The morphology of physiologically identified GABAergic neurons in the somatic sensory part of the thalamic reticular nucleus in the cat

TLDR

The study used electrophysiological recordings of sensory‑responsive neurons in the cat thalamic reticular nucleus and intracellular horseradish peroxidase labeling to reveal thin axons with intrareticular collaterals and diffuse branches throughout the ventral posterior and posterior thalamic nuclei. These GABAergic reticular nucleus cells exhibited larger receptive fields, longer response latencies, and dendritic processes resembling synaptic terminals, and were shown by immunocytochemistry to receive synapses from at least three distinct non‑GABAergic input types.

Abstract

Neurons with somatic sensory receptive fields were examined electrophysiologically in the thalamic reticular nucleus of the cat. All cells had receptive fields much larger than those of neurons in the ventral posterior nucleus and were driven by less readily defined somesthetic stimuli. Response latencies to peripheral or medial lemniscal stimulation were, on average, longer than in the ventral posterior nucleus and suggested activation of the reticular nucleus cells by collaterals of thalamocortical relay cell axons arising in the ventral posterior nucleus. When injected intracellularly with horseradish peroxidase, reticular nucleus cells displayed thin axons with intrareticular collaterals and diffuse branches through much of the ventral posterior and posterior thalamic nuclei. Dendrites ended in processes resembling synaptic terminals. Electron microscopic immunocytochemistry of the same part of the reticular nucleus revealed processes immunoreactive for glutamic acid decarboxylase and identifiable as both collateral axon terminals and presynaptic dendrites of GABAergic reticular nucleus cells. These synaptically linked reticular nucleus cells and, in addition, immunoreactive somata and presynaptic dendrites received synapses from at least three varieties of nonimmunoreactive profiles.