Spontaneous and cortically-evoked unit activity in the caudate nucleus after systemic morphine

Area of Science:

• Neuroscience
• Pharmacology

Background:

• The caudate nucleus plays a crucial role in motor control and reward pathways.
• Understanding how opioids like morphine affect neuronal activity in the caudate nucleus is vital for pain management and addiction research.

Purpose of the Study:

• To investigate the effects of systemically administered morphine on spontaneous and cortically-evoked single unit activity in the rat caudate nucleus.
• To determine the role of naloxone in reversing morphine-induced changes in neuronal activity.

Main Methods:

• Rats were surgically implanted with microelectrode guide cannulas and cortical stimulating electrodes.
• Morphine was administered intravenously in incremental doses (1-30 mg/kg).
• Neuronal activity (spontaneous and evoked) was recorded, and the effects of naloxone (1 mg/kg) were assessed.

Main Results:

• Morphine altered spontaneous activity in a significant portion of caudate nucleus neurons, with depression observed in 12/33 cells and stimulation in 5/33 cells.
• Cortically-evoked neuronal firing was also affected, with reduction in 7/36 units and enhancement in 9/36 units.
• A substantial number of morphine-induced responses, particularly those affecting evoked firing, were not reversed by naloxone.

Conclusions:

• Systemic administration of morphine induces diverse changes in both spontaneous and cortically-evoked activity of caudate nucleus neurons.
• The incomplete reversal of these effects by naloxone suggests complex interactions and potentially non-opioid receptor-mediated actions of morphine in this brain region.