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

Exogenous Sonic hedgehog modulates the pool of GABAergic interneurons during cerebellar development

All cerebellar GABAergic interneurons were derived from a common pool of precursor cells residing in the embryonic ventricular zone (VZ) and migrating in the prospective white matter (PWM) after birth, where both intrinsic and extrinsic factors contribute to regulate their amplification. Among the environmental factors, we focused on Sonic hedgehog (Shh), a morphogen well known to regulate neural progenitor cell proliferation. We asked if and how exogenous Shh treatment affects the lineage of cerebellar GABAergic interneurons. To address these issues, exogenous Shh was administered to embryonic and postnatal organotypic slices. We found that Shh is able to expand the pool of interneuron progenitors residing in the embryonic epithelium and in the postnatal PWM. In particular, Shh signalling pathway was highly mitogenic at early developmental stages of interneuron production, whereas its effect decreased after the first postnatal week. Gene expression analysis of sorted cells and in situ hybridization further showed that immature interneurons express both the Shh receptor patched and the Shh target gene Gli1. Thus, within the interneuron lineage, Shh might exert regulatory functions also in postmitotic cells. On the whole, our data enlighten the role of Shh during cerebellar maturation and further broaden our knowledge on the amplification mechanisms of the interneuron progenitor pool.

"Hairy baskets" associated with degenerative Purkinje cell changes in essential tremor

Essential tremor (ET) is one of the most common neurologic diseases. Increased numbers of torpedoes and Purkinje cell (PC) loss have been documented in the brains of patients with ET. We recently observed a dense and tangled appearance ("hairiness") of the basket cell axonal plexuses that surround PC soma in Bielschowsky preparations of cerebellar cortex in ET brains. Here, we assessed basket cell "hairiness" in 37 ET (32 cerebellar ET; 5 Lewy body variant ET), 21 nondisease control, and 48 disease control brains using a semiquantitative scale. In 8 cerebellar ET cases (25%), there were high basket scores (rating = 3), whereas no Lewy body variant ET, 1 nondisease control (4.8%), and 2 diseased controls (4.2%) had high basket scores (p = 0.001). The hairy basket scores correlated with numbers of torpedoes (p < 0.001) and inversely with numbers of PCs (p = 0.06). Axonal plexus density obtained by image analysis of basket cell processes traced from digitized images was higher in ET than in nondiseased control cases (p = 0.016). Closely spaced sites of synaptic contact between basket cell processes and PCs were identified by electron microscopy in ET cases. These data indicate that structural changes are not restricted to PCs in ET, and that other neurons within their functional network may be involved in its pathogenesis.

Chromosome 16q22.1-linked autosomal dominant cerebellar ataxia: an autopsy case report with some new observations on cerebellar pathology

An autopsy case of chromosome 16q22.1-linked autosomal dominant cerebellar ataxia is reported. The patient was a 77-year-old man who died after a clinical course of about 19 years characterized by pure cerebellar ataxia. Main neuropathological findings included moderate loss of Purkinje cells, variegated degenerative features of the remaining Purkinje cells, finely fibrillary material surrounding the perikarya of Purkinje cells, and ubiquitin-immunoreactive small dots in the molecular layer and cerebellar white matter. Neuritic hyperplasia surrounding the perikarya of Purkinje cells was also a prominent finding. Golgi impregnation study demonstrated poor dendritic arborization of some Purkinje cells. It is our assumption that the pathological processes leading to Purkinje cell death in this disorder are not singular because the intracellular functions of the protein coded by the mutant gene are manifold, and the multiplicity of the pathological processes is reflected in diverse cytomorphological changes seen in degenerating Purkinje cells.