A simplified and rapid procedure for in situ hybridization on human, flash-frozen, post-mortem brain and its combination with immunohistochemistry

A method to image brain tissue frozen at autopsy

Magnetic Resonance Imaging (MRI) can provide the location and signal characteristics of pathological regions within a postmortem tissue block, thereby improving the efficiency of histopathological studies. However, such postmortem-MRI guided histopathological studies have so far only been performed on fixed samples as imaging tissue frozen at the time of extraction, while preserving its integrity, is significantly more challenging. Here we describe the development of cold-postmortem-MRI, which can preserve tissue integrity and help target techniques such as transcriptomics. As a first step, RNA integrity number (RIN) was used to determine the rate of tissue biomolecular degradation in mouse brains placed at various temperatures between -20 °C and +20 °C for up to 24 h. Then, human tissue frozen at the time of autopsy was immersed in 2-methylbutane, sealed in a bio-safe tissue chamber, and cooled in the MRI using a recirculating chiller to determine MRI signal characteristics. The optimal imaging temperature, which did not show significant RIN deterioration for over 12 h, at the same time giving robust MRI signal and contrast between brain tissue types was deemed to be -7 °C. Finally, MRI was performed on human tissue blocks at this optimal imaging temperatures using a magnetization-prepared rapid gradient echo (MPRAGE, isotropic resolution between 0.3-0.4 mm) revealing good gray-white matter contrast and revealing subpial, subcortical, and deep white matter lesions. RINs measured before and after imaging revealed no significant changes (n = 3, p = 0.18, paired t-test). In addition to improving efficiency of downstream processes, imaging tissue at sub-zero temperatures may also improve our understanding of compartment specificity of MRI signal.

Postmortem MRI of Tissue Frozen at Autopsy

Introduction

Postmortem MRI provides insight into location of pathology within tissue blocks, enabling efficient targeting of histopathological studies. While postmortem imaging of fixed tissue is gaining popularity, imaging tissue frozen at the time of extraction is significantly more challenging.

Methods

Tissue integrity was examined using RNA integrity number (RIN), in mouse brains placed between -20 °C and 20 °C for up to 24 hours, to determine the highest temperature that could potentially be used for imaging without tissue degeneration. Human tissue frozen at the time of autopsy was sealed in a tissue chamber filled with 2-methylbutane to prevent contamination of the MRI components. The tissue was cooled to a range of temperatures in a 9.4T MRI using a recirculating aqueous ethylene glycol solution. MRI was performed using a magnetization-prepared rapid gradient echo (MPRAGE) sequence with inversion time of 1400 ms to null the signal from 2-methylbutane bath, isotropic resolution between 0.3-0.4 mm, and scan time of about 4 hours was used to study the anatomical details of the tissue block.

Results and Discussion

A temperature of -7 °C was chosen for imaging as it was below the highest temperature that did not show significant RIN deterioration for over 12 hours, at the same time gave robust imaging signal and contrast between brain tissue types. Imaging performed on various human tissue blocks revealed good gray-white matter contrast and revealing subpial, subcortical, and deep white matter lesions typical of multiple sclerosis enabling further spatially targeted studies.

Conclusion

Here, we describe a new method to image cold tissue, while maintaining tissue integrity and biosafety during scanning. In addition to improving efficiency of downstream processes, imaging tissue at sub-zero temperatures may also improve our understanding of compartment specificity of MRI signal.

Experimental study of different dehydration methods in the process of preparing frozen brain sections

This study aimed to provide a recommendable protocol for the preparation of brain cryosections of rats to reduce and avoid ice crystals. We have designed five different dewatering solutions (Scheme 1: dehydrate with 15%, 20%, and 30% sucrose-phosphate-buffered saline solution; Scheme 2: 20% sucrose and 30% sucrose; Scheme 3: 30% sucrose; Scheme 4: 10%, 20%, and 30% sucrose; and Scheme 5: the tissue was dehydrated with 15% and 30% sucrose polyacetate I until it sank to the bottom, followed by placement in 30% sucrose polyacetate II) to minimize the formation of ice crystals. Cryosections from different protocols were stained with Nissl staining and compared with each other by density between cells and the distance of intertissue spaces. The time required for the dehydration process from Scheme 1 to Scheme 5 was 24, 23, 24, 24, and 33 h, respectively. Density between cells gradually decreased from Scheme 1 to Scheme 5, and the distance of intertissue spaces was differentiated and irregular in different schemes according to the images of Nissl staining. We recommend the dewatering method of Scheme 4 (the brain tissues were dehydrated in 10%, 20% and 30% sucrose solution in turn until the tissue samples were completely immersed in the solution and then immersed in the next concentration solution for dehydration).

Quantitative expression and localization of GABAB receptor protein subunits in hippocampi from patients with refractory temporal lobe epilepsy

This study investigates GABA_B protein expression and mRNA levels in three types of specimens. Two types of specimens from patients with temporal lobe epilepsy (TLE), secondary to hippocampal sclerosis, sclerotic hippocampal samples (TLE-HS), and tissue from the structurally preserved non-spiking ipsilateral superior temporal gyrus (TLE-STG) removed from the same patient during epilepsy surgery; and third specimen is hippocampal tissue from individuals with no history of epilepsy (post-mortem controls, PMC). mRNA expression of GABA_B subunits was quantified in TLE-HS, TLE-STG and PMC specimens by qRT-PCR. Qualitative and quantitative Western blot (WB) and immunohistochemistry techniques were employed to quantify and localize GABA_B proteins subunits. qRT-PCR data demonstrated an overall decrease of both GABA_B1 isoforms in TLE-HS compared to TLE-STG. These results were mirrored by the WB findings. GABA_B2 mRNA and protein were significantly reduced in TLE-HS samples compared to TLE-STG; however they appeared to be upregulated in TLE-HS compared to the PMC samples. Immunohistochemistry (IHC) showed that GABA_B proteins were widely distributed in PMC and TLE-HS hippocampal sections with regional differences in the intensity of the signal. The higher expression of mature GABA_B protein in TLE-HS than PMC is in agreement with previous studies. However, these findings could be due to post-mortem changes in PMC specimens. The TLE-STG samples examined here represent a better 'control' tissue compared to TLE-HS samples characterised by lower than expected GABA_B expression. This interpretation provides a better explanation for previous functional studies suggesting reduced inhibition in TLE-HS tissue due to attenuated GABA_B currents. This article is part of the "Special Issue Dedicated to Norman G. Bowery".

Brain banking for neurological disorders

Brain banks are used to gather, store, and provide human brain tissue for research and have been fundamental to improving our knowledge of the brain in health and disease. To maintain this role, the legal and ethical issues relevant to the operations of brain banks need to be more widely understood. In recent years, researchers have reported that shortages of high-quality brain tissue samples from both healthy and diseased people have impaired their efforts. Closer collaborations between brain banks and improved strategies for brain donation programmes will be essential to overcome these problems as the demand for brain tissue increases and new research techniques become more widespread, with the potential for substantial scientific advances in increasingly common neurological disorders.

Nitric oxide production in striatum and pallidum of cirrhotic rats

Ammonium and manganese are neurotoxic agents related to brain metabolic disturbances observed after prolonged liver damage. The aim of this study was to assess the production of nitric oxide (NO) in the brain of cirrhotic rats exposed to manganese. We induced cirrhosis by bile duct ligation for 4 weeks in rats. From brain, striatum and globus pallidus were dissected out, and NO synthase activity and the content of nitrites plus nitrates (NOx) were determined. In pallidum we found a diminished constitutive NO synthase activity from cirrhotic rats, independently of manganese exposure. This result was confirmed by low levels of NOx in the same brain area (P<0.05, two-way ANOVA). This finding was not related to protein expression of NO synthase since no differences were observed in immunoblot signals between cirrhotic and sham-operated animals. Results from present study suggest that the production of NO is reduced in basal ganglia during cirrhosis.

Alteration in α-synuclein mRNA expression in Parkinson's disease

The presynaptic protein alpha-synuclein is considered to play an important role in the pathophysiology of Parkinson's disease (PD). Point mutations in the alpha-synuclein gene have been demonstrated in familial PD and alpha-synuclein is a major component of Lewy bodies, the pathological hallmark of the sporadic disease. It is not clear whether abnormal accumulation of alpha-synuclein is the result of abnormal levels of expression of the gene in neurodegenerative conditions. Expression of alpha-synuclein mRNA was therefore studied in control and PD brain using semiquantitative in situ hybridization. alpha-synuclein was expressed widely and hybridization signal was seen in most cortical regions, hippocampus, cerebellum, and brain stem. There was little mRNA in the striatum and no hybridization signal was detected in glia. High levels of alpha-synuclein mRNA expression in neurons did not seem to be a marker for Lewy body formation. Abundant signal was seen both in regions in which Lewy body deposition occurs commonly in idiopathic PD (PD), such as substantia nigra and frontal and temporal cortex, as well as in less susceptible regions, e.g. visual cortex. Quantitative comparison of mRNA expression in regions of predilection for Lewy body formation showed that mRNA expression was reduced significantly in melanized substantia nigra neurons and frontal cortex neurons in Parkinson's disease. In substantia nigra neurons there seemed to be a negative correlation between cellular mRNA expression and disease duration. These findings are in broad agreement with other studies of the expression of alpha-synuclein mRNA in human brain and suggest that Lewy body formation is unlikely to be the result of overexpression of alpha-synuclein.

Temporal and spatial expression of integrins and their extracellular matrix ligands at the maternal-fetal interface in the rhesus monkey during pregnancy

The integrin and extracellular matrix protein (ECM)-mediated adhesion and invasion of the receptive maternal uterine endometrium by trophoblasts is a critical event in the complex physiological process of pregnancy. Although the process has been largely characterized in mice, the relevant mechanism in primates remains unclear. We investigated the expression patterns and dynamic alterations of integrin subunits (alpha1, alpha5, alpha6, beta1, and beta4) and their ECM ligands, such as laminin (LN), type IV collagen (Col IV), and fibronectin (FN), at the maternal-fetal interface during Gestational Days 15, 25, 50, and 100 and at full term in 20 pregnant rhesus monkeys. Immunohistochemistry and in situ hybridization revealed that a relatively high expression of integrins occurred in trophoblast cells at Gestational Day 15, with the peak level occurring at Day 25. The expression level decreased from Day 50 to term. Along the invasive pathway, expression levels of integrin alpha1, alpha5, and beta1 subunits were gradually elevated from the proximal to distal column, reaching peak level in the trophoblast shell, but were reduced in those invasive extravillous cytotrophoblast (EVCT) cells in contact with the decidua. Integrin alpha1, alpha5, beta1, and beta4 subunits were also highly expressed in decidual stromal cells and moderately expressed in the maternal epithelium and endothelium. Immunoreactive FN, LN, and Col IV were distributed in EVCT and decidual stromal cells and part of the uterine epithelial and endothelial cells. These data suggest that the correlated expression of integrins and their ECM ligands at the maternal-fetal interface might be involved in regulation of cell proliferation and differentiation and the counterbalanced invasion-accelerating and invasion-restraining processes in trophoblast cells during the early stage of pregnancy.

Deficits in a tricarboxylic acid cycle enzyme in brains from patients with Parkinson's disease

Parkinson's disease (PD) is associated with mitochondrial dysfunction, specifically a deficiency of complex I of the electron transport chain. Most, although not all, studies indicate that this deficiency is limited to brain regions with neurodegeneration. The current studies tested for deficiencies in other mitochondrial components in PD brain in a neuropathologically unaffected region where the abnormality cannot be attributed to secondary effects of neurodegeneration. The activity of a key (and arguably rate-limiting) tricarboxylic acid cycle enzyme, the alpha-ketoglutarate dehydrogenase complex (KGDHC), was measured in the cerebellum of patients with PD. Activity in 19 PD brains was 50.5% of that in 18 controls matched for age, sex, post-mortem interval, and method of preservation (P<0.0019). The protein subunits of KGDHC were present in normal amounts in PD brains, indicating a relatively discrete abnormality in the enzyme. The activities of another mitochondrial enzyme, glutamate dehydrogenase (GDH), were normal in PD brains. These results demonstrate that specific reductions in KGDHC occur even in pathologically unaffected areas in PD, where the decline is unlikely to be a non-specific result of neurodegeneration. Reductions in the activity of this enzyme, if widespread in the brain, may predispose vulnerable regions to further damage.

Immunohistochemical identification of multipotent adult progenitor cells from human bone marrow after transplantation into the rat brain

In the immunohistochemical analysis of the brain, tissue preparation and fixation are critical steps. During our studies of transplanting human bone marrow multipotent adult progenitor cells (hMAPCs) into the rat brain, we noticed that various methods of brain tissue preparation and fixation differentially influenced antigenic preservation in the transplants and in the host brain. Here, we report a simple, effective and reproducible method of tissue preparation and fixation that results in the immunohistochemical labeling of transplanted and host cells.

GABA(B1a), GABA(B1b) AND GABA(B2) mRNA variants expression in hippocampus resected from patients with temporal lobe epilepsy

The aim of this study was to investigate the mRNA expression of the two GABA(B1) receptor isoforms and the GABA(B2) subunit, in human postmortem control hippocampal sections and in sections resected from epilepsy patients using quantitative in situ hybridisation autoradiography. Utilising human control hippocampal sections it was shown that the oligonucleotides employed were specific to the receptor. Hippocampal slices from surgical specimens obtained from patients with hippocampal sclerosis and temporal lobe epilepsy were compared with neurologically normal postmortem control subjects for neuropathology and GABA(B) mRNA expression. Neuronal loss was observed in most of the hippocampal subregions, but in the subiculum no significant difference was detected. The localisation of GABA(B1a) and GABA(B1b) isoform mRNAs in human control hippocampal sections supported and extended earlier studies using the GABA(B1) pan probe, which does not distinguish between the two GABA(B1) isoforms. Moreover, the GABA(B2) mRNA location confirmed the heterodimerisation of the receptor. Thus, although there was an apparent correlation between GABA(B1b) and GABA(B2), GABA(B1a) exhibited no such relationship. GABA(B1b) and GABA(B2) showed a similar intensity of expression whilst GABA(B1a) displayed a lower hybridisation signal. Comparison of the expression of the three mRNAs between control and epileptic subjects showed significant decreases or increases in different hippocampal subregions.GABA(B) isoforms and subunit mRNA expression per remaining neuron was significantly increased in the hilus and dentate gyrus. These results demonstrate that altered GABA(B) receptor mRNA expression occurs in human TLE; possibly the observed changes may also serve to counteract ongoing hyperexcitability.

Studies of GABA(B) receptors labelled with [(3)H]-CGP62349 in hippocampus resected from patients with temporal lobe epilepsy

1 The aim of this study was to investigate the binding of a novel GABA(B) receptor radioligand, [(3)H]-CGP62349, to human post-mortem control and epileptic hippocampal sections using quantitative receptor autoradiography. Utilizing human control hippocampal sections it was shown that [(3)H]-CGP62349 bound with high affinity (K(D) 0.5 nM) to this tissue. 2 Hippocampal slices from surgical specimens obtained from patients with hippocampal sclerosis (HS) and temporal lobe epilepsy (TLE) were compared with neurologically normal post-mortem control subjects for neuropathology and GABA(B) receptor density and affinity. Neuronal loss was observed in most of the hippocampal subregions, but in the subiculum no significant difference was detected. 3 The localization of GABA(B) receptors with the antagonist [(3)H]-CGP62349 in human control hippocampal sections supported and extended earlier studies using the agonist ligand [(3)H]-GABA. 4 The kinetics of binding to the GABA(B) receptor in human hippocampus using this novel compound was comparable to previous data obtained in rat hippocampal membranes. 5 GABA(B) receptor density (B(max)) was significantly reduced in CA3, hilus, and dentate gyrus (DG); the affinity was increased exclusively in DG. The trend is identical in all the hippocampal subregions with the agonist and the antagonist, although significant differences with the antagonist where recorded in CA3 and hilus, whereas with the agonist a significant reduction was reported in all of the hippocampal subfields. 6 GABA(B) receptor expression per remaining neuron appeared significantly increased in CA3 and hilus. These results suggest altered GABA(B) receptor function may occur in human TLE, possibly as a result of synaptic reorganization, and may contribute to epileptogenesis.

A simplified method for combined immunohistochemistry and in-situ hybridization in fresh-frozen, cryocut mouse brain sections

A method is described to perform combined immunohistochemistry and in situ hybridization in mouse brain sections. The protocol is specific to sections mounted on glass slides. In contrast to earlier methods that require either paraffin embedding or perfusion of the brain with paraformaldehyde, this protocol can be carried out on fresh-frozen, cryostat cut post-fixed sections. This simple and concise protocol increases the applicability of the technique as the RNAse-free immunodetection of antigen is useful by itself for immunologically identifying specific cells of interest and then examining gene expression in those cells using techniques such as real-time PCR and microarray analysis. The use of fresh-frozen, cryocut sections enables reliable detection of easily perturbable post-translational modifications such as phosphorylation and improves the quality of results obtained in subsequent in situ hybridization by reducing the background signal and interference from lower cell layers. Inducible transgenic mice that express either a dominant negative mutant form of the cAMP response element binding protein (mCREB) or CREB, in discrete brain regions, were used in this study. The combined immunohistochemistry and in situ hybridization protocol was used to examine colocalization of enkephalin or dynorphin mRNA, both downstream targets of CREB-mediated gene expression, in cells expressing transgenic mCREB or CREB.

Metabolic enzyme expression in dopaminergic neurons in Parkinson's disease: an in situ hybridization study

To clarify the role of neuronal complex 1 activity in idiopathic Parkinson's disease (IPD), expression of mitochondrial mRNA encoding the ND1 subunit of mitochondrial complex I was examined by semiquantitative in situ hybridization histochemistry in melanized neurons of human substantia nigra in IPD cases and control subjects. Expression of mRNA encoding the glycolytic enzyme, aldolase C, was also examined in substantia nigra and other neurons of the midbrain and brain stem. ND1 mRNA expression was strong in melanized substantia nigra neurons but undetectable in nigral glia. Levels of expression in nigral neurons were higher than in neurons of the red nucleus or cranial nerve nuclei, but similar values were obtained in pontine neurons. ND1 mRNA expression was reduced by about 25% in melanized neurons in IPD. There was no relationship between ND1 expression per cell and disease duration or L-DOPA dosage in the IPD group. No change in ND1 expression was observed in pontine neurons in IPD, and ND1 expression in the locus ceruleus was also unchanged. Melanized nigral neurons expressed lower levels of aldolase C mRNA than other midbrain or brain stem populations in both control and IPD material. These findings suggest that dopamine neurons are more strongly dependent on mitochondrial energy metabolism and oxidative phosphorylation than other brain stem populations. Because mitochondrial complex I activity is significantly reduced in IPD, intrinsically low expression of glycolytic enzymes, together with disease-related reduction in complex I activity, may be a contributory factor predisposing nigral neurons

Up-regulation of tyrosine hydroxylase mRNA in a sub-population of A10 dopamine neurons in Parkinson's disease

Neuronal injury has been consistently found in A10 midbrain dopamine neurons in Parkinson's disease (PD). To assess changes in neurotransmitter-related gene transcription, in these neurons in PD, tyrosine hydroxylase (TH) mRNA expression was examined in the ventral tegmental area (VTA) of seven PD cases and seven control subjects, using in situ hybridization histochemistry (ISHH). In controls, TH mRNA expression was found in both melanised and non-melanised neurons in the VTA. Neither population expressed dopamine beta-hydroxylase (DBH). Of the melanised neurons, 99% were TH mRNA positive. The level of the TH mRNA signal (expressed as grain density per cell) was similar in the two populations (melanised: 0.129+/-0.004 (mean+/-S.E.M.), n=142 vs. non-melanised: 0.138+/-0.006, n=89, P>0.05, Student's t-Test). In PD cases there was no significant change in TH mRNA expression in melanised neurons (0.138+/-0.003, n=196), and the proportion of positively labeled melanised neurons was 98%. However, non-melanised neurons showed significantly higher TH mRNA (0.163+/-0.006, n=87) than non-melanised neurons in control subjects (P<0.005) and melanised neurons in the PD cases (P<0.0005). This up-regulation of TH mRNA expression in non-melanised neurons may suggest the existence of a compensatory mechanism at presynaptic level.

Freeze-drying allows double nonradioactive ISH and antigenic labeling

Because tissue freeze-drying is an excellent way to preserve antigenic conformation, we have tested the feasibility of this technique to reveal nonradioactive in situ hybridization (ISH) of tissue mRNA. We have compared mRNA detection after different methods of tissue preservation, freeze-drying, cryosectioning, and formaldehyde or methanol fixation. Our results show that nonradioactive ISH is more sensitive for tissues preserved by freeze-drying than for other tissue preparations. We have demonstrated that freeze-drying allows combination of ISH and immunohistochemistry for simultaneous detection of mRNA and antigen because with this technique of tissue preservation ISH does not affect the sensitivity or the amount of the detected antigens. This work underscores the fact that tissue freeze-drying is an easy, convenient, and reliable technique for both ISH and immunohistochemistry and achieves excellent structural conditions for nonradioactive detection.

The vulnerability of nigral neurons to Parkinson's disease is unrelated to their intrinsic capacity for dopamine synthesis: an in situ hybridization study

The contribution of the dopamine-synthetic capacity of nigral neuronal subregions to their vulnerability to degeneration in idiopathic Parkinson's disease (IPD) was explored using semiquantitative in situ hybridization to study expression of mRNA encoding the rate-limiting dopamine synthetic enzyme, tyrosine hydroxylase (TH). Expression of mRNA, the structural protein, beta-tubulin, and the glycolytic enzyme, fructose-1,6, biphosphate aldolase (aldolase C) was studied in parallel in individual neurons of the substantia nigra pars compacta (SNc) in matched groups of IPD and control subjects. TH mRNA expression was found to be heterogeneously expressed in nigral neurons in control and IPD subjects. There was no significant difference in mean values for TH mRNA expression between control and IPD cases and none between nigral subregions, either in control subjects or in established IPD subjects in this study, but there was evidence for a selective upregulation of TH mRNA expression in non-melanized neurons in IPD. There was no relationship between TH mRNA expression disease duration or L-dopa dosage in the IPD group. Mean TH mRNA values for two additional 40-year-old control subjects fell within the range of values of the aged-control group. Aldolase C and beta-tubulin expression did not differ between control and IPD groups or between nigral subregions. These findings suggest that regulation of dopamine synthesis at the level of the cell body does not play a part in determining the pattern of nigral cell vulnerability in IPD. The heterogeneous pattern of TH synthesis was not age-dependent and may be of physiological significance in nigral function. There was no evidence for compensatory upregulation of TH synthesis in surviving melanized neurons in IPD but non-melanized neurons may be involved in this process. Surviving nigral neurons in IPD appear to retain the capacity for normal aldolase C and beta-tubulin peptide synthesis. Long-term L-dopa treatment does not appear to compromise normal function of nigral dopaminergic neurons.

Basal ganglia neuronal nitric oxide synthase mRNA expression in Parkinson's disease

Expression of nitric oxide synthase (NOS) mRNA in post mortem brain was studied in putamen, globus pallidus and subthalamic nucleus (STN) of neurologically normal control subjects and patients with Parkinson's disease (PD) using in situ hybridization histochemistry. In PD, a significant increase in NOS mRNA expression was observed in the dorsal two-thirds of the STN with respect to the ventral one-third of the STN. A significant increase in NOS mRNA expression per cell in the medial medullary lamina of the globus pallidus was also observed in PD. NOS mRNA expression was significantly reduced in PD putamen. These findings provide evidence of increased activity of STN neurotransmitter systems in PD and demonstrate for the first time in any species that basal ganglia nitric oxide systems can be selectively regulated in response to changes in dopaminergic input.