Voltage-dependent conductances in a non-spiking neuron of the leech nervous system

LORENA RELA; LIDIA SZCZUPAK

New Orleans, LA, Estados Unidos

Congreso; Society for Neuroscience Annual Meeting; 2003

Society for Neuroscience

Non-spiking neurons codify signals in the nervous system through graded changes in membrane potential. Since their electrical activity cannot be detected using extracellular recordings, they can only be studied using intracellular recordings in preparations where they can be identified. NS neurons are a pair of non-spiking neurons that can be clearly identified in each midbody ganglion of the leech nervous system. We have previously shown that these neurons regulate the coordinated activity of leech motoneurons.The present work reports the presence of voltage-dependent conductances in the NS neurons, describes their properties and evaluates their role in synaptic integration.The experiments were performed in isolated midbody ganglia of Hirudo medicinalis under constant superfusion and the electrical activity of neurons was studied by means of intracellular electrodes. We show that NS neurons generate spike-like depolarizations in response to specific patterns of electrical stimulation that reach threshold.Spike-like responses depended on external sodium and calcium, since their replacement with non-permeant cations or specific blockers abolished the responses. Furthermore, increasing external calcium increased the amplitude of the spike-like responses.The repolarizing phase of the spike-like responses depended on TEA-sensitive conductances, as the injection of TEA into the NS neurons turned these responses into long-lasting plateaus. This effect of TEA correlated with an increment in synaptic responses. P mechanosensory neurons produce depolarizing potentials in NS neurons, and these synaptic potentials were magnified after TEA injection.The spike-like responses of NS neurons are generated neither spontaneously nor by stimulation of their afferents; we propose that they result from the activation of voltage-dependent conductances that shape the graded signals in these non-spiking neurons.