[Response characteristics of fast-adapting units innervating cat oral mucosa to ramp-shaped pressure and triangular...

In this study, responses of fast-adapting sensory units to ramp-shaped pressure and triangular vibratory stimuli were recorded in the molar lingual gingiva and the alveolar mucosa isolated from the cat mandible via the air-gap method. The receptors of the fast-adapting units were classified into five types by a morphological study and the response characteristics of the individual sensory unit were investigated by electrophysiological methods. 1. Fast-adapting units of cat oral mucosa were found to have had five types of encapsulated endings (Type I-V) via a microscopical study. Among the 1,609 endings observed, the occurrence frequency of the individual receptor type was as follows: Type I 64.1%, Type II 9.5%, Type III 13.9%, Type IV 1.2% and Type V 11.3%. Although Type V a-d receptors had not been observed in the cat oral mucosa, their presence was demonstrated in whole thickness preparation stained with methylene blue. 2. The impulse frequency-displacement velocity curves (long-long coordinated) of 32 fast-adapting units (20 animals) showed four different patterns. 9.3% of the fast-adapting units showed a proportional relationship over all ranges of displacement velocity in the impulse frequency-displacement velocity relation. 25.0% showed a proportional relationship in an initial narrow range of displacement velocity and attained a steady state in the higher range. In 21.9% of these units, the impulse frequency remained steady over all the ranges. In the remaining 43.8%, the impulse frequency remained steady in singular range over all displacement velocities tested, however their response times decreased when the displacement velocity was increased. 3. The fast-adapting units were divided into two groups by response mode: a unit group with a Type I receptor and the other with Type II-V receptors (represented by a Type III receptor). The slopes were measured from their relations (log-log coordinates) in threshold amplitude vs. displacement caused by single triangular stimulus. The slope for the Type I group was -0.796 +/- 0.099 (mean +/- S. D.) (Range: -0.593(-)-1.017, n = 22). The slope for the other group was -0.658 +/- 0.024 (Range: -0.607(-)-0.758, n = 6). The slope of the former was larger than that of the latter. 4. The threshold-frequency curves (tuning curve; semilog coordinates) for the Type I group and the other group were analyzed. Both tuning curves of these sensory units revealed no plateaus between the lower-frequency limits and the upper-frequency limits.(ABSTRACT TRUNCATED AT 250 WORDS)