Abstract
Purpose: :
Connexin 36 (Cx36)-containing gap junctions are found in various retinal circuitries in adult mammals, particularly in the primary rod signaling pathway. In contrast to their roles in mature retinas, the functions of gap junctions in developing retinas have not been carefully explored. Previous studies have shown that the Cx36 gene and protein expressions are developmentally regulated in both rodent and rabbit retinas, and the temporal pattern of Cx36 protein expression in AII amacrine cells are correlated with the maturation of glutamatergic neurotransmission in the developing retina. Given the importance of Cx36-containing gap junctions for rod signaling, it is of great interest to examine the relationship between chemical synaptic maturation via glutamate receptors and the electrical synaptic transmission via gap junctions.
Methods: :
The retinas from New Zealand White rabbits aged around postnatal day 10 (eye-opening) were isolated and cultured in the interphase/perfusion chamber system. CNQX (AMPA receptor antagonist) was added in the culture medium to block AMPA receptor mediated glutamatergic neurotransmission for several days. Alternatively, CNQX was injected intraocularly into the eyes in a daily manner. The wholemount and sliced retinas were then processed to determine the Cx36-containing gap junction expression using immunocytochemistry.
Results: :
In both wholemount and slice preparations, the Cx36 protein expression in the inner plexiform layer was up-regulated after treating AMPA receptor antagonists for 2-3 days. The colocalization pattern of Cx36-positive puncta and calretinin-positive AII amacrine processes in the sublamina b was apparently normal in cultured retinas when compared with the freshly isolated retinas with and without intraocular injection of CNQX.
Conclusions: :
The up-regulation of Cx36 protein expression in AII amacrine cells resulted from blockade of AMPA receptor-driven activity after eye opening indicates that the functional maturation of Cx36-containing gap junction in the primary rod signaling pathway is dependent on glutamatergic neurotransmission during retinal development. This finding also suggests that neural activity may play some roles in rod pathway maturation.
Keywords: gap junctions/coupling • retinal development • retinal connections, networks, circuitry