Drug-driven AMPA receptor redistribution mimicked by selective dopamine neuron stimulation

Background

Addictive drugs have in common that they cause surges in dopamine (DA) concentration in the mesolimbic reward system and elicit synaptic plasticity in DA neurons of the ventral tegmental area (VTA). Cocaine for example drives insertion of GluA2-lacking AMPA receptors (AMPARs) at glutamatergic synapes in DA neurons. However it remains elusive which molecular target of cocaine drives such AMPAR redistribution and whether other addictive drugs (morphine and nicotine) cause similar changes through their effects on the mesolimbic DA system.

Methodology / Principal Findings

We used in vitro electrophysiological techniques in wild-type and transgenic mice to observe the modulation of excitatory inputs onto DA neurons by addictive drugs. To observe AMPAR redistribution, post-embedding immunohistochemistry for GluA2 AMPAR subunit was combined with electron microscopy. We also used a double-floxed AAV virus expressing channelrhodopsin together with a DAT Cre mouse line to selectively express ChR2 in VTA DA neurons. We find that in mice where the effect of cocaine on the dopamine transporter (DAT) is specifically blocked, AMPAR redistribution was absent following administration of the drug. Furthermore, addictive drugs known to increase dopamine levels cause a similar AMPAR redistribution. Finally, activating DA VTA neurons optogenetically is sufficient to drive insertion of GluA2-lacking AMPARs, mimicking the changes observed after a single injection of morphine, nicotine or cocaine.

Conclusions / Significance

We propose the mesolimbic dopamine system as a point of convergence at which addictive drugs can alter neural circuits. We also show that direct activation of DA neurons is sufficient to drive AMPAR redistribution, which may be a mechanism associated with early steps of non-substance related addictions.     

Cholinergic mediation in the ventral tegmental area of alpha-melanotropin induced excessive grooming: changes of the dopamine activity in the nucleus accumbens and caudate putamen

The effect of alpha-melanotropin (alpha-MSH) on the rat mesolimbic dopaminergic activity was estimated by measuring the changes in dihydroxyphenyl acetic acid (DOPAC) and dopamine (DA) endogenous levels in the nucleus accumbens (Ac) and caudate putamen (CP). A marked increase of DOPAC/DA ratios resulting from an increase in DOPAC and decrease in DA levels was found in the Ac 30 and 65 min after bilateral alpha-MSH-injections (1 microgram) into the ventral tegmental area (VTA). Similar changes were observed in the CP 65 min post-injections. These peptide-induced changes were completely inhibited by a previous VTA injection of atropine (1 microgram), at a dose that totally blocked the alpha-MSH-induced excessive grooming and motor activation. These results confirms that alpha-MSH affects a cholinergic afferent to the VTA which modifies the mesolimbic dopaminergic system involved in the alpha-MSH/ACTH-induced behaviors.     

Role for mTOR signaling and neuronal activity in morphine-induced adaptations in ventral tegmental area dopamine neurons

While the abuse of opiate drugs continues to rise, the neuroadaptations that occur with long-term drug exposure remain poorly understood. We describe here a series of chronic morphine-induced adaptations in ventral tegmental area (VTA) dopamine neurons, which are mediated via downregulation of AKT-mTORC2 (mammalian target of rapamycin complex-2). Chronic opiates decrease the size of VTA dopamine neurons in rodents, an effect seen in humans as well, and concomitantly increase the excitability of the cells but decrease dopamine output to target regions. Chronic morphine decreases mTORC2 activity, and overexpression of Rictor,?a component of mTORC2, prevents morphine-induced changes in cell morphology and activity. Further, local knockout of Rictor in VTA decreases DA soma size and reduces rewarding responses to morphine, consistent with the hypothesis that these adaptations represent a mechanism of reward tolerance. Together, these findings demonstrate a novel role for AKT-mTORC2 signaling in mediating neuroadaptations to opiate drugs of abuse.     

Leptin Acts via Leptin Receptor-Expressing Lateral Hypothalamic Neurons to Modulate the Mesolimbic Dopamine System and Suppress Feeding

The lateral hypothalamic area (LHA) acts in concert with the ventral tegmental area (VTA) and other components of the mesolimbic dopamine (DA) system to control motivation, including the incentive to feed. The anorexigenic hormone leptin modulates the mesolimbic DA system, although the mechanisms underlying this control have remained incompletely understood. We show that leptin directly regulates a population of leptin receptor (LepRb)-expressing inhibitory neurons in the LHA and that leptin action via these LHA LepRb neurons decreases feeding and body weight. Furthermore, these LHA LepRb neurons innervate the VTA, and leptin action on these neurons restores VTA expression of the rate-limiting enzyme in DA production along with mesolimbic DA content in leptin-deficient animals. Thus, these findings reveal that LHA LepRb neurons link anorexic leptin action to the mesolimbic DA system.     

Mimicking synaptic effects of addictive drugs with selective dopamine neuron stimulation

The synaptic changes induced by initial drug exposure leave a trace on neural systems that can eventually manifest in compulsive drug-seeking behavior. A single injection of cocaine has been shown to induce a change in the AMPA receptor (AMPAR) subunit composition at glutamatergic synapses onto ventral tegmental area (VTA) dopamine (DA) neurons. This change is long-lasting (up to months following self-administration) and represents an important functional change at the synaptic level following cocaine use. We recently published findings that cocaine's action at the DA transporter (DAT) is necessary for the induction of AMPAR redistribution and that this can also be mimicked by selective DA neuron stimulation. The stimulation effect is dependent on D1 receptors within the VTA. Furthermore other addictive drugs, although they act through distinct mechanisms, also induce this synaptic change. Here we discuss literature that expands on these observations in an attempt to further clarify the synaptic changes following early drug use.     

Role of excitatory amino acids in the ventral tegmental area for central actions of non-competitive NMDA-receptor antagonists and nicotine

Summary The putative role of non-NMDA excitatory amino acid (EAA) receptors in the ventral tegmental area (VTA) for the increase in dopamine (DA) release in the nucleus acumbens (NAC) and the behavioural stimulation induced by systemically administered dizocilpine (MK-801) was investigated. Microdialysis was utilized in rats with probes in the VTA and NAC. The VTA was perfused with the AMPA and kainate receptor antagonist CNQX (0.3 or 1.0 mM) or vehicle and dialysates from the NAC were analyzed with high-performance liquid chromatography for DA. Forty min after onset of CNQX or vehicle perfusion of the VTA MK-801 (0.1 mg/kg) was injected subcutaneously (sc). Subsequently, typical MK-801 induced behaviours were assessed. The MK-801 induced hyperlocomotion was associated with a 50% increase of DA levels in NAC dialysates. Both the MK-801 evoked hyperlocomotion and DA release in the NAC were effectively antagonized by CNQX perfusion of the VTA. However, by itself the CNQX or vehicle perusion of the VTA did not affect DA levels in NAC or the rated behaviours. The results indicate that MK-801 induced hyperlocomotion and increased DA release in the NAC are largely elicited within the VTA via activation of non-NMDA EAA receptors, tentatively caused by locally increased EAA release. In contrast, the enhanced DA output in the NAC induced by systemic nicotine (0.5 mg/kg sc) was not antagonized by intra VTA infusion of CNQX (0.3 or 1.0 mM), but instead by infusion of the NMDA receptor antagonist AP-5 (0.3 or 1.0 mM) into the VTA, which by itself did not alter DA levels in the NAC. Thus, the probably indirect, EAA mediated activation of the mesolimbic DA neurons in the VTA by MK-801 and nicotine, respectively, seems to be mediated via different glutamate receptor subtypes.     

Modulation of the Mesolimbic Dopamine System by Glutamate

Glutamate has been shown to modulate motor behavior, probably via N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors that are involved in the control of the mesolimbic dopamine (DA) system, that is, the ventral tegmental area (VTA)-nucleus accumbens (NAC). In the present study, we investigated the effects of uncompetitive (MK-801) and competitive [DL-2-amino-5-phosphonopentanoic acid (AP-5), CGP 40116] NMDA receptor antagonists and NMDA and AMPA on DA release in the mesolimbic system and on motor behavior. Systemic injection and intrategmental infusion of MK-801 increased DA levels in the VTA, but the systemic administration enhanced DA exclusively in the NAC and increased motor behavior. In contrast, intrategmental infusion of AP-5, but not the systemic administration of its lipophilic analogue CGP 40116, decreased the DA release in the two regions without affecting motor behavior. NMDA and AMPA infusion into the VTA increased DA levels in both areas. This increase was accompanied by a strong motor behavioral stimulation after NMDA but only a moderate increase after AMPA infusion. The present results indicate that mesolimbic DA neurons are controlled by the glutamatergic system and that the effects of uncompetitive and competitive NMDA receptor antagonists on DA release are mediated by an interaction with different brain areas. These findings may account for the different effects of NMDA receptor ligands on motor behavior.     

The role of dopamine in the nucleus accumbens in analgesia

Opioid and psychostimulant drugs have long been used for the relief of chronic pain in the clinical situation. Animal studies confirm that these drugs alleviate persistent or tonic pain. Little is known, however, about the neural systems underlying the suppression of tonic pain except that they are different from those mediating the suppression of phasic (i.e., sharp and short-lasting) pain. Although spinal and brainstem-descending pain suppression mechanisms play a role in mediating the inhibition of tonic pain, it appears that this response is additionally mediated by the activation of mechanisms lying rostral to the brainstem. Recent studies suggest that the activation of mesolimbic dopamine (DA) neurons, arising from the cell bodies of the ventral tegmental area (VTA) and projecting to the nucleus accumbens (NAcc), plays an important role in mediating the suppression of tonic pain. Other studies suggest that this pain-suppression system involving the activation of mesolimbic DA neurons is naturally triggered by exposure to stress, through the endogenous release of opioids and substance P (SP) in the midbrain.     

NMDA Receptors on Non-Dopaminergic Neurons in the VTA Support Cocaine Sensitization

Background

The initiation of behavioral sensitization to cocaine and other psychomotor stimulants is thought to reflect N-methyl-D-aspartate receptor (NMDAR)-mediated synaptic plasticity in the mesolimbic dopamine (DA) circuitry. The importance of drug induced NMDAR mediated adaptations in ventral tegmental area (VTA) DA neurons, and its association with drug seeking behaviors, has recently been evaluated in Cre-loxp mice lacking functional NMDARs in DA neurons expressing Cre recombinase under the control of the endogenous dopamine transporter gene (NR1^DATCre mice).

Methodology and Principal Findings

Using an additional NR1^DATCre mouse transgenic model, we demonstrate that while the selective inactivation of NMDARs in DA neurons eliminates the induction of molecular changes leading to synaptic strengthening, behavioral measures such as cocaine induced locomotor sensitization and conditioned place preference remain intact in NR1^DATCre mice. Since VTA DA neurons projecting to the prefrontal cortex and amygdala express little or no detectable levels of the dopamine transporter, it has been speculated that NMDA receptors in DA neurons projecting to these brain areas may have been spared in NR1^DATCre mice. Here we demonstrate that the NMDA receptor gene is ablated in the majority of VTA DA neurons, including those exhibiting undetectable DAT expression levels in our NR1^DATCre transgenic model, and that application of an NMDAR antagonist within the VTA of NR1^DATCre animals still blocks sensitization to cocaine.

Conclusions/Significance

These results eliminate the possibility of NMDAR mediated neuroplasticity in the different DA neuronal subpopulations in our NR1^DATCre mouse model and therefore suggest that NMDARs on non-DA neurons within the VTA must play a major role in cocaine-related addictive behavior.     

Orexinergic Input to Dopaminergic Neurons of the Human Ventral Tegmental Area

The mesolimbic reward pathway arising from dopaminergic (DA) neurons of the ventral tegmental area (VTA) has been strongly implicated in reward processing and drug abuse. In rodents, behaviors associated with this projection are profoundly influenced by an orexinergic input from the lateral hypothalamus to the VTA. Because the existence and significance of an analogous orexigenic regulatory mechanism acting in the human VTA have been elusive, here we addressed the possibility that orexinergic neurons provide direct input to DA neurons of the human VTA. Dual-label immunohistochemistry was used and orexinergic projections to the VTA and to DA neurons of the neighboring substantia nigra (SN) were analyzed comparatively in adult male humans and rats. Orexin B-immunoreactive (IR) axons apposed to tyrosine hydroxylase (TH)-IR DA and to non-DA neurons were scarce in the VTA and SN of both species. In the VTA, 15.0±2.8% of TH-IR perikarya in humans and 3.2±0.3% in rats received orexin B-IR afferent contacts. On average, 0.24±0.05 and 0.05±0.005 orexinergic appositions per TH-IR perikaryon were detected in humans and rats, respectively. The majority (86–88%) of randomly encountered orexinergic contacts targeted the dendritic compartment of DA neurons. Finally, DA neurons of the SN also received orexinergic innervation in both species. Based on the observation of five times heavier orexinergic input to TH-IR neurons of the human, compared with the rat, VTA, we propose that orexinergic mechanism acting in the VTA may play just as important roles in reward processing and drug abuse in humans, as already established well in rodents.     

Suppression of the morphine-induced rewarding effect in the rat with neuropathic pain: implication of the reduction in mu-opioid receptor functions in the ventral tegmental area

The present study was designed to investigate the rewarding effect, G-protein activation and dopamine (DA) release following partial sciatic nerve ligation in the rat. Here we show for the first time that morphine failed to produce a place preference in rats with nerve injury. Various studies provide arguments to support that the mesolimbic dopaminergic system, which projects from the ventral tegmental area (VTA) to the nucleus accumbens (N.Acc), is critical of the motivational effects of opioids. In the present study, there were no significant differences between sham-operated and sciatic nerve-ligated rats in the increases in guanosine-5'-o-(3-[35S]thio)triphosphate ([35S]GTPgammaS) binding to membranes of the N.Acc stimulated by either DA, the D1 receptor agonist SKF81297, the D2 receptor agonist N-propylnoraporphine or the D3 receptor agonist 7-hydroxy-2-dipropylaminotetralin (7-OH DPAT). In contrast, the increases in [35S]GTPgammaS binding to membranes of the VTA induced by either morphine or a selective micro -opioid receptor agonist [d-Ala2, NMePhe4, Gly(ol)5]enkephalin were significantly attenuated in nerve-ligated rats as compared with sham- operated rats. Furthermore, the enhancement of DA release in the N.Acc stimulated by morphine was significantly suppressed by sciatic nerve ligation. These findings suggest that attenuation of the morphine-induced place preference under neuropathic pain may result from a decrease in the morphine-induced DA release in the N.Acc with reduction in the mu-opioid receptor-mediated G-protein activation in the VTA.     

Feedback control of mesolimbic somatodendritic dopamine release in rat brain

The objective of this study was to examine the role of dopamine (DA) receptors in the nucleus accumbens (ACB) in controlling feedback regulation of mesolimbic somatodendritic DA release in the ventral tegmental area (VTA) of Wistar rats using ipsilateral dual-probe in vivo microdialysis. Perfusion of the ACB for 60 min with the DA uptake inhibitor GBR-12909 (10-1,000 microM) or nomifensine (10-1,000 microM) dose-dependently increased the extracellular levels of DA in ACB and concomitantly reduced the extracellular levels of DA in the VTA. Coperfusion of 100 microM nomifensine with either 100 microM SCH-23390 (SCH), a D1 antagonist, or 100 microM sulpiride (SUL), a D2 receptor antagonist, produced either an additive (for SCH) or a synergistic (for SUL) elevation in the extracellular levels of DA in the ACB, whereas the reduction in the extracellular levels of DA in the VTA produced by nomifensine alone was completely prevented by addition of either antagonist. Application of 100 microM SCH or SUL alone through the microdialysis probe in the ACB increased the extracellular levels of DA in the ACB, whereas the extracellular levels of DA in the VTA remained unchanged. Overall, the results suggest that (a) increasing the synaptic levels of DA in the ACB activates a long-loop negative feedback pathway to the VTA involving both D1 and D2 postsynaptic receptors and (b) terminal DA release within the ACB is regulated directly by D2 autoreceptors and may be indirectly regulated by D1 receptors, possibly on interneurons and/or through postsynaptic inhibition of the negative feedback loop.     

Synaptic plasticity in the mesolimbic dopamine system

Long-term potentiation (LTP) and long-term depression (LTD) are thought to be critical mechanisms that contribute to the neural circuit modifications that mediate all forms of experience-dependent plasticity. It has, however, been difficult to demonstrate directly that experience causes long-lasting changes in synaptic strength and that these mediate changes in behaviour. To address these potential functional roles of LTP and LTD, we have taken advantage of the powerful in vivo effects of drugs of abuse that exert their behavioural effects in large part by acting in the nucleus accumbens (NAc) and ventral tegmental area (VTA); the two major components of the mesolimbic dopamine system. Our studies suggest that in vivo drugs of abuse such as cocaine cause long-lasting changes at excitatory synapses in the NAc and VTA owing to activation of the mechanisms that underlie LTP and LTD in these structures. Thus, administration of drugs of abuse provides a distinctive model for further investigating the mechanisms and functions of synaptic plasticity in brain regions that play important roles in the control of motivated behaviour, and one with considerable practical implications.     

Leptin action via neurotensin neurons controls orexin, the mesolimbic dopamine system and energy balance

Leptin acts on leptin receptor (LepRb)-expressing neurons throughout the brain, but the roles for many populations of LepRb neurons in modulating energy balance and behavior remain unclear. We found that the majority of LepRb neurons in the lateral hypothalamic area (LHA) contain neurotensin (Nts). To investigate the physiologic role for leptin action via these LepRb(Nts) neurons, we generated mice null for LepRb specifically in Nts neurons (Nts-LepRbKO mice). Nts-LepRbKO mice demonstrate early-onset obesity, modestly increased feeding, and decreased locomotor activity. Furthermore, consistent with the connection of LepRb(Nts) neurons with local orexin (OX) neurons and the ventral tegmental area (VTA), Nts-LepRbKO mice exhibit altered regulation of OX neurons and the mesolimbic DA system. Thus, LHA LepRb(Nts) neurons mediate physiologic leptin action on OX neurons and the mesolimbic DA system, and contribute importantly to the control of energy balance.     

D1-D2 dopamine receptor interaction within the nucleus accumbens mediates long-loop negative feedback to the ventral tegmental area (VTA)

The objective of the present study was to examine the effects of perfusion of dopamine (DA) D1- and D2-like receptor agonists in the nucleus accumbens (ACB) on the long-loop negative feedback regulation of mesolimbic somatodendritic DA release in the ventral tegmental area (VTA) of Wistar rats employing ipsilateral dual probe in vivo microdialysis. Perfusion of the ACB for 60 min with the D1-like receptor agonist SKF 38393 (SKF, 1-100 microM) dose-dependently reduced the extracellular levels of DA in the ACB, whereas the extracellular levels of DA in the VTA were not changed. Similarly, application of the D2-like receptor agonist quinpirole (Quin, 1-100 microM) through the microdialysis probe in the ACB reduced the extracellular levels of DA in the ACB in a concentration-dependent manner, whereas extracellular levels of DA in the VTA were not altered. Co-application of SKF (100 microM) and Quin (100 microM) produced concomitant reductions in the extracellular levels of DA in the ACB and VTA. The reduction in extracellular levels of DA in the ACB and VTA produced by co-infusion of SKF and Quin was reversed in the presence of either 100 microM SCH 23390 (D1-like antagonist) or 100 microM sulpiride (D2-like antagonist). Overall, the results suggest that (a) activation of dopamine D1- or D2-like receptors can independently regulate local terminal DA release in the ACB, whereas stimulation of both subtypes is required for activation of the negative feedback pathway to the VTA.     

Differential effects after repeated treatment with haloperidol, clozapine, thioridazine and tefludazine on SNC and VTA dopamine neurones in rats

The effects of repeated treatment (21 days) with different antipsychotic compounds (haloperidol, clozapine, thioridazine and tefludazine) on dopamine (DA) neurones in substantia nigra pars compacta (SNC) and ventral tegmental area (VTA) were studied in rats using single unit recording techniques. A dose-dependent decrease in the number of spontaneously active DA neurones in SNC and in VTA was observed with haloperidol. Clozapine showed no significant effect on the activity in SNC while a dose-dependent decrease in the number of active DA neurones in VTA was observed. Thioridazine showed no or weak effect in SNC while repeated treatment induced a marked inhibitory effect on the DA neurones in VTA. Tefludazine, a potential antipsychotic compound, induced a dose-dependent decrease in both SNC and VTA DA activity. However, the effect on the DA neurones in VTA was more pronounced at all doses. Since the classical neuroleptic haloperidol is equally effective in both regions, while the atypical neuroleptics clozapine and thioridazine have selective or predominant effect in the VTA area it has previously been thought that the inhibition of spontaneously active DA neurones in VTA should indicate an antipsychotic effect of a compound while the inhibition of DA neurones in SNC should account for the development of neurological side effects. The data suggests that the potential antipsychotic compound tefludazine should not induce neurological side effects at lower doses but still has an antipsychotic activity while repeated treatment with higher doses of tefludazine might cause extrapyramidal side effects.     

Peri-Pubertal Emergence of UNC-5 Homologue Expression by Dopamine Neurons in Rodents

Puberty is a critical period in mesocorticolimbic dopamine (DA) system development, particularly for the medial prefrontal cortex (mPFC) projection which achieves maturity in early adulthood. The guidance cue netrin-1 organizes neuronal networks by attracting or repelling cellular processes through DCC (deleted in colorectal cancer) and UNC-5 homologue (UNC5H) receptors, respectively. We have shown that variations in netrin-1 receptor levels lead to selective reorganization of mPFC DA circuitry, and changes in DA-related behaviors, in transgenic mice and in rats. Significantly, these effects are only observed after puberty, suggesting that netrin-1 mediated effects on DA systems vary across development. Here we report on the normal expression of DCC and UNC5H in the ventral tegmental area (VTA) by DA neurons from embryonic life to adulthood, in both mice and rats. We show a dramatic and enduring pubertal change in the ratio of DCC:UNC5H receptors, reflecting a shift toward predominant UNC5H function. This shift in DCC:UNC5H ratio coincides with the pubertal emergence of UNC5H expression by VTA DA neurons. Although the distribution of DCC and UNC5H by VTA DA neurons changes during puberty, the pattern of netrin-1 immunoreactivity in these cells does not. Together, our findings suggest that DCC:UNC5H ratios in DA neurons at critical periods may have important consequences for the organization and function of mesocorticolimbic DA systems.     

Regulation of Phospholipase Cγ in the Mesolimbic Dopamine System by Chronic Morphine Administration

Neurotrophic signaling pathways have been implicated in the maintenance of the mesolimbic dopamine system, as well as in changes in this system induced by chronic morphine exposure. We found that many of these signaling pathway proteins are expressed at appreciable levels within the ventral tegmental area (VTA) and related regions, although with substantial regional variation. Moreover, phospholipase Cgamma1 (PLCgamma1) was significantly and specifically up-regulated within the VTA by 30% following chronic exposure to morphine. PLCgamma1 mRNA expression is enriched in dopaminergic neurons within the VTA; however, the up-regulation of PLCgamma1 in this region was not seen at the mRNA level. In contrast to PLCgamma1, insulin receptor substrate (IRS)-2, a protein involved in phosphatidylinositol 3-kinase signaling, and another putative IRS-like protein were significantly down-regulated within the VTA by 49 and 45%, respectively. Levels of several proteins within the Ras-ERK pathway were not altered. Regulation of neurotrophic factor signaling proteins may play a role in morphine-induced plasticity within the mesolimbic dopamine system.     

Reduced levels of Cacna1c attenuate mesolimbic dopamine system function

Genetic variation in CACNA1C, which codes for the L‐type calcium channel (LTCC) Ca_v1.2, is associated with clinical diagnoses of bipolar disorder, depression and schizophrenia. Dysregulation of the mesolimbic‐dopamine (ML‐DA) system is linked to these syndromes and LTCCs are required for normal DAergic neurotransmission between the ventral tegmental area (VTA) and nucleus accumbens (NAc). It is unclear, however, how variations in CACNA1C genotype, and potential subsequent changes in expression levels in these regions, modify risk. Using constitutive and conditional knockout mice, and treatment with the LTCC antagonist nimodipine, we examined the role of Cacna1c in DA‐mediated behaviors elicited by psychomotor stimulants. Using fast‐scan cyclic voltammetry, DA release and reuptake in the NAc were measured. We find that subsecond DA release in Cacna1c haploinsufficient mice lacks normal sensitivity to inhibition of the DA transporter (DAT). Constitutive haploinsufficiency of Cacna1c led to attenuation of hyperlocomotion following acute administration of stimulants specific to DAT, and locomotor sensitization of these mice to the DAT antagonist GBR12909 did not reach the same level as wild‐type mice. The maintenance of sensitization to GBR12909 was attenuated by administration of nimodipine. Sensitization to GBR12909 was attenuated in mice with reduced Cacna1c selectively in the VTA but not in the NAc. Our findings show that Cacna1c is crucial for normal behavioral responses to DA stimulants and that its activity in the VTA is required for behavioral sensitization. Cacna1c likely exerts these effects through modifications to presynaptic ML‐DA system function.