RESUMO
Degeneration of dopamine (DA) neurons in Parkinson's disease (PD) causes hypokinesia, but DA replacement therapy can elicit exaggerated voluntary and involuntary behaviors that have been attributed to enhanced DA receptor sensitivity in striatal projection neurons. Here we reveal that in hemiparkinsonian mice, striatal D1 receptor-expressing medium spiny neurons (MSNs) directly projecting to the substantia nigra reticulata (SNr) lose tonic presynaptic inhibition by GABAB receptors. The absence of presynaptic GABAB response potentiates evoked GABA release from MSN efferents to the SNr and drives motor sensitization. This alternative mechanism of sensitization suggests a synaptic target for PD pharmacotherapy.
Assuntos
Corpo Estriado/patologia , Neurônios GABAérgicos/fisiologia , Atividade Motora/fisiologia , Transtornos Parkinsonianos/patologia , Transtornos Parkinsonianos/fisiopatologia , Substância Negra/patologia , Adrenérgicos/toxicidade , Animais , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Channelrhodopsins , Modelos Animais de Doenças , Dopamina/metabolismo , Antagonistas de Aminoácidos Excitatórios/farmacologia , GABAérgicos/farmacologia , Humanos , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Proteínas Luminescentes/genética , Proteínas Luminescentes/metabolismo , Feixe Prosencefálico Mediano/lesões , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Atividade Motora/efeitos dos fármacos , Oxidopamina/toxicidade , Transtornos Parkinsonianos/induzido quimicamente , Terminações Pré-Sinápticas/efeitos dos fármacos , Terminações Pré-Sinápticas/fisiologia , Compostos de Piridínio/metabolismo , Compostos de Amônio Quaternário/metabolismo , Quinoxalinas/farmacologia , Ácido gama-Aminobutírico/metabolismoRESUMO
We recently introduced fluorescent false neurotransmitters (FFNs) as optical tracers that enable the visualization of neurotransmitter release at individual presynaptic terminals. Here, we describe a pH-responsive FFN probe, FFN102, which as a polar dopamine transporter substrate selectively labels dopamine cell bodies and dendrites in ventral midbrain and dopaminergic synaptic terminals in dorsal striatum. FFN102 exhibits greater fluorescence emission in neutral than acidic environments, and thus affords a means to optically measure evoked release of synaptic vesicle content into the extracellular space. Simultaneously, FFN102 allows the measurement of individual synaptic terminal activity by following fluorescence loss upon stimulation. Thus, FFN102 enables not only the identification of dopamine cells and their processes in brain tissue, but also the optical measurement of functional parameters including dopamine transporter activity and dopamine release at the level of individual synapses. As such, the development of FFN102 demonstrates that, by bringing together organic chemistry and neuroscience, molecular entities can be generated that match the endogenous transmitters in selectivity and distribution, allowing for the study of both the microanatomy and functional plasticity of the normal and diseased nervous system.
Assuntos
Encéfalo/metabolismo , Dopamina/metabolismo , Corantes Fluorescentes , Sinapses/metabolismo , Anfetamina/farmacologia , Animais , Axônios/metabolismo , Corpo Estriado/metabolismo , Dendritos/metabolismo , Proteínas da Membrana Plasmática de Transporte de Dopamina/metabolismo , Corantes Fluorescentes/química , Concentração de Íons de Hidrogênio , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Microscopia de Fluorescência por Excitação Multifotônica , Processos Fotoquímicos , Terminações Pré-Sinápticas/metabolismo , Sinapses/efeitos dos fármacos , Transmissão SinápticaRESUMO
Optical imaging is a valuable tool for investigating alterations in membrane turnover and vesicle trafficking. Established techniques can easily be adapted to study the mechanisms of synaptic dysfunction in models of neuropsychiatric disorders and neurodegenerative diseases, such as drug addiction, Parkinsonism, and Huntington's disease. Fluorescent endocytic tracers, including FM1-43, have been used to optically monitor synaptic vesicle fusion and measure synaptic function in various preparations, including chromaffin cells, dissociated cell cultures, and brain slices. In this chapter, we describe a technique that provides a direct measure of pathway-specific exocytosis from glutamatergic corticostriatal terminals.