Activation of mGluR6 declines more slowly in rod spherules than in a similar-size sphere with a narrow neck. (A) Illustration of the sphere model for rod 2 showing 200 mGluR6 (yellow spheres) in a transparent plane just beneath a release site at the apex. Glutamate molecules following the release of a vesicle are shown in white. (B) Illustration of rod 1 with mGluR6 (yellow spheres) on BP dendrites (purple and red). Glutamate molecules are in white when in front of the semitransparent ribbon and shaded when behind the ribbon. (C) Activation of mGluR6 in the sphere and the four rod spherules in the presence of 3,000 EAAT5. The decay time courses in reconstructed rods were fit with two exponentials. The decay in the sphere was fit with a single exponential. Best-fit time constants are given in Table 2. (D) Activation of mGluR6 in the sphere and four rod spherules without EAAT5. All simulations in this figure are the average of 25 runs using different seed values (±SD).