Renal sympathetic preganglionic neurons in the spinal cord of rabbits were transneuronally retrogradely labelled by injection of Herpes simplex virus type 1 into the renal nerve and immunohistochemical demonstration of viral antigen. The morphology of the labelled neurons was examined, particularly with respect to the shape and extent of their dendritic trees. Double-labelling immunohistochemical studies were performed to determine the relationship of neuropeptide Y-immunoreactive axons to virus-labelled perikarya and dendrites. The shape of the renal sympathetic preganglionic neurons differed according to whether the neurons were located in the intermediolateral cell column or in other sympathetic areas. The neurons in the intermediolateral cell column had very long dendrites, extending in the rostrocaudal and mediolateral directions. The medially oriented processes extended towards and beyond the central canal. The laterally oriented dendritic processes projected within the dorsolateral funiculus, towards the edge of the spinal cord. Neuropeptide Y-immunoreactive fibres were concentrated in regions containing renal sympathetic preganglionic neurons of the spinal segments examined (T7-L2). Immunoreactive varicose terminals were closely opposed to individual preganglionic neurons, especially to the dendritic processes of these neurons. Our findings indicate that neurotransmitter candidates such as neuropeptide Y are likely to influence renal preganglionic neurons by an input to dendritic processes at some distance from the perikarya. Electrophysiological and other functional studies utilizing applications of neurotransmitter candidates onto these neurons should take this into account.
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