The Journal of Neuroscience, April 15, 2001, 21(8):2820-2832
Regulation of Limbic Information Outflow by the Subthalamic
Nucleus: Excitatory Amino Acid Projections to the Ventral Pallidum
Michael S.
Turner1,
Antonieta
Lavin2,
Anthony
A.
Grace3, and
T. Celeste
Napier1
1 Department of Pharmacology, and the Neuroscience
Program, Loyola University Chicago, School of Medicine, Maywood,
Illinois 60153, 2 Department of Physiology and
Neuroscience, Medical University of South Carolina, Charleston, South
Carolina 29425, and 3 Departments of Neuroscience and
Psychiatry, University of Pittsburgh, Pittsburgh, Pennsylvania
15260
The subthalamic nucleus (STN), a component of the basal ganglia
motor system, sends an excitatory amino acid (EAA)-containing projection to the ventral pallidum (VP), a major limbic system output
region. The VP contains both NMDA and AMPA subtypes of EAA receptors.
To characterize the physiology of the subthalamic pathway to the VP,
and to determine the influence of EAA receptor subtypes, in
vivo intracellular recordings, and in vivo
extracellular recordings combined with microiontophoresis, were made
from VP neurons in anesthetized rats. Of the intracellularly recorded neurons, 86% responded to STN stimulation, and these displayed EPSPs
with an onset of 8.7 msec, consistent with a monosynaptic input. The
EPSPs evoked in spontaneously firing neurons were nearly twice the
amplitude of those in nonfiring cells (13.1 vs 6.8 mV, respectively).
As neurons were depolarized by current injection, the latency
for spiking decreased from 24.2 to 14.2 msec, although EPSP latency was
unaffected. Eighty-seven percent of the extracellularly recorded VP
neurons responded to STN stimulation with a rapid and robust
enhancement of spiking; the response onset, like the EPSP onset,
equaled 8.7 msec. Firing rate was enhanced by NMDA in 94% of the
STN-excited cells, and AMPA increased firing in 94% as well. The
NMDA-selective antagonist AP-5 attenuated 67% of the STN-evoked
excitatory responses, and the AMPA-selective antagonist CNQX attenuated
52%. Both antagonists attenuated 33% of responses, and 78% were
attenuated by at least one. This evidence suggests that a great
majority of VP neurons are directly influenced by STN activation and
that both NMDA and non-NMDA receptors are involved. Moreover, the VP
response to STN stimulation appears to be strongly dependent on the
depolarization state of the neuron.
Key words:
ventral pallidum; subthalamic nucleus; basal ganglia; NMDA; AMPA; CNQX; AP-5; electrophysiology
Copyright © 2001 Society for Neuroscience 0270-6474/01/2182820-13$05.00/0