Neurochemical evidence for histamine acting as a transmitter in mammalian brain.

HA, besides its function in immune processes, is probably a neurotransmitter in mammalian brain. It is synthesized by a specific decarboxylase localized in the cytoplasm of nerve endings. It is stored in synaptic vesicles. Its release might depend on nerve-impulse flow; specific receptors to this amine have been evidenced both electrophysiologically and by the activation of cyclic AMP formation. Lesion studies indicate that histamine-containing neurons might constitute an ascending bundle arising from the brainstem and widely projecting into the whole telencephalon. This disposition, together with neuropharmacological data, suggests that histaminergic neurons, like the monoaminergic ones, might be involved in the control of arousal mechanisms, an idea consistent with the observed fluctuations of the endogenous amine content during the day-night cycle. On the other hand, the investigation of the effect of stress situations on the turnover of HA in brain leads to the conclusion that histaminergic neurons are specifically affected.