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Localization of pancreatic preganglionic neurons within the rat dorsal vagal nucleus

The dorsal vagal nucleus (DVN) is the main source of the vagal innervation of the pancreas. In vitro studies have demonstrated that the DVN consists of a heterogeneous neuronal population with distinct morphological and electrophysiological characteristics. The aims of this study were (i) to identify DVN pancreatic preganglionic neurons (PPNs) in vivo and (ii) to characterize their responses to cholecystokinin (CCK), a major regulator of pancreatic secretion. Male Sprague Dawley rats anaesthetised with isoflurane (1.5%/100% O2) were used in all experiments. Extracellular single unit recording techniques were used to record the activity of PPNs within the DVN and their locations were marked using Pontamine Sky Blue. PPNs were identified by antidromic activation in response to stimulation of the pancreatic vagus nerve (0.5 Hz, 0.5 ms pulse width, 500μA). They had axonal conduction velocities in the C‐fibre range (< 1 m/s). Twenty‐five PPNs were identified within the rostral, medial and caudal DVN and twenty were tested for responsiveness to CCK. CCK (0.01–10 μg/kg, i.v.) produced three types of responses: (i) PPNs in the medial DVN were completely inhibited by CCK (0.7 ± 0.02 m/s, n = 16), (ii) PPNs in the caudal DVN were slightly activated by CCK (0.6 ± 0.08 m/s, n = 2) and (iii) CCK had no effect on the PPNs in the rostral DVN (0.6 ± 0.01 m/s, n = 2). CCK has complex actions on PPNs that may be related to its effect on exocrine and endocrine secretion. Further investigation of PPNs may allow identification of sub‐groups of DVN neurons that control the pancreas.