title: Role of serotonin and cyclic AMP on facilitation of the fast conducting system activity in the leech Hirudo medicinalis.
abstract: In the nervous system of the leech Hirudo medicinalis it has been possible to study short-term plastic changes. Depression and facilitation have been demonstrated in the fast conducting system (FCS) activity; this pathway consists of a chain of electrically linked neurons present in each ganglion. In semi-intact animals or in preparation of nerve cord and segments of body wall, both electrical stimulation of peripheral roots and tactile stimulation of the skin induced, after repetitive stimulation (0.1/s) a prolonged decrement of FCS response. Strong nociceptive stimulation applied onto the head or the body wall produced a sustained facilitation of the waned response. The same potentiation has been observed by perfusing the isolated ganglion with serotonin (5 x 10(-5) M). Such a potentiation is abolished by preincubation with methysergide, an antagonist of serotonin, and with imidazole, a cAMP-phosphodiesterase activator. Such an effect is mimicked by an analog of cAMP, db-cAMP. Simultaneous recordings of both T neurons (intracellularly) and FCS firing discharge showed that, during FCS response decrement, the T cell activity remained unchanged and no modification of conductance occurred, excluding therefore a detectable involvement of sensory neurons in the depression. These results suggest that short-term plastic changes of the FCS of the leech are due to a prolonged potentiation of synaptic transmission as a result of serotonin-mediated increase in cAMP.
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000494:pharmacology*; D004553:Electric Conductivity; D004558:Electric Stimulation; D007093:Imidazoles / Q000494:pharmacology; D007865:Leeches / Q000502:physiology*; D009420:Nervous System / Q000187:drug effects*; D010812:Physical Stimulation; D012701:Serotonin / Q000494:pharmacology*; D013601:T-Lymphocytes / Q000502:physiology; D013997:Time Factors
chemical_list: D007093:Imidazoles; D012701:Serotonin; D000242:Cyclic AMP