Ultrastructural localization of molecular subtypes of immunoreactive neural cell adhesion molecule (NCAM) in the adult rodent striatum

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Abstract
Neural cell adhesion molecule (NCAM) is a plasma membrane glycoprotein that is thought to mediate adhesion between neuronal elements and play an important role in neural development. Although NCAM has been found in the adult brain, as well as the developing brain, little is known about its function or ultrastructural distribution. A monoclonal antibody which was directed against embryonic (E15-E17) mouse brain and identified 180 and 140 kDa molecular weight forms of NCAM was used to examine the immunohistochemical localization of NCAM in the rodent striatum. Light microscopic results in the adult mouse and rat showed that most NCAM180,140 immunoreactivity was localized to the relatively small population of medium and large-sized aspiny interneurons of the caudate nucleus and to the majority of neurons in the globus pallidus. Ultrastructural analysis revealed that reaction product in aspiny somata was present in discrete, closely spaced patches of cytoplasm along the inner face of the plasma membrane and was also prominent in somatic protrusions which were frequently apposed to synapsing axons. Distal aspiny and pallidal dendrites containing NCAM180,140 received numerous synaptic inputs. Within caudate neuropil NCAM180,140 was also present in spines with thin necks and small spine heads which were postsynaptic to unlabeled axon terminals and in preterminal (unmyelinated) axons and terminal boutons that issued from myelinated bundles and formed asymmetric synapses with unlabeled dendritic spines. This study provides the first evidence in adult brain that NCAM180,140 varies in extent and location within neurons. The heterogeneous distribution of NCAM180,140 in neurons of the basal ganglia may be related to a number of functions such as maintaining or modulating the density and distribution of synaptic inputs and the formation of new contacts on dendritic spines.