): The objective of our research is to understand how the retina of mammals analyzes the visual world and encodes its spatial, temporal and chromatic contrast into a message of action potentials for safe sending to the brain. In the retina, dopamine is the modulator responsible for many of the events that lead to neural adaptation to light. To identify the mechanisms and neural networks that control the release of dopamine, we labeled dopaminergic cells (DA cells) by introducing into the mouse genome the cDNA of human placental alkaline phosphatase linked to a promoter sequence of the gene for tyrosine hydroxylase. Because of the presence of the reporter gene product, we could study the synaptic connections of DA cells, identify their receptors and channels by single-cell RT-PCR and investigate their physiology by patch clamping. We have thus shown that DA cells spontaneously fire action potentials in a rhythmic fashion in absence of synaptic inputs and that this activity cause extrasynaptic release of dopamine. The present application has the following aims: By single-cell RT-PCR we have found that DA cells contain the transcripts for the sodium channels Scn8a and we are planning to establish whether it is responsible for the pacemaker current of DA cells in mice homozygous for a null mutation of its gene. To investigate the light responses of DA cells in the intact retina, we have produced a transgenic line in which these neurons are labeled with the green fluorescent protein (GFP). In these animals, we will study the effects of light stimulation on DA cells responses in the isolated retina maintained in vitro. We will continue our analysis of the receptors and ion channels of DA cells to identify mechanisms and networks that control dopamine release. To this purpose, we will combine the techniques of single-cell RT-PCR, electrophysiology, and immunocytochemistry. We have begun to develop methods for obtaining representative cDNA probes of receptors and channels from single, identified, retinal neurons and test them by hybridization on high density cDNA microarrays. Hopefully, this approach will speed up and enrich our functional studies of DA cells and other types of retinal neurons.
| Hirasawa, Hajime; Contini, Massimo; Raviola, Elio (2015) Extrasynaptic release of GABA and dopamine by retinal dopaminergic neurons. Philos Trans R Soc Lond B Biol Sci 370: |
| Hirasawa, Hajime; Betensky, Rebecca A; Raviola, Elio (2012) Corelease of dopamine and GABA by a retinal dopaminergic neuron. J Neurosci 32:13281-91 |
| Contini, Massimo; Lin, Bin; Kobayashi, Kazuto et al. (2010) Synaptic input of ON-bipolar cells onto the dopaminergic neurons of the mouse retina. J Comp Neurol 518:2035-50 |
| Hirasawa, Hajime; Puopolo, Michelino; Raviola, Elio (2009) Extrasynaptic release of GABA by retinal dopaminergic neurons. J Neurophysiol 102:146-58 |
| Storch, K-F; Paz, C; Signorovitch, J et al. (2007) Physiological importance of a circadian clock outside the suprachiasmatic nucleus. Cold Spring Harb Symp Quant Biol 72:307-18 |
| Puopolo, Michelino; Raviola, Elio; Bean, Bruce P (2007) Roles of subthreshold calcium current and sodium current in spontaneous firing of mouse midbrain dopamine neurons. J Neurosci 27:645-56 |
| Dorenbos, Ronald; Contini, Massimo; Hirasawa, Hajime et al. (2007) Expression of circadian clock genes in retinal dopaminergic cells. Vis Neurosci 24:573-80 |
| Puopolo, Michelino; Bean, Bruce P; Raviola, Elio (2005) Spontaneous activity of isolated dopaminergic periglomerular cells of the main olfactory bulb. J Neurophysiol 94:3618-27 |
| MacNeil, Margaret A; Heussy, John K; Dacheux, Ramon F et al. (2004) The population of bipolar cells in the rabbit retina. J Comp Neurol 472:73-86 |
| Gustincich, Stefano; Contini, Massimo; Gariboldi, Manuela et al. (2004) Gene discovery in genetically labeled single dopaminergic neurons of the retina. Proc Natl Acad Sci U S A 101:5069-74 |
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