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  • Society for Neuroscience  (12)
  • 1
    Online Resource
    Online Resource
    Society for Neuroscience ; 1985
    In:  The Journal of Neuroscience Vol. 5, No. 1 ( 1985-01-01), p. 72-80
    In: The Journal of Neuroscience, Society for Neuroscience, Vol. 5, No. 1 ( 1985-01-01), p. 72-80
    Abstract: Sensitization of the gill withdrawal reflex in Aplysia californica is an elementary form of learning, in part resulting from presynaptic facilitation of the LE mechanoreceptor neurons of the abdominal ganglion. It has previously been established that either application of serotonin or direct stimulation of a group of facilitatory neurons, the L29 cells of the abdominal ganglion, can simulate the effect of physiological stimulation in producing presynaptic facilitation. Because the evidence that serotonin serves as a facilitatory transmitter was indirect, we examined the distribution of serotonin- immunoreactive fibers and cell bodies in the abdominal ganglion in order to answer two questions: (1) do the sensory neurons receive serotonergic innervation and (2) are the L29 cells serotonergic? We observed two distinctive patterns of serotonergic innervation within the ganglion, sparse and dense. The sparse pattern is correlated with a serotonin-stimulated increase in cAMP in identified target cells, while the dense innervation is not. We found a sparse distribution of serotonin-immunoreactive fibers with varicosities close to both cell bodies and processes of identified LE sensory cells. It therefore is likely that the sensory neurons do receive serotonergic innervation. We also mapped the population of serotonergic neuronal cell bodies in the ganglion, and found five clusters of neurons. Cells in one of these clusters, the identified RB neurons, had previously been shown to synthesize serotonin from tryptophan and to contain the neurotransmitter in high concentration. Identified L29 facilitator cells marked by injection with Lucifer Yellow do not contain serotonin immunoreactivity and therefore evidently are not a source of serotonergic input onto sensory cells.
    Type of Medium: Online Resource
    ISSN: 0270-6474 , 1529-2401
    Language: English
    Publisher: Society for Neuroscience
    Publication Date: 1985
    detail.hit.zdb_id: 1475274-8
    SSG: 12
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  • 2
    Online Resource
    Online Resource
    Society for Neuroscience ; 1991
    In:  The Journal of Neuroscience Vol. 11, No. 5 ( 1991-05-01), p. 1275-1281
    In: The Journal of Neuroscience, Society for Neuroscience, Vol. 11, No. 5 ( 1991-05-01), p. 1275-1281
    Abstract: The purpose of this study was to determine the synaptic actions of the bursting peptidergic neuron R15 in Aplysia. R15 is known to be excited by the neuroendocrine bag cells, which trigger egg laying. In the two companion papers, we show that R15 mediates some of the effects of the bag cells on respiratory and reproductive organs. In this paper, we demonstrate that R15 excites L7, a multimodal motoneuron located in the abdominal ganglion. Although L7 excites several types of muscle fibers as well as neurons, the excitation of L7 by R15 is probably strong enough to cause contraction only of the sheath muscle of the pleuroabdominal connectives, which has an exceptionally low threshold for activation. The excitatory actions of R15 on L7, which desensitize profoundly, appear to be mediated by R15 alpha 1 peptide. The synaptic action of R15 on L7 and on the respiratory pumping system (Alevizos et al., 1991a) can be fully expressed only if R15 is first silenced for 2 hr by injection of hyperpolarizing current. A similar protocol for eliminating desensitization may prove to be generally useful for revealing the synaptic actions of other spontaneously active neurons that have rapidly desensitizing postsynaptic actions.
    Type of Medium: Online Resource
    ISSN: 0270-6474 , 1529-2401
    Language: English
    Publisher: Society for Neuroscience
    Publication Date: 1991
    detail.hit.zdb_id: 1475274-8
    SSG: 12
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  • 3
    Online Resource
    Online Resource
    Society for Neuroscience ; 1989
    In:  The Journal of Neuroscience Vol. 9, No. 11 ( 1989-11-01), p. 4078-4088
    In: The Journal of Neuroscience, Society for Neuroscience, Vol. 9, No. 11 ( 1989-11-01), p. 4078-4088
    Abstract: The purpose of this study was to begin to describe the neural circuit within the abdominal ganglion that modulates renal functioning in Aplysia. We found that the previously described cholinergic neuron L10 and peptidergic left upper quadrant (LUQ) neurons have important roles in the control of the kidney. Cell L10 and a subset of the LUQ cells branch extensively within the kidney and send major processes to the renal pore, a sphincter that controls the efflux of urine. The renal pore has circular (closer) and radial (opener) muscle fibers that act as antagonists. Embedded within the wall of the renal pore is a newly identified peripheral neuron, RPO, which is a renal pore opener motoneuron. L10 activity causes opening of the renal pore by directly exciting pore opener muscle, inhibiting closer muscle, and exciting RPO. When RPO is active, it generates synchronous, discrete twitches in the opener muscle fibers. The action potentials recorded in RPO exhibit pronounced broadening at physiological rates of firing. LUQ cells that project to the renal pore cause it to close, and they antagonize the opening generated by an L10 burst. The pore closing caused by the LUQ cells is mediated in part by heterosynaptic inhibition of the L10 to RPO excitatory connection. The previously described central inhibitory connections from L10 to the LUQ cells ensure that these 2 classes of antagonists fire out of phase with each other. Our data, along with those from earlier studies demonstrating that L10 plays an important role in controlling the circulatory system, suggest that L10 and the LUQ cells modulate various aspects of renal function in Aplysia, including filtration and micturition.
    Type of Medium: Online Resource
    ISSN: 0270-6474 , 1529-2401
    Language: English
    Publisher: Society for Neuroscience
    Publication Date: 1989
    detail.hit.zdb_id: 1475274-8
    SSG: 12
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  • 4
    Online Resource
    Online Resource
    Society for Neuroscience ; 1991
    In:  The Journal of Neuroscience Vol. 11, No. 5 ( 1991-05-01), p. 1263-1274
    In: The Journal of Neuroscience, Society for Neuroscience, Vol. 11, No. 5 ( 1991-05-01), p. 1263-1274
    Abstract: The purpose of the study described in this and the following two companion papers was to determine the synaptic actions of neuron R15, an endogenously bursting neurosecretory cell in Aplysia, as a step toward determining its physiological function. The results described in this paper demonstrate that activity in R15 increases the frequency of bursting in the R25/L25 network that triggers respiratory pumping. This excitatory modulatory effect appears to be mediated by R15 alpha 1 peptide. R15 activates both strong and weak modes of respiratory pumping. In contrast, the two R20 cells, which are thought to use the neuropeptides SCPA and SCPB as transmitters, elicit only strong episodes of respiratory pumping. The synaptic actions of R15 also differ from those of the R20 cells in being longer lasting and in exhibiting profound desensitization. Chronic recording of R15 activity in vivo indicates that it does not burst spontaneously in the intact animal, so the synaptic actions of R15 are not chronically desensitized. The neuroendocrine bag cells, which initiate egg laying, had been shown by others to excite R15 and the R25/L25 network that triggers respiratory pumping. Our data indicate that the excitatory effects of the bag cells on the R25/L25 cells are mediated in part by R15.
    Type of Medium: Online Resource
    ISSN: 0270-6474 , 1529-2401
    Language: English
    Publisher: Society for Neuroscience
    Publication Date: 1991
    detail.hit.zdb_id: 1475274-8
    SSG: 12
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  • 5
    In: The Journal of Neuroscience, Society for Neuroscience, Vol. 20, No. 11 ( 2000-06-01), p. 4037-4049
    Abstract: We have used site-directed mutagenesis in conjunction with homologous recombination to generate two mouse lines carrying point mutations in the glycine binding site of the NMDAR1 subunit ( Grin1 ). Glycine concentration–response curves from acutely dissociated hippocampal neurons revealed a 5- and 86-fold reduction in receptor glycine affinity in mice carrying Grin1 D481N and Grin1 K483Q mutations, respectively, whereas receptor glutamate affinity remained unaffected. Homozygous mutant Grin1 D481N animals are viable and fertile and appear to develop normally. However, homozygous mutant Grin1 K483Q animals are significantly lighter at birth, do not feed, and die within a few days. No gross abnormalities in CNS anatomy were detected in either Grin1 D481N or Grin1 K483Q mice. Interestingly, in situ hybridization and Western blot analysis revealed changes in the expression levels of NMDA receptor subunits in Grin1 D481N mice relative to wild type that may represent a compensatory response to the reduction in receptor glycine affinity. Grin1 D481N mice exhibited deficits in hippocampal theta burst-induced long-term potentiation (LTP) and spatial learning and also a reduction in sensitivity to NMDA-induced seizures relative to wild-type controls, consistent with a reduced activation of NMDA receptors. Mutant mice exhibited normal prepulse inhibition but showed increased startle reactivity. Preliminary analysis indicated that the mice exhibit a decreased natural aversion to an exposed environment. The lethal phenotype of Grin1 K483Q animals confirms the critical role of NMDA receptor activation in neonatal survival. A milder reduction in receptor glycine affinity results in an impairment of LTP and spatial learning and alterations in anxiety-related behavior, providing further evidence for the role of NMDA receptor activation in these processes.
    Type of Medium: Online Resource
    ISSN: 0270-6474 , 1529-2401
    Language: English
    Publisher: Society for Neuroscience
    Publication Date: 2000
    detail.hit.zdb_id: 1475274-8
    SSG: 12
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  • 6
    Online Resource
    Online Resource
    Society for Neuroscience ; 2003
    In:  The Journal of Neuroscience Vol. 23, No. 8 ( 2003-04-15), p. 3243-3250
    In: The Journal of Neuroscience, Society for Neuroscience, Vol. 23, No. 8 ( 2003-04-15), p. 3243-3250
    Type of Medium: Online Resource
    ISSN: 0270-6474 , 1529-2401
    Language: English
    Publisher: Society for Neuroscience
    Publication Date: 2003
    detail.hit.zdb_id: 1475274-8
    SSG: 12
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  • 7
    Online Resource
    Online Resource
    Society for Neuroscience ; 1995
    In:  The Journal of Neuroscience Vol. 15, No. 10 ( 1995-10-01), p. 6720-6734
    In: The Journal of Neuroscience, Society for Neuroscience, Vol. 15, No. 10 ( 1995-10-01), p. 6720-6734
    Abstract: We studied frequency-dependent spike broadening in the two electrically coupled R20 neurons in the abdominal ganglion of Aplysia. The peptidergic R20 cells excite the R25/L25 interneurons (which trigger respiratory pumping) and inhibit the RB cells. When fired at 1–10 Hz, the duration of the falling phase of the action potential in R20 neurons increases 2-10 fold during a spike train. Spike broadening recorded from the somata of the R20 cells affected synaptic transmission to nearby follower cells. Chemically mediated synaptic output was reduced by approximately 50% when recorded trains of nonbroadened action potentials were used as command signals for a voltage-clamped R20 cell. Electrotonic EPSPs between the R20 cells, which normally facilitated by two- to fourfold during a high frequency spike train, showed no facilitation when spike broadening was prevented under voltage-clamp control. To examine the mechanism of frequency- dependent spike broadening, we applied two-electrode voltage-clamp and pharmacological techniques to the somata of R20 cells. Several voltage- gated ionic currents were isolated, including INa, a multicomponent ICa, and three K+ currents--a high threshold, fast transient A-type K+ current (IAdepol), a delayed rectifier K+ current (IK-V), and a Ca(2+)- sensitive K+ current (IK-Ca), made up of two components. The influences of different currents on spike broadening were determined by using the recorded train of gradually broadening action potentials as the command for the voltage clamp. We found the following. (1) IAdepol is the major outward current that contributes to repolarization of nonbroadened spikes. It undergoes pronounced cumulative inactivation that is a critical determinant of spike broadening. (2) Activity-dependent changes in IK-V, IK-Ca, and ICa have complex effects on the kinetics and extent of broadening. (3) The time integral of ICa during individual action potentials increases approximately threefold during spike broadening.
    Type of Medium: Online Resource
    ISSN: 0270-6474 , 1529-2401
    Language: English
    Publisher: Society for Neuroscience
    Publication Date: 1995
    detail.hit.zdb_id: 1475274-8
    SSG: 12
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  • 8
    Online Resource
    Online Resource
    Society for Neuroscience ; 1989
    In:  The Journal of Neuroscience Vol. 9, No. 9 ( 1989-09-01), p. 3058-3071
    In: The Journal of Neuroscience, Society for Neuroscience, Vol. 9, No. 9 ( 1989-09-01), p. 3058-3071
    Abstract: Respiratory pumping in Aplysia consists of transient, synchronous pumping actions of the gill, siphon, mantle shelf, and parapodia. This behavior has previously been shown to be driven by a network of coupled interneurons in the abdominal ganglion, the R25 and the L25 cells. We describe here a pair of electrically coupled cells, the R20 cells, which when active can initiate respiratory pumping or increase its spontaneous rate of occurrence. This action is mediated by a slow, long- lasting excitation of the endogenous burst mechanism of the cells in the R25/L25 network. The R20 cells, which are located in the abdominal ganglion, also make slow inhibitory connections to the RB cells and to the RG cells in that ganglion, and to the gill motoneurons in the branchial ganglion. The R20 cells are immunoreactive to SCPB, a molluscan neuropeptide. Biochemical purification studies demonstrate that each of the R20 cells synthesizes not only SCPB, but also SCPA, a closely related molecule known to be encoded by the same gene as SCPB. The R20 cells also synthesize in abundance several other low-molecular- weight, methionine-containing peptides. The excitatory actions of the R20 cells on the R25/L25 network are mimicked by SCPA and SCPB. However, the inhibitory actions of the R20 cells on the RB cells, the RG cells, and on the cells of the branchial ganglion are not mimicked by the SCPs. Thus, the data support the hypothesis that the R20 cells release SCPA and SCPB and at least one other unidentified transmitter.
    Type of Medium: Online Resource
    ISSN: 0270-6474 , 1529-2401
    Language: English
    Publisher: Society for Neuroscience
    Publication Date: 1989
    detail.hit.zdb_id: 1475274-8
    SSG: 12
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  • 9
    Online Resource
    Online Resource
    Society for Neuroscience ; 1991
    In:  The Journal of Neuroscience Vol. 11, No. 5 ( 1991-05-01), p. 1282-1290
    In: The Journal of Neuroscience, Society for Neuroscience, Vol. 11, No. 5 ( 1991-05-01), p. 1282-1290
    Abstract: The purpose of the study described in this and the preceding two companion papers was to determine the synaptic actions of neuron R15, an endogenously bursting neurosecretory cell in Aplysia, as a step toward determining its physiological function. The results described in this paper demonstrate that activity in R15 activates anterograde peristaltic movements in the segment of the large hermaphroditic duct through which eggs move during egg-laying behavior. This action is mimicked by R15 alpha 1 peptide, a putative transmitter of R15. The neuroendocrine bag cells, which initiate egg laying when they fire in a population burst, have been shown by others to excite R15. Our data suggest that R15 mediates excitatory effects of the bag cells on the large hermaphroditic duct. Taken with the results of the two companion papers, these data support the hypothesis that R15 integrates various aspects of egg-laying behavior. The desensitization of R15's postsynaptic actions may complement the long-lasting refractoriness of the bag cells described by others, with both effects contributing to the episodic nature of egg laying.
    Type of Medium: Online Resource
    ISSN: 0270-6474 , 1529-2401
    Language: English
    Publisher: Society for Neuroscience
    Publication Date: 1991
    detail.hit.zdb_id: 1475274-8
    SSG: 12
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  • 10
    Online Resource
    Online Resource
    Society for Neuroscience ; 1997
    In:  The Journal of Neuroscience Vol. 17, No. 7 ( 1997-04-01), p. 2445-2458
    In: The Journal of Neuroscience, Society for Neuroscience, Vol. 17, No. 7 ( 1997-04-01), p. 2445-2458
    Abstract: Projection neurons throughout the mature mammalian neocortex extend efferent axons either through the ventrolaterally positioned internal capsule to subcortical targets or through the dorsally located midline corpus callosum to the contralateral cortex. In rats, the internal capsule is pioneered on E14, but the corpus callosum is not pioneered until E17, even though these two types of projection neurons are generated at the same time. Here we use axonal markers to demonstrate that early cortical axon growth is directed toward the nascent internal capsule, which could account for the timing difference in the development of the two efferent pathways. This directed axon growth may be due to a chemoattractant and/or a chemorepellent secreted by intermediate targets of cortical efferent axons, the nascent internal capsule, or the medial wall of the dorsal telencephalon (MDT), respectively. To test for these soluble activities, explants of E15 rat neocortex and intermediate targets were cocultured in collagen gels. Cortical axon outgrowth was directed toward the internal capsule, but outgrowth was nondirected and suppressed when cocultured with MDT, suggesting that the internal capsule releases a chemoattractant for cortical axons, whereas the MDT releases a chemosuppressant. Because the chemoattractant Netrin-1 is expressed in the internal capsule, we cocultured cortical explants with E13 rat floor plate, which expresses Netrin-1, or with Netrin-1-transfected or control-transfected 293T cells. Cortical axon growth was directed toward both floor plate and Netrin-1-transfected 293T cells, as it had been toward the internal capsule, but not toward control-transfected 293T cells. These findings suggest that early events in cortical axon pathfinding may be controlled by a soluble activity which attracts initial axon growth toward the internal capsule and that this activity may be due to Netrin-1.
    Type of Medium: Online Resource
    ISSN: 0270-6474 , 1529-2401
    Language: English
    Publisher: Society for Neuroscience
    Publication Date: 1997
    detail.hit.zdb_id: 1475274-8
    SSG: 12
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