Pre-feeding NNS can improve gastric motility in the preterm infant. It also modulates state control and decreases apneic and/or bradycardic events. I refer you to the linked article and many of the citations referenced therein.
The article below addresses gastric motility.
Abbasi, S., Sivieri, E., Samuel-Collins, N., et al. (2008). Effect of non-nutritive sucking on gastric motility of preterm infants. Abstract for Pediatric Academic Society, 5840.22.