Morphological analysis of the hyperpolarization-activated cyclic nucleotide-gated cation channel 1 (HCN1) immunoreactive bipolar cells in the rabbit retina.
Hyperpolarization-activated cation currents (I(h)) have been identified in neurons in the central nervous system, including the retina. There is growing evidence that these currents, mediated by the hyperpolarization-activated cyclic nucleotide-gated cation channel (HCN), may play important roles in visual processing in the retina. This study was conducted to identify and characterize HCN1-immunoreactive (IR) bipolar cells by immunocytochemistry, quantitative analysis, and electron microscopy. The HCN1-IR bipolar cells were a subtype of OFF-type cone bipolar cells and comprised 10% of the total number of cone bipolar cells. The axons of the HCN1-IR cone bipolar cells ramified narrowly in the border of strata 1 and 2 of the inner plexiform layer (IPL). These cells formed a regular distribution, with a density of 1,825 cells/mm(2) at a position 1 mm ventral to the visual streak, falling to 650 cells/mm(2) in the ventral periphery. Double-labeling experiments demonstrated that their axons stratified narrowly within and slightly proximal to the OFF-starburst amacrine cell processes. In the IPL, they were presynaptic to amacrine cell processes. The most frequent postsynaptic dyads formed of HCN1-IR bipolar cell axon terminals are pairs composed of both amacrine cell processes. These results suggest that these HCN1-IR cone bipolar cells might be the same as the DAPI-Ba1 bipolar population, and might therefore be involved in a direction-selective mechanism, providing inputs to the OFF-starburst amacrine cells and/or the OFF-plexus of the ON-OFF ganglion cells.
Kim
In-Beom
IB
Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul 137-701, Korea.
Lee
Eun-Jin
EJ
Kang
Tae-Hoon
TH
Chung
Jin-Woong
JW
Chun
Myung-Hoon
MH
D025042:Amacrine Cells / Q000737:chemistry / Q000166:cytology; D000818:Animals; D054815:Cyclic Nucleotide-Gated Cation Channels; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007120:Immunochemistry; D007473:Ion Channels / Q000032:analysis*; D009419:Nerve Tissue Proteins / Q000032:analysis*; D010786:Photoreceptor Cells / Q000737:chemistry / Q000166:cytology; D015221:Potassium Channels; D011817:Rabbits; D012160:Retina / Q000737:chemistry* / Q000166:cytology*
D054815:Cyclic Nucleotide-Gated Cation Channels; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D009419:Nerve Tissue Proteins; D015221:Potassium Channels