Voltammetry In Slices Research Articles

Fentanyl self-administration is accelerated by methamphetamine co-use and results in worsened hypodopaminergia in male, but not female rats.

Combined use of fentanyl and methamphetamine (FENT + METH) has increased in recent years and has been documented in a growing number overdose deaths each year. The impact of FENT + METH on behavior and neurobiology is not well understood. In this study, male and female Long Evans rats were tested on a limited access, fixed ratio 1 self-administration schedule for increasing doses (1.25-5 μg/kg/infusion; iv) of fentanyl, with and without a single dose (0.1 mg/kg/infusion; iv) of methamphetamine, for 15 days. FENT + METH abolished dose responsiveness to fentanyl in all rats and accelerated intake in males, resulting in patterns of responding that may be more likely to result in adverse effects. Ex vivo slice voltammetry in the nucleus accumbens core showed decreases in dopamine release and reuptake (Vmax) following FENT + METH exposure, compared with saline, fentanyl, and methamphetamine alone groups at baseline parameters. Further, significant decreases in dopamine release were observed across a range of stimulation intensities following FENT + METH exposure. Overall, male and female rats displayed sex-specific behavioral and neurobiological responses to FENT + METH exposure, with males displaying increased vulnerability.

Greater ethanol inhibition of presynaptic dopamine release in C57BL/6J than DBA/2J mice: Role of nicotinic acetylcholine receptors

The mesolimbic dopamine system, originating in the ventral tegmental area (VTA) and projecting to the nucleus accumbens (NAc), has been heavily implicated in the reinforcing effects of ethanol. Recent slice voltammetry studies have shown that ethanol inhibits dopamine release selectively during high-frequency activity that elicits phasic dopamine release shown to be important for learning and reinforcement. Presently, we examined ethanol inhibition of electrically evoked NAc dopamine in two mouse strains with divergent dopamine responses to ethanol, C57BL/6 (C57) and DBA/2J (DBA) mice. Previous electrophysiology and microdialysis studies have demonstrated greater ethanol-induced VTA dopaminergic firing and NAc dopamine elevations in DBA compared to C57 mice. Additionally, DBA mice have greater ethanol responses in dopamine-related behaviors, including hyperlocomotion and conditioned place preference. Currently, we demonstrate greater sensitivity of ethanol inhibition of NAc dopamine signaling in C57 compared to DBA mice. The reduced sensitivity to ethanol inhibition in DBA mice may contribute to the overall greater ethanol-induced dopamine signaling and related behaviors observed in this strain. NAc cholinergic activity is known to potently modulate terminal dopamine release. Additionally, ethanol is known to interact with multiple aspects of nicotinic acetylcholine receptor activity. Therefore, we examined ethanol-mediated inhibition of dopamine release at two ethanol concentrations (80 and 160mM) during bath application of the non-selective nicotinic receptor antagonist mecamylamine, as well as compounds selective for the β2-(dihydro-β-erythroidine hydrobromide; DhβE) and α6-(α-conotoxin MII [H9A; L15A]) subunit-containing receptors. Mecamylamine and DhβE decreased dopamine release and reduced ethanol’s inhibitory effects on dopamine in both DBA and C57 mice. Further, α-conotoxin also reduced the dopamine release and the dopamine-inhibiting effects of ethanol at the 80mM, but not 160mM, concentration. These data suggest that ethanol is acting in part through nicotinic acetylcholine receptors, or downstream effectors, to reduce dopamine release during high-frequency activity.

Potentiated Striatal Dopamine Release Leads to Hyperdopaminergia in Female Brain-Derived Neurotrophic Factor Heterozygous Mice

The goal of this study was to determine whether a reduction in brain-derived neurotrophic factor (BDNF) levels in female mice leads to dopaminergic system dysregulation. Through a series of in vivo brain microdialysis and slice voltammetry experiments, we discerned that female BDNF heterozygous (BDNF(+/-)) mice are hyperdopaminergic, similar to their male BDNF(+/-) counterparts. Zero-net flux microdialysis results showed that female BDNF(+/-) mice had increased striatal extracellular dopamine levels, while stimulated regional release by high potassium concentrations potentiated dopamine release through vesicular-mediated depolarization. Using the complementary technique of fast scan cyclic voltammetry, electrical stimulation evoked greater dopamine release in the female BDNF(+/-) mice, whereas dopamine uptake remained unchanged relative to that of female wildtype mice. Following psychostimulant methamphetamine administration, female BDNF(+/-) mice showed potentiated dopamine release compared to their wildtype counterparts. Taken together, these dopamine release impairments in female mice appear to result in a hyperdopaminergic phenotype without concomitant alterations in dopamine uptake.

Extended access of cocaine self‐administration results in tolerance to the dopamine‐elevating and locomotor‐stimulating effects of cocaine

Tolerance to the neurochemical and psychoactive effects of cocaine after repeated use is a hallmark of cocaine addiction in humans. However, comprehensive studies on tolerance to the behavioral, psychoactive, and neurochemical effects of cocaine following contingent administration in rodents are lacking. We outlined the consequences of extended access cocaine self-administration as it related to tolerance to the psychomotor activating, dopamine (DA) elevating, and DA transporter (DAT) inhibiting effects of cocaine. Cocaine self-administration (1.5 mg/kg/inj; 40 inj; 5 days), which resulted in escalation of first hour intake, caused reductions in evoked DA release and reduced maximal rates of uptake through the DAT as measured by slice voltammetry in the nucleus accumbens core. Furthermore, we report reductions in cocaine-induced uptake inhibition and a corresponding increase in the dose of cocaine required for 50% inhibition of DA uptake (Ki ) at the DAT. Cocaine tolerance at the DAT translated to reductions in cocaine-induced DA overflow as measured by microdialysis. In addition, cocaine-induced elevations in locomotor activity and stereotypy were reduced, while rearing behavior was enhanced in animals with a history of cocaine self-administration. Here, we demonstrate both neurochemical and behavioral cocaine tolerance in an extended-access rodent model of cocaine abuse, which allows for a better understanding of the neurochemical and psychomotor tolerance that develops to cocaine in human addicts. We demonstrate tolerance to the neurochemical and behavioral effects of cocaine following extended-access cocaine self-administration. With respect to neurochemistry, we show reduced cocaine-induced dopamine uptake inhibition, an increased dose of cocaine required for 50% inhibition of the dopamine transporter, and reduced cocaine-induced dopamine overflow. In addition, we show escalation of cocaine intake and reduced cocaine-induced locomotor activity following cocaine self-administration.

Examining the Complex Regulation and Drug-Induced Plasticity of Dopamine Release and Uptake Using Voltammetry in Brain Slices

Fast scan cyclic voltammetry in brain slices (slice voltammetry) has been used over the last several decades to increase substantially our understanding of the complex local regulation of dopamine release and uptake in the striatum. This technique is routinely used for the study of changes that occur in the dopamine system associated with various disease states and pharmacological treatments, and to study mechanisms of local circuitry regulation of dopamine terminal function. In the context of this Review, we compare the relative advantages of voltammetry using striatal slice preparations versus in vivo preparations, and highlight recent advances in our understanding of dopamine release and uptake in the striatum specifically from studies that use slice voltammetry in drug-naïve animals and animals with a history of psychostimulant self-administration.

Enduring increases in anxiety‐like behavior and rapid nucleus accumbens dopamine signaling in socially isolated rats

Social isolation (SI) rearing, a model of early life stress, results in profound behavioral alterations, including increased anxiety-like behavior, impaired sensorimotor gating and increased self-administration of addictive substances. These changes are accompanied by alterations in mesolimbic dopamine function, such as increased dopamine and metabolite tissue content, increased dopamine responses to cues and psychostimulants, and increased dopamine neuron burst firing. Using voltammetric techniques, we examined the effects of SI rearing on dopamine transporter activity, vesicular release and dopamine D2-type autoreceptor activity in the nucleus accumbens core. Long-Evans rats were housed in group (GH; 4/cage) or SI (1/cage) conditions from weaning into early adulthood [postnatal day (PD) 28-77]. After this initial housing period, rats were assessed on the elevated plus-maze for an anxiety-like phenotype, and then slice voltammetry experiments were performed. To study the enduring effects of SI rearing on anxiety-like behavior and dopamine terminal function, another cohort of similarly reared rats was isolated for an additional 4 months (until PD 174) and then tested. Our findings demonstrate that SI rearing results in lasting increases in anxiety-like behavior, dopamine release and dopamine transporter activity, but not D2 activity. Interestingly, GH-reared rats that were isolated as adults did not develop the anxiety-like behavior or dopamine changes seen in SI-reared rats. Together, our data suggest that early life stress results in an anxiety-like phenotype, with lasting increases in dopamine terminal function.

No role of the dopamine transporter in acute ethanol effects on striatal dopamine dynamics

The acute effects of ethanol on dopamine (DA) release and clearance in the caudate-putamen were evaluated in wild-type and dopamine transporter (DAT) knockout (DAT-KO) mice, using microdialysis and voltammetry. Dialysate DA levels were elevated, approximately 80% above baseline levels, after administration of 2 g/kg ethanol in both wild-type and DAT-KO mice. In brain slices containing the caudate-putamen, a low (20 mM) concentration of ethanol produced no change in electrically stimulated DA release in either wild-type or DAT-KO mice. A high concentration (200 mM) of ethanol caused a similar decrease in DA release in slices from both types of mice. DA clearance was unaltered across the genotypes at low and high concentrations of ethanol. The fact that ethanol had similar effects in wild-type and DAT-KO mice, measured by in vivo microdialysis or brain slice voltammetry, supports the idea that acute ethanol does not interact with the DAT to produce its effects on the DA system.

Detection of dopamine overflow and diffusion with voltammetry in slices of rat brain

Voltammetric electrodes have been used to monitor extracellular dopamine in rat brain slices. The electrode tips are small enough to be immersed inside the slice. Specificity for dopamine is increased through the use of voltammetry and a cation exchange membrane at the electrode tip. Dopamine overflow is observed in the caudate nucleus following electrical stimulation (60 Hz, 1 s, 3 V) with an adjacent bipolar electrode. The amount of overflow observed is increased when the tissue is perfused with 10 μM cocaine or nomifensine, both recognized inhibitors of dopamine uptake. The ability of dopamine in the perfusion buffer to permeate the slice was monitored with two voltammetric electrodes, one in the cerebral cortex and the other in the caudate nucleus. At a high concentration (100 μM), dopamine rapidly appeared (2.7 ± 0.4 min) in the interior of the cortex, but dopamine was not observed in the caudate until a significantly later time (8.9 ± 1.0 min). To examine whether this difference is a reflection of the presence of different uptake systems in the two regions, pressure ejection was employed. In this experiment a double-barelled pipette was used to eject dopamine or DOPAC at a fixed distance (∼70 μm) from the voltammetric electrode. Ejection of small amounts of both substances could be detected in the cortex. When the ejector-detector assembly was moved to the caudate, dopamine could only be observed following pressure ejection after perfusion of the slice with 10 μM nomifensine. Detection of DOPAC was unaffected. All of these experiments indicate that uptake systems in the caudate keep dopamine concentrations very low in the extracellular fluid of the slice.