Purpose in life as a resilience factor for brain health: diffusion MRI findings from the Midlife in the U.S. study

Introduction

A greater sense of purpose in life is associated with several health benefits relevant for active aging, but the mechanisms remain unclear. We evaluated if purpose in life was associated with indices of brain health.

Methods

We examined data from the Midlife in the United States (MIDUS) Neuroscience Project. Diffusion weighted magnetic resonance imaging data (n=138; mean age 65.2 years, age range 48-95; 80 females; 37 black, indigenous, and people of color) were used to estimate microstructural indices of brain health such as axonal density, and axonal orientation. The seven-item purpose in life scale was used. Permutation analysis of linear models was used to examine associations between purpose in life scores and the diffusion metrics in white matter and in the bilateral hippocampus, adjusting for age, sex, education, and race.

Results and discussion

Greater sense of purpose in life was associated with brain microstructural features consistent with better brain health. Positive associations were found in both white matter and the right hippocampus, where multiple convergent associations were detected. The hippocampus is a brain structure involved in learning and memory that is vulnerable to stress but retains the capacity to grow and adapt through old age. Our findings suggest pathways through which an enhanced sense of purpose in life may contribute to better brain health and promote healthy aging. Since purpose in life is known to decline with age, interventions and policy changes that facilitate a greater sense of purpose may extend and improve the brain health of individuals and thus improve public health.

Midline spikes

Midline spikes are characterized by spike foci recorded at Cz, Fz, or Pz with amplitude ranging from 20 to 350 microvolts. Out of 7,929 EEGs performed at the Neurodiagnostics Laboratory, Kaiser Permanente Medical Center, Anaheim, California, between 1996 and 2006, 17 EEGs (0.21%) were identified as having interictal midline spikes with or without other epileptiform discharges. Eight EEGs showed midline spikes at Cz, 2 at Fz, 2 at Cz and Fz, 1 at Cz and C3, 1 at Cz, C3, and P3, 1 at Cz and F8, 1 at Cz and T4, and 1 at Cz with 2 Hz generalized spike and slow wave complex. Midline spikes were recorded in 10 males and 7 females. The age ranged from 4 days to 38-years-old with a mean age of 10.8 years. Twelve patients (70.6%) were children. Twelve patients (70.6%) had generalized tonic-clonic seizures and 5 had partial motor seizures. Of the 17 patients, 14 had no known causes, 1 had an agenesis of corpus callosum, 1 had a left frontal arteriovenous malformation, and 1 had a left frontal area stroke. We postulate that the mechanism for the genesis of midline spikes may be heterogeneous. Midline spikes may be triggered by thalamocortical network in a generalized tonic-clonic seizure, or may originate in the parasagittal cortex in a partial motor seizure.

Protein-protein interactions in a higher-order structure direct lambda site-specific recombination

The highly directional site-specific recombination of bacteriophage lambda is tightly regulated by the binding of three different proteins to a complex array of sites. The manner in which these reactions are both stimulated and inhibited by co-operative binding of proteins to specific sites on the P arm of attP and AttR has been elucidated by correlation of nuclease protection with recombination studies of both wild-type and mutant DNAs. In addition to co-operative forces, there is a specific competitive interaction that allows the protein-DNA complex to serve as a "biological switch". This switch does not depend upon the simple occlusion of DNA binding sites by neighboring proteins; but, rather, the outcome of this competition is dependent on long-range interactions that vary between the higher-order structures of attP and attR. These higher-order structures are dependent on cooperative interactions involving three proteins binding to five or more sites.

A spectrophotometric assay for strictosidine synthase

A spectrophotometric assay for strictosidine synthase is described. Strictosidine is extracted with ethyl acetate and, where high substrate concentrations are used, the organic extract is washed with dilute ammonia to remove coextracted secologanin; after evaporation of the solvent, the residue is heated with 5 M H2SO4 for 45 min and the A348 value is measured. Strictosidine production is calculated from the response of similarly treated standards. A minimum production of 10-25 nmol of strictosidine may be determined. The assay is demonstrated using extracts of cultured Cinchona ledgeriana cells.

Chloramphenicol acetyltransferase gene of staphylococcal plasmid pC221. Nucleotide sequence analysis and expression studies

The nucleotide sequence of the inducible chloramphenicol acetyltransferase gene (cat) of Staphylococcus aureus plasmid pC221 has been determined. The deduced primary structure for the 215 residue polypeptide (25.9 kDa) is in agreement with partial amino acid sequence data on the purified protein, previously designated as the type C variant of CAT. In common with the inducible cat elements of pC194 and B. pumilus, the 5' non-coding region of the cat of pC221 contains an inverted complementary repeat ('stem-loop' or 'hairpin') which may sequester the predicted ribosome bonding site of the mRNA. The likely transcription initiation site has been determined in vitro using purified B. subtilis RNA polymerase. Recombinant plasmids carrying the cat of pC221 on a 1156 bp TaqI fragment are expressed inefficiently in Escherichia coli, wherein induction is both poor and orientation-specific.