Locomotor sensitization to [D-Trp(11)]neurotensin after repeated injections of the dopamine uptake inhibitor GBR12783 in rats

Cocaine induces locomotor sensitization through a dopamine-dependent VTA-mPFC-FrA cortico-cortical pathway in male mice

As a central part of the mammalian brain, the prefrontal cortex (PFC) has been implicated in regulating cocaine-induced behaviors including compulsive seeking and reinstatement. Although dysfunction of the PFC has been reported in animal and human users with chronic cocaine abuse, less is known about how the PFC is involved in cocaine-induced behaviors. By using two-photon Ca²⁺ imaging to simultaneously record tens of intact individual networking neurons in the frontal association cortex (FrA) in awake male mice, here we report that a systematic acute cocaine exposure decreased the FrA neural activity in mice, while the chemogenetic intervention blocked the cocaine-induced locomotor sensitization. The hypoactivity of FrA neurons was critically dependent on both dopamine transporters and dopamine transmission in the ventromedial PFC (vmPFC). Both dopamine D1R and D2R neurons in the vmPFC projected to and innervated FrA neurons, the manipulation of which changed the cocaine-induced hypoactivity of the FrA and locomotor sensitization. Together, this work demonstrates acute cocaine-induced hypoactivity of FrA neurons in awake mice, which defines a cortico-cortical projection bridging dopamine transmission and cocaine sensitization.

Mechanisms of locomotor sensitization to drugs of abuse in a two-injection protocol

A single exposure to psychostimulants or morphine is sufficient to induce persistent locomotor sensitization, as well as neurochemical and electrophysiological changes in rodents. Although it provides a unique model to study the bases of long-term behavioral plasticity, sensitization mechanisms remain poorly understood. We investigated in the mouse, a species suited for transgenic studies, the mechanisms of locomotor sensitization showed by the increased response to a second injection of drug (two-injection protocol of sensitization, TIPS). The first cocaine injection induced a locomotor sensitization that was completely context-dependent, increased during the first week, and persisted 3 months later. The induction of sensitized responses to cocaine required dopamine D1 and glutamate NMDA receptors. A single injection of the selective dopamine transporter blocker GBR12783 was sufficient to activate extracellular signal-regulated kinase (ERK) in the striatum to the same level as cocaine and to induce sensitization to cocaine, but not to itself. The induction of sensitization was sensitive to protein synthesis inhibition by anisomycin after cocaine administration. Morphine induced a pronounced context-dependent sensitization that crossed with cocaine. Sensitization to morphine injection was prevented in knockin mutant mice bearing a Thr-34-Ala mutation of DARPP-32, which suppresses its ability to inhibit protein phosphatase-1 (PP1), but not mutation of Thr-75 or Ser-130. These results combined with previous ones show that TIPS in mouse is a context-dependent response, which involves an increase in extracellular dopamine, stimulation of D1 and NMDA receptors, regulation of the cAMP-dependent and ERK pathways, inhibition of PP1, and protein synthesis. It provides a simple and sensitive paradigm to study the mechanisms of long-term effects of drugs of abuse.

Blockade of neurotensin receptors during amphetamine discontinuation indicates individual variability

Psychostimulant-induced locomotor sensitization has been related to changes within the mesolimbic dopamine system and has been suggested to be useful to study mechanisms underlying drug craving. Neurotensin is a neuropeptide co-localized with dopamine in the mesolimbic system. The response to novelty has been suggested to be a predictor of enhanced vulnerability to behavioral sensitization. The effects of repeated treatment with the neurotensin antagonist SR48692 after amphetamine discontinuation were investigated in mice previously classified as high responders (HRs) or low responders (LRs) to novelty. Mice were repeatedly treated with 2.0mg/kg amphetamine, every other day for 11 days. During the first 7 days after amphetamine discontinuation, the animals received a daily injection of saline or 0.3mg/kg SR48692. On the eighth day after amphetamine discontinuation all subjects received a 2.0mg/kg amphetamine challenge injection. Then, mice were tested for an open field behavior and after 90min, were sacrificed for Fos expression quantification in the nucleus accumbens. Both HRs and LRs expressed amphetamine-induced sensitized locomotor activation and increased expression of Fos protein. Treatment with SR48692 prevented behavioral sensitization and Fos protein expression enhancement in LRs but not in HRs mice. These data suggest that neurotensin plays a role in individual variability to amphetamine-induced sensitization.

Brain neurotensin, psychostimulants, and stress--emphasis on neuroanatomical substrates

Neurotensin (NT) is a peptide that is widely distributed throughout the brain. NT is involved in locomotion, reward, stress and pain modulation, and in the pathophysiology of drug addiction and depression. In its first part this review brings together relevant literature about the neuroanatomy of NT and its receptors. The second part focuses on functional-anatomical interactions between NT, the mesotelencephalic dopamine system and structures targeted by dopaminergic projections. Finally, recent data about the actions of NT in processes underlying behavioral sensitization to psychostimulant drugs and the involvement of NT in the regulation of the hypothalamo-pituitary-adrenal gland axis are considered.

The neurotensin receptor antagonist, SR48692, attenuates the expression of amphetamine-induced behavioural sensitisation in mice

The effects of acute administration of the neurotensin receptor antagonist, SR48692 (2-[[1-(7-chloroquinolin-4-yl)-5-(2,6-dimethoxyphenyl)-1H-pyrazol-3-carbonyl]amino]adamantane-2-carboxylic acid), on amphetamine-induced behavioural sensitisation were studied with the locomotor activity of mice in an open-field as an experimental parameter. The animals were repeatedly pretreated with saline or amphetamine (2.0 mg/kg, i.p. once a day, every other day for 13 days) and 2, 9 and 16 days after the last injection they received an acute i.p. administration of saline or 0.3 mg/kg SR48692 15 min before a challenge i.p. injection of 2.0 mg/kg amphetamine. Locomotor activity of the amphetamine-challenged mice was significantly higher in amphetamine-pretreated animals than in saline-pretreated mice on days 9 and 16 after withdrawal. SR48692 prevented the expression of this behavioural sensitisation. In addition, in saline-pretreated mice, the first two challenge injections of amphetamine sufficed to induce a sensitized locomotor response to the third challenge injection of the drug. SR48692 administration before amphetamine challenge injections prevented the development of this challenge injection-induced sensitisation in saline-pretreated mice but not in amphetamine-pretreated animals. In order to determine the effects of SR48692 on the expression of amphetamine-induced behavioural sensitisation in the absence of this challenge injection-induced sensitisation, the experiment was redone with a single challenge test 9 days after pretreatment. Once again, SR48692 prevented the expression of amphetamine-induced behavioural sensitisation. These results suggest that neurotensinergic transmission has a critical role in both the initiation and expression of locomotor sensitisation to amphetamine.

Distinct and interactive effects of d-amphetamine and haloperidol on levels of neurotensin and its mRNA in subterritories in the dorsal and ventral striatum of the rat

Striatal tissue concentrations of neurotensin, expression of neurotensin/neuromedin N (NT/N) mRNA, and numbers of neurotensin-immunoreactive neurons are increased by d-amphetamine (amph), which stimulates dopamine release in the striatum, and haloperidol (hal), a dopamine receptor antagonist with high affinity for D2-like receptors. The possibility that the effects of these drugs involve distinct subpopulations of striatal neurons was addressed in this study, in which the relative numbers and distributions of striatal neuron profiles containing neurotensin immunoreactivity and/or NT/N mRNA were compared following administrations of hal, amph, hal and amph co-administered, and vehicle. Fourteen striatal subterritories in caudate-putamen, nucleus accumbens, and olfactory tubercle were evaluated. Amph produced increases in the expression of neurotensin preferentially in the ventromedial and caudodorsal subterritories of the caudate-putamen, the rostrobasal cell cluster and lateral shell of the nucleus accumbens, and the olfactory tubercle. Haloperidol produced increased neurotensin expression in much of dorsal and ventral striatum, most prominently in the rostral, dorsomedial and ventrolateral quadrants of the caudate-putamen, and in the rostrobasal cell cluster, rostral pole, medial and lateral shell of the nucleus accumbens and the olfactory tubercle. The numbers of neurons responding to amph and hal in all subterritories following co-administration of the two drugs were significantly less than the summed numbers responding individually to amph and hal. Furthermore, in the subterritories where immunohistochemically detectable responses elicited by amph exceeded those produced by hal, co-administration of the two drugs resulted in responses comparable to those elicited by hal given alone. It is suggested that some of the reported anti-dopaminergic behavioral effects of basal ganglia neurotensin may be attenuated in conditions of reduced dopamine neurotransmission.