PANCREATIC PREGANGLIONIC NEURONS: DIFFERENTIAL RESPONSES TO CCK1 AND 5‐HT3 RECEPTOR STIMULATION

Abstract

The dorsal motor nucleus of the vagus (DMV) is the main source of vagal input to the pancreas. In vitro studies have shown that the DMV contains a mixed population of pancreatic preganglionic neurons (PPNs) but little is known about their responses to pancreatic secretagogues such as cholecystokinin (CCK) and serotonin (5‐HT) in vivo. The aims of this study were (i) to identify DMV PPNs in vivo and (ii) to characterize their responses to CCK and 5‐HT3 receptor activation. Male Sprague‐Dawley rats anesthetised with isoflurane (1.7–2.0%) were used in all experiments. PPNs were recorded extracellularly and their locations were marked using pontamine sky blue. Only PPNs that had an axon in the pancreatic vagus (collision test positive) were studied. Forty‐four PPNs were identified within the rostral, medial and caudal DMV and thirty eight were tested for responses to CCK‐8 and phenylbiguanide (PBG; 5‐HT3 receptor agonist). Their axonal conduction velocities were in the C‐fibre range (< 1 m/s). CCK and PBG (0.1–10 μg/kg, i.v.) produced three types of response: (i) PPNs in the intermediate DMV were inhibited by CCK (n = 18) and PBG (n = 10), (ii) PPNs in the caudal DMV were activated by CCK (n = 5) and PBG (n = 2) and (iii) rostral DMV neurons were not affected significantly by CCK (n = 9) or PBG (n = 7). Pancreatic secretagogues have complex actions on PPNs that may be related to their effects on pancreatic exocrine and endocrine secretion.