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Although the striatal dopamine (DA) is reportedly involved in impulsive action, little is known about the DA subtype receptors of dorsal striatum (dSTR) in the impulsive control involved in differential reinforcement of low-rate-responding (DRL) behavior. We examined the receptor-specific dopaminergic modulation of d-amphetamine (AMP)-altered DRL 10 s (DRL-10 s) performance by locally infusing SCH23390 (SCH) and raclopride (RAC), DA D1 and D2 receptor antagonists, respectively, into the rat's dSTR. Systemic injection of AMP significantly affected DRL-10 s behavior by increasing total, non-reinforced, and bust responses, as well as by decreasing reinforced responses, which correspondingly caused a leftward shift of the inter-response-time distribution curve as confirmed by a profound decrease in peak time (i.e., <10 s). Neither SCH nor RAC into dSTR pharmacologically reversed the timing impulsivity produced by AMP as measured by non-reinforced responses and peak time. However, the increase in total responses and the decrease in reinforced responses by AMP were reversed by intra-dSTR SCH or RAC. These results suggest that the D1 and D2 receptors of the dSTR may be involved in behavioral components apart from the timing impulsivity produced by AMP on a DRL task, which components are distinctly different from those in other terminal areas of midbrain DA systems., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Background: Preclinical and human positron emission tomography studies have produced inconsistent results regarding the effects of opioids on mesolimbic dopamine (DA). Here, we quantify striatal DA release (measured by [ 11 C]raclopride displacement) in response to an intravenous infusion of morphine, and its relationship with morphine-induced subjective effects, in healthy, nondependent opioid-experienced participants., Methods: Fifteen healthy male participants were initially included. Sessions were on separate days. On session 1, participants received intravenous morphine (10 mg/70 kg) in the clinic to ensure tolerability. Participants without adverse reactions (n = 10) then received intravenous morphine and placebo (saline) sessions, in counterbalanced order, while undergoing [ 11 C]raclopride positron emission tomography scans. Subjective and physiological responses were assessed. Region-of-interest and voxelwise image analyses were used to assess changes in [ 11 C]raclopride nondisplaceable binding potential., Results: Morphine produced marked subjective and physiological effects and induced a significant decrease in [ 11 C]raclopride nondisplaceable binding potential, particularly in the nucleus accumbens and globus pallidus, where the change in [ 11 C]raclopride nondisplaceable binding potential was approximately 9%. However, the subjective effects of morphine did not show a simple pattern of correlation with DA release., Conclusions: This is, to our knowledge, the first study providing in vivo human evidence that DA transmission in the ventral striatum is affected by morphine. Further studies are required to fully delineate the DA contribution to the reinforcing effects of opioids., (Copyright © 2019 Society of Biological Psychiatry. All rights reserved.)

The non-selective muscarinic receptor agonist oxotremorine-M has been found to decrease impulsive choice in high-impulsive (HI) rats and increase impulsive choice in low-impulsive (LI) rats, but little is known about the muscarinic M 1 receptor agonist N-desmethylclozapine (NDMC). This study investigated effects of NDMC on impulsive choice, and the effect of co-administration of NDMC with the dopamine D 1 -like receptor antagonist SCH 23390 or D 2 -like receptor antagonist raclopride on impulsive choice in HI and LI rats, characterized by basal levels of impulsive choice in a delay-discounting task. The results revealed that NDMC (1 and 2 mg/kg) significantly increased impulsive choice in HI, but not LI rats. SCH 23390 significantly promoted impulsive choice in HI rats at 0.01 mg/kg, and in LI rats at 0.0075 and 0.01 mg/kg. Moreover, SCH 23390 (0.005 and 0.0075 mg/kg) significantly inhibited the increase in impulsive choice induced by NDMC (1 mg/kg) in HI rats, whereas the increase in impulsive choice produced by SCH 23390 (0.0075 mg/kg) was significantly reversed by NDMC (1 mg/kg) in LI rats. Raclopride (0.04, 0.08, and 0.12 mg/kg) did not affect choice in both HI and LI rats, but significantly antagonized the increase in impulsive choice induced by NDMC (1 mg/kg) in HI rats. These findings suggest that D 1 - and D 2 -like receptors might be involved in different effects of the M 1 receptor agonist on impulsive choice between HI and LI rats., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Aripiprazole's effects on cognitive function in patients with schizophrenia are unclear because of the difficulty in disentangling specific effects on cognitive function from secondary effects due to the improvement in other schizophrenic symptoms. One approach to address this is to use an intermediate biomarker to investigate the relationship between the drug's effect on the brain and change in cognitive function. This study aims to investigate aripiprazole's effect on working memory by determining the correlation between dopamine D2/3 (D2/3) receptor occupancy and working memory of patients with schizophrenia. Seven patients with schizophrenia participated in the study. Serial positron emission tomography (PET) scans with [ 11 C]raclopride were conducted at 2, 26, and 74 h after the administration of aripiprazole. The subjects performed the N-back task just after finishing the [ 11 C]raclopride PET scan. The mean (±SD) D2/3 receptor occupancies were 66.9 ± 6.7% at 2 h, 65.0 ± 8.6% at 26, and 57.7 ± 11.2% at 74 h after administering aripiprazole. Compared with performance on the zero-back condition, performance in memory-loaded conditions (one-, two-, and three-back conditions) was significantly related to D2/3 receptor occupancy by aripiprazole (error rate: ß = -2.236, t = -6.631, df = 53.947, and p = 0.001; reaction time: ß = -9.567, t = -2.808, df = 29.967, and p = 0.009). Although the sample size was relatively small, these results suggest that aripiprazole as a dopamine-partial agonist could improve cognitive function in patients with schizophrenia.

Intranasal drug delivery is a noninvasive drug delivery route that can enhance systemic delivery of therapeutics with poor oral bioavailability by exploiting the rich microvasculature within the nasal cavity. The intranasal delivery route has also been targeted as a method for improved brain uptake of neurotherapeutics, with a goal of harnessing putative, direct nose-to-brain pathways. Studies in rodents, nonhuman primates, and humans have pointed to the efficacy of intranasally delivered neurotherapeutics, while radiolabeling studies have analyzed brain uptake following intranasal administration. In the present study, we employed carbon-11 radioactive methylation to assess the pharmacokinetic mechanism of intranasal delivery of Orexin A, a native neuropeptide and prospective antinarcoleptic drug that binds the orexin receptor 1. Using physicochemical and pharmacological analysis, we identified the methylation sites and confirmed the structure and function of methylated Orexin A (CH 3 -Orexin A) prior to monitoring its brain uptake following intranasal administration in rodent and nonhuman primate. Through positron emission tomography (PET) imaging of [ 11 C]CH 3 -Orexin A, we determined that the brain exposure to Orexin A is poor after intranasal administration. Additional ex vivo analysis of brain uptake using [ 125 I]Orexin A indicated intranasal administration of Orexin A affords similar brain uptake when compared to intravenous administration across most brain regions, with possible increased brain uptake localized to the olfactory bulbs.

The medial preoptic area (mPOA) is a brain structure classically related to both non-REM (NREM) sleep and maternal behavior. Although the dopaminergic system is known to play a role in the control of the states of sleep and wakefulness, its effects within the mPOA on sleep are still not clear. Microinjection of the dopamine D2 receptor antagonist Raclopride into the mPOA has been shown to promote nursing postures in lactating dams with no effects on active maternal behavior. We hypothesized that the facilitation of nursing postures may be also associated with the promotion of NREM sleep. In order to test the hypothesis, Raclopride was microinjected into the mPOA and maternal behavior and sleep were assessed in lactating rats. The changes observed included a reduction of the latency to start nursing and an increase of the time to reunite the entire litter. Contrary to our hypothesis, NREM sleep was not affected by Raclopride. On the other hand, REM sleep and its transitional stage from NREM sleep, were significantly reduced by this pharmacological agent. These data suggest that dopamine D2 receptors within the mPOA are involved in the transition from NREM to REM sleep., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Research in humans and nonhuman animals indicates that social affiliation, and particularly maternal bonding, depends on reward circuitry. Although numerous mechanistic studies in rodents demonstrated that maternal bonding depends on striatal dopamine transmission, the neurochemistry supporting maternal behavior in humans has not been described so far. In this study, we tested the role of central dopamine in human bonding. We applied a combined functional MRI-PET scanner to simultaneously probe mothers' dopamine responses to their infants and the connectivity between the nucleus accumbens (NAcc), the amygdala, and the medial prefrontal cortex (mPFC), which form an intrinsic network (referred to as the "medial amygdala network") that supports social functioning. We also measured the mothers' behavioral synchrony with their infants and plasma oxytocin. The results of this study suggest that synchronous maternal behavior is associated with increased dopamine responses to the mother's infant and stronger intrinsic connectivity within the medial amygdala network. Moreover, stronger network connectivity is associated with increased dopamine responses within the network and decreased plasma oxytocin. Together, these data indicate that dopamine is involved in human bonding. Compared with other mammals, humans have an unusually complex social life. The complexity of human bonding cannot be fully captured in nonhuman animal models, particularly in pathological bonding, such as that in autistic spectrum disorder or postpartum depression. Thus, investigations of the neurochemistry of social bonding in humans, for which this study provides initial evidence, are warranted.

Dysregulation of the stress response system is a potential etiological factor in the development of and relapse to multiple neuropsychiatric disorders. Previously we reported that repeated intermittent d-amphetamine administration can lead to progressively greater dopamine release, thereby providing evidence of drug-induced neurochemical sensitization. Here, we test the hypothesis that repeated exposure to d-amphetamine increases dopaminergic responses to stress; that is, produces cross-sensitization. Using positron emission tomography, we measured in 17 healthy male volunteers (mean ± s.d. = 22.1 ± 3.4 years) [(11)C]raclopride binding responses to a validated psychosocial stress task before and 2 weeks after a regimen of repeated d-amphetamine (3 × 0.3 mg kg(-1), by mouth; n = 8) or placebo (3 × lactose, by mouth; n = 9). Mood and physiological measurements were recorded throughout each session. Before the d-amphetamine regimen, exposure to the stress task increased behavioral and physiological indices of stress (anxiety, heart rate, cortisol, all P ⩽ 0.05). Following the d-amphetamine regimen, the stress-induced cortisol responses were augmented (P < 0.04), and voxel-based analyses showed larger stress-induced decreases in [(11)C]raclopride non-displaceable binding potential across the striatum. In the placebo group, re-exposure to stress led to smaller clusters of decreased [(11)C]raclopride binding, primarily in the sensorimotor striatum (P < 0.05). Together, this study provides evidence for drug × stress cross-sensitization; moreover, random exposure to stimulants and/or stress cumulatively, while enhancing dopamine release in striatal areas, may contribute to a lowered set point for psychopathologies in which altered dopamine neurotransmission is invoked.

Rationale: The only systematic in vivo studies comparing antipsychotic (AP) effects on nucleus accumbens (NAc) shell and core dopamine (DA) transmission are voltammetric studies performed in pargyline-pretreated, halothane-anaesthetized rats. Studies in freely moving rats not pretreated with pargyline are not available. This study was intended to fill this gap by the use of in vivo microdialysis in freely moving rats., Methods: Male Sprague-Dawley rats were implanted with microdialysis probes in the NAc shell and core and medial prefrontal cortex (PFCX). The next day, rats were administered intravenously with two or three doses of APs, and dialysate DA was monitored in 10-min samples. Some rats were pretreated with pargyline (75 mg/kg i.p.) and after 1 h were given clozapine or risperidone., Results: Clozapine, risperidone, quetiapine, raclopride, sulpiride and amisulpride increased DA preferentially in the NAc shell. Such preferential effect on shell DA was not observed after haloperidol, chlorpromazine and olanzapine. In contrast to voltammetric studies, a preferential effect on NAc core DA was not observed after any dose of AP. Pargyline pretreatment did not reduce but actually amplified the preferential effect of clozapine and risperidone on NAc shell DA., Conclusions: Apart from raclopride and olanzapine, the APs with lower extrapyramidal effects could be distinguished from typical APs on the basis of their ability to preferentially stimulate DA transmission in the NAc shell. There was no relationship between stimulation of PFCX DA and atypical APs profile. The differences between this study and voltammetry studies were not attributable to pargyline pretreatment.

High-resolution anatomical image data in preclinical brain PET and SPECT studies is often not available, and inter-modality spatial normalization to an MRI brain template is frequently performed. However, this procedure can be challenging for tracers where substantial anatomical structures present limited tracer uptake. Therefore, we constructed and validated strain- and tracer-specific rat brain templates in Paxinos space to allow intra-modal registration. PET [18F]FDG, [11C]flumazenil, [11C]MeDAS, [11C]PK11195 and [11C]raclopride, and SPECT [99mTc]HMPAO brain scans were acquired from healthy male rats. Tracer-specific templates were constructed by averaging the scans, and by spatial normalization to a widely used MRI-based template. The added value of tracer-specific templates was evaluated by quantification of the residual error between original and realigned voxels after random misalignments of the data set. Additionally, the impact of strain differences, disease uptake patterns (focal and diffuse lesion), and the effect of image and template size on the registration errors were explored. Mean registration errors were 0.70 ± 0.32 mm for [18F]FDG (n = 25), 0.23 ± 0.10mm for [11C]flumazenil (n = 13), 0.88 ± 0.20 mm for [11C]MeDAS (n = 15), 0.64 ± 0.28 mm for [11C]PK11195 (n = 19), 0.34 ± 0.15 mm for [11C]raclopride (n = 6), and 0.40 ± 0.13 mm for [99mTc]HMPAO (n = 15). These values were smallest with tracer-specific templates, when compared to the use of [18F]FDG as reference template (p<0.001). Additionally, registration errors were smallest with strain-specific templates (p<0.05), and when images and templates had the same size (p ≤ 0.001). Moreover, highest registration errors were found for the focal lesion group (p<0.005) and the diffuse lesion group (p = n.s.). In the voxel-based analysis, the reported coordinates of the focal lesion model are consistent with the stereotaxic injection procedure. The use of PET/SPECT strain- and tracer-specific templates allows accurate registration of functional rat brain data, independent of disease specific uptake patterns and with registration error below spatial resolution of the cameras. The templates and the SAMIT package will be freely available for the research community [corrected].

Ethanol increases the interstitial dopamine (DA) concentration in the nucleus accumbens (NAcc) of experimental animals, but positron emission tomography (PET) studies using the single-bolus protocol of the [(11)C]-raclopride competition paradigm have yielded conflicting results in humans. To resolve disparate previous findings, we utilized the bolus-plus-infusion (B/I) method, allowing both baseline and intervention quantification of [(11)C]raclopride binding during a single 105-minute PET scan, to investigate possible ethanol-induced DA release in nine healthy male subjects. A 25-minute intravenous ethanol (7.6%) infusion, resulting in a 1.3 g/L mean blood ethanol concentration, was administered using masked timing during the PET scan. Automated region-of-interest analysis testing the difference between baseline (40-50 minutes) and intervention (60-85 minutes) revealed an average 12.6% decrease in [(11)C]raclopride binding in the ventral striatum (VST, P=0.003) including the NAcc. In addition, a shorter time interval from the start of ethanol infusion to the first subjective effect was associated with a greater binding potential decrease bilaterally in the VST (r=0.92, P=0.004), and the feeling of pleasure was associated with a decrease in binding potential values in both the caudate nucleus (r=-0.87, P=0.003) and putamen (r=-0.74; P=0.02). These results confirm that ethanol induces rapid DA release in the limbic striatum, which can be reliably estimated using the B/I method in one imaging session.

Background: Food addiction is a debated topic in neuroscience. Evidence suggests diabetes is related to reduced basal dopamine levels in the nucleus accumbens, similar to persons with drug addiction. It is unknown whether insulin sensitivity is related to endogenous dopamine levels in the ventral striatum of humans. We examined this using the agonist dopamine D2/3 receptor radiotracer [(11)C]-(+)-PHNO and an acute dopamine depletion challenge. In a separate sample of healthy persons, we examined whether dopamine depletion could alter insulin sensitivity., Methods: Insulin sensitivity was estimated for each subject from fasting plasma glucose and insulin using the Homeostasis Model Assessment II. Eleven healthy nonobese and nondiabetic persons (3 female) provided a baseline [(11)C]-(+)-PHNO scan, 9 of which provided a scan under dopamine depletion, allowing estimates of endogenous dopamine at dopamine D2/3 receptor. Dopamine depletion was achieved via alpha-methyl-para-tyrosine (64mg/kg, P.O.). In 25 healthy persons (9 female), fasting plasma and glucose was acquired before and after dopamine depletion., Results: Endogenous dopamine at ventral striatum dopamine D2/3 receptor was positively correlated with insulin sensitivity (r(7)=.84, P=.005) and negatively correlated with insulin levels (r(7)=-.85, P=.004). Glucose levels were not correlated with endogenous dopamine at ventral striatum dopamine D2/3 receptor (r(7)=-.49, P=.18). Consistently, acute dopamine depletion in healthy persons significantly decreased insulin sensitivity (t(24)=2.82, P=.01), increased insulin levels (t(24)=-2.62, P=.01), and did not change glucose levels (t(24)=-0.93, P=.36)., Conclusion: In healthy individuals, diminished insulin sensitivity is related to less endogenous dopamine at dopamine D2/3 receptor in the ventral striatum. Moreover, acute dopamine depletion reduces insulin sensitivity. These findings may have important implications for neuropsychiatric populations with metabolic abnormalities., (© The Author 2015. Published by Oxford University Press on behalf of CINP.)

Purpose: This study was conducted to directly compare the high-resolution research tomograph (HRRT) (high-resolution brain) and HR+ (standard whole-body) positron emission tomography (PET) only scanners for quantitative brain studies using three tracers with vastly different tracer distributions., Procedures: Healthy volunteers underwent successive scans on HR+ and HRRT scanners (in random order) using either (R)-[(11)C]verapamil (n = 6), [(11)C]raclopride (n = 7) or [(11)C]flumazenil (n = 7). For all tracers, metabolite-corrected plasma-input functions were generated., Results: After resolution matching, HRRT-derived kinetic parameter values correlated well with those of HR+ for all tracers (intraclass correlation coefficients ≥0.78), having a good absolute interscanner test-retest variability (≤15 %). However, systematic differences can be seen for HRRT-derived kinetic parameter values (range -13 to +15 %)., Conclusion: Quantification of kinetic parameters based on plasma-input models leads to comparable results when spatial resolution between HRRT and HR+ data is matched. When using reference-tissue models, differences remain that are likely caused by differences in attenuation and scatter corrections and/or image reconstruction.

Purpose: The partial saturation approach (PSA) is a simple, single injection experimental protocol that will estimate both B(avail) and appK(D) without the use of blood sampling. This makes it ideal for use in longitudinal studies of neurodegenerative diseases in the rodent. The aim of this study was to increase the range and applicability of the PSA by developing a data driven strategy for determining reliable regional estimates of receptor density (B(avail)) and in vivo affinity (1/appK(D)), and validate the strategy using a simulation model., Methods: The data driven method uses a time window guided by the dynamic equilibrium state of the system as opposed to using a static time window. To test the method, simulations of partial saturation experiments were generated and validated against experimental data. The experimental conditions simulated included a range of receptor occupancy levels and three different B(avail) and appK(D) values to mimic diseases states. Also the effect of using a reference region and typical PET noise on the stability and accuracy of the estimates was investigated., Results: The investigations showed that the parameter estimates in a simulated healthy mouse, using the data driven method were within 10±30% of the simulated input for the range of occupancy levels simulated. Throughout all experimental conditions simulated, the accuracy and robustness of the estimates using the data driven method were much improved upon the typical method of using a static time window, especially at low receptor occupancy levels. Introducing a reference region caused a bias of approximately 10% over the range of occupancy levels., Conclusions: Based on extensive simulated experimental conditions, it was shown the data driven method provides accurate and precise estimates of B(avail) and appK(D) for a broader range of conditions compared to the original method., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Moves to legalize marijuana highlight the urgency to investigate effects of chronic marijuana in the human brain. Here, we challenged 48 participants (24 controls and 24 marijuana abusers) with methylphenidate (MP), a drug that elevates extracellular dopamine (DA) as a surrogate for probing the reactivity of the brain to DA stimulation. We compared the subjective, cardiovascular, and brain DA responses (measured with PET and [(11)C]raclopride) to MP between controls and marijuana abusers. Although baseline (placebo) measures of striatal DA D2 receptor availability did not differ between groups, the marijuana abusers showed markedly blunted responses when challenged with MP. Specifically, compared with controls, marijuana abusers had significantly attenuated behavioral ("self-reports" for high, drug effects, anxiety, and restlessness), cardiovascular (pulse rate and diastolic blood pressure), and brain DA [reduced decreases in distribution volumes (DVs) of [(11)C]raclopride, although normal reductions in striatal nondisplaceable binding potential (BPND)] responses to MP. In ventral striatum (key brain reward region), MP-induced reductions in DVs and BPND (reflecting DA increases) were inversely correlated with scores of negative emotionality, which were significantly higher for marijuana abusers than controls. In marijuana abusers, DA responses in ventral striatum were also inversely correlated with addiction severity and craving. The attenuated responses to MP, including reduced decreases in striatal DVs, are consistent with decreased brain reactivity to the DA stimulation in marijuana abusers that might contribute to their negative emotionality (increased stress reactivity and irritability) and addictive behaviors.

AKT1 (also known as protein kinase B, α), a serine/threonine kinase of AKT family, has been implicated in both schizophrenia and methamphetamine (Meth) use disorders. AKT1 or its protein also has epistatic effects on the regulation of dopamine-dependent behaviors or drug effects, especially in the striatum. The aim of this study is to investigate the sex-specific role of Akt1 in the regulation of Meth-induced behavioral sensitization and the alterations of striatal neurons using Akt1(-/-) mice and wild-type littermates as a model. A series of 4 Experiments were conducted. Meth-induced hyperlocomotion and Meth-related alterations of brain activity were measured. The neural properties of striatal medium spiny neurons (MSNs) were also characterized. Further, 17β-estradiol was applied to examine its protective effect in Meth-sensitized male mice. Our findings indicate that (1) Akt1(-/-) males were less sensitive to Meth-induced hyperlocomotion during Meth challenge compared with wild-type controls and Akt1(-/-) females, (2) further sex differences were revealed by coinjection of Meth with raclopride but not SCH23390 in Meth-sensitized Akt1(-/-) males, (3) Meth-induced alterations of striatal activity were confirmed in Akt1(-/-) males using microPET scan with (18)F-flurodeoxyglucose, (4) Akt1 deficiency had a significant impact on the electrophysiological and neuromorphological properties of striatal MSNs in male mice, and (5) subchronic injections of 17β-estradiol prevented the reduction of Meth-induced hyperactivity in Meth-sensitized Akt1(-/-) male mice. This study highlights a sex- and region-specific effect of Akt1 in the regulation of dopamine-dependent behaviors and implies the importance of AKT1 in the modulation of sex differences in Meth sensitivity and schizophrenia.

In the model with a choice of reinforcements of different value animals were able to "impulsive" and "self-controlled" behavior with an equal probability. Five adult cats were tested. A local application of agonists of 5-HT(1A) and 5-HT(2A/C) receptors (8-OH-DPAT, DOI) in the frontal cortex have resulted in a significant decrease of the "impulsive" reactions and an increase of omissions. The administration of antagonists of 5-HT(2A/C) receptors (ketanserin) and D1/D2 receptors (SCH 23390, raclopride) have impaired the "impulsive" behavior. However the combined administration of agonists/antagonists of 5-HT(2A/C) receptors and antagonists of D1/D2 receptors have not shown the significant changes in behavior as compared with control experiments. The data showed the realization of the optimal behavior with the "impulsive" and "self-controled" reactions in ambivalent animals requires the involvement of both dopaminergic and serotoninergic systems for the regulation of the activity of neurons in frontal cortex areas.

Rationale: Methamphetamine (METH) induces hyperthermia in warm and hypothermia in cool environments. Our first goal was to further study the role of ambient temperature in METH's effect on core temperature in rats. Previously, these effects were primarily demonstrated in high doses; we extended this investigation to the low-dose range (1 mg/kg METH). Our second goal was to identify the role of the D2 receptor in METH's effects in cool ambient temperatures., Method: Rats received METH (saline, 1, 5, and 10 mg/kg), raclopride (saline, 0.3, 0.6, and 1.2 mg/kg), or a combination (all doses of raclopride combined with 10 mg/kg METH). Treatments occurred in ambient temperatures of 18, 24, or 30 °C., Results and Conclusions: Consistent with prior research, 5 and 10 mg/kg METH caused hyperthermia or hypothermia in a dose- and ambient temperature-dependent manner (60 min after METH). In contrast, 1 mg/kg produced similar levels of hyperthermia at all ambient temperatures. These findings suggest that a threshold METH dose exists; below this dose, METH still changes core temperature, but CNS control over temperature regulation is left intact. In our experiments regarding D2 blockade, raclopride decreased METH-induced core temperature at 30 and 24 °C (60 min after METH), consistent with previous findings. We extended these findings by demonstrating that in a cool ambient temperature (18 °C), raclopride pretreatment also lowered the core temperature response to METH. Although the D2 receptor is known to mediate hypothermia, the combination of METH and D2 blockade suggests a complex mediation of the core temperature response, perhaps involving neurotransmitter interactions.

This study employed simultaneous neuroimaging with positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) to demonstrate the relationship between changes in receptor occupancy measured by PET and changes in brain activity inferred by fMRI. By administering the D2/D3 dopamine receptor antagonist [(11)C]raclopride at varying specific activities to anesthetized nonhuman primates, we mapped associations between changes in receptor occupancy and hemodynamics [cerebral blood volume (CBV)] in the domains of space, time, and dose. Mass doses of raclopride above tracer levels caused increases in CBV and reductions in binding potential that were localized to the dopamine-rich striatum. Moreover, similar temporal profiles were observed for specific binding estimates and changes in CBV. Injection of graded raclopride mass doses revealed a monotonic coupling between neurovascular responses and receptor occupancies. The distinct CBV magnitudes between putamen and caudate at matched occupancies approximately matched literature differences in basal dopamine levels, suggesting that the relative fMRI measurements reflect basal D2/D3 dopamine receptor occupancy. These results can provide a basis for models that relate dopaminergic occupancies to hemodynamic changes in the basal ganglia. Overall, these data demonstrate the utility of simultaneous PET/fMRI for investigations of neurovascular coupling that correlate neurochemistry with hemodynamic changes in vivo for any receptor system with an available PET tracer.

In Sprague-Dawley rats by means of in vivo microdialysis it was shown that stress, evoked by conditioned fear response acquisition, resulted in inhibition of exploratory behavior and produced a reduction of exploration-induced rise in extracellular levels of citrulline (an NO co-product) in the nucleus accumbens which were observed 24 hours after the stress. Intra-accumbal infusion of dopamine D2 receptor antagonist raclopride (10 μM), made after the conditioned fear response acquisition, in 24 hours after the infusion, restore the exploratory behavior and exploration-induced rise of extracellular levels of citrulline in this brain area. The data obtained indicate for the first time that stress-induced inhibition of the exploratory behavior might be mediated by inhibition of the nucleus accumbens nitrergic system occurring under the control of D2 receptors of this brain area.

To elucidate the dynamic effects of deep brain stimulation (DBS) in the subthalamic nucleus (STN) during activity on the dopaminergic system, 12 PD patients who had STN-DBS operations at least 1 month prior, underwent two positron emission tomography scans during right-foot movement in DBS-off and DBS-on conditions. To quantify motor performance changes, the motion speed and mobility angle of the foot at the ankle were measured twice. Estimations of the binding potential of [(11)C]raclopride (BP(ND)) were based on the Logan plot method. Significant motor recovery was found in the DBS-on condition. The STN-DBS during exercise significantly reduced the [(11)C]raclopride BP(ND) in the caudate and the nucleus accumbens (NA), but not in the dorsal or ventral putamen. The magnitude of dopamine release in the NA correlated negatively with the magnitude of motor load, indicating that STN-DBS facilitated motor behavior more smoothly and at less expense to dopamine neurons in the region. The lack of dopamine release in the putamen and the significant dopamine release in the ventromedial striatum by STN-DBS during exercise indicated dopaminergic activation occurring in the motivational circuit during action, suggesting a compensatory functional activation of the motor loop from the nonmotor to the motor loop system.

We have developed a feedback-controlled bolus plus infusion (FC-B/I) method for monitoring the interaction between positron emission tomography (PET) ligands and their specific target molecules with PET. The usefulness of the FC-B/I method was evaluated by the direct interaction between [(11)C]raclopride, a dopamine D(2) receptor (D(2)R) ligand, and cold raclopride (10 and 100 μg/kg) in the brains of conscious monkeys. The present results demonstrated that the FC-B/I method could achieve the equilibrium state of [(11)C]raclopride in the striatum of monkey brain, and also that the cold raclopride-induced reduction of [(11)C]raclopride binding to D(2)R was observed in a dose-dependent manner. Good correlations of distribution volume ratio of the striatum to cerebellum between the conventional bolus plus infusion (B/I) method and the FC-B/I method as well as between the conventional bolus injection method and the FC-B/I method were observed. These results indicated that the system could be a useful tool for the evaluation of interaction between drug candidates and their target molecules like enzymes, receptors, and transporters by using of their specific PET ligands.

Positron emission tomography (PET) is an imaging technique that provides direct measurements of receptor binding in neurons. The present study was performed to find reasons for the common observation of rapid metabolism of receptor radioligands during time of a brain PET scan. To this aim, the 1-h phase during which imaging-data are acquired was evaluated by using a pharmacokinetic approach. The values of half-lives, volumes of distribution, and dilution calculated for a set of metabolite corrected plasma curves of D2-receptor radioligand [(11)C]raclopride (PETc) during 50 min after radioligand injection in tracer dose were compared with the reference values obtained from a set of plasma curves (REFc) during 30 h after i.v. infusion of unlabelled raclopride in pharmacological doses. We found that the half-life of PETc correspond to the distribution half-life of REFc. Accordingly, the distribution volume during the terminal phase of PETc (13.6 ± 10.8 L) was significantly lower than that during the terminal phase (82.2 ± 30.5 L) and at steady state (59.4 ± 20 L) for REFc, and the dilution of raclopride in body for PETc at 50 min was 38 L, whereas it was 1015 L for REFc at 30 h. The [(11)C]raclopride in plasma at 50 min was higher (10% of dose) than the value for unlabelled raclopride at 30 h (4%). We concluded that the kinetic behavior of the radiolabelled drug [(11)C]raclopride during the 1 h time of a PET corresponds to the distribution phase. The high percentage of [(11)C]raclopride in plasma during this phase is a likely reason for the observed rapid radioligand metabolism., (Copyright © 2011 Wiley Periodicals, Inc.)

Although D2/3 agonists have been used as a first-line medication for idiopathic restless legs syndrome (iRLS), findings on D2/3 receptors have been inconsistent. Here, we aimed to clarify the contribution of D2/3 receptor function to the clinical symptoms of iRLS by comparing the binding potential (BP(ND)) of [(11)C]raclopride with clinical improvements after D2/3 stimulation by pramipexole. Eight drug-naïve, iRLS patients and eight age-matched healthy subjects were scanned with positron emission tomography (PET). After PET scans, all patients received pramipexole (0.125 mg) orally for 2 weeks. Patients were evaluated every day with several standardized clinical tests. The BP(ND) values were compared using regions of interest and voxel-based methods. Results showed that the mean magnitude of [(11)C]raclopride BP(ND) in the mesolimbic dopamine region (nucleus accumbens (NA) and caudate) was significantly lower in the iRLS group. No significant differences between groups were observed in the putamen. The NA [(11)C]raclopride BP(ND) levels correlated negatively with clinical severity scores and positively with the degree of posttreatment improvement in iRLS. The present results suggest that alterations in mesolimbic D2/3 receptor function reflect the pathophysiology of iRLS, and the baseline availability of D2/3 receptors may predict the clinical outcome after D2/3 agonist treatment.

In Sprague-Dawley rats, by means of in vivo microdialysis combined with HPLC analysis it was shown that the infusion into the n. accumbens of the D2-receptor antagonist raclopride (20, 100 microM) did not affect extracellular level ofcitrulline (an NO co-product) in this brain area. The intraaccumbal infusion of NMDA, an NMDA receptor agonist (100 microM) caused a rise of the extracellular citrulline level in this brain area. This rise was prevented by intraaccumbal infusion of 0.5 mM 7-nitroindazole, a neuronal NO-synthase inhibitor, and it was significantly reduced by the infusion of raclopride (20, 100 microM) into this brain area. The data obtained suggest that the D2-receptors of the n. accumbens are implicated in the regulation of neuronal NO-synthase activity induced by local NMDA receptor stimulation.

Rationale: Receptor occupancy study has been performed to evaluate pharmacokinetic profiles in new antipsychotic drug development. While these findings highlight the value of positron emission tomography (PET) for dose-finding study, what is unclear is if it is necessary to conduct these studies in patients with schizophrenia or whether studies in healthy volunteers are adequate., Objectives: To determine if it is necessary to conduct dopamine receptor occupancy studies in patients with schizophrenia or whether studies in healthy volunteers are adequate for dose-finding study, we compared the concentration-occupancy relationship in terms of EC(50) between patients and healthy volunteers., Methods: Ten healthy volunteers and eight patients with schizophrenia participated in the study. We measured dopamine receptor occupancy using [(11)C]raclopride PET and plasma concentration of YKP1358, a novel antipsychotic drug under clinical development, at a number of time points after the administration of YKP1358. Pharmacokinetic data including area under the plasma concentration versus time curve, elimination half-life, maximum observed plasma concentration, and the time to reach the maximum observed plasma concentration were obtained. We explored the relationship between plasma concentration and dopamine D(2) receptor occupancy using E (max) model and calculated EC(50)., Results: The elimination half-life was longer in healthy volunteers than in patients. Other pharmacokinetic parameters were not significantly different between two groups. The EC(50) was 7.6 ng/ml (95% confidence interval (CI) 6.2-9.0) in healthy volunteers and 8.6 (95% CI 7.4-9.9) in patients., Conclusions: The antipsychotic concentration-occupancy relationship in patients can be estimated from the EC(50) data of healthy volunteers.

Selective antagonists of D1 and D2 receptors (SCH 23 390 and raclopride respectively) were injected to rats divided on the basis of preliminary experiments into groups of"self-controlled" (preference of valuable but delayed reinforcement) and "impulsive" (choice of less valuable but immediate reinforcement) animals. Number of omissions of reactions and their latencies were recorded. In "self-controlled" rats, both drugs increased the number of reactions for less valuable immediate reinforcement, i.e., increased impulsiveness, whereas practically did not change the behavior of "impulsive" animals. Introduction of SCH 23 390 to animals ofboth groups increased the number of reaction omissions the effect being stronger in "self-controlled" animals. Raclopride also increased the number of reaction omissions in "self-controlled" rats but only on the next day after the injection. In "impulsive" animals, both drugs increased the latencies of reactions.

The present study examined the roles of dopamine and D(1)- and D(2)-like dopamine receptors in ventrolateral orbital cortex (VLO)-evoked antinociception in rats with persistent inflammatory pain. Following formalin injection into the rat unilateral hindpaw pad, the effects of dopamine receptor agonist and antagonist microinjections into the VLO on nociceptive behavior were observed. Results demonstrated that VLO microinjection of the non-selective dopamine receptor agonist apomorphine (R(-)-apomorphine hydrochloride, 1.0, 2.5 and 5.0μg) depressed later-phase nociceptive behavior induced by formalin injection; this effect was attenuated by the D(2)-like dopamine receptor antagonist S(-)-raclopride(+)-tartrate salt (raclopride, 3.0μg), but not by the D(1)-like dopamine receptor antagonist R(+)-SCH-23390 hydrochloride (SCH-23390, 1.0μg). Apomorphine-induced antinociception was mimicked by microinjection of the D(2)-like dopamine receptor agonist (-)-quinpirole hydrochloride (2.0 and 5.0μg) into the same VLO site, and this effect was antagonized by raclopride (3.0μg). In addition, microinjection of the D(1)-like dopamine receptor agonist R(+)-SKF-38393 hydrochloride (5.0μg) had no effect on formalin-induced nociceptive behavior during the later phase. However, the D(1)-like dopamine receptor antagonist SCH-23390 (2.5, 5.0 and 10μg) depressed nociceptive behavior in a dose-dependent manner. These results suggested that dopamine mediated VLO-induced antinociception via different mechanisms in the persistent inflammatory pain model; D(2)-like receptors mediated dopamine-induced antinociception, while D(1)-like dopamine receptors exhibited tonic facilitatory action on nociceptive behavior, thereby blocking D(1)-like dopamine receptors could induce antinociception., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Effects of direct injections of amphetamine into the shell of the nucleus accumbens were studied in three lines of Long-Evans rats, two of which had been selected for low and high rates of 50 kHz calls in adolescence in response to a standard social stimulation, and compared to results from randomly selected rats. Injections of amphetamine into the medial shell of the nucleus accumbens significantly increased the number of 50 kHz vocalizations in the high line but not low line, as compared to the random controls. This response was shell specific and antagonized by raclopride. Rats of the high line emitted significantly more frequency-modulated calls, with broader bandwidth and higher mean peak frequency than rats of all other lines. It is concluded that the high line of Long-Evans rats represents animals prone to positively valenced emotional states dependent on endogenous shell dopamine, as compared to the low line animals. Low line rats were less vocal than high and random line rats and not significantly responsive to intraaccumbens amphetamine. Selection of rats on the basis of the number of emitted 50 kHz calls is a useful model for studying brain mechanisms of different emotional phenotypes. The results also indicate that accumbens shell dopamine responsivity may be critical in determining the positive or negative emotional phenotype of the organism., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Background: The analysis of licking microstructure provides measures, such as duration and number of licking bouts, which might reveal the former an evaluation process and the latter an approach response. Dopamine D2-like receptor antagonists reduce the duration of licking bouts and mimic the effect of reducing sucrose concentration, while conflicting results are reported on the effects of dopamine D1-like receptor antagonists. The aim of this study is to examine the roles of dopamine D1-like and D2-like receptors in the activation of reward-associated responses and in reward evaluation, through the study of licking microstructure., Methods: The effects of the dopamine D2-like receptor antagonists raclopride (0.025-0.25 mg/kg), the D1-like antagonist SCH 23390 (0.01-0.04 mg/kg) and the antipsychotic drug haloperidol (0.02-0.05 mg/kg), have been examined on the microstructure of licking for a 10% sucrose solution in rats., Results: The results confirm that dopamine D2-like receptor antagonists reduce the duration of licking bouts and reveal that while SCH 23390 reduced licking exclusively by reducing bout number, raclopride produced on this measure an extinction mimicry effect similar to that observed in instrumental responding for different rewards., Discussion: These results are consistent with the hypothesis that the level of activation of the responses to the reward-associated cues depends on dopamine D1-like receptor stimulation, and is updated, or "reboosted", on the basis of a dopamine D2-like receptor-mediated evaluation process occurring during the consummatory transaction with the reward., ((c) 2010 Elsevier Ltd. All rights reserved.)

We examined interval timing in mice that underexpress the dopamine transporter (DAT) and have chronically higher levels of extracellular dopamine (Zhuang et al., 2001). The dopaminergic system has been proposed as a neural substrate for an internal clock, with transient elevations of dopaminergic activity producing underestimation of temporal intervals. A group of DAT knockdown (KD) and littermate wild type (WT) mice were tested with a dual peak procedure. Mice obtained reinforcement by pressing one of two levers after a fixed amount of time (30 or 45 s) had elapsed since lever extension. Only one lever was available at a time, and each lever was associated with a single duration. On occasional probe trials, the DAT KD mice began responding earlier in the interval than WT mice, but showed maximal responding and terminated responding around the same time as the WT mice. Administration of raclopride (0.2, 0.6, and 1.2 mg/kg), a D2 antagonist, eliminated most of the differences between DAT KD and WT mice, suggesting that the effects of chronic DAT downregulation on interval timing were mediated by the D2 receptors. Another cohort of DAT KD mice was trained on a visual attention task, and no deficits were observed, confirming that the changes in timed behavior were not attentionally mediated. Our data are consistent with the view that tonic dopamine affects the sensitivity of an organism to external reward signals, and that this increased motivation for reward of DAT KD mice lowers the threshold for initiating responding in a timing task., (Copyright 2010 Elsevier B.V. All rights reserved.)

Systemic administration of dopamine D1-like (SCH23390) and, to a lesser degree D2-like (raclopride), receptor antagonists significantly reduce the acquisition and expression of fructose-conditioned flavor preferences (CFP) in rats. Given the role of dopamine in the amygdala (AMY) in the processing and learning of food reward, the present study examined whether dopamine D1-like or D2-like antagonists in this site altered acquisition and/or expression of a fructose-CFP. In Experiment 1, food-restricted rats with bilateral AMY cannulae were trained to drink a fructose (8%)+saccharin (0.2%) solution mixed with one flavor (e.g., grape, CS+/Fs) and a less-preferred 0.2% saccharin solution mixed with another flavor (e.g., cherry, CS-/s) during one-bottle (16 ml) sessions. Two-bottle tests with the two flavors mixed in saccharin solutions (CS+/s, CS-/s) occurred 10 min following total bilateral AMY doses of 0, 12, 24 and 48 nmol of SCH23390 or raclopride. Preference for CS+/s over CS-/s was significantly reduced relative to vehicle baseline by the 48 nmol doses of SCH23390 and raclopride (from 77% to 66% and 68%), but not lower doses. In Experiment 2, rats received bilateral AMY injections (12 nmol) of SCH23390 (D1 group) or raclopride (D2 group) 10 min prior to one-bottle training sessions with CS+/Fs and CS-/s. Yoked Control rats received vehicle and were limited to the CS intakes of the D1 and D2 groups; untreated controls were not injected or limited to drug group intakes during training. Subsequent two-bottle tests revealed initial preferences of CS+/s over CS-/s in all groups that remained stable in untreated and Yoked Controls, but were lost over the 6 tests sessions in the D1 group, but not in the D2 group. These data indicate that dopamine D1-like and D2-like antagonists significantly attenuated the expression of the previously acquired fructose-CFP, and did not block acquisition of the fructose-CFP. D1-like antagonism during training hastened extinction of the fructose-CFP. The results are similar to those produced by dopamine D1-like and D2-like antagonist injections into the nucleus accumbens shell which suggests that flavor conditioning involves a regionally distributed brain network.

Experimentally induced and parkinsonian disruptions in dopamine (DA) transmission are associated with motor abnormalities that include a reduced likelihood of behavioral response initiation and an increased duration of executed responses. Here we investigated the dopamine receptor subtypes involved in regulating these two aspects of behavior. We examined the effects of D1 family (D1/D5) antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH23390; 0, 0.04, 0.08, or 0.16 mg/kg) and D2/D3 antagonist 3,5-dichloro-N-(1-ethylpyrrolidin-2-ylmethyl)-2-hydroxy-6-methoxybenzamide (+)-tartrate salt (raclopride; 0, 0.2, or 0.4 mg/kg) on the likelihood and duration of a cued Pavlovian approach and a cued operant lever-press response. While the high doses of the D1 and D2 antagonists produced similar levels of overall locomotor suppression, only the D2 antagonist increased the duration of time that animals' heads remained in the food compartment during both Pavlovian and operant task performance. In contrast, D1 antagonist SCH23390 decreased the proportion of trials in which animals executed both the Pavlovian approach and operant lever-press, while raclopride did not. The results suggest that D2 receptor blockade preferentially increases response duration, and, under the simple discrete-trial procedures employed here, D1 receptor blockade preferential reduces Pavlovian and operant response likelihood.

Positron emission tomography (PET) with [(11)C]raclopride is widely used to investigate temporal changes in the dopamine D(2) receptor system attributed to the dopamine release. The simplified reference tissue model (SRTM) can be used to determine the binding potential (BP(ND)) value using the time-activity curve (TAC) of the reference region as input function. However, in assessing temporal changes in BP(ND) using the SRTM, multiple [(11)C]raclopride PET scans are required, and a second scan must be performed after the disappearance of the [(11)C]raclopride administered in the first scan. In this study, we have developed an extended multiple-injection SRTM to estimate the BP(ND) change, from a single PET scan with multiple injections of [(11)C]raclopride, and we have validated this approach by performing numerous simulations and studies on monkeys. In the computer simulations, TACs were generated for dual injections of [(11)C]raclopride, in which binding conditions changed during the scans, and the BP(ND) values before, and after, the second injection were estimated by the proposed method. As a result, the reduction in BP(ND) was correlated, either with the integral of released dopamine, or with the administered mass of raclopride. This method was applied to studies on monkeys, and was capable of determining two identical BP(ND) values when there were no changes in binding conditions. The BP(ND) after the second injection decreased when binding conditions changed due to an increase in administered raclopride. An advantage of the proposed method is the shortened scan period for the quantitative assessment of the BP(ND) change for neurotransmitter competition studies.

Increased responsiveness to stress plays an important role in the manifestation of schizophrenia symptoms. Evidence indicates that the prefrontal cortex (PFC), and dopamine neurotransmission in the PFC in particular, is involved in the modulation of stress responsiveness. Decreased dopaminergic activity and loss of dopamine fibres have been reported in PFC in schizophrenia patients. Consequently, it was hypothesized that depletion of dopamine in PFC may facilitate increased stress responsiveness. Adult Sprague-Dawley rats received injections of 6-hydroxydopamine or saline bilaterally into the medial PFC (mPFC) following desipramine pretreatment to selectively deplete dopaminergic fibres. Following a 3-wk recovery period, the lesioned and control rats received injections of a D1 or D2 dopamine receptor agonist or vehicle into the mPFC and were immediately subjected to forced swimming as a stressor. Results showed that frequency of locomotion and rearing, behavioural measures indicative of increased dopaminergic activity in the nucleus accumbens (NAc), were significantly increased following stress in prefrontal cortical dopamine-depleted rats. This effect was significantly ameliorated by infusions of a D1 dopamine receptor agonist directly into the mPFC in a dose-dependent manner but not by infusion of a D2 dopamine receptor agonist. In addition, stress-induced behavioural changes in prefrontal cortical dopamine-depleted rats were significantly reduced following selective discrete infusions of a D2 dopamine receptor antagonist into the NAc shell. The results suggest that dopaminergic transmission via D1 receptors in the mPFC modulates D2 dopamine receptor-mediated stress responsiveness in the NAc, a feature that may be disrupted in schizophrenia patients.

Background: The effect of self-administered cocaine on extracellular dopamine (DA) levels has not been measured in humans., Methods: Ten nondependent cocaine users underwent positron emission tomography [11C]raclopride scans following intranasal self-administration of cocaine hydrochloride (1.0 mg/kg) and placebo powder., Results: Compared with placebo, intranasal cocaine self-administration decreased [11C]raclopride binding values in the ventral limbic striatum and putamen. Individual differences in the magnitude of the [11C]raclopride response in the ventral striatum were predicted by lifetime histories of stimulant drug use., Conclusions: The results suggest that 1) intranasal cocaine self-administration increases synaptic DA levels in human striatum and 2) prior use of stimulant drugs on the street is associated with progressively greater cocaine-induced DA responses. These dopaminergic effects might influence susceptibility to drug-seeking behavior and the progression to substance abuse.

Adenosine A2A receptor agonists produce a hypokinetic state (catalepsy) that is believed to reflect antagonistic interaction of A2A and dopamine D2 receptors in the basal ganglia. In addition to catalepsy, pharmacological blockade of D2 receptors produces rigidity. However there are conflicting data about the effect of A2A agonists on muscle tone, with some reports indicating an increase, while other data suggest that A2A catalepsy is dominated by muscle hypotonia. We investigated the effect on resistance to imposed movements of systemic cataleptic doses of the selective A2A agonist CGS21680 (5 mg/kg), and compared it with the effect of the D2 antagonist raclopride (5 mg/kg), in rats. Total resistance is made up of elastic and viscous components. The elastic component is velocity independent, and is referred to as "stiffness," whereas viscosity, which dampens responses to imposed movements, is velocity dependent. Using a method for quantifying total joint resistance that enabled separate identification of stiffness and viscosity, we found that during catalepsy evoked by either drug there was a clear increase in joint rigidity. Both CGS21680 and raclopride significantly increased joint stiffness, the velocity independent component of rigidity that is most affected in Parkinsonism. In contrast, the effect of CGS21680 on the velocity-dependent viscosity component was less robust than for raclopride, and did not reach significance, possibly reflecting an interaction with sedative effects via extrastriatal receptors. The effect of CGS21680 and raclopride on joint stiffness is thus consistent with previous findings suggesting functional antagonism of A2A and D2 receptors in the basal ganglia.

Many central nervous system (CNS) drug discovery programs require the successful collection of cerebrospinal fluid (CSF) for assessing CNS penetration and distribution of new chemical entities. The objective of the present investigation was to simplify the technique for collecting maximum CSF from cisterna magna of the rats. Rat was anesthetized with 5% halothane and positioned in a stereotaxic frame. The rat head was flexed downward at approximately 45 degrees , a depressible surface with the appearance of a rhomb between occipital protuberances and the spine of the atlas becomes visible. The 23 G needle was punctured into the cisterna magna for CSF collection without making any incision at this region. The blunt end of the needle was inserted into a 10 in. length of PE-50 tubing and other end of the tubing was connected to a collection syringe. The non-contaminated sample was drawn into the syringe by simple aspiration. This technique is simple and can be performed by one person. The technique has a greater than 95% success rate of CSF collection and it was free of red blood cell contamination. In addition, it yielded 100-120 microL of CSF per rat. This method is simple, effective, and easy to perform and has been successfully applied in preclinical screening of novel chemical entities in neuropharmacotherapy for CNS use. The present method is demonstrated by studying the CSF concentrations of carbamazepine and raclopride.

Striatal dopamine (DA) release has been shown during behavioural tasks, but the relative contribution of motor, reward, and cognitive components is unclear. Dopamine release was quantified using [(11)C]-raclopride in two studies using a triple-scan approach, comprising active task, motor control, and rest. In the first, bolus radiotracer was delivered during a sequential motor learning paradigm; in the second, a spatial planning task, bolus plus constant infusion was applied. [(11)C]-raclopride binding potentials (BP(ND)s) in striatal functional subdivisions were compared across conditions. [(11)C]-raclopride BP(ND) was significantly reduced in active task compared with rest in both the sensorimotor and associative striatum in both studies, because of differences between rest and motor control conditions. In both regions, the motor control BP(ND) fell between the rest and active task in the planning study, but the difference between motor control and active task conditions was not significant. No such changes were observed in the limbic striatum. Using rigorous methodology, this study validates earlier evidence that striatal DA release occurs during behavioural challenges. Increased DA release during movement was reliably detected in the sensorimotor and associative striatum, supporting use of the functional subdivision model in humans. No additional DA release was observed specific to the cognitive component of either task.

Background: The mechanism of the antinociceptive effects of nitrous oxide (N(2)O) has not been completely elucidated. On the other hand, numerous studies have indicated that mesolimbic dopaminergic neurons, which are thought to be involved in rewarding and reinforcement processes, play important roles in the supraspinal pain-suppression system. We hypothesized that the mesolimbic dopaminergic system is involved in the antinociceptive effect of N(2)O., Methods: Adult male Fischer rats were used in this study. To examine whether the dopaminergic system is activated by N(2)O, frozen sections of the ventral tegmental area of rats exposed to 75% N(2)O were double-stained for c-Fos and tyrosine hydroxylase. To clarify whether the dopaminergic system is involved in the antinociceptive action of N(2)O, saline or raclopride, a dopamine D(2)-like receptor antagonist, was injected into the nucleus accumbens (NAc) shell region. After exposure to 25% oxygen-75% nitrogen or 25% oxygen-75% N(2)O for 30 min, rats were subjected to formalin test, and the spinal cord was examined immunohistochemically., Results: Exposure to 75% N(2)O increased c-Fos expression in tyrosine hydroxylase-positive cells in the ventral tegmental area. Raclopride, injected into the NAc shell region, attenuated the antinociceptive effect of N(2)O in the formalin test, and blocked the suppressive effect of N(2)O on the formalin-induced c-Fos expression in the dorsal horn of the spinal cord by N(2)O., Conclusion: It is possible that inhalation of N(2)O activates mesolimbic dopaminergic neurons, and that the antinociceptive effect of N(2)O is at least partially mediated by dopamine D(2)-like receptors in the NAc shell region.

The purpose of this study was to quantify D2 receptors density and affinity in living rats using [11C]raclopride and to validate the multiinjection modelling approach. To this aim, we used an intracerebral beta+-sensitive probe as a highly sensitive system to quantify the radioligand activity using a single three-injection experimental paradigm. The study was divided into three main parts: (i) [11C]raclopride catabolism evaluation without and with cimetidine pretreatment (cytochrome P450 inhibitor); (ii) quantification of kinetics parameters in the striatum, enthorinal cortex, and cerebellum of living rats using a three-compartment model with an arterial input function; (iii) correlation study of in vivo and in vitro binding density and affinity values in the same striatal tissues. (i) raclopride catabolism was very reproducible between individuals; cimetidine pre-treatment resulted in a 30% reduction of raclopride metabolites. (ii) D2 striatal B'max and KdVr estimates obtained by compartmental modelling were 19.87+/-6.45 and 6.2+/-3.3 nmol/L, respectively. Cerebellum is the best candidate as a reference region with no specific binding detectable in vivo. (iii) When comparing density (Bmax/B'max) and affinity (Kd/KdVr) values in vivo and in vitro for each striatum, a high strict correlation was found (r2=0.90 and 0.72, for density and affinity, respectively). These results validate the multi-injection modelling approach coupled to beta-microprobe acquisitions as a mean to provide accurate and separate estimates of dopamine D2-receptor density and affinity, in the living rodent striatum.

Experiments were performed on cats to study the effects of systemic administration of antagonists of dopaminergic transmission on food-related and defensive (an escape response) operant conditioned reflexes acquired on the basis of the innate response of placing the forepaw on a support. Selective blockade of D1 receptors with SCH23390 (0.005-0.1 mg/kg) completely and selective blockade of D2/D3 receptors with raclopride (0.1-0.25 mg/kg) partially suppressed both reflexes. At these doses, both blockers had stronger actions on the defensive conditioned escape reflex than the food-related reflex: SCH23390 had significantly stronger inhibitory effects on both reflexes than raclopride.

In this study, we propose and evaluate new methods for automatic extraction of the brain surface and the mid-sagittal plane from functional positron emission tomography (PET) images. Designing methods for these segmentation tasks is challenging because the spatial distribution of intensity values in a PET image depends on the applied radiopharmaceutical and the contrast to noise ratio in a PET image is typically low. We extracted the brain surface with a deformable model which is based on a global optimization algorithm. The global optimization allows reliable automation of the extraction task. Based on the extracted brain surface, the mid-sagittal plane was determined. The method was tested with the image of the Hoffman brain phantom (FDG) and the images from the brain studies with the FDG (17 images) and the C11-Raclopride tracers (4 images). In addition to the brain surfaces, we applied the deformable model for extraction of the coarse cortical structure based on the tracer uptake from FDG-PET brain images. The proposed segmentation methods provide a promising direction for automatic processing and analysis of PET brain images.

Objective: Substantial evidence from animal models demonstrates that dopamine release in the ventral striatum underlies the reinforcing properties of nicotine. The authors used [(11)C]raclopride bolus-plus-continuous-infusion positron emission tomography (PET) to determine smoking-induced ventral striatum dopamine release in humans., Method: Twenty nicotine-dependent smokers (who smoked > or =15 cigarettes/day) underwent a [(11)C]raclopride bolus-plus-continuous-infusion PET session. During the session, subjects had a 10-minute break outside the PET apparatus during which 10 subjects smoked a cigarette and 10 did not smoke (as a control condition)., Results: The group that smoked had greater reductions in [(11)C]raclopride binding potential in ventral striatum regions of interest than the group that did not smoke, particularly in the left ventral caudate/nucleus accumbens and left ventral putamen (range for smoking group=-25.9% to -36.6% reduction). Significant correlations were found between change from before to after the smoking break in craving ratings and change from before to after the break in binding potential for these two regions., Conclusions: Nicotine-dependent subjects who smoked during a break in PET scanning had greater reductions in [(11)C]raclopride binding potential (an indirect measure of dopamine release) than nicotine-dependent subjects who did not smoke. The magnitude of binding potential changes was comparable to that found in studies that used similar methods to examine the effects of other addictive drugs.

Systemic administration of the specific antagonists of D1 (SCH23390, 0.005-0.1 mg/kg) and D2/D3 (raclopride, 0.1-0.25 mg/kg) dopamine receptors leeds to dose-dependent increase of the reaction time and decrease of conditined reflex probability up to full blocking (in the case of SCH23390) of alimentary and escape conditioned placing reaction in cats. The action of both antagonists was far more suppressive regarding conditioned escape reflex. The action of SCH23390 was far more effective than that of raclopride concerning both types of conditioned reflexes.

The authors assessed the behavioral effects of dopamine (DA) receptor antagonists, Cis (Z) flupentixol and S(+)-raclopride L-tartrate, on conditioned place preference (CPP) induced by paced mating behavior. Ovariectomized female rats of the Wistar strain were used. The administration of amphetamine (1 mg/kg) induced a clear CPP that was completely blocked by the DA antagonists flupentixol (0.25 mg/kg) or raclopride (0.125 mg/kg). These doses had no effect on motor coordination. Female rats that mated in a pacing chamber developed a clear CPP. Neither flupentixol nor raclopride blocked the reward state induced by paced mating behavior. These results indicate that DA is not involved in the reward state induced by paced mating behavior in female rats.

Chronic experiments were performed on four dogs using a model of an operant defensive reflex associated with maintaining a flexion posture to study the effects of bilateral intraneostriatal microinjection of the non-selective muscarinic receptor agonist carbachol, the selective D2 dopamine receptor blocker raclopride, and the selective M1 muscarinic receptor blocker pirenzipine on the performance of the operant defensive reflex and differentiation of signals. The results show that microinjection of carbachol induced increases in the tonic component and inhibition of the phasic component of the reflex, an ordering rearrangement of the posture, and increases in the amplitudes of its components. Raclopride microinjection gave similar but less marked results. The greatest effects with both substances were seen using differential stimuli. There were sharp increases in the process of differentiation of sound signals. Pirenzipine microinjections gave the opposite result. These data are assessed on the basis of concepts of the existence of two efferent outputs from the neostriatum with opposite effects on their targets and the roles of muscarinic and dopamine receptors in triggering and blocking these effects.

Abnormal repetitive behaviors are often associated with specific developmental, genetic, and neuropsychiatric disorders. Repetitive motor behaviors, often referred to as stereotypies, have been studied extensively as they can be readily induced by certain drugs (e.g., amphetamine). Recent work has shown, however, that such drug-induced models of stereotypy may not accurately reflect the neurobiological perturbations responsible for the spontaneous manifestation of these behaviors. The present study employed the deer mouse model of spontaneous and persistent stereotypy to evaluate the capacity of several selective dopaminergic agonists (apomorphine, SKF81297, and quinpirole) to exacerbate levels of spontaneously emitted stereotypic topographies when administered intrastriatally. Additionally, the effects of intrastriatal administration of the D(2)R antagonist raclopride on the expression of spontaneous stereotypic jumping were evaluated. No induction or exacerbation of stereotypy was observed following administration of the selective D(1)- or D(2)- receptor agonists, and the mixed agonist apomorphine induced hyperlocomotion and excessive grooming but failed to exacerbate spontaneous stereotypy. Thus, a dissociation was observed between spontaneously emitted and drug-induced stereotypy, suggesting significant limitations to the use of dopamine agonist-induced stereotypy as a model of clinical stereotyped movement disorder. Furthermore, an unexpected and statistically significant (P<.05) potentiation of locomotor activity was observed following intrastriatal raclopride administration, suggesting major alterations to the modulatory characteristics of the striatal dopaminergic system in these spontaneously stereotypic animals.

The complex mesolimbic-mesocortical system involved with behavioral selection has been implicated in the control of ethanol self-administration. However, the nature of the interactions within this multiple-structured system in ethanol intake regulation remains unclear. Although the role of dopamine (DA) in the prefrontal cortex and the nucleus accumbens has been examined individually, the interaction of DA activity in both structures at the same time remains to be examined. Male, Long-Evans rats were initiated to self-administer ethanol in an operant situation using the sucrose-substitution procedure. Following initiation, bilateral cannula guides were located to allow microinjection in the medial prefrontal cortex (mPFC) and the core of the nucleus accumbens. The DA D2/D3 agonist quinpirole (10.0-microg dose in the prefrontal cortex; 4.0-microg dose in n. accumbens) and the D2 antagonist raclopride (0.05-microg dose in prefrontal cortex; 1.0-microg dose in the nucleus accumbens) were then tested in each site alone and in combination in both sites in each rat. Changes in total responding, ethanol intake, and the pattern of responding were analyzed. Single-site injections replicated most of our previous findings for these doses. Changes in single-site effects were found when dual-site injections were performed, with altered input from the prefrontal areas impacting the effects of accumbens injections. Based on these interactions, our hypothesis that the prefrontal area is involved with the onset and offset of drinking, while the nucleus accumbens is involved with maintaining the ongoing behavior, remains viable.

Functional imaging of small animals, such as mice and rats, using ultra-high-resolution positron emission tomography (PET) and single-photon emission tomography (SPET) should be a valuable tool in studies of drug occupancy of cerebral binding sites. In this study we aimed to demonstrate the feasibility of using ultra-high-resolution SPET to measure the occupancy of dopamine D2 receptors by a competing drug, using the dopamine D2 receptor-specific radioligand iodine-123 5-iodo-7-N-[(1-ethyl-2-pyrrolidinyl) methyl] carboxamido-2,3-dihydrobenzofuran ([123I]IBF). Fourteen normal male mice (CD-1) were jugular vein-cannulated and a bolus infusion protocol was used to deliver 360 MBq [123I]IBF into the mouse (bolus-to-infusion ratio 1.8:1). The mice were scanned using an ultra-high-resolution triple-headed SPET system equipped with pinhole collimators. After sustained equilibrium had been achieved, varying doses of raclopride, a potent dopamine D2 receptor antagonist, were injected through the tail vein and the tracer was allowed to regain equilibrium. A simple equilibrium ratio of striatum to cerebellum provided a measure of D2 receptor binding both before and after injection of raclopride. Following raclopride administration, the system returned to equilibrium with lower specific binding in the striatum, while the counts in the cerebellum were unaffected. Receptor occupancy was 5.2% +/- 2.9% (control), 52.1% +/- 11.1% (0.3 mg/kg), 79.3% +/- 4.8% (1.0 mg/kg), and 94.7% +/- 2.2% (3.0 mg/kg), which gave an ED50=0.26 +/- 0.03 mg/kg using a single receptor site saturation model. This study has demonstrated clearly that ultra-high-resolution SPET of small animals is capable of measuring displacement and occupancy of dopamine D2 receptors by competing ligands.