Neurotransmitter modulation of Fos‐ and Jun‐like proteins in the turtle retina

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Abstract
The expression of the Fos and Jun families of nuclear phosphoproteins can be induced by a variety of extracellular stimuli and is known to participate in the transcriptional regulation of target genes. To examine the role of these transcription factors in retinal function, we used polyclonal antisera to localize these protein families in the turtle retina. Fos‐like immunoreactivity was in many somata in the inner nuclear and ganglion cell layers. In contrast, Jun‐like immunoreactivity was in a smaller number of amacrine cells and many somata in the ganglion cell layer. The monostratified dendritic arbors of one prominent amacrine cell type with Jun‐like immunoreactivity were also labeled. There were no dramatic differences in the levels of Fos‐like immunoreactivity or Jun‐like immunoreactivity between light‐ or dark‐adapted retinas. We examined the effects of excitatory amino acids and γ‐aminobutyric acid (GABA) on the expression of these proteins in vitro. In some experiments, cobalt was used to block synaptic transmission. The excitatory amino acids increased both Fos‐ and Jun‐like immunoreactivity, while GABA generally showed no such stimulatory effect. In cobalt‐treated retinas, the same cell types had Jun‐like immunoreactivity as seen in the controls, but overall levels of immunoreactivity were increased. In cobalt‐treated dark‐adapted retinas, some excitatory amino acids increased cytoplasmic Fos‐like immunoreactivity in the somata and processes of large cells in the ganglion cell layer. Our results suggest that Fos‐ and Jun‐related proteins may play an important role in the postsynaptic responses to amino acid transmitters in a wide variety of amacrine and ganglion cells.