THE ACTIVITY OF ON AND OFF CELLS AT THE ROSTROVENTROMEDIAL MEDULLA ISMODULATED BY VAGINO-CERVICAL STIMULATION

In anesthetized rats it was tested whether or not the activity of the ON and OFF cells within the rostral ventromedial medulla (RVM) is modu lated by the mechanical stimulation of the uterine cervix (VS). ON cel ls were identified by an abrupt increase in their firing rate before t he tail flick in response to a noxious heat. OFF cells were identified by a sudden decrease in their firing rate before the tail flick. All (27 out of 27) identified ON cells decreased their firing rate immedia tely after VS was applied. The effect of VS on the activity of the cel ls persisted for the entire stimulation period. On the other hand, all (19 out of 19) identified OFF cells increased their firing rate immed iately after VS. The effect of VS on the activity of these cells also persisted for the entire stimulation period. The activity of the neutr al cells showed no change, neither during the application of noxious h eat, nor during VS. These results suggest that the analgesic-like effe ct produced by VS can be mediated by the activity of the antinocicepti ve circuit at the RVM. Alternatively, it can be suggested that the aff erent inflow from the genital tract can induce the activity of the ant inociceptive circuit ar RVM, either by projections to the periaqueduct al gray matter or by direct projections to RVM. (C) 1998 International Association for the Study of Pain. Published by Elsevier Science B.V.