Invaginating Blue Bipolar

References

By a large majority, this cell is encountered as an On-center variety. Only Kolb et al '92 reports ever seeing a putative off-center variety.

Kouyama & Marshak describe this cell as characteristically providing the central element of the dendritic triad at the blue cone pedicles. They also describe unknown dendritic elements which form "triad-associated flat contacts". Since, as they acknowledge, these are likely to be other bipolar types, I refer to this type as the invaginating blue bipolar.

• Postsynaptic connections (Input)
  • Cones
    • 1-3 (average,SD: 1.22 +- .56) Blue Cones (see morphology below)
  • Horizontal Cells
    • H2 Horizontal Cell

• Presynaptic connections (Output)
  • Rodieck 1988 points out that the blue bipolars are described as having axons terminate in the *inner* half of the IPL while the blue ganglion cells De Monasterio stained had dendritic fields that ramified in the *outer* part of the IPL.
  • Bistratified On Blue Ganglion cell
  • Off Midget Amacrine cell

• Function

• Morphology
  • Kolb et al 1992
    • Axon terminal arborizing in stratum 5 of the IPL
    • "two sturdier dendrites converging on the same cone and finer, wispy branches ending either on another cone or in the neuropil of the OPL."
    • "the axon terminal.... widely ramifying varicose structure ending in stratum 5 of the IPL"
  • Kouyama and Marshak (1992)
    • A single dendrite which runs vertically through the INL and branched upon reaching the OPL. Diameter of at least 2 um.
    • In periphery, somata sometimes extended into the OPL where 2 or more dendrites branched directly from the soma. After this dendrites rarely branched and ranged from .2um to 2um in diameter.
    • In periphery: dendrites made 1-4 major dendrites, dendrites length 10-50 um, axons had 1-3 branches ranging from 5-35 um in length and were typically shorter than the dendrites.
    • Dendrites usually avoided the closest cone, but reached cone pedicles 10-50 um from the soma.
    • Upon reaching the target cone pedicle, the dendrites tapered to less than 1 um in diameter and divided.
    • Final invaginating dendrites varied from .1um to um in diameter and deeply invaginated the cone pedicle.
    • Somas 7-9 um in diameter in 1st or 2nd row of INL
    • Axons less than 1 um in diameter and didn't ramify in the strata where similarly stained amacrines were found.
    • Axons branched 75%-95% depth in IPL ~ 5th stratum
    • Central retina
      • Their technique didn't work to well in the fovea because the dye didn't disperse to well. In other words the fovea was to tightly packed.
      • Somas were mostly in the outer half of the INL. They were smaller than those in the periphery and more densly packed.
      • The axon reached stratum 5 of the IPL where they had expansions similar to those of peripheral blue bipolars.
      • A single main dendrite which was longer than the peripheral dendrite since the INL was thicker.
      • Typically the dendrite ended at a single cone with several terminal bifurcations and swellings.
      • Some bipolars did contact 2 cones.
      • Dendrites were oriented toward the fovea and axons toward the periphery.
      • Soma diameters were 6.3 +- .4 um (mean+-sd)
    • Eccentricity changes
      • Fitted line to soma diameter data
        • Temporal: Y = .064X + 6.15 (R2 = .938)
        • Nasal: Y = .035X + 6.34 (R2 = .989)
        • X : eccentricity in degrees
        • Y : diameter in um
    • As many as 4 bipolars contacted a single cone.
    • As many as 3 cones were contacted by a single bipolar.
    • On average 1.84 +- .7 bipolars contacted each cone
    • On average 1.22 +- .56 cones provided input to a single bipolar
    • Electron Microscopy
      • 2 um from the target pedicle, the dendrite usually bifurcated several times forming terminal specializations.
      • The dendrite ends were separated from the ribbon synapse by about .1 um by lateral dendrites from other cells.
  • Both Koyama and Marshak and Mariani noted dendrites which taper and end without any specialization in the middle of the OPL. Some cells had exclusively these dendrites. K & M suggest that this resulted from degeneration of blue cones and not from contacts with other cone types.

• Array characteristics
  • bipolar cells/blue cones = 1.4+-.2 in ventral retina
  • Density
    • 140 bipolars/degree2 in central periphery
    • ~5 @ 60 degrees temporally
    • ~35 @ 60 degrees nasally
    • Density in nasal half was consistently higher than temporal half.

• Compartmental Model Characteristics

• Location

• Subclasses

• Synapse types

• Synapse Receptors

• Neurotransmitters

• Immunoreactivity/Stain
  • Antisera that recognize glycine-extended cholecystokinin (CCK) precursors

• Nomenclature

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