Calcium transients evoked by action potentials in the somata of chick ciliary neurons

Dual-parameter cell biosensor for real-time monitoring of effects of propionic acid on neurons

Currently, only a few small devices are capable of continuously recording the physiological states of neurons in real time. Micro-electrode arrays (MEAs) are widely used as electrophysiological technology to detect the excitability of neurons non-invasively. However, the development of miniaturized and multi-parameter MEAs capable of real-time recording remains challenging. In this study, an on-chip micro-electrode and platinum resistor array (MEPRA) biosensor was designed and fabricated to monitor both the electrical and temperature signals of cells synchronously in real time. Such on-chip sensor maintains high sensitivity and stability. The MEPRA biosensor was further used to investigate the effects of propionic acid (PA) on primary neurons. The results demonstrate that PA affects the temperature and firing frequency of primary cortical neurons in concentration-dependent manners. The changes of temperature and firing frequency work in tandem with neuronal physiological status, including neuron viability, intracellular calcium concentration, neural plasticity, and mitochondrial function. This highly biocompatible, stable, and sensitive MEPRA biosensor may provide high-precision reference information for investigating the physiological responses of neuron cells under various conditions.

Removal of Ca(2+) following depolarization-evoked cytoplasmic Ca(2+) transients in freshly dissociated pyramidal neurones of the rat dorsal cochlear nucleus

Cytoplasmic [Ca(2+)] ([Ca(2+)](i)) was measured using Fura-2 in pyramidal neurones isolated from the rat dorsal cochlear nucleus (DCN). The kinetic properties of Ca(2+) removal following K(+) depolarization-induced Ca(2+) transients were characterized by fitting exponential functions to the decay phase. The removal after small transients (<82 nM peak [Ca(2+)](i)) had monophasic time course (time constant of 6.43 +/- 0.48 s). In the cases of higher Ca(2+) transients biphasic decay was found. The early time constant decreased (from 3.09 +/- 0.26 to 1.46 +/- 0.11 s) as the peak intracellular [Ca(2+)] increased. The value of the late time constant was 18.15 +/- 1.60 s at the smallest transients, and showed less dependence on [Ca(2+)](i). Blockers of Ca(2+) uptake into intracellular stores (thapsigargin and cyclopiazonic acid) decreased the amplitude of the Ca(2+) transients and slowed their decay. La(3+) (3 mM) applied extracellularly during the declining phase dramatically changed the time course of the Ca(2+) transients as a plateau developed and persisted until the La(3+) was present. When the other Ca(2+) removal mechanisms were available, reduction of the external [Na(+)] to inhibit the Na(+)/Ca(2+) exchange resulted in a moderate increase of the time constants. It is concluded that in the isolated pyramidal neurones of the DCN the removal of Ca(2+) depends mainly on the activity of Ca(2+) pump mechanisms.

Synaptically driven calcium transients via nicotinic receptors on somatic spines

Dendritic spines commonly receive glutamatergic innervation at postsynaptic densities and compartmentalize calcium influx arising from synaptic signaling. Recently, it was shown that a class of nicotinic acetylcholine receptors containing alpha7 subunits is concentrated on somatic spines emanating from chick ciliary ganglion neurons. The receptors have a high relative calcium permeability and contribute importantly to synaptic currents, although they appear to be excluded from postsynaptic densities. Here we show that low-frequency synaptic stimulation of the alpha7-containing receptors induces calcium transients confined to the spines. High-frequency stimulation induces a transient calcium elevation in the spines and a more sustained cell-wide elevation. The high-frequency transient elevation again depends on alpha7-containing receptors, whereas the sustained elevation can be triggered by other nicotinic receptors and depends on calcium release from internal stores and probably influx through voltage-gated L-type calcium channels as well. Retrograde axonal stimulation of the neurons at high frequency mimics synaptic stimulation in producing sustained cell-wide calcium increases that depend on L-type channels and release from internal stores, but it does not produce calcium transients in the spines. Thus frequent action potentials are sufficient to generate the cell-wide increases, but alpha7-containing receptors are needed for spine-specific effects. Patch-clamp recording indicates that alpha7-containing receptors preferentially desensitize at high-frequency stimulation, accounting for the inability of the stimulation to sustain high calcium levels in the spines. The spatial and temporal differences in the patterns of calcium elevation could enable the neurons to monitor their own firing histories for regulatory purposes.