Intracisternal TRH and RX 77368 potently activate gastric vagal efferent discharge in rats

The influence of intracisternal (ic) TRH and the stable TRH analog, RX 77368, on gastric vagal efferent discharge (GVED) was investigated in urethane-anesthetized rats. Consecutive IC injections of TRH (3, 30, and 300 ng) at 60 min intervals stimulated dose dependently multi-unit GVED with a peak increase of 90 +/- 21%, 127 +/- 18% and 145 +/- 16% respectively. In two separate studies, IC injection of RX 77368 at 1.5 or 15 ng stimulated multi-unit GVED by 142 +/- 24% and 244 +/- 95% respectively. Saline injection IC had no effect on GVED. RX 77368 (1.5 ng, ic) action was long lasting (84 +/- 13 min) compared with TRH (3 ng: 44 +/- 7 min). Single-unit analysis also showed that 13 of 13 units responded to ic RX 77368 (1.5 ng) by an increase in activity. These data indicate that low doses of TRH injected ic stimulate vagal efferent outflow to the rat stomach and that RX 77368 action is more potent than TRH.