Jin-Hui Wang

Calcium–calmodulin signalling pathway up-regulates glutamatergic synaptic function in non-pyramidal, fast spiking rat hippocampal CA1 neurons

The role of Ca2+‐calmodulin (CaM) signalling cascades in modulating glutamatergic synaptic transmission on CA1 non‐pyramidal fast‐spiking neurons was investigated using whole‐cell recording and perfusion in rat hippocampal slices. Paired stimuli (PS), consisting of postsynaptic depolarization to 0 mV and presynaptic stimulation at 1 Hz for 30 s, enhanced excitatory postsynaptic currents (EPSCs) on non‐pyramidal neurons in the stratum pyramidale (SP). The potentiation was reduced by the extracellular application of d‐amino‐5‐phosphonovaleric acid (DAP‐5, 40 μm), and blocked by the postsynaptic perfusion of 1,2‐bis(2‐aminophenoxy)‐ethane‐N,N,N′,N′‐tetraacetic acid (BAPTA, 10 mm), a CaM‐binding peptide (100 μm) or CaMKII (281–301) (an autoinhibitory peptide of CaM‐dependent protein kinases, 100 μm). The application of adenophostin, an agonist of inositol trisphosphate receptors (IP3Rs) that evokes Ca2+ release, into SP non‐pyramidal neurons via the patch pipette (1 μm) enhanced EPSCs and occluded PS‐induced synaptic potentiation. The co‐application of BAPTA (10 mm) with adenophostin blocked synaptic potentiation. In addition, Ca2+‐CaM (40:10 μm) induced synaptic potentiation, which occluded PS‐induced potentiation and was attenuated by introducing CaMKII (281–301) (100 μm). EPSCs were sensitive to an antagonist of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid receptor (AMPAR). Application of Ca2+‐CaM into SP non‐pyramidal neurons induced the emergence of AMPAR‐mediated EPSCs that were not evoked by low stimulus intensity before perfusion. Ca2+‐CaM also increased the amplitude and frequency of spontaneous EPSCs. A scavenger of nitric oxide, carboxy‐PTIO (30 μm in slice‐perfusion solution), did not affect these increases in sEPSCs. The magnitude of PS‐, adenophostin‐ or Ca2+‐CaM‐induced synaptic potentiation in SP non‐pyramidal neurons increased during postnatal development. These results indicate that Ca2+‐CaM signalling pathways in CA1 SP non‐pyramidal neurons up‐regulate glutamatergic synaptic transmission probably through the conversion of inactive‐to‐active synapses.

Short-term cerebral ischemia causes the dysfunction of interneurons and more excitation of pyramidal neurons in rats.

Neural excitotoxicity is a typical factor in the early phase pathogenesis of cerebral ischemia. Its cellular and molecular mechanisms are still unclear and clinical approaches are still lacking of promising therapies. We have examined the vulnerability of cortical neurons to short-term ischemia in rats by simultaneously analyzing the activities of inhibitory and principal neurons in brain slices. Our results demonstrate that short-term in vitro ischemia permanently impairs the excitability of inhibitory neurons (IN) and synaptic transmission mediated by gamma-aminobutyric acid (GABA). However, principal neurons appear to be more exciting during the reperfusion. The vulnerability of inhibitory neurons to ischemia acquires during postnatal development. Our findings signify a major contribution of the ischemic dysfunction of inhibitory neurons to neural excitotoxicity as well as a strategy to prevent the progress of ischemic stroke by protecting inhibitory neurons.

Cellular and molecular bases of memory: synaptic and neuronal plasticity.

Discoveries made during the past decade have greatly improved our understanding of how the nervous system functions. This review article examines the relation between memory and the cellular mechanisms of neuronal and synaptic plasticity in the central nervous system. Evidence indicating that activity-dependent short- and long-term changes in strength of synaptic transmission are important for memory processes is examined. Focus is placed on one model of synaptic plasticity called long-term potentiation, and its similarities with memory processes are illustrated. Recent studies show that the regulation of synaptic strength is bidirectional (e.g., synaptic potentiation or depression). Mechanisms involving intracellular signaling pathways that regulate synaptic strength are described, and the specific roles of calcium, protein kinases, protein phosphatases, and retrograde messengers are emphasized. Evidence suggests that changes in synaptic ultrastructure, dendritic ultrastructure, and neuronal gene expression may also contribute to mechanisms of synaptic plasticity. Also discussed are recent findings about postsynaptic mechanisms that regulate short-term synaptic facilitation and neuronal burst-pattern activity, as well as evidence about the subcellular location (presynaptic or postsynaptic) of mechanisms involved in long-term synaptic plasticity.

Essential role of axonal VGSC inactivation in time-dependent deceleration and unreliability of spike propagation at cerebellar Purkinje cells

BackgroundThe output of the neuronal digital spikes is fulfilled by axonal propagation and synaptic transmission to influence postsynaptic cells. Similar to synaptic transmission, spike propagation on the axon is not secure, especially in cerebellar Purkinje cells whose spiking rate is high. The characteristics, mechanisms and physiological impacts of propagation deceleration and infidelity remain elusive. The spike propagation is presumably initiated by local currents that raise membrane potential to the threshold of activating voltage-gated sodium channels (VGSC).ResultsWe have investigated the natures of spike propagation and the role of VGSCs in this process by recording spikes simultaneously on the somata and axonal terminals of Purkinje cells in cerebellar slices. The velocity and fidelity of spike propagation decreased during long-lasting spikes, to which the velocity change was more sensitive than fidelity change. These time-dependent deceleration and infidelity of spike propagation were improved by facilitating axonal VGSC reactivation, and worsen by intensifying VGSC inactivation.ConclusionOur studies indicate that the functional status of axonal VGSCs is essential to influencing the velocity and fidelity of spike propagation.

Homeostasis established by coordination of subcellular compartment plasticity improves spike encoding

Homeostasis in cells maintains their survival and functions. The plasticity at neurons and synapses may destabilize their signal encoding. The rapid recovery of cellular homeostasis is needed to secure the precise and reliable encoding of neural signals necessary for well-organized behaviors. We report a homeostatic process that is rapidly established through Ca2+-induced coordination of functional plasticity among subcellular compartments. An elevation of cytoplasmic Ca2+ levels raises the threshold potentials and refractory periods of somatic spikes, and strengthens the signal transmission at glutamatergic and GABAergic synapses, in which synaptic potentiation shortens refractory periods and lowers threshold potentials. Ca2+ signals also induce an inverse change of membrane excitability at the soma versus the axon. The integrative effect of Ca2+-induced plasticity among the subcellular compartments is homeostatic in nature, because it stabilizes neuronal activities and improves spike timing precision. Our study of neuronal homeostasis that is fulfilled by rapidly coordinating subcellular compartments to improve neuronal encoding sheds light on exploring homeostatic mechanisms in other cell types.

Inhibition of phosphatase 2b prevents expression of hippocampal long-term potentiation

The induction of long-term potentiation (LTP) in the CA1 region of the hippocampus is mediated by N-methyl-D-aspartate (NMDA) receptor-coupled calcium influx. In addition, calcium/calmodulin (CaM) has been demonstrated to play an essential role in the induction process. In the present study, a possible role of CaM-dependent phosphatase (phosphatase 2B, PP-2B, calcineurin) in the LTP process was examined by intracellular recordings in apical dendrites of CA1 pyramidal cells of adult guinea-pigs. In dendrites in which cypermethrin, a potent and specific inhibitor of PP-2B (IC50 40 pM), was intracellularly applied, tetanization generated only short-term increases (15-30 min) of excitatory responses. In the intracellular presence of allethrin, a weak inhibitor of PP-2B, LTP expression was not affected. These findings demonstrate that activation of PP-2B is a necessary condition for the expression of LTP in CA1 pyramidal cell dendrites.

Interleukin-2 gene therapy of chronic neuropathic pain

Previous research has revealed an antinociceptive (analgesic) effect of interleukin-2 (IL-2) in central and peripheral nervous systems. Unfortunately IL-2 is very short-lived in vivo, so it is impractical to apply IL-2 for analgesia in clinic. This study was performed to evaluate the effect of intrathecal delivery of human IL-2 gene on rat chronic neuropathic pain induced by chronic constriction injury of the sciatic nerve. Human IL-2 cDNA was cloned into pcDNA3 containing a cytomegalovirus promoter. The paw-withdrawal latency induced by radiant heat was used to measure the pain threshold. The results showed that recombinant human IL-2 had a dose-dependent antinociceptive effect, but that this only lasted for 10-25 min. The pcDNA3-IL-2 or pcDNA3-IL-2/lipofectamine complex in contrast also showed dose-dependent antinociceptive effects, but these reached a peak at day 2-3 and were maintained for up to 6 days. Liposome-mediated pcDNA3-IL-2 produced a more powerful antinociceptive effect than pcDNA3-IL-2 alone. The paw-withdrawal latencies were not affected by control treatments such as vehicle, lipofectamine, pcDNA3, or pcDNA3-lipofectamine. In the experimental groups, human IL-2 mRNA was detected by reverse transcription-polymerase chain reaction in the lumbar spinal pia mater, dorsal root ganglion, sciatic nerve, and spinal dorsal horn, but not in gastrocnemius muscle. The expressed IL-2 profile detected by western blot coincided with its mRNA profile except it was present in the spinal dorsal horn at a higher level. Furthermore, human IL-2 assayed by enzyme-linked immunosorbent assay in cerebrospinal fluid could still be detected at day 6, but lower than day 3. The antinociceptive effect of pcDNA3-IL-2 could be blocked by naloxone, showing some relationship of the antinociceptive effect produced by IL-2 gene to the opioid receptors. It is hoped that the new delivery approach of a single intrathecal injection of the IL-2 gene described here may be of some practical use as a part of a gene therapy for treating neuropathic pain.

Upregulation of Barrel GABAergic Neurons Is Associated with Cross-Modal Plasticity in Olfactory Deficit

BACKGROUND Loss of a sensory function is often followed by the hypersensitivity of other modalities in mammals, which secures them well-awareness to environmental changes. Cellular and molecular mechanisms underlying cross-modal sensory plasticity remain to be documented. METHODOLOGY/PRINCIPAL FINDINGS Multidisciplinary approaches, such as electrophysiology, behavioral task and immunohistochemistry, were used to examine the involvement of specific types of neurons in cross-modal plasticity. We have established a mouse model that olfactory deficit leads to a whisking upregulation, and studied how GABAergic neurons are involved in this cross-modal plasticity. In the meantime of inducing whisker tactile hypersensitivity, the olfactory injury recruits more GABAergic neurons and their fine processes in the barrel cortex, as well as upregulates their capacity of encoding action potentials. The hyperpolarization driven by inhibitory inputs strengthens the encoding ability of their target cells. CONCLUSION/SIGNIFICANCE The upregulation of GABAergic neurons and the functional enhancement of neuronal networks may play an important role in cross-modal sensory plasticity. This finding provides the clues for developing therapeutic approaches to help sensory recovery and substitution.

Gain and fidelity of transmission patterns at cortical excitatory unitary synapses improve spike encoding

Neuronal spike encoding and synaptic transmission in the brain need be precise and reliable for well-organized behavior and cognition. Little is known about how a unitary synapse reliably transmits presynaptic sequential spikes and how multiple unitary synapses precisely drive their postsynaptic neurons to encode spikes. To address these questions, we investigated the dynamics of glutamatergic unitary synapses as well as their role in driving the encoding of cortical fast-spiking neurons. Synaptic transmission patterns randomly fluctuate among facilitation, depression and parallel over time. The postsynaptic calmodulin-signaling pathway enhances initial responses and converts this fluctuation to a synaptic depression. We integrated current pulses mathematically based on synaptic plasticity and found that they improve spike capacity and timing precision by shortening the spike refractory period at postsynaptic neurons. Our results indicate that the gain and fidelity of synaptic patterns enable reliable transmission of presynaptic signals by the synapse and precise encoding of spikes by postsynaptic neurons. These reproducible neural codes may be involved in controlling well-organized behavior.

Physiological synaptic signals initiate sequential spikes at soma of cortical pyramidal neurons.

The neurons in the brain produce sequential spikes as the digital codes whose various patterns manage well-organized cognitions and behaviors. A source for the physiologically integrated synaptic signals to initiate digital spikes remains unknown, which we studied at pyramidal neurons of cortical slices. In dual recordings from the soma vs. axon, the signals recorded in vivo induce somatic spikes with higher capacity, which is associated with lower somatic thresholds and shorter refractory periods mediated by voltage-gated sodium channels. The introduction of these parameters from the soma and axon into NEURON model simulates sequential spikes being somatic in origin. Physiological signals integrated from synaptic inputs primarily trigger the soma to encode neuronal digital spikes.