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Supraspinal FMRFamide antagonizes morphine-induced horizontal, but not vertical, locomotor activity
1Department of Biological Research, Janssen Research Foundation, Spring House, PA 19477-0776.
Abstract:
Morphine and the molluscan neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) were administered to mice alone or in combination intracerebroventricularly (ICV) and the effect on locomotor activity was measured. Morphine given alone (0.5 micrograms) significantly increased horizontal locomotor activity compared to vehicle-treated controls. FMRFamide at low doses (0.01-10 micrograms) had no effect of its own, but blocked the morphine-induced increase in horizontal locomotor activity. Unlike the opiate antagonist naloxone (1.0 micrograms), FMRFamide (up to 10 micrograms) had no effect on morphine-induced decrease in vertical activity. These data further support a role for FMRFamide as a modulator of opiate action, but comparison to naloxone suggests that FMRFamide might not act as a pure competitive antagonist of this opiate effect.
Insights
The neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) modulates morphine
Area of Science:
- Neuroscience
- Pharmacology
- Behavioral Science
Background:
- Opiates like morphine are known to affect locomotor activity.
- The molluscan neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) has been suggested to interact with opiate systems.
Purpose of the Study:
- To investigate the modulatory role of FMRFamide on morphine's effects on locomotor activity in mice.
- To compare FMRFamide's effects to that of naloxone, a known opiate antagonist.
Main Methods:
- Morphine and FMRFamide were administered intracerebroventricularly (ICV) to mice, alone or in combination.
- Locomotor activity, including horizontal and vertical components, was measured.
- Effects were compared to vehicle-treated controls and naloxone treatment.
Main Results:
- Morphine (0.5 micrograms) significantly increased horizontal locomotor activity.
- FMRFamide (0.01-10 micrograms) alone had no effect but blocked the morphine-induced increase in horizontal activity.
- FMRFamide did not affect the morphine-induced decrease in vertical activity, unlike naloxone.
Conclusions:
- FMRFamide acts as a modulator of opiate action, specifically on horizontal locomotor activity.
- FMRFamide's distinct effect profile compared to naloxone suggests it may not be a pure competitive antagonist.
- These findings highlight a potential role for FMRFamide in regulating opiate-mediated behaviors.