Abstract
BackgroundMast cells (MCs) in the brain can respond to environmental cues and relay signals to neurons that may directly influence neuronal electrical activity, calcium signaling, and neurotransmission. MCs also express receptors for neurotransmitters and consequently can be activated by them. Here, we developed a coculture model of peritoneal MCs, incubated together with dissociated hippocampal neurons for the study of cellular mechanisms involved in the mast cell-neuron interactions.MethodsCalcium imaging was used to simultaneously record changes in intracellular calcium [Ca2+]i in neurons and MCs. To provide insight into the contribution of MCs on neurotransmitter release in rat hippocampal neurons, we used analysis of FM dye release, evoked by a cocktail of mediators from MCs stimulated by heat.ResultsBidirectional communication is set up between MCs and hippocampal neurons. Neuronal depolarization caused intracellular calcium [Ca2+]i oscillations in MCs that produced a quick response in neurons. Furthermore, activation of MCs with antigen or the secretagogue compound 48/80 also resulted in a neuronal [Ca2+]i response. Moreover, local application onto neurons of the MC mediator cocktail elicited Ca2+ transients and a synaptic release associated with FM dye destaining. Neuronal response was partially blocked by D-APV, a N-methyl-D-aspartate receptor (NMDAR) antagonist, and was inhibited when the cocktail was pre-digested with chondroitinase ABC, which induces enzymatic removal of proteoglycans of chondroitin sulfate (CS).ConclusionsMC-hippocampal neuron interaction affects neuronal [Ca2+]i and exocytosis signaling through a NMDAR-dependent mechanism.
Highlights
Mast cells (MCs) in the brain can respond to environmental cues and relay signals to neurons that may directly influence neuronal electrical activity, calcium signaling, and neurotransmission
Bidirectional communication between hippocampal neurons and MCs in coculture When in a coculture of mixed hippocampal neurons and MCs, loaded with FURA-2 AM, we stimulated a neuron by direct depolarizing stimuli applying a pressure pulse of K+-enriched solution (70 mM KCl with iso-osmotic reduction of NaCl) (Fig. 1a), a high [Intracellular calcium concentration (Ca2+]i) transient was evoked upon the onset of the stimulus in neuronal cell body, as it was expected (Fig. 1b)
This neuronal signal only occurred in neurons cocultured with MCs but not in isolated hippocampal neurons, and it could be reproduced for a second time when a new depolarizing pulse of high K+ was again applied, suggesting that MC mediators feedback on neuronal activity
Summary
Mast cells (MCs) in the brain can respond to environmental cues and relay signals to neurons that may directly influence neuronal electrical activity, calcium signaling, and neurotransmission. We developed a coculture model of peritoneal MCs, incubated together with dissociated hippocampal neurons for the study of cellular mechanisms involved in the mast cell-neuron interactions. Mast cells (MCs) are resident in the brain of all mammalian species studied [5] and located in the meninges and Flores et al Journal of Neuroinflammation (2019) 16:107 temperature and pressure sensitive, degranulating in response to noxious physical stimuli through a mechanism dependent on transient-receptor-potential channel 2 [11]. In addition to inducing the release of preformed granule constituents, MC activation leads to de novo synthesis of many bioactive compounds, including lipid mediators such as leukotrienes or prostaglandins or a variety of cytokines, chemokines, and growth factors [10, 12]. Exposure of MCs to lipopolysaccharide can cause the release of cytokines without observable degranulation [13]
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