| Abstract No.: | B-C2123 |
| Country: | Canada |
| | |
| Title: | REGENERATING AXONS FROM CAT PROPRIOSPINAL COMMISSURAL INTERNEURONS FORM FUNCTIONAL SYNAPTIC CONNECTIONS: ELECTROPHYSIOLOGICAL AND ANATOMICAL EVIDENCE |
| | |
| Authors/Affiliations: | 1 Keith K. Fenrich*; 1 P. Ken Rose;
1 Queen's University, Kingston, ON, Canada
|
| | |
| Content: | Neurons of the mammalian central nervous system (CNS) do not typically regenerate following injury. We have recently presented evidence that axotomized propriospinal commissural interneurons (PCIs) of the cat do regenerate their axons through the inhibitory environment of the lesioned spinal cord and conduct action potentials (Society for Neuroscience 2008 – Prog# 136.12). However, whether these regenerated axons form functional synaptic connections is unclear. To test the functional capacity of regenerated PCIs we used anatomical, immunohistochemical, and electrophysiological techniques.
PCI somata are located primarily within the ventral horn and have axons which project to the contralateral spinal cord through the ventral commissure. These axons were cut at the ventral commissure by a 4 mm long dorsal midsagittal lesion at C3. At 10 weeks post-lesion, tungsten stimulating electrodes were placed in the ventral horn adjacent to the lesion on one side of the spinal cord and multiple extracellular injections of Neurobiotin were made within the ventral horn on the other side of the spinal cord. Analysis of Neurobiotin stained regenerated PCI axons indicate that these axons form collaterals with bouton-like structures that are apposed to dendrites. To test whether the bouton-like structures of regenerated PCIs had biochemical features typical of functional synapses, we stained PCIs for synaptophysin. Synaptophysin is a synaptic vesicle glycoprotein, and a key protein involved in neurotransmitter release. Like functional synapses, bouton-like structures on regenerating PCI axons have a punctuate distribution of synaptophysin. To test the capacity of regenerated PCIs to excite or inhibit neurons, we recorded intracellular responses of motoneurons and interneurons following micro-stimulation of PCIs located in the contralateral spinal cord. To ensure that only regenerating PCIs were stimulated, only responses generated from stimulating electrodes well within the rostral-caudal length of the lesion site were included and stimulus strengths were minimized to prevent current-spread to unlesioned PCIs. Using these criteria, we recorded both excitatory and inhibitory post-synaptic potentials in a small proportion (2/26) of the impaled neurons. Taken together, our data show that regenerated PCI axons have morphological, biochemical, and electrical features consistent with functional synaptic connectivity.
|
| | |
| Back |
|
