ganglion cells, melanopsin, is excited by light mainly in the blue portion of the visible spectrum (absorption peaks at ~480 nanometers). The phototransduction mechanism in these cells is not fully understood, but seems likely to resemble that in invertebrate rhabdomeric photoreceptors. In addition to responding directly to light, these cells may receive excitatory and inhibitory influences from rods and cones by way of synaptic connections in the retina. The axons from these ganglia innervate regions of the brain related to object recognition, including the superior colliculus and dorsal lateral geniculate nucleus. Structure ipRGC receptor These photoreceptor cells project both throughout the retina and into the brain. They contain the photopigment melanopsin in varying quantities along the cell membrane, including on the axons up to the optic disc, the soma, and dendrites of the cell. ipRGCs contain membrane receptors for the neurotransmitters glutamate, glycine, and GABA. Photosensitive ganglion cells respond to light by depolarizing, thus increasing the rate at which they fire nerve impulses, which is opposite to that of other photoreceptor cells, which hyperpolarize in response to light. Results of studies in mice suggest that the axons of ipRGCs are unmyelinated. Melanopsin Unlike other photoreceptor pigments, melanopsin has the ability to act as both the excitable photopigment and as a photoisomerase. Unlike the visual opsins in rod cells and cone cells, which rely on the standard visual cycles for recharging all-trans-retinal back into the photosensitive 11-cis-retinal, melanopsin is able to isomerize all-trans-retinal into 11-cis-retinal itself when stimulated with another photon. An ipRGC therefore does not rely on Müller cells and/or retinal pigment epithelium cells for this conversion. The two isoforms of melanopsin differ in their spectral sensitivity, for the 11-cis-retinal isoform is more responsive to shorter wavelengths of light, while the all-trans isoform is more responsive to longer wavelengths of light. Synaptic inputs and outputs Inputs ipRGCs are both pre- and postsynaptic to dopaminergic amacrine cells (DA cells) via reciprocal synapses, with ipRGCs sending excitatory signals to the DA cells, and the DA cells sending inhibitory signals to the ipRGCs. These inhibitory signals are mediated through GABA, which is co-released from the DA cells along with dopamine. Dopamine has functions in the light-adaptation process by up-regulating melanopsin transcription in ipRGCs and thus increasing the photoreceptor's sensitivity. In parallel with the DA amacrine cell inhibition, somatostatin-releasing amacrine cells, themselves inhibited by DA amacrine cells, inhibit ipRGCs. Other synaptic inputs to ipRGC