A forward genetic screen identifies Dolk as a regulator of startle magnitude through the potassium channel subunit Kv1.1

The acoustic startle response is an evolutionarily conserved avoidance behavior. Disruptions in startle behavior, particularly startle magnitude, are a hallmark of several human neurological disorders. While the neural circuitry underlying startle behavior has been studied extensively, the repertoire of genes and genetic pathways that regulate this locomotor behavior has not been explored using an unbiased genetic approach. To identify such genes, we took advantage of the stereotypic startle behavior in zebrafish larvae and performed a forward genetic screen coupled with whole genome analysis. We uncovered mutations in eight genes critical for startle behavior, including two genes encoding proteins associated with human neurological disorders, Dolichol kinase (Dolk), a broadly expressed regulator of the glycoprotein biosynthesis pathway, and the potassium Shaker-like channel subunit Kv1.1. We demonstrate that Kv1.1 and Dolk play critical roles in the spinal cord to regulate movement magnitude during the startle response and spontaneous swim movements. Moreover, we show that Kv1.1 protein is mislocalized in dolk mutants, suggesting they act in a common genetic pathway. Combined, our results identify a diverse set of eight genes, all associated with human disorders, that regulate zebrafish startle behavior and reveal a previously unappreciated role for Dolk and Kv1.1 in regulating movement magnitude via a common genetic pathway.

Postural freezing foretells startle-potentiation in a human fear-conditioning paradigm

Freezing to impending threat is a core defensive response. It has been studied primarily using fear-conditioning in non-human animals, thwarting advances in translational human anxiety-research. Here we examine postural freezing as a human conditioning-index for translational anxiety-research. We show (n=28) that human freezing is highly sensitive to fear-conditioning, generalizes to ambiguous contexts, and amplifies with threat-imminence. Intriguingly, stronger parasympathetically-driven freezing under threat, but not sympathetically-mediated skin conductance, predicts subsequent startle magnitude. These results demonstrate that humans show fear-conditioned animal-like freezing responses, known to aid in active preparation for unexpected attack, and that freezing captures real-life anxiety-expression. Conditioned freezing offers a promising new, non-invasive, and continuous, readout for human fear-conditioning, paving the way for future translational studies into human fear and anxiety.

The Effects of Brief Mindfulness Training on Attentional Processes: Mindfulness Increases Prepulse Facilitation but Not Prepulse Inhibition

Mindfulness is intentional focus of one’s attention on emotions, thoughts, or sensations occurring in the present moment with a nonjudgmental attitude. Recently there has been increased interest in the effects of mindfulness practice on psychological processes such as concentration, focus, and attention. In the present study, a prepulse inhibition/facilitation (PPI/PPF) paradigm was employed to investigate the effect of brief mindfulness practice on automatic attention regulation processes. PPI occurs when a relatively weak prepulse (e.g., a tone) is presented 30–500 ms before a startle-inducing stimulus, and reduces the magnitude of the startle response. Prepulse facilitation (PPF) is the increase in startle magnitude when the prepulse is presented 500 ms or more before the startle-eliciting stimulus. In the present study, the effect of engaging in a 23-min mindfulness exercise on PPI and PPF was investigated. Participants listened to either a mindfulness instruction (mindfulness group) or relaxing music (control group). In a PPI/PPF pretest and posttest, a startle-eliciting noise was presented at lead intervals of 60, 120, and 2,000 ms. Results showed that engaging in brief mindfulness practice increased prepulse facilitation at the 2,000 ms lead interval in the posttest compared to the pretest. The amount of PPI did not differ between tests.

A forward genetic screen identifies Dolk as a regulator of startle magnitude through the potassium channel subunit Kv1.1

The acoustic startle response is an evolutionary conserved avoidance behavior. Disruptions in startle behavior, in particular startle magnitude, are a hallmark of several human neurological disorders. While the neural circuitry underlying startle behavior has been studied extensively, the repertoire of genes and genetic pathways that regulate this locomotor behavior has not been explored using an unbiased genetic approach. To identify such genes, we took advantage of the stereotypic startle behavior in zebrafish larvae and performed a forward genetic screen coupled with whole genome analysis. This identified mutants in eight genes critical for startle behavior, including two genes encoding proteins associated with human neurological disorders, Dolichol kinase (Dolk), a broadly expressed regulator of the glycoprotein biosynthesis pathway, and the potassium Shaker-like channel subunit Kv1.1. We demonstrate that Kv1.1 acts independently of supraspinal inputs to regulate locomotion, suggesting its site of action is within spinal circuitry. Moreover, we show that Kv1.1 protein is mis-localized in dolk mutants, suggesting they act in a common genetic pathway to regulate movement magnitude. Combined, our results identify a diverse set of eight genes all associated with human disorders that regulate zebrafish startle behavior and reveal a previously unappreciated role for Dolk and Kv1.1 in regulating movement magnitude via a common genetic pathway.Author summaryUnderlying all animal behaviors are neural circuits, which are controlled by numerous molecular pathways that direct neuron development and activity. To identify and study these molecular pathways that control behavior, we use a simple vertebrate behavior, the acoustic startle response, in the larval zebrafish. In response to an intense noise, larval zebrafish will quickly turn and swim away to escape. From a genetic screen, we have identified a number of mutants that behave in abnormal ways in response to an acoustic stimulus. We cloned these mutants and identified eight genes that regulate startle behavior. All eight genes are associated with human disorders, and here we focus on two genes, dolk and kcna1a, encoding Dolk, a key regulator of protein glycosylation, and the potassium channel Kv1.1, respectively. We demonstrate that loss of dolk or kcna1a causes larval zebrafish to perform exaggerated swim movements and that Dolk is required for Kv1.1 protein localization to axons of neurons throughout the nervous system, providing strong evidence that dolk and kcna1a act in a common molecular pathway. Combined, our studies provide new insights into the genetic regulation of startle behavior.

Do young adolescents with first-episode psychosis or ADHD show sensorimotor gating deficits?

BackgroundEarly identification is important for patients with early-onset schizophrenia (SZ). Assessment of (candidate) endophenotypic markers for SZ, such as prepulse inhibition of the startle reflex (PPI), may help distinguish between the early-onset SZ and other psychiatric disorders. We explored whether PPI deficits usually seen in adult-onset SZ are present in young adolescents with either early-onset psychosis or attention deficit/hyperactivity disorder (ADHD).MethodsTwenty-five adolescents with first-episode, non-affective psychosis (FEP), 28 adolescents with ADHD and 43 healthy controls (HC), aged 12–17 years, were assessed with an auditory PPI paradigm.ResultsNo significant group differences were found in PPI. However, when the FEP group was divided into those already diagnosed with SZ (n = 13) and those without (N-SZ) (n = 12), and all four groups (SZ, N-SZ, ADHD and HC) were compared on percentage PPI in the 85/60 trials, significantly less PPI was found in patients with SZ than in the HC as well as the ADHD group. No significant group differences were found in explorative analyses on the other trial types. Additionally, startle magnitude was significantly higher in SZ than in N-SZ patients.ConclusionYoung adolescents with SZ showed sensorimotor gating deficits similar to those usually found in adults with SZ and had larger startle magnitude than patients with other types of non-affective early-onset psychosis. No sensorimotor gating deficits were found in adolescents with ADHD. Our findings support the theory that deficient PPI is endophenotypic for SZ.

The neurofunctional basis of affective startle modulation in humans – evidence from combined facial EMG-fMRI

The startle reflex, a protective response elicited by an immediate, unexpected sensory event, ispotentiatedwhen evoked during threat andinhibitedduring safety. In contrast to skin conductance responses or pupil dilation, modulation of the startle reflex is valence-specific and consideredthecross-species translational tool for defensive responding.Rodent models implicate a modulatory pathway centering on the brainstem (i.e., nucleus reticularis pontis caudalis, PnC) and the centromedial amygdala (CeM) as key hubs for flexibly integrating valence information into differential startle magnitude.We employed innovative combined EMG-fMRI measurements in two independent experiments and samples and provide converging evidence for the involvement of these key regions in the modulatory acoustic startle reflex pathway in humans. Furthermore, we provide the crucial direct link between EMG startle eye-blink magnitude and neural response strength.We argue that startle-evoked amygdala responding and its affective modulation may hold promise as an important novel tool for affective neuroscience.

Reactivity to unpredictable threat as a treatment target for fear-based anxiety disorders

BackgroundHeightened reactivity to unpredictable threat (U-threat) is a core individual difference factor underlying fear-based psychopathology. Little is known, however, about whether reactivity to U-threat is a stable marker of fear-based psychopathology or if it is malleable to treatment. The aim of the current study was to address this question by examining differences in reactivity to U-threat within patients before and after 12-weeks of selective serotonin reuptake inhibitors (SSRIs) or cognitive-behavioral therapy (CBT).MethodsParticipants included patients with principal fear (n = 22) and distress/misery disorders (n = 29), and a group of healthy controls (n = 21) assessed 12-weeks apart. A well-validated threat-of-shock task was used to probe reactivity to predictable (P-) and U-threat and startle eyeblink magnitude was recorded as an index of defensive responding.ResultsAcross both assessments, individuals with fear-based disorders displayed greater startle magnitude to U-threat relative to healthy controls and distress/misery patients (who did not differ). From pre- to post-treatment, startle magnitude during U-threat decreased only within the fear patients who received CBT. Moreover, within fear patients, the magnitude of decline in startle to U-threat correlated with the magnitude of decline in fear symptoms. For the healthy controls, startle to U-threat across the two time points was highly reliable and stable.ConclusionsTogether, these results indicate that startle to U-threat characterizes fear disorder patients and is malleable to treatment with CBT but not SSRIs within fear patients. Startle to U-threat may therefore reflect an objective, psychophysiological indicator of fear disorder status and CBT treatment response.