Astrocytic connexin distributions and rapid, extensive dye transfer via gap junctions in the inferior colliculus: Implications for [¹⁴C]glucose metabolite trafficking

Abstract

The inferior colliculus has the highest rates of blood flow and metabolism in brain, and functional metabolic activity increases markedly in response to acoustic stimulation. However, brain imaging with [1- and 6-(14)C]glucose greatly underestimates focal metabolic activation that is readily detected with [(14)C]deoxyglucose, suggesting that labeled glucose metabolites are quickly dispersed and released from highly activated zones of the inferior colliculus. To evaluate the role of coupling of astrocytes via gap junctions in dispersal of molecules within the inferior colliculus, the present study assessed the distribution of connexin (Cx) proteins in the inferior colliculus and spreading of Lucifer yellow from single microinjected astrocytes in slices of adult rat brain. Immunoreactive Cx43, Cx30, and Cx26 were heterogeneously distributed; the patterns for Cx43 and Cx 30 differed and were similar to those of immunoreactive GFAP and S100beta, respectively. Most Cx43 was phosphorylated in resting and acoustically stimulated rats. Dye spreading revealed an extensive syncytial network that included thousands of cells and perivasculature endfeet; with 8% Lucifer yellow VS and a 5-min diffusion duration, about 6,100 astrocytes (range 2,068-11,939) were labeled as far as 1-1.5 mm from the injected cell. The relative concentration of Lucifer yellow fell by 50% within 0.3-0.8 mm from the injected cell with a 5-min diffusion interval. Perivascular dye labeling was readily detectable and often exceeded dye levels in nearby neuropil. Thus, astrocytes have the capability to distribute intracellular molecules quickly from activated regions throughout the large, heterogeneous syncytial volume of the inferior colliculus, and rapid trafficking of labeled metabolites would degrade resolution of focal metabolic activation.

Connexin 43-Mediated Astroglial Metabolic Networks Contribute to the Regulation of the Sleep-Wake Cycle

“…Since each astrocyte can contact over 100,000 synapses (Bushong et al, 2002) and enwrap 4 to 8 neuronal somata (Halassa et al, 2007), the demand on one astrocyte for energy metabolite supply might be overwhelming. Thus, by increasing the effective volume of the intracellular compartment (De Pina-Benabou et al, 2001) and allowing glucose/lactate trafficking towards areas of high neuronal activity (Ball et al, 2007; Cruz et al, 2007; Rouach et al, 2008; Gandhi et al, 2009), gap junctional communication between astrocytes could provide better metabolic support to neurons than could be achieved by individual uncoupled astrocytes.…”

Trafficking of Glucose, Lactate, and Amyloid-β from the Inferior Colliculus through Perivascular Routes

“…Astrocytes exhibit selective gap junctional trafficking of glycolytic intermediates, and have a 2–4-fold faster and higher capacity for lactate uptake from extracellular fluid and for lactate dispersal via the astrocytic syncytium compared to neuronal lactate uptake from extracellular fluid or shuttling of lactate to neurons from neighboring astrocytes (Gandhi et al, 2009a, b). Astrocytes in the inferior colliculus are gap junction-coupled to thousands of other astrocytes and quickly transfer Lucifer yellow dye to the colliculus-meninges boundary and to their endfeet (Ball et al, 2007); gap junction-coupled astrocytic endfeet form an extensive perivascular surface area containing various transporters. Our working model for metabolite clearance (Fig.…”

Contributions of glycogen to astrocytic energetics during brain activation

“…Coupled astrocytes not only regulate their own metabolic activity, they can also share glucose, downstream metabolites, and redox and signaling compounds with other coupled astrocytes. The large syncytium is comprised of as many as 10,000 cells, and it is linked to the vasculature via endfeet (Gandhi et al 2009a; Gandhi et al 2009b; Ball et al 2007). Astrocytes are crossroads of metabolite trafficking to and from blood.…”