Quantification of dopamine D1 and D2 receptor mRNA levels associated with the development of behavioral sensitization in amphetamine treated rats

Striatal phosphodiesterase 10A availability is altered secondary to chronic changes in dopamine neurotransmission

Background

Phosphodiesterase 10A (PDE10A) is an important regulator of nigrostriatal dopamine (DA) neurotransmission. However, little is known on the effect of alterations in DA neurotransmission on PDE10A availability. Here, we used [¹⁸F]JNJ42259152 PET to measure changes in PDE10A availability, secondary to pharmacological alterations in DA release and to investigate whether these are D₁- or D₂-receptor driven.

Results

Acute treatment of rats using D-amphetamine (5 mg, s.c. and 1 mg/kg i.v.) did not result in a significant change in PDE10A BP_ND compared to baseline conditions. 5-day D-amphetamine treatment (5 mg/kg, s.c.) increased striatal PDE10A BP_ND compared to the baseline (+24 %, p = 0.03). Treatment with the selective D2 antagonist SCH23390 (1 mg/kg) and D-amphetamine decreased PDE10A binding (-22 %, p = 0.03). Treatment with only SCH23390 further decreased PDE10A binding (-26 %, p = 0.03). No significant alterations in PDE10A mRNA levels were observed.

Conclusions

Repeated D-amphetamine treatment significantly increased PDE10A binding, which is not observed upon selective D₁ receptor blocking. This study suggests a potential pharmacological interaction between PDE10A enzymes and drugs modifying DA neurotransmission. Therefore, PDE10A binding in patients with neuropsychiatric disorders might be modulated by chronic DA-related treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s41181-016-0005-5) contains supplementary material, which is available to authorized users.

Amphetamine alters behavior and mesocorticolimbic dopamine receptor expression in the monogamous female prairie vole

We have recently established the socially monogamous prairie vole (Microtus ochrogaster) as an animal model with which to investigate the involvement of mesocorticolimbic dopamine (DA) in the amphetamine (AMPH)-induced impairment of social behavior. As the majority of our work, to date, has focused on males, and sex differences are commonly reported in the behavioral and neurobiological responses to AMPH, the current study was designed to examine the behavioral and neurobiological effects of AMPH treatment in female prairie voles. We used a conditioned place preference (CPP) paradigm to determine a dose-response curve for the behavioral effects of AMPH in female prairie voles, and found that conditioning with low to intermediate (0.2 and 1.0 mg/kg), but not very low (0.1 mg/kg), doses of AMPH induced a CPP. We also found that exposure to a behaviorally relevant dose of AMPH (1.0 mg/kg) induced an increase in DA concentration in the nucleus accumbens (NAcc) and caudate putamen but not the medial prefrontal cortex or ventral tegmental area (VTA). Finally, repeated AMPH exposure (1.0 mg/kg once per day for 3 consecutive days; an injection paradigm that has been recently shown to alter DA receptor expression and impair social bonding in male prairie voles) increased D1, but not D2, receptor mRNA in the NAcc, and decreased D2 receptor mRNA and D2-like receptor binding in the VTA. Together, these data indicate that AMPH alters mesocorticolimbic DA neurotransmission in a region- and receptor-specific manner, which, in turn, could have profound consequences on social behavior in female prairie voles.

Up-regulation of dopamine D(2)L mRNA levels in the ventral tegmental area and dorsal striatum of amphetamine-sensitized C57BL/6 mice: role of Ca(v)1.3 L-type Ca(2+) channels

Dopamine D(2) long (D(2)L) and D(2) short (D(2)S) isoforms of the D(2) receptor play an important role in psychostimulant-induced neuronal adaptations. In this study, we used quantitative real-time PCR to specifically amplify these two splice variants to examine their mRNA expression in the dorsal striatum (dStr), nucleus accumbens (NAc) and the ventral tegmental area (VTA) of amphetamine-sensitized C57BL/6 mice. We found a significant increase in D(2)L mRNA in the VTA and dStr of amphetamine-treated mice that positively correlated with the sensitized locomotor response. We also found a significant increase in D(2)S mRNA in the VTA. We further examined the role of the Ca(v)1.3 subtype of L-type Ca(2+) channels in up-regulation of D(2)L and D(2)S mRNA in the VTA. Amphetamine-pretreated Ca(v)1.3 wild-type (Ca(v)1.3(+/+)) mice exhibited sensitized behavior and a significant increase in D(2)L and D(2)S mRNA compared with saline-pretreated mice Amphetamine-pretreated homozygous Ca(v)1.3 knockout (Ca(v)1.3(-/-)) mice did not exhibit sensitized behavior. There was a significant increase in D(2)S mRNA, but not D(2)L mRNA. In conclusion, our results find that amphetamine increases D(2)L mRNA expression in the dStr and the VTA, an adaptation that correlates with expression of sensitized behavior and dependence on Ca(v)1.3 Ca(2+) channels.

Reversal of methamphetamine-induced behavioral sensitization by repeated administration of a dopamine D1 receptor agonist

Repeated intermittent administration of methamphetamine (MAP) produces an enduring hypersensitivity to the motor stimulant effect of MAP, termed behavioral sensitization. Dopamine plays a critical role in the development and expression of behavioral sensitization. Here, we investigated whether a dopamine D1 receptor agonist could reverse behavioral sensitization to MAP. Administration of MAP (1.0 mg/kg, i.p.) to rats once every 3 days for a total of 5 times (days 1-13) induced the enhancement of locomotor activity after MAP challenge (0.5 mg/kg, i.p.) on day 20, verifying the development of behavioral sensitization. The MAP-sensitized rats then received a dopamine D1 agonist, R-(+)-SKF38393 (3.0 mg/kg, i.p.), once a day for 7 consecutive days (days 21-27). Behavioral analysis on days 30 and 41 revealed that the enhanced locomotor activity was reversed by repeated R-(+)-SKF38393 administration. Moreover, repeated R-(+)-SKF38393 administration reversed the increased dopamine release in the striatum after MAP challenge on day 41. Thus, repeated administration of the dopamine D1 receptor agonist induces the reversal of established behavioral sensitization to MAP and of increased dopamine release in the striatum, lasting for at least 2 weeks. Dopamine D1 receptor agonists may be useful therapeutic agents for the treatment of psychostimulant addiction.

Repeated apomorphine administration alters dopamine D1 and D2 receptor densities in pigeon basal telencephalon

When pigeons are repeatedly administered a dose of apomorphine they show an increasing behavioral response, much as rodents do. In birds this expresses itself in an augmented pecking response. This sensitization is assumed to be largely due to a conditioning process. Here we present evidence that sensitization is accompanied by an alteration of the D(1) to D(2) dopamine receptor densities. An experimental group of pigeons was repeatedly injected with apomorphine, and a control group with saline. The basal forebrain tissue, known to be rich in dopamine receptors, was subjected to binding assays using tritiated specific D(1) and D(2) dopamine receptor antagonists. There was a trend towards an increase in D(1) and a significant decrease in D(2) receptor densities in apomorphine-treated birds compared to the saline-treated controls. We conclude that extended apomorphine treatment modifies the D(1) dopamine receptor density in the opposite manner to the D(2) dopamine receptor density.

Behavioral Sensitization to Apomorphine in Pigeons (Columba livia): Blockade by the D₁ Dopamine Antagonist SCH-23390

Repeated administration of apomorphine leads to a context-dependent pecking response sensitization. Previously sensitized pigeons (Columba livia) challenged with saline in the same context show a conditioned response (CR). The authors studied the effects of intrastriatal injections of the dopamine (D(1)) antagonist SCH-23390 on both the sensitized response and the CR. When coadministered with apomorphine, SCH-23390 inhibited the initial response to apomorphine, prevented the development of sensitization, and impaired the maintenance of an already developed sensitization. However, SCH-23390 had no effect on the retrieval of a previously established CR. It is concluded that the activation of D(1) receptors in the caudal avian striatum is necessary for the acquisition and maintenance of the sensitization, but not for the expression, of the CR.

Regression modeling of rodent locomotion data

We present the case for a model-based approach to the statistical analysis of rodent locomotion data for which previous research has established that the time course of behavioral change follows a specified parametric form. Inadequacies of statistical methods commonly applied to such data are described. Regression models can reveal time-dependent aspects of response that might escape more elementary analyses, as we illustrate with experimental data regarding the locomotion response to amphetamine. Inter-individual variation in response profiles is incorporated through the use of random coefficients (i.e. mixed effects models). These models provide an effective means of quantifying the extent of individual differences in behavioral response to stimulant drugs not attributable to treatment. The need to adjust for multiple comparisons when searching for regions of significant difference is discussed. We present specific models that we have found useful for characterizing responses to low doses of amphetamine or cocaine (the log-logistic random effects model) and higher or repetitive doses of amphetamine or cocaine (the polynomial random effects model). Code for performing these analyses with standard statistical software is provided.

Differential behavioral responses to chronic amphetamine in adult male and female rats exposed to postnatal cocaine treatment

The impact of cocaine exposure during development on behavioral sensitization as measured by locomotor activity and stereotypy following repeated intermittent administration of amphetamine is examined. Male and female Sprague-Dawley rats were exposed to cocaine at 50 mg/kg/day during postnatal days (PND) 11-20 and, as adults (PND193-212), were administered seven daily injections of 2.0 mg/kg amphetamine. Both locomotor activity and stereotypic behavior were assessed following the first and seventh injections. Control males and females showed sensitized behavior following repeated amphetamine injections with females showing greater locomotion while males showed increased stereotypy. Male rats pretreated with cocaine failed to develop sensitized locomotor or stereotypic responses following repeated amphetamine injections consistent with dampened D(1) receptor activity. Females pretreated with cocaine did not show a sensitized locomotor response but did display sensitization of stereotypy following repeated amphetamine administration. Thus, it appears that postnatal cocaine treatment produces differential effects on the circuits mediating sensitization behavior in male and female rats.

Long-term effects of postnatal amphetamine treatment on striatal protein kinase A activity, dopamine D(1)-like and D(2)-like binding sites, and dopamine content

The purpose of the present study was to determine whether exposure to amphetamine during the preweanling period would alter dopaminergic functioning in the dorsal striatum of adult rats. In three experiments, we assessed the effects of repeated amphetamine treatment on striatal protein kinase A (PKA) activity, dopamine (DA) D(1)-like and D(2)-like binding sites, and DA content. Rats were pretreated with saline or amphetamine (2.5 mg/kg, ip) for 7 consecutive days starting on postnatal day (PD) 11. At PD 90, rats were killed and their dorsal striata (i.e., caudate-putamen) were removed and frozen until time of assay. Amphetamine pretreatment produced long-term reductions in both striatal PKA activity and DA content. Early amphetamine exposure also resulted in an upregulation of D(2)-like binding sites, while leaving D(1)-like binding sites unaffected. It is likely that the upregulation of D(2)-like binding sites was stimulated by the persistent decline in striatal DA levels. Although speculative, it is possible that excess striatal D(2)-like receptors were responsible for inhibiting PKA activity through actions on the cAMP signal transduction pathway. The behavioral relevance of these amphetamine-induced neurochemical changes has not yet be determined.

Perinatal asphyxia induces region-specific long-term changes in mRNA levels of tyrosine hydroxylase and dopamine D(1) and D(2) receptors in rat brain

To study the effects of neonatal asphyxia on gene expression of the dopaminergic systems, we determined quantitatively the mRNA levels of tyrosine hydroxylase, dopamine transporter, dopamine D(1) and D(2) receptors in substantia nigra/ventral tegmental area, striatum and limbic area. The mRNA levels were determined at one and 4 weeks after asphyxia by a quantitative reverse transcription polymerase chain reaction method. Spontaneously and Caesarean section born rats showed similar mRNA levels with the exception of an increase of tyrosine hydroxylase mRNA levels in the limbic area of 4-week-old animals. Five min of asphyxia did not change the mRNA levels in any region compared to that in the spontaneously born rats. Fifteen and twenty min of asphyxia induced region-specific alterations in mRNA levels. In SN/VTA an increase of tyrosine hydroxylase mRNA levels in the 1-week-old rats and in striatum an increase of D(1) and D(2) dopamine receptor mRNA levels in the 4-week-old rats were observed. Fifteen min of asphyxia induced a selective increase of D(1) and D(2) dopamine receptor mRNA levels in the limbic area of 4-week-old rats. These observations indicate that neonatal asphyxia triggers a cascade of gene expressions for tyrosine hydroxylase and D(1) and D(2) dopamine receptors. In 1-week-old rats, the gene expression of tyrosine hydroxylase increased in the cell body region substantia nigra/ventral tegmental area. This change may increase the D(1) and D(2) dopamine receptor expression in the target regions striatum and limbic area during further development.

Quantification of dopamine D3 receptor mRNA level associated with the development of amphetamine-induced behavioral sensitization in the rat brain

We hypothesized that changes in expression of dopamine (DA) D3 receptor gene in the rat brain would correlate with the behavioral sensitization induced by amphetamine (AMPH). In order to test this hypothesis, we measured D3 receptor mRNA levels in the striatum, nucleus accumbens and prefrontal cortex, in individual rats following AMPH treatment (2.5 mg/kg s.c., for 5 consecutive days) using a ribonuclease protection assay method. We observed similar levels of D3 receptor mRNA in saline and AMPH treated animals in each brain region examined. These results suggest behavioral sensitization to AMPH is not mediated through postsynaptic transcriptional regulation of D3 receptor.