Beta-endorphin in experimental canine spinal ischemia

Subcutaneous administration of tramadol after elective surgery is as effective as intravenous administration in relieving acute pain and inflammation in dogs

Subcutaneous (SC) administration of tramadol was compared with intravenous (IV) administration to evaluate analgesia following canine ovariohysterectomy (OHE). Healthy female dogs (n = 12) between 1 and 3 years of age (1.95 ± 0.65 years), weighing between 10.5 and 17.1 kg (13.12 ± 1.95 kg), were used. Pain was assessed at baseline before surgery and then hourly for 8 hr after surgery. Tramadol was administered both SC and IV at a dose of 3 mg/kg and provided significant postoperative analgesia, as indicated by analgesiometry, β-endorphin levels, and interleukin 6 (IL-6) levels. The respiratory rates and rectal temperatures remained normal and were not significantly different between or within the groups. A significant increase in heart rate was observed at 4 hr for dogs in both groups relative to the baseline, but there was no significant difference in heart rates between the groups at any time point. A significant decrease in mechanical pain threshold was observed within each group after surgery, but both groups responded similarly, suggesting that SC administration of tramadol is as effective as IV administration. Increased serum levels of both IL-6 and β-endorphin 3 hr postoperatively further indicate that both routes of administration achieve similar pain control. Thus, the relative analgesic efficacy of SC tramadol is comparable to that of IV administration and can be used to achieve similar effects for postsurgical pain management in dogs undergoing OHE.

Treatment methods for spinal cord injury caused by acute type B aortic dissection

Acute distal aortic dissection rarely causes spinal cord ischemia presenting with paraplegia or paraparesis. Spinal cord involvement has poor outcomes, and there is no established effective treatment for this disorder. In this report we describe the acute conservative treatment of two cases of paraplegia/paraparesis due to acute type B aortic dissection. Early reversal of lower-limb dysmobility was achieved.

Mu and delta, but not kappa, opioid agonists induce spastic paraparesis after a short period of spinal cord ischaemia in rats

BACKGROUND

Intrathecal (IT) morphine given after a short interval of aortic occlusion in a rodent model induced transient spastic paraparesis via opioid receptor-predicted actions in spinal cord. To determine the role(s) of spinal opioid receptor subtypes we investigated whether IT administration of various selective opioid receptor agonists can induce paraparesis following a short period of spinal cord ischaemia in rats.

METHODS

In Sprague-Dawley rats implanted with an IT catheter, spinal cord ischaemia was induced for 6 min using an intraaortic balloon. Mu ([D-Ala2, N-Me Phe4, Gly-ol5] enkephalin), kappa (U50488H) or delta ([D-Pen(2,5)] enkephalin) selective agonists were injected intrathecally 30 min after reperfusion. A separate group of animals was used to investigate the dose-response effect on this motor dysfunction. For this purpose, three doses of mu, kappa, or delta agonists were injected intrathecally after ischaemia. After IT injection, recovery of motor function was assessed periodically using the motor deficit index (0=complete recovery; 6=complete paraplegia).

RESULTS

IT administration of mu and delta but not kappa agonists produced dose-dependent effects in the induction of spastic paraparesis. In addition, this spasticity induced by IT mu and delta agonists was reversed completely by IT naloxone and naltrindole, respectively.

CONCLUSION

These results suggest that the effect of various opioids on motor function after a short period of spinal cord ischaemia depends upon individual opioid receptor subtypes.

Intrathecal administration of morphine, but not small dose, induced spastic paraparesis after a noninjurious interval of aortic occlusion in rats

We sought to investigate the dose-response relationship for the effect of intrathecal morphine on the transient spastic paraparesis after short-lasting spinal ischemia in rats. Spinal ischemia was induced by aortic occlusion for 6 min with a balloon catheter in rats previously implanted with an intrathecal catheter for drug delivery. After ischemia, the animals were allowed to recover, and 3, 10, or 30 microg of morphine or saline was injected intrathecally at 30 min after reperfusion. In a separate group, the quantal bioassay for the effect of intrathecal morphine on neurological function after ischemia was performed to calculate 50% effective dose values for inducing paraparesis at 2 h of reperfusion. Subsequently, histopathology of the spinal cord was assessed at 48 h of reperfusion. Intrathecal injection of 30 or 10 micro g of morphine, but 3 micro g of neither morphine nor saline, caused a progressive development of hindlimb spasticity. The 50% effective dose values for inducing paraparesis were 16.1 +/- 1.5 microg in assessing behavioral analysis at 2 h after intrathecal morphine. Histopathological analysis of spinal cords in the 30- microg group revealed the presence of dark-staining alpha-motoneurons in lumbosacral segments. We conclude that spinal administration of a large dose of morphine after transient aortic occlusion may be associated with a potential risk of paraparesis and the corresponding development of neurological dysfunction. Careful attention should be paid when intrathecal morphine is used for pain control after thoracoabdominal aortic aneurysm repair.

IMPLICATIONS

Spinal administration of large-dose morphine after transient aortic occlusion may be associated with a potential risk of irreversible spinal neuronal degeneration and the corresponding development of neurological dysfunction.

Spinal cord protection during surgical procedures on the descending thoracic and thoracoabdominal aorta: a critical overview

During the past three decades, significant advances have been made in the surgical treatment of the diseases affecting the aorta. Despite these important advances, paraplegia remains a devastating complication of the surgical procedures on the thoracic and thoracoabdominal aorta. Paraparesis and paraplegia occur as a direct result of the interruption of blood flow to the spinal cord during the surgical procedures. A number of techniques have been advocated for the prevention of spinal cord ischemic injury. This article critically reviews our current understanding of the extent of this problem, the mechanism of injury, and the methods that have been devised to reduce the frequency of paraplegia following surgical procedures on the descending aorta.

Combined use of cerebral spinal fluid drainage and naloxone reduces the risk of paraplegia in thoracoabdominal aneurysm repair

PURPOSE

This report summarizes our experience with the use of cerebral spinal fluid drainage (CSFD) and naloxone for prevention of postoperative neurologic deficit (paraplegia or paraparesis).

METHODS

We reviewed 110 consecutive patients with 86 thoracoabdominal aneurysms and 24 thoracic aneurysms. The status of 47 patients (43%) was acute (rupture or dissection), and the status of 52 (47%) was Crawford type I or II. None of the patients had intercostal artery reimplantation. There were two patient groups for analysis of neurologic deficit risk. Group A (61 patients) received naloxone and CSFD, and group B (49 patients) did not.

RESULTS

One deficit occurred in group A and 11 deficits occurred in group B (p = 0.001). By multiple logistic regression analysis, the variables acute status, Crawford type II, or group B classification were significant factors for deficit risk. Use of the same logistic regression analysis on the subgroup of 47 patients with acute aneurysms and 33 patients with Crawford type 2 aneurysms confirmed the protective effect of combined CSFD and naloxone (group A) and that clinical presentation and extent of aorta replaced are the primary risk factors for development of deficit. To test this conclusion we developed a highly predictive model (correlation coefficient 0.997 with 16 series of thoracoabdominal aneurysms) for neurologic deficit. We applied our data to this model. Group B had the predicted number of deficits, and group A had substantially fewer deficits than predicted.

CONCLUSIONS

We conclude that the combined use of CSFD and naloxone offers significant protection from neurologic deficits in patients undergoing thoracoabdominal and thoracic aortic replacement.

The effects of naloxone on retinal ischemia in rats

The efficacy of naloxone (NL), a broad spectrum opioid antagonist, on retinal ischemia, was evaluated in a rat model of retinal ischemia with histopathologic and morphometric criteria. Two intraperitoneal injections of naloxone 3 mg/kg given immediately and 6 hr after reperfusion showed beneficial effects to the retina as evaluated at 2, 7, and 14 days after reperfusion. Morphologically, the naloxone-treated group showed better-preserved ganglion cells, nerve fiber layer, and inner nuclear layer. Morphometrically, in the treated groups, inner retinal thickness at all three time points and ganglion cell counts at 7 days showed higher values than vehicle controls. This beneficial effect of naloxone was dose-dependent with a minimal effective total dose of 6 mg/kg. A possible role of opiate receptors in retinal ischemia is suggested.

Endogenous opiates: 1989

This paper is the twelfth installment of our annual review of the research published during 1989 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal functions; mental illness; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; locomotor activity; sex, development, pregnancy, and aging; immunological responses; and other behavior.