The lemniscal–cuneate recurrent excitation is suppressed by strychnine and enhanced by GABA_A antagonists in the anaesthetized cat

Abstract

In the somatosensory system, cuneolemniscal (CL) cells fire high frequency doublets of spikes facilitating the transmission of sensory information to diencephalic target cells. We studied how lemniscal feedback affects ascending transmission of cutaneous neurons of the middle cuneate nucleus. Electrical stimulation of the contralateral medial lemniscus and of the skin at sites evoking responses with minimal threshold induced recurrent activation of CL cells at a latency of 1-3.5 ms. The lemniscal feedback activation was suppressed by increasing the stimulating intensity at the same sites, suggesting recurrent-mediated lateral inhibition. The glycine antagonist strychnine blocked the recurrent excitatory responses while GABAA antagonists uncovered those obscured by stronger stimulation. CL cells sharing a common receptive field (RF) potentiate one another by recurrent activation and disinhibition, the disinhibition being produced by serial interactions between glycinergic and GABAergic interneurons. Conversely, CL cells with different RFs inhibit each other through recurrent GABA-mediated inhibition. The lemniscal feedback would thus enhance the surround antagonism of a centre response by increasing the spatial resolution and the transmission of weak signals.

Quantitative stereological evaluation of the gracile and cuneate nuclei and their projection neurons in the rat

“…Coupling between interneurons takes place at chemical and electrical synapses at or near the soma (Fricker and Miles, 2001), so that, for effective coupling to occur, it is necessary that intersomatic distance in the cortex remains below 200 m (Amitai et al, 2002). Synchronization and rhythm generation in the DCN have only recently began to be explored, but it is becoming clear that those processes depend on cellular and circuit properties that are not fundamentally different from those of the cortex (Schwark et al, 1999;Nuñ ez et al, 2000;Aguilar et al, 2002). The low number of interneurons in the DCN makes more pressing the questions of how they are spatially organized and how they influence the much larger population of projection neurons.…”

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).…”

Spike Timing, Spike Count, and Temporal Information for the Discrimination of Tactile Stimuli in the Rat Ventrobasal Complex

“…Primary afferents could thus exploit the spike timing precision of their responses only to discriminate between close locations within the body area they represent, e.g., within a fingertip (Johansson and Birznieks, 2004), but not to discriminate between separate locations such as different digits or different whiskers. Temporal information conveyed by spike timing about stimulus location between digits or between whiskers in the ventrobasal complex is thus a product of the basic transformations that occur in the brainstem (Panetsos et al, 1997;Aguilar et al, 2002Aguilar et al, , 2003Fernández de Sevilla et al, 2006;Soto et al, 2006), which determine the enlargement of receptive fields at thalamic level. Importantly, the receptive field size of thalamocortical neurons is particularly large in active or awake states (Nicolelis et al, 1993;Nicolelis and Chapin, 1994;Friedberg et al, 1999;Aguilar and Castro-Alamancos, 2005).…”