Glutamatergic Synaptic Inputs to Mouse Supraoptic Neurons in Calcium‐Free Medium in vitro/e1

Abstract

The effects of Ca2+-free perfusion medium on excitatory postsynaptic currents (EPSCs) and potentials (EPSPs) were studied by whole-cell recordings from neurons of the supraoptic nucleus (SON) in trimmed slice preparations of mouse hypothalamus. EPSCs evoked with either focal stimulation to the SON or perfusion of slices with high K+-medium, spontaneous EPSCs (sEPSCs) and miniature EPSCs (mEPSCs) recorded from neurons of the SON were blocked by the glutamate receptor antagonist kynurenic acid (1 mM). While EPSCs evoked by focal stimulation were abolished in the presence of Ca2+-free perfusion medium; sEPSCs and mEPSCs remained. Neither the frequency nor the amplitude of the sEPSCs and mEPSCs significantly changed during the application of Ca2+-free perfusion medium. Perfusion of slices with high K+-medium increased the mEPSC frequency compared with that recorded in normal Ca2+-containing perfusion medium. In contrast, mEPSC frequency did not change during perfusion with Ca2+-free high K+-medium. In current-clamp mode sEPSPs were observed during the perfusion with Ca2+-free medium. Some sEPSPs recorded in Ca2+-free medium were sufficiently large to evoke action potentials. These results imply that spontaneous glutamatergic synaptic inputs to the hypothalamic neurosecretory cells exist in Ca2+-free perfusion medium. Thus, the present study suggests that Ca2+-free medium does not always block the synaptic transmission in hypothalamic slice preparations.

Derivation and Expansion Using Only Small Molecules of Human Neural Progenitors for Neurodegenerative Disease Modeling

“…The average amplitude of miniature spontaneous postsynaptic currents was 21.18±2.47 pA (peak value; n = 7 cells, 360 events analyzed). Representative trace and offline analysis results are shown in Figure S8A– F. The offline analysis revealed that recorded miniature spontaneous postsynaptic currents have the amplitude or kinetic parameters comparable to those of human neurons [26], [27], [28]. These results demonstrate that smNPC-derived neurons have acquired the electrical properties of excitable neurons and developed synaptic contacts between neurons.…”

Astrocyte-Mediated Distributed Plasticity at Hypothalamic Glutamate Synapses

“…The advantage of this strategy is that by examining changes in the amplitude distributions of sEPSCs or mEPSCs it is possible to determine whether changes in synaptic efficacy occur at all synapses or whether these changes are limited to a subset of synapses (Turrigiano et al, 1998). Under control recording conditions sEPSCs and mEPSCs recorded from MNCs are equivalent; both arise from the activation of postsynaptic AMPA/KA receptors as they are completely blocked by DNQX (1 μM), and both represent the stochastic release of glutamate-filled vesicles as TTX has no effect on sEPSC frequency or amplitude (Gordon and Bains, 2003;Inenaga et al, 1998). Here, we refer to both sEPSC and mEPSCs as ‘quantal’ glutamate neurotransmission.…”

Retrograde Opioid Signaling Regulates Glutamatergic Transmission in the Hypothalamus

“…First, the -opioid receptor agonist, U69593, produces a large reduction in the frequency of both asynchronous release events and mEPSCs but has no effect on their mean amplitude. Second, mEPSCs in MNCs are independent of external Ca 2ϩ (Inenaga et al, 1998), and since the inhibition of mEPSC frequency persisted when all Ca 2ϩ was removed/buffered, this suggests that the target of inhibition is Figure 5. -Opioid-mediated inhibition does not require presynaptic potassium channels.…”

“…Finally, since the frequency of mEPSCs recorded in MNCs is independent of external Ca 2ϩ (Inenaga et al, 1998), we next tested whether the -opioid inhibition of mEPSC frequency persisted in the absence of Ca 2ϩ . To remove Ca 2ϩ , slices were incubated in 0 mM Ca 2ϩ /4 mM Mg 2ϩ , 100 M EGTA, and 50 M BAPTA-AM for 1-2 h. During whole-cell recordings, slices were perfused continually with 0 mM external Ca 2ϩ and 100 M EGTA.…”