Neurotensin and its amide analogue [Gln4]-neurotensin: effects on brain monoamine turnover

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Abstract
Intracerebroventricularly administered neurotensin and [Gln4]-neurotensin (50–200 μg) increased the formation of Dopa in different brain regions of rats after inhibition of the aromatic l-amino acid decarboxylase. For both neuropeptides these increases were dose dependent (20–150%). In the corpus striatum [Gln4]-neurotensin was twice as active as neurotensin and it tended to be more active also in other brain regions. The brain tyrosine concentrations were also increased. [Gln4]-neurotensin (100–200 μg) following inhibition of the aromatic l-amino acid decarboxylase, increased the accumulation of 5-hydroxytryptophan in all brain regions by 30–60%. In contrast, neurotensin was completely inactive. In both cases the brain tryptophan concentrations were increased. Both neurotensin and [Gln4]-neurotensin also accelerated the disappearance of dopamine, noradrenaline and 5-hydroxytryptamine after inhibition of monoamine synthesis. These results show an increased brain monoamine turnover induced by both neuropeptides.