The Relationship Between Physical Activity and Non-Modifiable Risk Factors on Alzheimer's Disease and Brain Health Markers: A UK Biobank Study.

Background: Modifiable (physical activity) and non-modifiable (sex and genotype) risk factors interact to affect Alzheimer's disease (AD) risk. Further investigation is necessary to understand if these factors influence brain volume and cognition. Objective: The study aimed to assess the effect of physical activity, APOE genotype, and sex on AD risk, brain volume, and cognition. Methods: UK Biobank data from 2006 to 2023 was accessed. Physical activity was measured by accelerometers, and International Physical Activity Questionnaire. Outcomes were AD incidence; brain volume (ventricular cerebrospinal fluid and total brain); and cognition (executive function, memory, visuospatial ability, processing speed, and reaction time). Logistic and linear regression models were conducted. Results: 69,060 participants met inclusion criteria (mean age: 62.28 years, SD: 7.84; 54.64% female). Higher self-reported (OR = 0.63, 95% CI [0.40, 1.00], p = 0.047) and accelerometer-assessed (OR = 0.96 [0.93, 0.98], p = 0.002) physical activity was associated with lower disease incidence. Smaller ventricular cerebrospinal fluid volume (ß= - 65.43 [- 109.68, - 17.40], p = 0.007), and larger total brain volume (ß= 4398.46 [165.11, 8631.82], p <  0.001) was associated with increased accelerometer-assessed and self-reported physical activity respectively. Both brain volume analyses were moderated by sex. Increased accelerometer-assessed physical activity levels were associated with faster reaction time (ß= - 0.43 [- 0.68, - 0.18], p = 0.001); though poorer visuospatial ability (ß= - 0.06 [- 0.09, - 0.03], p <  0.001), and executive function (ß= 0.49 [0.31, 0.66], p <  0.001; ß= 0.27 [0.10, 0.45], p = 0.002) was related to self-reported physical activity levels. Conclusions: Higher levels of physical activity reduce AD risk independently of non-modifiable risk factors. Moderation of sex on brain volume highlighted the importance of incorporating non-modifiable risk factors in analysis.

Attenuation of Stimulated Accumbal Dopamine Release by NMDA Is Mediated through Metabotropic Glutamate Receptors.

Electrically stimulated dopamine release from the nucleus accumbens is attenuated following application of N-methyl-d-aspartate (NMDA), which is likely to be mediated indirectly through intermediary neuronal mechanisms rather than by a direct action on dopamine terminals. On the basis of known modulatory processes in nucleus accumbens, the current experiments sought to test whether the effect of NMDA was mediated through cholinergic, GABA-ergic, or metabotropic glutamatergic intermediate mechanisms. Fast-scan cyclic voltammetry was used to measure electrically stimulated dopamine release in nucleus accumbens of rat brain slices in vitro. Stimulated dopamine release was attenuated by NMDA, confirming previous findings, but this attenuation was unaffected by either cholinergic or GABA-ergic antagonists. However, it was completely abolished by the nonselective group I/II/III metabotropic glutamate receptor antagonist α-methyl-4-carboxyphenylglycine (MCPG) and by the selective group II antagonist LY 341396. Therefore, group II metabotropic glutamate receptors, but not acetylcholine or GABA receptors, mediate the attenuation of stimulated dopamine release caused by NMDA, probably by presynaptic inhibition through receptors located extra-synaptically on dopamine terminals. This provides a plausible mechanism for the documented role of metabotropic glutamate receptor systems in restoring deficits induced by NMDA receptor antagonists, modeling schizophrenia, underlining the potential for drugs affecting these receptors as therapeutic agents in treating schizophrenia.