PSYCHOPHARMACOLOGY OF CENTRAL SEROTONERGIC SYSTEMS

Serotonin neurons in the rostral and caudal brainstem raphe nuclear gr oups give rise to collateralized ascending and descending projections which provide modulatory input into most networks throughout the entir e neuraxis, The rostral raphe system is interconnected with target for ebrain areas through reciprocal limbic-midbrain loops, which suggests that serotonin has a role in the regulation of complex intelligent ada ptive behavior. Serotonergic pathways sensitize brainstem and spinal c ord central rhythmic pattern generators which organize repetitive auto nomic and motor activities, e.g, oral-buccal and nutritive behaviors, facilitate tonically active motor neurons innervating antigravity musc les, and disfacilitate somatosensory information processing. Serotonin effects are mediated by multiple receptor subtypes with distinct pre- and postsynaptic localization and regional distribution pattern. They belong to the G protein superfamily, coupling to adenylate cyclase (5 -HT1,4,5,6,7) or phospholipase C (5-HT2), and to the ligand-gated ion channel superfamily (5-HT3). Drugs acting at these receptors are known to modulate various aspects of cooperative social behavior and respon ding latency, i.e. impulsivity, in a variety of experimental models of anxiety and depression. The clinical efficacy of the so-called select ive serotonin reuptake inhibitors (SSRIs) in disorders characterized b y poor impulse control, e.g, bulimia nervosa, obsessive-compulsive dis order (OCD) and violent suicidal or homicidal behavior, may likewise b e due to improved responding latency.