Persistent increases of PKMζ in memory-activated neurons trace LTP maintenance during spatial long-term memory storage.

PKMζ is an autonomously active PKC isoform crucial for the maintenance of synaptic long-term potentiation (LTP) and long-term memory. Unlike other kinases that are transiently stimulated by second messengers, PKMζ is persistently activated through sustained increases in protein expression of the kinase. Therefore, visualizing increases in PKMζ expression during long-term memory storage might reveal the sites of its persistent action and thus the location of memory-associated LTP maintenance in the brain. Using quantitative immunohistochemistry validated by the lack of staining in PKMζ-null mice, we examined the amount and distribution of PKMζ in subregions of the hippocampal formation of wild-type mice during LTP maintenance and spatial long-term memory storage. During LTP maintenance in hippocampal slices, PKMζ increases in the pyramidal cell body and stimulated dendritic layers of CA1 for at least 2 hr. During spatial memory storage, PKMζ increases in CA1 pyramidal cells for at least 1 month, paralleling the persistence of the memory. During the initial expression of the memory, we tagged principal cells with immediate-early gene Arc promoter-driven transcription of fluorescent proteins. The subset of memory-tagged CA1 cells selectively increases expression of PKMζ during memory storage, and the increase persists in dendritic compartments within stratum radiatum for 1 month, indicating long-term storage of information in the CA3-to-CA1 pathway. We conclude that persistent increases in PKMζ trace the molecular mechanism of LTP maintenance and thus the sites of information storage within brain circuitry during long-term memory.

Rheumatoid meningitis and infection in absence of rheumatoid arthritis history: review of 31 cases.

A 62-year-old healthy male presents with leg weakness and fever. Imaging revealed leptomeningeal enhancement (LE). After cerebrospinal fluid (CSF) cultures were negative, he was discharged with a diagnosis of aseptic meningitis, but was readmitted due to worsening symptoms. Brain biopsy suggested rheumatoid leptomeningitis associated with elevated serum rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibodies (ACPA). Following discharge, the New York State Department of Health (NYSDOH) reported a polymerase chain reaction (PCR) on CSF and brain DNA consistent with Naegleria fowleri (NF). After dramatic improvement on steroids, the patient declined antimicrobial treatment. Upon prednisone taper, symptoms recurred which responded to rituximab (RTX). This case highlights a possible association between rheumatoid leptomeningitis (RM) onset and infection, in a patient without a history of rheumatoid arthritis (RA). Our goal is to assess whether this association is present in 69 RM cases reported since 2000. We also describe diagnosis and treatment of 31 new cases (January 2017 to March 2020). We did not identify evidence of active/latent infection in patients with RM and previous RA; however, patients without RA history appeared to have a significantly higher rate. This finding could demonstrate the necessity of evaluating for infection in de novo RM cases without antecedent RA history. We also describe characteristic clinical patterns for each group. More studies are needed to corroborate these results and expand into a possible distinct natural history of RM in each group, which might have an impact upon the clinical outcome.