Synaptic plasticity and sensory information processing through the thalamus and the cortex of the rodent barrel field

Resumen

Sensory information from rodent whiskers is sent from the whisker follicle to the contralateral area of the thalamus and from thalamus to the barrel cortex (BC) through two different pathways: the lemniscal and the paralemniscal pathways. Sensory information processing depends on processes as synaptic plasticity which is involved in memory and learning. In this Doctoral Thesis we performed extracellular in vivo recordings in the BC and thalamus of urethane anesthetized rats and mice in order to unravel the mechanisms of synaptic plasticity and sensory processing. We saw that repetitive stimulation at frequencies at which the animal explores the environment induced long-termpotentiation (LTP). In addition, low frequency stimulation could induce LTP or long-termdepression (LTD) depending on the intracellular Ca2+ concentration during the stimulation time period. This long-termplasticity depended on N-methyl-D-aspartate (NMDA) receptors activation and the activation of muscarinic and nicotinic cholinergic receptors. Through an optogenetic study we showed that the basal forebrain (BF), the main source of acetylcholine (ACh) to the neocortex, sent its projections in a very specific manner. Consequently, the ACh-depending facilitation of cortical responses occurs in a very specific manner. Sensory information arrives to the BC through two thalamic nuclei that process differently this information. While ventro-postero-medial (VPM) nucleus carry out precise information from one whisker, postero-medial (POM) nucleus carry out sensory information from several whiskers. We found that POM regulated BC whisker responses through GABAergic (°-aminobutyric-acid: GABA) neurons located in upper cortical layers. We have also described different firing patterns in the mouse BC through multichannel recordings. We found that the distribution of these different firing patters was not uniform, probably this fact may contribute to sensory processing.