Abstract
Purpose: :
Immediately after birth and until eye opening (P14), the juvenile rodent retina undergoes morphological and functional maturation. During early postnatal development, acetylcholine and glutamate, released by one or more populations of retinal progenitor cells, trigger short bursts of action potentials that propagate across the retina. In wildtype mice, between P4 and P7, phase II cholinergic waves dominate retinal waves. Around P7 cholinergic waves disappear and phase III glutamatergic waves dominate. Phase III waves disappear shortly before eye opening around P13. Earlier reports show that melanopsin containing intrinsically photosensitive retinal ganglion cells (ipRGCs) cause an increase in the number of action potentials in each burst. We show here, in addition to previous findings, light stimulation of melanopsin containing ipRGCs control the temporal disappearance of phase II retinal waves and also the time when rod and cone mediated light responses appear developmentally.
Methods: :
Multi-electrode array extracellular recording was used to record spontaneous activity and retinal waves from the ganglion cell layer of wildtype and melanopsin knockout mice retina, in dark, light and in presence of various pharmacological agonists / antagonists.
Results: :
In melanopsin knockout (mko) mice raised in cyclic light/dark condition, the phase III wave appear at least 1 day later compared to wildtype. Furthermore, in mko mice, the phase II cholinergic waves remain active even after the phase III waves are initiated. In dark reared animals the appearance of rod/cone mediated fast ON/OFF responses is delayed in wildtype. The appearance of the short latency ON/OFF responses is delayed in cyclic light/dark reared mko mice as well.
Conclusions: :
We conclude that light stimulation of ipRGCs under cyclic light/dark conditions accelerates the disappearance of phase II retinal waves and the appearance of phase III retinal waves. Furthermore, light stimulation of ipRGCs under cyclic light/dark conditions accelerates the onset of short latency ON/OFF visual signaling recorded in retinal ganglion cells.
Keywords: retinal development • ganglion cells • retinal connections, networks, circuitry