RESUMEN
Alterations of serotonin type 4 receptor levels are linked to mood disorders and cognitive deficits in several conditions. However, few studies have investigated 5-HT4R alterations in movement disorders. We wondered whether striatal 5-HT4R expression is altered in experimental parkinsonism. We used a brain bank tissue from a rat and a macaque model of Parkinson's disease (PD). We then investigated its in vivo PET imaging regulation in a cohort of macaques. Dopaminergic depletion increases striatal 5-HT4R in the two models, further augmented after dyskinesia-inducing L-Dopa. Pending confirmation in PD patients, the 5-HT4R might offer a therapeutic target for dampening PD's symptoms.
Asunto(s)
Discinesia Inducida por Medicamentos , Enfermedad de Parkinson , Trastornos Parkinsonianos , Humanos , Ratas , Animales , Enfermedad de Parkinson/tratamiento farmacológico , Receptores de Serotonina 5-HT4/uso terapéutico , Discinesia Inducida por Medicamentos/diagnóstico por imagen , Discinesia Inducida por Medicamentos/etiología , Discinesia Inducida por Medicamentos/tratamiento farmacológico , Trastornos Parkinsonianos/tratamiento farmacológico , Levodopa/uso terapéutico , Modelos Animales de Enfermedad , Oxidopamina , Antiparkinsonianos/uso terapéuticoRESUMEN
Selective serotonin reuptake inhibitors (SSRIs) are widely used to treat psychiatric disorders with affective biases such as depression and anxiety. How SSRIs exert a beneficial action on emotions associated with life events is still unknown. Here we ask whether and how the effectiveness of the SSRI fluoxetine is underpinned by neural mechanisms in the ventral striatum. To address these issues, we studied the spiking activity of neurons in the ventral striatum of monkeys during an approach-avoidance task in which the valence assigned to sensory stimuli was manipulated. Neural responses to positive and negative events were measured before and during a 4-week treatment with fluoxetine. We conducted PET scans to confirm that fluoxetine binds within the ventral striatum at a therapeutic dose. In our monkeys, fluoxetine facilitated approach of rewards and avoidance of punishments. These beneficial effects were associated with changes in tonic and phasic activities of striatal neurons. Fluoxetine increased the spontaneous firing rate of striatal neurons and amplified the number of cells responding to rewards versus punishments, reflecting a drug-induced positive shift in the processing of emotionally valenced information. These findings reveal how SSRI treatment affects ventral striatum neurons encoding positive and negative valence and striatal signaling of emotional information. In addition to a key role in appetitive processing, our results shed light on the involvement of the ventral striatum in aversive processing. Together, the ventral striatum appears to play a central role in the action of SSRIs on emotion processing biases commonly observed in psychiatric disorders.
Asunto(s)
Inhibidores Selectivos de la Recaptación de Serotonina , Estriado Ventral , Afecto , Animales , Cuerpo Estriado , Fluoxetina/farmacología , Primates , Inhibidores Selectivos de la Recaptación de Serotonina/farmacología , Estriado Ventral/diagnóstico por imagenRESUMEN
The aim of this study was to investigate the causal role of an early serotonin injury on parkinsonian-like motor symptomatology. Monkeys were pretreated with 3,4-methylenedioxy-N-methamphetamine (MDMA, or "ecstasy"), known to lesion serotonergic fibers, before being administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We combined behavioural assessment, PET imaging, and immunohistochemistry. Strikingly, prior MDMA administration aggravated MPTP-induced Parkinsonism and associated dopaminergic injury. Monkeys with early MDMA lesions developed parkinsonian deficits more rapidly and more severely. Interestingly, not all symptoms were impacted. Bradykinesia, rigidity and freezing were not affected by early MDMA lesions, whereas spontaneous activities, tremor and abnormal posture were significantly aggravated. Finally, as expected, MDMA induced a decrease of the serotonergic transporter availability. More surprisingly, we found that MDMA evoked also a decreased availability of the dopaminergic transporter to a lesser extent. Altogether, these results show that MDMA administration in non-human primates not only damage serotonergic terminals, but also injure dopaminergic neurons and enhance MPTP neurotoxic action, a completely new result in primates.