A comparison of the subsecond dynamics of neurotransmission of dopamine and serotonin

Influence of intra-abomasal administration of L-DOPA on circulating catecholamines and feed intake in cattle

Dopamine has multiple physiological functions including feed intake control in which it can act as an anorectic or orexigenic agent. This study had the objective to evaluate intra-abomasal administration of L-DOPA (levodopa; L-3,4-dihydroxyphenylalanine) from -Mucuna pruriens on circulating catecholamines, indicators of energy metabolism and feed intake in cattle. Eight Holstein steers (340 ± 20 kg) fitted with ruminal cannula were used in a replicated 4 x 4 Latin Square design experiment. Intra-abomasal infusion of L-DOPA at 0, 0.5, 1 and 2 mg/kg BW was carried out for seven days and blood samples were collected at 0, 30, 60, 120, 240 and 480 min from L-DOPA infusion on day 7. The area under the curve (AUC) of plasma L-DOPA and free dopamine increased quadratically with the administration of L-DOPA. However, the AUC of plasma total dopamine had a positive linear response with the increase of L-DOPA. Conversely, the serum 5-hydroxytriptophan (5-HTP), plasma serotonin, serum serotonin, serum tyrosine, plasma glucose and plasma free fatty acids were not affected by the intra-abomasal infusion of L-DOPA. The circulating concentration of the epinephrine, norepinephrine, serotonin, glucose and free fatty acids did not change with L-DOPA infusion. It can be concluded that intra-abomasal L-DOPA administration produced a strong increase in circulating dopamine with no change in energy metabolites and feed intake in cattle.

5-HT modulation of a medial septal circuit tunes social memory stability

Social memory-the ability to recognize and remember familiar conspecifics-is critical for the survival of an animal in its social group^1,2. The dorsal CA2 (dCA2)^3-5 and ventral CA1 (vCA1)⁶ subregions of the hippocampus, and their projection targets^6,7, have important roles in social memory. However, the relevant extrahippocampal input regions remain poorly defined. Here we identify the medial septum (MS) as a dCA2 input region that is critical for social memory and reveal that modulation of the MS by serotonin (5-HT) bidirectionally controls social memory formation, thereby affecting memory stability. Novel social interactions increase activity in dCA2-projecting MS neurons and induce plasticity at glutamatergic synapses from MS neurons onto dCA2 pyramidal neurons. The activity of dCA2-projecting MS cells is enhanced by the neuromodulator 5-HT acting on 5-HT_1B receptors. Moreover, optogenetic manipulation of median raphe 5-HT terminals in the MS bidirectionally regulates social memory stability. This work expands our understanding of the neural mechanisms by which social interactions lead to social memory and provides evidence that 5-HT has a critical role in promoting not only prosocial behaviours^8,9, but also social memory, by influencing distinct target structures.

Serotonergic Modulation of Persistent Inward Currents in Serotonergic Neurons of Medulla in ePet-EYFP Mice

Serotonergic (5-HT) neurons in the medulla play multiple functional roles associated with many symptoms and motor activities. The descending serotonergic pathway from medulla is essential for initiating locomotion. However, the ionic properties of 5-HT neurons in the medulla remain unclear. Using whole-cell patch-clamp technique, we studied the biophysical and modulatory properties of persistent inward currents (PICs) in 5-HT neurons of medulla in ePet-EYFP transgenic mice (P3–P6). PICs were recorded by a family of voltage bi-ramps (10-s duration, 40-mV peak step), and the ascending and descending PICs were mirrored to analyze the PIC hysteresis. PICs were found in 77% of 5-HT neurons (198/258) with no significant difference between parapyramidal region (n = 107) and midline raphe nuclei (MRN) (n = 91) in either PIC onset (−47.4 ± 10 mV and −48.7 ± 7 mV; P = 0.44) or PIC amplitude (226.9 ± 138 pA and 259.2 ± 141 pA; P = 0.29). Ninety-six percentage (191/198) of the 5-HT neurons displayed counterclockwise hysteresis and four percentage (7/198) exhibited the clockwise hysteresis. The composite PICs could be differentiated as calcium component (Ca_PIC) by bath application of nimodipine (25 μM), sodium component (Na_PIC) by tetrodotoxin (TTX, 2 μM), and TTX- and dihydropyridine-resistance component (TDR_PIC) by TTX and nimodipine. Ca_PIC, Na_PIC and TDR_PIC all contributed to upregulation of excitability of 5-HT neurons. 5-HT (15 μM) enhanced the PICs, including a 26% increase in amplitude of the compound currents of Ca_PIC and TDR_PIC (P < 0.001, n = 9), 3.6 ± 5 mV hyperpolarization of Na_PIC and TDR_PIC onset (P < 0.05, n = 12), 30% increase in amplitude of TDR_PIC (P < 0.01), and 2.0 ± 3 mV hyperpolarization of TDR_PIC onset (P < 0.05, n = 18). 5-HT also facilitated repetitive firing of 5-HT neurons through modulation of composite PIC, Na_PIC and TDR_PIC, and Ca_PIC and TDR_PIC, respectively. In particular, the high voltage-activated TDR_PIC facilitated the repetitive firing in higher membrane potential, and this facilitation could be amplified by 5-HT. Morphological data analysis indicated that the dendrites of 5-HT neurons possessed dense spherical varicosities intensively crossing 5-HT neurons in medulla. We characterized the PICs in 5-HT neurons and unveiled the mechanism underlying upregulation of excitability of 5-HT neurons through serotonergic modulation of PICs. This study provided insight into channel mechanisms responsible for the serotonergic modulation of serotonergic neurons in brainstem.

Lu(iii) bis-phthalocyanines containing carbazole moieties: synthesis, characterization, electrochemical properties and sensor applications

In this study, the synthesis and characterization of sandwich type Lu(iii) bis-phthalocyanines bearing electropolymerizable carbazole groups were evaluated and their electrochemical sensing properties studied towards DA, UA and AA.

Rewiring of the Serotonin System in Major Depression

Serotonin is a key neurotransmitter that is implicated in a wide variety of behavioral and cognitive phenotypes. Originating in the raphe nuclei, 5-HT neurons project widely to innervate many brain regions implicated in the functions. During the development of the brain, as serotonin axons project and innervate brain regions, there is evidence that 5-HT plays key roles in wiring the developing brain, both by modulating 5-HT innervation and by influencing synaptic organization within corticolimbic structures. These actions are mediated by 14 different 5-HT receptors, with region- and cell-specific patterns of expression. More recently, the role of the 5-HT system in synaptic re-organization during adulthood has been suggested. The 5-HT neurons have the unusual capacity to regrow and reinnervate brain regions following insults such as brain injury, chronic stress, or altered development that result in disconnection of the 5-HT system and often cause depression, anxiety, and cognitive impairment. Chronic treatment with antidepressants that amplify 5-HT action, such as selective serotonin reuptake inhibitors (SSRIs), appears to accelerate the rewiring of the 5-HT system by mechanisms that may be critical to the behavioral and cognitive improvements induced in these models. In this review, we survey the possible 5-HT receptor mechanisms that could mediate 5-HT rewiring and assess the evidence that 5-HT-mediated brain rewiring is impacting recovery from mental illness. By amplifying 5-HT-induced rewiring processes using SSRIs and selective 5-HT agonists, more rapid and effective treatments for injury-induced mental illness or cognitive impairment may be achieved.

Pharmacokinetics of N-ethylpentylone and its effect on increasing levels of dopamine and serotonin in the nucleus accumbens of conscious rats

N-Ethylpentylone (NEP) is one of the most confiscated synthetic cathinones in the world. However, its pharmacology and pharmacokinetics remain largely unknown. In this study, the pharmacokentics of NEP in rat nucleus accumbens (NAc) was assessed via brain microdialysis after the intraperitoneal (ip) administration of NEP (20 or 50 mg/kg). The concentrations of dopamine (DA) and serotonin (5-HT) and their metabolites, including 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT), and 5-hydroxyindoleacetic acid (5-HIAA), were simultaneously monitored to elucidate the pharmacological effect of NEP. In addition, the plasma levels of NEP were also assessed. The pharmacokinetics of NEP showed a dose-related pattern, with NEP rapidly passing through the blood-brain barrier and reaching a maximum concentration (C_max ) at approximately 40-minutes postdose. Approximately 4% of plasma NEP was distributed to the NAc, and considering a homogeneous brain distribution, over 90% of plasma NEP was potentially distributed to the brain. High values of area under curve (AUC) and mean residence time (MRT) of NEP were observed in both the NAc and plasma, indicating large and long-lasting effects. NEP elicited dose-related increases in microdialysate DA and 5-HT and increased the concentration of 3-MT in a dose-related manner. However, the rate of DA converted into 3-MT was unaffected. NEP had a negative effect on the rates of which DA and 5-HT were transformed into DOPAC and 5-HIAA, respectively. In summary, NEP rapidly entered the NAc and showed a long-lasting effect. In addition, DA increased more significantly than 5-HT, indicating a large potential for NEP abuse.

Dynamic control of neurochemical release with ultrasonically-sensitive nanoshell-tethered liposomes

The unique surface plasmon resonance of hollow gold nanoshells can be used to achieve drug release from liposomes upon laser stimulation, and adapted to mimic the intricate dynamics of neurotransmission ex vivo in brain preparations. However, to induce a physiological response in vivo requires the degree of temporal precision afforded by laser stimulation, but with a greater depth of penetration through tissue. Here we report that the attachment of hollow gold nanoshells to the surface of robust liposomes results in a construct that is highly sensitive to ultrasonic stimulation. The resulting construct can be remotely triggered by low intensity, therapeutic ultrasound. To our knowledge, this is the first example of nanoparticle-liposome system that can be activated by both laser and acoustic stimulation. The system is capable of encapsulating the neurochemical dopamine, and repeatedly releasing small amounts on-demand in a circulating environment, allowing for precise spatiotemporal control over the release profile.

Recent advances in graphene-based nanomaterials: properties, toxicity and applications in chemistry, biology and medicine

This review (with 239 refs.) summarizes the progress that has been made in applications of graphene-based nanomaterials (such as plain graphene, graphene oxides, doped graphene oxides, graphene quantums dots) in biosensing, imaging, drug delivery and diagnosis. Following an introduction into the field, a first large section covers the toxicity of graphene and its derivatives (with subsections on bacterial toxicity and tissue toxicity). The use of graphene-based nanomaterials in sensors is reviewed next, with subsections on electrochemical, FET-based, fluorescent, chemiluminescent and colorimetric sensors and probes. The large field of imaging is treated next, with subchapters on optical, PET-based, and magnetic resonance based methods. A concluding section summarizes the current status, addresses current challenges, and gives an outlook on potential future trends. Graphical Abstract Schematic presentation of the potential applications of graphene-based materials in life science and biomedicine, emphatically reflected in some vital areas such as DNA analysis, biological monitoring, drug delivery, in vitro labelling, in vivo imaging, tumor target, etc.

Chronic methylphenidate treatment during adolescence has long-term effects on monoaminergic function

BACKGROUND

Psychostimulants like methylphenidate or D-amphetamine are often prescribed for attention deficit and hyperactivity disorders in children. Whether such drugs can be administered into a developing brain without consequences in adulthood is still an open question.

METHODS

Here, using in vivo extracellular electrophysiology in anesthetised preparations, combined with behavioural assays, we have examined the long-term consequences in adulthood of a chronic methylphenidate oral administration (5 mg/kg/day, 15 days) in early adolescent (post-natal day 28) and late adolescent (post-natal day 42) rats, by evaluating body weight change, sucrose preference (indicator of anhedonia), locomotor sensitivity to D-amphetamine and electrical activities of ventral tegmental area dopamine and dorsal raphe nucleus serotonin neurons.

RESULTS

Chronic methylphenidate treatment during early or late adolescence did not induce weight deficiencies and anhedonia-like behaviours at adulthood. However, it increased bursting activities of dorsal raphe nucleus serotonin neurons. Furthermore, chronic methylphenidate treatment during early but not during late adolescence enhanced D-amphetamine-induced rearing activity, as well as ventral tegmental area dopamine cell excitability (firing, burst and population activity), associated with a partial desensitisation of dopamine D₂ auto-receptors.

CONCLUSIONS

We have demonstrated here that early, but not late, adolescent exposure to oral methylphenidate may induce long-lasting effects on monoamine neurotransmission. The possible clinical implication of these data will be discussed.

Somato-Dendritic Regulation of Raphe Serotonin Neurons; A Key to Antidepressant Action

Several lines of evidence implicate serotonin (5-hydroxytryptamine, 5-HT)in regulating personality traits and mood control. Serotonergic neurons are classically thought to be tonic regular-firing, “clock-like” neurons. Neurotransmission by serotonin is tightly regulated by the serotonin transporter (SERT) and by autoreceptors (serotonin receptors expressed by serotonin neurons) through negative feedback inhibition at the cell bodies and dendrites (5-HT_1A receptors) of the dorsal raphe nuclei or at the axon terminals (5-HT_1B receptors). In dorsal raphe neurons, the release of serotonin from vesicles in the soma, dendrites, and/or axonal varicosities is independent of classical synapses and can be induced by neuron depolarization, by the stimulation of L-type calcium channels, by activation of glutamatergic receptors, and/or by activation of 5-HT₂ receptors. The resulting serotonin release displays a slow kinetic and a large diffusion. This process called volume transmission may ultimately affect the rate of discharge of serotonergic neurons, and their tonic activity. The therapeutic effects induced by serotonin-selective reuptake inhibitor (SSRI) antidepressants are initially triggered by blocking SERT but rely on consequences of chronic exposure, i.e., a selective desensitization of somatodendritic 5-HT_1A autoreceptors. Agonist stimulation of 5-HT_2B receptors mimicked behavioral and neurogenic SSRI actions, and increased extracellular serotonin in dorsal raphe. By contrast, a lack of effects of SSRIs was observed in the absence of 5-HT_2B receptors (knockout-KO), even restricted to serotonergic neurons (Htr2b^5-HTKO mice). The absence of 5-HT_2B receptors in serotonergic neurons is associated with a higher 5-HT_1A-autoreceptor reactivity and thus a lower firing activity of these neurons. In agreement, mice with overexpression of 5-HT_1A autoreceptor show decreased neuronal activity and increased depression-like behavior that is resistant to SSRI treatment. We propose thus that the serotonergic tone results from the opposite control exerted by somatodendritic (Gi-coupled) 5-HT_1A and (Gq-coupled) 5-HT_2B receptors on dorsal raphe neurons. Therefore, 5-HT_2B receptors may contribute to SSRI therapeutic effects by their positive regulation of adult raphe serotonergic neurons. Deciphering the molecular mechanism controlling extrasynaptic release of serotonin, and how autoreceptors interact in regulating the tonic activity of serotonergic neurons, is critical to fully understand the therapeutic effect of SSRIs.

Perturbed Developmental Serotonin Signaling Affects Prefrontal Catecholaminergic Innervation and Cortical Integrity

Proper development of the medial prefrontal cortex (mPFC), crucial for correct cognitive functioning, requires projections from, among others, the serotonergic (5-HT) and catecholaminergic systems, but it is unclear how these systems influence each other during development. Here, we describe the parallel development of the 5-HT and catecholaminergic prefrontal projection systems in rat and demonstrate a close engagement of both systems in the proximity of Cajal-Retzius cells. We further show that in the absence of the 5-HT transporter (5-HTT), not only the developing 5-HT but also the catecholaminergic system, including their projections towards the mPFC, are affected. In addition, the layer identity of the mPFC neurons and reelin-positive interneuron number and integration are altered in the absence of the 5-HTT. Together, our data demonstrate a functional interplay between the developing mPFC 5-HT and catecholaminergic systems, and call for a holistic approach in studying neurotransmitter systems-specific developmental consequences for adult behavior, to eventually allow the design of better treatment strategies for neuropsychiatric disorders.

New dimensions of connectomics and network plasticity in the central nervous system

Cellular network architecture plays a crucial role as the structural substrate for the brain functions. Therefore, it represents the main rationale for the emerging field of connectomics, defined as the comprehensive study of all aspects of central nervous system connectivity. Accordingly, in the present paper the main emphasis will be on the communication processes in the brain, namely wiring transmission (WT), i.e. the mapping of the communication channels made by cell components such as axons and synapses, and volume transmission (VT), i.e. the chemical signal diffusion along the interstitial brain fluid pathways. Considering both processes can further expand the connectomics concept, since both WT-connectomics and VT-connectomics contribute to the structure of the brain connectome. A consensus exists that such a structure follows a hierarchical or nested architecture, and macro-, meso- and microscales have been defined. In this respect, however, several lines of evidence indicate that a nanoscale (nano-connectomics) should also be considered to capture direct protein-protein allosteric interactions such as those occurring, for example, in receptor-receptor interactions at the plasma membrane level. In addition, emerging evidence points to novel mechanisms likely playing a significant role in the modulation of intercellular connectivity, increasing the plasticity of the system and adding complexity to its structure. In particular, the roamer type of VT (i.e. the intercellular transfer of RNA, proteins and receptors by extracellular vesicles) will be discussed since it allowed us to introduce a new concept of 'transient changes of cell phenotype', that is the transient acquisition of new signal release capabilities and/or new recognition/decoding apparatuses.

Serotonin and brain function: a tale of two receptors

Previous attempts to identify a unified theory of brain serotonin function have largely failed to achieve consensus. In this present synthesis, we integrate previous perspectives with new and older data to create a novel bipartite model centred on the view that serotonin neurotransmission enhances two distinct adaptive responses to adversity, mediated in large part by its two most prevalent and researched brain receptors: the 5-HT1A and 5-HT2A receptors. We propose that passive coping (i.e. tolerating a source of stress) is mediated by postsynaptic 5-HT1AR signalling and characterised by stress moderation. Conversely, we argue that active coping (i.e. actively addressing a source of stress) is mediated by 5-HT2AR signalling and characterised by enhanced plasticity (defined as capacity for change). We propose that 5-HT1AR-mediated stress moderation may be the brain's default response to adversity but that an improved ability to change one's situation and/or relationship to it via 5-HT2AR-mediated plasticity may also be important - and increasingly so as the level of adversity reaches a critical point. We propose that the 5-HT1AR pathway is enhanced by conventional 5-HT reuptake blocking antidepressants such as the selective serotonin reuptake inhibitors (SSRIs), whereas the 5-HT2AR pathway is enhanced by 5-HT2AR-agonist psychedelics. This bipartite model purports to explain how different drugs (SSRIs and psychedelics) that modulate the serotonergic system in different ways, can achieve complementary adaptive and potentially therapeutic outcomes.

Silica stationary phase-based on-line sample enrichment coupled with LC-MS/MS for the quantification of dopamine, serotonin and their metabolites in rat brain microdialysates

Accurate measurement of trace levels of endogenous compounds remains challenging despite advancements in analytical technologies. In particular, monoamine neurotransmitters such as dopamine (DA) and serotonin (5-HT) are polar compounds with low molecular weights, which complicates the optimization of retention and detection on liquid chromatography-mass spectrometry (LC-MS). Microdialysis is an important sampling technique to collect extracellular fluid from the brain of living animals. However, the very low basal concentrations of the neurotransmitters, small sample volume (maximum 30 μL) and the absence of matrix-matching calibrators are limitations of a microdialysate as an analytical sample. In the present study, an LC-MS/MS method was developed and fully validated for the quantification of DA, 5-HT and their main metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), in microdialysates from the rat nucleus accumbens shell. To improve the method sensitivity and accuracy, on-line sample enrichment using silica stationary phase was employed, before which any other sample pretreatment was not performed. The validation results proved the method to be selective, sensitive, accurate and precise, with acceptable linearity within calibration ranges. The lower limits of quantification were 0.025, 0.1, 0.5, 25 and 2.5 ng/mL for 5-HT, DA, 5-HIAA, HVA and DOPAC, respectively. This is a powerful analytical method to determine endogenous concentrations of those compounds in microdialysates from the rat nucleus accumbens and will be very useful to further study on the pathophysiological functions of monoamine neurotramsmitters in vivo.

Mechanisms of 5-HT1A receptor-mediated transmission in dorsal raphe serotonin neurons

KEY POINTS

In the dorsal raphe nucleus, it is known that serotonin release activates metabotropic 5-HT1A autoreceptors located on serotonin neurons that leads to an inhibition of firing through the activation of G-protein-coupled inwardly rectifying potassium channels. We found that in mouse brain slices evoked serotonin release produced a 5-HT1A receptor-mediated inhibitory postsynaptic current (IPSC) that resulted in only a transient pause in firing. While spillover activation of receptors contributed to evoked IPSCs, serotonin reuptake transporters prevented pooling of serotonin in the extrasynaptic space from activating 5-HT1A -IPSCs. As a result, the decay of 5-HT1A -IPSCs was independent of the intensity of stimulation or the probability of transmitter release. These results indicate that evoked serotonin transmission in the dorsal raphe nucleus mediated by metabotropic 5-HT1A autoreceptors may occur via point-to-point synapses rather than by paracrine mechanisms.

ABSTRACT

In the dorsal raphe nucleus (DRN), feedback activation by Gαi/o -coupled 5-HT1A autoreceptors reduces the excitability of serotoninergic neurons, which decreases serotonin release both locally within the DRN and in projection regions. Serotonin transmission within the DRN is thought to occur via transmitter spillover and paracrine activation of extrasynaptic receptors. Here, we tested the volume transmission hypothesis in mouse DRN brain slices by recording 5-HT1A receptor-mediated inhibitory postsynaptic currents (5-HT1A -IPSCs) generated by the activation of G-protein-coupled inwardly rectifying potassium channels (GIRKs). We found that in the DRN of ePET1-EYFP mice, which selectively express enhanced yellow fluorescent protein in serontonergic neurons, the local release of serotonin generated 5-HT1A -IPSCs in serotonin neurons that rose and fell within a second. The transient activation of 5-HT1A autoreceptors resulted in brief pauses in neuron firing that did not alter the overall firing rate. The duration of 5-HT1A -IPSCs was primarily shaped by receptor deactivation due to clearance via serotonin reuptake transporters. Slowing diffusion with dextran prolonged the rise and reduced the amplitude the IPSCs and the effects were potentiated when uptake was inhibited. By examining the decay kinetics of IPSCs, we found that while spillover may allow for the activation of extrasynaptic receptors, efficient uptake by serotonin reuptake transporters (SERTs) prevented the pooling of serotonin from prolonging the duration of transmission when multiple inputs were active. Together the results suggest that the activation of 5-HT1A receptors in the DRN results from the local release of serotonin rather than the extended diffusion throughout the extracellular space.

The coaction of tonic and phasic dopamine dynamics

Tonic neurochemical dopamine activity underlies many brain functions; however a consensus on this important concentration has not yet been reached. In this work, we introduce in vivo fast-scan controlled-adsorption voltammetry to report tonic dopamine concentrations (90 ± 9 nM) and the dopamine diffusion coefficient (1.05 ± 0.09 × 10(-6) cm(2) s(-1)) in the mouse brain.

Highly sensitive detection of quantal dopamine secretion from pheochromocytoma cells using neural microelectrode array electrodeposited with polypyrrole graphene

For the measurement of events of dopamine (DA) release as well as the coordinating neurotransmission in the nerve system, a neural microelectrode array (nMEA) electrodeposited directionally with polypyrrole graphene (PG) nanocomposites was fabricated. The deposited graphene significantly increased the surface area of working electrode, which led to the nMEA (with diameter of 20 μm) with excellent selectivity and sensitivity to DA. Furthermore, PG film modification exhibited low detection limit (4 nM, S/N = 3.21), high sensitivity, and good linearity in the presence of ascorbic acid (e.g., 13933.12 μA mM(-1) cm(-2) in the range of 0.8-10 μM). In particular, the nMEA combined with the patch-clamp system was used to detect quantized DA release from pheochromocytoma cells under 100 mM K(+) stimulation. The nMEA that integrates 60 microelectrodes is novel for detecting a large number of samples simultaneously, which has potential for neural communication research.

Applying Time-sharing technique in a multimodal compact low-power CMOS neurochip for simultaneous neurochemical and action potential recording

Brain is an electrochemical system and recent studies suggest simultaneous measurement of interrelated brain's electrical and neurochemical activity may lead to better understanding of brain function in addition to developing optimal neural prosthetics. By exploiting opamp Time-sharing technique to minimized power dissipation and silicon area, we have fabricated a power efficient implantable CMOS microsystem for simultaneous measurement of Action Potential (AP) and neurotransmitter concentration. Both AP-recording and neurotransmitter sensing subsystems share a single 653 nW amplifier which senses picoscale to microscale current that corresponds to micromolar neurotransmitter concentration and microscale AP voltage. This microsystem is fabricated in CMOS 0.18 μm technology and tested using recorded signals from dorsal premotor cortex (PMd) area of a macaque monkey in our lab.

Fast-scan controlled-adsorption voltammetry for the quantification of absolute concentrations and adsorption dynamics

Fast-scan cyclic voltammetry has depended on background subtraction to quantify small changes in neurotransmitter concentration. Because of this requirement, measurements of absolute concentrations using fast-scan cyclic voltammetry have been limited. Here we develop and characterize fast-scan controlled-adsorption voltammetry (FSCAV), which enables direct measurements of absolute concentrations in vitro without the use of flow injection to change the concentration. This enables probing the diffusion-controlled adsorption dynamics of biogenic amines and other adsorbing species. An implicit finite-difference model of mass-transport-limited adsorption was developed and is in agreement with experimental results. Optimization of FSCAV yielded a sensitivity of 81 ± 11 nA/μM for dopamine, corresponding to a limit of detection of 3.7 ± 0.5 nM. Through the combination of novel instrumentation and validated computer simulations, we show that FSCAV is an important measurement tool that can be used to determine absolute concentrations and study mass-transport-limited adsorption.