New Corticocuneate Cellular Mechanisms Underlying the Modulation of Cutaneous Ascending Transmission in Anesthetized Cats

Abstract

The ascending cutaneous transmission through the middle cuneate nucleus is subject to cortico-feedback modulation. This work studied the intracuneate cellular mechanisms underlying the corticocuneate influence. Single unit extracellular records combined with iontophoresis showed that the corticocuneate input activates cuneo-lemniscal (CL) and noncuneo-lemniscal (nCL) cells via N-methyl-D-aspartate (NMDA) and non-NMDA receptors as shown by the decrease of the cortical-induced activation on ejection of CNQX and APV, either alone or in combination. These results were confirmed by in vivo intracellular recordings. Two subgroups of nCL cells were distinguished according to their sensitivity to iontophoretic ejection of glycine and its antagonist, strychnine. Finally, the corticalevoked activation of CL cells was decreased by GABA and increased by glycine acting at a strychnine-sensitive site, indicating that glycine indirectly affects the cuneo-lemniscal transmission. A model is proposed whereby the cortex influences CL cells through three different mechanisms, producing 1) activation via non-NMDA and NMDA receptors, 2) inhibition through GABAergic nCLs, and 3) disinhibition via serial glycinergic-GABAergic nCL cells. These corticocuneate feedback effects serve to potentiate the activity of CL cells topographically aligned through direct activation and disinhibition, while inhibiting, via GABAergic cells, other CL neurons not topographically aligned.

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

“…The ML antidromic latencies of the 188 proprioceptive neurons were compared with the antidromic latencies of a different sample of 261 CL cells with cutaneous receptive fields recorded more dorsally, in the cluster region of the medial cuneate nucleus, in previous work from our laboratory (Aguilar et al, 2002(Aguilar et al, , 2003Soto et al, 2004Soto et al, , 2006. The antidromic latencies of these samples were significantly different ( p Ͻ 0.001, Mann-Whitney).…”

“…3A-C, for proprioceptive cells). Table 2 shows some of the distinctive properties of cutaneous and proprioceptive neurons at the middle main cuneate nucleus derived from the present and previous work (Aguilar et al, 2003).…”

“…Finally, strychnine-sensitive glycine receptors were homogeneously distributed throughout the main cuneate nucleus, but their functional role on ascending transmission appears to vary in different loci, since whereas in the cluster region they disinhibit ascending cutaneous output through GABAergic interneurons (Aguilar et al, 2003), in the mvCN they play a pure inhibitory role.…”

Corticofugal Modulation of the Tactile Response Coherence of Projecting Neurons in the Gracilis Nucleus

“…Recently, it has been reported that the sensorimotor cortex exerts a selective control of the somatosensory transmission at the DCN (Aguilar et al 2003;Canedo and Aguilar 2000;Nuñez 1998, 2004). Indeed, the corticofugal input facilitates sensory responses of gracile neurons with overlapping receptive fields and inhibits sensory responses of cells with separate receptive fields, probably providing a synaptic mechanism for the enhancement of contrast between sensory signals.…”

“…The wavelet transform has been used to analyze brain signals from the very beginning in neuroscience. Most of its applications are in electroencephalographic recordings (see e.g., Alegre et al 2003;Castellanos and Makarov 2006;Goelz et al 2000;Mäkinen et al 2004;Mormann et al 2005;Murata 2005;Quiroga and Garcia 2003;Schiff et al 1994). However, there are few studies on synchronization between pairs of spike trains (e.g., stimulus-neural response).…”