Self-biting induced by activation of L-type calcium channels in mice: serotonergic influences

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.

L-methionine and the L-type Ca2+ channel agonist BAY K 8644 collaboratively contribute to the reduction of depressive-like behavior in mice

The L-type Ca2+ channel (LTCC, also known as Cav1,2) is involved in the regulation of key neuronal functions, such as dendritic information integration, cell survival, and neuronal gene expression. Clinical studies have shown an association between L-type calcium channels and the onset of depression, although the precise mechanisms remain unclear. The development of depression results from a combination of environmental and genetic factors. DNA methylation, a significant epigenetic modification, plays a regulatory role in the pathogenesis of psychiatric disorders such as posttraumatic stress disorder (PTSD), depression, and autism. In our study, we observed reduced Dnmt3a expression levels in the hippocampal DG region of mice with LPS-induced depression compared to control mice. The antidepressant Venlafaxine was able to increase Dnmt3a expression levels. Conversely, Bay K 8644, an agonist of the L-type Ca2+ channel, partially ameliorated depression-like behaviors but did not elevate Dnmt3a expression levels. Furthermore, when we manipulated DNA methylation levels during Bay K 8644 intervention in depression-like models, we found that enhancing the expression of Dnmt3a could improve LPS-induced depression/anxiety-like behaviors, while inhibiting DNA methylation exacerbated anxiety-like behaviors, the combined use of BAY K 8644 and L-methionine can better improve depressive-like behavior. These findings indicate that DNA methylation plays a role in the regulation of depression-like behaviors by the L-type Ca2+ channel, and further research is needed to elucidate the interactions between DNA methylation and L-type Ca2+ channels.

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.

In vivo effects of abused 'bath salt' constituent 3,4-methylenedioxypyrovalerone (MDPV) in mice: drug discrimination, thermoregulation, and locomotor activity

In recent years, synthetic analogues of naturally occurring cathinone have emerged as psychostimulant-like drugs of abuse in commercial 'bath salt' preparations. 3,4-Methylenedioxypyrovalerone (MDPV) is a common constituent of these illicit products, and its structural similarities to the more well-known drugs of abuse 3,4-methylenedioxymethamphetamine (MDMA), and methamphetamine (METH) suggest that it may have similar in vivo effects to these substances. In these studies, adult male NIH Swiss mice were trained to discriminate 0.3 mg/kg MDPV from saline, and the interoceptive effects of a range of substitution doses of MDPV, MDMA, and METH were then assessed. In separate groups of mice, surgically implanted radiotelemetry probes simultaneously monitored thermoregulatory and locomotor responses to various doses of MDPV and MDMA, as a function of ambient temperature. We found that mice reliably discriminated the MDPV training dose from saline and that cumulative doses of MDPV, MDMA, and METH fully substituted for the MDPV training stimulus. All three drugs had similar ED(50) values in this procedure. Stimulation of motor activity was observed following administration of a wide range of MDPV doses (1-30 mg/kg), and the warm ambient temperature potentiated motor activity and elicited profound stereotypy and self-injurious behavior at 30 mg/kg. In contrast, MDPV-induced hyperthermic effects were observed in only the warm ambient environment. This pattern of effects is in sharp contrast to MDMA, where ambient temperature interacts with thermoregulation, but not locomotor activity. These studies suggest that although the interoceptive effects of MDPV are similar to those of MDMA and METH, direct effects on thermoregulatory processes and locomotor activity are likely mediated by different mechanisms than those of MDMA.

Self-mutilation induced by psychotropic substances: a systematic review

Self-mutilation (SM) not only occurs among patients with schizophrenia, personality disorders or transsexuality but also as a phenomenon induced by psychotropic substances (PS). We intended to find characteristics of patients at risk to perform SM induced by PS (SMIPS), frequent PS within this phenomenon and typical presentations of SMIPS. A systematic review of the literature (including Medline, the Cochrane Database of Systematic Reviews, the Cochrane Central Register of Controlled Trials and Scopus) was conducted. On October 2011 we identified 26 cases (23 publications) of SM related to PS. Majority of patients (85%) was male, mean age was 30 years (median 41 years). Seventy-three percent of patients developed SM subsequent to the use of one PS, 27% presented SM after the use of more than one PS. Alcohol (25%), hallucinogens (25%) and amphetamines (22%) were found most frequently among the reported substances. Major impairment was present in 80%. Our findings suggest male sex, young age, a previous history of abuse of PS and the current use of alcohol, hallucinogens or amphetamines to favour SMIPS.

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.

Treatment of a patient with traumatic brain injury-related severe self-injurious behavior

OBJECTIVE

Report a case of severe self-injurious behavior (SIB), paying special attention to treatment.

DESIGN

Case report.

PARTICIPANT

A 26-year-old woman (H.S.) 8 years post-traumatic brain injury with a history of severe SIB.

METHODS

H.S. was treated over a 22-week period with combined behavioral and psychopharmacological interventions.

RESULTS

Marked reduction in SIB was noted after the interventions were initiated.

CONCLUSION

Behavioral treatment and medications may be useful tools in the treatment of SIB after traumatic brain injury.

Expression of L-type calcium channel alpha(1)-1.2 and alpha(1)-1.3 subunits on rat sacral motoneurons following chronic spinal cord injury

In the presence of the monoamines serotonin and norepinephrine, motoneurons readily generate large persistent inward currents (PICs). The resulting plateau potentials amplify and sustain motor output. Monoaminergic input to the cord originates in the brainstem and the sharp reduction in monoamine levels that occurs following acute spinal cord injury greatly decreases motoneuron excitability. However, recent studies in the adult sacral cord of the rat have shown that motoneurons reacquire the ability to generate PICs and plateau potentials within 1-2 months following spinal transection. Ca(v)1.3 L-type calcium channels are involved in generating PICs in both healthy and injured animals. Additionally, expression of Ca(v)1.2 and Ca(v)1.3 L-type calcium channels is altered in several pathological conditions. Therefore, in this paper we analyzed the expression of L-type calcium channel alpha(1) subunits within the motoneuron pool following a complete transection of the spinal cord at the level of the sacral vertebra (S)2 segment. The analysis was done both caudally (S4 segment) and rostrally [thoracic vertebra (T)6 segment] from the injury site. The S4 segment was significantly reduced in diameter when compared with control animals, and this reduction was more evident in the white matter. Ca(v)1.2 alpha(1) subunit expression significantly increased (26%) in the motoneuron pool located caudally but not rostrally from the injury site. In contrast, the expression of Ca(v)1.3 alpha(1) subunit remained unchanged in both S4 and T6 segments. The differential expression of the two alpha(1) subunits in spinal injury suggests that Ca(v)1.2 and Ca(v)1.3 channels have different functions in neuronal adaptation following spinal cord injury.

The role of dopamine receptors in the neurobehavioral syndrome provoked by activation of L-type calcium channels in rodents

In rodents, activation of L-type calcium channels with +/-BayK 8644 causes an unusual behavioral syndrome that includes dystonia and self-biting. Prior studies have linked both of these behaviors to dysfunction of dopaminergic transmission in the striatum. The current studies were designed to further elucidate the relationship between +/-BayK 8644 and dopaminergic transmission in the expression of the behavioral syndrome. The drug does not appear to release presynaptic dopamine stores, since microdialysis of the striatum revealed dopamine release was unaltered by +/-BayK 8644. In addition, the behaviors were preserved or even exaggerated in mice or rats with virtually complete dopamine depletion. On the other hand, pretreatment of mice with D(3) or D(1/5) dopamine receptor antagonists attenuated the behavioral effects of +/-BayK 8644, while pretreatment with D(2) or D(4) antagonists had no effect. In D(3) receptor knockout mice, +/-BayK 8644 elicited both dystonia and self-biting, but these behaviors were less severe than in matched controls. In D(1) receptor knockout mice, behavioral responses to +/-BayK 8644 appeared exaggerated. These results argue that the behavioral effects of +/-BayK 8644 are not mediated by a presynaptic influence. Instead, the behaviors appear to result from a postsynaptic activation of the drug, which does not require but can be modified by D(3) or D(1/5) receptors.

Nifedipine suppresses self-injurious behaviors in animals

Self-injurious behavior is a common problem in many developmental disorders. The neurobiology of this behavior is not well understood, but the differing behavioral manifestations and associations with different disorders suggest that the underlying biological mechanisms are heterogeneous. The behavioral and biological heterogeneity is also evident in several animal models, where different manifestations can be provoked under different experimental conditions. Identifying commonalities among the different mechanisms is likely to be helpful in the design of treatments useful for the broadest populations of patients. The current studies reveal that nifedipine suppresses self-injurious behavior in 4 unrelated animal models: acute administration of high doses of +/-BayK 8644 or methamphetamine in mice, dopamine agonist treatment in rats with lesions of dopamine pathways during early development and repeated administration of pemoline in rats. The effect of nifedipine does not appear to be due to nonspecific mechanisms, such as sedation, since other classes of behaviors are unaffected or exaggerated. These results suggest that nifedipine may target a common biological mechanism in the expression of self-injurious behavior, and they suggest it should be considered in the treatment of self-injury in humans.

Expression of c-fos in the Brain after Activation of L-Type Calcium Channels

In rodents, administration of the L-type calcium channel activators, +/-Bay K 8644 and FPL 64176, causes an unusual neurobehavioral syndrome that includes dystonia and self-injurious biting. To determine the regional influence of these drugs in the brain, the induction of c-FOS was mapped after administration of these drugs to mice. In situ hybridization with an antisense riboprobe directed to c-FOS mRNA revealed widespread induction, with the highest levels in the striatum, cortex, hippocampus, locus coeruleus, and cerebellum. The induction of c-FOS mRNA was dose dependent, reached maximal expression approximately 60 min after drug treatment, and could be blocked by pretreatment with the L-type calcium channel antagonist, nifedipine. Immunohistochemical stains with an antibody directed to c-FOS protein revealed a pattern of induction similar to that obtained with in situ hybridization in most brain regions. These results demonstrate a very heterogeneous influence of L-type calcium channel activation in different brain regions, despite the nearly universal expression of these channels implied by more classical anatomical methods.

Self-biting induced by activation of L-type calcium channels in mice: dopaminergic influences

The L-type calcium channel activator +/-Bay K 8644 induces repetitive self-biting and self-injurious behavior in young mice. Since dopaminergic systems have been implicated in prior studies of these behaviors in both humans and animals, the present experiments were designed to test whether drugs influencing the dopaminergic systems could modify the behavioral responses to +/-Bay K 8644. The ability of +/-Bay K 8644 to provoke self-biting and self-injurious behavior was increased by amphetamine and GBR 12909, drugs that augment synaptic dopaminergic concentrations by blocking the reuptake and/or stimulating the release of dopamine. Conversely, self-biting and self-injurious behavior were decreased by tetrabenazine or reserpine, two drugs that deplete vesicular stores of dopamine. These results suggest that dopaminergic systems may play a role in the ability of +/-Bay K 8644 to provoke self-biting and self-injurious behavior.