NEUROTENSIN-INDUCED MODULATION OF SPINAL NEURONS AND FICTIVE LOCOMOTION IN THE LAMPREY

1. Neurotensin containing interneurons are present in the spinal cord of both mammalian and nonmammalian vertebrates, but as yet little is known about their functional role. In this study we examine the effect of neurotensin on spinal cells and on the central pattern generator for locomotion in the lamprey spinal cord. 2. Bath application of neurotensin (10(-8) to 10(-6) M) slowed down the fictive locomotor activity induced by the glutamate agonist N-methyl-D-aspartate in the isolated spinal cord. The duration of the bursts of activity in the ventral roots increased in proportion to the increase of the locomotor cycle duration. 3. Intracellular recordings from grey matter neurons and intraspinal stretch receptors neurons showed that neurotensin induced a depolarization [4.4 +/- 0.5 (SE) mV, n = 19]. This depolarization could still be obtained after a blockade of voltage-sensitive sodium channels with tetrodotoxin (1.5 +/- 0.5 mV; n = 6), and after removal of calcium (2.8 +/- 0.4 mV; n = 5). Moreover no consistent change occurred in the fast and slow phase of the afterhyperpolarization (AHP) both of which are carried by potassium currents.