Loss of Dopamine D2 Receptors Increases Parvalbumin-Positive Interneurons in the Anterior Cingulate Cortex

Abstract

Disruption to dopamine homeostasis during brain development has been implicated in a variety of neuropsychiatric disorders, including depression and schizophrenia. Inappropriate expression or activity of GABAergic interneurons are common features of many of these disorders. We discovered a persistent upregulation of GAD67+ and parvalbumin+ neurons within the anterior cingulate cortex of dopamine D2 receptor knockout mice, while other GABAergic interneuron markers were unaffected. Interneuron distribution and number were not altered in the striatum or in the dopamine-poor somatosensory cortex. The changes were already present by postnatal day 14, indicating a developmental etiology. D2eGFP BAC transgenic mice demonstrated the presence of D2 receptor expression within a subset of parvalbumin-expressing cortical interneurons, suggesting the possibility of a direct cellular mechanism through which D2 receptor stimulation regulates interneuron differentiation or survival. D2 receptor knockout mice also exhibited decreased depressive-like behavior compared with wild-type controls in the tail suspension test. These data indicate that dopamine signaling modulates interneuron number and emotional behavior and that developmental D2 receptor loss or blockade could reveal a potential mechanism for the prodromal basis of neuropsychiatric disorders.

Behavioral and Neuroanatomical Consequences of Cell-Type Specific Loss of Dopamine D2 Receptors in the Mouse Cerebral Cortex

“…Although quantitative cell counts were not obtained in individual cortical layers, the increase in PV+ cells appears to be homogeneous across the depth of the cortex and therefore not lamina-specific. This change in GABAergic interneurons is specific to both the GABAergic interneuron subtype as well as the brain region, as there were no differences in the number of SST+ neurons in the ACC ( Figure 12G ; t (21) = 0.1408, p = 0.8894), despite the presence of recombination in SST+ neurons ( Figures 1E–H ), nor the number of PV+ neurons between genotypes in the DA-poor SSC ( Figure 12H ; t (34) = 0.03426, p = 0.9729), similar to our previous findings (Graham et al, 2015b ). Our results suggest that there is an increased PV interneuron density specifically in the ACC upon deleting D2Rs from cortical GABAergic interneurons from the Nkx2.1 lineage.…”

“…However, there are limitations in our understanding of D2R signaling and its effect on brain circuitry function and structure, which may be explained in part by opposing functions of D2Rs in the two major neuronal subtypes within the cerebral cortex: excitatory glutamatergic pyramidal neurons and inhibitory GABAergic interneurons. As previously demonstrated by our group, D2Rs play a role in determining PV+ interneuron number and distribution in the frontal cortex (Graham et al, 2015b ). This interneuron subpopulation is crucial in the regulation of synchronized neuronal activity (Cardin, 2018 ), and dysregulation of PV+ interneurons has been linked previously to the pathophysiology of schizophrenia, bipolar illness, and substance abuse (Rotaru et al, 2012 ).…”

“…Previously, our lab has reported increased numbers of PV interneurons and overall GABAergic interneurons in the ACC from adult mice with marked differences as early as P14 following the global deletion of D2Rs in all cells throughout development (Graham et al, 2015b ). Studies have also consistently reported reduced GAD67 levels in schizophrenic patient brains as well as in other subtypes of GABAergic interneurons, including PV and SST, which is believed to contribute to impaired inhibitory inputs onto excitatory pyramidal cells (Gonzalez-Burgos et al, 2010 ).…”

“…Sections were analyzed per region of interest × hemisphere by an observer blinded to genotype. For GAD67 and PV cell counts, sections were imaged at 20× as previously described (Graham et al, 2015b ). For each hemisphere in each D2R-cKO line, two non-overlapping fields of ACC (dorsal and ventral portions) were counted.…”

Deletion of Gαq in the telencephalon alters specific neurobehavioral outcomes

“…Briefly, images of the ACC (10× magnification) were analyzed and scored based on the following rating system: 0 = very straight processes; can be traced in single focal plane from cell body to pial surface; no significant deviations in x‐y coordinates as well; 1 = occasional fragmented or bent dendritic bundle; 2 = ∼50% of dendritic processes show deviation in either the x‐y or z coordinate systems; 3 = majority of processes appear “wavy” and take tortuous routes to the pial surface. For GAD67 and PV cell counts, sections were imaged at 20× as previously described (Graham et al, ). Cells counts were corrected for profile size (Abercrombie, ).…”