Figure 3.

[Ca²⁺]_i oscillations occur by direct activation of mGluRs on neurons. (A) Neurons and glia can be readily distinguished in fluo-3-loaded slices. A biocytin-filled neuron in a P3 neocortical slice shown in comparison to a biocytin-filled glial cell from an older slice (P15) highlights the difference in size and morphological features between these cell types (main panels). The size difference can be appreciated on visualization of fluo-3-loaded neurons and glia (Insets). (B) Cells with neuronal morphology exhibit oscillatory [Ca²⁺]_i dynamics on direct activation of mGluRs when indirect stimulation of these cells is blocked with TTX (1 μM), DNQX (10 μM), and d-AP5 (100 μM). Given the exclusive expression of NMDA receptors by neurons in the neocortex, we subsequently confirmed neuronal identity by observing direct calcium responses of these same cells to NMDA (30 μM) in the presence of TTX (1 μM) and DNQX (10 μM).