From Fruit Flies to Barnacles, Histamine Is the Neurotransmitter of Arthropod Photoreceptors

Photoreceptor synapses of both vertebrate and invertebrate eyes are unconventional. These synapses release transmitter continuously yet never fatigue, and they transmit tiny presynaptic signals faithfully, often over a wide intensity range. Insight into these processes may now come with the identification of histamine as the neurotransmitter used by the photoreceptors of arthropod eyes. This minireview calls attention to peculiarities of arthropod photoreceptor synapses, reviews the evidence that histamine is the transmitter, and points out what we know of how histaminergic transmission is adapted to photoreceptor function