Presynaptic NMDA receptors cooperate with local action potentials to implement activity-dependent GABA release from the reciprocal olfactory bulb granule cell spine

Abstract

<jats:title>Abstract</jats:title><jats:p>In the rodent olfactory bulb the smooth dendrites of the principal glutamatergic mitral cells (MCs) form reciprocal dendrodendritic synapses with large spines on GABAergic granule cells (GC), where unitary release of glutamate can trigger postsynaptic local activation of voltage-gated Na<jats:sup>+</jats:sup>-channels (Na<jats:sub>v</jats:sub>s), i.e. a spine spike. Can such single MC inputs evoke reciprocal release? We find that unitary-like activation via two-photon uncaging of glutamate causes GC spines to release GABA both synchronously and asynchronously onto MC dendrites. This release indeed requires activation of Na<jats:sub>v</jats:sub>s and high-voltage-activated Ca<jats:sup>2+</jats:sup>-channels (HVACCs), but also of NMDA receptors (NMDAR). Simulations show temporally overlapping HVACC- and NMDAR-mediated Ca<jats:sup>2+</jats:sup>-currents during the spine spike, and ultrastructural data prove NMDAR presence within the GABAergic presynapse. The cooperative action of presynaptic NMDARs allows to implement synapse-specific, activity-dependent and non-topographical lateral inhibition and thus could provide an efficient solution to combinatorial percept synthesis in a sensory system with many receptor channels.</jats:p>

Local postsynaptic signalling on slow time scales in reciprocal olfactory bulb granule cell spines matches asynchronous release

“…It is often observed at repetitively stimulated synapses (Wen et al, 2013), which would also hold true for the classical DDI protocol, where voltage-clamped mitral cells are being depolarized for 20-50 ms and thus ongoing release of glutamate from mitral cells is likely to happen over dozens of ms and subsequent asynchronous release of GABA has been documented by many groups (see Introduction). Thus it is at first surprising that local, unitary-like stimulation of GC spines by TPU would suffice to elicit asynchronous release, which we have recently documented (Lage-Rupprecht et al, 2020). However, the temporal extent of this asynchronous release was shorter than in the classical DDI experiments (maximal extent of ~500 ms vs > 1 s) and therefore there might be additional mechanisms involved whenever GCs are activated more strongly.…”

“…Since on the other hand there is also a fast, synchronous component of reciprocal release (Halabisky et al, 2000;Lage-Rupprecht et al, 2020), GC spines are obviously capable of parallel processing on multiple time scales, a property that appears to be further refined with maturation. (C) Cumulative plots of (ΔF/F) TPU amplitudes in dendrite and spine pairs (highly significantly different: P < 0.001, Wilcoxon test), and of rise times and half durations t 1/2 of (ΔF/F) TPU within the spine heads (mostly not detectable in the dendrites).…”

“…The underlying asynchronous release is at least to a major extent due to processing in GCs, since asynchronous responses were demonstrated following flash photolysis of Ca 2+ in mitral cell lateral dendrites (Chen et al, 2000). Moreover, while the massive release of glutamate during the commonly used protocol for mitral cell excitation (20-50 ms depolarization in the voltage-clamp mode) might result in activation of slow release pathways not accessible to unitary transmission, we have shown recently, that local, unitary-like two-photon uncaging of glutamate (TPU) can still cause prolonged release of GABA within a time window of up to 500 ms post uncaging (Lage-Rupprecht et al, 2020).…”

Dendritic integration in olfactory bulb granule cells upon simultaneous multispine activation: Low thresholds for nonlocal spiking activity

“…Dendritic excitability in granule cells already sets in with single-spine activation, because a single mitral/tufted cell input can trigger a local Na + -spike within the spine [15]. This spine spike can cause reciprocal release of GABA via gating of high-voltage-activated Ca v s [16]. Activation of larger numbers of spines is observed to result in global low-threshold Ca 2+ -spikes, which are mediated by T-type Ca v s [17][18][19].…”

Mapping Functional Protein Neighborhoods in the Mouse Brain

“…Though the complex as a whole is undescribed, several members are known to interact, physically or functionally. For instance, N-cadherin and AMPA receptors interact at the cell surface (Nuriya and Huganir, 2006;Saglietti et al, 2007;Silverman et al, 2007) , AMPA receptors and Na v channels are both involved in postsynaptic depolarization (Bywalez et al, 2015;Lage-Rupprecht et al, 2019) , and EFR3b is a membrane scaffolding protein involved in the synthesis of PIP2, a lipid that regulates AMPA receptor activity (Seebohm et al, 2014) and trafficking (McCartney et al, 2014) . In flies, knock-down of the EFR3 homolog "rolling blackout" severely affects neuronal function, but primarily in the pre-synapse (Huang et al, 2004(Huang et al, , 2006 .…”