Fig. 1.

In vivo: effects of the endogenous agonist, gamma-aminobutyric acid (GABA), and the selective agonist, gaboxadol (GBX), application onto medial geniculate body (MGB) units. MGB unit is sensitive to application of the endogenous agonist GABA (A–C, Db, Gb). Ab: 5 nA GABA resulted in a near 50% decrease in spike rate, as shown in dot raster display. B: GABA application showed a selective suppression at or near rate best-modulated frequency (rBMF). C: average total spike change by low-dose GABA (less than 10 nA) for 23 units was 46.24 ± 2.97%. Application of the δ-subunit selective agonist GBX onto MGB units showed varying responses. Average total spikes were 32.59 ± 4.86% under GABA application and 67.15 ± 4.62% under GBX application. F: GABA showed greater reduction of spike rate than GBX for majority units (11/15). The representative unit in D showed profound spike suppression with 0 nA (leaking) GABA and a smaller effect with 20 nA GBX onto the same unit. F: group data indicated that applied GABA was almost twice as potent as GBX (**P < 0.01, independent t-test). There was a small number of units (4/15) that had similar levels of suppression with applied GABA and GBX (G–I). In the representative mixed type unit (G), GABA and GBX show a similar pattern of reduction in discharge rate (15.91% vs. 17.42%) across different modulation frequencies (H). I: group data for this response type indicated the same effects for GABA and GBX (P > 0.5, independent t-test). Data shown as means ± SE. N, number of spikes; n, number of units in all figures.