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Making high‐quality dopamine (DA)‐producing cells for basic biological or small molecule screening studies is critical for the development of novel therapeutics for disorders of the ventral midbrain. Currently, many ventral midbrain assays have low signal‐to‐noise ratio due to low levels of cellular DA and the rate‐limiting enzyme of DA synthesis, tyrosine hydroxylase (TH), hampering discovery efforts. Using intensively characterized ventral midbrain cells derived from human skin, which demonstrate calcium pacemaking activity and classical electrophysiological properties, we show that an L‐type calcium agonist can significantly increase TH protein levels and DA content and release. Live calcium imaging suggests that it is the immediate influx of calcium occurring simultaneously in all cells that drives this effect. Genome‐wide expression profiling suggests that L‐type calcium channel stimulation has a significant effect on specific genes related to DA synthesis and affects expression of L‐type calcium receptor subunits from the CACNA1 and CACNA2D families. Together, our findings provide an advance in the ability to increase DA and TH levels to improve the accuracy of disease modeling and small molecule screening for disorders of the ventral midbrain, including Parkinson's disease. Using intensively characterized ventral midbrain cells derived from humans, we show that an L‐type calcium agonist can significantly increase tyrosine hydroxylase protein levels and dopamine release. Genome‐wide expression profiling suggests that L‐type calcium channel stimulation has a significant effect on specific genes related to dopamine synthesis and affects expression of L‐type calcium receptor subunits from the CACNA1 and CACNA2D families.

Dopamine (DA) neurons in the ventral tegmental area (VTA) help mediate stress susceptibility and resilience. However, upstream mechanisms controlling these neurons remain unknown. Noradrenergic (NE) neurons in the locus coeruleus, implicated in the pathophysiology of depression, have direct connections within the VTA. Here we demonstrate that NE neurons regulate vulnerability to social defeat through inhibitory control of VTA DA neurons.

Stress stimulates dopamine (DA) release in nucleus accumbens (NAcc) but will do so more strongly in medial prefrontal cortex (PFC). Evidence indicates, however, that the cortical DA response to stress acts to dampen the concurrent increase in NAcc DA release. In the present study, we used voltammetry to investigate the role of PFC GABA in regulating the NAcc DA response to stress. The results of Experiment 1 show that the NAcc stress response is inhibited following bilateral cortical microinjections of baclofen (GABABreceptor agonist). While phaclofen (GABABreceptor antagonist) blocked the effect of baclofen, it had no significant effect of its own. Intra‐PFC injections of muscimol (GABAAreceptor agonist) and bicuculline (GABAAreceptor antagonist) had no effect on the DA stress response in NAcc. In Experiment 2, we explored the possibility that GABA influences the NAcc DA stress response indirectly by modulating stress‐induced DA release in PFC. None of the drugs tested had an effect on the PFC stress response at a dose (1 nmol) that produced reliable effects on the NAcc stress response. At an order of magnitude higher dose, however, locally applied phaclofen and muscimol enhanced and attenuated, respectively, the DA stress response in PFC. These results were validated in Experiment 3 by showing that intra‐PFC injections of GBR‐12395 (DA uptake blocker) and quinpirole (D2/D3receptor agonist) dose‐dependently enhanced and inhibited, respectively, the local DA stress response. Together, these findings indicate that increased GABA transmission in PFC exerts an inhibitory influence on the NAcc DA response to stress, and that this action is mediated primarily but not exclusively by GABABreceptors which may be located both on cortical output neurons and on DA terminals. Synapse 32:288–300, 1999. © 1999 Wiley‐Liss, Inc.

Stress stimulates dopamine (DA) release in nucleus accumbens (NAcc) but will do so more strongly in medial prefrontal cortex (PFC). Evidence indicates, however, that the cortical DA response to stress acts to dampen the concurrent increase in NAcc DA release. In the present study, we used voltammetry to investigate the role of PFC GABA in regulating the NAcc DA response to stress. The results of Experiment 1 show that the NAcc stress response is inhibited following bilateral cortical microinjections of baclofen (GABAB receptor agonist). While phaclofen (GABAB receptor antagonist) blocked the effect of baclofen, it had no significant effect of its own. Intra-PFC injections of muscimol (GABAA receptor agonist) and bicuculline (GABAA receptor antagonist) had no effect on the DA stress response in NAcc. In Experiment 2, we explored the possibility that GABA influences the NAcc DA stress response indirectly by modulating stress-induced DA release in PFC. None of the drugs tested had an effect on the PFC stress response at a dose (1 nmol) that produced reliable effects on the NAcc stress response. At an order of magnitude higher dose, however, locally applied phaclofen and muscimol enhanced and attenuated, respectively, the DA stress response in PFC. These results were validated in Experiment 3 by showing that intra-PFC injections of GBR-12395 (DA uptake blocker) and quinpirole (D2/D3 receptor agonist) dose-dependently enhanced and inhibited, respectively, the local DA stress response. Together, these findings indicate that increased GABA transmission in PFC exerts an inhibitory influence on the NAcc DA response to stress, and that this action is mediated primarily but not exclusively by GABAB receptors which may be located both on cortical output neurons and on DA terminals. Synapse 32:288–300, 1999. © 1999 Wiley-Liss, Inc.

Converging evidence suggests that dopamine (DA) transmission in nucleus accumbens (NAcc) is modulated locally by an excitatory amino acid (EAA)-containing input possibly originating in medial prefrontal cortex (PFC). In the present study, we examined the effects of intra-NAcc administration of EAA receptor antagonists on stress-induced increases of NAcc DA levels and of dendritically released DA in the ventral tegmental area (VTA). Local injection of the NMDA receptor antagonist—AP-5 (0.05, 0.5, and 5.0 nmoles)—dose-dependently potentiated increases in NAcc DA levels elicited by 15 min of restraint stress. In contrast, local application of equivalent doses of the kainate/AMPA receptor antagonist—DNQX—failed to alter the NAcc DA stress response reliably. In a separate experiment, we found that intra-NAcc injection of AP-5 also potentiated stress-induced increases in VTA DA levels. These results indicate that EAAs acting at NMDA receptors in NAcc can modulate stress-induced DA release in this region. Our data indicate, however, that this action exerts an inhibitory influence on the NAcc DA stress response, suggesting that the relevant population of NMDA receptors are not located on NAcc DA terminals. The fact that intra-NAcc AP-5 injections also potentiated the DA stress response in VTA suggests instead an action mediated by NMDA receptors located on NAcc neurons that feedback, directly or indirectly, to cell bodies of the mesocorticolimbic DA system. Synapse 26:225–234, 1997. © 1997 Wiley-Liss Inc.

Converging evidence suggests that dopamine (DA) transmission in nucleus accumbens (NAcc) is modulated locally by an excitatory amino acid (EAA)‐containing input possibly originating in medial prefrontal cortex (PFC). In the present study, we examined the effects of intra‐NAcc administration of EAA receptor antagonists on stress‐induced increases of NAcc DA levels and of dendritically released DA in the ventral tegmental area (VTA). Local injection of the NMDA receptor antagonist—AP‐5 (0.05, 0.5, and 5.0 nmoles)—dose‐dependently potentiated increases in NAcc DA levels elicited by 15 min of restraint stress. In contrast, local application of equivalent doses of the kainate/AMPA receptor antagonist—DNQX—failed to alter the NAcc DA stress response reliably. In a separate experiment, we found that intra‐NAcc injection of AP‐5 also potentiated stress‐induced increases in VTA DA levels. These results indicate that EAAs acting at NMDA receptors in NAcc can modulate stress‐induced DA release in this region. Our data indicate, however, that this action exerts an inhibitory influence on the NAcc DA stress response, suggesting that the relevant population of NMDA receptors are not located on NAcc DA terminals. The fact that intra‐NAcc AP‐5 injections also potentiated the DA stress response in VTA suggests instead an action mediated by NMDA receptors located on NAcc neurons that feedback, directly or indirectly, to cell bodies of the mesocorticolimbic DA system. Synapse 26:225–234, 1997. © 1997 Wiley‐Liss Inc.