Stephen J. Divers

Specialized stem cell niche enables repetitive renewal of alligator teeth

Reptiles and fish have robust regenerative powers for tooth renewal. However, extant mammals can either renew their teeth one time (diphyodont dentition) or not at all (monophyodont dentition). Humans replace their milk teeth with permanent teeth and then lose their ability for tooth renewal. Here, we study tooth renewal in a crocodilian model, the American alligator, which has well-organized teeth similar to mammals but can still undergo life-long renewal. Each alligator tooth is a complex family unit composed of the functional tooth, successional tooth, and dental lamina. Using multiple mitotic labeling, we map putative stem cells to the distal enlarged bulge of the dental lamina that contains quiescent odontogenic progenitors that can be activated during physiological exfoliation or artificial extraction. Tooth cycle initiation correlates with β-catenin activation and soluble frizzled-related protein 1 disappearance in the bulge. The dermal niche adjacent to the dermal lamina dynamically expresses neural cell adhesion molecule, tenascin-C, and other molecules. Furthermore, in development, asymmetric β-catenin localization leads to the formation of a heterochronous and complex tooth family unit configuration. Understanding how these signaling molecules interact in tooth development in this model may help us to learn how to stimulate growth of adult teeth in mammals.

Pharmacokinetics of meloxicam following intravenous and oral administration in green iguanas (Iguana iguana)

OBJECTIVE To determine pharmacokinetics of meloxicam in healthy green iguanas following PO and IV administration and assess potential toxicity. ANIMALS 21 healthy green iguanas (Iguana iguana). PROCEDURES To assess pharmacokinetics, 13 iguanas were administered a single dose (0.2 mg/kg) of meloxicam PO and, 14 days later, the same dose IV. To assess potential toxicity, 4 iguanas were given meloxicam at a dosage of 1 or 5 mg/kg, PO, every 24 hours for 12 days, and results of histologic examination were compared with results for another 4 iguanas given a single dose of meloxicam (0.2 mg/kg). RESULTS There were no significant differences between PO and IV administration with regard to terminal half-life (mean ± SD, 12.96 ± 8.05 hours and 9.93 ± 4.92 hours, respectively), mean area under the curve to the last measured concentration (5.08 ± 1.62 μg•h/mL and 5.83 ± 2.49 μg•h/mL), volume of distribution (745 ± 475 mL/kg and 487 ± 266 mL/kg), or clearance (40.17 ± 10.35 mL/kg/h and 37.17 ± 16.08 mL/kg/h). Maximum plasma concentration was significantly greater following IV (0.63 ± 0.17 μg/mL) versus PO (0.19 ± 0.07 μg/mL) administration. Time from administration to maximum plasma concentration and mean residence time were significantly longer following PO versus IV administration. Daily administration of high doses (1 or 5 mg/kg) for 12 days did not induce any histologic changes in gastric, hepatic, or renal tissues. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that administration of meloxicam at a dose of 0.2 mg/kg IV or PO in green iguanas would result in plasma concentrations > 0.1 μg/mL for approximately 24 hours.

Sterilisation of hybrid Galapagos tortoises (Geochelone nigra) for island restoration. Part 2: phallectomy of males under intrathecal anaesthesia with lidocaine

Lidocaine intrathecal anaesthesia was used to perform phallectomies in 15 hybrid Galapagos tortoises (Geochelone nigra) in a field setting as part of a conservation and ecosystem restoration project in the Galapagos Islands. The intrathecal injection was performed in the dorsal intercoccygeal region of the tail. Once the tail and hindlimbs were relaxed and the phallus was easily exteriorised, phallectomy was performed in a routine manner. All the animals recovered well from the procedure and were walking 30 to 60 minutes after surgery. No adverse effects were noted as a result of lidocaine intrathecal anaesthesia. One of the larger animals had evidence of haemorrhage from the surgical site 48 hours postoperatively. All tortoises continued to make full recoveries and were released on to the island of Pinta in May 2010.

Reptile diagnostic endoscopy and endosurgery.

The 2.7-mm telescope commonly used in avian practice has transitioned into an invaluable diagnostic tool for the reptile clinician. Previously plagued by vague medical histories, nonpathognomonic physical examinations, indistinct diagnostic images, and less than conclusive clinical pathology results, the reptile clinician often has had trouble making a definitive, antemortem diagnosis. A definitive diagnosis generally relies on the demonstration of a host pathologic response and the causative agent. The ability to examine internal structures and collect biopsies has enabled many postmortem diagnoses to now be appreciated in the living animal, and along with accurate diagnosis comes accurate prognosis and improved case management. The advent of 3-mm human pediatric laparoscopy equipment has fueled interest in minimally invasive endosurgery in exotic pets, including reptiles. However, the chelonian shell has also served as a catalyst to speed the development of surgical approaches to the coelom that do not involve major shell surgery. This article summarizes the most common endoscopic approaches in lizards, chelonians, and snakes for the purposes of making a diagnosis and increasingly performing endosurgery.

Sterilisation of hybrid Galapagos tortoises (Geochelone nigra) for island restoration. Part 1: endoscopic oophorectomy of females under ketamine-medetomidine anaesthesia

An endoscopic sterilisation technique for use in Galapagos tortoises (Geochelone nigra) was developed as part of a conservation and ecosystem restoration project. Fifteen female giant Galapagos tortoises were anaesthetised, intubated and positioned in dorsal recumbency. A bilateral prefemoral approach was made and the ovaries were identified using a 5 mm × 33 cm rigid telescope. In the case of endoscope-assisted oophorectomy, the ovaries were exteriorised through the same incision, the vasculature was ligated and the mesovarium was transected. Two tortoises had immature ovaries that could not be exteriorised. In these animals, endoscopic oophorectomy was performed using radiosurgery. Closure of the incisions was routine. All tortoises except one recovered well from surgery. There were no reported complications six weeks and six months postoperatively, and all were successfully released on to Pinta Island in May 2010.

Exotic mammal diagnostic endoscopy and endosurgery.

Despite the extensive use of endoscopy in avian and domestic animal practice, inclusion of exotic mammals (rabbits, rodents, ferrets, and so forth) in the endoscopists case load is a much more recent phenomenon. Initially used as a means for the detailed evaluation of the oral cavity, rigid endoscopy has also become invaluable for the evaluation of the nasal cavity, urogenital tract, and increasingly for laparoscopic procedures. This article summarizes the most common procedures used by the author for first opinion and referral cases, and introduces some of the recent developments that are expected to become the standard of care in exotic animal practice in the future.

Clinical Evaluation of Reptiles

A detailed history and physical examination usually provides the veterinarian with a list of possible differential diagnoses and indicates which further investigations may be necessary to make a definitive diagnosis. Radiography, ultrasonography, endoscopy, hematology, blood biochemistry, and microbiological and parasitologic investigations are all proven techniques that are used extensively in reptile medicine. A logical case workup enables the clinician to make a previously elusive reptile diagnosis and offers this interesting group of animals veterinary services comparable with that already expected for more domesticated pets.

Cardiomyopathy and Right-sided Congestive Heart Failure in a Red-tailed Hawk (Buteo jamaicensis)

Abstract A 15-year-old female red-tailed hawk (Buteo jamaicensis) was evaluated because of dyspnea, anorexia, and coelomic distension. Diagnostic imaging results confirmed severe coelomic effusion and revealed a markedly dilated right ventricle. The diagnosis was right-sided congestive heart failure. Results of measurements of vitamin E, selenium, lead, zinc, and cardiac troponin levels were normal or nondiagnostic. The hawk was treated with furosemide, antifungal and antimicrobial agents, and supplemental fluids and oxygen, but euthanasia was elected because of the poor prognosis and the practical difficulties associated with intensive case management. To our knowledge, this is the first described case of cardiomyopathy and congestive heart failure in a captive red-tailed hawk.

Avian diagnostic endoscopy.

Unlike most animals, birds are blessed by an air sac system that essentially provides the endoscopist with a preinsufflated patient. Thanks to this unique anatomy and the pioneering work of Greg Harrison, Michael Taylor, and other avian veterinarians, rigid endoscopy has enjoyed considerable popularity in avian practice over the past 30 years. Indeed, endoscopy now is considered an essential component of the avian investigation for many clinical presentations, and indeed few could argue that high-quality avian medicine is possible without rigid endoscopy. The ability to examine the internal viscera, respiratory, gastrointestinal, and reproductive tracts, and collect samples for definitive diagnosis continues to play a central role in avian practice, and this article summarizes the most common diagnostic endoscopic approaches likely to be undertaken in companion species.

Endoscopy equipment and instrumentation for use in exotic animal medicine.

The first descriptions of endoscopy date back to the times of Hippocrates (460-377 BC), who described the use of a rectal speculum in humans. Since that time, technologic advances have fueled the development of endoscopy equipment. The application of human pediatric instruments in exotic pet medicine has enabled these minimally invasive techniques to be applied to birds, reptiles, amphibians, fish, and small mammals. This article aims to summarize the development of endoscopy equipment and focuses on recent developments in miniature laparoscopy equipment that have found use in zoologic companion animal practice.