Fig. 7: A model shows the mechanisms of Ca²⁺ transients affecting EPSPs during sleep and waking states.

Left: During sleep, whisker stimulation induces glutamate release from neurons and activates mGluR (metabotropic glutamate receptor) and phospholipase C to release inositol trisphosphate (IP3) and diacylglycerol (DAG), which possibly open transient receptor potential ion channels (TRP channels) to obtain Ca²⁺ influx into astrocytes. The Ca²⁺ increase would in turn increase intracellular Na⁺, activating the Na⁺ pump to take up K⁺ and hyperpolarizing the neuron. Right: During waking states, norepinephrine (NE) activates G protein-coupled receptors (Gq receptors) that prime astrocytes and synergistically works with metabotropic glutamate (mGLu) to activate Gq receptors to release even more IP₃, which induces Ca²⁺ release from the endoplasmic reticulum (ER) and gliotransmitter release (such as ATP, glutamate, or glutamine) and induces emotional arousal states. Note: Glu glutamine; NCX, the Na⁺/Ca²⁺ exchanger or the sodium-calcium exchanger.