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Effect of systemic morphine on neurons in the lateral reticular nucleus area of the rat
1Neurophysiology Laboratory, Xian Medical University, Shaanxi, People's Republic of China.
Abstract:
The present study is undertaken to investigate the effect of systemic morphine on neurons in the lateral reticular nucleus (LRN) using extracellular recording techniques. The spontaneous activities of 64 neurons in the LRN area were tested with morphine (3-5 mg/kg, IV). Morphine excited 23 and inhibited 28 neurons tested, and 13 neurons were not affected. Of the 28 neurons inhibited, 20 were identified as nociceptive and the remaining 6 were nonnociceptive. Of the 23 neurons excited by morphine, 18 were nociceptive and 5 were nonociceptive. Systemic naloxone (0.3-0.5 mg/kg) significantly reversed the morphine effect in 15 out of 19 neurons excited and 19 out of 20 neurons inhibited by morphine. Thirteen out of 64 neurons were further identified as reticulospinal neurons, of which four were excited and four were inhibited by morphine. The remaining five were not affected. The results demonstrate that a similar proportion of neurons in the LRN area were either excited or inhibited by systemic morphine, and the majority of them are nociceptive neurons. It is suggested that different types of neurons in the LRN area may have different functions in morphine analgesia.
Insights
Systemic morphine affects lateral reticular nucleus (LRN) neurons, exciting or inhibiting them, primarily nociceptive neurons. Naloxone reversed these morphine-induced changes, suggesting complex roles in analgesia.
Area of Science:
- Neuroscience
- Pharmacology
Background:
- The lateral reticular nucleus (LRN) plays a role in motor control and sensory processing.
- Opioid analgesics, like morphine, exert their effects through complex neural pathways.
Purpose of the Study:
- To investigate the effects of systemic morphine on neuronal activity within the lateral reticular nucleus (LRN).
- To determine the proportion of nociceptive and non-nociceptive neurons affected by morphine in the LRN.
- To examine the role of naloxone in reversing morphine's effects on LRN neurons.
Main Methods:
- Extracellular recording techniques were used to monitor the spontaneous activity of 64 LRN neurons.
- Neurons were tested with systemic administration of morphine (3-5 mg/kg, IV).
- Naloxone (0.3-0.5 mg/kg) was administered to assess reversal of morphine's effects.
Main Results:
- Morphine excited 23 neurons (18 nociceptive, 5 non-nociceptive) and inhibited 28 neurons (20 nociceptive, 6 non-nociceptive).
- Thirteen neurons were identified as reticulospinal neurons, with morphine exciting 4 and inhibiting 4.
- Naloxone significantly reversed morphine's effects in the majority of affected neurons.
Conclusions:
- Systemic morphine differentially affects neuronal activity in the LRN, with a significant proportion of neurons being either excited or inhibited.
- The majority of morphine-affected neurons in the LRN are nociceptive.
- These findings suggest that different neuronal populations within the LRN contribute to morphine's analgesic effects.