Figure 3.

Model of connectivity between wake-active TMN neurons and sleep-active VLPO neurons. During wakefulness, histamine release from TMN neurons acts at H3 receptors to suppress inhibitory GABAergic inputs, such as those arising from the VLPO. Histamine also acts at H1 receptors to increase inhibitory output from GABAergic interneurons to the VLPO, thereby producing a feedforward inhibition of VLPO neurons. During sleep, when TMN neurons are inactive, VLPO neurons are disinhibited and can inhibit the TMN.