Neurotensin actions in the retina: mechanisms and variability

The effects of neurotensin on mudpuppy retinal cells were studied using extracellular and intracellular electrophysiological recording techniques and bath application of the peptide. Ganglion and amacrine cells (but not bipolar or horizontal cells) were reversibly depolarized by low micromolar concentrations of neurotensin. Depolarizations also occurred with neurotensin application during cobalt block of synaptic transmission and were accompanied by decreased input resistances. This suggests neurotensin may act directly on amacrine and ganglion cells as a conventional excitatory transmitter. However, in many retinas, cells responded to light stimuli and to other drugs but not to neurotensin. These negative results are important in considering the peptide's normal role in retinal function.