COX-2-Derived Prostaglandin E2 Produced by Pyramidal Neurons Contributes to Neurovascular Coupling in the Rodent Cerebral Cortex.

Vasodilatory prostaglandins play a key role in neurovascular coupling (NVC), the tight link between neuronal activity and local cerebral blood flow, but their precise identity, cellular origin and the receptors involved remain unclear. Here we show in rats that NMDA-induced vasodilation and hemodynamic responses evoked by whisker stimulation involve cyclooxygenase-2 (COX-2) activity and activation of the prostaglandin E2 (PgE2) receptors EP2 and EP4. Using liquid chromatography-electrospray ionization-tandem mass spectrometry, we demonstrate that PgE2 is released by NMDA in cortical slices. The characterization of PgE2 producing cells by immunohistochemistry and single-cell reverse transcriptase-PCR revealed that pyramidal cells and not astrocytes are the main cell type equipped for PgE2 synthesis, one third expressing COX-2 systematically associated with a PgE2 synthase. Consistent with their central role in NVC, in vivo optogenetic stimulation of pyramidal cells evoked COX-2-dependent hyperemic responses in mice. These observations identify PgE2 as the main prostaglandin mediating sensory-evoked NVC, pyramidal cells as their principal source and vasodilatory EP2 and EP4 receptors as their targets. SIGNIFICANCE STATEMENT: Brain function critically depends on a permanent spatiotemporal match between neuronal activity and blood supply, known as NVC. In the cerebral cortex, prostaglandins are major contributors to NVC. However, their biochemical identity remains elusive and their cellular origins are still under debate. Although astrocytes can induce vasodilations through the release of prostaglandins, the recruitment of this pathway during sensory stimulation is questioned. Using multidisciplinary approaches from single-cell reverse transcriptase-PCR, mass spectrometry, to ex vivo and in vivo pharmacology and optogenetics, we provide compelling evidence identifying PgE2 as the main prostaglandin in NVC, pyramidal neurons as their main cellular source and the vasodilatory EP2 and EP4 receptors as their main targets. These original findings will certainly change the current view of NVC.

Lactate is an energy substrate for rodent cortical neurons and enhances their firing activity.

Glucose is the mandatory fuel for the brain, yet the relative contribution of glucose and lactate for neuronal energy metabolism is unclear. We found that increased lactate, but not glucose concentration, enhances the spiking activity of neurons of the cerebral cortex. Enhanced spiking was dependent on ATP-sensitive potassium (KATP) channels formed with KCNJ11 and ABCC8 subunits, which we show are functionally expressed in most neocortical neuronal types. We also demonstrate the ability of cortical neurons to take-up and metabolize lactate. We further reveal that ATP is produced by cortical neurons largely via oxidative phosphorylation and only modestly by glycolysis. Our data demonstrate that in active neurons, lactate is preferred to glucose as an energy substrate, and that lactate metabolism shapes neuronal activity in the neocortex through KATP channels. Our results highlight the importance of metabolic crosstalk between neurons and astrocytes for brain function.

Tissue Plasminogen Activator Expression Is Restricted to Subsets of Excitatory Pyramidal Glutamatergic Neurons.

Although the extracellular serine protease tissue plasminogen activator (tPA) is involved in pathophysiological processes such as learning and memory, anxiety, epilepsy, stroke, and Alzheimer's disease, information about its regional, cellular, and subcellular distribution in vivo is lacking. In the present study, we observed, in healthy mice and rats, the presence of tPA in endothelial cells, oligodendrocytes, mastocytes, and ependymocytes, but not in pericytes, microglial cells, and astrocytes. Moreover, blockage of the axo-dendritic transport unmasked tPA expression in neurons of cortical and hippocampal areas. Interestingly, combined electrophysiological recordings, single-cell reverse transcription polymerase chain reaction (RT-PCR), and immunohistological analyses revealed that the presence of tPA is restricted to subsets of excitatory pyramidal glutamatergic neurons. We further evidenced that tPA is stored in synaptobrevin-2-positive glutamatergic synaptic vesicles. Based on all these data, we propose the existence of tPA-ergic neurons in the mature brain.