Aging affects isoproterenol-induced water drinking, astrocyte density, and central neuronal activation in female Brown Norway rats

Aging pattern of the brainstem based on volumetric measurement and optimized surface shape analysis

The brainstem, a small and crucial structure, is connected to the cerebrum, spinal cord, and cerebellum, playing a vital role in regulating autonomic functions, transmitting motor and sensory information, and modulating cognitive processes, emotions, and consciousness. While previous research has indicated that changes in brainstem anatomy can serve as a biomarker for aging and neurodegenerative diseases, the structural changes that occur in the brainstem during normal aging remain unclear. This study aimed to examine the age- and sex-related differences in the global and local structural measures of the brainstem in 187 healthy adults (ranging in age from 18 to 70 years) using structural magnetic resonance imaging. The findings showed a significant negative age effect on the volume of the two major components of the brainstem: the medulla oblongata and midbrain. The shape analysis revealed that atrophy primarily occurs in specific structures, such as the pyramid, cerebral peduncle, superior and inferior colliculi. Surface area and shape analysis showed a trend of flattening in the aging brainstem. There were no significant differences between the sexes or sex-by-age interactions in brainstem structural measures. These findings provide a systematic description of age associations with brainstem structures in healthy adults and may provide a reference for future research on brain aging and neurodegenerative diseases.

Mapping internal brainstem structures using T1 and T2 weighted 3T images

Background

Many neurodegenerative diseases affect the brainstem and often do so in an early stage. The overall goal of this project was (a) to develop a method to segment internal brainstem structures from T1 and T2 weighted sequences by taking advantage of the superior myelin contrast of the T1/T2 ratio image (RATIO) and (b) to test if this approach provides biological meaningful information by investigating the effects of aging on different brainstem gray matter structures.

Methods

675 T1 and T2 weighted images were obtained from the Human Connectome Project Aging. The intensities of the T1 and T2 images were re-scaled and RATIO images calculated. The brainstem was isolated and k-means clustering used to identify five intensity clusters. Non-linear diffeomorphic mapping was used to warp the five intensity clusters in subject space into a common space to generate probabilistic group averages/priors that were used to inform the final probabilistic segmentations at the single subject level. The five clusters corresponded to five brainstem tissue types (two gray matters, two mixed gray/white, and 1 csf/tissue partial volume).

Results

These cluster maps were used to calculate Jacobian determinant maps and the mean Jacobians of 48 brainstem gray matter structures extracted. Significant linear or quadratic age effects were found for all but five structures.

Conclusions

These findings suggest that it is possible to obtain a biologically meaningful segmentation of internal brainstem structures from T1 and T2 weighted sequences using a fully automated segmentation procedure.

Thirst: neuroendocrine regulation in mammals

Animals can sense their changing internal needs and then generate specific physiological and behavioural responses in order to restore homeostasis. Water-saline homeostasis derives from balances of water and sodium intake and output (drinking and diuresis, salt appetite and natriuresis), maintaining an appropriate composition and volume of extracellular fluid. Thirst is the sensation which drives to seek and consume water, regulated in the central nervous system by both neural and chemical signals. Water and electrolyte homeostasis depends on finely tuned physiological mechanisms, mainly susceptible to plasma Na+ concentration and osmotic pressure, but also to blood volume and arterial pressure. Increases of osmotic pressure as slight as 1-2% are enough to induce thirst ("homeostatic" or cellular), by activation of specialized osmoreceptors in the circumventricular organs, outside the blood-brain barrier. Presystemic anticipatory signals (by oropharyngeal or gastrointestinal receptors) inhibit thirst when fluids are ingested, or stimulate thirst associated with food intake. Hypovolemia, arterial hypotension, Angiotensin II stimulate thirst ("hypovolemic thirst", "extracellular dehydration"). Hypervolemia, hypertension, Atrial Natriuretic Peptide inhibit thirst. Circadian rhythms of thirst are also detectable, driven by suprachiasmatic nucleus in the hypothalamus. Such homeostasis and other fundamental physiological functions (cardiocircolatory, thermoregulation, food intake) are highly interdependent.

The neuroinflammatory role of glucocerebrosidase in Parkinson's disease

The lysosomal enzyme glucocerebrosidase (GCase), encoded by the GBA1 gene, is a membrane-associated protein catalyzing the cleavage of glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph). Homologous GBA1 mutations cause Gaucher disease (GD) and heterologous mutations cause Parkinson's disease (PD). Importantly, heterologous GBA1 mutations are recognized as the second risk factor of PD. The pathological features of PD are Lewy neurites (LNs) and Lewy bodies (LBs) composed of pathological α-synuclein. Oxidative stress, inflammatory response, autophagic impairment, and α-synuclein accumulation play critical roles in PD pathogenic cascades, but the pathogenesis of PD has not yet been fully elucidated. What's more, PD treatment drugs can only relieve symptoms to a certain extent, but cannot alleviate neurodegenerative progression. Therefore, it's urgent to explore new targets that can alleviate the neurodegenerative process. Deficient GCase can cause lysosomal dysfunction, obstructing the metabolism of α-synuclein. Meanwhile, GCase dysfunction causes accumulation of its substrates, leading to lipid metabolism disorders. Subsequently, astrocytes and microglia are activated, releasing amounts of pro-inflammatory mediators and causing extensive neuroinflammation. All these cascades can induce neuron damage and death, eventually promoting PD pathology. This review aims to summarize these points and the potential of GCase as an original target to provide some ideas for elucidating the pathogenesis of PD.

Principles of Astrogliopathology

The role of astrocytes in the nervous system pathology was early on embraced by neuroscientists at end of the nineteenth and the beginning of the twentieth century, only to be pushed aside by neurone-centric dogmas during most of the twentieth century. However, the last decade of the twentieth century and the twenty-first century have brought the astroglial "renaissance", which has put astroglial cells as key players in pathophysiology of most if not all disorders of the nervous system and has regarded astroglia as a fertile ground for therapeutic intervention.Astrocytic contribution to neuropathology can be primary, whereby cell-autonomous changes, such as mutations in gene encoding for glial fibrillary acidic protein, can drive the pathologic progression, in this example, Alexander disease. They can also be secondary, when astrocytes respond to a variety of insults to the nervous tissue. Regardless of their origin, being cell-autonomous or not, changes in astroglia that occur in pathology, that is, astrogliopathology, can be contemporary and arbitrary classified into four forms: (i) reactive astrogliosis, (ii) astrocytic atrophy with loss of function, (iii) pathological remodelling of astrocytes and (iv) astrodegeneration morphologically manifested as clasmatodendrosis. Inevitably, as with any other classification, this classification of astrogliopathology awaits its revision that shall be rooted in new discoveries and concepts.

The anti-dipsogenic and anti-natriorexigenic effects of estradiol, but not the anti-pressor effect, are lost in aged female rats

Estradiol (E2) inhibits fluid intake in several species, which may help to defend fluid homeostasis by preventing excessive extracellular fluid volume. Although this phenomenon is well established using the rat model, it has only been studied directly in young adults. Because aging influences the neuronal sensitivity to E2 and the fluid intake effects of E2 are mediated in the brain, we tested the hypothesis that aging influences the fluid intake effects of E2 in female rats. To do so, we examined water and NaCl intake in addition to the pressor effect after central angiotensin II treatment in young (3-4 months), middle-aged (10-12 months), and old (16-18 months) ovariectomized rats treated with estradiol benzoate (EB). As expected, EB treatment reduced water and NaCl intake in young rats. EB treatment, however, did not reduce water intake in old rats, nor did it reduce NaCl intake in middle-aged or old rats. The ability of EB to reduce blood pressure was, in contrast, observed in all three age groups. Next, we also measured the gene expression of estrogen receptors (ERs) and the angiotensin type 1 receptor (AT1R) in the areas of the brain that control fluid balance. ERβ, G protein estrogen receptor (GPER), and AT1R were reduced in the paraventricular nucleus of the hypothalamus in middle-aged and old rats, compared to young rats. These results suggest the estrogenic control of fluid intake is modified by age. Older animals lost the fluid intake effects of E2, which correlated with decreased ER and AT1R expression in the hypothalamus.

Astroglial asthenia and loss of function, rather than reactivity, contribute to the ageing of the brain

Astroglia represent a class of heterogeneous, in form and function, cells known as astrocytes, which provide for homoeostasis and defence of the central nervous system (CNS). Ageing is associated with morphological and functional remodelling of astrocytes with a prevalence of morphological atrophy and loss of function. In particular, ageing is associated with (i) decrease in astroglial synaptic coverage, (ii) deficits in glutamate and potassium clearance, (iii) reduced astroglial synthesis of synaptogenic factors such as cholesterol, (iv) decrease in aquaporin 4 channels in astroglial endfeet with subsequent decline in the glymphatic clearance, (v) decrease in astroglial metabolic support through the lactate shuttle, (vi) dwindling adult neurogenesis resulting from diminished proliferative capacity of radial stem astrocytes, (vii) decline in the astroglial-vascular coupling and deficient blood-brain barrier and (viii) decrease in astroglial ability to mount reactive astrogliosis. Decrease in reactive capabilities of astroglia are associated with rise of age-dependent neurodegenerative diseases. Astroglial morphology and function can be influenced and improved by lifestyle interventions such as intellectual engagement, social interactions, physical exercise, caloric restriction and healthy diet. These modifications of lifestyle are paramount for cognitive longevity.

Astrocytes in the nucleus of the solitary tract: Contributions to neural circuits controlling physiology

The nucleus of the solitary tract (NTS) is the primary brainstem centre for the integration of physiological information from the periphery transmitted via the vagus nerve. In turn, the NTS feeds into downstream circuits regulating physiological parameters. Astrocytes are glial cells which have key roles in maintaining CNS tissue homeostasis and regulating neuronal communication. Recently an increasing number of studies have implicated astrocytes in the regulation of synaptic transmission and physiology. This review aims to highlight evidence for a role for astrocytes in the functions of the NTS. Astrocytes maintain and modulate NTS synaptic transmission contributing to the control of diverse physiological systems namely cardiovascular, respiratory, glucoregulatory, and gastrointestinal. In addition, it appears these cells may have a role in central control of feeding behaviour. As such these cells are a key component of signal processing and physiological control by the NTS.

Neuroglia in Ageing

Ageing reduces the functional capacity of all organs, so does that of the nervous system; the latter is evident in the reduction of cognitive abilities, learning and memory. While the exact mechanisms of ageing of the nervous system remain elusive, it is without doubt that morpho-functional changes in a variety of neuroglial cells contribute to this process. The age-dependent changes in neuroglia are characterised by a progressive loss of function. This reduces glial ability to homeostatically nurture, protect and regenerate the nervous tissue. Such neuroglial paralysis also facilitates neurodegenerative processes. Ageing of neuroglia is variable and can be affected by environmental factors and comorbidities.