Figure 2.

Activation of mAChR mediates long lasting and cumulative excitation. (A) Repeated injections of ACh into the central protocerebrum released stridulation of progressively increasing duration. Changes were most pronounced with stimulus intervals of 15 s (Left), still highly significant with intervals of 30 s (Center), but absent with stimulus intervals of 60 s (Right) (one-way ANOVA for repeated measures). (B) Reducing the activation of mACh receptors by coinjection of the muscarinic receptor antagonist scopolamine caused a highly significant (two-way ANOVA, P = 0.0001) reduction in the progressive increase of stridulation in comparison to ACh alone. Data were obtained from six animals, in which both treatments were repeatedly tested at identical injection sites. (C) Increases in the duration of stridulation were also seen with repeated injections of muscarine at intervals of 5 min. (D) Injections of muscarine and forskolin stimulated stridulation of equal duration. (E) Injection of the adenylate cyclase inhibitor SQ22536 reversibly reduced the duration of stridulation stimulated by identical muscarine injections (P < 0.001, one-way ANOVA for repeated measures). All drugs were used at concentrations of 10⁻³ M in the pipet. The mean duration of stridulation at a specific stimulation site was set to 100% as follows: using the first stimulation of a series (A–C), muscarine alone (D), and muscarine before SQ22536 (E).