Model for reduced brain dopamine in Lesch-Nyhan syndrome and the mentally retarded: Neurobiology of neonatal-6-hydroxydopamine-lesioned rats

Pharmacological interventions for self-injurious behaviour in adults with intellectual disabilities

BACKGROUND

Self-injurious behaviour among people with intellectual disability is relatively common and often persistent. Self-injurious behaviour continues to present a challenge to clinicians. It remains poorly understood and difficult to ameliorate despite advances in neurobiology and psychological therapies. There is a strong need for a better evidence base in prescribing and monitoring of drugs in this population, especially since none of the drugs are actually licensed for self-injurious behaviour.

OBJECTIVES

To determine clinical effectiveness of pharmacological interventions in management of self-injurious behaviour in adults with intellectual disability.

SEARCH METHODS

We searched the following databases on 19 February 2012: CENTRAL, MEDLINE, EMBASE, PsycINFO, CINAHL, Science Citation Index, Social Science Citation Index, Conference Proceedings Citation Index - Science, Conference Proceedings Citation Index - Social Science and Humanities, ZETOC and WorldCat. We also searched ClinicalTrials.gov, ICTRP and the reference lists of included trials.

SELECTION CRITERIA

We included randomised controlled trials that examined drug interventions versus placebo for self-injurious behaviour (SIB) in adults with intellectual disability.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed risk of bias for each trial using a data extraction form. We present a narrative summary of the results is presented. We did not consider meta-analysis was appropriate due to differences in study designs, differences between interventions and heterogeneous outcome measures.

MAIN RESULTS

We found five double-blind placebo-controlled trials that met our inclusion criteria. These trials assessed effectiveness and safety of drugs in a total of 50 people with intellectual disability demonstrating SIB. Four trials compared the effects of naltrexone versus placebo and one trial compared clomipramine versus placebo.One of the naltrexone versus placebo trials reported that naltrexone had clinically significant effects (≥ 33% reduction) on the daily rates of three of the four participants' most severe form of SIB and modest to substantial reductions in SIB for all participants; however, this study did not report on statistical significance. Another trial reported that naltrexone attenuated SIB in all four participants, with 25 mg and 50 mg doses producing a statistically significant decrease in SIB (P value < 0.05). Another trial (eight people) indicated that naltrexone administration was associated with significantly fewer days of high frequency self injury and significantly more days with low frequency self injury. Naltrexone had different effects depending on the form and location of self injury. Another trial with only 26 participants found that neither single-dose (100 mg) nor long-term (50 and 150 mg) naltrexone treatment had any therapeutic effect on SIB.Comparison of clomipramine versus placebo found no statistically significant benefit for any outcome measure, which included SIB rate and intensity, stereotypy and adverse events. However, it showed clinically significant improvement in the rate and intensity of SIB and stereotypy.There were very few noteworthy adverse events to report in any of the four trials in which these were reported.All trials were at high risk of bias, apart from one trial (Lewis 1996), which was probably at low risk of bias. The short period of follow-up was a significant drawback in the design of all five trials, as it did not allow long-term assessment of behaviour over time.We were unable to examine the efficacy of antidepressants other than clomipramine, antipsychotics, mood stabilisers or beta-blockers as we did not identify any relevant placebo-controlled trials.

AUTHORS' CONCLUSIONS

There was weak evidence in included trials that any active drug was more effective than placebo for people with intellectual disability demonstrating SIB. Due to sparse data, an absence of power and statistical significance, and high risk of bias for four of the included trials, we are unable to reach any definite conclusions about the relative benefits of naltrexone or clomipramine compared to placebo.

Self-injurious behavior in neurodevelopmental disorders: relevance of nociceptive and immune mechanisms

Self-injurious behavior (SIB) among individuals with intellectual and related neurodevelopmental disorders (IDD) is a clinical challenge and scientific puzzle. The physiological mechanisms regulating the sensory components of SIB remain a mystery with no clear understanding of the underlying pathophysiology. The central dogma regarding sensory processing in general and pain in particular among individuals with IDD and chronic SIB is that sensory processing is reduced and pain is absent or blunted. In this paper, recent findings challenging some of the conventional wisdom regarding pain and sensory function among individuals with IDD and SIB are reviewed. It seems that at least a subgroup of individuals with IDD and chronic SIB may be in a physiological state similar to neuropathic pain in which hyperalgesia is mediated by plasticity mechanisms regulating inflammatory, immune, and nociceptive systems. In response to repeated tissue damage associated with chronic self-injury, innate immune cells may be producing pro-inflammatory and pro-nociceptive cytokines that act on the brain to cause sickness-like behavior and sensitize primary sensory nerve afferents contributing to pain hypersensitivity (i.e., hyperalgesia).

[Self-injurious-behavior in children and adolescents with intellectual disabilities]

10% of the children and teenagers with intellectual disability develop self-injurious behavior during lifespan. The causes for this are investigated, often various and reach from learn-theoretical up to neurobiological conditions. The available work gives overview of the current state of research to the etiology, further factors of influence as well as the process of self-injurious behavior by intellectual disability. Beyond that current diagnostics procedures, standard of treatment of the last thirty years and their effectiveness are presented and discussed finally.

The effects of methylphenidate on the classroom behavior of elementary school-age children with cerebral palsy: a preliminary observational analysis

High- and low-dose methylphenidate administration was evaluated prospectively for 3 elementary school-age children with cerebral palsy, cognitive impairments, and attention-deficit hyperactivity disorder (ADHD) symptoms using single-case, randomized, double-blind, placebo-controlled designs. An observational time sampling protocol was used to directly measure and quantify classroom behavior. Summary level analysis showed that (1) low-dose (0.3 mg/kg/dose) administration was associated with clinically significant (>50%) reductions in stereotyped and disruptive behavior relative to baseline and placebo conditions, (2) high-dose (0.5 mg/kg/dose) administration was associated with exacerbated amounts of stereotyped and disruptive behavior, and (3) no changes were directly observed for task-related behavior at either dose. Results are discussed with respect to previous research with methylphenidate administration and cerebral palsy, and the suggestion is made that further work using larger, randomly selected study samples with complementary measures of behavior and performance appears warranted.

Self-injurious behavior and the efficacy of naltrexone treatment: a quantitative synthesis

People with mental retardation, autism, and related developmental disabilities who self-injure are treated with a wide array of behavioral techniques and psychotropic medications. Despite numerous reports documenting short-term and some long-term changes in self-injury associated with the opiate antagonist naltrexone hydrochloride, no quantitative review of its efficacy has been reported. We conducted a quantitative synthesis of the peer-reviewed published literature from 1983 to 2003 documenting the use of naltrexone for the treatment of self-injurious behavior (SIB). Individual-level results were analyzed given subject and study characteristics. A sample of 27 research articles involving 86 subjects with self-injury was reviewed. Eighty percent of subjects were reported to improve relative to baseline (i.e., SIB reduced) during naltrexone administration and 47% of subjects SIB was reduced by 50% or greater. In studies reporting dose levels in milligrams, males were more likely than females to respond. No significant relations were found between treatment outcomes and autism status or form of self-injury. Results are discussed with respect to future efficacy work related to study outcomes and the pharmacological treatment of self-injury.

The neonate-6-hydroxydopamine-lesioned rat: a model for clinical neuroscience and neurobiological principles

In 1973, a technique of administering 6-hydroxydopamine (2,4,5-trihydroxyphenylethylamine) intracisternally to neonate rats was introduced to selectively reduce brain dopamine (neonate-lesioned rat). This neonate treatment proved unique when compared to rats lesioned as adults with 6-hydroxydopamine--prompting the discovery of differing functional characteristics resulting from the age at which brain dopamine is reduced. A realization was that neonate-lesioned rats modeled the loss of central dopamine and the increased susceptibility for self-injury in Lesch-Nyhan disease, which allowed identification of drugs useful in treating self-injury in mentally retarded patients. The neonate-lesioned rat has also been proposed to model the hyperactivity observed in attention-deficit hyperactivity disorder. Because the neonate-lesioned rat exhibits enhanced sensitization to repeated NMDA receptor antagonist administration and has functional changes characteristic of schizophrenia, the neonate lesioning is believed to emulate the hypothesized NMDA hypofunction in this psychiatric disorder. Besides modeling features of neurological and psychiatric disorders, important neurobiological concepts emerged from pharmacological studies in the neonate-lesioned rats. One was the discovery of coupling of D1/D2-dopamine receptor function. Another was the progressive increase in responsiveness to repeated D1-dopamine agonist administration referred to as "priming" of D1-dopamine receptor function. Additionally, a unique profile of signaling protein expression related to neonate reduction of dopamine has been identified. Thus, from modeling characteristics of disease to defining adaptive mechanisms related to neonatal loss of dopamine, the neonate-lesioned rat has had a persisting influence on neuroscience. Despite an extraordinary legacy from studies of the neurobiology of this treatment, a host of unknowns remain that will inspire future investigations.

The use of clozapine in adults with intellectual disability

BACKGROUND

There are not many studies on the use of clozapine in patients with intellectual disability (ID). The authors describe a case series of patients treated with clozapine, drawn from a medium secure unit, a low secure assessment and treatment service and a community team in the London region.

METHOD

A retrospective file-review of patients treated in these three settings during the time period March-June 2002 was performed (n = 24). Information was collected using a semistructured proforma.

RESULTS

Of the 24 patients, 67% had schizophrenia, 17% had schizoaffective disorder and 8% had bipolar disorder. Patients had been unwell for a mean of 6 years and had been tried on a mean of four antipsychotics. The mean maximum dose of clozapine was 488 mg. The outcomes on the clinical global impression (CGI) scale showed 29% very much improved, 42% much improved, 21% minimally improved and 8% no change. 54% of the whole sample and 53% of those from the medium secure unit were discharged to homes in the community. The drug had to be stopped in four patients, of which three were because of neutropaenia.

CONCLUSION

Clozapine appears to be safe and efficacious in many people with ID. Careful monitoring of side-effects is needed during therapy.

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.