Fixed ratio discrimination training increases in vivo striatal dopamine in neonatal 6-OHDA-lesioned rats

Neonatal 6-OHDA lesion model in mouse induces Attention-Deficit/ Hyperactivity Disorder (ADHD)-like behaviour

Attention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder characterized by impaired attention, impulsivity and hyperactivity. The "neonatal 6-hydroxydopamine" (6-OHDA) lesion is a commonly used model of ADHD in rat. However, a comprehensive assessment of ADHD-like symptoms is still missing, and data in mouse remain largely unavailable. Our aim was to analyse symptoms of ADHD in the mouse neonatal 6-OHDA model. 6-OHDA mice exhibited the major ADHD-like symptoms, i.e. hyperactivity (open field), attention deficit and impulsivity (five-choice serial reaction time task). Further, the model revealed discrete co-existing symptoms, i.e. anxiety-like (elevated plus maze test) and antisocial (social interaction) behaviours and decreased cognitive functioning (novel object recognition). The efficacy of methylphenidate, a classical psychostimulant used in the treatment of ADHD, was also evaluated. A histological analysis further supports the model validity by indicating dopamine depletion, changes in cortical thickness and abnormalities in anterior cingulate cortex neurons. A principal component analysis of the behaviour profile confirms that the 6-OHDA mouse model displayed good face and predictive validity. We conclude that neonatal dopamine depletion results in behavioural and morphological changes similar to those seen in patients and therefore could be used as a model for studying ADHD pathophysiological mechanisms and identifying therapeutic targets.

Rodent models of ADHD

The neonatal 6-OHDA-lesioned rat, coloboma mouse, DAT-KO mouse, and spontaneously hypertensive rat (SHR) models all bear a phenotypic resemblance to ADHD in that they express hyperactivity, inattention, and/or impulsivity. The models also illustrate the heterogeneity of ADHD: the initial cause (chemical depletion or genetic abnormality) of the ADHD-like behaviors is different for each model. Neurochemical and behavioral studies of the models indicate aberrations in monoaminergic neurotransmission. Hyperdopaminergic neurotransmission is implicated in the abnormal behavior of all models. Norepinephrine has a dual enhancing/inhibitory role in ADHD symptoms, and serotonin acts to inhibit abnormal dopamine and norepinephrine signaling. It is unlikely that symptoms arise from a single neurotransmitter dysfunction. Rather, studies of animal models of ADHD suggest that symptoms develop through the complex interactions of monoaminergic neurotransmitter systems.

Weaver mutant mice exhibit long-term learning deficits under several measures of instrumental behavior

Homozygous weaver mutant mice (wv/wv) exhibit symptoms that parallel Parkinson's disease, including motor deficits and the destruction of dopaminergic neurons as well as degeneration in the cerebellum and hippocampus. To develop a more complete behavioral profile of these organisms, groups of wv/wv, wv/+ mice and C57BL/6 mice were observed on a within-subjects basis under a fixed-interval schedule of reinforcement, a differential-reinforcement-of-low-rate-of-responding schedule, and a discrimination task in which a saccharin solution and tap water were concurrently available from two food cups. Under both reinforcement schedules, the wv/wv mice responded as frequently as the comparison subjects, but they responded in a manner that was inappropriate to the contingencies. Rather than respond with increasing frequency as the upcoming reinforcer became temporally proximate, wv/wv mice responded with decreasing probability as a function of the time since the previous reinforcer. Under the discrimination task, the wv/wv mice, unlike the controls, obtained saccharin over tap water at the level of chance. The findings suggest that weaver mutant mice express learning deficits similar to those found in other dopamine-deficient organisms.

High-throughput automated post-processing of separation data

The development of an efficient method for high-throughput analysis of multiple electropherograms or chromatograms collected in series is presented. The method, encoded in a computer program designated "Cutter", utilizes batch processing for determining chromatographic figures of merit (CFOM) including peak centroid times, heights, areas, signal-to-noise ratios (S/N), variance (sigma2), skew, excess, and plate number (N) across a set of separations collected serially. The software was validated using simulated data with varying S/N, skew, and excess. The accuracy of the analysis was comparable to or improved over commercial software with area calculation relative errors (RE) below 5% for simulated data with S/N = 5. File sets containing 1300 electropherograms were analyzed in 5 min, representing a nearly 200-fold reduction in analysis time from other methods. Incorporated within the program is a novel method for automated peak deconvolution using an Empirically Transformed Gaussian function. Area measurements of deconvoluted peaks were within 3% of the true value of a simulated data set with S/N = 5 and resolution (R(S)) = 1 for equivalent peaks, and within 10% when the ratio of the overlapped peak heights was 10:1.