Long term worsening of amyloid pathology, cerebral function, and cognition after a single inoculation of beta-amyloid seeds with Osaka mutation

Alzheimer's disease (AD) is characterized by intracerebral deposition of abnormal proteinaceous assemblies made of amyloid-β (Aß) peptides or tau proteins. These peptides and proteins induce synaptic dysfunctions that are strongly correlated with cognitive decline. Intracerebral infusion of well-defined Aβ seeds from non-mutated Aβ_1-40 or Aβ_1-42 peptides can increase Aβ depositions several months after the infusion. Familial forms of AD are associated with mutations in the amyloid precursor protein (APP) that induce the production of Aβ peptides with different structures. The Aβ Osaka (Aβ_osa mutation (E693Δ)) is located within the Aβ sequence and thus the Aβ_osa peptides have different structures and properties as compared to non-mutated Aβ_1-42 peptides (Aβ_wt). Here, we wondered if a single exposure to this mutated Aβ can worsen AD pathology as well as downstream events including cognition, cerebral connectivity and synaptic health several months after the inoculation. To answer this question we inoculated Aβ_1-42-bearing Osaka mutation (Aβ_osa) in the dentate gyrus of APP_swe/PS1_dE9 mice at the age of two months. Their cognition and cerebral connectivity were analyzed at 4 months post-inoculation by behavioral evaluation and functional MRI. Aβ pathology as well as synaptic density were evaluated by histology. The impact of Aβ_osa peptides on synaptic health was also measured on primary cortical neurons. Remarkably, the intracerebral administration of Aβ_osa induced cognitive and synaptic impairments as well as a reduction of functional connectivity between different brain regions, 4 months post-inoculation. It increased Aβ plaque depositions and increased Aβ oligomers. This is the first study showing that a single, sporadic event as Aβ_osa inoculation can worsen the fate of the pathology and clinical outcome several months after the event. It suggests that a single inoculation of Aβ regulates a large cascade of events for a long time.

Induced Obsessive Compulsive Symptoms (OCS) in schizophrenia patients under Atypical 2 Antipsychotics (AAPs): review and hypotheses

The prevalence of OCS and OCD is higher in schizophrenic patients than in the general population. These disorders are sometimes induced by AAPs. There is higher frequency of OCS and greater severity in patients treated with antipsychotics with predominant anti-serotoninergic profiles opposed to those with predominant dopaminergic blockade. Induced OCS may be due to complex neuromodulation involving many serotonin, dopamine and glutamate receptors and several subtypes. Concerning connectivity, AAPs differentially influence the BOLD signal, depending on the intensity of D2 receptor blockade. The OFC could play a significant role, on account of its involvement in inhibitory control. There is a paradox: AAPs are efficient as augmentation to SSRI in treatment resistant OCD, some of them such as risperidone or aripiprazole have favourable effects in schizoptypic OCD, but AAPs cause induced OCS in schizophrenic patients. When prescribing AAPs, we should inform patients about this potential side effect and assess systematically OCS with Y-BOCS assessment after 1 month of treatment. Afterwards there are different strategies: Aripiprazole in combination can reduce OCS induced by clozapine, SSRI are slightly effective and CBT shows a few encouraging results. OCS are sometimes dose-dependent, so we also recommend prescribing the minimum effective dose and gradual introduction.

Structural and functional correlates of epileptogenesis - does gender matter?

In the majority of neuropsychiatric conditions, marked gender-based differences have been found in the epidemiology, clinical manifestations, and therapy of disease. One possible reason is that sex differences in cerebral morphology, structural and functional connections, render men and women differentially vulnerable to various disease processes. The present review addresses this issue with respect to the functional and structural correlates to some forms of epilepsy.