Selective tolerance to the hypothermic and anticataleptic effects of a neurotensin analog that crosses the blood–brain barrier

doi:10.1016/S0006-8993(03)03227-X

Brain Research

Volume 987, Issue 1, 10 October 2003, Pages 39-48

https://doi.org/10.1016/S0006-8993(03)03227-X Get rights and content

Abstract

NT69L, a neurotensin analog that crosses the blood–brain barrier, reduces body temperature, reverses apomorphine-induced climbing, haloperidol-induced catalepsy, and d-amphetamine- and cocaine-induced locomotor activity in rats. In this study we tested the development of tolerance to these effects of NT69L in rats. The blockade of apomorphine-induced climbing behavior and d-amphetamine- and cocaine-induced hyperactivity seen after a single acute injection did not show significant change with repeated daily injections of NT69L. Thus, for example, NT69L after five daily injections at a fixed dosage was as effective at reversing cocaine-induced hyperactivity as after the first injection. On the other hand, repeated daily injections of NT69L resulted in a diminished hypothermic response and a diminished anticataleptic effect against haloperidol. The effect of NT69L on blood glucose, cortisol, and thyroxine (T₄) were all back to control levels after five daily injections. Thus, tolerance developed to NT69L after the first injection, when it was tested for causing hypothermia, blockade of haloperidol-induced catalepsy, and change in blood glucose, cortisol and T₄ levels. Since tolerance did not develop to the effects of drugs acting as direct (apomorphine) or indirect (d-amphetamine and cocaine) agonists at dopamine receptors over the course of 5 days, these findings suggest a selective role of neurotensin in the modulation of dopamine neurotransmission. Furthermore, due to the lack of development of tolerance, NT69L or similar analogs might be useful in modulating certain behavioral effects of psychostimulants or have potential use as an antipsychotic drug in humans.

Introduction

Neurotensin is an endogenous tridecapeptide neurotransmitter that was discovered by Carraway and Leeman in bovine hypothalami [5]. It is found in the central nervous system as well as in the gastrointestinal tract. Neurotensin exerts potent central nervous system effects including hypothermia [1], antinociception [19], modulation of dopamine neurotransmission [9], [16], [20], [21], and stimulation of anterior pituitary hormone secretion [18], [22], [25]. Peripherally, neurotensin acts as a paracrine and endocrine peptide of both the digestive and cardiovascular systems. All known effects of NT(1–13) are mediated by the smaller fragment, NT(8–13).

For neurotensin to exert its central nervous system effects, it needs to be delivered directly into the brain. This is due in part to its rapid degradation by peptidases upon systemic administration [6]. Although peptides generally do not cross the blood–brain barrier [23], many groups have worked on developing a neurotensin agonist that could be delivered systemically and cross this highly selective barrier.

Our laboratory has been working on developing neurotensin peptide analogs that are resistant to peptidase degradation and can cross the blood–brain barrier. Because neurotensin has neuroleptic-like effects in animal models, our aim has been to develop a potential, novel antipsychotic for human use. Such a novel neuroleptic would lack the dopamine receptor blocking effects of currently available antipsychotics and therefore, would not likely produce extrapyramidal side effects, including tardive dyskinesia.

Previously, we reported on a NT(8–13) analog, called NT69L, that crosses the blood–brain barrier [31]. NT69L causes hypothermia, antinociception, and has neuroleptic-like properties, similar to those of atypical neuroleptics. Thus, for this latter property, NT69L blocks the climbing behavior in rats induced by the dopamine agonist apomorphine at a high dose (600 μg/kg) [7]. It also reverses haloperidol-induced catalepsy [7]. Due to its potential use as an atypical neuroleptic, we were interested to learn if repeated injections of NT69L would result in the development of tolerance to its various effects. Here we report on the selective development of tolerance to some, but not to all of the effects of NT69L.

Section snippets

Drugs

NT69L was synthesized as previously described [7]. Haloperidol (H-1512), apomorphine (4393-), d-amphetamine (A-5880) and cocaine (C-5776) were purchased from Sigma (St. Louis, MO, USA).

Animals

Male Sprague–Dawley rats weighing 150–250 g were used for all experiments. Rats were housed in a temperature controlled room with free access to food and water. The animals were kept on a 12 h light–dark cycle. All tests were performed during the light cycle. The rats in each group were used only for one

Hypothermia

After the first daily injection of NT69L (1 mg/kg), there was a marked reduction in body temperature (Fig. 1) as we have reported previously, with an ED₅₀ of 390 μg/kg [7]. However, body temperature did not deviate from normal after the third or fifth daily injection of this peptide (P=0.008). Challenging the rats with five times the dose resulted in a drop of body temperature similar to that found after the first day’s injection (results not shown) indicating development of tolerance.

Haloperidol-induced catalepsy

NT69L

Discussion

Chronic stimulation of neurotransmitter receptors may lead to adaptive changes that result in a decreased responsiveness to the neurotransmitter. If the agent that is stimulating the receptor is a drug, then the phenomenon that occurs is called tolerance. More generally, tolerance is defined as a decreased responsiveness to a drug after repeated exposure, requiring higher dosages of the drug to cause the same level of effect. At the molecular level, mechanisms explaining tolerance to a drug are

References (38)

M. Boules et al.
A novel neurotensin peptide analog given extracranially decreases food intake and weight in rodents
Brain Res.
(2000)
M. Boules et al.
Antiparkinson-like effects of a novel neurotensin analog in unilaterally 6-hydroxydopamine lesioned rats
Eur. J. Pharmacol.
(2001)
M. Boules et al.
A novel neurotensin analog blocks cocaine- and d-amphetamine-induced hyperactivity
Eur. J. Pharmacol.
(2001)
R. Carraway et al.
The isolation of a new hypotensive peptide, neurotensin, from bovine hypothalami
J. Biol. Chem.
(1973)
B. Cusack et al.
Effects of a novel neurotensin peptide analog given extracranially on CNS behaviors mediated by apomorphine and haloperidol
Brain Res.
(2000)
A.D. Drumheller et al.
Effects of neurotensin on regional brain concentrations of dopamine, serotonin and their main metabolites
Neuropeptides
(1990)
I. Dubuc et al.
Tolerance to the hypothermic but not to the analgesic effect of [d-Trp11]neurotensin during the semichronic intracerebroventricular infusion of the peptide in rats
Peptides
(1994)
J.A. Gilbert et al.
Desensitization of neurotensin receptor-mediated cyclic GMP formation in neuroblastoma clone N1E-115
Biochem. Pharmacol.
(1988)
P. Hertel et al.
Induction of tolerance to the suppressant effect of the neurotensin analogue NT69L on amphetamine-induced hyperactivity
Eur. J. Pharm.
(2001)
F.B. Jolicoeur et al.
Differential neurobehavioral effects of neurotensin and structural analogues
Peptides
(1981)

B. Kinkead et al.

Does neurotensin mediate the effects of antipsychotic drugs?

Biol. Psychiatry

(1999)

C.B. Nemeroff et al.

Neurotensin: central nervous system effects of a hypothalamic peptide

Brain Res.

(1977)

G.J. Rinkel et al.

Elective tolerance to behavioral effects of neurotensin

Physiol. Behav.

(1983)

P. Sarret et al.

Pharmacology and functional properties of NTS2 neurotensin receptors in cerebellar granule cells

J. Biol. Chem.

(2002)

B. Scatton

Differential regional development of tolerance to increase in dopamine turnover upon repeated neuroleptic administration

Eur. J. Pharmacol.

(1977)

B. Scatton et al.

Dopamine metabolism in the mesolimbic and mesocortical dopaminergic systems after single or repeated administrations of neuroleptics

Brain Res.

(1976)

B. Scatton et al.

Effects of thioproperazine and apomorphine on dopamine synthesis in the mesocortical dopaminergic systems

Brain Res.

(1975)

R.E. See

Striatal dopamine metabolism increases during long-term haloperidol administration in rats but shows tolerance in response to acute challenge with raclopride

Neurosci. Lett.

(1991)

B.M. Tyler et al.

In vitro binding and CNS effects of novel neurotensin agonists that cross the blood–brain barrier

Neuropharmacology

(1999)

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Activation of neurotensin receptor type 1 attenuates locomotor activity
2014, Neuropharmacology
Intracerebroventricular administration of neurotensin (NT) suppresses locomotor activity. However, the brain regions that mediate the locomotor depressant effect of NT and receptor subtype-specific mechanisms involved are unclear. Using a brain-penetrating, selective NT receptor type 1 (NTS1) agonist PD149163, we investigated the effect of systemic and brain region-specific NTS1 activation on locomotor activity. Systemic administration of PD149163 attenuated the locomotor activity of C57BL/6J mice both in a novel environment and in their homecage. However, mice developed tolerance to the hypolocomotor effect of PD149163 (0.1 mg/kg, i.p.). Since NTS1 is known to modulate dopaminergic signaling, we examined whether PD149163 blocks dopamine receptor-mediated hyperactivity. Pretreatment with PD149163 (0.1 or 0.05 mg/kg, i.p.) inhibited D2R agonist bromocriptine (8 mg/kg, i.p.)-mediated hyperactivity. D1R agonist SKF-81297 (8 mg/kg, i.p.)-induced hyperlocomotion was only inhibited by 0.1 mg/kg of PD149163. Since the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC) have been implicated in the behavioral effects of NT, we examined whether microinjection of PD149163 into these regions reduces locomotion. Microinjection of PD149163 (2 pmol) into the NAc, but not the mPFC suppressed locomotor activity. In summary, our results indicate that systemic and intra-NAc activation of NTS1 is sufficient to reduce locomotion and NTS1 activation inhibits D2R-mediated hyperactivity. Our study will be helpful to identify pharmacological factors and a possible therapeutic window for NTS1-targeted therapies for movement disorders.
Repeated effects of the neurotensin receptor agonist PD149163 in three animal tests of antipsychotic activity: Assessing for tolerance and cross-tolerance to clozapine
2014, Pharmacology Biochemistry and Behavior
Neurotensin is an endogenous neuropeptide closely associated with the mesolimbic dopaminergic system and shown to possess antipsychotic-like effects. In particular, acute neurotensin receptor activation can inhibit conditioned avoidance response (CAR), attenuate phencyclidine (PCP)-induced prepulse inhibition (PPI) disruptions, and reverse PCP-induced hyperlocomotion. However, few studies have examined the long term effects of repeated neurotensin receptor activation and results are inconsistent. Since clinical administration of antipsychotic therapy often requires a prolonged treatment schedule, here we assessed the effects of repeated activation of neurotensin receptors using an NTS1 receptor selective agonist, PD149163, in 3 behavioral tests of antipsychotic activity. We also investigated whether reactivity to the atypical antipsychotic clozapine was altered following prior PD149163 treatment. Using both normal and prenatally immune activated rats generated through maternal immune activation with polyinosinic:polycytidylic acid, we tested PD149163 in CAR, PCP (1.5 mg/kg)-induced PPI disruption, and PCP (3.2 mg/kg)-induced hyperlocomotion. For each paradigm, rats were first repeatedly tested with vehicle or PD149163 (1.0, 4.0, 8.0 mg/kg, sc) along with vehicle or PCP for PPI and hyperlocomotion tests, then challenged with PD149163 after 2 drug-free days. All rats were then challenged with clozapine (5.0 mg/kg, sc). During the repeated test period, PD149163 exhibited antipsychotic-like effects in all three models. On the PD149163 challenge day, prior drug treatment only caused a tolerance effect in CAR. This tolerance in CAR was transferrable to clozapine, as it enhanced clozapine tolerance in the same group of animals. Although no tolerance effect was seen in the PD149163 challenge for the PCP-induced hyperlocomotion test, the clozapine challenge showed increased sensitivity in groups previously exposed to repeated PD149163 treatment. Our findings suggest that repeated exposure to NTS1 receptor agonists can induce a dose-dependent tolerance and cross-tolerance to clozapine to some of its behavioral effects but not others.
Acute, but not repeated, administration of the neurotensin NTS<inf>1</inf> receptor agonist PD149163 decreases conditioned footshock-induced ultrasonic vocalizations in rats
2014, Progress in Neuro-Psychopharmacology and Biological Psychiatry
Neurotensin is an endogenous neuropeptide that has significant interactions with monoamine neurotransmitter systems. To date, neurotensin NTS₁ receptor agonists, such as PD149163, have been primarily evaluated for the treatment for schizophrenia, drug addiction, and pain. Recently, PD149163 was found to attenuate fear-potentiated startle in rats, an experimental procedure used for screening anxiolytic drugs. The present study sought to assess these findings through testing PD149163 in a conditioned footshock-induced ultrasonic vocalization (USV) model. Conditioning was conducted in male Wistar rats using chambers equipped with shock grid floors and an ultrasonic vocalization detector. PD149163 and the 5-HT_1A receptor partial agonist buspirone produced a statistically significant reduction of 22 kHz USV counts. The typical antipsychotic haloperidol also reduced 22 kHz USV counts, but did so at cataleptic doses. Ten days of repeated administration of PD149163 abolished the inhibitory effects of PD149163 on 22 kHz USVs. These findings further support an anxiolytic profile for PD149163. However, tolerance to these effects may limit the utility of these drugs for the treatment of anxiety.
The role of NTS2 in the development of tolerance to NT69L in mouse models for hypothermia and thermal analgesia
2011, Behavioural Brain Research
Citation Excerpt :
These data support the theory that repeated activation of NTS1 leads to tolerance. Also, these data confirm previous reports of tolerance to NT-mediated [43] and NT69L-mediated [19] hypothermia in rats. By contrast, mice deficient in NTS2 failed to develop tolerance to NT69L-mediated hypothermia or thermal analgesia.
NT69L is a neurotensin (NT)(8-13) analog that binds the two major NT receptors, NTS1 and NTS2, and elicits similar behavioral effects as endogenous NT. Tolerance develops rapidly to some, but not to all of NT69L's effects, and to date, little is known about the mechanisms responsible for this tolerance. The development of tolerance appears to be more prevalent in behavioral effects mediated by NTS1 than by those mediated by NTS2, including hypothermia and thermal analgesia. However, we hypothesize that both NTS1 and NTS2 have important roles in mediating the effects of NT69L. Here, we investigate the role of NTS2 on NT69L-mediated hypothermia and thermal analgesia with the use of NTS2 knock-out mice. We show that tolerance develops to NT69L-mediated hypothermia and thermal analgesia following sub-chronic treatment in wild-type (WT) mice, and that NTS2 is necessary for the development of that tolerance. Additionally, we suggest potential means by which NTS2 influences these NT69L-mediated behaviors.
Chronic NT69L potently prevents drug-induced disruption of prepulse inhibition without causing tolerance
2010, Behavioural Brain Research
NT69L is a neurotensin receptor agonist with antipsychotic-like activity. NT69L blocks apomorphine-induced climbing in rats with no effect on stereotypic behavior, attenuates d-amphetamine-induced hyperactivity, and blocks pharmacologically induced disruption of prepulse inhibition (PPI) of the startle response. Repeated administration of NT69L results in tolerance to some, but not to all of its effects. Because schizophrenic patients require long-term treatment, chronic (21-day) administration of NT69L was tested in PPI with comparisons to chronic haloperidol and clozapine treatment.
Sprague–Dawley rats received acute or 21 daily, subcutaneous injections of NT69L (1.0 mg/kg). On days 1 and 21 the NT69L injection was followed 30 min later by treatment with either saline; the dopamine agonist, d-amphetamine (5.0 mg/kg); or the serotonin 5-HT_2A psychotomimetic receptor agonist [1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane] DOI (0.5 mg/kg). Experiments were repeated with either haloperidol (1 mg/kg) or clozapine (20 mg/kg) in place of NT69L. Acute injection of NT69L significantly blocked d-amphetamine and DOI disruption of PPI. As with the acute injection, 21 daily administrations of NT69L also blocked d-amphetamine- and DOI-induced disruption of PPI. The data show that animals do not develop tolerance to the antipsychotic-like effects of NT69L when tested in the PPI of the startle response. The persistent efficacy of NT69L with chronic treatment provides further support for the therapeutic use of neurotensin (NT) agonists to treat schizophrenia and possibly other disorders that are characterized by PPI deficits. The modulatory role of NT69L on the dopaminergic and serotonergic neurotransmission systems both of which are implicated in the pathophysiology of schizophrenia is discussed.
The novel neurotensin analog NT69L blocks phencyclidine (PCP)-induced increases in locomotor activity and PCP-induced increases in monoamine and amino acids levels in the medial prefrontal cortex
2010, Brain Research
Citation Excerpt :
Moreover, a large amount of evidence suggests that targeting the neurotensin system may provide a novel treatment for schizophrenia (Breslin et al., 1994; Garver et al., 1991; Sharma et al., 1997). Our group has been developing analogs of NT that can be administered peripherally, pass into brain, and induce behavioral effects and neurochemical changes similar to those of native NT directly injected into brain (Boules et al., 2003; Boules et al., 2006). Since all known activity of NT is mediated by the 8–13 fragment, we have focused our efforts on this part of the molecule.
Schizophrenia is a life-long, severe, and disabling brain disorder that requires chronic pharmacotherapy. Because current antipsychotic drugs do not provide optimal therapy, we have been developing novel treatments that focus on receptors for the neuropeptide neurotensin (NT). NT69L, an analog of neurotensin(8-13), acts like an atypical antipsychotic drug in several dopamine-based animal models used to study schizophrenia. Another current animal model utilizes non-competitive antagonists of the NMDA/glutamate receptor, such as the psychotomimetic phencyclidine (PCP). In the present study, we investigated the effects of NT69L on PCP-induced behavioral and biochemical changes in the rat. The top of an activity chamber was modified to allow us to perform microdialysis in rat brain, while simultaneously recording the locomotor activity of a rat. PCP injection significantly increased activity as well as the extracellular concentration of norepinephrine (NE), 5-HT, dopamine (DA), and glutamate in the medial prefrontal cortex (mPFC). Pretreating with NT69L blocked the PCP-induced hyperactivity as well as the increase of DA, 5-HT, NE, and glutamate in mPFC. Interestingly and unexpectedly, NT69L markedly increased glycine levels, while PCP was without effect on glycine levels. Thus, NT69L showed antipsychotic-like effects in this glutamate-based animal model for studying schizophrenia. Previous work from our group suggests that NT69L also has antipsychotic-like effects in dopaminergic and serotonergic rodent models. Taken together, these data suggest that NT69L in particular and NT receptor agonists in general, will be useful as broad-spectrum antipsychotic drugs.

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Research reportSelective tolerance to the hypothermic and anticataleptic effects of a neurotensin analog that crosses the blood–brain barrier

Abstract

Introduction

Section snippets

Drugs

Animals

Hypothermia

Haloperidol-induced catalepsy

Discussion

Brain Res.

Eur. J. Pharmacol.

Eur. J. Pharmacol.

J. Biol. Chem.

Brain Res.

Neuropeptides

Peptides

Biochem. Pharmacol.

Eur. J. Pharm.

Peptides

Biol. Psychiatry

Brain Res.

Physiol. Behav.

J. Biol. Chem.

Eur. J. Pharmacol.

Brain Res.

Brain Res.

Neurosci. Lett.

Neuropharmacology

Research report
Selective tolerance to the hypothermic and anticataleptic effects of a neurotensin analog that crosses the blood–brain barrier