Elvira De Leonibus

Targeting Group III Metabotropic Glutamate Receptors Produces Complex Behavioral Effects in Rodent Models of Parkinson's Disease

Drugs activating group III metabotropic glutamate receptors (mGluRs) represent therapeutic alternatives to l-DOPA (l-3,4-dihydroxyphenylalanine) for the treatment of Parkinsons disease (PD). Their presynaptic location at GABAergic and glutamatergic synapses within basal ganglia nuclei provide a critical target to reduce abnormal activities associated with PD. The effects of selective group III mGluR agonists (1S,3R,4S)-1-aminocyclopentane-1,3,4-tricarboxylic acid (ACPT-I) and l-(+)-2-amino-4-phosphonobutyric acid (l-AP4) infused into the globus pallidus (GP) or the substantia nigra pars reticulata (SNr) were thus studied in rat models of PD. Bilateral infusions of ACPT-I (1, 2.5, and 5 nmol/μl) into the GP fully reverse the severe akinetic deficits produced by 6-hydroxydopamine nigrostriatal dopamine lesions in a reaction-time task without affecting the performance of controls. Similar results were observed after l-AP4 (1 nmol) or picrotoxin, a GABAA receptor antagonist, infused into the GP. In addition, intrapallidal ACPT-I counteracts haloperidol-induced catalepsy. This effect is reversed by concomitant administration of a selective group III receptor antagonist (RS)-α-cyclopropyl-4-phosphonophenylglycine. In contrast, ACPT-I (0.05, 0.1, and 0.25 nmol) infusions into the SNr enhance the lesion-induced akinetic deficits in control and lesioned rats and do not reverse haloperidol-induced catalepsy. l-AP4 (0.05 nmol) and picrotoxin in the SNr produce the same effects. Together, these results show that activation of group III mGluRs in the GP provides benefits in parkinsonian rats, presumably by modulating GABAergic neurotransmission. The opposite effects produced by group III mGluR activation in the SNr, also observed with a selective mGluR8 agonist, support the use of subtype-selective group III mGluR agonists as a potential antiparkinsonian strategy.

Area-specific temporal control of corticospinal motor neuron differentiation by COUP-TFI

Transcription factors with gradients of expression in neocortical progenitors give rise to distinct motor and sensory cortical areas by controlling the area-specific differentiation of distinct neuronal subtypes. However, the molecular mechanisms underlying this area-restricted control are still unclear. Here, we show that COUP-TFI controls the timing of birth and specification of corticospinal motor neurons (CSMN) in somatosensory cortex via repression of a CSMN differentiation program. Loss of COUP-TFI function causes an area-specific premature generation of neurons with cardinal features of CSMN, which project to subcerebral structures, including the spinal cord. Concurrently, genuine CSMN differentiate imprecisely and do not project beyond the pons, together resulting in impaired skilled motor function in adult mice with cortical COUP-TFI loss-of-function. Our findings indicate that COUP-TFI exerts critical areal and temporal control over the precise differentiation of CSMN during corticogenesis, thereby enabling the area-specific functional features of motor and sensory areas to arise.

Loss of COUP-TFI Alters the Balance between Caudal Ganglionic Eminence- and Medial Ganglionic Eminence-Derived Cortical Interneurons and Results in Resistance to Epilepsy

In rodents, cortical interneurons originate from the medial ganglionic eminence (MGE) and caudal ganglionic eminence (CGE) according to precise temporal schedules. The mechanisms controlling the specification of CGE-derived interneurons and their role in cortical circuitry are still unknown. Here, we show that COUP-TFI expression becomes restricted to the dorsal MGE and CGE at embryonic day 13.5 in the basal telencephalon. Conditional loss of function of COUP-TFI in subventricular precursors and postmitotic cells leads to a decrease of late-born, CGE-derived, VIP (vasoactive intestinal peptide)- and CR (calretinin)-expressing bipolar cortical neurons, compensated by the concurrent increase of early-born MGE-derived, PV (parvalbumin)-expressing interneurons. Strikingly, COUP-TFI mutants are more resistant to pharmacologically induced seizures, a phenotype that is dependent on GABAergic signaling. Together, our data indicate that COUP-TFI controls the delicate balance between MGE- and CGE-derived cortical interneurons by regulating intermediate progenitor divisions and ultimately affecting the activity of the cortical inhibitory circuitry.

Spatial deficits in a mouse model of Parkinson disease

RationaleAccumulating evidence in humans demonstrated that visuo-spatial deficits are the most consistently reported cognitive abnormalities in Parkinson disease (PD). These deficits have been generally attributed to cortical dopamine degeneration. However, more recent evidence suggests that dopamine loss in the striatum is responsible for the visuo-spatial abnormalities in PD. Studies based on animal models of PD did not specifically address this question.ObjectivesThus, the first goal of this study was to analyze the role of dopamine within the dorsal striatum in spatial memory. We tested bilateral 6-OHDA striatal lesioned CD1 mice in an object–place association spatial task. Furthermore, to see whether the effects were selective for spatial information, we measured how the 6-OHDA-lesioned animals responded to a non-spatial change and learned in the one-trial inhibitory avoidance task.ResultsThe results demonstrated that bilateral (approximately 75%) dopamine depletion of the striatum impaired spatial change discrimination. On the contrary, no effect of the lesion was observed on non-spatial novelty detection or on passive avoidance learning.ConclusionsThese results confirm that dopamine depletion is accompanied by cognitive deficits and demonstrate that striatal dopamine dysfunction is sufficient to induce spatial information processing deficits.

Metabotropic Glutamate Receptors 5 Blockade Reverses Spatial Memory Deficits in a Mouse Model of Parkinson's Disease

Visuo-spatial deficits are the most consistently reported cognitive abnormalities in Parkinsons disease (PD), and they are frequently associated to motor symptoms in the early stages of the disease when dopamine loss is moderate and still restricted to the caudate–putamen. The metabotropic glutamate receptor 5 (mGluR5) antagonist, 2-methyl-6-(phenylethynyl)-pyridine (MPEP), has beneficial effects on motor symptoms in animal models of PD. However, the effects of MPEP on the cognitive deficits of the disease have never been investigated. Thus, the purpose of this study was to explore its therapeutic potentials by investigating its effects on the visuo-spatial deficits induced by 6-hydroxydopamine (6-OHDA) lesions of dorsal striatum in CD1 mice. The results demonstrated that systemic injections of MPEP (6, 12, and 24u2009mg/kg, i.p.) impair visuo-spatial discrimination in intact mice at high concentrations, whereas lower doses (1.5 and 3u2009mg/kg, i.p.) were void of effects. Nevertheless, when an ineffective dose (MPEP 3u2009mg/kg) was injected, either acutely or subchronically (8 days), it antagonized the visuo-spatial discrimination deficit induced by bilateral dopamine lesion of the striatum. Furthermore, the same treatment increased contralateral turning induced by L-DOPA in mice bearing unilateral 6-OHDA lesion. These results confirm the therapeutic potential of mGluR5 blockade on motor symptoms induced by reduced striatal dopamine function. Further, they demonstrate that mGluR5 blockade may also have beneficial effects on cognitive deficits induced by dopamine depletion.

Lack of Mid1, the Mouse Ortholog of the Opitz Syndrome Gene, Causes Abnormal Development of the Anterior Cerebellar Vermis

Opitz G/BBB syndrome (OS) is a genetic disorder characterized by midline developmental defects. Male patients with the X-linked form of OS, caused by loss-of-function mutations in the MID1 gene, show high variability of the clinical signs. MID1 encodes a ubiquitin ligase that controls phosphatase 2A, but its role in the pathogenesis of the disease is still unclear. Here, we report a mouse line carrying a nonfunctional ortholog of the human MID1 gene, Mid1. Mid1-null mice show the brain anatomical defect observed in patients (i.e., hypoplasia of the anterior portion of the medial cerebellum, the vermis). We found that the presence of this defect correlates with motor coordination and procedural and nonassociative learning impairments. The defect is limited to the most anterior lobes of the vermis, the region of the developing cerebellum adjacent to the dorsal midbrain. Analyses at midgestation reveal that lack of Mid1 causes the shortening of the posterior dorsal midbrain, the rostralization of the midbrain/cerebellum boundary, and the downregulation of a key player in the development of this region, Fgf17. Thus, lack of Mid1 causes a misspecification of the midbrain/cerebellar boundary that results in an abnormal development of the most anterior cerebellar lobes. This animal model provides a tool for additional in vivo studies of the physiological and pathological role of the Mid1 gene and a system to investigate the development and function of anterior cerebellar domains.

Role of Dopamine Receptors Subtypes, D1-Like and D2-Like, within the Nucleus Accumbens Subregions, Core and Shell, on Memory Consolidation in the One-Trial Inhibitory Avoidance Task.

Recent evidence demonstrated that dopamine within the nucleus accumbens mediates consolidation of both associative and nonassociative memories. However, the specific contribution of the nucleus accumbens subregions, core and shell, and of D1 and D2 receptors subtypes has not been yet clarified. The aim of this study was, therefore, to directly compare the effect of D1 and D2 dopamine receptor blockade within the core and the shell subregions of the nucleus accumbens on memory consolidation. Using the one-trial inhibitory avoidance task in CD1 mice, we demonstrated that SCH 23390 (vehicle, 12.5, 25, 50 ng/side) administration within the core, but not the shell, impaired step-through latency 24 h after the administration if injected immediately, but not 120 min post-training. Interestingly, sulpiride (vehicle, 25, 50 ng/side) injection in both the core and the shell of the accumbens affected step-through latency 24 h later; also, in this case the impairment was time dependent. These data provide the most complete and direct demonstration to date that early consolidation of aversive memory requires D2 receptor activation in both nucleus accumbens subregions, and D1 activation selectively in the nucleus accumbens core.

Distinct kinds of novelty processing differentially increase extracellular dopamine in different brain regions

Behaviourally relevant novel stimuli are known to activate the mesocorticolimbic dopaminergic (DAergic) system. In this study we tested the reactivity of this system in response to distinct kinds of novelty processing. Using the in vivo microdialysis technique, we measured extracellular amounts of dopamine (DA) in different DAergic terminal regions during a social learning task in rats. In the first session (40u2003min) rats were exposed to two never previously encountered juveniles (i.e. unconditional novelty). Afterwards, the animals were divided into three groups: Control group was not exposed to any other stimulus; Discrimination group was exposed to one familiar and one new juvenile (i.e. novel stimulus discrimination); and Recognition group was re‐exposed to the two familiar juveniles (i.e. familiarity recognition). In both the medial prefrontal cortex and the nucleus accumbens shell DA increased in response to the first presentation of the juveniles, showing that both structures are involved in processing unconditional social novelty. During the novel stimulus discrimination, we found no change in the prefrontal cortex, although DA increased in the accumbal shell in comparison with the group exposed to two familiar juveniles, showing that the shell is also involved in processing novel social stimulus discrimination. None of the stimuli presented affected DA in the accumbal core. This study provided the original evidence that DA in the various terminal regions is differentially coupled to distinct aspects of novelty processing.

Long-term amelioration of feline Mucopolysaccharidosis VI after AAV-mediated liver gene transfer.

Mucopolysaccharidosis VI (MPS VI) is caused by deficient arylsulfatase B (ARSB) activity resulting in lysosomal storage of glycosaminoglycans (GAGs). MPS VI is characterized by dysostosis multiplex, organomegaly, corneal clouding, and heart valve thickening. Gene transfer to a factory organ like liver may provide a lifetime source of secreted ARSB. We show that intravascular administration of adeno-associated viral vectors (AAV) 2/8-TBG-felineARSB in MPS VI cats resulted in ARSB expression up to 1 year, the last time point of the study. In newborn cats, normal circulating ARSB activity was achieved following delivery of high vector doses (6 × 10(13) genome copies (gc)/kg) whereas delivery of AAV2/8 vector doses as low as 2 × 10(12) gc/kg resulted in higher than normal serum ARSB levels in juvenile MPS VI cats. In MPS VI cats showing high serum ARSB levels, independent of the age at treatment, we observed: (i) clearance of GAG storage, (ii) improvement of long bone length, (iii) reduction of heart valve thickness, and (iv) improvement in spontaneous mobility. Thus, AAV2/ 8-mediated liver gene transfer represents a promising therapeutic strategy for MPS VI patients.

Rats that differentially respond to cocaine differ in their dopaminergic storage capacity of the nucleus accumbens

Cocaine (COC) inhibits the re‐uptake of dopamine. However, the dopamine response to COC also depends on dopamine inside storage vesicles. The aim of this study was to investigate whether rats that differentially respond to COC differ in their dopaminergic storage capacity of the nucleus accumbens. Total and vesicular levels of accumbal dopamine as well as accumbal vesicular monoamine transporter‐2 levels were established in high (HR) and low responders (LR) to novelty rats. Moreover, the effects of reserpine (RES) on the COC‐induced increase of extracellular accumbal dopamine were investigated. HR displayed higher accumbal levels of total and vesicular dopamine than LR. Moreover, HR displayed more accumbal vesicular monoamine transporters‐2 than LR. COC increased extracellular accumbal dopamine more strongly in HR than in LR. A low dose of RES prevented the COC‐induced increase of accumbal dopamine in LR, but not in HR. A higher dose of RES was required to inhibit the COC‐induced increase of accumbal dopamine in HR. These data demonstrate that HR were marked by a larger accumbal dopaminergic storage pool than LR. It is hypothesized that HR are more sensitive to COC than LR, because COC can release more dopamine from accumbal storage vesicles in HR than in LR.