Specific Radioligand Research Articles

Cytotoxic Effects of 4-Hydroxynonenal In Pc12 Cells: Involvement of Neurotransmitter Receptors

Effect of 4-hydroxynonenal (HNE) was studied on the sensitivity of various neurotransmitter receptors in PC-12 cells. Initially, cytotoxicity profiling of HNE was carried out using HNE concentrations 0.1–50mM for 30min to 24h. The endpoints selected were, trypan blue dye exclusion, MTT, LDH release and neutral red uptake (NRU) assays. Significant cytotoxic responses were observed by minimum 2h of exposure, except for HNE at 50mM, where cytotoxicity was exerted even at 90min. HNE concentrations 10–50mM were found to be cytotoxic, 2–5mM cytostatic and 0.1-lmM non-cytotoxic. Neurotransmitter receptors studies were carried out using specific radioligands with selected doses of HNE (1,10,25 and 50mM for l-8h). Significant decrease in binding of 3 H-QNB, 3 H-Fluinitrazepam and 3 H-Ketanserin, known to label cholinergic-muscarinic, benzodiazepine and serotonin 5HT 2A receptors respectively was observed even at lh exposure with 25 and 50mM concentrations of HNE. Whereas, significant inhibition in binding of 3 H-Spiperone to DA-D2 receptor was started at 4h of exposure and continued till 8h. Specific binding with 3 H-Fluinitrazepam and 3 H-Ketanserin was reached to saturation at dose of 50mM for 4h and onwards. PC-12 cells have shown particular vulnerability to cytotoxic concentrations of HNE. Experimental HNE exposure provides an intriguing model of toxicant-cell interactions, which likely involved receptors in HNE neurotoxicity, lead neurodegeneration. doi: 10.5214/ans.0972.7531.2007.140401

Dual-isotope SPECT imaging of striatal dopamine: A comparative study between never treated and haloperidol treated first episode schizophrenic patients

Background: The aim of this investigation was to evaluate the striatal dopamine transporter (DAT) and D2 receptor availability by dual-isotope SPECT imaging in first episode schizophrenic patients in the never treated and haloperidol treated state compared to healthy control persons. Methods: Two groups of each 12 acutely ill drug naive inpatients suffering from a first acute schizophrenic episode and 12 healthy control persons were analyzed. One patient group was treated with haloperidol for a 14 days steady state treatment. The other group underwent the SPECT protocol in the drug naïve state. The dual-isotope SPECT protocol used combined application of [99mTc]TRODAT-1 and [123I]IBZM. Psychopathology was assessed in the patient group by specific scales including PANSS. Results: With respect to D2 availability to the specific radioligand, drug naïve patients did not differ to the control group while there was a significant reduction of D2 availability in the haloperidol treated compared to the drug naïve patients and the healthy control group. Availability of the DAT was significantly reduced in the treated patients, too. DAT availability correlated positively with the haloperidol dose. Discussion: The data obtained with the new dual-isotope SPECT technique reveal a direct effect of haloperidol not only postsynaptically but at the at the presynaptic DAT, too.

123I] ADAM and SPECT in patients with borderline personality disorder and healthy control subjects

Background: Impulsive behaviour, a key feature in borderline personality disorder (BPD), is associated with an impairment of the central serotonergic system. We hypothesized that the serotonin transporter availability is altered in patients with BPD and that there is an association between scores of impulsive aggression and serotonin transporter availability. Methods: In a group of eight female patients with BPD and nine healthy female controls, single photon emission computed tomography (SPECT) was conducted by using the serotonin specific radioligand [123I] ADAM. Using an occipital reference region, brain serotonin transporter availability was measured and ratios of specific to nonspecific [123I] ADAM binding for the brainstem and hypothalamus were calculated. Impulsiveness, anger and depressive symptoms were assessed using the Barratt Impulsiveness Scale, the State-Trait Anger Expression Inventory and the Beck Depression Inventory. Results: Mean specific-to-nonspecific ratios showed a 27% higher brainstem and a 29% higher hypothalamus [123I] ADAM binding in BPD patients compared to healthy controls. Significant correlations were found between ADAM binding and age, impulsiveness, and anger, but not depression. Conclusion: Our results are consistent with previous data suggesting a serotonergic dysfunction in the pathophysiology of BPD. Scores of impulsiveness and anger seemed to be associated with serotonin transporter availability in patients and in healthy controls.

SPECT neuroimaging in translational research of CNS disorders

High resolution SPECT imaging is an emerging field and there are only limited studies as yet available in this direction. Still there is continuous effort to achieve better spatial and temporal resolution in order to obtain detailed structural and functional information of different brain regions in small experimental animals. Recently, SPECT imaging system has been used to perform in vivo imaging using specific radioligands to further elucidate the role of dopaminergic, serotonergic, and cholinergic neurotransmission in relation to regional cerebral blood flow in various human CNS disorders and in gene-manipulated mouse models of neurodegeneration. Although in vivo and non-invasive translational research can be performed by high-resolution microPET imaging system, its limited spatial resolution restricts detailed anatomical and functional information of different brain regions involved in disease process. Recently developed NanoSPECT/CT imaging system has a better spatial resolution hence can be used to correlate and confirm microPET imaging data and determine the precise structural and functional anatomy of CNS disorders and their remission. Moreover SPECT imaging system reduces the cost and number of animals and provides detailed information of CNS disorders at the cellular, molecular and genetic level. Furthermore, SPECT system is economical, provides less radiation burden, and can be used to study bio-distribution of newly synthesized radioligands with increased target to non-target ratios, quality control, and clinical applications. It is envisaged that high-resolution SPECT imaging system will further improve in vivo non-invasive translational research on CNS disorders of unknown etiopathogenesis and their treatment in future.

Preclinical evaluation of [99mTc/EDDA/tricine/HYNIC0, 1-Nal3, Thr8]-octreotide as a new analogue in the detection of somatostatin-receptor-positive tumors

Radiolabeled somatostatin analogues are important tools for the in vivo localization and targeted radionuclide therapy of somatostatin-receptor-positive tumors. The aim of this study was to evaluate a new somatostatin analogue designed for the labeling with (99m)Tc: [6-hydrazinopyridine-3-carboxylic acid (HYNIC(0)), 1-Nal(3), Thr(8)]-octreotide ([HYNIC]-NATE), using ethylenediamine-N,N'-diacetic acid (EDDA) and tricine as coligands. Synthesis was preformed on a solid phase using a standard Fmoc strategy. Labeling with (99m)Tc was performed at 100 degrees C for 10 min using SnCl(2) as a reductant. Radiochemical analysis involved ITLC and high-performance liquid chromatography methods. Peptide conjugate affinity was determined in AR4-2J cell membranes. The internalization and externalization rates were studied in sstr(2)-expressing AR4-2J cells. Biodistribution of radiopeptide was studied in rats bearing the AR4-2J tumor. Radiolabeling was performed at high specific activities, and radiochemical purity was >95%. Peptide conjugate showed high affinity binding for sstr(2). The radioligand showed a moderate and specific internalization into AR4-2J cells (14.13+/-0.61% at 4 h). In animal biodistribution studies, a receptor-specific uptake of radioactivity was observed in somatostatin-receptor-positive organs. After 4 h, uptake in the AR4-2J tumor was 1.33+/-0.23%ID/g (percentage of injected dose per gram of tissue). These data show that [(99m)Tc/EDDA/tricine/HYNIC]-NATE is a specific radioligand for the somatostatin-receptor-positive tumors and is a suitable candidate for clinical studies.

Differential regulation on human skin fibroblast by α 1 adrenergic receptor subtypes

Alpha 1 adrenoceptor (α 1-AR) regulation of DNA synthesis was studied in human neonatal foreskin fibroblast. Saturation assay with a specific radioligand for α 1 adrenergic [ 3H]-prazosin revealed two saturated and specific binding sites with high or low affinity. Competitive binding assay with different antagonist subtypes, defined pharmacologically three major types of α 1-AR. The α 1-AR agonists (from 1 × 10 −10 to 1 × 10 −4 M) triggered a biphasic action on DNA synthesis reaching maximal stimulation at 1 × 10 −9 M and maximal inhibition at 1 × 10 −6 M. Prazosin, abolished the stimulatory (pA 2: 9.24) and inhibitory (pA 2: 8.80) actions of α 1-AR agonists. The α 1-AR stimulation resulted in the activation of phosphoinositide turnover (InsP) via phospholipase C (PLC) involving calcium/calmodulin (CaM) and nitric oxide synthase (NOS) that correlates with the DNA synthesis increment; whereas the inhibition resulted in a decrease of cyclic AMP (cAMP) accumulation via adenylate cyclase inhibition. The potency displayed by the specific antagonists tested in binding, DNA synthesis, InsP and NOS at low agonist concentration suggests that they can be elicited by the activation of the same receptor (α 1B-AR subtype); while the decrement in DNA synthesis and cAMP at high concentration account by the activation of α 1D-AR coupled to G i protein. Non-functional α 1A-AR in neonatal human foreskin fibroblast was observed. Results suggest that the expression of α 1-AR subtypes on human skin fibroblast may differentially activate signaling pathways that modulate physiological response of the cells.

Imagerie moléculaire dans les démences

Nuclear neuroimaging, with single photon emission computed tomography (SPECT) or with positron emission tomography (PET), allows study of functional and neurochemical aspects of human brain. It provides in vivo informations about pathophysiology in dementia. The routinely available tracers are perfusional tracers ( 99mTc-HMPAO/GE Healthcare and 99mTc-ECD/BMS). In June 2006, a new indication for the DaTSCAN ® (GE Healthcare) has been adopted. DaTSCAN ® could now be used to help differentiate probable dementia with Lewy bodies from Alzheimer's disease. Since a few years, there have been tremendous efforts expended to develop specific radioligands for several neurochemical systems and for imaging of beta-amyloid plaques. The aim of this paper is to review the most common radiotracers for SPECT and PET brain imaging in dementia and to focus on the new tracers.

Acute S-ketamine application does not alter cerebral [18F]altanserin binding: a pilot PET study in humans

Modeling short-term psychotic states with subanaesthetic doses of ketamine provides substantial experimental evidence in support of the glutamate hypothesis of schizophrenia. Ketamine exerts its pharmacological effects both directly via interactions with glutamate receptors and indirectly by stimulating presynaptic release of endogenous serotonin (5-HT). The aim of this feasibility study was to examine whether acute ketamine-induced 5-HT release interferes with the binding of the 5-HT(2A) receptor (5-HT(2A)R) radioligand [(18)F]altanserin and positron emission tomography (PET). Two subjects treated with ketamine and one subject treated with placebo underwent [(18)F]altanserin PET at distribution equilibrium conditions. Robust physiological, psychopathological and cognitive effects were present at ketamine plasma concentrations exceeding 100 microg/l during >70 min. Notwithstanding, we observed stable radioligand binding (changes +/-95% CI of -1.0 +/- 1.6% and +4.1 +/- 1.8% versus -1.2 +/- 2.6%) in large cortical regions presenting high basal uptake of both, [(18)F]altanserin and ketamine. Marginal decreases of 4% of radioligand binding were observed in the frontal lobe, and 8% in a posteriorily specified frontomesial subregion. This finding is not compatible with a specific radioligand displacement from 5-HT(2A)R which should occur proportionally throughout the whole brain. Instead, the spatial pattern of these minor reductions was congruent with ketamine-induced increases in cerebral blood flow observed in a previous study using [(15)O]butanol PET. This may caused by accelerated clearance of unspecifically bound [(18)F]altanserin from cerebral tissue with increased perfusion. In conclusion, this study suggests that [(18)F]altanserin PET is not sensitive to acute neurotransmitter fluctuations under ketamine. Advantageously, the stability of [(18)F]altanserin PET towards acute influences is a prerequisite for its future use to detect sub-acute and chronic effects of ketamine.

Phase-dependent roles of reactive microglia and astrocytes in nervous system injury as delineated by imaging of peripheral benzodiazepine receptor

Elevated levels of peripheral benzodiazepine receptor (PBR) in glia have been documented in diverse nervous system injuries, while the identity and spatiotemporal characteristics of the cells showing upregulation of PBR remain elusive. We examined the astrocytic and microglial expressions of PBR in rat brains during the duration of ethanol-induced neuronal insults in order to clarify the significance of PBR as a biomarker capable of detecting a distinctive subpopulation of these glial cells involved in the impairment and protection of neurons. The levels of PBR, as determined by autoradiographic analysis using a specific radioligand, [ 11C]DAA1106, began to significantly increase at 3 days after intrastriatal injection of ethanol, and peaked at 7 days. This was consistent with the results of double immunofluorescence staining and high-resolution emulsion autoradiography, which revealed upregulation of PBR in both microglia and astrocytes proliferating in nonoverlapping compartments of the injury site. Notably, increased expression of PBR in astrocytes was transiently observed in a manner parallel to the centripetal migration of these cells to the inflammatory lesion, which may be a response indispensable to the protection of intact tissue. Thereafter, astrocytic PBR was barely detectable, despite the presence of numerous glial fibrillary acidic protein-immunoreactive astrocytes forming glial scarring. By contrast, intense PBR signals were persistently present in microglia localized to the injury epicenter up to 90 days, notwithstanding a gradual reduction in the number of ionized calcium binding adapter molecule-1-positive amoeboid microglia between 7 and 90 days. The long-lasting PBR expression in microglia was finally supported by in vivo positron emission tomography imaging, and suggests that inflammatory tissue damage is potentially expandable unless it is tightly sealed by astrocytic scar. The present findings collectively support the utility of PBR in identifying a unique temporal pattern of astrocytic and microglial activation that conventional glial markers hardly pursue.

N-(5-Fluoro-2-phenoxyphenyl)-N-(2-[131I]iodo-5-methoxybenzyl)acetamide: A Potent Iodinated Radioligand for the Peripheral-type Benzodiazepine Receptor in Brain

To image the peripheral-type benzodiazepine receptor (PBR) in vivo, we previously developed two positron emission tomography (PET) ligands, N-(2-[11C],5-dimethoxybenzyl)-N-(5-fluoro-2-phenoxyphenyl)acetamide ([11C]1a) and its [18F]fluoroethyl analogue ([18F]1b), for the investigation of PBR in the living human brain. This time, using 1a as a leading compound, we designed two novel iodinated analogues, N-(5-fluoro-2-phenoxyphenyl)-N-(2-iodo-5-methoxybenzyl)acetamide (3a) and N-(2,5-dimethoxybenzyl)-N-(5-iodo-2-phenoxyphenyl)acetamide (3b) for the PBR imaging. Ligands 3 were synthesized by the iodination of tributystannyl precursors 10. Radiolabeling for 3 with 131I was carried out by the reaction of 10 with [131I]NaI using H2O2 as an oxidizing agent. In vitro competition experiments determined that 3a exhibited both high affinity and selectivity for PBR (IC50: 7.8 nM) vs CBR (>1 microM). Biodistribution study in mice determined that [131I]3a had a high radioactivity level (1.69% dose/g) in the brain, and its distribution pattern in the brain was consistent with the known distribution of PBR in rodents. Ex vivo autoradiography of the rat brain gave visual evidence that [131I]3a was a potent and specific radioligand for PBR.

Sigma Receptor Ligands: Possible Application as Therapeutic Drugs and as Radiopharmaceuticals

Sigma receptors are classified into sigma(1) and sigma(2) subtypes. These subtypes display a different tissue distribution and a distinct physiological and pharmacological profile in the central and peripheral nervous system. The characterization of these subtypes and the discovery of new specific sigma receptor ligands demonstrated that sigma receptors are novel targets for the therapeutic treatment of neuropsychiatric diseases (schizophrenia, depression, and cognition), brain ischemia, and cocaine addiction. Furthermore, imaging of sigma(1) receptors in the human brain using specific PET radioligands has started. In addition, the two sigma receptor subtypes are also expressed on tumor cells, where they could be of prognostic relevance. The ability of sigma(2) receptor agonists to inhibit tumor cell proliferation through mechanisms that might involve apoptosis, intracellular Ca(2+), and sphingolipids has promoted the development of sigma(2) receptor agonists as novel therapeutic drugs for treating cancer. Consequently, sigma(2) receptor ligands have been demonstrated to be potentially useful tumor imaging ligands. In this article, we focus on the sigma receptor ligands as therapeutic agents and as radiopharmaceuticals.

Modulation of dopamine D 1 receptor signaling by adenosine A 1 receptors in Sf9 cells requires expression of G i proteins

There are several evidences that some functions of D 1 dopamine receptors can be modulated by colocalized adenosine A 1 receptors. To elucidate the role of particular components of the receptor complex in the ligand binding and second messenger activation level we have used Sf9 cell expression system. The expression of D 1 and A 1 receptors was confirmed by proper binding of specific radioligands [ 3 H]SCH23390 ( K d = 1.1 ± 0.1 nM, B max = 2.2 ± 0.1 pmol/mg protein) and [ 3 H]DPCPX ( K d = 2.1 ± 0.8 nM, B max = 2.9 ± 0.4 pmol/mg protein), respectively. The kinetics of [ 3 H]SCH23390 binding corresponded to the simplest reversible bimolecular binding reaction of complex formation, with k on = 0.20 ± 0.02 min −1 nM −1 and k off = 0.13 ± 0.01 min −1. Dopaminergic agonists increased the accumulation of cAMP in the transfected cells in concentration-dependent manner, indicating a correct coupling of receptor to second messenger system. The coupling of the A 1 receptor to G i proteins was confirmed by both GTPγS dependent agonist binding and inhibition of cAMP accumulation by N-cyclopentyladenosine (NCPA). Activation of the A 1 receptor by NCPA had no significant influence on neither affinities of dopaminergic ligands nor the radioligand binding kinetics to the co-exprssed D 1 receptors in Sf9 cell membranes. On the other hand, the activation of the A 1 receptors inhibited the D 1 receptor-specific accumulation of cAMP, but only in cells where G i proteins were expressed with the receptors.

Characterization of Kir1.1 Channels with the Use of a Radiolabeled Derivative of Tertiapin

Inward rectifier potassium channels (Kir) play critical roles in cell physiology. Despite representing the simplest tetrameric potassium channel structures, the pharmacology of this channel family remains largely undeveloped. In this respect, tertiapin (TPN), a 21 amino acid peptide isolated from bee venom, has been reported to inhibit Kir1.1 and Kir3.1/3.4 channels with high affinity by binding to the M1-M2 linker region of these channels. The features of the peptide-channel interaction have been explored electrophysiologically, and these studies have identified ways by which to alter the composition of the peptide without affecting its biological activity. In the present study, the TPN derivative, TPN-Y1/K12/Q13, has been synthesized and radiolabeled to high specific activity with (125)I. TPN-Y1/K12/Q13 and mono-iodo-TPN-Y1/K12/Q13 ([(127)I]TPN-Y1/K12/Q13) inhibit with high affinity rat but not human Kir1.1 channels stably expressed in HEK293 cells. [(125)I]TPN-Y1/K12/Q13 binds in a saturable, time-dependent, and reversible manner to HEK293 cells expressing rat Kir1.1, as well as to membranes derived from these cells, and the pharmacology of the binding reaction is consistent with peptide binding to Kir1.1 channels. Studies using chimeric channels indicate that the differences in TPN sensitivity between rat and human Kir1.1 channels are due to the presence of two nonconserved residues within the M1-M2 linker region. When these results are taken together, they demonstrate that [(125)I]TPN-Y1/K12/Q13 represents the first high specific activity radioligand for studying rat Kir1.1 channels and suggest its utility for identifying other Kir channel modulators.

Peripheral benzodiazepine receptors on platelets of fibromyalgic patients

Objective: The aim of the present study was to analyze if alterations of peripheral-type benzodiazepine receptor (PBR) characteristics occurred in platelet membranes of patients affected by primary fibromyalgia (FM). Design and methods: Platelets were obtained from 30 patients with FM. Evaluation of kinetic parameters of PBR was performed using [ 3H] PK11195 as specific radioligand compared with 16 healthy volunteers. Results: The results showed a significant increase of PBR binding sites value in platelet membranes from FM patients ( B max was 5366 ± 188 fmol/mg vs. controls, 4193 ± 341 fmol/mg, mean ± SEM) (** p < 0.01) but not for affinity value ( K d was 4.90 ± 0.39 nM vs. controls, 4.74 ± 0.39 nM, mean ± SEM) ( p > 0.05). Symptom severity scores (pain and tiredness) were positively correlated with B max. Conclusions: Our results showed an up-regulation of PBR in platelets of FM patients, and this seems to be related to the severity of fibromyalgic symptoms.

A 1 adenosine receptor PET using [ 18F]CPFPX: Displacement studies in humans

Background. Imaging of cerebral A 1 adenosine receptors (A 1AR) with positron emission tomography (PET) has recently become available for neurological research. To date, it has still not been unraveled if there is a valid reference region without specific radioligand binding that may be used to improve image quantification. We conducted in vivo displacement studies in humans to elucidate this important question using the A 1AR ligand [ 18F]CPFPX. Methods. Five healthy male volunteers underwent [ 18F]CPFPX bolus/infusion PET with short infusion of unlabelled CPFPX as competitor ( n = 4; 0.9 to 4.0 mg) or vehicle ( n = 1; control condition) after equilibrium of [ 18F]CPFPX distribution was attained. Results. Infusion of CPFPX induced a rapid displacement of [ 18F]CPFPX binding in all regions, including the cerebellum (region with lowest binding). Even at the highest competitor dose, no full displacement was reached. Displacement was dose-dependent in all regions except the cerebellum where floor effects and/or noise might have obscured dose dependency. Specific binding was estimated to account for about one third and two thirds of total equilibrium uptake in cerebellum and cortex, respectively. Conclusions. Although the cerebellum is the region with lowest in vivo [ 18F]CPFPX binding, it is not an ideal reference region devoid of specific binding. Nevertheless, as will be discussed, the use of a reference region analysis may be a useful, non-invasive alternative analysis method in carefully selected applications.

3-Aza-6,8-dioxabicyclo[3.2.1]octanes as new enantiopure heteroatom-rich tropane-like ligands of human dopamine transporter

CNS diseases such as Parkinson, schizophrenia, and attention deficit hyperactivity disorder (ADHD) are characterized by a significant alteration of dopamine transporter (DAT) density. Thus, the development of compounds that are able to selectively interact with DAT is of great interest. Herein we describe the design and synthesis of a new set of 3-aza-6,8-dioxabicyclo[3.2.1]octanes having a tropane-like structure with additional heteroatoms at positions 3 and 6. The compounds were evaluated for their in vitro receptor binding properties toward human dopamine (hDAT) and serotonin (hSERT) transporters using [ 3H]WIN35,428 and [ 3H]citalopram as specific radioligands, respectively. Biological assays revealed that some compounds having the N-3 atom substituted with aryl groups possess significant affinity and selectivity for monoamine transporters, and in particular, compound 5d displayed an IC 50 of 21 nM toward DAT, and a good selectivity toward SERT (IC 50 = 1042 nM). These results suggest that 3-aryl-3-aza-6,8-dioxabicyclo[3.2.1]octanes may represent a new class of DAT ligands.

A Novel Nicotinic Acetylcholine Receptor Antagonist Radioligand for PET Studies.

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Brain Serotonin Reuptake Did not Change During One Year in Overtrained Athletes

Brain 5-HT neurotransmission has been described to be down-regulated in depressed people, and also suspected to be changed in overtraining state, the consequence of long-term physical overloading and stress in athletes. We studied brain serotonin (5-HT) transporter binding i.e., 5-HT reuptake with the specific radioligand (123-I-labelled 2beta-carbomethoxy-3beta[4-iodopenyl]-nortropane, Nor-beta-CIT), and with single photon emission tomography (SPET) in severely overtrained athletes and their controls at the baseline and after a one-year recovery period. Twelve overtrained (6 women and 6 men, mean age 27 yrs, range 16 - 39 yrs) and 11 healthy (6 women, 5 men, 26 yrs, 20 - 39 yrs) athletes were examined. Overtrained athletes 1) had suffered from an unexplained decrement in physical performance and fatigue for several weeks to many months and continued to have the same symptoms even after a recovery time of weeks to months, 2) had been examined to be otherwise healthy, and 3) had a suitable training history for overtraining. Nor-beta-CIT SPET was acquired 5 min, and 3, 6, and 24 h after the injection of the radioligand. 5-HT reuptake in ml/ml in midbrain (raphe nuclei) was calculated as (midbrain - cerebellum)/cerebellum. According to two-way analysis of variance, no changes inside the groups or group differences in 5-HT reuptake were found. Male athletes had significantly higher 5-HT reuptake than female athletes at the baseline (p = 0.034). The overtrained athletes were moderately depressed, while their scores in standardized Hamilton and Montgomery-Asberg Depression Rating Scales were 16 +/- 2 (mean +/- SEM, range 8 - 29) and 17 +/- 2 (7 - 28), respectively. In the CA, the scores were 6 +/- 1 (range 2 - 18) and 6 +/- 2 (1 - 19), respectively. 5-HT reuptake did not correlate with the depression scores either in the whole group or in the OA. The finding of the present study does not support the idea of long-term changes in 5-HT neurotransmission in overtraining state, in this case serotonin reuptake in midbrain, the regulating area of brain serotonin neurotransmission. Furthermore, depression of overtrained athletes may be its own variant having no correlation with 5-HT reuptake in midbrain. Sex may have effect on chronic stress response at the brain level in athletes, which may be a confusing factor in the overtraining studies, and has to be taken into consideration in the future.

Distribution of PK11195 binding sites in porcine brain studied by autoradiography in vitro and by positron emission tomography

The cerebral distribution of peripheral-type benzodiazepine binding sites (PBBS) in human brain has been investigated by positron emission tomography (PET) with the specific radioligand [11C]PK11195 in diverse neuropathological conditions. However, little is known about the pattern of PK11195 binding sites in healthy brain. Therefore, we used quantitative autoradiography to measure the saturation binding parameters for [3H]PK11195 in cryostat sections from young Landrace pigs. Specific binding was lowest in the cerebellar white matter (85 fmol mg(-1)) and highest in the caudate nucleus (370 fmol mg(-1)), superior colliculus (400 fmol mg(-1)), and anterior thalamic nucleus (588 fmol mg(-1)). The apparent affinity was in the range of 2-6 nM in vitro, predicting high specific binding in PET studies of living brain. However, the distribution volume (V(d), ml g(-1)) of high specific activity [11C]PK11195 was nearly homogeneous (3 ml g(-1)) throughout brain of healthy Landrace pigs, and was nearly identical in studies with lower specific activity, suggesting that factors in vivo disfavor the detection of PBBS in Landrace pigs with this radioligand. In young, adult Göttingen minipig brain, the magnitude of V(d) for [11C]PK11195 was in the range 5-10 ml g(-1), and had a heterogeneous distribution resembling the in vitro findings in Landrace pigs. There was a trend toward globally increased V(d) in a group of minipigs with acute MPTP-induced parkinsonism, but no increase in V(d) was evident in the same pigs rescanned at 2 weeks after grafting of fetal mesencephalon to the partially denervated striatum. Thus, [11C]PK11195 binding was not highly sensitive to constituitively expressed PBBS in brain of young Landrace pigs, and did not clearly demonstrate the expected microglial activation in the MPTP/xenograft model of minipigs.

P.1.d.002 Aggressive and hyperactive behavioural characteristics is increased in maternal social separated rat

Lurasidone is a novel antipsychotic agent with high affinity for dopamine D2 and serotonin 5-HT7, 5-HT2A, and 5-HT1A receptors. We previously reported that in addition to its antipsychotic action, lurasidone shows beneficial effects on mood and cognition in rats, likely through 5-HT7 receptor antagonistic actions. In this study, we evaluated binding of lurasidone to 5-HT7 receptors in the rat brain by autoradiography using [3H]SB-269970, a specific radioligand for 5-HT7 receptors. Brain slices were incubated with 4 nM [3H]SB-269970 at room temperature and exposed to imaging plates for 8 weeks before phosphorimager analysis. Using this method, we first investigated 5-HT7 receptor distribution. We found that 5-HT7 receptors are abundantly localized in brain limbic structures, including the lateral septum, thalamus, hypothalamus, hippocampus, and amygdala. On the other hand, its distribution was moderate in the cortex and low in the caudate putamen and cerebellum. Secondly, binding of lurasidone, a selective 5-HT7 receptor antagonist SB-656104-A and an atypical antipsychotic olanzapine to this receptor was examined. Lurasidone, SB-656104-A (10–1000 nM), and olanzapine (100–10,000 nM) showed concentration-dependent inhibition of [3H]SB-269970 binding with IC50 values of 90, 49, and 5200 nM, respectively. Similar inhibitory actions of these drugs were shown in in vitro [3H]SB-269970 binding to 5-HT7 receptors expressed in Chinese hamster ovary cells. Since there was no marked species difference in rat and human 5-HT7 receptor binding by lurasidone (Ki = 1.55 and 2.10 nM, respectively), these findings suggest that binding to 5-HT7 receptors might play some role in its beneficial pharmacological actions in schizophrenic patients.