Complementary immunohistochemical distribution of the neurofilament triplet and novel intermediate filament proteins in the autonomic and sensory nervous system of the guinea-pig

Neurofilament triplet proteins are restricted to a subset of neurons in the rat neocortex

The cellular localisation of neurofilament triplet subunits was investigated in the rat neocortex. A subset of mainly pyramidal neurons showed colocalisation of subunit immunolabelling throughout the neocortex, including labelling with the antibody SMI32, which has been used extensively in other studies of the primate cortex as a selective cellular marker. Neurofilament-labelled neurons were principally localised to two or three cell layers in most cortical regions, but dramatically reduced labelling was present in areas such as the perirhinal cortex, anterior cingulate and a strip of cortex extending from caudal motor regions through the medial parietal region to secondary visual areas. However, quantitative analysis demonstrated a similar proportion (10-20%) of cells with neurofilament triplet labelling in regions of high or low labelling. Combining retrograde tracing with immunolabelling showed that cellular content of the neurofilament proteins was not correlated with the length of projection. Double labelling immunohistochemistry demonstrated that neurofilament content in axons was closely associated with myelination. Analysis of SMI32 labelling in development indicated that content of this epitope within cell bodies was associated with relatively late maturation, between postnatal days 14 and 21. This study is further evidence of a cell type-specific regulation of neurofilament proteins within neocortical neurons. Neurofilament triplet content may be more closely related to the degree of myelination, rather than the absolute length, of the projecting axon.

Neurochemical classification of myenteric neurons in the guinea-pig ileum

A strategy has been developed to identify and quantify the different neurochemical populations of myenteric neurons in the guinea-pig ileum using double-labelling fluorescence immunohistochemistry of whole-mount preparations. First, six histochemical markers were used to identify exclusive, non-overlapping populations of nerve cell bodies. They included immunoreactivity for the calcium binding proteins calbindin and calretinin, the neuropeptides vasoactive intestinal polypeptide, substance P and somatostatin, and the amine, 5-hydroxytryptamine. The sizes of these populations of neurons were established directly or indirectly in double-labelling experiments using a marker for all nerve cell bodies. Each of these exclusive populations was further subdivided into classes by other markers, including immunoreactivity for enkephalins and neurofilament protein triplet. The size of each class was then established directly or by calculation. These distinct, neurochemically-identified classes were related to other published work on the histochemistry, electrophysiology and retrograde labelling of enteric neurons and to the simple Dogiel morphological classification. A classification scheme, consistent with previous studies, is proposed. It includes 14 distinct classes of myenteric neurons and accounts for nearly all neurons in the myenteric plexus of the guinea-pig ileum.

Regional differences in the number of neurons in the myenteric plexus of the guinea pig small intestine and colon: an evaluation of markers used to count neurons

BACKGROUND

Subsets of myenteric neurons have been identified. To determine the proportional representation of neurons in each, it is necessary to relate the number of neurons in the subset to that of the complete set. Prior estimates of total numbers of neurons, obtained with many different markers, have varied widely.

METHODS

Markers were compared for counting myenteric neurons in dissected laminar preparations of guinea pig duodenum, jejunum-ileum, and colon; the effect of stretching preparations on these counts was also determined. Markers included the visualization of single-stranded nucleic acid with cuprolinic blue and the immunocytochemical demonstration of neuron specific enolase (NSE), PGP9.5, S-100, and the constitutive expression of a Fos related antigen (FRA).

RESULTS

Neurons could not be counted accurately by demonstrating NSE, PGP9.5, or S-100. The number of neurons detected by demonstrating FRA was consistently less than that determined with cuprolinic blue (approximately 65%). Cuprolinic blue-derived estimates of neuron numbers were higher than most reported in the literature, but comparable to those recently obtained with "a nerve cell body" antiserum. Ganglionic area was found to be stretch independent. The rank order of neurons/cm2 and ganglionic area/ unit resting length was colon > duodenum >> jejunum-ileum; more neurons were found in the myenteric plexus of the colon (7.3 x 10(6)) than in that of the entire small intestine (6.5 x 10(6)).

CONCLUSIONS

Prior studies that have obtained denominators for estimating the proportions of myenteric neuronal subsets with markers that do not reveal the entire population should be re-evaluated. The guinea pig colon contains a surprisingly large number of neurons, the physiological significance of which must be determined.

Distribution of immunoreactivity for cytoskeletal (microtubule, microtubule-associated, and neurofilament) proteins in adult human dorsal root ganglia

BACKGROUND

The cytoskeleton of mature neurons consists of three main types of filamentous structures: microtubules (or neurotubules) neurofilaments and microfilaments, and of the so-called associated proteins. Neurotubules are formed by alpha- and beta-tubulin; neurofilaments are comprised of three protein subunits (68, 160, and 200 kDa of molecular weight), referred to here as neurofilament proteins (NFPs). The microtubule-associated proteins (MAPs) and tau-proteins form cross bridges between microtubules and other cytoskeletal constituents, as well as cellular organelles. This study analyzes the distribution of several cytoskeletal proteins in adult human dorsal root ganglia (DRG).

METHODS

Sections of formaldehyde-fixed, paraffin-embedded adult human DRG were processed for PAP immunohistochemistry. Mouse monoclonal antibodies against specific epitopes of alpha- and beta-tubulin, MAP-1, MAP-2, MAP-5, tau-protein, and NFPs (68, 160, and 200 kDa) were used. Furthermore, a quantitative image analysis (optic microdensitometry) was performed to establish the relationship between neuronal size and intensity of immunostaining.

RESULTS

Most of DRG neuron cell bodies displayed immunoreactivity for all assessed antibodies, with the exception of MAP2, which was absent. Nevertheless, the neuronal perikarya showed an heterogeneous pattern of immunoreactivity, which was not related to neuronal profile size. Positive immunolabelling was also observed in satellite cells and Schwann cells for microtubule and MAP1 proteins, and for tau-protein in Schwann cells.

CONCLUSIONS

Adult human primary sensory neurons in DRG express immunoreactivity for neurotubule and neurofilament proteins, as well as for some microtubule-associated proteins. However, since large heterogeneity was observed in the expression of those proteins, we conclude that the expression of cytoskeletal proteins is not a criterion to establish DRG neuronal subtypes.

Immunoreactivity for phosphorylated 200-kDa neurofilament subunit is heterogeneously expressed in human sympathetic and primary sensory neurons

This study was undertaken to investigate whether human sensory and sympathetic neurons contain phosphorylated neurofilament proteins, and whether they may be classified on the basis of this property, as in other mammalian species. The distribution of the phosphorylated 200-kDa neurofilament protein subunit (p200-NFP) was investigated in lumbar sympathetic and dorsal root ganglia by means of the RT97 monoclonal antibody (against p200-NFP). The intensity of immunostaining, and the size of neuronal body profiles were measured in order to define different neuron subclasses. In dorsal root ganglia, most of the neuronal profiles (96%) were p200-NFP immunoreactive, and the intensity of immunostaining was not related to neuronal perikarya size. In the lumbar paravertebral sympathetic ganglia, virtually all neurons displayed p200-NFP immunoreactivity, and the intensity of immunolabelling was also independent of the size of the neuronal somata. These results demonstrate heterogeneity in the expression of p200-NFP immunoreactivity in human sympathetic and sensory neurons. In contrast to other mammalian species, RT97 immunolabelling cannot be used as a discriminative marker for the two main types of human primary sensory neurons. On the other hand, our findings provide evidence for the occurrence of phosphorylated neurofilaments within peripheral neuron cell bodies.

Distribution of protein gene product 9.5 (PGP 9.5) immunoreactivity in the dorsal root ganglia of adult rat

The rat dorsal root ganglia (DRG) contain heterogeneous subpopulations of sensory neurons as demonstrated by ultrastructural, histochemical and immunohistochemical methods. In this study we investigated whether phenotypic heterogeneity occurs in the distribution of protein gene product 9.5 (PGP 9.5) in DRG neurons of adult rats by combined immunohistochemical and image analysis (neuron-size and intensity of immunostaining) techniques. Moreover, the effect of different fixatives on the expression of PGP 9.5 was analyzed. PGP 9.5 immunoreactivity (IR) was observed in all primary sensory neurons and in the axons of the ganglionic nerve fibres, but not in the satellite glial cells or Schwann cells. Data from a quantitative study demonstrated that DRG neurons displayed a homogeneous pattern of PGP 9.5 IR which was not affected by fixatives, and no correlation between neuron size and intensity of immunostaining was encountered. Thus, as reported for other neuronal and neuroendocrine cell proteins, no heterogeneity exists in the phenotypic expression of immunohistochemically demonstrable PGP 9.5 in sensory neurons of the adult rat DRG.

Neuronal intermediate filaments: new progress on an old subject

Neurofilaments (NFs) are the major intermediate filaments in most mature neurons. Genetic approaches have now proven that NFs are an essential determinant for radial growth of axons. NF phosphorylation most probably plays an important role in this function. Further, forced over-expression of NF subunits in transgenic mice yields NF misaccumulation in motor neurons and, subsequently, causes motor neuron dysfunction. This has important implications for human motor neuron diseases because similar accumulations are nearly universally found in the early stages of many motor neuron disorders.

The distribution of novel intermediate filament proteins defines subpopulations of myenteric neurons in rat intestine

BACKGROUND/AIMS

Recent studies with neurofilament antibodies as neuronal markers have shown subpopulations of myenteric neurons that do not contain neurofilament proteins. Novel neuronal intermediate filament proteins alpha-internexin, peripherin, and nestin have been identified. The aim of this study was to examine the distribution of these novel intermediate filaments in comparison with neurofilaments in myenteric plexus neurons.

METHODS

Using indirect immunofluorescence techniques in whole-mount cryostat sections from neonate and adult rat small intestine and in primary cultures of myenteric neurons, the distribution of neurofilaments, alpha-internexin, peripherin, and nestin was studied in comparison with the neuronal marker protein gene product (PGP) 9.5 in myenteric neurons.

RESULTS

Sixty-five percent of neurons contained neurofilament triplet proteins. alpha-Internexin and/or peripherin were found in the neurofilament-negative neurons. PGP 9.5 was present in 80% of the myenteric neurons. Of the neurons that were PGP negative, > 95% contained peripherin or alpha-internexin. Nestin was not found in either neonate or adult myenteric neurons but was seen in glial cells in culture.

CONCLUSIONS

The results suggest that a subpopulation of myenteric neurons lacks neurofilament triplet proteins but contains either peripherin, alpha-internexin, or both. This selective distribution of intermediate filaments in subpopulations of enteric neurons may support differential roles in these structurally unique neurons.

Substance P, neurofilament, peripherin and SSEA4 immunocytochemistry of human dorsal root ganglion neurons obtained from post-mortem tissue: a quantitative morphometric analysis

Immunocytochemical studies on lumbar dorsal root ganglia obtained at routine postmortem 24-36 h after death were carried out, and neuronal cross-sectional areas measured. The subjects were elderly (76-81 years), of both sexes, had died from heart attack or haemorrhage, and had no clinical evidence of clinical neuropathy or of disease known to be associated with neuropathy. The data were consistent between ganglia from the three subjects. There were striking similarities with data from other species. Two populations of cell profiles with overlapping size distributions were distinguished with an anti-neurofilament antibody, neurofilament-rich (45% of cell profiles) with a large mean area and neurofilament-poor with a smaller mean area. Anti-substance P and anti-peripherin antibodies both labelled a population with a small mean area, with extensive co-localization between them. There were also some differences between these human dorsal root ganglia and dorsal root ganglia from some other species. More neuronal profiles were labelled for substance P in humans (44%) than in rat (20%). More neuronal profiles were labelled for SSEA4 (stage specific embryonic antigen 4) in human (40.5%) than in rat dorsal root ganglia (10%), and the SSEA4-positive profiles were relatively smaller in human than in rat. No selective accumulation of lipofusin in profiles of large cells was apparent. This study also shows that quantitative morphometric analysis of immunocytochemically labelled dorsal root ganglion neuronal profiles can be carried out successfully on human sensory ganglia obtained at post-mortem. This is the first demonstration of the two main subgroups of dorsal root ganglia neurones with neurofilament-rich and poor somata in human tissue. The size distributions of neurons with neurofilament, substance P and peripherin are consistent with these neuronal populations having similar functional properties to those described in other species. From the known sensory and fibre loss with aging, it is speculated that the loss of some large diameter neurones with myelinated fibres and low mechanical thresholds, might account for the high percentage of neurones expressing substance P.

Alterations in neurofilament protein immunoreactivity in human hippocampal neurons related to normal aging and Alzheimer's disease

The distribution of immunoreactivity for the neurofilament triplet class of intermediate filament proteins was examined in the hippocampus of young, adult and elderly control cases and compared to that of Alzheimer's disease cases. In a similar fashion to non-human mammalian species, pyramidal neurons in the CA1 region showed a very low degree of neurofilament triplet immunoreactivity in the three younger control cases examined. However, in the other control cases of 49 years of age and older, many CA1 pyramidal neurons showed elevated neurofilament immunoreactivity. In the Alzheimer's disease cases, most of the surviving CA1 neurons showed intense labeling for the neurofilament triplet proteins, with many of these neurons giving off abnormal "sprouting" processes. Double labeling demonstrated that many of these neurons contained tangle-like or granular material that was immunoreactive for abnormal forms of tau and stained with thioflavine S, indicating that these neurons are in a transitional degenerative stage. An antibody to phosphorylated neurofilament proteins labeled a subset of neurofibrillary tangles in the Alzheimer's disease cases. However, following formic acid pre-treatment, the number of neurofibrillary tangles showing phosphorylated neurofilament protein immunoreactivity increased, with double labeling confirming that all of the tau-immunoreactive neurofibrillary tangles were also immunoreactive for phosphorylated neurofilament proteins. Immunoblotting demonstrated that there was a proportionately greater amount of the neurofilament triplet subunit proteins in hippocampal tissue from Alzheimer's disease cases as compared to controls. These results indicate that there are changes in the cytoskeleton of CA1 neurons associated with age which are likely to involve an increase in the level of neurofilament proteins and may be a predisposing factor contributing towards their high degree of vulnerability in degenerative conditions such as Alzheimer's disease. The cellular factors affecting hippocampal neurons during aging may be potentiated in Alzheimer's disease to result in even higher levels of intracellular neurofilament proteins and the progressive alterations of neurofilaments and other cytoskeletal proteins that finally results in neurofibrillary tangle formation and cellular degeneration.

A subpopulation of chicken primary sensory neurons defined by complete co-localization of peripherin-and ovalbumin-immunoreactivities

In a previous study, we have demonstrated that an ovalbumin-like antigen is present within approximately one-half of all neurons of chicken spinal ganglia. The current study demonstrates this antigen co-localizes absolutely with neural intermediate filament protein (Peripherin) in small to medium-sized neurons of spinal ganglia. While the function of ovalbumin in neurons is unknown, its precise co-localization with Peripherin suggests a functional role restricted to neurons of a defined phenotype.

Progressive transformation of the cytoskeleton associated with normal aging and Alzheimer's disease

Transitional and end-stage forms of neurofibrillary tangles associated with normal aging and Alzheimer's disease were identified using thioflavine staining combined with tau and neurofilament protein immunofluorescence. Normal aging was marked by transitional pathology in layer II of the entorhinal cortex but no neurofibrillary tangles in prefrontal cortex, whereas, in Alzheimer's disease cases, layer II entorhinal neurons had progressed to end-stage neurofibrillary tangles and the prefrontal cortex contained a high representation of transitional forms of the neurofibrillary tangle.

Subpopulations of neurons in the guinea-pig inferior mesenteric ganglia distinguished by the differential distribution of neurofilament triplet epitopes

The distribution of the neurofilament protein triplet was examined in neurochemically identified subpopulations of neurons in the guinea-pig inferior mesenteric ganglion. A majority of the catecholamine-containing nerve cell bodies also contained the neurofilament protein triplet. However, a major proportion of the noradrenergic, neuropeptide Y-immunoreactive neurons did not contain neurofilament protein triplet immunoreactivity. Furthermore, a specific subpopulation of neurons that lacked catecholamines and were associated with the hypogastric nerve could be distinguished by the unusual feature of cell body content of post-translationally modified neurofilament protein triplet epitopes. These studies indicate that neurons in the inferior mesenteric ganglia can be distinguished by the presence of specific neurofilament protein triplet epitopes, and thus this class of intermediate filament proteins may confer specific properties to the neurons in which it is contained.

Selective distribution of the 66-kDa neuronal intermediate filament protein in the sensory and autonomic nervous system of the guinea-pig

The immunohistochemical distribution of a recently identified 66-kDa neurofilament protein (NF-66) was investigated in peripheral and autonomic ganglia of the guinea-pig where it has been previously established that other neuronal intermediate filament proteins have a selective distribution. NF-66 immunoreactivity was observed in distinct subpopulations of neurons and did not coexist completely with either the neurofilament triplet or a 57-kDa intermediate filament protein (peripherin). NF-66 labelling was identical to that observed with an antibody to a 150-kDa intermediate filament or associated protein (CH1). These results further demonstrate that different neuronal intermediate filament proteins are present in selective subpopulations of neurons and that these proteins are, therefore, likely to have cell type-specific roles.

The neurofilament triplet is present in distinct subpopulations of neurons in the central nervous system of the guinea-pig

It is commonly assumed that most, if not all, neurons contain the intermediate filament protein class known as the neurofilament protein-triplet. The following study investigated the distribution of neurofilament protein-triplet immunoreactivity in selected regions of the guinea-pig central nervous system using monoclonal antibodies directed against phosphorylation-independent epitopes on the three subunits under optimal tissue processing conditions. Neurofilament protein-triplet immunoreactivity was present in distinct subpopulations of neurons in the cerebellar cortex, neocortex, hippocampal formation, retina, striatum and medulla oblongata. In many of these regions, labelled neurons represented only a small proportion of the total. The selective distribution of this intermediate filament protein class was confirmed in double-labelling experiments using antibodies to the neurofilament protein-triplet in combination with antibodies to other neuronal markers. The distribution of neurofilament protein-triplet immunoreactivity also correlated with the distribution of staining observed with a silver impregnation method based on Bielschowsky. The present results in combination with previous observations have demonstrated that the neurofilament protein-triplet is found in specific subclasses of neurons in different regions of the nervous system. Content of this intermediate filament protein class does not appear to be correlated with neuronal size or length of projection. These results also suggest that the selectivity of staining between neuronal classes observed with classical silver impregnation methods may be due to the presence or absence of the neurofilament protein-triplet. The present results may also provide a new perspective on the basis of the selective vulnerability of neurons in degenerative diseases.

A neurofilament protein antibody selectively labels a large ganglion cell type in the human retina

An antibody (SMI-32) raised against the non-phosphorylated form of the neurofilament protein triplet (NFP) revealed immunoreactivity in the soma and dendritic arborization of a group of large ganglion cells in the human retina. In addition, a population of smaller somas was also faintly labeled with this antibody in the ganglion cell layer. The completely stained cells amounted to 44,000 and were non-uniformly distributed across the retina with a peak density of 100 cells/mm2 in the retinal periphery. The soma sizes increased about two-fold and dendritic field sizes about 3-fold with retinal eccentricity. The immunoreactive dendrites branched in the vitread sublamina of the inner plexiform layer. The dendritic branching pattern of these cells indicated that they correspond to the previously described shrub cells. Antibodies against NFP and neuropeptide Y showed colocalization of these markers in all of the completely stained cells.