KETAMINE MODULATION OF THE TEMPORAL PATTERN OF DISCHARGES AND SPIKE TRAIN INTERACTIONS IN THE RAT SUBSTANTIA-NIGRA PARS RETICULATA

This study compares the temporal pattern of discharges of extracellula rly recorded substantia nigra pars reticulata (SNr) single units in tw o experimental conditions: Equithesin- and ketamine-induced anesthesia . The analysis of the statistical properties of the spike trains recor ded in the Equithesin group of animals showed that this experimental c ondition could be considered as a control condition with respect to pr evious data reported in the literature. We investigated the glutamater gic modulation of SNr activity at spike train level in a steady-state condition by using the anesthetic agent ketamine, which is a noncompet itive antagonist of the N-methyl-D-aspartate (NMDA) glutamatergic rece ptors. The most relevant effect of ketamine at single unit level was t o induce burst discharges, with an intraburst frequency rate near 50 H z, specifically in units characterized by an initial long refractorine ss in the Equithesin condition. The other classes of single units tend ed to discharge at a higher rate without any significant change in the ir temporal pattern of firing. Simultaneous recording of the spike tra ins of 108 SNr pairs (46 and 62 during Equithesin and ketamine conditi on, respectively) were equally distributed between pairs of units simu ltaneously recorded from the same electrode and from distinct electrod es at a distance up to 400 mu m in the same hemisphere. Ketamine induc ed a significant increase in the number of pairs with synchronous firi ng (from 4 to 49%), which was strongly, but not exclusively, associate d with an increased tendency to fire in bursts. Neighboring cells tend ed to fire with a similar pattern in either condition of recording, wh ereas synchronous firing between distant cells was observed only durin g ketamine condition. (C) 1997 Elsevier Science Inc.