bluuebunny/crossref_metadata_2025 huggingface dataset:
Three types of early transient potassium currents in Aplysia neurons
Authors: Furukawa Y , Kandel ER , Pfaffinger P
Published: April 2018

In an attempt to categorize the various early transient K+ currents (A- type K+ currents) present in mature neurons, we have explored these currents in the identified neurons in the abdominal ganglion of the mollusk, Aplysia californica. Three distinct types of A-type K+ currents (IAfast, IAslow, and IAdepol) were found. The activation and the steady-state inactivation properties of two of these currents, IAfast and IAslow, were similar to conventional A-type K+ currents. By contrast, those of the third current, IAdepol, were shifted to more depolarized potentials. Whereas the decay time constants of IAfast were voltage dependent, those of IAslow and IAdepol were almost voltage independent. The recovery from inactivation of IAfast and IAslow was much faster than that of IAdepol. In addition, IAdepol was more sensitive to 4-aminopyridine (4-AP) than other currents and was almost completely blocked by 1 mM 4-AP. All the currents were depressed by forskolin or 1,9-dideoxyforskolin, but not by cAMP analogs. None of these currents were blocked by external tetraethylammonium (50 mM). These results indicate that there are at least three subtypes of A-type K+ currents in the Aplysia CNS. Of these, two currents, IAfast and IAslow, are conventional A-type K+ currents, whereas the third current, IAdepol, is a novel early transient K+ current.
The distribution of 13 GABAA receptor subunit mRNAs in the rat brain. II. Olfactory bulb and cerebellum
Authors: Laurie DJ , Seeburg PH , Wisden W
Published: April 2018

In an effort to determine subunit compositions of in vivo GABAA receptors, the cellular localization of 13 subunit encoding mRNAs (alpha 1-alpha 6, beta 1-beta 3, gamma 2-gamma 3, delta) was determined in the rat olfactory bulb and cerebellum. Cerebellar granule cells expressed significant quantities of alpha 1, alpha 6, beta 2, beta 3, gamma 2, and delta mRNAs. They contained very much lower levels of alpha 4, beta 1, and gamma 3 mRNAs, and the alpha 2, alpha 3, alpha 5, and gamma 1 genes appeared to be silent. Purkinje cells contained only the alpha 1, beta 2, beta 3, and gamma 2 mRNAs. Putative Bergmann glial cells were found to contain the gamma 1 mRNA and possibly the alpha 2 mRNA. In the molecular layer, only the alpha 1, beta 2 and gamma 2 mRNAs were expressed in stellate/basket cells. The alpha 3 probe hybridized weakly to targets in the molecular layer. The inferior olivary nucleus contained significant quantities of alpha 2, alpha 4, and gamma 1 transcripts, with the alpha 1, alpha 3, beta 2, beta 3, and gamma 2 mRNAs also present. In the olfactory bulb, mitral cells were found to express the alpha 1, beta 1, beta 2, beta 3, and gamma 2 mRNAs strongly and the alpha 3 mRNA weakly. Tufted cells contained alpha 1, alpha 3, beta 2, beta 3, and gamma 2 mRNAs and, occasionally, the alpha 2 mRNA. In the internal granule cells the alpha 2, alpha 4, alpha 5, beta 3, and delta mRNAs were all present. Low levels of alpha 3, gamma 1, gamma 2, and gamma 3 mRNAs were also noted in these cells. Periglomerular cells expressed low levels of alpha 2, alpha 3, alpha 4, beta 2, beta 3, gamma 1, gamma 2, and gamma 3 mRNAs. No alpha 6 mRNA was present in the olfactory bulb. Correlations that are general ones from other brain regions are the colocalizations of alpha 1 beta 2, alpha 2 beta 3, and alpha 4 delta mRNAs. In both the olfactory bulb and cerebellum, alpha 1 beta 2 gamma 2 receptor cores are probably employed. The delta-subunit mRNA appears to codistribute with alpha- subunit mRNAs (alpha 4 and alpha 6) associated with GABAA subunits that fail to bind benzodiazepine agonists.
In situ histochemical localization of type I interleukin-1 receptor messenger RNA in the central nervous system, pituitary, and adrenal gland of the mouse
Authors: Cunningham ET , Wada E , Carter DB , Tracey DE , Battey JF , De Souza EB
Published: April 2018

The cytokine interleukin-1 (IL-1) has a number of biologic activities, including pronounced effects on the nervous and neuroendocrine systems. In this study, in situ histochemical techniques were used to investigate the distribution of cells expressing type I IL-1 receptor mRNA in the CNS, pituitary, and adrenal gland of the mouse. Hybridization of 35S-labeled antisense cRNA probes derived from a murine T-cell IL-1 receptor cDNA revealed a distinct regional distribution of the type I IL-1 receptor, both in brain and in the pituitary gland. In the brain, an intense signal was observed over the granule cell layer of the dentate gyrus, over the entire midline raphe system, over the choroid plexus, and over endothelial cells of postcapillary venules throughout the neuraxis. A weak to moderate signal was observed over the pyramidal cell layer of the hilus and CA3 region of the hippocampus, over the anterodorsal thalamic nucleus, over Purkinje cells of the cerebellar cortex, and in scattered clusters over the external-most layer of the median eminence. In the pituitary gland, a dense and homogeneously distributed signal was observed over the entire anterior lobe. No autoradiographic signal above background was observed over the posterior and intermediate lobes of the pituitary, or over the adrenal gland. This study therefore provides evidence for discrete receptor substrates subserving the central effects of IL-1, thus supporting the notion that IL-1 acts as a neurotransmitter/neuromodulator in brain. It also supports studies suggesting that IL-1-mediated activation of the hypothalamic-pituitary- adrenal axis occurs primarily at the level of the brain and/or pituitary gland.
The development of ACh- and GABA-activated currents in embryonic chick ciliary ganglion neurons in the absence of innervation in vivo
Authors: Engisch KL , Fischbach GD
Published: April 2018

Chemical synaptic transmission in the chick ciliary ganglion is mediated by nicotinic ACh receptors. Ciliary ganglion neurons also express GABAA receptors, although there is no known source of GABAergic innervation of the ganglion, and the function of GABA receptors on these neurons is not known. We examined whether ACh and GABA receptors on embryonic chick ciliary ganglion neurons are regulated by presynaptic inputs. Whole-cell currents evoked by ACh or GABA in neurons soon after dissociation were taken to estimate the level of functional receptors in intact ganglia. We destroyed the accessory oculomotor nucleus (AON), the only source of synaptic input to the ganglion, on embryonic day (E) 4. We determined that 80% of the operations resulted in the virtual elimination of synaptic contacts in the ganglion, using P65 immunohistochemistry (a synaptic vesicle antigen) and direct ultrastructural examination. Previous experiments have shown that during normal development, ACh-activated currents increase over sevenfold between E6 and E18; GABA-activated currents increase only twofold, in proportion to cell size. We found that ACh- activated currents of uninnervated neurons at E14 and E18 were as large as control responses. Furthermore, ACh receptor-like molecules, visualized with monoclonal antibody 35 immunofluorescence, were concentrated in high density clusters on the surface of E18 neurons from AON-ablated embryos. GABA-activated currents were also not affected by AON destruction. We conclude that ACh and GABA receptors are not induced in embryonic chick ciliary ganglion neurons during development by contact with or soluble factors released from AON synaptic terminals.
A system for characterizing cellular and molecular events in programmed neuronal cell death
Authors: Pittman RN , Wang S , DiBenedetto AJ , Mills JC
Published: April 2018

A model system has been established in which PC12 cells are converted to neuronal-like cells that undergo transcription-dependent cell death following removal of NGF. Nineteen sublines of PC12 cells were tested to establish parameters for making cells dependent on NGF for survival. In most sublines, a relatively small percentage of cells become dependent on NGF for survival, and following removal of NGF, most of the cells begin proliferating in serum-containing medium. In several sublines, however, a significant percentage of cells die following removal of NGF. One of these sublines, PC6–3, can be grown under conditions in which 90% of the cells undergo transcription-dependent cell death following removal of NGF in either serum-free or serum- containing medium. Fourteen hours after removing NGF, 50% of the cells are committed to die, while initial morphological signs of cell death as determined by time-lapse videomicroscopy occur 2–6 hr later and include loss of neurites followed by a 1–3 hr period of active membrane “blebbing” and protrusions. Cell death can be blocked by the RNA synthesis inhibitor actinomycin D, the protein synthesis inhibitor cycloheximide, KCl, basic fibroblast growth factor, or dibutryl-cAMP, but not by epidermal growth factor, leupeptin, or the endonuclease inhibitor aurintricarboxylic acid (ATA). Removal of NGF activates an endonuclease that causes nucleosomal laddering of the DNA; however, endonuclease activity does not appear to be required for cell death. In agreement with previous studies (Batistatou and Greene, 1991; Rukenstein et al., 1991) demonstrating that naive PC12 cells undergo transcription-independent cell death when shifted into serum-free medium in the absence of growth factors, all cell lines tested except for one die when cultured in RPMI medium lacking growth factors. DNA fragmentation is a prominent feature of transcription-independent cell death, and death can be blocked with NGF, ATA, and dibutryl-cAMP but not with actinomycin D or KCl. The PC12 model system described here should be useful for identifying cell death genes and for characterizing cellular and molecular events in programmed neuronal cell death.
The modular organization of projections from areas V1 and V2 to areas V4 and TEO in macaques
Authors: Nakamura H , Gattass R , Desimone R , Ungerleider LG
Published: April 2018

In addition to the major anatomical pathways from V1 into the temporal lobe, there are other smaller, “bypass” routes that are poorly understood. To investigate the direct projection from V1 to V4 (bypassing V2) and from V2 to TEO (bypassing V4), we injected the foveal and parafoveal representations of V4 and TEO with different retrograde tracers in five hemispheres of four macaques and analyzed the distributions of labeled neurons in V1 and V2 using flattened preparations of the cortex. In V1, labeled neurons were seen after injections in V4 but not TEO. The V4-projecting neurons were located in the foveal representation of V1, in both cytochrome oxidase (CO)-rich blobs and CO-poor interblob regions. In V2, TEO-projecting neurons were intermingled with V4-projecting neurons, although the former were far sparser than the latter. Across the cases, 6–19% of the TEO-projecting neurons were double labeled, that is, also projected to area V4. Both V4- and TEO-projecting neurons formed bands that ran orthogonal to the V1/V2 border, and both were located in CO-rich thin stripes and CO-poor interstripe regions. In some cases, a continuous band of V4-projecting neurons was also found along the V1/V2 border in the foveal representation of V2. The results indicate that the pathways from V1 to V4 and from V2 to TEO involve anatomical subcompartments thought to be concerned with both color and form. These “bypass” routes may allow coarse information about color and form to arrive rapidly in the temporal lobe. The bypass route from V2 to TEO might explain the partial sparing of color and form vision that is seen after lesions of V4. By analogy, given the bypass route from the foveal representation of V1 to V4, lesions of V2 affecting the foveal visual field would also be insufficient to block color and form vision.
Contact-mediated mechanisms of motor axon segmentation
Authors: Oakley RA , Tosney KW
Published: April 2018

In the chick embryo, the segmental pattern of motor outgrowth depends on guidance cues provided by sclerotome cells. Motor axons preferentially invade the anterior sclerotome but avoid the posterior sclerotome. To determine how motor growth cone motility is influenced by these cells, we used videomicroscopy to analyze the behavior of motor growth cones as they confronted identified sclerotome cells in vitro. After contact, motor growth cones invariably avoided posterior sclerotome cells by either branching or turning. Both types of avoidance behavior were initiated by a local inhibition of veil protrusion: veils failed to progress along the contacting filopodia. This inhibition was specific to veils since contact failed to alter the number of filopodia protruded. Moreover, motor growth cones turned away from posterior cells despite more persistent filopodial contacts with these cells than with the laminin substratum. In no case did contact with posterior cells cause a complete loss of growth cone motility or a complete collapse of growth cone structure. In contrast, motor growth cones exhibited a selective affinity for anterior cells, preferring the surfaces of these cells to the laminin substratum. Contact with anterior cells stimulated a generalized increase in protrusive activity: contact caused a net increase in the extension of veils and filopodia both locally and at sites distant from the site of contact. Contact also elicited a localized thickening of contacting processes, suggesting that contact with anterior cells promotes neurite consolidation. This behavior of motor growth cones in vitro suggests that both an inhibition of veil formation by posterior cells and an enhancement of motility and axon consolidation by anterior cells contribute to the preferential advance of motor axons into anterior sclerotome in vivo. We suggest that patterned outgrowth results from the juxtaposition of two contrasting environments that differentially influence growth cone motility.
Spatial and behavioral correlates of striatal neurons in rats performing a self-initiated navigation task
Authors: Wiener SI
Published: April 2018

To investigate the spatial and behavioral correlates of striatal neurons during displacement movements, the rostromedial dorsal striata (AP 1.0–2.2, ML 1.5–2.0) of five rats were surgically implanted with advanceable bundles of fine wire electrodes. After recovery, the rats were deprived of water and trained in a square-walled open field in a dark room. The behavioral task required alternating visits to water reservoirs in the center and in the four corners. A certain corner contained the first reward for each trial; after this reward, a cue card appeared in this corner for the rest of the trial. The firing rates of striatal units were compared as the rat moved between the center and the four corners of the arena. Analyses were made of 30 units. Eight of these had firing rates that significantly increased or decreased by 62–480% while the rat was in one or more quadrants of the arena. Six of these manifested such firing rate changes only as the rat performed certain behavioral sequences in the quadrant. Three other units fired as the rat's head was in a certain orientation relative to the arena walls, in all parts of the arena. To determine the principal controlling cues and hence the frame of reference of spatial selectivity of these units, the arena, while the rat was still inside, was rotated in total darkness. The first water reward was then presented at the same position relative to the outside room as before the rotation. The cue card was then illuminated in this corner as a visual cue for the extra-arena reference frame. All 11 neurons demonstrated spatial selectivity that rotated with the arena; thus, this activity was in the frame of reference of the arena and was not controlled by the visual cue. Six other units fired at rates up to six times their resting discharge or stopped firing completely in synchrony with initiation or execution of displacement movements, and two of these were also location selective. Four other units were silent as the rat performed the task, but fired tonically following arena rotations or other interruptions of the session, independent of the rat's location or movements. Nine analyzed units had very low firing rates (< 1 impulse/sec) and showed no discernible changes in activity as the rat performed the task. These patterns of unit activity indicate that fundamental informational components required for navigation are coded in the striatum.(ABSTRACT TRUNCATED AT 400 WORDS)
Vulnerability of mossy fiber targets in the rat hippocampus to forebrain ischemia
Authors: Hsu M , Buzsaki G
Published: April 2018

Much of the work on forebrain ischemia in the hippocampus has focused on the phenomenon of delayed neuronal death in CA1. It is established that dentate granule cells and CA3 pyramidal cells are resistant to ischemia. However, much less is known about interneuronal involvement in CA3 or ischemic injury in the dentate hilus other than the fact that somatostatin neurons in the latter lose their immunoreactivity. We combined two sensitive methods--heat-shock protein (HSP72) immunocytochemistry and a newly developed Gallyas silver stain for demonstrating impaired cytoskeletal elements--to investigate the extent of ischemic damage to CA3 and the dentate hilus using the four-vessel- occlusion model for inducing forebrain ischemia. HSP72-like immunoreactivity was induced in neuronal populations previously shown to be vulnerable to ischemia. In addition, a distinct subset of interneurons in CA3 was also extremely sensitive to ischemia, even more so than the CA1 pyramidal cells. These neurons are located in the stratum lucidum of CA3 and possess a very high density of dendritic spines. In silver preparations, they were among the first to be impregnated as “dark” neurons, before CA1 pyramidal cells; microglial reaction was also initiated first in the stratum lucidum of CA3. Whereas CA1 damage was most prominent in the septal half of the hippocampus, hilar and CA3 interneuronal damage had a more extensive dorsoventral distribution. Our results also show a far greater extent of damage in hilar neurons than previously reported. At least four hilar cell types were consistently compromised: mossy cells, spiny fusiform cells, sparsely spiny fusiform cells, and long-spined multipolar cells. A common denominator of the injured neurons in CA3 and the hilus was the presence of spines on their dendrites, which in large part accounted for the far greater number of mossy fiber terminals they receive than their non-spiny neighbors. We suggest that the differential vulnerability of neuronal subtypes in these two regions may be attributed to their extremely dense innervation by the mossy fibers and/or the presence of non-NMDA receptor subtypes that are highly permeable to calcium. In addition, early impairment of these spiny CA3 cells and hilar neurons after ischemia may be causal to delayed neuronal death in the CA1 pyramidal cells.
Induction of noncatalytic TrkB neurotrophin receptors during axonal sprouting in the adult hippocampus
Authors: Beck KD , Lamballe F , Klein R , Barbacid M , Schauwecker PE , McNeill TH , Finch CE , Hefti F , Day JR
Published: April 2018

Brain-derived neurotrophic factor (BDNF) and its signal transducing receptor, the TrkB tyrosine protein kinase, are expressed at high levels in the hippocampus of the adult brain, suggesting a role for BDNF mechanisms in neuronal plasticity. To test this hypothesis, we used defined lesions of perforant path and fimbria-fornix, two major hippocampal afferents, to remove synapses on dendrites of dentate gyrus granule cells and pyramidal cells of Ammon's horn and induce synaptic rearrangements. These combined lesions remove afferent connections from entorhinal cortex and septum and produce massive sprouting of axons of the commissural/associational pathways into the molecular layer of the hippocampal dentate gyrus. At days 1, 3, and 6, the lesions decreased BDNF mRNA expression ipsilaterally to approximately 50% of control, with complete recovery at 14 d. The lesions did not alter trkB mRNA levels in neuronal layers of the hippocampus; however, they resulted in a pronounced induction of trkB mRNA expression in hippocampal non- neuronal cells 6–14 d after lesioning. The induction corresponded in time and place to the synaptic reorganization in the lesioned hippocampus. The mRNA species newly induced by the lesions corresponded to those transcripts encoding the noncatalytic TrkB receptor isoform that lacks the cytoplasmic protein kinase domain. Expression of mRNAs coding for neurotrophin-3 and the TrkC tyrosine protein kinase were not altered by the lesions. The findings suggest that truncated noncatalytic TrkB molecules expressed on the surface of glial cells play an important role in plasticity of the adult brain, possibly regulating the concentration of bioactive neurotrophins or the responsiveness of neurotrophin receptors. Alternatively, they may play a role in presenting neurotrophin molecules to growing axons.
Directionally selective mnemonic properties of neurons in the lateral dorsal nucleus of the thalamus of rats
Authors: Mizumori SJ , Williams JD
Published: April 2018

The hippocampal formation has been extensively studied for its special role in visual spatial learning and navigation. To ascertain the nature of the associations made, or computations performed, by hippocampus, it is important to delineate the functional contributions of its afferents. Therefore, single units were recorded in the lateral dorsal nucleus of the thalamus (LDN) as rats performed multiple trials on a radial maze. Many LDN neurons selectively discharged when an animal's head was aligned along particular directions in space, irrespective of its location in the test room. These direction-sensitive cells were localized to the dorsal aspect of the caudal two-thirds of the LDN, the site of innervation by retinal recipient pretectal and intermediate/deep-layer superior colliculus cells (Thompson and Robertson, 1987b). The directional specificity and preference of LDN cells were disrupted if rats were placed on the maze in darkness. If the room light was then turned on, the original preference was restored. If the light was again turned off, directional firing was maintained briefly. Normal directional firing lasted about 2–3 min. After this time, the directional preference (but not specificity) appeared to “rotate” systematically in either the clockwise or counterclockwise direction. The duration of normal directional discharge patterns in darkness could be extended to 30 min by varying the behavior of the animal. LDN cells required visual input to initialize reliable directional firing. After the rat viewed the environment, directional specificity was maintained in the absence of visual cues. Maximal directional firing was achieved only when the rat viewed the entire test room, and not just the scene associated with the directional preference of the cell. Thus, contextual information seems important. Also, a significant correlation was found between directional specificity and errors made on the maze during acquisition of the task. It was concluded that the LDN may pass on to the hippocampal formation directional information that is not merely a reflection of current sensory input. As such, the LDN may serve an important integrative function for limbic spatial learning systems.
Corticosteroid actions on amino acid-mediated transmission in rat CA1 hippocampal cells
Authors: Joels M , de Kloet ER
Published: April 2018

We here describe actions mediated by mineralo- and glucocorticoid receptors (MRs and GRs, respectively) on intracellularly recorded synaptic responses, evoked in rat CA1 pyramidal cells in vitro by stimulation of the Schaffer collaterals. Neurons in slices from adrenalectomized (ADX) rats, that is, where MRs and GRs are unoccupied, showed a synaptic response consisting of an EPSP, followed by a fast and a slow IPSP; the responses were apparently similar to those in slices from sham-operated rats. However, in the ADX rats, repeated electrical stimulation over a period of 80 min resulted in a gradual decline of the firing probability for synaptically driven action potentials and of the slow IPSP amplitude. Nonsynaptic responses (e.g., membrane potential, accommodation, and afterhyperpolarization) were stable during the 80 min period. Application of 3 nM aldosterone between 20 and 40 min after impalement of cells in slices from ADX rats, thus activating predominantly MRs, yielded stable synaptic and nonsynaptic responses for at least 1 hr after the onset of the steroid application. By contrast, corticosterone (30 nM), which occupies GRs in addition to MRs, reduced the amplitude of both the EPSP and slow IPSP, and the firing probability of synaptically driven action potentials, within 20 min; nonsynaptic properties remained stable. Similar results were obtained with the selective glucocorticoid RU 28362. The EPSP and fast and slow IPSPs of neurons in slices from ADX rats impaled with a time lag of 1–4 hr after the steroid application did not differ significantly from the responses of neurons impaled before steroid application.(ABSTRACT TRUNCATED AT 250 WORDS)
Developmental expression of trkC, the neurotrophin-3 receptor, in the mammalian nervous system
Authors: Lamballe F , Smeyne RJ , Barbacid M
Published: April 2018

The mammalian trkC gene encodes a tyrosine protein kinase that serves as a functional receptor for neurotrophin-3 (NT-3). Here, we report that trkC is widely expressed in the developing and adult nervous system. Using in situ hybridization, we first detect trkC transcripts in the telencephalon and spinal cord of embryonic day 9.5 mouse embryos. In later embryonic development, trkC is expressed in various structures of the CNS including the caudatoputamen, septal nuclei, cerebellum, and brainstem. In the PNS, trkC hybridization appears to correlate, both temporally and spatially, with the outgrowth of axons toward their peripheral targets. trkC transcripts were also identified in the autonomous enteric nervous system as well as in some non-neural tissues such as the wall of the aorta and the acini of the submaxillary and sublingual glands. In the adult mouse, trkC gene expression is heterogeneously distributed throughout the brain, with highest levels in limbic and diencephalic structures. These results indicate that the trkC gene is widely expressed in the three identified branches of the mammalian nervous system and appears to correlate with the expression of NT-3, its cognate ligand. The apparent colocalization of trkC transcripts with NT-3 raises the possibility this neurotrophin exerts its trophic effects by a paracrine and/or autocrine mechanism.
Aggregation of vasopressin mRNA in a subset of axonal swellings of the median eminence and posterior pituitary: light and electron microscopic evidence
Authors: Trembleau A , Morales M , Bloom FE
Published: April 2018

The mRNA encoding vasopressin has recently been documented within the magnocellular hypothalamo-neurohypophyseal projections of the rat such as the median eminence (ME) and the posterior pituitary (PP), suggesting the possibility of its axonal transport. To address the origin of this mRNA and to investigate the functional significance of this unexpected axonal transport of mRNA, we have examined its subcellular localization within both magnocellular perikarya and their axonal projections. For this purpose, we have used nonradioactive in situ hybridization techniques in order to localize the vasopressin mRNA with precision at the ultrastructural level in magnocellular perikarya, dendrites, and axons from control, salt-loaded, and lactating rats. This approach permitted us to demonstrate directly the axonal localization of vasopressin mRNA. Moreover, we were able to obtain novel information concerning vasopressin mRNA compartmentation within both perikarya and axons. At both light and electron microscopic levels, we observed vasopressin mRNA-containing cells in the hypothalamic magnocellular cell body groups, but not in the ME or in the PP. When vasopressin mRNA was detected in medium-size dendrites, it was always associated with the rough endoplasmic reticulum (RER). Within the labeled magnocellular perikarya, the abundant vasopressin mRNA was mainly associated with discrete areas of the RER. However, vasopressin mRNA was never detected in the Golgi apparatus or in association with neurosecretory granules, in perikarya or axons. These data suggest that vasopressin mRNA translation is restricted to certain segments within the RER, and that axonal transport of vasopressin mRNA does not involve the classical neurosecretory pathway, via the Golgi apparatus and the neurosecretory granules, as has been proposed. Within the magnocellular neuron axons, vasopressin mRNA could be detected only in a subset of axonal swellings, all of which were confined to the internal layer of the ME and the PP. The mRNA-containing swellings were numerous in 7 d salt-loaded animals, less abundant in lactating animals, and almost undetectable in control animals. In all groups of animals, no vasopressin mRNA was detectable in any other region of the magnocellular neuron axons, including undilated axonal segments or varicose swellings. These results strongly suggest that, under physiological activation such as chronic salt loading, axonal vasopressin mRNA is increased and becomes aggregated in a selected subset of swellings of the ME and the PP. Furthermore, these data indicate that along the magnocellular neuron axons, the swellings may differ in their biochemical and functional features. Further analysis focused on the mRNA-accumulating swellings may illuminate the function of RNA within the axonal compartment.
Basal forebrain lesions in monkeys disrupt attention but not learning and memory [published erratum appears in J Neurosci 1995 Mar;15(3): following table of contents]
Authors: Voytko ML , Olton DS , Richardson RT , Gorman LK , Tobin JR , Price DL
Published: April 2018

Cognitive impairments in humans and animals have been linked to dysfunction of neurons in the basal forebrain cholinergic system (BFCS). Degeneration of these cells may be, in part, responsible for some of the cognitive deficits observed in Alzheimer's disease (AD). Although memory deficits are associated with lesions of the BFCS in rats, impairments in memory have been more subtle following similar lesions in monkeys. To evaluate the effects of BFCS lesions on cognitive processes in monkeys, we have systematically investigated the behavioral effects of ibotenic acid injections in the medial septum, nucleus of the diagonal band of Broca, and nucleus basalis of Meynert in cynomolgus monkeys, using a large series of cognitive tasks that examined different mnemonic and attentional abilities. These lesions did not impair accuracy in delayed nonmatching-to-sample, delayed response, simple or concurrent visual discriminations, spatial discriminations, or discrimination reversals. However, these lesions disrupted attentional focusing. Similar impairments in attention have been noted in patients with AD. BFCS lesions increased sensitivity to injections of the cholinergic antagonist scopolamine in a delayed nonmatching-to-sample task, indicating that the central cholinergic system was compromised in these monkeys. In concert, the results of this study suggest that the primate basal forebrain may be more involved in attentional than mnemonic processes, and that degeneration of neurons in the BFCS in cases of AD may contribute to the attention deficits observed in these individuals.
Ca2+ entry via AMPA/KA receptors and excitotoxicity in cultured cerebellar Purkinje cells
Authors: Brorson JR , Manzolillo PA , Miller RJ
Published: April 2018

Initial studies of glutamate receptors activated by kainate (KA) found them to be Ca2+ impermeable. Activation of these receptors was thought to produce Ca2+ influx into neurons only indirectly by Na(+)-dependent depolarization. However, Ca2+ entry via AMPA/KA receptors has now been demonstrated in several neuronal types, including cerebellar Purkinje cells. We have investigated whether such Ca2+ influx is sufficient to induce excitotoxicity in cultures of cerebellar neurons enriched for Purkinje cells. Agonists at non-NMDA receptors induced Ca2+ influx in the majority of these cells, as measured by whole-cell voltage clamp and by fura-2 [Ca2+]i microfluorimetry. To assess excitotoxicity, neurons were exposed to agonists for 20 min and cell survival was evaluated by a fluorescence assay 24 hr later. KA (100 microM) reduced neuronal survival relative to controls to 43 +/- 3% when applied in Na(+)-containing solution and to 45 +/- 3% in Na(+)-free solution. This toxicity was blocked completely by CNQX but only slightly by 100 microM Cd2+ and 50 microM D-(-)-2-amino-5-phosphonovaleric acid. Both Purkinje neurons and non-Purkinje cell types present in the cultures were similarly vulnerable to toxic KA exposure, but the population marked by KA-induced Co2+ uptake was selectively diminished by the excitotoxicity. Na(+)-independent excitotoxicity could also be induced by domoate, AMPA, or glutamate. Compared to KA, NMDA was relatively ineffective in inducing cell death. Most of the KA-induced excitotoxicity could be blocked by removal of extracellular Ca2+ during the KA exposure and for a 5 min period thereafter. Furthermore, antagonists of the Ca(2+)-activated enzymes nitric oxide synthase and calpain significantly reduced the KA-induced cell death. These results show that non-NMDA receptor activation can cause excitotoxicity in cerebellar Purkinje neurons by mechanisms not involving Na+ influx, but rather depending on direct Ca2+ permeation and activation of Ca(2+)- dependent enzymatic processes.
Autosomal recessive neuromuscular disorder in a transgenic line of mice
Authors: Kelly D , Chancellor K , Milatovich A , Francke U , Suzuki K , Popko B
Published: April 2018

We have generated a line of transgenic mice that when homozygous for the transgene develop a severe, adult-onset neuromuscular disorder. This mutation is likely the result of the insertional inactivation of an endogenous gene by the transgene integration. The mutant mice have a gait abnormality with stiffened and/or splayed hind legs, and adopt a hunched posture with some exhibiting kyphosis of the thoracic spine. These symptoms progress gradually to severe motor dysfunction. Pathologic changes were found in skeletal muscle and peripheral nerve of the mutant animals. In young mice the muscles from both upper and lower extremities show necrosis and phagocytosis. In older mice, regeneration with muscle fiber splitting, internally located nuclei, and variable fiber size are conspicuous features. Interactions between Schwann cells and axons also appear disrupted in these animals. Although many peripheral axons are well myelinated, the nerve and nerve roots contain very large bundles of juxtaposed, bare axons, reminiscent of Schwann cell-axon interactions in early development. Within these bundles there are axons large enough to be myelinated. The relationship between the pathologic changes in the muscles and nerves is not clear. The phenotypic abnormalities of these animals resemble those that occur in the spontaneous mouse mutants dystrophia muscularis and myodystrophy. Nevertheless, the chromosomal position of the transgene integration site, which was mapped by fluorescent in situ hybridization to chromosome 11, indicates that this disorder represents a new neuromuscular mutation.
Increased deafferentation-induced cell death in chick brainstem auditory neurons following blockade of mitochondrial protein synthesis with chloramphenicol
Authors: Hyde GE , Durham D
Published: April 2018

Second-order auditory neurons in nucleus magnocellularis (NM) of the chick brainstem undergo a series of rapid metabolic changes following unilateral cochlea removal, culminating in the death of 25% of NM neurons. Within hours of cochlea removal, ipsilateral NM neurons show marked increases in histochemical staining for the mitochondrial enzymes succinate dehydrogenase and cytochrome oxidase (CO). We have shown previously in an ultrastructural study that these increases in oxidative capacity are mediated in part by a rapid increase in mitochondrial volume within deafferented neurons. In neurons that are destined to die as a result of deafferentation, mitochondria are smaller, stain poorly for CO, and often contain vacuoles associated with oxidative dysfunction. Our present set of experiments is designed to test the hypothesis that increases in oxidative metabolism are necessary for NM neuronal survival following removal of afferent input. We used chloramphenicol (CAP), a mitochondrial protein synthesis inhibitor, to block the characteristic increase in CO activity and mitochondrial proliferation following cochlea removal. We then studied the effects of CAP on NM neuronal survival following deafferentation. When CAP was administered continuously at 600 mg/kg/d for 5 d following cochlea removal, deafferentation-induced neuronal death in NM was significantly increased from 22% to 36%. Higher-dose (1200 mg/kg/d) pulses of CAP were administered for the first 6, 12, or 24 hr following cochlea removal. After 5 d survival, greater increases in neuronal cell death were found in animals treated for the first 12 or 24 hr (65% neuronal death). CAP administration for the first 6 hr had no significant effect on neuronal survival. The effects of CAP on neuronal cell death in NM are not likely to be due to systemic effects of the drug, but instead to a specific change in mitochondrial function. Our results suggest that enhanced oxidative enzyme function plays an important role in the survival of NM neurons during the first 24 hr after deafferentation. The nature of the signal(s) eliciting mitochondrial enhancement and the means by which it influences NM survival are not known.
Differential distribution of the synapsins in the rat olfactory bulb
Authors: Stone LM , Browning MD , Finger TE
Published: April 2018

The distribution of the different forms of synapsin in the rat olfactory bulb was investigated by biochemical and immunocytochemical methods. Western blots of tissue derived from microdissection of the surface and core regions of the olfactory bulb were performed using antibodies to synapsin I and synapsin II. The relative levels of the synapsins in the core region of the olfactory bulb were similar to the cerebral cortex. In contrast, the surface region of the olfactory bulb had significantly higher levels of synapsin IIa and significantly lower levels of synapsin I, relative to the cortex. Immunocytochemical localization of synapsin I and synapsin II revealed that synapsin I immunoreactivity was the most dense in the external plexiform layer and in the glomeruli; immunoreactivity was also present in the granule cell layer and the periglomerular regions. Synapsin II immunoreactivity was the most dense in the glomeruli. The external plexiform layer, internal plexiform layer, and granule cell layer exhibited much lower immunoreactivity. To determine the source of synapsin II immunoreactivity in the glomeruli, the olfactory epithelium was damaged to decrease the primary afferent input to the bulb. Three to four days later, olfactory bulb sections were double labeled with anti-olfactory marker protein (OMP) antibodies and anti-synapsin II antibodies. Following denervation, both OMP and synapsin II immunoreactivities were diminished, and continued to colocalize in regions retaining immunoreactivity. Individual puncta were immunoreactive for both OMP and synapsin II. Occasional puncta contained only synapsin II immunoreactivity. These results indicate that the distribution of the synapsins in the olfactory bulb differs from most other brain regions.(ABSTRACT TRUNCATED AT 250 WORDS)
Microtubule polarity in the peripheral processes of trigeminal ganglion cells: relevance for the retrograde transport of herpes simplex virus
Authors: Topp KS , Meade LB , LaVail JH
Published: April 2018

The directional movement of many cellular organelles in neurons is dependent on polarized microtubules and direction-specific motor molecules. Microtubules are also thought to mediate the retrograde transport of herpes simplex virus (HSV) in sensory neurons. To define the cellular machinery responsible for retrograde axonal transport of HSV, we have investigated the polarity of microtubules in the peripheral axons of trigeminal ganglion neurons. The long ciliary nerves of rabbits were prepared for a standard “hook assay” of microtubule polarity. Axons in cross-sectioned nerves contained microtubules with almost uniform orientation. The fast-growing, plus ends of these axonal microtubules are located distal to the cell body and the slow-growing, minus ends are directed centrally. To determine the role played by microtubules in the retrograde transport of HSV in these axons, we injected the retrobulbar space of mice with the microtubule-inhibiting drugs colchicine, vinblastine, or nocodazole or with the microfilament inhibitor cytochalasin D and 1 d later inoculated the cornea with HSV. We found that colchicine, vinblastine, or nocodazole reduced by 52–87% the amount of virus recovered from the ganglion 3 d postinoculation, compared to vehicle-treated animals. In contrast, cytochalasin D or beta-lumicolchicine did not significantly reduce the amount of HSV recovered from the ganglion. We conclude that the retrograde axonal transport of HSV from axon endings in the cornea to the trigeminal ganglion cell bodies requires intact microtubules and occurs in a plus-to-minus direction on the microtubules. Our data are consistent with the hypothesis that the retrograde axonal transport of HSV is mediated by a minus end-directed motor molecule, for example, cytoplasmic dynein.
Effects of prolonged darkness on light responsiveness and spectral sensitivity of cone horizontal cells in carp retina in vivo
Authors: Yang XL , Fan TX , Shen W
Published: April 2018

Light responses of cone- and rod-driven horizontal cells were recorded intracellularly from opened eyes of intact, immobilized carp and the effects of prolonged darkness on these cells were examined. When the retina was left in the dark, responses of cone horizontal cells to a moderate test flash presented once every 10 min gradually and steadily decreased in size (dark suppression effect). Following a repetitive presentation of the test flash, the light responsiveness of the cells was enhanced. In contrast, the rod horizontal cells did not show the dark suppression effect and the light responsiveness of these cells increased in the dark. Effects of prolonged darkness on the spectral sensitivity of L-type and R/G-type cone horizontal cells were also studied. The spectral sensitivity of L-type cells, determined just after background illumination was extinguished, agreed reasonably well with that of red-sensitive (R-) cones, but it matched better that of green-sensitive (G-) cones when determined in prolonged darkness. We further show that depolarizing responses of R/G-type cone horizontal cells to long-wavelength flashes, driven by R-cones, were abolished after prolonged darkness. Taken together, these results suggest that input from R-cones converging onto the cone horizontal cells is more significantly suppressed after prolonged dark adaptation than input from G-cones. Due to the suppression of the R-cone input, enhancement of responses of the L-type cone horizontal cells to long-wavelength stimulation in the presence of a green background light was no longer seen after prolonged darkness.(ABSTRACT TRUNCATED AT 250 WORDS)
Cytoskeletal movements and substrate interactions during initiation of neurite outgrowth by sympathetic neurons in vitro
Authors: Smith CL
Published: April 2018

The initial outgrowth of neurites from chick sympathetic neurons grown in vitro was investigated by time-lapse microscopy with laser-scanning and conventional light microscopes. Video-enhanced contrast, differential interference contrast optics (VECDIC) were used to monitor movements of neuronal cytoplasm, as well as the movements of small beads attached to the surface membrane, and interference reflection microscopy (IRM) was used to determine the concomitant pattern of attachment to the growth substrate (polyornithine or laminin). Related changes in the distributions of actin filaments, microtubules, and neurofilaments were determined by fluorescence labeling methods. Neurite formation on both substrates entailed invasion of the actin cores of filopodia by cytoplasm containing microtubules and neurofilaments. Small beads attached to the surface membrane surrounding the cytoplasm moved outward simultaneously with the cytoplasm. Cytoplasm invaded filopodia of neurons plated on laminin soon after attachment to the substrate or, for neurons generated in vitro, within as little as 3 min after cytokinesis. However, cytoplasm invaded filopodia of neurons grown on polyornithine only when they contacted a three-dimensional object such as another cell or a large, polyornithine-coated polystyrene bead. The observation that adhesion of filopodia to polyornithine-coated beads can initiate neurite formation is inconsistent with the commonly held view that neurite formation requires adhesion mediated by specific cell adhesion molecules. Simultaneous IRM and DIC imaging showed that cytoplasm invaded filopodia when only their tips were closely apposed to a substrate but not when they were closely apposed to a substrate along their entire lengths. These findings help to elucidate the mechanisms by which interactions between the cytoskeleton and the growth substrate initiate and produce the neuronal movements that lead to the formation of neurites.
Novel hyperpolarization-activated K+ current mediates anomalous rectification in crayfish muscle
Authors: Araque A , Buno W
Published: April 2018

The ionic current underlying anomalous rectification in opener muscle fibers of crayfish was studied under two-electrode voltage clamp. Opener muscle fibers showed a mean resting potential (RP) of -64.8 mV and an input resistance of 0.4 M omega. Hyperpolarizing voltage command pulses from a holding potential (H) of -60 mV evoked an instantaneous voltage-independent linear current (IL) followed by a time- and voltage- dependent inward current (IAB) that reached a steady state within 500 msec. The reversal potential of IAB (EAB) was estimated from tail current amplitudes. At an extracellular K+ concentration ([K+]o) of 5.4 mm the mean EAB was -61.8 mV. EAB shifted toward positive potentials by 50.8 mV for a 10-fold increase in [K+]o. The conductance underlying IAB (GAB) increased sigmoidally with hyperpolarization, starting close to the RP, saturating at a GAB,max of about -140 mV, and showing a mean half-activation at -94.4 mV. The activation curve of GAB shifted 53.6 mV toward positive potentials with a 10-fold increase in [K+]o. GAB,max did not increase in raised [K+]o. The activation and deactivation kinetics of IAB were accurately described by single exponentials with similar time constants (< 100 msec). Time constants changed as an exponential function of the membrane potential. IAB, its time course, GAB, and EAB were not modified in the following conditions: (1) Na(+)- and Ca(2+)-free solutions, (2) intracellular EGTA, (3) extracellular (100 mM) or intracellular tetraethylammonium, (4) extracellular Cs+ (up to 50 mM), Rb+ (up to 10 mM), Ba2+ (13.5 mM), or Mn2+ (13.5 mM). However, low extracellular concentrations of Cd2+ or Zn2+ strongly and reversibly reduced both IL and IAB. Therefore, we conclude that anomalous rectification in crayfish muscle is generated by a voltage- and time-dependent K+ current IAB. This current displayed many electrophysiological and pharmacological characteristics that distinguished it from all others mediating anomalous rectification described previously.