EFFETTO DELL’INIBIZIONE DELLA 5-ALFA REDUTTASI SULLE DISCINESIE IN UN MODELLO ANIMALE DI MALATTIA DI PARKINSON

Levodopa-induced dyskinesia (LID) is a disabling motor complication occurring in Parkinson's disease patients (PD) after long-term l-DOPA treatment. Although its etiology remains unclear, there is accumulating evidence that LID relies on an excessive dopamine receptor transmission, particularly at the downstream signaling of D1 receptors. We previously reported that the inhibition of 5-alpha reductase (5AR), the rate limiting enzyme in neurosteroids synthesis, rescued a number of behavioral aberrations induced by D1 receptor-selective and non-selective agonists, without inducing extrapyramidal symptoms. Thus, this study was aimed at investigating whether the pharmacological blockade of 5AR by the two prototypical irreversible inhibitors finasteride (FIN) and dutasteride (DUTA), might elicit antidyskinetic properties in a rodent model of Parkinson's disease. Specifically, we tested the effects of FIN and DUTA on dyskinesias induced by dopaminergic agonists in 6-hydroxydopamine (6-OHDA)-lesioned rats. Acute and chronic effect of different doses of FIN (30-60mg/kg) and DUTA (15-30 mg/Kg), was assessed on LID in male 6-OHDA-lesioned dyskinetic rats. Thereafter, to fully characterize the therapeutic potential of these inhibitors on LID and their impact on l-DOPA efficacy, we tested abnormal involuntary movements and forelimb use in hemiparkinsonian male rats chronically injected with FIN (30-60mg/kg/24days) and DUTA (30-60mg/kg/24days) either prior to- or concomitant with l-DOPA administration. In addition, to investigate whether the antidyskinetic properties on LID may be ascribed to a modulation of the D1- or D2/D3-receptor function, dyskinesias were assessed in l-DOPA-primed 6-OHDA-lesioned rats that received FIN in combination with selective direct dopaminergic agonists. Finally, we set to investigate whether FIN may produce similar effect in female hemiparkinsonian rats, as seen in males. The results indicated that both FIN and DUTA administrations significantly dampened LID in all tested treatment regimens, without interfering with the ability of l-DOPA to ameliorate forelimb use in the stepping test. The antidyskinetic effect appears to be due to modulation of both D1- and D2/D3-receptor function, as FIN also reduced abnormal involuntary movements induced by the selective D1 receptor agonist SKF-82958 and the D2/D3 receptor agonist ropinirole. Significant dampening of LID was also observed in female rats, although only at the higher tested dose. To our knowledge, these findings for the first time highlight 5AR enzyme as a new therapeutic target for the treatment of dyskinesia in PD. Clinical investigations are warranted to assess whether similar protection from dyskinesia might be reproduced also in PD patients

Effetti dell'astinenza da morfina in un modello computazionale di un neurone dopaminegico

Dopamine (DA) neurons of the ventral tegmental area (VTA) are involved in the neurobiological mechanisms underlying addictive processes. It has been shown that withdrawal from drugs of abuse, causes profound modifications in the morphology and physiology of these neurons, but the mechanisms underlying these modifications are poorly understood. Because of their high predictive value, computational models are a powerful tool in neurobiological research, and have been used to gain further insights and deeper understanding on the molecular and physiological mechanisms underlying the development of various psychiatric disorders. Here we present a biophysical model of a DA VTA neuron based on 3d morphological reconstruction and electrophysiological data from literature, showing how opiate withdrawal-driven morphological and electrophysiological changes could affect the firing rate and pattern of these neurons. The model is composed by 89 membrane segments, with sodium and calcium dynamics responsible for the basal in vivo activity of these neurons; the set of inputs is modeled adding GabaA and AMPA/NMDA synapses, activated in such a way to model the behavior of gabaergic and glutamatergic inputs, respectively. We modeled the opiate withdrawal state by applying to the model morphometric modifications observed experimentally and by modulating the balance of Gaba/Glu inputs as described by electrophysiological data. Our results suggest that changes in the balance of Gaba/Glu inputs could explain the hypofunction of VTA DA neurons with different effects on synaptic efficacy, while morphological changes could be responsible for their higher responsivity to opiate administration observed during opiate withdrawal

Influence of Amphetamine-type stimulants in the Central Nervous System: abuse and neurotoxicity

Amphetamines are synthetic drugs characterized by their psychostimulants effects on the central nervous system (CNS), and include a wide range of substances such as alpha-methylphenethylamine or amphetamine (AMPH), N-methylamphetamine or methamphetamine (METH) and 3,4 methylenedioxymethamphetamine (MDMA) also known as “ecstasy”. The ATS, structurally, are a group of substances related to the compound known as β-phenethylamine (β-PEA), a naturally neurotransmitter in the body. Structural modifications on the aromatic ring of β-PEA create multiple synthetic derivatives with different pharmacological properties. Various hypotheses regarding the mechanism responsible for METH and MDMA-induced neurotoxicity, have been proposed, including high release of monoamines (Dopamine (DA), serotonin (5-HT)), DA quinones formation synthesized by oxidation of the catechol ring of DA, excitatory amino acid glutamate (GLU) release and hyperthermia (Cadet et al., 2003; Miyazaki et al., 2006). It is likely that interactions between these factors trigger neurotoxicity induced by METH or MDMA. In addition, METH causes substantial changes in gene expression in some brain regions including the cortex, the dorsal caudate-putamen (CPu), and the midbrain (Cadet et al., 2009). These molecular changes include transient increases and decreases in the expression of various transcription factors, neuropeptides, and genes that participate in several biological functions (cell cycle, cell differentiation, signaling transduction), (Jayanthi et al., 2005). In order to better understand the molecular mechanism that control the compulsive drug use, in collaboration with National Institutes on Drug abuse (NIDA, Baltimore) we have used the Self-administration (SA) paradigm in association with footshocks to induce negative consequences during METH SA. We investigated whether the compulsive METH taking under punishment can increase the expression of immediate early genes (IEGs) in the rat Nucleus Accumbens (NAc) and Prefrontal cortex (PFC), that are important areas involved in reward, memory, executive function, motivation and contribute to some of the differences in the circuit of addiction (Volkow & Morales 2015; Volkow et al., 2012; Adinoff 2004). In the second and third study, performed at the University of Cagliari, we focused on MDMA treatment in mice in order to clarify the role played by this drug on neurotoxicity and motor behavior resulting from MDMA administration. Specifically, in the second study, considering the influence of the Ras Homolog enriched in striatum protein (Rhes) very important in the striatal functions, we studied the age-related survival of DA neurons in the substantia nigra (SNc) after MDMA treatment and the implication of this protein in neurodegenerative disease such as Parkinson Disease (PD). We have investigated the basal and the MDMA-induced neurotoxic effects in Rhes knock-out mice, male and female at different ages. Moreover, in an attempt to link neurochemical changes with behavioural modifications, this study investigated the motor activity. The third study investigated the possible neuroprotective effect of metformin, an antidiabetic drug, against short and long-term neurotoxicity induced by MDMA, together with its role on MDMA-induced hyperthermia

EFFECTS OF EARLY LIFE STRESS ON MESOCORTICOLIMBIC DOPAMINE SYSTEM FUNCTION AND RELATED DISORDERS IN PRE-ADOLESCENT HYPOMORPHIC MAOA MICE

Monoamine oxidase A (MAOA) is the degrading enzyme of monoamines (e.g., serotonin and dopamine (DA)), which plays an age-specific role in the etiopathogenesis of aggressive behavior (AB). AB is a multifaceted disorder based on the interaction between genetic (i.e., low activity of MAOA gene) and early life adversities (i.e., child neglect/abuse) (GxE). Furthermore, both early life adversities and AB display high comorbidity with substance abuse, raising the possibility that MAOA may act as a risk/predictive factor for subsequent drug abuse. In this thesis, we investigated the impact of this GxE interaction on DA function at pre-adolescence by exposing hypomorphic MAOA (MAONeo) mice to early life stress (ES). Then, we performed behavioral and ex vivo electrophysiological analyses in the ventral tegmental area (VTA) and the prefrontal cortex (PFC) to determine whether i) synaptic alterations of mesocorticolimbic DA system are necessary and sufficient for the genesis of AB during pre-adolescence and ii) GxE interaction enhances the vulnerability to psychostimulant effects of cocaine. We found that in MAOANeoES mouse DA neurons, the manifestation of AB is associated with enhanced post-synaptic responsiveness to excitatory inputs and aberrant plasticity in the PFC during pre-adolescence. Moreover, systemic administration of the selective antagonist at DA DAD1 receptors SCH23390 fully restored PFC function and rescued AB. On the other hand, we found that MAOANeo ES mice were more sensitive to psychostimulant effects of cocaine after subchronic administration and following one week of withdrawal. While the analysis of excitatory properties of VTA DA neurons did not reveal any significant difference in these synapses among groups, we showed that in MAOANeo ES mice, subchronic cocaine reduced synaptic efficacy of inhibitory inputs and the probability of GABA release, effects that persisted after one week of withdrawal. The study of the role of endocannabinoids (eCB) signaling in the regulation of these alterations revealed that cocaine enabled 2-arachidonoylglycerol (2-AG)-mediated depolarization-induced suppression of inhibition (DSI) in MAOANeo ES mice an effect that persisted also after one week of withdrawal. We also discovered that in vivo pretreatment with DAD2 and CB1 receptor antagonists, sulpiride and AM281 respectively, restored inhibitory synaptic efficacy and probability of GABA release in MAOANeo ES mice, as well as prevented DSI. Collectively, these results reveal that dysfunctional mesocortical DA signaling at pre-adolescence ties to AB in the MAOANeo ES mouse model and that it cross-sensitizes to psychostimulant effects of cocaine through a reduced GABA synaptic transmission on VTA DA neurons