Synchrony within the thalamocortical system is regulated in part by intranuclear synaptic inhibition within the reticular nucleus (RTN). Inhibitory postsynaptic currents (IPSCs) in RTN neurons are largely characterized by slow decay kinetics that result in powerful and prolonged suppression of spikes. Here we show that some individual RTN neurons are characterized by highly variable mixtures of fast, slow and mixed IPSCs. Heterogeneity arose largely through differences in the contribution of an initial decay component (τD∼10 ms) which was insensitive to loreclezole, suggesting involvement of the GABAA receptor β1 subunit. Single-cell RT-PCR revealed the presence of β1 subunit mRNA only in those neurons whose IPSCs were dominated by a rapid and prominent initial decay phase. These data show that brief, β1-dependent, loreclezole-insensitive IPSCs are present in a subpopulation of RTN neurons, and suggest that striking differences in IPSC heterogeneity within single neurons can result from of the presence or absence of a single GABAA receptor subunit.