CNTF inhibits high voltage activated Ca2+ currents in fetal mouse cortical neurones

Interleukin-6 inhibits L-type calcium channel activity of cultured cerebellar granule neurons

Our previous work has shown that interleukin-6 (IL-6) implements its neuroprotective effect by inhibiting the intracellular Ca(2+) overload in neurons. Here, we examined whether regulation of L-type calcium channels (LCCs) activities is involved in the neuroprotective action of IL-6. In cultured cerebellar granule neurons (CGNs), patch-clamp recording showed that the whole-cell Ca(2+) current and LCC current were significantly reduced by IL-6 pretreatment (120 ng/ml, for 24 h). Calcium imaging data indicated that IL-6 significantly suppressed high K(+)-induced intracellular Ca(2+) overload and LCC Ca(2+) influx. Moreover, expression of the LCC subunit, Ca(v)1.2, was remarkably downregulated by IL-6 in cultured CGNs. These findings suggest that IL-6 exerts a neurotrophic effect by preventing Ca(2+) overload, at least partly through inhibition of LCC activity in cultured CGNs.

Astrocytes and microglia: responses to neuropathological conditions

Activated astrocytes and microglia, hallmark of neurodegenerative diseases release different factors like array of pro and anti-inflammatory cytokines, free radicals, anti-oxidants, and neurotrophic factors during neurodegeneration which further contribute to neuronal death as well as in survival mechanisms. Astrocytes act as double-edged sword exerting both detrimental and neuroprotective effects while microglial cells are attributed more in neurodegenerative mechanisms. The dual and insufficient knowledge about the precise role of glia in neurodegeneration showed the need for further investigations and thorough review of the function of glia in neurodegeneration. In this review, we consolidate and categorize the glia-released factors which contribute in degenerative and protective mechanisms during neuropathological conditions.

Behavioral and neurochemical characterization of mice deficient in the N-type Ca2+ channel alpha1B subunit

N-type voltage-dependent calcium channels (VDCCs) play an important role in neurotransmission, synaptic plasticity, and brain development. They are composed of several subunits named alpha(1), alpha(2), delta, beta and gamma. The alpha(1) subunit is essential for channel functions and determines fundamental channel properties. Since N-type VDCC are critically involved in the release of neurotransmitters and clinical relevance, we predicted that alpha(1) subunit KO mice would show several alterations in behavior. In the present study, we investigated neuronal functions in mice lacking the alpha(1B) (Ca(V)2.2) subunit of the N-type calcium channels. Ca(V)2.2(-/-) mice exhibited a significant increase in locomotion on an activity wheel during the dark phase. Furthermore, when challenged with apomorphine, mutant mice showed enhanced locomotor activity. Cognitive functions were examined using a Y-maze task for short-term memory and a passive avoidance task for long-term memory. The Y-maze revealed no differences in spontaneous alternation behavior between mutant and wild-type mice. The passive avoidance test revealed that the latency time in mutant mice was significantly decreased. The mutant mice showed prepulse inhibition deficits reminiscent of the sensorimotor gating deficits observed in a large majority of schizophrenic patients. Decreases in baseline levels of dopamine and serotonin within the striata and frontal cortices of mutant mice were also observed. These results suggest that Ca(2+) in the central nervous system modulates various neurophysiological functions, such as locomotor activity, long-term memory, and sensorimotor gating through the alpha(1B) subunit of the N-type calcium channels.

Ciliary neurotrophic factor-treated astrocyte conditioned medium regulates the L-type calcium channel activity in rat cortical neurons

Astrocytes are activated by ciliary neurotrophic factor (CNTF) in vivo and in vitro, however, the consequences on the L-type calcium channel (LCC) of neurons are still poorly understood. Therefore, in the present study, whole-cell patch clamp, western-blot and RT-PCR assay were performed to evaluate the effects of CNTF-treated astrocyte conditioned medium (CNTF-ACM) on LCC current (I(Ca)-L) and the expression of Cav1.2 and Cav1.3 in Sprague-Dawley rat cortical neurons. The results revealed that CNTF-ACM enhanced the amplitude of Ica-L and the expression of Cav1.3 significantly, but had no effects on Cav1.2 expression. We also found an increase in the concentration of fibroblast growth factor-2 (FGF-2) in CNTF-ACM by ELISA assay. Taken together, these findings indicate that CNTF induces the release of factors, including FGF-2, from astrocytes, thereby potentiating the activity of LCC in cortical neurons.

Blockade of presynaptic voltage-gated calcium channels in the medial prefrontal cortex of neonatal rats leads to post-pubertal alterations in locomotor behavior

Although the etiology of neurodevelopmental mental disorders remains obscure, converging lines of evidence using animal modeling suggest a critical role for activity-dependent neurodevelopmental processes during neonatal life. Here, we report the behavioral effects of a novel technique designed to induce targeted, transient disruption of activity-dependent processes in early development via reduction of calcium-mediated neurotransmitter release. We examined the post-pubertal behavioral effects of neonatal (postnatal day 7) medial prefrontal cortex infusion of either vehicle or N-type and P/Q-type presynaptic voltage-dependent calcium channel blockers (omega-conotoxins MVIIA and MVIIC respectively; 6.8 and 45 pmol infused respectively) in rat pups. In a test of amphetamine-induced behavioral sensitization, neonatal omega-conotoxin MVIIA treatment significantly increased locomotion following repeated amphetamine injections (1.5 mg/kg i.p.) and significantly decreased locomotion following repeated saline injections relative to animals treated neonatally with vehicle. However, there was no effect of conotoxin treatment on the long-term expression of amphetamine sensitization. Neonatal treatment with omega-conotoxins had no effect on the other behaviors assayed, namely, acoustic startle response, prepulse inhibition of startle, novelty- and amphetamine-induced (1.5 mg/kg i.p.) locomotion, and anxiety-like behavior in the elevated plus-maze. These data confirm that transient, region-specific disruption of synaptic transmission during early development can have long-term effects on behaviors relevant to neurodevelopmental mental disorders.

Ciliary neurotrophic factor promotes inactivation of muscle Ca2+ channels via PKC

The actions of the ciliary neurotrophic factor (CNTF) were assessed on adult mouse skeletal muscle L-type Ca2+ currents and on Ca2+ release from sarcoplasmic reticulum. Currents were measured with the whole cell patch clamp technique. Ca2+ signals in response to single action potentials were recorded with Fluo3-AM. CNTF (20 ng/ml) reversibly reduced the amplitude of Ca2+ channel currents by 50% within 15 min. In addition, CNTF greatly increased the rate of inactivation during depolarizing pulses and shifted the steady state inactivation curve by -12 mV. The effects of CNTF were mimicked by the PKC activator PMA and prevented by the PKC-inhibitor chelerythrine. In contrast to the effects on the Ca2+ conductance, charge movement and Ca2+ signals remained unaffected by CNTF. These results suggest that CNTF can rapidly decrease muscle Ca2+ channel currents by promoting inactivation, probably through an intracellular PKC-dependent mechanism.

Rapid protein kinase C-dependent reduction of rat skeletal muscle voltage-gated sodium channels by ciliary neurotrophic factor

The ciliary neurotrophic factor (CNTF), known to exert long-term myotrophic effects, has not yet been shown to induce a rapid biological response in skeletal muscles. The present in vitro study gives rise to the possibility that CNTF could affect the sodium channel activity implied in the triggering of muscle fibre contraction. Therefore, we investigated the effects of an external CNTF application on macroscopic sodium current (I(Na)) in rat native fast-twitch skeletal muscle (flexor digitorum brevis, FDB) by using a cell-attached patch-clamp technique. The I(Na) peak amplitude measured at a depolarizing pulse from -100 to -10 mV is rapidly reduced in a time- and dose-dependent manner by CNTF (0.01-20 ng ml(-1)). The maximal decrease is 25% after 10 min incubation in 2 ng ml(-1) CNTF. There was no alteration in activation or inactivation kinetics, or in activation curves constructed from current-voltage relationships in the presence of CNTF. In contrast, the relative I(Na) inhibition induced by CNTF is accompanied by a hyperpolarizing shift in the midpoint of the inactivation curves: -6 and -10 mV for the steady-state fast and slow inactivation, respectively. Furthermore, CNTF induces a 5 mV hyperpolarization of the resting membrane potential of the fibres. The effects of CNTF are similar to those of 1-oleoyl-2-acetyl-sn-glycerol (OAG), a protein kinase C (PKC) activator, when no effect is observed in the presence of chelerythrine, a PKC inhibitor. These results suggest that, in skeletal muscle, CNTF can rapidly decrease sodium currents by altering inactivation gating, probably through an intracellular PKC-dependent mechanism that could lead to decreased membrane excitability. The present study contributes to a better understanding of the physiological role of endogenous CNTF.

Ciliary neurotrophic factor protects retinal ganglion cells from axotomy-induced apoptosis via modulation of retinal gliain vivo

Adenoviral-mediated transfer of ciliary neurotrophic factor (CNTF) to the retina rescued retinal ganglion cells (RGCs) from axotomy-induced apoptosis, presumably via activation of the high affinity CNTF receptor alpha (CNTFRalpha) expressed on RGCs. CNTF can also activate astrocytes, via its low affinity leukemia inhibitory receptor beta expressed on mature astrocytes, suggesting that CNTF may also protect injured neurons indirectly by modulating glia. Adenoviral-mediated overexpression of CNTF in normal and axotomized rat retinas was examined to determine if it could increase the expression of several glial markers previously demonstrated to have a neuroprotective function in the injured brain and retina. Using Western blotting, the expression of glial fibrillary acid protein (GFAP), glutamate/aspartate transporter-1 (GLAST-1), glutamine synthetase (GS), and connexin 43 (Cx43) was examined 7 days after intravitreal injections of Ad.CNTF or control Ad.LacZ. Compared to controls, intravitreal injection of Ad.CNTF led to significant changes in the expression of CNTFRalpha, pSTAT(3), GFAP, GLAST, GS, and Cx43 in normal and axotomized retinas. Taken together, these results suggest that the neuroprotective effects of CNTF may result from a shift of retinal glia cells to a more neuroprotective phenotype. Moreover, the modulation of astrocytes may buffer high concentrations of glutamate that have been shown to contribute to the death of RGCs after optic nerve transection.

Orchestrating neuronal differentiation: patterns of Ca2+ spikes specify transmitter choice

Appropriate specification of neurotransmitters is a key feature of neuronal network assembly. There is much evidence that genetic programs are responsible for this aspect of cell fate and neuronal differentiation. Are there additional ways in which these processes are shaped? Recent findings demonstrate that altering patterned Ca(2+) spike activity that is spontaneously generated by different classes of embryonic spinal neurons in vivo changes expression of neurotransmitters in a homeostatic manner, as if to achieve a constant level of excitation. Activity-dependent changes in presynaptic transmitter expression pose a matching problem: are there corresponding changes in postsynaptic transmitter receptor expression, or are axons rerouted to novel targets with which functional synapses can be formed?