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Electron microscopic observation of mu-opioid receptor in the rat area postrema
1Department of Anatomy, Showa University School of Medicine, Tokyo, Japan.
Abstract:
A simple preembedding avidin-biotin-peroxidase complex technique was used to study the ultrastructural localization of mu-opioid receptor in the rat area postrema. By using low concentrations of the first antiserum for incubation with a short reaction time to 3,3'-diaminobenzidine, the immunostaining was faint at the light microscopic level. However, at the electron microscopic level, strong immunoreaction was observed. Mu-Opioid receptors were found to be localized on the postsynaptic membrane of dendrites, extrasynaptic plasma membrane, and the surface of the small, clear vesicles in axon terminals. Of the total 283 immunopositive profiles observed, 68.2% (193 of 283) were dendrites, 29.3% (83 of 283) were axon terminals, and 2.5% (7 of 283) were myelinated axons. No immunostained neuron bodies were found in the present study; 109 mu-opioid receptor immunoreactive dendrites received synapses (56.5%, 109 of 193) from nonimmunoreactive (84.4%, 92 of 109) or immunoreactive (15.6%, 17 of 109) axon terminals, whereas 84 dendrites (43.5%, 84 of 193) were found without receiving synapses. The present study shows that the mu-opioid receptor in the area postrema plays a role mainly at the synapses.
Insights
This study reveals that mu-opioid receptors are primarily located at synapses in the rat area postrema, specifically on postsynaptic membranes and axon terminals. These receptors play a key role in synaptic transmission within this brain region.
Area of Science:
- Neuroscience
- Cell Biology
- Pharmacology
Background:
- The area postrema is a crucial chemosensory organ involved in regulating nausea and vomiting.
- Mu-opioid receptors are implicated in various physiological processes, including pain modulation and reward pathways.
Purpose of the Study:
- To investigate the ultrastructural localization of mu-opioid receptors in the rat area postrema.
- To elucidate the specific cellular and subcellular compartments where these receptors are found.
Main Methods:
- Utilized a pre-embedding avidin-biotin-peroxidase complex technique for electron microscopy.
- Employed immunocytochemistry with specific antisera against mu-opioid receptors.
- Analyzed 283 immunopositive profiles, categorizing them by cellular location (dendrites, axon terminals, etc.).
Main Results:
- Mu-opioid receptors were predominantly found on postsynaptic membranes of dendrites (68.2%) and on axon terminals (29.3%).
- Receptors were also observed on extrasynaptic plasma membranes and within synaptic vesicles.
- Immunoreactive dendrites frequently received synapses from both immunoreactive and non-immunoreactive axon terminals.
Conclusions:
- Mu-opioid receptors in the area postrema are mainly localized at synapses, suggesting a significant role in synaptic transmission.
- The findings highlight the importance of these receptors in the neurochemical signaling within this brain region.