Effects of L-DOPA on striatal iodine-123-FP-CIT binding and behavioral parameters in the rat

The 5-HT1A receptor agonist 8-OH-DPAT modulates motor/exploratory activity, recognition memory and dopamine transporter binding in the dorsal and ventral striatum

In the present studies, we assessed the effect of the 5-HT1A receptor (R) agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on motor and exploratory behaviors, object and place recognition and dopamine transporter (DAT) and serotonin transporter (SERT) binding in the rat brain. In Experiment I, motor/exploratory behaviors were assessed in an open field after injection of either 8-OH-DPAT (0.1 and 3 mg/kg) or vehicle for 30 min without previous habituation to the open field. In Experiment II, rats underwent a 5-min exploration trial in an open field with two identical objects. After injection of either 8-OH-DPAT (0.1 and 3 mg/kg) or vehicle, rats underwent a 5-min test trial with one of the objects replaced by a novel one and the other object transferred to a novel place. Subsequently, N-o-fluoropropyl-2b-carbomethoxy-3b-(4-[123I]iodophenyl)-nortropane ([123I]FP-CIT; 11 ± 4 MBq) was injected into the tail vein. Regional radioactivity accumulations were determined post mortem with a well counter. In both experiments, 8-OH-DPAT dose-dependently increased ambulation and exploratory head-shoulder motility, whereas rearing was dose-dependently decreased. In the test rial of Experiment II, there were no effects of 8-OH-DPAT on overall activity, sitting and grooming. 8-OH-DPAT dose-dependently impaired recognition of object and place. 8-OH-DPAT (3 mg/kg) increased DAT binding in the dorsal striatum relative to both vehicle and 0.1 mg/kg 8-OH-DPAT. Furthermore, in the ventral striatum, DAT binding was decreased after 3 mg/kg 8-OH-DPAT relative to vehicle. Findings indicate that motor/exploratory behaviors, memory for object and place and regional dopamine function may be modulated by the 5-HT1AR. Since, after 8-OH-DPAT, rats exhibited more horizontal and less (exploratory) vertical motor activity, while overall activity was not different between groups, it may be inferred, that the observed impairment of object recognition was not related to a decrease of motor activity as such, but to a decrease of intrinsic motivation, attention and/or awareness, which are relevant accessories of learning. Furthermore, the present findings on 8-OH-DPAT action indicate associations not only between motor/exploratory behavior and the recognition of object and place but also between the respective parameters and the levels of available DA in dorsal and ventral striatum.

Striatal serotonin transporter gain-of-function in L-DOPA-treated, hemi-parkinsonian rats

L-DOPA is the standard treatment for Parkinson's disease (PD), but chronic treatment typically leads to L-DOPA-induced dyskinesia (LID). LID involves a complex interaction between the remaining dopamine (DA) system and the semi-homologous serotonin (5-HT) system. Since serotonin transporters (SERT) have some affinity for DA uptake, they may serve as a functional compensatory mechanism when DA transporters (DAT) are scant. DAT and SERT's functional contributions in the dyskinetic brain have not been well delineated. The current investigation sought to determine how DA depletion and L-DOPA treatment affect DAT and SERT transcriptional processes, translational processes, and functional DA uptake in the 6-hydroxydopamine-lesioned hemi-parkinsonian rat. Rats were counterbalanced for motor impairment into equally lesioned treatment groups then given daily L-DOPA (0 or 6 mg/kg) for 2 weeks. At the end of treatment, the substantia nigra was processed for tyrosine hydroxylase (TH) and DAT gene expression and dorsal raphe was processed for SERT gene expression. The striatum was processed for synaptosomal DAT and SERT protein expression and ex vivo DA uptake. Nigrostriatal DA loss severely reduced DAT mRNA and protein expression in the striatum with minimal changes in SERT. L-DOPA treatment, while not significantly affecting DAT or SERT alone, did increase striatal SERT:DAT protein ratios. Using ex vivo microdialysis, L-DOPA treatment increased DA uptake via SERT when DAT was depleted. Overall, these results suggest that DA loss and L-DOPA treatment uniquely alter DAT and SERT, revealing implications for monoamine transporters as potential biomarkers and therapeutic targets in the hemi-parkinsonian model and dyskinetic PD patients.

A systematic review of the potential effects of medications and drugs of abuse on dopamine transporter imaging using [123I]I-FP-CIT SPECT in routine practice

PURPOSE

In routine practice, dopamine transporter (DAT) imaging is frequently used as a diagnostic tool to support the diagnosis of Parkinson's disease or dementia with Lewy bodies. In 2008, we published a review on which medications and drugs of abuse may influence striatal [123I]I-FP-CIT binding and consequently may influence the visual read of an [123I]I-FP-CIT SPECT scan. We made recommendations on which drugs should be withdrawn before performing DAT imaging in routine practice. Here, we provide an update of the original work based on published research since 2008.

METHODS

We performed a systematic review of literature without language restriction from January 2008 until November 2022 to evaluate the possible effects of medications and drugs of abuse, including the use of tobacco and alcohol, on striatal DAT binding in humans.

RESULTS

The systematic literature search identified 838 unique publications, of which 44 clinical studies were selected. Using this approach, we found additional evidence to support our original recommendations as well as some new findings on potential effect of other medications on striatal DAT binding. Consequently, we updated the list of medications and drugs of abuse that may influence the visual read of [123I]I-FP-CIT SPECT scans in routine clinical practice.

CONCLUSION

We expect that a timely withdrawal of these medications and drugs of abuse before DAT imaging may reduce the incidence of false-positive reporting. Nevertheless, the decision to withdraw any medication must be made by the specialist in charge of the patient's care and considering the pros and cons of doing so.

FMR1 deletion in rats induces hyperactivity with no changes in striatal dopamine transporter availability

Autism Spectrum Disorder (ASD) is a pervasive neurodevelopmental disorder emerging in early life characterized by impairments in social interaction, poor verbal and non-verbal communication, and repetitive patterns of behaviors. Among the best-known genetic risk factors for ASD, there are mutations causing the loss of the Fragile X Messenger Ribonucleoprotein 1 (FMRP) leading to Fragile X syndrome (FXS), a common form of inherited intellectual disability and the leading monogenic cause of ASD. Being a pivotal regulator of motor activity, motivation, attention, and reward processing, dopaminergic neurotransmission has a key role in several neuropsychiatric disorders, including ASD. Fmr1 ^Δexon 8 rats have been validated as a genetic model of ASD based on FMR1 deletion, and they are also a rat model of FXS. Here, we performed behavioral, biochemical and in vivo SPECT neuroimaging experiments to investigate whether Fmr1 ^Δexon 8 rats display ASD-like repetitive behaviors associated with changes in striatal dopamine transporter (DAT) availability assessed through in vivo SPECT neuroimaging. At the behavioral level, Fmr1 ^Δexon 8 rats displayed hyperactivity in the open field test in the absence of repetitive behaviors in the hole board test. However, these behavioral alterations were not associated with changes in striatal DAT availability as assessed by non-invasive in vivo SPECT and Western blot analyses.

Dopamine metabolism of the nucleus accumbens and fronto-striatal connectivity modulate impulse control

Impulsive-compulsive behaviours like pathological gambling or hypersexuality are a frequent side effect of dopamine replacement therapy in patients with Parkinson's disease. Multiple imaging studies suggest a significant reduction of presynaptic dopamine transporters in the nucleus accumbens to be a predisposing factor, reflecting either a reduction of mesolimbic projections or, alternatively, a lower presynaptic dopamine transporter expression per se. Here, we aimed to test the hypothesis of fewer mesolimbic projections as a risk factor by using dopamine synthesis capacity as a proxy of dopaminergic terminal density. Furthermore, previous studies have demonstrated a reduction of fronto-striatal connectivity to be associated with increased risk of impulsive-compulsive behaviour in Parkinson's disease. Therefore, another aim of this study was to investigate the relationship between severity of impulsive-compulsive behaviour, dopamine synthesis capacity and fronto-striatal connectivity. Eighty participants underwent resting state functional MRI and anatomical T1-weighted images [mean age: 68 ± 9.9 years, 67% male (patients)]. In 59 participants, 18F-DOPA-PET was obtained and voxel-wise Patlak slopes indicating dopamine synthesis capacity were calculated. All participants completed the QUIP-RS questionnaire, a well validated test to quantify severity of impulsive-compulsive behaviour in Parkinson's disease. A voxel-wise correlation analysis between dopamine synthesis capacity and QUIP-RS score was calculated for striatal regions. To investigate the relationship between symptom severity and functional connectivity, voxel-wise correlations were performed. A negative correlation was found between dopamine synthesis capacity and QUIP-RS score in the nucleus accumbens (r = -0.57, P = 0.001), a region functionally connected to the rostral anterior cingulate cortex. The connectivity strength was modulated by QUIP-RS, i.e. patients with more severe impulsive-compulsive behaviours had a weaker functional connectivity between rostral anterior cingulate cortex and the nucleus accumbens. In addition, cortical thickness and severity of impulsive-compulsive behaviour were positively correlated in the subgenual rostral anterior cingulate cortex. We found three factors to be associated with severity of impulsive-compulsive behaviour: (i) decreased dopamine synthesis capacity in the nucleus accumbens; (ii) decreased functional connectivity of the rostral anterior cingulate cortex with the nucleus accumbens; and (iii) increased cortical thickness of the subgenual rostral anterior cingulate cortex. Rather than a downregulation of dopamine transporters, a reduction of mesolimbic dopaminergic projections in conjunction with a dysfunctional rostral anterior cingulate cortex-a region known to play a key role in impulse control-could be the most crucial neurobiological risk factor for the development of impulsive-compulsive behaviours in patients with Parkinson's disease under dopamine replacement therapy.

GABAergic Control of Nigrostriatal and Mesolimbic Dopamine in the Rat Brain

Purpose: The present study assessed the effects of the GABA_A receptor (R) agonist muscimol (MUS), and the GABA_AR antagonist bicuculline (BIC) on neocortical and subcortical radioligand binding to dopamine D_2/3Rs in relation to motor and exploratory behaviors in the rat.

Methods: D_2/3R binding was measured with small animal SPECT in baseline and after challenge with either 1 mg/kg MUS or 1 mg/kg BIC, using [¹²³I]IBZM as radioligand. Motor/exploratory behaviors were assessed for 30 min in an open field prior to radioligand administration. Anatomical information was gained with a dedicated small animal MRI tomograph. Based on the Paxinos rat brain atlas, regions of interest were defined on SPECT-MRI overlays. Estimations of the binding potentials in baseline and after challenges were obtained by computing ratios of the specifically bound compartments to the cerebellar reference region.

Results: After MUS, D_2/3R binding was significantly reduced in caudateputamen, nucleus accumbens, thalamus, substania nigra/ventral tegmental area, and posterior hippocampus relative to baseline (0.005 ≤ p ≤ 0.012). In all these areas, except for the thalamus, D_2/3R binding was negatively correlated with grooming in the first half and positively correlated with various motor/exploratory behaviors in the second half of the testing session. After BIC, D_2/3R binding was significantly elevated in caudateputamen (p = 0.022) and thalamus (p = 0.047) relative to baseline. D_2/3R binding in caudateputamen and thalamus was correlated negatively with sitting duration and sitting frequency and positively with motor/exploratory behaviors in the first half of the testing time.

Conclusions: Findings indicate direct GABAergic control over nigrostriatal and mesolimbic dopamine levels in relation to behavioral action. This may be of relevance for neuropsychiatric conditions such as anxiety disorder and schizophrenia, which are characterized by both dopaminergic and GABAergic dysfunction.

Increased dopaminergic function in the thalamus is associated with excessive daytime sleepiness

OBJECTIVES/BACKGROUND

Excessive daytime sleepiness (EDS) is a common disorder, which can manifest in isolation or in combination with other neurological or psychiatric disorders. We know relatively little about the mechanisms underlying the development of EDS and the clinical management of patients with EDS remains an unmet need. In this study, we hypothesised that thalamic dopaminergic function would be altered in subjects with EDS and we sought to investigate this by assessing [¹²³I]FP-CIT Single Photon Emission Computed Tomography (SPECT) data, which is a molecular imaging marker of dopamine transporter (DAT).

PATIENTS/METHODS

We performed a case-control study using people registered as healthy subjects in the Parkinson's Progression Markers Initiative database. We assessed and compared semi-quantified [¹²³I]FP-CIT-SPECT in two groups of 21 healthy subjects with and without EDS, who were matched for age, gender, years of education and Rapid eyemovement (REM) sleep behaviour disorder (RBD) Questionnaire scores.

RESULTS

Our findings show increased thalamic DAT binding in people with EDS compared to matched healthy subjects without EDS. Higher thalamic DAT binding also correlated with worse EDS scores.

CONCLUSION

Our findings provide evidence that increased dopaminergic function in the thalamus may mediate excessive daytime sleepiness in humans.

Deep Transcranial Magnetic Stimulation of the Dorsolateral Prefrontal Cortex in Alcohol Use Disorder Patients: Effects on Dopamine Transporter Availability and Alcohol Intake

Repetitive Transcranial Magnetic Stimulation (rTMS) of the dorsolateral prefrontal cortex may affect neuro-adaptations associated with alcohol use disorder (AUD), potentially influencing craving and alcohol intake. We investigated alcohol intake and dopamine transporter (DAT) availability by Single Photon Emission Computed Tomography (SPECT) in the striatum of AUD patients before and after deep rTMS. Fourteen patients underwent baseline clinical and SPECT assessment. Eleven out of fourteen patients were randomized into two groups for the REAL (n.5) or SHAM (n.6) treatment. Clinical and SPECT evaluations were then carried out after four weeks of rTMS sessions (T1). At baseline, AUD patients showed higher striatal DAT availability than healthy control subjects (HC). Patients receiving the REAL stimulation revealed a reduction in DAT availability at T1, whereas the SHAM-treated group did not. In addition, patients receiving the REAL stimulation had a decrease in alcohol intake. The results of this longitudinal pilot study may suggest a modulatory effect of deep rTMS on dopaminergic terminals and a potential clinical efficacy in reducing alcohol intake in AUD patients. Further investigations are required to confirm these preliminary data.

GABAergic control of neostriatal dopamine D2 receptor binding and behaviors in the rat

PURPOSE

The present study assessed the influence of the GABA_A receptor agonist muscimol and the GABA_A receptor antagonist bicuculline on neostriatal dopamine D₂ receptor binding in relation to motor and exploratory behaviors in the rat.

METHODS

D₂ receptor binding was measured in baseline and after challenge with either 1mg/kg muscimol or 1mg/kg bicuculline. In additional rats, D₂ receptor binding was measured after injection of saline. After treatment with muscimol, bicuculline and saline, motor and exploratory behaviors were assessed for 30min in an open field prior to administration of [¹²³I]S-3-iodo-N-(1-ethyl-2-pyrrolidinyl)methyl-2-hydroxy-6-methoxybenzamide ([¹²³I]IBZM). For baseline and challenges, striatal equilibrium ratios (V₃″) were computed as estimation of the binding potential.

RESULTS

Muscimol but not bicuculline reduced D₂ receptor binding relative to baseline and to saline. Travelled distance, duration of rearing and frequency of rearing and of head-shoulder motility were lower after muscimol compared to saline. In contrast, duration of rearing and grooming and frequency of rearing, head-shoulder motility and grooming were elevated after bicuculline relative to saline. Moreover, bicuculline decreased duration of sitting and head-shoulder motility.

CONCLUSIONS

The muscimol-induced decrease of motor/exploratory behaviors can be related to an elevation of striatal dopamine levels. In contrast, bicuculline is likely to elicit a decline of synaptic dopamine, which, however, is compensated by the time of D₂ receptor imaging studies. The results indicate direct GABAergic control over D₂ receptor binding in the neostriatum in relation to behavioral action, and, thus, complement earlier pharmacological studies.

Intranasal Dopamine Reduces In Vivo [(123)I]FP-CIT Binding to Striatal Dopamine Transporter: Correlation with Behavioral Changes and Evidence for Pavlovian Conditioned Dopamine Response

Purpose: Dopamine (DA), which does not cross the blood-brain barrier, has central and behavioral effects when administered via the nasal route. Neither the mechanisms of central action of intranasal dopamine (IN-DA), nor its mechanisms of diffusion and transport into the brain are well understood. We here examined whether IN-DA application influences dopamine transporter (DAT) binding in the dorsal striatum and assessed the extent of binding in relation to motor and exploratory behaviors. We hypothesized that, based on the finding of increased extracellular DA in the striatum induced by application of IN-DA, binding of [¹²³I]FP-CIT to the DAT should be decreased due to competition at the receptor.

Methods: Rats were administered 3 mg/kg IN-DA and vehicle (VEH), with IN-DA injection either preceding or following VEH. Then motor and exploratory behaviors (traveled distance, velocity, center time, sitting, rearing, head-shoulder motility, grooming) were assessed for 30 min in an open field prior to administration of [¹²³I]FP-CIT. DAT binding after IN-DA and VEH was measured with small animal SPECT 2 h following administration of the radioligand.

Results: (1) After IN-DA application, striatal DAT binding was significantly lower as compared to VEH, indicating that the nasally delivered DA had central action and increased DA levels comparable to that found previously with L-DOPA administration; and (2) DAT binding in response to intranasal VEH was lower when IN-DA application preceded VEH treatment. This finding is suggestive of Pavlovian conditioning of DA at the level of the DAT, since the DA treatment modified (decreased) the binding in response to the subsequent VEH treatment. VEH treatment also reduced motor and exploratory behaviors more when applied before, as compared to when it followed IN-DA application, also indicative of behavioral Pavlovian conditioning akin to that found upon application of various psychostimulant drugs.

Conclusions: The results: (a) demonstrate a direct central action of intranasally applied DA on the DAT in the dorsal striatum, indicating enhanced DA availability; and (b) provide first evidence of a Pavlovian conditioned DA response at the DAT. The latter results have relevance to understanding neurochemical mechanisms that underlie placebo action in the treatment of Parkinsonian patients.

Relationship Between L-DOPA-Induced Reduction in Motor and Exploratory Activity and Striatal Dopamine D2 Receptor Binding in the Rat

Purpose: The present study assessed the influence of L-DOPA administration on neostriatal dopamine (DA) D₂ receptor binding in relation to motor and exploratory behaviors in the rat.

Methods: D₂ receptor binding was measured in baseline, after challenge with the aromatic L-amino acid decarboxylase inhibitor benserazide, and after challenge with either 5 or 10 mg/kg L-DOPA plus benserazide. Additional rats received injections of saline. For baseline and challenges, striatal equilibrium ratios (V3″) were computed as estimation of the binding potential. Motor and exploratory behaviors were assessed for 30 min in an open field prior to administration of [¹²³I]IBZM. D₂ receptor binding was measured with small animal SPECT 2 h after radioligand administration for 60 min.

Results: Both L-DOPA doses significantly reduced D₂ receptor binding relative to baseline and led to significantly less ambulation, less head-shoulder motility, and more sitting relative to saline. Moreover, 10 mg/kg L-DOPA induced less head-shoulder motility, more sitting, and more grooming than 5 mg/kg L-DOPA. Analysis of time-behavior curves showed that L-DOPA-treated animals relative to saline exhibited a faster rate of decrease of ambulation frequency and a slower rate of decrease of both duration and frequency of head-shoulder motility from a lower maximum level.

Conclusions: The reductions of striatal D₂ receptor binding after L-DOPA may be conceived to reflect elevated concentrations of synaptic DA. L-DOPA-treated animals showed less ambulation and less head-shoulder motility than saline-treated animals, indicating an association between less behavioral activity and increased availability of striatal DA. The faster rate of decrease of ambulation frequency and the lower maximum levels of both head-shoulder motility duration and frequency may be interpreted in terms of influence of increased DA availability on behavioral habituation to a novel environment.

Pharmacological treatment with L-DOPA may reduce striatal dopamine transporter binding in in vivo imaging studies

Numerous neurologic and psychiatric conditions are treated with pharmacological compounds, which lead to an increase of synaptic dopamine (DA) levels. One example is the DA precursor L-3,4-dihydroxyphenylalanine (L-DOPA), which is converted to DA in the presynaptic terminal. If the increase of DA concentrations in the synaptic cleft leads to competition with exogenous radioligands for presynaptic binding sites, this may have implications for DA transporter (DAT) imaging studies in patients under DAergic medication. This paper gives an overview on those findings, which, so far, have been obtained on DAT binding in human Parkinson's disease after treatment with L-DOPA. Findings, moreover, are related to results obtained on rats, mice or non-human primates. Results indicate that DAT imaging may be reduced in the striata of healthy animals, in the unlesioned striata of animal models of unilateral Parkinson's disease and in less severly impaired striata of Parkinsonian patients, if animal or human subjects are under acute or subchronic treatment with L-DOPA. If also striatal DAT binding is susceptible to alterations of synaptic DA levels, this may allow to quantify DA reuptake in analogy to DA release by assessing the competition between endogenous DA and the administered exogenous DAT radioligand.

PET imaging of dopamine transporters with [(18)F]FE-PE2I: Effects of anti-Parkinsonian drugs

PURPOSE

This study aimed to assess the striatal [(18)F]FE-PE2I binding and the immunohistochemical stain of tyrosine hydroxylase (TH) in the striatum, and to evaluate the effects of therapeutic drugs on [(18)F]FE-PE2I binding.

METHODS

Dynamic PET/CT of [(18)F]FE-PE2I was performed in Parkinson's disease (PD) rat models, induced by the unilateral injection of 6-OHDA into the striatum. A simplified reference tissue model method was used to calculate the striatal binding potential (striatal BPND). Each of the four normal rats was pretreated with pramipexole, amantadine, and escitalopram 30 min before [(18)F]FE-PE2I injection. The effect of L-DOPA combined with benserazide was assessed in the normal and PD rats.

RESULTS

The BPND was significantly lower in the lesioned striatum than in the striatum of the normal rats. After the pretreatment with pramipexole, amantadine, and escitalopram, the values of the striatal BPND did not differ from those of the controls. The pretreatment with L-DOPA/benserazide, however, significantly reduced the striatal BPND. The striatal BPND of the PD rats with L-DOPA/benserazide pretreatment was not different from that of the same PD rats with placebo treatment.

CONCLUSION

[(18)F]FE-PE2I may be used as a radioligand for the in-vivo imaging of the DAT. In the normal rats, [(18)F]FE-PE2I binding is unaffected by pramipexole, amantadine, and escitalopram. L-DOPA/benserazide does not affect the striatal [(18)F]FE-PE2I binding in PD rats.

Reduced Dopamine Transporter Availability and Neurocognitive Deficits in Male Patients with Alcohol Dependence

Dopamine plays an important role in the development of alcohol dependence, cognitive dysfunction, and is regulated via dopamine transporter activity. Although dopamine transporter activity is critically involved in alcohol dependence, studies observing this relationship are limited. Thus the current study examined whether dopamine transporter availability is associated with developing of alcohol dependence and cognitive dysfunction. Brain imaging with ^99mTc-TRODAT-1 as a ligand was used to measure dopamine transporter availability among 26 male patients with pure alcohol dependence and 22 age- and sex- matched healthy volunteers. The Wisconsin Card Sorting Test (WCST) and Tridimensional Personality Questionnaire (TPQ) were administered to assess neurocognitive functioning and personality traits, respectively. Compared to healthy controls, patients with alcohol dependence showed a significant reduction in dopamine transporter availability (p < 0.001), as well as diminished performance on the WCST (p < 0.001). Dopamine transporter availability was negatively correlated with both total and perseverative WCST errors among healthy controls, but only patients with alcohol dependence showed a positive correlation between dopamine transporter availability and a harm avoidance personality profile. Thus, reductions in dopamine transporter availability may play a pathophysiological role in the development of pure alcohol dependence, given its association with neurocognitive deficits. Moreover, personality may influence the development of pure alcohol dependence; however, additional clinical subgroups should be examined to confirm this possibility.

Relationship between L-DOPA-induced reduction in motor and exploratory activity and degree of DAT binding in the rat

Purpose: The present study assessed the influence of L-DOPA administration on neostriatal dopamine (DA) transporter (DAT) binding in relation to motor and exploratory behaviors in the rat.

Methods: Rats received injections of 5 mg/kg L-DOPA, 10 mg/kg L-DOPA or vehicle. Motor and exploratory behaviors were assessed for 30 min in an open field prior to administration of [¹²³I]FP-CIT. Dopamine transporter binding was measured with small animal single-photon emission computed tomography (SPECT) 2 h after radioligand administration for 60 min.

Results: Both L-DOPA doses significantly reduced DAT binding and led to significantly less head-shoulder motility and more sitting relative to vehicle. Moreover, 10 mg/kg L-DOPA induced less distance traveled and ambulation than 5 mg/kg L-DOPA. Analysis of time-behavior (t-b) curves showed that L-DOPA-treated animals relative to vehicle exhibited (1) a faster rate of increase in duration of sitting; (2) a slower rate of increase in duration of head-shoulder motility; and (3) a slower rate of decrease in frequency of head-shoulder motility.

Conclusions: The reductions of striatal DAT binding after L-DOPA challenges reflected elevated concentrations of synaptic DA. L-DOPA-treated animals showed less head-shoulder motility and more sitting than vehicle-treated animals, indicating an association between less behavioral activity and increased availability of striatal DA. The faster increase of sitting duration to a higher final level and the slower increase of head-shoulder motility to a lower final level relative to controls may be interpreted in terms on behavioral habituation to a novel environment.

Quantification of rat brain SPECT with (123)I-ioflupane: evaluation of different reconstruction methods and image degradation compensations using Monte Carlo simulation

SPECT studies with (123)I-ioflupane facilitate the diagnosis of Parkinson's disease (PD). The effect on quantification of image degradations has been extensively evaluated in human studies but their impact on studies of experimental PD models is still unclear. The aim of this work was to assess the effect of compensating for the degrading phenomena on the quantification of small animal SPECT studies using (123)I-ioflupane. This assessment enabled us to evaluate the feasibility of quantitatively detecting small pathological changes using different reconstruction methods and levels of compensation for the image degrading phenomena. Monte Carlo simulated studies of a rat phantom were reconstructed and quantified. Compensations for point spread function (PSF), scattering, attenuation and partial volume effect were progressively included in the quantification protocol. A linear relationship was found between calculated and simulated specific uptake ratio (SUR) in all cases. In order to significantly distinguish disease stages, noise-reduction during the reconstruction process was the most relevant factor, followed by PSF compensation. The smallest detectable SUR interval was determined by biological variability rather than by image degradations or coregistration errors. The quantification methods that gave the best results allowed us to distinguish PD stages with SUR values that are as close as 0.5 using groups of six rats to represent each stage.