Differential effects of cocaine and methamphetamine on neurotensin/neuromedin N and preprotachykinin messenger RNA expression in unique regions of the striatum

Neurotensin receptor 1 deletion decreases methamphetamine self-administration and the associated reduction in dopamine cell firing

We previously reported that a non-selective pharmacological blockade of neurotensin receptors in the ventral tegmental area (VTA) decreases methamphetamine (METH) self-administration in mice. Here, we explored the consequences of genetic deletion of neurotensin receptor 1 (NtsR1) on METH self-administration and VTA dopamine neuron firing activity. We implanted mice with an indwelling jugular catheter and trained them to nose-poke for intravenous infusions of METH. Mice with NtsR1 deletion (KO) acquired self-administration similar to wildtype (WT) and heterozygous (HET) littermates. However, in NtsR1 KO and HET mice, METH intake and motivated METH seeking decreased when the response requirement was increased to a fixed ratio 3 and when mice were tested on a progressive ratio protocol. After completion of METH self-administration, single cell in vivo extracellular recordings of dopamine firing activity in the VTA were obtained in anesthetized mice. Non-bursting dopamine neurons from KO mice fired at slower rates than those from WT mice, supporting an excitatory role for NtsR1 on VTA dopamine neuronal activity. In WT mice, a history of METH self-administration decreased dopamine cell firing frequency compared with cells from drug-naïve controls. NtsR1 KO and HET mice did not exhibit this decline in dopamine cell firing activity after METH experience. We also observed an increase in population activity following METH self-administration that was strongest in the WT group. Our results suggest a role for NtsR1 in METH-seeking behavior and indicate that ablation of NtsR1 prevents the detrimental effects of prolonged METH self-administration on VTA dopamine cell firing frequency.

Translational study of the whole transcriptome in rats and genetic polymorphisms in humans identifies LRP1B and VPS13A as key genes involved in tolerance to cocaine-induced motor disturbances

Motor disturbances strongly increase the burden of cocaine use disorder (CUDs). The objective of our translational study was to identify the genes and biological pathways underlying the tolerance to cocaine-induced motor effects. In a 5-day protocol measuring motor tolerance to cocaine in rats (N = 40), modeling the motor response to cocaine in patients, whole-genome RNA sequencing was conducted on the ventral and dorsal striatum to prioritize a genetic association study in 225 patients with severe CUD who underwent thorough phenotypic (cocaine-induced hyperlocomotion, CIH; and cocaine-induced stereotypies, CIS) and genotypic [571,000 polymorphisms (SNPs)] characterization. We provide a comprehensive description of the rat striatal transcriptomic response to cocaine in our paradigm. Repeated vs. acute cocaine binge administration elicited 27 differentially expressed genes in the ventral striatum and two in the dorsal striatum. One gene, Lrp1b, was differentially expressed in both regions. In patients, LRP1B was significantly associated with both CIS and CIH. CIH was also associated with VPS13A, a gene involved in a severe neurological disorder characterized by hyperkinetic movements. The LRP1B minor allele rs7568970 had a significant protective effect against CIS (558 SNPs, Bonferroni-corrected p = 0.02) that resisted adjustment for confounding factors, including the amount of cocaine use (adjusted beta = -0.965 and -2.35 for heterozygotes and homozygotes, respectively, p < 0.01). Using hypothesis-free prioritization of candidate genes along with thorough methodology in both the preclinical and human analysis pipelines, we provide reliable evidence that LRP1B and VPS13A are involved in the motor tolerance to cocaine in CUD patients, in line with their known pathophysiology.

Neurokinin receptors in drug and alcohol addiction

The neurokinins are a class of peptide signaling molecules that mediate a range of central and peripheral functions including pain processing, gastrointestinal function, stress responses, and anxiety. Recent data have linked these neuropeptides with drug-related behaviors. Specifically, substance P (SP) and neurokinin B (NKB), have been shown to influence responses to alcohol, cocaine, and/or opiate drugs. SP and NKB preferentially bind to the neurokinin-1 receptor (NK1R) and neurokinin-3 receptor (NK3R), respectively, but do have some affinity for all classes of neurokinin receptor at high concentrations. NK1R activity has been shown to influence reward and reinforcement for opiate drugs, stimulatory and neurochemical responses to cocaine, and escalated and stress-induced alcohol seeking. In reinstatement models of relapse-like behavior, NK1R antagonism attenuates stress-induced reinstatement for all classes of drugs tested to date. The NK3R also influences alcohol intake and behavioral/neurochemical responses to cocaine, but less research has been performed in regard to this particular receptor in preclinical models of addiction. Clinically, agents targeting these receptors have shown some promise, but have produced mixed results. Here, the preclinical findings for the NK1R and NK3R are reviewed, and discussion is provided to interpret clinical findings. Additionally, important factors to consider in regards to future clinical work are suggested.

ProSAAS-derived peptides are regulated by cocaine and are required for sensitization to the locomotor effects of cocaine

To identify neuropeptides that are regulated by cocaine, we used a quantitative peptidomic technique to examine the relative levels of neuropeptides in several regions of mouse brain following daily intraperitoneal administration of 10 mg/kg cocaine or saline for 7 days. A total of 102 distinct peptides were identified in one or more of the following brain regions: nucleus accumbens, caudate putamen, frontal cortex, and ventral tegmental area. None of the peptides detected in the caudate putamen or frontal cortex were altered by cocaine administration. Three peptides in the nucleus accumbens and seven peptides in the ventral tegmental area were significantly decreased in cocaine-treated mice. Five of these ten peptides are derived from proSAAS, a secretory pathway protein and neuropeptide precursor. To investigate whether proSAAS peptides contribute to the physiological effects of psychostimulants, we examined acute responses to cocaine and amphetamine in the open field with wild-type (WT) and proSAAS knockout (KO) mice. Locomotion was stimulated more robustly in the WT compared to mutant mice for both psychostimulants. Behavioral sensitization to amphetamine was not maintained in proSAAS KO mice and these mutants failed to sensitize to cocaine. To determine whether the rewarding effects of cocaine were altered, mice were tested in conditioned place preference (CPP). Both WT and proSAAS KO mice showed dose-dependent CPP to cocaine that was not distinguished by genotype. Taken together, these results suggest that proSAAS-derived peptides contribute differentially to the behavioral sensitization to psychostimulants, while the rewarding effects of cocaine appear intact in mice lacking proSAAS.

Effect of low doses of methamphetamine on rat limbic-related neurotensin systems

Administration of methamphetamine (METH) alters limbic-related (LR) neurotensin (NT) systems. Thus, through a D1-receptor mechanism, noncontingent high doses (5-15 mg kg(-1)), and likely self-administration, of METH appears to reduce NT release causing its accumulation and an elevation of NT-like immunoreactivity (NTLI) in limbic-related NT pathways. For comparison, we tested the effect of low doses of METH, that are more like those used in therapy, on NTLI in the core and shell of the nucleus accumbens (NAc and NAs), prefrontal cortex (PFC), ventral tegmental area (VTA), the lateral habenula (Hb) and basolateral amygdala (Amyg). METH at the dose of 0.25 mg kg(-1) in particular, but not 1.00 mg kg(-1), decreased NTLI concentration in all of the LR structures studied, except for the prefrontal cortex; however, these effects were rapid and brief being observed at 5 h but not at 24 h after treatment. In all of the LR areas where NTLI levels were reduced after the low dose of METH, the effect was blocked by pretreatment with either a D1 or a D2 antagonist. Thus, opposite to high doses like those associated with abuse, the therapeutic-like low-dose METH treatment induced reduction in NT tissue levels likely reflected an increase in NT release and a short-term depletion of the levels of this neuropeptide in LR structures, manifesting features comparable to the response of basal ganglia NT systems to similar low doses of METH.

Responses of the rat basal ganglia neurotensin systems to low doses of methamphetamine

RATIONALE

Administration of high doses of methamphetamine (METH) in a manner mimicking the binging patterns associated with abuse reduces NT release and causes its accumulation and elevated NT levels in extrapyramidal structures by a D1 mechanism. The relevance of these findings to the therapeutic use of METH needs to be studied.

OBJECTIVES

The effect of low doses (comparable to that used for therapy) of METH on basal ganglia NT systems was examined and compared to high-dose and self-administration effects previously reported.

METHODS

Rats were injected four times (2-h intervals) with either saline or low doses of METH (0.25, 0.50, or 1.00 mg/kg/subcutaneously (s.c.)). For the DA antagonist studies, animals were pretreated with a D1 (SCH23390) or D2 (eticlopride) antagonist 15 min prior to METH or saline treatments. Rats were sacrificed 5-48 h after the last injection.

RESULTS

METH at doses of 0.25 and 0.50, but not 1.00 mg/kg, rapidly and briefly decreased NTLI concentration in all basal ganglia structures studied. In the posterior dorsal striatum, the reduction in NT level after low-dose METH appeared to be caused principally by D2 stimulation, but both D2 and D1 stimulation were required for the NT responses in the other basal ganglia regions.

CONCLUSIONS

A novel finding from the present study was that opposite to abuse-mimicking high doses of METH, the therapeutically relevant low-dose METH treatment reduced NT tissue levels likely reflecting an increase in NT release and a short-term depletion of the levels of this neuropeptide in basal ganglia structures. The possible significance is discussed.

Neurotensin agonist attenuates nicotine potentiation to cocaine sensitization

Tobacco usage typically precedes illicit drug use in adolescent and young adult populations. Several animal studies suggest nicotine increases the risk for subsequent cocaine abuse, and may be a negative prognostic factor for treatment of cocaine addiction; i.e., a “gateway drug”. Neurotensin (NT) is a 13-amino acid neuropeptide that modulates dopamine, acetylcholine, glutamate, and GABA neurotransmission in brain reward pathways. NT69L, a NT(8-13) analog, blocks behavioral sensitization (an animal model for psychostimulant addiction) to nicotine, and nicotine self-administration in rats. The present study tested the effect of NT69L on the potentiating effects of nicotine on cocaine-induced locomotor sensitization. Male Wistar rats were injected daily for seven days with nicotine or saline (control) followed by four daily injections of cocaine. NT69L was administered 30 min prior to the last cocaine injection. Behavior was recorded with the use of activity chambers. Subchronic administration of nicotine enhanced cocaine-induced behavioral sensitization in Wistar rats, consistent with an hypothesized gateway effect. These behavioral effects of cocaine were attenuated by pretreatment with NT69L. The effect of the neurotensin agonist on cocaine sensitization in the nicotine treated group indicated a possible therapeutic effect for cocaine addiction, even in the presence of enhanced behavioral sensitization induced by nicotine.

Genome-wide profiling identifies a subset of methamphetamine (METH)-induced genes associated with METH-induced increased H4K5Ac binding in the rat striatum

BACKGROUND

METH is an illicit drug of abuse that influences gene expression in the rat striatum. Histone modifications regulate gene transcription.

METHODS

We therefore used microarray analysis and genome-scale approaches to examine potential relationships between the effects of METH on gene expression and on DNA binding of histone H4 acetylated at lysine 4 (H4K5Ac) in the rat dorsal striatum of METH-naïve and METH-pretreated rats.

RESULTS

Acute and chronic METH administration caused differential changes in striatal gene expression. METH also increased H4K5Ac binding around the transcriptional start sites (TSSs) of genes in the rat striatum. In order to relate gene expression to histone acetylation, we binned genes of similar expression into groups of 100 genes and proceeded to relate gene expression to H4K5Ac binding. We found a positive correlation between gene expression and H4K5Ac binding in the striatum of control rats. Similar correlations were observed in METH-treated rats. Genes that showed acute METH-induced increased expression in saline-pretreated rats also showed METH-induced increased H4K5Ac binding. The acute METH injection caused similar increases in H4K5Ac binding in METH-pretreated rats, without affecting gene expression to the same degree. Finally, genes that showed METH-induced decreased expression exhibited either decreases or no changes in H4K5Ac binding.

CONCLUSION

Acute METH injections caused increased gene expression of genes that showed increased H4K5Ac binding near their transcription start sites.

Response of neurotensin basal ganglia systems during extinction of methamphetamine self-administration in rat

Because of persistent social problems caused by methamphetamine (METH), new therapeutic strategies need to be developed. Thus, we investigated the response of central nervous system neurotensin (NT) systems to METH self-administration (SA) and their interaction with basal ganglia dopamine (DA) pathways. Neurotensin is a peptide associated with inhibitory feedback pathways to nigrostriatal DA projections. We observed that NT levels decreased in rats during extinction of METH SA when lever pressing resulted in intravenous infusions of saline rather than METH. Thus, 6 h after the first session of extinction, NT levels were 53, 42, and 49% of corresponding controls in the anterior dorsal striatum, posterior dorsal striatum, and globus pallidus, respectively. NT levels were also significantly reduced in corresponding yoked rats in the anterior dorsal striatum (64% of control), but not the other structures examined. The reductions in NT levels in the anterior dorsal striatum particularly correlated with the lever pressing during the first session of extinction (r =s; 0.745). These, and previously reported findings, suggest that the extinction-related reductions in NT levels were mediated by activation of D2 receptors. Finally, administration of the neurotensin receptor 1 (NTR1) agonist [PD149163 [Lys(CH2NH)Lys-Pro,Trp-tert-Leu-Leu-Oet]; 0.25 or 0.5 mg/kg] diminished lever pressing during the first extinction session, whereas the NTR1 antagonist [SR48692 [2-[(1-(7-chloro-4-quinolinyl)-5-(2,6-imethoxyphenyl)pyrazol-3-yl)carbonylamino]tricyclo(3.3.1.1.(3.7))decan-2-carboxylic acid]; 0.3 mg/kg per administration] attenuated the reduction of lever pressing during the second to fourth days of extinction. In summary, these findings support the hypothesis that some of the endogenous basal ganglia NT systems contribute to the elimination of contingent behavior during the early stages of the METH SA extinction process.

Addiction-related gene regulation: risks of exposure to cognitive enhancers vs. other psychostimulants

The psychostimulants methylphenidate (Ritalin, Concerta), amphetamine (Adderall), and modafinil (Provigil) are widely used in the treatment of medical conditions such as attention-deficit hyperactivity disorder and narcolepsy and, increasingly, as "cognitive enhancers" by healthy people. The long-term neuronal effects of these drugs, however, are poorly understood. A substantial amount of research over the past two decades has investigated the effects of psychostimulants such as cocaine and amphetamines on gene regulation in the brain because these molecular changes are considered critical for psychostimulant addiction. This work has determined in some detail the neurochemical and cellular mechanisms that mediate psychostimulant-induced gene regulation and has also identified the neuronal systems altered by these drugs. Among the most affected brain systems are corticostriatal circuits, which are part of cortico-basal ganglia-cortical loops that mediate motivated behavior. The neurotransmitters critical for such gene regulation are dopamine in interaction with glutamate, while other neurotransmitters (e.g., serotonin) play modulatory roles. This review presents (1) an overview of the main findings on cocaine- and amphetamine-induced gene regulation in corticostriatal circuits in an effort to provide a cellular framework for (2) an assessment of the molecular changes produced by methylphenidate, medical amphetamine (Adderall), and modafinil. The findings lead to the conclusion that protracted exposure to these cognitive enhancers can induce gene regulation effects in corticostriatal circuits that are qualitatively similar to those of cocaine and other amphetamines. These neuronal changes may contribute to the addiction liability of the psychostimulant cognitive enhancers.

Activation of mu opioid receptors in the striatum differentially augments methamphetamine-induced gene expression and enhances stereotypic behavior

Mu opioid receptors are densely expressed in the patch compartment of striatum and contribute to methamphetamine-induced patch-enhanced gene expression and stereotypy. To further elucidate the role of mu opioid receptor activation in these phenomena, we examined whether activation of mu opioid receptors would enhance methamphetamine-induced stereotypy and prodynorphin, c-fos, arc and zif/268 expression in the patch and/or matrix compartments of striatum, as well as the impact of mu opioid receptor activation on the relationship between patch-enhanced gene expression and stereotypy. Male Sprague-Dawley rats were intrastriatally infused with d-Ala(2)-N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO; 1 μg/μL), treated with methamphetamine (0.5 mg/kg) and killed at 45 min or 2 h later. DAMGO augmented methamphetamine-induced zif/268 mRNA expression in the patch and matrix compartments, while prodynorphin expression was increased in the dorsolateral patch compartment. DAMGO pre-treatment did not affect methamphetamine-induced arc and c-fos expression. DAMGO enhanced methamphetamine-induced stereotypy and resulted in greater patch versus matrix expression of prodynorphin in the dorsolateral striatum, leading to a negative correlation between the two. These findings indicate that mu opioid receptors contribute to methamphetamine-induced stereotypy, but can differentially influence the genomic responses to methamphetamine. These data also suggest that prodynorphin may offset the overstimulation of striatal neurons by methamphetamine.

Response of limbic neurotensin systems to methamphetamine self-administration

Methamphetamine (METH) abuse is personally and socially devastating. Although effects of METH on dopamine (DA) systems likely contribute to its highly addictive nature, no medications are approved to treat METH dependence. Thus, we and others have studied the METH-induced responses of neurotensin (NT) systems. NT is associated with inhibitory feedback action on DA projections, and NT levels are elevated in both the nucleus accumbens and dorsal striatum after noncontingent treatment with high doses of METH. In the present study, we used a METH self-administration (SA) model (linked to lever pressing) to demonstrate that substitution of an NT agonist for METH, while not significantly affecting motor activity, dramatically reduced lever pressing but was not self-administered per se. We also found that nucleus accumbens NT levels were elevated via a D1 mechanism after five sessions in rats self-administering METH (SAM), with a lesser effect in corresponding yoked rats. Extended (15 daily sessions) exposure to METH SA manifested similar NT responses; however, more detailed analyses revealed (i) 15 days of METH SA significantly elevated NT levels in the nucleus accumbens shell and dorsal striatum, but not the nucleus accumbens core, with a lesser effect in the corresponding yoked METH rats; (ii) the elevation of NT in both the nucleus accumbens shell and dorsal striatum significantly correlated with the total amount of METH received in the self-administering, but not the corresponding yoked METH rats; and (iii) an NT agonist blocked, but an NT antagonist did not alter, lever-pressing behavior on day 15 in SAM rats. After 5 days in SAM animals, NT levels were also elevated in the ventral tegmental area, but not frontal cortex of rats self-administering METH.

Basal Ganglia disorders associated with imbalances in the striatal striosome and matrix compartments

The striatum is composed principally of GABAergic, medium spiny striatal projection neurons (MSNs) that can be categorized based on their gene expression, electrophysiological profiles, and input–output circuits. Major subdivisions of MSN populations include (1) those in ventromedial and dorsolateral striatal regions, (2) those giving rise to the direct and indirect pathways, and (3) those that lie in the striosome and matrix compartments. The first two classificatory schemes have enabled advances in understanding of how basal ganglia circuits contribute to disease. However, despite the large number of molecules that are differentially expressed in the striosomes or the extra-striosomal matrix, and the evidence that these compartments have different input–output connections, our understanding of how this compartmentalization contributes to striatal function is still not clear. A broad view is that the matrix contains the direct and indirect pathway MSNs that form parts of sensorimotor and associative circuits, whereas striosomes contain MSNs that receive input from parts of limbic cortex and project directly or indirectly to the dopamine-containing neurons of the substantia nigra, pars compacta. Striosomes are widely distributed within the striatum and are thought to exert global, as well as local, influences on striatal processing by exchanging information with the surrounding matrix, including through interneurons that send processes into both compartments. It has been suggested that striosomes exert and maintain limbic control over behaviors driven by surrounding sensorimotor and associative parts of the striatal matrix. Consistent with this possibility, imbalances between striosome and matrix functions have been reported in relation to neurological disorders, including Huntington’s disease, L-DOPA-induced dyskinesias, dystonia, and drug addiction. Here, we consider how signaling imbalances between the striosomes and matrix might relate to symptomatology in these disorders.

Methamphetamine induces striatal neurokinin-1 receptor endocytosis primarily in somatostatin/NPY/NOS interneurons and the role of dopamine receptors in mice

Methamphetamine (METH) is a psychostimulant that induces long-term deficits of dopamine terminal markers and apoptotic cell death in the striatum. Our laboratory demonstrated that pharmacological blockade of the neurokinin-1 receptor attenuated the METH-induced damage to the striatal dopamine terminals and the apoptotic cell death of some striatal neurons. Here, we used histological methods to assess the effect of METH on neurokinin-1 receptor trafficking in the striatum as an indirect index of signaling by the neuropeptide substance P (natural ligand for this receptor). Male mice received a single injection of METH (30 mg/kg, i.p.) and were sacrificed 30 min later. Immunohistofluorescence confocal microscopy confirmed that the neurokinin-1 receptor is located on cholinergic and somatostatin interneurons of the striatum. METH induced the trafficking of the neurokinin-1 receptor from the membrane into cytoplasmic endosomes primarily in the somatostatin/NPY/NOS interneurons, and this phenomenon was attenuated by antagonists of the dopamine D1 (SCH-23390), D2 (raclopride), or neurokinin-1 (WIN-51,708) receptors. These data demonstrate that METH induces the trafficking of the striatal neurokinin-1 receptors principally in the somatostatin/NPY/NOS interneurons and that this phenomenon is dependent on the activity of dopamine D1 and D2 receptors.

Methamphetamine-induced dopamine-independent alterations in striatal gene expression in the 6-hydroxydopamine hemiparkinsonian rats

Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle are used extensively as a model of Parkinson's disease. The present experiments sought to identify genes that were affected in the dopamine (DA)-denervated striatum after 6-hydroxydopamine-induced destruction of the nigrostriatal dopaminergic pathway in the rat. We also examined whether a single injection of methamphetamine (METH) (2.5 mg/kg) known to cause changes in gene expression in the normally DA-innervated striatum could still influence striatal gene expression in the absence of DA. Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle resulted in METH-induced rotational behaviors ipsilateral to the lesioned side and total striatal DA depletion on the lesioned side. This injection also caused decrease in striatal serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels. DA depletion was associated with increases in 5-HIAA/5-HT ratios that were potentiated by the METH injection. Microarray analyses revealed changes (±1.7-fold, p<0.025) in the expression of 67 genes on the lesioned side in comparison to the intact side of the saline-treated hemiparkinsonian animals. These include follistatin, neuromedin U, and tachykinin 2 which were up-regulated. METH administration caused increases in the expression of c-fos, Egr1, and Nor-1 on the intact side. On the DA-depleted side, METH administration also increased the expression of 61 genes including Pdgf-d and Cox-2. There were METH-induced changes in 16 genes that were common in the DA-innervated and DA-depleted sides. These include c-fos and Nor-1 which show greater changes on the normal DA side. Thus, the present study documents, for the first time, that METH mediated DA-independent changes in the levels of transcripts of several genes in the DA-denervated striatum. Our results also implicate 5-HT as a potential player in these METH-induced alterations in gene expression because the METH injection also caused significant increases in 5-HIAA/5-HT ratios on the DA-depleted side.

NK-3 receptor antagonism prevents behavioral sensitization to cocaine: a role of glycogen synthase kinase-3 in the nucleus accumbens

Repeated administration of cocaine induces heightened behavioral hyperactivity termed sensitization. Although NK-3 receptors have been shown to modulate acute cocaine-induced behaviors, their role in behavioral sensitization is unknown. The present study investigated whether NK-3 receptor blockade altered behavioral sensitization to cocaine. Additionally, glycogen synthase kinase-3 (GSK3) has been shown to be involved in dopamine receptor signaling and in development of sensitization; therefore regulation of GSK3 activity in the nucleus accumbens was also investigated. Administration of the NK-3 receptor antagonist SB 222200 (5 mg/kg, s.c.) prior to repeated cocaine (20 mg/kg, i.p.) prevented the development of sensitized responses after a cocaine challenge. Pre-treatment with SB 222200 before a cocaine challenge also blocked expression of sensitization. Decrease in GSK3 activity demonstrated by increased phosphorylation of GSK3α and GSK3β was detected 20 mins after an acute cocaine injection. In contrast, a cocaine challenge failed to alter phosphorylation of GSK3α and GSK3β in sensitized mice. SB 222200 prior to repeated cocaine resulted in increased phosphorylation of GSK3α and GSK3β akin to changes following acute cocaine. Collectively, these findings demonstrate the involvement of NK-3 receptors in development and expression of behavioral sensitization and in regulation of GSK3 activity in the nucleus accumbens after repeated cocaine.

Methamphetamine-induced stereotypy correlates negatively with patch-enhanced prodynorphin and arc mRNA expression in the rat caudate putamen: the role of mu opioid receptor activation

Amphetamines induce stereotypy, which correlates with patch-enhanced c-Fos expression the patch compartment of caudate putamen (CPu). Methamphetamine (METH) treatment also induces patch-enhanced expression of prodynorphin (PD), arc and zif/268 in the CPu. Whether patch-enhanced activation of any of these genes correlates with METH-induced stereotypy is unknown, and the factors that contribute to this pattern of expression are poorly understood. Activation of mu opioid receptors, which are expressed by the neurons of the patch compartment, may underlie METH-induced patch-enhanced gene expression and stereotypy. The current study examined whether striatal mu opioid receptor blockade altered METH-induced stereotypy and patch-enhanced gene expression, and if there was a correlation between the two responses. Animals were intrastriatally infused with the mu antagonist CTAP (10 microg/microl), treated with METH (7.5 mg/kg, s.c.), placed in activity chambers for 3h, and then sacrificed. CTAP pretreatment attenuated METH-induced increases in PD, arc and zif/268 mRNA expression and significantly reduced METH-induced stereotypy. Patch-enhanced PD and arc mRNA expression in the dorsolateral CPu correlated negatively with METH-induced stereotypy. These data indicate that mu opioid receptor activation contributes to METH-induced gene expression in the CPu and stereotypy, and that patch-enhanced PD and arc expression may be a homeostatic response to METH treatment.

The neurokinin-1 receptor modulates the methamphetamine-induced striatal apoptosis and nitric oxide formation in mice

In a previous study we showed that pharmacological blockade of the neurokinin-1 receptors attenuated the methamphetamine (METH)-induced toxicity of the striatal dopamine terminals. In the present study we examined the role of the neurokinin-1 receptors on the METH-induced apoptosis of some striatal neurons. To that end, we administered a single injection of METH (30 mg/kg, i.p.) to male mice. METH induced the apoptosis (terminal deoxyncleotidyl transferase-mediated dUTP nick end labeling) of approximately 20% of striatal neurons. This percentage of METH-induced apoptosis was significantly attenuated by either a single injection of the neurokinin-1 receptor antagonist, 17-beta-hydroxy-17-a-ethynyl-5-a-androstano[3,2-beta]pyrimido[1,2-a]benzimidazole (WIN-51,708) (5 mg/kg, i.p.), or the ablation of the striatal interneurons expressing the neurokinin-1 receptors (cholinergic and somatostatin) with the selective neurotoxin [Sar(9),Met(O(2))(11)] substance P-saporin. Next we assessed the levels of striatal 3-nitrotyrosine (3-NT) by HPLC and immunohistochemistry. METH increased the levels of striatal 3-NT and this increase was attenuated by pre-treatment with WIN-51,708. Our data support the hypothesis that METH-induced striatal apoptosis occurs via a mechanism involving the neurokinin-1 receptors and the activation of nitric oxide synthesis. Our findings are relevant for the treatment of METH abuse and may be relevant to certain neurological disorders involving the dopaminergic circuitry of the basal ganglia.

Intra-accumbens shell injections of SR48692 enhanced cocaine self-administration intake in rats exposed to an environmentally-elicited reinstatement paradigm

Neurotensin (NT) is a neuropeptide involved in cocaine reward, and in learning and memory processes related to drug use within the mesolimbic dopamine (DA) system. Studies have demonstrated that NT receptor antagonists have potential as pharmacotherapeutical tools for cocaine abuse. Therefore, it is important to understand the molecular profile of NT within mesolimbic neurons and the behavioral effects of NT receptor inhibitors on environmentally-elicited cocaine seeking behavior. To address this issue, male Sprague Dawley rats were trained to self-administer cocaine and to discriminate between environmental cues signaling cocaine vs. saline availability. Then, following extinction, these cues were used to induce reinstatement of cocaine seeking behavior. A differential expression profile was observed throughout the experiment. Particularly, a significant increase of NT levels was observed within the nucleus accumbens (NAc) shell subregion during the acquisition phase of training. To further examine the implications of this increase, separate groups of animals received intra NAc shell injections of one of three doses (25, 50, 100 nM) of the NT1 receptor antagonist SR48692 after reaching stable self-administration. Animals were injected prior to placement in the operant conditioning chambers for four consecutive sessions. An increase in lever pressing was observed following antagonist treatment, whereas no major changes in locomotor activity were observed. We propose that the observed increase in lever pressing may be a compensatory response to a decrease in reinforcement, possibly due to decreased DA release, as previous studies show that chronic SR48692 decreases basal DA release in the NAc shell.

Responses of limbic and extrapyramidal substance P systems to nicotine treatment

RATIONALE

Neuropeptides are linked to the psychopathology of stimulants of abuse, principally through dopamine mechanisms. Substance P (SP) is one of these neuropeptides and is associated with both limbic and extrapyramidal dopaminergic pathways and likely contributes to the pharmacology of these stimulants. The effects of nicotine on these dopamine systems have also been extensively studied; however, its effects on the associated SP pathways have received little attention.

OBJECTIVES

In the present study, we elucidated the effects of nicotine treatment on limbic and extrapyramidal SP systems by measuring changes in associated SP tissue concentrations.

MATERIALS AND METHODS

Male Sprague-Dawley rats received (+/-)nicotine 4.0 mg/kg/day (0.8 mg/kg, intraperitoneally; five injections at 2-h intervals) in the presence or absence of selective dopamine D1 and D2 receptor antagonists or a nonselective nicotinic acetylcholine receptor antagonist.

RESULTS

The nicotine treatment significantly but temporarily decreased substance P-like immunoreactivity (SPLI) content in the ventral tegmental area (VTA) and substantia nigra 12-18 h after drug exposure. The nicotine-mediated changes in SPLI were selectively blocked by pretreatment with mecamylamine as well as a dopamine D1, D2, or both receptor antagonists. Other brain areas that also selectively demonstrated nicotine-related declines in SPLI content included prefrontal cortex, the nucleus accumbens shell, and the very posterior caudate.

CONCLUSIONS

These findings indicate that some limbic and basal ganglia SP systems are significantly affected by exposure to nicotine through processes mediated by nicotinic and dopaminergic receptors, suggesting a role for SP pathways in nicotine's limbic and extrapyramidal effects.

Neurokinin3 receptor modulation of the behavioral and neurochemical effects of cocaine in rats and monkeys

Neurokinin3 (NK3) receptors and their endogenous ligands (e.g. the neuropeptide substance P and its C-terminal fragment) have been implicated in psychomotor activity and reinforcement mechanisms. We review here recent findings on the involvement of NK3 receptors in the behavioral and neurochemical effects of cocaine. Although NK3 receptors can modulate dopamine (DA) activity in the brain, recent results suggest that this modulation does not occur during spontaneous behavioral activity. However, NK3 receptors play a role in the regulation of cocaine-induced DA responses in the nucleus accumbens core and shell subregions. NK3 receptor agonism as well as antagonism potentiate cocaine's effects on nucleus accumbens DA subregions specifically, and modulate the acute behavioral effects of cocaine in rats and non-human primates (Callithrix penicillata). However, conditioned place preference studies in rats have, so far, failed to provide evidence for an involvement of NK3 receptors in the reinforcing effects of cocaine.

Striatal and ventral pallidum dynorphin concentrations are markedly increased in human chronic cocaine users

Interest in development of therapeutics targeting brain neuropeptide systems for treatment of cocaine addiction (e.g., kappa opioid agonists) is based on animal data showing interactions between the neuropeptides, brain dopamine, and cocaine. In this autopsied brain study, our major objective was to establish by radioimmunoassay whether levels of dynorphin and other neuropeptides (e.g., metenkephalin, neurotensin and substance P) are increased in the dopamine-rich caudate, putamen, and nucleus accumbens of human chronic cocaine users (n=12) vs. matched control subjects (n=17) as predicted by animal findings. Changes were limited to markedly increased dynorphin immunoreactivity in caudate (+92%), decreased caudate neurotensin (-49%), and a trend for increased dynorphin (+75%) in putamen. In other examined subcortical/cerebral cortical areas dynorphin levels were normal with the striking exception of the ventral pallidum (+346%), whereas cerebral cortical metenkephalin levels were generally decreased and neurotensin variably changed. Our finding that, in contradistinction to animal data, the other striatal neuropeptides were not increased in human cocaine users could be explained by differences in pattern and contingency between human drug users and the animal models. However, the human dynorphin observations parallel well animal findings and suggest that the dynorphin system is upregulated, manifested as elevated neuropeptide levels, after chronic drug exposure in striatum and ventral pallidum. Our postmortem brain data suggest involvement of striatal dynorphin systems in human cocaine users and should add to the interest in the testing of new dynorphin-related therapeutics for the treatment of cocaine addiction.

Brain levels of neuropeptides in human chronic methamphetamine users

Animal data show that neuropeptide systems in the dopamine-rich brain areas of the striatum (caudate, putamen, and nucleus accumbens) are influenced by exposure to psychostimulants, suggesting that neuropeptides are involved in mediating aspects of behavioral responses to drugs of abuse. To establish in an exploratory study whether levels of neuropeptides are altered in brain of human methamphetamine users, we measured tissue concentrations of dynorphin, metenkephalin, neuropeptide Y, neurotensin, and substance P in autopsied brains of 16 chronic methamphetamine users and 17 matched control subjects. As expected, levels of most neuropeptides were enriched in dopamine-linked brain regions such as the nucleus accumbens and striatum of normal human brain. In contrast to animal findings of increased neuropeptide levels following short-term methamphetamine exposure, striatal neuropeptide concentrations were either normal or moderately decreased in the methamphetamine users. In other examined dopamine-poor cortical and subcortical brain areas, neuropeptide levels were generally either normal or variably reduced. Although the neuropeptide differences might be explained by methamphetamine-induced damage to neuropeptide-containing neurons, our human data are consistent with the possibility that, at least in the human striatum, long-term methamphetamine exposure leads to an adaptive process that is distinct from that which increases neuropeptide levels after acute methamphetamine exposure.

Quantitative peptidomics in mice: effect of cocaine treatment

We recently developed a quantitative peptidomics method using stable isotopic labels and mass spectrometry to both quantify and identify a large number of peptides. To test this approach and screen for peptides regulated by cocaine administration, 32 Cpefat/fat mice and 16 wild-type mice were treated twice daily for 5 d either with saline or 10 mg/kg cocaine. Peptides were extracted from striatum, hypothalamus, hippocampus, and prefrontal cortex, and extracts from groups of eight mice were labeled with the N-hydroxysuccinimide ester of trimethylammonium butyrate containing either nine deuterium or nine hydrogen atoms. Pools of heavy- and light-labeled peptides were combined, purified on an anhydrotrypsin affinity column, and analyzed on a reversephase column coupled to an electrospray ionization quadrapole time-of-flight mass spectrometer. Changes in peptide levels upon cocaine treatment were determined from the relative peak intensities of the cocaine versus saline peaks, and peptides were identified from collision-induced dissociation spectra. Ten peptides were found to increase or decrease in each of two separate analyses from distinct groups of mice. Peptides found to increase corresponded to fragments of proenkephalin, prothyrotropin-releasing hormone, provasopressin, proSAAS, secretogranin II, chromogranin B, and peptidyl-glycine-alpha-amidating mono-oxygenase in the hypothalamus. The same peptidyl-glycine-alpha-amidating mono-oxygenase peptide decreased in the prefrontal cortex, along with striatal neurokinin B and two unidentified peptides. Thirty other peptides were not substantially affected by cocaine treatment in both replicates. Taken together, the quantitative peptidomics approach provides an efficient method to screen for changes in a large number of peptides.

Co-localization of GABA with other neuroactive substances in the basal ganglia

The dorsal striatum (caudate putamen) contains two types of GABAergic medium spiny neurons (MSNs) that are distinguished by the expression of either the opioid peptide, enkephalin, or the opioid peptide, dynorphin, as well as the tachykinin substance P. Pharmacological studies suggest that these peptides modulate local neurotransmission in the striatum in response to direct and indirect dopamine agonists. In contrast, GABA appears to have minimal impact within the striatum under these conditions. The actions of the peptide cocktail are dependent on the cellular distribution of their receptors in the striatal network. The net result of their actions is a homeostatic response that regulates striatal output and balances dopamine and glutamate receptor stimulation.

Effects of acute and subchronic d-amphetamine on ventral striatal concentrations of neurotensin and neuropeptide Y in rats treated with antipsychotic drugs

We have reported that acute d-amphetamine increases extracellular concentrations (efflux) of neurotensin-like immunoreactivity (NT-LI) and neuropeptide Y-LI (NPY-LI) in the ventral striatum (VSTR) of freely moving rats, effects that are abolished by chronic administration of haloperidol and risperidone admixed to food pellets. In this study we further investigated the d-amphetamine effects on NT-LI and NPY-LI efflux in VSTR and their content in selected brain regions. Rats received haloperidol, risperidone or vehicle for 30days and saline or d-amphetamine either on days 22-29 and/or day 30. Seven day d-amphetamine administration decreased basal NT-LI and NPY-LI efflux in vehicle-treated rats; pretreatment with haloperidol counteracted these effects, while pretreatment with risperidone had effect only on NT-LI. Acute d-amphetamine after the seven day d-amphetamine increased NT-LI only. Pretreatment with haloperidol or risperidone abolished the effects of acute d-amphetamine on NT-LI and NPY-LI. Acute and seven day d-amphetamine increased NT-LI and NPY-LI contents in striatum; seven day d-amphetamine also increased NT-LI in frontal and occipital cortex and both NT-LI and NPY-LI in hippocampus. Our results suggest that NT and NPY are involved in both the pathophysiology and the therapeutics of schizophrenia.

Differential effects of methamphetamine and cocaine on behavior and extracellular levels of dopamine and 3,4-dihydroxyphenylalanine in the nucleus accumbens of conscious rats

The central dopamine system plays a prominent role in the effect of psychostimulants such as methamphetamine, cocaine and nicotine. l-3,4-Dihydroxyphenylalanine (DOPA), a precursor of dopamine, has been proposed as a neurotransmitter in the central nervous system. We have studied the effects of these psychostimulants on the release of DOPA and dopamine from the nucleus accumbens shell in conscious rats using in vivo microdialysis. Methamphetamine and cocaine increase the extracellular levels of dopamine. The effect of methamphetamine (1 mg/kg s.c.) on the release of dopamine was almost comparable to that of cocaine (10 mg/kg i.p.). However, methamphetamine increases, but cocaine decreases the extracellular levels of DOPA. In a behavioral study, methamphetamine (1 mg/kg s.c.) induced chewing, walking and sniffing behavior. Cocaine (10 mg/kg i.p.) produces weak effects on these behavioral parameters, when compared to the effects of methamphetamine (1 mg/kg s.c.). The behavioral changes produced by methamphetamine are suppressed by DOPA cyclohexyl ester (30 mg/kg i.p.), a competitive DOPA antagonist. Endogenous DOPA in the nucleus accumbens thus appears to be in involved in the behavioral responses to these psychomotor stimulants.

Neurotensin: role in psychiatric and neurological diseases

Neurotensin (NT), an endogenous brain-gut peptide, has a close anatomical and functional relationship with the mesocorticolimbic and neostriatal dopamine system. Dysregulation of NT neurotransmission in this system has been hypothesized to be involved in the pathogenesis of schizophrenia. Additionally, NT containing circuits have been demonstrated to mediate some of the mechanisms of action of antipsychotic drugs, as well as the rewarding and/or sensitizing properties of drugs of abuse. NT receptors have been suggested to be novel targets for the treatment of psychoses or drug addiction.

Interaction of the tachykinin NK3 receptor agonist senktide with behavioral effects of cocaine in marmosets (Callithrix penicillata)

Brain neuropeptide transmitters of the tachykinin family are involved in the organization of many behaviors. However, little is known about their contribution to the behavioral effects of drugs of abuse. Recently, antagonism of the tachykinin NK3-receptor (NK3-R), one of the three tachykinin receptors in the brain, was shown to attenuate the acute and chronic behavioral effects of cocaine in rats and the acute effects in non-human primates. In order to expand these findings we investigated the effects of the NK3-R agonist, succinyl-[Asp6, Me-Phe8]SP(6-11) (senktide), on the acute behavioral effects of cocaine in marmoset monkeys (Callithrix penicillata) using a figure-eight maze procedure. Animals were pretreated with senktide (0, 0.1, 0.2, 0.4 mg/kg, s.c.), and received either a treatment with cocaine (10 mg/kg) or saline (i.p.). Cocaine increased locomotor activity and the duration of aerial scanning behavior, but reduced exploratory activity, bodycare activity, the frequency of aerial scanning, and terrestrial glance behavior. Senktide blocked the effects of cocaine on locomotor activity, but enhanced the cocaine effects on exploratory activity, aerial scanning frequency, and terrestrial glance behavior. Senktide alone did not significantly influence monkey behavior in this study. These data expand previous findings suggesting a complex role of the NK3-R in the acute behavioral effects of cocaine in non-human primates.

C/EBPβ couples dopamine signalling to substance P precursor gene expression in striatal neurones

Dopamine-induced changes in striatal gene expression are thought to play an important role in drug addiction and compulsive behaviour. In this study we report that dopamine induces the expression of the transcription factor CCAAT/Enhancer Binding Protein beta (C/EBP)-beta in primary cultures of striatal neurones. We identified the preprotachykinin-A (PPT-A) gene coding for substance P and neurokinin-A as a potential target gene of C/EBPbeta. We demonstrated that C/EBPbeta physically interacts with an element of the PPT-A promoter, thereby facilitating substance P precursor gene transcription. The regulation of PPT-A gene by C/EBPbeta could subserve many important physiological processes involving substance P, such as nociception, neurogenic inflammation and addiction. Given that substance P is known to increase dopamine signalling in the striatum and, in turn, dopamine increases substance P expression in medium spiny neurones, our results implicate C/EBPbeta in a positive feedback loop, changes of which might contribute to the development of drug addiction.

Association of paradoxical sleep deprivation and ecstasy (MDMA) enhances genital reflexes in male rats

Ecstasy ((+/-)3,4-methylenedioxymethamphetamine, MDMA) is a psychostimulant and a synthetic derivative of amphetamine that, according to its consumers, promotes the enhancement of sexual pleasure. This study sought to investigate the effects of ecstasy in the genital reflexes of paradoxical sleep deprived (PSD) male rats. Distinct groups of PSD rats were administered with saline or different doses of ecstasy. The incidence of genital reflexes was verified for 100 min. The four doses that were used induced genital reflexes in PSD animals and these significantly differed from their respective treated control groups. Under the influence of two intermediary doses (2.5 and 5mg/kg), all animals displayed erection and ejaculation. The frequency of genital reflexes was also significantly greater than in relation to the PSD-saline group. The comparison between cocaine and ecstasy in PSD rats revealed that ecstasy induced more erections and ejaculations than cocaine. Thus, the present results showed a great enhancement of the genital reflexes of PSD rats that might have occurred due to serotoninergic alterations induced by this illicit substance when associated to sleep deprivation.

Genetic analysis of the hypothalamic neurotensin system

This study used B x D recombinant inbred mice to detect and localize genes that control the hypothalamic neurotensin (NT) system. Abundance of transcripts that encode NT and NT receptors 1, 2, and 3 (NTR1, NTR2, and NTR3) in total hypothalamic RNA was the quantitative trait measured. Analysis of transcript abundance data revealed associations with quantitative trait loci (QTL) for NT transcript abundance (NTta) on chromosome 1, 3, 6, 7, 8, and 9; for NTR1ta on chromosome 3, 8, 12, and X; for NTR2ta on chromosome 2, 4, 9, 10, 12, 13, and 17; for NTR3ta on chromosome 1, 7, 11, and 12. NTta QTL on chromosomes 3, 7, and 8 coincide with QTL previously identified that impact NT peptide content and NTR2ta QTL on chromosome 2 and 12 coincide with genes previously associated with NTR2 receptor abundance. The NTta, NTR1ta, and NTR3ta QTL were not linked to their respective structural genes, but there is a highly significant (p<0.001) association for NTR2ta on chromosome 12 that includes the Ntsr2 structural gene. There are areas of potential shared genetic regulation between NTta and NTR3ta on chromosome 1 and 7 and for all three receptors on proximal chromosome 12. The NTta QTL on chromosome 9 includes the dopamine D2 receptor (Drd2) gene and QTL involved in responses to dopaminergic agents (Hts), antipsychotics (Hpic1) and cocaine (Cocrb8), and ethanol (Etohc3). These results further strengthen the hypothesis that the NT system is involved in mediating the actions of antipsychotic agents and drugs of abuse.

Single-cell RT-PCR, in situ hybridization histochemical, and immunohistochemical studies of substance P and enkephalin co-occurrence in striatal projection neurons in rats

Single-cell RT-PCR studies in 3-4-week-old rats have raised the possibility that as many as 20% of striatal projection neurons may be a unique type that contains both substance P (SP) and enkephalin (ENK). We used single-cell RT-PCR, retrograde labeling, in situ hybridization histochemistry, and immunolabeling to characterize the abundance of this cell type, its projection target(s), and any developmental changes in its frequency. We found by RT-PCR that 11% of neurons containing either SP or ENK contained both in 4-week-old rats, while in 4-month-old rats SP/ENK colocalization was only 3%. SP-only neurons tended to co-contain dynorphin and ENK-only neurons neurotensin, while SP/ENK neurons tended to contain dynorphin. Single-cell RT-PCR showed SP/ENK co-occurrence in 4-week-old rats to be no more common among striatal neurons retrogradely labeled from the substantia nigra than among those retrogradely labeled from globus pallidus. Double-label in situ hybridization showed SP/ENK perikarya to be scattered throughout striatum, making up 8% of neurons containing either SP or ENK at 4 weeks, but only 4% at 4 months. Immunolabeling showed that presumptive striatal terminals in globus pallidus externus, globus pallidus internus and substantia nigra pars reticulata that colocalized SP and ENK were scarce. Terminals colocalizing SP and ENK were, however, abundant in the substantia nigra pars compacta. Thus, SP-only and ENK-only neurons make up the vast majority of striatal projection neurons in rats, the frequency of SP/ENK colocalizing striatal neurons is low in adult rats (3-4%), and SP/ENK colocalizing neurons primarily project to SNc but do not appear to be confined to striosomes.

Failure of MK-801 to suppress D1 receptor-mediated induction of locomotor activity and striatal preprotachykinin mRNA expression in the dopamine-depleted rat

N-methyl-D-aspartate receptor antagonism exerts suppressive influences over dopamine D1 receptor-mediated striatal gene expression and locomotor behavior in the intact rat. The present study examined the effects of the N-methyl-D-aspartate receptor antagonist MK-801 on locomotor activity and striatal preprotachykinin mRNA expression stimulated by the D1 agonist (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide in rats with bilateral dopamine lesions. Two months after neonatal dopamine lesions with 6-hydroxydopamine, rats were challenged with (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (1.0 mg/kg) 15 min after administration of the N-methyl-D-aspartate receptor antagonist MK-801 (0.1 mg/kg). In the intact rat, MK-801 prevented the induction of striatal preprotachykinin mRNA by D1 agonism. Similarly, direct infusion of (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (3.0 microg) into the intact striatum produced an increase in locomotor activity that was suppressed by MK-801 (1.0 microg) co-infusion. In the dopamine-depleted rat, MK-801 (0.1 mg/kg) administered prior to (+/-)6-chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (1.0 mg/kg) increased, rather than suppressed, striatal preprotachykinin mRNA levels. Intrastriatal infusion of MK-801 (1.0 microg) failed to inhibit D1-mediated induction of motor activity in dopamine-depleted animals. Together, these data provide further support that N-methyl-D-aspartate receptor antagonists lose their ability to block D1-mediated behavioral activation following dopamine depletion. The activation, rather than suppression, of tachykinin neurons of the direct striatonigral pathway may play a facilitatory role in this mechanism.

Differential neurotensin responses to low and high doses of methamphetamine in the terminal regions of striatal efferents

Neurotensin is a neuropeptide associated with basal ganglia dopaminergic neurons. Because levels of neurotensin in striatal tissue are differentially affected by low or high doses of methamphetamine, we employed microdialysis to assess the dose-dependent effects of methamphetamine on neurotensin release from the terminals of striatonigral and striatopallidal neurons. A low (0.5 mg/kg), but not high (10 mg/kg), dose of methamphetamine significantly increased nigral extracellular levels of neurotensin. The low-dose effect on extracellular nigral neurotensin levels was blocked by pretreatment with either a dopamine D1 or D2 receptor antagonist. In the globus pallidus, only half of the animals demonstrated increased neurotensin release after the low dose of methamphetamine. These findings suggest that low and high doses of methamphetamine differentially affect the release of neurotensin from the terminals of striatonigral neurons and that both dopamine D1 and D2 receptor activation contributes to the low-dose methamphetamine effects in the substantia nigra.

Topography of methylphenidate (ritalin)-induced gene regulation in the striatum: differential effects on c-fos, substance P and opioid peptides

Dopamine action alters gene regulation in striatal neurons. Methylphenidate increases extracellular levels of dopamine. We investigated the effects of acute methylphenidate treatment on gene expression in the striatum of adult rats. Molecular changes were mapped in 23 striatal sectors mostly defined by their predominant cortical inputs in order to determine the functional domains affected. Acute administration of 5 and 10 mg/kg (i.p.) of methylphenidate produced robust increases in the expression of the transcription factor c-fos and the neuropeptide substance P. Borderline effects were found with 2 mg/kg, but not with 0.5 mg/kg. For 5 mg/kg, c-fos mRNA levels peaked at 40 min and returned to baseline by 3 h after injection, while substance P mRNA levels peaked at 40-60 min and were back near control levels by 24 h. These molecular changes occurred in most sectors of the caudate-putamen, but were maximal in dorsal sectors that receive sensorimotor and medial agranular cortical inputs, on middle to caudal levels. In rostral and ventral striatal sectors, changes in c-fos and substance P expression were weaker or absent. No effects were seen in the nucleus accumbens, with the exception of c-fos induction in the lateral part of the shell. In contrast to c-fos and substance P, acute methylphenidate treatment had minimal effects on the opioid peptides dynorphin and enkephalin. These results demonstrate that acute methylphenidate alters the expression of c-fos and substance P preferentially in the sensorimotor striatum. These molecular changes are similar, but not identical, to those produced by other psychostimulants.

Blockade of stimulant-induced preprodynorphin mRNA expression in the striatal matrix by serotonin depletion

Cocaine and methamphetamine (METH) induce preprodynorphin (PPD) mRNA expression in the striatum. Cocaine induces PPD expression in both the patch and matrix compartments of the rostral striatum, whereas METH induces PPD expression in the patch compartment of the rostral striatum. In middle striatum, both stimulants increase PPD expression in the patch and matrix compartments. METH and cocaine treatment also increase extracellular serotonin (5-HT). Several studies have shown that 5-HT receptors are present on striatonigral neurons that express PPD mRNA, and that 5-HT is a positive regulator of striatal neuropeptide expression. The current study examined whether 5-HT plays a role in the patch/matrix expression of PPD mRNA induced by cocaine and METH in striatum. Male Sprague-Dawley rats were treated with p-chloroamphetamine (PCA; 8 mg/kg, i.p), a serotonin neurotoxin, 1 week prior to cocaine (30 mg/kg, i.p) and METH (15 mg/kg, s.c.) treatment. The 80% loss of 5-HT induced by PCA-pretreatment blocked cocaine-induced PPD expression in the rostral matrix compartment. Cocaine- and METH-induced PPD expression in the rostral patch compartment was unaffected by PCA-pretreatment. PCA-pretreatment also decreased both cocaine- and METH-induced PPD expression in the matrix, but not patch of middle striatum. PCA-induced 5-HT depletion did not affect stimulant-induced increases in PPT mRNA expression in the striatum. These data suggest that 5-HT plays a role in stimulant-induced PPD expression in the matrix compartment of rostral and middle striatum. Thus, 5-HT innervation may play a critical role in basal ganglia function.

Acute cocaine effects in paradoxical sleep deprived male rats

Cocaine is a psychomotor drug known to cause behavioural alterations. This study was conducted to characterize behavioural response to acute cocaine injection (7 mg/kg, ip) in paradoxical sleep deprived (PSD) male rats since sleep deprivation is also associated with several behavioural alterations. Cocaine or vehicle was administered to rats at the end of a 4-day period of sleep deprivation, and in home-cage control animals. Cocaine administration in control and PSD rats induced a significant increase in stereotyped behaviour in relation to saline-injected rats. PSD induced significant but heterogeneous effects in animals by increasing grooming while it had effect neither on stereotyped behaviours, locomotion nor on anxiety-like behaviours but significantly decreased rearing behaviour. PSD potentiates the action of cocaine on stereotyped behaviours suggesting supersensitivity of dopaminergic receptors. Thus, the present study indicated that the behavioural effects of cocaine could be modified by PSD. This in turn may have relevant implications in the cocaine effect in abusers under sleep deprived condition.

3,4-Methylenedioxymethamphetamine increases neuropeptide messenger RNA expression in rat striatum

The amphetamine analog 3,4-methylenedioxymethamphetamine (MDMA) is also known as the recreational drug of abuse, Ecstasy. Several neuropeptides are found in striatal neurons postsynaptic to dopamine and serotonin nerve terminals, and changes in neuropeptide neurotransmission may be important for behavioral effects of 3,4-methylenedioxymethamphetamine. This study used in situ hybridization to characterize the effects of 3,4-methylenedioxymethamphetamine on four neuropeptide mRNAs: preprodynorphin, preprotachykinin, neurotensin/neuromedin N, and preproenkephalin. Male, Sprague-Dawley rats received a single administration of 10 mg/kg 3,4-methylenedioxymethamphetamine and were sacrificed 30 min or 3 h later. Three hours after administration, 3,4-methylenedioxymethamphetamine increased preprodynorphin, preprotachykinin, and neurotensin/neuromedin N mRNAs. These increases were most prominent in ventral and medial aspects of the rostral-middle striatum, and then became more dorsally restricted in the caudal striatum. At the 30-minute time point, MDMA significantly decreased the signal for preproenkephalin mRNA in a general manner but did not affect the signal for the other neuropeptide precursors. These data suggest that 3,4-methylenedioxymethamphetamine has a generalized, transient, inhibitory effect on striatopallidal neuron gene expression, and then preferentially influences striatonigral neuropeptide systems at the later time point in a regionally selective manner.

Intranigral antagonism of neurokinin 1 and 3 receptors reduces intrastriatal dopamine D1 receptor-stimulated locomotion in the rat

Stimulation of striatal dopamine (DA) D1 receptors increases the activity of the direct striatonigral pathway resulting in movement. While GABA has long been considered the primary effector of this pathway, co-released tachykinin peptides and their respective nigral tachykinin receptors are also in position to influence movement. Therefore, the present studies determined to what extent nigral tachykinin receptor subtypes contribute to striatal D1-mediated locomotion. Adult male Sprague-Dawley rats bearing chronic cannulae in the dorsal striatum and/or substantia nigra (SN) were tested for locomotor responses to various drug infusions. Unilateral intranigral infusions of the neurokinin-1 (NK1) antagonist LY306740 (0 and 50 nmol) but not the neurokinin-3 (NK3) antagonist SR142801 (0 and 50 nmol) led to ipsilateral rotations. Bilateral intrastriatal infusions of the full D1 agonist SKF 82958 (0, 1.2 and 12.0 nmol) dose-dependently increased locomotion. Prior bilateral intranigral infusions of LY306740 or SR142801 (0, 5.0 and 50 nmol) dose-dependently attenuated locomotor activity induced by intrastriatal SKF 82958 (12.0 nmol). These findings indicate that NK1, but not NK3, receptors within the SN may be tonically stimulated. However, activation of both nigral NK1 and NK3 receptors appears to be required for increased locomotion in response to striatal D1 receptor stimulation.

Altered neurotensin mrna expression in mice lacking the dopamine transporter

Psychostimulants and antipsychotic drugs increase mRNA expression of the neuropeptide neurotensin (NT) in the striatum and nucleus accumbens. In the present study, we used mice lacking the dopamine transporter (DAT) to investigate the consequences of a chronic hyperdopaminergic state on NT gene expression. NT mRNA expression was examined under basal conditions and after administration of haloperidol or amphetamine using in situ hybridization with a digoxigenin-labeled NT cRNA probe. DAT-/- mice exhibited a striking increase in the number of NT mRNA-expressing perikarya in the substantia nigra and ventral tegmental area, as well as a less pronounced increase in the lateral septum compared with wild-type littermates. No changes were detected in other regions expressing NT mRNA. Acute administration of haloperidol (1 mg/kg) induced a significant increase in the number of NT mRNA-expressing neurons in the dorsomedial and dorsolateral striatum of wild-type mice but failed to stimulate NT gene expression in DAT mutants. In contrast, a higher dose of haloperidol (5 mg/kg) stimulated striatal NT mRNA expression both in DAT+/+ and DAT-/- mice. Amphetamine (10 mg/kg) increased the number of hybridized neurons in the nucleus accumbens shell and fundus striati of wild-type and DAT-/- mice, indicating that the drug acted through a target other than DAT, such as the serotonin or the norepinephrine transporters. The up-regulation of NT mRNA observed in DAT-/- mice may represent an adaptive mechanism in response to constitutive hyperdopaminergia. These results illustrate the profound alterations in the NT system induced by chronic stimulation of DA receptors and underscore the potential clinical relevance of NT/DA interactions in schizophrenia and drug abuse.

Identification of differentially regulated transcripts in mouse striatum following methamphetamine treatment - an oligonucleotide microarray approach

Methamphetamine is an addictive drug of abuse that can produce neurotoxic effects in dopamine nerve endings of the striatum. The purpose of this study was to identify new genes that may play a role in the highly complex cascade of events associated with methamphetamine intoxication. Using Affymetrix oligonucleotide arrays, 12 488 genes were simultaneously interrogated and there were 152 whose expression levels were changed following methamphetamine treatment. The genes are grouped into broad functional categories with inflammatory/immune response elements, receptor/signal transduction components and ion channel/transport proteins among the most populated. Many genes within these categories can be linked to ion regulation and apoptosis, both of which have been implicated in methamphetamine toxicity, and numerous factors associated with microglial activation emerged with significant changes in expression. For example, brain-derived neurotrophic factor (BDNF), chemokine (C-C) receptor 6 (CCr6) and numerous chemokine transcripts were increased or decreased in expression more than 2.8-fold. These results point to activated microglia as a potential source of the reactive oxygen/nitrogen species and cytokines that have been previously associated with methamphetamine toxicity and other neurotoxic conditions.

Facilitation of ejaculation after methamphetamine administration in paradoxical sleep deprived rats

This study investigated the effects of methamphetamine (MA) on genital reflexes in paradoxical sleep deprived (PSD) rats. Different doses of MA (0, 4, 16 and 64 mg/kg) were acutely given after PSD or the equivalent time to control animals. We observed enhancement of spontaneous ejaculation in PSD rats with larger doses of MA, the highest of which induced ejaculation in 100% of the PSD rats. This was significantly higher than the 30% in the control. Although testosterone exerts motivational effects on male sexual behavior, our data shows that testosterone levels were lower after the PSD period in saline and in the 64 mg/kg MA groups, which present ejaculation at different rates (20% and 100%, respectively). Progesterone levels were significantly higher in PSD-saline in relation to control group and in the 16 and 64 mg/kg of MA groups compared to the other doses. Since PSD induces dopaminergic alterations and dopamine (DA) has a key role in male sexual behavior, plasma DA was also measured. The DA concentration was enhanced in all PSD groups compared with their control group. The mechanism that activates steroid hormones may represent an important physiological effect through which neurotransmitters can affect behavioral events. These data show that MA facilitates ejaculation in PSD rats, however, further studies need to be carried out in order to clarify the hormonal-neurochemical mechanisms involved.

Neurotensin agonists: possible drugs for treatment of psychostimulant abuse

Although many neuropeptides have been implicated in the pathophysiology of psychostimulant abuse, the tridecapeptide neurotensin holds a prominent position in this field due to the compelling literature on this peptide and psychostimulants. These data strongly support the hypothesis that a neurotensin agonist will be clinically useful to treat the abuse of psychostimulants, including nicotine. This paper reviews the evidence for a role for neurotensin in stimulant abuse and for a neurotensin agonist for its treatment.

Quantification of multiple mRNA levels in rat brain regions using real time optical PCR

TaqMan is significantly more sensitive than other methods of mRNA quantification and makes possible the simultaneous analysis of numerous genes in small brain regions. This technique was used to quantify levels of mRNAs of 21 genes in tissue extracts from caudate putamen and nucleus accumbens from individual rats after 1 day 'binge' cocaine or saline administration. Expression of glyceraldehyde-3-phosphate-dehydrogenase, cyclophilin and actin mRNAs as well as 18S ribosomal RNA were evaluated for normalization of levels of gene expression.

Topography of cocaine-induced gene regulation in the rat striatum: relationship to cortical inputs and role of behavioural context

Psychostimulants alter gene expression in projection neurons of the striatum, and such neuroplasticity is implicated in drug addiction and dependence. Evidence indicates that excitatory inputs from the cortex and thalamus are critical for these molecular changes. In the present study, we determined the topography of cocaine-induced changes in gene expression in the rat striatum and investigated whether these molecular alterations are associated with particular cortical inputs. Acute induction of c-fos (by 25 mg/kg of cocaine), and the c-fos response and dynorphin expression after repeated cocaine treatment (25 mg/kg, 4 days) were assessed as examples for short-term and longer-term molecular changes, respectively. In addition, we examined whether these molecular effects were influenced by the behaviour performed during cocaine action (running-wheel training vs. open field). Our results demonstrate that the overall topography of cocaine-induced gene regulation in the striatum is remarkably stable. Both acute and longer-term molecular changes were maximal in caudal dorsal striatal sectors that receive convergent inputs from the medial agranular and the sensorimotor cortex. In contrast, relatively minor or no effects were found in rostral and ventral striatal sectors. However, running-wheel training under the influence of cocaine enhanced the c-fos response to a subsequent cocaine challenge selectively in parts of the caudal sensorimotor striatum. These results indicate that cocaine produces molecular adaptations preferentially in cortico-basal ganglia circuits through the sensorimotor striatum, and that some of these neuronal changes are influenced by the behaviour performed during drug exposure.

Ciproxifan, a histamine H3-receptor antagonist/inverse agonist, modulates the effects of methamphetamine on neuropeptide mRNA expression in rat striatum

We have explored the effect of histamine H3-receptor ligands on the regulation of neuropeptide mRNA expression in the striatum by using in situ hybridization performed with proenkephalin, prodynorphin, substance P and proneurotensin riboprobes. Acute administration of ciproxifan, an H3-receptor antagonist/inverse agonist, or (R)-alpha-methylhistamine, an H3-receptor agonist, did not modify the striatal expression of the neuropeptides by itself. However, ciproxifan strongly and differentially modulated the effect of a single administration of 3 mg/kg methamphetamine on neuropeptide mRNA expression. This modulation was suppressed by the administration of (R)-alpha-methylhistamine and occurred in both the caudate-putamen and nucleus accumbens. Ciproxifan strongly potentiated the decrease of proenkephalin mRNA expression induced by methamphetamine. In contrast, it suppressed the increase in prodynorphin and substance P mRNA expression induced by methamphetamine. Methamphetamine alone or with ciproxifan did not modify proneurotensin mRNA expression. These neurochemical findings indicate that ciproxifan differentially regulates the effect of methamphetamine on the neuropeptides contained in striatonigral and striatopallidal neurons. They suggest that endogenous histamine and dopamine cooperate to modulate the activity of striatal projection neurons and strengthen the interest of H3-receptors as new targets for the treatment of psychotic disorders and drug abuse.

Distinct responses of basal ganglia substance P systems to low and high doses of methamphetamine

Substance P (SP) is a neuropeptide closely associated with basal ganglia dopaminergic neurons. Because some neuropeptide systems in the basal ganglia (i.e. neurotensin and metenkephalin) are differentially affected by treatment with low or high doses of methamphetamine, we determined if basal ganglia SP pathways were also differentially influenced in a dose-dependent manner by this psychostimulant. Employing in vivo microdialysis, it was observed that the low dose (0.5 mg/kg) of methamphetamine increased the extracellular concentration of SP in the substantia nigra, but not in globus pallidus or striatum. In contrast, the high dose (10 mg/kg) of methamphetamine did not increase extracellular SP content in any of these structures. The effect of the low-dose methamphetamine treatment on nigral extracellular SP levels was blocked by pre-treatment with either a D1 or D2 antagonist. In addition, 12 h after similar methamphetamine treatments, a dose-dependent differential response in SP tissue levels occurred in some of the regions examined. When these changes occurred, the low dose of methamphetamine usually reduced, whereas the high dose increased, SP tissue content. This study demonstrated opposite responses of the basal ganglia SP system to low and high doses of methamphetamine and suggested that a combination of dopamine D1 and D2 receptor activity contributed to these effects.