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The effects of intrathecal morphine and naltrexone on autotomy in sciatic nerve sectioned rats
1Department of Clinical Neurophysiology, Huddinge University Hospital, S-141 86 HuddingeSweden.
Abstract:
Rats were implanted with an intrathecal catheter aimed at the lumbar enlargement (LE). Morphine hydrochloride (240 micrograms/day) was infused continuously on the spinal cord for 14 days with an osmotic minipump delivering 0.5 microliter/h solution or a bolus dose of naltrexone (37.5, 75 or 150 micrograms) was injected intrathecally. Intrathecally infused morphine delivered on the dorsum of the LE induced analgesia, as tested on the hot plate, whereas normal saline was without effect. Naltrexone caused hyperalgesia revealed as decreased threshold for vocalization to electrical stimulation of the tail. Rats with unilaterally sectioned sciatic nerves that were continuously infused with morphine on the dorsum of the LE autotomized significantly less than saline controls. Nerve sectioned rats injected with naltrexone had an overall level of autotomy similar to saline controls. However, autotomy had a somewhat earlier onset and was more severe with naltrexone than with saline. It is therefore concluded that intrathecal infusion of opiates specifically reduces autotomy, a behavior that may occur as a result of chronic discomfort or pain following nerve injury. Furthermore, the endogenous opiate system at the spinal level may be involved in the control of autotomy.
Insights
Intrathecal morphine infusion reduced autotomy, a sign of nerve injury pain in rats. This suggests spinal opiates may help manage chronic pain following nerve damage.
Area of Science:
- Neuroscience
- Pharmacology
- Pain Research
Background:
- Chronic pain and autotomy (self-mutilation) are significant issues following nerve injury.
- The role of the endogenous opioid system in modulating pain behaviors after nerve injury requires further investigation.
Purpose of the Study:
- To investigate the effects of intrathecal morphine and naltrexone on pain behaviors and autotomy in rats with sciatic nerve injury.
- To explore the involvement of the spinal endogenous opioid system in controlling autotomy.
Main Methods:
- Rats received continuous intrathecal morphine infusion or bolus naltrexone injections targeting the lumbar enlargement.
- Pain was assessed using hot plate tests and vocalization thresholds.
- Autotomy behavior was quantified in rats with unilaterally sectioned sciatic nerves.
Main Results:
- Intrathecal morphine induced analgesia on the hot plate, while naltrexone caused hyperalgesia.
- Continuous morphine infusion significantly reduced autotomy in nerve-injured rats compared to saline controls.
- Naltrexone administration led to an earlier onset and more severe autotomy, though overall levels were similar to saline controls.
Conclusions:
- Intrathecal opiate infusion effectively reduces autotomy, indicating a specific role in mitigating pain associated with nerve injury.
- The endogenous opioid system at the spinal level appears to play a role in the control of autotomy following nerve injury.
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