Gackiere, F. | bioRxiv Science

bioRxiv2023

D--hydroxybutyrate stabilizes the hippocampal CA3-CA1 circuit during acute insulin resistance.

1.The brain primarily relies on glycolysis for mitochondrial respiration but switches to alternative fuels such as ketone bodies (KBs) when less glucose is available. Neuronal KB uptake, which does not rely on glucose transporter 4 (GLUT4) or insulin, has shown promising clinical applicability in alleviating the neurological and cognitive effects of disorders with hypometabolic components. However, the specific mechanisms by which such interventions affect neuronal functions are poorly understood. In this study, we pharmacologically blocked GLUT4 to investigate the effects of exogenous KB D--hydroxybutyrate (D-Hb) on mouse brain metabolism during acute insulin resistance (AIR). We found that both AIR and D-Hb had distinct impacts across neuronal compartments: AIR decreased synaptic activity and long-term potentiation (LTP) and impaired axonal conduction, synchronization, and action potential (AP) properties, while D-Hb rescued neuronal functions associated with axonal conduction, synchronization, and LTP. 2. Significance statementThis study investigates the impact of acute insulin resistance on the functionality of the hippocampal circuit and the potential protective effects of ketone body supplementation. By inhibiting GLUT4 receptors to induce acute insulin resistance, we reveal several detrimental changes caused by impaired neuronal glucose uptake. These changes include impairments in synaptic activity, axonal conduction, and neuronal firing properties. The study further examines the distinctive effects of acute insulin resistance and the rescue agent D-{beta}Hb on synaptic activity, long-term potentiation, axonal conduction, synchronization, and neuronal firing. By shedding light on neuronal responses during insulin resistance, this investigation advances our understanding of neurological disorders associated with hypometabolism and highlights the potential therapeutic value of D-{beta}Hb.

neuroscience↗

bioRxiv2017

Variability of quantal NMDA to AMPA current ratio in nucleus tractus solitarii neurons

The ratio between AMPA and NMDA receptors is a key factor governing integrative and plastic properties of excitatory glutamatergic synapses. To determine whether the respective proportions of AMPA and NMDA receptors are similar or vary across a neuron's synapse, we analyzed the variability of NMDA and AMPA currents in quantal responses recorded from neurons located in the nucleus tractus solitarii. We found that the average NMDA to AMPA current ratio strongly differed between recorded neurons and that most of the intra-neuronal current ratio variability was attributable to fluctuations in NMDA current. We next performed computer simulations with a Monte Carlo model of a glutamatergic synapse to estimate the part of AMPA and NMDA currents fluctuations induced by stochastic factors. We found that NMDA current variability mainly resulted from strong channel noise with few influence of release variations. On the contrary, partly because of the presence of subconductance states, AMPA receptor channel noise was low and AMPA current fluctuations tightly reflected changes in the amount of glutamate released. We next showed that these two factors, channel noise and fluctuations in glutamate release, were sufficient to explain the observed variability of the NMDA to AMPA current ratio in quantal events recorded from the same neuron. We therefore concluded that the proportion of AMPA and NMDA receptors was similar, or roughly similar, across synapses onto the same target cell.

neuroscience↗