Abstract
Dendritic release of dopamine activates dopamine D2 autoreceptors, which are inhibitory G protein-coupled receptors (GPCRs), to decrease the excitability of dopamine neurons. This study used tagged D2 receptors to identify the localization and distribution of these receptors in living midbrain dopamine neurons. GFP-tagged D2 receptors were found to be unevenly clustered on the soma and dendrites of dopamine neurons within the substantia nigra pars compacta (SNc). Physiological signaling and desensitization of the tagged receptors were not different from wild type receptors. Unexpectedly, upon desensitization the tagged D2 receptors were not internalized. When tagged D2 receptors were expressed in locus coeruleus neurons, a desensitizing protocol induced significant internalization. Likewise, when tagged µ-opioid receptors were expressed in dopamine neurons they too were internalized. The distribution and lack of agonist-induced internalization of D2 receptors on dopamine neurons indicate a purposefully regulated localization of these receptors.
Highlights
Dopamine D2 receptors are crucial for many behavioral processes including movement and the response to rewarding stimuli[1,2,3] and are involved in a number of disease states including Parkinson’s disease, drug addiction, and schizophrenia
Within the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc), dopamine neurons communicate via dendrodendritic neurotransmission
The intensity of the superecliptic pHluorin GFP is less than GFP and without antibody amplification was below the limit of detection in both fixed and living slice preparations
Summary
Dopamine D2 receptors are crucial for many behavioral processes including movement and the response to rewarding stimuli[1,2,3] and are involved in a number of disease states including Parkinson’s disease, drug addiction, and schizophrenia. Dendritic dopamine release has since been directly measured using several methods[10,11,12,13,14] and the target of dopamine is the D2 autoreceptor[15,16,17,18]. Within midbrain nuclei, dopamine neuron excitability is regulated through somatodendritic release of dopamine acting on G protein-coupled D2 receptors[21]. Are there synapses containing paired release sites and receptors or is volume transmission the primary mode of communication between midbrain neurons? A novel mouse model with a superecliptic pHluorin (GFP) knocked-in to the N-terminus of the endogenous D2 receptor ( GFP-D2; Supplementary Figure 1) was used to examine the distribution and functional consequences of D2 autoreceptor activation in live neurons from the SNc. The tagged receptor www.nature.com/scientificreports/. D2 receptors in dopamine neurons do not readily internalize upon agonist exposure
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