Novelty-evoked elevations of nucleus accumbens dopamine: dependence on impulse flow from the ventral subiculum and glutamatergic neurotransmission inthe ventral tegmental area

In vivo microdialysis in freely moving rats was used to monitor novelty-evo ked elevations in extracellular dopamine in the nucleus accumbens septi (NA S) and to examine the role of the ventral subiculum of the hippocampus and glutamatergic transmission in the ventral tegmental area (VTA) on these ele vations. Exposure to novel stimuli evoked investigatory activity and increa sed nucleus accumbens dopamine. Unilateral injections of the sodium channel blocker tetrodotoxin (0.16 ng/0.5 muL) into the ventral subiculum ipsilate ral to the dialysed NAS abolished novelty-evoked elevations in dopamine. In jections of tetrodotoxin into the contralateral VS did not prevent novelty- evoked elevations in nucleus accumbens dopamine. Unilateral perfusion (via microdialysis) of the ionotropic glutamate receptor antagonists kynurenic a cid (1 mm) into the ipsilateral but not the contralateral VTA blocked novel ty-evoked elevations in nucleus accumbens dopamine. Neither unilateral inje ctions of tetrodotoxin nor unilateral perfusion of kynurenic acid disrupted investigatory behaviour. These data indicate that phasic elevations in nuc leus accumbens dopamine evoked by exposure to unconditioned novel stimuli a re dependent on impulse flow from the hippocampus and glutamatergic transmi ssion in the VTA.