IN-VIVO CHARACTERIZATION OF 2 CELL-TYPES IN THE RAT GLOBUS-PALLIDUS WHICH HAVE OPPOSITE RESPONSES TO DOPAMINE-RECEPTOR STIMULATION - COMPARISON OF ELECTROPHYSIOLOGICAL PROPERTIES AND RESPONSES TO APOMORPHINE, DIZOCILPINE, AND KETAMINE ANESTHESIA

Extracellular single-unit recording techniques were used to examine th e rat globus pallidus (GP). In both locally anesthetized, paralyzed ra ts and ketamine-anesthetized rats, we observed two distinct biphasic e xtracellular waveforms, which we have labeled Type I (negative/positiv e waveform) and Type II (positive/negative waveform). No significant d ifferences were observed in the firing pattern or number of cells per track between these cell types, although the Type II neurons had a fas ter mean firing rate in the locally anesthetized animal. A portion of both cell types could be antidromically activated from the subthalamic nucleus, although Type II neurons had significantly slower conduction velocities. The most striking pharmacological difference between the two cell types was that Type I GP neurons were inhibited by systemic a dministration of the dopamine agonist apomorphine; previous studies ha ve repeatedly shown that Type II GP cells are excited by this treatmen t. Pretreatment with a subthreshold dose of apomorphine reduced the re sponsiveness of Type I cells to a subsequent high dose of apomorphine, as has been shown for Type II cells. However, pretreatment with the N MDA antagonist dizocilpine (MK 801) produced a significant change in t he pattern of response to apomorphine for Type II GP neurons only. Rel ative to observations in locally anesthetized, paralyzed rats, ketamin e anesthesia reduced the firing rate of both cell types, but did not s ignificantly alter their direction of response to apomorphine. Thus, t his study has confirmed the existence of two GP cell types with distin ct extracellular waveforms and different responses to dopamine recepto r stimulation. These data may necessitate a reevaluation of general th eoretical models of basal ganglia function in order to account for the se opposite effects of dopamine receptor stimulation on pallidal outpu t. (C) 1995 Wiley-Liss, Inc.