Developing pigeon retina: Light‐evoked responses and ultrastructure of outer segments and synapses

Abstract

Morphological development of photoreceptor outer segments and synapses in the foveal region of the pigeon retina was studied by electron microscopy. In addition, the maturation of outer retina function was investigated by recording electroretinographic (ERG) responses to either flash or pattern stimuli. The first ERGs to unpatterned or patterned stimulation can be recorded at 4-6 days posthatching. These results are consistent with anatomical analysis of pigeon photoreceptor and synapse development. Indeed, photosensitive lamellae in the outer segments can be observed simultaneously with the appearance of the first retinal responses to light. A few synapses can already be seen in the outer plexiform layer at the time photoreceptor disks first appear. In contrast, numerous synapses are already present in the inner plexiform layer when photoreceptor lamellae have yet to appear. A comparable maturation pattern has been reported to occur in chicks toward the end of the incubation time.

Interaction between photoreceptors and pigment epithelium in developing pigeon retina: an electrophysiological and ultrastructural study

“…This intensity was sufficient to obtain near-maximal ERG responses in the whole range of tested ages. This result is consistent with a previous study on a a-b-wave maturation in pigeons, in which a strobe flash of stronger intensity has been used (Bagnoli et al, 1985). We cannot exclude the possibility, however, that a very strong light stimulus might elicit a recordable response at the very earliest stage of outer segment development.…”

“…The first ERG can be recorded simultaneously with the appearance of photosensitive lamellae in the receptor outer segments. At the appearance of photoreceptor disks, numerous synapses in the inner plexiform layer were present, whereas synapses in the outer plexiform layer increased in number as the lamellar structures completed their maturation (Bagnoli et al, 1985).…”

Ultrastructural study of retinal development in the turtle Trachemys scripta elegans

“…These results confirm the observations in other vertebrates (Grun 1982), such as chickens (Morris et al 1976), pigeons (Bagnoli et al 1985), shrews (Foeli x et al 1987), monkeys (Hendrickson 1996) and zebrafish (Schmitt and Dowling 1999). At embryonic stage 18, it is poorly differentiated and lamination is incomplete, because the OPL is still incipient.…”

“…This result has also been reported for peripheral retina of pigeons (Bagnoli et al 1985), chickens (Morris et al 1976;Drenhaus et al 2007), ,\!accaca mulata (Smelser et al 1974 ), tree shrews (Poelix et al 1987), and monkeys (Hendrickson 1996). However, this finding contrasts with those of other animals: in rodents synapses formed in the OPL sli ghtly earlier than in the IPL.…”

Development of the Visual System in a Burrow-Nesting Seabird: Leach's Storm Petrel

“…However, altricial rock dove (Columba livia) chicks do not open their eyelids until 4 days after hatching (i.e., "day 4"), and the ERG response reaches adult-like expression only on day 20 [Bagnoli et al, 1985]. In chickens, the optokinetic head reflex (a series of slow head movements interchanged with fast saccadic repositions on coherently moving objects in a large part of the visual field) is present 2 days after hatching [Schmid and Wildsoet, 1998].…”