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Development of acute opioid tolerance and dependence in rat striatal neurones
Abstract:
Striatal neurones in the rat were frequently observed to develop tachyphylaxis to the specific, naloxone-antagonisable depressant effects of methionine- and leucine-enkephalin on spontaneous and L-glutamate-evoked activity. This loss of responsiveness to the enkephalins occurred within a few minutes of the repeated or prolonged application of these peptides and is suggested to reflect a form of acute tolerance. As with chronic opiate tolerance, the acute tolerance of single striatal neurones to the enkephalins appeared to be associated with dependence on these opioids, as evinced by the withdrawal-like hyperactivity that occurred upon terminating the application of the peptides or upon the microelectrophoresis of naloxone.
Insights
Rats developed acute tolerance to enkephalins, opioid peptides affecting striatal neurons. This tolerance, similar to chronic opiate use, involved withdrawal-like hyperactivity upon peptide removal or naloxone administration.
Area of Science:
- Neuroscience
- Pharmacology
- Neurobiology
Background:
- Striatal neurons play a crucial role in motor control and reward processing.
- Enkephalins are endogenous opioid peptides with inhibitory effects on neuronal activity.
- Understanding neuronal responses to opioid peptides is vital for neuropharmacological research.
Purpose of the Study:
- To investigate the development of acute tolerance to enkephalins in rat striatal neurons.
- To examine the relationship between acute enkephalin tolerance and opioid dependence.
Main Methods:
- Electrophysiological recordings of striatal neuronal activity in rats.
- Application of methionine- and leucine-enkephalin.
- Administration of naloxone to assess receptor antagonism and withdrawal effects.
Main Results:
- Striatal neurons exhibited rapid tachyphylaxis (acute tolerance) to the depressant effects of enkephalins.
- This tolerance developed within minutes of repeated or prolonged peptide application.
- Neuronal dependence was indicated by withdrawal-like hyperactivity upon peptide withdrawal or naloxone administration.
Conclusions:
- Acute tolerance to enkephalins can rapidly develop in striatal neurons.
- This acute tolerance is associated with opioid dependence, mirroring aspects of chronic opiate tolerance.
- Findings suggest complex adaptive mechanisms in opioid peptide signaling within the striatum.