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PubMed1988

The effects of intrauterine growth retardation on the development of the Purkinje cell dendritic tree in the cerebellar cortex of fetal sheep: a note on the ontogeny of the Purkinje cell.

The development of the fetal sheep cerebellum at 80, 100, 120 and 140 days gestation (term = 146 days) and 3 months postnatally was studied using Nissl stained sections and rapid Golgi preparations. The most rapid expansion of the Purkinje cell dendritic tree occurred between 100 and 120 days of gestation (5-6 fold increase in area). By 140 days it had acquired its adult form after which time growth continued mainly in the vertical direction. The effects of intrauterine growth retardation on the growth of granule and Purkinje cell dendrites in the cerebellar cortex of fetal sheep (140 days) were investigated in Golgi preparations. Compared with control cerebella the length (but not the number) of granule cell dendrites was reduced by 14% (P less than 0.01); the area of the Purkinje cell dendritic field was reduced by 20% (P less than 0.01); the branching density was reduced by 8% (P less than 0.01); the total branch length was reduced by 27% (P less than 0.002); the density of dendritic spines per row was not affected. These factors resulted in a decrease of 26% (P less than 0.002) in the total number of dendritic spines per row per Purkinje cell. These findings show that the growth of granule cell dendrites and the Purkinje cell dendritic tree have been significantly affected by chronic intrauterine deprivation. Such structural abnormalities could affect the pattern of neuronal connectivity and could be associated with functional deficits.

Animals↗
PubMed1984

Persistent, differential alterations in developing cerebellar cortex of male and female mice after methylmercury exposure.

Developing animals have long been believed to be more sensitive to methylmercury toxicity than adults, but the reasons for differential effects are not well understood. In the present study, 2-day-old mice received a single per os dose of 4 mg Hg/kg methylmercury and were sacrificed 24 h or 19 days later. This resulted in a mean brain concentration of 1.8 micrograms Hg/g tissue on day 3 and less than 0.1 micrograms Hg/g on day 21. Compared to littermate vehicle controls, the methylmercury-treated mice exhibited a significant reduction in cell numbers in 1 of 4 regions of the developing cerebellar external granular layer 24 h after treatment. Although the mitotic index over the same 4 regions was not significantly altered by methylmercury treatment, the total number of mitotic figures per section of cerebellum was significantly reduced in the treated group. The ratio of late mitotic figures to total mitotic figures was significantly reduced, indicating mitotic arrest. Both of these antimitotic effects were greater in males than females. Cerebellar structure was also examined 19 days after methylmercury treatment. The number of cells in the molecular layer and thickness of the molecular layer and internal granular layer were significantly reduced in males; the number of Purkinje cells in both sexes and all measures in females remained unaltered. This suggests that early cell loss results in persistent reductions in cell number. Although the basis for the differential effect in males and females is not known, the antimitotic effect of methylmercury is most likely the mechanism underlying the reduced cellularity in treated animals.

Animals↗
PubMed2006

Alternative splicing of the voltage-gated Ca2+ channel beta4 subunit creates a uniquely folded N-terminal protein binding domain with cell-specific expression in the cerebellar cortex.

Ca2+ channel beta subunits regulate cell-surface expression and gating of voltage-dependent Ca2+ channel alpha1 subunits. Based on primary sequence comparisons, beta subunits are predicted to be modular structures composed of five domains (A-E) that are related to the large family of membrane-associated guanylate kinase proteins. The crystal structure of the beta subunit core B-D domains has been reported recently; however, little is known about the structures of the A and E domains. The N-terminal A domain differs among the four subtypes of Ca2+ channel beta subunits (beta1-beta4) primarily as the result of two duplications of an ancestral gene containing multiple alternatively spliced exons. At least nine A domain sequences can be generated by alternative splicing. In this report, we focus on one A domain sequence, the highly conserved beta4a A domain. We solved its three-dimensional structure and show that it is expressed in punctate structures throughout the molecular layer of the cerebellar cortex. We also demonstrate that it does not participate directly in Cav2.1 Ca2+ channel gating but serves as a binding site in protein-protein interactions with synaptotagmin I and the LC2 domain of microtubule-associated protein 1A. With respect to beta4 subunits, the interactions are specific for the beta4a splice variant, because they do not occur with the beta4b A domain. These results have strong bearing on our current understanding of the structure of alternatively spliced Ca2+ channel beta subunits and the cell-specific roles they play in the CNS.

Alternative Splicing↗
PubMed1971

The form and distribution of the surface evoked responses in cerebellar cortex from intercostal nerves in the cat.

1. The form and distribution of the cerebellar evoked responses to electrical stimulation of intercostal and other thoracic segmental nerves were investigated in anaesthetized cats.2. Low intensity stimulation (< 2 x nerve threshold) evoked short latency, low amplitude (< 20 muV), initially surface positive responses which could only be distinguished with certainty from the electrocorticogram with averaging.3. On the basis of experiments involving sectioning of afferent tracts it is concluded that intercostal evoked responses of less than 7.0 msec latency are conducted in dorsal spino-cerebellar, ventral spino-cerebellar and dorsal column (cuneo-cerebellar) pathways.4. The surface positive waves have a highly punctate distribution with a steep potential gradient extending over an area of about 1 mm diameter. It is postulated that these small fields represent activation of single or few mossy fibre inputs.5. Short latency responses to thoracic inputs were found only in the ipsilateral intermediate cortex and lateral margin of the vermis of the anterior lobe (lateral two thirds of Larsell's lobules IV and V of the accessible cortex). The responses were distributed throughout the fore and hind limb areas of the anterior lobe and no rostro-caudal or medio-lateral segmental organization was seen.6. It is suggested that the overlapping distribution of thoracic and fore and hind limb mossy fibre inputs within the cerebellar cortex provides an anatomical basis for the integration of information from the trunk and from the limbs.

Animals↗