GABAA receptor immunoreactivity is transiently expressed in the developing outer retina
Extensive evidence has suggested a trophic role of [gamma]-aminobutyric acid (GABA) on developing cone photoreceptors in postnatal retina. In a previous study, we showed that GABA raises intracellular calcium levels in the developing cones via activation of GABAA receptors. Using confocal microscopy in conjunction with immunocytochemistry, we have now demonstrated that (1) GABAA receptor subunits are localized on cone cell bodies as well as on cone pedicles, indicating that GABA has a direct, rather than indirect, effect on cones and (2) the temporal expression of GABAA receptor subunits coincides with the developmental effects of GABA on cone synaptogenesis. An antibody against the [beta] 2/3 subunits of the GABAA receptor and a specific cone marker peanut-agglutinin lectin (PNA) were used to double-label wholemount neonatal retinal preparations. Results show that GABAA receptors are transiently expressed on cone photoreceptors in the early stages of postnatal retinal development. GABAA receptor immunoreactivity is clearly present on cone cell bodies and their processes and on other—as yet unidentified—elements (horizontal cells?) in the outer plexiform layer. Immunoreactivity decreases within cone photoreceptor somata after postnatal day 5, but persists in the processes of the outer plexiform layer until day 7. Our results provide support for the hypothesis that GABA acts as an important developmental regulator of cone photoreceptor maturation.(Received August 4 1998)
(Accepted June 16 1999)
Key Words: Retinal development; Outer plexiform layer; Horizontal cells; PNA; GABA.
c1 Address correspondence and reprint requests to: Dianna A. Redburn-Johnson, Department of Opthalmology, The University of Tennessee, Memphis, College of Medicine, 855 Monroe Avenue, Room 515 Link Building, Memphis, TN 38163, USA.
p1 Current address: Department of Opthalmology, The University of Tennessee, Memphis, College of Medicine, 855 Monroe Avenue, Room 515 Link Building, Memphis, TN 38163, USA. E-mail: firstname.lastname@example.org.