Dopamine Restores Limbic Memory Loss, Dendritic Spine Structure, and NMDAR-Dependent LTD in the Nucleus Accumbens of Alcohol-Withdrawn Rats.

Alcohol abuse leads to aberrant forms of emotionally salient memory, i.e., limbic memory, that promote escalated alcohol consumption and relapse. Accordingly, activity-dependent structural abnormalities are likely to contribute to synaptic dysfunctions that occur from suddenly ceasing chronic alcohol consumption. Here we show that alcohol-dependent male rats fail to perform an emotional-learning task during abstinence but recover their functioning by l-3,4-dihydroxyphenylalanin (l-DOPA) administration during early withdrawal. l-DOPA also reverses the selective loss of dendritic "long thin" spines observed in medium spiny neurons of the nucleus accumbens (NAc) shell of alcohol-dependent rats during abstinence, as well as the reduction in tyrosine hydroxylase immunostaining and postsynaptic density-95-positive elements. Patch-clamp experiments in NAc slices reveal that both in vivo systemic l-DOPA administration and in vitro exposure to dopamine can restore the loss of long-term depression (LTD) formation, counteract the reduction in NMDAR-mediated synaptic currents and rectify the altered NMDAR/AMPAR ratio observed in alcohol-withdrawn rats. Further, in vivo microdialysis experiments show that blunted dopaminergic signaling is revived after l-DOPA treatment during early withdrawal. These results suggest a key role of an efficient dopamine signaling for maintaining, and restore, neural trophism, NMDA-dependent LTD, and ultimately optimal learning.SIGNIFICANCE STATEMENT Blunted dopamine signaling and altered glutamate connectivity in the nucleus accumbens represent the neuroanatomical basis for the impairment in aversive limbic memory observed during withdrawal in alcohol dependence. Supplying l-DOPA during withdrawal re-establishes synaptic morphology and functional neuroadaptations, suggesting a complete recovery of nucleus accumbens glutamatergic synaptic plasticity when dopamine is revived. Importantly, restoring dopamine transmission allows those synapses to encode emotionally relevant information and rescue flexibility in the neuronal circuits that process limbic memory formation. Under these conditions, drugs capable of selectively boosting the dopaminergic function during the "fluid" and still responsive state of the early withdrawn maladaptive synapses may help in the treatment of alcohol addiction.

Modeling Parkinson's Disease Neuropathology and Symptoms by Intranigral Inoculation of Preformed Human α-Synuclein Oligomers.

The accumulation of aggregated α-synuclein (αSyn) is a hallmark of Parkinson's disease (PD). Current evidence indicates that small soluble αSyn oligomers (αSynOs) are the most toxic species among the forms of αSyn aggregates, and that size and topological structural properties are crucial factors for αSynOs-mediated toxicity, involving the interaction with either neurons or glial cells. We previously characterized a human αSynO (H-αSynO) with specific structural properties promoting toxicity against neuronal membranes. Here, we tested the neurotoxic potential of these H-αSynOs in vivo, in relation to the neuropathological and symptomatic features of PD. The H-αSynOs were unilaterally infused into the rat substantia nigra pars compacta (SNpc). Phosphorylated αSyn (p129-αSyn), reactive microglia, and cytokine levels were measured at progressive time points. Additionally, a phagocytosis assay in vitro was performed after microglia pre-exposure to αsynOs. Dopaminergic loss, motor, and cognitive performances were assessed. H-αSynOs triggered p129-αSyn deposition in SNpc neurons and microglia and spread to the striatum. Early and persistent neuroinflammatory responses were induced in the SNpc. In vitro, H-αSynOs inhibited the phagocytic function of microglia. H-αsynOs-infused rats displayed early mitochondrial loss and abnormalities in SNpc neurons, followed by a gradual nigrostriatal dopaminergic loss, associated with motor and cognitive impairment. The intracerebral inoculation of structurally characterized H-αSynOs provides a model of progressive PD neuropathology in rats, which will be helpful for testing neuroprotective therapies.

Immunomodulatory drugs alleviate l-dopa-induced dyskinesia in a rat model of Parkinson's disease.

BACKGROUND: Thalidomide and closely related analogues are used clinically for their immunomodulatory and antiangiogenic properties mediated by the inhibition of the proinflammatory cytokine tumor necrosis factor α. Neuroinflammation and angiogenesis contribute to classical neuronal mechanisms underpinning the pathophysiology of l-dopa-induced dyskinesia, a motor complication associated with l-dopa therapy in Parkinson's disease. The efficacy of thalidomide and the more potent derivative 3,6'-dithiothalidomide on dyskinesia was tested in the 6-hydroxydopamine Parkinson's disease model. METHODS: Three weeks after 6-hydroxydopamine infusion, rats received 10 days of treatment with l-dopa plus benserazide (6 mg/kg each) and thalidomide (70 mg/kg) or 3,6'-dithiothalidomide (56 mg/kg), and dyskinesia and contralateral turning were recorded daily. Rats were euthanized 1 hour after the last l-dopa injection, and levels of tumor necrosis factor-α, interleukin-10, OX-42, vimentin, and vascular endothelial growth factor immunoreactivity were measured in their striatum and substantia nigra reticulata to evaluate neuroinflammation and angiogenesis. Striatal levels of GLUR1 were measured as a l-dopa-induced postsynaptic change that is under tumor necrosis factor-α control. RESULTS: Thalidomide and 3,6'-dithiothalidomide significantly attenuated the severity of l-dopa-induced dyskinesia while not affecting contralateral turning. Moreover, both compounds inhibited the l-dopa-induced microgliosis and excessive tumor necrosis factor-α in the striatum and substantia nigra reticulata, while restoring physiological levels of the anti-inflammatory cytokine interleukin-10. l-Dopa-induced angiogenesis was inhibited in both basal ganglia nuclei, and l-dopa-induced GLUR1 overexpression in the dorsolateral striatum was restored to normal levels. CONCLUSIONS: These data suggest that decreasing tumor necrosis factor-α levels may be useful to reduce the appearance of dyskinesia, and thalidomide, and more potent derivatives may provide an effective therapeutic approach to dyskinesia. © 2019 International Parkinson and Movement Disorder Society.

Neuroinflammation in L-DOPA-induced dyskinesia: beyond the immune function.

Neuroinflammation is a main component of Parkinson's disease (PD) neuropathology, where unremitting reactive microglia and microglia-secreted soluble molecules such as cytokines, contribute to the neurodegenerative process as part of an aberrant immune reaction. Besides, pro-inflammatory cytokines, predominantly TNF-α, play an important neuromodulatory role in the healthy and diseased brain, being involved in neurotransmitter metabolism, synaptic scaling and brain plasticity. Recent preclinical studies have evidenced an exacerbated neuroinflammatory reaction in the striatum of parkinsonian rats that developed dyskinetic responses following L-DOPA administration. These findings prompted investigation of non-neuronal mechanisms of L-DOPA-induced dyskinesia (LID) involving glial cells and glial-secreted soluble molecules. Hence, besides the classical mechanisms of LID that include abnormal corticostriatal neurotransmission and maladaptive changes in striatal medium spiny neurons (MSNs), here we review studies supporting a role of striatal neuroinflammation in the development of LID, with a focus on microglia and the pro-inflammatory cytokine TNF-α. Moreover, we discuss several mechanisms that have been involved in the development of LID, which are directly or indirectly under the control of TNF-α, and might be abnormally affected by its chronic overproduction and release by microglia in PD. It is proposed that TNF-α may contribute to the altered neuronal responses occurring in LID by targeting receptor trafficking and function in MSNs, but also dopamine synthesis in preserved dopaminergic terminals and serotonin metabolism in serotonergic neurons. Therapeutic approaches specifically targeting glial-secreted cytokines may represent a novel target for preventing or treating LID.

Hampered long-term depression and thin spine loss in the nucleus accumbens of ethanol-dependent rats.

Alcoholism involves long-term cognitive deficits, including memory impairment, resulting in substantial cost to society. Neuronal refinement and stabilization are hypothesized to confer resilience to poor decision making and addictive-like behaviors, such as excessive ethanol drinking and dependence. Accordingly, structural abnormalities are likely to contribute to synaptic dysfunctions that occur from suddenly ceasing the use of alcohol after chronic ingestion. Here we show that ethanol-dependent rats display a loss of dendritic spines in medium spiny neurons of the nucleus accumbens (Nacc) shell, accompanied by a reduction of tyrosine hydroxylase immunostaining and postsynaptic density 95-positive elements. Further analysis indicates that "long thin" but not "mushroom" spines are selectively affected. In addition, patch-clamp experiments from Nacc slices reveal that long-term depression (LTD) formation is hampered, with parallel changes in field potential recordings and reductions in NMDA-mediated synaptic currents. These changes are restricted to the withdrawal phase of ethanol dependence, suggesting their relevance in the genesis of signs and/or symptoms affecting ethanol withdrawal and thus the whole addictive cycle. Overall, these results highlight the key role of dynamic alterations in dendritic spines and their presynaptic afferents in the evolution of alcohol dependence. Furthermore, they suggest that the selective loss of long thin spines together with a reduced NMDA receptor function may affect learning. Disruption of this LTD could contribute to the rigid emotional and motivational state observed in alcohol dependence.

Enhanced endocannabinoid-mediated modulation of rostromedial tegmental nucleus drive onto dopamine neurons in Sardinian alcohol-preferring rats.

The progressive predominance of rewarding effects of addictive drugs over their aversive properties likely contributes to the transition from drug use to drug dependence. By inhibiting the activity of DA neurons in the VTA, GABA projections from the rostromedial tegmental nucleus (RMTg) are well suited to shift the balance between drug-induced reward and aversion. Since cannabinoids suppress RMTg inputs to DA cells and CB1 receptors affect alcohol intake in rodents, we hypothesized that the endocannabinoid system, by modulating this pathway, might contribute to alcohol preference. Here we found that RMTg afferents onto VTA DA neurons express CB1 receptors and display a 2-arachidonoylglycerol (2-AG)-dependent form of short-term plasticity, that is, depolarization-induced suppression of inhibition (DSI). Next, we compared rodents with innate opposite alcohol preference, the Sardinian alcohol-preferring (sP) and alcohol-nonpreferring (sNP) rats. We found that DA cells from alcohol-naive sP rats displayed a decreased probability of GABA release and a larger DSI. This difference was due to the rate of 2-AG degradation. In vivo, we found a reduced RMTg-induced inhibition of putative DA neurons in sP rats that negatively correlated with an increased firing. Finally, alcohol failed to enhance RMTg spontaneous activity and to prolong RMTg-induced silencing of putative DA neurons in sP rats. Our results indicate functional modifications of RMTg projections to DA neurons that might impact the reward/aversion balance of alcohol attributes, which may contribute to the innate preference observed in sP rats and to their elevated alcohol intake.

Dynamic changes in pro- and anti-inflammatory cytokines in microglia after PPAR-γ agonist neuroprotective treatment in the MPTPp mouse model of progressive Parkinson's disease.

Neuroinflammatory changes play a pivotal role in the progression of Parkinson's disease (PD) pathogenesis. Recent findings have suggested that activated microglia may polarize similarly to peripheral macrophages in the central nervous system (CNS), assuming a pro-inflammatory M1 phenotype or the alternative anti-inflammatory M2 phenotype via cytokine production. A skewed M1 activation over M2 has been related to disease progression in Alzheimer disease, and modulation of microglia polarization may be a therapeutic target for neuroprotection. By using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-probenecid (MPTPp) mouse model of progressive PD, we investigated dynamic changes in the production of pro-inflammatory cytokines, such as tumor necrosis factor (TNF)-α and interleukin (IL)-1ß, and anti-inflammatory cytokines, such as transforming growth factor (TGF)-ß and IL-10, within Iba-1-positive cells in the substantia nigra compacta (SNc). In addition, to further characterize changes in the M2 phenotype, we measured CD206 in microglia. Moreover, in order to target microglia polarization, we evaluated the effect of the peroxisome-proliferator-activated receptor (PPAR)-γ agonist rosiglitazone, which has been shown to exert neuroprotective effects on nigral dopaminergic neurons in PD models, and acts as a modulator of cytokine production and phenotype in peripheral macrophages. Chronic treatment with MPTPp induced a progressive degeneration of SNc neurons. The neurotoxin treatment was associated with a gradual increase in both TNF-α and IL-1ß colocalization with Iba-1-positive cells, suggesting an increase in pro-inflammatory microglia. In contrast, TGF-ß colocalization was reduced by the neurotoxin treatment, while IL-10 was mostly unchanged. Administration of rosiglitazone during the full duration of MPTPp treatment reverted both TNF-α and IL-1ß colocalization with Iba-1 to control levels. Moreover, rosiglitazone induced an increase in TGF-ß and IL-10 colocalization compared with the MPTPp treatment. CD206 was gradually reduced by the chronic MPTPp treatment, while rosiglitazone restored control levels, suggesting that M2 anti-inflammatory microglia were stimulated and inflammatory microglia were inhibited by the neuroprotective treatment. The results show that the dopaminergic degeneration was associated with a gradual microglia polarization to the inflammatory over the anti-inflammatory phenotype in a chronic mouse model of PD. Neuroprotective treatment with rosiglitazone modulated microglia polarization, boosting the M2 over the pro-inflammatory phenotype. PPAR-γ agonists may offer a novel approach to neuroprotection, acting as disease-modifying drugs through an immunomodulatory action in the CNS.

Nestin and vimentin colocalization affects the subcellular location of glucocorticoid receptor in cutaneous melanoma.

AIMS: Nestin (a neuronal stem cell/progenitor cell marker of central nervous system development), vimentin (which is ubiquitously expressed in mesenchymal cells), and the glucocorticoid receptor (GR, which is involved in the immune response, cell proliferation, and apoptosis) have been shown to interact in embryonic and undifferentiated tissues in modulating cell proliferation. The aim of this study was to analyse nestin, vimentin and GR expression in tumour tissue (melanoma), and their association with clinicopathological variables, to evaluate any effect on tumour progression. METHODS AND RESULTS: Immunohistochemistry, double-label immunofluorescence and confocal laser scanning microscopy were performed on biopsy specimens of cutaneous melanoma from 81 patients. Fisher's and Pearson's tests showed a correlation between nestin, vimentin and subcellular GR location (P = 0.008). Their concomitant expression also correlated with Clark level and thickness (P = 0.02 and P = 0.029, respectively). Kaplan-Meier analysis revealed a poorer outcome for stage III and IV patients with associated expression of nestin, vimentin and cytoplasmic GR in tumour tissue (P = 0.02). CONCLUSIONS: These results suggest the presence in melanoma of growth mechanisms involving nestin, vimentin, and GR, similarly to that occurring in embryonic and undifferentiated cells, and may help in understanding tumour biology to provide a molecular basis for clinical therapies.

Ontogenetic changes in the tyrosine hydroxylase immunoreactive preoptic area in the small-spotted catshark Scyliorhinus canicula (L., 1758) females: catecholaminergic involvement in sexual maturation.

Introduction: The catecholaminergic component of the brain-pituitary-gonadal axis, which mediates the influence of external and internal stimuli on the central nervous system and gonad development in vertebrates, is largely unexplored in Chondrichthyes. We considered Scyliorhinus canicula (L., 1758) females as a model for this vertebrate's class, to assess the involvement of the catecholaminergic system of the brain in its reproduction. Along the S. canicula reproductive cycle, we characterized and evaluated differences in somata morphometry and the number of putative catecholaminergic neurons in two brain nuclei: the periventricular preoptic nucleus, hypothesized to be a positive control for ovarian development, and the suprachiasmatic nucleus, examined as a negative control. Materials and methods: 16 S. canicula wild females were sampled and grouped in maturity stages (immature, maturing, mature, and mature egg-laying). The ovary was histologically processed for the qualitative description of maturity stages. Anti-tyrosine hydroxylase immunofluorescence was performed on the diencephalic brain sections. The immunoreactive somata were investigated for morphometry and counted using the optical fractionator method, throughout the confocal microscopy. Results and discussions: Qualitative and quantitative research confirmed two separate populations of immunoreactive neurons. The modifications detected in the preoptic nucleus revealed that somata were more numerous, significantly smaller in size, and more excitable during the maturing phase but decreased, becoming slightly bigger and less excitable in the egg-laying stage. This may indicate that the catecholaminergic preoptic nucleus is involved in the control of reproduction, regulating both the onset of puberty and the imminent spawning. In contrast, somata in the suprachiasmatic nucleus grew in size and underwent turnover in morphometry, increasing the total number from the immature-virgin to maturing stage, with similar values in the more advanced maturity stages. These changes were not linked to a reproductive role. These findings provide new valuable information on Chondrichthyes, suggesting the existence of an additional brain system implicated in the integration of internal and environmental cues for reproduction.

Changes in Dendritic Spine Morphology and Density of Granule Cells in the Olfactory Bulb of Anguilla anguilla (L., 1758): A Possible Way to Understand Orientation and Migratory Behavior.

Olfaction could represent a pivotal process involved in fish orientation and migration. The olfactory bulb can manage olfactive signals at the granular cell (GC) and dendritic spine levels for their synaptic plasticity properties and changing their morphology and structural stability after environmental odour cues. The GCs' dendritic spine density and morphology were analysed across the life stages of the catadromous Anguilla anguilla. According to the head and neck morphology, spines were classified as mushroom (M), long thin (LT), stubby (S), and filopodia (F). Total spines' density decreased from juvenile migrants to no-migrant stages, to increase again in the adult migrant stage. Mean spines' density was comparable between glass and silver eels as an adaptation to migration. At non-migrating phases, spines' density decreased for M and LT, while M, LT, and S density increased in silver eels. A great dendritic spine development was found in the two migratory phases, regressing in trophic phases, but that could be recreated in adults, tracing the migratory memory of the routes travelled in juvenile phases. For its phylogenetic Elopomorph attribution and its complex life cycle, A. anguilla could be recommended as a model species to study the development of dendritic spines in GCs of the olfactory bulb as an index of synaptic plasticity involved in the modulation of olfactory stimuli. If olfaction is involved in the orientation and migration of A. anguilla and if eels possess a memory, these processes could be influenced by the modification of environmental stimuli (ocean alterations and rapid climate change) contributing to threatening this critically endangered species.

The Intranigral Infusion of Human-Alpha Synuclein Oligomers Induces a Cognitive Impairment in Rats Associated with Changes in Neuronal Firing and Neuroinflammation in the Anterior Cingulate Cortex.

Parkinson's disease (PD) is a complex pathology causing a plethora of non-motor symptoms besides classical motor impairments, including cognitive disturbances. Recent studies in the PD human brain have reported microgliosis in limbic and neocortical structures, suggesting a role for neuroinflammation in the development of cognitive decline. Yet, the mechanism underlying the cognitive pathology is under investigated, mainly for the lack of a valid preclinical neuropathological model reproducing the disease's motor and non-motor aspects. Here, we show that the bilateral intracerebral infusion of pre-formed human alpha synuclein oligomers (H-αSynOs) within the substantia nigra pars compacta (SNpc) offers a valid model for studying the cognitive symptoms of PD, which adds to the classical motor aspects previously described in the same model. Indeed, H-αSynOs-infused rats displayed memory deficits in the two-trial recognition task in a Y maze and the novel object recognition (NOR) test performed three months after the oligomer infusion. In the anterior cingulate cortex (ACC) of H-αSynOs-infused rats the in vivo electrophysiological activity was altered and the expression of the neuron-specific immediate early gene (IEG) Npas4 (Neuronal PAS domain protein 4) and the AMPA receptor subunit GluR1 were decreased. The histological analysis of the brain of cognitively impaired rats showed a neuroinflammatory response in cognition-related regions such as the ACC and discrete subareas of the hippocampus, in the absence of any evident neuronal loss, supporting a role of neuroinflammation in cognitive decline. We found an increased GFAP reactivity and the acquisition of a proinflammatory phenotype by microglia, as indicated by the increased levels of microglial Tumor Necrosis Factor alpha (TNF-α) as compared to vehicle-infused rats. Moreover, diffused deposits of phospho-alpha synuclein (p-αSyn) and Lewy neurite-like aggregates were found in the SNpc and striatum, suggesting the spreading of toxic protein within anatomically interconnected areas. Altogether, we present a neuropathological rat model of PD that is relevant for the study of cognitive dysfunction featuring the disease. The intranigral infusion of toxic oligomeric species of alpha-synuclein (α-Syn) induced spreading and neuroinflammation in distant cognition-relevant regions, which may drive the altered neuronal activity underlying cognitive deficits.

Acetaldehyde elicits ERK phosphorylation in the rat nucleus accumbens and extended amygdala.

Recent advances suggest that acetaldehyde mediates some of the neurobiological properties of ethanol. In a recent study, we have shown that ethanol elicits the phosphorylation of extracellular signal-regulated kinase (pERK) in the nucleus accumbens and extended amygdala, via a dopamine D(1) receptor-mediated mechanism. The aim of this study was to determine whether acetaldehyde and ethanol-derived acetaldehyde elicit the activation of ERK in the nucleus accumbens and extended amygdala. The effects of acetaldehyde (10 and 20 mg/kg) and ethanol (1 g/kg), administered to rats intragastrically, were assessed by pERK peroxidase immunohistochemistry. To establish the role of ethanol-derived acetaldehyde, the alcohol dehydrogenase inhibitor, 4-methylpyrazole (90 mg/kg), and the acetaldehyde-sequestering agent, D-penicillamine (50 mg/kg), were administered before ethanol. Acetaldehyde increased pERK immunoreactivity in the nucleus accumbens and extended amygdala. Inhibition of ethanol metabolism and sequestration of newly synthesized acetaldehyde completely prevented ERK activation by ethanol. In addition, to establish the role of D(1) receptors stimulation in acetaldehyde-elicited ERK phosphorylation, we studied the effect of the D(1) receptor antagonist, SCH 39166. Pretreatment with the D(1) receptor antagonist (50 µg/kg) fully prevented acetaldehyde-elicited ERK activation. Overall, these results indicate that ethanol activates ERK by means of its metabolic conversion into acetaldehyde and strengthen the view that acetaldehyde is a centrally acting compound with a pharmacological profile similar to ethanol.

Role of dopamine D(1) receptors in caffeine-mediated ERK phosphorylation in the rat brain.

The aim of this research was to study the role of dopamine D(1) receptors in caffeine elicited ERK phosphorylation in the prefrontal and other cortical (cingulate and motor) and subcortical (shell and core of the nucleus accumbens) regions. To this end, caffeine (3 and 10 mg/kg) was administered before phosphoERK immunohistochemistry. Caffeine dose-dependently increased the number of phosphoERK-positive neurons in the prefrontal and cingulate cortices but not in the secondary motor cortex and in the nucleus accumbens shell and core. The dopamine D(1) receptor antagonist, SCH 39166 (50 microg/kg), fully prevented phosphoERK activation by caffeine (10 mg/kg) in the superficial and deep layers of the prefrontal cortex but failed to prevent it in the cingulate cortex. Given that phosphoERK can be regarded as a postsynaptic marker of neuronal activation, the present results indicate that psychotropic properties of caffeine may result from the activation of prefrontal, via dopamine D(1) receptors, and cingulate cortices. Failure of caffeine to activate ERK in the nucleus accumbens further supports, indirectly, the observation that caffeine fails to activate dopamine transmission in this structure and is consistent with the tenet that caffeine lacks of true addictive properties.

Role of dopamine D1 receptors and extracellular signal regulated kinase in the motivational properties of acetaldehyde as assessed by place preference conditioning.

BACKGROUND: The role of dopamine D1 receptors and Extracellular signal Regulated Kinase (ERK) in the motivational properties of drugs can be studied by place-conditioning. Recent advances have shown that the motivational properties of ethanol, determined by place-conditioning, are mediated by its metabolic conversion into acetaldehyde. To date, the role of D1 receptors and ERK activation in acetaldehyde-elicited place preference has not been determined. The aim of this study was to assess the role of D1 receptors blockade and MEK inhibition in the acquisition of acetaldehyde-elicited conditioned place preference. METHODS: Male Sprague-Dawley rats were subjected to repeated pairings with 1 compartment of the conditioning apparatus immediately following acetaldehyde (20 mg/kg i.g.) or ethanol (1 g/kg i.g.) administration. The D1 receptor antagonist, SCH 39166 (50 microg/kg s.c.), was administered 10 minutes before acetaldehyde or ethanol administration. In order to study the role of activated ERK in the acetaldehyde-elicited place preference, rats were administered the MEK inhibitor, PD98059 (1, 30, and 90 microg i.c.v.), 10 or 30 minutes before acetaldehyde. To verify the specificity of these effects, we also studied whether PD98059 pretreatment could affect morphine (1 mg/kg s.c.)-elicited place preference. RESULTS: Both acetaldehyde and ethanol elicited significant place preferences and these were prevented by pretreatment with SCH 39166. In addition, pretreatment with PD98059, dose (30 and 90 but not 1 microg i.c.v.) and time (10 but not 30 minutes before) dependently, prevented the acquisition of acetaldehyde- and significantly reduced the acquisition of morphine-elicited conditioned place preference. CONCLUSIONS: These results confirm that acetaldehyde and ethanol elicit conditioned place preference and demonstrate that D1 receptors are critically involved in these effects. Furthermore, the finding that PD98059 prevents the acquisition of acetaldehyde-elicited conditioned place preference highlights the importance of the D1 receptor-ERK pathway in its motivational effects.

Altered architecture and functional consequences of the mesolimbic dopamine system in cannabis dependence.

Cannabinoid withdrawal produces a hypofunction of mesencephalic dopamine neurons that impinge upon medium spiny neurons (MSN) of the forebrain. After chronic treatment with two structurally different cannabinoid agonists, Delta(9)-tetrahydrocannabinol and CP55 940 (CP) rats were withdrawn spontaneously and pharmacologically with the CB1 antagonist SR141716A (SR). In these two conditions, evaluation of tyrosine hydroxylase (TH)-positive neurons revealed significant morphometrical reductions in the ventrotegmental area but not substantia nigra pars compacta of withdrawn rats. Similarly, confocal analysis of Golgi-Cox-stained sections of the nucleus accumbens revealed a decrease in the shell, but not the core, of the spines' density of withdrawn rats. Administration of the CB1 antagonist SR to control rats, provoked structural abnormalities reminiscent of those observed in withdrawal conditions and support the regulatory role of cannabinoids in neurogenesis, axonal growth and synaptogenesis by acting as eu-proliferative signals through the CB1 receptors. Further, these measures were incorporated into a realistic computational model that predicts a strong reduction in the excitability of morphologically altered MSN, yielding a significant reduction in action potential output. These pieces of evidence support the tenet that withdrawal from addictive compounds alters functioning of the mesolimbic system and provide direct morphological evidence for functional abnormalities associated with cannabinoid dependence at the level of dopaminergic neurons and their postsynaptic counterpart and are coherent with recent hypothesis underscoring a hypodopaminergic state as a distinctive feature of the 'addicted brain'.

Ethanol-induced extracellular signal regulated kinase: role of dopamine D1 receptors.

BACKGROUND: Addictive drugs activate extracellular signal regulated kinase (ERK) in brain regions critically involved in their affective and motivational properties. The aim of this study was to demonstrate the ethanol-induced activation of ERK in the nucleus accumbens (Acb) and in the extended amygdala [bed nucleus of the stria terminalis lateralis (BSTL) and central nucleus of the amygdala (CeA)] and to highlight the role of dopamine (DA) D(1) receptors in these effects. METHODS: Ethanol (0.5, 1, and 2 g/kg) was administered by gavage and ERK phosphorylation was determined in the nucleus Acb (shell and core), BSTL, and CeA by immunohistochemistry. The DA D(1) receptor antagonist, SCH 39166 (SCH) (50 microg/kg), was administered 10 minutes before ethanol (1 g/kg). RESULTS: Quantitative microscopic examination showed that ethanol, dose-dependently increased phospho-ERK immunoreactivity (optical and neuronal densities) in the shell and core of nucleus Acb, BSTL, and CeA. Pretreatment with SCH fully prevented the increases elicited by ethanol (1 g/kg) in all brain regions studied. CONCLUSIONS: The results of this study indicate that ethanol, similar to other addictive drugs, activates ERK in nucleus Acb and extended amygdala via a DA D(1) receptor-mediated mechanism. Overall, these results suggest that the D(1) receptors/ERK pathway may play a critical role in the motivational properties of ethanol.

Noradrenergic terminals are the primary source of α2-adrenoceptor mediated dopamine release in the medial prefrontal cortex.

In various psychiatric disorders, deficits in dopaminergic activity in the prefrontal cortex (PFC) are implicated. Treatments involving selective augmentation of dopaminergic activity in the PFC primarily depend on the inhibition of α2-adrenoreceptors singly or in combination with the inhibition of the norepinephrine transporter (NET). We aimed to clarify the relative contribution of dopamine (DA) release from noradrenergic and dopaminergic terminals to DA output induced by blockade of α2-adrenoreceptors and NET. To this end, we assessed whether central noradrenergic denervation modified catecholamine output in the medial PFC (mPFC) of rats elicited by atipamezole (an α2-adrenoreceptor antagonist), nisoxetine (an NET inhibitor), or their combination. Intraventricular administration of anti-dopamine-beta-hydroxylase-saporin (aDBH) caused a loss of DBH-positive fibers in the mPFC and almost total depletion of tissue and extracellular NE level; however, it did not reduce tissue DA level but increased extracellular DA level by 70% in the mPFC. Because noradrenergic denervation should have caused a loss of NET and reduced NE level at α2-adrenoceptors, the actual effect of an aDBH-induced lesion on DA output elicited by blockade of α2-adrenoceptors and NET was evaluated by comparing denervated and control rats following blockade of α2-adrenoceptors and NET with atipamezole and nisoxetine, respectively. In the control rats, extracellular NE and DA levels increased by approximately 150% each with 3 mg/kg atipamezole; 450% and 230%, respectively, with 3 mg/kg nisoxetine; and 2100% and 600%, respectively, with combined atipamezole and nisoxetine. In the denervated rats, consistent with the loss of NET, nisoxetine failed to modify extracellular DA level, whereas atipamezole, despite the lack of NE-induced stimulation of α2-adrenoceptors, increased extracellular DA level by approximately 30%. Overall, these results suggest that atipamezole-induced DA release mainly originated from noradrenergic terminals, possibly through the inhibition of α2-autoreceptors. Furthermore, while systemic and local administration of the α2-adrenoceptor agonist clonidine into the mPFC of the controls rats reduced extracellular NE level by 80% and 60%, respectively, and extracellular DA level by 50% and 60%, respectively, it failed to reduce DA output in the denervated rats, consistent with the loss of α2-autoreceptors. To eliminate the possibility that denervation reduced DA release potential via the effects at dopaminergic terminals in the mPFC, the effect of systemic administration of the D2-DA antagonist raclopride (0.5 mg/kg IP) on DA output was analyzed. In the control rats, raclopride was found to be ineffective when administered alone, but it increased extracellular DA level by 380% following NET inhibition with nisoxetine. In the denervated rats, as expected due to the loss of NET, raclopride-alone or with nisoxetine-increased DA release to approximately the same level as that observed in the control rats after NET inhibition. Overall, these results suggest that noradrenergic terminals in the mPFC are the primary source of DA released by blockade of α2-adrenoreceptors and NET and that α2-autoreceptors, and not α2-heteroreceptors, mediate DA output induced by α2-adrenoceptor blockade.

Boosting phagocytosis and anti-inflammatory phenotype in microglia mediates neuroprotection by PPARγ agonist MDG548 in Parkinson's disease models.

BACKGROUND AND PURPOSE: Microglial phenotype and phagocytic activity are deregulated in Parkinson's disease (PD). PPARγ agonists are neuroprotective in experimental PD, but their role in regulating microglial phenotype and phagocytosis has been poorly investigated. We addressed it by using the PPARγ agonist MDG548. EXPERIMENTAL APPROACH: Murine microglial cell line MMGT12 was stimulated with LPS and/or MDG548, and their effect on phagocytosis of fluorescent microspheres or necrotic neurons was investigated by flow cytometry. Cytokines and markers of microglia phenotype, such as mannose receptor C type 1; MRC1), Ym1 and CD68 were measured by elisa and fluorescent immunohistochemistry. Levels of Beclin-1, which plays a role in microglial phagocytosis, were measured by Western blotting. In the in vivo MPTP-probenecid (MPTPp) model of PD in mice, MDG548 was tested on motor impairment, nigral neurodegeneration, microglial activation and phenotype. KEY RESULTS: In LPS-stimulated microglia, MDG548 increased phagocytosis of both latex beads and necrotic cells, up-regulated the expression of MRC1, CD68 and to a lesser extent IL-10, while blocking the LPS-induced increase of TNF-α and iNOS. MDG548 also induced Beclin-1. Chronic MPTPp treatment in mice down-regulated MRC1 and TGF-ß and up-regulated TNF-α and IL-1ß immunoreactivity in activated CD11b-positive microglia, causing the death of nigral dopaminergic neurons. MDG548 arrested MPTPp-induced cell death, enhanced MRC1 and restored cytokine levels. CONCLUSIONS AND IMPLICATIONS: This study adds a novel mechanism for PPARγ-mediated neuroprotection in PD and suggests that increasing phagocytic activity and anti-inflammatory markers may represent an effective disease-modifying approach.

Preferential increase of extracellular dopamine in the rat nucleus accumbens shell as compared to that in the core during acquisition and maintenance of intravenous nicotine self-administration.

RATIONALE: It has been reported that passive administration of nicotine increases preferentially extracellular dopamine (DA) release in the shell as compared to that in the core of the nucleus accumbens (NAc). To date, no information is available if this also applies to active, response-contingent nicotine administration. OBJECTIVE: This study was aimed to monitor the changes of extracellular DA in the NAc shell and core during active intravenous nicotine self-administration (SA). METHODS: Rats were bilaterally implanted with chronic cannulae and were trained to self-administer nicotine (0.03 mg/kg, i.v.) in single daily 1-h session for 6 weeks, with an initial fixed ratio (FR) 1 schedule increased to FR 2. Dialysate DA from the NAc shell and core was monitored before and for 90 min after the start of SA. RESULTS: Significant increases of active nose-pokes over inactive ones were found starting from the 16th SA session. No differences were found in basal extracellular DA in the NAc subdivisions. Data analysis showed (1) significant increases over basal of dialysate DA in the NAc subdivisions during nicotine SA, starting from the first week in the shell and from the second week in the core, (2) preferential increase of extracellular DA during nicotine SA in the shell (24-43%) compared to that in the core (10-23%) and (3) no change in dialysate DA in NAc subdivisions during extinction. CONCLUSIONS: Response-contingent nicotine SA preferentially increases the DA output in the NAc shell as compared to that in the core, independently from the duration of the nicotine exposure. Increase in NAc DA is strictly related to nicotine action since is not observed during extinction in spite of active responding.

Persistent and reversible morphine withdrawal-induced morphological changes in the nucleus accumbens.

Morphine withdrawal produces a hypofunction of mesencephalic dopamine (DA) neurons which impinge upon medium spiny neurons (MSN) of the forebrain. After chronic treatment rats were either spontaneously or pharmacologically withdrawn from chronic morphine: under these two distinct conditions we studied the effects of withdrawal on spine density of MSN of the core and shell of the nucleus accumbens (NAcc) at various times (1-3-7-14 days). MSN were stained with the Golgi-Cox procedure and analyzed by a confocal laser-scanning microscope. Our analysis shows that both spontaneous and naloxone-induced withdrawal produces a long-lasting but reversible reduction in spines' density in shell MSN, as compared with core MSN. This effect is selectively localized at the level of second-order dendritic trunks and persists up to 14 days when spine density was found within control (pretreatment) values. By contrast, spine density counts of NAcc MSN from rats chronically treated with morphine, did not reveal any change over time. Collectively, the results of the present article suggest that spontaneous and pharmacologically precipitated withdrawal, but not chronic morphine, persistently but reversibly reduce spines' density under a condition of reduced mesolimbic DA transmission, and the reduction of spines' density in second-order dendritic trunks is selectively segregated in the MSN of the shell of the NAcc. Morphine withdrawal dramatically, lastingly, and reversibly reduces spine density, selectively in second-order dendritic trunks of NAcc shell MSN, thereby further impoverishing the already abated DA transmission. These results may be relevant in the most harmful consequences of drug addiction such as craving and loss of control over intake and are in line with recent views suggesting the hypodopaminergic state as a cardinal feature of drug dependence.