Intracellular study of lemniscal and non-specific synaptic interactions in thalamic ventrobasal neurons

Abstract

The effects of low frequency repetitive stimulation of medial thalamic (MTh) non-specific nuclei have been examined in intracellular studies of neurons of the ventrobasal (VB) thalamic complex. VB relay cells identified by medial lemniscus (ML) stimulation were relatively uninfluenced during recruiting responses elicited by MTh stimulation. VB neurons exhibiting long latency EPSPs or IPSP-EPSP sequences in response to ML stimulation were more consistently affected by MTh stimulation. Interactions observed in these elements were characteristically inhibitory in nature although in some cells facilitation of discharge without significant change in membrane potential occurred during MTh stimulation. Potentiation or enhancement of ML evoked IPSPs was observed in a small proportion of identified VB relay cells during 3nd as an after-effect of MTh stimulation. Spontaneosly developing 6–12/sec spindle waves in posterior sigmoid gyrus were associated with prominent IPSP and EPSP-IPSP sequences in VB relay cells. Stimulation of posterior sigmoid gyrus, corona radiata or internal capsule elicited prominent, variable latency, IPSPs or EPSP-IPSP sequences in relay cells and other neurons of the VB complex. The characteristics of these PSPs suggest the operation of complex interneuronal systems acting on VB relay cells via corticofugal projections. The intracellular data indicate marked differences in the distribution of synaptic pathways to VB relay and non-relay cells from medial non-specific nuclei. These results are considered in the light of previous findings on the effects of medial thalamic stimulation on specific neurons of the ventrolateral thalamic nucleus.