Mitochondrial transport in processes of cortical neurons is independent of intracellular calcium

Mitochondria show extensive movement along neuronal processes, but the mechanisms and function of this movement are not clearly understood. We have used high-resolution confocal microscopy to simultaneously monitor movement of mitochondria and changes in intracellular [Ca2+] ([Ca2+]i) in rat cortical neurons. A significant percentage (27%) of the total mitochondria in cortical neuronal processes showed movement over distances of >2 μM. The average velocity was 0.52 μm/s. The velocity, direction, and pattern of mitochondrial movement were not affected by transient increases in [Ca2+]i associated with spontaneous firing of action potentials. Stimulation of Ca2+ transients with forskolin (10 μM) or bicuculline (10 μM), or sustained elevations of [Ca2+]i evoked by glutamate (10 μM) also had no effect on mitochondrial transit. Neither removal of extracellular Ca2+, depletion of intracellular Ca2+ stores with thapsigargin, or inhibition of synaptic activity with TTX (1 μM) or a cocktail of CNQX (10 μM) and MK801 (10 μM) affected mitochondrial movement. These results indicate that movement of mitochondria along processes is a fundamental activity in neurons that occurs independently of physiological changes in [Ca2+]i associated with action potential firing, synaptic activity, or release of Ca2+ from intracellular stores.

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Ca2+ Influx, But Not Ca2+ Release From Internal Stores, Is Required for the PACAP-Induced Increase in Excitability in Guinea Pig Intracardiac Neurons

Journal of Neurophysiology ◽

10.1152/jn.01077.2005 ◽

2006 ◽

Vol 95 (4) ◽

pp. 2134-2142 ◽

Cited By ~ 23

Author(s):

John D. Tompkins ◽

Jean C. Hardwick ◽

Sarah A. Locknar ◽

Laura A. Merriam ◽

Rodney L. Parsons

Keyword(s):

Guinea Pig ◽

Action Potentials ◽

Action Potential Firing ◽

Pituitary Adenylate Cyclase ◽

Whole Mount ◽

Voltage Dependent ◽

Potential Firing ◽

Intracellular Ca ◽

Indicator Dye ◽

Intracardiac Neurons

Mechanisms modulating the pituitary adenylate cyclase activating polypeptide (PACAP)-induced increase in excitability have been studied using dissociated guinea pig intrinsic cardiac neurons and intact ganglion preparations. Measurements of intracellular calcium (Ca2+) with the fluorescent Ca2+ indicator dye fluo-3 indicated that neither PACAP nor vasoactive intestinal polypeptide (VIP) at either 100 nM or 1 μM produced a discernible elevation of intracellular Ca2+ in dissociated intracardiac neurons. For neurons in ganglion whole mount preparations kept in control bath solution, local application of PACAP significantly increased excitability, as indicated by the number of action potentials generated by long depolarizing current pulses. However, in a Ca2+-deficient solution in which external Ca2+ was replaced by Mg2+ or when cells were bathed in control solution containing 200 μM Cd2+, PACAP did not enhance action potential firing. In contrast, in a Ca2+-deficient solution with Ca2+ replaced by strontium (Sr2+), PACAP increased excitability. PACAP increased excitability in cells treated with a combination of 20 μM ryanodine and 10 mM caffeine to interrupt release of Ca2+ from internal stores. Experiments using fluo-3 showed that ryanodine/caffeine pretreatment eliminated subsequent caffeine-induced Ca2+ release from intracellular stores, whereas exposure to the Ca2+-deficient solution did not. In dissociated intracardiac neurons voltage clamped with the perforated patch recording technique, 100 nM PACAP decreased the voltage-dependent barium current ( IBa). These results show that, in the guinea pig intracardiac neurons, the PACAP-induced increase in excitability apparently requires Ca2+ influx through Cd2+-sensitive calcium permeable channels other than voltage-dependent Ca2+ channels, but not Ca2+ release from internal stores.

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Zinc Enhances the Inhibitory Effects of Strychnine-Sensitive Glycine Receptors in Mouse Hippocampal Neurons

Journal of Neurophysiology ◽

10.1152/jn.00500.2007 ◽

2007 ◽

Vol 98 (6) ◽

pp. 3666-3676 ◽

Cited By ~ 8

Author(s):

Hai Xia Zhang ◽

Liu Lin Thio

Keyword(s):

Action Potential ◽

Action Potentials ◽

Hippocampal Neurons ◽

Neuronal Excitability ◽

Hippocampal Slices ◽

Glycine Receptors ◽

Inhibitory Effects ◽

Action Potential Firing ◽

Embryonic Mouse ◽

Potential Firing

Although extracellular Zn2+ is an endogenous biphasic modulator of strychnine-sensitive glycine receptors (GlyRs), the physiological significance of this modulation remains poorly understood. Zn2+ modulation of GlyR may be especially important in the hippocampus where presynaptic Zn2+ is abundant. Using cultured embryonic mouse hippocampal neurons, we examined whether 1 μM Zn2+, a potentiating concentration, enhances the inhibitory effects of GlyRs activated by sustained glycine applications. Sustained 20 μM glycine (EC25) applications alone did not decrease the number of action potentials evoked by depolarizing steps, but they did in 1 μM Zn2+. At least part of this effect resulted from Zn2+ enhancing the GlyR-induced decrease in input resistance. Sustained 20 μM glycine applications alone did not alter neuronal bursting, a form of hyperexcitability induced by omitting extracellular Mg2+. However, sustained 20 μM glycine applications depressed neuronal bursting in 1 μM Zn2+. Zn2+ did not enhance the inhibitory effects of sustained 60 μM glycine (EC70) applications in these paradigms. These results suggest that tonic GlyR activation could decrease neuronal excitability. To test this possibility, we examined the effect of the GlyR antagonist strychnine and the Zn2+ chelator tricine on action potential firing by CA1 pyramidal neurons in mouse hippocampal slices. Co-applying strychnine and tricine slightly but significantly increased the number of action potentials fired during a depolarizing current step and decreased the rheobase for action potential firing. Thus Zn2+ may modulate neuronal excitability normally and in pathological conditions such as seizures by potentiating GlyRs tonically activated by low agonist concentrations.

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Discovery of a heme-binding domain in a neuronal voltage-gated potassium channel

Journal of Biological Chemistry ◽

10.1074/jbc.ra120.014150 ◽

2020 ◽

Vol 295 (38) ◽

pp. 13277-13286

Author(s):

Mark J. Burton ◽

Joel Cresser-Brown ◽

Morgan Thomas ◽

Nicola Portolano ◽

Jaswir Basran ◽

...

Keyword(s):

Cortical Neurons ◽

Normal Function ◽

Pas Domain ◽

Heme Binding ◽

Channel Activity ◽

Action Potential Firing ◽

Voltage Gated ◽

Conserved Domain ◽

Potential Firing ◽

Eag Channels

The EAG (ether-à-go-go) family of voltage-gated K+ channels are important regulators of neuronal and cardiac action potential firing (excitability) and have major roles in human diseases such as epilepsy, schizophrenia, cancer, and sudden cardiac death. A defining feature of EAG (Kv10–12) channels is a highly conserved domain on the N terminus, known as the eag domain, consisting of a Per–ARNT–Sim (PAS) domain capped by a short sequence containing an amphipathic helix (Cap domain). The PAS and Cap domains are both vital for the normal function of EAG channels. Using heme-affinity pulldown assays and proteomics of lysates from primary cortical neurons, we identified that an EAG channel, hERG3 (Kv11.3), binds to heme. In whole-cell electrophysiology experiments, we identified that heme inhibits hERG3 channel activity. In addition, we expressed the Cap and PAS domain of hERG3 in Escherichia coli and, using spectroscopy and kinetics, identified the PAS domain as the location for heme binding. The results identify heme as a regulator of hERG3 channel activity. These observations are discussed in the context of the emerging role for heme as a regulator of ion channel activity in cells.

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Nicotine suppresses hyperexcitability of colonic sensory neurons and visceral hypersensivity in mouse model of colonic inflammation

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00411.2011 ◽

2012 ◽

Vol 302 (7) ◽

pp. G740-G747 ◽

Cited By ~ 2

Author(s):

Galya R. Abdrakhmanova ◽

Minho Kang ◽

M. Imad Damaj ◽

Hamid I. Akbarali

Keyword(s):

Mouse Model ◽

Action Potential ◽

Action Potentials ◽

Drg Neurons ◽

Action Potential Firing ◽

Colonic Inflammation ◽

Single Action ◽

Nicotine Administration ◽

Potential Firing

Recently, we reported that nicotine in vitro at a low 1-μM concentration suppresses hyperexcitability of colonic dorsal root ganglia (DRG; L1-L2) neurons in the dextran sodium sulfate (DSS)-induced mouse model of acute colonic inflammation ( 1 ). Here we show that multiple action potential firing in colonic DRG neurons persisted at least for 3 wk post-DSS administration while the inflammatory signs were diminished. Similar to that in DSS-induced acute colitis, bath-applied nicotine (1 μM) gradually reduced regenerative multiple-spike action potentials in colonic DRG neurons to a single action potential in 3 wk post-DSS neurons. Nicotine (1 μM) shifted the activation curve for tetrodotoxin (TTX)-resistant sodium currents in inflamed colonic DRG neurons (voltage of half-activation changed from −37 to −32 mV) but did not affect TTX-sensitive currents in control colonic DRG neurons. Further, subcutaneous nicotine administration (2 mg/kg b.i.d.) in DSS-treated C57Bl/J6 male mice resulted in suppression of hyperexcitability of colonic DRG (L1-L2) neurons and the number of abdominal constrictions in response to intraperitoneal injection of 0.6% acetic acid. Collectively, the data suggest that neuronal nicotinic acetylcholine receptor-mediated suppression of hyperexcitability of colonic DRG neurons attenuates reduction of visceral hypersensitivity in DSS mouse model of colonic inflammation.

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Temporal coupling of field potentials and action potentials in the neocortex

10.1101/214650 ◽

2017 ◽

Cited By ~ 2

Author(s):

Brendon O. Watson ◽

Mingxin Ding ◽

György Buzsáki

Keyword(s):

Action Potential ◽

Action Potentials ◽

Field Potential ◽

Electromyographic Activity ◽

Action Potential Firing ◽

Firing Rates ◽

Potential Firing ◽

Temporal Coupling ◽

Potential Activity ◽

The Relationship

AbstractThe local field potential (LFP) is an aggregate measure of group neuronal activity and is often correlated with the action potentials of single neurons. In recent years investigators have found that action potential firing rates increase during elevations in power high-frequency band oscillations (50-200 Hz range). However action potentials also contribute to the LFP signal itself, making the spike–LFP relationship complex. Here we examine the relationship between spike rates and LFPs in varying frequency bands in rat neocortical recordings. We find that 50-180Hz oscillations correlate most consistently with high firing rates, but that other LFPs bands also carry information relating to spiking, including in some cases anti-correlations. Relatedly, we find that spiking itself and electromyographic activity contribute to LFP power in these bands. The relationship between spike rates and LFP power varies between brain states and between individual cells. Finally, we create an improved oscillation-based predictor of action potential activity by specifically utilizing information from across the entire recorded frequency spectrum of LFP. The findings illustrate both caveats and improvements to be taken into account in attempts to infer spiking activity from LFP.

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Dopamine modulates the integrity of the perisynaptic extracellular matrix at excitatory synapses

10.1101/722454 ◽

2019 ◽

Cited By ~ 2

Author(s):

Jessica Mitlöhner ◽

Rahul Kaushik ◽

Hartmut Niekisch ◽

Armand Blondiaux ◽

Christine E. Gee ◽

...

Keyword(s):

Extracellular Matrix ◽

Cortical Neurons ◽

Receptor Activation ◽

Synaptic Activity ◽

Excitatory Synapses ◽

Intracellular Calcium Signaling ◽

Rat Cortical Neurons ◽

Synaptic Receptors

SummaryIn the brain, Hebbian-type and homeostatic forms of plasticity are affected by neuromodulators like dopamine (DA). Modifications of the perisynaptic extracellular matrix (ECM), controlling functions and mobility of synaptic receptors as well as diffusion of transmitters and neuromodulators in the extracellular space, are crucial for the manifestation of plasticity. Mechanistic links between synaptic activation and ECM modifications are largely unknown. Here, we report that neuromodulation via D1-type DA receptors can induce targeted ECM proteolysis specifically at excitatory synapses of rat cortical neurons via proteases ADAMTS-4 and -5. We show that receptor activation induces increased proteolysis of brevican (BC) and aggrecan, two major constituents of the adult ECM, in vivo and in vitro. ADAMTS immunoreactivity is detected near synapses, and shRNA-mediated knockdown reduced BC cleavage. We outline a molecular scenario how synaptic activity and neuromodulation are linked to ECM rearrangements via increased cAMP levels, NMDA receptor activation, and intracellular calcium signaling.

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Neuron-Derived Extracellular Vesicles Modulate Microglia Activation and Function

Biology ◽

10.3390/biology10100948 ◽

2021 ◽

Vol 10 (10) ◽

pp. 948

Author(s):

Hui Peng ◽

Brock T. Harvey ◽

Christopher I. Richards ◽

Kimberly Nixon

Keyword(s):

Extracellular Vesicles ◽

Cortical Neurons ◽

Molecular Mechanisms ◽

Proinflammatory Response ◽

Tnf Α ◽

Rat Cortical Neurons ◽

The Central Nervous System ◽

And Function ◽

And Control ◽

Brain Homeostasis

Microglia act as the immune cells of the central nervous system (CNS). They play an important role in maintaining brain homeostasis but also in mediating neuroimmune responses to insult. The interactions between neurons and microglia represent a key process for neuroimmune regulation and subsequent effects on CNS integrity. However, the molecular mechanisms of neuron-glia communication in regulating microglia function are not fully understood. One recently described means of this intercellular communication is via nano-sized extracellular vesicles (EVs) that transfer a large diversity of molecules between neurons and microglia, such as proteins, lipids, and nucleic acids. To determine the effects of neuron-derived EVs (NDEVs) on microglia, NDEVs were isolated from the culture supernatant of rat cortical neurons. When NDEVs were added to primary cultured rat microglia, we found significantly improved microglia viability via inhibition of apoptosis. Additionally, application of NDEVs to cultured microglia also inhibited the expression of activation surface markers on microglia. Furthermore, NDEVs reduced the LPS-induced proinflammatory response in microglia according to reduced gene expression of proinflammatory cytokines (TNF-α, IL-6, MCP-1) and iNOS, but increased expression of the anti-inflammatory cytokine, IL-10. These findings support that neurons critically regulate microglia activity and control inflammation via EV-mediated neuron–glia communication. (Supported by R21AA025563 and R01AA025591).

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Interconnection and synchronization of neuronal populations in the mouse medial septum/diagonal band of Broca

Journal of Neurophysiology ◽

10.1152/jn.00367.2014 ◽

2015 ◽

Vol 113 (3) ◽

pp. 971-980 ◽

Cited By ~ 12

Author(s):

Richardson N. Leão ◽

Zé H. Targino ◽

Luis V. Colom ◽

André Fisahn

Keyword(s):

Action Potentials ◽

Theta Rhythm ◽

Medial Septum ◽

Gabaergic Neurons ◽

Action Potential Firing ◽

Neuronal Populations ◽

Diagonal Band ◽

Potential Firing ◽

Diagonal Band Of Broca ◽

Hippocampal Theta

The medial septum/diagonal band of Broca (MS/DBB) is crucial for hippocampal theta rhythm generation (4–12 Hz). However, the mechanisms behind theta rhythmogenesis are still under debate. The MS/DBB consists, in its majority, of three neuronal populations that use acetylcholine, GABA, or glutamate as neurotransmitter. While the firing patterns of septal neurons enable the MS/DBB to generate rhythmic output critical for the generation of the hippocampal theta rhythm, the ability to synchronize these action potentials is dependent on the interconnectivity between the three major MS/DBB neuronal populations, yet little is known about intraseptal connections. Here we assessed the connectivity between pairs of MS/DBB neurons with paired patch-clamp recordings. We found that glutamatergic and GABAergic neurons provide intraseptal connections and produce sizable currents in MS/DBB postsynaptic cells. We also analyzed linear and nonlinear relationships between the action potentials fired by pairs of neurons belonging to various MS/DBB neuronal populations. Our results show that while the synchrony index for action potential firing was significantly higher in pairs of GABAergic neurons, coherence of action potential firing in the theta range was similarly low in all pairs analyzed. Recurrence analysis demonstrated that individual action potentials were more recurrent in cholinergic neurons than in other cell types. Implementing sparse connectivity in a computer model of the MS/DBB network reproduced our experimental data. We conclude that the interplay between the intrinsic membrane properties of different MS/DBB neuronal populations and the connectivity among these populations underlie the ability of the MS/DBB network to critically contribute to hippocampal theta rhythmogenesis.

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