Neuronal and subcellular localization of acetylcholine in the posterior pituitary of the rabbit.

1. Acetylcholine and neurohypophysial hormones were measured in subcellular fractions of rabbit neurohypophysis.2. Differential and density gradient centrifugation, followed by bio-assay and electron microscopy were used to separate and characterize the subcellular particles, or isolated nerve endings.3. Acetylcholine in the rabbit neurohypophysis was found to occur in small vesicles of about 40 nm diameter which had similar characteristics to the synaptic vesicles from central nervous tissue.4. Examination of intact nerve endings isolated from the rabbit neurohypophysis indicated that at least some acetylcholine and neurohypophysial hormones occurred in separate nerve endings.