Mitochondrial DNA deletions and depletion within paraspinal muscles

Aims

Although mitochondrial abnormalities have been reported within paraspinal muscles in patients with axial weakness and neuromuscular disease as well as with ageing, the basis of respiratory deficiency in paraspinal muscles is not known. This study aimed to determine the extent and basis of respiratory deficiency in paraspinal muscles from cases undergoing surgery for degenerative spinal disease and post mortem cases without a history of spinal disease, where age-related histopathological changes were previously reported.

Methods

Cervical and lumbar paraspinal muscles were obtained peri-operatively from 13 patients and from six post mortem control cases (age range 18–82 years) without a neurological disease. Sequential COX/SDH (mitochondrial respiratory chain complex IV/complex II) histochemistry was performed to identify respiratory-deficient muscle fibres (lacking complex IV with intact complex II activity). Real-time polymerase chain reaction, long-range polymerase chain reaction and sequencing were used to identify and characterize mitochondrial DNA (mtDNA) deletions and determine mtDNA copy number status. Mitochondrial respiratory chain complex subunits were detected by immunohistochemistry.

Results

The density of respiratory-deficient fibres increased with age. On average, 3.96% of fibres in paraspinal muscles were respiratory-deficient (range 0–10.26). Respiratory deficiency in 36.8% of paraspinal muscle fibres was due to clonally expanded mtDNA deletions. MtDNA depletion accounted for further 13.5% of respiratory deficiency. The profile of immunohistochemically detected subunits of complexes was similar in respiratory-deficient fibres with and without mtDNA deletions or mtDNA depletion.

Conclusions

Paraspinal muscles appeared to be particularly susceptible to age-related mitochondrial respiratory chain defects. Clonally expanded mtDNA deletions and focal mtDNA depletion may contribute towards the development of age-related postural abnormalities.

Detection of cytochrome c oxidase activity and mitochondrial proteins in single cells

Cytochrome c oxidase or mitochondrial respiratory chain complex IV is where over 90% of oxygen is consumed. The relationship between complex IV activity and mitochondrial proteins, which provides a guide to understanding the mechanisms in primary mitochondrial disorders, has been determined by histochemistry (activity) and immunohistochemistry in serial sections. In the central nervous system (CNS), mitochondrial activity and immunoreactivity have been determined in populations of cells in serial sections as capturing cells in more than one section is difficult. In this report we describe a method to determine complex IV activity in relation to mitochondrial proteins at a single cell level in the CNS. We performed complex IV histochemistry and immunohistochemistry consecutively in snap frozen sections. Although the product of complex IV histochemistry reduces the sensitivity of standard immunohistochemistry (secondary antibody and ABC method) the biotin-free Menapath polymer detection system (A. Menarini Diagnostics, Wokingham, UK) enables mitochondrial proteins to be detected following complex IV histochemistry. The co-occurring chromogens may then be separately visualised and analysed using multi-spectral imaging (Nuance system CRi, Woburn, MA). Our technique is applicable for exploring mitochondrial defects within single cells in a variety of CNS disorders and animal models of those diseases.

Differences in neuropathologic characteristics across the Lewy body dementia spectrum

BACKGROUND

The objective of this comparative neuropathologic study was to determine the extent to which dementia with Lewy bodies (DLB) and Parkinson disease dementia (PDD) are distinct entities or part of a continuum with respect to the duration of parkinsonism.

METHODS

We evaluated the relationship between cortical alpha-synuclein pathology, plaques (Consortium to Establish a Registry for Alzheimer's Disease [CERAD]), tangles (Braak staging), and cholinergic deficits (choline acetyltransferase in temporal cortex) in 57 prospectively assessed patients (29 DLB, 28 PDD), confirmed at autopsy. The PDD group was divided according to the median duration of parkinsonism prior to dementia.

RESULTS

There was an association between longer duration of parkinsonism prior to dementia and less severe cortical alpha-synuclein pathology (chi(2) 10.4, df 2, p = 0.006) and lower CERAD plaque scores (chi(2) 26.6, df 9, p = 0.002), but not Braak staging. These findings were confirmed in a further correlation analysis, which also identified an unexpected correlation between more pronounced cortical cholinergic deficits and longer duration of parkinsonism prior to dementia (R = -0.37, p = 0.04).

CONCLUSION

While there is a clear relationship between the duration of Parkinson disease prior to the onset of dementia and key neuropathologic and neurochemical characteristics, there is a gradation of these differences across the dementia with Lewy bodies/Parkinson disease dementia spectrum and the findings do not support an arbitrary cut-off between the two disorders.

Absence of cholinergic deficits in "pure" vascular dementia

Choline acetyltransferase in temporal cortex was evaluated as a marker of cholinergic function in autopsied dementia cases (9 vascular dementia [VaD] cases, 12 "mixed" VaD and Alzheimer disease [AD] cases, 10 AD cases, 12 control subjects). Patients with AD (t = 2.5, p = 0.02) and "mixed" VaD and AD (t = 3.8, p = 0.001) had greater cholinergic deficits than age-matched control subjects and patients with "pure" VaD. The absence of cholinergic deficits in "pure" VaD may be relevant to the pharmacologic treatment of these patients.

Mother's voice "buffers" separation-induced receptor changes in the prefrontal cortex of octodon degus

Although the potential vulnerability of the postnatally developing brain toward adverse environmental influences is generally recognized, relatively little is known about the basic mechanisms involved. The plasticity and adaptability of the postnatally developing brain in response to adverse emotional experiences was analyzed in the South American Octodon degus. Our study revealed that repeated brief separation from the parents and exposure to an unfamiliar environment induces an up-regulation of dopamine (D1) and 5-hydroxytrytamine (5HT1(A))-receptor density in the precentral medial, anterior cingulate, prelimbic and infralimbic cortices in female pups. No significant changes of gamma aminobutyric acid (GABA(A)) receptor density were found in deprived animals of both genders. The acoustic presence of the mother during parental separation suppressed the D1-receptor up-regulation as well as the 5-HT1(A)-receptor up-regulation, again only in the female pups. These results demonstrate that that early adverse emotional experience alters aminergic function within the prefrontal cortex in the female but not the male brain. The mother's voice, a powerful emotional signal, can protect the developing cortex from separation-induced receptor changes.