[Functional characteristics of rapidly adapting mechanoreceptor units of the rat mammary gland nipple].

Two types of rapidly adapting mechanosensitive units were found in the teat of the rat mammary gland (RAI and RAII). Neither was spontaneously active. 10% of the units were RAII and had the functional characteristics of "transient" receptors. The relation between the average frequency of discharge and the velocity of displacement at a constant displacement amplitude was linear for RAI. The latency of the first spike decreased when indentation velocity increased. The number and frequency of afferent impulses decreased at a repeated mechanical stimulation. Vibratory tuning points were in the range 10--25 Hz for RAI. RAI units were not directionally sensitive to the teat displacement.