title: Graded boosting of synaptic signals by low-threshold voltage-activated calcium conductance.
abstract: Low-threshold voltage-activated calcium conductances (LT-VACCs) play a substantial role in shaping the electrophysiological attributes of neurites. We have investigated how these conductances affect synaptic integration in a premotor nonspiking (NS) neuron of the leech nervous system. These cells exhibit an extensive neuritic tree, do not fire Na(+)-dependent spikes, but express an LT-VACC that was sensitive to 250 μM Ni(2+) and 100 μM NNC 55-0396 (NNC). NS neurons responded to excitation of mechanosensory pressure neurons with depolarizing responses for which amplitude was a linear function of the presynaptic firing frequency. NNC decreased these synaptic responses and abolished the concomitant widespread Ca(2+) signals. Coherent with the interpretation that the LT-VACC amplified signals at the postsynaptic level, this conductance also amplified the responses of NS neurons to direct injection of sinusoidal current. Synaptic amplification thus is achieved via a positive feedback in which depolarizing signals activate an LT-VACC that, in turn, boosts these signals. The wide distribution of LT-VACC could support the active propagation of depolarizing signals, turning the complex NS neuritic tree into a relatively compact electrical compartment.
authors.affiliation: Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina; and Instituto de Fisiología, Biología Molecular y Neurociencias, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Ciudad Universitaria, Buenos Aires, Argentina.
authors.forename: Martín
authors.initials: M
authors.lastname: Carbó Tano
authors.affiliation: Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina; and Instituto de Fisiología, Biología Molecular y Neurociencias, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Ciudad Universitaria, Buenos Aires, Argentina.
authors.forename: María Eugenia
authors.initials: ME
authors.lastname: Vilarchao
authors.affiliation: Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina; and Instituto de Fisiología, Biología Molecular y Neurociencias, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Ciudad Universitaria, Buenos Aires, Argentina szczupak@retina.ar.
authors.forename: Lidia
authors.initials: L
authors.lastname: Szczupak
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D007865:Leeches; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D056969:Voltage-Sensitive Dye Imaging
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002118:Calcium
keywords: calcium conductance; dendritic integration; nonspiking; synaptic amplification; window current