Non-phosphorylated and phosphorylated neurofilaments in the cerebellum of the rat: an immunocytochemical study using monoclonal antibodies. Development in normal and thyroid-deficient animals

The third wave: Intermediate filaments in the maturing nervous system

Intermediate filaments are critical for the extreme structural specialisations of neurons, providing integrity in dynamic environments and efficient communication along axons a metre or more in length. As neurons mature, an initial expression of nestin and vimentin gives way to the neurofilament triplet proteins and α-internexin, substituted by peripherin in axons outside the CNS, which physically consolidate axons as they elongate and find their targets. Once connection is established, these proteins are transported, assembled, stabilised and modified, structurally transforming axons and dendrites as they acquire their full function. The interaction between these neurons and myelinating glial cells optimises the structure of axons for peak functional efficiency, a property retained across their lifespan. This finely calibrated structural regulation allows the nervous system to maintain timing precision and efficient control across large distances throughout somatic growth and, in maturity, as a plasticity mechanism allowing functional adaptation.

Postnatal development of cerebellar zones revealed by neurofilament heavy chain protein expression

The cerebellum is organized into parasagittal zones that control sensory-motor behavior. Although the architecture of adult zones is well understood, very little is known about how zones emerge during development. Understanding the process of zone formation is an essential step toward unraveling how circuits are constructed to support specific behaviors. Therefore, we focused this study on postnatal development to determine the spatial and temporal changes that establish zonal patterns during circuit formation. We used a combination of wholemount and tissue section immunohistochemistry in mice to show that the cytoskeletal protein neurofilament heavy chain (NFH) is a robust marker for postnatal cerebellar zonal patterning. The patterned expression of NFH is initiated shortly after birth, and compared to the domains of several known zonal markers such as zebrin II, HSP25, neurogranin, and phospholipase Cβ4 (PLCβ4), NFH does not exhibit transient expression patterns that are typically remodeled between stages, and the adult zones do not emerge after a period of uniform expression in all lobules. Instead, we found that throughout postnatal development NFH gradually reveals distinct zones in each cerebellar lobule. The boundaries of individual NFH zones sharpen over time, as zones are refined during the second and third weeks after birth. Double labeling with neurogranin and PLCβ4 further revealed that although the postnatal expression of NFH is spatially and temporally unique, its pattern of zones respects a fundamental and well-known molecular topography in the cerebellum. The dynamics of NFH expression support the hypothesis that adult circuits are derived from an embryonic map that is refined into zones during the first 3-weeks of life.

Neurofilament heavy chain expression reveals a unique parasagittal stripe topography in the mouse cerebellum

Despite the general uniformity in cellular composition of the adult cerebellum (Cb), the expression of proteins such as ZebrinII/AldolaseC and the small heat shock protein HSP25 reveal striking patterns of parasagittal Purkinje cell (PC) stripes. Based on differences in the stripe configuration within subsets of lobules, the Cb can be further divided into four anterior-posterior transverse zones: anterior zone (AZ) = lobules I-V, central zone (CZ) = lobules VI-VII, posterior zone (PZ) = lobules VIII and anterior IX, and the nodular zone (NZ) = lobules posterior IX-X. Here we used whole-mount and tissue section immunohistochemistry to show that neurofilament heavy chain (NFH) expression alone divides all lobules of the mouse Cb into a complex series of parasagittal stripes of PCs. We revealed that the striped pattern of NFH in the vermis of the AZ and PZ was complementary to ZebrinII and phospholipase C ß3 (PLCß3), and corresponded to phospholipase C ß4 (PLCß4). In the CZ and NZ the stripe pattern of NFH was complementary to HSP25 and corresponded to PLCß3. The boundaries of the NFH stripes were not always sharply delineated. Instead, a gradual decrease in NFH expression was observed toward the edges of particular stripes, resulting in domains comprised of overlapping expression patterns. Furthermore, the terminal field distributions of mossy and climbing fibers had a complex but consistent topographical alignment with NFH stripes. In summary, NFH expression reveals an exquisite level of Cb stripe complexity that respects the transverse zone divisions and delineates an intricately patterned target field for Cb afferents.

Cerebellar basket cells of Creutzfeldt-Jakob disease: immunohistochemical and ultrastructural study

To elucidate possible abnormalities of cerebellar basket cells of Creutzfeldt-Jakob disease (CJD), seven sporadic cases were examined neuropathologically. Recently, parvalbumin-positive, GABAergic cerebral interneurons have been demonstrated to show early, selective loss in CJD, and the phenomenon is postulated as a cause of characteristic neurological symptoms of CJD. In this study, however, we demonstrated that the basket cells, cerebellar counterparts, were resistant even in patients with severe brain atrophy, and their processes showed intense argyrophilia and immunopositivity to phosphorylated neurofilament. They can newly be listed as CJD-resistant neurons similar to those of the hippocampus and brainstem nuclei. The mechanism to escape cell loss is of great interest, and there might be unknown factors modulating susceptibility within parvalbumin-positive neuronal subgroups. Furthermore, one case showed abnormal positivity with hematoxylin, crystal violet and pyronin in the basket cells. The pyronin positivity was reduced after ribonuclease digestion, suggesting that the causative substance was composed of RNA. Ultrastructurally, the fibers contained free ribosomes and amorphous electron-dense deposits. To our knowledge, such a finding has also not been previously reported.

Postnatal expressions of non-phosphorylated and phosphorylated neurofilament proteins in the rat hippocampus and the Timm-stained mossy fiber pathway

Neurofilament proteins (NFPs), the cytoskeletal proteins that are essential for axogenesis and maintenance of neuron shape in the nervous system, were studied for their spatial distributions at nine postnatal days (PN 3, 5, 7, 10, 14, 17, 21, 28, and 120). Simultaneously non-phosphorylated (SMI-32; 150/200 kDa; Sternberger) and phosphorylated (SMI-31; 200 kDa) NFP immunoreactivity in the entire developing rat hippocampus was studied, quantified, and compared to that of mossy fiber (MF) axons and terminals using Neo-Timm's histochemistry, the most selective, sensitive, and reproducible technique. Differential developmental expressions were observed between the two NFP states. SMI-32 was initially expressed on PN 3 only in the perikarya of pyramidal neurons in CA3. As early as PN 5, SMI-31 appeared in the MF pathway, in parallel to the growth of MF axons. By contrast, SMI-32 did not appear at any age in the MF pathway, including the MF terminal zone of stratum lucidum. At PN 14, the distribution of both NFPs in the MF system (MFs and their target neurons, i.e., CA3/CA4 pyramidal neurons and hilar neurons) was nearly complete; however, the peak densities of SMI-32 and SMI-31 were later at PN 21 and statistically equal to the most adult level (PN 120). The temporal regulation and maximal levels of SMI-32 and SMI-31 expressions on MF target neurons (CA3: SMI-32) and in the MF terminal zone (stratum lucidum: SMI-31) were nearly parallel to the progressive and rapid PN growth of the MF axons and terminals occurring between PN 14 and PN 17, suggesting that the mechanisms for maturation of MF synaptogenesis occur after PN 17.

Changes in the cerebellar cortex of hairless Rhino-J mice (hr-rh-j)

A mutation in the hr gene is responsible for typical epithelium phenotype in hairless mice. As this gene is expressed at high levels not only in the skin but also in the brain, the aim of the study was to clarify its role in the central nervous system. We have analyzed by morphological and immunocytochemical methods (calbindin D-28k, phosphorylated and 200 kDa neurofilament protein) the cerebellum of a mutated mouse strain, the hairless (hr-rh-j) type carrying the homozygous hr gene rhino mutation. The cerebellar cortex was studied in young (3 months) and adult (9 months) wild type and mutated mice. No major structural change was found in any of the groups and neuronal density or neuronal arrangement were similar in mutated animals to their age-matched controls. Nevertheless there were changes in shape and size of the Purkinje neurons in the old mutated animals respect to their normal littermates, while the molecular and the granule cell layers were apparently invariable. Calbindin (CB) immunohistochemistry revealed a significant decrease in the expression of this protein in the Purkinje cells of the aged mutated mice. Immunohistochemistry for a neurofilament protein (NFP) showed a reduction of staining in all the cerebellar cortex layers in the older animals, which was much more evident in the (hr-rh-j) mutated mice. These results suggest that hr gene is involved in the structural maintenance of the mature cerebellar cortex, rather than in the development. Our findings may also be consistent with an accelerated aging of the central nervous system in rh-rh-j mice.

Differential expression and modification of neurofilament triplet proteins during cat cerebellar development

Neurofilament (NF) proteins consist of three subunits of different molecular weights defined as NF-H, NF-M, and NF-L. They are typical structures of the neuronal cytoskeleton. Their immunocytochemical distribution during postnatal development of cat cerebellum was studied with several monoclonal and polyclonal antibodies against phosphorylated or unmodified sites. Expression and distribution of the triplet neurofilament proteins changed with maturation. Afferent mossy and climbing fibers in the medullary layer contained NF-M and NF-L already at birth, whereas NF-H appeared later. Within the first three postnatal weeks, all three subunits appeared in mossy and climbing fibers in the internal granular and molecular layers and in the axons of Purkinje cells. Axons of local circuit neurons such as basket cells expressed these proteins at the end of the first month, whereas parallel fibers expressed them last, at the beginning of the third postnatal month. Differential localization was especially observed for NF-H. Depending on phosphorylation, NF-H proteins were found in different axon types in climbing, mossy, and basket fibers or additionally in parallel fibers. A nonphosphorylated NF-H subunit was exclusively located in some Purkinje cells at early developmental stages and in some smaller interneurons later. A novel finding is the presence of a phosphorylation site in the NF-H subunit that is localized in dendrites of Purkinje cells but not in axons. Expression and phosphorylation of the NF-H subunit, especially, is cell-type specific and possibly involved in the adult-type stabilization of the axonal and dendritic cytoskeleton.

Biology of the congenitally hypothyroid hyt/hyt mouse

The hyt/hyt mouse has an autosomal recessive, fetal onset, characterized by severe hypothyroidism that persists throughout life and is a reliable model of human sporadic congenital hypothyroidism. The hypothyroidism in the hyt/hyt mouse reflects the hyporesponsiveness of the thyroid gland to thyrotropin (TSH). This is attributable to a point mutation of C to T at nucleotide position 1666, resulting in the replacement of a Pro with Leu at position 556 in transmembrane domain IV of the G protein-linked TSH receptor. This mutation leads to a reduction in all cAMP-regulated events, including thyroid hormone synthesis. The diminution in T3/T4 in serum and other organs, including the brain, also leads to alterations in the level and timing of expression of critical brain molecules, i.e. selected tubulin isoforms (M beta 5, M beta 2, and M alpha 1), microtubule associated proteins (MAPs), and myelin basic protein, as well as to changes in important neuronal cytoskeletal events, i.e. microtubule assembly and SCa and SCb axonal transport. In the hyt/hyt mouse, fetal hypothyroidism leads to reductions in M beta 5, M beta 2, and M alpha 1 mRNAs, important tubulin isoforms, and M beta 5 and M beta 2 proteins, which comprise the microtubules. These molecules are localized to layer V pyramidal neurons in the sensorimotor cortex, a site of differentiating neurons, as well as a site for localization of specific thyroid hormone receptors. These molecular abnormalities in specific cells and at specific times of development or maturation may contribute to the observed neuroanatomical abnormalities, i.e. altered neuronal process growth and maintenance, synaptogenesis, and myelination, in hypothyroid brain. Abnormal neuroanatomical development in selected brain regions may be the factor underlying the abnormalities in reflexive, locomotor, and adaptive behavior seen in the hyt/hyt mouse and other hypothyroid animals.

Phosphorylated and non-phosphorylated neurofilament proteins: distribution in the rat hippocampus and early changes after kainic acid induced seizures

The regional distribution of neurofilament proteins in the rat hippocampus and their early changes after kainic acid induced seizures were investigated immunocytochemically with antibodies against light weight neurofilament, phosphorylated and non-phosphorylated heavy weight neurofilament. The light weight and non-phosphorylated heavy weight neurofilaments were distributed more unevenly than the phosphorylated neurofilament. The perikarya and processes of pyramidal cells in the CA3 field contained the highest light weight and non-phosphorylated heavy weight neurofilaments, while the perikarya of granule cells contained only few light weight neurofilament and the perikarya of CA1 pyramidal cells were even devoid of immunoreactivity of both light and heavy weight neurofilaments. The fiber staining of the light weight and non-phosphorylated heavy weight neurofilaments, especially the former, was less in the CA1 field and molecular layer of dentate gyrus. The phosphorylated neurofilament immunoreactivity was identified only in axons. Mossy fibers, the axons of granule cells, contained the light weight and phosphorylated heavy weight neurofilaments, but not the non-phosphorylated neurofilament. Seven days after the kainic acid induced seizures, the phosphorylated neurofilament staining was greatly reduced in the CA1 and inner molecular layer of the dentate gyrus, probably resulting from the axonal degeneration of the Schaffer collaterals and the commissural/associational fibers. Furthermore, the nonphosphorylated neurofilament appeared in the mossy fibers of the CA3 stratum lucidum, which normally do not express such immunoreactivity. The results indicate that the neurofilaments are altered following the neuronal degeneration and postlesional plasticity caused by the kainic acid administration. Therefore, the examination of various phosphorylated neurofilaments may offer a comprehensive understanding of major hippocampal pathways, axonal plasticity and the possible roles of neurofilaments in the hippocampus following excitotoxic insults.

Phosphorylation of neurofilament H subunit as related to arrangement of neurofilaments

To find out what causes differences in phosphorylation states in neurofilaments (NF), we selected two types of dendrite, one provided with very few NFs (Purkinje cell) and the other with relatively many (anterior horn cell). We examined these with four monoclonal antibodies selected by the Western blot analysis, two (NE14 and SMI31) recognizing only phosphorylated, SMI32 recognizing only nonphosphorylated, and N52 recognizing phosphorylation-independent epitopes of NF-H. The immunoperoxidase labeling of dendrites, and also of perikarya, in both neurons was detectable with all four antibodies. After the tissue was treated with Triton X-100, the labeling was still detectable with SMI32 or N52, but undetectable with NE14 and SMI31. The brain homogenate Triton-extracted supernatant after centrifugation at 100,000g for 1 hr showed the staining of NE14, SMI31, and N52 but not that of SMI32. In Purkinje cell dendrite and perikaryon, NFs always appeared singly. In the immunogold labeling, they were labeled only with SMI32 or N52. Labeling by NE14 or SMI31 was distributed throughout the cytoplasm and hardly associated with NFs. In the anterior horn cell dendrite and perikaryon, NFs appeared both singly and in bundles. They were predominantly labeled with SMI32 or N52 when they were single, and with NE14, SMI31, or N52 when they were bundled. Even in one NF, portions that appeared single were labeled mostly with SMI32 or N52, while the remainder, to which other NFs approached closely, were labeled mostly with NE14, SMI31, or N52. Thus, when NFs appear singly, NF-H in their projections or cross-bridges with other organelles is not phosphorylated, while when NFs are bundled, NF-H is phosphorylated in crossbridges between NF core filaments. These data may explain why the NF-H is heavily phosphorylated in axons, where NFs are abundant, and not in dendrites and perikarya, where NFs are sparse.

Effects of social deprivation in prepubescent rhesus monkeys: immunohistochemical analysis of the neurofilament protein triplet in the hippocampal formation

Social deprivation during early postnatal life has profound and long-lasting effects on the behavior of primates, including prolonged and exaggerated responses to stress as well as impaired performance on a variety of learning tasks. Although the cellular changes that underlie such alterations in behavior are unknown, environmentally induced psychopathology may involve morphologic or biochemical changes in select neuronal populations. The hippocampal formation of both socially deprived and socially reared prepubescent rhesus monkeys was selected for immunocytochemical investigation because of its association with the behavioral stress response and learning. Immunocytochemical analysis using antibodies specific for the neurofilament protein triplet was performed since these proteins are modified within degenerating neurons in a variety of neurodegenerative disorders. Results from optical density measurements indicate an increase in the intensity of non-phosphorylated neurofilament protein immunoreactivity in the dentate gyrus granule cell layer of socially deprived monkeys in comparison with that of socially reared animals, suggesting that early social deprivation may result in an increase in the amount of non-phosphorylated neurofilament protein in these cells. This phenotypic difference in dentate granule cells between differentially reared monkeys supports the notion that specific subpopulations of neurons in brain regions that subserve complex behaviors may undergo long-term modifications induced by environmental conditions. Furthermore, the data suggest that constitutive chemical components related to structural integrity may be as susceptible to early environmental manipulations as the more traditionally viewed measures of cellular perturbations, such as neurotransmitter dynamics, cell density and the establishment of connectivity. The observed modifications may serve as an anatomical substrate for behavioral abnormalities that persist in later life.

Hypothyroidism selectively reduces the rate and amount of transport for specific SCb proteins in the hyt/hyt mouse optic nerve

Thyroid hormone significantly affects molecular and neuroanatomical properties of the developing nervous system. Altered connectivity in hypothyroidism may reflect reductions in process growth, alterations in process maintenance, or changes in synaptogenesis or synaptic maintenance. These events are dependent on microtubules, neurofilaments, microfilaments, and associated molecular components. Reductions in delivery of microtubules and neurofilaments to the distal axon by slow component a (SCa) of axonal transport may contribute to the neuroanatomical abnormalities of hypothyroidism (Stein et al., J Neurosci Res 28:121-133, 1991). However, hypothyroidism might also affect the axon and synaptic connections by altering slow component b (SCb), which includes actin microfilaments and proteins that contribute to synaptic function, i.e., clathrin, HSC70 (clathrin uncoating ATPase), spectrin, and calmodulin. To determine the effect of hypothyroidism on SCb proteins, slow axonal transport was analyzed in optic nerves of hyt/hyt hypothyroid mice, which have severe primary hypothyroidism, and euthyroid control mice. Clathrin, spectrin, HSC70, and actin showed significant reductions in transport velocity in hyt/hyt optic nerves relative to euthyroid nerves, but the transport rate for calmodulin was less affected. However, the amount of calmodulin was significantly elevated in hyt/hyt nerve over euthyroid nerves. Hypothyroidism selectively reduces transport of SCb proteins, which are thought to play significant roles in synaptic function and in the growth cone. The effects of hypothyroidism on microtubules and neurofilaments combined with actions on SCb suggest that changes in neuronal function associated with reduced thyroid hormone during development and maturity (i.e., alterations in neuronal connectivity, nerve conduction, and synaptic function) may be mediated in part by effects on slow axonal transport.

Hypothyroidism reduces the rate of slow component A (SCa) axonal transport and the amount of transported tubulin in the hyt/hyt mouse optic nerve

Thyroid hormone deficiency in the developing brain leads to disorders of neuronal process growth. This is evidenced by reduced axonal and dendritic size and complexity (Garza et al.: Developmental Brain Research 43:287-297, 1988; Ruiz-Marcos: Iodine and the Brain. New York: Plenum Press, pp 91-102, 1989). These findings may be related to alterations in the neuronal cytoskeleton in hypothyroidism, such as reduced or abnormal microtubular number and density (Faivre et al.: Developmental Brain Research 8: 21-30, 1983), and altered assembly, stabilization, and composition of microtubule protein in the hypothyroid brain. Neurofilaments also contribute to axonal caliber and process stability. Similar to microtubules, certain properties of neurofilaments are altered in developing hypothyroid axons (Marc and Rabie: International Journal of Developmental Neuroscience 3: 353-358, 1985; Faivre et al.: Developmental Brain Research 8:21-30, 1983) that may affect axonal caliber and process stability. Normal process growth is predicted on formation of appropriate numbers of microtubules and on the normal synthesis and axonal transport of cytoskeletal components [tubulin, microtubule associated proteins (MAPs), and neurofilament proteins]. Hypothyroidism might alter the neuronal cytoskeleton and neuronal growth either by affecting the developmental programs for expression of specific isoforms of cytoskeletal proteins or by changing the delivery of cytoskeletal proteins via slow axonal transport, particularly slow component a (SCa). Previous studies had demonstrated changes in the amount of specific microtubule protein isoforms and mRNAs (Stein et al.: Iodine and the Brain. New York: Plenum Press, pp 59-78, 1989a). To further elucidate the molecular basis for process growth abnormalities in the hypothyroid brain, we investigated slow axonal transport in the mouse to determine the effects of thyroid hormone deficiency on the rate and composition of SCa. Comparisons of SCa in the optic nerve of hyt/hyt hypothyroid mouse and euthyroid hyt/+ littermates and euthyroid progenitor strain, BALB/cBY +/+ mice, indicated that the velocity of SCa was significantly reduced in hyt/hyt optic nerve relative to hyt/+ and +/+. The axonal transport rate for tubulin, which is carried in SCa, was 0.118 mm/day in the hyt/hyt optic nerves. This rate was significantly different for the tubulin rates for the hyt/+ optic nerves (0.127 mm/day) and for the +/+ optic nerves (0.138 mm/day). Neurofilament proteins, as measured by the 140,000 daltons component, NFM, also appeared to be reduced in velocity in the hyt/hyt versus the hyt/+ and +/+ optic nerves.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of thyroid deficiency on glial fibrillary acidic protein (GFAP) and GFAP-mRNA in the cerebellum and hippocampal formation of the developing rat

The concentrations of glial fibrillary acidic protein (GFAP) and its encoding mRNA in the cerebellum and hippocampal formation were assayed during the development of normal and hypothyroid rats. Neonatal hypothyroidism induced a significant reduction in the GFAP concentration in both regions from day 14. The reduction was especially marked on day 35 in the cerebellum (-43%) and the hippocampal formation (-55%). The immunocytochemical study of vimentin showed that the developmental disappearance of this protein from the Bergmann and internal astrocytes is greatly delayed in the cerebellum of the hypothyroid rats. The reduction in GFAP concentration together with the delayed vimentin-GFAP transition could explain how astrocyte morphogenesis is impaired by neonatal thyroid deficiency. The GFAP-mRNA concentration in the hippocampal formation was reduced throughout the development of thyroid-deficient rats, while the GFAP-mRNA concentration in the cerebellum first increased between birth and day 14 to reach a peak well above the normal value (+78%) and decreased thereafter to reach 53% of the normal value by day 35. This transient increase in the cerebellar GFAP-mRNA concentration may be related to the astroglial hyperplasia that occurs in these animals. The difference between the developmental profile of GFAP and its encoding mRNA, especially under pathological conditions, indicates that two distinct mechanisms control the synthesis or stability of the protein and its messenger RNA, as was previously found in the forebrain of the developing normal rat.

Glial and neuronal differentiation in the human fetal brain 9-23 weeks of gestation

Nineteen human fetal brains ranging from 9-23 weeks of gestation were examined immunocytochemically for evidence of glial and neuronal differentiation. Radial glia were positive for vimentin and glial fibrillary acidic protein (GFAP) throughout the age range. S100-positive cells which were presumed to be astrocytes were present from 9 weeks; they were always more widespread in the cerebrum and the brainstem than GFAP-positive mature astrocytes, which could be detected with certainty only at 14 weeks. Carbonic anhydrase II (CA II)-positive oligodendrocytes were present in the brainstem in small numbers from 17 weeks. Neuronal fibre tracts in the cerebrum were positive for 160 kD phosphorylated neurofilament protein (BF10) from 9 weeks, but negative for 200 kD phosphorylated neurofilament protein (RT97) and for 70 and 200 kD non-phosphorylated neurofilament protein (NFP) whereas most tracts in the brainstem were positive for BF10 from 9 weeks and positive for the other neurofilament proteins from 14 weeks. Corticospinal tracts differed in remaining negative for neurofilament proteins other than BF10, which showed positive reaction throughout. Perikarya of differentiated neurons in all areas of the brain were neurofilament-negative but neuron specific enolase (NSE)-positive. Germinal eminence cells were focally vimentin-positive from 15 weeks, focally GFAP-positive from 17 weeks, and negative for all NFP and for NSE. The value of a short fixation time and pretreatment with trypsin in the immunocytochemical demonstration of GFAP is stressed.

Prenatal exposure to ethanol causes a delay in the developmental expression of neurofilament epitopes in cerebellum

The expression of nonphosphorylated neurofilaments (nPNFs) and phosphorylated neurofilaments (PNFs) was examined in cerebella during development of C57/Bl/6J mice prenatally exposed to ethanol. The length of nPNF immunoreactive portions of primary and secondary dendrites of Purkinje neurons was reduced during early postnatal developmental stages. This difference disappeared by 2 months of age. These results indicate a delay in the maturation of nPNFs in Purkinje neurons of ethanol-exposed mice. There also appeared to be some underdevelopment of basket cell axons in terms of PNF expression, during early postnatal stages, as compared to normal control litters. These findings may reflect a general delay in neuronal maturation after ethanol exposure. Prenatal exposure to ethanol may, therefore, have profound effects on developmental events occurring during early postnatal life. We could not, however, exclude the possibility that the disturbances in neurofilament expression were due to malnutrition in the alcohol-treated animals.

Expression of neurofilament proteins in granule cells of the cerebellum

We have used a panel of monoclonal antibodies directed against the low, middle and high molecular weight subunits of neurofilament triplet, to study their expression in mouse cerebellar granule cells. We demonstrate that in situ such cells only express the 2 lower molecular weight subunits either at various developmental stages or in the adult. The same results were obtained in vitro. This pattern of neurofilament protein expression in adult granule cells is therefore similar to that observed in developing neurons but differs from most neurons in the adult brain. The retention of such 'immature' pattern of neurofilament protein expression throughout adulthood could explain the lack of cytologically identifiable intermediate filaments in these neurons when examined with conventional electron microscopic techniques. It furthermore suggests that various neuronal populations might be characterized by the expression of specific subsets of neuronal intermediate filaments.

Maturation of the corpus callosum of the rat: II. Influence of thyroid hormones on the number and maturation of axons

Quantitative electron microscopy has been used to study the number of callosal axons in the corpus callosum of normal and hypothyroid rats during postnatal development. At birth, the normal corpus callosum contains 4.4 x 10(6) axons. This number increases to 11.4 x 10(6) by 5 days of age (P5) and then, in contrast to cats and primates, remains constant until at least P60, the oldest age examined. The number of axons in the corpus callosum of hypothyroid animals is not significantly different from the values observed in normal rats at all ages studied, although the callosal axons of hypothyroid rats remain structurally immature. As extensive elimination of callosal axons has been shown to occur in normal rats past P5, we conclude that new callosal processes grow through the corpus callosum past this age that compensate numerically for the loss. Moreover, as the number of callosally projecting neurons seems to be higher in hypothyroid rats than in normal controls, it seems that the constant axon number derives from more parent neurons, and thus that there are more axon collaterals per callosal neuron in a normal animal than in a hypothyroid one. Taken together, these data indicate that although hypothyroidism does not alter the total number of callosally projecting axons, it interferes with the normal processes that define or sculpt the projection fields, thereby leading to a numerically normal projection with abnormal topography.

Effect of thyroid deficiency on actin mRNA content in the developing rat cerebellum

The actin mRNA content of the cerebellum was determined in normal and hypothyroid developing rats using RNA dot hybridization with a beta-actin cDNA probe. The decline in actin mRNA content occurring during the second postnatal week in normal development was delayed by about 1 week in hypothyroid rats. Since this effect coincides exactly with the delay in actin filament formation recently reported in thyroid-deficient rats, it strengthens the hypothesis of an inverse relationship in the developing brain between the polymerization state of actin and the production of actin mRNA.

Immunohistochemistry with anti-calbindin and anti-neurofilament antibodies in the cerebellum of methylazoxymethanol-treated mice

Mice pups were injected with methylazoxymethanol at birth (MAM0) or on the fifth postnatal day (MAM5) and their cerebella were examined when adult. Immunohistochemistry with an antiserum directed against calbindin, a protein specific for Purkinje cells, was used to survey more easily Purkinje cell position and orientation. For a general view of basket cell axon distribution, we used a monoclonal antibody that recognized the phosphorylated form of the 200 kD constituent protein of neurofilaments, which is axon specific. The present results confirm that in MAM5 the cytoarchitecture was preserved, some Purkinje cells degenerated, and the pericellular basket around the Purkinje cells was apparently normal. In MAM0 animals, the Purkinje cells appeared malpositioned and disoriented, the pinceau around the Purkinje cell hillock was absent, but basket cell axons were present. This indicated that the absence of pinceau was not due to the absence of basket cells, but probably to alterations of cell interactions, which hindered the proper pericellular basket formation.

Expression of neurofilament proteins by Purkinje cells: ultrastructural immunolocalization with monoclonal antibodies

Purkinje cell bodies in rodent cerebellum have been shown to express neurofilament protein epitopes but neurofilaments are rarely seen in these perikarya by classical morphological approaches. In an attempt to solve this enigma the ultrastructural distribution of two neurofilament epitopes was studied by immunoelectron microscopy with two monoclonal antibodies (Mabs) of divergent specificity: one, Mab 04-7 recognized a phosphorylated epitope, the other, Mab 02-135 a non-phosphorylated epitope. Longitudinal filamentous elements were heavily labeled in basket cell axons and afferent nerve fibers with both Mabs. While Mab 04-7 was unreactive with Purkinje cells, the immunoperoxidase reaction product with Mab 02-135 was distributed in the form of patches with no filamentous substructure throughout the cytoplasm of these cells. The data complement the results of other immunocytochemical studies showing the presence of all 3 neurofilament constituent proteins in Purkinje cell bodies, and lead to the conclusion that in these perikarya the majority of neurofilament proteins are not assembled in the form of neurofilaments.

Progressive supranuclear palsy with hypertrophy of the olives. An immunocytochemical study of the cytoskeleton of argyrophilic neurons

In a patient with progressive supranuclear palsy (PSP) and hypertrophy of the olives, neurons with different forms of argyrophilic degeneration were detected by means of Bodian's silver staining method, i.e., neurofibrillary tangle-bearing neurons in the basal ganglia and brain stem, ballooned argyrophilic neurons in the brain stem, and hypertrophied neurons in the olives. In these cells, the cytoskeleton was investigated to ascertain whether neurons with different cytoskeletal changes contained phosphorylated neurofilaments (P-Nf) in the perikaryon. This study, carried out using two monoclonal antibodies that recognize phosphorylated epitopes of the neurofilament high molecular weight subunits, showed that hypertrophied olivary neurons, most ballooned neurons and a small aliquot of tangle-bearing neurons were labelled. The immunostaining of hypertrophied and ballooned neurons was localized in the whole perikaryon and dendrites, whereas that of tangle-bearing neurons was confined to the tangle. These findings were reproduced in five additional patients (one with hypertrophy of the olives, four with PSP) and demonstrated that, in PSP, the mechanism responsible for tangle formation does not affect the ability of neurons to accumulate P-Nf. This fact suggested that perikaryonal P-Nf accumulation is likely to be part of the cell reaction to abnormal conditions affecting the neuronal cytoskeleton.

Thyroid hormone modulates the expression of a neurofilament antigen in the cerebellar cortex: premature induction and overexpression by basket cells in hyperthyroidism and a critical period for the correction of hypothyroidism

Neurofilament expression by basket cells of the cerebellar cortex is suppressed in hypothyroidism. By using a monoclonal antibody (mabN210) that selectively recognizes an epitope associated with the 210-kDa neurofilament subunit, we have explored the relationship between thyroid hormone levels and basket cell maturation. In animals rendered hypothyroid by inclusion of propylthiouracil in the maternal drinking water from embryo age E17, there is a complete absence of mabN210 immunoreactivity in the basket cell axons, while the other immunoreactive axons in the cerebellar cortex, primarily Purkinje cell axons and mossy fibers, are apparently unaffected. This deficit can be corrected by treatment with thyroid hormone but there seems to be a critical period for full recovery, for animals treated from birth recover normally whereas there is a gradual diminution in the efficacy of treatment the later it begins. Thyroid hormone therapy begun after postnatal day 30 (P30) leads only to very minor recovery. By contrast, animals on a hyperthyroid regime show premature mabN210-antigen induction in the basket cells and supranormal levels of expression at P25, despite the severe reduction in the number of basket cell somata. This suggests either abnormal compensatory sprouting of axon collaterals by the remaining basket cells or the occurrence, during normal cerebellar corticogenesis, of competition between basket cell axons for a limited number of Purkinje cell targets followed by the elimination of the excess collaterals.

Down's syndrome. Precocious neurofilament antigen expression

Neuronal cytoskeletal abnormalities may be a common factor in the neurobiologic causes of diverse forms of mental deficiency including Down's syndrome (DS). MabN210 which recognizes the 210 kDa subunit of neurofilaments was applied to sections of autopsy-derived DS and control central nervous system tissue. The findings included precocious and possibly aberrant neurofilament antigen expression during the first few months of life in DS cerebellar basket cell axons. Staining of central white matter tracts revealed an increased caliber of immunoreactive axons suggesting a widespread abnormality in mabN210 antigen expression in DS neurons. This abnormal regulation of normal neurofilament antigenic epitopes may be causally related to the development of Alzheimer's disease in DS.

Non-phosphorylated and phosphorylated neurofilaments in hypothyroid rat cerebellum

Purkinje cell baskets in hypothyroid rat cerebellum were studied with antibodies reacting with phosphorylated or non-phosphorylated neurofilament epitopes. Compared to normal rats, Purkinje cell baskets were fewer in number and less developed in hypothyroid rat cerebellum. However, no differences were observed as to their immunoreactivity with monoclonal antibodies reacting with phosphorylated or non-phosphorylated neurofilament epitopes.

The effects of thyroid hormone on differentiation and neurofilament expression in rat brain aggregating cultures

The effects of thyroid hormone on neural development in vitro were studied using rat fetal forebrain aggregating cultures. They were examined morphologically after growth for 21 days in medium containing fetal calf serum (S+), in a chemically defined medium (S-), or in serum-free medium containing 30 nM triiodothyronine (T3). Aggregates grown in S+ showed certain morphological differences compared to those grown in the absence of serum: a glia limitans was present in the former, but not the latter, which were further characterized by a marginal zone rich in fibres and containing few cells. Immunocytochemistry using a monoclonal antibody against neurofilaments showed that immunostaining was most pronounced in aggregates grown in T3 (especially in the marginal zone) and weakest in those grown in S+. Quantitative estimation using an immunoadsorbent assay confirmed that T3 medium increased the amount of neurofilament protein in the aggregates, consistent with the view that thyroid hormone promotes neural development in vitro.