Dopamine depletion of the prefrontal cortex induces dendritic spine loss: reversal by atypical antipsychotic drug treatment

Ultrasound Stimulation Attenuates CRS-Induced Depressive Behavior by Modulating Dopamine Release in the Prefrontal Cortex

Depression is one of the most serious mental disorders affecting modern human life and is often caused by chronic stress. Dopamine system dysfunction is proposed to contribute to the pathophysiology of chronic stress, especially the ventral tegmental area (VTA) which mainly consists of dopaminergic neurons. Focused ultrasound stimulation (FUS) is a promising neuromodulation modality and multiple studies have demonstrated effective ultrasonic activation of cortical, subcortical, and related networks. However, the effects of FUS on the dopamine system and the potential link to chronic stress-induced depressive behaviors are relatively unknown. Here, we measured the effects of FUS targeting VTA on the improvement of depression-like behavior and evaluated the dopamine concentration in the downstream region - medial prefrontal cortex (mPFC). We found that targeting VTA FUS treatment alleviated chronic restraint stress (CRS) -induced anhedonia and despair behavior. Using an in vivo photometry approach, we analyzed the dopamine signal of mPFC and revealed a significant increase following the FUS, positively associated with the improvement of anhedonia behavior. FUS also protected the dopaminergic neurons in VTA from the damage caused by CRS exposure. Thus, these results demonstrated that targeting VTA FUS treatment significantly rescued the depressive-like behavior and declined dopamine level of mPFC induced by CRS. These beneficial effects of FUS might be due to protection in the DA neuron of VTA. Our findings suggest that FUS treatment could serve as a new therapeutic strategy for the treatment of stress-related disorders.

Hub architecture of the human structural connectome: Links to aging and processing speed

The human structural brain network, or connectome, has a rich-club organization with a small number of brain regions showing high network connectivity, called hubs. Hubs are centrally located in the network, energy costly, and critical for human cognition. Aging has been associated with changes in brain structure, function, and cognitive decline, such as processing speed. At a molecular level, the aging process is a progressive accumulation of oxidative damage, which leads to subsequent energy depletion in the neuron and causes cell death. However, it is still unclear how age affects hub connections in the human connectome. The current study aims to address this research gap by constructing structural connectome using fiber bundle capacity (FBC). FBC is derived from Constrained Spherical Deconvolution (CSD) modeling of white-matter fiber bundles, which represents the capacity of a fiber bundle to transfer information. Compared to the raw number of streamlines, FBC is less bias for quantifying connection strength within biological pathways. We found that hubs exhibit longer-distance connections and higher metabolic rates compared to peripheral brain regions, suggesting that hubs are biologically costly. Although the landscape of structural hubs was relatively age-invariant, there were wide-spread age effects on FBC in the connectome. Critically, these age effects were larger in connections within hub compared to peripheral brain connections. These findings were supported by both a cross-sectional sample with wide age-range (N = 137) and a longitudinal sample across 5 years (N = 83). Moreover, our results demonstrated that associations between FBC and processing speed were more concentrated in hub connections than chance level, and FBC in hub connections mediated the age-effects on processing speed. Overall, our findings indicate that structural connections of hubs, which demonstrate greater energy demands, are particular vulnerable to aging. The vulnerability may contribute to age-related impairments in processing speed among older adults.

Olanzapine Ameliorates Ischemic Stroke-like Pathology in Gerbils and H2O2-Induced Neurotoxicity in SH-SY5Y Cells via Inhibiting the MAPK Signaling Pathway

Olanzapine (OLNZ) is used to treat psychotic disorders. To look into the neurological basis of this phenomenon, we investigated the neuroprotective effects of OLNZ in gerbils and SH-SY5Y cells. Gerbils were subjected to transient global cerebral ischemia (TGCI) by blocking both common carotid arteries, and OLNZ (10 mg/kg) was injected intraperitoneally. Hydrogen peroxide (H₂O₂) was used to induce oxidative-stress-mediated damage in the SH-SY5Y cells. The results indicated that OLNZ administration markedly reduced neuron damage and glial cell triggering within CA1 zone of the hippocampus. We used RNA sequencing to assess the numbers of up-and downregulated genes involved in TGCI. We found that OLNZ treatment downregulated the expression of complement-component-related genes and the expression of mitogen-activated protein kinases (MAPKs) in the hippocampus. In cells, OLNZ co-treatment significantly improved cell viability and reduced lactate dehydrogenase (LDH), and reactive oxygen species (ROS) generation. Expression of antioxidant superoxide dismutase-1,2 enzymes (SOD-1, SOD-2) was also intensely upregulated by OLNZ, while the expression of MAPKs and NF-κB were reduced. Co-incubation with OLNZ also regulated apoptosis-related proteins Bax/Bcl-2 expression. Finally, the results demonstrated that treatment with OLNZ showed neuroprotective effects and that the MAPK pathway could involve in the protective effects.

Corticotropin-releasing factor receptor 1 in infralimbic cortex modulates social stress-altered decision-making

Chronic stress could lead to a bias in behavioral strategies toward habits. However, it remains unclear which neuronal system modulates stress-induced behavioral abnormality during decision making. The corticotropin-releasing factor (CRF) system in the medial prefrontal cortex (mPFC), which has been implicated in governing strategy choice, is involved in the response to stress. The present study aimed to clarify whether altered function in cortical CRF receptors is linked to abnormal behaviors after chronic stress. In results, mice subjected to a 10-day social defeat preferred to use a habitual strategy. The infralimbic cortex (IL), but not the prelimbic cortex (PL) or anterior cingulate cortex (ACC), showed higher cFos expression in stress-subjected mice than in control mice, which may be associated with habitual behavior choice. Furthermore, CRF receptor 1 (CRFR1) agonist and antagonist infusion in IL during behavioral training mimicked and rescued stress-caused behavioral change in the decision-making assessment, respectively. An electrophysiological approach showed that the frequencies of both spontaneous IPSC and spontaneous EPSC, but not their amplitude, increased after stress and were modulated by CRFR1 agents. Further recordings revealed that an increased ratio of excitation to inhibition (E/I ratio) of IL by stress was rescued under conditions with CRFR1 antagonist. Collectively, these data indicate that CRFR1 plays a critical role in stress-permitted or enhanced glutamatergic and GABAergic presynaptic transmission in direct or indirect ways, as well as the modulation for E/I ratio in the IL. Thus, CRFR1 in the mPFC may be a proper target for treating cases of chronic stress-altered behavior.

Plasma Orexin-A Levels in Patients With Schizophrenia: A Systematic Review and Meta-Analysis

BACKGROUND

Orexins are polypeptides regulating appetite, sleep-wake cycle, and cognition functions, which are commonly disrupted in patients with schizophrenia. Patients with schizophrenia show a decreased connectivity between the prefrontal cortex and midline-anterior thalamus, and orexin can directly activate the axon terminal of cells within the prefrontal cortex and selectively depolarize neurons in the midline intralaminar nuclei of the thalamus. To address the relationship between orexin and schizophrenia, this study performed a meta-analysis on the alteration of plasma orexin-A levels in patients with schizophrenia.

METHOD

We searched eligible studies in PubMed, Embase, Cochrane, and China National Knowledge Infrastructure (CNKI) from 1998 to September 3, 2021. A total of 8 case-control studies were included in the meta-analyses, providing data on 597 patients with schizophrenia and 370 healthy controls. The Stata version 16.0 software was used to calculate the Hedges's adjusted g with 95% confidence intervals (CI).

RESULTS

The plasma orexin-A levels were not altered in subjects with schizophrenia (n = 597) when compared to healthy controls (n = 370). Subgroup analyses of gender (male and female vs. only male), country (China vs. other countries), medication (medication vs. non-medication), and the measurement of plasma orexin-A (Enzyme-linked immunosorbent assay vs. radioimmunoassay) revealed heterogeneity ranging from 30.15 to 98.15%, but none showed a significant alteration of plasma orexin-A levels in patients with schizophrenia. Heterogeneity was lower in the other countries and radioimmunoassay subgroup, while other subgroups remained to be highly heterogeneous. No significant evidence of publication bias was found either in Begg's test or the Egger's test.

CONCLUSION

The present meta-analysis indicated that patients with schizophrenia did not show abnormal plasma levels of orexin-A.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021283455, identifier: CRD42021283455.

Impact of Pharmacological and Non-Pharmacological Modulators on Dendritic Spines Structure and Functions in Brain

Dendritic spines are small, thin, hair-like protrusions found on the dendritic processes of neurons. They serve as independent compartments providing large amplitudes of Ca²⁺ signals to achieve synaptic plasticity, provide sites for newer synapses, facilitate learning and memory. One of the common and severe complication of neurodegenerative disease is cognitive impairment, which is said to be closely associated with spine pathologies viz., decreased in spine density, spine length, spine volume, spine size etc. Many treatments targeting neurological diseases have shown to improve the spine structure and distribution. However, concise data on the various modulators of dendritic spines are imperative and a need of the hour. Hence, in this review we made an attempt to consolidate the effects of various pharmacological (cholinergic, glutamatergic, GABAergic, serotonergic, adrenergic, and dopaminergic agents) and non-pharmacological modulators (dietary interventions, enriched environment, yoga and meditation) on dendritic spines structure and functions. These data suggest that both the pharmacological and non-pharmacological modulators produced significant improvement in dendritic spine structure and functions and in turn reversing the pathologies underlying neurodegeneration. Intriguingly, the non-pharmacological approaches have shown to improve intellectual performances both in preclinical and clinical platforms, but still more technology-based evidence needs to be studied. Thus, we conclude that a combination of pharmacological and non-pharmacological intervention may restore cognitive performance synergistically via improving dendritic spine number and functions in various neurological disorders.

Dopamine: The Neuromodulator of Long-Term Synaptic Plasticity, Reward and Movement Control

Dopamine (DA) is a key neurotransmitter involved in multiple physiological functions including motor control, modulation of affective and emotional states, reward mechanisms, reinforcement of behavior, and selected higher cognitive functions. Dysfunction in dopaminergic transmission is recognized as a core alteration in several devastating neurological and psychiatric disorders, including Parkinson's disease (PD), schizophrenia, bipolar disorder, attention deficit hyperactivity disorder (ADHD) and addiction. Here we will discuss the current insights on the role of DA in motor control and reward learning mechanisms and its involvement in the modulation of synaptic dynamics through different pathways. In particular, we will consider the role of DA as neuromodulator of two forms of synaptic plasticity, known as long-term potentiation (LTP) and long-term depression (LTD) in several cortical and subcortical areas. Finally, we will delineate how the effect of DA on dendritic spines places this molecule at the interface between the motor and the cognitive systems. Specifically, we will be focusing on PD, vascular dementia, and schizophrenia.

Levodopa Improves Cognitive Function and the Deficits of Structural Synaptic Plasticity in Hippocampus Induced by Global Cerebral Ischemia/Reperfusion Injury in Rats

The cognitive impairment caused by cerebral ischemia/reperfusion is an unsolved problem in the field of international neural rehabilitation. Not only ameliorates the consciousness level of certain patients who suffered from ischemia-reperfusion injury and were comatose for a long time period after cerebral resuscitation treatment, but levodopa also improves the symptoms of neurological deficits in rats with global cerebral ischemia-reperfusion injury. However, Levodopa has not been widely used as a brain protection drug after cardiopulmonary resuscitation, because of its unclear repair mechanism. Levodopa was used to study the neuroplasticity in the hippocampus of global cerebral ischemia/reperfusion injury rat model, established by Pulsinelli's four-vessel occlusion method. Levodopa was injected intraperitoneally at 50 mg/kg/d for 7 consecutive days after 1st day of surgery. The modified neurological function score, Morris water maze, magnetic resonance imaging, Nissl and TH staining, electron microscopy and western blot were used in the present study. The results showed that levodopa improved the neurological function and learning and memory of rats after global cerebral ischemia/reperfusion injury, improved the integrity of white matter, and density of gray matter in the hippocampus, increased the number of synapses, reduced the delayed neuronal death, and increased the expression of synaptic plasticity-related proteins (BDNF, TrkB, PSD95, and Drebrin) in the hippocampus. In conclusion, levodopa can improve cognitive function after global cerebral ischemia/reperfusion injury by enhancing the synaptic plasticity in the hippocampus.

Allosteric Modulators of G Protein-Coupled Dopamine and Serotonin Receptors: A New Class of Atypical Antipsychotics

Schizophrenia was first described by Emil Krapelin in the 19th century as one of the major mental illnesses causing disability worldwide. Since the introduction of chlorpromazine in 1952, strategies aimed at modifying the activity of dopamine receptors have played a major role for the treatment of schizophrenia. The introduction of atypical antipsychotics with clozapine broadened the range of potential targets for the treatment of this psychiatric disease, as they also modify the activity of the serotoninergic receptors. Interestingly, all marketed drugs for schizophrenia bind to the orthosteric binding pocket of the receptor as competitive antagonists or partial agonists. In recent years, a strong effort to develop allosteric modulators as potential therapeutic agents for schizophrenia was made, mainly for the several advantages in their use. In particular, the allosteric binding sites are topographically distinct from the orthosteric pockets, and thus drugs targeting these sites have a higher degree of receptor subunit specificity. Moreover, “pure” allosteric modulators maintain the temporal and spatial fidelity of native orthosteric ligand. Furthermore, allosteric modulators have a “ceiling effect”, and their modulatory effect is saturated above certain concentrations. In this review, we summarize the progresses made in the identification of allosteric drugs for dopamine and serotonin receptors, which could lead to a new generation of atypical antipsychotics with a better profile, especially in terms of reduced side effects.

Microglial Pruning of Synapses in the Prefrontal Cortex During Adolescence

Exaggerated synaptic elimination in the prefrontal cortex (PFC) during adolescence has been suggested to contribute to the neuropathological changes of schizophrenia. Recent data indicate that microglia (MG) sculpt synapses during early postnatal development. However, it is not known if MG contribute to the structural maturation of the PFC, which has a protracted postnatal development. We determined if MG are involved in developmentally specific synapse elimination in the PFC, focusing on adolescence. Layer 5 PFC pyramidal cells (PCs) were intracellularly filled with Lucifer Yellow for dendritic spine measurements in postnatal day (P) 24, P30, P35, P39, and P50 rats. In the contralateral PFC we evaluated if MG engulfed presynaptic (glutamatergic) and postsynaptic (dendritic spines) elements. Dendritic spine density increased from P24 to P35, when spine density peaked. There was a significant increase in MG engulfment of spines at P39 relative to earlier ages; this subsided by P50. MG also phagocytosed presynaptic glutamatergic terminals. These data indicate that MG transiently prune synapses of PFC PCs during adolescence, when the symptoms of schizophrenia typically first appear. An increase in MG-mediated synaptic remodeling of PFC PCs may contribute to the structural changes observed in schizophrenia.

Effects of the 5-HT2A and DRD3 genotypes on cortical morphology and functional connectivity density in drug-naïve first episode schizophrenia

The 5-hydroxytryptamine 2A receptor (5-HT2A) and dopamine D3 receptor (DRD3) have been extensively studied as promising candidate genes for schizophrenia. Magnetic resonance imaging studies have demonstrated that schizophrenia is associated with widespread structural and functional abnormalities in the brain. Serotonin and dopamine receptors play crucial roles in the development of the human cerebral cortex and brain activity. However, how the 5-HT2A and DRD3 genes impact brain structure and function in schizophrenia remains unknown. In the present study, we investigated the main effect of disease state and the interaction effect between disease state and genotype of these two genes on cortical volume, thickness, surface area and functional connectivity density (FCD) in fifty-five drug-naïve first episode schizophrenia patients and fifty-three healthy controls. We found that the differences in local FCD (lFCD) and global FCD (gFCD) between patients and healthy controls were predominantly located in brain hub regions. The significant interaction effects of disease state and 5-HT2A and DRD3 genes on brain structure and function were mainly located in the temporal cortex. Our findings may help to improve the understanding of the relationship between 5-HT2A and DRD3 genotypes and schizophrenia pathogenesis.

Inefficient neural system stabilization: a theory of spontaneous resolutions and recurrent relapses in psychosis

A striking feature of psychosis is its heterogeneity. Presentations of psychosis vary from transient symptoms with no functional consequence in the general population to a tenacious illness at the other extreme, with a wide range of variable trajectories in between. Even among patients with schizophrenia, who are diagnosed on the basis of persistent deterioration, marked variation is seen in response to treatment, frequency of relapses and degree of eventual recovery. Existing theoretical accounts of psychosis focus almost exclusively on how symptoms are initially formed, with much less emphasis on explaining their variable course. In this review, I present an account that links several existing notions of the biology of psychosis with the variant clinical trajectories. My aim is to incorporate perspectives of systems neuroscience in a staging framework to explain the individual variations in illness course that follow the onset of psychosis.

Neuroprotective effects of the second generation antipsychotics

BACKGROUND

In contrast to over 30 studies reporting neurotoxicity associated with the first-generation antipsychotics (FGAs), several published studies have reported multiple neuroprotective effects associated with the second generation antipsychotics (SGAs). This prompted us to conduct a review of the reported neuroprotective mechanisms of the SGA class of antipsychotics compared to the FGAs.

METHODS

A PubMed search was conducted using the keywords antipsychotic, neuroprotection, neuroplasticity, neurogenesis, neurotoxicity, toxicity, brain volume, neuroinflammation, oxidative stress, myelin, and oligodendrocyte. No restrictions were placed on the date of the articles or language. Studies with a clearly described methodology were included.

RESULTS

Animal, cell culture, and human clinical studies were identified. Twenty-four reports met the criteria for the search. All studies included at least one SGA (aripiprazole, clozapine, lurasidone, olanzapine, paliperidone, perospirone, quetiapine, risperidone, and/or ziprasidone). A few also included FGAs as a comparator (predominantly haloperidol). All studies demonstrated at least one neuroprotective mechanism of one or more SGAs, while some studies also showed that FGAs ranged from having no neuroprotective effects to actually exerting neurotoxic effects leading to neuronal death.

CONCLUSIONS

A review of the literature suggests that in addition to their antipsychotic efficacy and low motoric side effects, SGAs exert measurable neuroprotective effects mediated via multiple molecular mechanisms and often in a dose-dependent manner. The neuroprotective effects of SGAs range from preventative to restorative and may play a salutary role in ameliorating the neurodegenerative effects of psychosis.

Dopamine Synthesis Capacity is Associated with D2/3 Receptor Binding but Not Dopamine Release

Positron Emission Tomography (PET) imaging allows the estimation of multiple aspects of dopamine function including dopamine synthesis capacity, dopamine release, and D2/3 receptor binding. Though dopaminergic dysregulation characterizes a number of neuropsychiatric disorders including schizophrenia and addiction, there has been relatively little investigation into the nature of relationships across dopamine markers within healthy individuals. Here we used PET imaging in 40 healthy adults to compare, within individuals, the estimates of dopamine synthesis capacity (K_i) using 6-[¹⁸F]fluoro-l-m-tyrosine ([¹⁸F]FMT; a substrate for aromatic amino acid decarboxylase), baseline D2/3 receptor-binding potential using [¹¹C]raclopride (a weak competitive D2/3 receptor antagonist), and dopamine release using [¹¹C]raclopride paired with oral methylphenidate administration. Methylphenidate increases synaptic dopamine by blocking the dopamine transporter. We estimated dopamine release by contrasting baseline D2/3 receptor binding and D2/3 receptor binding following methylphenidate. Analysis of relationships among the three measurements within striatal regions of interest revealed a positive correlation between [¹⁸F]FMT K_i and the baseline (placebo) [¹¹C]raclopride measure, such that participants with greater synthesis capacity showed higher D2/3 receptor-binding potential. In contrast, there was no relationship between [¹⁸F]FMT and methylphenidate-induced [¹¹C]raclopride displacement. These findings shed light on the nature of regulation between pre- and postsynaptic dopamine function in healthy adults, which may serve as a template from which to identify and describe alteration with disease.

Mapping pathologic circuitry in schizophrenia

Schizophrenia is a complex disorder lacking an effective treatment option for the pervasive and debilitating cognitive impairments experienced by patients. Working memory is a core cognitive function impaired in schizophrenia that depends upon activation of distributed neural network, including the circuitry of the dorsolateral prefrontal cortex (DLPFC). Accordingly, individuals diagnosed with schizophrenia show reduced DLPFC activation while performing working-memory tasks. This lower DLPFC activation appears to be an integral part of the disease pathophysiology, and not simply a reflection of poor performance. Thus, the cellular and circuitry alterations that underlie lower DLPFC neuronal activity in schizophrenia must be determined in order to identify appropriate therapeutic targets. Studies using human postmortem brain tissue provide a robust way to investigate and characterize these cellular and circuitry alterations at multiple levels of resolution, and such studies provide essential information that cannot be obtained either through in vivo studies in humans or through experimental animal models. Studies examining neuronal morphology, protein expression and localization, and transcript levels indicate that a microcircuit composed of excitatory pyramidal cells and inhibitory interneurons containing the calcium-binding protein parvalbumin is altered in the DLPFC of subjects with schizophrenia and likely contributes to DLPFC dysfunction.

Risperidone and aripiprazole alleviate prenatal valproic acid-induced abnormalities in behaviors and dendritic spine density in mice

RATIONALE

Rodents exposed prenatally to valproic acid (VPA) exhibit autism spectrum disorder (ASD)-like behavioral abnormalities. We recently found that prenatal VPA exposure causes hypofunction of the prefrontal dopaminergic system in mice. This suggests that the dopaminergic system may be a potential pharmacological target for treatment of behavioral abnormalities in ASD patients.

OBJECTIVES

In the present study, we examined the effects of antipsychotic drugs, which affect the dopaminergic system, on the social interaction deficits, recognition memory impairment, and reduction in dendritic spine density in the VPA mouse model of ASD.

RESULTS

Both acute and chronic administrations of the atypical antipsychotic drugs risperidone and aripiprazole increased prefrontal dopamine (DA) release, while the typical antipsychotic drug haloperidol did not. Chronic risperidone and aripiprazole, but not haloperidol, increased the expression of c-Fos in the prefrontal cortex, although they all increased c-Fos expression in the striatum. Chronic, but not acute, administrations of risperidone and aripiprazole improved the VPA-induced social interaction deficits and recognition memory impairment, as well as the reduction in dendritic spine density in the prefrontal cortex and hippocampus. In contrast, chronic administration of haloperidol did not ameliorate VPA-induced abnormalities in behaviors and dendritic spine density.

CONCLUSIONS

These findings indicate that chronic risperidone and aripiprazole treatments improve VPA-induced abnormalities in behaviors and prefrontal dendritic spine density, which may be mediated by repeated elevation of extracellular DA in the prefrontal cortex. Our results also imply that loss of prefrontal dendritic spines may be involved in the abnormal behaviors in the VPA mouse model of ASD.

Risperidone and aripiprazole alleviate prenatal valproic acid-induced abnormalities in behaviors and dendritic spine density in mice

RATIONALE

Rodents exposed prenatally to valproic acid (VPA) exhibit autism spectrum disorder (ASD)-like behavioral abnormalities. We recently found that prenatal VPA exposure causes hypofunction of the prefrontal dopaminergic system in mice. This suggests that the dopaminergic system may be a potential pharmacological target for treatment of behavioral abnormalities in ASD patients.

OBJECTIVES

In the present study, we examined the effects of antipsychotic drugs, which affect the dopaminergic system, on the social interaction deficits, recognition memory impairment, and reduction in dendritic spine density in the VPA mouse model of ASD.

RESULTS

Both acute and chronic administrations of the atypical antipsychotic drugs risperidone and aripiprazole increased prefrontal dopamine (DA) release, while the typical antipsychotic drug haloperidol did not. Chronic risperidone and aripiprazole, but not haloperidol, increased the expression of c-Fos in the prefrontal cortex, although they all increased c-Fos expression in the striatum. Chronic, but not acute, administrations of risperidone and aripiprazole improved the VPA-induced social interaction deficits and recognition memory impairment, as well as the reduction in dendritic spine density in the prefrontal cortex and hippocampus. In contrast, chronic administration of haloperidol did not ameliorate VPA-induced abnormalities in behaviors and dendritic spine density.

CONCLUSIONS

These findings indicate that chronic risperidone and aripiprazole treatments improve VPA-induced abnormalities in behaviors and prefrontal dendritic spine density, which may be mediated by repeated elevation of extracellular DA in the prefrontal cortex. Our results also imply that loss of prefrontal dendritic spines may be involved in the abnormal behaviors in the VPA mouse model of ASD.

Levodopa treatment and dendritic spine pathology

Parkinson's disease (PD) is a neurodegenerative disorder associated with the progressive loss of nigrostriatal dopaminergic neurons. Levodopa is the most effective treatment for the motor symptoms of PD. However, chronic oral levodopa treatment can lead to various motor and nonmotor complications because of nonphysiological pulsatile dopaminergic stimulation in the brain. Examinations of autopsy cases with PD have revealed a decreased number of dendritic spines of striatal neurons. Animal models of PD have revealed altered density and morphology of dendritic spines of neurons in various brain regions after dopaminergic denervation or dopaminergic denervation plus levodopa treatment, indicating altered synaptic transmission. Recent studies using rodent models have reported dendritic spine head enlargement in the caudate‐putamen, nucleus accumbens, primary motor cortex, and prefrontal cortex in cases where chronic levodopa treatment following dopaminergic denervation induced dyskinesia‐like abnormal involuntary movement. Hypertrophy of spines results from insertion of alpha‐amino‐2,3‐dihydro‐5‐methyl‐3‐oxo‐4‐isoxazolepropanoic acid receptors into the postsynaptic membrane. Such spine enlargement indicates hypersensitivity of the synapse to excitatory inputs and is compatible with a lack of depotentiation, which is an electrophysiological hallmark of levodopa‐induced dyskinesia found in the corticostriatal synapses of dyskinetic animals and the motor cortex of dyskinetic PD patients. This synaptic plasticity may be one of the mechanisms underlying the priming of levodopa‐induced complications such as levodopa‐induced dyskinesia and dopamine dysregulation syndrome. Drugs that could potentially prevent spine enlargement, such as calcium channel blockers, N‐methyl‐D‐aspartate receptor antagonists, alpha‐amino‐2,3‐dihydro‐5‐methyl‐3‐oxo‐4‐isoxazolepropanoic acid receptor antagonists, and metabotropic glutamate receptor antagonists, are candidates for treatment of levodopa‐induced complications in PD. © 2017 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Differential Associations between Cortical Thickness and Striatal Dopamine in Treatment-Naïve Adults with ADHD vs. Healthy Controls

Alterations in catecholamine signaling and cortical morphology have both been implicated in the pathophysiology of attention deficit/hyperactivity disorder (ADHD). However, possible links between the two remain unstudied. Here, we report exploratory analyses of cortical thickness and its relation to striatal dopamine transmission in treatment-naïve adults with ADHD and matched healthy controls. All participants had one magnetic resonance imaging (MRI) and two [¹¹C]raclopride positron emission tomography scans. Associations between frontal cortical thickness and the magnitude of d-amphetamine-induced [¹¹C]raclopride binding changes were observed that were divergent in the two groups. In the healthy controls, a thicker cortex was associated with less dopamine release; in the ADHD participants the converse was seen. The same divergence was seen for baseline D2/3 receptor availability. In healthy volunteers, lower D2/3 receptor availability was associated with a thicker cortex, while in the ADHD group lower baseline D2/3 receptor availability was associated with a thinner cortex. Individual differences in cortical thickness in these regions correlated with ADHD symptom severity. Together, these findings add to the evidence of associations between dopamine transmission and cortical morphology, and suggest that these relationships are altered in treatment-naïve adults with ADHD.

The modulation of adult neuroplasticity is involved in the mood-improving actions of atypical antipsychotics in an animal model of depression

Depression is a prevalent psychiatric disorder with an increasing impact in global public health. However, a large proportion of patients treated with currently available antidepressant drugs fail to achieve remission. Recently, antipsychotic drugs have received approval for the treatment of antidepressant-resistant forms of major depression. The modulation of adult neuroplasticity, namely hippocampal neurogenesis and neuronal remodeling, has been considered to have a key role in the therapeutic effects of antidepressants. However, the impact of antipsychotic drugs on these neuroplastic mechanisms remains largely unexplored. In this study, an unpredictable chronic mild stress protocol was used to induce a depressive-like phenotype in rats. In the last 3 weeks of stress exposure, animals were treated with two different antipsychotics: haloperidol (a classical antipsychotic) and clozapine (an atypical antipsychotic). We demonstrated that clozapine improved both measures of depressive-like behavior (behavior despair and anhedonia), whereas haloperidol aggravated learned helplessness in the forced-swimming test and behavior flexibility in a cognitive task. Importantly, an upregulation of adult neurogenesis and neuronal survival was observed in animals treated with clozapine, whereas haloperidol promoted a downregulation of these processes. Furthermore, clozapine was able to re-establish the stress-induced impairments in neuronal structure and gene expression in the hippocampus and prefrontal cortex. These results demonstrate the modulation of adult neuroplasticity by antipsychotics in an animal model of depression, revealing that the atypical antipsychotic drug clozapine reverts the behavioral effects of chronic stress by improving adult neurogenesis, cell survival and neuronal reorganization.

Cortical brain volume abnormalities associated with few or multiple neuropsychiatric symptoms in Alzheimer's disease

New research on assessing neuropsychiatric manifestations of Alzheimer´s Disease (AD) involves grouping neuropsychiatric symptoms into syndromes. Yet this approach is limited by high inter-subject variability in neuropsychiatric symptoms and a relatively low degree of concordance across studies attempting to cluster neuropsychiatric symptoms into syndromes. An alternative strategy that involves dichotomizing AD subjects into those with few versus multiple neuropsychiatric symptoms is both consonant with real-world clinical practice and can contribute to understanding neurobiological underpinnings of neuropsychiatric symptoms in AD patients. The aim of this study was to address whether the number of neuropsychiatric symptoms (i.e., presence of few [≤2] versus multiple [≥3] symptoms) in AD would be associated with degree of significant gray matter (GM) volume loss. Of particular interest was volume loss in brain regions involved in memory, emotional processing and salience brain networks, including the prefrontal, lateral temporal and parietal cortices, anterior cingulate gyrus, temporo-limbic structures and insula. We recruited 19 AD patients and 13 healthy controls, which underwent an MRI and neuropsychiatric assessment. Regional brain volumes were determined using voxel-based morphometry and other advanced imaging processing methods. Our results indicated the presence of different patterns of GM atrophy in the two AD subgroups relative to healthy controls. AD patients with multiple neuropsychiatric manifestations showed more evident GM atrophy in the left superior temporal gyrus and insula as compared with healthy controls. In contrast, AD subjects with few neuropsychiatric symptoms displayed more GM atrophy in prefrontal regions, as well as in the dorsal anterior cingulate ad post-central gyri, as compared with healthy controls. Our findings suggest that the presence of multiple neuropsychiatric symptoms is more related to the degree of atrophy in specific brain networks rather than dependent on the global severity of widespread neurodegenerative brain changes.

Spine Enlargement of Pyramidal Tract-Type Neurons in the Motor Cortex of a Rat Model of Levodopa-Induced Dyskinesia

Growing evidence suggests that abnormal synaptic plasticity of cortical neurons underlies levodopa-induced dyskinesia (LID) in Parkinson's disease (PD). Spine morphology reflects synaptic plasticity resulting from glutamatergic transmission. We previously reported that enlargement of the dendritic spines of intratelencephalic-type (IT) neurons in the primary motor cortex (M1) is linked to the development of LID. However, the relevance of another M1 neuron type, pyramidal-tract (PT) neurons, to LID remains unknown. We examined the morphological changes of the dendritic spines of M1 PT neurons in a rat model of LID. We quantified the density and size of these spines in 6-hydroxydopamine-lesioned rats (a model of PD), 6-hydroxydopamine-lesioned rats chronically treated with levodopa (a model of LID), and control rats chronically treated with levodopa. Dopaminergic denervation alone had no effect on spine density and head area. However, the LID model showed significant increases in the density and spine head area and the development of dyskinetic movements. In contrast, levodopa treatment of normal rats increased spine density alone. Although, chronic levodopa treatment increases PT neuron spine density, with or without dopaminergic denervation, enlargement of PT neuron spines appears to be a specific feature of LID. This finding suggests that PT neurons become hyperexcited in the LID model, in parallel with the enlargement of spines. Thus, spine enlargement, and the resultant hyperexcitability of PT pyramidal neurons, in the M1 cortex might contribute to abnormal cortical neuronal plasticity in LID.

Dopaminergic control of anxiety in young and aged zebrafish

Changes in the expression of the dopamine transporter (DAT), or the sensitivity of dopamine receptors, are associated with aging and substance abuse and may underlie some of the symptoms common to both conditions. In this study, we explored the role of the dopaminergic system in the anxiogenic effects of aging and acute cocaine exposure by comparing the behavioral phenotypes of wild type (WT) and DAT knockout zebrafish (DAT-KO) of different ages. To determine the involvement of specific dopamine receptors in anxiety states, antagonists to D1 (SCH23390) and D2/D3 (sulpiride) were employed. We established that DAT-KO results in a chronic anxiety-like state, seen as an increase in bottom-dwelling and thigmotaxis. Similar effects were produced by aging and acute cocaine administration, both leading to reduction in DAT mRNA abundance (qPCR). Inhibition of D1 activity counteracted the anxiety-like effects associated with DAT deficit, independent of its origin. Inhibition of D2/D3 receptors reduced anxiety in young DAT-KO, and enhanced the anxiogenic effects of cocaine in WT, but did not affect aged WT or DAT-KO fish. These findings provide new evidence that the dopaminergic system plays a critical role in anxiety-like states, and suggest that adult zebrafish provide a sensitive diurnal vertebrate model for elucidating the molecular mechanisms of anxiety and a platform for anxiolytic drug screens.

Effects of Chronic Dopamine D2R Agonist Treatment and Polysialic Acid Depletion on Dendritic Spine Density and Excitatory Neurotransmission in the mPFC of Adult Rats

Dopamine D2 receptors (D2R) in the medial prefrontal cortex (mPFC) are key players in the etiology and therapeutics of schizophrenia. The overactivation of these receptors contributes to mPFC dysfunction. Chronic treatment with D2R agonists modifies the expression of molecules implicated in neuronal structural plasticity, synaptic function, and inhibitory neurotransmission, which are also altered in schizophrenia. These changes are dependent on the expression of the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), a plasticity-related molecule, but nothing is known about the effects of D2R and PSA-NCAM on excitatory neurotransmission and the structure of mPFC pyramidal neurons, two additional features affected in schizophrenia. To evaluate these parameters, we have chronically treated adult rats with PPHT (a D2R agonist) after enzymatic removal of PSA with Endo-N. Both treatments decreased spine density in apical dendrites of pyramidal neurons without affecting their inhibitory innervation. Endo-N also reduced the expression of vesicular glutamate transporter-1. These results indicate that D2R and PSA-NCAM are important players in the regulation of the structural plasticity of mPFC excitatory neurons. This is relevant to our understanding of the neurobiological basis of schizophrenia, in which structural alterations of pyramidal neurons and altered expression of D2R and PSA-NCAM have been found.

Control of Dendritic Spine Morphological and Functional Plasticity by Small GTPases

Structural plasticity of excitatory synapses is a vital component of neuronal development, synaptic plasticity, and behaviour. Abnormal development or regulation of excitatory synapses has also been strongly implicated in many neurodevelopmental, psychiatric, and neurodegenerative disorders. In the mammalian forebrain, the majority of excitatory synapses are located on dendritic spines, specialized dendritic protrusions that are enriched in actin. Research over recent years has begun to unravel the complexities involved in the regulation of dendritic spine structure. The small GTPase family of proteins have emerged as key regulators of structural plasticity, linking extracellular signals with the modulation of dendritic spines, which potentially underlies their ability to influence cognition. Here we review a number of studies that examine how small GTPases are activated and regulated in neurons and furthermore how they can impact actin dynamics, and thus dendritic spine morphology. Elucidating this signalling process is critical for furthering our understanding of the basic mechanisms by which information is encoded in neural circuits but may also provide insight into novel targets for the development of effective therapies to treat cognitive dysfunction seen in a range of neurological disorders.

Antioxidant treatments for schizophrenia

BACKGROUND

There is accumulating evidence that progressive changes in brain structure and function take place as schizophrenia unfolds. Among many possible candidates, oxidative stress may be one of the mediators of neuroprogression, grey matter loss and subsequent cognitive and functional impairment. Antioxidants are exogenous or endogenous molecules that mitigate any form of oxidative stress or its consequences. They may act from directly scavenging free radicals to increasing anti-oxidative defences. There is evidence that current treatments impact oxidative pathways and may to some extent reverse pro-oxidative states in schizophrenia. The existing literature, however, indicates that these treatments do not fully restore the deficits in antioxidant levels or restore levels of oxidants in schizophrenia. As such, there has been interest in developing interventions aimed at restoring this oxidative balance beyond the benefits of antipsychotics in this direction. If antioxidants are to have a place in the treatment of this serious condition, the relevant and up-to-date information should be available to clinicians and investigators.

OBJECTIVES

To evaluate the effect of antioxidants as add-on treatments to standard antipsychotic medication for improving acute psychotic episodes and core symptoms, and preventing relapse in people with schizophrenia.

SEARCH METHODS

We searched the Cochrane Schizophrenia Group's Study-Based Register of Trials which is based on regular searches of CINAHL, BIOSIS, AMED, Embase, PubMed, MEDLINE, PsycINFO, and registries of clinical trials. There are no language, time, document type, or publication status limitations for inclusion of records in the register. We ran this search in November 2010, and again on 8 January 2015. We also inspected references of all identified studies for further trials and contacted authors of trials for additional information.

SELECTION CRITERIA

We included reports if they were randomised controlled trials (RCTs) involving people with schizophrenia who had been allocated to either a substance with antioxidant potential or to a placebo as an adjunct to standard antipsychotic treatment.

DATA COLLECTION AND ANALYSIS

We independently extracted data from these trials and we estimated risk ratios (RR) or mean differences (MD), with 95% confidence intervals (CI). We assessed risk of bias for included studies and created a 'Summary of findings' table using GRADE.

MAIN RESULTS

The review includes 22 RCTs of varying quality and sample size studying Ginkgo biloba, N-acetyl cysteine (NAC), allopurinol, dehydroepiandrosterone (DHEA), vitamin C, vitamin E or selegiline. Median follow-up was eight weeks. Only three studies including a minority of the participants reported our a priori selected primary outcome of clinically important response. Short-term data for this outcome (measured as at least 20% improvement in scores on Positive and Negative Syndrome Scale (PANSS)) were similar (3 RCTs, n = 229, RR 0.77, 95% CI 0.53 to 1.12, low quality evidence). Studies usually reported only endpoint psychopathology rating scale scores. Psychotic symptoms were lower in those using an adjunctive antioxidant according to the PANSS ( 7 RCTS, n = 584, MD -6.00, 95% CI -10.35 to -1.65, very low quality evidence) and the Brief Psychiatric Rating Scale (BPRS) (8 RCTS, n = 843, MD -3.20, 95% CI -5.63 to -0.78, low quality evidence). There was no overall short-term difference in leaving the study early (16 RCTs, n = 1584, RR 0.73, 95% CI 0.48 to 1.11, moderate quality evidence), or in general functioning (2 RCTs, n = 52, MD -1.11, 95% CI -8.07 to 5.86, low quality evidence). Adverse events were generally poorly reported. Three studies reported useable data for 'any serious adverse effect', results were equivocal (3 RCTs, n = 234, RR 0.65, 95% CI 0.19 to 2.27, low quality evidence). No evidence was available for relapse, quality of life or service use.

AUTHORS' CONCLUSIONS

Although 22 trials could be included in this review, the evidence provided is limited and mostly not relevant to clinicians or consumers. Overall, although there was low risk of attrition and selective data reporting bias within the trials, the trials themselves were not adequately powered and need more substantial follow-up periods. There is a need for larger trials with longer periods of follow-up to be conducted. Outcomes should be meaningful for those with schizophrenia, and include measures of improvement and relapse (not just rating scale scores), functioning and quality of life and acceptability and, importantly, safety data.

Chronic stress effects on working memory: association with prefrontal cortical tyrosine hydroxylase

Chronic stress causes deficits in cognitive function including working memory, for which transmission of such catecholamines as dopamine and noradrenaline transmission in the prefrontal cortex (PFC) are crucial. Since catecholamine synthesis depends on the rate-limiting enzyme, tyrosine hydroxylase (TH), TH is thought to play an important role in PFC function. In this study, we found that two distinct population existed in Sprague-Dawley rats in terms of working memory capacity, one with higher working memory capacity, and the other with low capacity. This distinction of working memory capacity became apparent after rats were exposed to chronic stress. In addition, such working memory capacity and alterations of working memory function by chronic stress were associated with TH expression in the PFC.

Subtle alterations in brain anatomy may change an individual's personality in chronic pain

It is well established that gross prefrontal cortex damage can affect an individual’s personality. It is also possible that subtle prefrontal cortex changes associated with conditions such as chronic pain, and not detectable until recent advances in human brain imaging, may also result in subtle changes in an individual’s personality. In an animal model of chronic neuropathic pain, subtle prefrontal cortex changes including altered basal dendritic length, resulted in altered decision making ability. Using multiple magnetic resonance imaging techniques, we found in humans, although gray matter volume and on-going activity were unaltered, chronic neuropathic pain was associated with reduced free and bound proton movement, indicators of subtle anatomical changes, in the medial prefrontal cortex, anterior cingulate cortex and mediodorsal thalamus. Furthermore, proton spectroscopy revealed an increase in neural integrity in the medial prefrontal cortex in neuropathic pain patients, the degree of which was significantly correlated to the personality temperament of novelty seeking. These data reveal that even subtle changes in prefrontal cortex anatomy may result in a significant change in an individual’s personality.

Treating Parkinson's disease in the 21st century: can stem cell transplantation compete?

The characteristic and selective degeneration of a unique population of cells—the nigrostriatal dopamine (DA) neurons—that occurs in Parkinson’s disease (PD) has made the condition an iconic target for cell replacement therapies. Indeed, transplantation of fetal ventral mesencephalic cells into the DA-deficient striatum was first trialled nearly 30 years ago, at a time when other treatments for the disease were less well developed. Over recent decades standard treatments for PD have advanced, and newer biological therapies are now emerging. In the 21st century, stem cell technology will have to compete alongside other sophisticated treatments, including deep brain stimulation and gene therapies. In this review we examine how stem cell–based transplantation therapies compare with these novel and emerging treatments in the management of this common condition. J. Comp. Neurol. 522:2802–2816, 2014.

Dendritic spines: the locus of structural and functional plasticity

The introduction of high-resolution time lapse imaging and molecular biological tools has changed dramatically the rate of progress towards the understanding of the complex structure-function relations in synapses of central spiny neurons. Standing issues, including the sequence of molecular and structural processes leading to formation, morphological change, and longevity of dendritic spines, as well as the functions of dendritic spines in neurological/psychiatric diseases are being addressed in a growing number of recent studies. There are still unsettled issues with respect to spine formation and plasticity: Are spines formed first, followed by synapse formation, or are synapses formed first, followed by emergence of a spine? What are the immediate and long-lasting changes in spine properties following exposure to plasticity-producing stimulation? Is spine volume/shape indicative of its function? These and other issues are addressed in this review, which highlights the complexity of molecular pathways involved in regulation of spine structure and function, and which contributes to the understanding of central synaptic interactions in health and disease.

Antipsychotic drug effects in schizophrenia: a review of longitudinal FMRI investigations and neural interpretations

The evidence that antipsychotics improve brain function and reduce symptoms in schizophrenia is unmistakable, but how antipsychotics change brain function is poorly understood, especially within neuronal systems. In this review, we investigated the hypothesized normalization of the functional magnetic resonance imaging (fMRI) blood oxygen level dependent signal in the context of antipsychotic treatment. First, we conducted a systematic PubMed search to identify eight fMRI investigations that met the following inclusion criteria: case-control, longitudinal design; pre- and post-treatment contrasts with a healthy comparison group; and antipsychotic-free or antipsychotic-naive patients with schizophrenia at the start of the investigation. We hypothesized that aberrant activation patterns or connectivity between patients with schizophrenia and healthy comparisons at the first imaging assessment would no longer be apparent or "normalize" at the second imaging assessment. The included studies differed by analysis method and fMRI task but demonstrated normalization of fMRI activation or connectivity during the treatment interval. Second, we reviewed putative mechanisms from animal studies that support normalization of the BOLD signal in schizophrenia. We provided several neuronal-based interpretations of these changes of the BOLD signal that may be attributable to long-term antipsychotic administration.

Morphological and electrophysiological changes in intratelencephalic-type pyramidal neurons in the motor cortex of a rat model of levodopa-induced dyskinesia

Levodopa-induced dyskinesia (LID) is a major complication of long-term dopamine replacement therapy for Parkinson's disease, and becomes increasingly problematic in the advanced stage of the disease. Although the cause of LID still remains unclear, there is accumulating evidence from animal experiments that it results from maladaptive plasticity, resulting in supersensitive excitatory transmission at corticostriatal synapses. Recent work using transcranial magnetic stimulation suggests that the motor cortex displays the same supersensitivity in Parkinson's disease patients with LID. To date, the cellular mechanisms underlying the abnormal cortical plasticity have not been examined. The morphology of the dendritic spines has a strong relationship to synaptic plasticity. Therefore, we explored the spine morphology of pyramidal neurons in the motor cortex in a rat model of LID. We used control rats, 6-hydroxydopamine-lesioned rats (a model of Parkinson's disease), 6-hydroxydopamine-lesioned rats chronically treated with levodopa (a model of LID), and control rats chronically treated with levodopa. Because the direct pathway of the basal ganglia plays a central role in the development of LID, we quantified the density and size of dendritic spines in intratelencephalic (IT)-type pyramidal neurons in M1 cortex that project to the striatal medium spiny neurons in the direct pathway. The spine density was not different among the four groups. In contrast, spine size became enlarged in the Parkinson's disease and LID rat models. The enlargement was significantly greater in the LID model than in the Parkinson's disease model. This enlargement of the spines suggests that IT-type pyramidal neurons acquire supersensitivity to excitatory stimuli. To confirm this possibility, we monitored miniature excitatory postsynaptic currents (mEPSCs) in the IT-type pyramidal neurons in M1 cortex using whole-cell patch clamp. The amplitude of the mEPSCs was significantly increased in the LID model compared with the control. This indicates that the IT-type pyramidal neurons become hyperexcited in the LID model, paralleling the enlargement of spines. Thus, spine enlargement and the resultant hyperexcitability of IT-type pyramidal neurons in M1 cortex might contribute to the abnormal cortical neuronal plasticity in LID.

Developmental origins of brain disorders: roles for dopamine

Neurotransmitters and neuromodulators, such as dopamine, participate in a wide range of behavioral and cognitive functions in the adult brain, including movement, cognition, and reward. Dopamine-mediated signaling plays a fundamental neurodevelopmental role in forebrain differentiation and circuit formation. These developmental effects, such as modulation of neuronal migration and dendritic growth, occur before synaptogenesis and demonstrate novel roles for dopaminergic signaling beyond neuromodulation at the synapse. Pharmacologic and genetic disruptions demonstrate that these effects are brain region- and receptor subtype-specific. For example, the striatum and frontal cortex exhibit abnormal neuronal structure and function following prenatal disruption of dopamine receptor signaling. Alterations in these processes are implicated in the pathophysiology of neuropsychiatric disorders, and emerging studies of neurodevelopmental disruptions may shed light on the pathophysiology of abnormal neuronal circuitry in neuropsychiatric disorders.

Long-term effects of cocaine experience on neuroplasticity in the nucleus accumbens core of addiction-prone rats

Repeated exposure to drugs of abuse is associated with structural plasticity in brain reward pathways. Rats selectively bred for locomotor response to novelty differ on a number of neurobehavioral dimensions relevant to addiction. This unique genetic animal model was used here to examine both pre-existing differences and long-term consequences of repeated cocaine treatment on structural plasticity. Selectively bred high-responder (bHR) and low-responder (bLR) rats received repeated saline or cocaine injections for 9 consecutive days. Escalating doses of cocaine (7.5, 15 and 30 mg/kg) were administered on the first (day 1) and last (day 9) days of treatment and a single injection of the intermediate dose (15 mg/kg) was given on days 2-8. Motor activity in response to escalating doses of cocaine was compared on the first and last days of treatment to assess the acute and sensitized response to the drug. Following prolonged cocaine abstinence (28 days), spine density was examined on terminal dendrites of medium spiny neurons in the nucleus accumbens core. Relative to bLRs, bHRs exhibited increased psychomotor activation in response to both the acute and repeated effects of cocaine. There were no differences in spine density between bHR and bLR rats under basal conditions or following repeated saline treatment. However, spine density differed markedly between these two lines following prolonged cocaine abstinence. All spine types were decreased in cocaine-treated bHRs, while only mushroom spines were decreased in bLRs that received cocaine. Changes in spine density occurred specifically near the branch point of terminal dendrites. These findings indicate that structural plasticity associated with prolonged cocaine abstinence varies markedly in two selected strains of rats that vary on numerous traits relevant to addiction. Thus, genetic factors that contribute to individual variation in the behavioral response to cocaine also influence cocaine-induced structural plasticity.

Loss of asymmetric spine synapses in prefrontal cortex of motor-asymptomatic, dopamine-depleted, cognitively impaired MPTP-treated monkeys

Parkinson's disease is usually characterized as a movement disorder; however, cognitive abilities that are dependent on the prefrontal cortex decline at an early stage of the disease in most patients. The changes that underlie cognitive deficits in Parkinson's disease are not well understood. We hypothesize that reduced dopamine signalling in the prefrontal cortex in Parkinson's disease is a harbinger of detrimental synaptic changes in pyramidal neurons in the prefrontal cortex, whose function is necessary for normal cognition. Our previous data showed that monkeys exposed to the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), but not exhibiting overt motor deficits (motor-asymptomatic), displayed cognitive deficits in prefrontal cortex-dependent tasks. The present results demonstrate that motor-asymptomatic MPTP-treated monkeys have a reduced dopamine concentration and a substantially lower number (50%) of asymmetric (excitatory) spine synapses in layer II/III, but not layer V, of the dorsolateral prefrontal cortex, compared to controls. In contrast, neither dopamine concentration nor asymmetric synapse number was altered in the entorhinal cortex of MPTP-treated monkeys. Together, these findings suggest that the number of asymmetric spine synapses on dendrites in the prefrontal cortex is dopamine-dependent and that the loss of synapses may be a morphological substrate of the cognitive deficits induced by a reduction in dopamine neurotransmission in this region.

Chronic administration of risperidone in a rat model of schizophrenia: a behavioural, morphological and molecular study

In the present work we analyzed the effect of the chronic administration of risperidone (2mg/kg over 65 days) on behavioural, morphological and molecular aspects in an experimental model of schizophrenia obtained by bilateral injection of ibotenic acid into the ventral hippocampus of new-born rats. Our results show that during their adult lives the animals with hippocampal lesions exhibit different alterations, mainly at behavioural level and in the gene expression of dopamine D(2) and 5-HT(2A) receptors. However, at morphological level the study performed on the prefrontal cortex did not reveal any alterations in either the thickness or the number of cells immunoreactive for c-Fos, GFAP, CBP or PV. Overall, risperidone administration elicited a trend towards the recovery of the values previously altered by the hippocampal lesion, approaching the values seen in the animals without lesions. It may be concluded that the administration of risperidone in the schizophrenia model employed helps to improve the altered functions, with no significant negative effects.

Prevention of the phencyclidine-induced impairment in novel object recognition in female rats by co-administration of lurasidone or tandospirone, a 5-HT(1A) partial agonist

Hypoglutamatergic function may contribute to cognitive impairment in schizophrenia (CIS). Subchronic treatment with the N-methyl-D-aspartate receptor antagonist, phencyclidine (PCP), induces enduring deficits in novel object recognition (NOR) in rodents. Acute treatment with atypical antipsychotic drugs (APDs), which are serotonin (5-HT)(2A)/dopamine D(2) antagonists, but not typical APDs, eg, haloperidol, reverses the PCP-induced NOR deficit in rats. We have tested the ability of lurasidone, an atypical APD with potent 5-HT(1A) partial agonist properties, tandospirone, a selective 5-HT(1A) partial agonist, haloperidol, a D(2) antagonist, and pimavanserin, a 5-HT(2A) inverse agonist, to prevent the development of the PCP-induced NOR deficit. Rats were administered lurasidone (0.1 or 1 mg/kg), tandospirone (5 mg/kg), pimavanserin (3 mg/kg), or haloperidol (1 mg/kg) b.i.d. 30 min before PCP (2 mg/kg, b.i.d.) for 7 days (day1-7), followed by a 7-day washout (day 8-14). Subchronic treatment with PCP induced an enduring NOR deficit. Lurasidone (1 mg/kg) but not 0.1 mg/kg, which is effective to acutely reverse the deficit due to subchronic PCP, or tandospirone, but not pimavanserin or haloperidol, significantly prevented the PCP-induced NOR deficit on day 15. The ability of lurasidone co-treatment to prevent the PCP-induced NOR deficit was enduring and still present at day 22. The preventive effect of lurasidone was blocked by WAY100635, a selective 5-HT(1A) antagonists, further evidence for the importance of 5-HT(1A) receptor stimulation in the NOR deficit produced by subchronic PCP. Further study is needed to determine whether these results concerning mechanism and dosage can be the basis for prevention of the development of CIS in at risk populations.

Increased prefrontal cortical D₁ receptors in drug naive patients with schizophrenia: a PET study with [¹¹C]NNC112

D₁ receptors are the main mediators of dopamine transmission in the cortex and subserve cognitive functions that are affected in patients with schizophrenia. Prior imaging studies have suggested abnormalities in the expression of these receptors in schizophrenia, but no conclusive picture has emerged yet. One source of discrepancy may have been prior antipsychotic exposure. We used positron emission tomography (PET) and a D1 radiotracer, [¹¹C]NNC112, in drug naïve (DN, n = 12) and drug free (DF, n = 13) patients with schizophrenia and 40 healthy control subjects (HC, n = 40 total, n = 24 per comparison group) matched for age, gender, ethnicity, parental socioeconomic status and cigarette smoking. We measured the binding potential BPP, corrected for partial volume effects. The outcome measure was obtained in cortical and striatal subregions outlined on coregistered individual MRIs. Partial volume effect corrected BPP measures were significantly higher in DN vs controls in cortical regions. No such increases were found in the DF versus controls comparison. Furthermore, in the DF group, DF interval correlated positively with cortical BPP. We conclude that upregulation of D1 receptors in schizophrenia is related to the illness itself and may be corrected and normalized by chronic antipsychotic treatment.

Dendritic spine pathology in schizophrenia

Schizophrenia is a neurodevelopmental disorder whose clinical features include impairments in perception, cognition and motivation. These impairments reflect alterations in neuronal circuitry within and across multiple brain regions that are due, at least in part, to deficits in dendritic spines, the site of most excitatory synaptic connections. Dendritic spine alterations have been identified in multiple brain regions in schizophrenia, but are best characterized in layer 3 of the neocortex, where pyramidal cell spine density is lower. These spine deficits appear to arise during development, and thus are likely the result of disturbances in the molecular mechanisms that underlie spine formation, pruning, and/or maintenance. Each of these mechanisms may provide insight into novel therapeutic targets for preventing or repairing the alterations in neural circuitry that mediate the debilitating symptoms of schizophrenia.

Arg kinase regulates prefrontal dendritic spine refinement and cocaine-induced plasticity

Adolescence is characterized by vulnerability to the development of neuropsychiatric disorders including drug addiction, as well as prefrontal cortical refinement that culminates in structural stability in adulthood. Neuronal refinement and stabilization are hypothesized to confer resilience to poor decision making and addictive-like behaviors, although intracellular mechanisms are largely unknown. We characterized layer V prefrontal dendritic spine development and refinement in adolescent wild-type mice and mice lacking the cytoskeletal regulatory protein Abl-related gene (Arg) kinase. Relative to hippocampal CA1 pyramidal neurons, which exhibited a nearly linear increase in spine density up to postnatal day 60 (P60), wild-type prefrontal spine density peaked at P31, and then declined by 18% by P56-P60. In contrast, dendritic spines in mice lacking Arg destabilized by P31, leading to a net loss in both structures. Destabilization corresponded temporally to the emergence of exaggerated psychomotor sensitivity to cocaine. Moreover, cocaine reduced dendritic spine density in wild-type orbitofrontal cortex and enlarged remaining spine heads, but arg(-/-) spines were unresponsive. Local application of Arg or actin polymerization inhibitors exaggerated cocaine sensitization, as did reduced gene dosage of the Arg substrate, p190RhoGAP. Genetic and pharmacological Arg inhibition also retarded instrumental reversal learning and potentiated responding for reward-related cues, providing evidence that Arg regulates both psychomotor sensitization and decision-making processes implicated in addiction. These findings also indicate that structural refinement in the adolescent orbitofrontal cortex mitigates psychostimulant sensitivity and support the emerging perspective that the structural response to cocaine may, at any age, have behaviorally protective consequences.

Development of disease-modifying treatment of schizophrenia

Development of disease-modifying therapies requires an innovative approach to drug development where novel drugs are designed to target mechanisms of interest rather than to produce preclinical effects similar to those of currently used antipsychotics. Application of such novel strategy will undoubtedly require a very deep understanding of the disease biology that is just starting to emerge. Alternatively, one may let environmental experiences of the diseased individual guide the repair process and use drugs only to facilitate the effects of experience. Such an approach would bring together functional experience that is age-, environment- and disease-dependent with the plasticity resources that may otherwise not be available. There are currently no preclinical drug-environment interaction models that can be claimed to have significant degrees of validity. Therefore, from a drug development perspective, principles that combine acute symptomatic and disease-modifying properties are clearly preferred. The question arises then how such treatments can be differentiated from those that have only symptomatic effects (i.e., most currently used antipsychotic medications). One expectation is that the former will show superior and broader efficacy (especially with longer treatment duration). Another possibility is that disease-modifying drugs will be particularly useful at the very earliest stages of the disease. Society and medical communities may not be ready yet to initiate the treatment as early as during the prodromal phase, but the situation may change by the time the science advances enough to bring a convincing case of a drug with disease-modification potential.

Regulation of the actin cytoskeleton in dendritic spines

Spine morphogenesis is largely dependent on the remodeling of the actin cytoskeleton. Actin dynamics within spines is regulated by a complex network of signaling molecules, which relay signals from synaptic receptors, through small GTPases and their regulators, to actin-binding proteins. In this chapter, we will discuss molecules involved in dendritic spine plasticity beginning with actin and moving upstream toward neuromodulators and trophic factors that initiate signaling involved in these plasticity events. We will place special emphasis on small GTPase pathways, as they have an established importance in dendritic spine plasticity and pathology. Finally, we will discuss some epigenetic mechanisms that control spine morphogenesis.

Reversal of stress-induced dendritic atrophy in the prefrontal cortex by intracranial self-stimulation

The mammalian prefrontal cortex (PFC) has been implicated in a variety of motivational and emotional processes underlying working memory, attention and decision making. The PFC receives dopaminergic projections from the ventral tegmental area (VTA) and contains high density of D1 and D2 receptors and these projections are important in higher integrative cortical functions. The neurons of the PFC have been shown to undergo atrophy in response to stress. In an earlier study, we demonstrated that the chronic stress-induced atrophy of hippocampal neurons and behavioral impairment in the T-maze task were reversed by the activation of dopaminergic pathway by intracranial self-stimulation (ICSS) of the VTA. The stress-induced decrease in hippocampal dopamine (DA) levels was also restored by ICSS. Whether the reversal of stress-induced behavioral deficits by ICSS involves changes in the morphology of PFC neurons is unknown and the current study addresses this issue. Male Wistar rats underwent 21 days of restraint stress followed by ICSS for 10 days. The dendritic morphology of the PFC neurons was studied in Golgi-impregnated sections. Stress produced atrophy of the layer II/III and V PFC pyramidal neurons and ICSS to naïve rats significantly increased the dendritic arborization of these neurons compared to control. Interestingly, ICSS of stressed rats resulted in the reversal of the dendritic atrophy. Further, these structural changes were associated with a restored tissue levels of DA, norepinephrine and serotonin in the PFC. These results indicate that the behavioral restoration in stressed rats could involve changes in the plasticity of the PFC neurons and these results further our understanding of the role of dopaminergic neurotransmitter system in the amelioration of stress-induced deficits.

Loss of asymmetric spine synapses in dorsolateral prefrontal cortex of cognitively impaired phencyclidine-treated monkeys

Schizophrenia patients, long-term abusers of phencyclidine (PCP), and monkeys treated with PCP all exhibit enduring cognitive deficits. Evidence indicates that loss of prefrontal cortex spine synapses results in cognitive dysfunction, suggesting the presence of synaptic pathology in the monkey PCP model; however, there is no direct evidence of such changes. In this study we use the monkey PCP model of schizophrenia to investigate at the ultrastructural level whether remodelling of dorsolateral prefrontal cortex (DLPFC) asymmetric spine synapses occurs following PCP. Subchronic PCP treatment resulted in a decrease in the number of asymmetric spine synapses, which was greater in layer II/III than layer V of DLPFC, compared to vehicle-treated controls. This decrease may contribute to PCP-induced cognitive dysfunction in the non-human primate model and perhaps in schizophrenia. Thus, the synapse loss in the PCP model provides a novel target for the development of potential treatments of cognitive dysfunction in this model and in schizophrenia.

Phencyclidine-induced loss of asymmetric spine synapses in rodent prefrontal cortex is reversed by acute and chronic treatment with olanzapine

Enduring cognitive deficits exist in schizophrenic patients, long-term abusers of phencyclidine (PCP), as well as in animal PCP models of schizophrenia. It has been suggested that cognitive performance and memory processes are coupled with remodeling of pyramidal dendritic spine synapses in prefrontal cortex (PFC), and that reduced spine density and number of spine synapses in the medial PFC of PCP-treated rats may potentially underlie, at least partially, the cognitive dysfunction previously observed in this animal model. The present data show that the decrease in number of asymmetric (excitatory) spine synapses in layer II/III of PFC, previously noted at 1-week post PCP treatment also occurs, to a lesser degree, in layer V. The decrease in the number of spine synapses in layer II/III was sustained and persisted for at least 4 weeks, paralleling the observed cognitive deficits. Both acute and chronic treatment with the atypical antipsychotic drug, olanzapine, starting at 1 week after PCP treatment at doses that restore cognitive function, reversed the asymmetric spine synapse loss in PFC of PCP-treated rats. Olanzapine had no significant effect on spine synapse number in saline-treated controls. These studies demonstrate that the effect of PCP on asymmetric spine synapse number in PFC lasts at least 4 weeks in this model. This spine synapse loss in PFC is reversed by acute treatment with olanzapine, and this reversal is maintained by chronic oral treatment, paralleling the time course of the restoration of the dopamine deficit, and normalization of cognitive function produced by olanzapine.

The netrin receptor DCC is required in the pubertal organization of mesocortical dopamine circuitry

Netrins are guidance cues involved in neural connectivity. We have shown that the netrin-1 receptor DCC (deleted in colorectal cancer) is involved in the functional organization of the mesocorticolimbic dopamine (DA) system. Adult mice with a heterozygous loss-of-function mutation in dcc exhibit changes in indexes of DA function, including DA-related behaviors. These phenotypes are only observed after puberty, a critical period in the maturation of the mesocortical DA projection. Here, we examined whether dcc heterozygous mice exhibit structural changes in medial prefrontal cortex (mPFC) DA synaptic connectivity, before and after puberty. Stereological counts of tyrosine-hydroxylase (TH)-positive varicosities were increased in the cingulate 1 and prelimbic regions of the pregenual mPFC. dcc heterozygous mice also exhibited alterations in the size, complexity, and dendritic spine density of mPFC layer V pyramidal neuron basilar dendritic arbors. Remarkably, these presynaptic and postsynaptic partner phenotypes were not observed in juvenile mice, suggesting that DCC selectively influences the extensive branching and synaptic differentiation that occurs in the maturing mPFC DA circuit at puberty. Immunolabeling experiments in wild-type mice demonstrated that DCC is segregated to TH-positive fibers innervating the nucleus accumbens, with only scarce DCC labeling in mPFC TH-positive fibers. Netrin had an inverted target expression pattern. Thus, DCC-mediated netrin-1 signaling may influence the formation/maintenance of mesocorticolimbic DA topography. In support of this, we report that dcc heterozygous mice exhibit a twofold increase in the density of mPFC DCC/TH-positive varicosities. Our results implicate DCC-mediated netrin-1 signaling in the establishment of mPFC DA circuitry during puberty.

Interaction of mGlu2/3 agonism with clozapine and lurasidone to restore novel object recognition in subchronic phencyclidine-treated rats

RATIONALE

Subchronic administration to rodents of the N-methyl-D-aspartate non-competitive antagonist, phencyclidine (PCP), impairs novel object recognition (NOR). Atypical antipsychotic drugs (APDs) reverse the effects of subchronic PCP on NOR. The effect of metabotropic glutamate₂/₃ receptor (mGlu₂/₃) agonists upon NOR is unknown.

OBJECTIVES AND METHODS

We tested the hypotheses that the mGlu₂/₃ agonist, LY379268, by itself, or in combination with APDs or pimavanserin, a 5-HT(2A) inverse agonist, would reverse the deficit in NOR induced by subchronic treatment with PCP (2 mg/kg, b.i.d., for 7 days).

RESULTS

The mGlu₂/₃ agonist LY379268 (1 or 3 mg/kg) did not attenuate the PCP-induced NOR deficit. However, together with sub-effective dose of the atypical APDs, clozapine (0.1 mg/kg) or lurasidone (0.03 mg/kg), but not the typical APD, haloperidol (0.1 mg/kg), or pimavanserin (3 mg/kg), LY379268, 1 mg/kg, significantly reversed the PCP-induced NOR deficit. Moreover, the effect of clozapine was blocked by the mGlu₂/₃ antagonist, LY341495 (1 mg/kg).

CONCLUSIONS

These results indicate that mGlu₂/₃ agonism can potentiate the ability of atypical, but not typical APDs, to ameliorate the effect of subchronic PCP on NOR, that mGlu₂/₃ agonism may contribute to the ability of atypical APDs to acutely reverse the effect of subchronic PCP on NOR, but that by itself, mGlu₂/₃ agonism, is ineffective in this model of cognitive impairment in schizophrenia. These results suggest that mGlu₂/₃ receptor agonism should be investigated as an adjunctive treatment of cognitive impairment in schizophrenia rather than as monotherapy, which may be effective for control of psychosis, but not for cognitive impairment.

Evolution of extra-nigral damage predicts behavioural deficits in a rat proteasome inhibitor model of Parkinson's disease

Establishing the neurological basis of behavioural dysfunction is key to provide a better understanding of Parkinson's disease (PD) and facilitate development of effective novel therapies. For this, the relationships between longitudinal structural brain changes associated with motor behaviour were determined in a rat model of PD and validated by post-mortem immunohistochemistry. Rats bearing a nigrostriatal lesion induced by infusion of the proteasome inhibitor lactacystin into the left-medial forebrain bundle and saline-injected controls underwent magnetic resonance imaging (MRI) at baseline (prior to surgery) and 1, 3 and 5 weeks post-surgery with concomitant motor assessments consisting of forelimb grip strength, accelerating rotarod, and apormorphine-induced rotation. Lactacystin-injected rats developed early motor deficits alongside decreased ipsilateral cortical volumes, specifically thinning of the primary motor (M1) and somatosensory cortices and lateral ventricle hypertrophy (as determined by manual segmentation and deformation-based morphometry). Although sustained, motor dysfunction and nigrostriatal damage were maximal by 1 week post-surgery. Additional volume decreases in the ipsilateral ventral midbrain; corpus striatum and thalamus were only evident by week 3 and 5. Whilst cortical MRI volume changes best predicted the degree of motor impairment, post-mortem tyrosine hydroxylase immunoreactivity in the striatum was a better predictor of motor behaviour overall, with the notable exception of performance in the accelerating rotarod, in which, M1 cortical thickness remained the best predictor. These results highlight the importance of identifying extra-nigral regions of damage that impact on behavioural dysfunction from damage to the nigrostriatal system.