Immunohistochemical localisation of nicotinic acetylcholine receptor subunits in human cerebellum.

ABSTRACT

Neuronal nicotinic acetylcholine receptors are members of the ligand-gated ion channel superfamily composed of alpha and beta subunits with specific structural, functional and pharmacological properties. In this study we have used immunohistochemistry to investigate the presence of nicotinic acetylcholine receptor subunits in human cerebellum. Tissue was obtained at autopsy from eight adult individuals (aged 36-56 years). Histological sections were prepared from formalin-fixed paraffin-embedded material. alpha 3, alpha 4, alpha 6, alpha 7, beta 2, and beta 4 subunits were present in this brain area associated with both neuronal and non-neuronal cell types. Most Purkinje cells were immunoreactive for all the above subunits, but most strongly for alpha 4 and alpha 7. A proportion of granule cell somata were immunoreactive for all subunits except alpha 3. Punctate immunoreactivity in Purkinje cell and granule cell layers was evident with antibodies against alpha 3, alpha 4, alpha 6, and alpha 7 in parallel with synaptophysin immunoreactivity, suggesting the presence of these subunits on nerve terminals in the human cerebellum. All subunits were present in the dentate nucleus associated with neurones and cell processes. Strong immunoreactivity of neuropil in both the molecular and granule cell layers and within the dentate nucleus was noted with alpha 4, alpha 7 and beta 4 subunits. Astrocytes and astrocytic cell processes appeared to be immunoreactive for alpha 7 and cell processes observed in white matter, also possibly astrocytic, were immunoreactive for beta2. Immunoreactivity to all subunits was noted in association with blood vessels. We suggest that nicotinic acetylcholine receptor subunits may be involved in the modulation of cerebellar activity. Further investigations are warranted to evaluate the participation of nicotinic acetylcholine receptors in cerebellar pathology associated with both developmental and age-related disorders.