Multifactorial White Matter Damage in the Acute Phase and Pre-Existing Conditions May Drive Cognitive Dysfunction after SARS-CoV-2 Infection: Neuropathology-Based Evidence

BACKGROUND

There is an urgent need to better understand the mechanisms underlying acute and long-term neurological symptoms after COVID-19. Neuropathological studies can contribute to a better understanding of some of these mechanisms.

METHODS

We conducted a detailed postmortem neuropathological analysis of 32 patients who died due to COVID-19 during 2020 and 2021 in Austria.

RESULTS

All cases showed diffuse white matter damage with a diffuse microglial activation of a variable severity, including one case of hemorrhagic leukoencephalopathy. Some cases revealed mild inflammatory changes, including olfactory neuritis (25%), nodular brainstem encephalitis (31%), and cranial nerve neuritis (6%), which were similar to those observed in non-COVID-19 severely ill patients. One previously immunosuppressed patient developed acute herpes simplex encephalitis. Acute vascular pathologies (acute infarcts 22%, vascular thrombosis 12%, diffuse hypoxic-ischemic brain damage 40%) and pre-existing small vessel diseases (34%) were frequent findings. Moreover, silent neurodegenerative pathologies in elderly persons were common (AD neuropathologic changes 32%, age-related neuronal and glial tau pathologies 22%, Lewy bodies 9%, argyrophilic grain disease 12.5%, TDP43 pathology 6%).

CONCLUSIONS

Our results support some previous neuropathological findings of apparently multifactorial and most likely indirect brain damage in the context of SARS-CoV-2 infection rather than virus-specific damage, and they are in line with the recent experimental data on SARS-CoV-2-related diffuse white matter damage, microglial activation, and cytokine release.

Histochemical and immunohistochemical study on muscle fibers in human extraocular muscle spindles

Human extraocular muscles are unique in several ways including their endowment with proprioceptive organs. Aim of this study was to establish a classification of intrafusal muscle fibers of human extraocular muscles based on their histochemical and immunohistochemical properties and to determine their relationship to extrafusal extraocular muscle fiber types in this respect. Using light microscopy, intrafusal muscle fibers were followed on consecutive cross-sections and classified according to the localization of their myonuclei and to their enzyme- and myosin-immunohistochemical characteristics. Sixteen muscle spindles in human extraocular muscles counted as 'true' spindles revealed 27% nuclear chain fibers [40.1 microm+/-10.4; perimeter+/-SD] and 73% anomalous fibers [44.1 microm+/-12]. Seven 'false' muscle spindles showed only anomalous fibers [43.8 microm+/-11.1] and entirely lacked nuclear chain fibers. Six fiber types were distinguished according to their histochemical and myosin heavy chain immunohistochemical properties. Fiber type 1 [46.3 microm+/-13.3] was made up of fast-twitch myosin heavy chain isoform. Fiber type 2 [39.5 microm+/-10] additionally expressed a developmental myosin heavy chain isoform. Fiber type 3 [42.8 microm+/-10.4] consisted of pure slow-twitch positive muscle fibers. Slow-twitch MHC and fast-twitch myosin heavy chain isoform were found in fiber type 4 [43.3 microm+/-9]. Fiber types 5 and 6 showed different myosin heavy chain patterns than fiber types 1-4. The vast majority of nuclear chain fibers displayed fiber type 2 features, but 12% of nuclear chain fibers were found to be of fiber type 1. Among anomalous fibers in true spindles the frequency of fiber type 1 was much higher than in false spindles. On the other hand, fiber type 4 was found more often in false than in true spindles. With regard to their histochemical and immunohistochemical properties intrafusal muscle fibers in human extraocular muscles differ both from intrafusal muscle fibers in other skeletal muscles and from extrafusal muscle fibers in extraocular eye muscles. These conspicuous differences to skeletal muscle spindles relate to their morphology and myosin heavy chain characteristics. In particular, the occurrence of anomalous fibers might reflect dynamic neuronal processes and might be necessary for modulating and adapting processes in advancing age, as well as maintaining proprioceptive input during the whole life.

Twitch and nontwitch motoneuron subgroups in the oculomotor nucleus of monkeys receive different afferent projections

Motoneurons in the primate oculomotor nucleus can be divided into two categories, those supplying twitch muscle fibers and those supplying nontwitch muscle fibers. Recent studies have shown that twitch motoneurons lie within the classical oculomotor nucleus (nIII), and nontwitch motoneurons lie around the borders. Nontwitch motoneurons of medial and inferior rectus are in the C group dorsomedial to nIII, whereas those of inferior oblique and superior rectus lie near the midline are in the S group. In this anatomical study, afferents to the twitch and nontwitch subgroups of nIII have been anterogradely labeled by injections of tritiated leucine into three areas and compared. 1) Abducens nucleus injections gave rise to silver grain deposits over all medial rectus subgroups, both twitch and nontwitch. 2) Laterally placed vestibular complex injections that included the central superior vestibular nucleus labeled projections only in twitch motoneuron subgroups. However, injections into the parvocellular medial vestibular nucleus (mvp), or Y group, resulted in labeled terminals over both twitch and nontwitch motoneurons. 3) Pretectal injections that included the nucleus of the optic tract (NOT), and the olivary pretectal nucleus (OLN), labeled terminals only over nontwitch motoneurons, in the contralateral C group and in the S group. Our study demonstrates that twitch and nontwitch motoneuron subgroups do not receive identical afferent inputs. They can be controlled either in parallel, or independently, suggesting that they have basically different functions. We propose that twitch motoneurons primarily drive eye movements and nontwitch motoneurons the tonic muscle activity, as in gaze holding and vergence, possibly involving a proprioceptive feedback system.

Presence and structure of innervated myotendinous cylinders in rabbit extraocular muscle

Innervated myotendinous cylinders (IMCs) in rabbit extraocular muscles (EOMs) were identified for the first time. The nature of IMC nerve terminals was demonstrated by means of electron microscopy and double fluorescent staining. The distal EOM portions of four rabbits of different age and sex were prepared for transmission electron microscopy and for double-fluorescent labelling. Antibody against neurofilament H and alpha-bungarotoxin were applied on longitudinal cryostat sections of distal myotendinous junction. IMCs were consistently and frequently observed at the distal myotendons of each EOM. More than 30 IMCs were counted in two medial recti of a 6 month and 3 year old rabbit. IMCs were enveloped by two to three layered capsules of fibrocytes. Each IMC contained the terminal portion of one multiply-innervated muscle fibre and its corresponding tendon. The tendon compartment of an IMC was entered by a single myelinated nerve fibre (2-3 microm in diameter). Inside the IMC, this nerve fibre ramified into up to four preterminal branches. Nerve terminals exclusively established contacts with the muscle fibre at its junction with the tendon fibrils. Nerve terminals contained mitochondria and a multitude of clear vesicles. Within the synaptic cleft a basal lamina was always present. alpha-Bungarotoxin labelled the muscle side of these myoneural contacts. Nerve terminals exhibited neither age nor sex differences. Among all species so far investigated, rabbit IMCs are unique by exhibiting exclusively myoneural terminal contacts. Based on fine structure and alpha-bungarotoxin binding, myoneural contacts in rabbit IMCs are almost certainly motor, as previously observed only in human IMCs. Thus, rabbit IMCs are supposed to have a predominant effector function.

Number, distribution, and morphologic particularities of encapsulated proprioceptors in pig extraocular muscles

PURPOSE

To analyze qualitatively and quantitatively the total complement of encapsulated proprioceptors (Golgi tendon organs [GTOs] and neuromuscular spindles) in pig extraocular muscles (EOMs).

METHODS

EOMs of four pigs of different ages were prepared for light microscopic histochemical and immunohistochemical analysis and for transmission electron microscopy.

RESULTS

GTOs and muscle spindles were numerous in pig EOMs. GTOs were found to be distributed in aponeurotic expansions of the distal and proximal EOM tendons, being more numerous in the distal aponeurosis than in the proximal aponeurosis. The total number of GTOs was higher in the recti EOMs (100-128) than in the oblique EOMs (45-61). Spindles were distributed over the entire muscle length. In each EOM the number of muscle spindles (142-333) exceeded those of GTOs. The morphology of the GTOs was variable. In addition to collagen bundles, approximately one third of the GTOs contained intracapsular muscle fibers that resembled the multiply innervated fiber type. Intracapsular muscle fibers entered the poles of the GTOs and either terminated inside the receptors in collagen bundles or exited the GTOs at the opposite poles. Nerve terminals were numerous in each GTO and established intimate contacts with collagen fibrils.

CONCLUSIONS

Most structural particularities formerly observed in GTOs of rhesus monkey and sheep EOMs are also present in GTOs of pig EOMs. The high number of GTOs with their typical nerve terminals indicates functional importance. During muscle activity, afferent signals from GTOs and muscle spindles may provide sufficient information about eye position.

Detection of herpes simplex virus type 1 in human vestibular nuclei

The distribution of herpes simplex virus type 1 (HSV-1) in human geniculate, vestibular ganglia, and vestibular nuclei was determined in 10 human temporal bones and brainstems of five individuals by PCR. HSV-1 was found in 3 of 10 of each ganglia and vestibular nuclei. The various patterns of HSV-1 infection of vestibular structures are compatible with virus migration from the vestibular ganglia to the vestibular nuclei and from the ipsilateral to the contralateral vestibular nucleus via commissural fibers.

The human anterior tympanic artery. A nutrient artery of the middle ear with highly variable origin

The variability of the origin of the anterior tympanic artery was investigated in 104 individuals of both sexes. A surprising laterality was found: thus, while the left anterior tympanic artery originated as a singular vessel from either the maxillary or the superficial temporal artery with almost equal frequencies (44.7 and 45.9%, respectively), the right anterior tympanic artery predominantly branched off from the maxillary artery (77.8% of cases). Besides the origin from either the maxillary artery or the superficial temporal artery, also anterior tympanic arteries branching off from the external carotid artery were found to occur (4% on the left and 1% on the right side). Although in the majority of individuals, a singular anterior tympanic artery occurred within the infratemporal fossa, duplications of the anterior tympanic artery were found to be present: in one case on the right and in 8 cases on their left side. In 1 female individual, a triplet of left anterior tympanic arteries was found to supply the tympanic cavity. Also in these cases, the anterior tympanic artery arose from either the external carotid, the superficial temporal or the maxillary artery. In singular cases, even several other branches of the maxillary artery, viz. the deep auricular, middle, and accessory meningeal, as well as the posterior deep temporal, inferior alveolar and masseteric arteries were found to form common trunks with the anterior tympanic artery.

Muscle fiber types of human extraocular muscles: a histochemical and immunohistochemical study

PURPOSE

To classify muscle fibers of human extraocular muscle (hEOM) and to compare them to previous studies on hEOM, as well as to nonhuman EOM classification schemes and skeletal muscle fiber types.

METHODS

Muscle fibers cut in different muscle planes were followed on consecutive cross sections and typed with regard to their oxidative profile in combination with their myosin-immunohistochemical characteristics.

RESULTS

Three zones were observed. In the global layer three muscle fiber types were observed: global layer singly innervated granular fibers, 79.4 +/- 8.1 microm (perimeter [values at midmuscle region] +/- SD); 59%; global layer singly innervated coarse fibers (80.3 +/- 10.8 microm; 21%); and global layer multiply innervated muscle fibers (4.1 +/- 9.7 microm; 21%). Two muscle fiber types were detected in the orbital layer: orbital layer singly innervated muscle fibers (54.1 +/- 8.5 microm; 83%) and orbital layer multiply innervated muscle fibers (53.5 +/- 7.6 microm; 17%). Three muscle fiber types were differed in the marginal zone: marginal zone singly innervated muscle fibers (83.1 +/- 15.8 microm; 56%), marginal zone multiply innervated low oxidative muscle fibers (84.4 +/- 23.3 microm; 7%), and marginal zone multiply innervated high oxidative muscle fibers (88.4 +/- 14.5 microm; 37%). Coexpressions of developmental myosin heavy chain isoforms and fast myosin heavy chain isoform were detected mainly in the marginal zone.

CONCLUSIONS

hEOMs resemble mammalian EOM with regard to their organization. However, in addition to an inner global layer and an orbital layer an external marginal zone was described for the first time in hEOM in the present study.

Presence and morphological variability of Golgi tendon organs in the distal portion of sheep extraocular muscle

This study was undertaken to demonstrate the presence of Golgi tendon organs (GTOs) in the distal portion of sheep extraocular muscle (EOM) and to describe the morphological variability of these receptors. Extraocular muscles of a young and an old sheep were perfusion fixed and/or immersion fixed. Tissue was prepared for light microscopy and transmission electron microscopy. Immunohistochemistry was done to demonstrate the myosin pattern of the intracapsular muscle fibers of the GTOs. All GTOs in the distal portions of the sheep EOMs were located in a distinct muscle layer which was designated in a former investigation as the so-called peripheral patch layer. Each EOM of the young sheep contained GTOs; between four and 15 GTOs were counted in the rectus EOMs. Eight GTOs were found in the superior rectus of the old sheep. Golgi tendon organs in EOMs of the young and the old sheep did not differ in their morphology. In the young sheep the mean length of the GTOs was 447 +/- 132 microm (n = 60) and their mean width 101 +/- 26 microm (n = 60). In the old sheep values were 576 +/- 188 microm (mean length, n = 8) and 103 +/- 18 microm (mean width, n = 8). The GTOs were encapsulated by perineurial cells. In 12 GTOs, only collagen bundles were inside. In the remaining GTOs (56), intracapsular muscle fibers were present. Muscle fibers entered the proximal poles of the GTOs and either terminated inside the receptors or muscle fibers left the GTOs at their distal poles. These intracapsular muscle fibers were of the multiply-innervated type. In the GTOs variably shaped nerve terminals were found which contained a high number of mitochondria. In two GTOs, additionally, nerve terminals with aggregates of densely packed vesicles were present.

Prognostic significance of tumor angiogenesis in primary fallopian tube cancer

Tumor angiogenesis has been found to be prognostically significant in many types of malignant tumors. We assessed tumor vascularity in 43 cases of histologically proven primary fallopian tube cancer, FIGO stage I-IV, using the highly specific endothelial cell marker CD34. Microvessel count was determined by counting CD34-positive cells at 200 x magnification. The 5-year disease-free survival probability was 43.8% (+/- 11.5%) in 24 patients whose tumors had a microvessel count < or = 19 microvessels/field and 19.7% (+/- 9.5%) in the > 19 microvessels/field group (P = 0.046). Stage and microvessel count were statistically significant for disease-free survival in univariate analysis. Therefore, a larger sample size would be required to detect an independent and statistically significant prognostic effect of microvessel density in primary fallopian tube cancer in multivariate analysis.

Prognostic significance of tumor angiogenesis in epithelial ovarian cancer

Since angiogenesis is considered essential for tumor growth and the development of metastasis, we assessed the correlation of microvessel density (MVD) with overall survival in patients with epithelial ovarian cancer. Histologic slides were immunostained for CD34-antigen. MVD was determined within each tumor by enumeration under a light microscope at 200x magnification and an examination area of 0.25 mm2. The Cox proportional-hazards model was used for multivariate analysis. In 63 patients with epithelial ovarian cancer the 5-year survival rate (OS-%) was as follows: 55.0% (+/-12.5) in 18 patients whose tumors had an MVD < 10/field, and 23.6% (+/-6.7) in 45 patients whose tumors had an MVD(10/field (log-rank P = 0.038). MVD showed a significant influence on survival in univariate analysis, but failed to attain a significant value after adjustment for established prognostic parameters such as patients' age at diagnosis, stage of disease, and histologic grading. High MVD was significantly associated with advanced patients' age at diagnosis. This and a considerable heterogenity in the vascular architecture of ovarian carcinoma tissue might be the reasons why MVD did not reveal prognostic significance in multivariate analysis. In contrast to a variety of solid neoplasms, MVD does not seem to be a useful predictor of survival in patients with epithelial ovarian cancer.

Prognostic significance of tumor angiogenesis in endometrial cancer

OBJECTIVE

To determine the prognostic effect of intratumor microvessel density in a series of unselected patients with endometrial carcinoma.

METHODS

We reviewed 93 consecutive patients treated surgically for endometrial cancer at the University Hospital of Vienna between 1983 and 1989. Histologic sections were obtained from original paraffin-embedded blocks and stained immunohistochemically for CD34 antigen. Microvessel density was determined by enumeration of intratumor CD34-positive cells under a light microscope at 200 x magnification using an examination area of 0.74 mm2. Log-rank test and Cox proportional-hazards models (univariate and multivariate) were applied for overall survival analysis.

RESULTS

Overall, the 25% quantile of survival was reached at 37.9 months. The 5-year survival rate was 82.2% in 69 patients whose tumors had microvessel counts no more than 100/0.74 mm2 field, and 52.0% in 24 patients whose tumors had microvessel counts of more than 100/0.74 mm2 field (log-rank P = .004). In the multiple Cox model, high microvessel counts (relative risk [RR] 1.2; 95% confidence interval [CI] 1.1, 1.4) as well as undifferentiated tumors (RR 6.1; CI 2.2, 16.8), and advanced stage of disease (RR 2.6; CI 1.3, 5.1) independently exerted an adverse influence on the survival of patients with endometrial cancer.

CONCLUSION

High intratumor microvessel count is associated with poor survival of patients with endometrial cancer.

Presence and structure of innervated myotendinous cylinders in sheep extraocular muscle

Innervated myotendinous cylinders (IMCs) were for the first time described in a sheep extraocular muscle (EOMs). They were found at the distal myotendinous junction of a medial rectus and were investigated by light and transmission electron microscopy. The IMCs are enveloped by a multi-layered capsule of fibrocytes and each contains the terminal portion of one multiply-innervated muscle fibre and its corresponding tendon. The tendinous compartment of the IMC is entered by a single nerve fibre which, inside, spreads into several terminal branches. Numerous terminal branches were found among the collagen fibrils but few on the muscle fibre tips. Nerve terminals contain mitochondria and are full of clear vesicles. Within the nerve terminals, vesicles are often concentrated in an area where the axolemma exhibits dense patches. Innervated myotendinous cylinders of sheep EOMs exhibit the same ultrastructural features as those earlier described as palisade endings or myotendinous cylinders in cat, monkey and man.