Intraventricular administration of substance P induces unattached Purkinje cell dendritic spines in rats.

Substance P was infused in the lateral ventricles of twenty Lewis rats for twenty days. The animals under the influence of the substance P demonstrated grooming of the head, the body and the forepaws. On the twentieth day the animals were sacrificed and the cerebellar cortex was processed for electron microscopy. The ultrastructural analysis revealed that although the granule cells, the parallel fibers and the systems of the afferent fibers were intact, numerous unattached Purkinje cell dendritic spines were seen embedded in the soma of the astrocytes, demonstrating postsynaptic differentiation. Numerous unattached spines of the secondary and tertiary dendritic branches of the Purkinje cells were also seen in the molecular layer surrounded by astrocytic sheath. Free unattached spines were also seen not surrounded by any astrocytic process, which did not demonstrate any postsynaptic specialization. The development of unattached Purkinje cell dendritic spines, in an otherwise intact cerebellar cortex, following the intraventricular administration of substance P, suggests that it may act as local growth factor, enforcing the preprogrammed-capability of the Purkinje cells in developing new synaptic surfaces.