In vitro evaluation of a closed-loop feedback system for dopamine concentration control

Introduction It is well known that Parkinson’s disease is related to a deficit of dopamine (DA) in the region of the brain called the corpus striatum. The aim of this work is to demonstrate the possibility of in vitro closed-loop control of the DA concentration levels. Methods By applying the electrochemical technique of fast scan cyclic voltammetry (FSCV), the measured values were compared with previously selected ones, and the system made decisions to control infusion pumps by dynamically adjusting the DA concentration in a continuous flow injection cell. Low-cost hardware was used for the acquisition and control signals (Arduino board), whereas for processing the collected data, graphical programming software (LabView) was used. Results The resolution of the system was approximately 0.4 µmol/L, with a time correction of the concentration adjustable between 1 and 90 seconds. The system allowed control of the DA concentration between 1 and 10 µmol/L with an error of approximately +/– 0.8 µmol/L. Conclusion Although designed to control the DA concentration, the system could be used to control, within the range of the developed FSCV, the concentration of other substances or to turn on brain stimulators. These results encourage the possibility of using the system in clinical studies (in vivo).

Antidepressant-like effect of the novel MAO inhibitor 2-(3,4-dimethoxy-phenyl)-4,5-dihydro-1H-imidazole (2-DMPI) in mice.

Monoamine oxidase (MAO) inhibitors were the first antidepressant drugs to be prescribed and are still used today with great success, especially in patients resistant to other antidepressants. In this study, we evaluated the MAO inhibitory properties and the potential antidepressant action of 2-(3,4-dimethoxy-phenyl)-4,5-dihydro-1H-imidazole (2-DMPI) in mice. We found that 2-DMPI inhibited both MAO isoforms (K(i) values were 1.53 (1.3-1.8) µM and 46.67 (31.8-68.4) µM for MAO-A and MAO-B, respectively) with 30-fold higher selectivity toward MAO-A. In relation to the nature of MAO-A inhibition, 2-DMPI showed to be a mixed and reversible inhibitor. The treatment with 2-DMPI (100-1000 µmol/kg, s.c.) caused a significant decrease in immobility time in the tail suspension test (TST) without affecting locomotor activity, motor coordination or anxiety-related activities. Conversely, moclobemide (1000 µmol/kg, s.c.) caused a significant increase in immobility time in the TST, which appeared to be mediated by a nonspecific effect on motor coordination function. 2-DMPI (300 µmol/kg, s.c.) decreased serotonin turnover in the cerebral cortex, hippocampus and striatum, whereas dopamine turnover was diminished only in the striatum, and norepinephrine turnover was not changed. The antidepressant-like effect of 2-DMPI was inhibited by the pretreatment of mice with methysergide (2 mg/kg, s.c., a non-selective serotonin receptor antagonist), WAY100635 (0.1 mg/kg, s.c., a selective 5-HT(1A) receptor antagonist) or haloperidol (0.05 mg/kg, i.p., a non-selective dopamine receptor antagonist). These results suggest that 2-DMPI is a prototype reversible and preferential MAO-A inhibitor with potential antidepressant activity, due to its modulatory effect on serotonergic and dopaminergic systems.

Microdialysis study of striatal dopamine in MPTP-hemilesioned rats challenged with apomorphine and amphetamine.

Motor impairments of Parkinson's disease (PD) appear only after the loss of more than 70% of the DAergic neurons of the substantia nigra pars compacta (SNc). An earlier phase of this disease can be modeled in rats that received a unilateral infusion of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine (MPTP) into the SNc. Though these animals do not present gross motor impairments, they rotate towards the lesioned side when challenged with DAergic drugs, like amphetamine and apomorphine. The present study aimed to test whether these effects occur because the drugs disrupt compensatory mechanisms that keep extracellular levels of dopamine in the striatum (DA(E)) unchanged. This hypothesis was tested by an in vivo microdialysis study in awake rats with two probes implanted in the right and left striatum. Undrugged rats did not present turning behaviour and their basal DA(E) did not differ between the lesioned and sham-lesioned sides. However, after apomorphine treatment, DA(E) decreased in both sides, but to a larger extent in the lesioned side at the time the animals started ipsiversive turning behaviour. After amphetamine challenge, DA(E) increased in both sides, becoming significantly higher in the non-lesioned side at the time the animals started ipsiversive turning behaviour. These results are in agreement with the hypothesis that absence of gross motor impairments in this rat model of early phase PD depends on maintenance of extracellular DA by mechanisms that may be disrupted by events demanding its alteration to higher or lower levels.

Non-motor function of the midbrain dopaminergic neurons.

The roles of the nigrostriatal pathway are far beyond the simple control of motor functions. The tonic release of dopamine in the dorsal and ventral striatum controls the choice of proper actions toward a given environmental situation. In the striatum, a specific action is triggered by a specific stimulus associated with it. When the subject faces a novel and salient stimulus, the phasic release of dopamine allows synaptic plasticity in the cortico-striatal synapses. Neurons of different regions of cortical areas make synapses that converge to the same medium spine neurons of the striatum. The convergent associations form functional units encoding body parts, objects, locations, and symbolic representations of the subject's world. Such units emerge in the striatum in a repetitive manner, like a mosaic of broken mirrors. The phasic release of dopamine allows the association of units to encode an action of the subject directed to an object or location with the outcome of this action. Reinforced stimulus-action-outcome associations will affect future decision making when the same stimulus (object, location, idea) is presented to the subject in the future. In the absence of a minimal amount of striatal dopamine, no action is initiated as seen in Parkinson's disease subjects. The abnormal and improper association of these units leads to the initiation of unpurposeful and sometimes repetitive actions, as those observed in dyskinetic patients. The association of an excessive reinforcement of some actions, like drug consumption, leads to drug addiction. Improper associations of ideas and unpleasant outcomes may be related to traumatic and depressive symptoms common in many diseases, including Parkinson's disease. The same can be said about the learning and memory impairments observed in demented and nondemented Parkinson's disease patients.

Inflammatory events induced by brown spider venom and its recombinant dermonecrotic toxin: a pharmacological investigation.

Accidents involving Brown spider (Loxosceles sp.) venom produce a massive inflammatory response in injured region. This venom has a complex mixture of different toxins, and the dermonecrotic toxin is the major contributor to toxic effects. The ability of Loxosceles intermedia venom and a recombinant isoform of dermonecrotic toxin to induce edema and increase in vascular permeability was investigated. These toxins were injected into hind paws and caused a marked dose and time-dependent edema and increase in vascular permeability in mice. Furthermore, the enzymatic activity of venom toxins may be primal for these effects. A mutated recombinant isoform of dermonecrotic toxin, that has only residual enzymatic activity, was not able to induce these inflammatory events. Besides the previous heating of toxins markedly reduced the paw edema and vascular permeability showing that thermolabile constituents can trigger these effects. In addition, the ability of these venom toxins to evoke inflammatory events was partially reduced in compound 48/80-pretreated animals, suggesting that mast cells may be involved in these responses. Pretreating mice with histamine (prometazine and cetirizine) and serotonin (methysergide) receptor antagonists significantly attenuated toxins induced edema and vascular permeability. Moreover, HPLC analysis of whole venom showed the presence of histamine sufficient to induce inflammatory responses. In conclusion, these inflammatory events may result from the activation of mast cells, which in turn release bioamines and may be related to intrinsic histamine content of venom.

Reversible inactivation of the dorsal raphe nucleus blocked the antipanic-like effect of chronic imipramine in the elevated T-maze.

Antidepressant drugs are effective in the treatment of panic in human panic disorder patients. One hypothesis is that the anti-panic effects of antidepressant drugs are mediated by an increase in the activity of serotonergic neurons within dorsal raphe nucleus (DRN) leading to an increase in serotonin-mediated inhibition of the dorsal periaqueductal gray (DPAG). In order to test this hypothesis, we investigated the effects of reversible inhibition of the DRN on behavior in the elevated T-maze (ETM) in control rats and rats chronically treated with imipramine. Rats were injected daily with imipramine (15 mg/kg i.p.) or saline for 24 days. A guide cannula was implanted in the DRN on day 14. Lidocaine (4%, 0.2 microL) or saline was injected into the DRN 10 min before the test in the ETM followed immediately by the open-field test (day 21). Three days later, the infusions were crossed-over, rats microinjected into the DRN with saline in the first trial received lidocaine and vice versa, and the behavioral tests were repeated (day 24). Chronic saline plus lidocaine in the DRN and chronic imipramine (plus saline or lidocaine in the DRN) impaired inhibitory avoidance, indicating an anxiolytic effect. In the one-way escape, lidocaine facilitated it, suggesting a panicogenic effect, while chronic imipramine impaired it, which is indicative of a panicolytic effect. Moreover, lidocaine blocked the facilitatory effect of chronic imipramine. The locomotor activity in the open field was not changed by any treatment compared to the control group. These effects were congruent with the hypothesis that the DRN has a dual effect on anxiety: increasing learned anxiety and decreasing innate anxiety. Moreover, they suggest that the DRN exerts a crucial role in the antipanic-like effect of chronic imipramine in the ETM.