Fig. 4.  Histologic examination of the lumbar spinal cord following intrathecal administration of saline or bupivacaine. Animals were injected with saline (A , C , E ) or bupivacaine (3.75 mg/kg) (B , D , F ) and 7 days later their lumbar spinal cords were embedded in plastic, sectioned, and analyzed for histopathology in a blinded fashion. n = 5 for ages P (postnatal day) P7 across both treatment groups and n = 4 for ages P14 and P21 across both treatment groups (total n = 26). As detailed in the Results, no differences were observed between the treatments for any age group: P7 (A  and B ), P14 (C  and D ), and P21 (E  and F ). The inset in panel A  shows a lower magnification image of the spinal cord with a box depicting the area in which the high-resolution analysis was performed. Scale bar 150 μm.