Reduction of fetal rat spinal cord volume following maternal morphine injection.

Previous studies have shown behavioral changes in pre- and postnatal rats exposed to morphine before and during gestation. The present study has attempted to discover morphological correlates of these changes in the fetal rat spinal cord. Pregnant Wistar rats were injected subcutaneously on days 12-18 of gestation with 5 mg/kg of morphine 4 times daily. Non-injected, saline-injected and pair-fed controls were prepared for comparison. On day 18 of gestation the fetuses were perfused and the volume of the first thoracic spinal cord segment was measured using planimetric measurements of histological sections. The following volumes were measured within the segment: hemisection, gray matter, white matter, dorsal horn, ventral horn and length. All volumes were reduced by 20% in morphine-exposed fetuses and 10% in pair-fed fetuses. The length of the spinal cord segment was not different from controls. In addition, body weights were not reduced in either the morphine-exposed or pair-fed fetuses. This is the first study of rats exposed prenatally to morphine, exhibiting a decrease in nervous system volume without an accompanying decrease in body weight.