Abdominal sensory neurons providing negative feedback to the feeding behavior of the blowfly

1. The anatomy of the abdominal nerves of the blowfly, Phormia regina, is briefly described. Five nerves connect the thoracico-abdominal ganglion (TAG) with the abdomen, an unpaired median abdominal nerve (MAN), a pair of medial accessory abdominal nerves (MAAN) and a pair of lateral accessory abdominal nerves (LAAN). 2. The affect on feeding of cutting the MAN, MAAN or LAAN immediately posterior to the TAG is reported. A significant increase in feeding is produced only by cutting the MAN. Cutting the MAN posterior to the second lateral branches arising from it has no affect on feeding. 3. A small population of cell bodies is located within the branches of the abdominal nerves. These cells are 15-20 microns in diameter and are usually situated at branch points. Approximately 4-8 such cells are located in the first and second lateral branches of the MAN. 4. Electrical recording from cells in peripheral abdominal nerves reveals steady activity which survives complete isolation of the cell from the CNS and the periphery. A unit can be activated by gentle stretch of the nerve containing it or branching in its immediate vicinity. Stretch was the only consistently effective stimulus found. 5. Recording from the cells in situ demonstrates that their net rate of firing is dependent on crop volume. The short-term temporal pattern of output can be modulated by crop contractions and expansions. It is suggested that the output of these cells acts in the CNS to reduce the probability of feeding.