[A new cerebellar neuron: the brush or monopolar cell. Characteristics and possible function]. / Nueva célula 'en cepillo' (brush cell) o célula monopolar del cerebelo. Características y posible función.

The basic neuronal structure and circuitry of the cerebellum has been well known since Cajal's time. In recent years, however, a number of new neuronal connections and new immunohistochemically defined neuronal subtypes and functional cerebellar modules have been described. This new morphofunctional concept of the cerebellum seems to be in agreement with its newly assumed roles in learning and memory. In this new functional structure, a new cell (the brush cell, monopolar cell or monodendritic cell, Altman and Bayer, 1977; Mugnaini, 1994) specific to the cerebellar cortex and cochlear nucleus, could be of great importance. In all species studied, including man, this cell shows very particular morphology, immunohistochemical reactivity (against calretinin, some glutamate receptors and some neurofilament antibodies) and synaptic connections. The main afferents of these neurons are the mossy fibres, which form giant synaptic structures with them. The axons of monopolar cells end either in contact with extracerebellar neurons, or terminate intracortically at other brush cells (in the form of mossy fibres) or other cortical neurons of still-unknown morphology. In every animal species examined, these monopolar cells show different embryological development. No involution of them has been seen either in senility or in neurodegenerative disease.

Nueva célula `en cepillo' (brush cell) o célula monopolar del cerebelo. Características y posible función / A new cerebellar neuron: the brush or monopolar cell. Characteristics and possible function

La estructura del cerebelo y los circuitos que forman sus neuronas se conocen muy bien desde la época de Cajal. En los últimos años se ha descrito un cierto número de nuevas conexiones neuronales y subtipos neuronales, así como compartimentos funcionales mediante técnicas inmunohistoquímicas. Esta nueva concepción morfofuncional del cerebelo se corresponde con las nuevas funciones que se le asignan en aprendizaje y memoria. Dentro de este esquema puede ser clave una nueva célula, mencionada por Altman y Bayer (1977) y descrita por Mugnaini (1994), la célula `en cepillo', monopolar o monodendrítica, específica de la corteza cerebelosa -junto a los núcleos cocleares-, que presenta en todas las especies, incluido el hombre, morfología, reacción inmunohistoquímica (anticalretinina, receptores para glutamato, neurofilamentos, etc.) y conexiones muy características. La formación de una sinapsis gigante con una fibra musgosa es su principal aferencia, y posee o puede poseer terminales extracerebelosos directos, intracorticales -sobre otras células en cepillo en forma de terminal musgosa, o sobre otras neuronas-. En cada especie animal tiene un desarrollo diferente y parece que no involucionan ni en la senilidad ni en las enfermedades neurodegenerativas (AU)

The basic neuronal structure and circuitry of the cerebellum has been well known since Cajal’s time. In recent years, however, a number of new neuronal connections and new immunohistochemically-defined neuronal subtypes and functional cerebellar modules have been described. This new morphofunctional concept of the cerebellum seems to be in agreement with its newly assumed roles in learning and memory. In this new functional structure, a new cell (the brush cell, monopolar cell or monodendritic cell, Altman and Bayer, 1977; Mugnaini, 1994) specific to the cerebellar cortex and cochlear nucleus, could be of great importance. In all species studied, including man, this cell shows very particular morphology, immunohistochemical reactivity (against calretinine, some glutamate receptors and some neurofilament antibodies) and synaptic connections. The main afferents of these neurons are the mossy fibres, which form giant synaptic structures with them. The axons of monopolar cells end either in contact with extracerebellar neurons, or terminate intracortically at other brush cells (in the form of mossy fibres) or other cortical neurons of still-unknown morphology. In every animal species examined, these monopolar cells show different embryological development. No involution of them has been seen either in senility or in neurodegenerative disease (AU)

Hypotheses concerning the aetiology of Alzheimer's disease.

Theories on the aetiology and pathogenesis of Alzheimer's disease (AD) are revised. After discussing senile involution, the principal characteristic alterations of AD are presented. These pathological changes include involutive morphological phenomena (neurofibrillar tangles, senile neuritic plaques with varying = amyloid content) and functional phenomena (alterations in energy metabolism, in protein synthesis, and in the neurotransmitter metabolism). Currently it is assumed that the neurons most affected seem to be primarily those of the ascending cholinergic activating system, whose somas are situated in Meinert's basal nucleus. Serotoninergic, adrenergic and peptidergic brainstem neurons and serotoninergic neurons of the cerebral cortex are also affected. Secondary to these, the main pathological alterations, triggered by these disfunctions, are observed in neurons of the neocortex, hippocampus and amygdala. These changes are responsible for the symptoms of AD. The aetiology of these changes may be genetic = (related to chromosoma 21), toxic (aluminium) or infective (slow agents similar to those that cause Creutzfeldt-Jakob disease, kuru and scrapie). Various aetiopathological theories emphasized on immunological or vascular phenomena, altered protein synthesis, etc. It seems to be important that certain neurons are affected in most of degenerative diseases: the high-risk neurons. These neurons could be affected by toxic and environmental factors.