Motion processing in the auditory cortex of the rufous horseshoe bat: role of GABAergic inhibition.
This study examined the influence of inhibition on motion-direction-sensitive responses of neurons in the dorsal fields of auditory cortex of the rufous horseshoe bat. Responses to auditory apparent motion stimuli were recorded extracellularly from neurons while microiontophoretically applying gamma-aminobutyric acid (GABA) and the GABAA receptor antagonist bicuculline methiodide (BMI). Neurons could respond with a directional preference exhibiting stronger responses to one direction of motion or a shift of receptive field (RF) borders depending on direction of motion. BMI influenced the motion direction sensitivity of 53% of neurons. In 21% of neurons the motion-direction sensitivity was decreased by BMI by decreasing either directional preference or RF shift. In neurons with a directional preference, BMI increased the spike number for the preferred direction by a similar amount as for the nonpreferred direction. Thus, inhibition was not direction specific. BMI increased motion-direction sensitivity by either increasing directional preference or magnitude of RF shifts in 22% of neurons. Ten percent of neurons changed their response from a RF shift to a directional preference under BMI. In these neurons, the observed effects could often be better explained by adaptation of excitation rather than inhibition. The results suggest, that adaptation of excitation, as well as cortex specific GABAergic inhibition, contribute to motion-direction sensitivity in the auditory cortex of the rufous horseshoe bat.
Firzlaff
U
U
Department Biologie II, Ludwig-Maximilians-Universität München, Luisenstr. 14, D-80333 München, Germany. firzlaff@zi.biologie.uni-muenchen.de
Schuller
G
G
D000161:Acoustic Stimulation; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001303:Auditory Cortex / Q000187:drug effects / Q000502:physiology*; D001640:Bicuculline / Q000494:pharmacology; D002685:Chiroptera / Q000033:anatomy & histology / Q000502:physiology*; D004455:Echolocation / Q000187:drug effects / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D009039:Motion Perception / Q000187:drug effects / Q000502:physiology*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D011963:Receptors, GABA-A / Q000378:metabolism*; D013017:Sound Localization / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism* / Q000494:pharmacology
D018756:GABA Antagonists; D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D001640:Bicuculline