Repair of the transected spinal cord at different stages of development in the North American opossum, Didelphis virginiana.

When the thoracic spinal cord is transected on postnatal day (PD) 5 in the North American opossum, descending and ascending axons grow through the lesion site. When the lesion is made on PD20, comparable growth is limited to a subset of descending axons. To better understand the mechanisms underlying these differences, we analyzed the transection site at different times after lesioning at both ages. Axons which crossed the lesion site could be identified using silver impregnation and immunostaining for neurofilament. Nissl stains revealed that abnormal appearing grey matter was also present in some of the PD5 cases. In many PD5 cases, however, and in all of the animals transected at PD20, grey matter was not present at the lesion site. Immunostaining with a neuron specific antibody supported that conclusion. However, immunostaining with phenotypic specific antibodies revealed that glial cells were present in all cases. Immunostaining for Schwann cells was negative. Fibronectin-positive cells were also present at the lesion site after transection of the thoracic cord at PD20, but their identity was uncertain. When injections of bromodeoxyuridine (BrdU), a thymidine analog, were made at different times after lesioning and the pups were sacrificed for BrdU immunohistochemistry up to 40 days later, labeled cells were found in the tissue which bridged the lesion site indicating that cell proliferation contributed to reconstruction at the lesion site.

Traumatic injuries occurring in possums and gliders in the Blue Mountains, New South Wales.

Twenty common brushtail possums (Trichosurus vulpecula), 23 ringtail possums (Pseudocheirus peregrinus) and five sugar gliders (Petaurus breviceps) from the Blue Mountains, New South Wales, Australia were evaluated for traumatic injuries between 1989 and 1990. Ten brushtail possums and five ringtail possums were hit by motor vehicles with injuries primarily to the anterior of the body. Fifteen ringtail possums and all sugar gliders were attacked by cats. Four brushtail possums were attacked by dogs. The remaining nine possums had evidence of intraspecific fighting (n = 2) or other types of trauma. Brushtail and ringtail possums were presented primarily during their main breeding seasons. There was no sex predilection. More ringtail than brushtail possums were subadults and these were injured primarily at the time of dispersal.