantly higher in females than in males. Values for quantal content in males can be increased by raising extracellular calcium concentration. There is no sex difference in miniature endplate potential amplitude suggesting that ACh receptor number or properties are not different in the sexes. Sex difference in synaptic strength thus appear presynaptic in origin; transmitter release is less in males. Ultrastructural analyses of the laryngeal motor terminal indicate that there is no sex difference in the length of active zones or in the number of channels per length of active zone. Thus, ultrastructural characteristics of the laryngeal motor terminal do not account for the pronounced sex difference in quantal content.
Polarization of myelinating Schwann cell surface membranes: role of microtubules and the trans-Golgi network
Authors: Trapp BD , Kidd GJ , Hauer P , Mulrenin E , Haney CA , Andrews SB
Published: April 2018

Schwann cells polarize their surface membranes into several biochemically and ultrastructurally discrete regions of the myelin internode. To form these membrane domains, Schwann cells must sort, transport, and target membrane proteins appropriately. In this study, microtubule disassembly, confocal microscopy, and electron microscopic immunocytochemistry were used to investigate mechanisms involved in targeting P0 protein (P0), the myelin-associated glycoprotein (MAG), and laminin to different plasma membrane domains in myelinating Schwann cells from 35-d-old rat sciatic nerve. After microtubule disassembly by colchicine, all three proteins accumulated in Schwann cell perinuclear cytoplasm, indicating that microtubules are necessary for their transport. The distributions of Golgi membranes, endoplasmic reticulum, and intermediate filaments were also altered by colchicine treatment. Electron microscopic immunocytochemical studies indicated that P0 and MAG are sorted into separate carrier vesicles as they exit the trans- Golgi network. Following microtubule disassembly, P0-rich carrier vesicles fused and formed myelin-like membrane whorls, whereas MAG-rich carrier vesicles fused and formed mesaxon-like membrane whorls. Microtubule disassembly did not result in mistargeting of either P0 or MAG to surface membranes. These results indicate that following sorting in the trans-Golgi network, certain carrier vesicles are transported along the myelin internode on microtubules; however, microtubules do not appear to target these vesicles selectively to specific sites. The targeting of P0-, MAG-, and laminin-rich carrier vesicles to specific sites most likely occurs by ligand receptor binding mechanisms that permit fusion of carrier vesicles only with the appropriate target membrane.
Neuronal regulation of c-fos, c-jun, and junB immediate-early genes in rat adrenal medulla
Authors: Pelto-Huikko M , Dagerlind A , Kononen J , Lundberg JM , Villar M , Koistinaho J , Bravo R , Hokfelt T
Published: April 2018

We have applied in situ hybridization histochemistry, Northern analysis, and immunocytochemistry to study the regulation of the immediate-early gene (IEG) c-fos, c-jun, and junB mRNAs and the respective proteins in the rat adrenal medulla. Electrophoresis mobility shift assay was used to examine changes in AP-1 DNA binding activity. In nontreated rats the mRNA and protein levels for these three IEGs were low. Reflex stimulation of adrenal medulla elicited by a single capsaicin injection induced a rapid and marked elevation in the mRNA levels for these IEGs. Stimulation with nicotine also caused a drastic increase in the mRNA levels, whereas muscarine only induced moderate elevations. c-fos and c-jun were induced strongly in adrenaline cells and only weakly in noradrenaline cells. junB was upregulated mainly in adrenaline cells. The AP-1 DNA binding activity was low in control adrenals, whereas a marked increase was observed after nicotine treatment. Treatment of the animals with a nicotinic (chlorisondamine) or a muscarinic (atropine) receptor antagonist did not change the expression of IEGs studied. The combination of the two drugs, however elevated the mRNA levels for all three IEGs, especially for junB. Pretreatment of the rats with chlorisondamine alone or in combination with atropine diminished the capsaicin-induced increase in c-fos, whereas atropine alone was less efficient. Increase in c-jun mRNA was not affected by these drugs. The capsaicin-induced elevation of junB mRNA levels was not influenced by chlorisondamine or atropine alone, whereas both combined potentiated the effect of capsaicin. The present results demonstrate that neurotransmitters released from splanchnic nerve terminals induce expression of c-fos, c-jun, and junB in adrenal chromaffin cells which results in increased AP-1 DNA binding activity. Although stimulation of both nicotinic and muscarinic cholinergic receptors may mediate the induction of these IEGs, it is possible that also another neurotransmitter(s), in addition to ACh, released from splanchnic nerve terminals is involved in the regulation of their expression, especially of c-jun and junB.
Developmental regulation of nicotinic ACh receptor subunit mRNAs in the rat central and peripheral nervous systems
Authors: Zoli M , Le Novere N , Hill JA , Changeux JP
Published: April 2018

In the present study we have investigated the anatomical distribution pattern of nAChR alpha 3, alpha 4, beta 2, and beta 4 subunit mRNAs during prenatal and perinatal development of the rat CNS and PNS. Three main developmental patterns have been recognized. (1) In the majority of cases studied (caudal brain, spinal cord, dorsal root ganglia, trigeminal and geniculate ganglia) all four subunit mRNAs are initially (E11–13) detected but, during subsequent prenatal development, the level of some of these subunit mRNAs (alpha 3 and beta 4 in the brain and spinal cord, alpha 4 and beta 4 in the dorsal root ganglia, alpha 4 in the visceral sensory ganglia, and alpha 3, alpha 4, and beta 4 in the somatic sensory ganglia) become undetectable. (2) In the case of the cerebral cortex a pair of subunit mRNAs (alpha 3-beta 2) is initially (E12–13) expressed followed by a repression of the alpha 3 subunit (E15) and the subsequent (E17–19) induction of the alpha 4 subunit. (3) Only some subunit mRNAs are initially (E13–15) expressed in the retina (alpha 3-alpha 4-beta 2-beta 4), parasympathetic or sympathetic motor ganglia (alpha 3-beta 2-beta 4), and vestibulo- cochlear ganglia (alpha 4-beta 2) and their level remains stable throughout prenatal and early postnatal development. Overall, in most central and peripheral structures the appearance of nAChR subunit mRNAs is precocious and temporally related to the timing of neuronal differentiation. In addition, in several structures the expression of certain subunits (alpha 3, alpha 4 or beta 4) is transient, although not beta 2. Finally, the comparison of the different regional distribution patterns suggests that a limited number of structure- specific receptor isoforms are functional during development of CNS and PNS.
Central neuronal circuit innervating the rat heart defined by transneuronal transport of pseudorabies virus
Authors: Standish A , Enquist LW , Escardo JA , Schwaber JS
Published: April 2018

We defined the central circuit innervating various regions of the rat heart using a neurotropic herpesvirus as a transneuronal tracer. Location of viral antigens in the brain after cardiac injection of three strains of pseudorabies virus (PRV) provided insight into vagal preganglionic neurons and their connected interneurons. At short survival times, labeled vagal preganglionic neurons were localized in both the nucleus ambiguus (NA) and the dorsal motor nucleus of the vagus (DMV), and in an arc-like band through the reticular formation between the NA and the DMV. The amount of DMV labeling was dependent on viral strain. Similar distributions of labeled neurons were observed following either ganglionic, sinoatrial node, or ventricular injections. At intermediate survival times postcardiac injection, the virus replicated in vagal preganglionic neurons and was trans- synaptically transported to interneurons observed primarily in the NA regions and in an arc-like band through the reticular formation. Labeled neurons were also observed in ventral regions of the nucleus of the solitary tract (NTS). At longer survival times, labeled neurons were found in various regions of the NTS with the most abundant label dorsal and dorsomedial to the solitary tract. Abundant neuronal labeling was also found in the intermediolateral cell column, the raphe nuclei, the caudal and rostral ventral lateral medulla, the A5 region, the locus coeruleus, and the lateral and paraventricular hypothalamic nuclei. These data define the central circuits including the interneuronal connections that innervate various cardiac targets.
Regulation of astrocyte proliferation by FGF-2 and heparan sulfate in vivo
Authors: Gomez-Pinilla F , Vu L , Cotman CW
Published: April 2018

The goal of this study was to examine the ability of basic fibroblast growth factor (FGF-2) to promote reactivity and/or proliferation of astrocytes in vivo following brain injury, and the possible mechanisms involved. A small bilateral lesion in the motor-sensory cortex was performed, and either FGF-2, FGF-2 plus heparan sulfate, heparan sulfate, or saline was applied unilaterally in a piece of Gelfoam within the wound cavity. Following lesions, there was an increase in FGF-2 and FGF receptor (FGFR) immunoreactivities in the area surrounding the lesion in all the treatment groups. Rats that received treatment with recombinant FGF-2 alone showed an increase in the density of astrocytes as compared to the control group. The same group of rats exhibited an increase in the density of cells displaying FGF-2 immunoreactivity and cells displaying FGFR-1 immunoreactivity and cells displaying FGFR-1 immunoreactivity, and also an induction of FGF-2 mRNA in the tissue surrounding the lesion. The group of rats that received FGF-2 combined with heparan sulfate showed a larger increase in the same cellular parameters. Our results suggest that the FGF-2/FGFR system is involved in the regulation of astrocytic reactivity and/or proliferation in the brain and its action is potentiated by heparan sulfate. The action of FGF-2 on CNS injury appears to be part of an autocrine cascade that involves induction of FGF-2 and its receptor, thereby enhancing the ability of astrocytes to respond to FGF-2.
Target neuron controls the integrity of afferent axon phenotype: a study on the Purkinje cell-climbing fiber system in cerebellar mutant mice
Authors: Rossi F , Jankovski A , Sotelo C
Published: April 2018

The effects of target loss on adult axonal arbors were investigated by comparing the morphological changes of adult climbing fibers in several mutant mouse strains where Purkinje cells slowly degenerate (namely, Lurcher, nervous, Purkinje cell degeneration, and tambaleante), with those occurring after a fast Purkinje cell death induced by mechanical lesions of the adult mouse cerebellum. In each of the different mutations, Purkinje cells displayed distinctive structural modifications. However, a set of regressive changes common to all strains could be disclosed, mostly dendritic atrophy and a progressive axonal retraction with the hypertrophy of recurrent collaterals. Climbing fibers that contacted such degenerating neurons also showed abnormal morphological features, consisting in the presence of extensive perisomatic plexuses, whereas peridendritic branches were atrophic or absent. In Lurcher mice, target-deprived climbing fibers were strictly confined around the granular-molecular layer interface and never penetrated into the molecular layer. Similar terminal plexuses at the level of the former Purkinje cell layer were observed in the other mutants. However, in the latter cases, atrophic terminal arbors were also present in the molecular layer, being confined to the deep portions in nervous, while spanning its whole extent in Purkinje cell degeneration and tambaleante mice. Following mechanical lesions, atrophic target-deprived climbing fibers were exclusively located in the molecular layer. In addition, some of the Purkinje cells that survived after the injury displayed regressive modifications similar to those observed in mutant mice, and their climbing fibers were characterized by perisomatic plexuses. These results show that the normal relationship between the climbing fiber and its Purkinje cell is already disrupted during the slow degeneration of the target neuron. As a consequence, the phenotypic pattern of target-deprived climbing fibers reflects the preceding interactions with their postsynaptic neurons and it is determined by the onset time and progression rate of Purkinje cell degeneration.
Extensive regeneration in vitro by early embryonic neurons on immature and adult CNS tissue
Authors: Shewan D , Berry M , Cohen J
Published: April 2018

The failure of axon regeneration in the injured adult CNS has been ascribed to axon growth inhibitory molecules expressed by the resident glial cell populations, especially oligodendrocytes. Unlike their adult counterparts, however, early embryonic neurons are able to send lengthy axons through myelinated fiber tracts when transplanted into the adult brain. One explanation is that they have yet to express receptors for factors that inhibit the growth of older neurons. To test this possibility, we have used the cryoculture technique to study the regeneration of rat central and peripheral neurons, over a developmental period that encompasses the stages before, during, and after target contact, when cultured on either unmyelinated (neonatal) or myelinated (adult) optic nerve tissue sections. Early embryonic (days 14–15) retinal ganglion cells extended neurites on neonatal optic nerve, but few grew on adult optic nerve. In the case of early embryonic dorsal root ganglion neurons, however, neurite outgrowth on either neonatal optic nerve or on adult optic nerve was extensive. This response declined sharply with age. In contrast, neurite outgrowth by dorsal root ganglion neurons on laminin substrata remained relatively constant (> 80% extended neurites) over the same period. This suggests that (a) inhibition of neurite outgrowth within the optic nerve is mediated not only by oligodendrocytes, but also by molecules expressed prior to the onset of myelination; (b) neurons acquire receptors for these inhibitors only late in embryonic development; (c) differences exist between developing central and peripheral neurons in the response to myelin-associated axon-growth inhibitors.
Differential influence of nerve growth factor on neuropeptide expression in vivo: a novel role in peptide suppression in adult sensory neurons
Authors: Verge VM , Richardson PM , Wiesenfeld-Hallin Z , Hokfelt T
Published: April 2018

In this study the actions of NGF in regulating peptide expression were examined in vivo in adult rat primary sensory neurons. The hypothesis that NGF might tonically inhibit expression of some peptides was tested specifically. In situ hybridization and immunohistochemistry were used to detect presence or absence of alpha-CGRP, beta-CGRP, SP, SOM, VIP, CCK, NPY, and GAL as well as their mRNAs. In neurons in normal lumbar DRG alpha-CGRP, beta-CGRP, SP, and SOM are abundantly and heterogeneously expressed whereas few neurons have detectable VIP, CCK, NPY, or GAL. Two weeks following sciatic nerve transection, concentrations of alpha-CGRP, beta-CGRP, SP, and SOM plus their mRNAs have decreased to background in all but a few neurons. In contrast, VIP, CCK, NPY, and GAL are now synthesized in many neurons. Delayed intrathecal infusion of NGF (125 ng/microliter/hr) for 7 d, starting 2 weeks after injury counteracted the decrease in expression of alpha- CGRP, beta-CGRP and SP expression, but not SOM. This lack of influence of NGF on SOM is consistent with the absence of high-affinity NGF receptors and trk mRNA in SOM-positive neurons. Delayed infusion of NGF also reduced the number of neurons expressing VIP, CCK, NPY, and GAL after injury by approximately one-half in each subpopulation. Therefore, we suggest that NGF suppresses expression of these four peptides but only if the neurons also have NGF receptors. The results show that NGF can regulate peptide expression differentially and may also be part of the signal that allows reversion to normal of responses to injury as axons regenerate.