Type: Imidazole amine
Receptors: H1–H4 (metabotropic)
Region-specific functions:

• Tuberomammillary nucleus (origin): Only histaminergic neurons

• Cortex: Promotes wakefulness, arousal

• Hypothalamus: Thermoregulation, appetite

• Basal forebrain: Modulates sleep-wake cycle

• Thalamus: Gates sensory input during arousal

• Antihistamines (H1 blockers) → drowsiness