Abstract: Objective To investigate the role of ventrolateral periaqueductal gray (VL-PAG) metabotropic glutamate receptors
subtype 7 and 8 (mGluR 7/8) in descending modulation of cardiosomatic motor reflex (CMR) in rats. Methods AMN082
(agonist of mGluR 7) and DCPG (agonist of mGluR 8) were injected into the VL-PAG of a rat model of CMR to observe their
effects in modulating CMR. The raphe magnus nucleus (NRM) or the gigantocellular reticular nucleus (Gi) was then damaged,
and the changes in VL-PAG descending modulation were observed. Results Selective activation of mGluR 7 of the VL-PAG by
AMN082 obviously facilitated capsaicin (CAP)-induced CMR (P<0.05), which was suppressed by DCPG-induced mGluR 8
activation (P<0.05). These facilitatory or inhibitory effects were completely reversed by group III mGluR antagonist MSOP.
Damaging the NRM of VL-PAG main relay nucleus did not significantly affect the facilitatory effect produced by AMN082
microinjection (P>0.05), but partially attenuated the inhibitory effect of DCPG microinjection (P<0.05). Both the facilitatory
effect of AMN082 and the inhibitory effect of DCPG were reduced obviously after bilateral Gi damage (P<0.05). Conclusion
VL-PAG mGluR 7 and mGluR 8 mediate biphasic regulation of CMR in rats probably through activation of different sub-nuclei
and different neurons in the rostroventral medulla.