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

Prenatal exposition to haloperidol: A preclinical narrative review

Pre-existing maternal mental disorders may affect the early interactions between mother and baby, impacting the child's psychoemotional development. The typical antipsychotic haloperidol can be used during pregnancy, even with some restrictions. Its prescription is not limited to psychotic disorders, but also to other psychiatric conditions of high incidence and prevalence in the woman's fertile period. The present review focused on the preclinical available data regarding the biological and behavioral implications of embryonic exposure to haloperidol. The understanding of the effects of psychotropic drugs during neurodevelopment is important for its clinical aspect since there is limited evidence regarding the risks of antipsychotic drug treatment in pregnant women and their children. Moreover, a better comprehension of the mechanistic events that can be affected by antipsychotic treatment during the critical period of neurodevelopment may offer insights into the pathophysiology of neurodevelopmental disorders. The findings presented in this review converge to the existence of several risks associated with prenatal exposure to such medication and emphasize the need for further studies regarding its dimensions.

Neuropeptide Y Signaling Regulates Recurrent Excitation in the Auditory Midbrain

Neuropeptides play key roles in shaping the organization and function of neuronal circuits. In the inferior colliculus (IC), which is in the auditory midbrain, Neuropeptide Y (NPY) is expressed by a class of GABAergic neurons that project locally and outside the IC. Most neurons in the IC have local axon collaterals; however, the organization and function of local circuits in the IC remain unknown. We previously found that excitatory neurons in the IC can express the NPY Y1 receptor (Y1R+) and application of the Y1R agonist, [Leu31, Pro34]-NPY (LP-NPY), decreases the excitability of Y1R+ neurons. As NPY signaling regulates recurrent excitation in other brain regions, we hypothesized that Y1R+ neurons form interconnected local circuits in the IC and that NPY decreases the strength of recurrent excitation in these circuits. To test this hypothesis, we used optogenetics to activate Y1R+ neurons in mice of both sexes while recording from other neurons in the ipsilateral IC. We found that nearly 80% of glutamatergic IC neurons express the Y1 receptor, providing extensive opportunities for NPY signaling to regulate local circuits. Additionally, Y1R+ neuron synapses exhibited modest short-term synaptic plasticity, suggesting that local excitatory circuits maintain their influence over computations during sustained stimuli. We further found that application of LP-NPY decreased recurrent excitation in the IC, suggesting that NPY signaling strongly regulates local circuit function in the auditory midbrain. Our findings show that Y1R+ excitatory neurons form interconnected local circuits in the IC, and their influence over local circuits is regulated by NPY signaling.SIGNIFICANCE STATEMENT Local networks play fundamental roles in shaping neuronal computations in the brain. The IC, localized in the auditory midbrain, plays an essential role in sound processing, but the organization of local circuits in the IC is largely unknown. Here, we show that IC neurons that express the Neuropeptide Y1 receptor (Y1R+ neurons) make up most of the excitatory neurons in the IC and form interconnected local circuits. Additionally, we found that NPY, which is a powerful neuromodulator known to shape neuronal activity in other brain regions, decreases the extensive recurrent excitation mediated by Y1R+ neurons in local IC circuits. Thus, our results suggest that local NPY signaling is a key regulator of auditory computations in the IC.

Acetylcholine waves and dopamine release in the striatum

Striatal dopamine encodes reward, with recent work showing that dopamine release occurs in spatiotemporal waves. However, the mechanism of dopamine waves is unknown. Here we report that acetylcholine release in mouse striatum also exhibits wave activity, and that the spatial scale of striatal dopamine release is extended by nicotinic acetylcholine receptors. Based on these findings, and on our demonstration that single cholinergic interneurons can induce dopamine release, we hypothesized that the local reciprocal interaction between cholinergic interneurons and dopamine axons suffices to drive endogenous traveling waves. We show that the morphological and physiological properties of cholinergic interneuron - dopamine axon interactions can be modeled as a reaction-diffusion system that gives rise to traveling waves. Analytically-tractable versions of the model show that the structure and the nature of propagation of acetylcholine and dopamine traveling waves depend on their coupling, and that traveling waves can give rise to empirically observed correlations between these signals. Thus, our study provides evidence for striatal acetylcholine waves in vivo, and proposes a testable theoretical framework that predicts that the observed dopamine and acetylcholine waves are strongly coupled phenomena.

Dystonia and Parkinson's disease: Do they have a shared biology?

Parkinsonism and dystonia co-occur across many movement disorders and are most encountered in the setting of Parkinson's disease. Here we aim to explore the shared neurobiological underpinnings of dystonia and parkinsonism through the clinical lens of the conditions in which these movement disorders can be seen together. Foregrounding the discussion, we briefly review the circuits of the motor system and the neuroanatomical and neurophysiological aspects of motor control and highlight their relevance to the proposed pathophysiology of parkinsonism and dystonia. Insight into shared biology is then sought from dystonia occurring in PD and other forms of parkinsonism including those disorders in which both can be co-expressed simultaneously. We organize these within a biological schema along with important questions to be addressed in this space.

Neuropeptide Y signaling regulates recurrent excitation in the auditory midbrain

Neuropeptides play key roles in shaping the organization and function of neuronal circuits. In the inferior colliculus (IC), which is located in the auditory midbrain, Neuropeptide Y (NPY) is expressed by a large class of GABAergic neurons that project locally as well as outside the IC. The IC integrates information from numerous auditory nuclei making the IC an important hub for sound processing. Most neurons in the IC have local axon collaterals, however the organization and function of local circuits in the IC remains largely unknown. We previously found that neurons in the IC can express the NPY Y1 receptor (Y 1 R + ) and application of the Y 1 R agonist, [Leu 31 , Pro 34 ]-NPY (LP-NPY), decreases the excitability of Y 1 R + neurons. To investigate how Y 1 R + neurons and NPY signaling contribute to local IC networks, we used optogenetics to activate Y 1 R + neurons while recording from other neurons in the ipsilateral IC. Here, we show that 78.4% of glutamatergic neurons in the IC express the Y1 receptor, providing extensive opportunities for NPY signaling to regulate excitation in local IC circuits. Additionally, Y 1 R + neuron synapses exhibit modest short-term synaptic plasticity, suggesting that local excitatory circuits maintain their influence over computations during sustained stimuli. We further found that application of LP-NPY decreases recurrent excitation in the IC, suggesting that NPY signaling strongly regulates local circuit function in the auditory midbrain. Together, our data show that excitatory neurons are highly interconnected in the local IC and their influence over local circuits is tightly regulated by NPY signaling.

Generalized and social anxiety disorder interactomes show distinctive overlaps with striosome and matrix interactomes

Mechanisms underlying anxiety disorders remain elusive despite the discovery of several associated genes. We constructed the protein-protein interaction networks (interactomes) of six anxiety disorders and noted enrichment for striatal expression among common genes in the interactomes. Five of these interactomes shared distinctive overlaps with the interactomes of genes that were differentially expressed in two striatal compartments (striosomes and matrix). Generalized anxiety disorder and social anxiety disorder interactomes showed exclusive and statistically significant overlaps with the striosome and matrix interactomes, respectively. Systematic gene expression analysis with the anxiety disorder interactomes constrained to contain only those genes that were shared with striatal compartment interactomes revealed a bifurcation among the disorders, which was influenced by the anterior cingulate cortex, nucleus accumbens, amygdala and hippocampus, and the dopaminergic signaling pathway. Our results indicate that the functionally distinct striatal pathways constituted by the striosome and the matrix may influence the etiological differentiation of various anxiety disorders.

CalDAG-GEFI mediates striatal cholinergic modulation of dendritic excitability, synaptic plasticity and psychomotor behaviors

CalDAG-GEFI (CDGI) is a protein highly enriched in the striatum, particularly in the principal spiny projection neurons (SPNs). CDGI is strongly down-regulated in two hyperkinetic conditions related to striatal dysfunction: Huntington’s disease and levodopa-induced dyskinesia in Parkinson’s disease. We demonstrate that genetic deletion of CDGI in mice disrupts dendritic, but not somatic, M1 muscarinic receptors (M1Rs) signaling in indirect pathway SPNs. Loss of CDGI reduced temporal integration of excitatory postsynaptic potentials at dendritic glutamatergic synapses and impaired the induction of activity-dependent long-term potentiation. CDGI deletion selectively increased psychostimulant-induced repetitive behaviors, disrupted sequence learning, and eliminated M1R blockade of cocaine self-administration. These findings place CDGI as a major, but previously unrecognized, mediator of cholinergic signaling in the striatum. The effects of CDGI deletion on the self-administration of drugs of abuse and its marked alterations in hyperkinetic extrapyramidal disorders highlight CDGI’s therapeutic potential.

Causal Evidence for Induction of Pessimistic Decision-Making in Primates by the Network of Frontal Cortex and Striosomes

Clinical studies have shown that patients with anxiety disorders exhibited coactivation of limbic cortices and basal ganglia, which together form a large-scale brain network. The mechanisms by which such a large-scale network could induce or modulate anxiety-like states are largely unknown. This article reviews our experimental program in macaques demonstrating a causal involvement of local striatal and frontal cortical sites in inducing pessimistic decision-making that underlies anxiety. Where relevant, we related these findings to the wider literature. To identify such sites, we have made a series of methodologic advances, including the combination of causal evidence for behavioral modification of pessimistic decisions with viral tracing methods. Critically, we introduced a version of the classic approach-avoidance (Ap-Av) conflict task, modified for use in non-human primates. We performed microstimulation of limbic-related cortical regions and the striatum, focusing on the pregenual anterior cingulate cortex (pACC), the caudal orbitofrontal cortex (cOFC), and the caudate nucleus (CN). Microstimulation of localized sites within these regions induced pessimistic decision-making by the monkeys, supporting the idea that the focal activation of these regions could induce an anxiety-like state, which subsequently influences decision-making. We further performed combined microstimulation and tract-tracing experiments by injecting anterograde viral tracers into focal regions, at which microstimulation induced increased avoidance. We found that effective stimulation sites in both pACC and cOFC zones projected preferentially to striosomes in the anterior striatum. Experiments in rodents have shown that the striosomes in the anterior striatum project directly to the dopamine-containing cells in the substantia nigra, and we have found evidence for a functional connection between striosomes and the lateral habenular region in which responses to reward are inhibitory. We present here further evidence for network interactions: we show that the pACC and cOFC project to common structures, including not only the anterior parts of the striosome compartment but also the tail of the CN, the subgenual ACC, the amygdala, and the thalamus. Together, our findings suggest that networks having pACC and cOFC as nodes share similar features in their connectivity patterns. We here hypothesize, based on these results, that the brain sites related to pessimistic judgment are mediated by a large-scale brain network that regulates dopaminergic functions and includes striosomes and striosome-projecting cortical regions.

Compartmental function and modulation of the striatum

The striatum plays a central role in guiding numerous complex behaviors, ranging from motor control to action selection and reward learning. The diverse responsibilities of the striatum are reflected by the complexity of its organization. In this review, we will summarize what is currently known about the compartmental layout of the striatum, an organizational principle that is crucial for allowing the striatum to guide such a diverse array of behaviors. We will focus on the anatomical and functional properties of striosome (patch) and matrix compartments of the striatum, and how the engagement of these compartments is uniquely controlled by their afferents, intrinsic properties, and neuromodulation. We will give examples of how advances in technology have opened the door to functionally dissecting the striatum's compartmental design, and close by offering thoughts on the future and relevance for human disease.

Analgesia by Deletion of Spinal Neurokinin 1 Receptor Expressing Neurons Using a Bioengineered Substance P-Pseudomonas Exotoxin Conjugate

Cell deletion approaches to pain directed at either the primary nociceptive afferents or second-order neurons are highly effective analgesic manipulations. Second-order spinal neurons expressing the neurokinin 1 (NK1) receptor are required for the perception of many types of pain. To delete NK1+ neurons for the purpose of pain control, we generated a toxin–peptide conjugate using DTNB-derivatized (Cys₀) substance P (SP) and a N-terminally truncated Pseudomonas exotoxin (PE35) that retains the endosome-release and ADP-ribosylation enzymatic domains but with only one free sulfhydryl side chain for conjugation. This allowed generation of a one-to-one product linked by a disulfide bond (SP-PE35). In vitro, Chinese hamster ovary cells stably transfected with the NK1 receptor exhibited specific cytotoxicity when exposed to SP-PE35 (IC₅₀ = 5 × 10⁻¹¹M), whereas the conjugate was nontoxic to NK2 and NK3 receptor-bearing cell lines. In vivo studies showed that, after infusion into the spinal subarachnoid space, the toxin was extremely effective in deleting NK1 receptor-expressing cells from the dorsal horn of the spinal cord. The specific cell deletion robustly attenuated thermal and mechanical pain sensations and inflammatory hyperalgesia but did not affect motoric capabilities. NK1 receptor cell deletion and antinociception occurred without obvious lesion of non–receptor-expressing cells or apparent reorganization of primary afferent innervation. These data demonstrate the extraordinary selectivity and broad-spectrum antinociceptive efficacy of this ligand-directed protein therapeutic acting via receptor-mediated endocytosis. The loss of multiple pain modalities including heat and mechanical pinch, transduced by different populations of primary afferents, shows that spinal NK1 receptor-expressing neurons are critical points of convergence in the nociceptive transmission circuit. We further suggest that therapeutic end points can be effectively and safely achieved when SP-PE35 is locally infused, thereby producing a regionally defined analgesia.

Dysfunctions in striatal microstructure can enhance perceptual decision making through deficits in predictive coding

An important brain function is to predict upcoming events on the basis of extracted regularities of previous inputs. These predictive coding processes can disturb performance in concurrent perceptual decision-making and are known to depend on fronto-striatal circuits. However, it is unknown whether, and if so, to what extent striatal microstructural properties modulate these processes. We addressed this question in a human disease model of striosomal dysfunction, i.e. X-linked dystonia-parkinsonism (XDP), using high-density EEG recordings and source localization. The results show faster and more accurate perceptual decision-making performance during distraction in XDP patients compared to healthy controls. The electrophysiological data show that sensory memory and predictive coding processes reflected by the mismatch negativity related to lateral prefrontal brain regions were weakened in XDP patients and thus induced less cognitive conflict than in controls as reflected by the N2 event-related potential (ERP). Consequently, attentional shifting (P3a ERP) and reorientation processes (RON ERP) were less pronounced in the XDP group. Taken together, these results suggests that striosomal dysfunction is related to predictive coding deficits leading to a better performance in concomitant perceptual decision-making, probably because predictive coding does not interfere with perceptual decision-making processes. These effects may reflect striatal imbalances between the striosomes and the matrix compartment.

Striatal Cholinergic Interneurons Modulate Spike-Timing in Striosomes and Matrix by an Amphetamine-Sensitive Mechanism

The striatum is key for action-selection and the motivation to move. Dopamine and acetylcholine release sites are enriched in the striatum and are cross-regulated, possibly to achieve optimal behavior. Drugs of abuse, which promote abnormally high dopamine release, disrupt normal action-selection and drive restricted, repetitive behaviors (stereotypies). Stereotypies occur in a variety of disorders including obsessive-compulsive disorder, autism, schizophrenia and Huntington's disease, as well as in addictive states. The severity of drug-induced stereotypy is correlated with induction of c-Fos expression in striosomes, a striatal compartment that is related to the limbic system and that directly projects to dopamine-producing neurons of the substantia nigra. These characteristics of striosomes contrast with the properties of the extra-striosomal matrix, which has strong sensorimotor and associative circuit inputs and outputs. Disruption of acetylcholine signaling in the striatum blocks the striosome-predominant c-Fos expression pattern induced by drugs of abuse and alters drug-induced stereotypy. The activity of striatal cholinergic interneurons is associated with behaviors related to sensory cues, and cortical inputs to striosomes can bias action-selection in the face of conflicting cues. The neurons and neuropil of striosomes and matrix neurons have observably separate distributions, both at the input level in the striatum and at the output level in the substantia nigra. Notably, cholinergic axons readily cross compartment borders, providing a potential route for local cross-compartment communication to maintain a balance between striosomal and matrix activity. We show here, by slice electrophysiology in transgenic mice, that repetitive evoked firing patterns in striosomal and matrix striatal projection neurons (SPNs) are interrupted by optogenetic activation of cholinergic interneurons either by the addition or the deletion of spikes. We demonstrate that this cholinergic modulation of projection neurons is blocked in brain slices taken from mice exposed to amphetamine and engaged in amphetamine-induced stereotypy, and lacking responsiveness to salient cues. Our findings support a model whereby activity in striosomes is normally under strong regulation by cholinergic interneurons, favoring behavioral flexibility, but that in animals with drug-induced stereotypy, this cholinergic signaling breaks down, resulting in differential modulation of striosomal activity and an inability to bias action-selection according to relevant sensory cues.

Substance P Weights Striatal Dopamine Transmission Differently within the Striosome-Matrix Axis

The mammalian striatum has a topographical organization of input-output connectivity, but a complex internal, nonlaminar neuronal architecture comprising projection neurons of two types interspersed among multiple interneuron types and potential local neuromodulators. From this cellular melange arises a biochemical compartmentalization of areas termed striosomes and extrastriosomal matrix. The functions of these compartments are poorly understood but might confer distinct features to striatal signal processing and be discretely governed. Dopamine transmission occurs throughout striosomes and matrix, and is reported to be modulated by the striosomally enriched neuromodulator substance P. However, reported effects are conflicting, ranging from facilitation to inhibition. We addressed whether dopamine transmission is modulated differently in striosome-matrix compartments by substance P.We paired detection of evoked dopamine release at carbon-fiber microelectrodes in mouse striatal slices with subsequent identification of the location of recording sites with respect to μ-opioid receptor-rich striosomes. Substance P had bidirectional effects on dopamine release that varied between recording sites and were prevented by inhibition of neurokinin-1 receptors. The direction of modulation was determined by location within the striosomal-matrix axis: dopamine release was boosted in striosome centers, diminished in striosomal-matrix border regions, and unaffected in the matrix. In turn, this different weighting of dopamine transmission by substance P modified the apparent center-surround contrast of striosomal dopamine signals. These data reveal that dopamine transmission can be differentially modulated within the striosomal-matrix axis, and furthermore, indicate a functionally distinct zone at the striosome-matrix interface, which may have key impacts on striatal integration.

Striatal patch compartment lesions reduce stereotypy following repeated cocaine administration

Stereotypy can be characterized as inflexible, repetitive behaviors that occur following repeated exposure to psychostimulants, such as cocaine (COC). Stereotypy may be related to preferential activation of the patch (striosome) compartment of striatum, as enhanced relative activation of the patch compartment has been shown to positively correlate with the emergence of stereotypy following repeated psychostimulant treatment. However, the specific contribution of the patch compartment to COC-induced stereotypy following repeated exposure is unknown. To elucidate the involvement of the patch compartment to the development of stereotypy following repeated COC exposure, we determined if destruction of this sub-region altered COC-induced behaviors. The neurons of the patch compartment were ablated by bilateral infusion of the neurotoxin dermorphin-saporin (DERM-SAP; 17 ng/μl) into the striatum. Animals were allowed to recover for eight days following the infusion, and then were given daily injections of COC (25mg/kg) or saline for one week, followed by a weeklong drug-free period. Animals were then given a challenge dose of saline or COC, observed for 2h in activity chambers and sacrificed. The number of mu-labeled patches in the striatum were reduced by DERM-SAP pretreatment. In COC-treated animals DERM-SAP pretreatment significantly reduced the immobilization and intensity of stereotypy but increased locomotor activity. DERM-SAP pretreatment attenuated COC-induced c-Fos expression in the patch compartment, while enhancing COC-induced c-Fos expression in the matrix compartment. These data indicate that the patch compartment contributes to repetitive behavior and suggests that alterations in activity in the patch vs matrix compartments may underlie to this phenomenon.

Melatonin inhibits manganese-induced motor dysfunction and neuronal loss in mice: involvement of oxidative stress and dopaminergic neurodegeneration

Excessive manganese (Mn) induces oxidative stress and dopaminergic neurodegeneration. However, the relationship between them during Mn neurotoxicity has not been clarified. The purpose of this study was to investigate the probable role of melatonin (MLT) against Mn-induced motor dysfunction and neuronal loss as a result of antagonizing oxidative stress and dopaminergic neurodegeneration. Mice were randomly divided into five groups as follows: control, MnCl2, low MLT + MnCl2, median MLT + MnCl2, and high MLT + MnCl2. Administration of MnCl2 (50 mg/kg) for 2 weeks significantly induced hypokinesis, dopaminergic neurons degeneration and loss, neuronal ultrastructural damage, and apoptosis in the substantia nigra and the striatum. These conditions were caused in part by the overproduction of reactive oxygen species, malondialdehyde accumulation, and dysfunction of the nonenzymatic (GSH) and enzymatic (GSH-Px, superoxide dismutase, quinone oxidoreductase 1, glutathione S-transferase, and glutathione reductase) antioxidative defense systems. Mn-induced neuron degeneration, astrocytes, and microglia activation contribute to the changes of oxidative stress markers. Dopamine (DA) depletion and downregulation of DA transporter and receptors were also found after Mn administration, this might also trigger motor dysfunction and neurons loss. Pretreatment with MLT prevented Mn-induced oxidative stress and dopaminergic neurodegeneration and inhibited the interaction between them. As a result, pretreatment with MLT significantly alleviated Mn-induced motor dysfunction and neuronal loss. In conclusion, Mn treatment resulted in motor dysfunction and neuronal loss, possibly involving an interaction between oxidative stress and dopaminergic neurodegeneration in the substantia nigra and the striatum. Pretreatment with MLT attenuated Mn-induced neurotoxicity by means of its antioxidant properties and promotion of the DA system.

Severe drug-induced repetitive behaviors and striatal overexpression of VAChT in ChAT-ChR2-EYFP BAC transgenic mice

In drug users, drug-related cues alone can induce dopamine release in the dorsal striatum. Instructive cues activate inputs to the striatum from both dopaminergic and cholinergic neurons, which are thought to work together to support motor learning and motivated behaviors. Imbalances in these neuromodulatory influences can impair normal action selection and might thus contribute to pathologically repetitive and compulsive behaviors such as drug addiction. Dopamine and acetylcholine can have either antagonistic or synergistic effects on behavior, depending on the state of the animal and the receptor signaling systems at play. Semi-synchronized activation of cholinergic interneurons in the dorsal striatum drives dopamine release via presynaptic nicotinic acetylcholine receptors located on dopamine terminals. Nicotinic receptor blockade is known to diminish abnormal repetitive behaviors (stereotypies) induced by psychomotor stimulants. By contrast, blockade of postsynaptic acetylcholine muscarinic receptors in the dorsomedial striatum exacerbates drug-induced stereotypy, exemplifying how different acetylcholine receptors can also have opposing effects. Although acetylcholine release is known to be altered in animal models of drug addiction, predicting whether these changes will augment or diminish drug-induced behaviors thus remains a challenge. Here, we measured amphetamine-induced stereotypy in BAC transgenic mice that have been shown to overexpress the vesicular acetylcholine transporter (VAChT) with consequent increased acetylcholine release. We found that drug-induced stereotypies, consisting of confined sniffing and licking behaviors, were greatly increased in the transgenic mice relative to sibling controls, as was striatal VAChT protein. These findings suggest that VAChT-mediated increases in acetylcholine could be critical in exacerbating drug-induced stereotypic behaviors and promoting exaggerated behavioral fixity.

Anti-nociceptive effect of a conjugate of substance P and light chain of botulinum neurotoxin type A

Neuropathic pain is a debilitating condition resulting from damage to sensory transmission pathways in the peripheral and central nervous system. A potential new way of treating chronic neuropathic pain is to target specific pain-processing neurons based on their expression of particular receptor molecules. We hypothesized that a toxin-neuropeptide conjugate would alter pain by first being taken up by specific receptors for the neuropeptide expressed on the neuronal cells. Then, once inside the cell the toxin would inhibit the neurons' activity without killing the neurons, thereby providing pain relief without lesioning the nervous system. In an effort to inactivate the nociceptive neurons in the trigeminal nucleus caudalis in mice, we targeted the NK1 receptor (NK1R) using substance P (SP). The catalytically active light chain of botulinum neurotoxin type A (LC/A) was conjugated with SP. Our results indicate that the conjugate BoNT/A-LC:SP is internalized in cultured NK1R-expressing neurons and also cleaves the target of botulinum toxin, a component-docking motif necessary for release of neurotransmitters called SNAP-25. The conjugate was next tested in a murine model of Taxol-induced neuropathic pain. An intracisternal injection of BoNT/A-LC:SP decreased thermal hyperalgesia as measured by the operant orofacial nociception assay. These findings indicate that conjugates of the light chain of botulinum toxin are extremely promising agents for use in suppressing neuronal activity for extended time periods, and that BoNT/A-LC:SP may be a useful agent for treating chronic pain.

Evaluating the role of neuronal nitric oxide synthase-containing striatal interneurons in methamphetamine-induced dopamine neurotoxicity

Production of nitric oxide (NO) has been implicated in methamphetamine (METH)-induced dopamine (DA) neurotoxicity. The source of this NO has not been clearly delineated, but recent evidence suggests that it arises from activation of neuronal nitric oxide synthase (nNOS), which is selectively expressed in a subpopulation of striatal interneurons. Our objective was to determine whether inhibiting activation of nNOS-containing interneurons in the striatum blocks METH-induced neurotoxicity. These interneurons selectively express the neurokinin-1 (NK-1) receptor, which is activated by substance P. One particular toxin, a conjugate of substance P to the ribosome-inactivating protein saporin (SSP-SAP), selectively destroys neurons expressing the NK-1 receptor. Thus, we examined the extent to which depletion of the nNOS-containing interneurons alters production of NO and attenuates METH-induced neurotoxicity. The SSP-SAP lesions resulted in significant loss of nNOS-containing interneurons throughout striatum. Surprisingly, this marked deletion did not confer resistance to METH-induced DA neurotoxicity, even in areas devoid of nNOS-positive cells. Furthermore, these lesions did not attenuate NO production, even in areas lacking nNOS. These data suggest that nNOS-containing interneurons either are not necessary for METH-induced DA neurotoxicity or produce NO that can diffuse extensively through striatal tissue and thereby still mediate neurotoxicity.

Pause and rebound: sensory control of cholinergic signaling in the striatum

Cholinergic interneurons have emerged as one of the key players controlling network functions in the striatum. Extracellularly recorded cholinergic interneurons acquire characteristic responses to sensory stimuli during reward-related learning, including a pause and subsequent rebound in spiking. However, the precise underlying cellular mechanisms have remained elusive. Here, we review recent advances in our understanding of the regulation of cholinergic interneuron activity. We discuss evidence of mechanisms that have been proposed to underlie sensory responses, including antagonistic actions by dopamine, recurrent inhibition via local interneurons, and an intrinsically generated membrane hyperpolarization in response to excitatory inputs. The review highlights outstanding questions and concludes with a model of the sensory responses and their downstream effects through dynamic acetylcholine receptor activation.

Raclopride or high-frequency stimulation of the subthalamic nucleus stops cocaine-induced motor stereotypy and restores related alterations in prefrontal basal ganglia circuits

Motor stereotypy is a key symptom of various neurological or neuropsychiatric disorders. Neuroleptics or the promising treatment using deep brain stimulation stops stereotypies but the mechanisms underlying their actions are unclear. In rat, motor stereotypies are linked to an imbalance between prefrontal and sensorimotor cortico-basal ganglia circuits. Indeed, cortico-nigral transmission was reduced in the prefrontal but not sensorimotor basal ganglia circuits and dopamine and acetylcholine release was altered in the prefrontal but not sensorimotor territory of the dorsal striatum. Furthermore, cholinergic transmission in the prefrontal territory of the dorsal striatum plays a crucial role in the arrest of motor stereotypy. Here we found that, as previously observed for raclopride, high-frequency stimulation of the subthalamic nucleus (HFS STN) rapidly stopped cocaine-induced motor stereotypies in rat. Importantly, raclopride and HFS STN exerted a strong effect on cocaine-induced alterations in prefrontal basal ganglia circuits. Raclopride restored the cholinergic transmission in the prefrontal territory of the dorsal striatum and the cortico-nigral information transmissions in the prefrontal basal ganglia circuits. HFS STN also restored the N-methyl-d-aspartic-acid-evoked release of acetylcholine and dopamine in the prefrontal territory of the dorsal striatum. However, in contrast to raclopride, HFS STN did not restore the cortico-substantia nigra pars reticulata transmissions but exerted strong inhibitory and excitatory effects on neuronal activity in the prefrontal subdivision of the substantia nigra pars reticulata. Thus, both raclopride and HFS STN stop cocaine-induced motor stereotypy, but exert different effects on the related alterations in the prefrontal basal ganglia circuits.

Activation of mu opioid receptors in the striatum differentially augments methamphetamine-induced gene expression and enhances stereotypic behavior

Mu opioid receptors are densely expressed in the patch compartment of striatum and contribute to methamphetamine-induced patch-enhanced gene expression and stereotypy. To further elucidate the role of mu opioid receptor activation in these phenomena, we examined whether activation of mu opioid receptors would enhance methamphetamine-induced stereotypy and prodynorphin, c-fos, arc and zif/268 expression in the patch and/or matrix compartments of striatum, as well as the impact of mu opioid receptor activation on the relationship between patch-enhanced gene expression and stereotypy. Male Sprague-Dawley rats were intrastriatally infused with d-Ala(2)-N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO; 1 μg/μL), treated with methamphetamine (0.5 mg/kg) and killed at 45 min or 2 h later. DAMGO augmented methamphetamine-induced zif/268 mRNA expression in the patch and matrix compartments, while prodynorphin expression was increased in the dorsolateral patch compartment. DAMGO pre-treatment did not affect methamphetamine-induced arc and c-fos expression. DAMGO enhanced methamphetamine-induced stereotypy and resulted in greater patch versus matrix expression of prodynorphin in the dorsolateral striatum, leading to a negative correlation between the two. These findings indicate that mu opioid receptors contribute to methamphetamine-induced stereotypy, but can differentially influence the genomic responses to methamphetamine. These data also suggest that prodynorphin may offset the overstimulation of striatal neurons by methamphetamine.

Distribution of GABAergic interneurons and dopaminergic cells in the functional territories of the human striatum

Background

The afferent projections of the striatum (caudate nucleus and putamen) are segregated in three territories: associative, sensorimotor and limbic. Striatal interneurons are in part responsible for the integration of these different types of information. Among them, GABAergic interneurons are the most abundant, and can be sorted in three populations according to their content in the calcium binding proteins calretinin (CR), parvalbumin (PV) and calbindin (CB). Conversely, striatal dopaminergic cells (whose role as interneurons is still unclear) are scarce. This study aims to analyze the interneuron distribution in the striatal functional territories, as well as their organization regarding to the striosomal compartment.

Methodology/Principal Findings

We used immunohistochemical methods to visualize CR, PV, CB and tyrosine hydroxylase (TH) positive striatal neurons. The interneuronal distribution was assessed by stereological methods applied to every striatal functional territory. Considering the four cell groups altogether, their density was higher in the associative (2120±91 cells/mm³) than in the sensorimotor (959±47 cells/mm³) or limbic (633±119 cells/mm³) territories. CB- and TH-immunoreactive(-ir) cells were distributed rather homogeneously in the three striatal territories. However, the density of CR and PV interneurons were more abundant in the associative and sensorimotor striatum, respectively. Regarding to their compartmental organization, CR-ir interneurons were frequently found in the border between compartments in the associative and sensorimotor territories, and CB-ir interneurons abounded at the striosome/matrix border in the sensorimotor domain.

Conclusions/Significance

The present study demonstrates that the architecture of the human striatum in terms of its interneuron composition varies in its three functional territories. Furthermore, our data highlight the importance of CR-ir striatal interneurons in the integration of associative information, and the selective role of PV-ir interneurons in the motor territory. On the other hand, the low density of dopaminergic cells casts doubts about their role in the normal human striatum.

Basal Ganglia disorders associated with imbalances in the striatal striosome and matrix compartments

The striatum is composed principally of GABAergic, medium spiny striatal projection neurons (MSNs) that can be categorized based on their gene expression, electrophysiological profiles, and input–output circuits. Major subdivisions of MSN populations include (1) those in ventromedial and dorsolateral striatal regions, (2) those giving rise to the direct and indirect pathways, and (3) those that lie in the striosome and matrix compartments. The first two classificatory schemes have enabled advances in understanding of how basal ganglia circuits contribute to disease. However, despite the large number of molecules that are differentially expressed in the striosomes or the extra-striosomal matrix, and the evidence that these compartments have different input–output connections, our understanding of how this compartmentalization contributes to striatal function is still not clear. A broad view is that the matrix contains the direct and indirect pathway MSNs that form parts of sensorimotor and associative circuits, whereas striosomes contain MSNs that receive input from parts of limbic cortex and project directly or indirectly to the dopamine-containing neurons of the substantia nigra, pars compacta. Striosomes are widely distributed within the striatum and are thought to exert global, as well as local, influences on striatal processing by exchanging information with the surrounding matrix, including through interneurons that send processes into both compartments. It has been suggested that striosomes exert and maintain limbic control over behaviors driven by surrounding sensorimotor and associative parts of the striatal matrix. Consistent with this possibility, imbalances between striosome and matrix functions have been reported in relation to neurological disorders, including Huntington’s disease, L-DOPA-induced dyskinesias, dystonia, and drug addiction. Here, we consider how signaling imbalances between the striosomes and matrix might relate to symptomatology in these disorders.

Targeting neuronal populations of the striatum

The striatum is critically involved in motor and motivational functions. The dorsal striatum, caudate–putamen, is primarily implicated in motor control and the learning of habits and skills, whereas the ventral striatum, the nucleus accumbens, is essential for motivation and drug reinforcement. The GABA medium-sized spiny neurons (MSNs, about 95% of striatal neurons), which are targets of the cerebral cortex and the midbrain dopaminergic neurons, form two pathways. The dopamine D₁ receptor-positive (D₁R) striatonigral MSNs project to the medial globus pallidus and substantia nigra pars reticulata (direct pathway) and co-express D₁R and substance P, whereas dopamine D₂ receptor-positive (D₂R) striatopallidal MSNs project to the lateral globus pallidus (indirect pathway) and co-express D₂R, adenosine A_2A receptor (A_2AR) and enkephalin (Enk). The specific role of the two efferent pathways in motor and motivational control remained poorly understood until recently. Indeed, D₁R striatonigral and D₂R striatopallidal neurons, are intermingled and morphologically indistinguishable, and, hence, cannot be functionally dissociated with techniques such as chemical lesions or surgery. In view of the still debated respective functions of projection D₂R striatopallidal and D₁R striatonigral neurons and striatal interneurons, both in motor control and learning but also in more cognitive processes such as motivation, the present review sum up the development of new models and techniques (bacterial artificial chromosome transgenesis, optogenetic, viral transgenesis) allowing the selective targeting of these striatal neuronal populations in adult animal brain to understand their specific roles.

Distribution of tyrosine hydroxylase-expressing interneurons with respect to anatomical organization of the neostriatum

We have recently shown in vitro that striatal tyrosine hydroxylase-expressing interneurons identified in transgenic mice by expression of enhanced green fluorescent protein (TH-eGFP) display electrophysiological profiles that are distinct from those of other striatal interneurons. Furthermore, striatal TH-eGFP interneurons show marked diversity in their electrophysiological properties and have been divided into four distinct subtypes. One question that arises from these observations is whether striatal TH-eGFP interneurons are distributed randomly, or obey some sort of organizational plan as has been shown to be the case with other striatal interneurons. An understanding of the striatal TH-eGFP interneuronal patterning is a vital step in understanding the role of these neurons in striatal functioning. Therefore, in the present set of studies the location of electrophysiologically identified striatal TH-eGFP interneurons was mapped. In addition, the distribution of TH-eGFP interneurons with respect to the striatal striosome–matrix compartmental organization was determined using μ-opioid receptor (MOR) immunofluorescence or intrinsic TH-eGFP fluorescence to delineate striosome and matrix compartments. Overall, the distribution of the different TH-eGFP interneuronal subtypes did not differ in dorsal versus ventral striatum. However, striatal TH-eGFP interneurons were found to be mostly in the matrix in the dorsal striatum whereas a significantly higher proportion of these neurons was located in MOR-enriched domains of the ventral striatum. Further, the majority of striatal TH-eGFP interneurons was found to be located within 100 μm of a striosome–matrix boundary. Taken together, the current results suggest that TH-eGFP interneurons obey different organizational principles in dorsal versus ventral striatum, and may play a role in communication between striatal striosome and matrix compartments.

Shifting responsibly: the importance of striatal modularity to reinforcement learning in uncertain environments

We propose here that the modular organization of the striatum reflects a context-sensitive modular learning architecture in which clustered striosome-matrisome domains participate in modular reinforcement learning (RL). Based on anatomical and physiological evidence, it has been suggested that the modular organization of the striatum could represent a learning architecture. There is not, however, a coherent view of how such a learning architecture could relate to the organization of striatal outputs into the direct and indirect pathways of the basal ganglia, nor a clear formulation of how such a modular architecture relates to the RL functions attributed to the striatum. Here, we hypothesize that striosome-matrisome modules not only learn to bias behavior toward specific actions, as in standard RL, but also learn to assess their own relevance to the environmental context and modulate their own learning and activity on this basis. We further hypothesize that the contextual relevance or "responsibility" of modules is determined by errors in predictions of environmental features and that such responsibility is assigned by striosomes and conveyed to matrisomes via local circuit interneurons. To examine these hypotheses and to identify the general requirements for realizing this architecture in the nervous system, we developed a simple modular RL model. We then constructed a network model of basal ganglia circuitry that includes these modules and the direct and indirect pathways. Based on simple assumptions, this model suggests that while the direct pathway may promote actions based on striatal action values, the indirect pathway may act as a gating network that facilitates or suppresses behavioral modules on the basis of striatal responsibility signals. Our modeling functionally unites the modular compartmental organization of the striatum with the direct-indirect pathway divisions of the basal ganglia, a step that we suggest will have important clinical implications.

Protective effect of Zhen-Wu-Tang (ZWT) through keeping DA stable and VMAT 2/DAT mRNA in balance in rats with striatal lesions induced by MPTP

ETHNOPHARMACOLOGICAL RELEVANCE

Zhen-Wu-Tang (ZWT), the modified formulation of a classical Chinese prescription from "Treaties on Febrile Disease", was clinically employed to treat Parkinson's disease.

AIM OF THE STUDY

To investigate the neuroprotective effect of ZWT on intra-striatum injection of MPTP-induced Parkinson's disease in rats.

MATERIALS AND METHODS

The effect of ZWT on the behavioral changes (open-field test, Ladder walking, spontaneous alternation in Y maze), the dopamine transmitter systems of substantia nigra, striatum and frontal cortex of rats by HPLC-ECD, mRNA expression of tyrosine hydroxylase (TH), dopamine transporter (DAT) and vesicular monoamine transporter 2 (VMAT 2) of the above three brain regions was investigated.

RESULTS

This study showed that ZWT not only ameliorated the behavior induced by the administration of MPTP in striatum, but also increased DA in the brain, prevented the decreasing of TH and balanced the ratio of VMAT 2/DAT in mRNA level.

CONCLUSIONS

These results suggest that ZWT possesses neuroprotective and anti-parkinsonism properties.

Key role of striatal cholinergic interneurons in processes leading to arrest of motor stereotypies

Motor stereotypy is a key symptom of various disorders such as Tourette's syndrome and punding. Administration of nicotine or cholinesterase inhibitors is effective in treating some of these symptoms. However, the role of cholinergic transmission in motor stereotypy remains unknown. During strong cocaine-induced motor stereotypy, we showed earlier that increased dopamine release results in decreased acetylcholine release in the territory of the dorsal striatum related to the prefrontal cortex. Here, we investigated the role of striatal cholinergic transmission in the arrest of motor stereotypy. Analysis of N-methyl-d-aspartic acid-evoked release of dopamine and acetylcholine during declining intensity of motor stereotypy revealed a dissociation between dopamine and acetylcholine release. Whereas dopamine release remained increased, the inhibition of acetylcholine release decreased, mirroring the time course of motor stereotypy. Furthermore, pharmacological treatments restoring striatal acetylcholine release (raclopride, dopamine D2 antagonist; intraperitoneal or local injection in prefrontal territory of the dorsal striatum) rapidly stopped motor stereotypy. In contrast, pharmacological treatments that blocked the post-synaptic effects of acetylcholine (scopolamine, muscarinic antagonist; intraperitoneal or striatal local injection) or induced degeneration of cholinergic interneurons (AF64A, cholinergic toxin) in the prefrontal territory of the dorsal striatum robustly prolonged the duration of strong motor stereotypy. Thus, we propose that restoration of cholinergic transmission in the prefrontal territory of the dorsal striatum plays a key role in the arrest of motor stereotypy.

Developmental exposure to manganese increases adult susceptibility to inflammatory activation of glia and neuronal protein nitration

Chronic exposure to manganese (Mn) produces a neurodegenerative disorder affecting the basal ganglia characterized by reactive gliosis and expression of neuroinflammatory genes including inducible nitric oxide synthase (NOS2). Induction of NOS2 in glial cells causes overproduction of nitric oxide (NO) and injury to neurons that is associated with parkinsonian-like motor deficits. Inflammatory activation of glia is believed to be an early event in Mn neurotoxicity, but specific responses of microglia and astrocytes to Mn during development remain poorly understood. In this study, we investigated the effect of juvenile exposure to Mn on the activation of glia and production of NO in C57Bl/6J mice, postulating that developmental Mn exposure would lead to heightened sensitivity to gliosis and increased expression of NOS2 in adult mice exposed again later in life. Immunohistochemical analysis indicated that Mn exposure caused increased activation of both microglia and astrocytes in the striatum (St), globus pallidus (Gp), and substantia nigra pars reticulata (SNpr) of treated mice compared with controls. More robust activation of microglia was observed in juveniles, whereas astrogliosis was more prominent in adult mice preexposed during development. Co-immunofluorescence studies demonstrated increased expression of NOS2 in glia located in the Gp and SNpr. Additionally, greater increases in the level of 3-nitrotyrosine protein adducts were detected in dopamine- and cAMP-regulated phosphoprotein-32-positive neurons of the St of Mn-treated adult mice preexposed as juveniles. These data indicate that subchronic exposure to Mn during development leads to temporally distinct patterns of glial activation that result in elevated nitrosative stress in distinct populations of basal ganglia neurons.

Oxidative damage and neurodegeneration in manganese-induced neurotoxicity

Exposure to excessive manganese (Mn) levels results in neurotoxicity to the extrapyramidal system and the development of Parkinson's disease (PD)-like movement disorder, referred to as manganism. Although the mechanisms by which Mn induces neuronal damage are not well defined, its neurotoxicity appears to be regulated by a number of factors, including oxidative injury, mitochondrial dysfunction and neuroinflammation. To investigate the mechanisms underlying Mn neurotoxicity, we studied the effects of Mn on reactive oxygen species (ROS) formation, changes in high-energy phosphates (HEP), neuroinflammation mediators and associated neuronal dysfunctions both in vitro and in vivo. Primary cortical neuronal cultures showed concentration-dependent alterations in biomarkers of oxidative damage, F2-isoprostanes (F2-IsoPs) and mitochondrial dysfunction (ATP), as early as 2 h following Mn exposure. Treatment of neurons with 500 microM Mn also resulted in time-dependent increases in the levels of the inflammatory biomarker, prostaglandin E2 (PGE2). In vivo analyses corroborated these findings, establishing that either a single or three (100 mg/kg, s.c.) Mn injections (days 1, 4 and 7) induced significant increases in F2-IsoPs and PGE2 in adult mouse brain 24 h following the last injection. Quantitative morphometric analyses of Golgi-impregnated striatal sections from mice exposed to single or three Mn injections revealed progressive spine degeneration and dendritic damage of medium spiny neurons (MSNs). These findings suggest that oxidative stress, mitochondrial dysfunction and neuroinflammation are underlying mechanisms in Mn-induced neurodegeneration.

Blockade of neurokinin-3 receptors modulates dopamine-mediated behavioral hyperactivity

Acute activation or blockade of neurokinin-3 (NK-3) receptors has been shown to alter dopamine-mediated function and behaviors, however long-term effects of NK-3 receptor blockade remain largely unknown. The present study investigated whether acute and repeated administration of the NK-3 receptor antagonist SB 222200 altered hyperactivity induced by cocaine, and examined its effects on dopamine D1 receptor density in the striatum. Adult male CD-1 mice received either vehicle or SB 222200 (2.5 or 5 mg/kg, s.c.) 30 min before a cocaine injection (20 mg/kg, i.p.) and behavioral responses were recorded. Mice that were administered SB 222200 had an attenuated stereotypic response to cocaine compared to vehicle treated mice. Mice were also injected once daily with either vehicle or SB 222200 (5 mg/kg, s.c.) for 5 days, and after a 7-day drug-free period they were challenged with either saline, cocaine or the dopamine D1 receptor agonist SKF 82958 (0.125 or 0.25 mg/kg, i.p.). Mice injected with SB 222200 had significantly enhanced hyperactivity when challenged with cocaine or a low dose of SKF 82958 (0.125 mg/kg, i.p.) compared to control mice. Brains of mice administered vehicle or SB 222200 for 5 days were harvested after a 7-day drug-free period for dopamine D1 receptor quantification by radioligand binding. [(3)H] SCH 23390 homogenate binding studies showed a 19.7% increase in dopamine D1 receptor density in the striatum of SB 222200 treated mice. These data suggest that repeated blockade of NK-3 receptors enhances subsequent dopamine-mediated behaviors possibly resulting from dopamine D1 receptor up-regulation in the striatum.

Interplay of beta2* nicotinic receptors and dopamine pathways in the control of spontaneous locomotion

Acetylcholine (ACh) is a known modulator of the activity of dopaminergic (DAergic) neurons through the stimulation of nicotinic ACh receptors (nAChRs). Yet, the subunit composition and specific location of nAChRs involved in DA-mediated locomotion remain to be established in vivo. Mice lacking the beta2 subunit of nAChRs (beta2KO) display striking hyperactivity in the open field, which suggests an imbalance in DA neurotransmission. Here, we performed the selective gene rescue of functional beta2*-nAChRs in either the substantia nigra pars compacta (SNpc) or the ventral tegmental area (VTA) of beta2KO mice. SNpc rescued mice displayed normalization of locomotor activity, both in familiar and unfamiliar environments, whereas restoration in the VTA only rescued exploratory behavior. These data demonstrate the dissociation between nigrostriatal and mesolimbic beta2*-nAChRs in regulating unique locomotor functions. In addition, the site-directed knock-down of the beta2 subunit in the SNpc by RNA interference caused hyperactivity in wild-type mice. These findings highlight the crucial interplay of nAChRs over the DA control of spontaneous locomotion.

Participation of mu-opioid, GABA(B), and NK1 receptors of major pain control medullary areas in pathways targeting the rat spinal cord: implications for descending modulation of nociceptive transmission

Several brain areas modulate pain transmission through direct projections to the spinal cord. The descending modulation is exerted by neurotransmitters acting both at spinally projecting neurons and at interneurons that target the projection neurons. We analyzed the expression of mu-opioid (MOR), gamma-aminobutyric acid GABA(B), and NK1 receptors in spinally projecting neurons of major medullary pain control areas of the rat: rostroventromedial medulla (RVM), dorsal reticular nucleus (DRt), nucleus of the solitary tract, ventral reticular nucleus, and lateralmost part of the caudal ventrolateral medulla. The retrograde tracer cholera toxin subunit B (CTb) was injected into the spinal dorsal horn, and medullary sections were processed by double immunocytochemistry for CTb and each receptor. The RVM contained the majority of double-labeled neurons followed by the DRt. In general, high percentages of MOR- and NK1-expressing neurons were retrogradely labeled, whereas GABA(B) receptors were mainly expressed in neurons that were not labeled from the cord. The results suggest that MOR and NK1 receptors play an important role in direct and indirect control of descending modulation. The co-localization of MOR and GABA(B) in DRt neurons also demonstrated by the present study suggests that the pronociceptive effects of this nucleus may be controlled by local opoidergic and GABAergic inhibition of the pronociception increased during chronic pain.

Roles of micro-opioid receptors in GABAergic synaptic transmission in the striosome and matrix compartments of the striatum

The striatum is divided into two compartments, the striosomes and extrastriosomal matrix, which differ in several cytochemical markers, input-output connections, and time of neurogenesis. Since it is thought that limbic, reward-related information and executive aspects of behavioral information may be differentially processed in the striosomes and matrix, respectively, intercompartmental communication should be of critical importance to proper functioning of the basal ganglia-thalamocortical circuits. Cholinergic interneurons are in a suitable position for this communication since they are preferentially located in the striosome-matrix boundaries and are known to elicit a conditioned pause response during sensorimotor learning. Recently, micro-opioid receptor (MOR) activation was found to presynaptically suppress the amplitude of GABAergic inhibitory postsynaptic currents in striosomal cells but not in matrix cells. Disinhibition of cells in the striosomes is further enhanced by inactivation of the protein kinase C cascade. We discuss in this review the possibility that MOR activation in the striosomes affects the activity of cholinergic interneurons and thus leads to changes in synaptic efficacy in the striatum.

Chemical architecture of the posterior striatum in the human brain

The neurochemical organization of the posterior caudate nucleus (CN) (body, gyrus and tail) and putamen (Put) was analyzed in the human brain using adjacent sections stained for acetylcholinesterase (AChE), limbic system-associated membrane protein (LAMP), enkephalin (ENK), parvalbumin (PV), calbindin (CB) and tyrosine hydroxylase (TH). Striosomes were visualized in all striatal regions but the anterior two thirds of the CN tail. They were highly immunoreactive (-ir) for ENK and LAMP, devoid of PV and AChE staining, and surrounded by a ring of tissue with pale TH- and CB-ir neuropil. In the Put, other rings of tissue completely free of ENK labeling surrounded certain striosomes (clear septa). In the CN body, gyrus and tail some markers revealed gradients and heterogeneities along the dorsoventral and mediolateral axes. A rim of striatal tissue densely stained for ENK and LAMP and poorly labeled for PV was noticeable along the lateral edge of the Put and the dorsolateral sector of the CN body. Our results illustrate a chemical architecture in the posterior striatum that is heterogeneous and slightly different from that found in the more anterior striatum.

Impact of 6-hydroxydopamine lesions and cocaine exposure on mu-opioid receptor expression and regulation of cholinergic transmission in the limbic-prefrontal territory of the rat dorsal striatum

Information processing within the striatum is regulated by local circuits involving dopamine, cholinergic interneurons and neuropeptides released by recurrent collaterals of striatal output neurons. In the limbic-prefrontal territory of the dorsal striatum, enkephalin inhibits the NMDA-evoked release of acetylcholine directly through micro-opioid receptors (MORs) located on cholinergic interneurons and indirectly through MORs of output neurons of striosomes. In this territory, we investigated the consequence of changes in dopamine transmission, bilateral 6-hydroxydopamine-induced degeneration of striatal dopaminergic innervation or cocaine (acute and chronic) exposure on (i) MOR expression in both cholinergic interneurons and output neurons of striosomes, and (ii) the direct and indirect enkephalin-MOR regulations of the NMDA-evoked release of acetylcholine. Expression of MORs in cholinergic interneurons was preserved after 6-hydroxydopamine and down-regulated after cocaine treatments. Accordingly, the direct enkephalin-MOR control of acetylcholine release was preserved after 6-hydroxydopamine treatment and lost after cocaine exposure. Expression of MORs in output neurons of striosomes was down-regulated in the 6-hydroxydopamine situation and either preserved or up-regulated after acute or chronic cocaine exposure, respectively. Accordingly, the indirect enkephalin-MOR control of acetylcholine release disappeared in the 6-hydroxydopamine situation but surprisingly, despite preservation of MORs in striosomes, disappeared after cocaine treatment. Showing that MORs of striosomes are still functional in this situation, the MOR agonist [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin inhibited the NMDA-evoked release of acetylcholine after cocaine exposure. Therefore, alteration in the regulation of cholinergic transmission by the enkephalin-MOR system might play a major role in the motivational and cognitive disorders associated with dopamine dysfunctions in fronto-cortico-basal ganglia circuits.

Sensitization of spinal cord nociceptive neurons with a conjugate of substance P and cholera toxin

Background

Several investigators have coupled toxins to neuropeptides for the purpose of lesioning specific neurons in the central nervous system. By producing deficits in function these toxin conjugates have yielded valuable information about the role of these cells. In an effort to specifically stimulate cells rather than kill them we have conjugated the neuropeptide substance P to the catalytic subunit of cholera toxin (SP-CTA). This conjugate should be taken up selectively by neurokinin receptor expressing neurons resulting in enhanced adenylate cyclase activity and neuronal firing.

Results

The conjugate SP-CTA stimulates adenylate cyclase in cultured cells that are transfected with either the NK1 or NK2 receptor, but not the NK3 receptor. We further demonstrate that intrathecal injection of SP-CTA in rats induces the phosphorylation of the transcription factor cyclic AMP response element binding protein (CREB) and also enhances the expression of the immediate early gene c-Fos. Behaviorally, low doses of SP-CTA (1 μg) injected intrathecally produce thermal hyperalgesia. At higher doses (10 μg) peripheral sensitivity is suppressed suggesting that descending inhibitory pathways may be activated by the SP-CTA induced sensitization of spinal cord neurons.

Conclusion

The finding that stimulation of adenylate cyclase in neurokinin receptor expressing neurons in the spinal cord produces thermal hyperalgesia is consistent with the known actions of these neurons. These data demonstrate that cholera toxin can be targeted to specific cell types by coupling the catalytic subunit to a peptide agonist for a g-protein coupled receptor. Furthermore, these results demonstrate that SP-CTA can be used as a tool to study sensitization of central neurons in vivo in the absence of an injury.

Single unit and population responses during inhibitory gating of striatal activity in freely moving rats

The striatum is thought to be an essential region for integrating diverse information in the brain. Rapid inhibitory gating (IG) of sensory input is most likely an early factor necessary for appropriate integration to be completed. Gating is currently evaluated in clinical settings and is dramatically altered in a variety of psychiatric illnesses. Basic neuroscience research using animals has revealed specific neural sites involved in IG including the hippocampus, thalamus, brainstem, amygdala and medial prefrontal cortex. The present study investigated local IG in the basal ganglia structure of the striatum using chronic recording microwires. We obtained both single unit activations and local field potentials (LFPs) in awake behaving rats from each wire during the standard two-tone paradigm. Single units responded with different types of activations including a phasic and sustained excitation, an inhibitory response and a combination response that contained both excitatory and inhibitory components. IG was observed in all the response types; however, non-gating was observed in a large proportion of responses as well. Positive wave field potentials at 50-60 ms post-stimulus (P60) showed consistent gating across the wire arrays. No significant correlations were found between single unit and LFP measures of gating during the initial baseline session. Gating was strengthened (Tamp/Camp ratios approaching 0) following acute stress (saline injection) at both the single unit and LFP level due to the reduction in the response to the second tone. Alterations in sensory responding reflected by changes in the neural response to the initial tone were primarily observed following long-term internal state deviation (food deprivation) and during general locomotion. Overall, our results support local IG by single neurons in striatum but also suggest that rapid inhibition is not the dominant activation profile observed in other brain regions.

Manganese-Induced Neurotoxicity: The Role of Astroglial-Derived Nitric Oxide in Striatal Interneuron Degeneration

Chronic exposure to excessive manganese (Mn) is the cause of a neurodegenerative movement disorder, termed manganism, resulting from degeneration of neurons within the basal ganglia. Pathogenic mechanisms underlying this disorder are not fully understood but involve inflammatory activation of glial cells within the basal ganglia. It was postulated in the present studies that reactive astrocytes are involved in neuronal injury from exposure to Mn through increased release of nitric oxide. C57Bl/6 mice subchronically exposed to Mn by intragastric gavage had increased levels of Mn in the striatum and displayed diminutions in both locomotor activity and striatal DA content. Mn exposure resulted in neuronal injury in the striatum and globus pallidus, particularly in regions proximal to the microvasculature, indicated by histochemical staining with fluorojade and cresyl fast violet. Neuropathological assessment revealed marked perivascular edema, with hypertrophic endothelial cells and diffusion of serum albumin into the perivascular space. Immunofluorescence studies employing terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate (DUTP)-biotin nick-end labeling revealed the presence of apoptotic neurons expressing neuronal nitric oxide synthase (NOS), choline acetyltransferase, and enkephalin in both the striatum and globus pallidus. In contrast, soma and terminals of dopaminergic neurons were morphologically unaltered in either the substantia nigra or striatum, as indicated by immunohistochemical staining for tyrosine hydroxylase. Regions with evident neuronal injury also displayed increased numbers of reactive astrocytes that coexpressed inducible NOS2 and localized with areas of increased neuronal staining for 3-nitrotyrosine protein adducts, a marker of NO formation. These data suggest a role for astrocyte-derived NO in injury to striatal-pallidal interneurons from Mn intoxication.

Phasic dopaminergic transmission increases NO efflux in the rat dorsal striatum via a neuronal NOS and a dopamine D(1/5) receptor-dependent mechanism

Dysfunctional neurotransmission within striatal networks is believed to underlie the pathophysiology of several neurological and psychiatric disorders. Nitric oxide (NO)-producing interneurons have been shown to play a critical role in modulating striatal synaptic transmission. These interneurons receive synaptic contacts from midbrain dopamine (DA) neurons and may be regulated by DA receptor activation. In the current study, striatal NO efflux was measured in anesthetized male rats using an NO-selective electrochemical microsensor and the role of DA in modulating NO synthase (NOS) activity was assessed during electrical or chemical (bicuculline) stimulation of the substantia nigra (SN). Electrical stimuli were patterned to approximate the natural single spike or burst firing activity of midbrain DA neurons. Electrical stimulation of the SN at low frequencies induced modest increases in striatal NO efflux. In contrast, train stimulation of the SN robustly increased NO efflux in a stimulus intensity-dependent manner. NO efflux evoked by SN stimulation was similar in chloral hydrate- and urethane-anesthetized rats. The facilitatory effect of train stimulation on striatal NO efflux was transient and attenuated by systemic administration of the neuronal NOS inhibitor 7-nitroindazole and the nonselective NOS inhibitor methylene blue. Moreover, the increase in NO efflux observed during chemical and train stimulation of the SN was attenuated following systemic administration of the DA D(1/5) receptor antagonist SCH 23390. SCH 23390 also blocked NO efflux induced by systemic administration of the D(1/5) agonist SKF 81297. These results indicate that neuronal NOS is activated in vivo by nigrostriatal DA cell burst firing via a DA D(1/5)-like receptor-dependent mechanism.

Possible Mechanisms of the Involvement of Dopaminergic Cells and Cholinergic Interneurons in the Striatum in the Conditioned-Reflex Selection of Motor Activity

A possible mechanism for the involvement of cholinergic interneurons in the striatum and dopaminergic cells in the substantia nigra in the selection from among several types of motor activity during learning is proposed. Selection is triggered by simultaneous increases in the activity of dopaminergic neurons and a pause in the activity of cholinergic interneurons in response to the conditioned signal. The appearance of the pause may facilitate activation of GABAergic interneurons in the striatum and the action of dopamine on D2 receptors on cholinergic interneurons. Differently directed changes in dopamine and acetylcholine levels synergistically modulate the efficiency of corticostriatal inputs, such that the rules for modulation of the "strong" and "weak" inputs are opposite in sign. The subsequent reorganization of neuron activity in the cortex-basal ganglia-thalamus-cortex circuit leads to increased activity in those cortical neurons providing "strong" innervation to the striatum with simultaneous decreases in the activity of neurons providing "weak" innervation to the striatum, which may underlie the selection of the movement reaction, in which the neocortex is involved. It follows from this model that if the delay between the conditioned and unconditioned stimuli is not longer than the latent period of the reactions of dopaminergic and cholinergic cells (about 100 msec), selection of movement activity in response to the conditioned signal and learning is hindered.

Involvement of the transmitter systems of the neostriatum in automation of motor skills in dogs

Chronic experiments were performed on six dogs to address the influence of automation of a motor skill on the components of an operant defensive reflex, rearrangement of posture, and the characteristics of the projection of the center of mass on a tensometric platform by the forepaws; the effects of activation and blockade of muscarinic and dopamine receptors on the process of automation of the motor skill were also studied. Despite high criteria for execution of the operant reflex, the reproducibility of reflex performance, increases in the tonic component of the response, and the clear diagonal pattern of the postural rearrangement, a local (as opposed to diffuse) projection of the position of the center of mass on the tensometric platform by the forepaws was seen only after prolonged training leading to automation of the skill. The effect of automation of the operant response could be obtained immediately following bilateral microinjection of the muscarinic receptor agonist carbachol into the neostriatum. The same effect, but weaker, was obtained using bilateral microinjections of the dopamine D2 receptor blocker raclopride into the neostriatum. Conversely, bilateral microinjections of the selective muscarinic M1 receptor blocker pirenzepine into the neostriatum gave the opposite result, with increases in the phasic component of the response, impairment of the diagonal pattern of the postural rearrangement, and diffuseness of the projection of the center of mass on the tensometric platform by the forelimbs. It is concluded that the indirect efferent output of the neostriatum has an important role in the process of learning the motor operant reflex involving maintenance of a defined degree of flexion (where the main role is played by the tonic component of the movement) and during the process of automation of the motor skill.

Regulation of psychostimulant-induced preprodynorphin, c-fos and zif/268 messenger RNA expression in the rat dorsal striatum by mu opioid receptor blockade

Several studies have shown that psychostimulants can induce differential immediate early gene and neuropeptide expression in the patch versus matrix compartments of dorsal striatum. The patch compartment contains a high density of mu opioid receptors and activation of these receptors may contribute to psychostimulant-induced gene expression in the patch versus matrix compartments of dorsal striatum. However, the contribution of mu opioid receptor activation to psychostimulant-induced changes in gene expression in the patch compartment of dorsal striatum has not been examined. The current study examined the role of mu opioid receptors in psychostimulant induction of preprodynorphin, c-fos and zif/268 messenger RNA expression in the patch versus matrix compartments of dorsal striatum. Male Sprague-Dawley rats were treated with the mu opioid receptor antagonist, clocinnamox (1 mg/kg, s.c.), 24 h prior to treatment with cocaine (30 mg/kg, i.p.) or methamphetamine (15 mg/kg, s.c.) and sacrificed 45 min or 3 h later. Mu opioid receptor antagonism blocked psychostimulant-induced preprodynorphin messenger RNA expression only in the rostral patch compartment, whereas psychostimulant-induced zif/268 messenger RNA expression in the patch and matrix compartments was attenuated throughout the dorsal striatum. Clocinnamox pretreatment had no effect on stimulant-induced increases in c-fos expression. These data suggest that mu opioid receptor activation plays a specific role in psychostimulant-induced preprodynorphin messenger RNA expression in the rostral patch compartment and zif/268 messenger RNA expression throughout dorsal striatum.

Morphological abnormalities in nitric-oxide-synthase-positive striatal interneurons of schizophrenic patients

Schizophrenia has been suggested to be a neurodevelopmental disorder, and nitric-oxide-synthase (NOS)-positive neurons were shown to be involved in distorted cortical development in schizophrenia. Here we investigated whether nitrinergic neurons in the striatum of schizophrenic patients also display abnormalities regarding distribution or morphology. To do so, postmortem putaminal sections of schizophrenic subjects were examined by means of nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) staining and NOS immunohistochemistry. NOS-positive neurons were counted and analyzed morphologically. Abnormalities regarding morphology or number of NOS-containing neurons could be found in the putamen of schizophrenics (n = 3), but not controls (n = 5). Neurons were either of abnormal size and branching pattern, or they were markedly reduced (130 +/- 44 vs. 54 +/- 62 NADPHd-positive somata/mm(3) putamen; p < 0.0001). Striatal nitrinergic interneurons might thus be involved in the pathogenesis of at least some forms of schizophrenia. Studies on larger samples are however needed to further corroborate this finding.