Abstract
Electrical stimulation of the central end of the vagal communicating branch in the thorax at frequencies between 2 and 20 Hz elicited, after a latency of 7.2 +/- 0.8 s, large-amplitude colonic contractions. 5 Hz stimulation gave near maximal contractions and, because vomiting was more likely to occur at higher stimulus frequencies, was used as the standard stimulus for subsequent experiments. At this frequency the peak colonic contraction was 6.5 +/- 0.9 kPa. Following atropine the characteristics of the response to central vagal stimulation differed from that seen before atropinization. The latency was longer (45.7 +/- 8.2 s) and the amplitude greatly attenuated (0.7 +/- 0.2 kPa). Cooling the vagus nerves to 2 degrees C at a level either above or below the site of stimulation completely abolished both the cholinergic and the atropine-resistant colonic responses to central vagal stimulation. These results are consistent with the vagus containing two motor pathways to the colon which are reflexly stimulated by a vagal afferent input. The functional significance of these reflexes is discussed.