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The sub-cellular localization of stereo-specific opiate binding in mouse brain
Research Communications in Chemical Pathology and Pharmacology
|October 1, 1976
Summary
Mouse brain P3 fractions exhibit high stereo-specific opiate receptor binding, comparable to purified synaptosomal membranes. This suggests opiate receptors are broadly distributed on nerve cells, not just at synapses.
Area of Science:
- Neuroscience
- Pharmacology
- Cell Biology
Background:
- Opiate receptors are crucial for pain modulation and neurotransmission.
- Previous research suggested opiate receptors are concentrated at synaptic regions.
Purpose of the Study:
- To investigate the sub-cellular distribution of stereo-specific opiate receptors in mouse brain homogenates.
- To determine if opiate receptors are localized to nerve endings or more diffusely distributed.
Main Methods:
- Differential centrifugation of mouse brain homogenates to isolate sub-cellular fractions (P3, microsomal).
- Radioligand binding assays using [3H]-dihydromorphine and [3H]-naloxone.
- Characterization of binding properties (affinity, agonist potency, ion/enzyme sensitivity) and comparison with synaptosomal plasma membranes (SPM).
Main Results:
- The P3 (microsomal) fraction demonstrated high-capacity, stereo-specific binding of [3H]-dihydromorphine, nearly matching purified SPM.
- Binding in P3 was significantly higher than in SPM and localized to a different sucrose density band, ruling out SPM contamination.
- Binding characteristics (KD, agonist displacement, Na+/trypsin effects) in P3 were indistinguishable from those in nerve endings.
Conclusions:
- Stereo-specific opiate receptors are not exclusively concentrated at synaptic regions.
- Opiate receptors appear to be diffusely distributed across the entire surface of nerve cells.
- This finding challenges the traditional view of opiate receptor localization.