same tissue samples evaluated by single cell or single nuclei RNA profiling [61, 63]. Notably, in many of the above cases, transcriptome differences appear to occur among reactive astrocytes that do not exhibit obvious differences in other features such as cell morphology, proliferation or cellular interactions. Hence there is a need for conceptually evaluating changes in reactive astrocyte molecular expression and function; these would be plastic, context-dependent, and can change over time without changing other basic cell characteristics (Key Figure, Figure 2B–E). When such changes and differences are observed among reactive astrocytes, it seems more appropriate to refer to them as differences in reactive astrocyte states rather than to regard the myriad and highly nuanced molecular differences among reactive astrocytes as being indicative of different subtypes. Such changes in reactive astrocyte states may be finely graded and directly continuous with diverse functional states observed in healthy tissue (Key Figure, Figure 2A).; they may evolve over time after or during disorders; and they may in certain instances, resolve over time, if triggering cues are removed (Key Figure, Figure 2B–E). In this regard, it may be useful to regard differentially expressed genes and other molecular changes as interchangeable tools used by the
