Effects of a novel neurotensin peptide analog given extracranially on CNS behaviors mediated by apomorphine and haloperidol

Neurotensin (NT) is a neuropeptide neurotransmitter in the central nervous system. It has been implicated in the therapeutic and in the adverse effects of neuroleptics. Activity of NT in brain can only be shown by direct injection of the peptide into that organ. However, we have developed a novel analog of NT(8-13), NT69L, which is active upon intraperitoneal (i.p.) injection. Like atypical neuroleptics, NT69L blocked the climbing behavior in rats, but not the licking and sniffing behaviors of a high close (600 mu g/kg) of the non-selective dopamine agonist apomorphine. Its blockade of climbing was very potent with an ED50 (effective dose at 50% of maximum) of 16 mu g/kg. Both apomorphine and NT69L caused a long-lasting hypothermia, which was greater with the peptide bur nor synergistic in combination with apomorphine. The ED,, of NT69L for hypothermia was 390 mu g/kg. NT69L (up to 5 mg/kg i.p.) did nut produce catalepsy. However, when given before haloperidol, NT69L, but not clozapine, completely prevented catalepsy. When given after haloperidol, NT69L, but not clozapine, reversed haloperidol's cataleptic effects with an ED50 of 260 mu g/kg. There was no significant difference between the ED(50)s for hypothermia and anticataleptic effects of NT69L. However, the ED50 for blocking the effects of apomorphine was significantly lower than the other two. These data suggest that NT69L may have neuroleptic properties in humans and may be useful in the treatment of extrapyramidal side effects caused by typical neuroleptics such as haloperidol. (C) 2000 Elsevier Science B.V. All rights reserved.