THE ROLE OF SEROTONIN IN BEHAVIOR MODULAT ION

The central projection systems represent an expansive and important co mponent of the brainstem reticular core which provide modulatory input into multiple target networks throughout the entire vertebrate neurax is. Most of the afferent input into the cranial raphe originates withi n sensory uni- and polymodal, associative and limbic cortices suggesti ng that serotonin modulates preprocessed information. The serotonergic neurons discharge in a remarkably stable and tonic fashion during wak efulness. Some 5-HT neurons increase their discharge rate phasically i n association with the activation of central rhythmic pattern generato rs involved in consummatory and grooming behaviour. In concert with en hancing motor functions, the serotonergic systems discretely deamplify sensory attentiveness and pain processing, thereby establishing an es sential and protective filter mechanism against distracting and irrita ting noise effects of sensory afferent input level. In addition, serot onin restrains the latency to responding, i. e, impulsivity. These eff ects of serotonin are mediated by multiple receptor subtypes with dist inct pre- and postsynaptic localisation and regional distribution patt ern, acting via amplifying (5-HT2 receptors) or desamplifying (5-HT1 r eceptors) G-protein-dependent transduction mechanisms. The breakdown o f these protective and adaptive functions of 5-HT in complex behaviour and in basic aspects of sensorimotor integration may have a pathogene tic role in disorders of impulse control (e. g. bulimia nervosa and OC D) which have been found to respond to high-dose, long-term treatment with selective serotonin reuptake inhibitors.