Feeding and Amines Stimulate the Growth of the Salivary Gland following Short-Term Starvation in the Black Field Cricket, Teleogryllus commodus

SIMPLE SUMMARY: Biting and chewing insects, such as crickets, may not have regular meals. They have a foregut with a crop that permits food to be stored, and also for further processing of previously ingested food if they cannot find food. Does this short period of starvation cause any further changes in other parts of the digestive system? We found that the salivary glands of crickets decreased in size as a result of a decrease in the size of one type of salivary cell, the zymogen cell. Amines (serotonin and dopamine) that stimulate gland secretion appeared to be stored with those cells, rather than in the parietal cells that are involved in salivation. Upon feeding, the glands immediately increase in size and the amines are then found in the parietal cells. This work appears to show that feeding and starving can affect parts of the digestive system as shown in animals such as snakes that can go long periods without feeding. The salivary glands of insects may have several different control mechanisms that require further work. ABSTRACT: The salivary gland of the black field cricket, Teleogryllus commodus Walker changed size between being starved and fed. Crickets without access to food for 72 h showed a reduction in both wet and dry mass of the glands compared with the glands from continuously fed animals at 72 h. Glands returned to size following ingestion within 10 min. Salivary glands of starved crickets (72 h) were incubated in saline containing either serotonin (5-HT) or dopamine (DA). Glands increased to pre-starvation size after 1 h incubation in situ with either 10(−4) moles L(−1) 5-HT or 10(−4) moles L(−1) DA, although lower concentrations (10(−5) moles L(−1)) did not affect gland size. From immunohistochemistry, amines appeared to shift from zymogen cells during starvation to parietal cells following feeding. High-performance liquid chromatography showed that serotonin concentration is higher than dopamine in the salivary gland removed from starved and fed crickets, but the quantity of these compounds was not dependent upon feeding state; the amine quantities increased as gland size increased. Further work is necessary to determine what might be the stimulus for gland growth and if dopamine and serotonin play a role in the stimulation of salivary gland growth after a period of starvation.