ABSTRACT
Lack of dystrophin is known to reduce several cerebral fiber systems. To investigate if the loss of fibers is progressive, we analyzed projections of the trigeminal sensory system to the red nucleus in 3, 6, and 12 month old dystrophin-deficient mdx mice. The retrograde tracer fluorogold was injected in the magnocellular part of the red nucleus, and the number of labeled neurons in the oral part of the spinal trigeminal nucleus (Sp5O) was counted. We found that the number of labeled Sp5O neurons was reduced by 50% in mdx mice compared to age-matched control mice. The number of labeled Sp5O neurons did not change significantly between 3 and 12 months neither in mdx nor in control mice. In addition, the number of labeled neurons in the interstitial system of the trigeminal nerve was reduced by 43% in mdx mice. We conclude that fiber loss did not continue beyond the age of 3 months. Our data suggest that lack of full-length dystrophin impairs neuronal migration or axonal outgrowth, or increases neuronal death during fetal or early life.
Subject(s)
Axons/metabolism , Dystrophin/genetics , Nerve Degeneration/metabolism , Red Nucleus/abnormalities , Trigeminal Nucleus, Spinal/abnormalities , Animals , Axons/ultrastructure , Brain Mapping , Cell Count , Cell Death/genetics , Disease Models, Animal , Male , Mice , Mice, Inbred C57BL , Mice, Inbred mdx , Nerve Degeneration/genetics , Nerve Degeneration/physiopathology , Nervous System Malformations/genetics , Nervous System Malformations/metabolism , Nervous System Malformations/physiopathology , Neural Pathways/abnormalities , Neural Pathways/cytology , Neural Pathways/metabolism , Red Nucleus/cytology , Red Nucleus/metabolism , Stilbamidines , Trigeminal Nerve/abnormalities , Trigeminal Nerve/cytology , Trigeminal Nerve/metabolism , Trigeminal Nucleus, Spinal/cytology , Trigeminal Nucleus, Spinal/metabolism , Wallerian Degeneration/genetics , Wallerian Degeneration/metabolism , Wallerian Degeneration/physiopathologyABSTRACT
The neurons of the lateral spinal nucleus in the spinal cord of young adult rats were studied in transverse and longitudinal planes using the Golgi-Kopsch method and electron microscope. The perikarya were mainly polygonal or spindle shaped, and measured 20 to 35 pm in the longest diameter. They formed a dense column in the dorsolateral funiculus underneath the pial surface. The dendrites followed three patterns. Several of them turned laterally and approached the surface of the spinal cord. Another group of dendrites ran longitudinally within the column of the perikarya. A third group of dendrites turned medially or ventromedially and coursed towards the reticulated portion of the gray matter. Medium-sized neurons located at the margin of this latter portion of the spinal cord sent some of their straight dendrites into the dorsolateral funiculus. Thus, the dendrites of these two populations of neurons appeared as rungs of a ladder in longitudinally-cut spinal cord specimens. Only the initial portions of the axons of the LSN neurons could be impregnated. They originated with a regular axon hillock from either the perikaryon or from one of the primary dendrites and became unimpregnated after a 20 to 40 ?m long course, indicating their myelinated character. Preliminary ultrastructural observations revealed that the laterally directed dendrites of the neurons in the lateral spinal nucleus approached the free surface of the spinal cord and ended immediately underneath the pia mater. Large numbers of fine, unmyelinated fibers were found in the dorsolateral funiculus coursing perpendicular to the laterally and medially oriented dendrites (AU)
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