Dietary nitrate supplementation and cognitive health: the nitric oxide-dependent neurovascular coupling hypothesis.

Diet is currently recognized as a major modifiable agent of human health. In particular, dietary nitrate has been increasingly explored as a strategy to modulate different physiological mechanisms with demonstrated benefits in multiple organs, including gastrointestinal, cardiovascular, metabolic, and endocrine systems. An intriguing exception in this scenario has been the brain, for which the evidence of the nitrate benefits remains controversial. Upon consumption, nitrate can undergo sequential reduction reactions in vivo to produce nitric oxide (•NO), a ubiquitous paracrine messenger that supports multiple physiological events such as vasodilation and neuromodulation. In the brain, •NO plays a key role in neurovascular coupling, a fine process associated with the dynamic regulation of cerebral blood flow matching the metabolic needs of neurons and crucial for sustaining brain function. Neurovascular coupling dysregulation has been associated with neurodegeneration and cognitive dysfunction during different pathological conditions and aging. We discuss the potential biological action of nitrate on brain health, concerning the molecular mechanisms underpinning this association, particularly via modulation of •NO-dependent neurovascular coupling. The impact of nitrate supplementation on cognitive performance was scrutinized through preclinical and clinical data, suggesting that intervention length and the health condition of the participants are determinants of the outcome. Also, it stresses the need for multimodal quantitative studies relating cellular and mechanistic approaches to function coupled with behavior clinical outputs to understand whether a mechanistic relationship between dietary nitrate and cognitive health is operative in the brain. If proven, it supports the exciting hypothesis of cognitive enhancement via diet.

Impairment of neurovascular coupling in the hippocampus due to decreased nitric oxide bioavailability supports early cognitive dysfunction in type 2 diabetic rats.

Numerous epidemiological and preclinical studies have established a strong correlation between type 2 diabetes (T2DM) and cognitive impairment and T2DM is now established as an undisputable risk factor in different forms of dementia. However, the mechanisms underlying cognitive impairment in T2DM are still not fully understood. The temporal and spatial coupling between neuronal activity and cerebral blood flow (CBF) - neurovascular coupling (NVC) - is essential for normal brain function. Neuronal-derived nitric oxide (⦁NO) produced through the nNOS-NMDAr pathway, is recognized as a key messenger in NVC, especially in the hippocampus. Of note, impaired hippocampal perfusion in T2DM patients has been closely linked to learning and memory dysfunction. In this study, we aimed to investigate the functionality of NVC, in terms of neuronal-•NO signaling and spatial memory performance, in young Goto-Kakizaki (GK) rats, a non-obese model of T2DM. For that, we performed direct and simultaneous measurements of •NO concentration dynamics and microvascular CBF changes in the hippocampus upon glutamatergic activation. We found that limited •NO bioavailability, connected to shorter and faster •NO transients in response to glutamatergic neuronal activation, is associated with decreased hemodynamic responses and a decline in spatial memory performance. This evidence supports a close mechanistic association between neuronal-triggered •NO concentration dynamics in the hippocampus, local microvascular responses, and cognitive performance in young diabetic animals, establishing the functionality of NVC as a critical early factor to consider in the cascade of events leading to cognitive decline in T2DM. These results suggest that strategies capable to overcome the limited •NO bioavailability in early stages of T2DM and maintaining a functional NVC pathway may configure pertinent therapeutic approaches to mitigate the risk for cognitive impairment in T2DM.

Dietary nitrite induces occludin nitration in the stomach.

The clinical implications of the nitrate-nitrite-nitric oxide pathway have been extensively studied in recent years. However, the physiological impact of bioactive nitrogen oxides produced from dietary nitrate has remained largely elusive. Here, we report a hitherto unrecognized nitrite-dependent nitrating pathway that targets tight junction proteins in the stomach. Inorganic nitrate, nitrite or saliva obtained after the consumption of lettuce were administered by oral gavage to Wistar rats. The enterosalivary circulation of nitrate was allowed to occur for 4 h after which the animals were euthanized and the stomach collected. Nitrated occludin was detected by immunoprecipitation in the gastric epithelium upon inorganic nitrite administration (p < .05) but was not observed in the case of inorganic nitrate or human saliva administration. This observation, along with differences in •NO production rates from inorganic and salivary nitrite under simulated gastric conditions, suggests that competing reactions at acidic pH determine the production of nitrating agents (•NO2) or other, more stable, oxides. Accordingly, it is shown in vitro that salivary nitrite yields higher steady state concentrations of •NO (0.37 ± 0.01 µM) than sodium nitrite (0.12 ± 0.03 µM). Dietary-dependent reactions involving the production of nitrogen oxides should be further investigated as, in the context of occludin nitration, the consumption of green leafy vegetables (with high nitrate content), if able to modulate gut barrier function, may have important implications in the context of leaky gut disorders.

Hallucinations and related concepts-their conceptual background.

Prior to the seventeenth century, the experiences we now name hallucinations were valued within a cultural context, they could bring meaning to the subject or the world. From mid-seventeenth to eighteenth centuries, they acquire a medical quality in mental and organic illnesses. However, the term was only fully integrated in psychiatry by Esquirol in the eighteenth-nineteenth centuries. By then, a controversy begins on whether hallucinations have a perceptual or intellectual origin. Esquirol favors the intellectual origin, describing them as an involuntary exercise of memory and imagination. By the twentieth century, some authors maintain that hallucinations are a form of delusion (Ey), while others describe them as a change in perception (Jaspers, Fish). More integrated perspectives like those proposed by Alonso Fernandez and Luque, highlights the heterogeneity of hallucinations and the multiplicity of their types and causes. The terms pseudohallucination, illusion, and hallucinosis are grafted into the concept of hallucination. Since its introduction the term pseudohallucination has been used with different meanings. The major characteristics that we found associated with pseudohallucinations were "lack of objectivity" and "presence of insight" (differing from hallucinations). Illusions are unanimously taken as distortions of real objects. Hallucinosis, first described in the context of alcohol consumption, is generally considered egodystonic, in which insight is preserved. These and other controversial aspects regarding the evolution of the term hallucination and all its derivative concepts are discussed in this paper.