Characterization of responses mediated by low threshold calcium conductances in a nonspiking neuron

MARTÍN CARBÓ TANO; LIDIA SZCZUPAK

Huerta Grande

Congreso; XXIX Reunión Annual de la Sociedad Argentina de Investigación en Neurociencias.; 2014

Sociedad Argentina de Investigación en Neurociencias

Voltage activated conductances boost distal synaptic signals counteracting electrotonic decay, increasing their chances to summate with other events in the neuritic tree. We study how a low threshold voltage-activated Ca2+ conductance (LT-VACC) shapes the synaptic response in the neuritic tree of the leech premotor nonspiking (NS) neurons, which express low threshold spikes (LTS). We show that NNC 55-0396 dihydrochloride, a specific blocker of LT-VACC in vertebrates, blocked the conductance that underlies the LTS of NS neurons. This allowed us to evaluate the role of LT-VACC in the amplification and propagation of synaptic signals in NS neuron. Inhibition of LT-VACC reduced the magnitude of NS synaptic responses and hindered its fast components. Blocking LT-VACC had a larger effect the larger were the responses, leaving unaffected responses that were slower and smaller. When NS neurons were stimulated with sinusoidal current waves, the successive cycles exhibited temporal summation that could be recorded in the contralateral soma. NNC strongly diminished this temporal summation, diminishing the maximal amplitude of the response, and reduced its ability to propagate. Literature shows that LT-VACC either supports local graded amplification of synaptic signals or global all-or-none effects. This work presents the first description of a neuron in which LT-VACC produces a graded boosting of synaptic signals while supporting an effective active propagation.