A general role for serotonin in the control of behavior: studies with intracerebral 5,7-dihydroxytryptamine

Multiple injections of 5,7-dihydroxytryptamine (5,7-DHT) into the rat brainstem reduced forebrain levels of serotonin and 5-hydroxyindoleacetic acid to 3–10% of the levels observed in control rats that had received intrabrainstem injection of a Locke's solution vehicle. This treatment reduced or abolished atropine-resistant cerebral activation (ARCA) in most cases. In rats in which ARCA was impaired or lost, a number of behavioral abnormalities were observed. These included: high levels of locomotion in an open field test; a deficiency in swimming to, and climbing upon, a visible platform in a water-filled tank; deficient social behavior; and impaired performance in a simple test of active avoidance. These deficits were not due to low level motor impairment. The 5,7-DHT-treated rats displayed a circadian rhythm of activity in running wheels. It is proposed that ascending serotonergic projections are an important component in the cerebral control of the Type 1 behavior with which the occurrence of ARCA is closely linked. Since Type 1 behavior includes such motor patterns as walking and manipulation of objects with the limbs, which are essential components of a great variety of behavioral performances, it is to be expected that a loss of ascending serotonergic function will result in a generalized deficit in behavior.