GABAA and GABAB receptors mediated inhibition affect the pattern adaptation of relay cells in the dorsal lateral geniculate nucleus (LGNd) of cats

Pattern adaptation is very important for visual function, while the mechanisms that mediate pattern adaptation, especially in the dorsal lateral geniculate nucleus (LGNd), are still unclear. Iontophoresis of the antagonists and agonists of GABA receptors were employed to separately investigate the contribution of GABA(A) and GABA(B) receptors to pattern adaptation of LGNd cells. When GABA(A) receptors were blocked by bicuculline both the response amplitude of LGNd cells and the degree of adaptation increased significantly. Many neurons showing no pattern adaptation under the normal condition became adapted to a prolonged stimulus. Moreover, the proportion of cells showing adaptation doubled (from 40 to 88%). The mean adaptation index (AI, adapted response amplitude/original response amplitude) was 0.82 during bicuculline application, compared with 0.92 under the control condition. In additional, iontophoresis of baclofen, a selective GABA(B) receptor agonist, decreased the mean response amplitude to grating stimuli to 53% of normal. Nearly half of the neurons increased their adaptation index following baclofen administration and the mean AI increased from 0.89 to 1.01. Iontophoresis of GABA(B) receptor antagonist (CGP35348) could abolish this effect, though it had no significant effect on visual response amplitude and pattern adaptation itself. Iontophoresis of another GABA(B) receptor antagonist, 2-OH-saclofen, also had no significant effect on visual response amplitude and pattern adaptation. These results suggest that both GABA(A) receptors and GABA(B) receptors modulate the pattern adaptation of LGNd cells and are involved in synaptic plasticity.

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