Localization of cb1 receptors in rat`s periaqueductal gray after immobilization stress and effects of peptide tyr-w-mif- 1. immunocytochemical study

Abstract

Periaqueductal gray (PAG) is a midbrain structure closely involved in the stress-induced analgesia. It suppresses nociception by the descending efferent pathways to the dorsal horn of the spinal cord. Except stimulation of opioid receptors, the PAG is specialized to produce cannabinoid-mediated stress-induced analgesia. Attractive candidates for opiate modulators are neuropeptides from Tyr-MIF-1 family. These peptides also are involved in the development of stress. Based on behavioral and anatomical data about direct interactions of cannabinoid type 1 (CB1) receptors and μ-receptors in the PAG we decided to investigate the effects of the Tyr-W-MIF-1 neuropeptide on expression of CB1 immunoreactive neurons in rat`s PAG after immobilization stress. Light microscopic study was used to determine the distribution of CB1 receptor immunoreactivity. The obtained results showed that stress itself increased the expression of CB1 immunoreactive neurons in the PAG compared with intact animals, while Tyr-W-MIF-1 decreased stress-induced CB1 expression mentioned above probably by opioid/cannabinoid interaction. Further studies are needed to understand the exact role of Tyr-W-MIF-1 on CB1 receptors in response to immobilization stress.