1. Effects of cocaine, lignocaine, benzocaine and tetrodotoxin (TTX) on the simultaneously measured pressure‐ and diameter‐discharge frequency relations of single fibre baroreceptors were compared in rat in vitro aortic arch‐aortic nerve preparations. 2. Between 1 and 10 microM, cocaine produced selective increases in the pressure threshold shifting the pressure‐response curve without altering the gain or threshold frequency. At near‐blocking concentrations, gain was depressed as well. Cocaine experiments were done in nitroprusside (NP, 1 microM). Neither NP or NP with cocaine altered diameter (P > 0.36). 3. Lignocaine (at > 10 microM) and benzocaine (at > 100 microM) shifted pressure‐response curves to higher pressures and generally depressed discharge by increasing pressure threshold and decreasing maximum discharge frequency (P < 0.05). Gain decreased and threshold frequency increased at higher concentrations. Diameter was unaffected by lignocaine or benzocaine (P > 0.14). 4. TTX increased thresholds and discharge frequencies at threshold but did not shift pressure‐discharge curve locations. This produced superimposable discharge curves with changes occurring as losses of discharge points in the threshold region. Diameter was unaffected by TTX (P > 0.80). 5. The contrasting patterns of effects between TTX and local anaesthetics suggest that blockade of TTX‐sensitive sodium channels alone may not be responsible for the effects of cocaine, lignocaine and benzocaine.
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