Isolation of synaptosomal fractions from rabbit retina.

Homogenization of rabbit retina in isotonic sucrose and differential rate centrifugation yielded two morphologically distinct synaptosomal fractions. One fraction was enriched in photoreceptor cell synaptosomes; the second fraction contained small synaptosomes derived from conventional sized synapses most abundant in the inner plexiform layer. Attempts to further purify these fractions using a variety of density gradients proved unsuccessful due to poor viability of photoreceptor cell synaptosomes. The synaptosomes prepared by our method are functionally stable as they demonstrate high affinity uptake for putative retinal neurotransmitters, neurotransmitter-sensitive adenylate cyclase activity, and calcium-dependent, potassium-stimulated release of [14C]GABA and [3H]dopamine.