Sensory Axon Terminals Research Articles

Rapid degeneration of developing rat Pacinian corpuscles after denervation

The effect of denervation upon the development of Pacinian corpuscles was investigated in the crural interosseous membrane of the rat during the early postnatal period. When the sciatic nerve was transected in 1-day-old rats, further development of immature Pacinian corpuscles,was arrested and their structure rapidly disintegrated. In the main cluster of corpuscles, Pacinian axon terminals degenerated within 12 h after the operation and were phagocytised by the inner core cells. Subsequently large dense inclusion bodies and vacuoles with dense debris appeared in the innercore and capsule, and cell autolysis and pyknosis ensued from the 2nd day onwards. The debris of degenerated cells was removed by macrophages and the disintegration of individual corpuscles was completed 2–5 days after nerve section. Normal interosseous membranes of 2–6-day-old rats contained54.9 ± 1.2 (±S.E.) Pacinian corpscles, as revealed by staining for cholinesterase. The total number of corpuscles decreased to about 70% of the control values during the first 2 days after denervation, dropped to 38% on day 3, decreased further to 15% on day 4 and reached zero values on day 5 after nerve section. The experiments demonstrate that the postnatal development and growth of the non-nervous components of Pacinian corpuscles is completely dependent upon the neuronal induction exerted by sensory axon terminals.

Uptake of horseradish peroxidase of sensory terminals of lamellated corpuscles in mouse foot pads.

Uptake of horseradish peroxidase (HRP) by sensory axon terminals was studied in lamellated corpuscles of mouse plantar foot pads after i.v. and local s.c. HRP injections. The corpuscles, considered to be rapidly adapting mechanoreceptors, are localized in dermal papillae and have discoid axon terminals enclosed in 1-5 lamellae of lamellar cells. The injected HRP diffused into interlamellar and adaxonal clefts and was taken up by sensory terminals, being incorporated in coated pits and coated vesicles formed by the axolemma. The tracer further appeared in the axoplasm in smooth vesicles, multivesicular bodies, and vacuoles. Similar incorporation of HRP into vesicles, inclusion bodies, and vacuoles was observed in the lamellae and perinuclear cytoplasm of lamellar cells. Vibratory stimulation considered to be adequate for this type of mechanoreceptors did not result in any perceptible increase in HRP uptake by sensory terminals. It is suggested that endocytosis by sensory terminals may serve for incorporation of regulatory macromolecules that presumably mediate information to the perikaryon about conditions of the distant terminals and their microenvironment.

Regeneration of olfactory axons and synapse formation in the forebrain after bulbectomy in neonatal mice.

We removed the right olfactory bulb in neonatal mice, leaving the bulb on the left side intact as an internal control. At 5 days of survival time, we observed that the right cerebral hemisphere was displaced forward to occupy the region made vacant by removal of the bulb. The frontal cortex was, consequently, in close proximity to the lamina cribrosa. As a result of bulb ablation and severance of the fila olfactoria, the sensory perikarya underwent total retrograde degeneration, which peaked at 8 days. New neurons differentiated in the neuroepithelium from basal stem cells and, at 30 days of survival, mature sensory neurons were reconstituted. These new elements sent their axons through the lamina cribrosa to reach the protruding cerebral hemisphere, penetrating it and forming glomeruli-like structures directly in the host tissue. The "glomerulization" of the sensory fibers persisted and actually expanded between 60 and 120 days. The new glomeruli were organized intimately within the brain tissue, and large neurons of the cortex were observed to be in close proximity. Ultrastructural observations of the newly formed glomeruli demonstrated that typical sensory axon terminals profusely branched and synapsed with unidentified postsynaptic processes that penetrated the glomeruli from the surrounding cerebral tissue.