[Properties of mechanoreceptor units of mammary gland parenchyma]

Two types of mechanosensitive units were found in the parenchyma of the rat mammary gland (SA and RA). Most of SA units had a spontaneous activity 1-3/sec. and responded to an abrupt displacement with a decline in the activity for 5-10 sec. RA had no such a response. The relation between average firing rate and displacement velocity at a constant displacement amplitude was linear for both SA and RA. RA however had the velocity threshold higher than SA. The number and frequency of SA afferent impulses decreased at a repeated stimulation. Electron microscopy revealed that free nerve endings correspond to SA and RA.