Abstract
Serotonin neurons in the rostral and caudal brainstem raphe nuclear groups give rise
to collateralized ascending and descending projections which provide modulatory input
into most networks throughout the entire neuraxis. The rostral raphe system is interconnected
with target forebrain areas through reciprocal limbic-midbrain loops, which suggests
that serotonin has a role in the regulation of complex intelligent adaptive behavior.
Serotonergic pathways sensitize brainstem and spinal cord central rhythmic pattern
generators which organize repetitive autonomic and motor activities, e. g. oral-buccal
and nutritive behaviors, facilitate tonically active motor neurons innervating anti-gravity
muscles, 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 C protein super-family, coupling
to adenylate cyclase (5-HT 1, 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 responding latency, i.e. impulsivity,
in a variety of experimental models of anxiety and depression. The clinical efficacy
of the so-called selective serotonin reuptake inhibitors (SSRls) in disorders characterized
by poor impulse control, e. g. bulimia nervosa, obsessive-compulsive disorder (OCD)
and violent suicidal or homicidal behavior, may likewise be due to improved responding
latency.
