Lemniscal recurrent and transcortical influences on cuneate neurons

Abstract

Intracellular recordings were obtained from cuneate neurons of chloralose-anesthetized, paralysed cats to study the synaptic responses induced by electrical stimulation of the contralateral medial lemniscus. From a total of 178 cells sampled, 109 were antidromically fired from the medial lemniscus, 82 of which showed spontaneous bursting activity. In contrast, the great majority (58/69) of the non-lemniscal neurons presented spontaneous single spike activity. Medial lemniscus stimulation induced recurrent excitation and inhibition on cuneolemniscal and non-lemniscal cells. Some non-lemniscal neurons were activated by somatosensory cortex and inhibited by motor cortex stimulation. Some other non-lemniscal cells that did not respond to medial lemniscus stimulation in control conditions were transcortically affected by stimulating the medial lemniscus after inducing paroxysmal activity in the sensorimotor cortex. These findings indicate that different sites in the sensorimotor cortex can differentially influence the sensory transmission through the cuneate, and that the distinct available corticocuneate routes are selected within the cerebral cortex. From a total of 92 cells tested, the initial effect induced by low-frequency stimulation of the sensorimotor cortex was inhibition on most of the cuneolemniscal neurons (32/52) and excitation on the majority of the non-lemniscal cells (25/40). The fact that a substantial proportion of cuneolemniscal and non-lemniscal cells was excited and inhibited, respectively, suggests that the cerebral cortex may potentiate certain inputs by exciting and disinhibiting selected groups of cuneolemniscal cells. Finally, evidence is presented demonstrating that the tendency of the cuneolemniscal neurons to fire in high-frequency spike bursts is due to different mechanisms, including excitatory synaptic potentials, recurrent activation through lemniscal axonal collaterals, and via the lemnisco-thalamo-cortico-cuneate loop.A corticocuneate network circuit to explain the results is proposed.

Processing Afferent Proprioceptive Information at the Main Cuneate Nucleus of Anesthetized Cats

“…8 A, Control). This presumed recurrent suppression (Kelly and Renaud, 1973;Canedo et al, 2000) was observed at stimulating frequencies of up to 20 -25 Hz and was canceled by application of BiCu (Fig. 8 A, right) and/or strychnine.…”

Cortical modulation of dorsal column nuclei: A computational study

“…In this Section we explain how we modeled the circuit proposed by Canedo et al (2000) and shown in Fig. 1.…”

“…On the other hand, it was also demonstrated that SMC could directly excite CT cells (Darian-Smith, 1966;Winter, 1965). Recent experiments in the cuneate nucleus, based on intracellular recordings in vivo Canedo et al, 2000) have confirmed the results of some of the classical studies, have questioned others and have added new insights about synaptic connections and relationships between the cerebral cortex and the CN. With regard to cuneate interneurons, in addition to excitatory effects, cortical inhibitory effects have also been observed .…”

“…It has been proposed that, during wakefulness, SMC could control the flow of information through the DCN by two complementary mechanisms (Mountcastle and Darian-Smith, 1968;Canedo et al, 2000): (1) facilitation of the transmission of information originating in those cutaneous areas that either process a high intensity stimulus or are inside the window of cortical attention; and (2) filtering of irrelevant information. Recent findings have also shown that during sleep, descending cortical fibers play an important role by imposing oscillatory rhythms on the DCN (Mariño et al, 1996.…”

“…Three possible synaptic connections are depicted: cortical excitation and inhibition on interneurons (inset 1), cortical inhibition on cuneothalamic neurons (inset 2), and cortical excitation on cuneothalamic neurons (inset 3). Scheme adapted from Canedo et al (2000) The aim of the present study was to analyze the behaviour of the circuit proposed by Canedo et al (2000) under different synaptic configurations, and particularly, to find out which synaptic parameters explain the behaviour observed in vivo in sleep as well as wakefulness. We present: (1) the computational methods used in the present study, (2) a computational model for the circuitry proposed by Canedo et al (2000), (3) computer experiments performed with the model, and predictions derived from them, and (4) a final discussion.…”