Astrocyte Regulation of Spinal Circuit Function

The spinal cord stands as a crucial nexus in the central nervous system (CNS), integrating and modulating signals that ultimately shape our everyday interactions with the world. Its gray matter is arranged into discrete laminae spanning the dorsal-ventral axis that encompass circuit-specific modalities. Concurrently, extensive interconnected interneuron networks within and between these laminae confer remarkable flexibility in the behavioral outputs for a given input. The flexibility of spinal cord information processing in light of its organized architecture makes it a particularly intriguing region to explore the neuronal computations underlying behaviors, particularly as they relate to neurological dysfunction. At the same time, astrocytes engage in highly dynamic interactions with underlying neuronal circuitries, suggesting they may add another dimension to spinal cord information processing. Technical limitations specific to the spinal cord have long limited our ability to interrogate the relationship between astrocyte-neuron interactions and ongoing spinal cord function. In this review, we highlight emerging insights-particularly those from recent in vivo studies-that illustrate astrocytes actively shape spinal cord behavioral outputs in both health and disease. We briefly review the spinal cord's neuronal organization to provide a structural foundation for assessing the relative spatial relationship between astrocyte and neuron activity as it relates to different spinal cord outputs. Within this architectural framework, we review growing evidence that spinal cord astrocytes respond to activity associated with spinal cord function and, in turn, modulate underlying neuronal circuits to alter future behavioral outputs. Moreover, we propose an overall conceptual framework for understanding circuit-specific spinal cord modulations through the lens of astrocyte-neuron interactions and underscore how it can be leveraged to uncover novel ways of targeting spinal cord disease states. Finally, we put forth key outstanding questions related to this conceptual framework and emphasize the technological advances that will facilitate future studies addressing them.