[Ultrastructural changes of receptor endings in prolonged action of local anesthetics]

Ultrastructural changes of the terminal plates of the bushy receptors in the frog urinary bladder have been studied after two hours' exposition in 0.05% novocaine solution and one hour's exposition in 0.05% dicaine and trimecaine solution. During these periods a steady block of the receptor impulse activity develops. The local anesthetics essentially change ultramicroscopic structure of the terminals. The reaction to the anesthetics investigated has both some features in common and certain peculiarities. At each effect three types of changes can be determined, characterized with various degree of rearrangement in neurilemma, neuroplasm and organelles. Each type of the changes is supposed to reflect a certain phase of the plate reactive response. Specificities of the reaction to novocaine are minimal changes of mitochondria, accumulation of glycogen granules, deformity and decreasing amount of vesicles. Under dicaine effect mitochondria do not change, amount of vesicles increases, their form does not change; under trimecaine effect mitochondria undergo most noticeable alterations. The changes of the terminal plates observed are interpreted as adaptive. The effect of the local anesthetics on the receptors is not limited with the blockade of the sodium canals of the afferent fibers, in parallel, biochemical processes, occurring in cytosol of the terminals also change; their morphological manifestations are the ultrastructural changes observed.