Glycolysis selectively shapes the presynaptic action potential waveform

Abstract

Mitochondria are major suppliers of cellular energy in neurons; however, utilization of energy from glycolysis vs. mitochondrial oxidative phosphorylation (OxPhos) in the presynaptic compartment during neurotransmission is largely unknown. Using presynaptic and postsynaptic recordings from the mouse calyx of Held, we examined the effect of acute selective pharmacological inhibition of glycolysis or mitochondrial OxPhos on multiple mechanisms regulating presynaptic function. Inhibition of glycolysis via glucose depletion and iodoacetic acid (1 mM) treatment, but not mitochondrial OxPhos, rapidly altered transmission, resulting in highly variable, oscillating responses. At reduced temperature, this same treatment attenuated synaptic transmission because of a smaller and broader presynaptic action potential (AP) waveform. We show via experimental manipulation and ion channel modeling that the altered AP waveform results in smaller Ca influx, resulting in attenuated excitatory postsynaptic currents (EPSCs). In contrast, inhibition of mitochondria-derived ATP production via extracellular pyruvate depletion and bath-applied oligomycin (1 μM) had no significant effect on Ca influx and did not alter the AP waveform within the same time frame (up to 30 min), and the resultant EPSC remained unaffected. Glycolysis, but not mitochondrial OxPhos, is thus required to maintain basal synaptic transmission at the presynaptic terminal. We propose that glycolytic enzymes are closely apposed to ATP-dependent ion pumps on the presynaptic membrane. Our results indicate a novel mechanism for the effect of hypoglycemia on neurotransmission. Attenuated transmission likely results from a single presynaptic mechanism at reduced temperature: a slower, smaller AP, before and independent of any effect on synaptic vesicle release or receptor activity.

Chronic inhibition of brain glycolysis initiates epileptogenesis

“…For instance, Sada et al showed that inhibition of LDH resulted in a 70% reduction in excitatory postsynaptic currents, most likely due to a decrease in synaptic transmitter release (as the postsynaptic target cells were recorded in whole‐cell configuration with 4 mM ATP in the intracellular solution, preventing any energy shortage from LDH blockade). Presynaptic machinery presumably relies mostly on glycolysis‐provided ATP (Lujan et al, ), and therefore the reported LDH effect was most likely underlain by presynaptic glycolysis inhibition. Thus, similar to the acute effects of 2‐DG, the initial decrease in network activity induced by energy deprivation can cause a short‐term antiseizure effect, although an opposite proseizure effect cannot be excluded (see Gasior et al, ).…”

Presynaptic GCaMP expression decreases vesicle release probability at the calyx of Held

“…Adeno‐associated virus encoding the GECI GCaMP6m (T. W. Chen et al, ) was procured from the Penn Vector Core in the Gene Therapy Program of the University of Pennsylvania (#AV‐1‐PV2823, 1.78 × 10 13 GC/mL, in sterile PBS). This virus was injected into the ventral cochlear nucleus of neonatal (P1) mice, using procedures previously described (Chen, Cooper, Kalla, Varoqueaux, & Young, ; Lujan, Kushmerick, Das Banerjee, Dagda, & Renden, ; Pilpel, Landeck, Klugmann, Seeburg, & Schwarz, ). Briefly, mice were anesthetized via hypothermia on ice for 5 min until unresponsive, then fixed on a stereotaxic surgery platform.…”

“…Transverse brainstem slices containing the medial nucleus of the trapezoid body (MNTB) were cut at 200 µm using a vibratome (VT 1200S, Leica Microsystems, Germany), as previously described (Lujan et al, ; Singh, Miura, & Renden, ). The slicing solution contained (in mM): 85 NaCl, 2.5 KCl, 25 glucose, 25 NaHCO 3 , 1.25 NaH 2 PO 4 , 75 sucrose, 0.5 CaCl 2 , 7 MgCl 2 , 3 myo‐inositol, 2 Na‐pyruvate, and 0.4 ascorbic acid; the pH was 7.4 when continuously bubbled with carbogen gas (95% O 2 –5% CO 2 ).…”

Lack of appropriate stoichiometry: Strong evidence against an energetically important astrocyte–neuron lactate shuttle in brain

“…Cox, Bachelard, and colleagues (see references cited above), Okada and Lipton (), and, more recently, Ivanov et al () concluded that glycolysis plays a key role in neuronal activity in brain slices, as observed by Bak and colleagues () in cultured neurons. Examples of preferred functions for glycolysis in neurons include vesicular glutamate loading (Ikemoto et al, ; Ueda and Ikemoto, ), calcium clearance (Ivannikov et al, ), and presynaptic action potential waveform (Lujan et al, ).…”