Effects of bromocriptine in developing rat pups after 6-hydroxydopamine

Animal Models of ADHD?

To describe animals that express abnormal behaviors as a model of Attention-Deficit Hyperactivity Disorder (ADHD) implies that the abnormalities are analogous to those expressed by ADHD patients. The diagnostic features of ADHD comprise inattentiveness, impulsivity, and hyperactivity and so these behaviors are fundamental for validation of any animal model of this disorder. Several experimental interventions such as neurotoxic lesion of neonatal rats with 6-hydroxydopamine (6-OHDA), genetic alterations, or selective inbreeding of rodents have produced animals that express each of these impairments to some extent. This article appraises the validity of claims that these procedures have produced a model of ADHD, which is essential if they are to be used to investigate the underlying cause(s) of ADHD and its abnormal neurobiology.

Motor hyperactivity caused by a deficit in dopaminergic neurons and the effects of endocrine disruptors: a study inspired by the physiological roles of PACAP in the brain

Recent studies have revealed that the pituitary adenylate cyclase-activating polypeptide (PACAP) might act as a psychostimulant. Here we investigated the mechanisms underlying motor hyperactivity in patients with pervasive developmental disorders, such as autism, and attention-deficit hyperactivity disorder (ADHD). We studied the effects of intracisternal administration of 6-hydroxydopamine (6-OHDA) or endocrine disruptors (EDs) on spontaneous motor activity (SMA) and multiple gene expression in neonatal rats. Treatment with 6-OHDA caused significant hyperactivity during the dark phase in rats aged 4-5 weeks. Motor hyperactivities also were observed after treatment with endocrine disruptors, such as bisphenol A, nonylphenol, diethylhexyl phthalate and dibutyl phthalate, during both dark and light phases. Gene-expression profiles produced using cDNA macroarrays of 8-week-old rats with 6-OHDA lesions revealed the altered expression of several classes of gene, including the N-methyl-D-aspartate (NMDA) receptor 1, glutamate/aspartate transporter, gamma-aminobutyric-acid transporter, dopamine transporter 1, D4 receptor, and peptidergic elements such as the galanin receptor, arginine vasopressin receptor, neuropeptide Y and tachykinin 2. The changes in gene expression caused by treatment with endocrine disruptors differed from those induced by 6-OHDA. These results suggest that the mechanisms underlying the induction of motor hyperactivity and/or compensatory changes in young adult rats might differ between 6-OHDA and endocrine disruptors.

Amphetamine reverses learning deficits in 6-hydroxydopamine-treated rat pups

At 5 days of age, rat pups were treated with a combination of desmethylimipramine (DMI) and 6-hydroxydopamine (6-OHDA) to selectively deplete brain dopamine (DA) or with vehicle (saline) control solutions. Two days later, all animals received conditioning to a novel odor by pairing the odor with intraoral milk. When the odor was anise, treated pups spent less time near the conditioned stimulus than did controls, but there were no 6-OHDA effects when the stimulus was a lemon odor (Experiment I). The difference in performance between the treated and control animals was not attributable to alterations in activating effects of the reinforcer (Experiment I), changes in olfactory sensitivity or olfactory preference (Experiment II), or sensitization to the stimulus (Experiment III). In Experiment IV, animals received d-amphetamine sulfate (0.5 mg/kg) prior to conditioning, testing, or both conditioning and testing. Amphetamine treatment before conditioning produced an improvement in performance in animals previously treated with 6-OHDA/DMI, but it impaired performance in controls, regardless of the time of injection. The results indicate a role of brain DA in learning in young rats.

Effects of apomorphine on appetitive conditioning in 6-hydroxydopamine treated rat pups

Rat pups were treated on postnatal day 5 either with the combination of desmethylimipramine (DMI) and 6-hydroxydopamine (6-OHDA) to produce depletion of brain dopamine, or with control injections of saline. Two days later they were presented a novel anise odor paired with intraoral baby formula, and on the next day were tested for preference for the novel odor. Before conditioning and testing, animals were treated with either apomorphine (0.05 mg/kg) or isotonic saline. Performance of the conditioned appetitive response was impaired in dopamine depleted animals. In DMI/6-OHDA treated pups, apomorphine administration prior to conditioning produced an improvement in performance, but drug treatment prior to testing had no effect. In normal pups, apomorphine administration either before conditioning or testing produced impaired performance at testing.