Journal of Neuroscience, Vol 6, 120-126, Copyright © 1986 by Society for Neuroscience
Endogenous dopamine can modulate inhibition of substantia nigra pars reticulata neurons elicited by GABA iontophoresis or striatal stimulation
BL Waszczak and JR Walters
Previous reports from this laboratory have described an ability of
iontophoretically applied dopamine to attenuate the inhibitory effects of
iontophoresed GABA on neurons of the substantia nigra pars reticulata. This
finding raised the question of whether endogenous dopamine, released from
dendrites of neighboring pars compacta dopamine neurons, might act as a
neuromodulator which diminishes the inhibition of pars reticulata neurons
evoked by either GABA iontophoresis or electrical stimulation of the
striatonigral GABAergic pathway. Extracellular, single-unit activity of
pars reticulata neurons was recorded in male rats anesthetized with chloral
hydrate. In one set of studies, d-amphetamine, a drug reported to release
dopamine from nigral dendrites, was administered intravenously (1.6 mg/kg)
during regular, intermittent iontophoretic pulses of GABA. As had been
previously observed with iontophoresed dopamine, i.v. amphetamine
significantly lessened the inhibition of reticulata neurons produced by
GABA application. This change was reflected by a decrease in GABA's
inhibitory potency by 22% relative to the control level of inhibition
achieved prior to amphetamine administration. Amphetamine caused no
decreases in GABA's effectiveness, however, in animals that had previously
received treatments that depleted or destroyed nigral dopamine stores,
i.e., in rats pretreated with reserpine and alpha- methyl-p-tyrosine, or in
rats with 6-hydroxydopamine lesions of the nigrostriatal dopamine pathway.
In a second set of experiments, amphetamine or dopamine was delivered
iontophoretically while monitoring the GABA-mediated
(bicuculline-reversible) inhibition of reticulata neurons that can be
elicited by striatal stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)