Effects of stimulation of the chorda tympani in bursts on submaxillary responses in the cat.

1. The effects of continuous preganglionic stimulation of the chorda tympani at 2 Hz for 10 min were compared with those of stimulation at 20 Hz in 1 sec bursts at 10 sec intervals for the same period in cats treated with atropine (0.5 mg/kg). Both the fall in mean submaxillary vascular resistance (s.v.r.) and the rise in mean vasoactive intestinal peptide (VIP) output from the gland were increased significantly (P < 0.01; P < 0.02) when the same total number of impulses were delivered in the form of bursts at the higher frequency.2. Both responses were also consistently increased by stimulating the post-ganglionic innervation in bursts in atropinized cats, or by stimulating the preganglionic innervation in bursts in the absence of atropine.3. The effects of stimulation of the chorda tympani in 1 sec bursts at 10 sec intervals for 2-3 min were investigated over the frequency range 2-160 Hz. The change in mean s.v.r. under these conditions was significantly reduced by administration of atropine at frequencies between 2 and 20 Hz, but not at higher frequencies. In atropinized cats, the fall in mean s.v.r. was linearly related to stimulus frequency (r = 0.993) over the range 2-60 Hz and a maximal response was obtained during stimulation at 80 Hz. In the same experiments the fall in mean s.v.r. was linearly related to log mean VIP output over the frequency range 20-160 Hz (r = 0.998).4. Closely similar changes in mean s.v.r occurred in response to both pre- and post-ganglionic stimulation at all frequencies tested between 2 and 160 Hz in atropinized cats when the stimuli were delivered in bursts. The changes in mean s.v.r. were not significantly affected by varying the duration of individual stimuli over the range 0.1-25.0 msec.5. The flow of submaxillary saliva was also linearly related to stimulus frequency over the range 2-40 Hz (r = 0.997) when the stimuli were delivered in bursts in the absence of atropine and secretion of saliva was maximal at 60 Hz.6. It is concluded that release of VIP from the submaxillary gland of the cat is optimal in response to stimulation of the chorda tympani at relatively high frequencies, when the impulses are delivered in bursts. Flow of saliva which is mediated by acetyl choline, may also be potentiated under the same conditions.