Selective Dysregulation of Hippocampal Inhibition in the Mouse Lacking Autism Candidate Gene CNTNAP2.

Mutations in the human gene encoding contactin-associated protein-like 2 (CNTNAP2) have been strongly associated with autism spectrum disorders (ASDs). Cntnap2(-/-) mice recapitulate major features of ASD, including social impairment, reduced vocalizations, and repetitive behavior. In addition, Cntnap2(-/-) mice show reduced cortical neuronal synchrony and develop spontaneous seizures throughout adulthood. As suggested for other forms of ASDs, this phenotype could reflect some form of synaptic dysregulation. However, the impact of lifelong deletion of CNTNAP2 on synaptic function in the brain remains unknown. To address this issue, we have assessed excitatory and inhibitory synaptic transmission in acute hippocampal slices of Cntnap2(-/-) mice. We found that although excitatory transmission was mostly normal, inhibition onto CA1 pyramidal cells was altered in Cntnap2(-/-) mice. Specifically, putative perisomatic, but not dendritic, evoked IPSCs were significantly reduced in these mice. Whereas both inhibitory short-term plasticity and miniature IPSC frequency and amplitude were normal in Cntnap2(-/-) mice, we found an unexpected increase in the frequency of spontaneous, action potential-driven IPSCs. Altered hippocampal inhibition could account for the behavioral phenotype Cntnap2(-/-) mice present later in life. Overall, our findings that Cntnap2 deletion selectively impairs perisomatic hippocampal inhibition while sparing excitation provide additional support for synaptic dysfunction as a common mechanism underlying ASDs.

Lack of galectin-3 speeds Wallerian degeneration by altering TLR and pro-inflammatory cytokine expressions in injured sciatic nerve.

Wallerian degeneration (WD) comprises a series of events that includes activation of non-neuronal cells and recruitment of immune cells, creating an inflammatory milieu that leads to extensive nerve fragmentation and subsequent clearance of the myelin debris, both of which are necessary prerequisites for effective nerve regeneration. Previously, we documented accelerated axon regeneration in animals lacking galectin-3 (Gal-3), a molecule associated with myelin clearance. To clarify the mechanisms underlying this enhanced regeneration, we focus here on the early steps of WD following sciatic nerve crush in Gal-3(-/-) mice. Using an in vivo model of nerve degeneration, we observed that removal of myelin debris is more efficient in Gal-3(-/-) than in wild-type (WT) mice; we next used an in vitro phagocytosis assay to document that the phagocytic potential of macrophages and Schwann cells was enhanced in the Gal-3(-/-) mice. Moreover, both RNA and protein levels for the pro-inflammatory cytokines IL-1ß and TNF-α, as well as for Toll-like receptor (TLR)-2 and -4, show robust increases in injured nerves from Gal-3(-/-) mice compared to those from WT mice. Collectively, these data indicate that the lack of Gal-3 results in an augmented inflammatory profile that involves the TLR-cytokine pathway, and increases the phagocytic capacity of Schwann cells and macrophages, which ultimately contributes to speeding the course of WD.

Activation of D1/D5 dopamine receptors protects neurons from synapse dysfunction induced by amyloid-beta oligomers.

Soluble oligomers of the amyloid-ß peptide (AßOs) accumulate in the brains of Alzheimer disease (AD) patients and are implicated in synapse failure and early memory loss in AD. AßOs have been shown to impact synapse function by inhibiting long term potentiation, facilitating the induction of long term depression and inducing internalization of both AMPA and NMDA glutamate receptors, critical players in plasticity mechanisms. Because activation of dopamine D1/D5 receptors plays important roles in memory circuits by increasing the insertion of AMPA and NMDA receptors at synapses, we hypothesized that selective activation of D1/D5 receptors could protect synapses from the deleterious action of AßOs. We show that SKF81297, a selective D1/D5 receptor agonist, prevented the reduction in surface levels of AMPA and NMDA receptors induced by AßOs in hippocampal neurons in culture. Protection by SKF81297 was abrogated by the specific D1/D5 antagonist, SCH23390. Levels of AMPA receptor subunit GluR1 phosphorylated at Ser(845), which regulates AMPA receptor association with the plasma membrane, were reduced in a calcineurin-dependent manner in the presence of AßOs, and treatment with SKF81297 prevented this reduction. Establishing the functional relevance of these findings, SKF81297 blocked the impairment of long term potentiation induced by AßOs in hippocampal slices. Results suggest that D1/D5 receptors may be relevant targets for development of novel pharmacological approaches to prevent synapse failure in AD.

Amyloid-beta oligomers increase the localization of prion protein at the cell surface.

In Alzheimer's disease, the amyloid-ß peptide (Aß) interacts with distinct proteins at the cell surface to interfere with synaptic communication. Recent data have implicated the prion protein (PrP(C)) as a putative receptor for Aß. We show here that Aß oligomers signal in cells in a PrP(C)-dependent manner, as might be expected if Aß oligomers use PrP(C) as a receptor. Immunofluorescence, flow cytometry and cell surface protein biotinylation experiments indicated that treatment with Aß oligomers, but not monomers, increased the localization of PrP(C) at the cell surface in cell lines. These results were reproduced in hippocampal neuronal cultures by labeling cell surface PrP(C). In order to understand possible mechanisms involved with this effect of Aß oligomers, we used live cell confocal and total internal reflection microscopy in cell lines. Aß oligomers inhibited the constitutive endocytosis of PrP(C), but we also found that after Aß oligomer-treatment PrP(C) formed more clusters at the cell surface, suggesting the possibility of multiple effects of Aß oligomers. Our experiments show for the first time that Aß oligomers signal in a PrP(C)-dependent way and that they can affect PrP(C) trafficking, increasing its localization at the cell surface.

N-methyl-D-aspartate receptors are required for synaptic targeting of Alzheimer's toxic amyloid-ß peptide oligomers.

Soluble amyloid-ß peptide (Aß) oligomers, known to accumulate in Alzheimer's disease brains, target excitatory post-synaptic terminals. This is thought to trigger synapse deterioration, a mechanism possibly underlying memory loss in early stage Alzheimer's disease. A major unknown is the identity of the receptor(s) targeted by oligomers at synapses. Because oligomers have been shown to interfere with N-methyl-d-aspartate receptor (NMDAR) function and trafficking, we hypothesized that NMDARs might be required for oligomer binding to synapses. An amplicon vector was used to knock-down NMDARs in mature hippocampal neurons in culture, yielding 90% reduction in dendritic NMDAR expression and blocking neuronal oxidative stress induced by Aß oligomers, a pathological response that has been shown to be mediated by NMDARs. Remarkably, NMDAR knock-down abolished oligomer binding to dendrites, indicating that NMDARs are required for synaptic targeting of oligomers. Nevertheless, oligomers do not appear to bind directly to NMDARs as indicated by the fact that both oligomer-attacked and non-attacked neurons exhibit similar surface levels of NMDARs. Furthermore, pre-treatment of neurons with insulin down-regulates oligomer-binding sites in the absence of a parallel reduction in surface levels of NMDARs. Establishing that NMDARs are key components of the synaptic oligomer binding complex may illuminate the development of novel approaches to prevent synapse failure triggered by Aß oligomers.

Analysis of the antinociceptive effect of the proanthocyanidin-rich fraction obtained from Croton celtidifolius barks: evidence for a role of the dopaminergic system.

In a previous study, we demonstrated the antinociceptive effect of 63SF, a proanthocyanidin-rich fraction obtained from Croton celtidifolius barks, in chemical and thermal behavioural models of pain in mice. The current study now investigate the possible mechanisms underlying the antinociceptive activity of 63SF in the formalin test, by using drugs which interfere with systems that are implicated in descending control of nociception. The antinociceptive effect of 63SF (11 mg/kg, i.p., given 30 min prior to 2.5% formalin) was not altered by pre-treatment of animals 45-50 min beforehand with either prazosin (alpha(1)-adrenergic antagonist; 0.15 mg/kg, i.p.), yohimbine (alpha(2)-adrenergic antagonist; 0.15 mg/kg, i.p.), ketanserin (5-HT(2A)-receptor antagonist; 1.0 mg/kg, i.p.), or l-arginine (substrate for NO synthase, 600 mg/kg, i.p.). On the other hand, treatment with sulpiride, an antagonist of dopaminergic D(2)-receptors (1.0 mg/kg, i.p., 45 min of pre-treatment), reversed the antinociceptive activity of 63SF. Pre-treatment of animals with reserpine (5 mg/kg, i.p., 24 h beforehand) did not alter the antinociceptive effect of 63SF. The current results support the view that the 63SF exerts antinociceptive effects by enhancing the activity of descending control, possibly by direct stimulation of dopaminergic D(2) receptors.

Involvement of 5-HT2 receptors in the antinociceptive effect of Uncaria tomentosa.

Uncaria tomentosa (Willd.) DC (Rubiaceae) is a vine that grows in the Amazon rainforest. Its bark decoctions are used by Peruvian Indians to treat several diseases. Chemically, it consists mainly of oxindole alkaloids. An industrial fraction of U. tomentosa (UT fraction), containing 95% oxindole alkaloids, was used in this study in order to characterize its antinociceptive activity in chemical (acetic acid-induced abdominal writhing, formalin and capsaicin tests) and thermal (tail-flick and hot-plate tests) models of nociception in mice. UT fraction given by the i.p. route dose-dependently suppressed the behavioural response to the chemical stimuli in the models indicated and increased latencies in the thermal stimuli models. The antinociception caused by UT fraction in the formalin test was significantly attenuated by i.p. treatment of mice with ketanserin (5-HT2 receptor antagonist), but was not affected by naltrexone (opioid receptor antagonist), atropine (a nonselective muscarinic antagonist), l-arginine (precursor of nitric oxide), prazosin (alpha1-adrenoceptor antagonist), yohimbine (alpha2-adrenoceptor antagonist), and reserpine (a monoamine depleter). Together, these results indicate that UT fraction produces dose-related antinociception in several models of chemical and thermal pain through mechanisms that involve an interaction with 5-HT2 receptors.

Antinociceptive effect of proanthocyanidins from Croton celtidifolius bark.

The chemical composition of the chromatography 63 subfraction (63SF) from the ethyl acetate soluble fraction of the crude extract of Croton celtidifolius bark presented a high content of total proanthocyanidins (75.0+/-2.3%). HPLC analysis of 63SF revealed a dimeric profile (e.g.catechin-(4alpha-->8)-catechin and gallocatechin-(4alpha-->8)-catechin) and polymeric proanthocyanidins. In pharmacological investigations, 63SF administered intraperitoneally exhibited dose-dependent antinociceptive activity against several chemical stimuli, including the intraperitoneal injection of acetic acid (ID50 (the dose of 63SF which was able to reduce the nociceptive response by 50% relative to the control value)=0.9 (0.5-1.6)) and the intraplantar injection of capsaicin (ID50=13.0 (10.0-17.0)), glutamate (ID50=4.0 (2.0-7.0)) and formalin (ID50 first phase=36.0 (24.0-53.0) and late phase=11.0 (8.0-14.0)). 63SF administered orally exhibited an antinociceptive effect in the formalin test (ID50 first phase=125.0 (89.0-177.0) and late phase=65.0 (33.0-95.0)). In the same test, 63SF was effective when given soon after the first phase, as well as exhibiting therapeutic activity. Furthermore, 63SF was effective in models of thermal nociception including tail-flick and hot-plate tests. When the mice were treated in the neonatal period with capsaicin, the antinociceptive effect of 63SF in the first phase of the formalin test was abolished, but pretreatment with naltrexone did not change the antinociceptive effect of 63SF. Together, these results provide evidence that 63SF exerted a pronounced systemic antinociception against chemical (acetic acid, formalin, glutamate and capsaicin tests) and thermal (hot-plate and tail-flick tests) nociceptive models of pain in mice at a dose that did not interfere with the locomotor activity. The mechanism by which this sub-fraction produced antinociception remains unclear, but it is unlikely to involve the activation of the opioid system. However, unmyelinated C-fibres sensitive to treatment with capsaicin are likely to participate in antinociception caused by 63SF.

A combination of Schwann-cell grafts and aerobic exercise enhances sciatic nerve regeneration.

BACKGROUND: Despite the regenerative potential of the peripheral nervous system, severe nerve lesions lead to loss of target-organ innervation, making complete functional recovery a challenge. Few studies have given attention to combining different approaches in order to accelerate the regenerative process. OBJECTIVE: Test the effectiveness of combining Schwann-cells transplantation into a biodegradable conduit, with treadmill training as a therapeutic strategy to improve the outcome of repair after mouse nerve injury. METHODS: Sciatic nerve transection was performed in adult C57BL/6 mice; the proximal and distal stumps of the nerve were sutured into the conduit. Four groups were analyzed: acellular grafts (DMEM group), Schwann cell grafts (3×105/2 µL; SC group), treadmill training (TMT group), and treadmill training and Schwann cell grafts (TMT + SC group). Locomotor function was assessed weekly by Sciatic Function Index and Global Mobility Test. Animals were anesthetized after eight weeks and dissected for morphological analysis. RESULTS: Combined therapies improved nerve regeneration, and increased the number of myelinated fibers and myelin area compared to the DMEM group. Motor recovery was accelerated in the TMT + SC group, which showed significantly better values in sciatic function index and in global mobility test than in the other groups. The TMT + SC group showed increased levels of trophic-factor expression compared to DMEM, contributing to the better functional outcome observed in the former group. The number of neurons in L4 segments was significantly higher in the SC and TMT + SC groups when compared to DMEM group. Counts of dorsal root ganglion sensory neurons revealed that TMT group had a significant increased number of neurons compared to DMEM group, while the SC and TMT + SC groups had a slight but not significant increase in the total number of motor neurons. CONCLUSION: These data provide evidence that this combination of therapeutic strategies can significantly improve functional and morphological recovery after sciatic injury.

Nicotinic receptors, amyloid-beta, and synaptic failure in Alzheimer's disease.

Dysfunctional cholinergic transmission is thought to underlie, at least in part, memory impairment and cognitive deficits in Alzheimer's disease (AD). However, it is still unclear whether this is a consequence of the loss of cholinergic neurons and elimination of nicotinic acetycholine receptors (nAChRs) in AD brain or of a direct impact of molecular interactions of the amyloid-beta (Abeta) peptide with nAChRs, leading to dysregulation of receptor function. This review examines recent progress in our understanding of the roles of nicotinic receptors in mechanisms of synaptic plasticity, molecular interactions of Abeta with nAChRs, and how Abeta-induced dysregulation of nicotinic receptor function may underlie synaptic failure in AD.