Fig. 2.

Spontaneous activity of smooth muscle and low-threshold rectal mechanoreceptors. A: preparation of rectum from a control guinea pig, pretreated with a saline enema 6 days previously, shows spontaneous contractions of circular muscle. Associated with the rising phase of most but not all of these contractions are bursts of mechanoreceptor firing. B: mean tension measured over 60 s was unaffected by TNBS treatment compared with saline. However, there was a significant increase with age (30 days after saline or TNBS enema, *P = 0.018; 2-way ANOVA). Numbers on histograms refer to the number of rectal preparations. C: frequency of contractions per minute was unaffected by TNBS treatment at both 6 days and 30 days after treatment (P = 0.26 2-way ANOVA for both). D: spontaneous firing of mechanoreceptors was not affected by either TNBS treatment or age.