ELECTROPHYSIOLOGY OF GLOBUS-PALLIDUS NEURONS IN-VITRO

1. We investigated the electrical properties of globus pallidus neurons intracellularly using brain slices from adult guinea pigs. Three types of neurons were identified according to their intrinsic electrophysiological properties. 2. Type I neurons (59%) were silent at the resting membrane level (-65 +/- 10 mV, mean +/- SD) and generated a burst of spikes, with strong accommodation, to depolarizing current injection. Calcium-dependent low-frequency (1-8 Hz) membrane oscillations were often elicited by membrane depolarization (-53 +/- 8 mV). A low-threshold calcium conductance and an A-current were also identified. The mean input resistance of this neuronal type was 70 +/- 22 M Omega. 3. Type II neurons (37%) fired spontaneously at the resting membrane level (-59 +/- 9 mV). Their repetitive firing (less than or equal to 200 Hz) was very sensitive to the amplitude of injected current and showed weak accommodation. Sodium-dependent high-frequency (20-100 Hz) subthreshold membrane oscillations were often elicited by membrane depolarization. This neuronal type demonstrated a low-threshold calcium spike and had the highest input resistance (134 +/- 62 M Omega) of the three neuron types. 4. Type III neurons (4%) did not fire spontaneously at the resting membrane level (-73 +/- 5 mV). Their action potentials were characterized by a long duration (2.3 +/- 0.6 ms). Repetitive firing elicited by depolarizing current injection showed weak or no accommodation. This neuronal type had an A-current and showed the lowest input resistance (52 +/- 35 M Omega) of the three neuron types. 5. Stimulation of the caudoputamen evoked inhibitory postsynaptic potentials (IPSPs) in Type I and II neurons. In Type II neurons the IPSPs were usually followed by rebound firing. Excitatory postsynaptic potentials and antidromic responses were also elicited in some Type I and II neurons. The estimated conduction velocity of the striopallidal projection was <1 m/s (Type I neurons, 0.49 +/- 0.37 m/s; Type II neurons, 0.33 +/- 0.13 m/s).