Opposite modulation of brain stimulation reward by NMDA and AMPA receptors in the ventral tegmental area.

Charles Ducrot, Emmanuel Fortier, Claude Bouchard, Pierre-Paul Rompré
Front. Syst. Neurosci.. 2013-01-01; 7:
DOI: 10.3389/fnsys.2013.00057

PubMed
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Ducrot C(1), Fortier E, Bouchard C, Rompré PP.

Author information:
(1)Département de Physiologie, Université de Montréal Montréal, QC, Canada.

Previous studies have shown that blockade of ventral tegmental area (VTA)
glutamate N-Methyl-D-Aspartate (NMDA) receptors induces reward, stimulates
forward locomotion and enhances brain stimulation reward. Glutamate induces two
types of excitatory response on VTA neurons, a fast and short lasting
depolarization mediated by α-amino-3-hydroxy-5-methyl-4-isoxazole propionate
(AMPA) receptors and a longer lasting depolarization mediated by NMDA receptors.
A role for the two glutamate receptors in modulation of VTA neuronal activity is
evidenced by the functional change in AMPA and NMDA synaptic responses that
result from repeated exposure to reward. Since both receptors contribute to the
action of glutamate on VTA neuronal activity, we studied the effects of VTA AMPA
and NMDA receptor blockade on reward induced by electrical brain stimulation.
Experiments were performed on rats trained to self-administer electrical pulses
in the medial posterior mesencephalon. Reward thresholds were measured with the
curve-shift paradigm before and for 2 h after bilateral VTA microinjections of
the AMPA antagonist, NBQX
(2,3,-Dioxo-6-nitro-1,2,3,4-tetrahydrobenzo(f)quinoxaline-7-sulfonamide, 0, 80,
and 800 pmol/0.5 μl/side) and of a single dose (0.825 nmol/0.5 μl/side) of the
NMDA antagonist, PPPA (2R,4S)-4-(3-Phosphonopropyl)-2-piperidinecarboxylic acid).
NBQX produced a dose-dependent increase in reward threshold with no significant
change in maximum rate of responding. Whereas PPPA injected at the same VTA sites
produced a significant time dependent decrease in reward threshold and increase
in maximum rate of responding. We found a negative correlation between the
magnitude of the attenuation effect of NBQX and the enhancement effect of PPPA;
moreover, NBQX and PPPA were most effective when injected, respectively, into the
anterior and posterior VTA. These results suggest that glutamate acts on
different receptor sub-types, most likely located on different VTA neurons, to
modulate reward.

 

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