Figure 2.

Characterization of the mAChRs mediating the inhibition of electrically evoked noradrenaline release. Primary cultures of rat SCG neurons were labelled with [³H]-noradrenaline for 1 h in the absence or presence of 100 nmol·L⁻¹ MT-7 and were then superfused. Subsequent to a 60 min washout period, 4 min fractions of superfusate were collected. Electrical field stimulation was applied at 73 (S1) and 113 (S3) min of superfusion. Either OxoM or bethanechol (Bech) was present as indicated by the arrow on the right hand side in (A); OxoM caused transient increases in the rate of spontaneous ³H outflow (S2) as shown in Figure 1A; as a control for statistical comparison, solvent was applied instead of OxoM or bethanechol. (A) The time course of fractional ³H outflow·min⁻¹ and its alteration by 100 µmol·L⁻¹ bethanechol on the right hand side (n= 3). For comparison, the effect of solvent is depicted on the left hand side (n= 3). (B) Indicates a lack of bethanechol-induced ³H overflow, as exemplified by S2% values. The indicated concentrations of bethanechol were applied as shown in (A) (n= 6 to 9). (C) The concentration-dependence of the inhibition of electrically evoked tritium overflow by bethanechol, as exemplified by S3/S1 ratios. The indicated concentrations of bethanechol were applied as shown in (A) (n= 6 to 9); *** indicates a significant difference versus the result obtained in the presence of solvent at P < 0.001. (D) ³H overflow induced by 10 µmol·L⁻¹ OxoM (as exemplified by S2% values) in either untreated or MT-7-treated cultures; its effect is compared with that of solvent (n= 9). (E) The inhibition of electrically evoked tritium overflow by 10 µmol·L⁻¹ OxoM in either untreated cultures or in cultures treated with 100 nmol·L⁻¹ MT-7 (as exemplified by S3/S1 ratios); the effect of OxoM is compared with that of solvent (n= 9). In (D) and (E) significances of differences between pairs of columns are indicated above the corresponding pairs. *** Indicates a significant difference versus the corresponding results obtained in untreated cultures at P < 0.001; n.s. indicates the lack of such a significance. mAChRs, muscarinic acetylcholine receptors; MT-7, muscarinic toxin 7; OxoM, oxotremorine M; SCG, superior cervical ganglia.