Autoreceptor Function of the Dopamine D2 Receptor Splice Variants D2S and D2L
Authors: Neve Kim Arthur , Robinson Brooks G , Condon Alec F , Yorgason Jordan T , McLain Duncan E , Asad Naeem , Dore Timothy M , Borrelli Emiliana , Williams John T 
Published: June 2021

The aim of this work is to evaluate a model of dopamine receptor function in which the short splice variant of the dopamine D2 receptor, D2S, is thought to be the autoreceptor that inhibits firing of dopamine neurons and dopamine release, and the long splice variant, D2L, is proposed to be the postsynaptic receptor that regulates the activity of medium spiny neurons (MSNs) in the basal forebrain. We obtained the results described here using two approaches. In the first, D2S and D2L were virally expressed in midbrain dopamine neurons of mice in which the D2 receptor was genetically deleted (D2‐KO) either globally or selectively in dopamine neurons. The second approach involved the use of mice constitutively expressing only D2S (D2L‐KO) or D2L (D2S‐KO) due to genetically preventing expression of one variant. Viral expression of either variant in dopamine neurons of D2‐KO mice restored inhibition of locomotor activity by a high dose of quinpirole (1 mg/kg) and quinpirole inhibition of electrically evoked dopamine release in neostriatal slices. Regulation of G protein‐regulated inward‐rectifying potassium channels (GIRKs) by the splice variants was indistinguishable when whole‐cell recordings were carried out using a strong calcium‐buffering solution (10 mM BAPTA) in slices containing the substantia nigra pars compacta (SNc), or in neostriatal slices from D2‐KO mice virally expressing both the D2 receptor and GIRK in MSNs. When recordings were made from SNC dopamine neurons virally or constitutively expressing only one splice variant and with a weak calcium‐buffering intracellular solution (0.1 mM EGTA), D2S desensitized more rapidly than D2L in the presence of bath‐applied quinpirole (10 μM). The D2S‐mediated GIRK current in midbrain slices was also found to have increased sensitivity to calcium buffering in the early phase of desensitization induced by a photoactivatable caged dopamine. Finally, D2‐GIRK IPSCs evoked with electrical stimulation (1/min) were studied in the receptor variants. Upon bath application of cocaine (30 μM), the IPSCs initially increase and then desensitize. The initial increase in amplitude was significantly less and the rate of desensitization significantly slower in slices from mice constitutively expressing D2L compared with mice expressing D2S. Beyond desensitization, this could also reflect splice variant differences in inhibition of dopamine release, dopamine transport, or activation of GIRKs. Overall, our results suggest that either variant can function as an autoreceptor, but that expression of D2S more closely models wild type D2 receptor under normal slice recording conditions.Support or Funding InformationMerit Review Award BX003279 from the US Department of Veterans Affairs, Veterans Health Administration, Office of Research and Development, Biomedical Laboratory Research and DevelopmentThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.