Kynurenic acid

1. We have identified a new type of NMDA channel in rat central neurones that express mRNA for the NR2D subunit. We have examined single NMDA channels in cerebellar Purkinje cells (which possess NR1 and 2D), deep cerebellar nuclei (NR1, 2A, 2B and 2D) and spinal cord dorsal horn neurones (NR1, 2B and 2D). 2. In Purkinje cells, NMDA opened channels with a main conductance of 37.9 +/- 1.1 pS and a subconductance of 17.8 +/- 0.7 pS, with frequent transitions between the two levels. 3. NMDA activated low-conductance ('38/18 pS') events (along with high-conductance--'50/40 pS'--openings) in some patches from deep cerebellar nuclei and dorsal horn neurones. Our evidence suggests that 38/18 pS and 50/40 pS events arose from distinct types of NMDA receptors. 4. The transitions for 38/18 pS events were asymmetrical: steps from 38 to 18 pS were more frequent (72.2%) than steps from 18 to 38 pS. This feature appeared common to the 38/18 pS events in all three cell types, sugges...

We obtained rat brain slices (550-650 microm) that contained part of the frontoparietal cortex along with a portion of the thalamic ventrobasal complex (VB) and of the reticular nucleus (RTN). Maintained reciprocal thalamocortical connectivity was demonstrated by VB stimulation, which elicited orthodromic and antidromic responses in the cortex, along with re-entry of thalamocortical firing originating in VB neurons excited by cortical output activity. In addition, orthodromic responses were recorded in VB and RTN following stimuli delivered in the cortex. Spontaneous and stimulus-induced coherent rhythmic oscillations (duration = 0.4-3.5 s; frequency = 9-16 Hz) occurred in cortex, VB, and RTN during application of medium containing low concentrations of the K(+) channel blocker 4-aminopyridine (0.5-1 microM). This activity, which resembled electroencephalograph (EEG) spindles recorded in vivo, disappeared in both cortex and thalamus during application of the excitatory amino acid re...