Fig 1.
Effects of a single dose of intrathecal (IT) morphine on residual locomotor function after mild thoracic spinal cord injury (SCI).
Locomotor function was measured by the 21-point Basso, Beattie, and Bresnahan (BBB) locomotor rating scale (0 = complete paralysis; 21 = normal locomotion) before SCI (time 0) and after administration of IT morphine (30 μg/10 μl) or IT normal saline (10 μl). IT morphine or IT saline was administered 6 hours after SCI. An arrow indicates the timing of administration of drugs (morphine or saline. n = 6 in each group. Data are presented as means ± SDs. * P < 0.05 compared to saline. # P < 0.05 compared to time 0.
Fig 2.
Locomotor function (a-d) and muscle tone (e-h) after intrathecal (IT) administration of morphine and μ- (DAMGO), δ- (DPDPE), and κ- (U50,488H) selective opioid receptor agonists after mild thoracic spinal cord injury (SCI). Locomotor function was evaluated using the 21-point Basso, Beattie, and Bresnahan (BBB) locomotor rating scale (0 = complete paralysis, 21 = normal locomotion) before SCI (pre SCI), 6 hours after SCI (SCI), after administration of each drug, and after IT administration of naloxone (60 μg). The panels show effects of (a) morphine, (b) DAMGO, (c) DPDPE, and (d) U50,488H. Data of the BBB score are presented as means ± SDs. The Ashworth scales (0 = no increase in tone; 4 = increase in muscle tone) were used to evaluate changes in muscle tone of the hindlimbs before SCI (pre SCI), 6 hours after SCI (SCI), after administration of each drug, and after administration of IT naloxone (60 μg). The panels show effects of (e) morphine, (f) DAMGO, (g) DPDPE, and (h) U50,488H. Data are presented as scatter dot plots of the Ashworth score displaying the median as a line and the 25–75 percentiles. n = 6 in each dose. * P < 0.05 compared to post SCI. # P < 0.05 compared to before naloxone.
Fig 3.
Effects of continuous infusion of intrathecal (IT) morphine on locomotor function and muscle tone after mild spinal cord injury (SCI).
Locomotor function (a) was evaluated using the 21-point Basso, Beattie, and Bresnahan (BBB) locomotor rating scale and muscle tone (b) was evaluated using the Ashworth scale before SCI (time 0) and 6 hours after the SCI or sham operation and after the start of continuous administration of IT morphine or normal saline up to day 14. A single dose of 30 μg of IT morphine was administered followed by continuous infusion of morphine (3 μg/hour with a concentration of 3 μg/1 μl of morphine in saline) for 72 hours to rats with SCI (SCI + morphine) and sham-operated rats without SCI (Sham + morphine). Physiological saline was continuously administered (1 μl/hour) for 72 hours to rats with SCI (SCI + saline) and sham-operated rats without SCI (Sham + saline). Data of the BBB scores are expressed as means ± SDs. n = 6 in each group. Data are presented as scatter dot plots of the Ashworth scores displaying the median as a line and the 25–75 percentiles. * P < 0.05 compared to SCI + saline group. # P < 0.05 compared to Sham + saline group.
Fig 4.
Effects of intrathecal (IT) naloxone, an opioid receptor antagonist, on locomotor function after administration of IT morphine to rats with mild spinal cord injury (SCI).
Locomotor function was evaluated using the 21-point Basso, Beattie, and Bresnahan (BBB) locomotor rating scale. Panel (a) shows effects of IT naloxone (60 μg), administered 30 min after the end of 72-hour continuous infusion of morphine, on locomotor function of rats. A single dose of 30 μg of IT morphine was administered followed by continuous infusion of 3 μg/hour morphine for 72 hours to rats with SCI. Panel (b) shows effects of IT naloxone on locomotor function after IT administration of a single dose of morphine. A single dose of 30 μg of IT morphine was administered 30 min after the end of 72-hour continuous infusion of normal saline to rats with SCI. After another 30 min, naloxone was intrathecally administered. The BBB scores on the third day were evaluated 30 min after administration of each drug. Data are shown as means ± SDs. n = 6 in each group. *P < 0.05 compared to data at 6 hours after thoracic SCI. # P < 0.05 compared to before IT naloxone.
Fig 5.
Effects of continuous administration of intrathecal (IT) morphine on α-motoneurons in the lumbar spinal cord after mild thoracic spinal cord injury (SCI).
The ventral horns in the lumbar spinal cord were stained by the Klüver-Barrera method after 72-hour continuous infusion of IT normal saline to rats without SCI (a, sham + saline), IT morphine to rats without SCI (b, sham + morphine), IT normal saline to rats with mild thoracic SCI (c, SCI + saline), or morphine (d, SCI + morphine) to rats with mild thoracic SCI. Images of the left ventral horns are shown in this figure. The number of α-motoneurons in the left ventral horn of the lumbar spinal cord (e) was counted. Dark-stained α-motoneurons (considered to be damaged) (arrowhead) were seen in all of the groups and the ratios of damaged /total α-motoneurons (f) were calculated. Data are expressed as means ± SDs. n = 6 in each group.