Dendritic mechanisms contribute to stimulus-specific adaptation in an insect neuron.
Reduced neuronal activation to repetitive stimulation is a common feature of information processing in nervous systems. Such stimulus-specific adaptation (SSA) occurs in many systems, but the underlying neural mechanisms are not well understood. The Neoconocephalus (Orthoptera, Tettigoniidae) TN-1 auditory neuron exhibits an SSA-like process, characterized by reliably detecting deviant pulses after response cessation to common standard pulses. Therefore, TN-1 provides a model system to study the cellular mechanisms underlying SSA with an identified neuron. Here we test the hypothesis that dendritic mechanisms underlie TN-1 response cessation to fast-pulse rate repeated signals. Electrically stimulating TN-1 with either high-rate or continuous-current pulses resulted in a decreased ability in TN-1 to generate action potentials but failed to elicit cessation of spiking activity as observed with acoustic stimulation. BAPTA injection into TN-1 delayed the onset of response cessation to fast-pulse rate acoustic stimuli in TN-1 but did not eliminate it. These results indicate that calcium-mediated processes contribute to the fast cessation of spiking activity in TN-1 but are insufficient to cause spike cessation on its own. Replacing normal saline with low-Na(+) saline (replacing sodium chloride with either lithium chloride or choline chloride) eliminated response cessation, and TN-1 no longer responded selectively to the deviant pulses. Sodium-mediated potassium channels are the most likely candidates underlying sodium-mediated response suppression in TN-1, triggered by Na(+) influx in dendritic regions activated by acoustic stimuli. On the basis of these results, we present a model for a cellular mechanism for SSA in a single auditory neuron.
Department of Biology, College of Charleston, Charleston, South Carolina; and.
Jeffrey D
JD
Triblehorn
Johannes
J
Schul
D000161:Acoustic Stimulation; D000200:Action Potentials; D000222:Adaptation, Physiological; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003712:Dendrites / Q000378:metabolism / Q000502:physiology*; D017952:Ganglia, Invertebrate / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D009475:Neurons, Afferent / Q000378:metabolism / Q000502:physiology*; D009987:Orthoptera; D015221:Potassium Channels / Q000378:metabolism; D012964:Sodium / Q000378:metabolism
D015221:Potassium Channels; D012964:Sodium; D002118:Calcium
auditory neuron; hearing; insect