Ultrastructural localization of insulin-like immunoreactivity in the rat spinal cord.

Insulin-like immunoreactive neurons were localized in the cervical, thoracic, lumbar and sacral segments of the rat spinal cord. Neurons from both the ventral and dorsal horns were labelled. The insulin-like reaction product was predominantly localized in the cell nucleus and the proximal and distal dendrites. In the labelled cell nucleus, the reaction product was scattered throughout the nucleoplasm and the inner and outer nuclear membranes but not within the nucleolus. In the labelled dendrites, the reaction product was closely associated with the parallel arrays of neurotubules. Most of the labelled distal dendrites were postsynaptic to non-labelled axon terminals. A labelled dendrite often formed the central element of a synaptic glomerulus with several non-labelled axon terminals. It is hypothesized that the insulin-like substance(s) may be modulating nuclear activities as well as neurotransmission at the synapse in the spinal cord.