Injections of N‐methyl‐D‐aspartate into the ventral hippocampus increase extracellular dopamine in the ventral tegmental area and nucleus accumbens

Chemical Stimulation of the Ventral Hippocampus Elevates Nucleus Accumbens Dopamine by Activating Dopaminergic Neurons of the Ventral Tegmental Area

“…The firing rates of ϳ50% of dopaminergic neurons were elevated by NMDA injections. These elevations were sustained for a minimum of 15 min, a time during which the same dose of NMDA increases locomotor activity and elevates both NAS and VTA DA collected from microdialysis samples in freely moving rats (Legault and Wise, 1999). The present electrophysiological results are in partial agreement with a recent report from Todd and Grace (1999) in which the number and firing rates of dopaminergic neurons were recorded during multiple electrode descents into the VTA after intra-VS injections of NMDA (0.75 g, comparable to the dose used in the present study) or TTX (1 M).…”

“…The present study confirms that chemical stimulation of the VS elevates NAS DA (Legault et al, 1995;Brudzynski and Gibson, 1997;Legault and Wise, 1999). The present results add to evidence that the hippocampus can modulate dopaminergic transmission by demonstrating that VS stimulation can increase impulse flow through VTA dopaminergic neurons and by demonstrating that impulse flow through VTA dopaminergic neurons is critical for VS stimulation to increase NAS DA.…”

“…Intra-VS injections of NMDA failed to increase NAS DA when impulse flow through dopaminergic neurons was disrupted by perfusion of TTX into the VTA (on day 1) but increased NAS DA during perfusion of aCSF the VTA (on day 2). VS-evoked elevations in NAS DA were comparable in both magnitude and duration, as we have previously reported (Legault and Wise, 1999). Electrophysiological recordings confirmed that injections of NMDA into the VS increases the firing rates of at least a subpopulation of identified VTA dopaminergic neurons.…”

Effects of hippocampal N-methyl-[D]-aspartate infusion on locomotor activity and prepulse inhibition: Differences between the dorsal and ventral hippocampus.

“…The pronounced hyperactivity seen after NMDA infusion into the ventral hippocampus is in line with numerous previous studies that found hyperactivity after chemical stimulation of the ventral hippocampus by NMDA or other excitatory neuroactive compounds (Bardgett & Henry, 1999;Bast et al, 2001a;Bast, Zhang, Heidbreder, & Feldon 2001;Brenner & Bardgett, 1998;Brudzynski & Gibson, 1997;Legault & Wise, 1999;Wu & Brudzynski, 1995;Yang & Mogenson, 1987). As in our previous study (Bast, Zhang, Heidbreder, & Feldon, 2001), the hyperactivity disappeared 24 hr after the infusion, demonstrating that hyperactivity was in fact due to a temporary change in activity of the ventral hippocampus and not to possible permanent cell damage.…”

Specific Effects of Characteristics of Enriched Environment on Innovative Problem Solving by Animals

“…An examination of the neural mechanisms behind the effects of novelty on mice’s innovate problem-solving ability provided further evidence for the involvement of exploratory motivation. The numbers of dopamine neurons and VTA to NA dopaminergic projections (a neural functional circuit that regulates novelty seeking and motivation in the mouse brain; Flaherty, 2005; Griffin & Guez, 2014; Kaufman et al, 2011; Legault & Wise, 1999) increased in response to environmental novelty, but not environmental complexity, similar to previous studies in rats that demonstrated the increased release of dopamine in the NA in response to novel stimuli (Hooks & Kalivas, 1995; Legault & Wise, 2001). These results further indicated that only the novelty (relative to the complexity) of the enrichment environment had the potential to enhance novel exploratory motivation, which promoted the innovative capability of mice.…”