Dopaminergic amacrine cells in rabbit retina: a confocal microscopic study

Objective: To demonstrate the relationship between dopamicergic amacrine (DA) cells and AII amacrine cells and to characterize DA cells of the rabbit retina. Methods: Retinal whole mounts were doubleor triple-labeled using antibodies against tyrosine hydroxylase (TH), calretinin (CR), and vesicular glutamate transporter 1 (VGLUT1) which selectively label DA cells, AII amacrine cells, and all bipolar axon terminals, respectively. Neurochemical property of DA cell was examined by doubleor triple-labeling using antibodies against γ-aminobutyric acid (GABA), vesicular GABA transporter (VGAT), and glutamic acid decarboxylase (GAD), all three of which are reliable markers for GABAergic neuron. Confocal images were taken and quantitatively analyzed. Result: In stratum 1, most of DA dendritic varicosities which are presumed sites of neurotransmitter release made contact with somata or lobular appendages of AII amacrine cells. In addition, some of varicosities in strata 3 and 5 contacted arboreal dendrites of AII amacrine cells. Numerous lobular appendages of AII amacrines localized at stratum 2 of the IPL (inner plexiform layer) showed little contact with DA varicosities. Doubleor triple-labeling experiment showed that GABAergic markers such as GABA, VGAT, and GAD were not expressed in DA cells of the rabbit retina. Conclusion: DA dendrites stratified at strata 1, 3 and 5 of the IPL; DA cells of the rabbit retina do not use GABA as a neurotransmitter, unlike other mammals.