Abstract
Opioids are generally believed to activate descending pain inhibitory pathways from the periaqueductal gray matter (PAG). Since opioids exert an inhibitory effect on neural excitability and transmitter release, an opioid-mediated inhibition of tonically active inhibitory γ-aminobutyric acid (GABA) neurons has been suggested to mediate this effect. The aim of the present microdialysis study was to investigate the effect of local administration of morphine on the extracellular GABA level in the PAG of awake rats. The recently developed and highly sensitive method of capillary electrophoresis with laser-induced fluorescence detection was used for GABA determination in microdialysate samples obtained from the PAG of freely moving rats. The basal GABA level was 54.5 ± 6.6 nM ( n = 8; mean ± SEM). Perfusion of the dialysis probe with morphine (100 μM) for 30 min significantly decreased the GABA level to 28.2 ± 4.2 nM ( n = 8; P < 0.05). The effect of morphine was reversed by coperfusion with naloxone (100 μM in the perfusion fluid). The present results thus provide direct experimental evidence for an opioid-induced inhibition of tonic GABA release in the PAG, which may in turn lead to a disinhibition of descending pain inhibitory pathways.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
