Long-Term Treatment of the Developing Retina with the Metabotropic Glutamate Agonist APB Induces Long-Term Changes in the Stratification of Retinal Ganglion Cell Dendrites

Abstract

The gradual restriction of initially multistratified retinal ganglion cell (RGC) dendrites into ON and OFF sublaminae of the inner plexiform layer (IPL) can be effectively blocked by treating the developing retina with 2-amino-4-phosphonobutyrate (APB), the metabotropic glutamate agonist, or by light deprivation. Previous studies have focused on the short-term consequences of such manipulations, so the long-term effects of arresting dendritic stratification on the structural development of RGCs are as yet unknown. In the present study, we have addressed this issue by performing a morphological analysis of α RGCs labeled by retrograde transport of horseradish peroxidase injected into the dorsal lateral geniculate nucleus of adult cats that received monocular injections of APB from postnatal (P) day 2 until P30. A large proportion of the α cells in the APB-treated eye (44%) were found to have multistratified dendrites that terminated in both the ON and OFF sublaminae of the IPL. The dendritic arborization pattern in the sublaminae of the IPL of these cells was asymmetric, showing a variety of forms. Immunolabeling of retinal cross-sections showed that mGLUR6 receptors appeared normal in density and location, while qualitative observation suggested an increase in the axonal arborization of rod bipolar cells. These findings indicate that long-term treatment of the neonatal retina with APB induces a long- lasting structural reorganization in retinal circuitry that most likely accounts for some of the previously described changes in the functional properties of RGCs.

Retinal ganglion cell dendrites undergo a visual activity‐dependent redistribution after eye opening

“…These results provided new insights into the possible synaptic mechanisms with which visual activity regulates the development of RGC dendrites. Fourth, in contrast to assuming that all RGCs with dendrites ramified in both sublaminae a and b of the IPL are regulated by the same mechanism and treated as a single group in our previous study (Tian and Copenhagen, 2003) and several other studies (Bodnarenko and Chalupa, 1993;Bodnarenko et al, 1995;1999;Wang et al, 2001;Deplano et al, 2004;Chalupa and Gü nhan, 2004), we found that the number of RGCs ramified in both sublaminae a and b of the IPL with a single layer of dendritic plexus decreased with age, whereas the number of RGCs ramified in both sublaminae a and b of the IPL with clear bistratified dendritic patterns increased with age. We interpreted these results as indicating that some monostratified ON-OFF RGCs and bistratified RGCs are likely to be in different developmental status and, therefore, ought to be considered separately.…”

“…Several previous studies have investigated the developmental segregation of ON and OFF synaptic pathways in the retina and found that the number of RGCs ramified in both sublaminae a and b of the IPL decreased with age during postnatal development (Bodnarenko and Chalupa, 1993;Bodnarenko et al, 1995Bodnarenko et al, , 1999Wang et al, 2001;Tian and Copenhagen, 2003;Deplano et al, 2004;Chalupa and Gü nhan, 2004). In these studies, all RGCs ramified in both sublaminae a and b of the IPL were considered as a single group regardless of whether their dendrites stratified into a single layer or two layers.…”

“…These cells are exclusively D2 RGCs in this study. It is worth noting that the definition of "bistratified" RGCs used in this study, which includes only RGCs with whole dendritic trees clearly separated into two layers of plexi, is different from that used in previous reports by us and by others (Bodnarenko and Chalupa, 1993;Bodnarenko et al, 1995Bodnarenko et al, , 1999Wang et al, 2001;Tian and Copenhagen, 2003;Deplano et al, 2004;Chalupa and The Journal of Comparative Neurology. DOI 10.1002/cne Gü nhan, 2004), in which all RGCs ramified in both sublaminae a and b of the IPL were considered as "bistratified" RGCs regardless of whether their dendrites stratified into a single layer or multiple layers.…”

Permanent Functional Reorganization of Retinal Circuits Induced by Early Long-Term Visual Deprivation

“…The possibility that visual deprivation might permanently alter retinal circuitry was first suggested by evidence that APB treatment during the first month of postnatal life of the cat induced permanent modifications in RGC function, including an increase in the proportion of RGCs with ON-OFF discharges and loss of surround inhibition (Bisti et al, 1998) and an increase in the percentage of multistratifying RGCs (Deplano et al, 2004). A recent report by Giovanelli et al (2008) showed that in LongEvans rats, early prolonged visual deprivation reduced the spontaneous synaptic activity recorded of RGCs.…”

Slow-release Drug Delivery through Elvax 40W to the Rat Retina: Implications for the Treatment of Chronic Conditions

“…APB has been used in physiological studies to control retinal function and measure its effect using electrophysiological methods such as electroretinography (ERG). In previous studies, APB has been used for both short-term 29 and long-term treatment of the developing retina; the latter involved giving a single dose via intraocular injection daily for 30 days 30 . The same amount of APB (0.092 mg in sterile saline, at a concentration of 50 µM) was used for all injections as suggested in previous work 28,29,31 .…”