Biomedical subjects

Carola G Schipke

Publications and source records attributed to Carola G Schipke.

6 recordsLinked to original sources

PubMed2005

Extracellular application of nicotinic acid adenine dinucleotide phosphate induces Ca2+ signaling in astrocytes in situ.

Nicotinic acid adenine dinucleotide phosphate (NAADP+) has been identified as a novel second messenger triggering Ca2+ release from intracellular stores. Here we report that murine cortical astrocytes in culture and in acute slices respond with transient intracellular Ca2+ increases to extracellularly applied NAADP+ and express the NAADP+-producing enzyme CD38. The Ca2+ transients triggered by NAADP+ occurred with an average delay of 35 s as compared with ATP-triggered Ca2+ signaling, suggesting that NAADP+ may have to enter the cell to act. Blockage of connexin hemichannels (a possible entry route for NAADP+ into the cell) reduced the number of astrocytes responding to NAADP+. Disruption of lysosomes as the suggested site of NAADP+ receptors reduced the number of astrocytes responding to NAADP+ strongly. The NAADP+-triggered Ca2+ signal also depended on intact endoplasmic reticulum Ca2+ stores linked to activation of inositol 1,4,5-trisphosphate receptors and on the activity of voltage-gated Ca2+ channels. Adenosine receptor-mediated signaling contributes to the NAADP+-evoked signal, since it is strongly reduced by the adenosine receptor blocker CGS-15943. Moreover, NAADP+ triggered responses in all other cell types (cultured cerebellar neurons, microglia, and oligodendrocytes) of the central nervous system.

ADP-ribosyl Cyclase 1↗

PubMed2005

Activity-dependent ATP-waves in the mouse neocortex are independent from astrocytic calcium waves.

In the corpus callosum, astrocytic calcium waves propagate via a mechanism involving ATP-release but not gap junctional coupling. In the present study, we report for the neocortex that calcium wave propagation depends on functional astrocytic gap junctions but is still accompanied by ATP-release. In acute slices obtained from the neocortex of mice deficient for astrocytic expression of connexin43, the calcium wave did not propagate. In contrast, in the corpus callosum and hippocampus of these mice, the wave propagated as in control animals. In addition to calcium wave propagation in astrocytes, ATP-release was recorded as a calcium signal from 'sniffer cells', a cell line expressing high-affinity purinergic receptors placed on the surface of the slice. The astrocyte calcium wave in the neocortex was accompanied by calcium signals in the 'sniffer cell' population. In the connexin43-deficient mice we recorded calcium signals from sniffer cells also in the absence of an astrocytic calcium wave. Our findings indicate that astrocytes propagate calcium signals by two separate mechanisms depending on the brain region and that ATP release can propagate within the neocortex independent from calcium waves.

Adenosine Triphosphate↗

PubMed2004

Astrocyte responses to neuronal activity.

During the past few years, it has been established that astrocytes sense neuronal activity and are involved in signal transmission. Neuronal stimulation triggered electrophysiological and/or Ca(2+) responses in astrocyte cultures and in acute brain slices. Present even within one given brain region, different pathways of neuron-to-astrocyte communication involving different receptor systems have been described. These mechanisms include glutamatergic and NO-mediated signaling. Neuron-to-astrocyte signaling can be confined to subcellular compartments, the microdomains, or it can activate the entire cell. It can even trigger a multicellular response in astrocytes, a Ca(2+) wave. This form of astrocyte long-range signal propagation can occur independently, in pure astrocyte cultures, but it can also be triggered by neuronal activity. Astrocytes also exhibit spontaneous Ca(2+) activity. Neuronal activity in acute brain slices can organize this activity into complex synchronous networks. One of the functional consequences of neuron-to-astrocyte signaling might be the neuronal control of microcirculation using astrocytes as a mediator.

Action Potentials↗

PubMed2003

Different mechanisms promote astrocyte Ca2+ waves and spreading depression in the mouse neocortex.

Cortical spreading depression (CSD) is thought to play an important role in different pathological conditions of the human brain. Here we investigated the interaction between CSD and Ca2+ waves within the astrocyte population in slices from mouse neocortex (postnatal days 10-14). After local KCl ejection as a trigger for CSD, we recorded the propagation of Ca2+ increases within a large population of identified astrocytes in synchrony with CSD measured as intrinsic optical signal (IOS) or negative DC-potential shift. The two events spread with 39.2 +/- 3.3 mum/sec until the IOS and negative DC-potential shift decayed after approximately 1 mm. However, the astrocyte Ca2+ wave continued to propagate for up to another 500 microm but with a reduced speed of 18.3 +/- 2.5 microm/sec that is also typical for glial Ca2+ waves in white matter or culture. While blocking CSD using MK-801 (40 microm), an NMDA-receptor antagonist, the astrocyte Ca2+ wave persisted with a reduced speed (13.2 +/- 1.5 microm/sec). The specific gap junction blocker carbenoxolon (100 microm) did not prevent CSD but decelerated the speed (2.9 +/- 0.9 microm/sec) of the astrocyte Ca2+ wave in the periphery of CSD. We also found that interfering with intracellular astrocytic Ca2+ signaling by depletion of internal Ca2+ stores does not affect the spread of the IOS. We conclude that CSD determines the velocity of an accompanying astrocytic Ca2+ response, but the astrocyte Ca2+ wave penetrates a larger territory and by this represents a self-reliant phenomenon with a different mechanism of propagation.

Animals↗

PubMed2003

GABAA receptor-expressing astrocytes in the supraoptic nucleus lack glutamate uptake and receptor currents.

An important function of astrocytes is the clearance of excess extracellular glutamate via specific carriers whose expression has become an astrocytic marker. In the present study, we found that a large population of astrocytes in the supraoptic nucleus (SON) of the rat hypothalamus lacks glutamate uptake currents and receptor responses but expresses GABAA receptors. Patch clamp recordings in acute hypothalamic slices that included the SON showed typical astrocytic membrane currents and demonstrated that GABA, via GABAA receptor activation, triggered a conductance increase with the reversal potential close to the Cl- equilibrium potential and a decrease in resting K+ conductance. Intracellular labeling with Lucifer Yellow revealed that these cells had a radial glia-like morphology, with cell bodies lined up along the base of the brain and long processes traversing the nucleus; they were not dye-coupled. Parallel immunocytochemical labelings showed that they expressed strong GABAA receptor and glial fibrillary acidic protein (GFAP) immunoreactivities. In addition, our electrophysiological and morphological analyses revealed another population of astrocytes in this nucleus, located next to the subarachnoid space. They were less numerous than the radial type, had a round morphology and few processes, and were dye-coupled. Unlike the radial astrocytes, they showed little immunoreactivity for GABAA receptor or GFAP. Moreover, they did not respond to GABA but to glutamate, a response that was partially mimicked by aspartate, indicating glutamate transporter expression. Taken together, our observations add to growing evidence illustrating heterogeneity of astrocytes in the adult brain, a heterogeneity that reflects striking differences in form and function of astrocytic populations in regions as discrete as the SON of the hypothalamus.

Action Potentials↗

PubMed2001

Astrocyte Ca2+ waves trigger responses in microglial cells in brain slices.

Pathologic impacts in the brain lead to a widespread activation of microglial cells far beyond the site of injury. Here, we demonstrate that glial Ca2+ waves can trigger responses in microglial cells. We elicited Ca2+ waves in corpus callosum glial cells by electrical stimulation or local adenosine triphosphate (ATP) ejection in acute brain slices. Macroglial cells, but not microglia, were bulk-loaded with Ca2+-sensitive dyes. Using a transgenic animal in which astrocytes were labeled by the enhanced green fluorescence protein (EGFP) allowed us to identify the reacting cell populations: the wave activated a Ca2+ response in both astrocytes and non-astrocytic glial cells and spread over hundreds of micrometers even into the adjacent cortical and ventricular cell layers. Regenerative ATP release and subsequent activation of metabotropic purinergic receptors caused the propagation of the glial Ca2+ wave: the wave was blocked by the purinergic receptor antagonist Reactive Blue 2 and was not affected by the gap junction blocker octanol, but enhanced in Ca2+ free saline. To test whether microglial cells respond to the wave, microglial cells were labeled with a dye-coupled lectin and membrane currents were recorded with the patch-clamp technique. When the wave passed by, a current with the characteristics of a purinergic response was activated. Thus, Ca2+ waves in situ are not restricted to astrocytic cells, but broadly activate different glial cell types.

Adenosine Triphosphate↗