Test-retest reproducibility of extrastriatal dopamine D2 receptor imaging with [123I]epidepride SPECT in humans

This study evaluated the test-retest reproducibility of D2 receptor quantification in the thalamus and temporal cortex using [123I]epidepride SPECT.

METHODS

Ten healthy volunteers (4 men, 6 women; age range, 19-46 y) underwent 2 SPECT studies (interval, 2-26 d) using a bolus-plus-constant-infusion paradigm (bolus-to-infusion ratio = 6 h; infusion time = 9 h). Plasma clearance (in liters per hour) and free fraction (f1) of the parent tracer were measured. Radioactivity (in becquerels per gram) in the thalamus, temporal cortex, and cerebellum were normalized to the infusion rate (in becquerels per hour). Normalized striatal radioactivity was also measured to assess reproducibility in regions with a high density of receptors and better counting statistics. The outcome measures obtained were V3 (receptor density [Bmax]/equilibrium dissociation constant [KD]), V3' (f1 x Bmax/KD), and RT (specific-to-nondisplaceable tissue ratio).

RESULTS

Test-retest variability and reliability (intraclass correlation coefficient) were 10.8% and 0.88, respectively, for plasma clearance and 15.3% and 0.77, respectively, for f1. The test-retest variability of brain-specific (target minus nondisplaceable) radioactivity was higher in the thalamus and temporal cortex than in the striatum, although reliability was comparable. Among the outcome measures, V3' showed better test-retest variability and reliability in the thalamus (13.3% and 0.75, respectively) and temporal cortex (13.4% and 0.86, respectively).

CONCLUSION

Brain radioactivity was the main source of variability for quantification of extrastriatal D2 receptors with [123I]epidepride. The reproducibility of outcome measures in extrastriatal regions was good. However, because receptor density was lower in extrastriatal regions than in the striatum, the counting statistics in these regions were low and reproducibility was affected by the higher test-retest variability of brain-specific radioactivity. Compared with V3 and V3', RT showed less test-retest variability in the thalamus and temporal cortex but lower reliability. Moreover, measurement of RT may be affected by the presence of potential lipophilic metabolites entering the brain.

Dopaminergic phenotype of hNT cells in vitro

We investigated the catecholaminergic nature of cultured hNT neurons previously treated either for 4 or 5 weeks with retinoic acid (RA). There were significantly more tyrosine hydroxylase (TH)-positive neurons (60%) in cultures treated for 4 weeks with RA compared to 5 week-treated cultures (</=15%). Furthermore, numerous TH-positive hNT cells were also immunoreactive to dopamine transporter (DAT), dopamine receptor (D2) and aldehyde dehydrogenase (AHD-2), an enzyme exclusively expressed by dopaminergic (DA) ventral mesencephalic (VM) precursors. Thus this cell line has all the necessary cellular machinery to produce functional DA neurons and therefore is a good alternative tissue source to fetal VM.

The ratio of striatal D1 to muscarinic receptors changes in aging rats housed in an enriched environment

The enriched environment (EC) causes morphological plasticity in striatal cells that express D1 and D2 receptors. We used radioligand binding assays to examine whether EC produces plasticity in striatal receptor density and receptor density ratios. After 30 days of EC, 2-year-old rats had a higher ratio of D1 to muscarinic receptors in striatum relative to singly housed rats. Assays also showed trends for a greater ratio of D1 to cannabinoid receptors and a greater density of D1 receptors in striatum after EC. D2 receptor density was unaffected by the EC condition.

Neuroprotection of nerve growth factor-loaded microspheres on the D2 dopaminergic receptor positive-striatal neurones in quinolinic acid-lesioned rats: a quantitative autoradiographic assessment with iodobenzamide

Huntington's disease (HD) results from the degeneration of striatal neurones, mainly gamma-aminobutyric acid (GABA)ergic projection neurones and lately cholinergic interneurones. The use of trophic factors as agents able to prevent such neural degeneration is a promising strategy. The aim of this study was to validate nerve growth factor-loaded (NGF-loaded) poly-D,L-lactide-co-glycolide (PLGA) microspheres for treatment of HD in a rat model with quinolinic acid lesion using autoradiographic study of D2 dopaminergic receptors (D2R). This target is expressed by about half of striatal neurones and its scintigraphic exploration has already been performed for the follow-up of this degenerative process. Ex vivo autoradiography of D2R performed with iodobenzamide, the widely used ligand for single photo emission computerized tomography, revealed slight neuroprotection. Moreover, tolerance of microspheres was demonstrated by in vitro autoradiography with the marker of gliosis, [(3)H]-PK 11195.

Selective attenuation of psychostimulant-induced behavioral responses in mice lacking A(2A) adenosine receptors

A(2A) adenosine receptors are highly expressed in the striatum where they modulate dopaminergic activity. The role of A(2A) receptors in psychostimulant action is less well understood because of the lack of A(2A)-selective compounds with access to the central nervous system. To investigate the A(2A) adenosinergic regulation of psychostimulant responses, we examined the consequences of genetic deletion of A(2A) receptors on psychostimulant-induced behavioral responses. The extent of dopaminergic innervation and expression of dopamine receptors in the striatum were indistinguishable between A(2A) receptor knockout and wild-type mice. However, locomotor responses to amphetamine and cocaine were attenuated in A(2A) knockout mice. In contrast, D(1)-like receptor agonists SKF81297 and SKF38393 produced identical locomotor stimulation and grooming, respectively, in wild-type and A(2A) knockout mice. Similarly, the D(2)-like agonist quinpirole produced motor-depression and stereotypy that were indistinguishable between A(2A) knockout and wild-type mice. Furthermore, attenuated amphetamine- (but not SKF81297-) induced locomotion was observed in pure 129-Steel as well as hybrid 129-SteelxC57BL/6 mice, confirming A(2A) receptor deficiency (and not genetic background) as the cause of the blunted psychostimulant responses in A(2A) knockout mice. These results demonstrate that A(2A) receptor deficiency selectively attenuates psychostimulant-induced behavioral responses and support an important role for the A(2A) receptor in modulating psychostimulant effects.

Cabergoline modulation of alpha-subunits and FSH secretion in a gonadotroph adenoma

Most non-functioning pituitary adenomas respond poorly to medical therapy. We describe the case of a 62-year-old man who presented with clinical features of an invasive macroadenoma. Baseline hormonal evaluation revealed increased FSH and alpha-subunit (alpha-SU) levels. Transsphenoidal exeresis followed by radiotherapy (RT) was performed. Almost all neoplastic cells were intensely immunoreactive for alpha-SU. On PCR analysis, specific amplification products were observed for somatostatin 2, 3 and 5 receptors as well as for both short and long isoforms of the dopamine D2 receptor. In vitro, alpha-SU and FSH were released into the medium by adenoma cells and increased after TRH stimulation. After surgery, alpha-SU and FSH levels were still elevated. Short-term slow-release lanreotide treatment did not modify either alpha-SU or FSH levels. Cabergoline was started and a fast and long-lasting decrease in alpha-SU and, to a lesser extent, in FSH was observed. The tumor remnant was unmodified on magnetic resonance imaging 3 years after surgery and RT. This case report shows that the in vitro expression of somatostatin receptors may not be directly associated to the in vivo response of alpha-SU and FSH to lanreotide, probably because of a functional uncoupling of the receptors. Cabergoline should be considered as an effective therapy for hormonal, and perhaps proliferative, control of gonadotroph adenoma remnants before the effects of RT are fully effective.

Dopamine D(1) and D(2) receptors in the forebrain of dystonia musculorum mutant mice: an autoradiographic survey in relation to dopamine contents

Dystonia musculorum (dt(J)/dt(J)) mutant mice suffer from a degeneration of spinocerebellar tracts as well as a dystrophy of peripheral sensory tracts. This neurological mutant has been proposed as an animal model of human cerebellar ataxia, in particular of the Friedreich's type; thus, it was deemed of interest to examine the endogenous contents of dopamine (DA) and metabolites as well as the distribution of DA receptors of the D(1) and D(2) subtypes, in order to delimit the biochemical characteristics of this pathological disorder, and determine an eventual dopaminergic dysfunction in this mutant. Tissue DA and its major metabolites 3, 4-dihydroxyphenylacetic acid, homovanillic acid and 3-methoxytyramine were measured by HPLC coupled to electrochemical detection in six cortical regions, in four divisions of rostral neostriatum and two halves of caudal neostriatum, as well as in olfactory bulb, nucleus accumbens, septum, amygdala, hippocampus, thalamus, hypothalamus, brainstem, cerebellum, substantia nigra, and ventral tegmental area. The only significant difference between dt(J)/dt(J) mice and wild-type controls was an increase in hypothalamic DA contents (+47%). Quantitative autoradiography with [(3)H]SCH23390 and [(3)H]raclopride, to label D(1) and D(2) receptors, respectively, revealed only moderate changes in receptor densities in a few localized regions. In dt(J)/dt(J) mutants, D(1) receptor numbers were found to be higher in thalamus (+27%) as well as in the medio-dorsal (+16%) and in the latero-dorsal (+16%) quadrants of rostral neostriatum, while D(2) receptor densities were greater in the medio-ventral (+32%) and the latero-dorsal (+17%) quadrants. The present results indicate an overall conservation of dopaminergic functions, albeit the few localized sites of increased D(1) and D(2) receptor densities, and that are seemingly independent of the DA innervation pattern, as revealed by the tissue measurements of DA and metabolites. They also rule out a major pathology linked to deficits in DA neurotransmission, and validate this mutant as an animal model of human cerebellar ataxia, probably of the Friedreich type.

Involvement of the direct striatonigral pathway in levodopa-induced sensitization in 6-hydroxydopamine-lesioned rats

Induction of dopamine D3 receptor gene expression in 6-hydroxydopamine-lesioned rats by repeated administration of levodopa had been suggested to be responsible for behavioural sensitization developing in these animals. Using double in situ hybridization techniques, we show that D3 receptor mRNA induction after repeated administration of levodopa took place mainly in dynorphin/substance P-expressing neurons of the direct striatonigral pathway. In agreement, induction of D3 receptor binding sites was evidenced, using 7-[3H]hydroxy-N,N-di-propyl-2-aminotetralin ([3H]7-OH-DPAT), in substantia nigra pars reticulata, the projection area of the direct nigrostriatonigral pathway. Changes in D3 receptor binding and behavioural sensitization during intermittent administration of levodopa paralleled changes in prodynorphin/preprotachykinin rather than preproenkephalin/prodynorphin and preproenkephalin/preprotachykinin mRNA ratios. Behavioural sensitization, induction of D3 receptor binding and changes in prodynorphin/preprotachykinin ratio were all prevented together when levodopa was continuously delivered or intermittently delivered in combination with R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4, 5-tetrahydro-1H-3-benzazepine (SCH 23390), a selective D1 receptor antagonist. Our results indicate that functional changes of the direct striatal output pathway, possibly through an interaction between D1 and D3 receptors at the level of terminals in the substantia nigra pars reticulata, are important for the development of behavioural sensitization.

Mechanisms and sites of ocular action of 7-hydroxy-2-dipropylaminotetralin: a dopamine(3) receptor agonist

The purpose of this study was to investigate mechanism(s) and site(s) of action involved in 7-hydroxy-2-dipropylaminotetralin (7-OH-DPAT)-induced ocular hypotension. As measured by pneumatonometry, the topical, unilateral application of 7-OH-DPAT (75 microg), a dopamine D(3)-preferring receptor agonist, decreased the intraocular pressure (IOP) bilaterally. The ocular hypotensive activity of 7-OH-DPAT was diminished in sympathetically denervated rabbits. Pretreatment with raclopride, a D(2)/D(3) receptor antagonist; UH232, a D(3) receptor antagonist; or U-99194A, a D(3) receptor antagonist antagonized 7-OH-DPAT-induced ocular hypotension. However, pretreatment with spiperone, a D(2) receptor antagonist, did not affect the 7-OH-DPAT-induced ocular hypotension. In addition, topically applied 7-OH-DPAT caused a reduction of aqueous humor flow rate. To examine sites of action, immunohistochemistry of D(3) dopamine receptors was performed. Dopamine D(3) receptors were found to be present on postganglionic sympathetic nerves in the ciliary body of normal rabbits but were virtually undetectable in the same tissue of sympathectomized rabbits. In summary, the IOP-lowering effect caused by 7-OH-DPAT was due, in part, to the suppression of aqueous humor flow. Immunohistochemical identification of D(3) receptors in the ciliary body, associated with the diminution of IOP-lowering effects by D(3) receptor agonist 7-OH-DPAT in sympathetically denervated rabbits provided evidence of neuronal site of action of 7-OH-DPAT. Suppression of 7-OH-DPAT-induced ocular hypotension by D(3) receptor antagonists (U-99194A and UH232) and sympathectomy, coupled with the immunohistochemical data, suggested that the primary site of D(3) receptor-mediated action of 7-OH-DPAT is located on postganglionic sympathetic nerve endings in the ciliary body of rabbit.

Dopamine D-5 receptor modulates hippocampal acetylcholine release

Dopamine is intimately involved in cognitive processes in the brain. Of the several subtypes of dopamine receptors, the possible role of dopamine D1-like receptors in brain functions, especially in learning and memory, has recently generated much interest. However, molecularly the D1-like receptors are comprised of at least two subtypes, namely D-1 and D-5, and it has not been possible to ascertain which of these two receptor classes is responsible for these functions due to the lack of selective ligands. In the present study, utilizing a combined antisense-in vivo dialysis approach, we show that the D-5 subtype is the dopamine D1-like receptor involved in modulating hippocampal acetylcholine (ACh) release, a transmitter implicated in a variety of cognitive processes. This is one of the first evidence for a functional role for the D-5 receptor.

Autoradiographic study of striatal dopamine re-uptake sites and dopamine D1 and D2 receptors in a 6-hydroxydopamine and quinolinic acid double-lesion rat model of striatonigral degeneration (multiple system atrophy) and effects of embryonic ventral mesencephalic, striatal or co-grafts

The influence of embryonic mesencephalic, striatal and mesencephalic/striatal co-grafts on amphetamine- and apomorphine-induced rotation behaviour was assessed in a rat model of multiple system atrophy/striatonigral degeneration type using dopamine D1 ([3H]SCH23390) and D2 ([3H]spiperone) receptor and dopamine re-uptake ([3H]mazindol) autoradiography. Male Wistar rats subjected to a sequential unilateral 6-hydroxydopamine lesion of the medial forebrain bundle followed by a quinolinic acid lesion of the ipsilateral striatum were divided into four treatment groups, receiving either mesencephalic, striatal, mesencephalic/striatal co-grafts or sham grafts. Amphetamine- and apomorphine-induced rotation behaviour was recorded prior to and up to 10 weeks following transplantation. 6-Hydroxydopamine-lesioned animals showed ipsiversive amphetamine-induced and contraversive apomorphine-induced rotation behaviour. Amphetamine-induced rotation rates persisted after the subsequent quinolinic acid lesion, whereas rotation induced by apomorphine was decreased. In 11 of 14 animals receiving mesencephalic or mesencephalic/striatal co-grafts, amphetamine-induced rotation scores were decreased by >50% at the 10-week post-grafting time-point. In contrast, only one of 12 animals receiving non-mesencephalic (striatal or sham) grafts exhibited diminished rotation rates at this time-point. Apomorphine-induced rotation rates were significantly increased following transplantation of mesencephalic, striatal or sham grafts. The largest increase of apomorphine-induced rotation rates approaching post-6-hydroxydopamine levels were observed in animals with striatal grafts. In contrast, in the co-graft group, there was no significant increase of apomorphine-induced rotation compared to the post-quinolinic acid time-point. Morphometric analysis revealed a 63-74% reduction of striatal surface areas across the treatment groups. Striatal [3H]mazindol binding on the lesioned side (excluding the demarcated graft area) revealed a marked loss of dopamine re-uptake sites across all treatment groups, indicating missing graft-induced dopaminergic re-innervation of the host. In eight (73%) of the 11 animals with mesencephalic grafts and reduced amphetamine-induced circling, discrete areas of [3H]mazindol binding ("hot spots") were observed, indicating graft survival. Dopamine D1 and D2 receptor binding was preserved in the remaining lesioned striatum irrespective of treatment assignment, except for a significant reduction of D2 receptor binding in animals receiving mesencephalic grafts. "Hot spots" of dopamine D1 and D2 receptor binding were observed in 10 (83%) and nine (75%) of 12 animals receiving striatal grafts or co-grafts, consistent with survival of embryonic primordial striatum grafted into a severely denervated and lesioned striatum. Our study confirms that functional improvement may be obtained from embryonic neuronal grafts in a double-lesion rat model of multiple system atrophy/striatonigral degeneration type. Co-grafts appear to be required for reversal of both amphetamine- and apomorphine-induced rotation behaviour in this model. We propose that the partial reversal of amphetamine-induced rotation asymmetry in double-lesioned rats receiving mesencephalic or mesencephalic/striatal co-grafts reflects non-synaptic graft-derived dopamine release. The changes of apomorphine-induced rotation following transplantation are likely to reflect a complex interaction of graft- and host-derived striatal projection pathways and basal ganglia output nuclei. Further studies in a larger number of animals are required to determine whether morphological parameters and behavioural improvement in the neurotransplantation multiple system atrophy rat model correlate.

Anatomical and physiological evidence for D1 and D2 dopamine receptor colocalization in neostriatal neurons

Despite the importance of dopamine signaling, it remains unknown if the two major subclasses of dopamine receptors exist on the same or distinct populations of neurons. Here we used confocal microscopy to demonstrate that virtually all striatal neurons, both in vitro and in vivo, contained dopamine receptors of both classes. We also provide functional evidence for such colocalization: in essentially all neurons examined, fenoldopam, an agonist of the D1 subclass of receptors, inhibited both the Na+/K+ pump and tetrodotoxin (TTX)-sensitive sodium channels, and quinpirole, an agonist of the D2 subclass of receptors, activated TTX-sensitive sodium channels. Thus D1 and D2 classes of ligands may functionally interact in virtually all dopamine-responsive neurons within the basal ganglia.

Applications of SPECT imaging of dopaminergic neurotransmission in neuropsychiatric disorders

Single photon emission computed tomography (SPECT) tracers selective for pre- and post-synaptic targets have allowed measurements of several aspects of dopaminergic (DA) neurotransmission. In this article, we will first review our DA transporter imaging in Parkinson's disease. We have developed the in vivo dopamine transporter (DAT) imaging with [123I]beta-CIT ((1R)-2beta-Carbomethoxy-3beta-(4-iodophenyl)tropane). This method showed that patients with Parkinson's disease have markedly reduced DAT levels in striatum, which correlated with disease severity and disease progression. Second, we applied DA imaging techniques in patients with schizophrenia. Using amphetamine as a releaser of DA, we observed the enhanced DA release, which was measured by imaging D2 receptors with [123I]IBZM (iodobenzamide), in schizophrenics. Further we developed the measurement of basal synaptic DA levels by AMPT (alpha-methyl-paratyrosine)-induced unmasking of D2 receptors. Finally, we expanded our techniques to the measurement of extrastriatal DA receptors using [123I]epidepride. The findings suggest that SPECT is a useful technique to measure DA transmission in human brain and may further our understanding of the pathophysiology of neuropsychiatric disorders.

Imaging extrastriatal dopamine D(2) receptor occupancy by endogenous dopamine in healthy humans

The effect of endogenous dopamine on in vivo measurement of dopamine D(2) receptors in extrastriatal regions (thalamus and temporal cortex) was evaluated with single photon emission computed tomography and the high affinity ligand [123I]epidepride by comparing the binding potential before and after acute dopamine depletion. Dopamine depletion was achieved by per-oral administration of 5.5 g/70 kg body weight alpha-methyl-para-tyrosine given in 37 h. The alpha-methyl-para-tyrosine treatment increased the binding potential significantly in the temporal cortex (13+/-15%, P=0.036) but not in the thalamus (2+/-9%). The increase of the binding potential in the temporal cortex correlated strongly with the increase of dysphoric mood evaluated by the Positive and Negative Symptom Scale (PANSS) (rho=0.88, P=0.004). These results imply that [123I]epidepride, coupled with acute dopamine depletion might provide estimates of synaptic dopamine concentration.

Dopamine D4 receptors

Initial investigations on dopamine D4 receptors generated much interest in the role of this receptor in schizophrenia and other aspects of human behavior, as well as new opportunities for novel therapeutics. However, attempts to treat patients suffering from schizophrenia with dopamine D4 agents have failed to yield satisfactory results so far. An examination of the dopamine D4 literature shows that contrasting and conflicting data seemed to be the norm in this field of research. This paper reviews the literature on the dopamine D4 receptor and discusses many of the associated methodological problems that might have contributed to the paradoxical findings.

Behavioral changes and [123I]IBZM equilibrium SPECT measurement of amphetamine-induced dopamine release in rhesus monkeys exposed to subchronic amphetamine

Previously we have shown that twelve weeks of repeated low-dose d-amphetamine (AMPH) exposure in rhesus monkeys induces a long-lasting enhancement of behavioral responses to acute low-dose challenge. The present study was designed to investigate the behavioral and neurochemical consequences of a six-week regimen of low-dose AMPH exposure (0.1-1.0 mg/kg, i.m., b.i.d.) in rhesus monkeys. SPECT imaging of AMPH's (0.4 mg/kg) ability to displace [123I]IBZM bound to D2 dopamine receptors in the striatum of saline control and AMPH-treated animals prior to and following chronic treatment was accomplished using a bolus/constant infusion paradigm. Following chronic AMPH treatment, all monkeys showed an enhanced behavioral response to acute AMPH challenge and a significant decrease in the percent of AMPH-induced displacement of [123I]IBZM in striatum compared to their pretreatment scans. These findings suggest that relatively small changes in presynaptic dopamine function may be reflected in significant alterations in the behavioral response to acute AMPH challenge.

Dopamine D3 receptor binding by D3 agonist 7-OH-DPAT (7-hydroxy-dipropylaminotetralin) and antipsychotic drugs measured ex vivo by quantitative autoradiography

Because the dopamine D3 receptor is primarily expressed in regions of the limbic system of brain, it was proposed that it may represent a target for antipsychotic drugs that is free of extrapyramidal side effects. An ex vivo receptor binding technique employing [3H]7-OH-DPAT was used to evaluate in vivo occupancy of dopamine D3 receptors in the rat nucleus accumbens by selective D3 agonist 7-OH-DPAT (7-hydroxy-dipropylaminotetralin) and various antipsychotic drugs. With an ID50 value of 0.07 mg/kg, the selective D3 agonist (+)-7-OH-DPAT had the most potent inhibitory effect on ex vivo binding of [3H]7-OH-DPAT among all drugs tested. Clinical doses of phenothiazine drugs, such as chlorpromazine and levomepromazine, induce binding to D3 receptors in vivo, while atypical antipsychotic drugs, such as clozapine, pimozide, and sulpiride, are very weak in inhibiting ex vivo binding of [3H]7-OH-DPAT, indicating that the role of D3 receptors as targets of antipsychotic drugs free of extrapyramidal side effects may not be important.

Association between age-related decline in brain dopamine activity and impairment in frontal and cingulate metabolism

OBJECTIVE

Despite the well-documented loss of brain dopamine activity with age, little is known about its functional consequences in healthy individuals. This study investigates the relationship between measures of brain dopamine D(2) receptors (molecules that transmit dopamine signals) and regional brain glucose metabolism (a marker of brain function) in healthy individuals.

METHOD

Thirty-seven healthy volunteers aged 24-86 years underwent positron emission tomography scans after injection of [(11)C]raclopride to assess dopamine D(2) receptors and [(18)]fluorodeoxyglucose to assess regional brain glucose metabolism. Two methods used to assess the correlations between metabolism and dopamine D(2) receptors-pixel-by-pixel correlations and correlations in preselected regions of interest-were then compared.

RESULTS

D(2) receptors as well as frontal and cingulate metabolism declined with age. Regardless of the method used, significant correlations between metabolism and D(2) receptors were found in the frontal cortex (Brodmann's areas 6, 7, 8, 9, 10, 11, 44, 45, 47), anterior cingulate gyrus (areas 24, 32), temporal cortex (area 21), and caudate. These correlations remained significant after removing age effects (partial correlation).

CONCLUSIONS

These results provide the first link between age-related declines in brain dopamine activity and frontal and cingulate metabolism, which supports the need to investigate the therapeutic utility of interventions that enhance dopamine function in the elderly. The fact that correlations remained significant after removing age effects suggests that dopamine may influence frontal, cingulate, and temporal metabolism regardless of age.

Influence of food restriction on dopamine receptor densities, catecholamine concentrations and dopamine turnover in chicken brain

To investigate further a putative role of dopamine in control of food restriction-induced behavioural stereotypies, chickens were fed during rearing on either a daily restricted ration recommended by a breeding company, twice the recommended restricted ration, or ad libitum food. They were killed at 60 days of age and their excised brains were dissected into six regions and homogenized. Densities of dopamine D1 and D2 receptors were assessed, after first estimating binding parameters for [3H]SCH 23390 (D1) and [3H]spiperone (D2) in chicken brain homogenates. Specific binding of both ligands was highest in basal telencephalon. Concentrations of dopamine and its metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid were also highest in basal telencephalon, whereas noradrenaline and adrenaline levels were highest in diencephalon. Dopamine concentration in basal telencephalon and noradrenaline concentration in diencephalon were increased significantly in response to food restriction, but no effect of feeding treatment was found in dopamine turnover, adrenaline levels, or D1 and D2 receptor densities in any brain region studied. The observed changes in brain catecholamine levels are consistent with roles for dopaminergic and adrenergic mechanisms in the control of food restriction-induced behavioural stereotypies in chickens.

Iodine-123 iodobenzofuran (I-123 IBF) SPECT in patients with parkinsonism

I-123 IBF is a dopaminergic antagonist which is suitable for SPECT imaging of D2 receptors. The purpose of this study is to evaluate the potential usefulness of semi-quantitative parameters obtained from brain SPECT data of I-123 IBF for differential diagnosis in patients with parkinsonism (PN). Subjects were 10 patients with PN: 2 patients with striato-nigral degeneration (SND), 5 patients with Parkinson's disease (PD), 2 patients with progressive supranuclear palsy (PSP) and one patient with olivo-ponto-cerebellar atrophy (OPCA). The data were acquired with a triple-head gamma camera at 2 hours after intravenous injection of 167 MBq of I-123 IBF. Transverse images were reconstructed by means of filtered backprojection, and attenuation correction was performed by Chang's method (mu = 0.08). The basal ganglia-to-frontal cortex ratio (GFR) and the basal ganglia-to-occipital cortex ratio(GOR) on slices of 5 different thicknesses were calculated. The GFR and GOR were lower in the SND group than in the other disease groups in all slices with different thicknesses (7.2 mm, 14.4 mm, 21.6 mm, 28.8 mm and 43.2 mm). The semiquantitative parameters (GFR and GOR) obtained from brain SPECT data at 2 hours after intravenous injection of I-123 IBF may be useful for differential diagnosis in patients with PN.

Graphical analysis and simplified quantification of striatal and extrastriatal dopamine D2 receptor binding with [123I]epidepride SPECT

The purpose of this study was to extend the graphical analysis of reversible tracer binding to account for labeled lipophilic metabolites (metabolites) in quantifying [123I]epidepride binding to striatal and extrastriatal D2 receptors and, additionally, to evaluate the feasibility of simplified analysis to measure the specific volume of distribution (V3') using single-sample blood data because the tissue ratio (RT) may be a less reliable measure of D2 binding in the presence of metabolites.

METHODS

Multilinear regression analysis (MLRA) and graphical analysis (GA) using plasma parent (P) plus metabolite (M) activities as input and time activities of receptor-free (RF, cerebellum) and receptor-containing regions (RR, striatum and temporal cortex) derived V3' = (alpha(RR)(P) - alpha(RF)(P)), V3' = (1 + delta) (alpha(RR) - alpha(RF)) and RT = V3'/(V2P' + deltaV2M'), where alpha is a regression coefficient, delta is the equilibrium area ratio of M and P, and (V2P'/V2M') are the corresponding nondisplaceable distribution volumes. V3' by simplified analysis (SA) was calculated from RT determined without blood data and (V2P' + deltaV2M') with single-blood sample data. The accuracy of these three V3' values was assessed relative to the metabolite-accounted kinetic analysis (KA) for [123I]epidepride SPECT studies of 11 healthy volunteers, in which each participant had 27 scans and 30 plasma samples drawn during the 14 h after injection.

RESULTS

All three V3' values (mL/g) significantly correlated with those by KA (r > or = 0.90) (striatum/temporal cortex: MLRA, 77.8 +/- 36.6/2.35 +/- 1.16; GA, 98.8 +/- 34.2/4.61 +/- 1.77; SA, 83.9 +/- 24.8/4.26 +/- 1.74; KA, 107.6 +/- 34.4/5.61 +/- 1.84). However, the correlation between RT and V3' was only moderate (r < or = 0.65) because of significant intersubject variability (23%) in (V2P' + deltaV2M').

CONCLUSION

The graphical analysis can be extended to account for metabolites in measuring D2 binding with [123I]epidepride SPECT for both high and low D2 density regions. Additionally, simplified V3' measurements with single blood sampling are feasible and may be a practical alternative to the tissue ratio RT because RT suffers as a measure of D2 binding from significant intersubject variability in the metabolite-contributed distribution volume of the nondisplaceable compartment.