Glutamatergic Spontaneous Excitatory Postsynaptic Currents Research Articles

Voltage-clamp recordings of postsynaptic currents in substantia gelatinosa neurons in vitro and its applications to assess synaptic transmission

We describe here procedures for recording postsynaptic currents in substantia gelatinosa neurons on a transverse spinal cord slice preparation with an attached dorsal root. At the holding potential of −70 mV, glutamatergic spontaneous excitatory postsynaptic currents (EPSCs) and dorsal root (Aδ and/or C fiber) stimulation-evoked EPSCs could be observed. Whereas at the holding potential of 0 mV, spontaneous inhibitory postsynaptic currents (IPSCs) and dorsal root Aδ fiber stimulation-evoked IPSCs could be encountered. The methods make it possible to evaluate synaptic transmission by analysing the postsynaptic currents on dorsal root attached spinal cord slice.

Oxytocin enhances presynaptic and postsynaptic glutamatergic transmission between rat olfactory bulb neurones in culture

Although oxytocin (OT) within the olfactory bulb has been implicated in maternal behaviour and olfactory recognition, the cellular mechanisms of action remain to be clarified. We examined the effects of OT on glutamatergic spontaneous excitatory postsynaptic currents (sEPSCs) in cultured granule cells with the use of whole-cell patch-clamp recordings. OT reversibly increased both the frequency and amplitude of sEPSCs. The effects of OT on sEPSCs were blocked by the selective OT receptor antagonist desGly-NH 2 9,d (CH 2) 5-[Thy(Me) 2,Thr 4]-ornithine vasotocin. OT had no detectable effect, however, on high voltage-activated Ca 2+ currents in mitral/tufted cells, suggesting that OT acts presynaptically on step(s) in the release process downstream from calcium influx. OT augmented the membrane current in granule cells evoked by exogenous application of glutamate, indicating a postsynaptic site of action. These results indicate that OT facilitates sEPSCs in granule cells by both pre- and postsynaptic mechanisms.

Oxytocin enhances spontaneous glutamatergic excitatory postsynaptic currents between mitral and granule cells in rat olfactory bulb cultures

Oxytocin enhances spontaneous glutamatergic excitatory postsynaptic currents between mitral and granule cells in rat olfactory bulb cultures

Serotonin, via 5-HT 2A receptors, increases EPSCs in layer V pyramidal cells of prefrontal cortex by an asynchronous mode of glutamate release

Previously, serotonin (5-HT) was found to induce a marked increase in glutamatergic spontaneous excitatory postsynaptic currents (EPSCs) in apical dendrites of layer V pyramidal cells of prefrontal cortex; this effect was mediated by 5-HT 2A receptors, a proposed site of action of hallucinogenic and atypical antipsychotic drugs. Unexpectedly, although the effect of 5-HT was Ca 2+-dependent and tetrodotoxin-sensitive, it did not appear to involve the activation of excitatory afferent impulse flow. This paradox prompted us to investigate (in rat brain slices) whether 5-HT was acting through an atypical mode of excitatory transmitter release. We found that the frequency of 5-HT-induced spontaneous EPSCs was fully supported by Sr 2+ in the absence of added Ca 2+, implicating the mechanism of asynchronous transmitter release which has been linked to the high-affinity Ca 2+-sensor synaptotagmin III. Although the early, synchronous component of electrically evoked EPSCs was reduced while 5-HT was being applied, late, nonsynchronous components were enhanced during 5-HT washout and also by the 5-HT 2 partial agonist 1-(2,5-dimethoxy-4-iodophenyl-2-aminopropane (DOI); the effect of DOI was blocked by a selective 5-HT 2A antagonist (MDL 100,907). This late, nonsynchronous component was distinct from conventional polysynaptic EPSCs evoked in the presence of the GABA A antagonist bicuculline, but resembled asynchronous glutamatergic excitatory postsynaptic potentials (EPSPs) evoked in the presence of Sr 2+. An enhancement of asynchronous EPSCs by a specific neurotransmitter receptor has not been reported previously. The possible role of excessive asynchronous transmission in the cerebral cortex in mediating the hallucinogenic effects of 5-HT 2A agonists such as DOI is discussed.

Chemokines regulate hippocampal neuronal signaling and gp120 neurotoxicity.

The HIV-1 envelope protein gp120 induces apoptosis in hippocampal neurons. Because chemokine receptors act as cellular receptors for HIV-1, we examined rat hippocampal neurons for the presence of functional chemokine receptors. Fura-2-based Ca imaging showed that numerous chemokines, including SDF-1alpha, RANTES, and fractalkine, affect neuronal Ca signaling, suggesting that hippocampal neurons possess a wide variety of chemokine receptors. Chemokines also blocked the frequency of spontaneous glutamatergic excitatory postsynaptic currents recorded from these neurons and reduced voltage-dependent Ca currents in the same neurons. Reverse transcription-PCR demonstrated the expression of CCR1, CCR4, CCR5, CCR9/10, CXCR2, CXCR4, and CX3CR1, as well as the chemokine fractalkine in these neurons. Both fractalkine and macrophage-derived chemokine (MDC) produced a time-dependent activation of extracellular response kinases (ERK)-1/2, whereas no activation of c-JUN NH2-terminal protein kinase (JNK)/stress-activated protein kinase, or p38 was evident. Furthermore, these two chemokines, as well as SDF-1alpha, activated the Ca- and cAMP-dependent transcription factor CREB. Several chemokines were able also to block gp120-induced apoptosis of hippocampal neurons, both in the presence and absence of the glial feeder layer. These data suggest that chemokine receptors may directly mediate gp120 neurotoxicity.

Capsaicin facilitates excitatory but not inhibitory synaptic transmission in substantia gelatinosa of the rat spinal cord

Actions of capsaicin were examined on synaptic transmissions in the substantia gelatinosa (SG) of adult rat spinal cord slices using the whole-cell patch-recording technique. Bath-applied capsaicin at a concentration of 2 μM activated a slow inward current (having an amplitude of 33 pA at −70 mV), which was accompanied by an increase in the frequency of glutamatergic spontaneous excitatory postsynaptic currents (sEPSCs; by 234%); these actions were blocked by a capsaicin-receptor antagonist, capsazepine (10 μM). The capsaicin-induced increase in sEPSC frequency was resistant to tetrodotoxin (0.5–1 μM). On the other hand, capsaicin (2 μM) did not affect either glycine- or γ-aminobutyric acid-mediated spontaneous synaptic transmission. The results indicate that capsaicin enhances excitatory but not inhibitory synaptic transmission, possibly through a direct action on primary afferent terminals in the SG. As the SG has been thought to participate in nociceptive pathway, it is suggested that such a presynaptic action of capsaicin contributes to nociceptive transmissions.