Project 16

Retinal circuitry in marsupials

Primates, including humans, have trichromatic colour vision, based on three cone photoreceptor types. Once light is absorbed by the photoreceptors, signals are transferred to the brain via a highly organised retinal circuitry (fig.1). As such, cones connect with bipolar cells, which in turn synapse with ganglion cells, whose axons form the optic nerve.

Studies of retinal circuitry in primates have identified cone-type-specific connections to cells in the inner retina. For instance, different bipolar cells are selective for SWS or M/LWS cones. In addition, primates are the only placental mammals (eutherians) that possess midget bipolar cells, thought to be related to their trichromatic colour vision.

Until recently, primates were thought to be the only trichromatic mammals. However, the discovery of three spectrally distinct cone types in Australian marsupials has provided evidence for a trichromatic colour system that may be distinct from that of mammals.

The aim of this project is to conduct an immunohistochemical investigation of retinal circuitry in two species of marsupials with different phylogenies, the Australian fat-tailed dunnart and South American grey short-tailed opossum, and to compare cone connections with those described for placental mammals, including primates with trichromacy