#Dendrite labeled serial#

Thus, analyzing DA circuits has required specific labeling, either with immunohistochemistry ( Bérubé-Carrière et al., 2012 Moss and Bolam, 2008 Omelchenko and Sesack, 2009 Liu et al., 2018) or with genetic targeting ( Dos Santos et al., 2018 Melchior et al., 2021 Mingote et al., 2019 Nasirova et al., 2021 Poulin et al., 2018). A second problem is that, unlike ionotropic excitatory or inhibitory connections, there is much less known about the ultrastructural characteristics of potential DA synapses, where they occur on neurons, or how frequently ( Liu et al., 2018 Rice and Cragg, 2008). Recent advances in automation of the data collection ( Hayworth et al., 2020 Kasthuri et al., 2015 Xu et al., 2017 Yin et al., 2020) and algorithms to analyze the resulting terabytes of data have made such approaches more accessible ( Funke et al., 2019 Januszewski et al., 2018 Saalfeld et al., 2012 Turaga et al., 2010).

One is that, until recently, collecting and analyzing large volumes of brain tissue with electron microscopy (EM), the gold standard for delineating neuronal connections, had been difficult and laborious. There were several problems preventing progress. However, while much is known about the molecular composition and functional roles of DA neurons in normal behavior and addiction ( Alcaro et al., 2007 Beeler et al., 2009 Berke and Hyman, 2000 Liu and Kaeser, 2019 Liu et al., 2018), much less is known about how DA neurons physically communicate with targets and how that communication changes with exposure to drugs of abuse. Moreover, alterations in DA circuitry in animal models and humans are a hallmark of addictive behaviors and are likely the result of changes in how DA neurons communicate with targets ( Berke and Hyman, 2000). The dopaminergic (DA) system, like many neuromodulatory systems of the brain, profoundly influences behaviors including learning risks and rewards, social cooperation, goal-directed behavior, and decision making ( Alcaro et al., 2007 Eskenazi et al., 2021 Liu et al., 2021). We conclude that DA axonal transmission is unlikely to be mediated via classical synapses in the NAc and that the major locus of anatomical plasticity of DA circuits after exposure to cocaine are large-scale axonal re-arrangements with correlated changes in mitochondria. Finally, mitochondrial lengths increased by ~2.2 times relative to control only in DA axons and NAc spiny dendrites after cocaine exposure. Days after a brief exposure to cocaine, DA axons were extensively branched relative to controls, formed blind-ended ‘bulbs’ filled with mitochondria, and were surrounded by elaborated glia. DA axon varicosities rarely make specific synapses (<2%, 6/410), but instead are more likely to form spinule-like structures (15%, 61/410) with neighboring neurons. Spatially ordering along individual axons further suggests that varicosity types are non-randomly organized. We find that individual DA axons contain different varicosity types based on their vesicle contents.

#Dendrite labeled serial#

We leverage cell type-specific labeling with large volume serial electron microscopy to detail DA connections in the nucleus accumbens (NAc) of the mouse ( Mus musculus) before and after exposure to cocaine. However, how DA axons communicate with target neurons and how those communications change with drug exposure remains poorly understood. Dopaminergic (DA) neurons exert profound influences on behavior including addiction.