Regional differences in striatal dopamine uptake and release associated with recovery from MPTP-induced parkinsonism: an in vivo electrochemical study

This study directly assessed striatal dopamine (DA) uptake rates and peak release in response to KCl in normal, symptomatic, and recovered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated cats using in vivo electrochemistry. DA uptake rates measured after direct application of known concentrations of DA to the striatum were slowed significantly in both dorsal and ventral striatum in symptomatic cats compared with rates recorded in normal animals. DA uptake rates remained significantly slowed in recovered cats and were not significantly different from the rates recorded in symptomatic animals. In symptomatic cats, both DA uptake rates and the signal recorded in response to KCl stimulation were significantly decreased from normal in all dorsal and ventral striatal regions sampled. Reduction/oxidation (redox) ratios recorded in response to KCl stimulation suggested DA to be the predominant electroactive species. In spontaneously recovered MPTP-treated cats, recordings in the ventral striatum subsequent to KCl stimulation again suggested DA to be the predominant electroactive species released, and peak levels were significantly higher than those recorded in symptomatic animals. In the dorsal striatum of recovered cats, redox ratios recorded subsequent to KCl stimulation suggested serotonin rather than DA to be the predominant electroactive species released. Peak levels of release in the dorsal striatum were not significantly greater than those recorded in symptomatic animals. These results suggest that in spontaneously recovered MPTP-treated cats, there is partial recovery of ventral striatal DAergic terminals, persistent loss of dorsal striatal DAergic terminals, and a down-regulation of DA transporter number/function throughout the striatum. These processes may contribute to volume transmission of DA in the striatum and promote functional recovery.

Effects of the method of drawing regions of interest on the differential diagnosis of extrapyramidal syndromes using 123I-iodolisuride SPET

Various parameters are currently used for the semi-quantitative assessment of dopamine D2 receptors and differ according to the delineation of the striatal region of interest (ROI) and the choice of the reference ROI. The aim of this study was to assess the value of different ROI approaches in differentiating patients with normal or increased numbers of D2 dopamine receptors (group 1 = Parkinson's disease, n = 8) from patients with decreased dopamine D2 receptors (group 2 = other extrapyramidal syndromes, n = 9) using 123I-iodolisuride SPET (ILIS-SPET). 123I-iodolisuride (190 +/- 31 MBq) and 99Tcm-ethyl cysteinate dimer (99Tcm-ECD) perfusion SPET were performed in the same position, with a dual-headed gamera camera equipped with fan beam collimators. Both a geometric approach (ellipse, circle or rectangle) and an anatomical approach using the CT scan and perfusion SPET as anatomical guides were used to draw striatal and reference ROIs. A total of 33 different parameters were calculated for each patient, indicating the ratio of counts between the striatal and reference ROIs (frontal, occipital cortex or cerebellum) and the asymmetry between the right and left striatum. More significant differences between group 1 and group 2 were found by using geometric ROIs than by using anatomical ROIs. The most discriminant ratios were the caudate/occipital, caudate/frontal and striatum/occipital ratios (P = 0.001, P = 0.002, P = 0.003 respectively). A close correlation was found between the striatum/caudate and striatum/occipital ratios, but not between the striatum/frontal and striatum/occipital ratios or between the striatum/frontal and striatum/caudate ratios. We conclude that the occipital cortex is the best reference for the semi-quantitative evaluation of dopamine D2 receptors as the frontal cortex could include some dopamine D2 receptor-bound radioligand, and that the caudate/occipital ratio is an appropriate parameter for differentiating Parkinson's disease from non-Parkinson extrapyramidal syndrome by 123I-iodolisuride SPET.

Use of magnetic resonance imaging for in vivo measurements of water content in human brain: method and normal values

OBJECT

The authors present a quantitative in vivo magnetic resonance (MR) imaging method and propose its use for the accurate assessment of brain water in humans.

METHODS

With this technique, a pure T1-weighted image of a selected brain slice in a patient is generated, and the image is subsequently converted to a pure water image by means of an equation derived from a tissue relaxation model. The image intensity in the resulting water map directly yields absolute measures of water expressed in grams of water per gram of tissue at a given anatomical location. The method has been validated previously in a series of phantom experiments and in an infusion model of brain edema in cats. In this report, the authors evaluate the method by using samples of tissue harvested from patients who underwent surgery for brain tumor removal and apply the technique to a series of normal volunteers, providing average regional brain water content (f(w)) values for a range of tissues. Application of the method in pathological conditions such as head trauma, tumor, and hydrocephalus allows quantification of regional or global increases in f(w) that result from edema.

CONCLUSIONS

It is now possible to obtain accurate brain water measurements with the anatomical resolution of MR imaging. This permits monitoring of the development and resolution of edema in a variety of clinical circumstances, thus enhancing understanding of the underlying pathophysiological processes.

Subgroups of parkinsonian patients differentiated by peptidergic immunostaining of caudate nucleus biopsies

In this study, Met-enkephalin (Met-enk), substance P (SP) and tyrosine hydroxylase (TH) immunostaining was assessed in caudate nucleus biopsies from 15 Parkinson's disease patients who were treated surgically. According to the combination of changes in Met-enk, SP and TH immunostaining, several subgroups of parkinsonian patients were disclosed. Group I: Patients showing low SP and normal Met-enk immunostaining, and variably reduced TH immunoreactivity. Group II: both SP and Met-enk immunostaining were apparently of normal intensity in these PD patients, but they showed the greatest decrease in TH labeling. Group III: PD patients that showed normal SP, very low Met-enk and variably reduced TH immunostaining. Low Met-enk immunostaining tended to correlate with the severity of the disease as judged by higher Unified Parkinson's disease Rating Scale and gait scores. These results suggest that different neurochemical phenotypes may exist among Parkinson's disease patients. Peptidergic deficits should be taken into account for therapeutic intervention.

Neuronal pathology in the wobbler mouse brain revealed by in vivo proton magnetic resonance spectroscopy and immunocytochemistry

Proton magnetic resonance spectroscopy (1H-MRS) was used to measure the in vivo signal of N-acetylaspartate (NAA), a putative neuronal marker, in the brain of the mutant wobbler mouse, a model of motor neuron disease. The ratio of NAA to creatine-phosphocreatine, an internal standard, was significantly lower in five affected wobbler mice (0.79+/-0.05; mean+/-s.d.) than in five unaffected littermates (0.98+/-0.10, p = 0.006). Ubiquitin and phosphorylated heavy neurofilament immunoreactivities were increased in cortical neurons of affected animals. This is the first demonstration of cerebral neuronal pathology in the wobbler mouse, supporting its use as a model of amyotrophic lateral sclerosis. In vivo IH-MRS and correlative postmortem study of wobbler mouse brain will allow temporal monitoring of neuronal degeneration and responsiveness to neuroprotective pharmacotherapies.

Regulation of extracellular dopamine by the norepinephrine transporter

There is growing evidence of an interaction between dopamine and norepinephrine. To test the hypothesis that norepinephrine terminals are involved in the uptake and removal of dopamine from the extracellular space, the norepinephrine uptake blocker desmethylimipramine (DMI) was infused locally while the extracellular concentrations of dopamine were simultaneously monitored. DMI increased the extracellular concentrations of dopamine in the medial prefrontal cortex and nucleus accumbens shell but had no effect in the striatum. The combined systemic administration of haloperidol and the local infusion of DMI produced an augmented increase in extracellular dopamine in the cortex compared with the increase produced by either drug alone. This synergistic increase in dopamine overflow is likely due to the combination of impulse-mediated dopamine release produced by haloperidol and blockade of the norepinephrine transporter. No such synergistic effects were observed in the nucleus accumbens and striatum. Local perfusion of the alpha2-antagonist idazoxan also increased the extracellular concentrations of dopamine in the cortex. Although the stimulation of extracellular dopamine by idazoxan and DMI could be due to the increased extracellular concentrations of norepinephrine produced by these drugs, an increase in dopamine also was observed in lesioned rats that were depleted of norepinephrine and challenged with haloperidol. This contrasted with the lack of an effect of haloperidol on cortical dopamine in unlesioned controls. These results suggest that norepinephrine terminals regulate extracellular dopamine concentrations in the medial prefrontal cortex and to a lesser extent in the nucleus accumbens shell through the uptake of dopamine by the norepinephrine transporter.

Determination of fluoxetine and its metabolite norfluoxetine in serum and brain areas using high-performance liquid chromatography with ultraviolet detection

A high-performance liquid chromatography (HPLC) method using only 0.1 ml of serum or homogenate from brain areas has been developed for the determination of fluoxetine (FLU) and its metabolite, norfluoxetine (N-FLU), with ultraviolet detection at 227 nm. The small volume of sample required in this method allows studies in small animals, such as mouse. The method provides recoveries of up to 90% for both compounds. Acceptable coefficients of variation were found for both within-run and day-to-day assays. The limit of detection was 5.0 ng/ml. No interferences were found with tricyclic antidepressant drugs and benzodiazepines, which allows this method to be used in clinical studies, Pharmacokinetic parameters for the two compounds are reported in mouse serum, frontal cortex and caudate nucleus. We also report the values of FLU and N-FLU in serum from humans who were treated once daily with 20 mg of FLU, obtained after 1, 14 and 28 days of treatment.

Diorthosubstituted polychlorinated biphenyls in caudate nucleus in Parkinson's disease

As it had previously been demonstrated that there were reduced brain dopamine concentrations in monkeys who had been given polychlorinated biphenyls (PCBs) chronically, we hypothesized that organochlorine compounds in general, and PCBs in particular, might be important in the pathogenesis of Parkinson's disease (PD). In a study of caudate nucleus obtained post mortem from patients with Parkinson's disease and from controls, there were significantly higher concentrations of the organochlorine insecticide dieldrin and the PCB congener 153 in the PD tissue. DDE, PCB congener 180, and total PCBs (matched with a commercial preparation) also tended to be higher in Parkinson's disease tissue. We think that this is important preliminary evidence that diorthosubstituted PCBs may contribute to the pathogenesis of Parkinson's disease, and a greater presence of organochlorine insecticides in the PD tissue suggests that this may be in part the explanation for the association between PD and rural living.

Kappa2 opioid receptors in limbic areas of the human brain are upregulated by cocaine in fatal overdose victims

Cocaine is thought to be addictive because chronic use leads to molecular adaptations within the mesolimbic dopamine (DA) circuitry that affect motivated behavior and emotion. Although the reinforcing effects of cocaine are mediated primarily by blocking DA reuptake into the presynaptic nerve terminal, reciprocal signaling between DA and endogenous opioids has important implications for cocaine dependence. The present study used the opioid antagonist 6 beta-[125iodo]-3,14-dihydroxy-17-cyclopropylmethyl-4,5 alpha-epoxymorphinan ([125I]IOXY) after pretreatment with the site-directed acylating agents 2-(p-ethoxybenzyl)-1-diethylaminoethyl-5-isothiocyanatobenzimid iazole -HCl (mu-selective) and N-phenyl-N-[1-(2-(4-isothiocyanato)-phenethyl)-4-piperidinyl]-p ropana mide-HCl (delta-selective) to examine the effect of cocaine exposure on the distribution and density of kappa2 receptors in autopsy studies of human cocaine fatalities. The selective labeling of the kappa2 receptor subtype was demonstrated by competition binding studies, which gave a pharmacological signature (IOXY >/= (+)-bremazocine >> U50,488 >/= U69,593) distinct from either the kappa1 or kappa3 receptor subtypes. Visualization of [125I]IOXY labeling revealed that kappa2 receptors localize to mesocortical and subcortical limbic areas, including the cingulate, entorhinal, insular, and orbitofrontal cortices and the nucleus accumbens and amygdala. The number of kappa2 receptors in the nucleus accumbens and other limbic brain regions from cocaine fatalities was increased twofold as compared with age-matched and drug-free control subjects. Cocaine overdose victims, who experienced paranoia and marked agitation before death, also had elevated densities of kappa2 receptors in the amygdala. These findings demonstrate for the first time that kappa2 receptor numbers are upregulated by cocaine exposure. The molecular adaptation of kappa2 receptor numbers may play a role in the motivational incentive associated with episodes of binge cocaine use and in the dysphoria that follows abrupt cocaine withdrawal.

Alterations in opioid receptor binding in Parkinson's disease patients with levodopa-induced dyskinesias

Levodopa-induced dyskinesias remain a major challenge in the therapeutic management of Parkinson's disease (PD). Their etiology is unknown although dysfunction of striatal opioid transmission has been implicated in experimental models of PD. To determine whether the opioid system is involved in human dyskinetic PD, we measured in vivo opioid receptor binding in PD patients with and without levodopa-induced dyskinesias, using positron emission tomography (PET) and the opioid receptor ligand [11C]diprenorphine. Striatal and thalamic/occipital uptake ratios were calculated using a region of interest (ROI) approach. In addition, we used statistical parametric mapping (SPM) and images reflecting the volume of distribution of [11C]diprenorphine to assess changes in cerebral receptor binding on a voxel-by-voxel basis. By using the ROI approach, we found significantly reduced striatal and thalamic opioid binding in dyskinetic, but not in nondyskinetic, PD patients. The SPM approach confirmed reduced availability in these areas and, in addition, showed decreased cingulate and increased prefrontal opioid receptor binding in the dyskinetic patients. Our findings confirm that altered opioid transmission is part of the pathophysiology of levodopa-induced dyskinesias in PD and support further investigation into the role of opioid agents in the management of these involuntary movements.

Neurochemical architecture of the human striatum

The striatum of the human brain has a highly differentiated neurochemical architecture visible in stains for many of the neurotransmitter-related molecules present in the striatum. The distributions for these chemical markers have never been analyzed comprehensively. We compared the distributions of multiple neurochemical markers in a serial-section analysis of the caudate nucleus, the putamen, and the ventral striatum in normal human brains. The cholinergic system was identified with choline acetyltransferase (ChAT). The organization of the cholinergic fiber system was compared with that of striatal systems expressing immunoreactivity for calbindin D28k, met-enkephalin, substance P, tyrosine hydroxylase, and parvalbumin. Each striatal region analyzed displayed a unique neurochemical organization. In the dorsal caudate nucleus, the distribution of all markers followed the classical striosome/matrix organization as previously reported. In the dorsal putamen, ChAT-staining was less intense, and striosomes were delineated primarily by unstained fiber bundles. In the ventral caudate nucleus/nucleus accumbens region, the boundaries of ChAT-stained regions were not always visible with stains for calbindin, enkephalin, and substance P. The ventral putamen displayed a similar organization, except in its lateral part, where ChAT-poor regions were often found adjacent to, rather than in register with, regions expressing low levels of the other markers (calbindin, enkephalin, substance P, and tyrosine hydroxylase). Our findings suggest that, in addition to the classical striosome-matrix organization visible in the dorsal caudate nucleus and putamen, there is further neurochemical differentiation in a large ventral part of the caudate nucleus and putamen and in the ventral striatum-nucleus accumbens proper. The more complex relationships among the different neurochemical systems in the ventral striatum may reflect the increase in size in the primate of striatal regions associated with association and limbic cortex.

Excitation of type II anterior caudate neurons by stimulation of dopamine D3 receptors

Previous studies have demonstrated that both direct- and indirect-acting dopamine (DA) receptor agonists excite type II neurons in the anterior caudate (CN) by stimulation of DA receptors belonging to the D2 receptor subfamily (D2, D3, D4 receptor subtypes). In the present study, pramipexole, a D3-preferring DA agonist effective in treating Parkinson's disease, excited type II anterior CN neurons. As with other direct-acting agonists, excitation of the CN neurons occurred only at doses above those that silenced DA neurons in the substantia nigra pars compacta (SNPC). Although more potent than pramipexole in inhibiting SNPC cells, PNU-91356A, a D2-preferring agonist, did not excite type II CN cells. The D3-preferring antagonist (+)-AJ76 was weaker than haloperidol, a D2-preferring antagonist, in reversing the effects of amphetamine on firing rates in dopaminergic neurons in both the SNPC and the CN. However, in relationship to its potency in the SNPC, (+)-AJ76 was more potent than haloperidol in the CN. PNU-101387, a selective D4 antagonist, did not alter amphetamine-induced stimulation of type II CN neurons. We conclude that DA agonists may excite type II anterior CN neurons via D3 receptor activation. The stimulation of these neurons may contribute to the anti-parkinsonian effects of pramipexole.

Expression of zinc finger immediate early genes in rat brain after permanent middle cerebral artery occlusion

The prolonged expression of the leucine zipper fos/jun immediate early genes (IEG) has been correlated with neuronal death after cerebral ischemia. In this study, the expression of six zinc finger IEG was examined using in situ hybridization in adult rats after middle cerebral artery occlusion (MCAO) with the suture model. NGFI-A, NGFI-B, NGFI-C, egr-2, egr-3, and Nurr1 mRNA were all induced throughout the ipsilateral cortex at 1 hour to 12 hours after MCAO. The cortical induction for most of the genes was greatest in the anterior cingulate and the anterior cerebral artery (ACA) and middle cerebral artery (MCA) transition zone. All of the zinc finger IEG were induced at 1 hour in all regions of hippocampus. NGFI-A and NGFI-B were induced in ipsilateral thalamus. Within areas of infarction, the basal IEG mRNA expression, and expression of the housekeeping gene cyclophilin A mRNA, decreased below control levels by 12 hours after the ischemia. Immediate early gene expression outside areas of infarction returned to control levels in most brain regions by 24 hours except for egr-3, which continued to be induced in the MCA/ ACA transition zone for 24 hours, and NGFI-A, which continued to be expressed in specific regions of the thalamus for 72 hours. The induction of these IEG in the cortex is likely caused by ischemia-induced cortical spreading depression, with the hippocampal and thalamic IEG induction being caused by activation of efferent cortical pathways to these regions. The prominent induction of NGFI-B, NGFI-C, egr-2, and egr-3 in the anterior cingulate cortex, the ACA/MCA transition zone, and medial striatum could reflect the ischemic regions around MCA infarcts. The prolonged NGFI-A expression observed in thalamus in this study, and in CA1 of hippocampus after global ischemia in the gerbil in a previous study, suggests that the prolonged NGFI-A, expression could be the result of or the cause of the delayed cell death. Prolonged NGFI-A expression, like c-fos and c-jun, seems to provide a marker for slowly dying neurons.

Rapid alteration of tau in oligodendrocytes after focal ischemic injury in the rat: involvement of free radicals

Glial inclusions containing the microtubule-associated protein tau are present in a variety of chronic neurodegenerative conditions. We now report a rapid and time-dependent increase of tau immunoreactivity within oligodendrocytes after focal cerebral ischemia in the rat. The number of tau positive oligodendrocytes in the ipsilateral subcortical white matter increased six- to eightfold by 40 minutes after permanent middle cerebral artery occlusion (MCAO). Tau was detected using antibodies that label both the N- and C-terminal of the protein, suggesting accumulation of full-length protein within these cells. Pretreatment with the spin trap agent alpha-phenyl-tert-butyl-nitrone (PBN)(100mg/kg) reduced the number of tau-positive oligodendrocytes by 55% in the subcortical white matter of the ischemic hemisphere compared with untreated animals at 40 minutes after MCAO. In contrast, pretreatment with glutamate receptor antagonists MK-801 (0.5 mg/kg) or 2,3-dihydroxy-6-nitro-7-sulpfamoyl-benzo(f)quinoxaline (NBQX) (2 x 30 mg/kg), failed to reduce the number of tau-positive oligodendrocytes after 40 minutes of ischemia. The results indicate that oligodendrocytes respond rapidly to an ischemic challenge and that free radical-mediated mechanisms are involved in the cascade leading to increased tau immunoreactivity.

Striatal dopaminergic loss without parkinsonism in a case of corticobasal degeneration

Neurochemical analyses of post-mortem brain from cases of corticobasal degeneration are extremely rare although nearly 100 cases have been reported in the literature. We detail findings of neurotransmitter derangement in the basal ganglia of a case of neuropathologically confirmed corticobasal degeneration, who presented with dementia. The implications of severe neuronal loss in the substantia nigra and extremely low levels of dopamine and its metabolites in the striatum are considered in relation to the absence of an intrinsic extrapyramidal syndrome.

In vivo monitoring of glutathione and cysteine in rat caudate nucleus using microdialysis on-line with capillary zone electrophoresis-laser induced fluorescence detection

A fully-automated method for monitoring thiols in vivo using microdialysis coupled on-line with capillary zone electrophoresis with laser-induced fluorescence detection was developed. Dialysates were derivatized on-line with monobromobimane and automatically transferred to the separation capillary by a flow-gated interface. Analytes were detected on-column using the 2 mW, 354 nm line of a He-Cd laser for excitation. Dialysis probes were perfused at 79 nl/min resulting in relative recoveries of nearly 100%, which allowed quantitative monitoring. On-line detection limits for these analytes were in the 20-40 nM range and the response was linear up to 20 microM. The system was applied to the measurement of glutathione and cysteine in the extracellular space of the caudate nucleus of anesthetized rats. The measured basal concentrations of glutathione and cysteine were 2.0 +/- 0.1 microM and 2.3 +/- 0.3 microM, respectively which agree well with literature values. Increases in glutathione and cysteine were monitored with 180 s temporal resolution during stimulation by infusion of potassium. The average concentration of glutathione and cysteine during stimulation was 3.0 +/- 0.9 and 3.3 +/- 0.5 microM (n = 3), respectively. This system is the first to obtain high relative recoveries and high temporal resolution simultaneously for multiple thiols with microdialysis sampling in the brain.

Four 5-hydroxytryptamine7 (5-HT7) receptor isoforms in human and rat produced by alternative splicing: species differences due to altered intron-exon organization

The serotonin (5-HT) 5-HT7 receptor subtype is thought to mediate a number of physiological effects in mammalian brain and periphery. Previous studies suggested that alternative splicing might contribute to 5-HT7 receptor diversity as well. We now report that alternative splicing in human and rat tissues produces four 5-HT7 receptor isoforms that differ in their predicted C-terminal intracellular tails. Human and rat partial 5-HT7 cDNAs and intronic sequences were identified and compared. In rat tissues, three 5-HT7 isoforms, here called 5-HT7(a), 5-HT7(b), and 5-HT7(c), are found. Rat 5-HT7(a) [448-amino acid (aa)] and 5-HT7(b) (435-aa) forms arise from alternative splice donor sites. A third new isoform found in rat, 5-HT7(c) (470-aa), results from a retained exon cassette. Three 5-HT7 mRNA isoforms were also identified in human tissues, where only one isoform was previously described. Two human isoforms represent 5-HT7(a) and 5-HT7(b) forms (445- and 432-aa), but the third form does not correspond to 5-HT7(c). Instead, it constitutes a distinct isoform, 5-HT7(d) (479-aa), resulting from retention of a separate exon cassette. 5-HT7(d) transcripts are not present in rat because the 5-HT7(d)-specifying exon is absent from the rat 5-HT7 gene. A frame-shifting homologue of the rat 5-HT7(c)-Specifying exon is present in the human gene but is not used in the human tissues examined. Tissue-specific splicing differences are present in human between brain and spleen. These studies suggest that alternative splicing may contribute to diversity of 5-HT7 receptor action and that the human and rat repertoires of 5-HT7 splice variants are substantially different.

Immunochemical analysis of dopamine transporter protein in Parkinson's disease

The plasma membrane dopamine transporter (DAT) is considered to be a reliable marker of presynaptic dopaminergic terminal loss. Previous in vivo imaging and postmortem binding studies have detected a loss in striatal DAT binding in Parkinson's diseased (PD) brain; however, these techniques have poor spatial resolution and may suffer from nonspecific binding of some ligands. In this study, we use novel highly specific monoclonal antibodies to distinct epitopes of human DAT to quantify and localize the protein. Western blot analysis revealed marked reductions in DAT immunoreactivity in putamen, caudate, and nucleus accumbens of PD brain compared with control cases, and the reductions were significantly correlated to disease duration. Immunohistochemistry revealed DAT-immunoreactive fibers and puncta that were dense throughout the striatum of control brains but that were drastically reduced in putamen of PD brains. Caudate from PD brains showed a significant degree of sparing along the border of the ventricle, and the nucleus accumbens was relatively preserved. An unexpected finding was that discrete islands of DAT immunoreactivity were preserved within the matrix of PD putamen. Thus, immunological analysis of DAT protein provides novel and sensitive means for localizing and quantifying DAT protein in PD and other neurological disorders involving dopaminergic systems.

Quantification of neuroreceptors in the living human brain: IV. Effect of aging and elevations of D2-like receptors in schizophrenia and bipolar illness

In a previous study of 10 drug-naive schizophrenic patients, the density of D2 dopamine receptors was found to be elevated in the caudate nucleus. The study raised questions about the influence of the age of the patients, the relationship of receptor density to psychosis, and the accuracy of the method used to obtain this evidence. Using positron emission tomography and constrained analysis of the brain uptake of the radioligand N-[11C]methyl-spiperone ([11C]NMSP), we tested four questions: Were the assumptions underlying the quantitation valid? Is there an age decline of the density of D2-like dopamine receptors in drug-naive schizophrenia and bipolar illness? If so, is it different from that observed in normal aging? Are D2-like dopamine receptors elevated at any age in either drug-naive schizophrenic or psychotic bipolar illness patients? NMSP and haloperidol partition volumes and plasma protein fractions were not significantly different among patient groups and normal volunteers. The model-derived assay of radioligand metabolites in plasma was confirmed by high-performance liquid chromatography in the patient groups. D2-like dopamine receptors declined with age, and the slope did not differ significantly between the schizophrenic patients, bipolar affective illness patients, and normal controls. Taking the effect of age into account, increases in D2 dopamine receptor density were found in seven psychotic patients with bipolar affective illness compared with seven nonpsychotic patients and 24 control subjects as well as in 22 drug-naive schizophrenic patients compared with the 24 control subjects.

Immuno-localization of serotonin 5-HT6 receptor-like material in the rat central nervous system

In order to map the recently cloned serotonin 5-HT6 receptor in the rat brain and spinal cord, polyclonal antibodies were raised against a synthetic octadecapeptide corresponding to a specific portion (Leu398-Val415) of the C-terminal domain of this receptor. Antibodies were detected by enzyme-linked immunosorbent assay as soon as one month after the first injection to rabbits of the peptide coupled to keyhole limpet hemocyanin. Immunoautoradiographic experiments with antibodies affinity-purified on Affi-Gel coupled to the peptide antigen showed that 5-HT6-like immunoreactive material was abundant in the olfactory tubercle (plexiform layer), cerebral cortex (frontal and entorhinal areas), nucleus accumbens, striatum, hippocampus (strata oriens and radiatum of the CA1 area, molecular layer of the dentate gyrus) and the molecular layer of the cerebellum. A specific immunolabeling, but at moderate intensity, was also observed in the thalamus, substantia nigra, superficial layer of the superior colliculus, motor trigeminal nucleus and facial nucleus. In contrast, no 5-HT6-like immunoreactive material was found in white matter areas. As the regional distribution of 5-HT6 receptor-like immunoreactivity matched generally that previously found for the 5-HT6 receptor mRNA, one could infer that this receptor protein is addressed in the vicinity of its synthesis site, i.e. on somas and/or dendrites. Indeed, immunohistochemistry at the light and electron microscope level showed that 5-HT6-like immunoreactivity was associated with dendritic processes in both the striatum and the dentate gyrus of the hippocampus. The relative abundance of 5-HT6 receptor-like immunoreactivity in extrapyramidal and limbic areas suggests that 5-HT6 receptors may participate in the serotoninergic control of motor function and mood-dependent behavior, respectively.

Demonstration of a new dopamine-containing cell group in the primate rostral telencephalon

The presence of dopaminergic neurons in the rostral forebrain has long been uncertain though the existence of tyrosine-hydroxylase (TH)-containing cells has been known in the region. Using an antibody to dopamine (DA), we demonstrated neurons immunoreactive (ir) to DA in the rostroventral striatum of the Japanese monkey (Macaca fuscata). The DA-ir cells were found at the ventral margin of the rostral part of the caudate nucleus, at the ventral margin of the rostral part of the nucleus accumbens, in the olfactory tubercle, and along the lateral margin of the putamen. These cells were intensely stained, small in size, and fusiform or ovoid in shape, and had one or two short processes. DA-ir cells were far smaller in number than TH-ir ones. The primates may possess a unique dopaminergic system in the rostral telencephalon.

Iodine-123-IPT SPECT imaging of CNS dopamine transporters: nonlinear effects of normal aging on striatal uptake values

Iodine-123-labeled IPT (N-(3-iodopropen-2-yl)-2 beta-carbomethoxy-3 beta-(4-chlorophenyl)tropane) is an analog of cocaine that selectively binds the presynaptic dopamine transporter. This study sought to characterize changes in the striatal uptake of IPT with normal aging.

METHODS

The sample included 18 healthy human volunteers. Their ages ranged from 19 to 67 yr. Dynamic SPECT scans of the brain were acquired with about 185 MBq (5 mCi) of IPT on a triple-headed camera. The images were reconstructed with a three-dimensional restorative filter and corrected for attenuation. The mean concentration of radioactivity [microCi/ml] was measured in the head of the caudate and body of the putamen. The remainder of the supratentorial brain was used as a reference.

RESULTS

The specific uptake of IPT was higher in the caudate than in the putamen of each subject. It decreased significantly with age in both regions. The mean specific uptake in seven volunteers who were less than 30 yr old was 17.6 +/- 4.9 in the caudate and 13.3 +/- 4.0 in the putamen, compared to only 11.97 +/- 3.30 and 7.8 +/- 2.68, respectively, in the six middle-aged subjects (t = 2.53 and 2.90, df = 11, p = 0.027 and 0.014). However, there were no significant differences between the six middle-aged subjects and the five volunteers who were older than 60 yr, whose respective means were 9.0 +/- 1.6 and 6.2 +/- 0.7 (t = 1.83 and 1.28, df = 9, p = 0.10 and 0.23). The results were supported by regression analysis, which indicated that changes with age were not optimally described as a linear function when compared to several nonlinear alternatives. The fit improved when the models accounted for relatively rapid rates of decline during young adulthood, followed by less rapid decline throughout middle age.

CONCLUSION

The results are consistent with the findings from previous studies that have shown that the specific uptake values for radiopharmaceuticals that bind the dopamine transporter decline with advancing age. However, results of this study suggest that the effects of aging may be nonlinear and regionally distinct.

Comparative dopamine-acetylcholine interactions in the ventral and dorsal striatum of rabbit and rat brain

The dopamine (DA)-acetylcholine (ACh) interactions were investigated in dorsal (nucleus caudate, NC) and ventral (olfactory tubercle, OT) striatal regions, of rats and rabbits. Both regions receive a dense dopaminergic innervation and have high ACh concentrations. Brain slices of NC and OT from both animal species were prelabeled with [3H]choline and superfused. In rat and rabbit OT and NC, higher ACh release per pulse was elicited by lower than higher stimulation frequencies; in addition, rabbit tissues released a greater fraction of tissue [3H]transmitter than rat tissues. Blockade of D2 DA-receptors with sulpiride (1 microM), did not modify ACh release in OT and NC of rats and rabbits; suggesting that the lower ACh release observed in rat tissues is not due to an inhibitory dopaminergic tone on cholinergic neurons. Apomorphine (APO), a D2 DA-receptor agonist, inhibited in a concentration-dependent manner the evoked release of ACh from rat and rabbit NC (maximal inhibition = 90%). In rabbit OT, maximal inhibition induced by APO was 49 +/- 2% and in the rat OT, it was 23 +/- 1%. Sulpiride antagonized APO-induced inhibition of ACh release from rat and rabbit NC; however, it failed to prevent APO-induced inhibition in rat OT, and in the rabbit OT reduced it from 47% to 20 +/- 5%. These results indicate differences in the wiring of DA and cholinergic neurons and terminals in dorsal and ventral striatal structures, as well as between rat and rabbit tissues. Cholinergic ventral striatal structures may not receive a direct DA input, and afferent cholinergic nerve terminals (rather than interneurons) predominate in the ventral striatum.

Quantitative in vivo monitoring of primary amines in rat caudate nucleus using microdialysis coupled by a flow-gated interface to capillary electrophoresis with laser-induced fluorescence detection

A method for monitoring primary amines in vivo using microdialysis coupled on-line with capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence detection was explored. Dialysates were derivatized on-line with o-phthaldialdehyde/beta-mercaptoethanol and automatically transferred to a separation capillary by a flow-gated interface. Analytes were detected on-column using the 2 mW, 354 nm line of a He-Cd laser for excitation. Dialysis probes were perfused at 79 nL/min, resulting in relative recoveries of nearly 100%, which allowed quantitative monitoring. On-line detection limits were in the 20-50 nM range, and the response was linear up to 50 microM. Temporal resolution was between 45 s and 3 min and was limited by separation time or broadening of sample zones during transfer to the separation capillary, depending on the operational parameters. The system was applied to measurement of primary amines in the caudate nucleus of anesthetized rats. Using CZE for separation, it was possible to resolve and monitor several compounds, including aspartate and glutamate. The measured basal concentrations of aspartate and glutamate were 1.2 +/- 0.1 and 5.0 +/- 0.4 microM, respectively, which agrees well with literature values. Increases in in vivo aspartate and glutamate were monitored with 90 s temporal resolution during K+ depolarization using dialysis flow rates of 79 nL/min; however, temporal resolution of 45 s was possible at the expense of lower relative recovery if the dialysis flow rate was increased to 155 nL/min. The use of MEKC as the separation mode significantly increased the number of compounds that could be resolved and detected. Using MEKC to separate the dialysate samples allowed aspartate, glutamate, isoleucine, leucine, lysine, methionine, phenylalanine, taurine, tyrosine, and valine to be resolved and detected. The basal concentrations for these compounds using MEKC were 1.9 +/- 0.2, 4.1 +/- 0.2, 4.6 +/- 0.7, 2.6 +/- 0.3, 5.4 +/- 0.4, 1.8 +/- 0.2, 2.0 +/- 0.2, 11.3 +/- 1.3, 3.3 +/- 0.9, and 5.3 +/- 0.3 microM, respectively. The concentrations of these primary amines in the striatum were monitored after K+ depolarization with 3 min temporal resolution. This is the first microdialysis system to generate high relative recoveries and good temporal resolution simultaneously for multiple neurotransmitters.

Distribution of radioiodinated recombinant human nerve growth factor in primate brain following intracerebroventricular infusion

The distribution of radioiodinated recombinant human nerve growth factor ([125I]rhNGF) was evaluated in adult cynomolgus monkeys following unilateral intracerebroventricular (icv) administration. Animals were cannulated into the right ventricle and recovered for 7 days. Monkeys were infused with 1.2 micrograms of [125I]rhNGF or [125I]rhNGF with a 140-fold excess of rhNGF. Twenty-four hours after infusion, animals were anesthetized and transcardially perfused with an aldehyde fixative. Coronal brain sections were processed for quantitative film autoradiography or for choline-acetyltransferase immunohistochemistry and then emulsion dipped. Specific radiolabel was distributed bilaterally and, with equal density, throughout the basal forebrain and was colocalized with choline acetyltransferase-positive neurons. Specific labeling was also present in the superficial ventral cortex. Nonspecific binding was observed surrounding the ventricles and lining blood vessels. These results demonstrate that unilateral icv infusion is an effective approach for delivering NGF to basal forebrain cholinergic neurons in primates and represents a viable drug delivery strategy for the therapeutic use of NGF in Alzheimer's Disease.