Figure 8

Spinal serotonin receptors contribute to descending facilitatory modulation from the ACC. (a, b) Microinjection of tACPD (0.25 μg in 0.5 μl) in the ACC facilitated the hot-plate responses (a, i.e., reduced response latency) and spinal nociceptive tail-flick reflex (b) in freely moving mice; (c, d) In freely moving (c) or anesthetized rats (d), tACPD microinjection in the ACC also facilitated the tail-flick reflex. Intrathecal injection of a serotonergic receptor antagonist methysergide (32.0 nmoles/10 μl) at a dose that blocked descending facilitation also blocked the facilitation of the tail-flick reflex.(e) A model explaining the neuronal pathways, which contribute to ACC activation, produced fear memory and descending facilitatory modulation of spinal nociception.