Micro‐iontophoretic studies on neurones in the cuneate nucleus

Abstract

Cuneate cells in anesthetized cats were strongly excited by L-glutamate, and somewhat less bv D-glutamate; cells which receive afferents from hair receptors were particularly sensitive. Glutamate could be used to demonstrate post-synaptic inhibitory inputs from the dorsal column, the medial lemniscus and the frontal cortex. Many cuneate cells were also strongly excited by ATP; this was probably due to the chelating action of ATP, as citric acid was also effective. [gamma]-Aminobutyric acid (GABA) readily blocked all forms of spontaneous and evoked activity, except antidromic invasion of cuneothalamic neurons; cells which receive proprioceptive afferents were particularly sensitive to GABA. Glycine had a comparable effect Acetylcholine (ACh), catecholamines, histamine, 5-hydroxytryptamine (5-HT) and an extract containing substance P mostly had only weak depressant actions. Cholinergic and mono-aminergic mechanisms are probably not very significant in the cuneate. Glutamate and GABA (or glycine), or some closely related compounds, are possibly the main excitatory and inhibitory transmitters in the cuneate nucleus. If ATP is released from afferent nerve endings, it could also play a significant role in excitation.