Stimulus-specific adaptation dendritic mechanisms

Stimulus-specific adaptation dendritic mechanisms 2 21 Abstract 22 23 Reduced neuronal activation to repetitive stimulation is a common feature of information 24 processing in nervous systems. Such stimulus-specific adaptation (SSA) occurs in many systems, 25 but the underlying neural mechanisms are not well understood. The Neoconocephalus 26 (Orthoptera: Tettigoniidae) TN-1 auditory neuron exhibits a SSA-like process, characterized by 27 reliably detecting deviant pulses after response cessation to common standard pulses. Therefore, 28 TN-1 provides a model system to study the cellular mechanisms underlying SSA using an 29 identified neuron. Here, we test the hypothesis that dendritic mechanisms underlie TN-1 30 response cessation to fast pulse rate repeated signals. Electrically stimulating TN-1 with either 31 high rate or continuous current pulses resulted in a decreased ability in TN-1 to generate action 32 potentials, but failed to elicit cessation of spiking activity as observed with acoustic stimulation. 33 BAPTA injection into TN-1 delayed the onset of response cessation to fast pulse rate acoustic 34 stimuli in TN-1, but did not eliminate it. These results indicate calcium-mediated processes 35 contribute to the fast cessation of spiking activity in TN-1, but are insufficient to cause spike 36 cessation on its own. Replacing normal saline with low-Na + saline (replacing sodium chloride 37 with either lithium chloride or choline chloride) eliminated response cessation and TN-1 no 38 longer responded selectively to the deviant pulses. Sodium-mediated potassium channels are the 39 most likely candidates underlying sodium-mediated response suppression in TN-1, triggered by 40 Na + influx in dendritic regions activated by acoustic stimuli. Based on these results, we present a 41 model for a cellular mechanism for SSA in a single auditory neuron. 42 Stimulus-specific adaptation dendritic mechanisms 3