Inhibitory synapses among interneurons in the glomerular layer of rat and frog olfactory bulbs

The patch-clamp technique was applied to periglomerular (PG) cells from slices of frog and rat olfactory bulbs to characterize whole cell and single- channel properties of inhibitory synaptic currents. Spontaneous and electrically driven bicuculline-sensitive synaptic events were recorded under ionic conditions that excluded any possible interference of excitatory synapses. The peak amplitude distribution of spontaneous events could be fitted by several Gaussians having the same interpeak distance. Spontaneous currents reversed polarity at the chloride equilibrium potential and were suppressed by 2 mM Co²⁺; the decay phase could be fitted with a single exponential having a time constant of ~10 ms at 0 mV. Bicuculline-sensitive monosynaptic responses could be evoked in PG cells by electrical stimulations delivered at the distance of several glomeruli within the glomerular layer. Finally, in excised outside-out patches, single-channel analysis revealed the presence of typical γ-aminobutyric acid-A receptor channels, with a single- channel conductance of 28 pS in symmetrical chloride and mean open times of 3-4 ms. The simplest explanation of these data, effectively supported by pristine anatomic findings, is that there could be inhibitory contacts among interneurons in the glomerular layer.