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Updated: May 25, 2026

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
Dopamine affects the change of pain-related electrical activity induced by morphine dependence
Ying Zhang1, Fengmin Zhang, Chunxiao Yang
1Department of Physiology, Harbin Medical University, Xuefu Road, No.194, Harbin 150081, People's Republic of China.
Abstract:
Morphine is among the most effective analgesics. However, many evidences suggest that, besides the well-know analgesic activity, repeated opioids treatment can induce some side effects such as dependence, hyperalgesia and tolerance. The mechanism of noxious information transmission in the central nervous system after dependence is not clear. An important neurotransmitter, dopamine (DA) participates not only in the process of opioid dependence but also in pain modulation in the central nervous system. In the present study we observed changes of electrical activities of pain-excitation neurons (PENs) and pain-inhibition neurons (PINs) in the caudate nucleus (Cd) following the development of morphine dependence. We also observed the role of DA on these changes. Our results revealed that both the latency of PEN discharges and the inhibitory duration of PIN discharges decreased, and the net increased values of PEN and PIN discharges increased in the Cd of morphine dependent rats. Those demonstrated that electrical activities of both PENs and PINs increased in morphine dependent rats. DA inhibited the electrical activities of PENs and enhanced those of PINs in morphine dependent rats.
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