Strong, reliable and precise synaptic connections between thalamic relay cells and neurones of the nucleus reticularis in juvenile rats.

The thalamic reticular nucleus (nRT) is composed entirely of GABAergic inhibitory neurones that receive input from pyramidal cortical neurones and excitatory relay cells of the ventrobasal complex of the thalamus (VB). It plays a major role in the synchrony of thalamic networks, yet the synaptic connections it receives from VB cells have never been fully physiologically characterised. Here, whole-cell current-clamp recordings were obtained from 22 synaptically connected VB-nRT cell pairs in slices of juvenile (P14-20) rats. At 34-36 degrees C, single presynaptic APs evoked unitary EPSPs in nRT cells with a peak amplitude of 7.4 +/- 1.5 mV (mean +/- S.E.M.) and a decay time constant of 15.1 +/- 0.9 ms. Only four out of 22 pairs showed transmission failures at a mean rate of 6.8 +/- 1.1 %. An NMDA receptor (NMDAR)-mediated component was significant at rest and subsequent EPSPs in a train were depressed. Only one out of 14 pairs tested was reciprocally connected; the observed IPSPs in the VB cell had a peak amplitude of 0.8 mV and were completely abolished in the presence of 10 microM bicuculline. Thus, synaptic connections from VB cells to nRT neurones are mainly 'drivers', while a small subset of cells form closed disynaptic loops.