Electrically and mechanically evoked nociceptive neuronal responses in the rat anterior cingulate cortex.

The present study examined nociceptive properties of anterior cingulate cortical (ACC) neurons following application of peripheral noxious electrical and mechanical stimulations to anesthetized rats. Among a total of 108 recorded neurons, 59 units were excited or inhibited by noxious electrical or mechanical stimulation. Of these 59 cells, 38% were located in area 24b, another 38% were located in area 8, and the remaining cells were located in areas 24a and 25. The noxious stimulus-responsive neurons were located predominately in layers V (58%) and III (30%), and the remaining cells were located in layers II and VI. The latency of evoked unit activities was 209.75 +/- 26.62 ms and the threshold of the ACC responses was 10 times greater than that in primary somatosensory cortex (SI). Morphine treatment (5 mg/kg, i.v.) increased activity in evoked ACC neurons. This effect was reversed by naloxone (2 mg, i.v.). Nociceptive neurons in the ACC were distributed in area 24 and motor related regions. The locations and properties of evoked responses indicated that ACC neurons may play a role in avoidance behavior in the context of affective aspects of nociceptive information processing.