The Effect Of NMDA Receptors On Thalamocortical Sensory Processing In Anesthetized Rat

Objective:N-methyl-D-aspartate receptors (NMDARs) are excitatory ionotropic glutamate receptors which are widely expressed in the central nervous system. Many anesthetics are known as NMDA receptor antagonists, but the local effects of these drugs on NMDA receptors are not clear. The sensory processing in thalamocortical circuit remains an open issue. In this study, we investigated the changes of tactile sensory processing in primary somatosensory cortex (S1) of rats by locally blocking the NMDA receptors in ventral posteromedial nucleus (VPM).Methods:The study included 24 rats. During experiment procedure, anaesthesia was induced and maintained by infusion propofol. After surgery an extracellular tungsten electrodes were inserted into S1 for recording spontaneous local field potentials (sLFPs) and Somatosensory evoked potentials (SEPs) and a micro glass electrode was inserted into VPM for infusions of the NMDA receptor antagonist D,L-2-amino-5-phosphonovaleric acid (AP-5) 1μl(5μg/lμl), ketamine 1μl (25μg/1μμl or 12.5μg/lμl) and saline solution 1μl. An extracellular AC amplifier was used and the raw electric signals were collected via an CDE 1401 interface to a personal computer. Whisker stimuli were performed by deflections of the optimal whisker on the contralateral face. spontaneous sLFPs power spectrum and SEPs were analysed before and after administration of NMDA receptor antagonists.Results:1. After administration of AP-51μl(5μg/μl), the amplitude of SEPs was lower andδ(1-4Hz),θ(4-8Hz),β(12-25Hz) and y (25-60Hz) powers of sLFPs decreased significantly.2. After administration of ketamine 1μl (25μg/μl), the amplitude of SEPs was reduced andβ(12-25Hz) and y (25-60Hz) powers of sLFPs decreased significantly.3. After administration of ketamine 1μl(12.5μg/μl), the amplitude of SEPs was reduced andδ(1-4Hz), a(8-12Hz),β(12-25Hz) and y (25-60Hz) powers of sLFPs decreased significantly.4. After administration of saline solution 1μ1 there was no significant deviation on sLFPs and SEPs than befor infusion.Conclusions:The findings indicate that locally blocking NMDA receptor in VPM can reduce the excitability of primary somatosensory cortex which may result in a loss of information capacity.