Selection of postsynaptic serotonin receptors during reinnervation of an identified leech neuron in culture.
Serotoninergic Retzius neurons reform an inhibitory synapse onto pressure-sensitive mechanosensory (P) neurons when the cells are removed from the nervous system of the leech and are juxtaposed in tissue culture. The somas of P cells in situ and single (uninnervated) P cells in culture have both a depolarizing and Cl-dependent hyperpolarizing response to application of the transmitter serotonin (5-HT). Synaptic release of 5-HT by a Retzius cell in situ and in culture evokes a Cl-dependent postsynaptic response but does not appear to activate the depolarizing receptors. We have characterized the ionic currents induced by synaptically released and applied 5-HT in voltage-clamped P cells in culture in order to determine the responses to transmitter and their modifications following innervation. When 5-HT was applied to single P cells, 2 types of channels were activated by 5-HT and could be distinguished by changing the ionic composition of the superfusion solution. In an impermeant cation (TrisCl) solution, a 5-HT-dependent Cl current was activated. When single P cells were superfused with a Cl-free solution (Cl replaced by impermeant SO4), 5-HT activated a monovalent cation current. Following innervation of a P cell by a cocultured Retzius cell, the reversal potential of the peak postsynaptic current depended on the Cl gradient and the synaptic response was blocked by the Cl channel blocker 9-anthracenecarboxylic acid. Thus, synaptic release of 5-HT activated solely the Cl channels and not the cationic channels. Pipette application of 5-HT onto innervated P cells activated a Cl conductance comparable in magnitude to the synaptic response. In contrast, the cationic conductance was reduced roughly 5-fold. It is concluded that innervation of a P cell by a Retzius cell resulted in clustering of the synaptic 5-HT receptors, which activate Cl channels and reduction of the nonsynaptic, cationic response. The result is a selection of receptors in the cultured P cell that mimics the pattern observed in vivo.
Drapeau
P
P
Neurosciences Unit, Montreal General Hospital Research Institute, Quebec, Canada.
Sanchez-Armass
S
S
D000818:Animals; D002414:Cations, Monovalent / Q000494:pharmacology; D002478:Cells, Cultured; D002712:Chlorides / Q000502:physiology; D004553:Electric Conductivity; D007865:Leeches; D008465:Mechanoreceptors / Q000502:physiology; D009416:Nerve Regeneration; D009474:Neurons / Q000502:physiology*; D011312:Pressure; D011985:Receptors, Serotonin / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000378:metabolism*
D002414:Cations, Monovalent; D002712:Chlorides; D011985:Receptors, Serotonin; D012701:Serotonin