Iodinated SCH 23390, 125I-SCH 23982 (DuPont-NEN), was examined using quantitative autoradiography for its potency, selectivity, and anatomical and neuronal localization of binding to the dopamine D1 receptor in rat brain sections. 125I-SCH 23982 bound to D1 sites in the basal ganglia with very high affinity (Kd values of 55-125 pM), specificity (70-85% of binding was displaced by 5 microM cis-flupenthixol), and in a saturable manner (Bmax values of 65-176 fmol/mg protein). Specific 125I-SCH 23982 binding was displaced by the selective D1 antagonists SCH 23390 (IC50 = 90 pM) and cis-flupenthixol (IC50 = 200 pM) and the D1 agonist SKF 38393 (IC50 = 110 nM) but not by D2-selective ligands (I-sulpiride, LY 171555) or the S2 antagonist cinanserin. Compared with 3H-SCH 23390, the 5- to 10-fold greater affinity for the D1 site and 50-fold greater specific radioactivity of 125I-SCH 23982 makes it an excellent radioligand for labeling the D1 receptor. The concentrations of D1 sites were greatest in the medial substantia nigra and exceeded by over 50% the concentration of D1 sites in the lateral substantia nigra, caudoputamen, nucleus accumbens, olfactory tubercle, and entopeduncular nucleus. Lower concentrations of D1 sites were present in the internal capsule, dorsomedial frontal cortex, claustrum, and layer 6 of the neocortex. D1 sites were absent in the ventral tegmental area. Intrastriatal injections of the axon-sparing neurotoxin, quinolinic acid, depleted by 87% and by 46-58% the concentrations of displaceable D1 sites in the ipsilateral caudoputamen and medial and central pars reticulata of the substantia nigra, respectively. No D1 sites were lost in the lateral substantia nigra. Destruction of up to 94% of the mesostriatal dopaminergic projection with 6-hydroxydopamine did not reduce D1 binding nor, with one exception, increase striatal or nigral D1 receptor concentrations. 125I-SCH 23982 selectively labels D1 binding sites on striatonigral neurons with picomolar affinity, and these neurons contain the majority of D1 sites in rat brain.

The African turquoise killifish uniquely combines a short lifespan with vertebrate-specific features, including age-dependent loss of neuroregenerative capacity, that are missing from the currently used model organisms. In this study, we investigate the cellular landscape that shapes adult neuro- and gliogenesis using single-cell sequencing. Our analysis identifies seventeen cell types including neuronal cells (NC), and progenitors (PC) of glial and non-glial nature in the adult killifish telencephalon. PC subclustering unveils four radial glia types, one atypical non-glial progenitor (NGP) and two clusters representing transitioning states. NC subclustering classified neurons into immature and mature excitatory or inhibitory sub-clusters. Using lineage inference analysis, we discovered neuroepithelial-like radial glia to be the source of neuro- and gliogenesis, and a central role for NGP. Our findings are evidence for specialized progenitors within telencephalon and the data is accessible via an online database, providing a resource to understand normal brain function, as well as the role of cellular relationships in response to injury and disease.

The aging central nervous system (CNS) of mammals displays progressive limited regenerative abilities. Recovery after loss of neurons is extremely restricted in the aged brain. Many research models fall short in recapitulating mammalian aging hallmarks or have an impractically long lifespan. We established a traumatic brain injury model in the African turquoise killifish (Nothobranchius furzeri), a regeneration-competent vertebrate model that evolved to naturally age extremely fast. Stab-wound injury of the aged killifish dorsal telencephalon unveils an impaired and incomplete regeneration response when compared to young individuals. Remarkably, killifish brain regeneration is mainly supported by atypical non-glial progenitors, yet their proliferation capacity appears declined with age. We identified a high inflammatory response and glial scarring to also underlie the hampered generation of new neurons in aged fish. These primary results will pave the way for further research to unravel the factor age in relation to neurorepair, and to improve therapeutic strategies to restore the injured and/or diseased aged mammalian CNS.