Electrophysiological actions of neurotensin in rat cerebellum

The electrophysiological actions of neurotensin (NT) and its analog D-Arg9-NT were studied in rat cerebellar Purkinje neurons. NT applied by pressure ejection was a potent depressant of Purkinje (P) neuron firing. In contrast, iontophoretically applied NT was a weak depressant. Pressure-ejected D-Arg9-NT, which is largely inactive in peripheral systems, had little effect on P neurons. The depressant effects of pressure-ejected NT were blocked by intraperitoneally administered haloperidol, iontophoretically applied magnesium or 6-OHDA pretreatment. After such treatments, locally applied NT evoked only excitations. The results of this study suggest that NT, when applied by pressure ejection, produces two effects on the Purkinje neuron. The potent inhibitory effects of locally applied NT appear to result from release of the inhibitory transmitter, norepinephrine from locus coeruleus-derived afferents. We postulate that the excitations, which appear when postsynaptic effects of norepinephrine are antagonized or release is reduced, may be the direct result of NT action at the postsynaptic P neuron membrane.