The GABAergic system in the retina of neonate and adult Octodon degus, studied by immunohistochemistry and electroretinography.
In the vertebrate retina, gamma-aminobutyric acid (GABA) mediates inhibitory processes that shape the visual response and is also thought to have neurotrophic functions during retinal development. To investigate the role of GABAergic signaling at the beginning of visual experience, we used immunohistochemistry to compare the distribution of GABA, the two isoforms of glutamic acid decarboxylase GAD65/67, and the GABA receptor types A, B, and C, in neonate versus adult Octodon degus, a native South American rodent with diurnal-crepuscular activity and a high cone-to-rod ratio. In parallel, we used electroretinography to evaluate retinal functionality and to test the contribution of fast GABAergic transmission to light responses at both developmental stages. Neonate O. degus opened their eyes on postnatal day (P)0 and displayed an adult-like retinal morphology at this time. GABA, its biosynthetic sources, and receptors had a similar cellular distribution in neonates and adults, but labeling of the outer plexiform layer and of certain amacrine and ganglion cells was more conspicuous at P0. In neonates, retinal sensitivity was 10 times lower than in adults, responses to ultraviolet light could not be detected, and oscillatory potentials were reduced or absent. Blockade of GABA(A/C) receptors by bicuculline and TPMPA had no noticeable effect in neonates, while it significantly altered the electroretinogram response in adults.


CONCLUSIONS
In spite of modest differences regarding retinal morphology and GABAergic expression, overall light response properties and GABAergic signaling are undeveloped in neonate O. degus compared to adults, suggesting that full retinal functionality requires a period of neural refinement under visual experience.
Centro de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Chile.
Luz M
LM
Delgado
Alex H
AH
Vielma
Thilo
T
Kähne
Adrián G
AG
Palacios
Oliver
O
Schmachtenberg
D000818:Animals; D000831:Animals, Newborn; D001640:Bicuculline / Q000494:pharmacology; D015153:Blotting, Western; D004596:Electroretinography; D018756:GABA Antagonists / Q000494:pharmacology; D005968:Glutamate Decarboxylase / Q000378:metabolism; D007150:Immunohistochemistry; D046329:Octodon; D010721:Phosphinic Acids / Q000494:pharmacology; D010775:Photic Stimulation; D011725:Pyridines / Q000494:pharmacology; D018079:Receptors, GABA / Q000378:metabolism; D012160:Retina / Q000254:growth & development* / Q000378:metabolism*; D012684:Sensory Thresholds; D015398:Signal Transduction; D014466:Ultraviolet Rays; D014785:Vision, Ocular; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
C101879:(1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid; D018756:GABA Antagonists; D010721:Phosphinic Acids; D011725:Pyridines; D018079:Receptors, GABA; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1; C401141:glutamate decarboxylase 2; D001640:Bicuculline