The expression and function of TRPV4 channels in primate retinal ganglion cells and bipolar cells.

The transient receptor potential vanilloid 4 (TRPV4) channel may be opened by mechanical stimuli to mediate Ca and Na influxes, and it has been suggested to mediate glaucoma retinopathy. However, it has been mostly unclear how TRPV4 activities affect the function of primate retinal ganglion cells (RGCs). We studied RGCs and bipolar cells (BCs) in the peripheral retina of the old-world primate using whole-cell current-clamp and voltage-clamp recordings, immunomarkers and confocal microscopy.

Cone synapses in mammalian retinal rod bipolar cells.

Some mammalian rod bipolar cells (RBCs) can receive excitatory chemical synaptic inputs from both rods and cones (DBC ), but anatomical evidence for mammalian cone-RBC contacts has been sparse. We examined anatomical cone-RBC contacts using neurobiotin (NB) to visualize individual mouse cones and standard immuno-markers to identify RBCs, cone pedicles and synapses in mouse and baboon retinas. Peanut agglutinin (PNA) stained the basal membrane of all cone pedicles, and mouse cones were positive for red/green (R/G)-opsin, whereas baboon cones were positive for calbindin D-28k.

Synaptic connections of amacrine cells containing vesicular glutamate transporter 3 in baboon retinas.

The goals of these experiments were to describe the morphology and synaptic connections of amacrine cells in the baboon retina that contain immunoreactive vesicular glutamate transporter 3 (vGluT3). These amacrine cells had the morphology characteristic of knotty bistratified type 1 cells, and their dendrites formed two plexuses on either side of the center of the inner plexiform layer. The primary dendrites received large synapses from amacrine cells, and the higher-order dendrites were both pre- and postsynaptic to other amacrine cells.

How do tonic glutamatergic synapses evade receptor desensitization?

Photoreceptor output synapses are the best known tonic chemical synapses in the nervous system, in which glutamate is continuously released in darkness, activating AMPA/kainate receptors in postsynaptic neurons. It has been shown that glutamate receptors in certain types of second-order retinal cells are largely desensitized in darkness, leading to small postsynaptic currents and reduced response dynamic ranges. Here we show that the tonic glutamatergic synapses between photoreceptors and rod-dominated hyperpolarizing bipolar cells (HBC(R)s) in the salamander retina evade postsynaptic receptor desensitization by using (1) multiple invaginating ribbon junctions as releasing sites for low-frequency, synchronized multiquantal release at each site; and (2) the GluR4 AMPA receptors as the postsynaptic receptors.