Stuttering associated with a pathogenic variant in the chaperone protein cyclophilin 40.

Stuttering is a common speech disorder that interrupts speech fluency and tends to cluster in families. Typically, stuttering is characterized by speech sounds, words or syllables which may be repeated or prolonged and speech that may be further interrupted by hesitations or 'blocks'. Rare variants in a small number of genes encoding lysosomal pathway proteins have been linked to stuttering. We studied a large four-generation family in which persistent stuttering was inherited in an autosomal dominant manner with disruption of the cortico-basal-ganglia-thalamo-cortical network found on imaging. Exome sequencing of three affected family members revealed the PPID c.808C>T (p.Pro270Ser) variant that segregated with stuttering in the family. We generated a Ppid p.Pro270Ser knock-in mouse model and performed ex vivo imaging to assess for brain changes. Diffusion-weighted MRI in the mouse revealed significant microstructural changes in the left corticospinal tract, as previously implicated in stuttering. Quantitative susceptibility mapping also detected changes in cortico-striatal-thalamo-cortical loop tissue composition, consistent with findings in affected family members. This is the first report to implicate a chaperone protein in the pathogenesis of stuttering. The humanized Ppid murine model recapitulates network findings observed in affected family members.

Reward motivation and cognitive flexibility in tau null-mutation mice.

The reduction of tau or hyperphosphorylated tau (p-tau) has been proposed as a therapeutic strategy for Alzheimer's disease (AD) and frontotemporal dementia (FTD). Cognitive decline and sleep-wake dysregulation seen in AD and FTD patients are mimicked in transgenic and null-mutation mouse models of tauopathy. Alterations in the reward system are additional symptoms of AD and FTD. However, the role of tau in reward processes is not well understood. The present study aimed to examine reward and reward-motivated cognitive processes in male and female tau knockout (tau-/-) and wild-type mice using progressive ratio and reversal learning tasks. Tau-/- mice were heavier, ate more in the home cage, and reached criterion in operant lever training faster than wild-type mice. Tau-/- mice had a higher breakpoint in progressive ratio but were unimpaired in reversal learning or reward sensitivity. These data indicate that tau loss of function alters reward processing. This may help to explain aberrant reward-related behaviors in tauopathy patients and highlights a potentially important area for consideration in the development of anti-tau therapies.

Paroxysmal and cognitive phenotypes in Prrt2 mutant mice.

Mutations in proline-rich transmembrane protein 2 (PRRT2) cause a range of episodic disorders that include paroxysmal kinesigenic dyskinesia and benign familial infantile epilepsy. Mutations are generally loss of function and include the c649dupC frameshifting mutation that is present in around 80% of affected individuals. To investigate how Prrt2 loss of function mutations causes disease, we performed a phenotypic investigation of a transgenic Prrt2 knockout (Prrt2 KO) mouse. We observed spontaneous paroxysmal episodes with behavioural features of both seizure and movement disorders, as well as unexplained deaths in KO and HET animals. KO mice showed spatial learning deficits in the Morris water maze, as well as gait abnormalities in the quantitative Digigait analysis; both of which may be representative of the more severe phenotypes experienced by homozygous patients. These findings extend the described phenotypes of Prrt2 mutant mice, further confirming their utility for in vivo investigation of the role of Prrt2 mutations in episodic diseases.

Separating Probability and Reversal Learning in a Novel Probabilistic Reversal Learning Task for Mice.

The exploration/exploitation tradeoff - pursuing a known reward vs. sampling from lesser known options in the hope of finding a better payoff - is a fundamental aspect of learning and decision making. In humans, this has been studied using multi-armed bandit tasks. The same processes have also been studied using simplified probabilistic reversal learning (PRL) tasks with binary choices. Our investigations suggest that protocols previously used to explore PRL in mice may prove beyond their cognitive capacities, with animals performing at a no-better-than-chance level. We sought a novel probabilistic learning task to improve behavioral responding in mice, whilst allowing the investigation of the exploration/exploitation tradeoff in decision making. To achieve this, we developed a two-lever operant chamber task with levers corresponding to different probabilities (high/low) of receiving a saccharin reward, reversing the reward contingencies associated with levers once animals reached a threshold of 80% responding at the high rewarding lever. We found that, unlike in existing PRL tasks, mice are able to learn and behave near optimally with 80% high/20% low reward probabilities. Altering the reward contingencies towards equality showed that some mice displayed preference for the high rewarding lever with probabilities as close as 60% high/40% low. Additionally, we show that animal choice behavior can be effectively modelled using reinforcement learning (RL) models incorporating learning rates for positive and negative prediction error, a perseveration parameter, and a noise parameter. This new decision task, coupled with RL analyses, advances access to investigate the neuroscience of the exploration/exploitation tradeoff in decision making.

Mice Lacking Brinp2 or Brinp3, or Both, Exhibit Behaviors Consistent with Neurodevelopmental Disorders.

Background:Brinps 1-3, and Astrotactins (Astn) 1 and 2, are members of the Membrane Attack Complex/Perforin (MACPF) superfamily that are predominantly expressed in the mammalian brain during development. Genetic variation at the human BRINP2/ASTN1 and BRINP1/ASTN2 loci has been implicated in neurodevelopmental disorders. We, and others, have previously shown that Brinp1-/- mice exhibit behavior reminiscent of autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD). Method: We created Brinp2-/- mice and Brinp3-/- mice via the Cre-mediated LoxP system to investigate the effect of gene deletion on anatomy and behavior. Additionally, Brinp2-/-Brinp3-/- double knock-out mice were generated by interbreeding Brinp2-/- and Brinp3-/- mice. Genomic validation was carried out for each knock-out line, followed by histological, weight and behavioral examination. Brinp1-/-Brinp2-/-Brinp3-/- triple knock-out mice were also generated by crossing Brinp2/3 double knock-out mice with previously generated Brinp1-/- mice, and examined by weight and histological analysis. Results:Brinp2-/- and Brinp3-/- mice differ in their behavior: Brinp2-/- mice are hyperactive, whereas Brinp3-/- mice exhibit marked changes in anxiety-response on the elevated plus maze. Brinp3-/- mice also show evidence of altered sociability. Both Brinp2-/- and Brinp3-/- mice have normal short-term memory, olfactory responses, pre-pulse inhibition, and motor learning. The double knock-out mice show behaviors of Brinp2-/- and Brinp3-/- mice, without evidence of new or exacerbated phenotypes. Conclusion:Brinp3 is important in moderation of anxiety, with potential relevance to anxiety disorders. Brinp2 dysfunction resulting in hyperactivity may be relevant to the association of ADHD with chromosome locus 1q25.2. Brinp2-/- and Brinp3-/- genes do not compensate in the mammalian brain and likely have distinct molecular or cell-type specific functions.

Brinp1(-/-) mice exhibit autism-like behaviour, altered memory, hyperactivity and increased parvalbumin-positive cortical interneuron density.

BACKGROUND: BMP/RA-inducible neural-specific protein 1 (Brinp1) is highly conserved in vertebrates, and continuously expressed in the neocortex, hippocampus, olfactory bulb and cerebellum from mid-embryonic development through to adulthood. METHODS: Brinp1 knock-out (Brinp1(-/-)) mice were generated by Cre-recombinase-mediated removal of the third exon of Brinp1. Knock-out mice were characterised by behavioural phenotyping, immunohistochemistry and expression analysis of the developing and adult brain. RESULTS: Absence of Brinp1 during development results in a behavioural phenotype resembling autism spectrum disorder (ASD), in which knock-out mice show reduced sociability and changes in vocalisation capacity. In addition, Brinp1(-/-) mice exhibit hyper-locomotor activity, have impaired short-term memory, and exhibit poor reproductive success. Brinp1(-/-) mice show increased density of parvalbumin-expressing interneurons in the adult mouse brain. Brinp1(-/-) mice do not show signs of altered neural precursor proliferation or increased apoptosis during late embryonic brain development. The expression of the related neuronal migration genes Astn1 and Astn2 is increased in the brains of Brinp1(-/-) mice, suggesting that they may ameliorate the effects of Brinp1 loss. CONCLUSIONS: Brinp1 plays an important role in normal brain development and function by influencing neuronal distribution within the cortex. The increased cortical PV-positive interneuron density and altered behaviour of Brinp1(-/-) mice resemble features of a subset of human neurological disorders; namely autism spectrum disorder (ASD) and the hyperactivity aspect of attention deficit hyperactivity disorder (ADHD).

'Neonatal' Nav1.2 reduces neuronal excitability and affects seizure susceptibility and behaviour.

Developmentally regulated alternative splicing produces 'neonatal' and 'adult' isoforms of four Na(+) channels in human brain, NaV1.1, NaV1.2, NaV1.3 and NaV1.6. Heterologously expressed 'neonatal' NaV1.2 channels are less excitable than 'adult' channels; however, functional importance of this difference is unknown. We hypothesized that the 'neonatal' NaV1.2 may reduce neuronal excitability and have a seizure-protective role during early brain development. To test this hypothesis, we generated NaV1.2(adult) mice expressing only the 'adult' NaV1.2, and compared the firing properties of pyramidal cortical neurons, as well as seizure susceptibility, between the NaV1.2(adult) and wild-type (WT) mice at postnatal day 3 (P3), when the 'neonatal' isoform represents 65% of the WT NaV1.2. We show significant increases in action potential firing in NaV1.2(adult) neurons and in seizure susceptibility of NaV1.2(adult) mice, supporting our hypothesis. At postnatal day 15 (P15), when 17% of the WT NaV1.2 is 'neonatal', the firing properties of NaV1.2(adult) and WT neurons converged. However, inhibitory postsynaptic currents in NaV1.2(adult) neurons were larger and the expression level of Scn2a mRNA was 24% lower compared with the WT. The enhanced seizure susceptibility of the NaV1.2(adult) mice persisted into adult age. The adult NaV1.2(adult) mice also exhibited greater risk-taking behaviour. Overall, our data reveal a significant impact of 'neonatal' NaV1.2 on neuronal excitability, seizure susceptibility and behaviour and may contribute to our understanding of NaV1.2 roles in health and diseases such as epilepsy and autism.

Quantification of phosphorylated cAMP-response element-binding protein expression throughout the brain of amphetamine-sensitized rats: activation of hypothalamic orexin A-containing neurons.

In the present study, using rats, we have examined acute, contextual, and sensitized patterns of activated or phosphorylated cAMP response element-binding protein (pCREB) expression in parallel, assaying across multiple nuclei that have been implicated in addiction. The paradigm used included a comparison of pretreatment dose of amphetamine upon patterns of cellular activation, following rechallenge. Because efferent orexinergic projections synapse on many targets through the mammalian brain, including mesotelencephalic regions and limbic systems involved in drug reward and reinforcement, we examined for coexpression of pCREB or c-Fos double labeling within orexin A-immunopositive neurons following sensitization. Acute challenge with amphetamine (1.5 mg/kg i.p.) resulted in an increase in the number of pCREB-immunoreactive (-IR) cells within the substantia nigra but a decrease of pCREB-IR cells in the central and medial subnuclei of the amygdala. Contextual re-exposure to the drug treatment environment altered pCREB expression, particularly in the basal ganglia and hypothalamus, although these effects were dictated by pretreatment dose of amphetamine. Sensitization to amphetamine resulted in robust increases in pCREB-IR cell numbers in the basal ganglia and lateral septum of rats that had been pretreated with high-dose (10 mg/kg i.p.) but not low-dose (2 mg/kg i.p.) amphetamine, despite a similar behavioral response. Orexin A-containing cells in the hypothalamus of sensitized rats did not coexpress pCREB; however, these cells double-labeled for c-Fos and orexin A. These data suggest that orexinergic neurons are activated during the expression of behavioral sensitization, although in a heterogenous manner with regard to afferent topologies and functional roles in the nervous system.