Midbrain and pons MRI shape analysis and its clinical and CSF correlates in degenerative parkinsonisms: a pilot study

OBJECTIVES

To conduct brainstem MRI shape analysis across neurodegenerative parkinsonisms and control subjects (CS), along with its association with clinical and cerebrospinal fluid (CSF) correlates.

METHODOLOGY

We collected demographic and clinical variables, performed planimetric and shape MRI analyses, and determined CSF neurofilament-light chain (NfL) levels in 84 participants: 11 CS, 12 with Parkinson's disease (PD), 26 with multiple system atrophy (MSA), 21 with progressive supranuclear palsy (PSP), and 14 with corticobasal degeneration (CBD).

RESULTS

MSA featured the most extensive and significant brainstem shape narrowing (that is, atrophy), mostly in the pons. CBD presented local atrophy in several small areas in the pons and midbrain compared to PD and CS. PSP presented local atrophy in small areas in the posterior and upper midbrain as well as the rostral pons compared to MSA. Our findings of planimetric MRI measurements and CSF NfL levels replicated those from previous literature. Brainstem shape atrophy correlated with worse motor state in all parkinsonisms and with higher NfL levels in MSA, PSP, and PD.

CONCLUSION

Atypical parkinsonisms present different brainstem shape patterns which correlate with clinical severity and neuronal degeneration. In MSA, shape analysis could be further explored as a potential diagnostic biomarker. By contrast, shape analysis appears to have a rather limited discriminant value in PSP.

KEY POINTS

• Atypical parkinsonisms present different brainstem shape patterns. • Shape patterns correlate with clinical severity and neuronal degeneration. • In MSA, shape analysis could be further explored as a potential diagnostic biomarker.

Chewing causes rapid changes in immunoreactive nerve patterns in rat molar teeth: Implications for dental proprioception and pain

OBJECTIVE

This study tests the hypothesis that normal use of teeth (chewing) causes changes in immunoreactive-(IR) patterns for endings of large Aβ and CGRP axons in rat molar cusps.

DESIGN

First, a new paradigm to test chewing in adult male rats was developed. Then IR patterns for large dental axons were analysed for a calcium-binding protein, parvalbumin (PV), heavy neurofilament protein-200 (NFP), and vesicle-release molecule synaptophysin (SYN) that all typify large dental axons and proprioceptors for comparison with endings of CGRP-IR neuropeptide axons. The behavior groups were: (1) daytime sleeping/fasting (Group:SF); (2) brief feeding after 8-11 h of daytime sleeping/fasting (Group:SF-C); (3) normal nocturnal feeding (Group:N); (4) nocturnal fasting (Group:NF); (5) brief feeding/chewing after nocturnal fasting (Group:NF-C).

RESULTS

Nerve endings with NFP-, PV-, or SYN-IR were lost or altered in pulp and dentin in all chewing groups. Other endings with CGRP-IR were near those with PV-, NFP- and SYN-IR at the pulp-dentin border and in dentin, and they also lost immunoreactivity in all chewing groups. The special beaded regions along the crown pulp/dentin borders lost neural labeling in all chewing groups. Nerves of molar roots and periodontal ligament were not changed.

CONCLUSIONS

Rapid neural reactions to chewing show extensive, reversible, non-nociceptive depletions of crown innervation. Those changes were rapid enough to occur during normal feeding followed by recovery during rest. The new dental paradigm related to chewing and fasting allows dissection of intradental proprioceptive-like mechanisms during normal tooth functions for comparison with nociceptive and mechanosensitive reactions after injury or inflammation.

Cerebrospinal fluid levels of glial marker YKL-40 strongly associated with axonal injury in HIV infection

BACKGROUND

HIV-1 infects the central nervous system (CNS) shortly after transmission. This leads to a chronic intrathecal immune activation. YKL-40, a biomarker that mainly reflects activation of astroglial cells, has not been thoroughly investigated in relation to HIV. The objective of our study was to characterize cerebrospinal fluid (CSF) YKL-40 in chronic HIV infection, with and without antiretroviral treatment (ART).

METHODS

YKL-40, neopterin, and the axonal marker neurofilament light protein (NFL) were analyzed with ELISA in archived CSF samples from 120 HIV-infected individuals (85 untreated neuroasymptomatic patients, 7 with HIV-associated dementia, and 28 on effective ART) and 39 HIV-negative controls.

RESULTS

CSF YKL-40 was significantly higher in patients with HIV-associated dementia compared to all other groups. It was also higher in untreated neuroasymptomatic individuals with CD4 cell count < 350 compared to controls. Significant correlations were found between CSF YKL-40 and age (r = 0.38, p < 0.001), CD4 (r = - 0.36, p < 0.001), plasma HIV RNA (r = 0.35, p < 0.001), CSF HIV RNA (r = 0.35, p < 0.001), CSF neopterin (r = 0.40, p < 0.001), albumin ratio (r = 0.44, p < 0.001), and CSF NFL (r = 0.71, p < 0.001). Age, CD4 cell count, albumin ratio, and CSF HIV RNA were found as independent predictors of CSF YKL-40 concentrations in multivariable analysis. In addition, CSF YKL-40 was revealed as a strong independent predictor of CSF NFL together with age, CSF neopterin, and CD4 cell count.

CONCLUSIONS

CSF YKL-40 is a promising biomarker candidate for understanding the pathogenesis of HIV in the CNS. The strong correlation between CSF YKL-40 and NFL suggests a pathogenic association between astroglial activation and axonal injury, and implies its utility in assessing the prognostic value of YKL-40.

Multiple complex somatosensory systems in mature rat molars defined by immunohistochemistry

OBJECTIVE

Intradental sensory receptors trigger painful sensations and unperceived mechanosensitivity, but the receptor bases for those functions are only partly defined. We present new evidence here concerning complex endings of myelinated axons in rat molars.

DESIGN

We sectioned mature rat jaws in sagittal and transverse planes to analyze neural immunoreactivity (IR) for parvalbumin, peripherin, neurofilament protein, neurotrophin receptors, synaptophysin, calcitonin gene-related peptide (CGRP), or mas-related g-protein-receptor-d (Mrgprd).

RESULTS

We found two complex sensory systems in mature rat molar dentin that labeled with neurofilament protein-IR, plus either parvalbumin-IR or peripherin-IR. The parvalbumin-IR system made extensively branched, beaded endings focused into dentin throughout each pulp horn. The peripherin-IR system primarily made unbeaded, fork-shaped dentinal endings scattered throughout crown including cervical regions. Both of these systems differed from neuropeptide CGRP-IR. In molar pulp we found peripherin- and parvalbumin-IR layered endings, either near special horizontal plexus arrays or in small coiled endings near tangled plexus, each with specific foci for specific pulp horns. Parvalbumin-IR nerve fibers had Aβ axons (5-7μm diameter), while peripherin-IR axons were thinner Aδ size (2-5μm). Mechano-nociceptive Mrgprd-IR was only found in peripherin-IR axons.

CONCLUSIONS

Complex somatosensory receptors in rat molars include two types of dentinal endings that both differ from CGRP-IR endings, and at least two newly defined types of pulpal endings. The PV-IR neurons with their widely branched, synaptophysin-rich, intradentinal beaded endings are good candidates for endodontic non-nociceptive, low threshold, unperceived mechanoreceptors. The complex molar dentinal and pulpal sensory systems were not found in rat incisors.

Neurofilament heavy chain expression and neuroplasticity in rat auditory cortex after unilateral and bilateral deafness

Deafness induces many plastic changes in the auditory neural system. For instance, dendritic changes cause synaptic changes in neural cells. SMI-32, a monoclonal antibody reveals auditory areas and recognizes non-phosphorylated epitopes on medium- and high-molecular-weight subunits of neurofilament proteins in cortical pyramidal neuron dendrites. We investigated SMI-32-immunoreactive (-ir) protein levels in the auditory cortices of rats with induced unilateral and bilateral deafness. Adult male Sprague-Dawley rats were divided into unilateral deafness (UD), bilateral deafness (BD), and control groups. Deafness was induced by cochlear ablation. All rats were sacrificed, and the auditory cortices were harvested for real-time quantitative polymerase chain reaction (RT-qPCR) and western blot analyses at 2, 4, 6, and 12 weeks after deafness was induced. Immunohistochemical staining was performed to evaluate the location of SMI-32-ir neurons. Neurofilament heavy chain (NEFH) mRNA expression and SMI-32-ir protein levels were increased in the BD group. In particular, SMI-32-ir protein levels increased significantly 6 and 12 weeks after deafness was induced. In contrast, no significant changes in protein level were detected in the right or left auditory cortices at any time point in the UD group. NEFH mRNA level decreased at 4 weeks after deafness was induced in the UD group, but recovered thereafter. Taken together, BD induced plastic changes in the auditory cortex, whereas UD did not affect the auditory neural system sufficiently to show plastic changes, as measured by neurofilament protein level.

Squid Giant Axon Contains Neurofilament Protein mRNA but does not Synthesize Neurofilament Proteins

When isolated squid giant axons are incubated in radioactive amino acids, abundant newly synthesized proteins are found in the axoplasm. These proteins are translated in the adaxonal Schwann cells and subsequently transferred into the giant axon. The question as to whether any de novo protein synthesis occurs in the giant axon itself is difficult to resolve because the small contribution of the proteins possibly synthesized intra-axonally is not easily distinguished from the large amounts of the proteins being supplied from the Schwann cells. In this paper, we reexamine this issue by studying the synthesis of endogenous neurofilament (NF) proteins in the axon. Our laboratory previously showed that NF mRNA and protein are present in the squid giant axon, but not in the surrounding adaxonal glia. Therefore, if the isolated squid axon could be shown to contain newly synthesized NF protein de novo, it could not arise from the adaxonal glia. The results of experiments in this paper show that abundant 3H-labeled NF protein is synthesized in the squid giant fiber lobe containing the giant axon's neuronal cell bodies, but despite the presence of NF mRNA in the giant axon no labeled NF protein is detected in the giant axon. This lends support to the glia-axon protein transfer hypothesis which posits that the squid giant axon obtains newly synthesized protein by Schwann cell transfer and not through intra-axonal protein synthesis, and further suggests that the NF mRNA in the axon is in a translationally repressed state.