Biology subjects

Gordon, G. R.

Publications and source records attributed to Gordon, G. R..

8 recordsLinked to original sources

bioRxiv2022

Bidirectional and reciprocal control of astrocyte free calcium by modest fluctuations in external potassium

Astrocytes sense and respond to changes in the concentration of extracellular K+, and separately contribute to multiple physiological processes through Ca2+ dependent mechanisms. Yet, whether a modest change in [K+]o impacts astrocyte free Ca2+ remains unclear. Using relative or quantitative two-photon fluorescence Ca2+ imaging in acute brain slices or in vivo in the somatosensory cortex from Sprague Dawley rats and C57Bl/6 mice, we showed that changes to external K+ (+/-1mM to 2.5mM) reciprocally controls the astrocyte Rhod-2 or OGB-1 Ca2+-dependent fluorescence in the soma, major processes and endfeet. The astrocyte Ca2+ decrease when [K+]o was elevated was sensitive to lowering the external concentration of Ca2+, Cl-, and HCO3-, but not Na+. Unexpectedly, the phenomenon was blocked by inhibiting K-Cl cotransport. Picrotoxin induced ictal neural activity drove an analogous decrease of astrocyte Ca2+. K+ mediated cerebral arteriole dilation in brain slices was also sensitive to inhibiting K-Cl cotransport as well as whole-cell patching a peri-arteriole astrocyte which perturbs normal Ca2+, Cl- and HCO3- concentration gradients. These data reveal subtle, bidirectional regulation of astrocyte free Ca2 via fluctuations of [K+]o within the physiological range.

neuroscience↗

bioRxiv2021

Spatiotemporal components of sustained functional hyperemia are differentially modulated by locomotion and silenced with vascular chemogenetics

Neural activity underlying sensation, movement or cognition drives regional blood flow enhancement - termed functional hyperemia - to increase the oxygen supply to respiring cells for as long as needed to meet energy demands. However, functional hyperemia is often studied under anesthesia which typically yields response profiles that appear temporally and spatially homogenous. We have insufficient understanding of the underlying kinetics of oxygen delivery in awake animals, especially during specific behaviours that may influence neurally-driven enhancements in cerebral blood flow. Using widefield intrinsic optical signal imaging in awake, head-fixed but active mice, we demonstrated distinct early and late components to changes in intravascular oxygenation in response to sustained (30s) whisker stimulation. We found that the late component (20-30s), but not the early component (1-5s), was strongly influenced by level of whisking/locomotion in the region of highest response and in surrounding regions. Optical flow analyses revealed complex yet stereotyped spatial properties of the early and late components that were related to location within the optical window and the initial state of the cerebral vasculature. In attempt to control these complex response characteristics, we drove a canonical microvasculature constriction pathway using mural cell Gq-chemogenetic mice. A low-dose of systemic C21 strongly limited both the magnitude and spatial extent of the sensory-evoked hemodynamic response, showing that functional hyperemia can be severely limited by direct mural cell activation. These data provide new insights into the cerebral microcirculation in the awake state and may have implications for interpreting functional imaging data.

neuroscience↗

bioRxiv2021

A genetically encoded fluorescent biosensor for extracellular L-lactate

To enable investigations of the emerging roles of cell-to-cell shuttling of L-lactate, we have developed an intensiometric green fluorescent genetically encoded biosensor for extracellular L-lactate. We demonstrate that this biosensor, designated eLACCO1.1, enables minimally invasive cellular resolution imaging of extracellular L-lactate in cultured mammalian cells and brain tissue.

molecular biology↗

bioRxiv2020

Astrocytes amplify cerebral blood flow elevation to sustained cortical activation in the awake mouse

Brain requires increased local cerebral blood flow (CBF) for as long as necessary during neuronal activation to match O2 and glucose supply with demand - termed functional hyperemia. Ca2+ elevation in astrocytes can drive arteriole dilation to increase CBF, yet affirmative evidence for the necessity of astrocytes in functional hyperemia in vivo is lacking. In awake and active mice, we discovered that functional hyperemia is bimodal with a distinct early and late component whereby arteriole dilation progresses as sensory stimulation is sustained. Clamping astrocyte Ca2+ signaling in vivo by expressing a high-affinity plasma membrane Ca2+ ATPase (CalEx) reduces sustained but not brief sensory-evoked arteriole dilation. Reciprocally, elevating astrocyte free Ca2+ using chemogenetics selectively augments sustained but not brief hyperemia. Neither locomotion, arousal, nor changes in neuronal signaling account for the selective effect of astrocyte Ca2+ on the late phase of the CBF response. Antagonizing NMDA-receptors or epoxyeicosatrienoic acid production reduces only the late component of functional hyperemia, leaving brief increases in CBF to sensory stimulation intact. We propose that a fundamental role of astrocyte Ca2+ is to amplify functional hyperemia when neuronal activation is prolonged.

neuroscience↗

bioRxiv2020

Deregulation of brain endothelial CD2AP in Alzheimer's disease impairs Reelin-mediated neurovascular coupling

Genetic variations in CD2-associated protein (CD2AP) predispose to Alzheimers disease (AD) but the underlying mechanisms remain unknown. Here, we show that a cerebrovascular loss of CD2AP is associated with cognitive decline in AD and that genetic downregulation of CD2AP in brain endothelial cells impairs memory function in two distinct mouse models. Mice with reduced CD2AP in brain microvessels display decreased resting cerebral blood flow, impaired functional hyperemia and vasomotion. In brain endothelial cells, CD2AP regulates the levels and signaling of ApoE receptor 2 elicited by Reelin glycoprotein. Activation of the CD2AP-ApoER2 pathway with Reelin mitigates the toxic effects of A{beta} on resting blood flow and vasomotion of brain vessels depleted of CD2AP. Thus, we demonstrate that deregulation of CD2AP perturbs specific functions and segments of the cerebral microvasculature and propose that targeting CD2AP molecular partners may offer refined therapeutic strategies for the treatment of AD.

neuroscience↗

bioRxiv2020

Spatiotemporal chloride dynamics in hypothalamic CRHPVN neurons

Chloride (Cl-) dynamics shape inhibitory neurotransmission in the brain. In the hypothalamus, GABA signalling onto corticotropin-releasing hormone (CRHPVN) neurons can switch from inhibitory to excitatory during stress. Although Cl- fluctuations mediate this stress-dependent shift in GABA signalling, the underlying Cl- dynamics are poorly understood. Here, using a novel optogenetic strategy to load intracellular Cl- using halorhodopsin, we demonstrate that KCC2 rapidly restores Cl- setpoints in CRHPVN neurons from naive animals, but that this process is slowed following stress. Further, we report that somatic Cl- homeostasis remains intact after stress. Our results strongly support the idea that KCC2 functions primarily to maintain Cl- setpoints and that inhibitory synapses onto dendritic and somatic compartments of CRHPVN neurons are differentially regulated during stress.

neuroscience↗

bioRxiv2020

Obesity-induced astrocyte dysregulation of heterosynaptic plasticity within the orbitofrontal cortex

SO_SCPLOWUMMARYC_SCPLOWOverconsumption of highly palatable, energy dense food is considered a key driver of the obesity pandemic. The orbitofrontal cortex (OFC) is critical for reward valuation of gustatory signals, yet how the OFC adapts to obesogenic diets is poorly understood. Here we show that extended access to a cafeteria diet impairs astrocyte glutamate clearance, which leads to a heterosynaptic depression of GABA transmission onto pyramidal neurons of the OFC. This decrease in GABA tone is due to an increase in extrasynaptic glutamate, which acts via metabotropic glutamate receptors to liberate endocannabinoids. This impaired the induction of endocannabinoid-mediated long-term plasticity. In obese rats, this cascade of synaptic impairments was rescued by restoring astrocyte glutamate transport with the nutritional supplement, N-acetylcysteine. Together, our findings indicate that obesity targets astrocytes to disrupt the delicate balance between excitatory and inhibitory transmission in the OFC. HO_SCPLOWIGHLIGHTSC_SCPLOWO_LIDiet-induced obesity induces hypertrophy of astrocytes and impairs their ability to transport glutamate. C_LIO_LIFailure of astrocytes to clear extrasynaptic glutamate drives endocannabinoid-mediated inhibitory long-term depression of principal output neurons in the OFC. C_LIO_LIAstrocytic glutamate transporter function is restored with NAC, which rescues the synaptic deficits. C_LI

neuroscience↗

bioRxiv2019

Seizures cause sustained microvascular constriction associated with astrocytic and vascular smooth muscle Ca2+ recruitment

Previously we showed that seizures result in a severe hypoperfusion/hypoxic attack that results in postictal memory and behavioral impairments (Farrell et al., 2016). However, neither postictal changes in microvasculature nor Ca2+ changes in key cell-types controlling blood perfusion have been visualized in vivo, leaving essential components of the underlying cellular mechanisms unclear. Here we use two-photon microvascular and Ca2+ imaging in awake mice to show that seizures result in a robust vasoconstriction of cortical penetrating arterioles, which temporally mirrors the prolonged postictal hypoxia. The vascular effect was dependent on cyclooxygenase-2, as pre-treatment with ibuprofen prevented postictal vasoconstriction. Seizures caused a rapid elevation in astrocyte endfoot Ca2+ that was confined to the seizure period. Vascular smooth muscle cells displayed a significant increase in Ca2+ both during and following seizures, lasting up to 75 minutes. The temporal activities of two cell-types within the neurovascular unit lead to seizure-induced hypoxia.\n\nHighlightsO_LISeizures lead to equivalent levels of postictal hypoxia in both male and female mice\nC_LIO_LICalcium elevation in astrocyte endfeet is confined to the seizure\nC_LIO_LIPostictal vasoconstriction in awake mice is mediated by cyclooxygenase-2\nC_LIO_LICalcium elevation in vascular smooth muscle cells is enduring and correlates with vasoconstriction.\nC_LI

neuroscience↗