Structure-activity studies with car☐y- and amino-terminal fragments of neurotensin on hypothalamic neurons in vitro

Abstract

The purpose of this study was to determine the structural requirements for the activity of neurotensin (NT 1–13) on preoptic/anterior hypothalamic (POAH) neurons in vitro. Standard explant culture electrophysiological techniques were employed. NT was administered to POAH cultures through the superfusion fluid, or, to the vicinity of individual neurons by pressure ejection (0.5–10 psi) from micropipettes. Computer-generated, peri-event histograms were used to quantitate neuronal responses. Pressure ejection of NT 1–13 (50 pM to 1 μM) consistently produced an excitatory effect on 30 of 42 neurons. The reamaining cells were either inhibited or unaffected. Application of the C-terminal hexapeptide, NT 8–13, but not the N-terminal octapeptide, NT 1–8 (</1 mM), produced an excitatory response in 21 of 30 neurons, but was less potent than NT 1–13. Application of an N-acetylated NT 8–13 fragment (NT AC8–13) produced a response that was similar to that produced by NT 8–13. The excitatory effects of NT 1–13 were maintained in medium which effectively blocked synaptic transmission (0 mM Ca 2+/12 mM Mg 2+ 1 mM EGTA). These data indicate that the C-terminal hexapeptide, but not the N-terminal octapeptide, produces a dose-related, excitatory effect on single neurons in the POAH in vitro. The persistence of these effects in Ca 2+-free medium supports a postsynaptic site of action for these peptides.