Local circuit neurons in the striatum regulate neural and behavioral responses to dopaminergic stimulation

Striatal glutamate release evoked in vivo by NMDA is dependent upon ongoing neuronal activity in the substantia nigra, endogenous striatal substance P and dopamine

The aim of the present microdialysis study was to investigate whether the increase in striatal glutamate levels induced by intrastriatal perfusion with NMDA was dependent on the activation of extrastriatal loops and/or endogenous striatal substance P and dopamine. The NMDA-evoked striatal glutamate release was mediated by selective activation of the NMDA receptor-channel complex and action potential propagation, as it was prevented by local perfusion with dizocilpine and tetrodotoxin, respectively. Tetrodotoxin and bicuculline, perfused distally in the substantia nigra reticulata, prevented the NMDA-evoked striatal glutamate release, suggesting its dependence on ongoing neuronal activity and GABA(A) receptor activation, respectively, in the substantia nigra. The NMDA-evoked glutamate release was also dependent on striatal substance P and dopamine, as it was antagonized by intrastriatal perfusion with selective NK(1) (SR140333), D(1)-like (SCH23390) and D(2)-like (raclopride) receptor antagonists, as well as by striatal dopamine depletion. Furthermore, impairment of dopaminergic transmission unmasked a glutamatergic stimulation by submicromolar NMDA concentrations. We conclude that in vivo the NMDA-evoked striatal glutamate release is mediated by activation of striatofugal GABAergic neurons and requires activation of striatal NK(1) and dopamine receptors. Endogenous striatal dopamine inhibits or potentiates the NMDA action depending on the strength of the excitatory stimulus (i.e. the NMDA concentration).

Classification of cDNA array genes that have a highly significant discriminative power due to their unique distribution in four brain regions

Novel statistical methods were used to distinguish functionally distinct brain regions using their cDNA array gene expression profiles, and it was found that one of four specific factors is often associated with the most regionally discriminative genes. The gene expression profiles for the substantia nigra (SN), striatum (STR), parietal cortex (PC), and posterolateral cortical amygdaloid nucleus (PLCo) brain regions were determined from each brain region. An F-test identified 339 genes of the 1185 array genes as having a P < or = 0.01 and applied a gene ranking and selection method based on Soft Independent Modeling of Class Analogy (SIMCA) to obtain 59 of the most discriminative genes. Their discriminative power was validated in three steps. The most convincing step showed their ability to correctly predict the brain regional classifications for 18 "test" gene expression sets obtained from the four regions. A two-way Hierarchical Cluster Analysis organized the 59 genes in six clusters according to their expression differences in the brain regions. Expression patterns in the SN and STR regions greatly differed from each other and the PC and PLCo. The closer similarity in the gene expression patterns of the PC and PLCo was probably due to their functional similarity. The important factors in determining differences in the regional gene expression profiles in six clusters were (1) regional myelin/oligodendrocyte levels, (2) resident neuron types, (3) neurotransmitter innervation profiles, and (4) Ca++-dependent signaling and second messenger systems.

Repetitive behaviors in monkeys are linked to specific striatal activation patterns

The spontaneous behavior of humans can be altered dramatically by repeated exposure to psychomotor stimulants. We have developed a primate model for analyzing the neurobiology underlying such drug-induced behavioral changes. We performed ethogram-based behavioral assays on squirrel monkeys given single or multiple cocaine treatments, and in the same monkeys made anatomical plots of striatal neurons that were activated to express early-gene proteins. A final cocaine challenge after chronic intermittent exposure to cocaine induced highly patterned behavioral changes in the monkeys, affecting individual behavioral motifs in distinct ways. In the striatum, the challenge dose induced striosome-predominant expression combined with intense dorsal early-gene expression, especially in the putamen. These patterns of gene expression were highly predictive of the levels of stereotypy exhibited by the monkeys in response to cocaine challenge. The total levels of expression, on the other hand, appeared to reflect increased spontaneous behavioral activation during the drug-free period after the cocaine exposure. We suggest that in the primate, compartmentally and regionally specific striatal activation patterns contribute to the striatal modulation of psychostimulant-induced behaviors. These observations in nonhuman primates raise the possibility that monitoring such basal ganglia activity patterns could help to delineate the neural mechanisms underlying drug-induced repetitive behaviors and related syndromes in which stereotypies are manifest.

Disrupted spermine homeostasis: a novel mechanism in polyglutamine-mediated aggregation and cell death

Our data suggest a novel mechanism whereby pathological-length polyglutamine (polyQ) proteins promote the spermine synthetic pathway, increasing polyQ-aggregation and cell death. As detected in a cell-free turbidity assay, spermine promotes aggregation of thio-polyQ62 in a dose-dependent manner. Using a stable neuronal cell line expressing pathological-length [polyQ57-yellow fluorescent protein (YFP) (Q57)] or non-pathological-length [polyQ19-YFP (Q19)] polyglutamine protein, we show that multiple steps in the production of polyamines are affected in Q57 cells, suggesting dysfunctional spermine homeostasis. As the building block for spermine synthesis, arginine transport is significantly increased in neuronal cell lines stably expressing Q57. Q57 lines displayed upregulated basal and inducible arginase I activities that were not seen in polyQ19-YFP lines. Normal induction of spermidine/spermine N-acetyltransferase in Q19 lines regulating back-conversion of spermine, thereby reducing spermine levels, however, was not observed in Q57 lines. Pharmacological activation of ornithine decarboxylase (ODC), a key enzyme of the polyamine synthetic pathway, increased cellular aggregates and increased cell death in Q57 cells not observed in Q19 cells. Inhibition of ODC by difluoromethylornithine prevented basal and induced cell death in Q57 cells, demonstrating a central role for polyamines in this process.

Morphological features, distribution and compartmental organization of the nicotinamide adenine dinucleotide phosphate reduced-diaphorase interneurons in the human striatum

Striatal nicotinamide adenine dinucleotide phosphate reduced-diaphorase (NADPH-d)-positive (+) cells are one of the major classes of striatal interneurons. The present study analyzes their somatodendritic morphology, distribution pattern, and compartmental organization in the caudate nucleus (CN) and putamen (Put) of nine normal human brains. The following striatal territories are examined: 1) the precommissural head of the CN; 2) the postcommissural head of the CN; 3) the body of the CN; 4) the gyrus of the CN; 5) the tail of the CN; 6) the precommissural Put; and 7) the postcommissural Put. Three morphologically distinct types of NADPH-d+ neurons were found in each of these territories. The two most common NADPH-d+ neurons displayed an ovoid or triangular perikaryon from which several thick primary dendrites emerged, although much less numerous, bipolar-shaped NADPH-d+ cells were also observed. The highest density of NADPH-d+ neurons was found in the gyrus of the CN, followed by the body of the CN, tail of the CN, postcommissural head of the CN, postcommissural Put, precommissural head of the CN, and precommissural Put. The matrix was the striatal compartment with the densest NADPH-d+ neuronal population. Some of these cells also occurred in the center and peripheral regions of the striosomes located in the head of the CN and in the Put. In the body and gyrus of the CN, the striosomes were largely devoid of these striatal interneurons. Knowledge of the density and distribution of these interneurons should advance our understanding of the organization of the normal human striatum and help to evaluate the effects of neurodegenerative processes on cell density.

Intrastriatal dopamine D1 receptor agonist-mediated motor behavior is reduced by local neurokinin 1 receptor antagonism

Recent evidence suggests that striatal neurokinin receptors modulate dopamine (DA)-induced motor behaviors. To further examine this, we studied the effects of intrastriatal neurokinin 1 receptor (NK1R) antagonism on motor behaviors induced by direct infusion of the full DA D1 receptor agonist SKF 82958. Adult male Sprague-Dawley rats received bilateral intrastriatal 0.8-mul infusions of the NK1R receptor antagonist LY 306,740 (0, 27, or 54 nmol/side) followed by intrastriatal infusions of SKF 82958 (0 or 24 nmol/side) into the dorsal striatum. Following each infusion, rats were placed into automated activity monitors for the quantification of horizontal activity, total distance traveled, movement bouts, and stereotypy counts. As expected, SKF 82958 increased motor activity on all behavioral measures. More importantly, whereas 27 nmol was without effect, prior infusion of 54 nmol LY 306,740 significantly reduced most aspects of behavior. The results of this study suggest that functional NK1Rs within the striatum play a permissive role in the motor behaviors induced by D1R stimulation.

Rationale for and use of NMDA receptor antagonists in Parkinson's disease

N-Methyl-d-aspartate (NMDA) glutamate receptors are a class of excitatory amino acid receptors, which have several important functions in the motor circuits of the basal ganglia, and are viewed as important targets for the development of new drugs to prevent or treat Parkinson's disease (PD). NMDA receptors are ligand-gated ion channels composed of multiple subunits, each of which has distinct cellular and regional patterns of expression. They have complex regulatory properties, with both agonist and co-agonist binding sites and regulation by phosphorylation and protein-protein interactions. They are found in all of the structures of the basal ganglia, although the subunit composition in the various structures is different. NMDA receptors present in the striatum are crucial for dopamine-glutamate interactions. The abundance, structure, and function of striatal receptors are altered by the dopamine depletion and further modified by the pharmacological treatments used in PD. In animal models, NMDA receptor antagonists are effective antiparkinsonian agents and can reduce the complications of chronic dopaminergic therapy (wearing off and dyskinesias). Use of these agents in humans has been limited because of the adverse effects associated with nonselective blockade of NMDA receptor function, but the development of more potent and selective pharmaceuticals holds the promise of an important new therapeutic approach for PD.

The basal ganglia: anatomy, physiology, and pharmacology

The basal ganglia are perceived as important nodes in cortico-subcortical networks involved in the transfer, convergence, and processing of information in motor, cognitive, and limbic domains. How this integration might occur remains a matter of some debate, particularly given the consistent finding in anatomic and physiologic studies of functional segregation in cortico-subcortical loops. More recent theories, however, have raised the notion that modality-specific information might be integrated not spatially, but rather temporally, by coincident processing in discrete neuronal populations. Basal ganglia neurotransmitters, given their diverse roles in motor performance, learning, working memory, and reward-related activity are also likely to play an important role in the integration of cerebral activity. Further work will elucidate this to a greater extent, but for now, it is clear that the basal ganglia form an important nexus in the binding of cognitive, limbic, and motor information into thought and action.

Network-level neuroplasticity in cortico-basal ganglia pathways

The striatum, the largest input nucleus of the basal ganglia, receives massive inputs from the neocortex and thalamus, and gives rise to the direct, indirect and striosomal pathways of the basal ganglia. Here, the view is developed that the striatum is a major site for adaptive plasticity in cortico-basal ganglia circuits, affecting in the normal state a broad range of behaviours. This plasticity can become a major source of maladaptive responses in disease states affecting the basal ganglia.

Overexpression of torsinA in PC12 cells protects against toxicity

Childhood-onset dystonia is an autosomal dominant movement disorder associated with a three base pair (GAG) deletion mutation in the DYT1 gene. This gene encodes a novel ATP-binding protein called torsinA, which in the central nervous system is expressed exclusively in neurons. Neither the function of torsinA nor its role in the pathophysiology of DYT1 dystonia is known. In order to better understand the cellular functions of torsinA, we established PC12 cell lines overexpressing wild-type or mutant torsinA and subjected them to various conditions deleterious to cell survival. Treatment of control PC12 cells with an inhibitor of proteasomal activity, an oxidizing agent, or trophic withdrawal, resulted in cell death, whereas PC12 cells that overexpressed torsinA were significantly protected against each of these treatments. Overexpression of mutant torsinA failed to protect cells against trophic withdrawal. These results suggest that torsinA may play a protective role in neurons against a variety of cellular insults.

Ablation of striatal interneurons influences activities of entopeduncular neurons

To characterize modulatory effects of striatal interneurons upon the output nucleus of the basal ganglia, we ablated striatal interneurons that express substance P receptors by using local injection of a selective neurotoxin, substance P-saporin, in rats. We then made extracellular recordings of the activity of entopeduncular neurons and examined their responses to stimulation in the motor cortex. In the interneuron-ablated animals, the spontaneous discharge rate of entopeduncular neurons was significantly decreased, and the proportion of entopeduncular neurons showing responses to cortical stimulation was significantly larger, in comparison with intact animals. It is suggested that striatal interneurons expressing substance P receptors are important for motor control mechanisms mediated by the cortico-basal ganglia pathways.

It could be habit forming: drugs of abuse and striatal synaptic plasticity

Drug addiction can take control of the brain and behavior, activating behavioral patterns that are directed excessively and compulsively toward drug usage. Such patterns often involve the development of repetitive and nearly automatic behaviors that we call habits. The striatum, a subcortical brain region important for proper motor function as well as for the formation of behavioral habits, is a major target for drugs of abuse. Here, we review recent studies of long-term synaptic plasticity in the striatum, emphasizing that drugs of abuse can exert pronounced influences on these processes, both in the striatum and in the dopaminergic midbrain. Synaptic plasticity in the ventral striatum appears to play a prominent role in early stages of drug use, whereas dopamine- and endocannabinoid-dependent synaptic plasticity in the dorsal striatum could contribute to the formation of persistent drug-related habits when casual drug use progresses towards compulsive drug use and addiction.

Muscarinic and nicotinic cholinergic mechanisms in the mesostriatal dopamine systems

The striatum and its dense dopaminergic innervation originating in the midbrain, primarily from the substantia nigra pars compacta and the ventral tegmental area, compose the mesostriatal dopamine (DA) systems. The nigrostriatal system is involved mainly in motor coordination and in disorders such as Tourette's syndrome, Huntington's disease, and Parkinson's disease. The dopaminergic projections from the ventral tegmental area to the striatum participate more in the processes that shape behaviors leading to reward, and addictive drugs act upon this mesolimbic system. The midbrain DA areas receive cholinergic innervation from the pedunculopontine tegmentum and the laterodorsal pontine tegmentum, whereas the striatum receives dense cholinergic innervation from local interneurons. The various neurons of the mesostriatal systems express multiple types of muscarinic and nicotinic acetylcholine receptors as well as DA receptors. Especially in the striatum, the dense mingling of dopaminergic and cholinergic constituents enables potent interactions. Evidence indicates that cholinergic and dopaminergic systems work together to produce the coordinated functioning of the striatum. Loss of that cooperative activity contributes to the dysfunction underlying Parkinson's disease.

Focused motor stereotypies do not require enhanced activation of neurons in striosomes

Stereotypic motor behavior is a widespread phenomenon of many neurologic and psychiatric disorders. Studies on the mechanisms controlling motor stereotypies have focused on the role of dopamine in modulating the activity of basal ganglia neuronal circuits, and recent results demonstrated that stereotypic motor responses characteristic of psychomotor stimulant sensitization correlate with an enhanced activation of neurons located in striatal striosomes that substantially exceeds that of the surrounding matrix. The present study tested whether predominant striosomal activation is a general predictor for stereotypy. Wild-type and dopamine D(2) and D(3) receptor knockout mice were treated either three times with methamphetamine (METH; 3 x 5 mg/kg every 2 hours) or once with a full D(1) agonist. Depending on the genotype, both treatments elicit the same focused stereotypy (taffy pulling). Repeated METH-treatment elicits intense stereotypy in wild-type and D(3) mutants but not in D(2) single and D(2)/D(3) double mutants. The stereotypic response of wild-type and D(3) mutants correlates with a predominant activation of neurons located in striosomes. No striosomal predominance is detected in METH-treated D(2) single and D(2)/D(3) double mutants. In contrast, D(2) single and D(2)/D(3) double mutants exhibited the most severe stereotypic response to D(1)-agonist treatment. However, this treatment did not result in enhanced striosomal activation. Thus, whereas the expression of stereotypy in response to repeated METH treatment requires D(2) receptor expression, D(2) receptor expression diminishes stereotypic responses to an acute dose of a D(1) agonist. Enhanced striosomal activation, however, is a reliable indicator of D(1)- and D(2)-receptor coactivation but not a predictor for repetitive motor behavior in general.

Concurrent activation of dopamine D1 and D2 receptors is required to evoke neural and behavioral phenotypes of cocaine sensitization

Repeated exposure to psychomotor stimulants produces a striking behavioral syndrome involving repetitive, stereotypic behaviors that occur if an additional exposure to the stimulant is experienced. The same stimulant exposure produces specific alterations in gene expression patterns in the striatum. To identify the dopamine receptor subtypes required for the parallel expression of these acquired neural and behavioral responses, we treated rats with different D1-class and D2-class dopamine receptor agonists and compared the responses of drug-naive rats with those of rats given previous intermittent treatment with cocaine. In rats exposed to repeated cocaine treatment, the effects of a subsequent challenge treatment with either a D1-class agonist (SKF 81297) or a D2-class agonist (quinpirole) were not significantly different from those observed in drug-naive animals: the drugs administered singly did not induce robust stereotyped motor behaviors nor produce significantly striosome-predominant expression of early genes in the striatum. In contrast, challenge treatment with the D1-class and D2-class agonists in combination led to marked and correlated increases in stereotypy and striosome-predominant gene expression in the striatum. Thus, immediately after repeated psychomotor stimulant exposure, only the concurrent activation of D1 and D2 receptor subclasses evoked expression of the neural and behavioral phenotypes acquired through repeated cocaine exposure. These findings suggest that D1-D2 dopamine receptor synergisms underlie the coordinate expression of both network-level changes in basal ganglia activation patterns and the repetitive and stereotypic motor response patterns characteristic of psychomotor stimulant sensitization.