Dorsal Neck Muscles Research Articles

Neck muscle function improves after neck exercises in individuals with whiplash-associated disorders: a case–control ultrasound study with speckle-tracking analyses

A whiplash injury can alter neck muscle function, which remains years after the injury and may explain why symptoms such as persistent pain and disability occur. There is currently limited knowledge about dynamic neck muscle function in chronic whiplash-associated disorders (WAD), and about the extent to which altered muscle function can improve after rehabilitation. Ultrasound can detect mechanical neck muscle function by measuring real-time deformation and deformation rate in the muscles. This method was used for five dorsal neck muscles in participants with chronic WAD versus matched controls in resistant neck rotation. We obtained real-time, non-invasive ultrasound measurements using speckle tracking, multivariate analyses, and mixed-design ANOVA analyses. The results showed altered deformation in the three deepest neck muscle layers, with less deformation area in the WAD group compared to controls in rotation to the most painful side at baseline. Participants in the WAD group performed three months of neck-specific exercises, resulting in improved deformation in the deep neck muscles in WAD and with a similar deformation pattern to controls, and the significant group differences ceased. We reveal new and important insights into the capability of ultrasound to diagnose altered neck muscle function and evaluate an exercise intervention.

Effect of neck-specific exercises with and without internet support on cervical range of motion and neck muscle endurance in chronic whiplash-associated disorders: analysis of functional outcomes of a randomized controlled trial.

To compare the effects of a neck-specific exercise programme with internet support and 4 physiotherapist sessions (NSEIT) and the same neck-specific exercises supervised by a physiotherapist (NSE) on neck muscle endurance and cervical range of motion. Randomized controlled trial. A total of 140 participants with chronic whiplash-associated disorders grade II or grade III were randomly assigned to the NSEIT or NSE groups. Outcomes were changes in active cervical range of motion, cranio-cervical flexion test, neck muscle endurance, and neck pain, at 3- and 15-month follow-ups. There were no significant differences between the NSEIT and NSE groups. There was a significant group-by-time inter-action effect in active cervical range of motion flexion/extension where the NSEIT group improved to 3-month follow-up, but the NSE group did not. Both groups were significantly improved over time in all other outcomes (p < 0.001) at 3- and 15-month follow-ups, with effect size between 0.64 and 1.35 in active cervical range of motion, cranio-cervical flexion test, dorsal neck muscle endurance, and neck pain, and effect size between 0.22 and 0.42 in ventral neck muscle endurance. Both NSE and NSEIT led to improved neck function. Depending on the patients' needs, either NSE or NSEIT could be used as treatment for patients with chronic whiplash-associated disorders.

Does vibration frequency and location influence the effect of neck muscle vibration on postural sway? A cross-sectional study in asymptomatic participants.

Postural control is of utmost importance for human functioning. Cervical proprioception is crucial for balance control. Therefore, any change to it can lead to balance problems. Previous studies used neck vibration to change cervical proprioception and showed changes in postural control, but it remains unknown which vibration frequency or location causes the most significant effect. Therefore, this study aimed to investigate the effect of different vibration frequencies and locations on postural sway and to serve as future research protocol guidance. Seventeen healthy young participants were included in the study. We compared postural sway without vibration to postural sway with six different combinations of vibration frequency (80, 100, and 150Hz) and location (dorsal neck muscles and sternocleidomastoid). Postural sway was evaluated using a force platform. The mean center of pressure (CoP) displacement, the root mean square (RMS), and the mean velocity in the anteroposterior and mediolateral direction were calculated, as well as the sway area. The aligned rank transform tool and a three-way repeated measures ANOVA were used to identify significant differences in postural sway variables. Neck vibration caused a significant increase in all postural sway variables (p < 0.001). Neither the vibration frequency (p > 0.34) nor location (p > 0.29) nor the interaction of both (p > 0.30) influenced the magnitude of the change in postural sway measured during vibration. Neck muscle vibration significantly changes CoP displacement, mean velocity, RMS, and area. However, we investigated and found that there were no significant differences between the different combinations of vibration frequency and location.

Fatty infiltrate and neck muscle volume in individuals with chronic whiplash associated disorders compared to healthy controls – a cross sectional case–control study

BackgroundThe underlying pathophysiological mechanisms of chronic Whiplash Associated Disorders (WAD) are not fully understood. More knowledge of morphology is needed to better understand the disorder, improve diagnostics and treatments. The aim was to investigate dorsal neck muscle volume (MV) and muscle fat infiltration (MFI) in relation to self-reported neck disability among 30 participants with chronic WAD grade II-III compared to 30 matched healthy controls.MethodsMV and MFI at spinal segments C4 through C7 in both sexes with mild- to moderate chronic WAD (n = 20), severe chronic WAD (n = 10), and age- and sex matched healthy controls (n = 30) was compared. Muscles: trapezius, splenius, semispinalis capitis and semispinalis cervicis were segmented by a blinded assessor and analyzed.ResultsHigher MFI was found in right trapezius (p = 0.007, Cohen’s d = 0.9) among participants with severe chronic WAD compared to healthy controls. No other significant difference was found for MFI (p = 0.22–0.95) or MV (p = 0.20–0.76).ConclusionsThere are quantifiable changes in muscle composition of right trapezius on the side of dominant pain and/or symptoms, among participants with severe chronic WAD. No other statistically significant differences were shown for MFI or MV. These findings add knowledge of the association between MFI, muscle size and self-reported neck disability in chronic WAD.Trial registrationNA. This is a cross-sectional case–control embedded in a cohort study.

Physical Load While Using a Tablet at Different Tilt Angles during Sitting and Standing.

Few standards and guidelines to prevent health problems have been associated with tablet use. We estimated the effects of posture and tablet tilt angle on muscle activity and posture in healthy young adults. Seventeen healthy young adults (age: 20.5 ± 3 years) performed a cognitive task using a tablet in two posture (sitting and standing) and tablet tilt angle (0 degrees and 45 deg) conditions. Segment and joint kinematics were evaluated using 16 inertial measurement unit sensors. Neck, trunk, and upper limb electromyography (EMG) activities were monitored using 12 EMG sensors. Perceived discomfort, kinematics, and EMG activities were compared between conditions using the Friedman test. The perceived discomfort in the standing-0 deg condition was significantly higher than in the remaining three conditions. Standing posture and tablet inclination significantly reduced the sagittal segment and joint angles of the spine, compared with sitting and flat tablet conditions. Similarly, standing posture and tablet inclination significantly reduced EMG activities of the dorsal neck, upper, and lower trunk muscles, while increasing EMG activity of shoulder flexors. Standing posture and tablet inclination reduced the sagittal flexion angle, and dorsal neck, upper, and lower trunk muscle activities, while potentially increasing the muscle activity of arm flexors.

Auditory perception is influenced by the orientation of the trunk relative to a sound source.

The study investigated how hearing depends on the whole body, head and trunk orientation relative to a sound source. In normal hearing humans we examined auditory thresholds and their ability to recognize logatomes (bi-syllabic non-sense words) at different whole body, head and trunk rotation relative to a sound source. We found that auditory threshold was increased and logatome recognition was impaired when the body or the trunk were rotated 40° away from a sound source compared to when the body or the trunk was oriented towards the sound source. Conversely, no effects were seen when only the head was rotated. Further, an increase of thresholds and impairment of logatome recognition were also observed after unilateral vibration of dorsal neck muscles that induces, per se, long-lasting illusory trunk displacement relative to the head. Thus, our findings support the idea that processing of acoustic signals depends on where a sound is located within a reference system defined by the subject's trunk coordinates.

Dorsal Neck Muscle Fatigue Affects Cervical Range of Motion and Proprioception in Adults with the Forward Head Posture

Dorsal Neck Muscle Fatigue Affects Cervical Range of Motion and Proprioception in Adults with the Forward Head Posture

Ultrasound Investigation of Dorsal Neck Muscle Deformation During a Neck Rotation Exercise

ObjectivesNeck-specific exercise can reduce neck pain and increase function, but information on how different neck muscle layers are activated during neck exercises is scarce. The aim of this study was to investigate deformation and deformation rate in 5 dorsal neck muscles and the correlation among these muscles during a loaded dynamic exercise used in clinical practice. MethodsDeformation and deformation rate were investigated in 5 dorsal right-sided neck muscles in 20 individuals without neck pain using ultrasonography and speckle-tracking analyses. Repeated-measures analysis of variance was used to measure differences between the muscles, and correlations between neck muscles were analyzed with Kendall's tau. ResultsDeformation in left (contralateral) rotation showed significant differences among the muscles (P = .01), with higher deformation of the semispinalis capitis muscle compared with the trapezius muscle (P = .02). There were no significant differences among the 5 neck muscles in right (unilateral) rotation (P = .46). There were significant differences in deformation rate among muscles in both right and left rotation (P < .01). The trapezius muscles have the lowest deformation rate in right rotation (P < .01). In left rotation, the trapezius and multifidus muscles showed lower deformation rates compared with most of the other muscles (P < .03). Almost all muscles were correlated in both deformation and deformation rate. ConclusionThe quadruped standing loaded dynamic neck exercise seemed to activate all the investigated neck muscles, with a tendency for more activation of the semispinalis capitis.

0001 Activation of Nociceptin/Orphanin-FQ Peptide (NOP) Receptors Produces an Increase in Non-REM Sleep in Rats and Constitutes a Novel and Attractive Target for the Treatment of Insomnia

Abstract Introduction Treatments for insomnia have targeted GABA, histamine, serotonin, melatonin and orexin receptors. The nociceptin/orphanin-FQ peptide (NOP) receptor is widely expressed in the nervous system. High doses of NOP agonists administered systemically or locally into the CNS can result in sedation, however, the utility of targeting this receptor to treat insomnia has not been fully described. Methods V117957 is a recently described investigational oral, potent and selective NOP receptor partial agonist. We determined the brain Kp in whole brain and multiple sub-regions (50mg/kg) and receptor occupancy in the hypothalamus (30, 300mg/kg) via in vivo displacement using [3H]-NOP-1A. EEG/EMG were determined in rats chronically implanted with electrodes (cortex and dorsal neck muscle) and recorded via telemetry following dosing (3, 30, 300mg/kg); sleep stage was determined from visual analysis of EEG level. Sleep parameters were also assessed in NOP receptor knock-out rats (300mg/kg). The side-effect profile for V117957 was determined by functional observation battery, whole-body plethysmography, Morris water maze (MWM) (up to 600mg/kg) and conditioned place preference (CPP) assay (up to 300mg/kg). Results V117957 displayed limited distribution into the CNS but achieved a high level of receptor occupancy (75% at 30mg/kg). Administration of V117957 produced dose-dependent and statistically significant increases in non-REM sleep with a minimally efficacious dose of 30mg/kg; a coincident dose-dependent and statistically significant decrease in wakefulness and a non-dose-dependent effect on REM sleep occurred. These changes were not seen in knock-out animals demonstrating effects are via NOP receptors. At doses higher than those that increased non-REM sleep, V117957 had no effects in a functional observational battery, did not affect escape latency in MWM or produce CPP; additionally, V117957 did not affect respiratory parameters. Conclusion We conclude that activation of NOP receptors decreases wakefulness and increases non-REM sleep in rats with an improved preclinical profile compared to historical profiles of current treatments and, therefore, may represent a novel and attractive target for the treatment of insomnia. Support Funded by Shionogi and Imbrium Therapeutics, a subsidiary of Purdue Pharma L.P.

The Relationship of Ultrasound Measurements of Muscle Deformation With Torque and Electromyography During Isometric Contractions of the Cervical Extensor Muscles

ObjectivesSpeckle tracking analysis (STA) of ultrasound (US) images quantifies the longitudinal deformation of a region of muscle tissue to provide a mechanical measure of muscle activity. As the validity and reliability of this method has not yet been adequately assessed, the aim of this study was to determine the validity and reliability of STA in the dorsal neck muscles during isometric neck extension contractions. MethodsTwenty volunteers performed 3 repetitions of isometric neck extension in a dynamometer at 10%, 20%, 40%, 60%, and 80% of maximal voluntary torque while US and surface electromyography (EMG) data were recorded. Speckle tracking analysis was then used to calculate measurements of muscle deformation. The relationship among torque, muscle deformation (separate for each muscle and summed), and EMG was evaluated using linear regressions and Spearman's correlation coefficients. The reliability of EMG and muscle deformation was determined using intraclass correlation coefficients (ICCs). ResultsMuscle deformation in 4 of the 5 muscles when examined separately and collectively was significantly related to torque (P < .05); however, the relationship was weak (r2 = 0.03-0.18). In contrast, a strong linear relationship was observed between torque and EMG (P < .001, r2 = 0.83). Poor to moderate reliability of muscle deformation measures (ICC: 0.02-0.69) was found compared with EMG, which was highly reliable (ICC: 0.67-0.90). ConclusionThese results suggest that the validity of US STA measurements for isometric contractions of the dorsal neck muscles is questionable. Further investigation into this method is required before it can be used as a tool to measure muscle activity.

Alteration in REM sleep and sleep spindles’ characteristics by a model of immobilization stress in rat

Investigation of sleep spindles’ oscillations is increasingly considered as a major avenue of inquiry in analyzing the microarchitecture of sleep. Previous studies highlight a strong mutual interaction between sleep and stress. In the present study, we investigated the effects of multiple stresses, provoked by animal immobilization in the narrow Plexiglas boxes with additional stress by placing some stones on the floor. Male Wistar rats (n = 14) were subjected to 2 h of immobilization per day in a narrow, uneven and stony place for 3 consecutive days. The electroencephalogram (EEG) was recorded with stainless steel screw electrodes placed over the skull and the electromyogram (EMG) was recorded from dorsal neck muscles. The sleep stages were recorded during 2 h before and 2 h after stress exposure for 3 days. Apart from sleep stages’ variations, sleep spindles’ density as well as their time- and frequency-domain characteristics were investigated rigorously by a semi-automatic sleep scoring method developed in MATLAB. Results indicate that multiple stresses containing immobilization as well as physical stress attenuate rapid eye movement sleep (REM). However, the stress effect on spindles is more sophisticated in NREM stages. Although spindle density does not undergo a significant change, spindle amplitude and sigma power of EEG during spindles raised significantly. Besides, a decrease in the mean frequency of spindles depicts a dramatic multiplication in delta slow oscillations. An especially mixed immobility including psychological and physical stress which we applied could affect sleep stability through an alteration in the sleep spindles’ amplitude and frequency but not the density of spindles and also through a reduction in REM sleep.

Neck Muscle Morphology and Function in Primates

The cervical spine lies at intersection between the cranium and postcranium and plays a crucial role in orienting the head relative to the substrate during locomotion. Previous work demonstrates that bony features of the cranial base and cervical spine are related to positional behavior in primates. How soft tissues of the neck vary across primate taxa is relatively unknown yet is critical for understanding function, head carriage, and locomotion in this clade. The objective of this study was to describe the relationship between the extrinsic and intrinsic muscles of the neck and postural and locomotor behaviors in primates. We collected and dissected 26 primate cadavers from 17 different genera representing each major primate clade. We hypothesized that trunk and neck posture, as well as forelimb dominated below‐branch suspensory behaviors and neck rotational capabilities all influence the attachment sites and size of the dorsal neck musculature.Using gross anatomical dissection, we qualitatively described and compared the attachment sites of the dorsal neck, back, and shoulder muscles of taxa that display contrasting behaviors and quantified muscle mass. Using the dissection data combined with contrast enhanced microCT data, we constructed 3D models of the head and neck to visualize the in situ neck muscle attachment sites for Propithecus, Aotus, and Carlito.Gross anatomical dissections demonstrate that among nonhuman apes, hylobatids lack cranial attachments of the trapezius and rhomboideus. Additionally, strepsirrhines display anatomy that is more nonprimate mammal‐like in the distribution of the trapezius, rhomboideus, and semispinalis muscles. Results of phylogenetic regressions indicate that neck muscle masses are best predicted by body size, but also demonstrated significant results for both postural and locomotor behaviors as predictors of overall muscle mass (p &lt; 0.05). This study represents the first comprehensive description of the functional anatomy of the neck muscles across primates. Future work will focus on quantifying biomechanically‐relevant variables such as physiological cross‐sectional area using novel fascicle‐tracking methods and estimating muscle moments to compare across taxa.Support or Funding InformationThis work was funded by the Leakey Foundation, National Science Foundation, American Association of Anatomists, Western University of Health Sciences, and University of Missouri.

Sniffing behaviour‐related changes in cardiac and cortical activity in rats

High-frequency (HF) sniffing represents active odour sampling and an increase in the animal's motivation. We examined how HF sniffing affects the physiological activity of the brain-body system. During HF sniffing, heart rates and the ratio of theta to delta critical local field potential power were comparable to those observed during motion periods. Vagus nerve spike rates did not vary depending on HF sniffing. Our results suggest that physiological factors in the central nervous system and the periphery are not simply determined by locomotion but are crucially associated with HF sniffing. Sniffing is a fundamental behaviour for odour sampling, and high-frequency (HF) sniffing, generally at a sniff frequency of more than 6Hz, is considered to represent an animal's increased motivation to explore external environments. Here, we examined how HF sniffing is associated with changes in physiological signals from the central and peripheral organs in rats. During HF sniffing while the rats were stationary, heart rates, the magnitude of dorsal neck muscle contraction, and the ratio of theta to delta local field potential power in the motor cortex were comparable to those observed during motion periods and were significantly higher than those observed during resting respiration periods. No pronounced changes in vagus nerve spike rates were detected in relation to HF sniffing. These results demonstrate that central and peripheral physiological factors are crucially associated with the emergence of HF sniffing, especially during quiescent periods. Behavioural data might be improved to more accurately evaluate an animal's internal psychological state if they are combined with a sniffing pattern as a physiological marker.

Ultrasound imaging of dorsal neck muscles with speckle tracking analyses \u2013 the relationship between muscle deformation and force

The development of methods of non-invasive measurement of neck muscle function remains a priority in the clinical sciences. In this study, dorsal neck muscle deformation vs time curves (deformation area) were evaluated against incremental force, recorded from non-invasive real-time ultrasound measurement. The results revealed subject-specific moderate to strong linear or non-linear relationships between deformation and force. Test-retest variability showed strong reliability for all five neck muscles summed together and fair to good reliability for the five muscles evaluated separately. Multivariate statistics were used to analyse the interactions between the dorsal neck muscles during different percentages of maximal voluntary contraction (MVC). Low force (10–20% MVC) was related to muscle shortening; higher force (40–80% MVC) showed combination of shortening and elongation deformation in the muscle interactions. The muscle interactions during isometric MVC test were subject-specific, with different combinations and deformations of the five neck muscles. Force ≥40% MVC were associated with a forward movement of the cervical spine that affected the ultrasound measurement of the dorsal neck muscles. Ultrasound with speckle-tracking analyses may be best used to detect low levels (<40% MVC) of neck muscle activity.

Splenius capitis: sensitive target for the cVEMP in older and neurodegenerative patients.

The vestibular evoked myogenic potential (VEMP) is a technique used to assess vestibular function. Cervical VEMPs (cVEMPs) are obtained conventionally from the sternocleidomastoid (SCM) muscle; however, the dorsal neck muscle splenius capitis (SPL) has also been shown to be a reliable target alongside the SCM in young subjects. This study aimed to compare cVEMPs from the SCM and SPL in two positions across young, older, and Parkinson's disease (PD) patients. Experiments were carried out using surface EMG electrodes placed over the SCM and SPL. cVEMPs were measured using a 30s, 126dB sound stimulus with 222 individual tone bursts, while subjects were in a supine and head-turned posture (also known as the head elevation method), and in a seated head-turned posture. When comparing cVEMPs across positions, the incidence of supine and seated SCM-cVEMPs diminished significantly in older and PD patients in comparison with young subjects. However, no statistically significant differences in incidences were found in seated SPL-cVEMPs when comparing young, older and PD patients. SPL-cVEMPs were present significantly more often than seated SCM-cVEMPs in PD patients. SPL-cVEMPs are not altered to the same extent that SCM-cVEMPs are by aging and disease and its addition to cVEMP testing may reduce false-positive tests for vestibulopathy.

Independent suboesophageal neuronal innervation of the defense gland and longitudinal muscles in the stick insect (Peruphasma schultei) prothorax

This study investigates the neuroanatomy of the defense gland and a related muscle in the stick insect Peruphasma schultei with axonal tracing and histological sections. The gland is innervated by three neurons through the Nervus anterior of the suboesophageal ganglion (SOG), the ipsilateral neuron (ILN), the contralateral neuron (CLN) and the prothoracic intersegmental neuron (PIN). The ILN has a large soma which is typical for motoneurons that cause fast contraction of large muscles and its dendrites are located in motor-sensory and sensory neuropile areas of the SOG. The CLN might be involved in the coordination of bilateral or unilateral discharge as its neurites are closely associated to the ILN of the contralateral gland. Close to the ejaculatory duct of the gland lies a dorsal longitudinal neck muscle, musculus pronoto-occipitalis (Idlm2), which is likely indirectly involved in gland discharge by controlling neck movements and, therefore, the direction of discharge. This muscle is innervated by three ventral median neurons (VMN). Thus, three neuron types (ILN, CLN, and PIN) innervate the gland muscle directly, and the VMNs could aid secretion indirectly. The cytoanatomy of motorneurons innervating the defense gland and neck muscle are discussed regarding the structure and functions of the neuropile in the SOG. As a basis for the neuroanatomical study on the defense gland we assembled a map of the SOG in Phasmatodea.

Alterations in the Mechanical Response of Deep Dorsal Neck Muscles in Individuals Experiencing Whiplash-Associated Disorders Compared to Healthy Controls: An Ultrasound Study.

The aim of this study was to investigate and compare the mechanical responses of dorsal neck muscles in individuals with whiplash-associated disorders (WAD) versus healthy individuals. This study included 36 individuals with WAD (26 women and 10 men) and 36 healthy controls (26 women and 10 men). Ultrasound imaging with speckle tracking was used to measure deformation and deformation rate in five dorsal neck muscles during a neck extension task. Compared with controls, individuals with WAD showed higher deformations of the semispinalis cervicis (P = 0.02) and multifidus (P = 0.002) muscles and higher deformation rates (P = 0.03 and 0.0001, respectively). Among individuals with WAD, multifidus deformation and deformation rate were significantly associated with pain, disability, and fatigue (r = 0.31-0.46, P = 0.0001-0.01). These findings indicate that the mechanical responses of the deep dorsal neck muscles differ between individuals with WAD and healthy controls, possibly reflecting that these muscles use altered strategies while performing a neck extension task. This finding provides new insight into neck muscles pathology in patients with chronic WAD and may help improve rehabilitation programs. Complete the self-assessment activity and evaluation online at http://www.physiatry.org/JournalCME CME OBJECTIVES: Upon completion of this article, the reader should be able to: (1) Summarize the mechanical responses of dorsal neck muscles during loading of the neck muscles via an extension task in individuals with chronic whiplash associated disorders and healthy volunteers; (2) Differentiate mechanical responses between five dorsal neck muscles while loading the neck via an extension task; and (3) Describe the relationships between the mechanical responses of the dorsal neck muscles with the patients' perception of neck pain, disability, and fatigue. Advanced ACCREDITATION: The Association of Academic Physiatrists is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.The Association of Academic Physiatrists designates this Journal-based CME activity for a maximum of 0.5 AMA PRA Category 1 Credit(s)™. Physicians should only claim credit commensurate with the extent of their participation in the activity.

Variability of peripheral and central organ activity patterns of mice in an elevated plus maze

Elevated plus maze (EPM) tests have been used to assess animal anxiety levels. Little information is known regarding how physiological activity patterns of the brain-body system are altered during EPM tests. Herein, we monitored cortical local field potentials of the prefrontal cortex and hippocampus, electrocardiograms from the intercostal muscle, electromyograms from the dorsal neck muscle, and respiratory signals from the olfactory bulb in individual mice that were repeatedly exposed to EPM tests. Heart rates of the mice were higher in the open arms. In the closed arms, the mice occasionally showed decreased heart and respiratory rates lasting for several seconds or minutes, characterized as low-peripheral activity (LP) states of peripheral signals. The LP states were observed only when the animals were in the closed arms, and the frequencies of the LP states increased as the testing days proceeded. The periods of LP states corresponded with those having significant lower amplitudes of electromyogram. The state more likely occurred in the distal part of the closed arms, which indicates that mice with LP states showed less locomotor activity. During the low-activity states, the delta and theta powers of cortical local field potentials were significantly increased and decreased, respectively. These results demonstrate that cortical oscillations crucially depend on whether an animal exhibits low-activity states in peripheral organs rather than the EPM arm in which the animal is located. These results suggest that combining behavioral tests with physiological makers enables an accurate evaluation of rodent mental states.

Multiple Identified Neurons and Peripheral Nerves Innervating the Prothoracic Defense Glands in Stick Insects Reveal Evolutionary Conserved and Novel Elements of a Chemical Defense System

The defense glands in the dorsal prothorax are an important autapomorphic trait of stick insects (Phasmatodea). Here, we study the functional anatomy and neuronal innervation of the defense glands in Anisomorpha paromalus (Westwood, 1859) (Pseudophasmatinae), a species which sprays its defense secretions when disturbed or attacked. We use a neuroanatomical approach to identify the nerves innervating the gland muscles and the motoneurons with axons in the different nerves. The defense gland is innervated by nerves originating from two segments, the suboesophageal ganglion and the prothoracic ganglion. Axonal tracing confirms the gland innervation via the anterior suboesophageal nerve, and two intersegmental nerves, the posterior suboesophageal nerve and the anterior prothoracic nerve. Axonal tracing of individual nerves reveals eight identified neuron types in the suboesophageal or prothoracic ganglion. The strongest innervating nerve of the gland is the anterior suboesophageal nerve, which also supplies dorsal longitudinal thorax muscles (neck muscles) by separate nerve branches. Tracing of individual nerve branches reveals different sets of motoneurons innervating the defense gland (one ipsilateral and one contralateral suboesophageal neuron) or the neck muscle (ventral median neurons). The ipsilateral and contralateral suboesophageal neurons have no homologs in related taxa like locusts and crickets, and thus evolved within stick insects with the differentiation of the defense glands. The overall innervation pattern suggests that the longitudinal gland muscles derived from dorsal longitudinal neck muscles. In sum, the innervating nerves for dorsal longitudinal muscles are conserved in stick insects, while the neuronal control system was specialized with conserved motoneurons for the persisting neck muscles, and evolutionarily novel suboesophageal and prothoracic motoneurons innervating the defense gland.

Functional morphology and neuronal innervation of the prothoracic defence gland in Timema

AbstractTimema is the most basal genus of Phasmatodea and the sister group to the remaining stick and leaf‐insects (Euphasmatodea). An autapomorphy of all phasmids is the paired prothoracic exocrine defence glands. In this study, the anatomy and innervation of the defence glands in Timema petita and Timema chumash are described and compared with the data on Euphasmatodea. In all phasmids, the glands consist of a cuticular epithelium, a secretory epithelium and muscular fibres that compress the lumen. In Timematodea, the muscular part of the gland is less developed than in Euphasmatodea and the ejection of the defence secretion depends on the dorsal longitudinal neck muscles. On the neuroanatomical level, Timema petita and Timema chumash lack neurons that are involved in the independent contraction of the gland in euphasmids. In both studied species of Timema, neck muscles play an active role in the gland function which is not observed in any other phasmid. Considering the basal position of this genus, this supports the hypothesis that in euphasmids, the muscular part of the gland evolved from the dorsal longitudinal neck muscles. Additionally, the same nerves that innervate the dorsal longitudinal neck muscles in all Polyneoptera also innervate the defence glands in phasmids.