Dopaminergic receptor supersensitivity in self-mutilatory behaviour of Lesch-Nyhan disease

Animal Models of Self-Injurious Behavior: An Update

Although self-injurious behavior is a common comorbid behavior problem among individuals with neurodevelopmental disorders, little is known about its etiology and underlying neurobiology. Interestingly, it shows up in various forms across patient groups with distinct genetic errors and diagnostic categories. This suggests that there may be shared neuropathology that confers vulnerability in these disparate groups. Convergent evidence from clinical pharmacotherapy, brain imaging studies, postmortem neurochemical analyses, and animal models indicates that dopaminergic insufficiency is a key contributing factor. This chapter provides an overview of studies in which animal models have been used to investigate the biochemical basis of self-injury and highlights the convergence in findings between these models and expression of self-injury in humans.

Animal models of self-injurious behaviour: an overview

Self-injurious behaviour is highly prevalent in neurodevelopmental disorders. Interestingly, it is not restricted to any individual diagnostic group. Rather, it is exhibited in various forms across patient groups with distinct genetic defects and classifications of disorders. This suggests that there may be shared neuropathology that confers vulnerability. Convergent evidence from clinical pharmacotherapy, brain imaging studies, postmortem neurochemical analyses, and animal models indicates that dopaminergic insufficiency is a key culprit. This chapter provides an overview of studies in which animal models have been used to investigate the biochemical basis of self-injury, and highlights the convergence in findings between these models and expression of self-injury in humans.

Neurotransmitter changes in the pathophysiology of Lesch-Nyhan syndrome

The neurological symptoms of Lesch-Nyhan syndrome (LNS) are assumed to result from the neurotransmitter changes in this disorder. Among them, the dopaminergic system is believed to play a role in the self-injurious behavior through receptor supersensitivity. However, the precise mechanism underlying the dopamine supersensitivity remains unclear. An increased serotonergic action in the striatum may be crucial for the appearance of self-injurious behavior, and pharmacological evidence suggests the efficacy of serotonin agonists/antagonists for the treatment of the self-mutilation in LNS.

Polysomnographic studies of Lesch-Nyhan syndrome

Three cases of Lesch-Nyhan syndrome (LNS) were examined by polysomnography to assess the brainstem function, and to determine the causes of the neurological manifestations and sudden death in this syndrome. In the two older cases, the amount of slow wave and rapid eye movement (REM) sleep, the REM density and the frequency of REM bursts were decreased. In the youngest case, symmetrical phasic movements of all four limbs were observed at all sleep stages other than REM sleep. Although movements other than these symmetrical body movements appeared to be normal in this case, the frequency of twitch movements showed an abnormal pattern in each sleep stage in the two older cases. These findings suggest that in the brainstems of younger cases with LNS the REM-non REM generator as well as multiple neurotransmitter systems influencing body movements during sleep remain relatively normal, but become progressively impaired in adult cases. Severe obstructive apnea was observed in one case with hypothyroidism, but there were no respiratory abnormalities in other two cases.

Analysis of abnormalities in purine metabolism leading to gout and to neurological dysfunctions in man

A modelling approach is used to analyse diseases associated with purine metabolism in man. The specific focus is on deficiencies in two enzymes, hypoxanthine:guanine phosphoribosyltransferase and adenylosuccinate lyase. These deficiencies can lead to a number of symptoms, including neurological dysfunctions and mental retardation. Although the biochemical mechanisms of dysfunctions associated with adenylosuccinate lyase deficiency are not completely understood, there is at least general agreement in the literature about possible causes. Simulations with our model confirm that accumulation of the two substrates of the enzyme can lead to significant biochemical imbalance. In hypoxanthine:guanine phosphoribosyltransferase deficiency the biochemical mechanisms associated with neurological dysfunctions are less clear. Model analyses support some old hypotheses but also suggest new indicators for possible causes of neurological dysfunctions associated with this deficiency. Hypoxanthine:guanine phosphoribosyltransferase deficiency is known to cause hyperuricaemia and gout. We compare the relative importance of this deficiency with other known causes of gout in humans. The analysis suggests that defects in the excretion of uric acid are more consequential than defects in uric acid synthesis such as hypoxanthine:guanine phosphoribosyltransferase deficiency.

Self-mutilation in the Lesch-Nyhan syndrome: a corporal consciousness problem?--a new hypothesis

The Lesch-Nyhan syndrome (LNS) has been extensively studied from the genetic and biochemical point of view. The main characteristic of the syndrome is the self-mutilation feature, which has been poorly studied and understood. We propose a new hypothesis about the self-mutilation physiopathology, which is related to the supersensitivity of the dopaminergic D1 receptors in the neuromatrix found in the cingulum cortex region. The LNS shows an increase of uric acid levels as a result of the deficiency of hypoxanthine phosphoribosyltransferase enzyme. This increase could induce damage to dopaminergic neurons. As a consequence, a decrease in dopamine synthesis during gestation and the early postnatal period could occur, producing a functional dopaminergic denervation of the D1 receptors, located on the prefrontal cortex, specifically in the cingulum bundle projections. This phenomenon could induce a codification disturbance in the 'genetic body' of the neuromatrix, that could be expressed functionally as anosognosia, giving rise to self-mutilation. We suggest that this self-mutilation is a pain consciousness problem.

Effects of REM sleep deprivation on the d-amphetamine-induced self-mutilating behavior

It is well known that self-mutilating behavior (SMB) is developed in rats and humans during the daily treatment with d-amphetamine. Accordingly, in this work it was found that the daily treatment with 7.5 mg/kg d-amphetamine induced in rats a progressive appearance of SMB. Lower doses (5.0 mg/kg) were uneffective and higher doses (10 mg/kg) produced a pattern of SMB in which the mutilation induced at the beginning of the d-amphetamine administration disappears completely as the treatment progresses. Interestingly, it was also found that REM sleep deprivation (48 h) potentiated significantly the SMB induced by the daily administration of 7.5 mg/kg d-amphetamine, and to lesser extent, the SMB induced by the daily treatment with 10 mg/kg d-amphetamine. R(+)-SCH-23390 a D1 dopamine (DA) receptor antagonist blocked completely or abolished the SMB induced by 7.5 mg/kg d-amphetamine in REM sleep deprived rats while (+/-)-sulpiride a D2 DA receptor antagonist had only a partial blocking effect. Haloperidol a D1/D2 DA receptor antagonist behaved as a D1 antagonist. Our results indicate that REM sleep deprivation enhances the SMB induced by the daily administration of d-amphetamine and suggest the involvement of D1 DA receptors in the mechanism underlying the SMB. A role of REM sleep deprivation is also suggested in the appearance of self-mutilating episodes in d-amphetamine addicts.

Presynaptic dopaminergic deficits in Lesch-Nyhan disease

BACKGROUND

Lesch-Nyhan disease is a rare, devastating, X-linked recessive disorder of purine synthesis. Patients present with hyperuricemia, choreoathetosis, dystonia, and aggressive and self-injurious behavior. Although the genetic and biochemical abnormalities have been identified, the causes of the neuropsychiatric syndrome remain unclear.

METHODS

We used positron-emission tomography to measure presynaptic accumulation of fluorodopa F 18 tracer in the dopaminergic regions of the brains of 12 patients with Lesch-Nyhan disease (age, 10 to 20 years) and 15 healthy controls (age, 12 to 23). The results were expressed as ratios of specific to nonspecific radioactive counts. A low ratio indicates decreased dopa decarboxylase activity and dopamine storage.

RESULTS

The fluorodopa F 18 ratio was significantly lower in the putamen (31 percent of control values), caudate nucleus (39 percent), frontal cortex (44 percent), and ventral tegmental complex (substantia nigra and ventral tegmentum; 57 percent) in the patients with Lesch-Nyhan disease than in the controls. Uptake of the tracer was abnormally low even in the youngest patients tested, and there was no overlap in the values between patients and controls.

CONCLUSIONS

Patients with Lesch-Nyhan disease have abnormally few dopaminergic nerve terminals and cell bodies. The abnormality involves all dopaminergic pathways and is not restricted to the basal ganglia. These dopaminergic deficits are pervasive and appear to be developmental in origin, which suggests that they contribute to the characteristic neuropsychiatric manifestations of the disease.

A dopamine deficiency model of Lesch-Nyhan disease--the neonatal-6-OHDA-lesioned rat

Lesch-Nyhan syndrome is characterized by a deficiency of the enzyme hypoxanthine phosphoribosyl transferase (HPRT), compulsive self-mutilatory behavior (SMB), and a loss of central dopaminergic neurons. In order to model the loss of central dopamine-containing neurons in this developmental disorder, neonatal rat pups 3 days of age were given the neurotoxin 6-OHDA intracisternally to reduce brain dopamine. Accompanying the profound loss of dopamine produced by this treatment was an increase in striatal serotonin content. When these neonatally lesioned rats were challenged as adults with systemically administered L-DOPA or with muscimol administration into substantia nigra reticulata (SNR), SMB was observed, a response not observed in unlesioned rats. Thus, the neonatally lesioned rats exhibit increased susceptibility for SMB. Since a D1-dopamine antagonist blocked the SMB response to L-DOPA, it was proposed that D1-dopamine receptors were critical to this behavioral response. Basic investigations concerning D1-dopamine receptor mechanisms in the lesioned rats have been performed and these are reviewed. The data in the neonatally lesioned rats provide convincing evidence that the absence of central dopaminergic neurons is responsible for at least some of the neurological symptoms of the Lesch-Nyhan syndrome, a finding consistent with data collected in mice with an HPRT deficiency.

Animal models of Lesch-Nyhan syndrome

In humans, deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT) is associated with a disorder known as Lesch-Nyhan syndrome which includes severe neurobehavioral abnormalities. Several animal models which have been developed to examine the neurobiologic substrates of this disorder have suggested a role for abnormal function in purine/dopamine neurotransmission, but the relationship between HPRT-deficiency and these abnormalities remains unknown. Recently, HPRT-deficient mice have been produced which appear to have similar, though more subtle changes in brain dopamine function. These mice will be useful in elucidating the relationship between HPRT-deficiency and the neurological deficits observed in patients with this disorder.

Lesch-Nyhan syndrome with delayed onset of self-mutilation: hyperactivity of interneurons at the brainstem and blink reflex

We studied a case of Lesch-Nyhan syndrome with delayed onset of self-mutilation. Athetotic cerebral palsy and mental retardation were diagnosed at 1 year old, but the disease was not suspected until age 8 years when he began biting his lips and fingers. There was no obvious alteration of catecholamine in urine and CSF. We attempted to induce a series of blink reflexes by electric, mechanical and photic procedures. The R1 amplitude increased and the latency of the R2 shortened compared with controls. This shows that not only orbicularis motoneuron itself, but also uncrossed interneurons, are in a state of hyperexcitability. The contralateral R2 was poor which was in favour of hypoexcitability of the crossed interneurons at the brainstem. The significant large response was obtained by photic procedure which was in favour of hyperexcitability of the motoneurons. Therefore, it is demonstrated that a thorough examination of blink reflexes provides a useful method for examination of a state of the underlying neural activity.

Self-injurious behaviour and the Gilles de la Tourette syndrome: a clinical study and review of the literature

Thirty (33%) of 90 patients with the Gilles de la Tourette syndrome exhibited self-injurious behaviour. Fourteen were head bangers, of whom two had cavum septum pellucidum. Clinical correlates of self-injury were the severity of Gilles de la Tourette syndrome symptoms and psychopathology, with special reference to obsessionality and hostility. We discuss an additional patient who died from a subdural haematoma as a result of head banging, and three who had permanent vision impairment from self inflicted eye injuries.

Lesch-Nyhan syndrome: a study of motor behavior and cerebrospinal fluid neurotransmitters

We studied 5 boys, 2 to 10 years old, with marked or complete deficiency of hypoxanthine-guanine phosphoribosyltransferase and Lesch-Nyhan syndrome with varying degrees of mental retardation, dysarthria, chorea, dystonia, spasticity, and ataxia. Four patients had marked reduction of homovanillic acid in the cerebrospinal fluid (CSF) and all showed low CSF 3-methoxy-4-hydroxy phenylethylene glycol, indicating reduced dopamine and norepinephrine turnover. Three patients showed high CSF 5-hydroxyindoleacetic acid, suggesting increased serotonin turnover. Some patients improved with carbidopa-levodopa, but others benefited from tetrabenazine, a monoamine-depleting agent. This study provides support for the theory of abnormal central monoamine metabolism in Lesch-Nyhan syndrome.

Opioid neuronal denervation in Gilles de la Tourette syndrome

Increased striatal dopaminergic functions with heightened postsynaptic receptor sensitivity has been proposed to underlie the major clinical symptoms of Tourette's syndrome (TS). The beneficial response of the majority of TS patients to haloperidol supports the hyperdopaminergic pathophysiological concept of TS. However, in 5 recently encountered TS patients, haloperidol failed to ameliorate self-injurious behavior (SIB) while the opiate antagonist, naloxone, attenuated SIB, implicating deranged endorphinergic mechanisms in the pathophysiology of this disorder. Brain damage is commonly associated with partial neuronal denervation, denervation supersensitivity and neuronal habituation (Cannon's Law). While the motor tics of TS possibly reflect neuronal denervation of striatal dopaminergic neurons. SIB may represent opioid denervation with alterations in opioid receptor sensitivity possibly involving striato-limbic-hypothalamic circuits. The effect of naloxone on SIB in TS could thus be explained on the basis of a modulatory effect of this drug on opioid receptor sensitivity.

The serotonin hypothesis of (auto)aggression. Critical appraisal of the evidence

Based on the relation found to exist between low CSF 5-HIAA and suicide attempt, in particular violent suicide attempt, both in depressed and in so-called nondepressed suicide attempters, the conclusion was drawn that decreased central 5-HT metabolism is related to (auto)aggression, rather than to depression. We challenged this conclusion and that for three reasons: Violent suicide attempt accumulates in certain types of depression making it impossible to conclude whether the biological variable relates to (auto)aggression or to that type of depression as such. Nondepressed suicide attempter is a diagnosis that should be based on presuicidal not on postsuicidal data, in order to avoid false-positive diagnoses. Suicide method is not a reliable index of seriousness of the attempt. Risk/rescue ratio should be used instead. Next the data are discussed that do support the hypothesis that diminished 5-HT metabolism in the brain is related to disregulation of aggression. Finally, the hypothesis is launched that both mood and aggression disorders are related to decreased 5-HT metabolism in the CNS. This would provide a biological explanation for the clinical observation that disorders in mood and in aggression often go hand in hand. Biological research of psychiatric disorders gains in informative value as the psychopathological analysis of the phenomena one studies is more comprehensive. Biological suicide research is no exception to this rule.