28 K cholecalcin (CaBP) levels in abnormal cerebella: studies on mutant mice and harmaline- and 3-acetylpyridine-treated rats

Cell Counts of Purkinje and Inferior Olivary Neurons in the 'Hyperspiny Purkinje Cells' Mutant Mouse

The mutant mouse 'hyperspiny Purkinje cells' (hpc) has morphologically abnormal Purkinje cells and below normal intracerebellar calbindin-D28k, a calcium-binding protein that, in the cerebellum, is found only in the Purkinje cells. We counted the Purkinje cells on serial sections stained with thionin or labelled with anti-calbindin-D28k antibodies to investigate whether the depletion of the cerebellar content of calbindin-D28k was correlated with a reduced number of Purkinje cells. We also counted the inferior olivary neurons, as they are one of the major afferents of the Purkinje cells and also contain calbindin-D28k. The hpc mutant mice had 27% fewer cerebellar Purkinje cells and 12% fewer inferior olivary neurons than did controls. Their Purkinje cells were evenly immunostained but slightly atrophic. These data suggest that the depleted cerebellar calbindin-D28k content could be explained both by the loss of some Purkinje cells and the reduced size of the remaining ones.

Dependence of parvalbumin expression on Purkinje cell input in the deep cerebellar nuclei

A complete loss of Purkinje cell (PC) input leads to an increase in expression of the calcium-binding protein parvalbumin (Parv) in neurons of the deep cerebellar nuclei (DCN) of PC degeneration (pcd) mutants. To verify this apparent dependence of Parv expression on PC input in the DCN, the patterns of expression in five other cerebellar mutants (weaver, staggerer, leaner, nervous, and lurcher) with differing grades and chronologies of PC loss were compared. Degree and time course of PC loss and the subsequent denervation of DCN neurons were monitored by using Calbindin D-28k (Calb) immunocytochemistry. Similar to pcd mice, somatal Parv in lurcher mutants increased massively throughout the cerebellar nuclei. In nervous and leaner mutants, somatal Parv was restricted to almost completely denervated nuclear areas, whereas areas with appreciable remnants of PC input were spared. The first appearance of Parv+ somata was closely correlated with the time course of PC degeneration--postnatal day 19 in lurcher mutants and postnatal day 23 in nervous mutants. In staggerer mice, neurons immunopositive for Parv as well as for Calb were present in outer DCN areas, likely representing ectopic PCs rather than DCN neurons. No Parv+ DCN somata were found in weaver mutants at any time. In conclusion, increased expression of somatal Parv in DCN neurons is not restricted to the specific histopathology in pcd mutants but is a common mechanism that is dependent on the topography and severeness of PC-input loss. The functional significance of the Parv increase and its possible contribution to the degree of motor disability among the different mutants are discussed.

A behavioral study of the development of hereditary cerebellar ataxia in the shaker rat mutant

shaker Mutant rats were first identified by their abnormal motor behaviors and degeneration of cerebellar Purkinje cells and brainstem inferior olivary neurons. After 6 generations of inbreeding 77% of shaker rat mutants are mildly ataxic (identified as mild shaker mutants) and 23% are ataxic and exhibit a whole body tremor (strong shaker mutants) by 3 months of age. This study of shaker mutants from birth to 3 months of age was designed to: (1) compare the somatic and motor development of shaker mutants with age matched normal rats; (2) identify the temporal onset of motor deficits; and (3) correlate qualitative differences in Purkinje cell degeneration between 3-month-old mild and strong shaker rat mutants. Shaker mutant rats consistently weighed less than age-matched control animals. Analysis of motor-development using the hindlimb splay test demonstrated the distance between hindpaws was significantly greater in shaker mutant rats than in controls starting at 42 postnatal days (PND) of age. Hindlimb stride width was greater for shaker than control rats at 42 PNDs. However, after 42 PNDS shaker mutant average hindlimb width was narrower than controls. Forelimb stride width was consistently narrower in shaker mutants than in normal rats. Hindlimb placement was impaired in shaker rat mutants after 15 PND. Forelimb placement, cliff avoidance and surface righting were only transiently impaired in shaker mutants. Mid-air righting, performance of a geotaxic response, and climbing and jumping postural reactions were similar in shaker and normal rats. The spatial extent of Purkinje cell survival/degeneration correlated with differences in abnormal motor activity seen in 3-month-old mild and strong shaker mutants. In mild shaker rat mutants, Purkinje cells appeared to have degenerated randomly throughout the cortex. In strong shaker mutants most Purkinje cells in the anterior lobe had degenerated. In the posterior lobe Purkinje cell degeneration appeared to be numerically significant, but many surviving cells were present. Although Purkinje cell loss was not numerically quantified in this study, a strong association between the extent and type of spatial loss of Purkinje cells, and the severity of clinical signs, appears to exist.

A study of cerebellar inositol 1,4,5-trisphosphate receptor following climbing and parallel fibre deafferentation

We have examined the influence of climbing fibre and parallel fibre afferent inputs on the inositol 1,4,5-trisphosphate (InsP3) receptor in rat cerebellum. Lesions of the inferior olive-climbing fibre projections to Purkinje cells by 3-acetylpyridine (3-AP) significantly reduced the [3H]InsP3 binding density (-20%) with no apparent changes in the binding affinity 21 days after treatment. No further reduction in binding density was found in rats given a second dose 7 days after the initial injection. A significant reduction in the binding density was evident as early as 7 days post-lesion. However, 3-AP (0.5 mM) failed to inhibit [3H]InsP3 binding in vitro. Cerebellar granule cells were lesioned by two consecutive injections of methylazoxymethanol acetate at birth. In these 60-day-old granuloprival rats, the density and affinity of [3H]InsP3 binding sites in the cerebellum remained comparable to the controls. Since lesions of the climbing fibres increase Purkinje cell activity, we suggest that changes in InsP3 receptor density may reflect an adaptative response to the heightened Purkinje cell activity. In addition, the results also indicate that expression of the InsP3 receptor in the cerebellum is largely independent of the presence of granule cell-parallel fibre synaptic innervation onto the Purkinje cells.

Detection of calbindin-D 28k mRNA in rat vestibular ganglion neurons by in situ hybridization

The cellular distribution of calbindin-D 28k mRNA in the rat vestibular ganglion was examined by in situ hybridization. Using a [35S]cDNA probe a neuronal subpopulation expressing calbindin-D 28k mRNA with a strong intensity has been identified. These findings confirm the presence of a subclass of calbindin-immunoreactive neurons in the rat vestibular ganglion.

Molecular cloning of a neuron-specific transcript and its regulation during normal and aberrant cerebellar development

PEP-19 is a brain-specific polypeptide whose levels increase dramatically during the late maturation of the rodent nervous system. By using immunocytochemistry, PEP-19 is shown to be localized to several regions of the central nervous system, notably cerebellum, thalamus caudate putamen, and olfactory bulb. We have isolated a 0.5-kilobase cDNA clone that encodes the entire PEP-19 protein sequence, making this one of the smallest primary transcripts and translation products ever identified in eukaryotes. The cDNA was used to investigate the developmental expression of PEP-19 in rodent brain. PEP-19 mRNA rises from low levels at embryonic day 17 of gestation in the rat to a plateau value by day 18 postpartum. This mirrored the levels of the protein determined by radioimmunoassay. Since the rise coincided with the formation of synaptic contacts onto Purkinje cells (a major site of PEP-19 expression), the hypothesis was tested that the activity and/or presence of afferent input modulated PEP-19 expression. Parallel fiber innervation was disrupted either by killing granule cells with the cytostatic agent methylazoxymethanol or by examining PEP-19 levels in cerebellar granuloprival mutant mice (reeler and weaver). The influence of climbing fiber input was assessed by either eliminating them with 3-acetylpyridine or stimulating them with harmaline in both neonatal and mature rats. None of the above altered PEP-19 gene expression in cerebellum, leading us to propose that the signals triggering the PEP-19 gene do not emanate from granule cells or neurons in the olivary nucleus. However, preliminary evidence suggests that PEP-19 is under posttranscriptional regulation.

Calbindin D-28k-immunoreactive neurons in chick dorsal root ganglion: ontogenesis and cytological characteristics of the immunoreactive sensory neurons

The expression of calbindin (28,000 mol. wt Vitamin D-dependent calcium binding protein) was studied in sensory neurons of the chick dorsal root ganglion by combining immunocytochemical and ultrastructural features. In the chick embryo at E10, about 20% of the neuroblasts were immunostained with antibodies raised to calbindin. After hatching, two subpopulations of primary sensory neurons were labeled with calbindin-antibodies and could be identified: the large Al cell bodies (6%) mainly characterized by huge blocks of rough endoplasmic reticulum and the small B1 cell bodies (14%) which contain parallel cisternae of rough endoplasmic reticulum. The other neuronal cell types A2 and B2 were devoid of any immunostaining. Thus, calbindin is an early and reliable marker of two subclasses of primary sensory neurons in the chick dorsal root ganglion.

Immuno-electronmicroscopic localization of 'vitamin D-dependent' calcium-binding protein (CaBP-28k) in the vestibular hair cells of the cat

The PAP immunohistochemical method was used to carry out a light- and electronmicroscopic study of the distribution of the vitamin D-dependent calcium-binding protein (CaBP-28k, calbindin, cholecalcin) in the vestibule of the young cat. It was found that the two types of hair cells, types I and II, were stained differently. Type II cells were intensely immunoreactive and their staining did not vary with the location of the cells within the crista ampullaris. Type I cells at the top of the cristae were lightly stained, or unstained, while the type I cells laterally or basally were frequently intensely stained. The nerve fibers arriving at the top of the cristae are highly immunoreactive while the fibers of the base are not stained. Immunostaining for CaBP was correlated with differences in the innervation of hair cells at the top and base of the cristae. This differential CaBP-immunostaining may reflect differences in the physiological activity of the cells. The electronmicroscopic study showed that CaBP is present throughout the cytoplasm of the hair cells but that its concentration was particularly high in the cuticular plate and stereocilia. This specific intracellular distribution of CaBP is discussed with the possible role of Ca2+ in the physiology of the vestibular hair cells.

Staggerer-specific protein SP47: a unique species among age- and genotype-dependent cerebellar proteins

Genotype- and age-specific proteins are found in the developing cerebellum of wildtype and staggerer (sg/sg) mutant mice by analysis of silver-stained one- and two-dimensional protein patterns. The methods used are suitable for gross inspection of protein patterns without previous purification, labeling, or immunochemistry. SP47, a polypeptide of 47 kD with a pI of 6.0, appears in the mature staggerer cerebellum, but not in the wildtype. SP47 is different from the astrocytic glial fibrillary acidic protein (GFAP) as shown by immunoblotting. Four polypeptides have been identified with distinct development- and genotype-dependent patterns in the cerebellum. Some of the changes are correlated with events during postnatal histogenesis.