Low-frequency noise impairs righting reflex behavior by disrupting central nervous system in the sea slug Onchidium reevesii

Anthropogenic noise has significantly increased due to human activities, posing a threat to the health and survival of marine organisms. However, current studies have often emphasized its effects on the physiological aspects of marine organisms, while ignored the relationship between the neuroendocrine system and behavior. This study aimed to evaluate the righting behavior and relevant physiological functions of the central nervous system (CNS) in sea slug (Onchidium reevesii) exposed to low-frequency noise and subsequent noise removal. The duration of the sea slugs' righting reflex increased with longer noise exposure time. The degree of neuronal cell damage and apoptosis were significantly increased and relevant gene expressions were affected (Glu, AChE, FMRFamide and CaMKII) (P < 0.05). After the removal of noise, the righting reflex speed gradually recovered, and the degree of neuronal cell damage, apoptosis and the expression levels of genes continued to decrease. Pearson correlation analysis showed that the righting time was positively correlated with CNS tissue and DNA damage, apoptosis rate, and negatively correlated with the expression levels of genes. Therefore, low-frequency noise exposure causes damage to the CNS of sea slugs, subsequently impairing their normal behavior. Sea slugs exhibited partial recovery within 384 h after removing noise. These findings provide valuable insights into the effects of low-frequency noise on the CNS and behavior of marine invertebrates.

Contact feedback helps snake robots propel against uneven terrain using vertical bending

Snakes can bend their elongate bodies in various forms to traverse various environments. We understand well how snakes use lateral body bending to push against asperities on flat ground for propulsion, and snake robots can do so effectively. However, snakes can also use vertical bending to push against uneven terrain of large height variation for propulsion, and they can adjust this bending to adapt to novel terrain presumably using mechano-sensing feedback control. Although some snake robots can traverse uneven terrain, few have used vertical bending for propulsion, and how to control this process in novel environments is poorly understood. Here we systematically studied a snake robot with force sensors pushing against large bumps using vertical bending to understand the role of sensory feedback control. We compared a feedforward controller and four feedback controllers that use different sensory information and generate distinct bending patterns and body-terrain interaction. We challenged the robot with increasing backward load and novel terrain geometry that break its contact with the terrain. We further varied how much the feedback control modulated body bending to conform to or push against the terrain to test their effects. Feedforward propagation of vertical bending generated large propulsion when the bending shape matched terrain geometry. However, when perturbations caused loss of contact, the robot easily lost propulsion or had motor overload. Contact feedback control resolved these issues by helping the robot regain contact. Yet excessive conformation interrupted shape propagation and excessive pushing stalled motors frequently. Unlike that using lateral bending, for propulsion generation using vertical bending, body weight that can help maintain contact with the environment but may also overload motors. Our results will help snake robots better traverse uneven terrain with large height variation and can inform how snakes use sensory feedback to control vertical body bending for propulsion.

Sedation and Anesthesia in Exotic Animal Critical Care

Sedation and anesthesia of exotic animals in inherently challenging, but often facilitates the best care for patients. Critical illness or injury adds on another layer of complexity to their management for obtaining diagnostics and providing treatments. This article serves to review some of the more recent literature of sedation and anesthesia within exotics practice, bringing to light some nuances and considerations for when those patients are critically ill or injured.

ULTRASONOGRAPHIC EVALUATION OF COELOMIC FLUID IN HEALTHY CORN SNAKES (PANTHEROPHIS GUTTATUS)

Free coelomic fluid can be a physiologic or pathologic finding in snakes. In this study, ultrasonography was used to assess the presence, volume, and type of coelomic fluid in 18 (16 females, 2 males) clinically healthy corn snakes (Pantherophis guttatus) using a semiquantitative scoring system. Each snake was divided into five equal regions (R1-R5) by length (from rostrum to vent) and fluid volume was scored on a scale of 0 to 4. Coelomic fluid was sampled when possible and cytologic analysis was performed. The majority of snakes (16/18) were found to have some degree of free coelomic fluid. The coelomic fluid samples that were collected (n= 6) were classified as transudates, acellular or primarily lymphocytic. Fluid was most likely to be found in R3 compared with all other regions and least likely to be found in R1 compared with R2, R3, and R4. A higher score of volume was found in R3 compared with R1 and R5. This study describes the distribution and abundance of coelomic fluid in snakes, as well as a method for point of care ultrasound (POCUS) in this species.

OPTIMIZING THE PHARMACODYNAMICS AND EVALUATING CARDIOGENIC EFFECTS OF THE INJECTABLE ANESTHETIC ALFAXALONE IN PRAIRIE RATTLESNAKES (CROTALUS VIRIDIS)

North American vipers are commonly housed in zoological institutions or studied as free-ranging populations. Because of their venomous predatory and defensive mechanism, sedation or anesthesia is frequently employed to facilitate safe handling and medical procedures, especially of the head. A new formulation of alfaxalone with proprietary preservatives was recently approved and indexed for 28-d use post-vial puncture. Pharmacodynamic effects of alfaxalone in its prior formulation have been researched in nonvenomous species, but the optimal dose and route of administration in vipers have not been reported. In part one, 10 prairie rattlesnakes (Crotalus viridis) participated in a complete four-route crossover study evaluating 20 mg/kg alfaxalone administered intracoelomically (ICo), SC cranial to the heart, IM cranial to the heart, and IV in the ventral coccygeal vein. HR significantly decreased from baseline during IV (P= 0.024), IM (P= 0.024), and SC (P= 0.028) administration. Respiratory rate significantly decreased following alfaxalone delivered IV (P = 0.027). Time to first effects was significantly faster in IV compared with IM (P= 0.01), SC (P= 0.001), and ICo (P= 0.036). All IV and IM administrations resulted in deep sedation, but 70% of the IV and 10% of the IM sedation events resulted in apnea and required intermittent positive ventilation via endotracheal tube. Fifty percent of the ICo sedation events and 10% of the SC sedation events did not result in sedation. One successful SC sedation event resulted in apnea. In part two, echocardiograms were performed in the same rattlesnakes at baseline and at maximum effect of sedation with 20 mg/kg alfaxalone administered IM. Cardiac contractility and output were unaffected. Administration of alfaxalone at 20 mg/kg IM cranial to the heart should facilitate safe handling and minimally invasive procedures in prairie rattlesnakes and related species.

Snake Sedation and Anesthesia

Snakes can be more challenging to anesthetize compared with other animals because of anatomic and physiologic differences, a wide range of patient sizes, and variable responses to anesthetic agents. Snakes have preferred optimal temperature zones, which, along with physiologic characteristics, such as the ability to shunt blood toward or away from the lungs, can have an impact on anesthesia. Injectable agents, including benzodiazepines, α₂-agonists, opioids, propofol, and alfaxalone, as well as inhalant anesthetics can be used to anesthetize snakes. Pain management must be incorporated to the anesthetic plan when performing procedures that are expected to produce nociception.

Comparison of isoflurane, sevoflurane, and desflurane as inhalant anesthetics in prairie rattlesnakes (Crotalus viridis)

OBJECTIVE

To characterize induction and recovery characteristics of 3 commonly used inhalant anesthetics in prairie rattlesnakes (Crotalus viridis): isoflurane, sevoflurane, and desflurane.

ANIMALS

12 healthy adult prairie rattlesnakes.

PROCEDURES

In a randomized crossover design, snakes underwent anesthetic induction with 5% isoflurane, 8% sevoflurane, or 18% desflurane, with a washout period of ≥ 7 days between anesthetic events. Anesthetic depth parameters were recorded throughout induction and recovery, including time to loss and return of righting reflex, muscle tone, ability to intubate, response to pressure, and time to return to spontaneous respiration. Every 5 minutes throughout the anesthetic procedures, heart rate, respiratory rate, and percentage expired anesthetic gas were recorded.

RESULTS

No snakes died during the study. Sevoflurane anesthesia resulted in anesthetic gas avoidance behavior in snakes during induction and had the significantly longest recovery time to extubation and time to return of pressure response, compared with the other inhalant anesthetics. Anesthesia with isoflurane resulted in a significantly longer time to return of righting reflex, compared with sevoflurane or desflurane. No significant difference was noted in time to loss of pressure response among the 3 anesthetic gases. Desflurane anesthesia resulted in the significantly quickest loss of righting reflex among the anesthetic protocols; despite this, 4 of 12 desflurane anesthetized snakes did not achieve an anesthetic plane deep enough for intubation.

CONCLUSIONS AND CLINICAL RELEVANCE

Isoflurane and sevoflurane, but not desflurane, inhalation anesthesia resulted in consistent and predictable loss of righting reflex and induction of anesthesia deep enough to allow intubation in snakes.

Evaluating the efficacy of alfaxalone in corn snakes (Pantherophis guttatus)

OBJECTIVE

Alfaxalone is a popular veterinary anesthetic; however, research on this anesthetic in snakes has been limited to ball pythons, garter snakes and several Australian species. The objective was to evaluate the anesthetic effects of alfaxalone in corn snakes (Pantherophis guttatus), a popular pet snake.

STUDY DESIGN

Prospective, randomized crossover study.

ANIMALS

A total of eight corn snakes.

METHODS

In phase I, snakes were subcutaneously administered three doses of alfaxalone (5, 10 and 15 mg kg^-1) in the cranial third of the body to determine the most effective dose. In phase II, a dose of 15 mg kg^-1 was administered in the cranial and caudal thirds of the snakes to determine if injection site affected anesthesia duration. Heart rate (HR), respiratory rate (f_R), righting reflex, escape response, tail pinch, needle prick and tongue flick were monitored at baseline and 5 minute intervals until the snakes fully recovered.

RESULTS

Duration of anesthesia differed significantly, with higher doses lasting longer than lower doses: 5 mg kg^-1 [23.8 ± 4.4 (15-30) minutes]; 10 mg kg^-1 [40.6 ± 9.4 (25-55) minutes]; and 15 mg kg^-1 [56.9 ± 8.4 (50-70) minutes], mean ± standard deviation (range). The tail pinch reflex was not completely lost in phase 1. There was a significant change in f_R over time, but this was not related to dose. HR was not different by time or dose. Duration of anesthesia was not different after administration of alfaxalone (15 mg kg^-1) in the cranial third versus the caudal third of the body; however, there was a significant decrease in HR and f_R at this dose, regardless of injection site.

CONCLUSIONS AND CLINICAL RELEVANCE

Based on these results, alfaxalone (15 mg kg^-1) provides adequate anesthesia for brief procedures or intubation; however, additional analgesia is required for painful procedures.

Effects of intracoelomic alfaxalone-dexmedetomidine on righting reflex in common garter snakes (Thamnophis sirtalis): preliminary data

OBJECTIVE

To evaluate the effect of dexmedetomidine on alfaxalone immobilization in snakes.

STUDY DESIGN

Nonblinded, crossover study.

ANIMALS

A total of eight mature common garter snakes (Thamnophis sirtalis).

METHODS

Snakes were administered each of three treatments intracoelomically: alfaxalone (30 mg kg^-1; treatment A), alfaxalone (30 mg kg^-1) combined with dexmedetomidine (0.05 mg kg^-1; treatment AD0.05); and alfaxalone (30 mg kg^-1) combined with dexmedetomidine (0.10 mg kg^-1; treatment AD0.10). A minimum of 10 days elapsed between experimental trials. Times to loss of righting reflex (LRR) and return of righting reflex (RRR) were recorded. Heart rate (HR) was recorded every 5 minutes throughout the period of LRR and averaged for each snake. Times to LRR and RRR, and mean HR in snakes that achieved LRR were reported.

RESULTS

LRR occurred in eight (100%), five (63%) and three (38%) snakes in treatments A, AD0.05 and AD0.10, respectively. For all treatments, time to LRR ranged 3-20 minutes. Median (range) times to RRR were 39 (30-46), 89 (62-128) and 77 (30-185) minutes for treatments A, AD0.05 and AD0.10, respectively. In animals where righting reflex was lost, mean HR was lower in all dexmedetomidine treatments compared with treatment A.

CONCLUSIONS AND CLINICAL RELEVANCE

In this pilot study, alfaxalone resulted in reliable immobilization, whereas dexmedetomidine and alfaxalone combinations resulted in highly variable durations of immobilization with low HR in immobilized animals. For snakes that achieved LRR, the addition of dexmedetomidine (0.05 mg kg^-1) to alfaxalone appeared to extend the period of immobilization compared with alfaxalone alone.