Fig. 11.

Neuronal targets of histaminergic neurons. H₁ receptor and H₂ receptor are located on many neurons where they modulate the activity in several ways (see text). H₃ receptors are located on histaminergic neuron somata, dendrites, and axons to control firing, histamine synthesis, and release acting as autoreceptors. As heteroreceptors they control transmitter release from a wide variety of nonhistaminergic axons and in some cases inhibit the activity of nonhistaminergic neurons. Modified from Haas and Panula (2003).