Pharmacological enhancement of mGlu5 receptors rescues behavioral deficits in SHANK3 knock-out mice.

SHANK3 (also called PROSAP2) genetic haploinsufficiency is thought to be the major cause of neuropsychiatric symptoms in Phelan-McDermid syndrome (PMS). PMS is a rare genetic disorder that causes a severe form of intellectual disability (ID), expressive language delays and other autistic features. Furthermore, a significant number of SHANK3 mutations have been identified in patients with autism spectrum disorders (ASD), and SHANK3 truncating mutations are associated with moderate to profound ID. The Shank3 protein is a scaffold protein that is located in the postsynaptic density (PSD) of excitatory synapses and is crucial for synapse development and plasticity. In this study, we investigated the molecular mechanisms associated with the ASD-like behaviors observed in Shank3Δ11-/- mice, in which exon 11 has been deleted. Our results indicate that Shank3 is essential to mediating metabotropic glutamate receptor 5 (mGlu5)-receptor signaling by recruiting Homer1b/c to the PSD, specifically in the striatum and cortex. Moreover, augmenting mGlu5-receptor activity by administering 3-Cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl)benzamide ameliorated the functional and behavioral defects that were observed in Shank3Δ11-/- mice, suggesting that pharmaceutical treatments that increase mGlu5 activity may represent a new approach for treating patients that are affected by PMS and SHANK3 mutations.

Phosphorylation of sodium channels mediated by protein kinase-C modulates inhibition by topiramate of tetrodotoxin-sensitive transient sodium current.

BACKGROUND AND PURPOSE: Topiramate is a novel anticonvulsant known to modulate the activity of several ligand- and voltage-gated ion channels in neurons. The mechanism of action of topiramate, at a molecular level, is still unclear, but the phosphorylation state of the channel/receptor seems to be a factor that is able to influence its activity. We investigated the consequences of phosphorylation of the sodium channel on the effect of topiramate on tetrodotoxin (TTX)-sensitive transient Na(+) current (I(NaT)). EXPERIMENTAL APPROACH: I(NaT) was recorded in dissociated neurons of rat sensorimotor cortex using whole-cell patch-clamp configuration. KEY RESULTS: We found that topiramate (100 microM) significantly shifted the steady-state I(NaT) inactivation curve in a hyperpolarized direction. In neurons pre-treated with a PKC-activator, 1-oleoyl-2-acetyl-sn-glycerol (OAG; 2 microM), the net effect of topiramate on steady-state I(NaT) inactivation was significantly decreased. In addition, OAG also slightly shifted the I(NaT) activation curve in a hyperpolarized direction, while perfusion with topiramate had no effect on the parameters of I(NaT) activation. CONCLUSIONS AND IMPLICATIONS: These data show that PKC-activation can modulate the effect of topiramate on I(NaT). This suggests that channel phosphorylation in physiological or pathological conditions (such as epiliepsy), can alter the action of topiramate on sodium currents.

Layer-specific properties of the persistent sodium current in sensorimotor cortex.

We evaluated the characteristics of the persistent sodium current (I(NaP)) in pyramidal neurons of layers II/III and V in slices of rat sensorimotor cortex using whole cell patch-clamp recordings. In both layers, I(NaP) began activating around -60 mV and was half-activated at -43 mV. The I(NaP) peak amplitude and density were significantly higher in layer V. The voltage-dependent I(NaP) steady-state inactivation occurred at potentials that were significantly more positive in layer V (V(1/2): -42.3 +/- 1.1 mV) than in layer II/III (V(1/2): -46.8 +/- 1.6 mV). In both layers, a current fraction corresponding to about 25% of the maximal peak amplitude did not inactivate. The time course of I(NaP) inactivation and recovery from inactivation could be fitted with a biexponential function. In layer V pyramidal neurons the faster time constant of development of inactivation had variable values, ranging from 158.0 to 1,133.8 ms, but it was on average significantly slower than that in layer II/III (425.9 +/- 80.5 vs. 145.8 +/- 18.2 ms). In both layers, I(NaP) did not completely inactivate even with very long conditioning depolarizations (40 s at -10 mV). Recovery from inactivation was similar in the two layers. Layer V intrinsically bursting and regular spiking nonadapting neurons showed particularly prolonged depolarized plateau potentials when Ca2+ and K+ currents were blocked and slower early phase of I(NaP) development of inactivation. The biexponential kinetics characterizing the time-dependent inactivation of I(NaP) in layers II/III and V indicates a complex inactivating process that is incomplete, allowing a residual "persistent" current fraction that does not inactivate. Moreover, our data indicate that I(NaP) has uneven inactivation properties in pyramidal neurons of different layers of rat sensorimotor cortex. The higher current density, the rightward shifted voltage dependency of inactivation as well the slower kinetics of inactivation characterizing I(NaP) in layer V with respect to layer II/III pyramidal neurons may play a significant role in their ability to fire recurrent action potential bursts, as well in the high susceptibility to generate epileptic events.