Volume 16, Number 23,
Issue of December 1, 1996
pp. 7505-7512
Copyright ©1996 Society for Neuroscience
Modulation of Inhibitory Transmission by Dopamine in Rat
Basal Forebrain Nuclei: Activation of Presynaptic
D1-like Dopaminergic Receptors
Received July 8, 1996; revised Sept. 10, 1996; accepted Sept. 16, 1996.
Toshihiko Momiyama1 and
J. A. Sim2
1 Department of Pharmacology, University College
London, London WC1E 6BT, United Kingdom, and 2 Department
of Neurobiology, Babraham Institute, Cambs CB2 4AT, United Kingdom
The effects of dopamine (DA) on inhibitory transmission onto
identified magnocellular neurons were examined in rat basal forebrain slices using whole-cell recording. IPSCs evoked by focal stimulation within basal forebrain nuclei were reversibly blocked by 10 µM bicuculline and had a decay time constant of 20.1 ± 0.77 msec in the presence of 6-cyano-7-nitroquinoxalline-2,3-dione
(5 µM). Bath application of DA reduced the amplitude of
IPSCs up to 71.1 ± 1.49% in a concentration-dependent manner
between 0.003 and 1 mM (the IC50 value being
6.6 µM), without any effect on the holding current at
70 mV. DA (10 µM) reduced the frequency of miniature
IPSCs (mIPSCs) recorded in the presence of TTX (0.5 µM),
without affecting their mean amplitude, rise time, and decay time
constant. Furthermore, the DA-induced effect on mIPSCs remained unaffected by 100 µM cadmium, suggesting a presynaptic
mechanism independent of calcium influx. SKF 81297, a
D1-like agonist, mimicked DA-induced effect on evoked IPSCs
(IC50, 10.9 µM), whereas R(
)-TNPA or
(
)-quinpirole, D2-like agonists (30 µM),
had little or no effect on the amplitude of evoked IPSCs. R(+)-SCH
23390, a D1-like antagonist, antagonized the DA-induced
effect on IPSCs (KB 0.82 µM),
whereas S(
)-eticlopride, a D2-like antagonist, showed
slight antagonism (KB 7.8 µM).
Forskolin (10 µM) reduced the amplitude of evoked IPSCs
to ~58% of the control and occluded the inhibitory effect of DA.
These findings indicate that DA reduces inhibitory transmission onto
magnocellular basal forebrain neurons by activating presynaptic
D1-like receptors.
Key words:
dopamine;
D1 receptor;
inhibitory
postsynaptic currents;
magnocellular basal forebrain nuclei;
presynaptic modulation