A neurotensin agonist and antagonist decrease and increase activity, respectively, but do not preclude discrete cue conditioning

The Neurotensin NTS1 Receptor Agonist PD149163 Produces Antidepressant-Like Effects in the Forced Swim Test: Further Support for Neurotensin as a Novel Pharmacologic Strategy for Antidepressant Drugs

Preclinical Research Neurotensin is a nonbrain penetrant neuropeptide neurotransmitter that alters dopaminergic and serotonergic neurotransmission. Previous animal behavioral studies have demonstrated that intra-ventral tegmental administration of neurotensin and system administration of the selective neurotensin NTS₁ receptor agonist, PD149163 produce antidepressant-like effects in a forced swim test and a differential reinforcement of low rate task, respectively. The present study sought to expand upon these past findings by assessing systemic administration of PD149163 in a forced swim test, a primary antidepressant preclinical screening model, in mice. The tricyclic antidepressant drug imipramine was tested for comparison, and both compounds were also assessed in an open field test. Both PD149163 and imipramine reduced time spent immobile, an antidepressant-like effect, in the forced swim test. The highest dose of each compound significantly reduced locomotor activity. These findings provide further evidence for the putative antidepressant effects for PD149163 and suggest that NTS₁ receptor activation may be a novel pharmacologic strategy for antidepressant drug development. Drug Dev Res 78 : 196-202, 2017. © 2017 Wiley Periodicals, Inc.

Systemic administration of the neurotensin NTS₁-receptor agonist PD149163 improves performance on a memory task in naturally deficient male brown Norway rats

Agonists for the neurotensin NTS₁ receptor consistently exhibit antipsychotic effects in animal models without producing catalepsy, suggesting that NTS₁-receptor agonists may be a novel class of drugs to treat schizophrenia. Moreover, studies utilizing NTS₁ agonists have reported improvements in some aspects of cognitive functioning, including prepulse inhibition and learning procedures, which suggest an ability of NTS₁-receptor agonists to diminish neurocognitive deficits. The present study sought to assess both baseline delay-induced memory performance and the effects of NTS₁-receptor activation on learning and memory consolidation in male Long-Evans and Brown Norway rats using a delayed nonmatch-to-position task radial arm-maze task. In the absence of drugs, Brown Norway rats displayed a significant increase in spatial memory errors following 3-, 7-, and 24-hr delay, whereas Long-Evans rats exhibited an increase in spatial memory errors following only a 7-, and 24-hr delay. With Brown Norway rats, administration of PD149163 before or after an information trial significantly reduced errors during a retention trial after a 24 hr delay. Administration of the NTS(1/2)-receptor antagonist SR142948 prior to the information trial did not affect retention-trial errors. These data are consistent with previous findings that Brown Norway rats have natural cognitive deficits and that they may be useful for assessing putative antipsychotic drugs for cognitive efficacy. Moreover, the results of this study support previous findings suggesting that NTS₁-receptor agonists may improve some aspects of cognitive functioning.

The role of endogenous neurotensin in psychostimulant-induced disruption of prepulse inhibition and locomotion

The neuropeptide neurotensin (NT) is closely associated with dopaminergic and glutamatergic systems in the rat brain. Central injection of NT into the nucleus accumbens (NAcc) or peripheral administration of NT receptor agonists, reduces many of the behavioral effects of psychostimulants. However, the role of endogenous NT in the behavioral effects of psychostimulants (e.g. DA agonists and NMDA receptor antagonists) remains unclear. Using a NTR antagonist, SR142948A, the current studies were designed to examine the role of endogenous NT in DA receptor agonist- and NMDA receptor antagonist-induced disruption of prepulse inhibition of the acoustic startle response (PPI), locomotor hyperactivity and brain-region specific c-fos mRNA expression. Adult male rats received a single i.p. injection of SR142948A or vehicle followed by D-amphetamine, apomorphine or dizocilpine challenge. SR142948A had no effect on baseline PPI, but dose-dependently attenuated d-amphetamine- and dizocilpine-induced PPI disruption and enhanced apomorphine-induced PPI disruption. SR142948A did not significantly affect either baseline locomotor activity or stimulant-induced hyperlocomotion. Systemic SR142948A administration prevented c-fos mRNA induction in mesolimbic terminal fields (prefrontal cortex, lateral septum, NAcc, ventral subiculum) induced by all three psychostimulants implicating the VTA as the site for NT modulation of stimulant-induced PPI disruption. Further characterization of the NT system may be valuable to find clinical useful compounds for schizophrenia and drug addiction.

The brattleboro rat displays a natural deficit in social discrimination that is restored by clozapine and a neurotensin analog

Cognitive deficits in schizophrenia are a major source of dysfunction for which more effective treatments are needed. The vasopressin-deficient Brattleboro (BRAT) rat has been shown to have several natural schizophrenia-like deficits, including impairments in prepulse inhibition and memory. We investigated BRAT rats and their parental strain, Long-Evans (LE) rats, in a social discrimination paradigm, which is an ethologically relevant animal test of cognitive deficits of schizophrenia based upon the natural preference of animals to investigate conspecifics. We also investigated the effects of the atypical antipsychotic, clozapine, and the putative antipsychotic, PD149163, a brain-penetrating neurotensin-1 agonist, on social discrimination in these rats. Adult rats were administered saline or one of the three doses of clozapine (0.1, 1.0, or 10 mg/kg) or PD149163 (0.1, 0.3, or 1.0 mg/kg), subcutaneously. Following drug administration, adult rats were exposed to a juvenile rat for a 4-min learning period. Animals were then housed individually for 30 min and then simultaneously exposed to the juvenile presented previously and a new juvenile for 4 min. Saline-treated LE rats, but not BRAT rats, exhibited intact social discrimination as evidenced by greater time spent exploring the new juvenile. The highest dose of clozapine and the two highest doses of PD149163 restored social discrimination in BRAT rats. These results provide further support for the utility of the BRAT rat as a genetic animal model relevant to schizophrenia and drug discovery. The potential of neurotensin agonists as putative treatments for cognitive deficits of schizophrenia was also supported.