RESUMEN
While the transporters that accumulate classical neurotransmitters in synaptic vesicles have been identified, little is known about how their expression regulates synaptic transmission. We have used adenoviral-mediated transfection to increase expression of the brain vesicular monoamine transporter VMAT2 and presynaptic amperometric recordings to characterize the effects on quantal release. In presynaptic axonal varicosities of ventral midbrain neurons in postnatal culture, VMAT2 overexpression in small synaptic vesicles increased both quantal size and frequency, consistent with the recruitment of synaptic vesicles that do not normally release dopamine. This was confirmed using noncatecholaminergic AtT-20 cells, in which VMAT2 expression induced the quantal release of dopamine. The ability to increase quantal size in vesicles that were already competent for dopamine release was shown in PC12 cells, in which VMAT2 expression increased the quantal size but not the number of release events. These results demonstrate that vesicle transporters limit the rate of transmitter accumulation and can alter synaptic strength through two distinct mechanisms.
Asunto(s)
Glicoproteínas de Membrana/biosíntesis , Proteínas de Transporte de Membrana , Neuropéptidos , Vesículas Sinápticas/metabolismo , Adenoviridae/genética , Animales , Axones/metabolismo , Células Cultivadas , Dopamina/metabolismo , Electroquímica , Exocitosis , Glicoproteínas de Membrana/genética , Ratones , Microelectrodos , Modelos Neurológicos , Neuronas/citología , Neuronas/metabolismo , Fenotipo , Distribución de Poisson , Terminales Presinápticos/metabolismo , ARN Mensajero/biosíntesis , Ratas , Transmisión Sináptica/fisiología , Transfección , Tirosina 3-Monooxigenasa/genética , Proteínas de Transporte Vesicular de Aminas Biógenas , Proteínas de Transporte Vesicular de MonoaminasRESUMEN
Peroxisomes were localized in the head of wild-type and mutant strains of Drosophila melanogaster by use of a cytochemical method for the demonstration of D-amino acid oxidase activity. With similar techniques we had found previously that vertebrate photoreceptors have few, if any, bodies with cytochemically demonstrable oxidase activity, but that the pigment epithelial cells adjacent to the photoreceptors have a substantial population of such bodies. Peroxisomes in Drosophila were very abundant in the fat body. Probable peroxisomes were also present in the peripheral retina of the eye, including in retinular (retinula) and pigment cells, but there were very few of them. Thus, our results suggest that the fat body, which lies adjacent to the eye, is the principal site of peroxisomal function in the head. Peroxisome functions in the Drosophila head may include participation in the genesis of eye pigments.