Figure 1. Catecholamine signaling in macrophage function.

A. Catecholamines are recognized by α and β-adrenergic receptors (1). Signaling through α-adrenergic receptors is pro-inflammatory and promotes LPS-induced gene expression whereas β-adrenergic receptor signaling inhibits this and induces expression of anti-inflammatory cytokines (2). Cold temperature induces macrophage synthesis of catecholamines which act to increase white to beige adipose tissue conversion and energy expenditure (3). B. Sciatic and vagus nerve stimulation promotes dopamine synthesis (1). Dopamine receptor signaling enhances GPCR activity leading to increased viral entry and replication (2). Dopamine signaling also inhibits pro-inflammatory cytokine production (3).