A NEW COMBINATION OF METHODS FOR THE LOCALIZATION, IDENTIFICATION, AND 3-DIMENSIONAL RECONSTRUCTION OF THE SENSORY ENDINGS OF ARTICULAR AFFERENTS CHARACTERIZED BY ELECTROPHYSIOLOGY

A combination of methods is described to identify and reconstruct corp uscular and non-corpuscular sensory endings of group II and group III nerve fibers following functional examination by electrophysiology. Af ferent units activated by electrical stimulation of the medial articul ar nerve of the cat's knee were analyzed by single fiber recordings an d characterized by their responsiveness to mechanical stimuli. The rec eptive fields of the units were closely demarcated by fine needles whe n the responses elicited by insertion of the needles were being record ed. After fixation, the tissue around the demarcated field was dissect ed and histologically processed. Series of semithin sections were cut from the embedded tissue blocks containing the receptive fields. Corpu scular endings of group II fibers and peripheral myelinated group III nerve fibers, presumably corresponding to the characterized units, wer e identified by light microscopy of semithin sections and localized wi thin the demarcated area. Non-corpuscular endings were identified by e lectron microscopy of ultrathin sections cut in alternation with, or a fter re-embedding of, semithin sections. Morphometric analysis of ultr athin section series allowed the measurement of parameters such as the mean axon diameter and the organelle content of the sensory endings. The methods described are appropriate for collecting data that correla te the structural and functional characteristics of sensory endings in deep tissues.