Abstract
Abstract: :
Purpose: Hyperpolarization-activated cation currents (Ih) have been found in cardiac pacemaker cells and neurons in several brain regions. To date, four members of a gene family encoding hyperpolarization-activated cyclic nucleotide-gated cation channels (HCN1-4) have been cloned. This study was conducted to identify and characterize the neurons expressing HCN1 in the rabbit retina. Methods: With immunocytochemistry using commercial antibody against HCN1, wholemount and 40µm-thick vibratome sections of the rabbit retina were examined. Results: Specific immunoreactivity was present within the outer nuclear layer (ONL), outer plexiform layer (OPL), inner nuclear layer (INL), inner plexiform layer (IPL), and ganglion cell layer (GCL). Immunoreactivity was found in nearly all somata of the ONL and in a few somata of the INL and the GCL. Weak immunoreactive processes from labeled photoreceptors and bipolar cells were present in the OPL, and strong immunoreactive processes from labeled processes originating from bipolar and amacrine cells ramified in the border of strata 1 and 2 of the IPL. Double-labeling experiments demonstrated that processes of the HCN1 immunoreactive neurons juxtapose to those of OFF-starburst cholinergic amacrine cells in the IPL, and that HCN1 immunoreactive amacrine cells are GABAergic. The postsynaptic elements at the ribbon synapses of HCN1 immunoreactive bipolar cells were amacrine/amacrine or ganglion in sublamina a of the IPL. The HCN1 immunoreactive amacrine cells received synaptic inputs from unlabeled cone bipolar cells and unlabeled amacrine cells, and made output synapses onto amacrine and ganglion cells in sublamina a of the IPL. Conclusions: These results demonstrate that HCN1 is expressed in photoreceptors and a certain type of bipolar, amacrine, and ganglion cells in the rabbit retina. Especially, HCN1 immunoreactive bipolar and amacrine cells might play a role in OFF-circuitry in the rabbit retina.
Keywords: retina: proximal(bipolar, amacrine, and gangli • amacrine cells • bipolar cells