Striatum Of Monkeys Research Articles

Protective Effects of Minocycline on the Reduction of Dopamine Transporters in the Striatum After Administration of Methamphetamine: A Positron Emission Tomography Study in Conscious Monkeys

Positron emission tomography (PET) studies of methamphetamine (METH) abusers suggest that psychotic symptoms of METH abusers may be attributable to the reduction of dopamine transporters (DAT) in the human brain. However, there are currently no particular pharmacological treatments for the wide range of symptoms associated with METH abuse. Using a PET study in conscious monkeys, we investigated whether the second generation antibiotic minocycline could protect against the reduction of DAT in monkeys treated with METH (2 mg/kg x 3, 3-hour intervals). Pretreatment and subsequent administration of minocycline significantly attenuated the reduction of DAT in the striatum of monkeys treated with METH. Furthermore, posttreatment and subsequent administration of minocycline also significantly attenuated the reduction of DAT. In contrast, repeated administration of minocycline alone did not alter the density of DAT in the striatum of monkeys treated with METH. Our findings suggest that minocycline protects against METH-induced neurotoxicity in the monkey brain. Therefore, minocycline is likely to be a promising therapeutic agent for the treatment of several symptoms associated with METH use in humans.

Influence of Spatial Information on Responses of Tonically Active Neurons in the Monkey Striatum

Previous studies have demonstrated that tonically active neurons (TANs) in the primate striatum play an important role in the detection of rewarding events. However, the influence of the spatial features of stimuli or actions required to obtain reward remains unclear. Here, we examined the activity of TANs in the striatum of monkeys trained to make spatially directed movements elicited by visual stimuli presented ipsilaterally or contralaterally to the moving arm. Among 181 neurons responding to the trigger stimulus, 127 (70%) were nonselective for stimulus location and 54 (30%) responded to only one location of the stimulus. Most of the selective responses (63%) occurred when the stimulus was presented contralaterally to the moving arm. To examine whether TAN responses are related to the location of the stimulus or to the direction of the movement, we tested a subset of the trigger-responsive neurons (n = 44) in a condition that elicited reaching toward or away from the stimulus. By comparing TAN activity between the two conditions, we found that half of the responses can be interpreted as being related to the location of the stimulus, one quarter to the direction of movement, and one quarter to the context in which stimulus-movement combination occurs. These results demonstrate that TANs are not limited to motivational processing, but may play a role in the processing of spatial attributes of stimulus and/or movement as well. These response properties suggest that TANs are involved in the flexible shifting of motor responses during spatially directed behavior.

Effects of N‐acetylcysteine on the behavioral‐stimulant, reinforcing, and neurochemical effects of cocaine in the squirrel monkey

The stimulant and reinforcing effects of cocaine have been attributed largely to its actions at the dopamine transporter. However, other neurotransmitters can modulate cocaine-induced increases in dopamine. In rodents, glutamate receptor function in the striatum and nucleus accumbens plays a major role in the behavioral pharmacology of cocaine. Withdrawal from repeated exposure to cocaine results in decreased levels of glutamate by decreased cystine-glutamate transporter function. Systemic administration of N-acetylcysteine (NAC), which restores cystine-glutamate function, normalized glutamate levels. In the present studies, we examined the stimulant effects of cocaine in squirrel monkeys using a fixed-interval schedule of reinforcement. Systemic administration of cocaine increased extracellular dopamine levels in the striatum of squirrel monkeys, as measured by in vivo microdialysis. Pretreatment with NAC did not alter the stimulant effects of cocaine, but dose-dependently decreased cocaine-induced increases in dopamine in the striatum. Self-administration behavior maintained by a second-order schedule of i.v. cocaine delivery in squirrel monkeys was not altered by pretreatment with NAC. Hence, drug interactions in neurochemistry were not reflected in behavioral measures. Supported by USPHS grants DA00517, DA15902, DA13326, DA12514 and RR00165.

Selective enhancement of associative learning by microstimulation of the anterior caudate

Primates have the remarkable ability to rapidly adjust or modify associations between visual cues and specific motor responses. Whereas little is known as to how such adjustments in behavioral policy are implemented, recent learning models suggest that the anterior striatum is optimally positioned to have a role in this process. We recorded from single units and delivered microstimulation in the striatum of rhesus monkeys performing an associative learning task. Caudate activity during reinforcement was closely correlated with the rate of learning and peaked during the steepest portion of the learning curve when new associations were being acquired. Moreover, delivering microstimulation in the caudate during the reinforcement period significantly increased the rate of learning without altering the monkeys' ultimate performance. These findings suggest that the caudate is responsible for implementing selective adjustments to the 'associative weights' between sensory cues and motor responses during learning, thus enhancing the likelihood of selecting profitable actions.

Synaptic microcircuitry of tyrosine hydroxylase‐containing neurons and terminals in the striatum of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐treated monkeys

A population of tyrosine hydroxylase (TH)-containing neurons that is up-regulated after lesion of the nigrostriatal dopaminergic pathway has been described in the primate striatum. The goal of this study was to examine the morphology, synaptology, and chemical phenotype of these neurons and TH-immunoreactive (-ir) terminals in the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated rhesus monkeys. TH-ir perikarya were small (10-12 microm), displayed nuclear invaginations, and received very few synaptic inputs. On the other hand, TH-containing dendrites were typically large in diameter (>1.0 microm) and received scarce synaptic innervation from putative excitatory and inhibitory terminals forming asymmetric and symmetric synapses, respectively. More than 70% of TH-positive intrastriatal cell bodies were found in the caudate nucleus and the precommissural putamen, considered as the associative functional territories of the primate striatum. Under 10% of these cells displayed calretinin immunoreactivity. TH-ir terminals rarely formed clear synaptic contacts, except for a few that established asymmetric axodendritic synapses. Almost two-thirds of TH-containing boutons displayed gamma-aminobutyric acid (GABA) immunoreactivity in the striatum of parkinsonian monkeys, whereas under 5% did so in the normal striatum. These findings provide strong support for the existence of a population of putative catecholaminergic interneurons in the associative territory of the striatum in parkinsonian monkeys. Their sparse synaptic innervation raises interesting issues regarding synaptic and nonsynaptic mechanisms involved in the regulation and integration of these neurons in the striatal microcircuitry. Finally, the coexpression of GABA in TH-positive terminals in the striatum of dopamine-depleted monkeys suggests dramatic neurochemical changes in the catecholaminergic modulation of striatal activity in Parkinson's disease.

New striatal dopamine neurons in MPTP-treated macaques result from a phenotypic shift and not neurogenesis

We investigated whether there is neurogenesis in the striatum of aged monkeys, and whether dopamine (DA) depletion induces the genesis of new DA neurons in this structure. Six aged macaques received repeated intraperitoneal injections of bromodeoxyuridine (BrdU) over a 3 week period to label dividing cells. Three macaques were injected in parallel with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to decrease dopaminergic innervation of the striatum. The brains were analysed 3 weeks after the last BrdU injection. In MPTP-treated aged macaques, the number of tyrosine hydroxylase (TH) immunoreactive (ir) striatal neurons increased 2.3-fold compared with controls. These TH-ir striatal cells did not express dopamine beta hydroxylase (DBH) but the dopamine transporter (DAT), suggesting that they are functional DA neurons. They were also negative for calbindin (CB), neuropeptide Y (NPY) and parvalbumin (PV), and a small proportion expressed calretinin (CR). This suggests that these cells stained for TH are interneurons. All these cells also co-expressed glutamic acid decarboxylase (GAD). They thus resemble the small, aspiny, GABAergic interneurons. None of the BrdU-labelled cells in the striatum expressed the neuronal markers neuronal nuclei (NeuN), or GAD or TH, and none of TH-ir cells incorporated BrdU. These data indicate that neurogenesis did not occur in the striatum of aged macaques. The new striatal TH-ir neurons observed after DA depletion was therefore derived from pre-existing GABAergic interneurons. Understanding of the molecular signals mediating this phenotypic shift might help in developing novel and elegant strategies for a cell-based therapy for Parkinson's disease that would avoid many of the drawbacks of cell transplantation.

Iron accumulation in the striatum predicts aging-related decline in motor function in rhesus monkeys

Changes in the nigrostriatal system may be involved with the motor abnormalities seen in aging. These perturbations include alterations in dopamine (DA) release, regulation and transport in the striatum and substantia nigra, striatal atrophy and elevated iron levels in the basal ganglia. However, the relative contribution of these changes to the motor deficits seen in aging is unclear. Thus, using the rhesus monkey as a model, the present study was designed to examine several of these key alterations in the basal ganglia in order to help elucidate the mechanisms contributing to age-related motor decline. First, 32 female rhesus monkeys ranging from 4 to 32 years old were evaluated for their motor capabilities using an automated hand-retrieval task. Second, non-invasive MRI methods were used to estimate brain composition and to indirectly measure relative iron content in the striatum and substantia nigra. Third, in vivo microdialysis was used to evaluate basal and stimulus-evoked levels of DA and its metabolites in the striatum and substantia nigra of the same monkeys. Our results demonstrated significant decreases in motor performance, decreases in striatal DA release, and increases in striatal iron levels in rhesus monkeys as they age from young adulthood. A comprehensive statistical analysis relating age, motor performance, DA release, and iron content indicated that the best predictor of decreases in motor ability, above and beyond levels of performance that could be explained by age alone, was iron accumulation in the striatum. This suggests that striatal iron levels may be a biomarker of motor dysfunction in aging; and as such, can be monitored non-invasively by longitudinal brain MRI scans. The results also suggest that treatments aimed at reducing accumulation of excess iron in the striatum during normal aging may have beneficial effects on age-related deterioration of motor performance.

242. Neuronal Specificity of α-Synuclein Toxicity and the Effect of Parkin Co-Expression in Primates

Top of pageAbstract Recombinant adeno-associated viral (rAAV) vector-mediated overexpression of |[alpha]|-synuclein (|[alpha]|Syn) protein has been shown to cause neurodegeneration of nigrostriatal dopaminergic pathway in rodents and primates. Using the serotype-2 rAAV vectors, we have recently reported the protective effect of Parkin on the |[alpha]|Syn-induced nigral dopaminergic neurodegeneration in a rat model. Here we investigated the neuronal specificity of |[alpha]|Syn toxicity and the effect of Parkin co-expression in a primate model. The serotype-1 rAAV (rAAV1) carrying |[alpha]|Syn cDNA (rAAV1-|[alpha]|Syn), and a cocktail of rAAV1-|[alpha]|Syn and rAAV1 carrying parkin cDNA (rAAV1-parkin) were unilaterally injected into the striatum of macaque monkeys, resulting in protein expression in striatonigral GABAergic and nigrostriatal dopaminergic neurons. The injection of rAAV1-|[alpha]|Syn alone caused a decrease of tyrosine hydroxylase- immunoreactivity in the striatum when compared to the contralateral side injected with a cocktail of rAAV1-|[alpha]|Syn and rAAV1-parkin. The immunostaining of the striatonigral GABAergic neurons showed no differences on each side. In the presence of overexpressed Parkin, |[alpha]|Syn protein seemed to be less accumulated and/or phosphorylated at Ser129 residue in GABAergic neurons. These results suggest that the toxicity of accumulated |[alpha]|Syn is not expressed in non- dopaminergic neurons but the |[alpha]|Syn-ablating effect of Parkin is exerted in all neurons introduced in primates.

Cellular and subcellular localization of PDE10A, a striatum-enriched phosphodiesterase

PDE10A is a recently identified phosphodiesterase that is highly expressed by the GABAergic medium spiny projection neurons of the mammalian striatum. Inhibition of PDE10A results in striatal activation and behavioral suppression, suggesting that PDE10A inhibitors represent a novel class of antipsychotic agents. In the present studies we further elucidate the localization of this enzyme in striatum of rat and cynomolgus monkey. We find by confocal microscopy that PDE10A-like immunoreactivity is excluded from each class of striatal interneuron. Thus, the enzyme is restricted to the medium spiny neurons. Subcellular fractionation indicates that PDE10A is primarily membrane bound. The protein is present in the synaptosomal fraction but is separated from the postsynaptic density upon solubilization with 0.4% Triton X-100. Immuno-electron microscopy of striatum confirms that PDE10A is most often associated with membranes in dendrites and spines. Immuno-gold particles are observed on the edge of the postsynaptic density but not within this structure. Our studies indicate that PDE10A is associated with post-synaptic membranes of the medium spiny neurons, suggesting that the specialized compartmentation of PDE10A enables the regulation of intracellular signaling from glutamatergic and dopaminergic inputs to these neurons.

Effect of age on markers for monoaminergic neurons of normal and MPTP-lesioned rhesus monkeys: A multi-tracer PET study

The binding of three tracers for monoaminergic terminals was mapped in the brain of healthy young ( N = 6) and healthy old rhesus monkeys ( N = 4), aged monkeys with mild unilateral intracarotid MPTP lesions ( N = 3), and monkeys of intermediate age with severe systemic MPTP lesions ( N = 6). The ligand for monoaminergic vesicles (+)-[ 11C]dihydrotetrabenazine (+DTBZ) had a mean binding potential ( pB) of 1.4 in striatum of the healthy young monkeys, which was reduced by 20% in putamen of the old monkeys. The catecholamine transporter ligand (+)-[ 11C]methylphenidate (+MP) had a mean pB of 1.3 in striatum of the young monkeys, which was reduced by 40% in caudate and putamen of the old monkeys. The DOPA decarboxylase substrate [ 18F]fluoro- l-DOPA (FDOPA) had a mean decarboxylation coefficient ( k 3 S) of 0.4 h −1 in striatum of the young group, and was not significantly reduced in the aged group. Of the three ligands, only +DTBZ pB was significantly reduced in striatum of the small group of animals with mild unilateral lesions. In the group with systemic MPTP lesions, the mean reduction of the binding of the three ligands was 80% in the caudate and putamen. However, the decline in +MP pB in the ventral striatum (−75%) exceeded the declines of +DTBZ pB and FDOPA k 3 S in that region (−65%), suggesting that compensatory down-modulation of uptake sites may occur in the striatal regions with the least dopamine depletion. Binding of all three ligands was reduced by 50% in the anterior cingulate cortex and in the thalamus, suggesting toxicity of MPTP for extrastriatal catecholamine innervations. +DTBZ binding in the hypothalamus, presumably mainly in serotonin fibers, was unaffected by systemic MPTP treatment. Of the three tracers, +DTBZ was most sensitive for detecting MPTP-induced dopamine depletion in monkey striatum.

Chemical characterization of newly generated neurons in the striatum of adult primates

We recently demonstrated the existence of neurogenesis in the striatum of adult monkeys, but the number of striatal neurons generated under normal conditions was too small to establish their chemical phenotype. We therefore used brain-derived neurotrophic factor (BDNF), which promotes neuronal differentiation and survival and induces striatal neurogenesis in rodents, in an attempt to increase the number of newborn neurons in monkey striatum and facilitate their chemical characterization. An adenoviral vector (AdBDNF), encoding the human BDNF cDNA under the control of a strong promoter, was injected into the lateral ventricles (LVs) of adult squirrel monkeys, which were then treated with bromodeoxyuridine (BrdU). Two weeks after viral injection, numerous BrdU-positive cells were found within the striatum and many expressed microtubule-associated protein 2 (MAP-2) and neuronal nuclear protein (NeuN), two markers of mature neurons. Newborn neurons also expressed glutamic acid decarboxylase (GAD(65/67)), calbindin (CB) and dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32), three markers of striatal projection neurons. We found no BrdU-positive neurons displaying the phenotype of striatal interneurons. Numerous BrdU-positive cells located near the subventricular zone (SVZ) coexpressed the migrating neuroblast markers polysialylated neural cell adhesion (PSA-NCAM) and doublecortin (DCX), suggesting that precursor cells could migrate from LVs to striatal parenchyma and develop a neuronal phenotype once they reach the striatum. However, many pairs of BrdU-positive nuclei were observed in the striatal parenchyma, suggesting that newborn neurons could also arise from resident progenitor cells. The present study demonstrates that a single injection of AdBDNF increases the number of newborn neurons into adult primate striatum and that newborn striatal neurons exhibit the chemical phenotype of medium-spiny projection neurons, which are specifically targeted in Huntington's disease.

Neuron Activity in the Monkey Striatum of Identifies Integration Sequential Actions into Functional Blocks

Spike activity in monkey striatum (putamen) neurons was recorded during the performance of a complex multistep operant task. Tonic responses propagating beyond a single action were recorded, along with phasic responses seen within a given action. The tonic type of response was recorded in 132 of 148 cells. Only 11 of these neurons showed exclusively this type of activity. The beginnings and ends of tonic responses were generally associated with key moments in the behavior, corresponding to the triggering and completion of immediate aims during the performance of the behavioral program as a whole. These results provide evidence that the role of the striatum is not limited to controlling single sequentially performed actions, but spreads to the whole structure of a behavioral act.

In vivo comparison of the reinforcing and dopamine transporter effects of local anesthetics in rhesus monkeys

Dopaminergic mechanisms are thought to play a central role in the reinforcing effects of cocaine. Similar to cocaine, other local anesthetics bind to the dopamine transporter (DAT) and inhibit DA uptake in rodent and monkey brain. Additionally, local anesthetics are self-administered in rhesus monkeys, indicative of abuse liability. The present study examined the reinforcing and DAT effects of the local anesthetics dimethocaine, procaine and cocaine using in vivo techniques. Monkeys were trained to respond under a second-order schedule for i.v. cocaine administration (0.10 or 0.30 mg/kg/infusion). When responding was stable, dimethocaine (0.030-1.7 mg/kg/ infusion) or procaine (0.10-10 mg/kg/ infusion) was substituted for the cocaine training dose. Dimethocaine administration produced higher response rates compared with that of procaine, and was a more potent reinforcer. Drug effects on behavior were related to DAT occupancy in monkey striatum during neuroimaging with positron emission tomography (PET). DAT occupancy was determined by displacement of 8-(2-[(18)F]fluroethyl)2beta-carbomethoxy-3beta-(4-chlorophenyl)nortropane (FECNT). DAT occupancy was between 66 and 82% and <10-41% for doses of dimethocaine and procaine that maintained maximum response rates, respectively. Finally, in vivo microdialysis in awake subjects determined drug-induced changes in extracellular DA in the caudate nucleus. There was close correspondence between peak increases in DA and DAT occupancy. Overall, reinforcing effects were consistent with DAT effects determined with in vivo techniques. The results further support a role for the DAT in the abuse liability of local anesthetics.

Enhanced proliferation of progenitor cells in the subventricular zone and limited neuronal production in the striatum and neocortex of adult macaque monkeys after global cerebral ischemia

Cerebral ischemia in adult rodent models increases the proliferation of endogenous neural progenitor cells residing in the subventricular zone along the anterior horn of the lateral ventricle (SVZ a) and induces neurogenesis in the postischemic striatum and cortex. Whether the adult primate brain preserves a similar ability in response to an ischemic insult is uncertain. We used the DNA synthesis indicator bromodeoxyuridine (BrdU) to label newly generated cells in adult macaque monkeys and show here that the proliferation of cells with a progenitor phenotype (double positive for BrdU and the markers Musashi 1, Nestin, and beta III-tubulin) in SVZ a increased during the second week after a 20-min transient global brain ischemia. Subsequent progenitor migration seemed restricted to the rostral migratory stream toward the olfactory bulb and ischemia increased the proportion of adult-generated cells retaining their location in SVZ a with a progenitor phenotype. Despite the lack of evidence for progenitor cell migration toward the postischemic striatum or prefrontal neocortex, a small but sustained proportion of BrdU-labeled cells expressed features of postmitotic neurons (positive for the protein Neu N and the transcription factors Tbr 1 and Islet 1) in these two regions for at least 79 days after ischemia. Taken together, our data suggest an enhanced neurogenic response in the adult primate telencephalon after a cerebral ischemic insult.

Variants of the primate vesicular monoamine transporter-2

The vesicular monoamine transporter-2 (VMAT2) sequesters monoamine neurotransmitters into vesicles and prevents neurotoxicity. Human or monkey striatum generated three VMAT2 immunoreactive proteins of ∼75 kDa, ∼52–55 kDa, and ∼45 kDa. The ∼55-kDa band is considered the unglycosylated native protein. Deglycosylation of the VMAT2 from striatum or human VMAT2 expressed in HEK293 cells yielded a ∼45-kDa, but not a 55-kDa immunoreactive band. We investigated this apparent mismatch between observed molecular size and predicted size.

942. Evaluation of Short (8 Weeks) and Long-Term (3 and 5 Years) Gene Transfer Following Brain Delivery of AAV-AADC Vector in Parkinsonian Monkeys

Parkinson's disease (PD) is well|[ndash]|defined brain disorder in which slow degeneration of nigrostriatal dopaminergic neurons in the pars compacta of the substantia nigra, results in neurological signs. Since dopamine cannot cross the blood|[ndash]|brain barrier (BBB), the current treatment for PD is a replacement strategy in which the dopamine precursor, L|[ndash]|dopa that crosses the BBB, is given orally several times a day. However, L|[ndash]|dopa efficacy decreases as the neurodegeneration of the dopaminergic innervation of the striatum progresses. Thus, patients are obliged to take higher doses of the drug, a process that leads to considerable fluctuations in L|[ndash]|dopa levels and a gradual decline of the therapeutic benefits. We have demonstrated that the delivery of AADC enzyme to the striatum of parkinsonian monkeys by means of adeno|[ndash]|associated viral vector|[ndash]|mediated AADC gene transfer (AAV-AADC) increases the efficiency of L|[ndash]|dopa conversion to dopamine. This approach improved motor behavioral of the parkinsonian monkeys in response to low otherwise sub|[ndash]|clinical doses of L|[ndash]|dopa. In the present study we used immunohistochemistry, stereology, quantitative PCR and positron emission tomography (PET) to quantify and compare the efficiency of gene transfer and distribution of AAV|[ndash]|AADC, 8 weeks, 3 years and 5 years after gene transfer. Two cohorts of hemi|[ndash]|parkinsonian monkeys received the same dose of AAV|[ndash]|AADC into the MPTP|[ndash]|lesioned hemisphere. Each monkey was infused by convection|[ndash]|enhanced delivery with AAV-AADC (2 |[times]| 1012 vg/ml; 30 |[mu]|l/site) at a total of 6 sites: 2 in the caudate and 4 in the putamen. We used immunochemical staining with anti|[ndash]|AADC antibodies to measure expression of AADC at 8 weeks and 3 years after gene transfer, and related this expression to the number of copies of vector DNA at each time point by quantitative PCR analysis. We demonstrated that gene transfer of AAV|[ndash]|AADC was strong and widespread at both 8 weeks and 3 years post|[ndash]|surgery. Interestingly, we observed a significant increase in the number of positive neurons in the striatum at 3 years compared to 8 weeks, suggesting perhaps that further transduction takes place many weeks after the gene transfer surgery. Furthermore, in a separate cohort of monkeys treated identically to those used for tissue analysis, PET scanning with the AADC|[ndash]|specific tracer FMT demonstrated continued stable expression for more than 5 years. This is to our knowledge the longest documented persistence of AAV|[ndash]|mediated gene transfer. In conclusion, we have shown that (i) AAV|[ndash]|AADC drives widespread and persistent expression of AADC in the striatum, and (ii) distribution of AADC immunoreactive cells is surprisingly more widespread and homogeneous 3 years after gene transfer.

Adeno‐associated virus‐mediated gene transfer of human aromatic l‐amino acid decarboxylase protects mixed striatal primary cultures from l‐DOPA toxicity

Although L-DOPA is the drug of choice for Parkinson's disease, prolonged L-DOPA therapy results in decreased drug effectiveness and the appearance of motor complications. This may be due in part to the progressive loss of the enzyme, aromatic L-amino acid decarboxylase (AADC). We have developed an adeno-associated virus vector (AAV-hAADC) that contains human AADC cDNA under the control of the cytomegalovirus promoter. Infusion of this vector into the striatum of parkinsonian rats and monkeys improves L-DOPA responsiveness by improving AADC-mediated conversion of L-DOPA to dopamine. This is now the basis of a proposed therapy for advanced Parkinson's disease. A key concern has been that over-production of dopamine in striatal neurons could cause dopamine toxicity. To investigate this possibility in a controlled system, mixed striatal primary rat neuronal cultures were prepared. Exposure of cultures to high concentrations of L-DOPA induced the following changes: cell death in nigral and striatal neurons, aggregation of neurofilaments and focal axonal swellings, abnormal expression of DARPP-32, and activation of astroglia and microglial cells. Transduction of cultures with AAV-hAADC resulted in efficient and sustained neuronal expression of the AADC protein and prevented all the L-DOPA-induced toxicities. The protective effects were due primarily to AADC-dependent conversion of L-DOPA to dopamine and an increase in induction of vesicular monoamine transporter resulting in dopamine storage in cultured cells. These results suggest a neuroprotective role for AADC gene transfer against L-DOPA toxicity.

Subunit composition of nicotinic receptors in monkey striatum: effect of treatments with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine or L-DOPA.

Nicotinic acetylcholine receptors (nAChRs) represent an important modulator of striatal function both under normal conditions and in pathological states such as Parkinson's disease. Because different nAChR subtypes may have unique functions, immunoprecipitation and ligand binding studies were done to identify their subunit composition. As in the rodent, alpha2, alpha4, alpha6, beta2, and beta3 nAChR subunit immunoreactivity was identified in monkey striatum. However, distinct from the rodent, the present results also revealed the novel presence of alpha3 nAChR subunit-immunoreactivity in this same region, but not that for alpha5 and beta4. Relatively high levels of alpha2 and alpha3 subunits were also identified in monkey cortex, in addition to alpha4 and beta2. Experiments were next done to determine whether striatal subunit expression was changed with nigrostriatal damage. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment decreased alpha6 and beta3 subunit immunoreactivity by approximately 80% in parallel with the dopamine transporter, suggesting that they are predominantly expressed on nigrostriatal dopaminergic projections. In contrast, alpha3, alpha4, and beta2 subunit immunoreactivity was decreased approximately 50%, whereas alpha2 was not changed. These data, together with those from dual immunoprecipitation and radioligand binding studies ([(3)H]cytisine, (125)I-alpha-bungarotoxin, and (125)I-alpha-conotoxin MII) suggest the following: that alpha6beta2beta3, alpha6alpha4beta2beta3, and alpha3beta2* nAChR subtypes are present on dopaminergic terminals and that the alpha4beta2 subtype is localized on both dopaminergic and nondopaminergic neurons, whereas alpha2beta2* and alpha7 receptors are localized on nondopaminergic cells in monkey striatum. Overall, these results suggest that drugs targeting non-alpha7 nicotinic receptors may be useful in the treatment of disorders characterized by nigrostriatal dopaminergic damage, such as Parkinson's disease.

Effects of N‐Acetyl‐l‐Cysteine on the Reduction of Brain Dopamine Transporters in Monkey Treated with Methamphetamine

Several lines of evidence suggest that oxidative stress might contribute to neurotoxicity in the dopaminergic nerve terminals after administration of methamphetamine (MAP). The present study undertakes to determine whether intravenous administration of N-acetyl-L-cysteine (NAC), a potent antioxidant drug, could attenuate the reduction of dopamine transporter (DAT) in the striatum of monkey brain after administration of MAP. Positron emission tomography (PET) studies demonstrated that repeated administration of MAP (2 mg/kg as a salt, four times at 2-h intervals) significantly decreased the accumulation of radioactivity in the striatum after intravenous administration of [11C]b-CFT (for DAT). In contrast, the binding of [11C]DASB to 5-hydroxytryptamine transporter (5-HTT) in the monkey brain was slightly decreased after the administration of MAP, although the difference was not statistically significant. The binding of [11C]SCH 23390 to dopamine D1 receptors in the striatum was also not altered after the administration of MAP. A bolus injection of NAC (150 mg/kg, i.v.) 30 min before administration of MAP and a subsequent continuous infusion of NAC (12 mg/kg/h, i.v.) over 8.5 h significantly attenuated the reduction of DAT in the monkey striatum 3 weeks after the administration of MAP. These results suggest that NAC could attenuate the reduction of DAT in the monkey striatum after repeated administration of MAP. Therefore, it is likely that NAC would be a suitable drug for treatment of neurotoxicity on dopaminergic nerve terminals related to chronic use of MAP in humans.

The distribution of m4 muscarinic acetylcholine receptors in the islands of Calleja and striatum of rats and cynomolgus monkeys

The distribution of m4 muscarinic acetylcholine receptors, and their relation to a number other markers, was examined using immunocytochemical techniques. Staining in the dorsal striatum tended to be more pronounced in the striosomal than the matrix compartment of both rats and cynomolgus monkeys. Within the ventral striatum, immunoreactivity was more pronounced within the olfactory tubercle and the shell region of the nucleus accumbens than in the nucleus accumbens core and was especially marked within the lateral striatal stripe. Modest staining was also seen in the external plexiform layer of the olfactory bulb. By far, the most intense staining in the forebrain of both rats and cynomolgus monkeys was found in islands of Calleja, where it appeared to be a selective marker for the core or hilus regions of the islands, or an analogous region found adjacent to them. The core regions of different islands appear to be continuous with each other so as to form a complex three-dimensional structure, which is largely encased by layers of granule cells. The neuronal elements in the islands of Calleja, which express m4 receptors, remain to be identified, but it is unlikely that cholinergic neurons are a major locus of these receptors. Although there are certain similarities between the islands of Calleja and other components of the striatal complex, the current studies emphasize the extent to which the islands are unique in terms of their architecture and chemical anatomy.