Histamine H1 Receptor - Neurophysiology

Neurophysiology

Histamine H₁ receptors are activated by endogenous histamine, which is released by neurons that have their cell bodies in the tuberomammillary nucleus of the hypothalamus. The histaminergic neurons of the tuberomammillary nucleus become active during the 'wake' cycle, firing at approximately 2 Hz; during slow wave sleep, this firing rate drops to approximately 0.5 Hz. Finally, during REM sleep, histaminergic neurons stop firing altogether. It has been reported that histaminergic neurons have the most wake-selective firing pattern of all known neuronal types.

In the cortex, activation of H₁ receptors leads to inhibition of cell membrane potassium channels. This depolarizes the neurons and increases the resistance of the neuronal cell membrane, bringing the cell closer to its firing threshold and increasing the excitatory voltage produced by a given excitatory current. H₁ receptor antagonists, or antihistamines, produce drowsiness because they oppose this action, reducing neuronal excitation.