Histaminergic projections from the brain shape retinal output

Although usually treated as an autonomous neuronal tissue, the mammalian retina receives input from the brain in the form of retinopetal axons, primarily from histaminergic neurons in the tuberomamillary nucleus (TMN) of the hypothalamus. These axons are the sole source of histamine in the retina. We investigated how histamine affects retinal processing.

We carried out two-photon calcium imaging of neurons in the ganglion cell layer. Responses to a battery of visual stimuli were recorded in control solution and following histamine application (20 µM). We found that histamine modified the activity and light responses of distinct subtypes of retinal cells.

As histaminergic neurons were shown to be silent during sleep and active during wakefulness, our data suggest that visual processing in the retina may change with arousal state.