Fig. (1). Schematic representations of the action of adrenoceptors that induce intrinsic plasticity.

a. β-adrenoceptor activation generally induces depolarization of postsynaptic neurons with an increase of input resistance. It reduces K⁺ currents (1) and facilitates Ih current via cAMP pathway (2) and the entry of Ca²⁺ (3).

b. α₁-adrenoceptors can also induce depolarization of neurons with an increase of input resistance. They reduce K⁺ currents (1) and act on Ca²⁺ entry via the activation of phosphoinositide turnover (2).

c. α₂-adrenoceptors generally induce hyperpolarization coupled to an increase or decrease of input resistance via blockade of Ih current (2) or opening of K⁺ channels (1) respectively. They also inhibit Ca²⁺ channels (3).

AC, adenylate cyclase; ATP, adenosine triphosphate; Ca²⁺, calcium; cAMP, cyclic adenosine monophosphate; DAG, diacylglyrerol; Ih, hyperpolarization-activated currents; IP3, inositol (1,4,5)-trisphosphate; K⁺, potassium; PIP2, phosphatidylinositol biphosphate; PLCβ, phospholipase Cβ.