Response of catecholaminergic neurons in the mouse hindbrain to glucoprivic stimuli is astrocyte dependent

Abstract

Hindbrain catecholaminergic (CA) neurons are required for critical autonomic, endocrine, and behavioral counterregulatory responses (CRRs) to hypoglycemia. Recent studies suggest that CRR initiation depends on hindbrain astrocyte glucose sensors (McDougal DH, Hermann GE, Rogers RC. Front Neurosci 7: 249, 2013; Rogers RC, Ritter S, Hermann GE. Am J Physiol Regul Integr Comp Physiol 310: R1102–R1108, 2016). To test the proposition that hindbrain CA responses to glucoprivation are astrocyte dependent, we utilized transgenic mice in which the calcium reporter construct (GCaMP5) was expressed selectively in tyrosine hydroxylase neurons (TH-GCaMP5). We conducted live cell calcium-imaging studies on tissue slices containing the nucleus of the solitary tract (NST) or the ventrolateral medulla, critical CRR initiation sites. Results show that TH-GCaMP5 neurons are robustly activated by a glucoprivic challenge and that this response is dependent on functional astrocytes. Pretreatment of hindbrain slices with fluorocitrate (an astrocytic metabolic suppressor) abolished TH-GCaMP5 neuronal responses to glucoprivation, but not to glutamate. Pharmacologic results suggest that the astrocytic connection with hindbrain CA neurons is purinergic via P2 receptors. Parallel imaging studies on hindbrain slices of NST from wild-type C57BL/6J mice, in which astrocytes and neurons were prelabeled with a calcium reporter dye and an astrocytic vital dye, show that both cell types are activated by glucoprivation but astrocytes responded significantly sooner than neurons. Pretreatment of these hindbrain slices with P2 antagonists abolished neuronal responses to glucoprivation without interruption of astrocyte responses; pretreatment with fluorocitrate eliminated both astrocytic and neuronal responses. These results support earlier work suggesting that the primary detection of glucoprivic signals by the hindbrain is mediated by astrocytes.

Dorsal vagal complex and hypothalamic glia differentially respond to leptin and energy balance dysregulation

“…Dual exposure images (i.e., 488 nm and 591 nm) were collected just prior to each experimental trial in order to confirm the cell types being recorded. All slices were then challenged with a cocktail of 100 μM ATP and 500 μM glutamate to determine which cells in the field were viable 39,44 . Viability was defined as a minimum increase in fluorescence of 7% in response to the ATP/ glutamate challenge 45 .…”

Revisiting How the Brain Senses Glucose—And Why

“…Indeed, a large (and somewhat contentious) literature suggests that astrocyte-derived lactate, rather than glucose, constitutes a primary fuel source for many neurons, particularly when they are activated (Magistretti and Allaman, 2018). Combined with evidence pointing to a role for astrocytes in the ARC and other brain areas as nutrient sensors (Rogers et al, 2018; Young and McKenzie, 2004) and that astrocytes also play an obligatory role in the response of hindbrain neurons to glucoprivation (Young and McKenzie, 2004), a potential role for astrocytes in brain glucose sensing and its role in glucose homeostasis can be considered. Indeed, work from Rossetti and colleagues (Lam et al, 2005) supports a model in which the glucose-lowering effect of intrahypothalamic glucose administration is dependent on its conversion to lactate by astrocytes.…”

Hindbrain astrocytes and glucose counter-regulation

“…Our results [86] show that approximately 90% of the TH-GCaMP5 neurons (both NST and VLM) were robustly activated by a glucoprivic challenge and that this response was dependent on functional astrocytes. Pretreatment of hindbrain slices with fluorocitrate (an astrocytic metabolic suppressor) abolished TH-GCaMP5 neuronal re-sponses to glucoprivation.…”