Ventral midbrain astrocytes display unique physiological features and sensitivity to dopamine D2 receptor signaling

Abstract

Astrocytes are ubiquitous CNS cells that support tissue homeostasis through ion buffering, neurotransmitter recycling, and regulation of CNS vasculature. Yet, despite the essential functional roles they fill, very little is known about the physiology of astrocytes in the ventral midbrain, a region that houses dopamine-releasing neurons and is critical for reward learning and motivated behaviors. Here, using a combination of whole-transcriptome sequencing, histology, slice electrophysiology, and calcium imaging, we performed the first functional and molecular profiling of ventral midbrain astrocytes and observed numerous differences between these cells and their telencephalic counterparts, both in their gene expression profile and in their physiological properties. Ventral midbrain astrocytes have very low membrane resistance and inward-rectifying potassium channel-mediated current, and are extensively coupled to surrounding oligodendrocytes through gap junctions. They exhibit calcium responses to glutamate but are relatively insensitive to norepinephrine. In addition, their calcium activity can be dynamically modulated by dopamine D2 receptor signaling. Taken together, these data indicate that ventral midbrain astrocytes are physiologically distinct from astrocytes in cortex and hippocampus. This work provides new insights into the extent of functional astrocyte heterogeneity within the adult brain and establishes the foundation for examining the impact of regional astrocyte differences on dopamine neuron function and susceptibility to degeneration.

Dopamine-induced calcium signaling in olfactory bulb astrocytes

“…Whether this effect in OB astrocytes is mediated by D 1 -D 2 heteromers, as shown in striatal neurons 34 , or by independent D 1 and D 2 receptors is not known and needs further investigation. In contrary to our results, studies in the hippocampus and ventral midbrain have shown that activation of D 2 receptors leads to a decrease in cytosolic calcium, whereas D 1 receptors mediate a calcium rise 29,35 . The D 2 -class receptor-mediated decrease in calcium in hippocampal astrocytes presumably results from modulation of L-type voltage-gated calcium channels 29 , which has also been shown in nucleus accumbens neurons 36 .…”

“…However, tuning of olfactory information processing and odor perception by neuromodulators such as dopamine, noradrenaline, acetylcholine and serotonin has moved into the focus of research on olfaction, in particular in recent years 23,[57][58][59] , and it is becoming increasingly clear that astrocytes have to be considered to take actively part in these processes. This hypothesis appears to be supported by findings showing interactions of dopamine and astrocytes in other regions of the CNS, such as ventral midbrain and hippocampus 29,35 .…”

“…There has been evidence for the presence of dopamine receptors leading to cAMP production and subsequent PKA activation as well as NADH modulation and calcium signaling mediated by D 1 -class receptors in cultured astrocytes of different brain regions [15][16][17] . In addition to the studies above describing dopamine-induced calcium transients in cultured astrocytes, Jennings et al (2017) and Xin et al (2019) could demonstrate that hippocampal and midbrain astrocytes in acute brain slices respond to dopamine with a cytosolic calcium rise. However, the effect of dopamine on astrocytes in other brain regions such as the olfactory bulb remains unknown and has been investigated in the present study.…”

Generation of homogeneous midbrain organoids with in vivo-like cellular composition facilitates neurotoxin-based Parkinson's disease modeling

“…Midbrain contains not only mDA neurons, a functional cell type representative of the midbrain, but also several other cell types, such as different neuronal subtypes, astrocytes, and oligodendrocytes, which exert roles in maintaining the functional homeostasis of the midbrain . Thus, we next investigated the cellular composition of DAC3.0 MOs.…”

Oligodendrocytes Support Neuronal Glutamatergic Transmission via Expression of Glutamine Synthetase

“…Some studies have indicated that oligodendrocytes express transporters that are permissible to glutamate and glutamine, such as EAAC1 (DeSilva et al, 2009), SNAT3 (Marques et al, 2018), and ASCT2 (Scopelliti et al, 2018), which would allow for a direct exchange of GS substrates with axons. Furthermore, we previously reported extensive gap junction coupling between midbrain oligodendrocytes and astrocytes (Xin et al, 2019). As molecules smaller than 1 kDa can theoretically pass freely through gap junctions (Berg et al, 2002), these structural connections may enable exchange of GS substrates between astrocytes and oligodendrocytes and thus neurons by way of astrocyte transporters.…”