Rodent models of mental retardation: Self-injury, aberrant behavior, and stress

Trichotillomania (hair pulling disorder), skin picking disorder, and stereotypic movement disorder: toward DSM-V

In DSM-IV-TR, trichotillomania (TTM) is classified as an impulse control disorder (not classified elsewhere), skin picking lacks its own diagnostic category (but might be diagnosed as an impulse control disorder not otherwise specified), and stereotypic movement disorder is classified as a disorder usually first diagnosed in infancy, childhood, or adolescence. ICD-10 classifies TTM as a habit and impulse disorder, and includes stereotyped movement disorders in a section on other behavioral and emotional disorders with onset usually occurring in childhood and adolescence. This article provides a focused review of nosological issues relevant to DSM-V, given recent empirical findings. This review presents a number of options and preliminary recommendations to be considered for DSM-V: (1) Although TTM fits optimally into a category of body-focused repetitive behavioral disorders, in a nosology comprised of relatively few major categories it fits best within a category of motoric obsessive-compulsive spectrum disorders, (2) available evidence does not support continuing to include (current) diagnostic criteria B and C for TTM in DSM-V, (3) the text for TTM should be updated to describe subtypes and forms of hair pulling, (4) there are persuasive reasons for referring to TTM as "hair pulling disorder (trichotillomania)," (5) diagnostic criteria for skin picking disorder should be included in DSM-V or in DSM-Vs Appendix of Criteria Sets Provided for Further Study, and (6) the diagnostic criteria for stereotypic movement disorder should be clarified and simplified, bringing them in line with those for hair pulling and skin picking disorder.

Cross-sensitization between footshock stress and apomorphine on self-injurious behavior and neostriatal catecholamines in a rat model of Lesch-Nyhan syndrome

The effects of footshock sensitization (priming), apomorphine (APO) priming and their combination on behavior and neostriatal and cortical catecholamines were examined in adult rats which had neonatally received bilateral intracerebroventricular injections with 6-hydroxydopamine (6-OHDA; a model of Lesch-Nyhan syndrome (LNS)) or vehicle (unlesioned rats). Lesioned (6-OHDA-treated) rats displayed self-biting (SB; 7/20 rats) and self-injurious behavior (SIB; 1/20 rats) during APO priming, but not during footshock priming. During subsequent acute cumulative APO dosing, 20-30% of lesioned rats primed with APO alone or footshock alone displayed SB and SIB. However, SB and SIB incidence in APO+footshock-primed lesioned rats was nearly tripled. Dopamine (DA) synthesis, metabolism and extracellular concentrations (disposition) in unlesioned rats and in cortices of lesioned animals were unaffected by priming. In lesioned rats primed with APO alone or footshock alone, only neostriatal 3-methoxytyramine (3-MT) was significantly increased. However, neostriatal DA and metabolite concentrations (and norepinephrine (NE)) were all significantly elevated in lesioned rats primed with both APO and footshock. These results confirm that neonatal 6-OHDA-induced neostriatal catecholamine depletion can be antagonized by experiential change, suggest that behavioral and neurochemical cross-sensitization between APO and footshock in such rats is unidirectional and support the view that stress can exacerbate the incidence of SIB in LNS.

Fixed-ratio discrimination training as replacement therapy in Parkinson's disease: studies in a 6-hydroxydopamine-treated rat model

Severe 6-hydroxydopamine (6-OHDA)-induced neostriatal dopamine (DA) depletion is generally held to be irreversible. Adult rats administered 6-OHDA soon after weaning, or neonatally, respectively model Parkinson's disease (PD) and Lesch-Nyhan syndrome (LNS). Prior studies in our laboratory indicate that prolonged training on incrementally more difficult fixed-ratio (FR) discriminations can reverse 'irreversible' 6-OHDA-induced neostriatal DA depletion in adult LNS rats. The present study evaluated the effects of such training on neostriatal DA depletion and its functional consequences in adult PD and control (vehicle-injected) rats. After recovery from 6-OHDA-induced hypophagia, rats were sacrificed to assess neostriatal DA depletion magnitude, or were food-deprived and either subjected to food-maintained operant FR discrimination training or allowed to remain in their home cages. 6-OHDA treatment antagonized amphetamine (AMP)-induced increases in brief rearing behavior and locomotor activity in 3-month-old PD rats prior to training, and reduced operant response rates throughout training without affecting learning rates. One week after training, AMP-increased locomotor and brief-rearing frequencies were augmented in all groups except trained controls, and the prior inhibitory effect of 6-OHDA treatment on AMP-increased behavioral frequencies was essentially eliminated. Cumulative apomorphine (APO) dose-effect curve (0.1-3.2 mg/kg) construction 3 weeks post-training revealed that 6-OHDA treatment abolished APO-induced intense licking behavior. However, training eliminated the hyperresponsiveness of 6-OHDA-treated rats to the locomotor- and brief-rearing stimulant effects of APO but did not affect the depletion of neostriatal DA. Nevertheless, 6-OHDA-induced increases in neostriatal DOPAC/DA and HVA/DA ratios were normalized by age/food-deprivation while that of 3MT/DA was not. These findings suggest that training reduces the functional responsiveness of at least some central DA receptors, FR discrimination training could be a useful adjunct to PD replacement therapy and that the neostriatal DA-repleting action of training in 6-OHDA-treated rats depend on the age at which 6-OHDA is administered.

FR discrimination training reverses 6-hydroxydopamine-induced striatal dopamine depletion in a rat model of Lesch-Nyhan syndrome

Five-day-old rats received 6-hydroxydopamine (6-HD; 100 micrograms base) or vehicle intracisternally. Striatal and cortical dopamine (DA) and metabolite levels were then determined when animals were three or 8.5 months of age and the latter rats had been weight-reduced for 5.5 months. In the latter animals these determinations were made 1 month following 4.5 months of home-cage confinement (untrained animals) or of food-maintained fixed-ratio (FR) discrimination training involving either a single discrimination (performance animals) or incrementally more difficult discriminations. Striatal DA levels in 3-month-old and 8.5-month-old (untrained) 6-HD-treated rats were, respectively, only 3% and 11% of those in untrained vehicle-treated animals (controls). Despite such large depletions, striatal DA levels in 6-HD-treated performance rats were 3-fold higher than those in untrained age-matched 6-HD-treated rats (i.e., were 32% of values in controls) while those in incrementally trained 6-HD-treated animals were even higher (i.e., were 60% of control values). Related changes occurred in levels of most metabolites. However, in incrementally trained rats, striatal 3-methoxytyramine concentrations were 154% of control values. Cortical DA and metabolite levels were little affected by 6-HD treatment. The present results confirm and extend our earlier observations suggesting that reversal of 'irreversible' neonatal 6-HD-induced striatal dopamine and metabolic depletion can be accomplished by environmental (training) manipulations in adult rats.