Fig. 1.

Gastric emptying rate in an awake, freely moving animal can be monitored by determining the rate of appearance of ¹³C in respired CO₂ that had been ingested as 13C-tagged sodium octanoate-doped meal. ¹³C in respired CO₂ is indicative of the transit of the carbohydrate meal from the stomach to the duodenum. This ¹³C method captures the entire time course of the transit event (samples taken at 15 min intervals) and is displayed in the right-hand graphs. Specific parameters of this transit can be extracted for comparisons: T_lag corresponds with the time at which rate of excretion of ¹³CO₂ is maximal, T_1/2 is the gastric half-emptying time (time when half of the label that is to be excreted has been excreted) and the GEC (a global index of rate of emptying). Each animal served as its own control. That is, the first session the animal receives the control injection (saline either i.p. or 4 V, as appropriate); the next session the animal receives the test injection. Therefore, paired t-test comparisons could be made between the saline control and the agonist condition for each animal. Examples of such paired gastric transit experiments of individual animals are seen in the right-hand graphs. In the left-hand column are group averages for the gastric transit parameters under each condition; statistical comparisons were only made within each condition group. Microinjection of the PAR1-selective agonist SFLLRN (10 nmol) into the fourth ventricle caused a significant reduction in gastric transit as measured by T_lag and T_1/2 as well as a slowed overall GEC compared with their respective saline controls. (Adapted from Hermann et al., J Neurosci, 2009, 29 [29]: 9292–9300).