Glutamate-mediated neuroplasticity in an animal model of self-injurious behaviour

The neuropathology of Self-Injurious Behavior: Studies using animal models

Self-injurious behavior is a debilitating characteristic that is highly prevalent in autism and other neurodevelopmental disorders. In these populations, self-injury has typically been interpreted in relation to behavioral reinforcement and/or sensory stimulation. However, self-injury is also commonly exhibited by people with a variety of neuropsychiatric disorders, where it is typically described in relation to emotional regulation and the presence or absence of suicidal ideation. Interestingly, self-injury has also been documented in many non-human animal species, especially when exposed to early environmental deprivation, isolation, and distress. Despite the propensity of animals to self-injure under adverse conditions, animal models of self-injury have not been the focus of much research, and translation of the data from these models has largely been limited to autism and neurodevelopmental disorders. This review summarizes evidence that common biological and environmental mechanisms may contribute to vulnerability for self-injury in neurodevelopmental disorders, psychiatric disorders, and distressed animals, and that investigations using animal models may be highly beneficial when considering self-injury as a behavioral phenotype that exists across diagnostic categories. Investigations using animal models have revealed that individual differences in stress responses and anxiety-related behavior contribute to vulnerability for self-injury. Animal models have implicated dysregulation of monoaminergic, glutamatergic, and other neurotransmitter systems in expression of self-injury, and these models have suggested neural targets for pharmacotherapy that have potential relevance for diverse clinical populations.

A mink (Neovison vison) model of self-injury: Effects of CBP-CREB axis on neuronal damage and behavior

Objective

Self-injurious behavior (SIB) is a clinically challenging problem in the general population and several clinical disorders. However, the precise molecular mechanism of SIB is still not clear. In this paper, the systematic investigation of the genesis and development of SIB is conducted based on behavioral and pathophysiology studies in mink (Neovison vison) models.

Method

The night-vision video was used to observe the mink behavior, and the duration was a month. HE stain was performed to characterize the pathology change in the brain of a mink. IHC assay was performed to conduct the protein level detection of Iba-1, p-CREB, CBP, and p300 in the brain tissues. Elisa assay was used to examine the levels of NfL and NfH in serum and CSF of mink. The qRT-PCR assay was used to detect the expression of Bcl-2, NOR1, FoxO4, c-FOS, CBP, and p300 in brain tissues. Western blot was used to detect the protein levels of p-CREB, CBP, and p300 in brain tissues. We also used Evans Blue as a tracer to detect whether the blood-brain barrier was impaired in the brain of mink.

Result

The behavioral test, histopathological and molecular biology experiments were combined in this paper, and the results showed that CBP was related to SIB. Mechanism analysis showed that the dysregulation of CBP in brain-activated CREB signaling will result in nerve damage of the brain and SIB symptoms in minks. More importantly, the CBP-CREB interaction inhibitor might help relieve SIB and nerve damage in brain tissues.

Conclusion

Our results illustrate that the induction of CBP and the activation of CREB are novel mechanisms in the genesis of SIB. This finding indicates that the CBP-CREB axis is critical for SIB and demonstrates the efficacy of the CBP-CREB interaction inhibitor in treating these behaviors.

Low-normal doses of methiopropamine induce aggressive behaviour in mice

Recreational use of illicit methiopropamine (MPA) is a public health concern because it produces neurochemical effects comparable with those induced by methamphetamine (METH). The present study investigated the effects of MPA on the expression of an aggressive behaviour. Eighty CD-1 male mice, after receiving intraperitoneal injection of saline, MPA (0.01-10 mg/kg), METH (0.01-10 mg/kg), or AMPH (0.01-10 mg/kg), once a week over a 5-week period, underwent the resident-intruder test and spontaneous locomotor activity measurement. Results showed that all psychostimulants induce aggressive behaviour even at low doses, with a dose-dependent increase and a time-dependent sensitisation. MPA potency was similar to METH and superior to AMPH. Therefore, MPA-induced aggressive behaviour may appear even at MPA dosages free of cardiovascular or other behavioural adverse effects and could become a non-intentional side effect that users experience after increasing and repeating MPA consumption.

The Pemoline Model of Self-Injurious Behavior: An Update

Neurodevelopmental disorders typically comprise a complex constellation of behavioral symptoms and neurochemical abnormalities. However, many of the symptoms are inconsistently expressed within any one particular patient group or overlap between patient groups. In other words, there is usually heterogeneity of symptoms between diagnostic groups, and there is often partial homogeneity of symptoms across these groups. These include cognitive deficits, emotional lability, and perseverative or aberrant behaviors. Animal models of neurodevelopmental disorders typically reproduce or mimic specific genetic, neurochemical, and/or behavioral sequelae, although they typically fail to replicate the entire spectrum of biological and behavioral characteristics. Indeed, it may be impractical or even impossible to model the entire spectrum of characteristics of a disorder in any single animal model. A focus on one or more specific behavioral characteristics that occur in multiple neurodevelopmental disorders (e.g., self-injury) may be a fruitful strategy. The development of these behaviorally focused models may yield increased understanding of the endogenous and environmental factors that confer vulnerability for aberrant behaviors that commonly occur in these disorders. One such behaviorally focused animal model is the pemoline model of self-injurious behavior.

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.

The role of neurotensin in vulnerability for self-injurious behaviour: studies in a rodent model

BACKGROUND

Self-injurious behaviour is a debilitating characteristic that is commonly expressed in people with autism and other neurodevelopmental disorders, but the neurobiological basis of this maladaptive behaviour is not understood. Abnormal dopaminergic and glutamatergic neurotransmission has been implicated, especially in relation to basal ganglia and mesocorticolimbic circuits. As neurotensin is an important modulator of dopamine and glutamate in these circuits, we investigated its potential role in vulnerability for self-injury, using the pemoline model in rats.

METHODS

Male Long-Evans rats were injected once daily with the psychostimulant pemoline or peanut oil vehicle on each of five consecutive days. Self-injury was quantified by measuring the area of injuries for each rat on each day of the experiment. Each brain was harvested on the sixth day, and the striatum and ventral tegmentum were dissected. Neurotensin-like immunoreactivity was quantified by radioimmunoassay from the dissected brain regions of some of the rats. Membrane and intracellular neurotensin receptor NTS₁ were assayed from the striata of the remaining pemoline-treated or vehicle-treated rats by Western blot. In an additional experiment, male Long-Evans rats were treated with daily injections of vehicle or pemoline, and the NTS₁ neurotensin receptor agonist PD149163 or the NTS₁ receptor antagonist SR48692 (or respective vehicle solutions) was co-administered twice daily throughout the pemoline treatment regimen. The areas of injured tissue were measured, and the duration of self-injurious oral contact was quantified by video-recorded time samples throughout each day.

RESULTS

Striatal neurotensin immunoreactivity was found to be significantly higher in pemoline-treated than in vehicle-treated rats. Moreover, both membrane-bound and intracellular levels of NTS₁ receptor were significantly higher in the striata of pemoline-treated rats than in the striata of the vehicle-treated controls. When the NTS₁ receptor agonist PD149163 was co-administered during the pemoline treatment regimen, it prolonged the daily durations of self-injurious oral contact and increased the severity of the injuries in the self-injurious rats. Conversely, co-administration of the NTS₁ receptor antagonist SR48692 diminished the daily durations of self-injurious oral contact and decreased the severity of the injuries.

CONCLUSIONS

The elevation of striatal neurotensin immunoreactivity during pemoline treatment, coupled with the effects of the NTS₁ agonist and antagonist, suggests that neurotensin transmission in the striatum may be an important modulator of self-injurious behaviour in the pemoline model. Overall, the convergence of the behavioural and biochemical findings suggests that neurotensin signalling could be an important target for pharmacotherapeutic interventions for self-injurious behaviour.

Effect of the Glutamate NMDA Receptor Antagonist Memantine as Adjunctive Treatment in Borderline Personality Disorder: An Exploratory, Randomised, Double-Blind, Placebo-Controlled Trial

BACKGROUND

Borderline personality disorder (BPD) is a complex, severe and highly stigmatised psychiatric illness. Several lines of evidence highlight the causal link between chronic stress, glucocorticoid response to stress and glutamatergic overactivity as a key event in the pathophysiology of BPD. Therefore, molecular mechanisms capable of regulating glutamate excitotoxicity represent novel and potentially promising treatment targets. Memantine-HCl is a voltage-dependent N-methyl-D-aspartate (NMDA) receptor 'channel blocker' that selectively blocks pathological glutamate overactivity.

OBJECTIVE

The aim of the current study was to determine if memantine can improve BPD symptoms.

METHOD

An 8-week, double-blind, placebo-controlled trial of adjunctive memantine to treatment as usual was conducted. Treatment as usual comprised antidepressants (selective serotonin reuptake inhibitors, tricyclic antidepressants, monoamine oxidase inhibitors, noradrenergic and specific serotonin antagonists and serotonin noradrenaline reuptake inhibitors), mood stabilisers and antipsychotics, as well as psychotherapy and other psychosocial interventions. Sixteen participants received oral placebo while 17 participants received daily oral memantine 10 mg for 7 days, with subsequent titration to daily oral memantine 20 mg. Eligibility criteria included men and women aged between 16-65 years, with a diagnosis of BPD according to the Diagnostic Interview for Borderline Patients. Primary outcome measures included the Zanarini Rating Scale for Borderline Personality Disorder (ZAN-BPD), assessed fortnightly. Secondary measures included an adverse effect questionnaire administered fortnightly to assess adverse effects known to be related to memantine use.

RESULTS

According to intention-to-treat, latent growth curve analyses, a significant change in total score of ZAN-BPD symptom severity was observed in the memantine group at 20 mg/daily across time, compared with placebo (p = 0.02). No adverse effects were significantly more frequent among participants receiving active memantine than among those receiving placebo.

CONCLUSION

Memantine at a 20-mg daily dose is a well tolerated drug that can improve BPD symptomatology and may be a promising novel therapeutic for its treatment. Further studies are needed to explore the efficacy of memantine versus placebo, as well as in comparison with other potential treatments for BPD. ClinicalTrials.gov identifier: NCT02097706.

The role of anxiety in vulnerability for self-injurious behaviour: studies in a rodent model

Self-injurious behaviour (SIB) is a debilitating characteristic that is highly prevalent in autism and other neurodevelopmental disorders. Pathological anxiety is also common, and there are reports of comorbid anxiety and self-injury in some children. We have investigated potential interactions between anxiety and self-injury, using a rat model of pemoline-induced self-biting. In one experiment, rats were pre-screened for trait anxiety by measuring expression of anxiety-related behaviour on the elevated plus maze and open field emergence test. The rats were then treated with pemoline once daily for ten days, and vulnerability for pemoline-induced self-injury was evaluated. This revealed modest correlations between innate levels of anxiety-related behaviour in the open field test (time in the start box, and latency to enter the open field), and vulnerability for pemoline-induced self-biting (total duration of self-injurious oral contact, and total size of tissue injury). Measures in the elevated plus maze were not significantly correlated with vulnerability for pemoline-induced self-injury. In a second experiment, rats were treated with the beta-carboline FG 7142 twice daily, during 5days of treatment with pemoline. The rats that were treated with this anxiogenic drug exhibited greater duration of self-injurious oral contact, and larger injuries than vehicle-treated controls did. Overall, these results suggest that anxiety may contribute to the etiology and/or expression of self-injurious behaviour, and indicate that further research is warranted.

Multidisciplinary assessment and treatment of self-injurious behavior in autism spectrum disorder and intellectual disability: integration of psychological and biological theory and approach

The objective of this review is to consider the psychological (largely behavioral) and biological [neurochemical, medical (including genetic), and pharmacological] theories and approaches that contribute to current thinking about the etiology and treatment of self-injurious behavior (SIB) in individuals with autism spectrum disorder and/or intellectual disability. Algorithms for the assessment and treatment of SIB in this context, respectively, from a multidisciplinary, integrative perspective are proposed and challenges and opportunities that exist in clinical and research settings are discussed.

Self-injurious behaviour in autistic children: a neuro-developmental theory of social and environmental isolation

RATIONALE

Self-injurious behaviour is not one of the three core symptoms that define autism. However, children on the autism spectrum appear to be particularly vulnerable. Afflicted children typically slap their faces, punch or bang their heads, and bite or pinch themselves. These behaviours can be extremely destructive, and they interfere with normal social and educational activities. However, the neurobiological mechanisms that confer vulnerability in children with autism have not been adequately described.

OBJECTIVES

This review explores behavioural and neurobiological characteristics of children with autism that may be relevant for an increased understanding of their vulnerability for self-injurious behaviour.

METHODS

Behavioural characteristics that are co-morbid for self-injurious behaviour in children with autism are examined. In addition, the contributions of social and environmental deprivation in self-injurious institutionalized orphans, isolated rhesus macaques, and additional animal models are reviewed.

RESULTS

There is extensive evidence that social and environmental deprivation promotes self-injurious behaviour in both humans (including children with autism) and animal models. Moreover, there are multiple lines of convergent neuroanatomical, neurophysiological, and neurochemical data that draw parallels between self-injurious children with autism and environmentally deprived humans and animals.

CONCLUSIONS

A hypothesis is presented that describes how the core symptoms of autism make these children particularly vulnerable for self-injurious behaviour. Relevant neurodevelopmental pathology is described in cortical, limbic, and basal ganglia brain regions, and additional research is suggested.

Pain and suicidality: insights from reward and addiction neuroscience

Suicidality is exceedingly prevalent in pain patients. Although the pathophysiology of this link remains unclear, it may be potentially related to the partial congruence of physical and emotional pain systems. The latter system's role in suicide is also conspicuous during setbacks and losses sustained in the context of social attachments. Here we propose a model based on the neural pathways mediating reward and anti-reward (i.e., allostatic adjustment to recurrent activation of the reward circuitry); both are relevant etiologic factors in pain, suicide and social attachments. A comprehensive literature search on neurobiology of pain and suicidality was performed. The collected articles were critically reviewed and relevant data were extracted and summarized within four key areas: (1) physical and emotional pain, (2) emotional pain and social attachments, (3) pain- and suicide-related alterations of the reward and anti-reward circuits as compared to addiction, which is the premier probe for dysfunction of these circuits and (4) mechanistically informed treatments of co-occurring pain and suicidality. Pain-, stress- and analgesic drugs-induced opponent and proponent states of the mesolimbic dopaminergic pathways may render reward and anti-reward systems vulnerable to sensitization, cross-sensitization and aberrant learning of contents and contexts associated with suicidal acts and behaviors. These findings suggest that pain patients exhibit alterations in the brain circuits mediating reward (depressed function) and anti-reward (sensitized function) that may affect their proclivity for suicide and support pain and suicidality classification among other "reward deficiency syndromes" and a new proposal for "enhanced anti-reward syndromes". We suggest that interventions aimed at restoring the balance between the reward and anti-reward networks in patients with chronic pain may help decreasing their suicide risk.

The pemoline model of self-injurious behaviour

Traditional models of neuropsychiatric disorders consist of attempts to replicate the broad spectrum of behavioural and neurochemical sequelae that characterize a specific disorder. However, these disorders comprise complex constellations of symptoms, including emotional instability, perseverative thoughts, and aberrant behaviours. Close examination often reveals heterogeneity of symptom expression within patient groups and homogeneity in expression of specific symptoms across diagnostic categories. Accordingly, it may not be possible to model the entire spectrum of characteristics for any one of these disorders in any single animal model. A focus on one or more specific behavioural characteristics (e.g. self-injury) may be a more fruitful strategy. Development of behaviourally focused models yields increased understanding of the genetic basis and biochemical abnormalities that underlie specific psychiatric dysfunctions. Furthermore, by revealing pathophysiology that underlies specific disease characteristics, behaviourally focused models improve translational power and help to identify targets for effective pharmacotherapies. One such behaviourally focused animal model is the pemoline model of self-injurious behaviour.

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.

Individual differences in vulnerability for self-injurious behavior: studies using an animal model

Self-injurious behavior (SIB) is a debilitating characteristic that is prevalent across a broad spectrum of neurodevelopmental disorders. In most of these disorders, some individuals exhibit SIB, whereas others do not. However, the neurobiological mechanisms that confer vulnerability are virtually unexplored. We examined innate characteristics that contribute to vulnerability or resistance for SIB in an animal model of the behavioral pathology. Eighteen outbred Long-Evans rats were screened for behavioral responsiveness to the mild stress of a novel environment. The rats were then categorized as high responders (HR; those rats that had the highest locomotor counts) or low responders (LR; those rats that had lower locomotor counts) by median split. All the rats were then given daily injections of the indirect monoamine agonist pemoline (150 mg/kg/day) for 10 days, and self-injury was evaluated. All 9 HR rats and 5 of the 9 LR rats exhibited self-injury. The HR rats spent more time self-injuring, injured more body sites, and caused larger areas of tissue damage than the LR rats did. Furthermore, the behavioral responsiveness to novelty stress was significantly correlated with each of these measures of self-injury. The HR rats did not exhibit substantially enhanced responses on other measures of psychostimulant action (stereotypy, grooming, locomotion, rearing). Accordingly, vulnerability to develop pemoline-induced SIB is positively correlated with, and can be predicted based upon, a behavioral measure of innate stress responsiveness. These findings suggest that characteristics that are common in developmental disorders may help predispose afflicted individuals to self-injure. The findings also extend the variety of behavioral pathologies (e.g. drug addiction) for which the HR/LR model predicts vulnerability.