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Cyclic nucleotides play critical roles in a variety of CNS functions. Many of their effects are mediated by protein kinase activation, but we hypothesized that an additional target may be represented by cyclic nucleotide-gated channels (CNGC). We previously demonstrated expression of CNGC in medial vestibular nucleus neurons where their activation causes membrane depolarization leading to increase of spontaneous firing rate. In the present study we focused on possible role of CNGC in astrocytes. Immunoblot and immunofluorescence demonstrated expression of olfactory type A subunit (CNGA2) in cultured rat cortical astrocytes. In voltage-clamp, currents elicited in these cells by -100 to +100 mV ramps in the presence of the cGMP analogue, dB-cGMP, were reduced by the CNGC blockers, L-cis-diltiazem (LCD) and Cd2+. Reversal potentials of the LCD- and Cd2+ sensitive-currents were compatible with a mixed cation current. The cGMP analogue, 8-Br-cGMP elicited tonic currents at both positive and negative potentials, which were reduced by LCD and were not affected by PKG inhibitor. Astrocytic CNGA2 expression was confirmed in situ. In addition, 8-Br-cGMP elicited, at -70 mV, tonic inward currents in astrocytes from brain slices and its effects were inhibited by LCD. Since CNGC may be activated by several physiologically important agent released by neurons and astrocytes, our data suggest that these channels could be involved in the bidirectional communication between these cell types

The involvement of metabotropic glutamate receptors type 5 (mGluR5) in drug-induced behaviours is well-established but limited information is available on their functional roles in addiction-relevant brain areas like the nucleus accumbens (NAc). This study demonstrates that pharmacological and synaptic activation of mGluR5 increases the spike discharge of medium spiny neurons (MSNs) in the NAc. This effect was associated with the appearance of a slow afterdepolarization (ADP) which, in voltage-clamp experiments, was recorded as a slowly inactivating inward current. Pharmacological studies showed that ADP was elicited by mGluR5 stimulation via G-protein-dependent activation of phospholipase C and elevation of intracellular Ca2+ levels. Both ADP and spike aftercurrents were significantly inhibited by the Na+ channel-blocker, tetrodotoxin (TTX). Moreover, the selective blockade of persistent Na+ currents (I-NaP), achieved by NAc slice pre-incubation with 20 nm TTX or 10 mu m riluzole, significantly reduced the ADP amplitude, indicating that this type of Na+ current is responsible for the mGluR5-dependent ADP. mGluR5 activation also produced significant increases in I-NaP, and the pharmacological blockade of this current prevented the mGluR5-induced enhancement of spike discharge. Collectively, these data suggest that mGluR5 activation upregulates I-NaP in MSNs of the NAc, thereby inducing an ADP that results in enhanced MSN excitability. Activation of mGluR5 will significantly alter spike firing in MSNs in vivo, and this effect could be an important mechanism by which these receptors mediate certain aspects of drug-induced behaviours.

Cyclic nucleotides play critical roles in a variety of CNS functions. Many of their effects are mediated by protein kinase activation, but we hypothesized that an additional target may be represented by cyclic nucleotide-gated channels (CNGC). We previously demonstrated expression of CNGC in medial vestibular nucleus neurons where their activation causes membrane depolarization leading to increase of spontaneous firing rate. In the present study we focused on possible role of CNGC in astrocytes. Immunoblot and immunofluorescence demonstrated expression of olfactory type A subunit (CNGA2) in cultured rat cortical astrocytes. In voltage-clamp, currents elicited in these cells by -100 to +100 mV ramps in the presence of the cGMP analogue, dB-cGMP, were reduced by the CNGC blockers, L-cis-diltiazem (LCD) and Cd2+. Reversal potentials of the LCD- and Cd2+ sensitive-currents were compatible with a mixed cation current. The cGMP analogue, 8-Br-cGMP elicited tonic currents at both positive and negative potentials, which were reduced by LCD and were not affected by PKG inhibitor. Astrocytic CNGA2 expression was confirmed in situ. In addition, 8-Br-cGMP elicited, at -70 mV, tonic inward currents in astrocytes from brain slices and its effects were inhibited by LCD. Since CNGC may be activated by several physiologically important agent released by neurons and astrocytes, our data suggest that these channels could be involved in the bidirectional communication between these cell types

Calcium signals generated through Cav1 channels activate intracellular pathways affecting the expression of genes controlling cell death and differentiation. Aim of our study was to determine the role of Cav1 channel signals in the pathophysiology of neurodegenerative diseases, and their impact on neurogenesis. We demonstrated that the different neurotoxicity of amyloid-β protein (Aβ) variants found in the brains of Alzheimer's disease patients depends on their ability to upregulate Cav1 channel expression and activate Ca2+-dependent pro-apoptotic pathways (1,2). Cav1 channels also gave a prominent contribution to intracellular Ca2+ signals triggered by the binding of herpes simplex virus type 1 (HSV-1) to the plasma membrane of neurons. These HSV-1-induced Ca2+ signals promoted amyloid precursor protein (APP) phosphorylation and processing, with consequent intracellular and extracellular accumulation of Aβ and other neurotoxic APP fragments (3,4). In neural stem cells (NSC) up-regulation of Cav1 channel signals caused opposite effects, i.e., increased in vitro NSC differentiation toward the neuronal phenotype and enhanced adult hippocampal neurogenesis in vivo (5,6). These effects are mediated by Cav1 channel-depended phosphorylation of CREB and increased expression of the pro-neuronal genes Mash1, NeuroD and Hes1. Collectively, our findings suggest that modulation of Cav1 channel signals have the potential to counteract neurodegeneration and promote brain repair.