A subgroup of dorsal raphe serotonergic neurons in the cat is strongly activated during oral-buccal movements

A subgroup of similar to 25% of dorsal raphe nucleus serotonergic neurons in cat was strongly activated in association with oral-buccal movements, such as chewing, licking, and grooming. The mean magnitude of increase in neuronal activity for these cells was approximately 100% above the spontaneous waking level. However, some of these cells were activated by as much as 200-300%. The neuronal activation frequently preceded the initiation of the movement and stopped abruptly in association with either pauses in the motor sequence or with its cessation. Most of the neurons in this subgroup were also strongly and preferentially activated by somatosensory stimuli applied to the head, neck, and face. During orientation to a strong or novel stimulus, the activity of these neurons fell silent for periods of 1-5 s. These data and results from our previous studies of medullary raphe neurons are discussed within the context of the general role of serotonin in tonic and central pattern generator-related motor activity.