Volume : 3
Issue : 4
Online ISSN : 2394-2126
Print ISSN : 2394-2118
Article First Page : 412
Article End Page : 418
Introduction: Recent studies have shown that amygdala plays a pivotal role in the emotional processing of pain. Opioids like morphine relieve pain by suppressing both the sensory and emotional components of pain. On chronic morphine administration, tolerance develops decreasing its analgesic effect. The underlying changes in the amygdala during morphine tolerance are not definitely known. Mu opioid receptors are binding sites for morphine while N-type voltage-gated calcium channels (VGCCs) directly control the release of neurotransmitters from presynaptic nerve endings.
Aims & Objectives: The present study was designed to investigate the status of mu receptors and N-type VGCCs in the amygdala of morphine tolerant rat by autoradiography and immunohistochemistry respectively.
Material & Methods: Wistar rats were made morphine tolerant by repeated administration of morphine for 5 days. Later, the rats were euthanized and cryostat sections of the brain were cut at the region of the amygdala. For autoradiographic localization, the sections were incubated with [3H] labeled DAMGO. For immunohistochemistry, the sections were exposed to primary antibody against N-type VGCCs.
Results: Using image analysis software, a significant down-regulation of mu receptors and an up-regulation of N-VGCCs were observed after tolerance. This differential change in expression would indicate a less effective antinociceptive action of morphine through / though higher neurotransmitter release after tolerance.
Conclusion: In conclusion, the study suggests that morphine tolerance could be associated with altered functional state of the amygdala.
Keywords: Amygdala, Mu-opioid receptor, Voltage-gated calcium channel, Autoradiography, Immunohistochemistry