Startle Behavior Research Articles

Transcriptional-profile changes in the medial geniculate body after noise-induced tinnitus.

Tinnitus is a disturbing condition defined as the occurrence of acoustic hallucinations with no actual sound. Although the mechanisms underlying tinnitus have been explored extensively, the pathophysiology of the disease is not completely understood. Moreover, genes and potential treatment targets related to auditory hallucinations remain unknown. In this study, we examined transcriptional-profile changes in the medial geniculate body after noise-induced tinnitus in rats by performing RNA sequencing and validated differentially expressed genes via quantitative polymerase chain reaction analysis. The rat model of tinnitus was established by analyzing startle behavior based on gap-pre-pulse inhibition of acoustic startles. We identified 87 differently expressed genes, of which 40 were upregulated and 47 were downregulated. Pathway-enrichment analysis revealed that the differentially enriched genes in the tinnitus group were associated with pathway terms, such as coronavirus disease COVID-19, neuroactive ligand-receptor interaction. Protein-protein-interaction networks were established, and two hub genes (Rpl7a and AC136661.1) were identified among the selected genes. Further studies focusing on targeting and modulating these genes are required for developing potential treatments for noise-induced tinnitus in patients.

A single base pair substitution in zebrafish distinguishes between innate and acute startle behavior regulation.

Behavioral thresholds define the lowest stimulus intensities sufficient to elicit a behavioral response. Establishment of baseline behavioral thresholds during development is critical for proper responses throughout the animal's life. Despite the relevance of such innate thresholds, the molecular mechanisms critical to establishing behavioral thresholds during development are not well understood. The acoustic startle response is a conserved behavior whose threshold is established during development yet is subsequently acutely regulated. We have previously identified a zebrafish mutant line (escapist) that displays a decreased baseline or innate acoustic startle threshold. Here, we identify a single base pair substitution on Chromosome 25 located within the coding sequence of the synaptotagmin 7a (syt7a) gene that is tightly linked to the escapist acoustic hypersensitivity phenotype. By generating animals in which we deleted the syt7a open reading frame, and subsequent complementation testing with the escapist line, we demonstrate that loss of syt7a function is not the cause of the escapist behavioral phenotype. Nonetheless, escapist mutants provide a powerful tool to decipher the overlap between acute and developmental regulation of behavioral thresholds. Extensive behavioral analyses reveal that in escapist mutants the establishment of the innate acoustic startle threshold is impaired, while regulation of its acute threshold remains intact. Moreover, our behavioral analyses reveal a deficit in baseline responses to visual stimuli, but not in the acute regulation of responses to visual stimuli. Together, this work eliminates loss of syt7a as causative for the escapist phenotype and suggests that mechanisms that regulate the establishment of behavioral thresholds in escapist larvae can operate independently from those regulating acute threshold regulation.

A novel locomotion-based prepulse inhibition assay in zebrafish larvae.

Sensory gating, measured using prepulse inhibition (PPI), is an endophenotype of neuropsychiatric disorders that can be assessed in larval zebrafish models. However, current PPI assays require high-speed cameras to capture rapid c-bend startle behaviours of the larvae. In this study, we designed and employed a PPI paradigm that uses locomotion as a read-out of zebrafish larval startle responses. PPI percentage was measured at a maximum of 87% and strongly reduced upon administration of the NMDA receptor antagonist, MK-801. This work provides the foundation for simpler and more accessible PPI assays using larval zebrafish to model key endophenotypes of neurodevelopmental disorders.

Effects of continuous drone herding on behavioral response and spatial distribution of grazing cattle

Robotic herding is expected to become a new technology for the management of grazing animals. We investigated the behavioral responses of cows to drone herding on consecutive days and the potential of this technology to manipulate grazing distribution in a pasture. A herd of ∼30 cows was stocked in a 1.1-ha pasture for 5 consecutive days each month from May to October 2022. The cows were herded using a drone for 10 days during the grazing period in August (days 1–5) and September (days 6–10). The pasture was divided into nine plots, with two and three plots assigned as the ‘herding area’ in August and September, respectively. When the cows were grazing in the herding area, the operator maneuvered the drone to move the animals out of the area. The drone first approached at an altitude of 10 m; if the cows did not move away, the altitude was gradually lowered to 3 m. The behavioral responses to the drone, success or failure of herding (whether the cows left the area or not), and drone altitude were classified based on videos recorded during herding. The behavior and location of the cows in the pasture were observed during this period. The utilization rates of the plots (percentage of grazing time) were calculated to evaluate the effects of herding and the number of herding days. The cows responded in 59% and 46% of the cases on days 1 and 2, respectively. Startle behavior was recorded in 23% of the responses on day 1. Herding was successful in 51–75% of the cases on days 1–3. However, these percentages decreased thereafter. The utilization rate of the herding area on day 1 was approximately half that on days without herding. It increased from day 2, and almost no effect on grazing distribution was observed on or after day 3. These findings suggest that the cows exhibited little fear of drones after 1-day herding, and responses to the drones decreased as the animals subsequently became habituated to frequently repeated stimuli. Even after a 24-day interval, responsiveness to drone herding barely recovered and then declined. Therefore, drone herding was hardly effective in manipulating grazing distribution. Further investigation of stimulation that persistently elicits desirable responses is needed for future applications in technologies for the autonomous control of animal movement.

Aging leads to impairment of spatial hearing abilities in the Mongolian Gerbil

Aging in humans is known to affect spatial hearing and speech in noise recognition, often even when hearing thresholds are normal. The Mongolian Gerbil (Meriones unguiculatus) can provide a model organism to investigate these changes. We performed auditory brainstem responses (ABRs), prepulse inhibition of the acoustic startle (PPI) behavior, and cochlear histology to assess age-related changes of the gerbil auditory brainstem. Aging (>33month) gerbils showed reduced ABR waveform amplitudes compared to young gerbils (2-10 months). Aging gerbils also show a reduced amplitude of the binaural interaction component (BIC), a biomarker for spatial hearing. However, ABR thresholds were not significantly different between cohorts. Aging gerbils showed impaired performance in our behavior tasks: young gerbils detected shorter gaps in noise and smaller minimum audible angles than aging animals, indicating that aging impairs temporal and spatial hearing abilities. Cochlear histology revealed an increase in cochlear synaptopathy in aging animals, revealing a potential mechanism for age-related dysfunction in the auditory pathway. Taken together, these data reveal structural and physiological changes in the auditory brainstem that underlie spatial hearing deficits in the gerbil. [Work supported by R01-DC017924.]

Genetic and genomic analyses of Drosophila melanogaster models of chromatin modification disorders.

Switch/sucrose nonfermentable (SWI/SNF)-related intellectual disability disorders (SSRIDDs) and Cornelia de Lange syndrome are rare syndromic neurodevelopmental disorders with overlapping clinical phenotypes. SSRIDDs are associated with the BAF (Brahma-Related Gene-1 associated factor) complex, whereas CdLS is a disorder of chromatin modification associated with the cohesin complex. Here, we used RNA interference in Drosophila melanogaster to reduce the expression of six genes (brm, osa, Snr1, SMC1, SMC3, vtd) orthologous to human genes associated with SSRIDDs and CdLS. These fly models exhibit changes in sleep, activity, startle behavior (a proxy for sensorimotor integration), and brain morphology. Whole genome RNA sequencing identified 9,657 differentially expressed genes (FDR < 0.05), 156 of which are differentially expressed in both sexes in SSRIDD- and CdLS-specific analyses, including Bap60, which is orthologous to SMARCD1, an SSRIDD-associated BAF component. k-means clustering reveals genes co-regulated within and across SSRIDD and CdLS fly models. RNAi-mediated reduction of expression of six genes co-regulated with focal genes brm, osa, and/or Snr1 recapitulated changes in the behavior of the focal genes. Based on the assumption that fundamental biological processes are evolutionarily conserved, Drosophila models can be used to understand underlying molecular effects of variants in chromatin-modification pathways and may aid in the discovery of drugs that ameliorate deleterious phenotypic effects.

Transcriptional Profile Changes after Noise-Induced Tinnitus in Rats

Tinnitus is an unpleasant symptom characterized by detective hearing without the actual sound input. Despite numerous studies elucidating a variety of pathomechanisms inducing tinnitus, the pathophysiology of tinnitus is not fully understood. The genes that are closely associated with this subtype of the auditory hallucination that could be utilized as potential treatment targets are still unknown. In this study, we explored the transcriptional profile changes of the auditory cortex after noise-induced tinnitus in rats using high throughput sequencing and verification of the detected genes using quantitative PCR (qPCR). Tinnitus models were established by analyzing startle behaviors through gap pre-pulse inhibition (PPI) of the acoustic startle. Two hundred and fifty-nine differential genes were identified, of which 162 genes were up-regulated and 97 genes were down-regulated. Analysis of the pathway enrichment indicated that the tinnitus group exhibited increased gene expression related to neurodegenerative disorders such as Huntington's disease and Amyotrophic lateral sclerosis. Based on the identified genes, networks of protein-protein interaction were established and five hub genes were identified through degree rank, including Fos, Nr4a1, Nr4a3, Egr2, and Egr3. Therein, the Fos gene ranked first with the highest degree after noise exposure, and may be a potential target for the modulation of noise-induced tinnitus.

Excess Dietary Vitamin B-6 Alters Startle Behavior of Rats

Excessive intakes of vitamin B-6 can produce peripheral nervous system abnormalities, but few reports of central nervous system effects exist. We measured startle response, a central nervous system reflex, in rats fed excess pyridoxine to determine if subtle effects on central nervous system function could be detected. Female Long-Evans rats (218 g; n = 12) were fed either 1, 10, 100, 200 or 300 times the requirement of pyridoxine HCl (7 mg/kg) for 7 wk. Startle behavior was assessed weekly in chambers that allowed quantification of movement in response to stimuli. Food intake and body weights did not differ among groups (P > 0.1), and urinary vitamin B-6 excretion reflected intake (P < 0.001). Overt toxicity was not observed. There was a marginally significant effect of pyridoxine intake over time (P = 0.053) on the amplitude of response to a startling acoustic stimulus (117 dB, 40 ms) administered alone; the response appeared attenuated at the three highest pyridoxine concentrations. When the same stimulus was preceded by either a 70- or 75-dB prepulse (40 ms), responses of groups fed the two highest pyridoxine concentrations were significantly reduced relative to those fed the two lowest concentrations (P < 0.05). No effect of diet was seen with a startling tactile stimulus. Changes in central nervous system function were detected in rats fed excess vitamin B-6 using techniques of startle behavior measurement.

Seismic sentinel? An analysis of captive giant panda behavior in response to the Lushan earthquake in China

It is widely believed that various animal species can sense and respond to the geophysical stimuli that precede earthquakes, especially electromagnetic fields, although supporting field evidence is mostly anecdotal. Here we report on the reactions of four female giant pandas under observation over the three days prior to the Lushan (30.1°N, 103.0°E) magnitude 7.0 earthquake that occurred in Sichuan province, China, on April 20, 2013. We observed no significant generalized behavioral anomalies indicative of them perceiving an impending earthquake. We also observed no startle behaviors in the 5 s prior to tremors commencing, indicating that these pandas either did not detect or did not respond to precursor P-waves. Our findings suggest that although giant pandas have evolved in, and continue to occupy exclusively, a seismically active range in central China, they do not appear to perceive pre-earthquake geophysical warning signs.

Survival and Axonal Outgrowth of the Mauthner Cell Following Spinal Cord Crush Does Not Drive Post-injury Startle Responses.

A pair of Mauthner cells (M-cells) can be found in the hindbrain of most teleost fish, as well as amphibians and lamprey. The axons of these reticulospinal neurons cross the midline and synapse on interneurons and motoneurons as they descend the length of the spinal cord. The M-cell initiates fast C-type startle responses (fast C-starts) in goldfish and zebrafish triggered by abrupt acoustic/vibratory stimuli. Starting about 70 days after whole spinal cord crush, less robust startle responses with longer latencies manifest in adult goldfish, Carassius auratus. The morphological and electrophysiological identifiability of the M-cell provides a unique opportunity to study cellular responses to spinal cord injury and the relation of axonal regrowth to a defined behavior. After spinal cord crush at the spinomedullary junction about one-third of the damaged M-axons of adult goldfish send at least one sprout past the wound site between 56 and 85 days postoperatively. These caudally projecting sprouts follow a more lateral trajectory relative to their position in the fasciculus longitudinalis medialis of control fish. Other sprouts, some from the same axon, follow aberrant pathways that include rostral projections, reversal of direction, midline crossings, neuromas, and projection out the first ventral root. Stimulating M-axons in goldfish that had post-injury startle behavior between 198 and 468 days postoperatively resulted in no or minimal EMG activity in trunk and tail musculature as compared to control fish. Although M-cells can survive for at least 468 day (∼1.3 years) after spinal cord crush, maintain regrowth, and elicit putative trunk EMG responses, the cell does not appear to play a substantive role in the emergence of acoustic/vibratory-triggered responses. We speculate that aberrant pathway choice of this neuron may limit its role in the recovery of behavior and discuss structural and functional properties of alternative candidate neurons that may render them more supportive of post-injury startle behavior.

Stress-activated leukocyte 12/15-lipoxygenase metabolite enhances struggle behaviour and tocotrienols relieve stress-induced behaviour alteration

Stress induces emotional arousal causing anxiety, irritability, exaggerated startle behaviour, and hypervigilance observed in patients with trauma and stress-related mental disorders, including acute stress disorder and post-traumatic stress disorder. Central norepinephrine release promotes stress-induced emotional arousal. However, the regulator of emotional arousal remains unknown. Here, we show that the arachidonate-derived metabolite produced by stress-activated leukocyte 12/15-lipoxygenase is remarkably elevated in the plasma and upregulates the central norepinephrine release, resulting in the enhancement of the struggle behaviour (= escape behaviour) in the tail suspension test. Struggle behaviour is mimicking a symptom of emotional arousal. This stress-induced struggle behaviour was absent in 12/15-lipoxygenase deficient mice; however, intravenous administration of a 12/15-lipoxygenase metabolite to these mice after stress exposure rekindled the struggle behaviour. Furthermore, tocotrienols and geranylgeraniol reduced stress-induced 12/15-lipoxygenase metabolite production and suppressed the struggle behaviour. Our findings indicate that arachidonate-derived 12/15-lipoxygenase metabolite is involved in the regulation of stress-enhanced central norepinephrine release and struggle behaviour. In addition, we propose 12/15-lipoxygenase as a potential therapeutic target for the treatment of emotional arousal observed in stress-related mental disorders.

Developmental Exposure to Domoic Acid Disrupts Startle Response Behavior and Circuitry in Zebrafish.

Harmful algal blooms produce potent neurotoxins that accumulate in seafood and are hazardous to human health. Developmental exposure to the harmful algal bloom toxin, domoic acid (DomA), has behavioral consequences well into adulthood, but the cellular and molecular mechanisms of DomA developmental neurotoxicity are largely unknown. To assess these, we exposed zebrafish embryos to DomA during the previously identified window of susceptibility and used the well-known startle response circuit as a tool to identify specific neuronal components that are targeted by exposure to DomA. Exposure to DomA reduced startle responsiveness to both auditory/vibrational and electrical stimuli, and even at the highest stimulus intensities tested, led to a dramatic reduction of one type of startle (short-latency c-starts). Furthermore, DomA-exposed larvae had altered kinematics for both types of startle responses tested, exhibiting shallower bend angles and slower maximal angular velocities. Using vital dye staining, immunolabeling, and live imaging of transgenic lines, we determined that although the sensory inputs were intact, the reticulospinal neurons required for short-latency c-starts were absent in most DomA-exposed larvae. Furthermore, axon tracing revealed that DomA-treated larvae also showed significantly reduced primary motor neuron axon collaterals. Overall, these results show that developmental exposure to DomA targets large reticulospinal neurons and motor neuron axon collaterals, resulting in measurable deficits in startle behavior. They further provide a framework for using the startle response circuit to identify specific neural populations disrupted by toxins or toxicants and to link these disruptions to functional consequences for neural circuit function and behavior.

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.

Analysis of behavioral changes in zebrafish (Danio rerio) larvae caused by aminoglycoside-induced damage to the lateral line and muscles

Zebrafish behavior is influenced by the lateral line hair cells and muscles. Drug-induced behavioral changes can serve as indicators in the evaluation of drug toxicity. The aminoglycoside family of antibiotics comprise a number of agents, including neomycin (NM) and gentamicin (GM). We hypothesized that NM and GM exert different effects on zebrafish larvae through their action on the lateral line and muscle fibers, inducing different swimming behavioral patterns such as locomotor behavior and the startle response. In this study, 125 μM NM and 5, 10, 20 μM GM induced hair cell damage in the anterior and posterior lateral lines of zebrafish larvae. However, unlike GM, 125 μM NM also caused muscle damage. Locomotor behavior was decreased in the 125 μM NM-exposed group compared to the group exposed to GM. Furthermore, 125 μM NM exposure induced significantly different patterns of various indices of startle behavior compared with the GM exposure groups. Additionally, the larvae exhibited different startle responses depending on the concentration of GM. These results suggest that GM may be the drug-of-choice for analyzing behavioral changes in zebrafish caused by damage to the lateral line alone. Our study highlights the importance of confirming muscle damage in behavioral analyses using zebrafish.

The duality of tyrosine receptor kinase B in stress‐induced hypervigilant phenotypes

Post‐traumatic stress disorder (PTSD) is an anxiety disorder resulting from exposure to traumatic or life‐threatening events. In addition to anxiety and hypervigilant behavioral deficits (i.e. increased startle), PTSD is also an independent risk factor for the development of cardiovascular disease (CVD). While stress is recognized to promote the emergence of behavioral dysfunction and co‐morbid CVD, the mechanism by which this occurs is largely unknown. Stress has been shown to promote the activation of tyrosine receptor kinase (Trk) B in the amygdala, a major brain nucleus that promotes the onset of anxiety‐like and hypervigilant behaviors while simultaneously stimulating cardiac sympathetic activity. However it has yet to be determined whether TrkB activation of the CeA directly contributes to the behavioral and CV responses induced by stress. As such the aim of the current project was to determine whether social stress‐induced increases of CeA TrkB signaling is the initiating factor that leads to the subsequent development of a hypervigilant phenotype. In order to address this hypothesis, two distinct studies were conducted utilizing male Sprague Dawley rats in conjunction with the resident‐intruder paradigm of social defeat (30 min for 5 consecutive days). Study 1 was focused on determining whether direct CeA administration of the selective TrkB inhibitor ANA‐12 (25 ug in 40%DMSO and 0.9% Saline; administered on days 1, 3, and 5) was capable of inhibiting the emergence of a stress‐induced hypervigilant phenotype (enhanced startle, increased blood pressure and heart rate). Study 2 focused on investigating the activation of downstream signaling pathways (i.e. MAPK, Akt, or CamKII) to identify which TrkB‐initiated pathway is upregulated in susceptible individuals and determined whether ANA‐12 (25 ug; administered on days 1, 3 and 5 of stress) blocks the stress‐induced activation of these pathways. Based on preliminary data, direct CeA infusion of ANA‐12 30 minutes prior to the onset of social defeat stress on days 1, 3 and 5 was capable of inhibiting social defeat‐induced phosphorylation of the TrkB receptor. This inhibition of TrkB phosphorylation was functionally associated with reduced anxiety‐like behaviors in the elevated plus maze. Moreover, our preliminary data further suggests that TrkB phosphorylation may also be important for the emergence of defensive behaviors during defeat that underlie resilience. Based on these preliminary behavioral and molecular data, it is probable that ANA‐12 will further protect against the development of hypervigilant startle behaviors and may also protect against the emergence of stress‐induced CVD.Support or Funding InformationThese studies were supported by the National Institute of Mental Health (1R01MH113892‐01A1 to SKW), the Behavior Research Foundation NARSAD Young Investigator Grant (26809 to SKW), and the American Heart Association (17PRE33670106 to JEF).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Maternal sensitivity during infancy and the regulation of startle in preschoolers

ABSTRACTCaregiving insensitivity and fear dysregulation predict anxiety symptoms in children. It is unclear, however, whether sensitive parental care during infancy predicts fear regulation later in childhood. To address this question, we asked whether observed maternal sensitivity, measured at 6 months, predicts 42-month-old children’s laboratory-induced fear responses (n=213) during a fear-eliciting episode. We predicted that higher levels of maternal sensitivity would be associated with greater fear regulation. We operationalized fear regulation as decreases in fear over repeated trials of a novel, potentially frightening, stimulus. Two aspects of fear responses were considered: expressed fear and startle. Expressed fear scores did not decrease over time but children exhibited less startle behavior in the second half of the task. Maternal sensitivity predicted this startle attenuation across trials. These findings highlight the contribution of maternal sensitivity during infancy to the development of fear regulation in early childhood, further suggesting its influence on offspring anxiety problems.

Transplantation of Ears Provides Insights into Inner Ear Afferent Pathfinding Properties.

Numerous tissue transplantations have demonstrated that otocysts can develop into normal ears in any location in all vertebrates tested thus far, though the pattern of innervation of these transplanted ears has largely been understudied. Here, expanding on previous findings that transplanted ears demonstrate capability of local brainstem innervation and can also be innervated themselves by efferents, we show that inner ear afferents grow toward the spinal cord mostly along existing afferent and efferent fibers and preferentially enter the dorsal spinal cord. Once in the dorsal funiculus of the spinal cord, they can grow toward the hindbrain and can diverge into vestibular nuclei. Inner ear afferents can also project along lateral line afferents. Likewise, lateral line afferents can navigate along inner ear afferents to reach hair cells in the ear. In addition, transplanted ears near the heart show growth of inner ear afferents along epibranchial placode-derived vagus afferents. Our data indicate that inner ear afferents can navigate in foreign locations, likely devoid of any local ear-specific guidance cues, along existing nerves, possibly using the nerve-associated Schwann cells as substrate to grow along. However, within the spinal cord and hindbrain, inner ear afferents can navigate to vestibular targets, likely using gradients of diffusible factors that define the dorso-ventral axis to guide them. Finally, afferents of transplanted ears functionally connect to native hindbrain vestibular circuitry, indicated by eliciting a startle behavior response, and providing excitatory input to specific sets of extraocular motoneurons.

Sensory Gating: Cellular Substrates of Surprise

Context modulates the brain's response to sensory input. Recent work has identified the neurons that implement contextual gating of a startle behavior in zebrafish and suggests a synaptic mechanism for this modulation.

Lrfn2-Mutant Mice Display Suppressed Synaptic Plasticity and Inhibitory Synapse Development and Abnormal Social Communication and Startle Response.

SALM1 (SALM (synaptic adhesion-like molecule), also known as LRFN2 (leucine rich repeat and fibronectin type III domain containing), is a postsynaptic density (PSD)-95-interacting synaptic adhesion molecule implicated in the regulation of NMDA receptor (NMDAR) clustering largely based on in vitro data, although its in vivo functions remain unclear. Here, we found that mice lacking SALM1/LRFN2 (Lrfn2-/- mice) show a normal density of excitatory synapses but altered excitatory synaptic function, including enhanced NMDAR-dependent synaptic transmission but suppressed NMDAR-dependent synaptic plasticity in the hippocampal CA1 region. Unexpectedly, SALM1 expression was detected in both glutamatergic and GABAergic neurons and Lrfn2-/- CA1 pyramidal neurons showed decreases in the density of inhibitory synapses and the frequency of spontaneous inhibitory synaptic transmission. Behaviorally, ultrasonic vocalization was suppressed in Lrfn2-/- pups separated from their mothers and acoustic startle was enhanced, but locomotion, anxiety-like behavior, social interaction, repetitive behaviors, and learning and memory were largely normal in adult male Lrfn2-/- mice. These results suggest that SALM1/LRFN2 regulates excitatory synapse function, inhibitory synapse development, and social communication and startle behaviors in mice.SIGNIFICANCE STATEMENT Synaptic adhesion molecules regulate synapse development and function, which govern neural circuit and brain functions. The SALM/LRFN (synaptic adhesion-like molecule/leucine rich repeat and fibronectin type III domain containing) family of synaptic adhesion proteins consists of five known members for which the in vivo functions are largely unknown. Here, we characterized mice lacking SALM1/LRFN2 (SALM1 KO) known to associate with NMDA receptors (NMDARs) and found that these mice showed altered NMDAR-dependent synaptic transmission and plasticity, as expected, but unexpectedly also exhibited suppressed inhibitory synapse development and synaptic transmission. Behaviorally, SALM1 KO pups showed suppressed ultrasonic vocalization upon separation from their mothers and SALM1 KO adults showed enhanced responses to loud acoustic stimuli. These results suggest that SALM1/LRFN2 regulates excitatory synapse function, inhibitory synapse development, social communication, and acoustic startle behavior.

The number of neurons in specific amygdala regions is associated with boldness in mink: a study in animal personality.

Conspecifics vary consistently in their behavioural responses towards environment stimuli such as exposure to novel objects; ethologists often refer to this variability as animal personality. The neurological mechanisms underlying animal personality traits remain largely unknown, but linking the individual variation in emotional expression to brain structural and neurochemical factors is attracting renewed interest. While considerable research has focused on hormonal and neurotransmitter effects on behavioural responses, less is known about how individual variation in the number of specific neuron populations contributes to individual variation in behaviour. The basolateral amygdala (BLA) and the central nuclei of the amygdala (CeA) mediate emotional processing by regulating behavioural responses of animals in a potentially threatening situation. As such, these structures are good candidates for evaluating the relationship between neuronal populations and behavioural traits. We now show that individual American mink (Neovison vison) reacting more boldly towards novelty have more neurons in the BLA than do their more timid conspecifics, suggesting that a developmental pattern of the number of amygdala neurons can influence behavioural traits of an adult animal. Furthermore, post hoc correlations revealed that individuals performing with higher arousal, as reflected by their frequency of startle behaviour, have more CeA neurons. Our results support a direct link between the number of neurons in amygdala regions and aspects of animal personality.