The effect of patterned preganglionic stimulation on acetylcholine (ACh) stores was studied in the superior cervical ganglion of the cat. 2. Patterns of stimulation based on 0.5 and 1.0 s trains at frequencies from 10 to 80/s and intervals between trains of 2-180 s increased ACh stores, over periods of 1-3 h stimulation, to the same extent (30-70%) as found earlier to result from continuous stimulation. 3. If the mean frequency of the overall pattern was greater than 5/s the increase in stores developed after termination of the stimulation. If the mean frequency was less than 5/s the increase developed progressively during stimulation and it was then maintained without accommodation over 7 h of stimulation. 4. The magnitude of the increase in ACh stores was linearly related to the frequency within the trains from 10 to 40/s, decreasing with further increase in frequency, and absent below 6-7/s. 5. The ACh stores were increased by patterns of stimulation that mimicked discharging of preganglionic neurones driven by the central respiratory drive under hypercapnic or asphyxial stress; and were increased similarly in animals respired with hypercapnic or partially asphyxial gas mixtures when the preganglionic innervation was intact, but not when it was severed. 6. The variance between ACh stores of ganglia from different animals was reduced in animals held in a controlled environment for 1-2 weeks before experimentation. 7. It is concluded that patterning of preganglionic inputs into high frequency trains is a code for the ongoing modulation of transmitter stores in a sympathetic ganglion. 8. The findings are discussed in relation to current knowledge of ganglionic transmission and to after-hyperpolarization in mammalian unmyelinated nerve fibres.
