Effects of adrenaline on nerve terminals in the superior cervical ganglion of the rabbit.

1. Adrenaline decreases the release of transmitter from the presynaptic nerves in the superior cervical ganglion of the rabbit. The presynaptic mechanism of adrenaline action was investigated with micro-electrode techniques.2. Adrenaline (10(-5)M) did not change the threshold of the presynaptic nerve terminals to a current stimulus.3. The effect of adrenaline on the excitatory postsynaptic potential (e.p.s.p.) was decreased when the calcium concentration of the perfusing solution was increased to 10 mM.4. The effect of adrenaline on a train of e.p.s.ps (30-50 Hz) was analysed. Adrenaline decreased the readily available stores of transmitter, but only slightly changed the probability of release.5. The probability of release was increased when the calcium concentration was increased to 5 mM.6. It was concluded that adrenaline acts directly on excitation release coupling in the presynaptic terminals.