Frontiers in Neuroanatomy最新文献

In the somatosensory cortex of transgenic mice, Cre-recombinase is expressed under the control of the dopamine receptor D1 (Drd1a) promoter in lower layer 6. These neurons selectively project to the higher-order thalamic nuclei and participate in the cortico-thalamo-cortical loops involved in sensory processing and stimulus representation. However, the role of dopaminergic modulation in activating this neuronal population during cortical arousal remains poorly understood. In this study, we examined the effects of D1 (SKF-81297) and D2 (Quinpirole) receptor agonists on cortical network activation. We further investigated the consequences of silencing these neurons using a Snap25 conditional knockout mouse model. We report a decrease in cellular and neuronal density in the subplate/L6b with normal development from P8 to adulthood. Conversely, the density of Drd1a-Cre+ neurons goes up in Snap25 cKO brains when comparing the same ages. Moreover, we observe that silencing of Drd1a-Cre+ neurons has no effect on microglial cells. Our results demonstrate that both D1 and D2 agonists require the Drd1a-Cre+ neurons to modulate cortical activity effectively. Our study provides new insights into the fundamental role of Drd1a-Cre+ neurons in cortical activation and sensory processing.

Alzheimer's disease (AD) is the most common neurodegenerative disorder in the elderly. Recent efforts have centered on understanding early events that trigger AD, aiming to facilitate early diagnosis and intervention for improved patient outcomes. The traditional histopathological features observed in AD encompass the extracellular accumulation of amyloid-beta protein and the intracellular abnormal phosphorylation of Tau protein (pTau). However, elucidating how these pathological hallmarks ultimately contribute to cognitive deficits remains a complex challenge. While AD is commonly conceptualized as a disorder characterized by synaptic failure, substantial knowledge gaps persist regarding the mechanisms underlying the onset and progression of the disease, underscoring the need for novel and more effective therapeutic approaches. In this context, the impairment of GABAergic paravalbumin (PV+) neurons has been proposed as a crucial factor contributing to neuronal network dysfunction and cognitive decline in AD. The presence of pTau in pyramidal neurons is directly linked to their impairment in AD; however, the effect of pTau in PV+ neurons remains unclear. In this present study, we analyzed the existence of PV+ neurons containing pTau using immunocytochemistry in the hippocampal formation and entorhinal cortex of human samples from diagnosed AD cases and individuals without neurological or psychiatric disorders. Two pTau isoforms, pTau_AT8 and pTau_pS396, corresponding to early and late stages of AD respectively, were examined. Our findings indicate that most PV+ neurons across the hippocampal formation and entorhinal cortex did not contain pTau in either group cases. Interestingly, while AD cases diagnosed with dementia exhibited a higher number of pTau+ neurons, the majority of PV+/pTau+ neurons were found in individuals with no neurological alterations. This suggests that the presence of pTau in PV+ neurons does not directly correlate with the overall abundance of pTau+ neurons. Given that PV+ neuron impairment is a key pathogenic mechanism in AD and is associated with cognitive decline, understanding the changes in PV+ neurons during AD progression could provide critical insights into the alterations of neuronal circuits underlying the disease.

Expression of the N-methyl-D-aspartate receptor, particularly when containing the GluN2B subunit (NMDAR-GluN2B), varies across the prefrontal cortex (PFC). In humans, the subgenual cingulate cortex (SGC) contains among the highest levels of NMDAR-GluN2B expression, while the dorsolateral prefrontal cortex (dlPFC) exhibits a more moderate level of NMDAR-GluN2B expression. NMDAR-GluN2B are commonly associated with ionotropic synaptic function and plasticity and are essential to the neurotransmission underlying working memory in the macaque dlPFC in the layer III circuits, which in humans are afflicted in schizophrenia. However, NMDAR-GluN2B can also be found at extrasynaptic sites, where they may trigger distinct events, including some linked to neurodegenerative processes. The SGC is an early site of tau pathology in sporadic Alzheimer's disease (sAD), which mirrors its high NMDAR-GluN2B expression. Additionally, the SGC is hyperactive in depression, which can be treated with NMDAR antagonists. Given the clinical relevance of NMDAR in the SGC and dlPFC, the current study used immunoelectron microscopy (immunoEM) to quantitatively compare the synaptic and extrasynaptic expression patterns of NMDAR-GluN2B across excitatory and inhibitory neuron dendrites in rhesus macaque layer III SGC and dlPFC. We found a larger population of extrasynaptic NMDAR-GluN2B in dendrites of putative pyramidal neurons in SGC as compared to the dlPFC, while the dlPFC had a higher proportion of synaptic NMDAR-GluN2B. In contrast, in putative inhibitory dendrites from both areas, extrasynaptic expression of NMDAR-GluN2B was far more frequently observed over synaptic expression. These findings may provide insight into varying cortical vulnerability to alterations in excitability and neurodegenerative forces.

Julius Caesar Arantius first described the hippocampus and proposed the term hippocampum. Years later, French anatomists called the structure ram's horns, and a decade later, it was named cornu ammonis. Although both concepts were first associated with the same structure, their use has expanded to include different but related structures. This situation can make understanding and applying the terminology more difficult. The objective of this work was to determine the presence of the terms hippocampus, cornu ammonis and their variants in Terminologia Anatomica, Terminologia Neuroanatomica, and Terminologia Histologica, evaluating their congruence in said terminologies, in addition to examining the etymology of both terms. We searched Terminologia Anatomica, Terminologia Neuroanatomica, and Terminologia Histologica for terms containing the concepts hippocampus, cornu ammonis, and their derivatives. We analyzed the terms hippocampus and cornu ammonis from their etymology by examining several Latin texts. This analysis included the dissection of the hippocampus and fornix and a review of the RAT rules. The etymological analysis indicated that the hippocampus refers to a sea horse; however, the term also has a mythological background. Cornu ammonis, on the other hand, refers to the horns of an Egyptian god. The terminologies present discrepancies regarding the terms derived from hippocampus and cornu ammonis. Although both terms appear in various terminologies, they are mythonyms that fail to describe the structure they refer to or meet the requirements set by FIPAT.

Fenestration of the intracranial artery is an anatomical remnant from the embryonic development of the vascular system. A cerebral aneurysm is a focal pathological dilation of the arterial wall. The occurrence of an aneurysm at the site of fenestration is rare in cerebral circulation but may have potential clinical implications. This study aimed to identify the frequencies of fenestrations and aneurysms, their locations, and their relationships. The vasculature of 35 adult brains was used for micromorphological dissection and analysis under a stereoscopic microscope, following an arterial injection with a mixture of formaldehyde, melted gelatin, and the solution of India ink. Additionally, we analyzed another group of vascular casts obtained from 15 brains injected with methyl methacrylate (MMA). A fenestration of the M1 segment of the middle cerebral artery (MCA) was sectioned for histological analysis. We also examined computed tomography (CT) angiograms of 1,230 patients, analyzed the data, and compared the findings with anatomical observations. In our group of 50 anatomical specimens, fenestrations were found in 12 brains (24%), affecting different cerebral arteries, with three cases showing double fenestrations on the same vessel. Aneurysms were observed in six brains (12%), always one per brain, with one case (2.00%) involving an aneurysm associated with the wall of a fenestration. Analysis of CT angiograms from 1,230 patients showed 26 arterial fenestrations (2.11%) in 26 patients, 28 aneurysms (2.28%), and one case (0.08%) where an aneurysm arose from a fenestration. The presence of an aneurysm on a fenestrated cerebral artery is a rare phenomenon, occurring far less frequently than isolated fenestrations or aneurysm formation.

Resting-state networks (RSNs) have been used as biomarkers of brain diseases and cognitive performance. However, age-related changes in the RSNs of macaques, a representative animal model, are still not fully understood. In this study, we measured the RSNs in macaques aged 3-20 years and investigated the age-related changes from both functional and structural perspectives. The proportion of structural connectivity in the RSNs relative to the total fibers in the whole brain significantly decreased in aged macaques, whereas functional connectivity showed an increasing trend with age. Additionally, the amplitude of low-frequency fluctuations tended to increase with age, indicating that resting-state neural activity may be more active in the RSNs may increase with age. These results indicate that structural and functional alterations in typical RSNs are age-dependent and can be a marker of aging in the macaque's brain.

This observational, descriptive anatomical cadaveric study aimed to identify, characterize, and analyze the morphometric parameters of the filum terminale (FT) and macroscopically describe the distal insertion of the FTE. The FT is a complex, three-dimensional, fibro-cellular structure of connective tissue and glial cells, extending from the conus medullaris (CM) to the dural sac (DS) and coccyx. It is divided into two segments: an intradural filum terminale internum (FTI) and extradural filum terminale externum (FTE). Few studies have comprehensively addressed its morphometric characteristics in the last decades. Thirty-eight embalmed (M = 16, F = 22) human cadavers were examined to determine the CM-FTI and DS-FTE vertebral levels and FT, FTI, and FTE lengths and widths. FTI and FTE segmental diameters, correlations, gross characteristics, tension, and mobility in situ and ex vivo were assessed. FTE distal insertion is thoroughly described. FT, FTI, and FTE mean lengths were 254.32 mm (±26.46), 152.75 mm (±22.02), and 106.64 mm (±12.21), respectively. The CM-FTI junction was observed at the L1-L2 disk space (32.1%), DS-FTE fusion in the upper third of S2 (39.3%), and FTI-DS fusion in the DS midline (46.4%). FT length and FTI, FTE lengths were directly correlated, as were all FTI diameters. FT gross characteristics were an irregular surface (71.4%), bright hue (57.1%), macroscopic FTI-CM contrast (64.3%), filiform shape (60.7%), and movement-resistance (53.6%). The FTE exhibited a flattened shape (64.3%), immobility (60.7%), distal insertion at Cx1 (67.8%) and one distal strand (60.7%). FTI segments ≥ 2 mm were uncommon (21.4%). The FTE distal insertion is variable, inserting as strands, with vascular tissue surrounding it. A distal coccygeal venous plexus and single or multiple strand-like insertions of the distal FTE are for the first time described in detail. Discrepancies in the morphometric parameters of the FT between studies highlight the need for standardized protocols, especially given the FT's anatomic-clinical importance and potential role as a neural progenitor niche. We provide a comprehensive basis for future standardized morphometric analyses, acknowledging the limitations of embalmed cadaveric studies.

Catecholaminergic (CA) neurons of the medial extended amygdala, preoptic region and adjacent alar hypothalamus have been involved in different aspects of social behavior, as well as in modulation of homeostasis in response to different stressors. Previous data suggested that at least some CA neurons of the medial extended amygdala could originate in a hypothalamic embryonic domain that expresses the transcription factor Otp. To investigate this, we used Otp-eGFP mice (with permanent labeling of GFP in Otp cells) to analyze coexpression of GFP and tyrosine hydroxylase (TH) throughout ontogenesis by way of double immunofluorescence. Our results provide evidence that some forebrain CA cells belong to the Otp lineage. In particular, we found small subpopulations of TH cells that coexpress GFP within the medial extended amygdala, the periventricular preoptic area, the paraventricular hypothalamus, the periventricular hypothalamus, as well as some subdivisions of the basal hypothalamus. In some of the Otp cells, such as those of extended amygdala, the expression of TH appears to be transitory, in agreement with previous studies. The results open interesting questions about the role of these Otp versus non-Otp catecholaminergic subpopulations during development, network integration and in modulation of different functions, including homeostasis and social behaviors.