(Brain) Food for Thought: How does Energetic Availability Change in Response to a Decrease in Synaptic Strength?

Synaptic plasticity, the process of altering the strength of neuronal connections by changing activity at the junction between two neurons, is essential for learning and memory formation but may be metabolically taxing. While... [ view full abstract ]

Synaptic plasticity, the process of altering the strength of neuronal connections by changing activity at the junction between two neurons, is essential for learning and memory formation but may be metabolically taxing. While glucose is undeniably the main source of energy in the brain, recent research implicates lactate as the preferred metabolic substrate for neurons during periods of increased energy consumption. We investigated how the availability of each substrate changes in response to reductions in synaptic strength. We recorded extracellular glucose and lactate concentrations and electroencephalographic (EEG) activity in the motor cortex of freely behaving rats in response to local reduction in synaptic strength induced by the drug ZIP. We hypothesize lactate, but not glucose, concentrations will decrease following ZIP injection due to a resultant decrease in synaptic potentiation and, correspondingly, neuronal energetic demands. Preliminary results support this hypothesis with lactate, but not glucose, concentrations changing in response to ZIP, suggesting that while glucose availability isn’t strongly affected by local synaptic strength, the pathway of glucose consumption may be. Our findings highlight the constraints of brain metabolism on processes central to learning and memory and may additionally provide a foundation for understanding common etiologies of neurological disorders.