Effects of an acute therapeutic or rewarding dose of amphetamine on acquisition of Pavlovian autoshaping and ventral striatal dopamine signaling.

Rewarding doses of amphetamine increase the amplitude, duration, and frequency of dopamine transients in the ventral striatum. Debate continues at the behavioral level about which component of reward, learning or incentive salience, is signaled by these dopamine transients and thus altered in addiction. The learning hypothesis proposes that rewarding drugs result in pathological overlearning of drug-predictive cues, while the incentive sensitization hypothesis suggests that rewarding drugs result in sensitized attribution of incentive salience to drug-predictive cues. Therapeutic doses of amphetamine, such as those used to treat attention-deficit hyperactivity disorder, are hypothesized to enhance the ventral striatal dopamine transients that are critical for reward-related learning and to enhance Pavlovian learning. However, the effects of therapeutic doses of amphetamine on Pavlovian learning are poorly understood, and the effects on dopamine transients are completely unknown. We determined the effects of an acute pre-training therapeutic or rewarding amphetamine injection on the acquisition of Pavlovian autoshaping in the intact rat. We also determined the effects of these doses on electrically evoked transient-like dopamine signals using fast-scan cyclic voltammetry in the anesthetized rat. The rewarding dose enhanced the amplitude and duration of DA signals, caused acute task disengagement, impaired learning for several days, and triggered incentive sensitization. The therapeutic dose produced smaller enhancements in DA signals but did not have similar behavioral effects. These results underscore the necessity of more studies using therapeutic doses, and suggest a hybrid learning/incentive sensitization model may be required to explain the development of addiction.

Amphetamine paradoxically augments exocytotic dopamine release and phasic dopamine signals.

Drugs of abuse hijack brain-reward circuitry during the addiction process by augmenting action potential-dependent phasic dopamine release events associated with learning and goal-directed behavior. One prominent exception to this notion would appear to be amphetamine (AMPH) and related analogs, which are proposed instead to disrupt normal patterns of dopamine neurotransmission by depleting vesicular stores and promoting nonexocytotic dopamine efflux via reverse transport. This mechanism of AMPH action, though, is inconsistent with its therapeutic effects and addictive properties, which are thought to be reliant on phasic dopamine signaling. Here we used fast-scan cyclic voltammetry in freely moving rats to interrogate principal neurochemical responses to AMPH in the striatum and relate these changes to behavior. First, we showed that AMPH dose-dependently enhanced evoked dopamine responses to phasic-like current pulse trains for up to 2 h. Modeling the data revealed that AMPH inhibited dopamine uptake but also unexpectedly potentiated vesicular dopamine release. Second, we found that AMPH increased the amplitude, duration, and frequency of spontaneous dopamine transients, the naturally occurring, nonelectrically evoked, phasic increases in extracellular dopamine. Finally, using an operant sugar reward paradigm, we showed that low-dose AMPH augmented dopamine transients elicited by sugar-predictive cues. However, operant behavior failed at high-dose AMPH, which was due to phasic dopamine hyperactivity and the decoupling of dopamine transients from the reward predictive cue. These findings identify upregulation of exocytotic dopamine release as a key AMPH action in behaving animals and support a unified mechanism of abused drugs to activate phasic dopamine signaling.

Functional reorganization of the presynaptic dopaminergic terminal in parkinsonism.

Whether dopamine (DA) release is compensated during the presymptomatic phase of Parkinson's disease (PD) is controversial. Here we use in vivo voltammetry in the parkinsonian rat and an electrical stimulation protocol established to fatigue nigrostriatal dopaminergic (DAergic) neurons to investigate the plasticity of DA-release mechanisms. Amplitudes of evoked voltammetric signals recorded in intact rat striata decreased with repetitive, high-frequency stimulation (60 Hz, every 5 min/60 min). Strikingly, DA levels were maintained during an identical "fatiguing" protocol in 6-hydroxydopamine-lesioned (<40% denervation) striata in the absence of enhanced DA synthesis. In contrast, more severely lesioned striata (>55% denervation) also appeared to sustain DA release, however, this was demonstrated in the presence of enhanced synthesis. Sustained release was replicated in intact animals after irreversible blockade of the dopamine transporter (DAT) via RTI-76, implicating neuronal uptake as a trigger. We further demonstrate through kinetic analysis that lesions and compromised uptake target a "long-term" (time constant of minutes) presynaptic depression, which underlies the maintenance of release. Taken together, our findings identify a denervation-induced maintenance of DA release that was independent of activated synthesis and driven by altered uptake. This novel neuroadaptation may contribute to early preclinical normalization of function and help resolve discrepant findings regarding compensatory changes in DA release during progression of the parkinsonian state.

In vivo dopamine release and uptake impairments in rats treated with 3-nitropropionic acid.

Recent evidence has suggested that mitochondrial dysfunction may lead to impaired neurotransmitter exocytosis in transgenic Huntington's disease (HD) model mice. To gain insight into the impact of mitochondrial impairment on striatal dopamine release in vivo, we used fast-scan cyclic voltammetry (FSCV) at carbon fiber microelectrodes to measure dopamine release and uptake kinetics in anesthetized Lewis rats continuously treated for 5 days with 3-nitropropionic acid (3NP). Our results indicate that, even though striatal dopamine content was unchanged, remotely stimulated dopamine release evoked per electrical stimulus pulse ([DA](p)) is decreased in 3NP-treated rats (33% of that observed in sham control rats) and that this decrease is uniform throughout all stereotaxic depths tested. Nevertheless, unlike data collected previously from transgenic HD model rodents, the maximum rate of dopamine uptake (V(max)) in 3NP-treated rats is diminished (30% of controls) while K(m) is unchanged. Treatment with 3NP also resulted in a corresponding decrease in locomotor activity, presumably due in part to the impaired dopamine release. These results indicate that dopamine release is degraded in this HD model, as is observed in transgenic HD model rodents; however, the results also imply that there are fundamental differences in dopamine uptake between 3NP-treated animals and transgenic animals.

A Wireless IC for Wide-Range Neurochemical Monitoring Using Amperometry and Fast-Scan Cyclic Voltammetry.

An integrated circuit for real-time wireless monitoring of neurochemical activity in the nervous system is described. The chip is capable of conducting measurements in both fast-scan cyclic voltammetry (FSCV) and amperometry modes for a wide input current range. The chip architecture employs a second-order DeltaSigma modulator (DeltaSigmaM) and a frequency-shift-keyed transmitter operating near 433 MHz. It is fabricated using the AMI 0.5-mum double-poly triple-metal n-well CMOS process, and requires only one off-chip component for operation. A measured current resolution of 12 pA at a sampling rate of 100 Hz and 132 pA at a sampling rate of 10 kHz is achieved in amperometry and 300-V/s FSCV modes, respectively, for any input current in the range of plusmn430 nA. The modulator core and the transmitter draw 22 and 400 muA from a 2.6-V power supply, respectively. The chip has been externally interfaced with a carbon-fiber microelectrode implanted acutely in the caudate-putamen of an anesthetized rat, and, for the first time, extracellular levels of dopamine elicited by electrical stimulation of the medial forebrain bundle have been successfully recorded wirelessly using 300-V/s FSCV.

A role for presynaptic mechanisms in the actions of nomifensine and haloperidol.

Psychomotor stimulants and neuroleptics exert multiple effects on dopaminergic signaling and produce the dopamine (DA)-related behaviors of motor activation and catalepsy, respectively. However, a clear relationship between dopaminergic activity and behavior has been very difficult to demonstrate in the awake animal, thus challenging existing notions about the mechanism of these drugs. The present study examined whether the drug-induced behaviors are linked to a presynaptic site of action, the DA transporter (DAT) for psychomotor stimulants and the DA autoreceptor for neuroleptics. Doses of nomifensine (7 mg/kg i.p.), a DA uptake inhibitor, and haloperidol (0.5 mg/kg i.p.), a dopaminergic antagonist, were selected to examine characteristic behavioral patterns for each drug: stimulant-induced motor activation in the case of nomifensine and neuroleptic-induced catalepsy in the case of haloperidol. Presynaptic mechanisms were quantified in situ from extracellular DA dynamics evoked by electrical stimulation and recorded by voltammetry in the freely moving animal. In the first experiment, the maximal concentration of electrically evoked DA ([DA](max)) measured in the caudate-putamen was found to reflect the local, instantaneous change in presynaptic DAT or DA autoreceptor activity according to the ascribed action of the drug injected. A positive temporal association was found between [DA](max) and motor activation following nomifensine (r=0.99) and a negative correlation was found between [DA](max) and catalepsy following haloperidol (r=-0.96) in the second experiment. Taken together, the results suggest that a dopaminergic presynaptic site is a target of systemically applied psychomotor stimulants and regulates the postsynaptic action of neuroleptics during behavior. This finding was made possible by a voltammetric microprobe with millisecond temporal resolution and its use in the awake animal to assess release and uptake, two key mechanisms of dopaminergic neurotransmission. Moreover, the results indicate that presynaptic mechanisms may play a more important role in DA-behavior relationships than is currently thought.

Determination of release and uptake parameters from electrically evoked dopamine dynamics measured by real-time voltammetry.

Quantifying mechanisms underlying extracellular signaling by the neurotransmitter dopamine (DA) is a difficult task, particularly in the complex extracellular microenvironment of the intact brain. In this study, two methods for evaluating release and uptake from DA dynamics monitored by real-time voltammetry are described. Both are based on a neurochemical model characterizing electrically evoked levels of DA as a balance between these opposing mechanisms. The theoretical basis of what is called here nonlinear regression and single curve analyses is given. Fitting simulated data tests the reliability of the methods. The two analyses are also compared with an experimental data set describing the effects of pharmacologically inhibiting the DA transporter in the caudate-putamen (CP) and nucleus accumbens (NAc). The results indicate that nonlinear regression and single curve analyses are suitable for quantifying release and uptake mechanisms underlying DA neurotransmission. Additionally, the most important experimental finding of this technical study was the independent confirmation of high affinity (approximately 0.2 microM) DA uptake in the intact striatum.

Sub-second changes in accumbal dopamine during sexual behavior in male rats.

Transient (200--900 ms), high concentrations (200--500 nM) of dopamine, measured using fast-scan cyclic voltammetry, occurred in the nucleus accumbens core of male rats at the presentation of a receptive female. Additional dopamine signals were observed during subsequent approach behavior. Background-subtracted cyclic voltammograms of the naturally-evoked signals matched those of electrically-evoked dopamine measured at the same recording sites. Administration of nomifensine amplified natural and evoked dopamine release, and increased the frequency of detectable signals. While gradual changes in dopamine concentration during sexual behavior have been well established, these findings dramatically improve the time resolution. The observed dopamine transients, probably resulting from neuronal burst firing, represent the first direct correlation of dopamine with sexual behavior on a sub-second time scale.

Preferential increases in nucleus accumbens dopamine after systemic cocaine administration are caused by unique characteristics of dopamine neurotransmission.

In vivo voltammetry was used to investigate the preferential increase of extracellular dopamine in the nucleus accumbens relative to the caudate-putamen after systemic cocaine administration. In the first part of this study, cocaine (40 mg/kg, i.p.) was compared with two other blockers of dopamine uptake, nomifensine (10 mg/kg, i.p.) and 3beta-(p-chlorophenyl)tropan-2beta-carboxylic acid p-isothiocyanatophenylmethyl ester hydrochloride (RTI-76; 100 nmol, i.c.v.), to assess whether the inhibitory mechanism of cocaine differed in the two regions. All three drugs robustly increased electrically evoked levels of dopamine, and cocaine elevated dopamine signals to a greater extent in the nucleus accumbens. However, kinetic analysis of the evoked dopamine signals indicated that cocaine and nomifensine increased the K(m) for dopamine uptake whereas the dominant effect of RTI-76 was a decrease in V(max). Under the present in vivo conditions, therefore, cocaine is a competitive inhibitor of dopamine uptake in both the nucleus accumbens and caudate-putamen. Whether the preferential effect of cocaine was mediated by regional differences in the presynaptic control of extracellular DA that are described by rates for DA uptake and release was examined next by a correlation analysis. The lower rates for dopamine release and uptake measured in the nucleus accumbens were found to underlie the preferential increase in extracellular dopamine after cocaine. This relationship explains the paradox that cocaine more effectively increases accumbal dopamine despite identical effects on the dopamine transporter in the two regions. The mechanism proposed for the preferential actions of cocaine may also mediate the differential effects of psychostimulant in extrastriatal regions and other uptake inhibitors in the striatum.

Partial, graded losses of dopamine terminals in the rat caudate-putamen: an animal model for the study of compensatory adaptation in preclinical parkinsonism.

Procedures to lesion dopamine (DA) neurons innervating the rat caudate-putamen (CP) in a partial, graded fashion are described in this study. The goal is to provide a lesion model that supports intra-animal comparisons of voltammetric recordings used to investigate compensatory adaptation of DA neurotransmission. Lesions exploited the topography of mesostriatal DA neurons, microinjections of the neurotoxin 6-hydroxydopamine (6-OHDA) into the medial and lateral edges of the ventral mesencephalon containing DA cell bodies and microdissection of the CP into six regions. Analysis of tissue DA content in these regions by HPLC-EC demonstrated that 6-OHDA injected into the lateral substantia nigra results in a significantly greater loss of DA in lateral versus medial regions of the CP. The direction of the graded loss of DA was reversed (i.e. a medial to lateral lesion gradient) by the injection of 6-OHDA into the ventral tegmental area near the medial SN. Extracellular concentrations of electrically evoked DA could be measured across the mediolateral axis of the CP in a single animal using the technique of in vivo voltammetry. More importantly, graded decreases in the amplitude of evoked DA levels generally followed the direction of the tissue DA gradient in lesioned animals. These results suggest that the graded loss of DA terminals in the CP, coupled to a spatially and temporally resolved technique for monitoring extracellular DA, is a viable tool for investigating compensatory adaptation in the mesostriatal DA system.

Dissociation of dopamine release in the nucleus accumbens from intracranial self-stimulation.

Mesolimbic dopamine-releasing neurons appear to be important in the brain reward system. One behavioural paradigm that supports this hypothesis is intracranial self-stimulation (ICS), during which animals repeatedly press a lever to stimulate their own dopamine-releasing neurons electrically. Here we study dopamine release from dopamine terminals in the nucleus accumbens core and shell in the brain by using rapid-responding voltammetric microsensors during electrical stimulation of dopamine cell bodies in the ventral tegmental area/substantia nigra brain regions. In rats in which stimulating electrode placement failed to elicit dopamine release in the nucleus accumbens, ICS behaviour was not learned. In contrast, ICS was acquired when stimulus trains evoked extracellular dopamine in either the core or the shell of the nucleus accumbens. In animals that could learn ICS, experimenter-delivered stimulation always elicited dopamine release. In contrast, extracellular dopamine was rarely observed during ICS itself. Thus, although activation of mesolimbic dopamine-releasing neurons seems to be a necessary condition for ICS, evoked dopamine release is actually diminished during ICS. Dopamine may therefore be a neural substrate for novelty or reward expectation rather than reward itself.

Utility of a tripolar stimulating electrode for eliciting dopamine release in the rat striatum.

The present study evaluated tripolar stimulating electrodes for eliciting dopamine release in the rat brain in vivo. Stimulating electrodes were placed either in the medial forebrain bundle or in the ventral mesencephalon associated with the ventral tegmental area and substantia nigra. The concentration of extracellular dopamine was monitored in dopamine terminal fields at 100-ms intervals using fast-scan cyclic voltammetry at carbon-fiber microelectrodes. To characterize the stimulated area, recordings were collected in several striatal regions including the caudate putamen and the core and shell of the nucleus accumbens. The tripolar electrode was equally effective in stimulating dopamine release in medial and lateral regions of the striatum. In contrast, responses evoked by a bipolar electrode were typically greater in one mediolateral edge versus the other. The added size of the tripolar electrode did not appear to cause complications as signals were stable over the course of the experiment (3 h). Subsets of mesostriatal dopamine neurons could also be selectively activated using the tripolar electrode in excellent agreement with previously described topography. Taken together, these results suggested that the tripolar stimulating electrode is well suited for studying the regulation of midbrain dopamine neurons in vivo.

Dopamine release and uptake rates both decrease in the partially denervated striatum in proportion to the loss of dopamine terminals.

The present study tested the hypothesis that normal concentrations of extracellular dopamine are preserved in the partially denervated striatum without active compensatory changes in dopamine uptake or release. One to four weeks after adult rats were unilaterally lesioned with 6-hydroxydopamine, fast-scan cyclic voltammetry at Nafion-coated, carbon-fiber microelectrodes was used to monitor extracellular dopamine levels in vivo, under urethane anesthesia. Simultaneous voltammetric recordings were collected in the lesioned and contralateral control striata. Extracellular dopamine was elicited by bilateral electrical stimulation of the medial forebrain bundle. A 20 Hz stimulation evoked similar concentrations of extracellular dopamine in both lesioned and control striata, although tissue dopamine was decreased 30-70% in lesioned striata, as determined subsequently by HPLC-EC. However, kinetic analysis of the voltammetric recordings revealed that the concentration of dopamine released per stimulus pulse and Vmax for dopamine uptake decreased in proportion to the magnitude of the lesion. These data support the hypothesis that normal extracellular dopamine levels can be generated in the partially lesioned striatum in the absence of active neuronal compensation. These results also suggest that passive mechanisms involved in the regulation of extracellular dopamine play an important role in maintaining function during the preclinical or presymptomatic phase of Parkinson's disease.

Real-time measurement of electrically evoked extracellular dopamine in the striatum of freely moving rats.

The real-time measurement of electrically evoked dopamine was established in brain extracellular fluid of freely moving rats. Dopamine was monitored by fast-scan cyclic voltammetry at carbon fiber microelectrodes lowered into the striatum by means of a detachable micromanipulator. A stimulating electrode, previously implanted in the substantia nigra, was used to evoke striatal dopamine efflux. Evoked extracellular dopamine was both current and frequency dependent. When low current intensities (+/-125 microA) and frequencies (10-20 Hz) were applied, detectable levels of dopamine were elicited without a perceptible behavioral response. Reproducible concentrations of extracellular dopamine could be evoked in the same rat for at least 2 months. These concentrations, moreover, were significantly higher in freely moving rats compared with rats anesthetized with Equithesin. Analysis of measured curves for dopamine uptake and release rates revealed that anesthesia inhibits release but does not affect uptake. It is concluded that (a) fast-scan cyclic voltammetry at carbon fiber microelectrodes is a viable technique for the measurement of electrically evoked dopamine in brain extracellular fluid of freely moving rats, (b) it is possible to determine in situ rate constants for dopamine release and uptake from these temporally and spatially resolved measurements of levels of dopamine, and (c) transient changes in extracellular dopamine levels elicited by electrical stimulation are affected by anesthesia.

Distinct pharmacological regulation of evoked dopamine efflux in the amygdala and striatum of the rat in vivo.

The pharmacological regulation of evoked extracellular dopamine was compared in the basolateral amygdaloid nucleus (BAN) and caudate-putamen (CP) of the urethane-anesthetized rat. The effects of drugs, which alter dopamine uptake, release or degradation, were examined. Dopamine efflux was elicited by electrical stimulation of ascending dopamine fibers and was monitored by fast-scan cyclic voltammetry at Nafion-coated, carbon-fiber microelectrodes. Dopamine uptake inhibitors, nomifensine (25 mg/kg) and cocaine (20 mg/kg), and the dopamine receptor antagonist, haloperidol (0.5 mg/kg), robustly increased evoked extracellular dopamine in the CP. In sharp contrast, these drugs were much less effective in the BAN. The relative potencies of the uptake inhibitors varied between the two regions. Nomifensine was more potent than cocaine in the CP, whereas cocaine was more potent that nomifensine in the BAN. The monoamine oxidase inhibitor, pargyline (75 mg/kg), and the catechol-O-methyltransferase (COMT) inhibitor, Ro 40-7592 (40 mg/kg), had small or negligible effects in either region. No electrochemical evidence was found for the formation of 3-methoxytyramine, the dopamine metabolite formed by the action of COMT on released dopamine, on the time scale of the measurements in control or after pharmacological manipulation of the degradative enzymes for dopamine. The conclusions reached are: (1) potent mechanisms for uptake and autoreceptor inhibition of release, which exist in the CP to tightly control the concentration of extracellular dopamine, are considerably weaker in the BAN; (2) the extracellular clearance of evoked dopamine in the BAN and CP is the result of cellular uptake and not degradation; and (3) these results support the view that the pharmacological regulation of extracellular dopamine is regionally distinct in the brain.

Different effects of cocaine and nomifensine on dopamine uptake in the caudate-putamen and nucleus accumbens.

The effects of cocaine and nomifensine on the uptake of dopamine have been compared in the caudate-putamen and nucleus accumbens of rat brain slices. Electrical stimulation of brain slices was used to evoke dopamine efflux and the changes in dopamine concentration in the extracellular fluid were monitored with fast-scan cyclic voltammetry with Nafion-coated, carbon-fiber electrodes. The disappearance of extracellular dopamine after the stimulation fit Michaelis-Menten kinetics in both regions. Cocaine and nomifensine were found to competitively inhibit dopamine uptake in both regions. The competitive mechanism of action was apparent in the primary data because the initial uptake rates were unchanged by low doses of inhibitor, but dopamine uptake was slowed at concentrations near the Km value. In both regions, the apparent Km value increased with higher concentrations of cocaine (0.01-60 microM) or nomifensine (0.01-30 microM) in the perfusion buffer. The apparent Km values were used to obtain inhibition constants (Ki values) for the uptake inhibitors in each region. This analysis showed that cocaine had a Ki of 0.29 microM in both regions. Nomifensine, however, had a significantly higher potency in the caudate-putamen (Ki = 0.09 microM) than in the nucleus accumbens (Ki = 0.21 microM). These results show that there are differential effects of uptake inhibitors in different brain regions, and suggest that the dopamine transporter exhibits cell-specific regulation.

Comparison of dopamine uptake in the basolateral amygdaloid nucleus, caudate-putamen, and nucleus accumbens of the rat.

Regional differences in the kinetics and pharmacological inhibition of dopamine uptake were investigated with fast-scan cyclic voltammetry in both the intact rat brain and a brain slice preparation. The regions compared were the basolateral amygdaloid nucleus, caudate-putamen, and nucleus accumbens. The frequency dependence of dopamine efflux evoked in vivo by electrical stimulation of the medial forebrain bundle was evaluated by nonlinear curve fitting with a Michaelis-Menten-based kinetic model. The Km for dopamine uptake was found to be significantly higher in the basolateral amygdala (0.6 microM) than in the other two regions (0.2 microM), whereas the Vmax value for dopamine uptake in the basolateral amygdala was significantly lower (0.49 microM/s vs. 3.8 and 2.4 microM/s in the caudate and accumbens, respectively). Similar kinetics were also obtained in brain slices. Addition of a dopamine uptake inhibitor, cocaine or nomifensine (10 microM), to the perfusion buffer increased the apparent Km value > 25-fold in slices of both the caudate-putamen and nucleus accumbens. In contrast, neither uptake inhibitor had an observable effect in the basolateral amygdaloid nucleus. Thus, dopamine uptake in the rat brain is regionally distinct with regard to rate, affinity, and sensitivity to competitive inhibition.

Efflux of dopamine from the synaptic cleft in the nucleus accumbens of the rat brain.

Synaptic release of dopamine in the nucleus accumbens of the intact rat brain elicited by a single electrical impulse applied to ascending dopaminergic fibers results in extracellular concentrations sufficient to bind the known dopamine receptors. The dopamine concentration observed after four rapid, sequential pulses is exactly four times greater and is unaffected by pharmacological antagonism of dopamine uptake and receptor sites at supramaximal concentrations. Thus, dopamine efflux from the synaptic cleft is not restricted by binding to intrasynaptic proteins on the time scale of the measurements (50-100 msec). The extracellular concentration, as a result of a single stimulus pulse, is 0.25 microM and is rapidly removed by extrasynaptic uptake. This maximal, transient concentration of dopamine is 60 times higher than steady-state concentrations reported previously using dialysis techniques, illustrating that dopamine extracellular concentrations are spatially and temporally heterogenous. In contrast to ACh transmission at the neuromuscular junction, the dopamine synapse in the telencephalon is designed for the effective efflux of dopamine from the synaptic cleft to the extrasynaptic compartment during neurotransmission.

In vivo voltammetric measurement of evoked extracellular dopamine in the rat basolateral amygdaloid nucleus.

1. The in vivo measurement of evoked extracellular dopamine was established in the basolateral amygdaloid nucleus (BAN) using fast-scan cyclic voltammetry at carbon-fibre microelectrodes. 2. The identification of evoked extracellular dopamine in the BAN was based on anatomical, electrochemical and pharmacological criteria. Electrochemical and pharmacological evidence indicated that the species was a catecholamine. Mesencephalic sites eliciting overflow and amygdaloid sites supporting overflow correlated well with the mesoamygdaloid dopamine innervation. 3. Marked differences in the dynamics and magnitude of evoked dopamine overflow were observed in the BAN, caudate-putamen and amygdalo-striatal transition area. The results underscore the importance of making spatially resolved measurements of extracellular dopamine in the amygdala. 4. Mesoamygdaloid dopamine neurons have similar release characteristics as mesostriatal dopamine neurons but share with mesoprefrontal cortical dopamine neurons the ability to use a greater percentage of intraneuronal dopamine stores for release.