| Abstract No.: | B-D2138 |
| Country: | Canada |
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| Title: | EXPRESSION OF THE GAP JUNCTION PROTEIN CONNEXIN-36 IN THE SPINAL CORD OF OPOSSUMS (MONODELPHIS DOMESTICA) DURING DEVELOPMENT |
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| Authors/Affiliations: | 1 Maxime Lemieux*; 1 Thérèse Cabana; 1 Jean-François Pflieger;
1 Université de Montréal, QC, Canada
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| Content: | Objectives: Opossums of the species Monodelphis domestica are born after a gestation of 13-14 days. At birth (P0), their forelimbs are just sufficiently developed to perform rhythmic, alternate movements allowing them to climb on the mother and reach a nipple where they attach. Their hindlimbs are little more than immobile buds that will start moving in the second week. The spinal cord enlargements have embryonic features, especially at lumbar levels. Motoneurons are recognized by their position and slightly larger size. Almost all projections from the brainstem will grow in postnatally. Moreover, few chemical synapses are present in the spinal enlargements at P0, but they occur in the entire grey matter by the third week, when most spinal reflexes appear, suggesting that evoked activity develops mostly postnatally. This led us to hypothesize that the initial spinal activity is mainly spontaneous and electrical, instead of chemical, and is mediated by gap junctions.
Materials and Methods: We have investigated immunohistochemically the presence of connexin36 (cx36), a neuron specific gap junction protein, and have used NeuN to identify neurons on sections of the spinal enlargements of postnatal opossums. The retina, a structure where cx36 is highly expressed in mammals, was used as positive control for antibodies. Results: On transverse sections of the spinal enlargements of P0 opossums, cx36 is expressed in the presumptive gray and white matter ventrally and to a lesser extent in the more immature dorsal region. At P5, punctate labeling is visible close to presumptive motoneurons and cx36 expression has increased dorsally. By P10, cx36 expression has disappeared from the presumptive white matter at cervical levels, except for a portion of the dorsolateral funiculi, but is still evidenced in all funiculi at lumbar levels. Labeling is moderate in the grey matter, but is more intense in the presumptive substantia gelatinosa. Larger puncta are seen in the vicinity of motoneurons, which can now be divided into medial and lateral pools. At P20, cx36 labeling is similar in the grey matter, but it has disappeared in the presumptive white matter, except dorsolaterally. By P50, cx36 is expressed only faintly in the grey matter and has disappeared entirely in the white matter. Cx36 is below detection level even in the spinal grey matter of adult opossums.
Conclusion: Cx36 is expressed in the spinal enlargements of newborn opossums. It increases afterwards along a ventrodorsal gradient and then decreases to a very low level in the grey matter and below detection in the white matter. The transient expression of cx36 at ages when no or only few chemical synapses are observed in the spinal enlargements suggests the existence of electrical synapses. Thus, electrotonic coupling could mediate neuronal activity underlying motor behaviors in neonatal opossums until chemical synapses are in place. |
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