title: Role of GABAergic inhibition in shaping the spatial frequency tuning of neurons and its contrast dependency in the dorsal lateral geniculate nucleus of cat.
abstract: To understand how GABAergic inhibition contributes to the elaboration of spatial frequency (SF) tuning of neurons in the lateral geniculate nucleus, we examined the effects of the microiontophoretic administration of bicuculline methiodide (BIC) and gabazine, both antagonists of GABAA receptors, on visual responses to grating stimuli with high or low contrasts. BIC administration changed the shape of the SF tuning curve of the spike response from band-pass to low-pass. We took the tuning curve obtained under the BIC condition as an estimated excitatory contribution to the control tuning curve and then estimated the difference between tuning curves recorded with and without BIC as the tuning curve of the estimated GABAergic inhibitory contribution. The SF tuning profile of estimated inhibition (Estimated-Inh) varied widely from cell to cell, as did estimated excitation (Estimated-Ex). Nonetheless, the relationship that Estimated-Inh exhibited more low-pass tuning than did Estimated-Ex was well conserved in the majority of cells, and the relationship refined the SF tuning of Estimated-Ex toward the band-pass tuning of the geniculate output. Lowering the stimulus contrast decreased the response magnitude, but did not change the degree of band-pass tuning. The GABAergic refinement of the SF tuning was also observed at low stimulus contrast, but was weaker than at high contrast, suggesting that GABAergic inhibition is regulated in coordination with excitatory inputs to keep the degree of the band-pass tuning constant. We therefore concluded that the degree of band-pass tuning is conserved contrast invariantly in the lateral geniculate nucleus on the basis of the dynamic regulatory action of GABAergic inhibition.
authors: Graduate School of Medicine, Osaka University, Toyonaka, Osaka, Japan.
authors: Akihiro
authors: A
authors: Kimura
authors: Satoshi
authors: S
authors: Shimegi
authors: Shin'ichiro
authors: S
authors: Hara
authors: Masahiro
authors: M
authors: Okamoto
authors: Hiromichi
authors: H
authors: Sato
mesh_terms: D000818:Animals; D002415:Cats; D015350:Contrast Sensitivity / Q000187:drug effects / Q000502:physiology*; D004594:Electrophysiology; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D005829:Geniculate Bodies / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010775:Photic Stimulation; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D058787:GABA-A Receptor Antagonists; D005680:gamma-Aminobutyric Acid