Repeated cocaine or methamphetamine treatment alters astrocytic CRF2 and GLAST expression in the ventral midbrain

Abstract Dopamine neurons in the substantia nigra (SN) and ventral tegmental area (VTA) play a central role in the reinforcing properties of abused drugs including methamphetamine and cocaine. Chronic effects of psychostimulants in the SN/VTA also involve non‐dopaminergic transmitters, including glutamate and the stress‐related peptide corticotropin‐releasing factor (CRF). In the SN/VTA, astrocytes express a variety of membrane‐bound neurotransmitter receptors and transporters that influence neurotransmission. CRF receptor type 2 (CRF2) activity in the VTA is important for stress‐induced relapse and drug‐seeking behaviour, but the localization of its effects is incompletely understood. Here, we first identified CRF2 transcript in astrocytes of the SN/VTA using RNA‐Seq in Aldh1l1;NuTRAP mice and confirmed it using in situ hybridization (RNAscope) in wild‐type mice. We then used immunofluorescence to quantify the astrocytic marker protein S100β, glial‐specific glutamate/aspartate transporter GLAST, and CRF2 in the SN/VTA following 12 days of treatment (i.p.) with methamphetamine (3 mg/kg), cocaine (10 mg/kg), or saline. We observed a significant decrease in GLAST immunofluorescence in brains of psychostimulant treated mice compared with saline controls. In addition, we observed increased labelling of CRF2 in drug treated groups, a decrease in the number of S100β positive cells, and an increase of co‐staining of CRF2 with both S100β and tyrosine hydroxylase (dopamine neurons). Our results suggest a significant interaction between CRF2, GLAST, and astrocytes in the midbrain that emerges with repeated exposure to psychostimulants. These findings provide rationale for future investigation of astrocyte‐based strategies for altering cellular and circuit function in response to stress and drug exposure.