Calcium oscillations in rhythmically active respiratory neurones in the brainstem of the mouse

The rhythmically active respiratory network in the brainstem slice of the mouse was investigated under in vitro conditions using patch clamp and microfluorometric techniques. Rhythmic respiratory activity persisted over the whole course of an experiment.Electrophysiologically recorded rhythmic activity in respiratory neurones was accompanied by oscillations in intracellular calcium, which displayed a maximal concentration of 300 nm and decayed to basal levels with a mean time constant of 1.6 ± 0.9 s.Elevations of calcium concentrations were highly correlated with the amplitude of rhythmic membrane depolarization of neurones, indicating that they were initiated by a calcium influx across the plasma membrane through voltage-gated calcium channels.Voltage clamp protocols activating either high voltage-activated (HVA) or both HVA and low voltage-activated (LVA) calcium channels showed that intracellular calcium responses were mainly evoked by calcium currents through HVA channels.Somatic calcium signals depended linearly on transmembrane calcium fluxes, suggesting that calcium-induced calcium release did not substantially contribute to the response.For calcium elevations below 1 μm, decay time constants were essentially independent of the amplitude of calcium rises, indicating that calcium extrusion was adequately approximated by a linear extrusion mechanism.Cytosolic calcium oscillations observed in neurones of the ventral respiratory group provide further evidence for rhythmic activation of calcium-dependent conductances or second messenger systems participating in the generation and modulation of rhythmic activity in the central nervous system

S100A6, a calcium- and zinc-binding protein, is overexpressed in SOD1 mutant mice, a model for amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterised by selective degeneration of motoneurones. Familial ALS is an age-dependent autosomal dominant disorder in which mutations in the homodimeric enzyme Cu/Zn superoxide dismutase 1 (SOD1) is linked to the disease. An animal model for this disease is a transgenic mouse expressing the mutated human SOD1(G93A) gene. Recent electrophysiological data emphasised that the striking selective vulnerability of motoneurones might be due to their differential calcium buffering capacities. Therefore we have investigated, using immunohistochemistry, the expression of different calcium binding proteins in brainstem and spinal cord from normal and SOD1 mutated mice. Among the 13 calcium-binding proteins screened, only one, S100A6, a homodimeric calcium-binding protein able to bind four Zn(2+), appeared to be highly expressed in the SOD1 mutated mice. In brainstem, reactive astrocytes, but not motoneurones, from several regions, including nerve 12 root, were highly S100A6-positive. Hypoglossal nucleus was negative for S100A6. In dorsal root, reactive astrocytes from both white matter and anterior horn were highly reactive. If overexpression of S100A6 is specific for ALS, it will be a valuable diagnostic marker for this disease.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe